12 environmental science of metals in the environment sources, fate and transport[2]

8/3/2019 12 Environmental Science of Metals in the Environment Sources, Fate and Transport[2]

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12. Environmental science of

metals in the environment:sources, fate and transport

Rodica G. StanescuPolitehnica University of Bucharest

IasiRomania

June 2009

Gheorghe Asachi Technical University of IasiInstitute of International Health, Michigan State University

Polytechnic University, BucharestAlexandru Ioan Cuza University of IaiInstitute of Public Health, Bucharest

John E. Fogarty International Center, U.S. National Institutesof Health
http://www.fic.nih.gov/index.htmhttp://www.uaic.ro/uaic/bin/view/Main/http://en.wikipedia.org/wiki/Image:Universitatea_Politehnica_Bucuresti_logo.png


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What We Know


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Source, Fate and Transport

ROCKS AND MINERALS

chemically altered andunaltered materials

weathering

(im)mobilization

Rock characteristics

Environment characteristics

Ion characteristics

Environment characteristics

(chemical)

IONS, OTHER METAL SPECIES

RECEPTOR

Ecosystems

transport


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Terrestrial Abundances of theElements

From Mineral and Energy Resources,Douglas G. Brookins, (1990).

From Planet Earth, Casare Emiliani,(1992).

CRUST: ~0.5% of Earths total mass


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What We Know

The abundant metallic - aluminum, iron, calcium,magnesium, sodium, potassium, and titanium --bound up in the various silicates, carbonates,

oxides, and other rocky materials that make upthe crust.

Silicates

- extremely stable in the chemical sense, and

- it requires prodigious amounts of energy to dissociateordinary rocks in order to retrieve pure metals fromthem.


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Metal Specificity

Metals cannot be destroyed by biological orchemical processes

Metals can only be reduced by physical removal (e.g.,leaching, biological uptake)

Metal speciation can influence metal distribution andbioavailability within the environment

Some metals are essential elements

Speciation (forms), transformations, and

geochemical environment need to be consideredwhen evaluating potential effects of metals onthe environment


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Heavy Metals

usually taken to mean those metallic elements that havea density equal to or greater than 6.0 g/cm3:

Cu, Cd, Cr, Hg, Ni, Pb and Zn

occur NATURALLY in soils, sedimentary deposits and

water bodies, normal background concentrations of these metals exist.

are considered to be contaminants relative tobackground concentrations

are considered to be pollutants relative to regulatedlimits of concentrations, where their concentrations haverisen to such an extent that they present a real orpotential risk to living organisms.


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Geoavailability

that portion of achemicalelements or acompounds totalcontent in anearth material

that can beliberated to thesurficial or near-surfaceenvironment (orbiosphere)throughmechanical,chemical, orbiologicalprocesses

(from Smith and

Huyck (1999))


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Weathering

Codrington, Stephen. Planet Geography 3rd Edition(2005)

Physical weathering Chemical weathering

Weathering is the breakdown and alteration of rocks andminerals at or near the Earth's surface into products thatare more in equilibrium with the conditions found in thisenvironment. Pidwirny, M. (2006). "Weathering". Fundamentals

of Physical Geography, 2nd Edition.
http://upload.wikimedia.org/wikipedia/commons/f/fc/YehliuTaiwan-HoneycombWeathering.jpghttp://en.wikipedia.org/wiki/Image:Weathering_9039.jpg


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Weathering Rate


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Chemical Weathering


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Processes and Geochemical Conditions thatRedistribute Cationic Dissolved Metals


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Mobility of Elements

Mobility refers to the capacity of an element tomove within fluids after dissolution

difficult to quantitatively predict in surficial

environmentsNeeds to be considered in a relative sense

empirically compare the behavior of elementsunder changing environmental conditions

geochemical barriers

Controlling factors include pH, solubility,sorption, and redox conditions


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Factors Affecting Mobility Speciation

Ions Cr(III), Cr(VI),As(III), As(V)

Complexes(Inorganicligands, Organicligands)

Mineralogy

Geochemical factorspH

Eh

Dissolved oxygen

Water chemistry

Microbial activity

Sorbents

Competition fromother ions

There are several computerprograms that perform chemical

speciation calculations(e.g., MINEQL+; MINTEQA2;

PHREEQ; GEOCHEM).

Speciation models andThermodynamic databases

http://chess.ensmp.fr/chemsites.html


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Mobility of Elements

in the surficial environmentis a function of ionicpotential (ratio of oxidationnumber to ionic radius)

from Rose et al. (1979)


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Relative Mobility of Chemical Elements underDifferent Environmental Conditions

(from Smith (2007))REE = Rare Earth Elements


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Metal Speciation

Key to understanding metal mobility, bioavailability,and toxicity

Different chemical species of a given metal often have differentmobility behavior and toxicological effects

Distinct chemical species are chemical compounds that differ inisotopic composition, conformation, oxidation or electronic state,or in the nature of their complexed or covalently boundsubstituents*

* from Templeton et al. (2000)

Physical and chemical properties of metals at the atomiclevel are responsible for differences in theirenvironmental behavior


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General Characteristics in AquaticSystems

after Smith and Huyck (1999)


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Metal Sorption Reactions

Largely control the fate of many traceelements in natural systems

Are strongly pH-dependent Are a function of metal-complex formation

and ionic strength At many mining sites there are abundant

iron-and aluminum-oxide precipitates can act as effective sorbents for a variety of

metals self-mitigating capacity of MIW (Mining Influenced

Waters) i.e., with pH increasing, dissolved iron can precipitate

and sorb trace elements


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Redox-Sensitive Metals

Generally undergo a change in mobilityunder different oxidizing or reducingconditions

uranium is immobile under reducing conditionsbut can be mobile under oxidizing conditions

Atmospheric oxygen generally is the primaryoxidant, and organic matter generally is the

primary reductant at mining sites, other reductants may include FeS,

FeS2, Fe2+, Mn2+, or H2S


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Metal Complexes

A metal complex - formed by thedonation of a lone pair of electronsfrom a negative ion, e.g. CN, ormolecule, e.g. H2O, to that metal.

The species donating the electronpair : a ligand.

The bond : co-ordinate chemicalbond.

The number of ligands : co-ordination number.

Ligands capable of co-ordinatingmore than once are termed

polydentate ligands, and arereferred to as chelating agents.(ethylenediaminetetraacetic acid)(EDTA)

Z=30


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Heavy Metal PollutantsSources and Cycles

pollutant concentration in agiven location typicallydepends on geochemicalcycling over multiple inputsources and pathways, withinter-reservoirexchange.


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Examples of metalforms or species that

are of potentialenvironmental and

toxicologicalimportance.

General schememetal speciation in

solution.


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Complex Ions in Sea Water

Metals Redox

condition

Insoluble

Compd

pKsp Soluble complex (%)

Cd (II) Oxidative CdCO3 13.59 CdCl+(56.5), CdCl2

0(15.2), CdCl42- (10.0),

CdCl64-

(9.1), CdCl3-

(9.0)

Cd (II) Reductive CdS 26.96 Cd(HS)20(97.2), Cd(HS)3

-(2.2), Cd(HS)42-(0.1),

Cd(HS)+(


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Heavy Metals in Soil

exchange withother cations on thesurface of thecolloidal clays andbecome adsorbed.

form complexeswith humic and fulvicacid groups.

react with anions

present and beprecipitated out ofsolution.

From emsi.stanford.edu/aboutEMSI.html


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pH role

mobility and bioavailability primarily determined by pH

mobility and bioavailability are enhanced under acidicconditions

Balance between acid-generating and acid-consumingreactions depends on:

relative rates of those reactions

accessibility of minerals that contribute to thosereactions


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pH role - Ficklin Diagram

from Plumlee et

al. (1999)


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Metal Speciation


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Bioavailability


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Metal Hydroxide

Solubility

Metal Sulfide

Solubility


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Single Variable Diagram: pH

What is the most abundant species of iron in natural waters?

Source: DeGraff, 2007 Understanding and Responding to Hazardous Substances at Mine Sites in the Western US


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Single Variable Diagrams:

pH

Most abundant species of arsenic innatural waters

Influence of pH on As distribution?

Source: DeGraff, 2007 Understanding and Responding to Hazardous

Substances at Mine Sites in the Western USHFO = hydrous ferric oxide


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Redox Potential

As Desorption andDissolutionduring changes ofthe reducingconditions

Insoluble Fe Soluble Fe


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Two Variable Diagrams:pE-pH

What is the most

abundant species ofarsenic in natural waters?

H3AsO4 H2AsO4- + H+

H2AsO4- + 3H+ + 2e- H3AsO3 + H2O

!!!!!! arsenite (III) is about 60 times more toxic than arsenate (V)


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Consequences: As Poisoning of

Groundwater

largest ever poisoning - 60 mil. atrisk, 700,000 poisoned (mostly inBangladesh)

1970s: 11m drinking wells

patchy contamination

one theory: As attached to reduced iron

oxides in peat deposits

anoxic microbes release Asduring respiration using Fe-ox

another theory:

As associate with pyrite

groundwater drawdown exposespyrite to O2, weathering releasesAs

UNSOLVED!!

arsenocosis cancer


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Redox Potential


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Redox PotentialAcid Mine Drainage

Sulfate reduction:CH2O + H2O CO2 + 4H

+ + 4e-

SO42- + 10H+ + 8e- HS- + 4H2O

SO42- + 2CH2O + 2H

+ H2S + 2H2O + 2CO2

With the presence of Fe2+

Fe2+ + H2S FeS + 2H+ And FeS + S FeS2

FeS2 + H2O + 7/2O2 Fe2+ + 2SO4

2- + 2H+

And

FeS2 + 14Fe3+ + 8H2O 15Fe

2+ + 8H2SO4

Later

4Fe2+ + O2 + 10H2O 4Fe(OH)3 + 8H+

Pyrite oxidationfrom the action of Acidithiobacillusbacteria

air

organics


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Acid DraiangeTerms

Acid Mine Drainage (AMD)

Water that is polluted fromcontact with mining activity

Acid Rock Drainage (ARD)

Natural rock drainage that isacidic

Both produce acidic waters

R k D i


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Rock Drainage

(general)

acid rock drainage neutral mine drainage

saline drainage

= contaminants are

released from solid toliquid phase by sulphidemineral oxidation

Includes: tailing, waste

rock, underground mineand pit walls, pit lakes,spent ore heaps andlow grade stockpiles


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Surface Water

Ground Water

Sediment/soil

Air

MediaSource

Smelters/ore processing

Tailings

Undergroundworkings

Waste rock

Heap leachpads

Pit lakes

Hg, Pb

As, Se

Cd, Sb,Ag, CNCu, ZnPb, UCr, Fe

Hg

Metals


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Acid Rock Drainage

Dissolution, sorption,nucleation, growth

Oxidation-Reductionreactions

Acid-Base reactions

Isotope exchange reactions

Modeling exercises Chemical Speciation

Saturation /equilibrium

Kinetics

Chemical Processes Physical & BiologicalProcesses

Transport

Water

Sediment Wind

Microbial

S-oxidizers, Fe-

oxidizers

S-reducers, Fe-reducers

Wetland Plants


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Pyrite Oxidation

Pyrite Dissolution/Overall Reaction

FeS2 + 15/4O2 + 7/2H2O = Fe(OH)3 + 2H2SO4

Low pH (high acidity)

Metal rich: As, Sb, Zn, Cu

Fe, Al, Mn rich

Sulfate rich


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Pyrite OxidationFeS2 + 7/2O2 + H2O = Fe

2+ + 2SO42- + 2H+

FeS2 + 14Fe3+ + 8H2O = 15Fe

2+ + 2SO42- +16H+

After Stumm and Singer (1980)

FeS (s) + O2

Fe(II) + S22-

+ O2

Fe (II) + SO42-

+ FeS (s)2

fast

fastmicrobial

+ O2

slowinorg.

Fe(III) = Fe(OH) (s)3


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Pyrite Oxidation

Chemical

oxygen, Fe(III), water, buffering

Physical texture, grain size Ore processing, framboidal pyrite

Biological

Fe- and S-oxidizing bacteria


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Mine Tailings, Sudbury Ontario
http://www.jurnalul.ro/librarie_fisiere/imagini/2008-07-16/5d2336169294c8f1024e15865688991c.jpg


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Almau Mare , Mina Hanes

S
http://www.jurnalul.ro/librarie_fisiere/imagini/2008-07-16/5d2336169294c8f1024e15865688991c.jpghttp://www.jurnalul.ro/librarie_fisiere/imagini/2008-07-16/5d2336169294c8f1024e15865688991c.jpg


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AMD Prediction

Assessment of Acid-generation and Acid-neutralization capacity (acid,

sulfate) Hydrologic Assessment:

Availability of Oxygen andWater (acid, sulfate)

Ore Deposit/Wasterock/TailingsCharacterization (metals)

T f O id i


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Transport of OxidationProducts to Surface Waters

Sorption trend onto Fe pptPb>Hg>Ag>As>Ni>Cu>Cd>Zn

Drainage Surface Water

H, Fe, SO

Mn,

+ 2-

4

M Mixing/dilution

pH increase

ppt of Fe(OH), Al(OH)sulfate diluted/sorbedMetals sorbed/co-ppt with

Fe and Al

3 3


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Wetland Processes

InputFe , SO , H , Me

3+ 2- +

4 Output=Cleaner

Plant uptake

ReducingSO to H S

ppt (Fe,Me)S4 2

2-

Oxidizingppt of Fe-OH-O-SO

adsorption4

[inc. pH]

See Kwong & Stempvoort (1994)

(Mt. Washington, B.C.)

Other ORD work at SPRD: T. Canfield et al.

Constructed Wetlands


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G d W t /A i Li t


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Ground Water/Anoxic LimestoneDrains

High Fe(II)/Fe(III)pH 2-6, low O2Al, Metals

GW

Limestone Drain

Calcite dissolutionAlkalinity production

Retain Anoxic [Fe(II)/Fe(III)]pH increase

High O2Fe(II)=>Fe(III)Fe(OH)3 ppt

alk takes up acid

Surface


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Thank you

12 environmental science of metals in the environment sources, fate and transport[2]

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