An ion exchanger is a solid material, often a resin, that can remove ions carrying a certain charge (cation or anion) in a solution by adsorption. These are replaced by an equivalent quantity of other ions with the same charge.
When the ion exchange material capacity is reached, i.e., when the material is saturated in ions or its stock of ions is exhausted, it ceases to have any action. It then has to be regenerated.
Ion exchangers are used to soften and demineralise water and to purify and depollute sewage.
Ion exchange column used to purify proteins. © Tim Vickers, Wikimedia public domain