Remediation Of Cr(Ⅵ)-Contaminated Soil Mixed with Chromite Ore Processing Residue (Copr) by Ferrous Sulphate and Biogas Solid Residue

The color of reduced Cr(Ⅵ)-contaminated soil and chromite ore processing residue (COPR) turned to yellow again due to the Cr(Ⅵ) incomplete reduction has gained wide attention. It is urgent to develop remediation techniques for complete Cr(Ⅵ) reduction. The combination of ferrous sulphate (FeSO4) and biogas solid residue (BSR) was used to the remediation of Cr(Ⅵ)-contaminated soil that mixed with COPR and reduced Cr(Ⅵ) content from 1498.05 to 104.63 mg/kg, which was lower than that reduced by single FeSO4 (413.61 mg/kg) or BSR (367.45 mg/kg). Compared to aerobic condition, the BSR or combined with FeSO4 have better Cr(Ⅵ) reduction performance under anaerobic condition, where the lower pH and redox potential were detected. The XRD and SEM results show that ettringite was decomposed into CaSO4(H2O)2 and Fe2(SO4)3 by the addition of FeSO4, and it was destroyed more completely with the combination treatment of FeSO4 and BSR. Metagenomic analysis indicated that microbial community (e.g., Acinetobacter) and genes (e.g., nemA)which are related with Cr(Ⅵ) and Fe(Ⅲ) reduction were enriched with the simultaneous treatment of FeSO4 and BSR, which contributes to the reinforcement of Cr(Ⅵ) remediation performance. This provides a promising method and theoretical guidance for the remediation of Cr(Ⅵ)-contaminated soil and COPR.