Enhanced immobilization of Cr(VI) by a Fe0–microorganisms composite system: Benchmark and pot experiments

In this study, a collaborative system of Fe 0 and mixed anaerobic microorganisms was established for remediating chromium (Cr)-contaminated soil and restraining the translocation of Cr from soil to swamp cabbage ( Ipomoea aquatica Forssk.). Solid phase characterization demonstrated that more reactive secondary minerals such as green rust, magnetite, and lepidocrocite were generated in the composite system as compared with the Fe 0 -only system. Hence, the Fe 0 –microorganisms composite system achieved a remarkably higher aqueous Cr(VI) removal of 85.6%, 2.9 times higher than that in the Fe 0 -only system. After 14 d remediation, easily available Cr(VI) and Cr total species such as water-soluble, exchangeable, and bound-to-carbonates were converted to less available Cr(III) and Cr total species (e.g., Fe–Mn oxides-bound and organic matter-bound species) because of the production of Cr–Fe hydroxides and oxides [Cr x Fe 1−x (OH) 3 or Cr x Fe 1−x OOH] on the Fe 0 surface. A pot experiment showed that Cr uptake by swamp cabbage after the composite system remediation was suppressed by 69.1%, two times higher than that after the Fe 0 -only system remediation. Excessive Fe uptake by swamp cabbage also was efficiently inhibited by the composite system treatment due to enhanced Fe hydroxides and oxides production on the Fe 0 surface because of biological corrosion and mineralization. These results indicated that Fe 0 –microorganisms composite system remediation could efficiently enhance Cr(VI) immobilization and decrease its bioavailability and bioaccumulation by plants, which is a promising technology in Cr-contaminated soil remediation.