Ion Exchange Resins
• General resin information
Functional Groups
Synthesis
Types
Structure
• Resin Data
Kinetics
Thermodynamics
Distribution
• Radiation effects
• Ion Specific Resins
7-1
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
7-2
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
7-3
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
7-4
Organic Resins
Functional group
Functionalize benzene
* Sulfonated to produce cation
exchanger
* Chlorinated to produce anion
exchanger
7-5
7-6
7-7
Resin Synthesis
HO
OH
HO
OH
NaOH, H 2 O
HCOH
n
resorcinol
OH
OH
OH
OH
NaOH, H 2 O
HCOH
catechol
n
7-8
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
7-9
Organic Resin groups
SO3 H
Linkage group
CH2 Cl
Chloride
Cation exchange
CH2 N(CH3 )3 Cl
Anion exchange
7-10
Resin
Structure
7-11
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
7-12
Zeolite
7-13
Inorganic Ion Exchanger
OPO(OH)2 OH
OH
Zr
O
Zr
O
Zr
OPO(OH)2
O
Zr
OPO(OH)2 OPO(OH)2 OPO(OH)2 OPO(OH)2
• Easy to synthesis
Metal salt with phosphate
Precipitate forms
Grind and sieve
• Zr can be replaced by other tetravalent metals
Sn, Th, U
7-14
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
7-15
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
7-16
7-17
7-18
7-19
7-20
7-21
7-22
7-23
7-24
7-25
7-26
7-27
7-28
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
7-29
7-30
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)
7-31
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
7-32
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
7-33
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
7-34
OH
HO
OH
OH
n
n
Resorcinol Formaldehyde Resin
OH
Catechol Formaldehyde Resin
OH
OH
N
x
n
m
x = 0, Phenol-8-Hydroxyquinoline Formaldehyde Resin
x = 1, Catechol-8-Hydroxyquinoline Formaldehyde Resin
7-35
x = 1, Resorcinol-8-Hydroxyquinoline Formaldehyde Resin
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
7-36
Moisture Regain and IEC
Resin
CF
RF
PQF
CQF
RQF
Moisture
%
20
40
10
20
19
IEC
meq/g
8.6
11.5
5.9
9.6
9.9
Theory IEC
%
55
74
80
70
70
•Phenolic resins have lower IEC
•8-hydroxyquinoline increase IEC
7-37
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 ICPAES or radiochemically
Distribution coefficient
Ci  Cf V
D
Ci = initial concentration
Cf
m
Cf = final solution concentration
V= solution volume (mL)
m = resin mass (g)
7-38
Cesium Extraction
1.8
catechol resorcinol
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
Li
Na
K
Rb
Cs
Alkali Metals
7-39
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)
Na
K
Rb
Resin
Li
PF
RF
CF
10.5 0.01
93.9 59.4
128.2 66.7
8.0
71.9
68.5
13.0
85.2
77.5
Cs
Selectivity
Cs/Na
Cs/K
79.8
229.5
112.8
7980
3.9
1.7
10
3.2
1.6
7-40
Cesium Column Studies with RF
pH 14, Na, Cs, K, Al, V, As
40
0.1 M HCl
1.0 M HCl
Eluant Concentration (g/mL)
35
30
25
20
Cs
Na
K
Al
15
10
5
0
0
2
4
6
8
10
Volume Eluant (mL)
12
14
16
7-41
Eu/La Competitive Extraction
Distribution Coefficients, 2.5 mM Eu,La, pH 4
Resin
CF
RF
PQF
CQF
RQF
La
2.38x106
2.59x106
64.4
98.1
78.4
Eu
2.03x106
2.18x106
400
672
817
Eu/La
0.85
0.84
6.21
6.85
9.91
7-42
[Eu] = [La] = 0.0025 mol L-1, T(shaking) = 20h, m = 0.05g
7-43
Eu-La Separation
12
10
D Eu/D
La
8
6
4
CQF
PQF
RQF
2
0
0
20
40
60
80
100
Mixing Time (Hours)
120
140
7-44
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
7-45
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
7-46