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Extension of conventional sodium-cycle softening to high-solids waters is restricted by the fundamental properties of ion-exchange systems. Resin performance is a function of water composition, both in regard to total dissolved salts and the fraction of hardness salts. Volume treated to hardness breakthrough, and hardness leakage can be estimated with a useful degree of accuracy by use of equilibrium relationships. Adjustment of performance for different levels of regeneration can be made by use of empirical data relating degree of regeneration to salt dosage.
Waters with total dissolved solids above 5000 ppm can be softened by use of weak acid resins in many cases. Depending on the nature of the salts present, a weak-acid resin may be used in either a sodium or hydrogen cycle. Although acid and base are required for regeneration, chemical costs are competitive with conventional softening in many situations.
Softening of saturated brines requires use of chelating resins showing high selectivity for hardness ions over sodium ion.
ion exchange, water, hardness, softening, brine, water injection
Senior research scientist, Diamond Shamrock Corporation, Redwood City, Calif.