Remediation of Cr(VI)-contaminated soil using combined chemical leaching and reduction techniques based on hexavalent chromium speciation

Hexavalent chromium [Cr(VI)] has strong mobility and it can enter into deep regions of soil. Cr(VI)contaminated soil remediation is the process of removing Cr(VI) present in deep soils and any residual Cr(VI). In this study, the Cr(VI)-contaminated soil in Chongqing was investigated, and the remediation and economic feasibility of chemical leaching and reduction combined with a soil repairing approach was explored. The results showed that the leaching reagent, liquid-solid ratio, leaching time, reduction agent dosage, reduction temperature and reduction time had significant (P < 0.05) effects on the remediation of Cr(VI). At 0.02 mol/L oxalic acid and citric acid using a liquid-solid ratio of 5:1 and leaching time of 45 min, the removal rate of Cr(VI) was 62.7%, the residual Cr(VI) in soil was 126 mg/kg, and the soil pH was 4.09 after leaching. Between 25 and 90 degrees C, and at a molar ratio of 25:1 of FeSO4 center dot 7 H2O to Cr(VI), the reduction rate of Cr(VI) in soil after reduction was 54.0-98.4%, and the leaching concentration of Cr(VI) in soil was 0.01-0.29 mg/L. The optimal reduction was at 90 degrees C for 60 min, resulting in only 2.7 mg/kg of residual Cr(VI) in soil. The cost of this technology to treat the area studied was 826 (sic)/ton of soil, which represents an economically feasible method for Cr(VI)-contaminated soil remediation.

Automated summary

The study found that using oxalic acid and citric acid at 0.02 mol/L, with a liquid-solid ratio of 5:1 and a leaching time of 45 minutes, the removal rate of Cr(VI) was 62.7%, with residual Cr(VI) in soil at 126 mg/kg and a soil pH of 4.09 after leaching. Between 25 and 90 degrees Celsius, with a molar ratio of 25:1 of FeSO4 center dot 7 H2O to Cr(VI), the reduction rate of Cr(VI) in soil ranged from 54.0% to 98.4%, with leaching concentration of Cr(VI) in soil at 0.01-0.29 mg/L. The most cost-effective reduction occurred at 90 degrees Celsius for 60 minutes, resulting in only 2.7 mg/kg of residual Cr(VI) in soil.