Ion exchange is a reversible exchange of ions between a solid ion exchanger and a liquid solution. The solid undergoes no structural change in the process. An ion exchanger, or ion exchange resin, can be a natural or synthetic substance which can exchange its own ions with the ions present in a solution which is passed through it. The ion exchanger is porous and allows for a solution to permeate through the material. As the solution passes through the ion exchanger and leaves as effluent, it contains ions different from those with which it began.

Ion exchange is usually associated with water treatment. The first industrial application of ion exchange technology was in 1905 when a sodium-aluminosilicate cation exchanger was used to soften water. As water passes through an ion exchange resin, harmful ions found in the water become attached to the resin, which releases its harmless...