Adsorptive remediation of hexavalent chromium from synthetic wastewater by a natural and ZnCl2 activated Sterculia guttata shell

The present study deals with the removal of Cr(VI) ions from aqueous solutions by raw Sterculia guttata shell waste (RSGS) and ZnCl2 activated S. guttata shell waste (ASGS). Effect of various process parameters like solution pH, adsorbent dose, initial Cr(VI) concentration and temperature has been studied in batch system. The experimental data were fitted to the isotherm models. Langmuir isotherm model best fitted the adsorption equilibrium data and the adsorption capacity of RSGS and ASGS was found as 45.45 and 90.90 mg/g respectively at 2.0 pH. The data were analyzed on the basis of pseudo-first-order, pseudo-second-order, intra-particle diffusion and Boyd models. Higher degree of coefficient of determination was obtained for the pseudo-second-order kinetic model. The calculated thermodynamic parameters such as Delta G degrees, Delta H degrees and Delta S degrees showed that the adsorption of Cr(VI) ions onto adsorbents was spontaneous, endothermic and increased randomness in nature. Desorption study was carried out with different concentrations of NaOH solutions. The results of the present study suggested that RSGS and ASGS can be used beneficially in treating industrial effluents containing hexavalent chromium. (C) 2015 Elsevier B.V. All rights reserved.