Chromium(VI) removal by mechanochemically sulfidated zero valent iron and its effect on dechlorination of trichloroethene as a co-contaminant

Mechanochemically sulfidatedmicroscale zero valent iron (S-mZVI(bm)) is a promising groundwater remediation material as it has been proven to be not only efficient in dechlorinating chlorinated compounds but also amenable to up-scaling. Yet, its efficiency in treating metal contaminants remains barely studied. In this study, we investigated the mechanism and efficiencies of Cr(VI) removal by S-mZVI(bm) and its effect on TCE dechlorination as a co-contaminant. The Cr(VI) removal by S-mZVI(bm) was mainly a chemisorption process and its kinetics was well fitted by a pseudo-second-order model. Alkaline pH inhibited Cr(VI) removal while dissolved oxygen slightly depressed the Cr(VI) removal. The Cr(VI) removal rapidly formed a non-conductive layer on S-mZVI(bm) surface to hinder further electron transfer from Fe-0 core before H+ was able to accept any electrons to produce H-2, which resulted in 100% electron efficiencies of Cr(VI) removal but <1% of Fe-0 utilization efficiency. The presence of Cr(VI) also dramatically inhibited the dechlorination of TCE and its electron efficiency as a co-contaminant by passivating the FeS surface. Therefore, Cr(VI) is likely to be an electron sink if present for remediation of other contaminants in groundwater. (C) 2018 Elsevier B.V. All rights reserved.