Mackinawite (FeS) plays an important role in reductive dechlorination, due to its high reactivity with chlorinated aliphatic contaminants. The primary objective of this research was to characterize the FeS oxidation products formed during reductive dechlorination of carbon tetrachloride (CT), tetrachloroethylene (PCE), and trichloroethylene (TCE). The FeS oxidation products formed during reductive dechlorination of CT, PCE, and TCE were characterized using microscopic and spectroscopic techniques. X-ray diffraction (XRD) analysis suggested the formation of greigite upon reaction of FeS with CT at pH 7. Results from scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) showed that after reaction with CT at pH 8, FeS surface had decreased sulfur and elevated oxygen compared to unreacted FeS; and the reaction led to the formation of abundant spherical particles with diameters between 50-400 nm on the FeS surface and in solution, which were proved to be poorly crystalline two-line ferrihydrite using selective area electron diffraction (SAED). The predominant Fe surface species after reaction with CT at pH 8 was Fe(III)-O, detected using X-ray photoelectron spectroscopy (XPS), consistent with ferrihydrite and other amorphous iron (hydr)oxides as major products. The oxidation products of FeS during reaction with PCE and TCE at pH 8 were mainly greigite within the time frame of the study, confirmed using high resolution transmission electron microscopy (HRTEM). Addition of sulfur compounds during the synthesis of ZVI (i.e., sulfidation) leads to the formation of a variety of materials, ranging from FeS coated ZVI core-shell structures to mixtures of ZVI and iron oxides and sulfides in discrete phases. The sulfidized materials have stronger reactivity towards the degradation of chlorinated solvents compared to untreated ZVI.

Material and reactivity characterization of iron sulfides and sulfidated zerovalent iron during reductive dechlorination

253rd National Meeting (2017)

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