Statistical design and kinetic and thermodynamic studies of Ni(II) adsorption on bentonite

The adsorption of the bentonite toward Ni(II) from aqueous solution was studied to obtain optimum conditions, equilibrium model, thermodynamic and kinetic parameters. Statistical method was used to evaluate maximum amount of adsorbed Ni (II). In this work, pH of solution during stirring, contact time, initial Ni (II) concentration, particle size of bentonite and amount of bentonite were considered as effective parameters which should be examined. The increase of temperature has negative effect on the Ni(II) adsorption. The equilibrium data were correlated well with Freundlich and Dubinin–Radushkevich isotherm models the correlation coefficients of which are (R2) 0.994 and 0.971, respectively. This model indicates heterogeneous and chemical absorption or ion exchange process. The values of thermodynamic parameters such as ΔH°, ΔS° and ΔG° of nickel adsorption reveal that it is a spontaneous, exothermic and associative process. The experimental data fit the pseudo-second-order kinetic very well with correlation coefficient (R2) more than 0.995.