Correlation Between the Structural-Activity of Sulfidated Nanoscale Zerovalent Iron and Its Enhanced Reactivity for Cr(VI) Reduction

Sulfidation has gained increasing attention due to its merits to improve the structural-activity of nanoscale zerovalent iron (nZVI) and thus enhance its reactivity toward contaminants. Few studies have been conducted to elucidate the correlation between the structural-activity and reactivity of nZVI, which is important for up-scaling such a decontamination strategy. Taking chromate (Cr(VI)) as the targeted contaminant, this study found that sulfidation enhanced the reactivity of nZVI toward Cr(VI) to varying extents, which was closely related to the degree and order of sulfidation. Particularly, the optimal rate constants of S-nZVI for Cr(VI) removal were 9.79 and 1.48 times higher than that of nZVI in the batch and column systems, respectively. In addition, this study suggested that sulfidation enhanced the electrical conductivity of nZVI by forming conductive iron sulfides (FeSx), while simultaneously reducing the particle aggregation and thus attenuating the settling rate of nZVI in water. More importantly, the reactivity of S-nZVI toward Cr(VI) exhibited negative correlations with its sedimentation activity and electrical conductivity. These relationships can be potentially used to predict the decontamination reactivity of S-nZVI if its sedimentation or conductivity activity was known in advance. Finally, this study clarified the sulfidation-induced improvement in reactivity of nZVI toward Cr(VI), which should be primarily associated with the improved reactive site of S-nZVI due to excellent dispersion and excellent conductivity due to FeSx introduction, ultimately facilitating the reduction of Cr(VI) by nZVI.