Properties and mechanism of Cr(VI) adsorption and reduction by K2FeO4 in presence of Mn(II)

To efficiently treat hexavalent chromium (Cr(VI)) wastewater, K2FeO4 was used to remove and reduce Cr(VI) in presence of Mn(II) in this paper. Batch removal experiments were carried out to study the effect of Fe/Mn molar ratios, initial pH, in-situ and ex-situ and co-existing ions on Cr(VI) removal. The results showed the removal efficiency of Cr(VI) was 97.7% for the initial Cr(VI) concentration of 10.0 mg/L at Fe/Mn molar ratio of 2:3 and initial pH 8.0. Meanwhile, the high removal efficiency of Cr(VI) had been maintained throughout the pH range of 3.0–8.0 in the experimental study. Moreover, the removal process was relatively stable regardless of in-situ and ex-situ, and co-existing ions such as Ca2+ and low concentration of HCO3− had no intense effect on Cr(VI) removal, while SO42− inhibited Cr(VI) removal in the reaction system. To investigate the removal mechanism of Cr(VI) by K2FeO4 in presence of Mn(II), the reaction products were characterized by the Fourier transformed infrared spectrometer, X-ray powder diffraction, Transmission electron microscopy and the high-resolution X-ray photoelectron spectroscopy. The results indicated the ferrate decomposition products of γ-FeOOH/γ-Fe2O3 had the ability to adsorb Cr(VI) and react with Mn(II) to form γ-Fe2O3-Mn(II) complex to adsorb and reduce Cr(VI).