a chemical process whereby ions are reversibly transferred between an insoluble solid, such as a resin, and a fluid mixture, usually an aqueous solution: widely used in water softening, recovery of metals from waste solutions, etc.
See ion exchange in American Heritage Dictionary 4
noun
A reversible chemical reaction between an insoluble solid and a solution during which ions may be interchanged, used in water softening and in the separation of radioactive isotopes.