Thermodynamics and Kinetics of Co (II) Adsorption onto Natural and Treated Bentonite

The present study examined the application of a commercial natural bentonite (untreated, NB) for the removal of Co (II) ions from aqueous solutions. Specific surface area of the sample was determined by means of N-2 adsorption-desorption at 77 K applying the BET method. X-ray powder diffraction (XRD) was also used to characterize the (NB). The effects of pH, adsorption time, cobalt ion concentration, bentonite doses, temperature and the NB treatment (calcination of NB at 700 degrees C and washing by water) on the adsorption process of Co (II) were examined. The optimum pH for adsorption was found to be 6.0. The data demonstrated that the amount of Co (II) adsorbed on bentonite increases rapidly during the first hour, thereafter adsorption becomes linear with time. Pseudo-second-order model described best the kinetics of the reaction. The thermodynamic parameters of the adsorption (the Gibbs free energy, entropy, and enthalpy) were determined and discussed. The adsorption of Co(II) on NB appeared to follow Langmuir adsorption. The process was found to be spontaneous and endothermic under normal conditions. The adsorbed amount of Co (II) on washed bentonite (WB) was increased by 100% compared to NB and bentonite calcined at 700 degrees C (CB). Our results show that bentonite could especially WB be considered as a potential adsorbent for Co (II) removal from aqueous solutions.