Sulfidation of Zero-Valent Iron by Direct Reaction with Elemental Sulfur in Water: Efficiencies, Mechanism, and Dechlorination of Trichloroethylene

Sulfidation can enhance both the reactivity and selectivity (i.e., electron efficiency, epsilon(e)) of zero-valent iron (ZVI) in contaminant removal, which may make this technology cost-effective for a wider range of water treatment applications. However, current sulfidation methods involve either hazardous or unstable sulfidation agents (e.g., Na2S, Na2S2O3, and Na2S2O4) or energy-intensive preparations (e.g., mechanochemical sulfidation with elemental sulfur). In this study, we demonstrate that very efficient sulfidation of microscale ZVI (mZVI) can be achieved at all S/Fe molar ratios (similar to 100% sulfidation efficiency, epsilon(s)) simply by direct reaction between elemental sulfur (S-0) and ZVI in an aqueous suspension at ambient temperature. In comparison, the epsilon(s) values obtained using Na2S, Na2S2O3, or Na2S2O4 as the sulfidation agents were only similar to 23, similar to 75, and similar to 38%, respectively. The sulfidated mZVI produced using the new method reacts with trichloroethylene (TCE) with very high rates and electron efficiencies: rate constants and electron efficiencies were 800- and 79-fold higher than those of the unsulfidated mZVI. The enhanced performance of this material, together with the operational advantages of S-0 for sulfidation (including safety, stability, and cost), may make it a desirable product for full-scale engineering applications.

Automated summary

Sulfidation of microscale ZVI using elemental sulfur as a reactant can achieve high efficiency in contaminant removal, with higher sulfidation efficiency compared to traditional sulfidation agents. The sulfidated mZVI has shown significantly enhanced reactivity and electron efficiency when reacting with trichloroethylene, making it a promising product for engineering applications.