ion exchange resinsradchem.nevada.edu/classes/rdch702/lectures/lect 7 ion exchange.pdf ·...
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7-1
Ion Exchange Resins• General resin information
Functional Groups SynthesisTypes Structure
• Resin DataKineticsThermodynamicsDistribution
• Radiation effects• Ion Specific Resins
7-2
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
7-3
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
7-4
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
7-5
Organic Resins
Functional groupFunctionalize benzene* Sulfonated to produce cation
exchanger* Chlorinated to produce anion
exchanger
7-9
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
7-10
Organic Resin groups
SO3H
Linkage group Cation exchange
Chloride
CH2ClCH2N(CH3)3Cl
Anion exchange
7-12
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
7-14
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
7-15
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
7-16
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
7-29
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
7-31
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)
7-32
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
7-33
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
7-34
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
7-35
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
7-36
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
7-37
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
7-38
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
7-39
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
7-40
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
7-41
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
7-42
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
7-44
Eu-La Separation
0
2
4
6
8
10
12
0 20 40 60 80 100 120 140
CQFPQFRQF
DEu
/DLa
Mixing Time (Hours)
7-45
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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