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Ion Exchange Resins

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  1. Ion Exchange Resins • General resin information • Functional Groups • Synthesis • Types • Structure • Resin Data • Kinetics • Thermodynamics • Distribution • Radiation effects • Ion Specific Resins

  2. 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

  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

  4. 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

  5. Organic Resins • Functional group • Functionalize benzene • Sulfonated to produce cation exchanger • Chlorinated to produce anion exchanger

  6. Resin Synthesis HO OH HO OH NaOH, H O 2 HCOH n resorcinol OH OH OH OH NaOH, H O 2 HCOH n catechol a a a

  7. 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 solutions • Can be used to make functionalized exchangers

  8. Organic Resin groups Linkage group Cation exchange Anion exchange Chloride

  9. Resin Structure

  10. 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

  11. Zeolite

  12. 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

  13. 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

  14. 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 resins • Need to determine site concentration

  15. Radioactive considerations • High selectivity • Cs from Na • Radiation effects • Not sensitive to radiation • Inorganics tend to be better than organics • High loading • Need to limit resin change • Limited breakthrough • Ease of change • Flushing with solution • Good waste form • Radioactive waste

  16. Hanford Tanks • 177 Tanks • Each Tank 3,800,000 Liters • Three sections • Salt cake • Sludge • Supernatant • Interested in extracting Cs, Sr, Tc, and Actinides with • Silicatitanates • Resorcinol formaldehyde • CS-100 (synthetic zeolite)

  17. Ion Selective Resins • Selected extraction of radionuclides • Cs for waste reduction • Am 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

  18. 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

  19. 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

  20. OH HO OH OH n n Catechol Formaldehyde Resin Resorcinol Formaldehyde Resin OH OH OH N x m n x = 0, Phenol-8-Hydroxyquinoline Formaldehyde Resin x = 1, Catechol-8-Hydroxyquinoline Formaldehyde Resin x = 1, Resorcinol-8-Hydroxyquinoline Formaldehyde Resin

  21. 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

  22. 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

  23. Experimental • Distribution studies • With H+ and Na+ forms • 0.05 g resin • 10 mL of 0.005-.1 M metal ion • Metal concentration determined by ICP-AES or radiochemically • Distribution coefficient Ci = initial concentration Cf = final solution concentration V= solution volume (mL) m = resin mass (g)

  24. Cesium Extraction

  25. 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) Selectivity Resin Li Na K Rb Cs Cs/Na Cs/K PF 10.5 0.01 8.0 13.0 79.8 7980 10 RF 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

  26. Cesium Column Studies with RF pH 14, Na, Cs, K, Al, V, As

  27. Eu/La Competitive Extraction Distribution Coefficients, 2.5 mM Eu,La, pH 4 Resin La Eu Eu/La CF 2.38x106 2.03x106 0.85 RF 2.59x106 2.18x106 0.84 PQF 64.4 400 6.21 CQF 98.1 672 6.85 RQF 78.4 817 9.91

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

  29. Eu-La Separation

  30. 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

  31. 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