pacific northwest national laboratory u.s. department of energy may 15, 2007 biogeochemistry of...
Post on 17-Dec-2015
219 Views
Preview:
TRANSCRIPT
Pacific Northwest National LaboratoryUS Department of Energy
May 15 2007May 15 2007
Biogeochemistry of Technetium Discriminating Microscopic Abiotic and
Microbiologic Reaction Processes and Their Implications to Fate and Transport
Biogeochemistry of Technetium Discriminating Microscopic Abiotic and
Microbiologic Reaction Processes and Their Implications to Fate and Transport
J M Zachara1 S M Heald2 J K Fredrickson1 T Peretyazhko1 R Kukkadapu1 and M Marshall1
1Pacific Northwest National Laboratory Richland WA2Argonne National Laboratory and Advanced Photon Source Argonne IL
J M Zachara1 S M Heald2 J K Fredrickson1 T Peretyazhko1 R Kukkadapu1 and M Marshall1
1Pacific Northwest National Laboratory Richland WA2Argonne National Laboratory and Advanced Photon Source Argonne IL
2
AcknowledgementsAcknowledgements
OBERERSD - 5 years + support for Tc biogeochemistry
DOEORP and CH2M-Hill Hanford - Tank farm samples and characterization data
EMSL and APS user facilities
Alex Beliaev and Frank Loeffler ERSP project for Anaeromyxobacter culture and conditions
3
ERSDrsquos Long Term MeasureERSDrsquos Long Term Measure
ldquoBy 2015 provide sufficient scientific understanding to allow a
significant fraction of DOE sites to incorporate biological chemical
and physical processes into decision making for environmental
remediationrdquo
4
TechnetiumTechnetium
Fission product of 235Uranium
Exists in oxidation states +7 to -1
Highly mobile as Tc(VII) pertechnetate ion TcO4-
Biological activity high (sulphate analogue)
Microbial reduction to insoluble Tc(IV) (widespread)
235Uranium 99TechnetiumFission
T12 = 70 x 108 years
-emitter
21 x 105 years
-emitter
5
400 Ci of 99Tc was Released to the BC-Crib Area Where is it
400 Ci of 99Tc was Released to the BC-Crib Area Where is it
CRIBS
Trenches
The SAC model forecasts that a growing plume of 99Tc should exist beneath the BC-cribs
99Tc 238ULithology
[Tc(VII)]max = 18x106 pCiL 10-6 molL
6
Different Scales ~ Different IssuesDifferent Scales ~ Different IssuesMolecular Microscopic Macroscopic Field
bull Bonding environment and local structure
bull Fundamental mechanisms
bull Energetics and structural controls
bull Solvation effects
bull Mineral residence phase identity amp composition
bull Reaction networks and kinetics
bull Morphologic and surface issues
bull Fundamental process coupling
bull Rate processesChemical MicrobiologicMass transfer
bull Advection effectsbull 1-D scaling issuesbull Pore scale process
coupling
bull Physical heterogeneityWater
velocitiesdirectionsReactants
bull Multi-scale mass transferbull Mixing amp averagingbull Distributed propertiesbull Seasonal issues (temperature precipitation)
7
Biogeochemical Cycles of Tc and Fe are LinkedBiogeochemical Cycles of Tc and Fe are Linked
Experimentsmeld environmentalmicrobiology geochemistryand mineralogy
Toolsbull Microscopyspectroscopybull X-ray diffraction and
scatteringbull Genomicsmutagenesisbull Controlled culture
Issuesbull Productsbull Mechanismsbull Kinetic controlsbull Indirect and direct
biologic effects
Impactsbull Weatheringbull Anoxic environmentsbull Contaminant behaviorbull Energy cycling
Fe(II)Fe(III) phases
Fe(III) oxides
Metal reducing organisms
abiotic reductants
Metal oxidizing organisms
abiotic oxidants
8
Solubility of TcO2Solubility of TcO2
TcO(OH)deg2(aq)
16784 pCiL
1678 pCiL
168 pCiL
Concentration of Tc(IV) fixed by solubililty at reduction pointDowngradient adsorption of Tc(IV) complexes or another reaction essential to reach MCL (900 pCiL)Adsorption behavior of TcO(OH)2deg(aq) unknown
MCL900 pCiL
Tc(VII)O4- + 4H+ + 3e- = Tc(IV)O2nH2O(s) + (2-n)H2O Eo = 0748 V
Tc(VII)O4- + 3Fe2+ + (n+7)H2O = Tc(IV)O2middotnH2O(s) + 3Fe(OH)3(s)+ 5H+
9
Technetium Redox Couples in Relation to Others at Standard State and pH = 7
Technetium Redox Couples in Relation to Others at Standard State and pH = 7
-10 -5 0 5 10 15 20 pe
H2(g) H2O H2O O2(g)
NH4 ι NO3-
MnCO3 ι MnO2-
Fe(aq) ι Fe(OH3)2+
HS ι SO42-
Fe(aq) ι FeOOH2+
Hemes
Tc(IV)O2 ι Tc(VII)Tc(V)(VI) ι Tc(VII)
ldquoCH2Ordquo ι CO2(g)
reducing oxidizing
10
Complex Redox Chemistry of 3e- Transfer for Tc(VII)
Complex Redox Chemistry of 3e- Transfer for Tc(VII)
Tc(VII)O4- + e- Tc(VI)O4
2- Tc(V) Tc(IV) [Tc(IV)OOHaq Tc(IV)O2nH2O(s)]
gelatin
rapid
tetrahedral tetrahedral octahedral
rapid
very
11
Disproportionation Rate Key to 3e- TransferDisproportionation Rate Key to 3e- Transfer
Tc(VII) Tc(VI) Fe(II) H+ log QK Gr
(molL) (kJmol)
100E-06 100E-12 0001 100E-07 26 14846100E-06 100E-13 0001 100E-07 16 9136100E-06 100E-14 0001 100E-07 06 3426100E-06 100E-15 0001 100E-07 -04 -2284100E-06 100E-16 0001 100E-07 -14 -7994100E-06 100E-17 0001 100E-07 -24 -13704
Reaction rate and extent increases with1 Disproportionation rate2 Concentration and redox potential of Fe(II)3 pH
Fe2+ + 3H2O + Tc(VII)O4- = Fe(III)(OH)3 + 3H+ + TcO4
2- log K = 266
Tc(VII)Tc(V)
Tc(IV)
12
Coupled Processes and ModelsCoupled Processes and Models
Reaction NetworkNecessary component reactions to define time evolution and steady stateComponent identities and concentrationsReaction parameters and dependencies
Coupled ProcessReactionMicrobiologic transformation (biogeochemical)Advectiondiffusion (water reactantproduct flux)Microbiologic speciation (ecologic)
13
Coupled ReactionsCoupled Reactions
Reaction Type Components Parameters
Electron transfer A + B rarr C + D Kdq=kfkb [A] [B] [X] [Y] [Z]Tc(VII)+Fe(II) = TcO22H2O+Fe(OH)3
Surface complexation B + E rarr F Ŝ [SOH]Fe(II)+FeOOH = Fe(II)-FeOOH
Electron transfer A + F rarr GTc(VII)+3Fe(II)-FeOOH rarr Tc(IV)-3Fe(III)Ox+FeOOH
Biological electron A + H rarr C biomass growth substrateTransfer specificity and kinetics
Tc(VII)+H2 = TcO2nH2O e-acceptordonor nutrients
Biologic reductive DE + J rarr B
FeOOHFe(OH3) + lactate = Fe(II) + CO2 + acetate
Aqueous complexation C + I rarr KTcO2nH2O + CO3
2- = TcOCO3(aq)
гbio
bio
г
14
Utilize dissolved and solid phase oxidized metals as electron acceptors for respiration when O2 becomes deplete
Strongly influence the composition and redox state of groundwaters and the valence state of polyvalent metals and radionuclides
Metal Reducing BacteriaMetal Reducing Bacteria
Bacterial mediation of geochemical reaction
Oxidized
Reduced
Oxidized
Reduced
Bacteria
Microorganisms mediate kinetically inhibited but thermodynamically favorable reactions
E for metabolism and growth
15
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Reduction (+ Fe(II) or MRB)
Tc(VII)O4-(aq)
Oxidation (+ O2 or MOB)
biologic (MRB)
+homogeneous
Fe(II)aq
heterogeneousFe(II)OH Fe(II)aq
Tc(IV)
bull speciationbull physical location
Fe(III) oxide
TcO4
t= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
Tc(IV)t
= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
medium
very slow
very fastmedium
16
Experimental Setup and Anoxic ChamberExperimental Setup and Anoxic Chamber
Glove box ldquoairrdquo is totally scrubbed of O2 using an oxygen trap based on heterogeneous reduction of O2 in Fe(II)Fe(OH)3 suspensions
lt 05 ppm
spectroscopypreparation
drying chamber
filtrationchamber
mineral and mineral-microbe
suspensions
oxygentrap
solids and liquid sampling
mineral solids and heterogeneous
precipitates
17
Probing Heterogeneous E-transferProbing Heterogeneous E-transfer
X-ray Adsorption Spectroscopy
57Fe-MossbauerSpectroscopy Combined Techniques
bull Valence statebull Local structurebull Tc-Obull Tc-Tcbull Tc-Fe
bull Valence bull Magnetic propertiesbull Bonding environmentbull Symmetry
APS EMSL In addition ndash HRTEM (EMSL)
(looking at Tc) (looking at Fe)
hFe 56Fe Al
57Fe h
57Fe
SO-Fe(II)OH + Tc(VII) rarr Г =
Heterogeneous Reduction of Pertechnetate [Tc(VII)O4
-] by Surface Complexed Fe(II) at pH = 7Heterogeneous Reduction of Pertechnetate
[Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
Dis
so
lved
Tc(
VII
)
mo
l L
-1
Dis
so
lved
Fe(
II)
mm
ol
L-1
To
tal
Fe
(II)
m
mo
l L
-1
Time daysTime days
Time days
+ FeOOH + Tc(VII)+ FeOOH
+ Tc(VII)
-6 to -2 day Fe(II)aq
-2 to 0 day FeO-Fe(II)OH0 day + FeO-Fe(II)OH+Tc(IV)Fe(III)
Issuesbull Stoichiometry of Fe(III) and Tc(IV)bull Nature of Fe(III) and Tc(IV) phasesbull Location and association of Fe(II)bull Speciation effects on heterogeneous
oxidation
3FeO-Fe(II)OH + Tc(VII)O4- = 3FeO-Fe(III)OH2 [] + Tc(IV)O2H2O []
19
Products of Heterogeneous Tc(VII)O4- Reduction
by Fe(II) on Goethite Products of Heterogeneous Tc(VII)O4
- Reduction by Fe(II) on Goethite
k A-1 R Aring
What is Fe(III)Tc(IV)Ox Where is readsorbed Fe(II)
56Fe- goethite(Moumlssbauer invisible)
57Fe(II)(Moumlssbauer visible)
bull Magnetic order and peak positions consistent with Fe(III) and goethite
bull No Fe(II)
bull ldquotwordquo Fe(II) sites
bull Spectra before Tc(IV) addition almost identical
20
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
2CP-C
Biogenic TcO2nH2O shows less Tc-Tc second neighbors and different long range order
Consistent with small size (2-3 nm) of biogenic precipitates
Tc-O
Tc-Tc
Tc-OTc-Tc
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
2
AcknowledgementsAcknowledgements
OBERERSD - 5 years + support for Tc biogeochemistry
DOEORP and CH2M-Hill Hanford - Tank farm samples and characterization data
EMSL and APS user facilities
Alex Beliaev and Frank Loeffler ERSP project for Anaeromyxobacter culture and conditions
3
ERSDrsquos Long Term MeasureERSDrsquos Long Term Measure
ldquoBy 2015 provide sufficient scientific understanding to allow a
significant fraction of DOE sites to incorporate biological chemical
and physical processes into decision making for environmental
remediationrdquo
4
TechnetiumTechnetium
Fission product of 235Uranium
Exists in oxidation states +7 to -1
Highly mobile as Tc(VII) pertechnetate ion TcO4-
Biological activity high (sulphate analogue)
Microbial reduction to insoluble Tc(IV) (widespread)
235Uranium 99TechnetiumFission
T12 = 70 x 108 years
-emitter
21 x 105 years
-emitter
5
400 Ci of 99Tc was Released to the BC-Crib Area Where is it
400 Ci of 99Tc was Released to the BC-Crib Area Where is it
CRIBS
Trenches
The SAC model forecasts that a growing plume of 99Tc should exist beneath the BC-cribs
99Tc 238ULithology
[Tc(VII)]max = 18x106 pCiL 10-6 molL
6
Different Scales ~ Different IssuesDifferent Scales ~ Different IssuesMolecular Microscopic Macroscopic Field
bull Bonding environment and local structure
bull Fundamental mechanisms
bull Energetics and structural controls
bull Solvation effects
bull Mineral residence phase identity amp composition
bull Reaction networks and kinetics
bull Morphologic and surface issues
bull Fundamental process coupling
bull Rate processesChemical MicrobiologicMass transfer
bull Advection effectsbull 1-D scaling issuesbull Pore scale process
coupling
bull Physical heterogeneityWater
velocitiesdirectionsReactants
bull Multi-scale mass transferbull Mixing amp averagingbull Distributed propertiesbull Seasonal issues (temperature precipitation)
7
Biogeochemical Cycles of Tc and Fe are LinkedBiogeochemical Cycles of Tc and Fe are Linked
Experimentsmeld environmentalmicrobiology geochemistryand mineralogy
Toolsbull Microscopyspectroscopybull X-ray diffraction and
scatteringbull Genomicsmutagenesisbull Controlled culture
Issuesbull Productsbull Mechanismsbull Kinetic controlsbull Indirect and direct
biologic effects
Impactsbull Weatheringbull Anoxic environmentsbull Contaminant behaviorbull Energy cycling
Fe(II)Fe(III) phases
Fe(III) oxides
Metal reducing organisms
abiotic reductants
Metal oxidizing organisms
abiotic oxidants
8
Solubility of TcO2Solubility of TcO2
TcO(OH)deg2(aq)
16784 pCiL
1678 pCiL
168 pCiL
Concentration of Tc(IV) fixed by solubililty at reduction pointDowngradient adsorption of Tc(IV) complexes or another reaction essential to reach MCL (900 pCiL)Adsorption behavior of TcO(OH)2deg(aq) unknown
MCL900 pCiL
Tc(VII)O4- + 4H+ + 3e- = Tc(IV)O2nH2O(s) + (2-n)H2O Eo = 0748 V
Tc(VII)O4- + 3Fe2+ + (n+7)H2O = Tc(IV)O2middotnH2O(s) + 3Fe(OH)3(s)+ 5H+
9
Technetium Redox Couples in Relation to Others at Standard State and pH = 7
Technetium Redox Couples in Relation to Others at Standard State and pH = 7
-10 -5 0 5 10 15 20 pe
H2(g) H2O H2O O2(g)
NH4 ι NO3-
MnCO3 ι MnO2-
Fe(aq) ι Fe(OH3)2+
HS ι SO42-
Fe(aq) ι FeOOH2+
Hemes
Tc(IV)O2 ι Tc(VII)Tc(V)(VI) ι Tc(VII)
ldquoCH2Ordquo ι CO2(g)
reducing oxidizing
10
Complex Redox Chemistry of 3e- Transfer for Tc(VII)
Complex Redox Chemistry of 3e- Transfer for Tc(VII)
Tc(VII)O4- + e- Tc(VI)O4
2- Tc(V) Tc(IV) [Tc(IV)OOHaq Tc(IV)O2nH2O(s)]
gelatin
rapid
tetrahedral tetrahedral octahedral
rapid
very
11
Disproportionation Rate Key to 3e- TransferDisproportionation Rate Key to 3e- Transfer
Tc(VII) Tc(VI) Fe(II) H+ log QK Gr
(molL) (kJmol)
100E-06 100E-12 0001 100E-07 26 14846100E-06 100E-13 0001 100E-07 16 9136100E-06 100E-14 0001 100E-07 06 3426100E-06 100E-15 0001 100E-07 -04 -2284100E-06 100E-16 0001 100E-07 -14 -7994100E-06 100E-17 0001 100E-07 -24 -13704
Reaction rate and extent increases with1 Disproportionation rate2 Concentration and redox potential of Fe(II)3 pH
Fe2+ + 3H2O + Tc(VII)O4- = Fe(III)(OH)3 + 3H+ + TcO4
2- log K = 266
Tc(VII)Tc(V)
Tc(IV)
12
Coupled Processes and ModelsCoupled Processes and Models
Reaction NetworkNecessary component reactions to define time evolution and steady stateComponent identities and concentrationsReaction parameters and dependencies
Coupled ProcessReactionMicrobiologic transformation (biogeochemical)Advectiondiffusion (water reactantproduct flux)Microbiologic speciation (ecologic)
13
Coupled ReactionsCoupled Reactions
Reaction Type Components Parameters
Electron transfer A + B rarr C + D Kdq=kfkb [A] [B] [X] [Y] [Z]Tc(VII)+Fe(II) = TcO22H2O+Fe(OH)3
Surface complexation B + E rarr F Ŝ [SOH]Fe(II)+FeOOH = Fe(II)-FeOOH
Electron transfer A + F rarr GTc(VII)+3Fe(II)-FeOOH rarr Tc(IV)-3Fe(III)Ox+FeOOH
Biological electron A + H rarr C biomass growth substrateTransfer specificity and kinetics
Tc(VII)+H2 = TcO2nH2O e-acceptordonor nutrients
Biologic reductive DE + J rarr B
FeOOHFe(OH3) + lactate = Fe(II) + CO2 + acetate
Aqueous complexation C + I rarr KTcO2nH2O + CO3
2- = TcOCO3(aq)
гbio
bio
г
14
Utilize dissolved and solid phase oxidized metals as electron acceptors for respiration when O2 becomes deplete
Strongly influence the composition and redox state of groundwaters and the valence state of polyvalent metals and radionuclides
Metal Reducing BacteriaMetal Reducing Bacteria
Bacterial mediation of geochemical reaction
Oxidized
Reduced
Oxidized
Reduced
Bacteria
Microorganisms mediate kinetically inhibited but thermodynamically favorable reactions
E for metabolism and growth
15
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Reduction (+ Fe(II) or MRB)
Tc(VII)O4-(aq)
Oxidation (+ O2 or MOB)
biologic (MRB)
+homogeneous
Fe(II)aq
heterogeneousFe(II)OH Fe(II)aq
Tc(IV)
bull speciationbull physical location
Fe(III) oxide
TcO4
t= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
Tc(IV)t
= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
medium
very slow
very fastmedium
16
Experimental Setup and Anoxic ChamberExperimental Setup and Anoxic Chamber
Glove box ldquoairrdquo is totally scrubbed of O2 using an oxygen trap based on heterogeneous reduction of O2 in Fe(II)Fe(OH)3 suspensions
lt 05 ppm
spectroscopypreparation
drying chamber
filtrationchamber
mineral and mineral-microbe
suspensions
oxygentrap
solids and liquid sampling
mineral solids and heterogeneous
precipitates
17
Probing Heterogeneous E-transferProbing Heterogeneous E-transfer
X-ray Adsorption Spectroscopy
57Fe-MossbauerSpectroscopy Combined Techniques
bull Valence statebull Local structurebull Tc-Obull Tc-Tcbull Tc-Fe
bull Valence bull Magnetic propertiesbull Bonding environmentbull Symmetry
APS EMSL In addition ndash HRTEM (EMSL)
(looking at Tc) (looking at Fe)
hFe 56Fe Al
57Fe h
57Fe
SO-Fe(II)OH + Tc(VII) rarr Г =
Heterogeneous Reduction of Pertechnetate [Tc(VII)O4
-] by Surface Complexed Fe(II) at pH = 7Heterogeneous Reduction of Pertechnetate
[Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
Dis
so
lved
Tc(
VII
)
mo
l L
-1
Dis
so
lved
Fe(
II)
mm
ol
L-1
To
tal
Fe
(II)
m
mo
l L
-1
Time daysTime days
Time days
+ FeOOH + Tc(VII)+ FeOOH
+ Tc(VII)
-6 to -2 day Fe(II)aq
-2 to 0 day FeO-Fe(II)OH0 day + FeO-Fe(II)OH+Tc(IV)Fe(III)
Issuesbull Stoichiometry of Fe(III) and Tc(IV)bull Nature of Fe(III) and Tc(IV) phasesbull Location and association of Fe(II)bull Speciation effects on heterogeneous
oxidation
3FeO-Fe(II)OH + Tc(VII)O4- = 3FeO-Fe(III)OH2 [] + Tc(IV)O2H2O []
19
Products of Heterogeneous Tc(VII)O4- Reduction
by Fe(II) on Goethite Products of Heterogeneous Tc(VII)O4
- Reduction by Fe(II) on Goethite
k A-1 R Aring
What is Fe(III)Tc(IV)Ox Where is readsorbed Fe(II)
56Fe- goethite(Moumlssbauer invisible)
57Fe(II)(Moumlssbauer visible)
bull Magnetic order and peak positions consistent with Fe(III) and goethite
bull No Fe(II)
bull ldquotwordquo Fe(II) sites
bull Spectra before Tc(IV) addition almost identical
20
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
2CP-C
Biogenic TcO2nH2O shows less Tc-Tc second neighbors and different long range order
Consistent with small size (2-3 nm) of biogenic precipitates
Tc-O
Tc-Tc
Tc-OTc-Tc
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
3
ERSDrsquos Long Term MeasureERSDrsquos Long Term Measure
ldquoBy 2015 provide sufficient scientific understanding to allow a
significant fraction of DOE sites to incorporate biological chemical
and physical processes into decision making for environmental
remediationrdquo
4
TechnetiumTechnetium
Fission product of 235Uranium
Exists in oxidation states +7 to -1
Highly mobile as Tc(VII) pertechnetate ion TcO4-
Biological activity high (sulphate analogue)
Microbial reduction to insoluble Tc(IV) (widespread)
235Uranium 99TechnetiumFission
T12 = 70 x 108 years
-emitter
21 x 105 years
-emitter
5
400 Ci of 99Tc was Released to the BC-Crib Area Where is it
400 Ci of 99Tc was Released to the BC-Crib Area Where is it
CRIBS
Trenches
The SAC model forecasts that a growing plume of 99Tc should exist beneath the BC-cribs
99Tc 238ULithology
[Tc(VII)]max = 18x106 pCiL 10-6 molL
6
Different Scales ~ Different IssuesDifferent Scales ~ Different IssuesMolecular Microscopic Macroscopic Field
bull Bonding environment and local structure
bull Fundamental mechanisms
bull Energetics and structural controls
bull Solvation effects
bull Mineral residence phase identity amp composition
bull Reaction networks and kinetics
bull Morphologic and surface issues
bull Fundamental process coupling
bull Rate processesChemical MicrobiologicMass transfer
bull Advection effectsbull 1-D scaling issuesbull Pore scale process
coupling
bull Physical heterogeneityWater
velocitiesdirectionsReactants
bull Multi-scale mass transferbull Mixing amp averagingbull Distributed propertiesbull Seasonal issues (temperature precipitation)
7
Biogeochemical Cycles of Tc and Fe are LinkedBiogeochemical Cycles of Tc and Fe are Linked
Experimentsmeld environmentalmicrobiology geochemistryand mineralogy
Toolsbull Microscopyspectroscopybull X-ray diffraction and
scatteringbull Genomicsmutagenesisbull Controlled culture
Issuesbull Productsbull Mechanismsbull Kinetic controlsbull Indirect and direct
biologic effects
Impactsbull Weatheringbull Anoxic environmentsbull Contaminant behaviorbull Energy cycling
Fe(II)Fe(III) phases
Fe(III) oxides
Metal reducing organisms
abiotic reductants
Metal oxidizing organisms
abiotic oxidants
8
Solubility of TcO2Solubility of TcO2
TcO(OH)deg2(aq)
16784 pCiL
1678 pCiL
168 pCiL
Concentration of Tc(IV) fixed by solubililty at reduction pointDowngradient adsorption of Tc(IV) complexes or another reaction essential to reach MCL (900 pCiL)Adsorption behavior of TcO(OH)2deg(aq) unknown
MCL900 pCiL
Tc(VII)O4- + 4H+ + 3e- = Tc(IV)O2nH2O(s) + (2-n)H2O Eo = 0748 V
Tc(VII)O4- + 3Fe2+ + (n+7)H2O = Tc(IV)O2middotnH2O(s) + 3Fe(OH)3(s)+ 5H+
9
Technetium Redox Couples in Relation to Others at Standard State and pH = 7
Technetium Redox Couples in Relation to Others at Standard State and pH = 7
-10 -5 0 5 10 15 20 pe
H2(g) H2O H2O O2(g)
NH4 ι NO3-
MnCO3 ι MnO2-
Fe(aq) ι Fe(OH3)2+
HS ι SO42-
Fe(aq) ι FeOOH2+
Hemes
Tc(IV)O2 ι Tc(VII)Tc(V)(VI) ι Tc(VII)
ldquoCH2Ordquo ι CO2(g)
reducing oxidizing
10
Complex Redox Chemistry of 3e- Transfer for Tc(VII)
Complex Redox Chemistry of 3e- Transfer for Tc(VII)
Tc(VII)O4- + e- Tc(VI)O4
2- Tc(V) Tc(IV) [Tc(IV)OOHaq Tc(IV)O2nH2O(s)]
gelatin
rapid
tetrahedral tetrahedral octahedral
rapid
very
11
Disproportionation Rate Key to 3e- TransferDisproportionation Rate Key to 3e- Transfer
Tc(VII) Tc(VI) Fe(II) H+ log QK Gr
(molL) (kJmol)
100E-06 100E-12 0001 100E-07 26 14846100E-06 100E-13 0001 100E-07 16 9136100E-06 100E-14 0001 100E-07 06 3426100E-06 100E-15 0001 100E-07 -04 -2284100E-06 100E-16 0001 100E-07 -14 -7994100E-06 100E-17 0001 100E-07 -24 -13704
Reaction rate and extent increases with1 Disproportionation rate2 Concentration and redox potential of Fe(II)3 pH
Fe2+ + 3H2O + Tc(VII)O4- = Fe(III)(OH)3 + 3H+ + TcO4
2- log K = 266
Tc(VII)Tc(V)
Tc(IV)
12
Coupled Processes and ModelsCoupled Processes and Models
Reaction NetworkNecessary component reactions to define time evolution and steady stateComponent identities and concentrationsReaction parameters and dependencies
Coupled ProcessReactionMicrobiologic transformation (biogeochemical)Advectiondiffusion (water reactantproduct flux)Microbiologic speciation (ecologic)
13
Coupled ReactionsCoupled Reactions
Reaction Type Components Parameters
Electron transfer A + B rarr C + D Kdq=kfkb [A] [B] [X] [Y] [Z]Tc(VII)+Fe(II) = TcO22H2O+Fe(OH)3
Surface complexation B + E rarr F Ŝ [SOH]Fe(II)+FeOOH = Fe(II)-FeOOH
Electron transfer A + F rarr GTc(VII)+3Fe(II)-FeOOH rarr Tc(IV)-3Fe(III)Ox+FeOOH
Biological electron A + H rarr C biomass growth substrateTransfer specificity and kinetics
Tc(VII)+H2 = TcO2nH2O e-acceptordonor nutrients
Biologic reductive DE + J rarr B
FeOOHFe(OH3) + lactate = Fe(II) + CO2 + acetate
Aqueous complexation C + I rarr KTcO2nH2O + CO3
2- = TcOCO3(aq)
гbio
bio
г
14
Utilize dissolved and solid phase oxidized metals as electron acceptors for respiration when O2 becomes deplete
Strongly influence the composition and redox state of groundwaters and the valence state of polyvalent metals and radionuclides
Metal Reducing BacteriaMetal Reducing Bacteria
Bacterial mediation of geochemical reaction
Oxidized
Reduced
Oxidized
Reduced
Bacteria
Microorganisms mediate kinetically inhibited but thermodynamically favorable reactions
E for metabolism and growth
15
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Reduction (+ Fe(II) or MRB)
Tc(VII)O4-(aq)
Oxidation (+ O2 or MOB)
biologic (MRB)
+homogeneous
Fe(II)aq
heterogeneousFe(II)OH Fe(II)aq
Tc(IV)
bull speciationbull physical location
Fe(III) oxide
TcO4
t= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
Tc(IV)t
= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
medium
very slow
very fastmedium
16
Experimental Setup and Anoxic ChamberExperimental Setup and Anoxic Chamber
Glove box ldquoairrdquo is totally scrubbed of O2 using an oxygen trap based on heterogeneous reduction of O2 in Fe(II)Fe(OH)3 suspensions
lt 05 ppm
spectroscopypreparation
drying chamber
filtrationchamber
mineral and mineral-microbe
suspensions
oxygentrap
solids and liquid sampling
mineral solids and heterogeneous
precipitates
17
Probing Heterogeneous E-transferProbing Heterogeneous E-transfer
X-ray Adsorption Spectroscopy
57Fe-MossbauerSpectroscopy Combined Techniques
bull Valence statebull Local structurebull Tc-Obull Tc-Tcbull Tc-Fe
bull Valence bull Magnetic propertiesbull Bonding environmentbull Symmetry
APS EMSL In addition ndash HRTEM (EMSL)
(looking at Tc) (looking at Fe)
hFe 56Fe Al
57Fe h
57Fe
SO-Fe(II)OH + Tc(VII) rarr Г =
Heterogeneous Reduction of Pertechnetate [Tc(VII)O4
-] by Surface Complexed Fe(II) at pH = 7Heterogeneous Reduction of Pertechnetate
[Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
Dis
so
lved
Tc(
VII
)
mo
l L
-1
Dis
so
lved
Fe(
II)
mm
ol
L-1
To
tal
Fe
(II)
m
mo
l L
-1
Time daysTime days
Time days
+ FeOOH + Tc(VII)+ FeOOH
+ Tc(VII)
-6 to -2 day Fe(II)aq
-2 to 0 day FeO-Fe(II)OH0 day + FeO-Fe(II)OH+Tc(IV)Fe(III)
Issuesbull Stoichiometry of Fe(III) and Tc(IV)bull Nature of Fe(III) and Tc(IV) phasesbull Location and association of Fe(II)bull Speciation effects on heterogeneous
oxidation
3FeO-Fe(II)OH + Tc(VII)O4- = 3FeO-Fe(III)OH2 [] + Tc(IV)O2H2O []
19
Products of Heterogeneous Tc(VII)O4- Reduction
by Fe(II) on Goethite Products of Heterogeneous Tc(VII)O4
- Reduction by Fe(II) on Goethite
k A-1 R Aring
What is Fe(III)Tc(IV)Ox Where is readsorbed Fe(II)
56Fe- goethite(Moumlssbauer invisible)
57Fe(II)(Moumlssbauer visible)
bull Magnetic order and peak positions consistent with Fe(III) and goethite
bull No Fe(II)
bull ldquotwordquo Fe(II) sites
bull Spectra before Tc(IV) addition almost identical
20
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
2CP-C
Biogenic TcO2nH2O shows less Tc-Tc second neighbors and different long range order
Consistent with small size (2-3 nm) of biogenic precipitates
Tc-O
Tc-Tc
Tc-OTc-Tc
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
4
TechnetiumTechnetium
Fission product of 235Uranium
Exists in oxidation states +7 to -1
Highly mobile as Tc(VII) pertechnetate ion TcO4-
Biological activity high (sulphate analogue)
Microbial reduction to insoluble Tc(IV) (widespread)
235Uranium 99TechnetiumFission
T12 = 70 x 108 years
-emitter
21 x 105 years
-emitter
5
400 Ci of 99Tc was Released to the BC-Crib Area Where is it
400 Ci of 99Tc was Released to the BC-Crib Area Where is it
CRIBS
Trenches
The SAC model forecasts that a growing plume of 99Tc should exist beneath the BC-cribs
99Tc 238ULithology
[Tc(VII)]max = 18x106 pCiL 10-6 molL
6
Different Scales ~ Different IssuesDifferent Scales ~ Different IssuesMolecular Microscopic Macroscopic Field
bull Bonding environment and local structure
bull Fundamental mechanisms
bull Energetics and structural controls
bull Solvation effects
bull Mineral residence phase identity amp composition
bull Reaction networks and kinetics
bull Morphologic and surface issues
bull Fundamental process coupling
bull Rate processesChemical MicrobiologicMass transfer
bull Advection effectsbull 1-D scaling issuesbull Pore scale process
coupling
bull Physical heterogeneityWater
velocitiesdirectionsReactants
bull Multi-scale mass transferbull Mixing amp averagingbull Distributed propertiesbull Seasonal issues (temperature precipitation)
7
Biogeochemical Cycles of Tc and Fe are LinkedBiogeochemical Cycles of Tc and Fe are Linked
Experimentsmeld environmentalmicrobiology geochemistryand mineralogy
Toolsbull Microscopyspectroscopybull X-ray diffraction and
scatteringbull Genomicsmutagenesisbull Controlled culture
Issuesbull Productsbull Mechanismsbull Kinetic controlsbull Indirect and direct
biologic effects
Impactsbull Weatheringbull Anoxic environmentsbull Contaminant behaviorbull Energy cycling
Fe(II)Fe(III) phases
Fe(III) oxides
Metal reducing organisms
abiotic reductants
Metal oxidizing organisms
abiotic oxidants
8
Solubility of TcO2Solubility of TcO2
TcO(OH)deg2(aq)
16784 pCiL
1678 pCiL
168 pCiL
Concentration of Tc(IV) fixed by solubililty at reduction pointDowngradient adsorption of Tc(IV) complexes or another reaction essential to reach MCL (900 pCiL)Adsorption behavior of TcO(OH)2deg(aq) unknown
MCL900 pCiL
Tc(VII)O4- + 4H+ + 3e- = Tc(IV)O2nH2O(s) + (2-n)H2O Eo = 0748 V
Tc(VII)O4- + 3Fe2+ + (n+7)H2O = Tc(IV)O2middotnH2O(s) + 3Fe(OH)3(s)+ 5H+
9
Technetium Redox Couples in Relation to Others at Standard State and pH = 7
Technetium Redox Couples in Relation to Others at Standard State and pH = 7
-10 -5 0 5 10 15 20 pe
H2(g) H2O H2O O2(g)
NH4 ι NO3-
MnCO3 ι MnO2-
Fe(aq) ι Fe(OH3)2+
HS ι SO42-
Fe(aq) ι FeOOH2+
Hemes
Tc(IV)O2 ι Tc(VII)Tc(V)(VI) ι Tc(VII)
ldquoCH2Ordquo ι CO2(g)
reducing oxidizing
10
Complex Redox Chemistry of 3e- Transfer for Tc(VII)
Complex Redox Chemistry of 3e- Transfer for Tc(VII)
Tc(VII)O4- + e- Tc(VI)O4
2- Tc(V) Tc(IV) [Tc(IV)OOHaq Tc(IV)O2nH2O(s)]
gelatin
rapid
tetrahedral tetrahedral octahedral
rapid
very
11
Disproportionation Rate Key to 3e- TransferDisproportionation Rate Key to 3e- Transfer
Tc(VII) Tc(VI) Fe(II) H+ log QK Gr
(molL) (kJmol)
100E-06 100E-12 0001 100E-07 26 14846100E-06 100E-13 0001 100E-07 16 9136100E-06 100E-14 0001 100E-07 06 3426100E-06 100E-15 0001 100E-07 -04 -2284100E-06 100E-16 0001 100E-07 -14 -7994100E-06 100E-17 0001 100E-07 -24 -13704
Reaction rate and extent increases with1 Disproportionation rate2 Concentration and redox potential of Fe(II)3 pH
Fe2+ + 3H2O + Tc(VII)O4- = Fe(III)(OH)3 + 3H+ + TcO4
2- log K = 266
Tc(VII)Tc(V)
Tc(IV)
12
Coupled Processes and ModelsCoupled Processes and Models
Reaction NetworkNecessary component reactions to define time evolution and steady stateComponent identities and concentrationsReaction parameters and dependencies
Coupled ProcessReactionMicrobiologic transformation (biogeochemical)Advectiondiffusion (water reactantproduct flux)Microbiologic speciation (ecologic)
13
Coupled ReactionsCoupled Reactions
Reaction Type Components Parameters
Electron transfer A + B rarr C + D Kdq=kfkb [A] [B] [X] [Y] [Z]Tc(VII)+Fe(II) = TcO22H2O+Fe(OH)3
Surface complexation B + E rarr F Ŝ [SOH]Fe(II)+FeOOH = Fe(II)-FeOOH
Electron transfer A + F rarr GTc(VII)+3Fe(II)-FeOOH rarr Tc(IV)-3Fe(III)Ox+FeOOH
Biological electron A + H rarr C biomass growth substrateTransfer specificity and kinetics
Tc(VII)+H2 = TcO2nH2O e-acceptordonor nutrients
Biologic reductive DE + J rarr B
FeOOHFe(OH3) + lactate = Fe(II) + CO2 + acetate
Aqueous complexation C + I rarr KTcO2nH2O + CO3
2- = TcOCO3(aq)
гbio
bio
г
14
Utilize dissolved and solid phase oxidized metals as electron acceptors for respiration when O2 becomes deplete
Strongly influence the composition and redox state of groundwaters and the valence state of polyvalent metals and radionuclides
Metal Reducing BacteriaMetal Reducing Bacteria
Bacterial mediation of geochemical reaction
Oxidized
Reduced
Oxidized
Reduced
Bacteria
Microorganisms mediate kinetically inhibited but thermodynamically favorable reactions
E for metabolism and growth
15
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Reduction (+ Fe(II) or MRB)
Tc(VII)O4-(aq)
Oxidation (+ O2 or MOB)
biologic (MRB)
+homogeneous
Fe(II)aq
heterogeneousFe(II)OH Fe(II)aq
Tc(IV)
bull speciationbull physical location
Fe(III) oxide
TcO4
t= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
Tc(IV)t
= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
medium
very slow
very fastmedium
16
Experimental Setup and Anoxic ChamberExperimental Setup and Anoxic Chamber
Glove box ldquoairrdquo is totally scrubbed of O2 using an oxygen trap based on heterogeneous reduction of O2 in Fe(II)Fe(OH)3 suspensions
lt 05 ppm
spectroscopypreparation
drying chamber
filtrationchamber
mineral and mineral-microbe
suspensions
oxygentrap
solids and liquid sampling
mineral solids and heterogeneous
precipitates
17
Probing Heterogeneous E-transferProbing Heterogeneous E-transfer
X-ray Adsorption Spectroscopy
57Fe-MossbauerSpectroscopy Combined Techniques
bull Valence statebull Local structurebull Tc-Obull Tc-Tcbull Tc-Fe
bull Valence bull Magnetic propertiesbull Bonding environmentbull Symmetry
APS EMSL In addition ndash HRTEM (EMSL)
(looking at Tc) (looking at Fe)
hFe 56Fe Al
57Fe h
57Fe
SO-Fe(II)OH + Tc(VII) rarr Г =
Heterogeneous Reduction of Pertechnetate [Tc(VII)O4
-] by Surface Complexed Fe(II) at pH = 7Heterogeneous Reduction of Pertechnetate
[Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
Dis
so
lved
Tc(
VII
)
mo
l L
-1
Dis
so
lved
Fe(
II)
mm
ol
L-1
To
tal
Fe
(II)
m
mo
l L
-1
Time daysTime days
Time days
+ FeOOH + Tc(VII)+ FeOOH
+ Tc(VII)
-6 to -2 day Fe(II)aq
-2 to 0 day FeO-Fe(II)OH0 day + FeO-Fe(II)OH+Tc(IV)Fe(III)
Issuesbull Stoichiometry of Fe(III) and Tc(IV)bull Nature of Fe(III) and Tc(IV) phasesbull Location and association of Fe(II)bull Speciation effects on heterogeneous
oxidation
3FeO-Fe(II)OH + Tc(VII)O4- = 3FeO-Fe(III)OH2 [] + Tc(IV)O2H2O []
19
Products of Heterogeneous Tc(VII)O4- Reduction
by Fe(II) on Goethite Products of Heterogeneous Tc(VII)O4
- Reduction by Fe(II) on Goethite
k A-1 R Aring
What is Fe(III)Tc(IV)Ox Where is readsorbed Fe(II)
56Fe- goethite(Moumlssbauer invisible)
57Fe(II)(Moumlssbauer visible)
bull Magnetic order and peak positions consistent with Fe(III) and goethite
bull No Fe(II)
bull ldquotwordquo Fe(II) sites
bull Spectra before Tc(IV) addition almost identical
20
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
2CP-C
Biogenic TcO2nH2O shows less Tc-Tc second neighbors and different long range order
Consistent with small size (2-3 nm) of biogenic precipitates
Tc-O
Tc-Tc
Tc-OTc-Tc
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
5
400 Ci of 99Tc was Released to the BC-Crib Area Where is it
400 Ci of 99Tc was Released to the BC-Crib Area Where is it
CRIBS
Trenches
The SAC model forecasts that a growing plume of 99Tc should exist beneath the BC-cribs
99Tc 238ULithology
[Tc(VII)]max = 18x106 pCiL 10-6 molL
6
Different Scales ~ Different IssuesDifferent Scales ~ Different IssuesMolecular Microscopic Macroscopic Field
bull Bonding environment and local structure
bull Fundamental mechanisms
bull Energetics and structural controls
bull Solvation effects
bull Mineral residence phase identity amp composition
bull Reaction networks and kinetics
bull Morphologic and surface issues
bull Fundamental process coupling
bull Rate processesChemical MicrobiologicMass transfer
bull Advection effectsbull 1-D scaling issuesbull Pore scale process
coupling
bull Physical heterogeneityWater
velocitiesdirectionsReactants
bull Multi-scale mass transferbull Mixing amp averagingbull Distributed propertiesbull Seasonal issues (temperature precipitation)
7
Biogeochemical Cycles of Tc and Fe are LinkedBiogeochemical Cycles of Tc and Fe are Linked
Experimentsmeld environmentalmicrobiology geochemistryand mineralogy
Toolsbull Microscopyspectroscopybull X-ray diffraction and
scatteringbull Genomicsmutagenesisbull Controlled culture
Issuesbull Productsbull Mechanismsbull Kinetic controlsbull Indirect and direct
biologic effects
Impactsbull Weatheringbull Anoxic environmentsbull Contaminant behaviorbull Energy cycling
Fe(II)Fe(III) phases
Fe(III) oxides
Metal reducing organisms
abiotic reductants
Metal oxidizing organisms
abiotic oxidants
8
Solubility of TcO2Solubility of TcO2
TcO(OH)deg2(aq)
16784 pCiL
1678 pCiL
168 pCiL
Concentration of Tc(IV) fixed by solubililty at reduction pointDowngradient adsorption of Tc(IV) complexes or another reaction essential to reach MCL (900 pCiL)Adsorption behavior of TcO(OH)2deg(aq) unknown
MCL900 pCiL
Tc(VII)O4- + 4H+ + 3e- = Tc(IV)O2nH2O(s) + (2-n)H2O Eo = 0748 V
Tc(VII)O4- + 3Fe2+ + (n+7)H2O = Tc(IV)O2middotnH2O(s) + 3Fe(OH)3(s)+ 5H+
9
Technetium Redox Couples in Relation to Others at Standard State and pH = 7
Technetium Redox Couples in Relation to Others at Standard State and pH = 7
-10 -5 0 5 10 15 20 pe
H2(g) H2O H2O O2(g)
NH4 ι NO3-
MnCO3 ι MnO2-
Fe(aq) ι Fe(OH3)2+
HS ι SO42-
Fe(aq) ι FeOOH2+
Hemes
Tc(IV)O2 ι Tc(VII)Tc(V)(VI) ι Tc(VII)
ldquoCH2Ordquo ι CO2(g)
reducing oxidizing
10
Complex Redox Chemistry of 3e- Transfer for Tc(VII)
Complex Redox Chemistry of 3e- Transfer for Tc(VII)
Tc(VII)O4- + e- Tc(VI)O4
2- Tc(V) Tc(IV) [Tc(IV)OOHaq Tc(IV)O2nH2O(s)]
gelatin
rapid
tetrahedral tetrahedral octahedral
rapid
very
11
Disproportionation Rate Key to 3e- TransferDisproportionation Rate Key to 3e- Transfer
Tc(VII) Tc(VI) Fe(II) H+ log QK Gr
(molL) (kJmol)
100E-06 100E-12 0001 100E-07 26 14846100E-06 100E-13 0001 100E-07 16 9136100E-06 100E-14 0001 100E-07 06 3426100E-06 100E-15 0001 100E-07 -04 -2284100E-06 100E-16 0001 100E-07 -14 -7994100E-06 100E-17 0001 100E-07 -24 -13704
Reaction rate and extent increases with1 Disproportionation rate2 Concentration and redox potential of Fe(II)3 pH
Fe2+ + 3H2O + Tc(VII)O4- = Fe(III)(OH)3 + 3H+ + TcO4
2- log K = 266
Tc(VII)Tc(V)
Tc(IV)
12
Coupled Processes and ModelsCoupled Processes and Models
Reaction NetworkNecessary component reactions to define time evolution and steady stateComponent identities and concentrationsReaction parameters and dependencies
Coupled ProcessReactionMicrobiologic transformation (biogeochemical)Advectiondiffusion (water reactantproduct flux)Microbiologic speciation (ecologic)
13
Coupled ReactionsCoupled Reactions
Reaction Type Components Parameters
Electron transfer A + B rarr C + D Kdq=kfkb [A] [B] [X] [Y] [Z]Tc(VII)+Fe(II) = TcO22H2O+Fe(OH)3
Surface complexation B + E rarr F Ŝ [SOH]Fe(II)+FeOOH = Fe(II)-FeOOH
Electron transfer A + F rarr GTc(VII)+3Fe(II)-FeOOH rarr Tc(IV)-3Fe(III)Ox+FeOOH
Biological electron A + H rarr C biomass growth substrateTransfer specificity and kinetics
Tc(VII)+H2 = TcO2nH2O e-acceptordonor nutrients
Biologic reductive DE + J rarr B
FeOOHFe(OH3) + lactate = Fe(II) + CO2 + acetate
Aqueous complexation C + I rarr KTcO2nH2O + CO3
2- = TcOCO3(aq)
гbio
bio
г
14
Utilize dissolved and solid phase oxidized metals as electron acceptors for respiration when O2 becomes deplete
Strongly influence the composition and redox state of groundwaters and the valence state of polyvalent metals and radionuclides
Metal Reducing BacteriaMetal Reducing Bacteria
Bacterial mediation of geochemical reaction
Oxidized
Reduced
Oxidized
Reduced
Bacteria
Microorganisms mediate kinetically inhibited but thermodynamically favorable reactions
E for metabolism and growth
15
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Reduction (+ Fe(II) or MRB)
Tc(VII)O4-(aq)
Oxidation (+ O2 or MOB)
biologic (MRB)
+homogeneous
Fe(II)aq
heterogeneousFe(II)OH Fe(II)aq
Tc(IV)
bull speciationbull physical location
Fe(III) oxide
TcO4
t= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
Tc(IV)t
= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
medium
very slow
very fastmedium
16
Experimental Setup and Anoxic ChamberExperimental Setup and Anoxic Chamber
Glove box ldquoairrdquo is totally scrubbed of O2 using an oxygen trap based on heterogeneous reduction of O2 in Fe(II)Fe(OH)3 suspensions
lt 05 ppm
spectroscopypreparation
drying chamber
filtrationchamber
mineral and mineral-microbe
suspensions
oxygentrap
solids and liquid sampling
mineral solids and heterogeneous
precipitates
17
Probing Heterogeneous E-transferProbing Heterogeneous E-transfer
X-ray Adsorption Spectroscopy
57Fe-MossbauerSpectroscopy Combined Techniques
bull Valence statebull Local structurebull Tc-Obull Tc-Tcbull Tc-Fe
bull Valence bull Magnetic propertiesbull Bonding environmentbull Symmetry
APS EMSL In addition ndash HRTEM (EMSL)
(looking at Tc) (looking at Fe)
hFe 56Fe Al
57Fe h
57Fe
SO-Fe(II)OH + Tc(VII) rarr Г =
Heterogeneous Reduction of Pertechnetate [Tc(VII)O4
-] by Surface Complexed Fe(II) at pH = 7Heterogeneous Reduction of Pertechnetate
[Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
Dis
so
lved
Tc(
VII
)
mo
l L
-1
Dis
so
lved
Fe(
II)
mm
ol
L-1
To
tal
Fe
(II)
m
mo
l L
-1
Time daysTime days
Time days
+ FeOOH + Tc(VII)+ FeOOH
+ Tc(VII)
-6 to -2 day Fe(II)aq
-2 to 0 day FeO-Fe(II)OH0 day + FeO-Fe(II)OH+Tc(IV)Fe(III)
Issuesbull Stoichiometry of Fe(III) and Tc(IV)bull Nature of Fe(III) and Tc(IV) phasesbull Location and association of Fe(II)bull Speciation effects on heterogeneous
oxidation
3FeO-Fe(II)OH + Tc(VII)O4- = 3FeO-Fe(III)OH2 [] + Tc(IV)O2H2O []
19
Products of Heterogeneous Tc(VII)O4- Reduction
by Fe(II) on Goethite Products of Heterogeneous Tc(VII)O4
- Reduction by Fe(II) on Goethite
k A-1 R Aring
What is Fe(III)Tc(IV)Ox Where is readsorbed Fe(II)
56Fe- goethite(Moumlssbauer invisible)
57Fe(II)(Moumlssbauer visible)
bull Magnetic order and peak positions consistent with Fe(III) and goethite
bull No Fe(II)
bull ldquotwordquo Fe(II) sites
bull Spectra before Tc(IV) addition almost identical
20
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
2CP-C
Biogenic TcO2nH2O shows less Tc-Tc second neighbors and different long range order
Consistent with small size (2-3 nm) of biogenic precipitates
Tc-O
Tc-Tc
Tc-OTc-Tc
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
6
Different Scales ~ Different IssuesDifferent Scales ~ Different IssuesMolecular Microscopic Macroscopic Field
bull Bonding environment and local structure
bull Fundamental mechanisms
bull Energetics and structural controls
bull Solvation effects
bull Mineral residence phase identity amp composition
bull Reaction networks and kinetics
bull Morphologic and surface issues
bull Fundamental process coupling
bull Rate processesChemical MicrobiologicMass transfer
bull Advection effectsbull 1-D scaling issuesbull Pore scale process
coupling
bull Physical heterogeneityWater
velocitiesdirectionsReactants
bull Multi-scale mass transferbull Mixing amp averagingbull Distributed propertiesbull Seasonal issues (temperature precipitation)
7
Biogeochemical Cycles of Tc and Fe are LinkedBiogeochemical Cycles of Tc and Fe are Linked
Experimentsmeld environmentalmicrobiology geochemistryand mineralogy
Toolsbull Microscopyspectroscopybull X-ray diffraction and
scatteringbull Genomicsmutagenesisbull Controlled culture
Issuesbull Productsbull Mechanismsbull Kinetic controlsbull Indirect and direct
biologic effects
Impactsbull Weatheringbull Anoxic environmentsbull Contaminant behaviorbull Energy cycling
Fe(II)Fe(III) phases
Fe(III) oxides
Metal reducing organisms
abiotic reductants
Metal oxidizing organisms
abiotic oxidants
8
Solubility of TcO2Solubility of TcO2
TcO(OH)deg2(aq)
16784 pCiL
1678 pCiL
168 pCiL
Concentration of Tc(IV) fixed by solubililty at reduction pointDowngradient adsorption of Tc(IV) complexes or another reaction essential to reach MCL (900 pCiL)Adsorption behavior of TcO(OH)2deg(aq) unknown
MCL900 pCiL
Tc(VII)O4- + 4H+ + 3e- = Tc(IV)O2nH2O(s) + (2-n)H2O Eo = 0748 V
Tc(VII)O4- + 3Fe2+ + (n+7)H2O = Tc(IV)O2middotnH2O(s) + 3Fe(OH)3(s)+ 5H+
9
Technetium Redox Couples in Relation to Others at Standard State and pH = 7
Technetium Redox Couples in Relation to Others at Standard State and pH = 7
-10 -5 0 5 10 15 20 pe
H2(g) H2O H2O O2(g)
NH4 ι NO3-
MnCO3 ι MnO2-
Fe(aq) ι Fe(OH3)2+
HS ι SO42-
Fe(aq) ι FeOOH2+
Hemes
Tc(IV)O2 ι Tc(VII)Tc(V)(VI) ι Tc(VII)
ldquoCH2Ordquo ι CO2(g)
reducing oxidizing
10
Complex Redox Chemistry of 3e- Transfer for Tc(VII)
Complex Redox Chemistry of 3e- Transfer for Tc(VII)
Tc(VII)O4- + e- Tc(VI)O4
2- Tc(V) Tc(IV) [Tc(IV)OOHaq Tc(IV)O2nH2O(s)]
gelatin
rapid
tetrahedral tetrahedral octahedral
rapid
very
11
Disproportionation Rate Key to 3e- TransferDisproportionation Rate Key to 3e- Transfer
Tc(VII) Tc(VI) Fe(II) H+ log QK Gr
(molL) (kJmol)
100E-06 100E-12 0001 100E-07 26 14846100E-06 100E-13 0001 100E-07 16 9136100E-06 100E-14 0001 100E-07 06 3426100E-06 100E-15 0001 100E-07 -04 -2284100E-06 100E-16 0001 100E-07 -14 -7994100E-06 100E-17 0001 100E-07 -24 -13704
Reaction rate and extent increases with1 Disproportionation rate2 Concentration and redox potential of Fe(II)3 pH
Fe2+ + 3H2O + Tc(VII)O4- = Fe(III)(OH)3 + 3H+ + TcO4
2- log K = 266
Tc(VII)Tc(V)
Tc(IV)
12
Coupled Processes and ModelsCoupled Processes and Models
Reaction NetworkNecessary component reactions to define time evolution and steady stateComponent identities and concentrationsReaction parameters and dependencies
Coupled ProcessReactionMicrobiologic transformation (biogeochemical)Advectiondiffusion (water reactantproduct flux)Microbiologic speciation (ecologic)
13
Coupled ReactionsCoupled Reactions
Reaction Type Components Parameters
Electron transfer A + B rarr C + D Kdq=kfkb [A] [B] [X] [Y] [Z]Tc(VII)+Fe(II) = TcO22H2O+Fe(OH)3
Surface complexation B + E rarr F Ŝ [SOH]Fe(II)+FeOOH = Fe(II)-FeOOH
Electron transfer A + F rarr GTc(VII)+3Fe(II)-FeOOH rarr Tc(IV)-3Fe(III)Ox+FeOOH
Biological electron A + H rarr C biomass growth substrateTransfer specificity and kinetics
Tc(VII)+H2 = TcO2nH2O e-acceptordonor nutrients
Biologic reductive DE + J rarr B
FeOOHFe(OH3) + lactate = Fe(II) + CO2 + acetate
Aqueous complexation C + I rarr KTcO2nH2O + CO3
2- = TcOCO3(aq)
гbio
bio
г
14
Utilize dissolved and solid phase oxidized metals as electron acceptors for respiration when O2 becomes deplete
Strongly influence the composition and redox state of groundwaters and the valence state of polyvalent metals and radionuclides
Metal Reducing BacteriaMetal Reducing Bacteria
Bacterial mediation of geochemical reaction
Oxidized
Reduced
Oxidized
Reduced
Bacteria
Microorganisms mediate kinetically inhibited but thermodynamically favorable reactions
E for metabolism and growth
15
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Reduction (+ Fe(II) or MRB)
Tc(VII)O4-(aq)
Oxidation (+ O2 or MOB)
biologic (MRB)
+homogeneous
Fe(II)aq
heterogeneousFe(II)OH Fe(II)aq
Tc(IV)
bull speciationbull physical location
Fe(III) oxide
TcO4
t= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
Tc(IV)t
= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
medium
very slow
very fastmedium
16
Experimental Setup and Anoxic ChamberExperimental Setup and Anoxic Chamber
Glove box ldquoairrdquo is totally scrubbed of O2 using an oxygen trap based on heterogeneous reduction of O2 in Fe(II)Fe(OH)3 suspensions
lt 05 ppm
spectroscopypreparation
drying chamber
filtrationchamber
mineral and mineral-microbe
suspensions
oxygentrap
solids and liquid sampling
mineral solids and heterogeneous
precipitates
17
Probing Heterogeneous E-transferProbing Heterogeneous E-transfer
X-ray Adsorption Spectroscopy
57Fe-MossbauerSpectroscopy Combined Techniques
bull Valence statebull Local structurebull Tc-Obull Tc-Tcbull Tc-Fe
bull Valence bull Magnetic propertiesbull Bonding environmentbull Symmetry
APS EMSL In addition ndash HRTEM (EMSL)
(looking at Tc) (looking at Fe)
hFe 56Fe Al
57Fe h
57Fe
SO-Fe(II)OH + Tc(VII) rarr Г =
Heterogeneous Reduction of Pertechnetate [Tc(VII)O4
-] by Surface Complexed Fe(II) at pH = 7Heterogeneous Reduction of Pertechnetate
[Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
Dis
so
lved
Tc(
VII
)
mo
l L
-1
Dis
so
lved
Fe(
II)
mm
ol
L-1
To
tal
Fe
(II)
m
mo
l L
-1
Time daysTime days
Time days
+ FeOOH + Tc(VII)+ FeOOH
+ Tc(VII)
-6 to -2 day Fe(II)aq
-2 to 0 day FeO-Fe(II)OH0 day + FeO-Fe(II)OH+Tc(IV)Fe(III)
Issuesbull Stoichiometry of Fe(III) and Tc(IV)bull Nature of Fe(III) and Tc(IV) phasesbull Location and association of Fe(II)bull Speciation effects on heterogeneous
oxidation
3FeO-Fe(II)OH + Tc(VII)O4- = 3FeO-Fe(III)OH2 [] + Tc(IV)O2H2O []
19
Products of Heterogeneous Tc(VII)O4- Reduction
by Fe(II) on Goethite Products of Heterogeneous Tc(VII)O4
- Reduction by Fe(II) on Goethite
k A-1 R Aring
What is Fe(III)Tc(IV)Ox Where is readsorbed Fe(II)
56Fe- goethite(Moumlssbauer invisible)
57Fe(II)(Moumlssbauer visible)
bull Magnetic order and peak positions consistent with Fe(III) and goethite
bull No Fe(II)
bull ldquotwordquo Fe(II) sites
bull Spectra before Tc(IV) addition almost identical
20
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
2CP-C
Biogenic TcO2nH2O shows less Tc-Tc second neighbors and different long range order
Consistent with small size (2-3 nm) of biogenic precipitates
Tc-O
Tc-Tc
Tc-OTc-Tc
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
7
Biogeochemical Cycles of Tc and Fe are LinkedBiogeochemical Cycles of Tc and Fe are Linked
Experimentsmeld environmentalmicrobiology geochemistryand mineralogy
Toolsbull Microscopyspectroscopybull X-ray diffraction and
scatteringbull Genomicsmutagenesisbull Controlled culture
Issuesbull Productsbull Mechanismsbull Kinetic controlsbull Indirect and direct
biologic effects
Impactsbull Weatheringbull Anoxic environmentsbull Contaminant behaviorbull Energy cycling
Fe(II)Fe(III) phases
Fe(III) oxides
Metal reducing organisms
abiotic reductants
Metal oxidizing organisms
abiotic oxidants
8
Solubility of TcO2Solubility of TcO2
TcO(OH)deg2(aq)
16784 pCiL
1678 pCiL
168 pCiL
Concentration of Tc(IV) fixed by solubililty at reduction pointDowngradient adsorption of Tc(IV) complexes or another reaction essential to reach MCL (900 pCiL)Adsorption behavior of TcO(OH)2deg(aq) unknown
MCL900 pCiL
Tc(VII)O4- + 4H+ + 3e- = Tc(IV)O2nH2O(s) + (2-n)H2O Eo = 0748 V
Tc(VII)O4- + 3Fe2+ + (n+7)H2O = Tc(IV)O2middotnH2O(s) + 3Fe(OH)3(s)+ 5H+
9
Technetium Redox Couples in Relation to Others at Standard State and pH = 7
Technetium Redox Couples in Relation to Others at Standard State and pH = 7
-10 -5 0 5 10 15 20 pe
H2(g) H2O H2O O2(g)
NH4 ι NO3-
MnCO3 ι MnO2-
Fe(aq) ι Fe(OH3)2+
HS ι SO42-
Fe(aq) ι FeOOH2+
Hemes
Tc(IV)O2 ι Tc(VII)Tc(V)(VI) ι Tc(VII)
ldquoCH2Ordquo ι CO2(g)
reducing oxidizing
10
Complex Redox Chemistry of 3e- Transfer for Tc(VII)
Complex Redox Chemistry of 3e- Transfer for Tc(VII)
Tc(VII)O4- + e- Tc(VI)O4
2- Tc(V) Tc(IV) [Tc(IV)OOHaq Tc(IV)O2nH2O(s)]
gelatin
rapid
tetrahedral tetrahedral octahedral
rapid
very
11
Disproportionation Rate Key to 3e- TransferDisproportionation Rate Key to 3e- Transfer
Tc(VII) Tc(VI) Fe(II) H+ log QK Gr
(molL) (kJmol)
100E-06 100E-12 0001 100E-07 26 14846100E-06 100E-13 0001 100E-07 16 9136100E-06 100E-14 0001 100E-07 06 3426100E-06 100E-15 0001 100E-07 -04 -2284100E-06 100E-16 0001 100E-07 -14 -7994100E-06 100E-17 0001 100E-07 -24 -13704
Reaction rate and extent increases with1 Disproportionation rate2 Concentration and redox potential of Fe(II)3 pH
Fe2+ + 3H2O + Tc(VII)O4- = Fe(III)(OH)3 + 3H+ + TcO4
2- log K = 266
Tc(VII)Tc(V)
Tc(IV)
12
Coupled Processes and ModelsCoupled Processes and Models
Reaction NetworkNecessary component reactions to define time evolution and steady stateComponent identities and concentrationsReaction parameters and dependencies
Coupled ProcessReactionMicrobiologic transformation (biogeochemical)Advectiondiffusion (water reactantproduct flux)Microbiologic speciation (ecologic)
13
Coupled ReactionsCoupled Reactions
Reaction Type Components Parameters
Electron transfer A + B rarr C + D Kdq=kfkb [A] [B] [X] [Y] [Z]Tc(VII)+Fe(II) = TcO22H2O+Fe(OH)3
Surface complexation B + E rarr F Ŝ [SOH]Fe(II)+FeOOH = Fe(II)-FeOOH
Electron transfer A + F rarr GTc(VII)+3Fe(II)-FeOOH rarr Tc(IV)-3Fe(III)Ox+FeOOH
Biological electron A + H rarr C biomass growth substrateTransfer specificity and kinetics
Tc(VII)+H2 = TcO2nH2O e-acceptordonor nutrients
Biologic reductive DE + J rarr B
FeOOHFe(OH3) + lactate = Fe(II) + CO2 + acetate
Aqueous complexation C + I rarr KTcO2nH2O + CO3
2- = TcOCO3(aq)
гbio
bio
г
14
Utilize dissolved and solid phase oxidized metals as electron acceptors for respiration when O2 becomes deplete
Strongly influence the composition and redox state of groundwaters and the valence state of polyvalent metals and radionuclides
Metal Reducing BacteriaMetal Reducing Bacteria
Bacterial mediation of geochemical reaction
Oxidized
Reduced
Oxidized
Reduced
Bacteria
Microorganisms mediate kinetically inhibited but thermodynamically favorable reactions
E for metabolism and growth
15
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Reduction (+ Fe(II) or MRB)
Tc(VII)O4-(aq)
Oxidation (+ O2 or MOB)
biologic (MRB)
+homogeneous
Fe(II)aq
heterogeneousFe(II)OH Fe(II)aq
Tc(IV)
bull speciationbull physical location
Fe(III) oxide
TcO4
t= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
Tc(IV)t
= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
medium
very slow
very fastmedium
16
Experimental Setup and Anoxic ChamberExperimental Setup and Anoxic Chamber
Glove box ldquoairrdquo is totally scrubbed of O2 using an oxygen trap based on heterogeneous reduction of O2 in Fe(II)Fe(OH)3 suspensions
lt 05 ppm
spectroscopypreparation
drying chamber
filtrationchamber
mineral and mineral-microbe
suspensions
oxygentrap
solids and liquid sampling
mineral solids and heterogeneous
precipitates
17
Probing Heterogeneous E-transferProbing Heterogeneous E-transfer
X-ray Adsorption Spectroscopy
57Fe-MossbauerSpectroscopy Combined Techniques
bull Valence statebull Local structurebull Tc-Obull Tc-Tcbull Tc-Fe
bull Valence bull Magnetic propertiesbull Bonding environmentbull Symmetry
APS EMSL In addition ndash HRTEM (EMSL)
(looking at Tc) (looking at Fe)
hFe 56Fe Al
57Fe h
57Fe
SO-Fe(II)OH + Tc(VII) rarr Г =
Heterogeneous Reduction of Pertechnetate [Tc(VII)O4
-] by Surface Complexed Fe(II) at pH = 7Heterogeneous Reduction of Pertechnetate
[Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
Dis
so
lved
Tc(
VII
)
mo
l L
-1
Dis
so
lved
Fe(
II)
mm
ol
L-1
To
tal
Fe
(II)
m
mo
l L
-1
Time daysTime days
Time days
+ FeOOH + Tc(VII)+ FeOOH
+ Tc(VII)
-6 to -2 day Fe(II)aq
-2 to 0 day FeO-Fe(II)OH0 day + FeO-Fe(II)OH+Tc(IV)Fe(III)
Issuesbull Stoichiometry of Fe(III) and Tc(IV)bull Nature of Fe(III) and Tc(IV) phasesbull Location and association of Fe(II)bull Speciation effects on heterogeneous
oxidation
3FeO-Fe(II)OH + Tc(VII)O4- = 3FeO-Fe(III)OH2 [] + Tc(IV)O2H2O []
19
Products of Heterogeneous Tc(VII)O4- Reduction
by Fe(II) on Goethite Products of Heterogeneous Tc(VII)O4
- Reduction by Fe(II) on Goethite
k A-1 R Aring
What is Fe(III)Tc(IV)Ox Where is readsorbed Fe(II)
56Fe- goethite(Moumlssbauer invisible)
57Fe(II)(Moumlssbauer visible)
bull Magnetic order and peak positions consistent with Fe(III) and goethite
bull No Fe(II)
bull ldquotwordquo Fe(II) sites
bull Spectra before Tc(IV) addition almost identical
20
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
2CP-C
Biogenic TcO2nH2O shows less Tc-Tc second neighbors and different long range order
Consistent with small size (2-3 nm) of biogenic precipitates
Tc-O
Tc-Tc
Tc-OTc-Tc
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
8
Solubility of TcO2Solubility of TcO2
TcO(OH)deg2(aq)
16784 pCiL
1678 pCiL
168 pCiL
Concentration of Tc(IV) fixed by solubililty at reduction pointDowngradient adsorption of Tc(IV) complexes or another reaction essential to reach MCL (900 pCiL)Adsorption behavior of TcO(OH)2deg(aq) unknown
MCL900 pCiL
Tc(VII)O4- + 4H+ + 3e- = Tc(IV)O2nH2O(s) + (2-n)H2O Eo = 0748 V
Tc(VII)O4- + 3Fe2+ + (n+7)H2O = Tc(IV)O2middotnH2O(s) + 3Fe(OH)3(s)+ 5H+
9
Technetium Redox Couples in Relation to Others at Standard State and pH = 7
Technetium Redox Couples in Relation to Others at Standard State and pH = 7
-10 -5 0 5 10 15 20 pe
H2(g) H2O H2O O2(g)
NH4 ι NO3-
MnCO3 ι MnO2-
Fe(aq) ι Fe(OH3)2+
HS ι SO42-
Fe(aq) ι FeOOH2+
Hemes
Tc(IV)O2 ι Tc(VII)Tc(V)(VI) ι Tc(VII)
ldquoCH2Ordquo ι CO2(g)
reducing oxidizing
10
Complex Redox Chemistry of 3e- Transfer for Tc(VII)
Complex Redox Chemistry of 3e- Transfer for Tc(VII)
Tc(VII)O4- + e- Tc(VI)O4
2- Tc(V) Tc(IV) [Tc(IV)OOHaq Tc(IV)O2nH2O(s)]
gelatin
rapid
tetrahedral tetrahedral octahedral
rapid
very
11
Disproportionation Rate Key to 3e- TransferDisproportionation Rate Key to 3e- Transfer
Tc(VII) Tc(VI) Fe(II) H+ log QK Gr
(molL) (kJmol)
100E-06 100E-12 0001 100E-07 26 14846100E-06 100E-13 0001 100E-07 16 9136100E-06 100E-14 0001 100E-07 06 3426100E-06 100E-15 0001 100E-07 -04 -2284100E-06 100E-16 0001 100E-07 -14 -7994100E-06 100E-17 0001 100E-07 -24 -13704
Reaction rate and extent increases with1 Disproportionation rate2 Concentration and redox potential of Fe(II)3 pH
Fe2+ + 3H2O + Tc(VII)O4- = Fe(III)(OH)3 + 3H+ + TcO4
2- log K = 266
Tc(VII)Tc(V)
Tc(IV)
12
Coupled Processes and ModelsCoupled Processes and Models
Reaction NetworkNecessary component reactions to define time evolution and steady stateComponent identities and concentrationsReaction parameters and dependencies
Coupled ProcessReactionMicrobiologic transformation (biogeochemical)Advectiondiffusion (water reactantproduct flux)Microbiologic speciation (ecologic)
13
Coupled ReactionsCoupled Reactions
Reaction Type Components Parameters
Electron transfer A + B rarr C + D Kdq=kfkb [A] [B] [X] [Y] [Z]Tc(VII)+Fe(II) = TcO22H2O+Fe(OH)3
Surface complexation B + E rarr F Ŝ [SOH]Fe(II)+FeOOH = Fe(II)-FeOOH
Electron transfer A + F rarr GTc(VII)+3Fe(II)-FeOOH rarr Tc(IV)-3Fe(III)Ox+FeOOH
Biological electron A + H rarr C biomass growth substrateTransfer specificity and kinetics
Tc(VII)+H2 = TcO2nH2O e-acceptordonor nutrients
Biologic reductive DE + J rarr B
FeOOHFe(OH3) + lactate = Fe(II) + CO2 + acetate
Aqueous complexation C + I rarr KTcO2nH2O + CO3
2- = TcOCO3(aq)
гbio
bio
г
14
Utilize dissolved and solid phase oxidized metals as electron acceptors for respiration when O2 becomes deplete
Strongly influence the composition and redox state of groundwaters and the valence state of polyvalent metals and radionuclides
Metal Reducing BacteriaMetal Reducing Bacteria
Bacterial mediation of geochemical reaction
Oxidized
Reduced
Oxidized
Reduced
Bacteria
Microorganisms mediate kinetically inhibited but thermodynamically favorable reactions
E for metabolism and growth
15
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Reduction (+ Fe(II) or MRB)
Tc(VII)O4-(aq)
Oxidation (+ O2 or MOB)
biologic (MRB)
+homogeneous
Fe(II)aq
heterogeneousFe(II)OH Fe(II)aq
Tc(IV)
bull speciationbull physical location
Fe(III) oxide
TcO4
t= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
Tc(IV)t
= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
medium
very slow
very fastmedium
16
Experimental Setup and Anoxic ChamberExperimental Setup and Anoxic Chamber
Glove box ldquoairrdquo is totally scrubbed of O2 using an oxygen trap based on heterogeneous reduction of O2 in Fe(II)Fe(OH)3 suspensions
lt 05 ppm
spectroscopypreparation
drying chamber
filtrationchamber
mineral and mineral-microbe
suspensions
oxygentrap
solids and liquid sampling
mineral solids and heterogeneous
precipitates
17
Probing Heterogeneous E-transferProbing Heterogeneous E-transfer
X-ray Adsorption Spectroscopy
57Fe-MossbauerSpectroscopy Combined Techniques
bull Valence statebull Local structurebull Tc-Obull Tc-Tcbull Tc-Fe
bull Valence bull Magnetic propertiesbull Bonding environmentbull Symmetry
APS EMSL In addition ndash HRTEM (EMSL)
(looking at Tc) (looking at Fe)
hFe 56Fe Al
57Fe h
57Fe
SO-Fe(II)OH + Tc(VII) rarr Г =
Heterogeneous Reduction of Pertechnetate [Tc(VII)O4
-] by Surface Complexed Fe(II) at pH = 7Heterogeneous Reduction of Pertechnetate
[Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
Dis
so
lved
Tc(
VII
)
mo
l L
-1
Dis
so
lved
Fe(
II)
mm
ol
L-1
To
tal
Fe
(II)
m
mo
l L
-1
Time daysTime days
Time days
+ FeOOH + Tc(VII)+ FeOOH
+ Tc(VII)
-6 to -2 day Fe(II)aq
-2 to 0 day FeO-Fe(II)OH0 day + FeO-Fe(II)OH+Tc(IV)Fe(III)
Issuesbull Stoichiometry of Fe(III) and Tc(IV)bull Nature of Fe(III) and Tc(IV) phasesbull Location and association of Fe(II)bull Speciation effects on heterogeneous
oxidation
3FeO-Fe(II)OH + Tc(VII)O4- = 3FeO-Fe(III)OH2 [] + Tc(IV)O2H2O []
19
Products of Heterogeneous Tc(VII)O4- Reduction
by Fe(II) on Goethite Products of Heterogeneous Tc(VII)O4
- Reduction by Fe(II) on Goethite
k A-1 R Aring
What is Fe(III)Tc(IV)Ox Where is readsorbed Fe(II)
56Fe- goethite(Moumlssbauer invisible)
57Fe(II)(Moumlssbauer visible)
bull Magnetic order and peak positions consistent with Fe(III) and goethite
bull No Fe(II)
bull ldquotwordquo Fe(II) sites
bull Spectra before Tc(IV) addition almost identical
20
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
2CP-C
Biogenic TcO2nH2O shows less Tc-Tc second neighbors and different long range order
Consistent with small size (2-3 nm) of biogenic precipitates
Tc-O
Tc-Tc
Tc-OTc-Tc
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
9
Technetium Redox Couples in Relation to Others at Standard State and pH = 7
Technetium Redox Couples in Relation to Others at Standard State and pH = 7
-10 -5 0 5 10 15 20 pe
H2(g) H2O H2O O2(g)
NH4 ι NO3-
MnCO3 ι MnO2-
Fe(aq) ι Fe(OH3)2+
HS ι SO42-
Fe(aq) ι FeOOH2+
Hemes
Tc(IV)O2 ι Tc(VII)Tc(V)(VI) ι Tc(VII)
ldquoCH2Ordquo ι CO2(g)
reducing oxidizing
10
Complex Redox Chemistry of 3e- Transfer for Tc(VII)
Complex Redox Chemistry of 3e- Transfer for Tc(VII)
Tc(VII)O4- + e- Tc(VI)O4
2- Tc(V) Tc(IV) [Tc(IV)OOHaq Tc(IV)O2nH2O(s)]
gelatin
rapid
tetrahedral tetrahedral octahedral
rapid
very
11
Disproportionation Rate Key to 3e- TransferDisproportionation Rate Key to 3e- Transfer
Tc(VII) Tc(VI) Fe(II) H+ log QK Gr
(molL) (kJmol)
100E-06 100E-12 0001 100E-07 26 14846100E-06 100E-13 0001 100E-07 16 9136100E-06 100E-14 0001 100E-07 06 3426100E-06 100E-15 0001 100E-07 -04 -2284100E-06 100E-16 0001 100E-07 -14 -7994100E-06 100E-17 0001 100E-07 -24 -13704
Reaction rate and extent increases with1 Disproportionation rate2 Concentration and redox potential of Fe(II)3 pH
Fe2+ + 3H2O + Tc(VII)O4- = Fe(III)(OH)3 + 3H+ + TcO4
2- log K = 266
Tc(VII)Tc(V)
Tc(IV)
12
Coupled Processes and ModelsCoupled Processes and Models
Reaction NetworkNecessary component reactions to define time evolution and steady stateComponent identities and concentrationsReaction parameters and dependencies
Coupled ProcessReactionMicrobiologic transformation (biogeochemical)Advectiondiffusion (water reactantproduct flux)Microbiologic speciation (ecologic)
13
Coupled ReactionsCoupled Reactions
Reaction Type Components Parameters
Electron transfer A + B rarr C + D Kdq=kfkb [A] [B] [X] [Y] [Z]Tc(VII)+Fe(II) = TcO22H2O+Fe(OH)3
Surface complexation B + E rarr F Ŝ [SOH]Fe(II)+FeOOH = Fe(II)-FeOOH
Electron transfer A + F rarr GTc(VII)+3Fe(II)-FeOOH rarr Tc(IV)-3Fe(III)Ox+FeOOH
Biological electron A + H rarr C biomass growth substrateTransfer specificity and kinetics
Tc(VII)+H2 = TcO2nH2O e-acceptordonor nutrients
Biologic reductive DE + J rarr B
FeOOHFe(OH3) + lactate = Fe(II) + CO2 + acetate
Aqueous complexation C + I rarr KTcO2nH2O + CO3
2- = TcOCO3(aq)
гbio
bio
г
14
Utilize dissolved and solid phase oxidized metals as electron acceptors for respiration when O2 becomes deplete
Strongly influence the composition and redox state of groundwaters and the valence state of polyvalent metals and radionuclides
Metal Reducing BacteriaMetal Reducing Bacteria
Bacterial mediation of geochemical reaction
Oxidized
Reduced
Oxidized
Reduced
Bacteria
Microorganisms mediate kinetically inhibited but thermodynamically favorable reactions
E for metabolism and growth
15
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Reduction (+ Fe(II) or MRB)
Tc(VII)O4-(aq)
Oxidation (+ O2 or MOB)
biologic (MRB)
+homogeneous
Fe(II)aq
heterogeneousFe(II)OH Fe(II)aq
Tc(IV)
bull speciationbull physical location
Fe(III) oxide
TcO4
t= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
Tc(IV)t
= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
medium
very slow
very fastmedium
16
Experimental Setup and Anoxic ChamberExperimental Setup and Anoxic Chamber
Glove box ldquoairrdquo is totally scrubbed of O2 using an oxygen trap based on heterogeneous reduction of O2 in Fe(II)Fe(OH)3 suspensions
lt 05 ppm
spectroscopypreparation
drying chamber
filtrationchamber
mineral and mineral-microbe
suspensions
oxygentrap
solids and liquid sampling
mineral solids and heterogeneous
precipitates
17
Probing Heterogeneous E-transferProbing Heterogeneous E-transfer
X-ray Adsorption Spectroscopy
57Fe-MossbauerSpectroscopy Combined Techniques
bull Valence statebull Local structurebull Tc-Obull Tc-Tcbull Tc-Fe
bull Valence bull Magnetic propertiesbull Bonding environmentbull Symmetry
APS EMSL In addition ndash HRTEM (EMSL)
(looking at Tc) (looking at Fe)
hFe 56Fe Al
57Fe h
57Fe
SO-Fe(II)OH + Tc(VII) rarr Г =
Heterogeneous Reduction of Pertechnetate [Tc(VII)O4
-] by Surface Complexed Fe(II) at pH = 7Heterogeneous Reduction of Pertechnetate
[Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
Dis
so
lved
Tc(
VII
)
mo
l L
-1
Dis
so
lved
Fe(
II)
mm
ol
L-1
To
tal
Fe
(II)
m
mo
l L
-1
Time daysTime days
Time days
+ FeOOH + Tc(VII)+ FeOOH
+ Tc(VII)
-6 to -2 day Fe(II)aq
-2 to 0 day FeO-Fe(II)OH0 day + FeO-Fe(II)OH+Tc(IV)Fe(III)
Issuesbull Stoichiometry of Fe(III) and Tc(IV)bull Nature of Fe(III) and Tc(IV) phasesbull Location and association of Fe(II)bull Speciation effects on heterogeneous
oxidation
3FeO-Fe(II)OH + Tc(VII)O4- = 3FeO-Fe(III)OH2 [] + Tc(IV)O2H2O []
19
Products of Heterogeneous Tc(VII)O4- Reduction
by Fe(II) on Goethite Products of Heterogeneous Tc(VII)O4
- Reduction by Fe(II) on Goethite
k A-1 R Aring
What is Fe(III)Tc(IV)Ox Where is readsorbed Fe(II)
56Fe- goethite(Moumlssbauer invisible)
57Fe(II)(Moumlssbauer visible)
bull Magnetic order and peak positions consistent with Fe(III) and goethite
bull No Fe(II)
bull ldquotwordquo Fe(II) sites
bull Spectra before Tc(IV) addition almost identical
20
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
2CP-C
Biogenic TcO2nH2O shows less Tc-Tc second neighbors and different long range order
Consistent with small size (2-3 nm) of biogenic precipitates
Tc-O
Tc-Tc
Tc-OTc-Tc
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
10
Complex Redox Chemistry of 3e- Transfer for Tc(VII)
Complex Redox Chemistry of 3e- Transfer for Tc(VII)
Tc(VII)O4- + e- Tc(VI)O4
2- Tc(V) Tc(IV) [Tc(IV)OOHaq Tc(IV)O2nH2O(s)]
gelatin
rapid
tetrahedral tetrahedral octahedral
rapid
very
11
Disproportionation Rate Key to 3e- TransferDisproportionation Rate Key to 3e- Transfer
Tc(VII) Tc(VI) Fe(II) H+ log QK Gr
(molL) (kJmol)
100E-06 100E-12 0001 100E-07 26 14846100E-06 100E-13 0001 100E-07 16 9136100E-06 100E-14 0001 100E-07 06 3426100E-06 100E-15 0001 100E-07 -04 -2284100E-06 100E-16 0001 100E-07 -14 -7994100E-06 100E-17 0001 100E-07 -24 -13704
Reaction rate and extent increases with1 Disproportionation rate2 Concentration and redox potential of Fe(II)3 pH
Fe2+ + 3H2O + Tc(VII)O4- = Fe(III)(OH)3 + 3H+ + TcO4
2- log K = 266
Tc(VII)Tc(V)
Tc(IV)
12
Coupled Processes and ModelsCoupled Processes and Models
Reaction NetworkNecessary component reactions to define time evolution and steady stateComponent identities and concentrationsReaction parameters and dependencies
Coupled ProcessReactionMicrobiologic transformation (biogeochemical)Advectiondiffusion (water reactantproduct flux)Microbiologic speciation (ecologic)
13
Coupled ReactionsCoupled Reactions
Reaction Type Components Parameters
Electron transfer A + B rarr C + D Kdq=kfkb [A] [B] [X] [Y] [Z]Tc(VII)+Fe(II) = TcO22H2O+Fe(OH)3
Surface complexation B + E rarr F Ŝ [SOH]Fe(II)+FeOOH = Fe(II)-FeOOH
Electron transfer A + F rarr GTc(VII)+3Fe(II)-FeOOH rarr Tc(IV)-3Fe(III)Ox+FeOOH
Biological electron A + H rarr C biomass growth substrateTransfer specificity and kinetics
Tc(VII)+H2 = TcO2nH2O e-acceptordonor nutrients
Biologic reductive DE + J rarr B
FeOOHFe(OH3) + lactate = Fe(II) + CO2 + acetate
Aqueous complexation C + I rarr KTcO2nH2O + CO3
2- = TcOCO3(aq)
гbio
bio
г
14
Utilize dissolved and solid phase oxidized metals as electron acceptors for respiration when O2 becomes deplete
Strongly influence the composition and redox state of groundwaters and the valence state of polyvalent metals and radionuclides
Metal Reducing BacteriaMetal Reducing Bacteria
Bacterial mediation of geochemical reaction
Oxidized
Reduced
Oxidized
Reduced
Bacteria
Microorganisms mediate kinetically inhibited but thermodynamically favorable reactions
E for metabolism and growth
15
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Reduction (+ Fe(II) or MRB)
Tc(VII)O4-(aq)
Oxidation (+ O2 or MOB)
biologic (MRB)
+homogeneous
Fe(II)aq
heterogeneousFe(II)OH Fe(II)aq
Tc(IV)
bull speciationbull physical location
Fe(III) oxide
TcO4
t= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
Tc(IV)t
= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
medium
very slow
very fastmedium
16
Experimental Setup and Anoxic ChamberExperimental Setup and Anoxic Chamber
Glove box ldquoairrdquo is totally scrubbed of O2 using an oxygen trap based on heterogeneous reduction of O2 in Fe(II)Fe(OH)3 suspensions
lt 05 ppm
spectroscopypreparation
drying chamber
filtrationchamber
mineral and mineral-microbe
suspensions
oxygentrap
solids and liquid sampling
mineral solids and heterogeneous
precipitates
17
Probing Heterogeneous E-transferProbing Heterogeneous E-transfer
X-ray Adsorption Spectroscopy
57Fe-MossbauerSpectroscopy Combined Techniques
bull Valence statebull Local structurebull Tc-Obull Tc-Tcbull Tc-Fe
bull Valence bull Magnetic propertiesbull Bonding environmentbull Symmetry
APS EMSL In addition ndash HRTEM (EMSL)
(looking at Tc) (looking at Fe)
hFe 56Fe Al
57Fe h
57Fe
SO-Fe(II)OH + Tc(VII) rarr Г =
Heterogeneous Reduction of Pertechnetate [Tc(VII)O4
-] by Surface Complexed Fe(II) at pH = 7Heterogeneous Reduction of Pertechnetate
[Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
Dis
so
lved
Tc(
VII
)
mo
l L
-1
Dis
so
lved
Fe(
II)
mm
ol
L-1
To
tal
Fe
(II)
m
mo
l L
-1
Time daysTime days
Time days
+ FeOOH + Tc(VII)+ FeOOH
+ Tc(VII)
-6 to -2 day Fe(II)aq
-2 to 0 day FeO-Fe(II)OH0 day + FeO-Fe(II)OH+Tc(IV)Fe(III)
Issuesbull Stoichiometry of Fe(III) and Tc(IV)bull Nature of Fe(III) and Tc(IV) phasesbull Location and association of Fe(II)bull Speciation effects on heterogeneous
oxidation
3FeO-Fe(II)OH + Tc(VII)O4- = 3FeO-Fe(III)OH2 [] + Tc(IV)O2H2O []
19
Products of Heterogeneous Tc(VII)O4- Reduction
by Fe(II) on Goethite Products of Heterogeneous Tc(VII)O4
- Reduction by Fe(II) on Goethite
k A-1 R Aring
What is Fe(III)Tc(IV)Ox Where is readsorbed Fe(II)
56Fe- goethite(Moumlssbauer invisible)
57Fe(II)(Moumlssbauer visible)
bull Magnetic order and peak positions consistent with Fe(III) and goethite
bull No Fe(II)
bull ldquotwordquo Fe(II) sites
bull Spectra before Tc(IV) addition almost identical
20
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
2CP-C
Biogenic TcO2nH2O shows less Tc-Tc second neighbors and different long range order
Consistent with small size (2-3 nm) of biogenic precipitates
Tc-O
Tc-Tc
Tc-OTc-Tc
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
11
Disproportionation Rate Key to 3e- TransferDisproportionation Rate Key to 3e- Transfer
Tc(VII) Tc(VI) Fe(II) H+ log QK Gr
(molL) (kJmol)
100E-06 100E-12 0001 100E-07 26 14846100E-06 100E-13 0001 100E-07 16 9136100E-06 100E-14 0001 100E-07 06 3426100E-06 100E-15 0001 100E-07 -04 -2284100E-06 100E-16 0001 100E-07 -14 -7994100E-06 100E-17 0001 100E-07 -24 -13704
Reaction rate and extent increases with1 Disproportionation rate2 Concentration and redox potential of Fe(II)3 pH
Fe2+ + 3H2O + Tc(VII)O4- = Fe(III)(OH)3 + 3H+ + TcO4
2- log K = 266
Tc(VII)Tc(V)
Tc(IV)
12
Coupled Processes and ModelsCoupled Processes and Models
Reaction NetworkNecessary component reactions to define time evolution and steady stateComponent identities and concentrationsReaction parameters and dependencies
Coupled ProcessReactionMicrobiologic transformation (biogeochemical)Advectiondiffusion (water reactantproduct flux)Microbiologic speciation (ecologic)
13
Coupled ReactionsCoupled Reactions
Reaction Type Components Parameters
Electron transfer A + B rarr C + D Kdq=kfkb [A] [B] [X] [Y] [Z]Tc(VII)+Fe(II) = TcO22H2O+Fe(OH)3
Surface complexation B + E rarr F Ŝ [SOH]Fe(II)+FeOOH = Fe(II)-FeOOH
Electron transfer A + F rarr GTc(VII)+3Fe(II)-FeOOH rarr Tc(IV)-3Fe(III)Ox+FeOOH
Biological electron A + H rarr C biomass growth substrateTransfer specificity and kinetics
Tc(VII)+H2 = TcO2nH2O e-acceptordonor nutrients
Biologic reductive DE + J rarr B
FeOOHFe(OH3) + lactate = Fe(II) + CO2 + acetate
Aqueous complexation C + I rarr KTcO2nH2O + CO3
2- = TcOCO3(aq)
гbio
bio
г
14
Utilize dissolved and solid phase oxidized metals as electron acceptors for respiration when O2 becomes deplete
Strongly influence the composition and redox state of groundwaters and the valence state of polyvalent metals and radionuclides
Metal Reducing BacteriaMetal Reducing Bacteria
Bacterial mediation of geochemical reaction
Oxidized
Reduced
Oxidized
Reduced
Bacteria
Microorganisms mediate kinetically inhibited but thermodynamically favorable reactions
E for metabolism and growth
15
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Reduction (+ Fe(II) or MRB)
Tc(VII)O4-(aq)
Oxidation (+ O2 or MOB)
biologic (MRB)
+homogeneous
Fe(II)aq
heterogeneousFe(II)OH Fe(II)aq
Tc(IV)
bull speciationbull physical location
Fe(III) oxide
TcO4
t= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
Tc(IV)t
= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
medium
very slow
very fastmedium
16
Experimental Setup and Anoxic ChamberExperimental Setup and Anoxic Chamber
Glove box ldquoairrdquo is totally scrubbed of O2 using an oxygen trap based on heterogeneous reduction of O2 in Fe(II)Fe(OH)3 suspensions
lt 05 ppm
spectroscopypreparation
drying chamber
filtrationchamber
mineral and mineral-microbe
suspensions
oxygentrap
solids and liquid sampling
mineral solids and heterogeneous
precipitates
17
Probing Heterogeneous E-transferProbing Heterogeneous E-transfer
X-ray Adsorption Spectroscopy
57Fe-MossbauerSpectroscopy Combined Techniques
bull Valence statebull Local structurebull Tc-Obull Tc-Tcbull Tc-Fe
bull Valence bull Magnetic propertiesbull Bonding environmentbull Symmetry
APS EMSL In addition ndash HRTEM (EMSL)
(looking at Tc) (looking at Fe)
hFe 56Fe Al
57Fe h
57Fe
SO-Fe(II)OH + Tc(VII) rarr Г =
Heterogeneous Reduction of Pertechnetate [Tc(VII)O4
-] by Surface Complexed Fe(II) at pH = 7Heterogeneous Reduction of Pertechnetate
[Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
Dis
so
lved
Tc(
VII
)
mo
l L
-1
Dis
so
lved
Fe(
II)
mm
ol
L-1
To
tal
Fe
(II)
m
mo
l L
-1
Time daysTime days
Time days
+ FeOOH + Tc(VII)+ FeOOH
+ Tc(VII)
-6 to -2 day Fe(II)aq
-2 to 0 day FeO-Fe(II)OH0 day + FeO-Fe(II)OH+Tc(IV)Fe(III)
Issuesbull Stoichiometry of Fe(III) and Tc(IV)bull Nature of Fe(III) and Tc(IV) phasesbull Location and association of Fe(II)bull Speciation effects on heterogeneous
oxidation
3FeO-Fe(II)OH + Tc(VII)O4- = 3FeO-Fe(III)OH2 [] + Tc(IV)O2H2O []
19
Products of Heterogeneous Tc(VII)O4- Reduction
by Fe(II) on Goethite Products of Heterogeneous Tc(VII)O4
- Reduction by Fe(II) on Goethite
k A-1 R Aring
What is Fe(III)Tc(IV)Ox Where is readsorbed Fe(II)
56Fe- goethite(Moumlssbauer invisible)
57Fe(II)(Moumlssbauer visible)
bull Magnetic order and peak positions consistent with Fe(III) and goethite
bull No Fe(II)
bull ldquotwordquo Fe(II) sites
bull Spectra before Tc(IV) addition almost identical
20
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
2CP-C
Biogenic TcO2nH2O shows less Tc-Tc second neighbors and different long range order
Consistent with small size (2-3 nm) of biogenic precipitates
Tc-O
Tc-Tc
Tc-OTc-Tc
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
12
Coupled Processes and ModelsCoupled Processes and Models
Reaction NetworkNecessary component reactions to define time evolution and steady stateComponent identities and concentrationsReaction parameters and dependencies
Coupled ProcessReactionMicrobiologic transformation (biogeochemical)Advectiondiffusion (water reactantproduct flux)Microbiologic speciation (ecologic)
13
Coupled ReactionsCoupled Reactions
Reaction Type Components Parameters
Electron transfer A + B rarr C + D Kdq=kfkb [A] [B] [X] [Y] [Z]Tc(VII)+Fe(II) = TcO22H2O+Fe(OH)3
Surface complexation B + E rarr F Ŝ [SOH]Fe(II)+FeOOH = Fe(II)-FeOOH
Electron transfer A + F rarr GTc(VII)+3Fe(II)-FeOOH rarr Tc(IV)-3Fe(III)Ox+FeOOH
Biological electron A + H rarr C biomass growth substrateTransfer specificity and kinetics
Tc(VII)+H2 = TcO2nH2O e-acceptordonor nutrients
Biologic reductive DE + J rarr B
FeOOHFe(OH3) + lactate = Fe(II) + CO2 + acetate
Aqueous complexation C + I rarr KTcO2nH2O + CO3
2- = TcOCO3(aq)
гbio
bio
г
14
Utilize dissolved and solid phase oxidized metals as electron acceptors for respiration when O2 becomes deplete
Strongly influence the composition and redox state of groundwaters and the valence state of polyvalent metals and radionuclides
Metal Reducing BacteriaMetal Reducing Bacteria
Bacterial mediation of geochemical reaction
Oxidized
Reduced
Oxidized
Reduced
Bacteria
Microorganisms mediate kinetically inhibited but thermodynamically favorable reactions
E for metabolism and growth
15
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Reduction (+ Fe(II) or MRB)
Tc(VII)O4-(aq)
Oxidation (+ O2 or MOB)
biologic (MRB)
+homogeneous
Fe(II)aq
heterogeneousFe(II)OH Fe(II)aq
Tc(IV)
bull speciationbull physical location
Fe(III) oxide
TcO4
t= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
Tc(IV)t
= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
medium
very slow
very fastmedium
16
Experimental Setup and Anoxic ChamberExperimental Setup and Anoxic Chamber
Glove box ldquoairrdquo is totally scrubbed of O2 using an oxygen trap based on heterogeneous reduction of O2 in Fe(II)Fe(OH)3 suspensions
lt 05 ppm
spectroscopypreparation
drying chamber
filtrationchamber
mineral and mineral-microbe
suspensions
oxygentrap
solids and liquid sampling
mineral solids and heterogeneous
precipitates
17
Probing Heterogeneous E-transferProbing Heterogeneous E-transfer
X-ray Adsorption Spectroscopy
57Fe-MossbauerSpectroscopy Combined Techniques
bull Valence statebull Local structurebull Tc-Obull Tc-Tcbull Tc-Fe
bull Valence bull Magnetic propertiesbull Bonding environmentbull Symmetry
APS EMSL In addition ndash HRTEM (EMSL)
(looking at Tc) (looking at Fe)
hFe 56Fe Al
57Fe h
57Fe
SO-Fe(II)OH + Tc(VII) rarr Г =
Heterogeneous Reduction of Pertechnetate [Tc(VII)O4
-] by Surface Complexed Fe(II) at pH = 7Heterogeneous Reduction of Pertechnetate
[Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
Dis
so
lved
Tc(
VII
)
mo
l L
-1
Dis
so
lved
Fe(
II)
mm
ol
L-1
To
tal
Fe
(II)
m
mo
l L
-1
Time daysTime days
Time days
+ FeOOH + Tc(VII)+ FeOOH
+ Tc(VII)
-6 to -2 day Fe(II)aq
-2 to 0 day FeO-Fe(II)OH0 day + FeO-Fe(II)OH+Tc(IV)Fe(III)
Issuesbull Stoichiometry of Fe(III) and Tc(IV)bull Nature of Fe(III) and Tc(IV) phasesbull Location and association of Fe(II)bull Speciation effects on heterogeneous
oxidation
3FeO-Fe(II)OH + Tc(VII)O4- = 3FeO-Fe(III)OH2 [] + Tc(IV)O2H2O []
19
Products of Heterogeneous Tc(VII)O4- Reduction
by Fe(II) on Goethite Products of Heterogeneous Tc(VII)O4
- Reduction by Fe(II) on Goethite
k A-1 R Aring
What is Fe(III)Tc(IV)Ox Where is readsorbed Fe(II)
56Fe- goethite(Moumlssbauer invisible)
57Fe(II)(Moumlssbauer visible)
bull Magnetic order and peak positions consistent with Fe(III) and goethite
bull No Fe(II)
bull ldquotwordquo Fe(II) sites
bull Spectra before Tc(IV) addition almost identical
20
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
2CP-C
Biogenic TcO2nH2O shows less Tc-Tc second neighbors and different long range order
Consistent with small size (2-3 nm) of biogenic precipitates
Tc-O
Tc-Tc
Tc-OTc-Tc
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
13
Coupled ReactionsCoupled Reactions
Reaction Type Components Parameters
Electron transfer A + B rarr C + D Kdq=kfkb [A] [B] [X] [Y] [Z]Tc(VII)+Fe(II) = TcO22H2O+Fe(OH)3
Surface complexation B + E rarr F Ŝ [SOH]Fe(II)+FeOOH = Fe(II)-FeOOH
Electron transfer A + F rarr GTc(VII)+3Fe(II)-FeOOH rarr Tc(IV)-3Fe(III)Ox+FeOOH
Biological electron A + H rarr C biomass growth substrateTransfer specificity and kinetics
Tc(VII)+H2 = TcO2nH2O e-acceptordonor nutrients
Biologic reductive DE + J rarr B
FeOOHFe(OH3) + lactate = Fe(II) + CO2 + acetate
Aqueous complexation C + I rarr KTcO2nH2O + CO3
2- = TcOCO3(aq)
гbio
bio
г
14
Utilize dissolved and solid phase oxidized metals as electron acceptors for respiration when O2 becomes deplete
Strongly influence the composition and redox state of groundwaters and the valence state of polyvalent metals and radionuclides
Metal Reducing BacteriaMetal Reducing Bacteria
Bacterial mediation of geochemical reaction
Oxidized
Reduced
Oxidized
Reduced
Bacteria
Microorganisms mediate kinetically inhibited but thermodynamically favorable reactions
E for metabolism and growth
15
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Reduction (+ Fe(II) or MRB)
Tc(VII)O4-(aq)
Oxidation (+ O2 or MOB)
biologic (MRB)
+homogeneous
Fe(II)aq
heterogeneousFe(II)OH Fe(II)aq
Tc(IV)
bull speciationbull physical location
Fe(III) oxide
TcO4
t= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
Tc(IV)t
= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
medium
very slow
very fastmedium
16
Experimental Setup and Anoxic ChamberExperimental Setup and Anoxic Chamber
Glove box ldquoairrdquo is totally scrubbed of O2 using an oxygen trap based on heterogeneous reduction of O2 in Fe(II)Fe(OH)3 suspensions
lt 05 ppm
spectroscopypreparation
drying chamber
filtrationchamber
mineral and mineral-microbe
suspensions
oxygentrap
solids and liquid sampling
mineral solids and heterogeneous
precipitates
17
Probing Heterogeneous E-transferProbing Heterogeneous E-transfer
X-ray Adsorption Spectroscopy
57Fe-MossbauerSpectroscopy Combined Techniques
bull Valence statebull Local structurebull Tc-Obull Tc-Tcbull Tc-Fe
bull Valence bull Magnetic propertiesbull Bonding environmentbull Symmetry
APS EMSL In addition ndash HRTEM (EMSL)
(looking at Tc) (looking at Fe)
hFe 56Fe Al
57Fe h
57Fe
SO-Fe(II)OH + Tc(VII) rarr Г =
Heterogeneous Reduction of Pertechnetate [Tc(VII)O4
-] by Surface Complexed Fe(II) at pH = 7Heterogeneous Reduction of Pertechnetate
[Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
Dis
so
lved
Tc(
VII
)
mo
l L
-1
Dis
so
lved
Fe(
II)
mm
ol
L-1
To
tal
Fe
(II)
m
mo
l L
-1
Time daysTime days
Time days
+ FeOOH + Tc(VII)+ FeOOH
+ Tc(VII)
-6 to -2 day Fe(II)aq
-2 to 0 day FeO-Fe(II)OH0 day + FeO-Fe(II)OH+Tc(IV)Fe(III)
Issuesbull Stoichiometry of Fe(III) and Tc(IV)bull Nature of Fe(III) and Tc(IV) phasesbull Location and association of Fe(II)bull Speciation effects on heterogeneous
oxidation
3FeO-Fe(II)OH + Tc(VII)O4- = 3FeO-Fe(III)OH2 [] + Tc(IV)O2H2O []
19
Products of Heterogeneous Tc(VII)O4- Reduction
by Fe(II) on Goethite Products of Heterogeneous Tc(VII)O4
- Reduction by Fe(II) on Goethite
k A-1 R Aring
What is Fe(III)Tc(IV)Ox Where is readsorbed Fe(II)
56Fe- goethite(Moumlssbauer invisible)
57Fe(II)(Moumlssbauer visible)
bull Magnetic order and peak positions consistent with Fe(III) and goethite
bull No Fe(II)
bull ldquotwordquo Fe(II) sites
bull Spectra before Tc(IV) addition almost identical
20
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
2CP-C
Biogenic TcO2nH2O shows less Tc-Tc second neighbors and different long range order
Consistent with small size (2-3 nm) of biogenic precipitates
Tc-O
Tc-Tc
Tc-OTc-Tc
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
14
Utilize dissolved and solid phase oxidized metals as electron acceptors for respiration when O2 becomes deplete
Strongly influence the composition and redox state of groundwaters and the valence state of polyvalent metals and radionuclides
Metal Reducing BacteriaMetal Reducing Bacteria
Bacterial mediation of geochemical reaction
Oxidized
Reduced
Oxidized
Reduced
Bacteria
Microorganisms mediate kinetically inhibited but thermodynamically favorable reactions
E for metabolism and growth
15
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Reduction (+ Fe(II) or MRB)
Tc(VII)O4-(aq)
Oxidation (+ O2 or MOB)
biologic (MRB)
+homogeneous
Fe(II)aq
heterogeneousFe(II)OH Fe(II)aq
Tc(IV)
bull speciationbull physical location
Fe(III) oxide
TcO4
t= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
Tc(IV)t
= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
medium
very slow
very fastmedium
16
Experimental Setup and Anoxic ChamberExperimental Setup and Anoxic Chamber
Glove box ldquoairrdquo is totally scrubbed of O2 using an oxygen trap based on heterogeneous reduction of O2 in Fe(II)Fe(OH)3 suspensions
lt 05 ppm
spectroscopypreparation
drying chamber
filtrationchamber
mineral and mineral-microbe
suspensions
oxygentrap
solids and liquid sampling
mineral solids and heterogeneous
precipitates
17
Probing Heterogeneous E-transferProbing Heterogeneous E-transfer
X-ray Adsorption Spectroscopy
57Fe-MossbauerSpectroscopy Combined Techniques
bull Valence statebull Local structurebull Tc-Obull Tc-Tcbull Tc-Fe
bull Valence bull Magnetic propertiesbull Bonding environmentbull Symmetry
APS EMSL In addition ndash HRTEM (EMSL)
(looking at Tc) (looking at Fe)
hFe 56Fe Al
57Fe h
57Fe
SO-Fe(II)OH + Tc(VII) rarr Г =
Heterogeneous Reduction of Pertechnetate [Tc(VII)O4
-] by Surface Complexed Fe(II) at pH = 7Heterogeneous Reduction of Pertechnetate
[Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
Dis
so
lved
Tc(
VII
)
mo
l L
-1
Dis
so
lved
Fe(
II)
mm
ol
L-1
To
tal
Fe
(II)
m
mo
l L
-1
Time daysTime days
Time days
+ FeOOH + Tc(VII)+ FeOOH
+ Tc(VII)
-6 to -2 day Fe(II)aq
-2 to 0 day FeO-Fe(II)OH0 day + FeO-Fe(II)OH+Tc(IV)Fe(III)
Issuesbull Stoichiometry of Fe(III) and Tc(IV)bull Nature of Fe(III) and Tc(IV) phasesbull Location and association of Fe(II)bull Speciation effects on heterogeneous
oxidation
3FeO-Fe(II)OH + Tc(VII)O4- = 3FeO-Fe(III)OH2 [] + Tc(IV)O2H2O []
19
Products of Heterogeneous Tc(VII)O4- Reduction
by Fe(II) on Goethite Products of Heterogeneous Tc(VII)O4
- Reduction by Fe(II) on Goethite
k A-1 R Aring
What is Fe(III)Tc(IV)Ox Where is readsorbed Fe(II)
56Fe- goethite(Moumlssbauer invisible)
57Fe(II)(Moumlssbauer visible)
bull Magnetic order and peak positions consistent with Fe(III) and goethite
bull No Fe(II)
bull ldquotwordquo Fe(II) sites
bull Spectra before Tc(IV) addition almost identical
20
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
2CP-C
Biogenic TcO2nH2O shows less Tc-Tc second neighbors and different long range order
Consistent with small size (2-3 nm) of biogenic precipitates
Tc-O
Tc-Tc
Tc-OTc-Tc
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
15
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Kinetic Pathways for Tc(VII) Reduction and Tc(IV) Oxidation
Reduction (+ Fe(II) or MRB)
Tc(VII)O4-(aq)
Oxidation (+ O2 or MOB)
biologic (MRB)
+homogeneous
Fe(II)aq
heterogeneousFe(II)OH Fe(II)aq
Tc(IV)
bull speciationbull physical location
Fe(III) oxide
TcO4
t= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
Tc(IV)t
= kbio[ ] + khomo[ ] + khet1[ ] + khet2[ ]
medium
very slow
very fastmedium
16
Experimental Setup and Anoxic ChamberExperimental Setup and Anoxic Chamber
Glove box ldquoairrdquo is totally scrubbed of O2 using an oxygen trap based on heterogeneous reduction of O2 in Fe(II)Fe(OH)3 suspensions
lt 05 ppm
spectroscopypreparation
drying chamber
filtrationchamber
mineral and mineral-microbe
suspensions
oxygentrap
solids and liquid sampling
mineral solids and heterogeneous
precipitates
17
Probing Heterogeneous E-transferProbing Heterogeneous E-transfer
X-ray Adsorption Spectroscopy
57Fe-MossbauerSpectroscopy Combined Techniques
bull Valence statebull Local structurebull Tc-Obull Tc-Tcbull Tc-Fe
bull Valence bull Magnetic propertiesbull Bonding environmentbull Symmetry
APS EMSL In addition ndash HRTEM (EMSL)
(looking at Tc) (looking at Fe)
hFe 56Fe Al
57Fe h
57Fe
SO-Fe(II)OH + Tc(VII) rarr Г =
Heterogeneous Reduction of Pertechnetate [Tc(VII)O4
-] by Surface Complexed Fe(II) at pH = 7Heterogeneous Reduction of Pertechnetate
[Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
Dis
so
lved
Tc(
VII
)
mo
l L
-1
Dis
so
lved
Fe(
II)
mm
ol
L-1
To
tal
Fe
(II)
m
mo
l L
-1
Time daysTime days
Time days
+ FeOOH + Tc(VII)+ FeOOH
+ Tc(VII)
-6 to -2 day Fe(II)aq
-2 to 0 day FeO-Fe(II)OH0 day + FeO-Fe(II)OH+Tc(IV)Fe(III)
Issuesbull Stoichiometry of Fe(III) and Tc(IV)bull Nature of Fe(III) and Tc(IV) phasesbull Location and association of Fe(II)bull Speciation effects on heterogeneous
oxidation
3FeO-Fe(II)OH + Tc(VII)O4- = 3FeO-Fe(III)OH2 [] + Tc(IV)O2H2O []
19
Products of Heterogeneous Tc(VII)O4- Reduction
by Fe(II) on Goethite Products of Heterogeneous Tc(VII)O4
- Reduction by Fe(II) on Goethite
k A-1 R Aring
What is Fe(III)Tc(IV)Ox Where is readsorbed Fe(II)
56Fe- goethite(Moumlssbauer invisible)
57Fe(II)(Moumlssbauer visible)
bull Magnetic order and peak positions consistent with Fe(III) and goethite
bull No Fe(II)
bull ldquotwordquo Fe(II) sites
bull Spectra before Tc(IV) addition almost identical
20
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
2CP-C
Biogenic TcO2nH2O shows less Tc-Tc second neighbors and different long range order
Consistent with small size (2-3 nm) of biogenic precipitates
Tc-O
Tc-Tc
Tc-OTc-Tc
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
16
Experimental Setup and Anoxic ChamberExperimental Setup and Anoxic Chamber
Glove box ldquoairrdquo is totally scrubbed of O2 using an oxygen trap based on heterogeneous reduction of O2 in Fe(II)Fe(OH)3 suspensions
lt 05 ppm
spectroscopypreparation
drying chamber
filtrationchamber
mineral and mineral-microbe
suspensions
oxygentrap
solids and liquid sampling
mineral solids and heterogeneous
precipitates
17
Probing Heterogeneous E-transferProbing Heterogeneous E-transfer
X-ray Adsorption Spectroscopy
57Fe-MossbauerSpectroscopy Combined Techniques
bull Valence statebull Local structurebull Tc-Obull Tc-Tcbull Tc-Fe
bull Valence bull Magnetic propertiesbull Bonding environmentbull Symmetry
APS EMSL In addition ndash HRTEM (EMSL)
(looking at Tc) (looking at Fe)
hFe 56Fe Al
57Fe h
57Fe
SO-Fe(II)OH + Tc(VII) rarr Г =
Heterogeneous Reduction of Pertechnetate [Tc(VII)O4
-] by Surface Complexed Fe(II) at pH = 7Heterogeneous Reduction of Pertechnetate
[Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
Dis
so
lved
Tc(
VII
)
mo
l L
-1
Dis
so
lved
Fe(
II)
mm
ol
L-1
To
tal
Fe
(II)
m
mo
l L
-1
Time daysTime days
Time days
+ FeOOH + Tc(VII)+ FeOOH
+ Tc(VII)
-6 to -2 day Fe(II)aq
-2 to 0 day FeO-Fe(II)OH0 day + FeO-Fe(II)OH+Tc(IV)Fe(III)
Issuesbull Stoichiometry of Fe(III) and Tc(IV)bull Nature of Fe(III) and Tc(IV) phasesbull Location and association of Fe(II)bull Speciation effects on heterogeneous
oxidation
3FeO-Fe(II)OH + Tc(VII)O4- = 3FeO-Fe(III)OH2 [] + Tc(IV)O2H2O []
19
Products of Heterogeneous Tc(VII)O4- Reduction
by Fe(II) on Goethite Products of Heterogeneous Tc(VII)O4
- Reduction by Fe(II) on Goethite
k A-1 R Aring
What is Fe(III)Tc(IV)Ox Where is readsorbed Fe(II)
56Fe- goethite(Moumlssbauer invisible)
57Fe(II)(Moumlssbauer visible)
bull Magnetic order and peak positions consistent with Fe(III) and goethite
bull No Fe(II)
bull ldquotwordquo Fe(II) sites
bull Spectra before Tc(IV) addition almost identical
20
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
2CP-C
Biogenic TcO2nH2O shows less Tc-Tc second neighbors and different long range order
Consistent with small size (2-3 nm) of biogenic precipitates
Tc-O
Tc-Tc
Tc-OTc-Tc
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
17
Probing Heterogeneous E-transferProbing Heterogeneous E-transfer
X-ray Adsorption Spectroscopy
57Fe-MossbauerSpectroscopy Combined Techniques
bull Valence statebull Local structurebull Tc-Obull Tc-Tcbull Tc-Fe
bull Valence bull Magnetic propertiesbull Bonding environmentbull Symmetry
APS EMSL In addition ndash HRTEM (EMSL)
(looking at Tc) (looking at Fe)
hFe 56Fe Al
57Fe h
57Fe
SO-Fe(II)OH + Tc(VII) rarr Г =
Heterogeneous Reduction of Pertechnetate [Tc(VII)O4
-] by Surface Complexed Fe(II) at pH = 7Heterogeneous Reduction of Pertechnetate
[Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
Dis
so
lved
Tc(
VII
)
mo
l L
-1
Dis
so
lved
Fe(
II)
mm
ol
L-1
To
tal
Fe
(II)
m
mo
l L
-1
Time daysTime days
Time days
+ FeOOH + Tc(VII)+ FeOOH
+ Tc(VII)
-6 to -2 day Fe(II)aq
-2 to 0 day FeO-Fe(II)OH0 day + FeO-Fe(II)OH+Tc(IV)Fe(III)
Issuesbull Stoichiometry of Fe(III) and Tc(IV)bull Nature of Fe(III) and Tc(IV) phasesbull Location and association of Fe(II)bull Speciation effects on heterogeneous
oxidation
3FeO-Fe(II)OH + Tc(VII)O4- = 3FeO-Fe(III)OH2 [] + Tc(IV)O2H2O []
19
Products of Heterogeneous Tc(VII)O4- Reduction
by Fe(II) on Goethite Products of Heterogeneous Tc(VII)O4
- Reduction by Fe(II) on Goethite
k A-1 R Aring
What is Fe(III)Tc(IV)Ox Where is readsorbed Fe(II)
56Fe- goethite(Moumlssbauer invisible)
57Fe(II)(Moumlssbauer visible)
bull Magnetic order and peak positions consistent with Fe(III) and goethite
bull No Fe(II)
bull ldquotwordquo Fe(II) sites
bull Spectra before Tc(IV) addition almost identical
20
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
2CP-C
Biogenic TcO2nH2O shows less Tc-Tc second neighbors and different long range order
Consistent with small size (2-3 nm) of biogenic precipitates
Tc-O
Tc-Tc
Tc-OTc-Tc
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
Heterogeneous Reduction of Pertechnetate [Tc(VII)O4
-] by Surface Complexed Fe(II) at pH = 7Heterogeneous Reduction of Pertechnetate
[Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
Dis
so
lved
Tc(
VII
)
mo
l L
-1
Dis
so
lved
Fe(
II)
mm
ol
L-1
To
tal
Fe
(II)
m
mo
l L
-1
Time daysTime days
Time days
+ FeOOH + Tc(VII)+ FeOOH
+ Tc(VII)
-6 to -2 day Fe(II)aq
-2 to 0 day FeO-Fe(II)OH0 day + FeO-Fe(II)OH+Tc(IV)Fe(III)
Issuesbull Stoichiometry of Fe(III) and Tc(IV)bull Nature of Fe(III) and Tc(IV) phasesbull Location and association of Fe(II)bull Speciation effects on heterogeneous
oxidation
3FeO-Fe(II)OH + Tc(VII)O4- = 3FeO-Fe(III)OH2 [] + Tc(IV)O2H2O []
19
Products of Heterogeneous Tc(VII)O4- Reduction
by Fe(II) on Goethite Products of Heterogeneous Tc(VII)O4
- Reduction by Fe(II) on Goethite
k A-1 R Aring
What is Fe(III)Tc(IV)Ox Where is readsorbed Fe(II)
56Fe- goethite(Moumlssbauer invisible)
57Fe(II)(Moumlssbauer visible)
bull Magnetic order and peak positions consistent with Fe(III) and goethite
bull No Fe(II)
bull ldquotwordquo Fe(II) sites
bull Spectra before Tc(IV) addition almost identical
20
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
2CP-C
Biogenic TcO2nH2O shows less Tc-Tc second neighbors and different long range order
Consistent with small size (2-3 nm) of biogenic precipitates
Tc-O
Tc-Tc
Tc-OTc-Tc
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
19
Products of Heterogeneous Tc(VII)O4- Reduction
by Fe(II) on Goethite Products of Heterogeneous Tc(VII)O4
- Reduction by Fe(II) on Goethite
k A-1 R Aring
What is Fe(III)Tc(IV)Ox Where is readsorbed Fe(II)
56Fe- goethite(Moumlssbauer invisible)
57Fe(II)(Moumlssbauer visible)
bull Magnetic order and peak positions consistent with Fe(III) and goethite
bull No Fe(II)
bull ldquotwordquo Fe(II) sites
bull Spectra before Tc(IV) addition almost identical
20
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
2CP-C
Biogenic TcO2nH2O shows less Tc-Tc second neighbors and different long range order
Consistent with small size (2-3 nm) of biogenic precipitates
Tc-O
Tc-Tc
Tc-OTc-Tc
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
20
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
Many Metal-Reducing Bacteria Change the Valence of Pertechnetate [Tc(VII)]
2CP-C
Biogenic TcO2nH2O shows less Tc-Tc second neighbors and different long range order
Consistent with small size (2-3 nm) of biogenic precipitates
Tc-O
Tc-Tc
Tc-OTc-Tc
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
21
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
HRTEM of TcO2H2O Precipitates on and within CN32 S putrefaciens
ΔG = 23 S
log Kso(s) = log Kso(s=o) +
log Kso(s) = log Kso(s=o) +
⅔23 RT
S
⅔23 RT
Md
Small biogenic precipitates are more soluble (eg 10-7 molL)
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
22
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Biogenic Products of Dissimilatory Iron Reduction are Reactive and Significant to
Trace Element Cycling
Fe2+(aq) helliphelliphelliphelliphelliphelliphelliphelliphellip reductant of Cr(VI)
and other dissolved oxidants
-FeOOH helliphelliphelliphelliphelliphelliphelliphelliphellip reactive crystalline Fe(III) oxide
-Fe(II) helliphelliphelliphelliphelliphelliphelliphelliphellip facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
FeCO3helliphelliphelliphelliphelliphelliphelliphelliphellip reversible repository of
divalent metals Co Zn Ni Cd
Fe3O4helliphelliphelliphelliphelliphelliphelliphelliphellip irreversible repository of divalent
metals Zn Ni Co heterogeneousreductant
[FeII(6-x)FeIII
x(OH)12] helliphellip unique anion exchanger withX+[(A2-)x2bullyH2O]x- reductant properties
Products Implications
aa
Starting Oxide
HFO
FeOOH + DIRB
Fe2O3
Products
Fe2+(aq)
Fe(ll)
FeCO3
Fe3O4
[FeII(6-x)FeIII
x(OH)12] x+[(A2-)x2bullyH2O]x-
Implications
reductant of Cr(VI)and other dissolved oxidants
facile reductant of chlorinatedsolvents nitroaromatics U(VI)Tc(VII) Cr(VI) etc
reversible repository ofdivalent metals Co Zn Ni Cd
irreversible repository of divalentmetals Zn Ni Co etc
unique anion exchangerwith reductant properties
SP980200235
+ DIRB
Starting Oxide
2LFH
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
23
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
Experiments to Assess Abiotic and Biotic Reaction Predominance
Tc and 2LFH Behavior in Anoxic Suspensions with MR-1 and H2 or Lactate
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
ID Experiment Product [Tc]aq
[Tc(IV]aq
Start 300x10-4
3 Tc(IV)-2LFH+Fe(II) ~70 goe 20 mag lt15x10-9
4 Tc(IV)-2LFH+AH2DS nanomagnetite 184x10-9
5 bio-Fe3O4+Tc(VII) 60 nm magnetite 193x10-9
6 Tc(VII)+MR-1+H2 TcO2nH2O 152x10-7
10 2LFH+Tc(VII)+MR-1+H2 large particle goethite 343x10-8
12 2LFH+Tc(VII)+MR-1+lactate 5LFH 378x10-6
499x10-7
14 Tc(IV)-2LFH+MR-1+H2 large particle goethite 411x10-8
15 Tc(IV)-2LFH+MR-1+lactate 5LFH 412x10-6
276x10-7
Hypothesis H2 would promote microbiologic reduction
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
24
What Reductive Process Dominates in Mineral-Microbe Suspension
What Reductive Process Dominates in Mineral-Microbe Suspension
MR-1
H2
Products display different EXAFS spectra from abiotic and biotic TcO2
Aqueous concentration tracks speciation and mineralogy
2-line ferrihydrite + Tc(VII)aq + MR-1 -FeOOH + Fe-O-Fe(II)OH + Tc(IV)(s)[]timeFe(II)
Tc-O
Tc-Tc
Tc-Fe
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
25
Biomineralization Products and Tc Concentrations with Shewanella Anaeromyxobacter and GeobacterBiomineralization Products and Tc Concentrations
with Shewanella Anaeromyxobacter and Geobacter
Reactants Product [Tc] [Fe(II)]-
05NHCl
(mol L-1)
2LFH + Tc(VII) + MR-1 + H2 rarr goethite 49x10-9 169x10-3
2LFH + Tc(VII) + CN-32 + H2 rarr goethite ge magnetite 81x10-9 336-x10-3
2LFH + Tc(VII) + 2CP-C + H2 rarr poorly crystalline goethite 117x10-8 264x10-3
2LFH + Tc(VII) + PCA + H2 rarr well crystalline goethite amp magnetite 849x10-9 312x10-3
Tc(VII) + PCA + H2 rarr TcO2nH2O 179x10-7[TcToT] = 302x10-4 [FeToT] = 302x10-2
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
26
XAS of Ferrihydrite Incubated with H2 and Various MRB
XAS of Ferrihydrite Incubated with H2 and Various MRB
Tc-O(ts)
Tc-Fe (ss)
Tc-Tc (ss)
Tc-O (fs)
heterogeneousreductionsignature
MR-1 CN32 ndash Shewanella2CP-C ndash AnaeromyxobacterPCA - Geobacter
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
27
EXAFS Interpretation Involves Various Tc(IV)O2 Models
EXAFS Interpretation Involves Various Tc(IV)O2 Models
Long chains Abiotic and biotic TcO2nH2O
Dimers and trimers coordinated to Fe-O with diffuse Fe scattering Sorbed Fe(II) on phyllosilicates (FRC)
Monomers and dimers coordinated to Fe-O with more intense Fe scattering Homogeneous Tc(IV) heterogeneous Tc(IV) on goethitehematite diasporecorundum and magnetite biotransformation products of ferrihydrite and Tc(IV)-ferrihydrite
Tc-TcTc-Fe
Dimeric surface complex
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
Tc(IV) Tc(IV)
H2O
H2O
Fe(III)
H2O
HO
HO
H2O
Fe(III)
Fe(III)
[Tc]aq
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
28
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Interfacial Speciation of both Tc and Fe Influence Oxidation Rate
Time hrs
T
c O
xidi
zed
Abiotic lt BioticH2 lt Bioticlactate lt TcO2nH2O
Tc(IV)(s) + O2(aq) rarr Tc(VII)(aq)
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
29
ConclusionsConclusions
Electron donor has a major role because of effects on enzymology and TcFe Lactate-enhances Fe(III) reduction slows Tc(VII) reduction and
complexes Tc(IV) H2 ndash stimulates Tc(VII) reduction and slows Fe(III) reduction
Heterogeneous Tc(VII) reduction predominates in Fe(III) oxide-microbe systems
Slower rates of heterogeneous reduction in phyllosilicate dominated systems may allow microbiologic reduction to predominate
Tc(VII) speciation varies in octahedra chain length Relatively insensitive to biogenic mineral phase Sensitive to apparent respiration rate and Fe(II) location
Tc(IV) oxidation rates slowed by mineral association difficult to interpret
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
30
Evolving Hydrology at HanfordEvolving Hydrology at Hanford
groundwater mounding fromSurface water discharge
W to E flowpath to Columbia River
bull Fast flowbull Contaminants migrate in
oxic layerbull Homo- or
heterogeneous reduction minimal
bull Tc(VII) migrates to Columbia
W to E flowpath to Columbia River
dep
th
dO2
dep
th
dO2
Past
Futurebull Slower flowbull Aerobic respiration
depletes O2 anaerobic sites
bull Mineral solubilization of Fe(II) heterogeneous reductants
bull Tc(VII) migration is retarded
high O2River water
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
31
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
Historic Releases of Processes Waters at Hanford Have Strongly Influenced Groundwater Composition
These will change in the future
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
32
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Secondary Fe(II)-Rich Saponite Results as a Weathering Product of Ferrous-Silicate Glass
in Basaltic Lithic Fragments
Fe(II)-glass Fe(II)OH
Fe(II)aq
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
33
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
57Fe Moumlssbauer Spectroscopy of Hanford Sediments
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
Velocity (mms)
-12 -9 -6 -3 0 3 6 9 12
Inte
nsity
(a
u)
124e+7
126e+7
128e+7
130e+7
132e+7
Experimental Simulated Phyllosilicate Fe(III) 8Phyllosilicate Fe(II) 17Clinochlore 6 7Mag-Fe(III) 8Mag-Fe(II)Fe(III) 5Goethite 47Hematite 2
-12 -9 -6 -3 0 3 6 9 12
T
rans
mis
sion
93
94
95
96
97
98
99
100
101
Bulk SampleMagnetic fraction
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
34
Future Research DirectionsFuture Research Directions
Focused on Tc-biogeochemistry in Hanford subsurface sediments and effects of the globally falling water table (lower O2 and slower flow rates)
Based on the observation that sorbed Fe(II) on certain surfaces is a strong reductant for Tc(VII) even when aqueous Fe(II) is near DL
Emphasizes effects of O2 consumption by indigenous microbes and ferrous-containing mineral solids on Fe(II) solubility surface complexed Fe(II) and in-situ heterogeneous Tc(VII) reduction
Will incorporate aquifer sediments along a flow-path from 200 A plateau to Columbia River
Involves laboratory studies with Hanford aquifer sediments (microbial ecology mineralogy biogeochemistry) and field experiments in pristine and Tc(VII)-contaminated groundwater plumes
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
35
Summary RemarksSummary Remarks
Basic ScienceBiotic and abiotic processes can leave distinct signatures at the molecular and microscopic level that allow process discrimination Unraveling bioticabiotic process coupling allows for understanding of non-linear combined effects less empiricism and improved extrapolation to other systemsProcess predominance strongly dependent on fundamental system parameters eg mineralogy and surface area respiration and metabolic rate that are conducive to modeling
HanfordIdentifying natural attenuation mechanisms and their rate and effectQuantifying biogeochemical processes that can reduce [Tc(VII)] to required regulatory needs (eg lt 10-9 molL)Bounding constraints imposed by natural processes as the site evolves in response to system changes
Contributions to ERSDs Long Term MeasureQuantifying coupled process effects that dominate fate and transport for some radionuclidesDevelopment of modelsparameters of appropriate phenomenology and complexitySupport decisions on need and approach for remediation
- Slide 1
- Heterogeneous Reduction of Pertechnetate [Tc(VII)O4-] by Surface Complexed Fe(II) at pH = 7
-
top related