Sulfidation of Magnetite for Superior Dechlorination of Trichloroethene

The reported contributions of magnetite to the abiotic natural attenuation of chlorinated ethenes have generated interest in its potential for soil and groundwater remediation. In this study, we investigated the impact of the two-step sulfidation method on the physicochemical properties and reactivity of magnetite with trichloroethene (TCE). We systematically evaluated the effect of different sulfur precursors (dithionite, thiosulfate, and sulfide) and sulfur-to-iron ([S/Fe]_dosed) molar ratios on the reactivity. Results were compared to those of sulfidated nZVI (S-nZVI) as a benchmark for assessing the efficacy of sulfidated magnetite (S-Fe₃O₄). The findings indicated limited reactivity of magnetite when sulfidated with dithionite and thiosulfate. However, sulfidation with sulfide yielded reaction rates comparable to those of S-nZVI, particularly at lower [S/Fe]_dosed ratios. At higher [S/Fe]_dosed ratios (>0.1), sulfide-sulfidated magnetite (S-Fe₃O_{4_S}) exhibited reaction rates surpassing those of S-nZVI, with the major dechlorination product being acetylene. Nonetheless, reusability experiments demonstrated that the performance of S-Fe₃O₄ diminished with aging. These results show that S-Fe₃O_{4_S} achieved complete transformation of TCE to acetylene, with reaction rates comparable to S-nZVI. Given its lower cost of production, engineered S-Fe₃O_{4_S} remediation systems could serve as a more affordable alternative for in situ chemical reduction of TCE with further research and development.