Demineralisation

Demineralisation removes dissolved salts by ion exchange. Cation resin swaps metal ions for hydrogen and anion resin swaps anions for hydroxide, which leaves very low conductivity water for boilers, laboratories and industrial processes. The resin trains are sized from the water analysis and the daily volume, and can run alone or after an RO stage.

RO removes most dissolved salts with membranes and suits large volumes. Demineralisation uses resin and reaches very low conductivity, but needs acid and caustic regeneration. EDI polishes RO water continuously without chemicals. Many plants combine RO with demineralisation or EDI.

When the resin is exhausted, the cation bed is regenerated with acid and the anion bed with caustic, then rinsed. Chemical storage, dosing and neutralisation of the regeneration water are part of the design and are sized from the water analysis and the volume treated.

A water analysis, the volume per day or hour, the conductivity or quality you need and how the water is used. If RO is already installed upstream, its permeate quality is the starting point. Space for chemical storage and the way regeneration water is handled on site also shape the design.