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Abstract: Iron and sulfur reducing conditions are generally created in permeable reactive barrier (PRB) systems constructed for groundwater treatment, which usually leads to formation of iron sulfide phases. Iron sulfides have been shown to play an important role in degrading chlorinated solvents and removing metals in these engineered systems. This study uses acid volatile sulfide (AVS) and chromium reducible sulfur (CRS) as probes to investigate iron sulfide formation and transformation in a column and PRB field study dealing with TCE degradation. Solid phase Fe speciation results show most Fe is reduced and S partitioning measurements show AVS and CRS coexist in all samples, with the conversion of AVS to CRS being most significant in locations with potential oxidants available. Microscopy reveals FeS, Fe3S4 and FeS2 formation in the column system, however, only pyrite formation was confirmed by X-ray diffraction. The polysulfide pathway is most likely the primary mechanism of FeS transformation in the system, with S0 as an intermediate species formed though H2S oxidation. Transformation of FeS to FeS2 could dramatically slow the natural degradation rate of chlorinated solvents.

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Study using acid volatile sulfide (AVS) and chromium reducible sulfur (CRS) as probes to investigate iron sulfide formation and transformation in a column and PRB field study dealing with TCE degradation.

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