Enhanced chromium(VI) removal by zero-valent iron in the presence of anions and a weak magnetic field: Batch and column tests

In this study, batch and column tests were conducted to evaluate the influence of selected anions (ClO₄⁻, NO₃⁻, Cl⁻ and SO₄²⁻) on Cr(VI) removal by zero-valent iron (ZVI) with and without a weak magnetic field (WMF). Batch kinetic experiments demonstrated a synergetic enhancing effect of WMF and each anion on Cr(VI) removal. In addition, the ratio of the Cr(VI) removal rate constant for each tested anion to that of deionized water (i.e., the promotion factor of the combined effect) exhibited a hyperbolic increase as a function of anion concentration. Based on the magnitudes of their enhancing effects, the anions were ranked from most to least enhancing: SO₄²⁻ > Cl⁻ > ClO₄⁻ > NO₃⁻. The synergetic effect of WMF and anions was also obvious in a continuous flow system, which could both dramatically extend the lifespan of ZVI systems and improve the efficiency of Cr(VI) removal. The influence of WMF and the tested anions on ZVI corrosion products was investigated by scanning electron microscopy and X-ray diffraction. These findings could encourage the application of ZVI/WMF technology in the field.