Iron particles have played a central role in water treatment because of its unique adsorption, redox and other properties than enable several important physico-chemical processes for removal of a diverse array of contaminants. Their low cost also enables its implementation in remote and poor communities. There has been significant interest over the last three decades in the use of zerovalent iron micro- and nano-particles for removal of heavy metals, and degradation of chlorinated hydrocarbons, nitrates and other common groundwater contaminants. Over the last decade, there has been considerable interest in the higher reactivity and longevity of zerovalent iron particles (ZVI) following their sulfidation. Numerous studies have focused on the role of S/Fe ratios, sulfidation agents and sulfidated ZVI (S-ZVI) synthesis methods on its reactivity. In the context of degradation of chlorinated hydrocarbons by S-ZVI, there has been much emphasis on trichloroethene as a model reactant. Although trichloroethene is a common groundwater contaminant of significant concern, it often co-exists with other chlorinated hydrocarbons of different molecular structures that are also highly toxic contaminants. However, current reaction mechanisms for degradation of chlorinated hydrocarbons by S-ZVI, such as direct electron transfer, are largely based on observations with reactivity to trichloroethene. A through investigation of the reactivity of S-ZVI with a suite of different chlorinated ethenes, ethanes and methanes, conducted in our laboratory through quantification of its reaction rate constants, degradation capacity, electron selectivity and degradation products, suggest that likely several distinct degradation mechanisms are involved and the dominant mechanisms are highly compound-specific. The knowledge gaps in our current understanding of reactivity of S-ZVI to chlorinated hydrocarbons, and its significance for successful application of S-ZVI for water treatment will be discussed.

Reactivity of sulfidated zerovalent iron nanoparticles to chlorinated hydrocarbons: Perspectives from degradation of compounds beyond trichloroethene

ACS Spring 2022

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