Ion Exchange Resins

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Ion Exchange Resins

• General resin information
• Functional Groups
• Synthesis
• Types
• Structure
• Resin Data
• Kinetics
• Thermodynamics
• Distribution
• 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

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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
• Z3 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
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
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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

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Organic Resin groups
Linkage group
Cation exchange
Anion exchange
Chloride
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Resin Structure
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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

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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
• DIon 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

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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 loading
• Need to limit resin change
• Limited breakthrough
• Ease of change
• Flushing with solution
• Good waste form
• Radioactive waste

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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)

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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

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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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Experimental

• IR spectroscopy
• Resin characterization
• OH, CCAromatic, CH2 , CO
• Moisture regain
• 24 hour heating of 0.1 g at 100C
• 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 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)

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Cesium Extraction
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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) 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

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Cesium Column Studies with RF
pH 14, Na, Cs, K, Al, V, As
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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
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Eu La 0.0025 mol L-1, T(shaking) 20h, m
0.05g
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Eu-La Separation
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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
• gt99 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