Ionebytting

Ionebytting, commonly known as ion exchange, is a reversible chemical process in which ions in a liquid phase are exchanged for ions bound to a solid phase, usually a resin or zeolite. The solid phase contains fixed exchange sites with complementary charges, and when a solution passes through, ions with higher affinity replace those on the solid until equilibrium is reached.

There are two main classes: cation exchange, which removes positively charged ions such as calcium and magnesium and replaces them with another cation (often sodium), and anion exchange, which removes negatively charged ions such as chloride or sulfate and replaces them with another anion (often hydroxide or bicarbonate). Mixed-bed systems combine both types in a single bed. Common media include organic polymer resins with sulfonic acid groups for strong cation exchange, carboxylic groups for weak cation exchange, and quaternary ammonium groups for strong anion exchange.

Applications are widespread in water treatment and purification. Ionebytting is used for water softening, demineralization and deionization, wastewater treatment, and selective removal of contaminants in biotech and pharmaceutical production. The process typically involves loading a resin with a solution, followed by rinsing to remove weakly bound ions, and regeneration, where a concentrated brine or caustic solution restores the resin’s capacity for reuse.

Key considerations include resin selectivity, competing ions, solution pH and temperature, flow rate, and the management of regeneration waste. Ionebytting has been developed and commercialized since the early 20th century and remains a fundamental technology in modern water systems.