INHIBITORY EFFECTS OF “ GREEN ” ADDITIVES ON THE CRYSTAL GROWTH OF SPARINGLY SOLUBLE SALTS

In this chapter the effects of environmentally friendly additives on formation and growth of sparingly soluble salts are presented in a concise way. Specifically, the influence of a biodegradable, environmentally friendly polysaccharide-based polycarboxylate, carboxymethyl inulin (CMI), on the crystal growth kinetics of calcium oxalate has been studied. The spontaneous crystallization method was used to delineate the crystallization kinetics of calcium oxalate (CaC2O4, CaOx). The results demonstrate that the retardation in crystal growth is controlled by the carboxylation degree of the CMI and its concentration. These studies also show that CMI additives direct calcium oxalate crystallization from calcium oxalate monohydrate (COM) to calcium oxalate dihydrate (COD). Colloidal silica is known to be a substantial problem in silica-laden process waters. Although silica “technically” is not a salt, it is often categorized with them, as it brings about the same problems as mineral scale deposits (reduced heat transfer, etc.). We also report a strategy to retard silicic acid condensation in supersaturated aqueous solutions by using non-toxic, “green”, zwitter-ionic phosphonomethylayed chitosan (PCH). An overview of the use of green additives in water treatment is also presented.