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Ion Exchange Resins• General resin information

Functional Groups SynthesisTypes Structure

• Resin DataKineticsThermodynamicsDistribution

• Radiation effects• Ion Specific Resins

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Ion Exchange Resins

• ResinsOrganic or inorganic polymer used to exchange cations or anions from a solution phase

• General StructurePolymer backbone not involved in bondingFunctional group for complexing anion or cation

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Resins• Properties

CapacityAmount of exchangeable ions per unit quantity of material

* Proton exchange capacity (PEC)Selectivity

Cation or anion exchange* Cations are positive ions* Anions are negative ions

Some selectivities within group* Distribution of metal ion can vary with solution

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Resins• Exchange proceeds on an equivalent basis

Charge of the exchange ion must be neutralizedZ=3 must bind with 3 proton exchanging groups

• Organic Exchange ResinsBackbone

Cross linked polymer chain* Divinylbenzene, polystyrene* Cross linking limits swelling, restricts cavity

size

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Organic Resins

Functional groupFunctionalize benzene* Sulfonated to produce cation

exchanger* Chlorinated to produce anion

exchanger

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Resin Synthesis

resorcinol

catechol

HO OH

HCOHNaOH, H 2O

HO OH

n

OHOH

HCOHNaOH, H 2O

OHOH

n

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Resins• Structure

Randomness in crosslinking produces disordered structure

Range of distances between sitesEnvironments

* Near organic backbone or mainly interacting with solution

Sorption based resins• Organic with long carbon chains (XAD resins)

Sorbs organics from aqueous solutionsCan be used to make functionalized exchangers

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Organic Resin groups

SO3H

Linkage group Cation exchange

Chloride

CH2ClCH2N(CH3)3Cl

Anion exchange

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Resin Structure

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Inorganic Resins• More formalized structures

Silicates (SiO4)Alumina (AlO4)

Both tetrahedralCan be combined

* (Ca,Na)(Si4Al2O12).6H2OAluminosilicates

* zeolite, montmorillonites* Cation exchangers* Can be synthesized

Zirconium, Tin- phosphate

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Zeolite

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Inorganic Ion Exchanger

• Easy to synthesisMetal salt with phosphatePrecipitate forms

Grind and sieve• Zr can be replaced by other tetravalent metals

Sn, Th, U

OH

OPO(OH)2

O

OPO(OH)2

OPO(OH)2

O

OH

OPO(OH)2

O

OPO(OH)2

OPO(OH)2

Zr ZrZrZr

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Kinetics• Diffusion controlled

Film diffusionOn surface of resin

Particle diffusionMovement into resin

• Rate is generally fast• Increase in crosslinking decrease rate• Theoretical plates used to estimate reactions

Swelling• Solvation increases exchange• Greater swelling decreases selectivity

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Selectivity• Distribution Coefficient

D=Ion per mass dry resin/Ion per volume• The stability constants for metal ions can be found

Based on molality (equivalents/kg solute)Ratio (neutralized equivalents)

Equilibrium constants related to selectivity constants

• Thermodynamic concentration based upon amount of sites available

Constants can be evaluated for resinsNeed to determine site concentration

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Radioactive considerations• High selectivity

Cs from Na• Radiation effects

Not sensitive to radiationInorganics tend to be better than organics

• High loadingNeed to limit resin changeLimited breakthrough

• Ease of changeFlushing with solution

• Good waste formRadioactive waste

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Hanford Tanks• 177 Tanks• Each Tank 3,800,000 Liters• Three sections

Salt cakeSludgeSupernatant

• Interested in extracting Cs, Sr, Tc, and Actinides withSilicatitanatesResorcinol formaldehydeCS-100 (synthetic zeolite)

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Ion Selective Resins• Selected extraction of radionuclides

Cs for waste reductionAm and Cm from lanthanides

ReprocessingTransmutation

• Separation based on differences in radii and ligandinteraction

size and ligand• Prefer solid-liquid extraction• Metal ion used as template

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Characteristics of Resins

• Ability to construct specific metal ion selectivity Use metal ion as template

• Ease of Synthesis• High degree of metal ion complexation • Flexibility of applications• Different functional groups

Phenol CatecholResorcinol8-Hydroxyquinoline

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Resin Synthesis

•Catechol-formaldehyde resin (CF)•Resorcinol-formaldehyde resin (RF)•Phenol-8-hydroxyquinoline formaldehyde resin (PQF)•Catechol-8-hydroxyquinoline formaldehyde resin (CQF)•Resorcinol-8-hydroxyquinoline formaldehyde resin (RQF)Resins analyzed by IR spectroscopy, moisture regain, and ion exchange capacity

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n

HO OH

Resorcinol Formaldehyde Resinn

OH

OH

Catechol Formaldehyde Resin

OH OH

N

n m

OH x

x = 0, Phenol-8-Hydroxyquinoline Formaldehyde Resinx = 1, Catechol-8-Hydroxyquinoline Formaldehyde Resinx = 1, Resorcinol-8-Hydroxyquinoline Formaldehyde Resin

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Experimental

• IR spectroscopyResin characterization

OH, C=CAromatic, CH2 , CO• Moisture regain

24 hour heating of 0.1 g at 100°C• Ion exchange capacity

Titration of 0.25g with 0.1 M NaOH

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Moisture Regain and IEC

Resin Moisture IEC Theory IEC% meq/g %

CF 20 8.6 55RF 40 11.5 74PQF 10 5.9 80CQF 20 9.6 70RQF 19 9.9 70

•Phenolic resins have lower IEC

•8-hydroxyquinoline increase IEC

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Experimental• Distribution studies

With H+ and Na+ forms0.05 g resin10 mL of 0.005-.1 M metal ionMetal concentration determined by ICP-AES or radiochemicallyDistribution coefficient

Ci = initial concentration Cf = final solution concentrationV= solution volume (mL)m = resin mass (g)

D =Ci − Cf

Cf

Vm

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Cesium Extraction

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Li Na K Rb CsAlkali Metals

catechol resorcinol

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Distribution Coefficients for Group 1 elements.

All metal ions as hydroxides at 0.02 M, 5 mL solution, 25 mg resin, mixing time 5 hours

D (mL/g (dry) SelectivityResin Li Na K Rb Cs Cs/Na Cs/K

PF 10.5 0.01 8.0 13.0 79.8 7980 10RF 93.9 59.4 71.9 85.2 229.5 3.9 3.2CF 128.2 66.7 68.5 77.5 112.8 1.7 1.6

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Cesium Column Studies with RF

0

5

10

15

20

25

30

35

40

0 2 4 6 8 10 12 14 16

CsNaKAl

Elua

nt C

once

ntra

tion

(g/m

L)

Volume Eluant (mL)

0.1 M HCl 1.0 M HCl

pH 14, Na, Cs, K, Al, V, As

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Eu/La Competitive Extraction

Resin La Eu Eu/LaCF 2.38x106 2.03x106 0.85RF 2.59x106 2.18x106 0.84PQF 64.4 400 6.21CQF 98.1 672 6.85RQF 78.4 817 9.91

Distribution Coefficients, 2.5 mM Eu,La, pH 4

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0123456789

10

CF RF PQF CQF RQF

Resin[Eu] = [La] = 0.0025 mol L-1, T(shaking) = 20h, m = 0.05g

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Eu-La Separation

0

2

4

6

8

10

12

0 20 40 60 80 100 120 140

CQFPQFRQF

DEu

/DLa

Mixing Time (Hours)

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Studies with 243Am

• Conditions similar to Eu studies10 mL solution0.05 g resin

RF, CF, PQF, RQF, CQFmillimolar Am concentration

• Analysis by alpha scintillation• >99% of Am removed by CF, RF, PQF• ≈ 95% of Am removed by CQF, RQF• 243Am removed from resin by HNO3

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Ion Specific Resins

• Effective column separation possible• Phenol exhibits selectivity• Incorporation of 8-hydroxyquinoline leads to

selectivity, but lower extraction• Eu/La separation possible• Possible to prepare ion specific resins for the

actinides