Synthesis of zeolites X and A from fly ashes for cadmium and zinc removal from aqueous solutions in single and binary ion systems

Abstract

Two different Brazilian fly ashes were used to selectively synthesize pure zeolites X and A by a two-step process. The zeolites were characterized in terms of mineralogical composition (XRD), morphological analysis (SEM), specific surface area (BET method), and cation exchange capacity (CEC). XRD and SEM results indicated that pure zeolites X and A were obtained from fly ash samples, possessing high CEC at 3.1–3.9 meq/g. The pure zeolites X and A were used in adsorption of zinc and cadmium in single and binary systems. The adsorption studies showed that zinc is more preferentially adsorbed on pure zeolites than cadmium in both single and binary systems under similar experimental conditions. Zeolite-A presented higher adsorption than zeolite-X. The adsorption isotherms followed the Langmuir model. The adsorption capacities for zinc and cadmium on the pure zeolites ranged 156–220 mg/g and 57–195 mg/g in the single and binary ion systems, respectively. The removal of both ions by zeolites A was less affected by the presence of a competitive ion, different from zeolites X.