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Ion exchange

Ion exchange is defined as an exchange of ions between two electrolytes. However, words ion exchange are more conventionally used to denote processes of purification, separation, and decontamination of aqueous and other ion-containing solutions with use of solid ion exchangers. In ion exchange processes ions are exchanged between a solution and an ion exchanger, a non-aqueous solid or gel. Typical ion exchangers are ion exchange resins, zeolite, montmorillonite, clay, and humus. Ion exchangers are either cation exchangers for positively charged cations or anion exchangers for negatively charged anions. There are also amphoteric exchangers that are able to exchange both cations and anions simultaneously. However, the simultaneous exchange of cations and anions is more efficiently performed in ion exchange reactors called mixed beds which contain mixed anion and cation exchange resins. Ion exchange is a reversible process and the ion exchanger can be regenerated or loaded with desirable ions by washing with an excess of these ions.

Ion exchange is a method widely used in household and industrial water purifications to produce soft water. This is accomplished by exchanging calcium Ca²⁺ and magnesium Mg²⁺ cations against sodium Na⁺ or hydrogen H⁺ cations (see Water softening). However, the field where ion exchange is the most economically efficient is ionic separations where a product of highest purity must be obtained, an ion contained in a low concentration must be extracted, or streams of varying composition must be treated. Thus a typical example of application is preparation of high purity water for electronic and nuclear industries.

Ion exchange chromatography is a chromatographical method that is widely used for chemical analysis and separation of ions. For example, in biochemistry it is widely used to separate charged molecules such as proteins.

Ion Exchange is also widely used in the food & beverage, hydrometallurgical, metals finishing, chemical & petrochemical, pharmaceutical, sugar & sweeteners, ground & potable water, nuclear, softening & industrial water, semiconductor, power, and a host of other industries.

References

• F. Helfferich, Ion Exchange, McGraw Hill, New York, 1962 (Bible of the subject).
• Ion Exchangers (K. Dorfner, ed.), Walter de Gruyter, Berlin, 1991.
• Ion exchange (D. Muraviev, V. Gorshkov, A. Warshawsky), M. Dekker, New York, 2000.
• A. A. Zagorodni, Ion Exchange Materials: Properties and Applications, Elsevier, Amsterdam, 2006.

External links

• Illustrated and well defined chemistry lab practical on ion exchange from Dartmouth College
• Some applets illustrating ion exchange processes

Contents

• References
• External links