Ion exchange resins for water treatment are polymer beads with fixed ionic groups that swap hardness, alkalinity, dissolved salts or single contaminants for harmless ions, and they work in 4 groups: cation, anion, mixed bed and selective resins. A strong acid cation resin holds about 2.0 eq/L and a weak acid cation resin about 4.2 eq/L, so how is the right resin, regenerant and dose chosen for a given water?
The 10 resin types run in the order of a demineralization train: strong acid cation (SAC), weak acid cation (WAC), strong base anion (SBA) Type 1 and Type 2, weak base anion (WBA), mixed bed, and the nitrate, PFAS, boron and iminodiacetic acid chelating resins. Sodium chloride, hydrochloric acid, sulfuric acid and sodium hydroxide regenerate them. Ion exchange resins form one of the 16 families of water treatment chemicals.
Capacity runs from 0.9 eq/L (SBA) to 4.5 eq/L (WAC), and regenerant doses from 40 to 240 g/L of resin (2.5 to 15 lb/ft3). Counter-current regeneration leaks about 10 times less than co-current regeneration and needs about 40 % less acid. Drinking-water resins are certified to NSF/ANSI/CAN 61 and listed in 21 CFR 173.25.
Every value on this page is checked against primary sources (eCFR, Federal Register, NSF listings, AWWA, CEN, UK DWI, resin manufacturers' technical manuals); see our methodology and fact-checking process.
What Is an Ion Exchange Resin in Water Treatment?#
An ion exchange resin is a cross-linked polymer bead whose fixed charged groups reversibly trade ions with the water passing through it, with no permanent change in the solid (DuPont Ion Exchange Fundamentals TechFact). Adams and Holmes made the first synthetic organic exchange resins in 1935. Today's water treatment resins are sulfonated polystyrene, polyacrylic or amine-functional beads.
Natural zeolite (clinoptilolite) is a mineral cation exchanger used mainly for ammonium and handled as a granular medium among the adsorbents and filter media for water treatment.
What does ion exchange remove from water?#
Ion exchange removes 5 groups of dissolved ions from water, listed below.
- Hardness: calcium and magnesium.
- Alkalinity: bicarbonate.
- All dissolved salts: down to below 0.1 µS/cm after mixed bed polishing.
- Silica and carbon dioxide.
- Single contaminants: nitrate, PFAS, boron and heavy metals.
Each target sets the resin type and the regenerant.
Gel and macroporous resin beads#
Ion exchange resins are spherical beads of 0.3 to 1.2 mm (50 to 16 mesh), made as transparent gels or as macroporous beads whose surface area reaches 500 m²/g or more, packed at 560 to 960 g/L (35 to 60 lb/ft3) with 35 to 40 % voids. Macroporous beads tolerate higher temperature and more chlorine (Table 6).
How Does Ion Exchange Work?#
Ion exchange works in 3 steps: the beads trade their mobile ions for ions in the water, the bed exhausts as its sites fill, and a concentrated regenerant reverses the exchange.
Exchange reactions and selectivity#
An ion exchange reaction swaps ions of the same charge in equivalent amounts: a sodium-form cation resin takes up one calcium ion and releases two sodium ions, 2RNa + Ca2+ → R2Ca + 2Na+. A hydrogen-form cation resin converts salts into their acids, and a mixed bed completes the reaction to water: RH + ROH + CA → RC + RA + H2O.
Why does regeneration need excess chemical? The selectivity coefficient K(Na/H) is 1.7 for strong acid cation resin and K(Cl/OH) is 22 for strong base anion resin, so caustic regeneration of SBA is inherently inefficient (Dardel ion exchange reference).
The service cycle: exhaustion, leakage and regeneration#
A resin bed runs until leakage of the target ion reaches a set endpoint, then it is regenerated, and the regenerant flow direction decides the leakage: co-current regeneration leaks about 10 times more than counter-current regeneration (DuPont Water Conditioning Manual). The same manual's softener reference design runs at 12 m/h (5 gpm/ft2) and 16 BV/h to a 15 mg/L hardness endpoint. A softener uses about 3 times as much salt as the hardness held on the resin (Veolia Water Technologies Handbook, chapter 8).
Types of Ion Exchange Resins#
The 10 ion exchange resin types used in water treatment fall into 4 groups: 2 cation resins (SAC, WAC), 3 anion resins (SBA Type 1, SBA Type 2, WBA), mixed bed resin and 4 selective or chelating resins for nitrate, PFAS, boron and metals. Table 1 compares the groups by functional group, ionic form and duty.
| Group | Resin types | Functional group | Ionic forms | Typical duty |
|---|---|---|---|---|
| Cation exchange resins | SAC, WAC | sulfonic acid; carboxylic acid | Na, H | softening, decationization, dealkalization |
| Anion exchange resins | SBA Type 1, SBA Type 2, WBA | quaternary ammonium; tertiary amine | OH, Cl, free base | demineralization, dealkalization, nitrate removal |
| Mixed bed ion exchange | SAC (H) + SBA (OH) | sulfonic acid + quaternary ammonium | H, OH | polishing, condensate polishing |
| Selective and chelating resins | nitrate, PFAS, boron, iminodiacetic | bulky or long-chain quaternary ammonium; N-methylglucamine; iminodiacetic acid | Cl, free base, Na | nitrate, PFAS, boron, metals |
1. Cation exchange resins#
Cation exchange resins carry negative fixed groups that exchange positive ions such as calcium, magnesium and sodium; this group has 2 resin types: strong acid cation and weak acid cation.
Strong acid cation (SAC) resin#
Strong acid cation (SAC) resin is sulfonated polystyrene whose sulfonic sites exchange cations across the entire pH range, softening in the sodium form and decationizing in the hydrogen form.
Weak acid cation (WAC) resin#
Weak acid cation (WAC) resin is a carboxylic polyacrylic resin that removes only the cations tied to alkalinity and regenerates with 105 to 115 % of the theoretical acid.
2. Anion exchange resins#
Anion exchange resins carry positive fixed groups that exchange negative ions such as chloride, sulfate, bicarbonate and silica; this group has 3 resin types: SBA Type 1, SBA Type 2 and weak base anion.
Strong base anion (SBA) Type 1 resin#
SBA Type 1 resin is the most basic and most heat-stable anion resin, removing silica and CO2 with about 20 µg/L (ppb) silica leakage after counter-current regeneration.
SBA Type 2 resin#
SBA Type 2 resin regenerates more efficiently than Type 1 but leaks more silica (about 50 µg/L) and tolerates only 35 °C (95 °F) in the hydroxide form. In the chloride form it is the dealkalizer resin, cutting alkalinity by about 90 %.
Weak base anion (WBA) resin#
Weak base anion (WBA) resin is an amine resin that absorbs mineral acids after cation exchange, regenerates with about 115 % of theoretical caustic and leaves CO2 and silica to the SBA.
3. Mixed bed resins#
Mixed bed resin is an intimate mixture of hydrogen-form SAC and hydroxide-form SBA beads that acts like many two-bed stages in series and polishes water to more than 10 MΩ·cm with less than 10 µg/L silica. The cation to anion volume ratio runs from 35 : 65 to 65 : 35, with more than 50 % cation for condensate polishing.
4. Selective and chelating resins#
Selective and chelating resins carry functional groups tuned to one ion or ion family; this group has 4 resin types for water treatment: nitrate-selective, PFAS-selective, boron-selective and iminodiacetic acid chelating resins. Thiol, thiourea and aminophosphonic groups serve industrial streams.
Nitrate-selective resin#
Nitrate-selective resin is a strong base anion resin with bulkier alkyl groups that prefers nitrate over sulfate, so it does not dump nitrate at the end of a run.
PFAS-selective resin#
PFAS-selective resin is a strong base anion resin with long-chain quaternary ammonium groups that binds PFAS by exchange and hydrophobic attraction and is normally used once.
Boron-selective resin#
Boron-selective resin carries N-methylglucamine groups that complex boric acid in desalinated water, against the EU boron value of 1.5 mg/L (2.4 mg/L where desalinated water predominates).
Iminodiacetic acid chelating resin#
Iminodiacetic acid chelating resin binds copper, lead, nickel, zinc and cadmium far ahead of calcium and sodium, but cannot remove metals held by EDTA or NTA.
Ion Exchange Resin Capacity#
Ion exchange resin capacity is the number of exchange sites per liter of resin, stated in eq/L: strong acid cation resins hold 1.7 to 2.2 eq/L and weak acid cation resins 3.7 to 4.5 eq/L of total capacity (Dardel). Table 2 compares total and operating capacity for the 4 basic resin types.
| Resin | Total, eq/L (most common) | Total, kgr/ft3 as CaCO3 | Operating, eq/L |
|---|---|---|---|
| SAC | 1.7 to 2.2 (2.0) | 37 to 48 | 0.6 to 1.7 (40 to 60 % of total) |
| WAC | 3.7 to 4.5 (4.2) | 81 to 98 (calc.) | 1.0 to 3.5 |
| SBA | 0.9 to 1.4 (1.2) | 20 to 31 (calc.) | 0.4 to 0.9 |
| WBA | 1.1 to 1.7 (1.3) | 24 to 37 (calc.) | 70 to 90 % of total |
Capacity per liter of wet resin and per kilogram of dry resin are never mixed: fully sulfonated SAC reaches about 5.5 eq/kg dry. Mixed bed and selective resin capacities are product-specific.
Total capacity and operating capacity#
Operating capacity is the part of total capacity a bed delivers per cycle, about 40 to 60 % for strong acid cation resin and 70 to 90 % for weak base anion resin, because regeneration level, flow, temperature and endpoint all cut into it. What margin does a design add? Designers subtract 5 % from cation and 10 % from anion operating capacity (DuPont Water Conditioning Manual).
Capacity and hardness units: eq/L, kgr/ft3, grains per gallon and bed volumes#
Resin capacity converts between metric and US units with one factor: 1 eq/L equals 21.8 kgr/ft3 as CaCO3, and 1 kgr/ft3 equals 45.8 meq/L. The 4 other conversions used in design are listed below.
- Hardness: 1 grain per US gallon (gpg) = 17.1 mg/L as CaCO3 = 0.342 meq/L.
- Degrees: 1 German degree = 17.9, 1 French degree = 10.0, 1 English degree = 14.3 mg/L as CaCO3.
- Bed volume: 1 BV = 7.5 US gal per ft3 of resin.
- Flow: 1 gpm/ft3 = 8.02 BV/h; 1 gpm/ft2 = 2.445 m/h.
Each hardness unit converts through the CaCO3 basis; calcium and magnesium units are explained under water hardness.
Worked example: softener throughput per regeneration#
Worked example: a sodium-cycle softener regenerated with 240 g/L (15 lb/ft3) of salt holds 30,000 grains per ft3, so at 171 mg/L (10 gpg) as CaCO3 it treats about 3,000 US gal per ft3 of resin, about 400 bed volumes, per cycle. The inputs are listed with each step below.
- Convert hardness: 171 mg/L as CaCO3 / 17.1 = 10 gpg.
- Divide capacity by hardness: 30,000 / 10 = 3,000 gal/ft3; 3,000 / 7.5 gal per BV = 400 BV.
- Apply the 5 % cation margin: about 2,850 gal/ft3, or 380 BV.
At 96 g/L (6 lb/ft3) the resin holds 18,000 gr/ft3, so 150 % more salt buys about 67 % more capacity (Veolia). Softening adds about 0.46 mg/L sodium per mg/L hardness as CaCO3, about 79 mg/L here, against the EU indicator value for sodium of 200 mg/L.
Ion Exchange Resin Regeneration: Chemicals, Doses and Efficiency#
Ion exchange resins are regenerated with 4 chemicals: sodium chloride for softeners and chloride-form anion resins, hydrochloric or sulfuric acid for hydrogen-form cation resins, and sodium hydroxide for hydroxide-form anion resins, each dosed in g/L of resin. Table 3 compares separate-bed doses as 100 % chemical (DuPont separate-beds TechFact); mixed beds need 15 to 20 % more.
| Regenerant (resin) | Co-current, g/L (lb/ft3) | Counter-current, g/L (lb/ft3) | Packed bed, g/L (lb/ft3) | Strength | Efficiency, % of theory (co / counter) |
|---|---|---|---|---|---|
| Sodium chloride (SAC softening) | 90 to 240 (5.6 to 15) | 70 to 120 (4.4 to 7.5) | 60 to 100 (3.7 to 6.2) | 10 % | salt about 3x hardness held |
| Hydrochloric acid (SAC, H form) | 75 to 150 (4.7 to 9.4) | 40 to 80 (2.5 to 5.0) | 40 to 70 (2.5 to 4.4) | 5 % | 200 to 250 / 120 to 150 |
| Sulfuric acid (SAC, H form) | 90 to 240 (5.6 to 15) | 60 to 100 (3.7 to 6.2) | 55 to 90 (3.4 to 5.6) | 0.8 to 6 % by feed calcium | 250 to 300 / 150 to 200 |
| Sodium hydroxide (SBA, OH form) | 75 to 160 (4.7 to 10) | 40 to 80 (2.5 to 5.0) | 40 to 70 (2.5 to 4.4) | 4 % (2 to 4 % counter-current) | Type 1: 250 to 300 / 140 to 220; Type 2: 150 to 200 / 125 to 140 |
| Acid (WAC) | 105 to 110 % of operating capacity | n/a | n/a | HCl 2 to 5 %; H2SO4 0.5 to 0.7 % | 105 to 115 |
| Caustic (WBA) | 115 % of ionic load (at least 130 % against organics) | n/a | n/a | 2 to 4 % | 120 to 150 |
Pound values are calculated at 16.0 g/L per lb/ft3 (240 g/L = 15 lb/ft3).
Regenerant chemicals and concentrations#
Each regenerant has its own working strength: about 10 % for sodium chloride, 5 % for hydrochloric acid, 4 % for sodium hydroxide and 0.8 to 6 % for sulfuric acid, kept dilute where calcium is high so calcium sulfate does not precipitate in the bed. Contact time stays above 20 minutes (below 60 minutes for sulfuric acid), and sulfuric acid goes in at no more than 25 °C (77 °F).
Sulfuric acid starts at 3 % below 15 % calcium in the feed cations and drops to 1 %, or gives way to hydrochloric acid, above 70 % calcium. These acids and caustic are compared on pH adjustment chemicals.
Co-current vs counter-current regeneration#
Counter-current regeneration needs about 40 % less hydrochloric acid than co-current regeneration for a strong acid cation bed: 120 to 150 % of theory against 200 to 250 % (DuPont Water Conditioning Manual). SBA Type 1 needs 140 to 220 % of theoretical caustic counter-current against 250 to 300 % co-current, because the freshest regenerant meets the outlet layer that polishes the water. The weak resins regenerate close to theory either way: WAC at 105 to 115 % and WBA at 120 to 150 %.
Regenerant quality limits#
Regenerant quality limits protect the resin: hydrochloric acid for regeneration carries no more than 0.01 % iron and no inhibitors, and caustic soda no more than 1.0 % sodium chloride, because 2 % salt in caustic cuts anion efficiency by 5 to 10 %. The same manual caps sulfuric acid at 50 mg/L iron and 0.2 mg/L arsenic, and caustic at 50 mg/L silica.
Which Ion Exchange Resin for Which Water? Selection by Process, Water Quality and Application#
Ion exchange resin selection follows 3 questions: which process the water needs, what the feed water contains, and which application sets the product-water target.
By treatment process#
Each ion exchange process pairs a resin with a regenerant: softening uses sodium-form SAC and salt, dealkalization uses WAC with acid or chloride-form SBA with salt, and demineralization runs hydrogen-form cation resin, a degasser and hydroxide-form anion resin in series. Two-bed units remove up to 99.5 % of salts and mixed beds 99.99 % (Water Quality Association). Counter-current demineralizers reach below 1 µS/cm and 5 to 40 µg/L silica, against 5 to 25 µS/cm and 50 to 200 µg/L co-current (Dardel). Table 4 compares the 4 processes.
| Process | Resin and form | Regenerant | Removes | Typical product |
|---|---|---|---|---|
| Water softening resin and softener salt | SAC, Na | NaCl 8 to 12 % | calcium, magnesium | below 1 to 2 mg/L hardness as CaCO3 |
| Dealkalization by ion exchange | WAC (H) + degasser, or SBA Type 2 (Cl) after a softener | acid; NaCl 5 % | alkalinity | about 90 % alkalinity reduction (Cl-form SBA) |
| Demineralization by ion exchange | SAC (H), degasser, SBA (OH); optional WAC, WBA, mixed bed | HCl or H2SO4; NaOH | all salts, CO2, silica | below 1 µS/cm, 5 to 40 µg/L SiO2 counter-current |
| Ion exchange resin regeneration | every regenerable resin | NaCl, HCl, H2SO4, NaOH | restores capacity | 105 to 300 % of theory |
By feed-water composition#
Feed-water composition decides the resin train: a weak acid cation resin goes ahead of the SAC when temporary hardness exceeds 40 % of the cations, and a weak base anion resin goes ahead of the SBA when chloride, nitrate and sulfate exceed about 60 % of the anions (DuPont Water Conditioning Manual). The 6 selection rules are listed below.
- WAC ahead of SAC: temporary hardness above 40 % of cations, low free mineral acidity (FMA).
- WBA ahead of SBA: FMA above about 60 % of anions.
- SBA Type 2 instead of Type 1: CO2 plus silica below 30 % of anions.
- SAC softening: 1 mg/L hardness leakage only below about 5,000 mg/L TDS.
- WAC softening: below 1 mg/L hardness up to 30,000 mg/L TDS.
- Mixed bed alone: feed below 1 meq/L, 100 mg/L TDS and 100 µS/cm; required above 5 MΩ·cm.
By application: boilers, cooling, drinking water, membranes and wastewater#
Each application has a default ion exchange duty: softening and dealkalization of boiler and cooling makeup, demineralization and mixed bed polishing of high-purity feed and RO permeate, condensate polishing, PFAS and nitrate removal in drinking water and chelating polishing of metal-bearing wastewater. Anion exchange is the most common municipal nitrate removal process (WHO), and US rules name ion exchange a best available technology for nitrate and regulated PFAS. Table 5 matches each application to its resins.
| Application | Duty | Resins | Key number |
|---|---|---|---|
| Boiler water treatment | makeup softening, dealkalization | SAC, WAC, SBA Type 2 (Cl) | below 2 mg/L hardness as CaCO3 |
| Condensate system treatment | condensate polishing | SAC, mixed bed | 30 to 120 BV/h; anion limit 60 °C (140 °F) |
| Cooling tower water treatment | makeup dealkalization | WAC + degasser | out of service above 10 % of influent alkalinity |
| Reverse osmosis and membrane chemicals | permeate polishing | mixed bed | 15 to 40 BV/h |
| Drinking water treatment chemicals | softening, nitrate, PFAS | SAC, SBA, selective | 0.46 mg/L sodium per mg/L hardness removed |
| PFAS removal in drinking water treatment | single-use resin | PFAS-selective | EBCT 2 to 5 min |
| Nitrate removal from drinking water | nitrate removal | SBA (Cl), nitrate-selective | MCL 10 mg/L as N |
| Heavy metal removal from wastewater | effluent polishing | iminodiacetic chelating | no removal from EDTA or NTA complexes |
| Deionized water | DI water | two-bed + mixed bed | below 0.1 µS/cm |
How Are Ion Exchange Resins Operated and Tested?#
Ion exchange resins stay in specification when 4 limits are kept: temperature per resin and form, free chlorine and oxidants, iron, turbidity and organic fouling, and a measured service endpoint. Table 6 compares temperature and chlorine limits (DuPont Water Conditioning Manual).
| Resin and form | Maximum temperature | Free chlorine at 15 to 20 °C |
|---|---|---|
| SAC, 8 % cross-linked gel | 120 °C (250 °F) | 0.1 mg/L as Cl2 |
| SAC, 10 % cross-linked gel | 130 °C (265 °F) | 0.2 mg/L as Cl2 |
| SAC, macroporous | 150 °C (300 °F) | 0.6 mg/L as Cl2 |
| WAC | 120 °C (250 °F) | not stated in the source |
| SBA Type 1, Cl / OH form | 100 °C (212 °F) / 60 °C (140 °F) | not stated in the source |
| SBA Type 2, Cl / OH form | 70 °C (158 °F) / 35 °C (95 °F) | not stated in the source |
| Acrylic SBA, Cl / OH form | 50 °C (122 °F) / 35 °C (95 °F) | not stated in the source |
| WBA | 100 °C (212 °F) | not stated in the source |
Anion-resin chlorine limits are not stated in the source, so feed water is dechlorinated ahead of every resin bed.
Temperature limits by resin type#
Temperature limits run from 150 °C (300 °F) for macroporous strong acid cation resin down to 35 °C (95 °F) for SBA Type 2 in the hydroxide form, so anion resins set the limit in hot service.
Chlorine, oxidants and dechlorination ahead of the resin#
Free chlorine is the main oxidant that shortens resin life: a standard gel cation resin tolerates about 0.1 mg/L as Cl2 at 15 to 20 °C, and its life falls from about 10 years below 0.2 mg/L to about 6 years at 1 mg/L. In theory, 1.78 g of sodium sulfite or 0.91 g of sulfur dioxide removes 1 g of chlorine as Cl2.
Strong oxidants, such as nitric acid, react violently with the organic polymer and never reach a resin bed.
Sulfite, bisulfite and thiosulfate ratios are compared on dechlorination chemicals.
Iron, turbidity and organic fouling#
Iron, suspended solids and natural organic matter foul ion exchange resins, so iron is stabilized or filtered out ahead of a softener, turbidity stays below 1.0 JTU, and fouled anion resin is cleaned with warm brine and 1 % caustic. Iron-fouled resin is cleaned with 5 % sodium dithionite, and organic-fouled anion resin with 10 % sodium chloride plus 1 % sodium hydroxide at about 50 °C (120 °F) for 4 to 16 hours. SBA damage hides until more than 25 % of its sites have turned weak base.
Service endpoints: hardness, conductivity and silica#
Each ion exchange unit ends its run on one measured endpoint: residual hardness for a softener, conductivity and silica for a demineralizer (for example 4 µS/cm or a 0.3 mg/L silica rise) and resistivity above 10 MΩ·cm for a mixed bed.
Resistivity is the reciprocal of conductivity, and 1 µS/cm is about 0.5 mg/L of dissolved solids, as explained under conductivity and TDS.
Which Standards and Regulations Apply to Ion Exchange Resins?#
Ion exchange resins for drinking water are governed in 4 layers: NSF/ANSI/CAN 61 process-media certification, FDA 21 CFR 173.25, standards for the regenerant salt, and drinking-water rules that name ion exchange as a treatment technology. Resins are never "NSF 60 certified", and the boiler-additive rule 21 CFR 173.310 does not cover them.
NSF/ANSI/CAN 61 and 21 CFR 173.25 for resins#
Ion exchange resins for public water systems are certified to NSF/ANSI/CAN 61 as process media, not to NSF/ANSI/CAN 60, and in the United States they must be one of the 20 resin chemistries listed in 21 CFR 173.25, with no more than 1 ppm of organic extractives. A listing may require a minimum flow of 2 gpm per ft3 of resin, about 16 BV/h.
Regenerant salt: NSF/ANSI/CAN 60 listing, AWWA B200-22 and EN 973#
Regenerant salt is certified as a chemical, not as media: NSF/ANSI/CAN 60 lists sodium chloride with the function Softener and no numeric maximum use level, and ANSI/AWWA B200-22 specifies sodium chloride for water treatment. The category holds 56 companies, 497 products and 680 product-function rows, 679 of them with maximum use "NA" (NSF listings, 2026-10-21). How listings and maximum use levels work is explained on NSF/ANSI/CAN 60.
ANSI/AWWA B200-22 took effect on 2022-07-01, replacing B200-17, and in Europe regeneration salt is specified in EN 973.
Drinking-water rules that name ion exchange: PFAS, nitrate and perchlorate#
US drinking-water rules name ion exchange a best available technology for nitrate (40 CFR 141.62) and for the PFAS regulated in 2024 (40 CFR 141.61(d)), whose PFOA and PFOS limits of 4.0 ng/L each apply from 2029-04-26. The nitrate MCL is 10 mg/L as N. Perchlorate is a proposal only: EPA proposed it on 2026-01-06 (91 FR 398) with co-proposed MCLs of 0.02, 0.04 or 0.08 mg/L.
Single-use resin vessels follow AWWA B104-24, listed with the other AWWA B-series standards.
EU and UK approval of ion exchange resins#
In the EU, ion exchange resins fall under Article 12 of Directive (EU) 2020/2184, and in the UK no BS EN standard covers them, so each resin needs Regulation 31 approval from the Drinking Water Inspectorate.
Article 12 duties for treatment chemicals and media are on EU Drinking Water Directive 2020/2184.
Complete List of Ion Exchange Resins and Regenerants#
The complete list below gives the 10 ion exchange resin types, the natural zeolite exchanger and the 5 chemicals that regenerate or protect them, with functional group or CAS number, role, systems and certification route.
| # | Resin or chemical | Functional group or CAS | Role in ion exchange | Certification | AWWA / EN |
|---|---|---|---|---|---|
| 1 | Strong acid cation (SAC) resin | sulfonic acid | softening, decationization, condensate polishing | NSF/ANSI/CAN 61 + 21 CFR 173.25 | none |
| 2 | Weak acid cation (WAC) resin | carboxylic acid | dealkalization, high-TDS softening | NSF/ANSI/CAN 61 + 21 CFR 173.25 | none |
| 3 | SBA Type 1 resin | quaternary ammonium | silica and CO2 removal | NSF/ANSI/CAN 61 + 21 CFR 173.25 | none |
| 4 | SBA Type 2 resin | quaternary ammonium | demineralization at low silica; Cl-form dealkalizer | NSF/ANSI/CAN 61 + 21 CFR 173.25 | none |
| 5 | Weak base anion (WBA) resin | tertiary amine | mineral-acid removal, organic trap | NSF/ANSI/CAN 61 + 21 CFR 173.25 | none |
| 6 | Mixed bed resin | SAC (H) + SBA (OH) | polishing | NSF/ANSI/CAN 61 + 21 CFR 173.25 | none |
| 7 | Nitrate-selective resin | bulky quaternary ammonium | nitrate removal | NSF/ANSI/CAN 61 + 21 CFR 173.25 | none |
| 8 | PFAS-selective resin | long-chain quaternary ammonium | single-use PFAS removal | NSF/ANSI/CAN 61 + 21 CFR 173.25 | AWWA B104-24 |
| 9 | Boron-selective resin | N-methylglucamine | boron removal | NSF/ANSI/CAN 61 + 21 CFR 173.25 | none |
| 10 | Iminodiacetic acid chelating resin | iminodiacetic acid | metal polishing, brine decalcification | not NSF listed | none |
| 11 | Natural zeolite (clinoptilolite) | 12173-10-3 | ammonium exchange, filtration | NSF/ANSI/CAN 61 | none |
| 12 | Sodium chloride (regenerant salt) | 7647-14-5 | SAC and Cl-form SBA regenerant; lay-up brine | NSF/ANSI/CAN 60, Softener (max use NA) | AWWA B200-22 / EN 973 |
| 13 | Hydrochloric acid | 7647-01-0 | SAC and WAC regenerant | NSF/ANSI/CAN 60 | none |
| 14 | Sulfuric acid | 7664-93-9 | SAC and WAC regenerant | NSF/ANSI/CAN 60 | none |
| 15 | Sodium hydroxide (caustic soda) | 1310-73-2 | SBA and WBA regenerant | NSF/ANSI/CAN 60 | AWWA B501-25 |
| 16 | Sodium sulfite | 7757-83-7 | dechlorination ahead of resin (1.78 g per g Cl2) | check the product listing | none |
Every chemical in this list is filterable by CAS number, function and NSF status in the water treatment chemical database.
Who Supplies Ion Exchange Resins and Ion Exchange Programs?#
Ion exchange resins reach plants through two routes: resin manufacturers and distributors supply new resin by type and ionic form, and program providers size the units, run regeneration and test the resin. Standard resins keep 2 years in storage and hydroxide-form anion resin no more than 1 year, at 0 to 30 °C (32 to 90 °F). Resin distributors and manufacturers by region are listed under water treatment chemical suppliers.
A resin order specifies the resin type, the ionic form (such as SAC in the sodium form), NSF/ANSI/CAN 61 certification and a chemistry listed in 21 CFR 173.25.
A supplier delivers resin to that specification, while a program provider also sets regeneration levels and tests capacity over the resin's life, as compared under water treatment companies.
Are Ion Exchange Resins Safe, and How Long Do They Last?#
Ion exchange resins are generally not classified as hazardous, and a well-protected cation resin lasts about 10 years, while the hazards and the wear come from the regenerants and oxidants around them.
Is ion exchange resin hazardous to handle?#
Ion exchange resin is generally not classified as hazardous, but hydrogen- and hydroxide-form beads irritate the eyes, and nitric acid or other strong oxidants can react violently with the polymer. Handling follows the supplier SDS; idle beds sit in 15 to 25 % brine.
How long does ion exchange resin last?#
A standard gel cation resin lasts about 10 years below 0.2 mg/L of chlorine and about 6 years at 1 mg/L, while unused resin keeps 2 years in storage and hydroxide-form anion resin no more than 1 year.
What is the difference between cation and anion exchange resins?#
Cation exchange resins remove positive ions such as calcium and sodium and regenerate with salt or acid, while anion exchange resins remove negative ions such as chloride, sulfate and silica and regenerate with salt or caustic.
What is an ion exchange softener?#
An ion exchange softener is a vessel of sodium-form strong acid cation resin that swaps calcium and magnesium for sodium and is regenerated with brine, producing water below 1 to 2 mg/L hardness as CaCO3 in industrial service.
What are the disadvantages of ion exchange?#
Ion exchange has 3 main disadvantages: it produces a salty regenerant waste, it adds sodium or chloride to treated water, and it removes some ions poorly, such as arsenic, fluoride and lithium. In nitrate plants, off-site brine disposal can exceed 80 % of operating cost (Purolite nitrate removal application guide, a supplier figure).
Does ion exchange remove colloidal silica?#
No: ion exchange removes dissolved silica only; colloidal silica passes the resin and needs RO, ultrafiltration or coagulation.
Reactive and colloidal forms are compared under silica in water.