Modified red mud tailored to chromium contaminated soil remediation

The modified red mud was prepared by thermal reduction with coconut shell for Cr(VI) contaminated soil remediation. Significant reduction of Cr(VI) in soil was achieved for the modified red mud with an efficiency up to 100%. The mass ratio of the modified red mud to soil presents the greatest impact on Cr(VI) reduction in soil, followed by pH, and then the soil moisture. Under the conditions of pH = 4%, and 40% water content, the reduction of Cr(VI) in soil reached 99.37%with 10 wt% of the modified red mud (RM1C-T800(1 h)). Based on the X-ray diffraction spectrum, zero valence iron (ZVI) was detected in RM1C-T800(1 h). The characterization analysis showed that the originally tight and porous surface of RM1C-T800(1 h) became loose and flocculation state after the soil remediation. It implied that internal ZVI particles had recombined with Cr and gradually separated from the parent by exposing to the external surface of RM1C-T800(1 h). The decrease of Cr(VI)in soil was probably attributed to the adsorption and reduction of the ZVI in RM1C-T800(1 h) when mixing the Cr(VI) contaminated soil with RM1C-T800(1 h). The work offers an effective strategy for the resource utilization of solid waste and contaminated site remediation.