Ion Exchange

Ion exchange is a reversible process in which one species of ion held in an insoluble solid is swapped for another ion of like charge present in a surrounding solution. It is carried out with ion exchangers such as synthetic ion-exchange resins, functionalized porous or gel polymers, as well as natural materials including zeolites, clay and soil humus; cation exchangers swap positively charged ions and anion exchangers swap negatively charged ones, while amphoteric exchangers, often arranged as mixed beds, can exchange both at once, with every exchanger selecting ions by size, charge and structure. The process is reversible, and an exhausted exchanger can be regenerated by washing it with an excess of the desired ion, which is why the technique is widely used to soften and demineralize water, purify chemicals and separate substances. The source consulted names no inventor or invention date.