Ammonium removal from aqueous solutions using microwave-treated natural Chinese zeolite

In this study, natural Chinese zeolite pretreated by sodium chloride solution under microwave irradiation was used to remove ammonium from aqueous solution. Adsorption kinetics, adsorption equilibrium isotherms and the effect of the individual presence of other cations and humic acid on the removal of ammonium were investigated by conducting a series of batch experiments. The zeolite treated under microwave irradiation had the highest ammonium adsorption capacity value, followed by the zeolite obtained by thermal process and the untreated zeolite. The kinetic studies confirmed that the adsorption of ammonium on the zeolite treated under microwave irradiation could be described by the pseudo-second-order kinetic model, and intra-particle diffusion controlled the limiting rate of the adsorption process. Five isotherm models were used to describe the isotherm data. Three-parameter isotherm models (Redlich-Peterson and Langmuir-Freundlich) provided much better isotherm data fitting than two-parameter isotherm models (Freundlich, Temkin and Langmuir). The presence of Na+, K+, Ca2+ and Mg2+ could reduce the uptake of ammonium onto the zeolite treated under microwave irradiation and the order of ammonium ion over other cations was Na+ > K+ > Ca2+ > Mg2+, while the presence of humic acid increased the uptake of ammonium. Due to their low cost, high adsorption capacity and selectivity, the zeolite treated under microwave irradiation has the potential to be utilized for cost-effective removal of ammonium from wastewater. (c) 2007 Elsevier B.V. All rights reserved.