Ion exchange in zeolites. Part 3.—Hydrolysis and trace 45Ca2+ and 22Na+ exchanges in zeolites X and Y

Abstract

The effects of hydrolysis on concurrent trace ⁴⁵Ca²⁺ and ²²Na⁺ 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.