Deals with the ion exchange process basics and design and with the applications of ion exchange process to water treatment.

1. Ion Exchange Process

2. Ions
• Electrically charged atoms or molecules (Cations and Anions) –
can have one or more charges (mostly 1 to 3), and can be
made of one or more atoms
– Mono-atomic ions: Mono-valent ions (Na+ and Cl-), divalent ions
(Ca+2), trivalent ions (Al+3)
– Polyatomic ions: Mono-valent ions (NH4
+1 and NO3
-1), Di-valent
ions (CO3
-2, and CrO4
-2)
• Mono-atomic divalent or trivalent anions are rare in water
• Soluble substances in water can be ionized or non-ionized
• Water is electrically neutral (sum of cation charges = sum of
anion charges)
• Ions move around in water freely (anions not attached to
cations) and are surrounded by water
– Cations are attracted by Oxygen atom and anions by Hydrogen
atoms of water
• Ionized substances can be removed from water by ion
exchange process

3. Ion Exchange Resins Ion Exchange Process
• Ion exchange materials
– Natural materials - Zeolites (alumino-silicates, NaOAl2O34SiO2),
proteins, soils, lignin, coal, and metal oxides
– Synthetic materials (zeolite gels and polymeric resins) – porous
phenolic polymer beads (~0.5 mm dia.)
• Soluble ionized substances are removed from water through
exchanging with the ions on the ion exchange materials
– Ion exchange process is appropriate for ions present in low
concentrations
• During the ion exchange process, electrical neutrality of water
is preserved
– Fixed ions of functional groups are neutralized by mobile ions
– Mobile ions of functional groups can be exchanged with the ions
of same charge (positive with positive and negative with negative)
• Functional groups of the resins determine the ion selectivity
and also the position of the ion exchange equilibrium

4. • Ion exchange resin is insoluble, inert and relatively rigid material
• Manufactured through copolymerization of styrene (neutral
organic molecules) and divinyl benzene (DVB)
– Polymerization of styrene to obtain polystyrene
– Cross linking the polystyrene chains with divinyl benzene
– Adding functional groups to the resultant skeletal framework by
chemical reaction procedures
• Increased cross linkages limit volume of the macro-reticular
spaces and reduce the ion exchange capacity - but can increase
the relative selectivity for smaller ions
Styrene
DVB
Skeletal framework

5. Ion Exchange Resins
• Basically two types: the cation and the anion exchange resins
(no resin exchanges both the cations and the anions)
• Cation exchange resins have anionic functional groups and
mobile caions (H+, Na+, etc.) are attached to them – two types
– Strongly Acidic Cation (SAC) exchange resins – have (SO-
3)
sulfonates (derived from sulfuric acid) as functional groups
• These remove hardness in the sodium form and all cations in the
hydrogen form
• Total exchange capacity is 1.9 to 2.2 eq/L [Na+]
– Weakly Acidic Cation (WCA) exchange resins – have R-COO-
(derived from carboxylic acid) as functional groups
• These are used in hydrogen form and these preferentially remove
divalent ions from solutions containing alkalinity
• Total exchange capacity is 3.7 to 4.5 eq/L [H+]

6. Ion Exchange Resins
• Anion exchange resins have cationic functional groups and
mobile anions (OH-, Cl-, SO4
2-) are attached to them – two types
– Strongly Basic Anion (SBA) exchange resins – have R-N+ (derived
from quaternary ammonia compounds) as functional groups
• These remove all anions in the hydroxide form and nitrates and
sulfates in the chloride form
• Total exchange capacity is 1.0 to 1.5 eq/L [Cl–]
– Weakly Basic Anion (WBA) exchange resins – have R-NH3
+ or R-
NH2
+ (derived from prim. and sec. amines) as functional groups
• After cation exchange, these remove chlorides, sulfates, nitrates
and other anions of strong acids, but do not remove anions of weak
acids (SiO2 and CO2)
• Total exchange capacity is 1.1 to 1.7 eq/L [free base]

7. Ion exchange resin types
Function group Ionic species removed
Triethylammonium NO3
Thiol Hg, Cd, etc.
Aminophosphonic Ca from brine
Iminodiacetic Ni, Cu, etc.
Methyl glucamine H3BO3
Bis-picolylamine Metals at low pH
Thiourea Hg, Cd, etc.
• Selective ion exchange resins
• Have many different types of functional groups and remove
different cations and different anions selectively
• Heavy metal selective chelating resins
– Functional group is usually EDTA (R-EDTA-Na)
– Behaves like weak acid cationic resin
– Exhibits high degree of selectivity for heavy metal cations

8. Ion Exchange Equilibrium

 HNaRSONaHRSO 33
  
 NaCaRSOCaNaRSO 22 23
2
3

 HRCOONaNaRCOOH

 NaCaRCOOCaRCOONa 2)(2 2
2
Weak acid cationic
Strong acid cationic

 OHNClRRClNOHRR '
3
'
3

 OHClRNHClOHRNH 33

 ClSORNHSOClRNH 2)(2 423
2
43
Weak base anionic resin
Strong base anionic resin
  
  
  
  
  
  
Ca
NaCaNa
Na
HNaH
B
ABA
KK
CaNa
CaNa
KK
NaH
NaH
KK
BA
BA












2
2
Resin phase is indicated by a bar
over letter
KA
B or KH
Na is selectivity coefficient
[…] denotes concentration

9. • Selectivity coefficient depends on
– Nature and valency (ionic charge number) of the ion (greater the
charge number higher the affinity)
– Type of the resin, and its saturation and functional groups
– Hydrated radius (smaller the radius greater the affinity)
– Ion concentration in the water/wastewater
• Selectivity coefficient is valid over a narrow pH range
• At low concentrations selectivity coefficient for the exchange
of mono-valent ions by divalent ions is larger than that for
exchange of mono-valent ions by mono-valent ions
Selectivity Coefficient

 nABRBAnR n
n
n
   
    nBAnn
n
n
n
K
BAR
BRA




KA
+
B
+n is selectivity coefficient
R-A+ is concentration of A on the resin
A+ is concentration of A in solution
Rn
- B+n is concentration of B+n on resin
B+n is concentration of B in solution

10. Anion Anion
Cation Cation

11. Ion exchange resin column

12. Ion exchange process
• Either a batch process or a continuous process
– Batch process: Resin is stirred with water for process
completion, and spent resin is removed, regenerated and reused
– Continuous process: water is passed through a packed resin
column, and, when exhausted, the resin is regenerated & reused
• Running (down-flow) and regeneration cycle
– Backwashing (up-flow and expansion/fluidization to remove
trapped solids)
– Regeneration chemical run (down flow)
• 2-5% solution (by weight) of H2SO4 or HCl (5-10% in case of
NaCl) is used for the cation exchange resin beds
regeneration
• 5-10% solution (by weight) of NaOH or NH4OH is used for
anion exchange resin beds regeneration
– Rinsing to remove residual regeneration chemical
– Rapid rinse (down-flow) till the quality becomes satisfactory

13. Characteristics of the ion exchange resins
1. Ion exchange capacity: Total capacity & Operating capacity
• Total capacity: Number of functional groups per unit volume
of the resin (expressed in equivalents per liter)
– Capacity of zeolite cation exchanger is 0.05 to 0.1 eq/kg
– Capacity of synthetic resins is 2 – 10 eq/kg
– SAC resin has 1.8 to 2.2 eq/L; WAC resin has 3.7 to 4.5 eq/L; and
WBA or SBA resin has 1.1 to 1.4 eq/L capacity
• Operating capacity: Difference of regenerated sites between
the beginning and the end of the ion exchange run
– Resin is 100% regenerated at the beginning of the run, but not
completely exhausted at the end of the run
– Usually 40-70% of the total capacity (functional groups are not
100% exhausted at the end of the run)
2. Size, density (wet), bulk density, porosity and shape factor of
the resin

14. For the estimation of the ion exchange capacity construct
breakthrough curve
– break through point and exhaustion points correspond to 5% and
95% of influent concentrations respectively)
Ion Exchange Capacity of Resins

15. Characteristics of the ion exchange resins
3. Ion exchange resin type and form of resin (hydrogen/ sodium/
hydroxide/ chloride forms)
– Strong/weak anion/cation exchange resins; selective ion
exchange resin; metal ion selective chelating resins
– Regeneration chemical used determines the form of resin
– Hydrochloric or sulfuric acid forms hydrogen form of cation
exchange resin
– Sodium chloride forms sodium form of cation exchange resin or
chloride form of anion exchange resin
– Sodium hydroxide or potassium hydroxide forms hydroxide form
of anion exchange resins
4. Selectivity coefficient and affinity differences among different
ionic species (with the mobile ions of resin functional groups!)
– The order affinity is
SO4
2- > NO3
- > Cl- > HCO3
- > OH- > F- for anions
Pb+ > Ca2+ > Mg2+ > Na+ > H+ for cations

16. Design
• Design of the process involves
– Resin selection and dimensioning of the resin bed and column
– Regeneration chemical selection and working out the
regeneration process
– Hydraulic design of the run and regeneration processes
• Analysis of the feed water
– Run a complete cation-anion analysis of the water (cations: Na+,
Ca+2, Mg+2, K+; Anions: HCO3
-, SO4
-2, Cl-. NO3
-)
– Obtain information on TDS, dissolved CO2 and SiO2 and pH
• Estimation of the volume of the selected resin required
– Operating ion exchange capacity of the selected resin
– Quantity of feed water to be processed per cycle
– Ionic strength of the feed water to be processed
• Decide on the number of resin columns
– Reliability of operation and enabling the use of the resin bed to
exhaustion point can be the bases

17. Design
• Decide on the resin bed and column dimensions
– Assume feed water application rate (12-24 m3/m2.hr) and work
out diameter and depth of the resin bed
– Decide on the freeboard to be provided (typically ~ 50% of the
resin bed depth)
– Make provisions for the under-drain system and for the
backwash water collection and drainage system
• Provide feed water (and regenerant) inlet, product water
outlet (backwash water and rinse water inlet) and backwash
water collection/energy dissipation structures
• Provide air vents, access manholes and sight glasses
• Estimate the regenerating chemical requirements
– Degree of attaining theoretical ion exchange capacity depends
on the amount (and concentration) of the regenerant employed
– Supplier of the resin, in this regard, may provide the
performance curves

18. Design
• Find backwash velocity and estimate the regeneration
wastewater generation rates
– Calculations for backwash velocity are similar to those for a rapid
gravity filter
– Water required for the backwashing (backwash velocity and
backwash duration are needed)
– Find out rinse water requirements (liters/unit volume of resin)
• Can be determined in laboratory or may also be available from the
resin manufacturers
– Find regeneration chemical solution volumes
• Regeneration wastewater management
– Segregation of the four streams of wastewater and management
– Internal recycling of the rapid rinse water and backwash water
– Recycle the later stage regeneration chemical solution in the
initial regeneration stage (in the next regeneration cycle)
• Design the resin column and its inlets/outlets for chemical
conservation and minimization of regeneration wastewater

19. • Problems associated with the ion exchange process
– Need for extensive pre-treatment of the feed water
• High influent TSS can clog or plug the ion-exchange beds
• Residual chlorine in water can be damaging to the resin
• Residual organics can cause resin binding
• pH and temperature of the feed water can influence the
process
– Fouling of ion exchange resin and limited life of the resin
• Pre-filtration, dechlorination and use of scavenger
exchange resin can be the pre-treatments
• Regenerants used should be capable of removing the
fouling (inorganic and organic) materials from the resin
during regeneration
Ion-exchange: Operational considerations

20. Ion exchange process applications
Removal of undesirable anions and cations from water/
wastewater
– Softening (removal of hardness)
– De-alkalisation (removal of bicarbonate)
– Decationisation (removal of all cations)
– Demineralisation (removal of all ions) - mixed bed for polishing
(effective and versatile means of conditioning boiler feed water)
– Nitrate removal
– Selective removal of various other contaminants
• Many of these require special resins, like chelating resins making
stable metal complexes
• Removal of boron (boric acid), perchlorate and heavy metals (from
wastewater), like, Cd, Cr, Fe, Hg, Ni, Pb and Zn
• Some contaminants (As, F, Li) are difficult to remove with ion
exchange, due to a poor selectivity of the resins
By adequate selection of ion exchangers most of the inorganic
wastewater problems can be handled

21. Softening of Water
• Strongly Acidic Cation (SAC) exchange resin in sodium form is
used in the water softening
2 R-Na + Ca++ → R2-Ca + 2 Na+ (here R represents resin)
• The resins, when exhausted, are regenerated with NaCl
R2-Ca + 2 Na+ → 2 R-Na + Ca++
• A small residual hardness still remains in the water

22. De-alkalization
• This process uses weakly acidic cation (WAC) exchange resin
• Used as first step before the SAC exchange in demineralization
• This resin is capable of removing hardness provided sufficient
bicarbonate alkalinity is present in water
2 R-H + Ca++(HCO3
–)2 → R2-Ca + 2 H+ + 2 HCO3
–
• The H+ ions combine with HCO3
- ions to produce CO2 and H2O
H+ + HCO3
– → CO2 + H2O
• The CO2 can be eliminated from water with a degassifier tower
• Salinity is decreased and temporary hardness is removed
• The cation resin is very efficiently regenerated with an acid
(HCl)
R2-Ca + + H+Cl- → 2 R-H + Ca+ + 2 Cl-

23. Raw water
Degassified water

24. Decationisation
• Practiced as a 1st stage of demineralization
• sometimes used for condensate polishing
• Strongly acidic cation (SAC) exchange resin in H+ form is used
for the exchange of all cations with H+ ions
R-H + Na+ ↔ R-Na + H+
• During regeneration (by using strong acid, HCl/H2SO4) the
reaction is reversed (R-Na + H+ ↔ R-H + Na+)
• In the 2nd step, a degassifier is used to remove the CO2
Raw water
SAC (H) (Degasifier)
Decat + degassed water
Decationized water

25. Demineralisation (deionization)
• In demineralization, all the cations dissolved in water are
replaced by H+ ions and all the anions by OH– ions
• A cation exchange resin in H+ form and an anion exchange resin
in OH- form are used in the demineralization process
– A WAC is often used ahead of SAC and a WBA ahead of SBA
• When water has significant levels of HCO3
-, degasifiers are used
for the CO2 (formed from cation exchange process) removal
• Cation resin is located before anion resin
– otherwise hardness, if present in water, can precipitate as CaCO3
or Ca(OH)2 in alkaline environment (created by anion resin)
• Reactions of the cation exchange resin are
2 R-H + Ca++ R2-Ca + 2 H+ R-H + Na+ R-Na + H+
• Reactions of the anion exchange resin are
R-OH + Cl– R-Cl + OH– 2 R-OH + SO4
= R-2SO4 + 2 OH–

27. Demineralisation
• Demineralised water is free of ions, except for traces of sodium
and silica (5 and 50 µg/L) - has about 1 µS/cm conductivity
– Salinity of the water is reduced to almost nothing, and only a few
ions may escape (ion leakage) from the resin columns
• pH should not be used for process control – monitoring pH is
impossible in waters with <5 µS/cm conductivity
• WBA resins remove only strong acids, and are not capable of
removing weak acids, such as, SiO2 and CO2
• Weak resins, WAC & WBA, are regenerated almost free of cost
– The regenerant first goes through the strong resin, which requires
an excess regenerant, and then through the weak resin
• Cation resins are regenerated preferably with HCl
– Use of H2SO4 as regenerant can precipitate calcium

28. Mixed bed polishing
• Used to treat pre-demineralized water (longer service run and
often off-site regeneration)
– Polish permeate of RO unit and the sea water distillate
– Treat the steam condensate of turbines and industrial process
– Produce ultra-pure water for semiconductors industry
• The last traces of salinity and silica can be removed on a mixed
resin bed with highly regenerated SAC and SBA resins
• Mixed bed polishing produces water with residual silica <1 µg/L
and conductivity < 0.1 µS/cm
– With sophisticated design and appropriate resins, conductivity of
~ 0.055 µS/cm can be achieved
• Mixed ion exchange resin beds are complicated to regenerate
– The resins must be separated by backwashing
– Regeneration requires large amounts of chemicals
– Hydraulic conditions for regeneration are not optimal

29. Raw water
tank
Activated
Carbon filter
SAC
Resin bed
Degassifier
WBA
Resin bed
SBA
Resin bed
Mixed
Resin bed
DI water
tank
Raw water from
Rawwater pump at ETP
A
A
DI water
to the boiler
as feed water
Rawwater
for backwash
Backwash water
30% HCl
Water for
regeneration Backwash water
Regeneration
chemcial waste
Rinse
wastewater
Blower
Air
Air & stripped
Carbon dioxide
Caustic
solution
Soft water
(1)
Soft water for
Regeneration (1)
Soft water
(1)
Regeneration
solution
Backwash water
Regeneration waste*
Regeneration waste
Backwash water
Rinse wastewater
Rinse wastewater
Regeneration waste
Backwash water
Rinse wastewaterBlower
Air
DI water
Caustic & HCl
solutions
Demineralized Water Plant

30. • Removal of sulfate, nitrate, nickel, chromate, arsenic,
perchlorate, lead, cadmium, iron, mercury, zinc, boron, and
fluoride from water is possible
– Some contaminants (arsenic, lithium and fluoride) are difficult to
remove with ion exchange due to poor selectivity of the resins
• Materials used include zeolites; weak and strong anion and
cation resins; and chelating resins
– Clinoptilolite and chabazite have been used to treat wastewater
with mixed metal backgrounds
– Chelating resins, aminophosphonic & iminodiacetic resins, have
high selectivity for metals such as Cu, Ni, Cd and Zn
• Selectivity of resin, pH, temperature, other ionic species and
chemical background all influence the exchange process
– Ion exchange process is highly pH dependent - most metals bind
better at higher pH
– Presence of oxidants, particles, solvents, and polymers may affect
the performance of the ion exchange resin
Ion-exchange process with selective resins

31. Nitrate removal
• Nitrate can be removed selectively using synthetic SBA resins
with –[N≡(CH3)3]+Cl- functional groups
RSBA-Cl + NO3
– → RSBA-NO3 + Cl–
• Conventional SBA resins can be used, but they also remove
sulphate from water
• Nitrate has lesser affinity than sulfate (but greater affinity over
chloride and bicarbonate)
• For higher sulfate levels (>25% of nitrate plus sulfate) NO3
-
selective resins are used
• Since the performance of NO3
- selective resins vary with the
water/wastewater composition, pilot testing is usually needed

32. SBA (Cl)
Denitrated waterRaw water
Nitrate removal

33. Selective removal of heavy metals
• Weakly basic anion exchange resins can be used
• The metals removed are Hg, Cu, Pb, Cd, Zn, and Ni, but the
water should not have Ca and Mg
• Regeneration of the resins is in two steps: first with an acid
(H2SO4) and then with a base (NaOH)
Uranium removal from water
• WBA and SBA resins can be used
– Application of weakly basic anion exchange resin
– Application of strongly basic anion exchange resin
• The resin used is not intended to be regenerated

34. Arsenic removal from drinking water
• Granular ferric hydroxide (GFH) in the form of inorganic
(amphoteric) ion exchanger is used
– SOLMETEX ion exchange resin (macroporous polystyrene with
incorporated ferric hydroxide nanoparticles) is used
• Treatment capacity is influenced by the pH of the water
• The resin is not regenerated

35. Fluoride removal from drinking water
• Activated alumina is used
2Al(OH)3 → Al2O3 + 3H2O (temp: 300 – 800°C
(Al2O3)nAl2O3 + 3H2O → (Al2O3)n2Al(OH)3
S-OH + H+ → S-OH2
+
S-OH2
+ + F- → S-OH2
+F-
• Treatment is efficient at 6.2 pH
• 14000 gallons with 5 mg/L of fluoride at 8.0 pH can be treated
to 0.8 mg/L fluoride level by 1.3 cubic feet of activated alumina
Boron removal from drinking water
• Boron specific ion exchangers are used
• Functional groups of the resin:
Methyl glucamine
• The resin is regenerated in two steps
– First with sulfuric acid
– Then with NaOH
Functional group: Methyl glucamine

36. Removal of natural organic matter
(NOM)/humic acids
• Magnetic micro ion exchange resins (SBA resins) (obtained by
adding magnetite or maghemite during synthesis) are used
• The ion exchange process is slower and for enhancing the
process smaller sorbent particles are used
• The ion exchange resin is mixed with the water and then
removed through Flocculation-Settling
• The resin is regenerated by NaCl
– Concentrated NOM is obtained in the regeneration waste
– Micro or ultrafiltraion can remove the NOM from the regeneration
waste

37. Technical pinciple for resin use