A stepwise processing strategy for treating manganese residue and the remediation of hexavalent chromium in water and soil by manganese residue-derived (Fe,Mn)C2O4

Abstract

This work provides a new approach for effective treatment and utilization of manganese residue (MR), including leaching, desulfurization, and recycling of iron and manganese. The secondary residue and the acidic filtrate (pH = 0.94) composed of H2SO4 and H2C2O4 could be used as a cement material and the medium and reductant for manganese sulfate production system, respectively. Approximately 94.5% of Fe and 97.5% of Mn were recovered to produce (Fe,Mn)C2O4 composite, which had a capacity of 122.7 mg g−1 for removing Cr(VI) and a good performance in a wide pH range of 2–9. The removal of Cr(VI) by (Fe,Mn)C2O4 was attributed to adsorption, reduction, and co-precipitation. What's more, the control experiment of FeC2O4 and MnC2O4 affirmed the synergism between Mn and Fe in (Fe,Mn)C2O4 composite, attributed to that the accelerated reduction of Mn(III) by Fe(Ⅱ) and the co-reduction effect of Fe with Mn on Cr(VI) synergistically promoted the reduction of Cr(VI). Furthermore, the ability of (Fe,Mn)C2O4 for immobilizing Cr(VI) in the soil was investigated, and the result proved that (Fe,Mn)C2O4 significantly reduced the leaching and releasing risk of Cr(VI). This strategy for treating and utilization of MR has great economic and ecological benefits.