![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+]](https://image.slidesharecdn.com/10-ionexchangeprocess-151119015726-lva1-app6892/85/10-ion-exchange-process-5-320.jpg)
![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]](https://image.slidesharecdn.com/10-ionexchangeprocess-151119015726-lva1-app6892/85/10-ion-exchange-process-6-320.jpg)
![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](https://image.slidesharecdn.com/10-ionexchangeprocess-151119015726-lva1-app6892/85/10-ion-exchange-process-8-320.jpg)
![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](https://image.slidesharecdn.com/10-ionexchangeprocess-151119015726-lva1-app6892/85/10-ion-exchange-process-31-320.jpg)
10 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
- 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-
- 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