A process in which ions are exchanged between a solution and an insoluble (usually resinous) solid; widely used in industrial processing WordNet 3.0 & Open English WordNet

Ion exchange is a reversible interchange of one kind of ion present in an insoluble solid with another of like charge present in a solution surrounding the solid with the reaction being used especially for softening or making water demineralised, the purification of chemicals and separation of substances. Wikipedia

Exchange of ions between two electrolytes or between an electrolyte solution and a complex Wikidata

A permanent insoluble material (usually a synthetic resin) which contains ions that will exchange reversibly with other ions in a surrounding solution. OmegaWiki

The process in which ions are exchanged between a solution and an insoluble solid, usually a resin. OmegaWiki

The reversible process whereby ions are exchanged between a solution and a solid or gel; cation exchange is the process used in a water softener. Wiktionary