Thermodynamics Analysis of Cesium Adsorption on Na₂Ti₂O₃SiO₄·2H₂O

Thermodynamical analysis of cesium adsorption on CST is considered to be one of the important approaches in studying the adsorption mechanism of cesium on CST. A series of parameters were obtained by measuring the change of the Cs⁺ ion concentration before and after the sorption. The CST sorption experiments were conducted with the CsNO₃ solution at different concentrations and temperatures. The saturation adsorption was found to be 212.8, 217.4 and 232.6 mg/g at 298.15, 313.15 and 328.15 K, respectively. The experimental data were fitted with the Langmuir model or the Freundlich model. The results showed that the Langmuir isotherm better fits this adsorption process. With the assumption that the adsorption enthalpy and adsorption entropy are independent of the temperature, the adsorption enthalpy and entropy were calculated to be 21.28 kJ/mol and 89.18 J·K^-1·mol^-1, respectively, with a negative adsorption free energy. The results indicated that the adsorption of cesium on CST is a spontaneous and endothermic process, with both physical and chemical adsorptions involved.