Remediation of Cr(VI) contaminated soil-groundwater using in-situ injection of calcium polysulfide: Results from a 3D sandbox model experiment

A self-designed 3D sandbox model was used in the study to investigate the in-situ injection of calcium polysulfide (CPS) for remediating chromium contamination. The remediation effect of in-situ injection of CPS on Cr(VI) contaminated soil and its effect on soil chemical properties were evaluated. The soil-groundwater environmental factors were monitored during the injection process, and a correlation analysis was conducted between the monitoring factors and the concentration of chromium. The remediation mechanism of CPS was explored in combination with microscopic experiments. The results indicate that the injection of CPS can significantly reduce Cr(VI) contamination at the simulated site and the Cr(VI) concentration in the aquifer was <0.05 mg/L (EPA standard) on the 7th day. In contrast, the removal rate of Cr(VI) in the soil at the top of the model box was lower. After 30 days of remediation, the TCLP concentration of soil was 18.172-28.362 mg/L. There is a sharp decrease observed in the ratio of Cr(VI)/Cr(total) as well as in the exchangeable state Cr. After 30 days of remediation, the ratios were 0.08 %-8.9 % and 5 %-10 %, respectively. Additionally, the strongest correlation with Cr(VI) concentration is found for the oxidation-reduction potential.