Sulfidation of zero-valent iron (ZVI) materials for enhanced reactivity towards chlorinated contaminants has attracted increasing attention due to the more sustainable nature of sulfided-iron versus other forms of ZVI materials that requires expensive catalytic additives or sophisticated procedures to attain improved reactive properties. In spite of the promise of sulfidation, the critical factors controlling the reactivity of sulfided iron and the mechanism of enhanced dechlorination rates caused by sulfur treatment (sulfidation) are not well understood. This study examines how sulfidation of laboratory synthesized iron nanoparticles (nZVI) as well as commercial brands of bulk ZVI particles influence the materials reactivity and selectivity for chlorinated ethenes (e.g., TCE and PCE). TCE dechlorination experiments indicate that the performance of sulfur-treated nZVI was relatively unaffected by the choice of sulfidation reagents (viz., sodium sulfide, dithionite, or thiosulfate), yet sulfur to iron (S/Fe) mole ratio was found to have a strong impact on the kinetics of TCE degradation by the sulfur-amended nZVI.  A small dose of sulfur led to a significant increase in TCE reduction rate, but the effect was saturated when S/Fe mole ratio exceeds 0.025. Using several lines of experimental evidence, we showed that the role of sulfidation lies essentially in its ability to poison hydrogen recombination on ZVI surface, which increases the production of atomic hydrogen relative to hydrogen gas. Consequently, sulfidation increases the selectivity of ZVI surface for the reduction of chlorinated ethenes relative to the competing process of water reduction. This new understanding points to the potential of sulfidation as a general surface engineering method to improve the reactivity and selectivity of ZVI materials for in situ chemical reduction applications.<br/> <br/>

Understanding the effect of sulfidation on the reactivity of zero-valent iron materials

253rd National Meeting (2017)

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