Ion Exchange Units: Cation Exchange (Softeners) And Anion ...

1 Page 1 Ion Exchange units are known primarily as watersofteners. But they can also remove nitrates, sul-fates, and various toxic metals from water. Under-standing how ion Exchange works and what contami-nants different units will remove can help you makeinformed decisions about water treatment by Ion Exchange Works Ions are atoms, small particles that are the build-ing blocks for molecules. Ions have a weak electricalcharge. The charge may be positive (for cations) ornegative (for anions). This positive and negativecharge is similar to the north or south pole of a mag-net or the positive or negative terminal of a car charged sodium ions are commonlyused to coat Cation Exchange resins. Negativelycharged chloride or hydroxide ions are commonlyused to coat Anion Exchange resins. Mixed bed resinscombine both positive and negative Exchange units actually Exchange ions fromthe resins with those in the water.

2 When water to betreated passes through the ion Exchange unit, ions inthe water are attracted by either a positive or a nega-tive charge to the ions in the resin bed. Since the ionsfrom the water are usually held more tightly by theresins than they were held in the water, they are, ineffect, removed from the water in the Exchange Exchange Units (Softeners)How Cation Exchange Works. Cation exchangeresins are usually coated with positively charged sodi-um ions. When water containing dissolved cationscontacts the resin, the cations are exchanged for ortrade places with the loosely held sodium ions on theresin. In this way the calcium and magnesium ionsresponsible for hardness are removed from the waterand placed on the Exchange resin, and the sodiumions from the resin are added to the water. This pro-cess makes the water soft. The calcium and magnesium, which cause hard-ness, are reported as grains per gallon (gpg), mil-ligrams per liter (mg/L), or parts per million (ppm).

3 Approximately 20 mg of sodium are added per gallonfor each grain of hardness a point is reached when very few sodi-um ions remain on the resin; thus, no more calcium ormagnesium ions can be removed from the incomingwater. The resin at this point is said to be exhausted or spent and cannot accomplish further water treat-ment until it is recharged or regenerated. This canbe done by backwashing with a sodium water in Alabama does not contain enoughminerals to require Cation Exchange Removes. Water softenersexchange calcium and magnesium with sodium. Thisexchange occurs as the hard water passes through aresin bed which attracts and holds calcium and mag-nesium in Exchange for sodium. Calcium and magne-sium cause hard water, and high levels can scalepipes, water heaters, boilers, and appliances, reducingwater flow and Exchange resins also remove barium, cad-mium, copper, iron, manganese, radium, zinc, andother metallic, positively-charged To Consider Before Buying A Water Sof-tener.

4 Consider the following factors before buying awater Of Water Softeners. Softeners are either manu-al, semi-automatic, or automatic. A manual water softener can be as simple as atank to hold the Exchange resin and appropriate pip-ing for raw (inlet) and treated (outlet) water. Tanksmust be constructed of corrosion-resistant materialbecause of the concentrated salt solutions that A&M AND AUBURN UNIVERSITIESIon Exchange Units: Cation Exchange (Softeners) And Anion ExchangePage 2 More sophisticated systems may include a sepa-rate tank for mixing and containing the brine solutionused for regenerating the resin, additional valves forbackwashing the Exchange resin, and switches forautomatic or semi-automatic operation. For semi-automatic operation, the homeownersets the system switches when recharging is neces-sary. The system completes the process without needfor further attention. For automatic operation, all steps of the recharg-ing process are controlled by a timing mechanismthat the homeowner sets based upon water models can measure water usage or remainingsoftening capacity and recharge themselves onlywhen of Cation Exchange unitsis largely confined to restocking the salt supply forthe brine solution.

5 With manual and semiautomaticmodels, the consumer will also have to start theregeneration Exchange resin lasts many years. However, ifit is not regenerated on a regular basis, it may becomecontaminated with slime or impurities from the rawwater and become unusable. If this happens, the resinmust be replaced with new can also become clogged with tiny parti-cles of iron if the raw water contains much dissolvediron. Backwashing or reversing the normal flow ofwater through the treatment unit may be required toremove the iron. Special additives may be included inthe brine regenerating solution to help minimize water is more corrosive than harderwater, and the waste brines may be a disposal prob-lem. Softening only the hot water tank lines or leav-ing the major cold water line for drinking waterunsoftened can help overcome this problem. Waterfor outdoor taps does not need to be softened. cost of a water softener can be balancedagainst the savings of soft water.

6 Softening hardwater can reduce the quantity of cleaning productsneeded by as much as 50 percent. The life of thehome s plumbing system and water-using appliancescan be extended. Other benefits include the timesaved in cleaning and removing scale and betterresults in laundry, dishwashing, and personal major disadvantage of watersofteners is that they remove beneficial calcium andmagnesium and substitute sodium. The sodium addedto softened water is normally a relatively small frac-tion of the sodium intake from other dietary sourcesand is probably not a problem for healthy , people on restricted salt diets should con-sult their physicians before using softened water fromion Exchange units for drinking and Exchange How Anion Exchange Works. Anion Exchange unitshave a resin that exchanges chloride or hydroxide forthe anions (the negatively charged atoms) that theyremove. Most use chloride, which increases the chlo-ride content of water and may cause a salty Anion Exchange exchangeunits can remove nitrate, sulfate, and other negativelycharged atoms called anions.

7 Researchers are devel-oping resins to selectively remove nitrate more effi-ciently than can now be done. Factors To Consider Before Buying An AnionExchange Unit. Frequent monitoring is suggested ifyou use Anion Exchange for nitrate removal. As theanion Exchange resin becomes spent, the nitratetrapped in the resin may be exchanged with sulfate inthe water if the water contains sulfate concentrationsthat are moderate to high. Under these circumstances,nitrate concentrations at times can be higher afterwater passes through the device than in the Bed Ion ExchangeOften called demineralizers, mixed bed ionexchange units combine resins for removal of bothpositive and negative ions. They do not removeorganic chemicals and they produce water similar todistilled water. Mixed bed units for industrial use are renewedwith hydrogen ions from an acidic solution for cationexchange and with hydroxyl ions from an alkalinesolution for Anion Exchange .

8 These acidic and alka-line solutions are too dangerous for home bed units for homes are usually notrechargeable. They must be discarded after a certainvolume of water has passed through them. Therefore,they are expensive. Water Softeners At A GlanceHow Water Softeners Work:Remove mineralswhich cause hardness and replace them with sodiumthrough Cation :Can pay for itself in savings in soap, hotwater. Not recommended for drinking water for indi-viduals on a salt-free diet. Must buy salt dispose of brine solution. Maintenance:Restock salt supply for brine solutionused to regenerate the resin. Start regeneration cyclefor manual and semi-automatic models. Backwash toremove iron or other particles that may clog system. Page 3 References Magette, William L. 1988. Using Ion ExchangeUnits To Soften Your Well Water. Water Resources19. Maryland cooperative extension Service. TheUniversity of Maryland. College Park, , Byron H.

9 , and James O. Peterson. Your Drinking Water Quality. cooperative extension Service. Universityof Wisconsin. Madison, , Michael P., James W. Bauder, and JeffreyS. Jacobsen. 1989. Groundwater: Household WaterTreatment. Montana cooperative extension State University. Bozeman, by James E. Hairston, extension Water Quality Scientist, assisted by Leigh Stribling, Technical Writer, and John M. Beck, extension more information,call your county extension office. Look in your telephone direc-tory under your county s name to find the in furtherance of cooperative extension work in agriculture and home economics, Acts of May8 and June 30, 1914, and other related acts, in cooperation with the Department of Alabama cooperative extension System (Alabama A&M University and Auburn University) offerseducational programs, materials, and equal opportunity employment to all people without regard torace, color, national origin, religion, sex, age, veteran status, or disability.

10 Last Modified 09/12/01