Equilibrium and Thermodynamic Studies of Cesium Adsorption on Natural Vermiculite and Optimization of Operation Conditions

Removal of cesium from synthetic aqueous solution through adsorption on vermiculite, under batch equilibrium experimental condition at six initial values of pH (۳, ۴, ۶, ۹, ۱۱ and ۱۲) and five temperatures (۲۵, ۵۰, ۷۵, ۸۵ and ۹۵ °C) has been investigated. It is necessary to propose a suitable model for a better understanding of the mechanism of cesium adsorption on vermiculite. For this propose the suitability of the Langmiur, Freundlich and Redlich-Peterson (R-P) adsorption models for equilibrium data were investigated. The parameters in the adopted adsorption isotherm models were determined by Eviews software. The study of equilibrium isotherm shows thatthe best model for analysis of experimental data is Redlich-Peterson model with correlation coefficient higher than ۰.۹۹(both for temperature and pH). The results showed that increasing of pH and temperature increased the adsorption ability of vermiculite.Optimum conditions for adsorption were determined as T=۷۵ °C, pH=۹, vermiculite dose=۱.۵ g and contact time of ۲۴ hr. Finally the thermodynamic constants of adsorption phenomena, DH° and DS° were found to be ۲.۶۷۲ kJ/mol and ۰.۵۶۳ kJ/mol K in the range of ۲۵-۹۵ °C respectively. The negative value of the Gibbs free energy DG demonstrates the spontaneous nature of cesium adsorption onto vermiculite.

کلیدواژه ها:

Adsorption ، Vermiculite ، Cesium ، equilibrium