Insights into the corrosion of sulfidated microscale zero valent iron in the presence of benzoic acid: Inhibited oxidation capacity and promoted zinc immobilization

Under oxic environment, the corrosion of zero valent iron (ZVI) connects with its oxidation and adsorption capacity, but little is known about the effects of sulfidation on those processes of ZVI. To assess the oxidant production from ball-milling unsulfidated and sulfidated microscale ZVI (mZVI bm and S-mZVI bm ), the transformation of benzoic acid (BA) to p-hydroxybenzoic acid (p-HBA) was used as the oxidation probe reaction. During the oxidation reaction, the concentration of p-HBA in S-mZVI bm /O 2 systems rapidly reached equilibrium (< 12 μM) within 40 min regardless of sulfur loading content, whereas it could gradually reach 26 μM in mZVI bm /O 2 system within 240 min despite the slower generation of p-HBA at initial stage. Combining with the characteristic analysis, the lower oxidation capacity of S-mZVI bm /O 2 system might be ascribed to the enhanced Fe(II) dissolution that caused a larger solution pH rise along with the loss of Fe(0) and FeS x sites and the formation of lepidocrocite , which was not beneficial for oxygen activation. Under the identical conditions such as material dosage and co-existing anions, the oxidation capacity of mZVI bm /O 2 system also exceeded S-mZVI bm /O 2 system. In addition, the comparative experiment of Zn 2+ immobilization by S-mZVI bm and S-mZVI bm with or without BA was investigated. mZVI bm showed insignificant Zn 2+ immobilization, whereas BA could enhance Zn 2+ immobilization by S-mZVI bm due to the enhanced corrosion that could provide more adsorption sites. Overall, this work is valuable for assessing the oxidation capacity of S-mZVI bm /O 2 system and BA effect on heavy metal immobilization of S-mZVI in wastewater treatment .