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 (FeS2) on zero-valent iron (Fe-0) corrosion for arsenic (As) removal was investigated in a combined-Fe-0/FeS2 system. The effects of different Fe-0/FeS2 composition, dosage and initial pH were evaluated by batch experiments. Results showed that the best combination ratio of Fe-0/FeS2 (w/w) was 1:1 and the optimal dosage of mixture was 2.0 g/L. The combination of Fe-0 and FeS2 in a system significantly enhanced the reactivity of Fe-0 for effective As removal within a broad pH range (3.0-9.0). The effective As removal in the combined-Fe-0/FeS2 system was primarily ascribed to being enhanced corrosion of Fe-0 by addition of FeS2. SEM and XRD characterizations strongly verified this point. Specifically, the mechanism study (the releases of Fe2+ and total Fe ion, variations of pH values as well as XPS characterization) suggested that FeS2 in the combined-Fe-0/FeS2 system could alleviate the passivation of Fe-0 (pH(ini) 3.0-5.0) and accelerate the dissolution of pristine oxide film that coated on Fe-0 surface (PHini 6.8-9.0). Besides, FeS2 in combined-Fe-0/FeS2 system could also accelerate the reactions between Fe-0 to O-2 at pH(ini) 3.0-9.0. These phenomena were well explained by a galvanic couple between Fe-0 and FeS2, where FeS2 was a cathode and Fe-0 was an anode. Consequently, electrons released from Fe-0 that mediated by FeS2 to oxide film, passivation layer and O-2 were accelerated in combined-Fe-0/FeS2 system and thereby enhanced the corrosion of Fe-0 for efficient As removal. Our findings suggest that utilizing FeS2 to enhance the corrosion of Fe-0 would be a promising technology for remediation of As-contaminated water. (C) 2019 Elsevier Ltd. All rights reserved.