De ionising resin, types, explanation.
The terms ion exchange, deionization and demineralization are often used synonymously to refer to the same process. However, deionization and demineralization may be accomplished by technologies other than ion exchange (see reverse osmosis). Ion exchange is a process used extensively in nuclear facilities, industrial processes and medical and pharmaceutical operations to control the purity and pH of water by removing undesirable ions and replacing them with acceptable ones. Specifically, it is the exchange of ions between a solid substance (called a resin) and an aqueous solution, typically municipal, potable water but it frequently involves process or even waste water (e.g., the plating industry). Depending on the identity of the ions that a resin releases to the water, the process may result in water purification or in control of the concentration of a particular ion in a solution. An ion exchange is the reversible exchange of ions between a liquid and a solid. This process is generally used to remove undesirable ions from a liquid and substitute acceptable ions from the solid (resin). The devices in which ion exchange occurs are commonly called demineralizers. This name is derived from the term demineralize, which means the process whereby impurities present in the incoming fluid (water) are removed by exchanging impure ions with H and OH ions, in the formation of pure water. H+ and OH- are present on the sites of resin beads contained in the demineralizer tanks or columns.
Ion Exchange Resins:
Cation Exchange Resins vs. Anion Exchange Resins
There are two general types of ion exchange resins: those that exchange positive ions, called cation exchange resins, and those that exchange negative ions, called anion exchange resins. A cation is an ion with a positive charge. Common cations include Ca+2, Mg+2, Fe+2, and H+1. A cation resin is one that exchanges positive ions. An anion is an ion with a negative charge. Common anions include Cl-1, SO4-2, and OH-1 . An anion resin is one that exchanges negative ions. Chemically, both types are similar and belong to a group of compounds called polymers, which are extremely large molecules that are formed by the combination of many molecules of one or two compounds in a repeating structure that produces long chains. A demineralizer is a vessel, usually with a volume of several cubic feet, that contains the resin. A demineralizer may contain an intimate mixture of both cation exchange resins and anion exchange resins and is called a mixed bed. Two-bed demineralizers have two vessels, the first containing cation resin followed by a separate vessel containing anion resin.
Physically, ion exchange resins are formed in the shape of very small beads, called resin beads, with an average diameter of about 0.5 millimeters. Wet resin has the appearance of damp, transparent, amber sand and is insoluble in water, acids, and bases. The ratio is normally 2 parts cation resin to 3 parts anion resin.
Alkaline water is negatively charged, acid water is positively charged.