Adsorption thermodynamic and kinetic studies of dissolved chromium onto humic acids

Adsorption thermodynamic characteristic and kinetics of dissolved chromium from aqueous solutions onto humic acids (HAs) were studied. The results showed that the Freundlich isotherm model described the equilibrium data well. The negative Delta G degrees confirmed the spontaneity of adsorption process. The positive Delta H degrees and Delta S degrees proved the endothermic nature and irreversibility of the sorption. Furthermore, the adsorption process followed the pseudo-second-order equation. With increasing initial concentration of Cr(VI), the adsorption rate constant decreased while the maximum adsorption capacity increased. (C) 2008 Elsevier B.V. All rights reserved.