Efficient Removal of Hexavalent Chromium in Aqueous Solution by Cationic Surfactant-Treated Natural Anatolian Clinoptilolite

Abstract

Sodium clinoptilolite-rich tuff from the Western Anatolia, Bigadic region was modified with octadecyltrimethylammonium bromide(ODTMA-Br) and hexadecyltrimethylammonium bromide (HDTMA-Br), and used for the first time to remove chromium(VI) from aqueous solution in a series of batch adsorption experiments. Various physico-chemical parameters affecting the adsorption process such as the contact time, pH, the optimum sorbent dosage and the initial concentration of chromium were studied. The Cr(VI) adsorption capacity of ODTMA-and HDTMA-treated clinoptilolite (Cp) was highly pH-dependent, and was found to be 3.65 mg/g and 2.85 mg/g at pH 2.0 and 3.0, and 0.25 g/50 mL sorbent dosage, 3 h equilibrium time and 25ºC, respectively. Langmuir, Freundlich and Dubinin-Radushkevich (D-R) models were applied to describe the adsorption isotherms. Langmuir's model fitted the equilibrium data better than the Freundlich isotherm. From the D-R isotherm model, the mean adsorption energy (E) calculated as 15.075 and 14.744 kJ/mol for ODTMA-Cp and HDTMA-Cp sorbents showed that the adsorption of chromium occurred by chemisorption. The kinetic data indicated that the sorption of hexavalent chromium onto modified Cp followed well the pseudo-first-order kinetics. The current study considers that further developments in this line of research should continue