The Remediation Technology Summit

March 7 - 9, 2017

Colorado Convention Center
Denver, CO

lanYing Lan
Post-Doctoral Researcher
Oregon Health and Science University

Dr. Ying Lan is a post-doctoral researcher in the Institute of Environmental Health at the Oregon Health and Science University. Her research at OHSU focuses on the assessment and enhancement of abiotic natural attenuation of groundwater contaminants. She received her Ph.D. degree in Environmental Science at the University of Oklahoma, where she investigated the iron mineral products formed during anaerobic remediation. She is also interested in the greenhouse gases mitigation, with a special focus on the carbon footprints studies in China using life cycle assessment. She received her master’s and bachelor’s degrees in Environmental Science at Jilin University, China.

FLASH POSTER PRESESNTER - Oxidative and Reductive Treatments

Iron Sulfide: Transformation During Reductive Dechlorination and its Role in the Sulfidation of Zero-Valent Iron

It is increasingly recognized that mackinawite (FeS), a reactive iron sulfide mineral with strong reductive dechlorination ability, can be either fortuitously or deliberately generated in situ as part of groundwater remediation strategies of chlorinated solvents. Remediation strategies that combine FeS with other treatments have been investigated. Reduced sulfur compounds were added during the synthesis of zero-valent iron (ZVI) (i.e. sulfidation of ZVI), to promote the formation of a mixture of ZVI and FeS, and to modulate the reactivity of ZVI towards treating chlorinated solvents. The objectives of this research were to characterize the FeS oxidation products formed during reductive dechlorination of carbon tetrachloride (CT), tetrachloroethylene (PCE), and trichloroethylene (TCE) and investigate the role of FeS in the sulfidation of zero-valent iron (ZVI). 

The FeS oxidation products formed during reductive dechlorination of CT, PCE, and TCE were characterized using microscopic and spectroscopic techniques. The formation of greigite upon reaction of FeS with CT at pH 7 was detected. 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 poorly crystalline two-line ferrihydrite on the FeS surface and in solution. The predominant Fe surface species after reaction with CT at pH 8 was Fe(III)-O, 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. Both ferrihydrite and Fe2+, which is a product of greigite dissolution, can react with dissolved HS- to form FeS, suggesting that, after oxidation by chlorinated aliphatic contaminants, FeS can be regenerated by addition or microbial generation of sulfide. Addition of sulfur compounds during the synthesis of ZVI leads to the formation of a variety of materials, ranging from FeS coated ZVI core-shell struct