Rapid Cr(VI) reduction and immobilization in contaminated soil by mechanochemical treatment with calcium polysulfide.

Mechanochemical treatment with calcium polysulfide (CPS) was applied to remediate the Cr(VI) contaminated soil. The effects of parameters including milling speed, milling time, ball to powder ratio (BPR) and dosage of CPS were investigated. The effectiveness of mechanical treatment with or without CPS is estimated by analyzing the leachable fraction of Cr(VI). The results show that mechanochemical treatment with CPS can decrease and immobilize Cr in soil more quickly and efficiently with comparison to the case without additive. Under a milling speed of 500 rpm, milling time of 2 h, BPR of 9 and CPS dosage of 3%, the Cr(VI) leaching concentration significantly decreased from 115 mg L-1 to 0.51 mg L-1, much lower than the regulatory limit of 5 mg L-1. Additionally, XPS results demonstrated that Cr(VI) can be converted into Cr(III) during ball milling with CPS. The high Cr(VI) removal and Cr immobilization capacity makes mechanochemical treatment a great potential in field remediation.