Surface interactions of Cs+ and Co2+ with bentonite
2018
Ozsoy, Omer | Bekbolet, Miray
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.
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