Ion exchange is a resin based process, the inner bids of resin carry either positive or negative ion which can be exchanged with the ion of incoming water. The dissolved salt or solids comprising of positive or negative ions are passed through cation and anion resins to achieve desired results.
There are various combinations of Ion exchange Columns depending upon raw water, product water and economy of operation. The demineralisation process can be carried out by 2 bed system, 3 bed system and combination of Degasser tower, as and when required. Another popular utility of ion exchange process is a softener. Softening resins have sodium ion concentration as an ion to be exchanged with calcium and magnesium ions. So by replacing calcium and magnesium ions, which constitutes hardness of the water. This type of resins can make the water soft. All types of resins are regeneratable by the help of weak acid, weak base and or salt solution.
Water softening is the removal of calcium, magnesium, and certain other metal cations in hard water. The resulting soft water is more compatible with soap and extends the lifetime of plumbing. Water softening is usually achieved using lime softening or ion-exchange resins. It is widely used in the food & beverage, hydrometallurgy, metals finishing, chemical & petrochemical, pharmaceutical, sugar & sweeteners, ground & potable water, nuclear, softening & industrial water, semiconductor, power, and a host of other industries.
Demineralization is often a term used interchangeably with deionization. Demineralization is essentially removing all the minerals that can be found in water. This process is usually done when the water is to be used for chemicals processes and the minerals present may interfere with the other chemicals. For eg. all chemistic and beauty products have to be made with demineralized water for this reason. With the demineralization process, the water is "softened" replacing the undesired minerals with different salts (NaCl). Demineralized water has a higher conductivity than deionized water.
Mixed bed deionization is a mixture of cation and anion resin combined in a single ion exchange column. With proper pretreatment, product water purified from a single pass through a mixed bed ion exchange column is the purest that can be made. Most commonly, mixed bed demineralizers are used for final water polishing to clean the last few ions within water prior to use.
Small mixed bed deionization units have no regeneration capability. Commercial mixed bed deionization units have elaborate internal water and regenerant distribution systems for regeneration. A control system operates pumps and valves for the regenerants of spent anions and cations resins within the ion exchange column. Each is regenerated separately, then remixed during the regeneration process. Because of the high quality of product water achieved, and because of the expense and difficulty of regeneration, mixed bed demineralizers are used only when the highest purity water is required.