Exchange of cadmium into the sodium and ammonium forms of the natural zeolites clinoptilolite, mordenite, and ferrierite

Abstract

The selectivity of three different natural zeolites for cadmium has been investigated using either chloride or nitrate as the co-anion in solution. The three zeolites examined (clinoptilolite, mordenite, and ferrierite) were prepared in both the sodium and ammonium forms before exchanges with cadmium were attempted, and the selectivities of these materials for cadmium were measured in terms of experimental ion-exchange isotherms at 298 K. With one exception [Cd/NH₄(Cl/NO₃)–clinoptilolite] all systems were shown to be reversible. Differences in selectivity when either chloride or nitrate is the co-anion are discussed, and thermodynamic data are derived for those systems shown to be reversible. In contrast to similar studies on clays, no over exchange of cadmium was observed on any of the zeolites. Of the systems studied, it is concluded that sodium clinoptilolite is the most suitable exchanger for the removal of cadmium from solution.