Ion exchange

"The replacement of undesirable ions with a certain charge by desirable ions of the same charge in a solution, by an ion-permeable absorbent." (Lenntech, 2019)

The reaction is used especially for softening or purifying drinking water by demineralising it. 

Sources

Lenntech. Water glossary: An explanation of  terminology concerning water related issues. Accessed March 4, 2019. Available at: https://www.lenntech.com/water-glossary.htm