What is an ion exchange process ?

Ion exchange can only take place between ions of the same charge namely anions for anions and cations for cations. Anion exchange resins have positively (+) charged exchange sites with anions attached. Cations -exchange resins have negatively (-) charged exchange sites with cations attached. In typical water supplies, the ion exchange resin is more selective for divalent (two positive or negative charges) and trivalent (three positive or negative charges) than monovalent ions. The ion exchange performance is largely dependent on the density of the beads, mechanical resistance, the grain size, the total capacity, break through capacity, porosity of a system, flow, rate, selectivity and the rate of exchange.

The dissolved salts in the natural waters pose serious problems in the industries. These salts form scales in the boiler tubes, corrode pipelines and interfere with many chemical processing. In the natural waters and in waste-waters, there are often undesirable ions and some of them may be worth recovering. So it is important to remove them when they are present in the drinking water.