Demineralization is typically described as the removal of all cations (e.g. calcium, magnesium, sodium, potassium, Iron and other heavy metals) and anions (e.g. bicarbonate alkalinity, chloride, sulfate, nitrate, silica and CO2) from a solution in exchange for H+ and OH- ions. This reduces the total dissolved solids of the solution. This is required for many sensitive processes, such as high pressure boiler operation, food and pharmaceutical applications, and electronics production.
Cation and anion resins can also be mixed together in a single vessel as a mixed bed for primary demineralization or as a polishing step following a two bed or multi-bed system.