ION-EXCHANGE IN ZEOLITES .3. HYDROLYSIS AND TRACE CA-45(2+) AND NA-22(+) EXCHANGES IN ZEOLITE-X AND ZEOLITE-Y

The effects of hydrolysis on concurrent trace Ca-45(2+) and Na-22+ exchanges have been studied in the Na forms (trace Ca2+ exchange) and the Ca forms (trace Na+ exchange) of zeolites X and Y in NaNO3 (Na forms) and Ca(NO3)2 (Ca forms) solutions at different concentrations. Based on the mass-action formulations of Gaines and Thomas, equations were derived for the prediction of hydrolysis and the trace exchange equilibria (distribution coefficient K(D)) in the zeolites. Predictions of hydrolysis equilibria (pH, Ca2+ and Na+ concentrations) were good in most cases, but for the trace Ca2+ and Na+ equilibria, K(D) predictions failed significantly at low concentrations of the macro-ions, as a strong decrease in selectivities for the trace ions took place. In theory, this could be explained by the presence of suspended zeolite particles, which could not be removed by centrifugation, in solution. The presence of such suspensions in solution could not, however, be established.