An investigation of Cu(II) adsorption by native and activated bentonite: Kinetic, equilibrium and thermodynamic study

In this study, the adsorption kinetics, equilibrium and thermodynamics of Cu(II) ions on native (NB) and acid activated (AAB) bentonites were examined. The specific surface areas, pore size and pore size distributions of the samples were fully characterized. The adsorption efficiency of Cu(II) onto the NB and AAB was observed to increase with increasing temperature. The kinetics of adsorption of Cu(II) ions was discussed using three kinetic models, namely: the pseudo-first-order, the pseudo-second-order and the intra-particle diffusion model. The experimental data fitted the pseudo-second-order kinetic model very well. The initial sorption rate and the activation energy were also calculated. Experimental results were also analyzed by the Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm equations at different temperatures. RL separation factor for Langmuir and the n value for Freundlich isotherm show that Cu(II) ions adsorbed favorably onto NB and AAB. Calculated thermodynamic quantities such as Gibbs free energy (ΔG), the enthalpy change (ΔH) and the entropy change of adsorption (ΔS) suggest that the adsorption processes were spontaneous, endothermic and controlled by physical mechanisms.