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

Abstract

<em>Removal of cesium from synthetic aqueous solution through adsorption on vermiculite, under batch equilibrium experimental condition at six initial values of pH </em><em>(3, 4, 6, 9, 11 and 12) </em><em>and five temperatures (</em><em>25, 50, 75, 85 and 95 </em><em>°</em><em>C</em><em>) 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 that</em><em>the best model for analysis of experimental data is </em><em>Redlich-Peterson </em><em>model with correlation coefficient higher than 0.99(both for temperature and pH). </em><em>The results showed that increasing of pH and temperature increased the adsorption ability of vermiculite.</em><em>Optimum conditions</em><em> for </em><em>adsorption were determined as T=75 °C, pH=9, vermiculite dose=1.5 g and contact time of 24 hr. Finally the thermodynamic constants of adsorption phenomena, </em><em>D</em><em>H° and </em><em>D</em><em>S° were found to be 2.672 kJ/mol and 0.563 kJ/mol K in the range of 25-95 °C respectively. The negative value of the Gibbs free energy </em><em>D</em><em>G demonstrates the spontaneous nature of cesium adsorption onto vermiculite.</em>