Effect of pyrite on enhancement of zero-valent iron corrosion for arsenic removal in water: A mechanistic study.

In this study, the enhanced effect of pyrite (FeS) on zero-valent iron (Fe) corrosion for arsenic (As) removal was investigated in a combined-Fe/FeS system. The effects of different Fe/FeS composition, dosage and initial pH were evaluated by batch experiments. Results showed that the best combination ratio of Fe:FeS (w/w) was 1:1 and the optimal dosage of mixture was 2.0 g/L. The combination of Fe and FeS in a system significantly enhanced the reactivity of Fe for effective As removal within a broad pH range (3.0-9.0). The effective As removal in the combined-Fe/FeS system was primarily ascribed to being enhanced corrosion of Fe by addition of FeS. SEM and XRD characterizations strongly verified this point. Specifically, the mechanism study (the releases of Fe and total Fe ion, variations of pH values as well as XPS characterization) suggested that FeS in the combined-Fe/FeS system could alleviate the passivation of Fe (pH 3.0-5.0) and accelerate the dissolution of pristine oxide film that coated on Fe surface (pH 6.8-9.0). Besides, FeS in combined-Fe/FeS system could also accelerate the reactions between Fe to O at pH 3.0-9.0. These phenomena were well explained by a galvanic couple between Fe and FeS, where FeS was a cathode and Fe was an anode. Consequently, electrons released from Fe that mediated by FeS to oxide film, passivation layer and O were accelerated in combined-Fe/FeS system and thereby enhanced the corrosion of Fe for efficient As removal. Our findings suggest that utilizing FeS to enhance the corrosion of Fe would be a promising technology for remediation of As-contaminated water.