2R SO3 NaCaHCO32R SO3Ca2NaHCO3(resin complex)(resin complex)DOE-HDBK-1015/2-93DISSOLVED GASES, SUSPENDED SOLIDS, AND pH CONTROLPrinciples of Water TreatmentCH-04Rev. 0Page 16Figure 6 A Typical Pretreatment SystemThe reactions that occur in the water softener include the removal of both Mg and Ca ions.++++The water softener contains resin in which the insoluble exchange site is the SO molecule, and3-the soluble ions attached to the exchange site are Na ions. When water containing Mg , Ca ,+++++and HCO ions is passed over the resin in the softener, the ions are exchanged by the following3-reaction (Mg removal is similar).++(4-6)Note that electrical neutrality is maintained before and after the exchange reaction. One calciumion with two positive charges is attached to two exchange sites that release two sodium ions withone positive charge each. The HCO ion is not affected by the reaction and passes through the3-resin of the softener.To obtain pure water, it is necessary to demineralize the water completely, which is accomplishedusing a cation exchanger, an aerator, and an anion exchanger.
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