Deionisation uses synthetic ion-exchange resins to chemically remove ions from feedwater. As the water passes through the ion exchange of hydrogen and hydroxide ions for dissolved minerals and then recombine to form water.
Deionisation resin beds or columns are typically made from cation-exchange resins and anion-exchange resins either in separate beds or packaged together. There are three types of deionisation: cocurrent, counter-current and mixed bed.
Co-current deionisation refers to the original downflow process where both input water and regeneration chemicals enter at top of an ion exchange column and exit at the bottom.
Counter current deionisation comes in two forms the first form is up flow columns where input water enters from the bottom and regenerants enter from the top of the exchange column. Second form is up flow regeneration where water enters from the top and regenerants enter from the bottom.
Mixed bed deionisation is a 50/50 mixture of carbon and anion resin combined in a single ion-exchange column.
Deionisation removes the following water impurities