Influence of Enhanced Corrosion of Microscale Zero-Valent Iron on Cr(Vi) Removal Efficiency and Mechanism: A Comparative Study

Abstract

In recent years, the countermeasures have developed for limitations of mZVI, such as pretreatment, surface modification, etc. Nevertheless, how to screen more appropriate countermeasures to better alleviate the limitations of mZVI are proposed to be based on the removal mechanism of pollutants. To deeply analyze the removal mechanism of Cr(VI) by mZVI, the study explored the influence of various factors  on the efficiency and path of Cr(VI) removal by mZVI. The results showed that H+, DO and SO42+ can promote the removal of Cr(VI) by mZVI, which was attributed to the fact that they can promote the corrosion of mZVI to release more secondary reductant Fe2+. Monitoring the release of Fe2+ during the reaction demonstrated that H+ and DO would be more likely to occupy the surface active sites of mZVI compared with Cr(VI), which indirectly indicated that the heterogeneous reduction of Cr(VI) was limited. The results of Cr valence analysis in liquid-solid phase and 1,10-phenanthroline shielding experiments revealed that Cr(VI) was mainly reduced to Cr(III) by Fe2+ through the homogeneous reaction, and then Cr(III) was better complexed with more Fe3+ and OH-, which promoted the sequestration of total Cr. Furthermore, the main role of mZVI was to release Fe2+ by self-corrosion and the reduction of Fe3+, and hardly participated directly in the reduction of Cr(VI). The study elucidated the fate and transport of Cr(VI) and total Cr, and provided helpful guidance for selecting appropriate countermeasures for enhancing activity or increasing electron utilization of mZVI in the Cr(VI) removal.

Keywords: mZVI, Cr(VI), Fe2+, Reduction, Sequestration