Synergistic effect of sulfidated nano zerovalent iron and proton-buffering montmorillonite in reductive immobilization of alkaline Cr(VI)-contaminated soil

Effective remediation of Cr(VI)-contaminated soil with strong alkalinity and high Cr(VI) concentration is a severe challenge. Herein, a proton-buffering montmorillonite-supported sulfidated nano zerovalent iron (nFeS/Fe 0 @H–Mt) was developed for remediation of alkaline Cr(VI)-contaminated soil. The reductive efficiencies of water-soluble Cr(VI) reached 99.7%, 99.3% and 99.8% in three tested soils with initial concentrations of 439.6, 3307.5 and 4626.7 mg kg −1 , respectively, after 15 d of nFeS/Fe 0 @H–Mt treatment. Further speciation analyses demonstrated most available Cr species (exchangeable and carbonate-bound Cr) were transformed into more stable Cr species. The leachable Cr(VI) and total Cr obtained by toxicity leaching procedures decreased to extremely low levels and maintained long-term stability for 120 d. Such superior reductive immobilization performance of FeS/Fe 0 @H–Mt was attributed to the synergistic effect of sulfidated nano zerovalent iron and proton-buffering montmorillonite , which induced the coordination of proton donation and electron transfer . The proton-buffering montmorillonite (H–Mt) could prevent the aggregation of nanoparticles and provide protons to accelerate the corrosion of Fe 0 . In addition, the FeS component improved electron selectivity and facilitated electron transfer of Fe 0 to Cr(VI). Our study demonstrated that the coordination of proton donation and electron transfer significantly enhanced the Cr(VI) reduction under the alkaline condition thus leading to effective remediation of alkaline Cr(VI)-contaminated soil.