Uptake of radioactive metal species from soils and solutions by clay particles could be a treatment option due to simplicity of operation and economic cost. In this concern, adsorption behavior of Cs+ or Co2+ onto bentonite as a function of contact time, pH, initial metal concentration, ionic strength, and temperature was studied by batch adsorption technique. Adsorption isotherm data were interpreted by Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models. Bentonite exhibited maximum adsorption capacity of 83.3 mg g-1 for Cs+ and 15.9 mg g-1 for Co2+. Presence of humic acid (HA) as a representative model of organic matter did not significantly affect the adsorption capacity of bentonite for Cs+, whereas it increased the adsorption capacity of bentonite for Co2+. Thermodynamic parameters, standard enthalpy (ΔH°), standard entropy (ΔS°), and standard free energy (ΔG°) were determined through batch adsorption experiments performed at four different temperatures of 288, 298, 318, and 338 K. Co2+ adsorption onto bentonite showed an endothermic reaction (ΔH° = 13.6 kJ mol-1) whereas Cs+ adsorption displayed an exothermic nature (ΔH° = -4.65 kJ mol-1). Negative values of ΔG° and positive values of ΔS° indicated the feasibility and spontaneous nature of adsorption processes and more disordered form after adsorption.
Keywords: Adsorption; Adsorption isotherm modeling; Bentonite; Cesium; Cobalt; Thermodynamic properties.