Mixedbed

A mixed-bed is an ion exchange resin configuration used for water deionization that combines cation exchange resin and anion exchange resin in a single bed or vessel. In a typical mixed-bed, a strong acid cation resin (in the hydrogen form) and a strong base anion resin (in the hydroxide form) are mixed and packed together. As water passes through, cations are exchanged for hydrogen ions and anions are exchanged for hydroxide ions; the resulting H+ and OH− combine to form water, yielding a deionized stream with very low electrical conductivity.

The term mixed-bed can refer to either a true mixed resin bed or a closely coupled arrangement of separate resin beds that operate as a single treatment stage. The goal is to remove nearly all ionic species from water, producing high-purity output useful for applications that require minimal ionic content. The bed’s performance depends on resin quality, the ratio of cation to anion resin, flow rate, and pretreatment to limit fouling.

Regeneration and maintenance involve restoring the resins to their original ionic forms. The cation resin is regenerated with a strong acid (commonly hydrochloric or sulfuric acid) to reestablish the hydrogen form, and the anion resin is regenerated with a strong base (commonly sodium hydroxide) to reestablish the hydroxide form. Mixed-bed systems require management of regenerated waste streams and are typically followed by polishing or monitoring to ensure consistent water quality.

Applications include ultrapure water production for power plant boiler makeup, laboratory and pharmaceutical use, semiconductor manufacturing, and other industries demanding very low ionic content. Compared with separate-bed deionization, mixed-bed systems offer higher deionization efficiency and smaller footprints but involve higher chemical handling, regeneration complexity, and waste management considerations.