SORPTIVE REMOVAL OF CADMIUM FROM AQUEOUS SOLUTION USING DERIVED AND THIOL-FUNCTIONALIZED SILICA: ISOTHERM, KINETIC AND THERMODYNAMIC STUDIES

Abstract

The present study explored the feasibility of using derived and thiol-functionalized silica as adsorbent for the removal of cadmium under different experimental conditions. Effects of various parameters such as function of point of zero charge (pHPZC), solution pH, sorbent-sorbate resident time and ratio, concentration and temperature were investigated. The sorption of cadmium followed pseudo-second-order rate kinetics. This was further supported by Elovich and Intra-particle diffusion model. Intra-particle diffusion was found not to be the sole rate-controlling step. Thermodynamic studies revealed that the sorption of cadmium was endothermic and spontaneous, with good affinity toward the sorbent. Various isotherm models viz. Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Harkins-Jura, and Halsey isotherms were used to analyze the equilibrium data at different temperatures. The Freundlich, Halsey, Langmuir, and Temkin models were found to be in good agreement with experimental data with high R2, low Root Mean Square Error (RMSE), and low χ2 values. The results show that the sorption capacity increases with an increase in solution temperature from 28 to 65 °C. The maximum sorption capacity calculated from Langmuir isotherm was 27.55 and 28.09 mg/g for derived and thiol-functionalized silica respectively at optimum condition of pH 5 and contact time of 120 min.