Polysulfide has been frequently used as an effective reductant to immobilize Cr(VI) in chromate-contaminated groundwater. This reductant is unique in that it can maintain the reducing area established in the subsurface for a prolonged time, allowing continuous treatment of residual chromate long after polysulfide is injected during site remediation. The mechanism behind this observed field phenomenon, however, is not completely understood. It is possible that iron (hydr)oxides commonly encountered in the sediment, would react with polysulfides on the mineral’s surface to produce additional reducing reagents such as Fe(II), FeS and/or related intermediate minerals that function not only to protect the established reducing area but also to serve as newly formed reductants for residual Cr(VI) fixation. In the current study, the redox reaction between maghemite (γ-Fe2O3) and polysulfide was studied in pH 9-11 under the anaerobic condition, and the capacity of the reduced maghemite (R-γM) for Cr(VI) immobilization was examined in pH 6-9. Experimental results indicated that total produced Fe(II) decreased with increasing solution pH, with more than 80% of the Fe(II) formed through the redox reaction with polysulfide distributed in the solid/sorbed forms. The reduced maghemite was found effective in further reducing Cr(VI), with higher reaction rates and removal efficiency generally observed at lower pH values. A reaction mechanism was proposed based on the XPS and XRD characterizations of R-γM and its reaction product with chromate, in agreement with the batch experimental results.

Reductive immobilization of Cr(VI) by Polysulfide-reduced Maghemite

2019 Spring National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.