Rapid removal of aqueous Cr(VI) and the removal mechanism using ZVI/Fe3O4/Fe2+ system

The treatment of chromium wastewater is a global environmental issue. In this paper, the influencing factors such as initial pH and Fe2+ concentration on the removal of Cr(VI) by the zero-valent iron (ZVI)/Fe3O4/Fe2+ system were studied. The comparison of Cr(VI) removal by hybrid ZVI/Fe3O4/Fe2+ system, non-hybrid, and partial-hybrid systems were studied. Fe(II)/FeT and Fe(III)/FeT changes, and Cr(III) concentration change were also investigated. X-ray powder diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were used to study the reaction mechanism between Cr(VI) and the ZVI/Fe3O4/Fe2+ system. The removal of Cr(VI) was accelerated with the increase of Fe2+ concentrations and decrease of initial pH. Cr(VI) from synthetic wastewater reduced from initial 20.0 to 0.1 mg/L in 30 min by 2.5 g/L ZVI, 2.5 g/L Fe3O4, and 0.4 mM Fe2+ at initial pH 3.0. At initial pH value of 3.0, Fe(II) and Fe(III) generation–consumption–regeneration cycle in the ZVI/Fe3O4/Fe2+ system was studied. The characterization of the ZVI/Fe3O4 after the reaction revealed that the removal of Cr(VI) is a complex process including surface adsorption and reduction. This study demonstrates that the ZVI/Fe3O4/Fe2+ system has a great potential to be applied in treating wastewater containing Cr(VI).