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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

• Resins

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

• General Structure

Polymer backbone not involved in bonding

Functional group for complexing anion or cation

7-3

Resins• Properties

Capacity Amount 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 neutralized Z=3 must bind with 3 proton exchanging groups

• Organic Exchange Resins

Backbone Cross linked polymer chain

* Divinylbenzene, polystyrene

* Cross linking limits swelling, restricts cavity size

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Organic Resins

Functional group Functionalize benzene

* Sulfonated to produce cation exchanger

* Chlorinated to produce anion exchanger

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Resin Synthesis

resorcinol

catechol

HO OH

HCOH

NaOH, H 2OHO OH

n

OH

OH

HCOH

NaOH, H 2OOH

OH

n

7-9

Resins• Structure

Randomness in crosslinking produces disordered structure Range of distances between sites Environments

* 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

aa

SO3H

Linkage group Cation exchange

Chloride

aa

CH2Cl

aa

CH2N(CH3)3Cl

Anion exchange

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Resin Structure

7-12

Inorganic Resins• More formalized structures

Silicates (SiO4)

Alumina (AlO4) Both tetrahedral Can be combined

* (Ca,Na)(Si4Al2O12).6H2O Aluminosilicates

* zeolite, montmorillonites* Cation exchangers* Can be synthesized

Zirconium, Tin- phosphate

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Zeolite

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Inorganic Ion Exchanger

• Easy to synthesis

Metal salt with phosphate

Precipitate forms Grind and sieve

• Zr can be replaced by other tetravalent metals

Sn, Th, U

aa

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 diffusion On surface of resin

Particle diffusion Movement 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 availableConstants can be evaluated for resins Need to determine site concentration

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Radioactive considerations• High selectivity

Cs from Na• Radiation effects

Not sensitive to radiation Inorganics 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 Reprocessing Transmutation

• Separation based on differences in radii and ligand interaction

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

Catechol

Resorcinol

8-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 Resin

n

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 spectroscopy

Resin 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 55

RF 40 11.5 74

PQF 10 5.9 80

CQF 20 9.6 70

RQF 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

V

m

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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 Cs

Alkali 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 3.2 CF 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

CsNaK

Al

Elu

an

t C

on

ce

ntr

ati

on

(g

/mL

)

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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0

1

2

3

4

5

6

7

8

9

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

DE

u/D

La

Mixing Time (Hours)

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Studies with 243Am

• Conditions similar to Eu studies

10 mL solution

0.05 g resin RF, CF, PQF, RQF, CQF

millimolar 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