Kinetic insights into the relationships between anaerobic corrosion and decontamination of nanoscale zerovalent iron improved by sulfidation

There is a trade-off between corrosion and decontamination of nanoscale zero-valent iron (nZVI), which can be modulated by the sulfidation. Despite that, the insights into the relationship between anaerobic corrosion and decontamination of sulfidated nZVI (S-nZVI) remain unclear from a kinetic point of view. Herein, we used the variation of open-circuit potential to explore the anaerobic corrosion kinetic of S-nZVI. Taking Cr(VI) as the targeted contaminant, a negative correlation between decontamination and the corrosion of S-nZVI was identified during the first 10 min of reaction (R² = 0.6919, slope = -0.7091) and after the 10 min of reaction (R² = 0.7556, slope = -0.1307). Based on the results of TEM mapping, electrochemical impedance spectroscopy and XPS, this study further revealed that sulfidation not only enhanced the mass transfer of Cr(VI) toward nZVI in the initial stage of reaction, but also improved the electron transfer of nZVI toward Cr(VI) in the later stage of reaction. The ultimately enhanced removal and reduction of Cr(VI) by S-nZVI should be attributed to the introduction of iron sulfides (FeS_x) that not only promoted the conductivity but also favored the affinity of nZVI toward Cr(VI). Overall, the kinetic insights presented in this study are valuable for understanding the process mechanisms of S-nZVI in anaerobic water and may extend to provide theoretical support for the development of enhanced methods for the remediation of contaminated groundwater using nZVI.