deionisaatio

Deionization, also spelled deionization, is a water purification process that removes dissolved ions from water to produce deionized water with very low electrical conductivity. It is a form of demineralization used in laboratories, manufacturing, and electronics where minerals would interfere with processes or analyses.

The primary method employs ion exchange resins. Cation resins exchange positively charged ions (such as Ca2+, Mg2+, Na+) for hydrogen ions, while anion resins exchange negatively charged ions (such as Cl−, SO4^2−, NO3−) for hydroxide ions. When used in series (separate cation and anion beds) or in a mixed-bed configuration, the exchanged ions recombine to form water (H2O) with greatly reduced ionic content. Mixed beds can achieve the highest purity, while two-bed systems are common for intermediate purity.

Pretreatment and maintenance are important. Water is pretreated to remove organics, iron, silica, and excessive hardness, often with carbon filtration and softening. Regeneration of the resins requires acids (for cation resins) and caustic solutions (for anion resins), producing waste streams that must be managed. A key limitation is that deionization primarily removes ionic species and does not eliminate non-ionic contaminants or microorganisms; additional treatment may be required for sterilization or organic removal. Resin performance can also be affected by carbon dioxide dissolution and resin fouling.

Applications include laboratory-grade water (Type I–III), semiconductor fabrication, pharmaceutical production, and certain cooling or process waters where mineral scaling must be avoided. Deionized water is typically measured by conductivity or resistivity to assess purity and is often part of a broader water purification system.