Physical and chemical factors affecting the adsorption of Cr(VI) via humic acids extracted from brown coals

The aim of this study is to demonstrate the potential of humic acids (HAs) as a low-cost reactive barrier material for environmental protection applications of toxic Cr(VI). Sorption of Cr(VI) on the HAs obtained from Ilgın, Beysehir and Ermenek lignites in Turkey were investigated and their sorption properties were compared with the activated carbon (AC) from Merck. The adsorption was carried out using a batch method. The sorption of Cr(VI) on the surface of HAs depends strongly on the pH and Cr(VI) sorption increased with a decreasing pH and increase in the concentration of this metal. The Freundlich adsorption isotherm was used to describe observed sorption phenomena. It was observed that the maximum adsorption capacity of 0.55 mmol Cr(VI)/g for Ilgın, 0.64 mmol Cr(VI)/g for Beysehir and 0.40 mmol Cr(VI)/g for Ermenek was achieved at pH of 3.2. The rise in temperature caused a slight decrease in the value of the equilibrium constant (Kc) for the sorption of Cr(VI). The Cr(VI) sorption capacities of Beysehir and Ilgın HAs were nearly as same as that of AC (0.58 mmol Cr(VI)/g). Therefore, HAs are used for the adsorption of Cr(VI) in wastewater treatment applications.