Highly efficient removal of hexavalent chromium in aqueous solutions via chemical reduction of plate-like micro/nanostructured zero valent iron

Abstract

The removal of hexavalent chromium [Cr(VI)] from aqueous solutions using plate-like micro/nanostructured zero valent iron (MNZVI), which is fabricated in mass production by ball-milling of reductive iron powders, is investigated in this study. It has been shown that this plate-like MNZVI has significantly enhanced ability to remove Cr(VI) from aqueous solutions as compared to commercial zero valent iron (CZVI). Cr(VI) in a concentration of 100 ppm at pH = 2 can be removed nearly completely within 20 min by the addition of 1.5 g L⁻¹ MNZVI. The time-dependent removal amount of Cr(VI) can be well described by a pseudo first-order kinetic model. The reaction rate constant for MNZVI is 20 times larger than that for CZVI. Further experiments have revealed that the Cr(VI) removal is also associated with the pH value and initial concentration of Cr(VI) in the solution, in addition to the iron dosage. These enhanced removal performances are attributed to the iron-induced reduction process of Cr(VI) and the high specific surface area of MNZVI. Further, electroplating wastewater was used to demonstrate the practical applications of MNZVI. The removal capacity is up to 330 mg g⁻¹ in the electroplating wastewater with a 556 ppm initial Cr(VI) content, which is more than 3 times higher than that of CZVI and also much higher than the previously reported results. This study has demonstrated that the ball milling-induced plate-like MNZVI is a good candidate material for efficient treatment of Cr(VI)-containing wastewater.