Effect of NaCl on Cr(VI) reduction by granular zero valent Iron (ZVI) in aqueous solutions

This study examined the effect of NaCl on the removal of Cr(VI) by ZVI in aqueous solutions and proposes a potential mechanism of Cr(VI) removal by ZVI in aqueous solutions with NaCl. A series of batch tests was conducted on ZVI using 100mg/L Cr(VI) solutions at an initial pH of 3 at various NaCl concentrations. The NaCl in aqueous solutions improved the removal efficiency for Cr(VI) by ZVI. Fe(III)Cr( III) (oxy)hydroxides were precipitated both on the ZVI surface and in the solution via the reduction reactions of Cr(VI) to Cr(III) in the presence of NaCl. The increase in the Cr(VI) removal efficiency in the solutions with NaCl was attributed to the Cl ions, which accumulate at the anodic sites of ZVI, thereby enhancing ZVI oxidation and colloidal particle formation. In the NaCl solutions, small grains were initially precipitated on the ZVI surface, via relatively fast reactions. The subsequent slowing of these reactions resulted in the precipitation of large grains on the ZVI surface and colloidal particles in the solutions.