Sulfidized zero-valent iron (S-nZVI) has recently gained much interest for subsurface remediation. This is because its core (Fe0) – shell (FeS) structure enables up to 10-fold faster degradation of organic pollutants in comparison to bare zero valent iron (ZVI), while keeping anaerobic Fe0 oxidation at a minimum. These enhanced properties have been well assessed in relatively simplified environments (i.e., testing only one contaminant, use of deionised water or single buffer solutions). However, limited information is known on how S-nZVI behaves once injected into contaminated groundwaters characterized by coexistence of multiple contaminants. In this study, we investigated the reactivity of S-nZVI, as a function of sulfidation treatment (i.e., FeS shell thickness), in the presence of anthropogenically contaminated natural groundwater. The groundwater exhibited a complex mixture of chlorinated hydrocarbons (CHCs). Batch reactivity tests show that S-nZVI sulfidation treatment time positively affected the reduction rate (kobs) of tetrachloroethene, trichloroethene, trans-dichloroethene, and 1,1-dichloroethene, while a negative response was observed for kobs determined for 1,1,2-trichloroethane (1,1,2-TCA), trichloromethane, and cis-dichloroethene. In contrast to bare ZVI, S-nZVI reactivity trends did not follow a linear free energy relationship based on CHCs one-electron reduction potential, highlighting differences in reduction pathways between ZVI and S-nZVI. Product differentiation of 1,1,2-TCA further showed that two sites exists in S-nZVI, namely FeS sites for direct electron transfer and Fe0/FeOx sites for hydrogen evolution mediated reaction. The study further proposes that sulfidation treatment duration may be a parameter to be fine-tuned during the synthesis in order to appropriately target the contaminants of concern.

Linking sulfidation treatment and contaminant selectivity of sulfidized zero-valent iron

2019 Fall National Meeting

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