Simultaneous Removal of Ammonium and Phosphate from Aqueous Solution by Calcium Chloride-Modified Zeolite

Abstract. In this study, the simultaneous adsorption characteristics of ammonium and phosphate from aqueous solution by calcium chloride-modified zeolite were investigated. Results showed that the adsorption kinetic data of ammonium and phosphate onto the calcium chloride-modified zeolite could be well described by a pseudo-second-order model. The adsorption equilibrium data of ammonium onto the calcium chloride-modified zeolite fitted to the Langmuir isotherm model better than the Freundlich and Dubinin-Radushkevich isotherm models. The phosphate removal efficiency of calcium chloride-modified zeolite increased with the initial concentration of ammonium in aqueous solution. The ammonium removal efficiency of calcium chloride-modified zeolite increased with increasing solution pH from 7.0 to 9.0, but decreased with increasing solution pH from 9.0 to 10.0. The phosphate removal efficiency of calcium chloride-modified zeolite increased dramatically with increasing solution pH from 7.0 to 9.0, but decreased with increasing solution pH from 9.0 to 10.0. The mechanism for the adsorption of ammonium onto the calcium chloride-modified zeolite was ions exchange, and the mechanism for the removal of phosphate by the calcium chloride-modified zeolite was chemical precipitation.