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Wastewater
Technologies
Jumbo DI service deionization cation anion or mixb
Ion Exchange
Ion exchange, deionization and demineralization are terms that are used synonymously to refer to the same process. Ion exchange is a process used extensively in nuclear facilities, industrial processes and medical and pharmaceutical operations to control the purity and pH of water by removing undesirable ions and replacing them with acceptable ones. Specifically, it is the exchange of ions between a solid substance (called a resin) and an aqueous solution, typically municipal, potable water but it frequently involves process or even waste water (e.g., the plating industry). Depending on the identity of the ions that a resin releases to the water, the process may result in purification of water or in control of the concentration of a particular ion in a solution. An ion exchange is the reversible exchange of ions between a liquid and a solid. This process is generally used to remove undesirable ions from a liquid and substitute acceptable ions from the solid (resin). The devices in which ion exchange occurs are commonly called demineralizers. This name is derived from the term demineralize, which means the process whereby impurities present in the incoming fluid (water) are removed by exchanging impure ions with H and OH ions, resulting + - in the formation of pure water. H and OH are present on the sites of resin beads contained in + - the demineralizer tank or column.
Ion Exchange Summary
Demineralize is defined as the process whereby impurities present in the incoming fluid (water) are removed by exchanging impure ions with H+ and OH- ions resulting in the formation of pure water.
Ion exchange is a process used to control the purity and pH of water by removing undesirable ions and replacing them with acceptable ones.
Mixed-bed demineralizer is a vessel containing resin that is a uniform mixture of cation and anion resins in a specific volume ratio depending on their specific gravities. Normally the ratio is 2 parts cation resin to 3 parts anion resin.
Cation is an ion with a positive charge. Common cations include Ca++, Fe++ and H+ . A cation resin is one that exchanges positive ions.
Anion is an ion with a negative charge. Common anions include Cl- , SO4--, and OH- . An anion resin is one that exchanges negative ions.
Decontamination factor (DF) is a ratio of the concentration (or activity) of the fluid at the inlet compared to the concentration (or activity) at the effluent, which defines the effectiveness of the ion exchange process.
Polymers are extremely large molecules that are formed by the combination of many molecules of one or two compounds in a repeating structure that produces long chains.
Affinity is often used to describe the attraction between a resin and a given ion. This affinity can be described quantitatively by experimental determination of a parameter called the relative affinity coefficient.. The general order of affinity serves as a useful guide in understanding many ion exchange processes. Cation and anion resins are named according to the identity of the ion occupying the exchange sites, such as hydrogen, hydroxyl, and chloride. Mixed-bed resins are used to remove both cations and anions. The effectiveness of any ion exchanger is directly related to the relative affinities between a resin and different ions. In order of decreasing strength, the relative affinities between a cation resin and various cations are: Ba > Sr > Ca > Co > Ni > Cu > Mg > Be +2 +2 +2 +2 +2 +2 +2 +2 Ag > Cs > Rb > K NH > Na > H > Li + + + + + + + + Similarly, the relative affinities of the anion resin for various anions are: SO > I > NO > Br > HSO > Cl > OH > HCO > F 4 3 3 3 -2 - - - - - - - - The higher the relative affinity the more effective the ion exchanger. This effectiveness is expressed by the Decontamination Factor.
Resin beads are long-chain cross-linked polymers that contain sites occupied by exchangeable ions
Adopted from the Department of Energy Publication: Principles of Water Treatment DOE-HDBK-1015/2-93 WATER TREATMENT PROCESSES Rev. 0 CH-04
with editing by the WaterProfessionals
WaterProfessionals™
Offices in Tennessee, North Carolina and South Carolina - Call 1-800-358-9981 “Waterprofessionals” is the licensed tradename and service mark of the following independent companies: Carolina Water Specialties, LLC (dba Culligan of the Piedmont, Upstate, SC) and McCollum Water Conditioning, Inc. (dba Culligan of Tri Cities).
