Anioninvaihtajia

Anioninvaihtajia, or anion exchangers in English, are porous, insoluble materials containing positively charged functional groups. These functional groups are capable of exchanging their mobile anions for other anions present in a solution that comes into contact with the exchanger. Typically, these materials are based on a polymer matrix, such as polystyrene, cross-linked with divinylbenzene to provide a stable structure. The functional groups are usually quaternary ammonium groups (-N(CH3)3+), which are strongly basic, or tertiary or secondary amine groups, which are weakly basic.

The process of anion exchange involves the reversible binding of anions from a liquid phase to the positively charged sites on the solid exchanger. When a solution containing anions is passed through a bed of anion exchanger, the anions in the solution will compete with the mobile counter-anions on the exchanger for binding sites. Anions with a higher affinity for the exchanger will displace those that are less strongly bound. This principle is utilized in various separation and purification processes.

Anion exchangers are widely employed in water treatment for demineralization, removing negatively charged ions like nitrates, sulfates, and carbonates. They are also used in the purification of pharmaceuticals, food products, and in analytical chemistry for pre-concentration of trace anions or removal of interfering species. The capacity and selectivity of an anion exchanger depend on the type and density of its functional groups, the nature of the polymer matrix, and the chemical environment, such as pH and ionic strength of the solution. Regeneration of the exchanger, to restore its capacity, is typically achieved by washing with a concentrated solution of a specific anion, such as chloride.