Britannica Sources used in this answer

How is an ion-exchange column regenerated after it is saturated?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

chemical structure of cation exchanger — ion-exchange reaction Figure 1: Chemical structure of cation exchanger. The exchangeable ions are marked ⁺. The whole structure is permeated by solvent molecules, usually water (not shown).

An ion-exchange column is regenerated by passing a solution containing the ions originally held by the exchanger through the column. This process restores the resin to its initial condition by using an excess of the original ions to displace the ions that were adsorbed during the column's operation.12

The specific regeneration method depends on the type of exchanger and its application:

Water Softening: A column saturated with calcium and magnesium ions is regenerated by passing a concentrated solution of common salt (sodium chloride) through it. The excess sodium ions displace the hardness-causing ions, and the column is then flushed with water to be ready for reuse.2
Deionization: Columns used for deionization are regenerated using strong acids for cation-exchange resins (which bear hydrogen ions) and strong alkalis for anion-exchange resins (which bear hydroxyl ions).2

Once the regeneration solution has passed through and the column has been flushed, the exchanger is restored to its original state and is ready for further use.12