Zn(II) Removal Using Natural Bentonite: Thermodynamics and Kinetic Studies

DOI : http://dx.doi.org/10.13005/msri/050104

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This paper describes the adsorption of Zn(II) from aqueous solutions by commercial natural bentonite (NB). The contact time, pH of the solution, metal ion concentration, Temperature, adsorbent doses, bentonite treatment (calcinations of NB at 700?C and washing by deionized water to remove the excess salt from bentonite surface) on the adsorption process were examined. The washed and calcined bentonite samples were labeled by WB and CB respectively. The adsorption process follows pseudo-second-order reaction kinetics. The Langmuir and Freundlich models were used to describe the adsorption equilibrium of zinc on NB and the adsorption followed the Langmuir isotherm. The Langmuir and Freundlich constants for adsorption of zinc on NB were determined. This work discusses the thermodynamic parameters of the adsorption (the Gibbs free energy, entropy, and enthalpy). Our results demonstrate that the adsorption process was spontaneous and endothermic under natural conditions. The results show that adsorption behavior of NB was strongly depending on the pH. The optimum pH for adsorption was found to be 6.0. Also the adsorption capacity of NB for Zn (II) increases with increased bentonite dose. The adsorbed amount of Zn (II) on WB was increased by 100% compared NB and CB. The results generally showed that bentonite could be considered as a potential adsorbent for Zn(II) removal from aqueous solutions especially WB.

Heavy metals; adsorption; isotherms; natural bentonite; kinetics; thermodynamics