Removal of chromate from water using surfactant modified Pohang clinoptilolite and Haruna chabazite

Two kinds of natural zeolite, Korea Pohang clinoptilolite (PC) and Japan Haruna chabazite (HC) were modified by hexadecyltrimethylammonium bromide (HDTMA) and used to remove chromate from water. The structures of HDTMA-zeolites were characterized by FTIR and XRD. The effects of contact time, initial Cr(VI) concentration, pH of solution, ionic strength and the coexisting ions on the chromate adsorption were evaluated. Our results show that Cr(VI) adsorption can reach equilibrium state very fast which can be described by pseudo-second order kinetic model. The Cr(VI) adsorption capacity of HDTMA-zeolites are significantly higher than that of PC and HC. In particular, the Cr(VI) removal of HDTMA-PC is optimized within a wide solution pH range of 3.0–11.0, while that of HDTMA-HC is very sensitive to pH value that it can only be optimized in a narrow pH range near 3.0; and HDTMA-HC shows a much higher Cr(VI) adsorption in comparison with HDTMA-PC and other HDTMA-chabazite. Meanwhile, ionic strength for solution has a significant effect on chromate removal for HDTMA-zeolites. The chromate removal is not affected by coexisting of chloride, nitrate, calcium and magnesium ions but is reduced in the presence of sulfate, bicarbonate and phosphate ions. Furthermore, HDTMA-zeolites can achieve high regeneration efficiency.