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 2 ) on zero-valent iron (Fe 0 ) corrosion for arsenic (As) removal was investigated in a combined-Fe 0 /FeS 2 system. The effects of different Fe 0 /FeS 2 composition, dosage and initial pH were evaluated by batch experiments. Results showed that the best combination ratio of Fe 0 :FeS 2 (w/w) was 1:1 and the optimal dosage of mixture was 2.0 g/L. The combination of Fe 0 and FeS 2 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 /FeS 2 system was primarily ascribed to being enhanced corrosion of Fe 0 by addition of FeS 2 . SEM and XRD characterizations strongly verified this point. Specifically, the mechanism study (the releases of Fe 2+ and total Fe ion, variations of pH values as well as XPS characterization) suggested that FeS 2 in the combined-Fe 0 /FeS 2 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 (pH ini 6.8–9.0). Besides, FeS 2 in combined-Fe 0 /FeS 2 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 FeS 2 , where FeS 2 was a cathode and Fe 0 was an anode. Consequently, electrons released from Fe 0 that mediated by FeS 2 to oxide film, passivation layer and O 2 were accelerated in combined-Fe 0 /FeS 2 system and thereby enhanced the corrosion of Fe 0 for efficient As removal. Our findings suggest that utilizing FeS 2 to enhance the corrosion of Fe 0 would be a promising technology for remediation of As-contaminated water.