Controlled Sulfidation to Optimize the Remediation Performance of Zero-Valent Iron and Related Materials

Presenter: Dr. Ying Lan

Dr. Ying Lan is a Postdoctoral Researcher in the OHSU-PSU School of Public Health at the Oregon Health & Science University. She has nine years of research experience in the fate and transformation of contaminants in natural and engineered systems. She is interested in the enhancement of abiotic remediation using iron-based materials, as well as the evaluation and characterization of iron-based materials using combined insights from meta-analyses, batch experiments, and advanced solid analyses. Ying received her Ph.D. degree in Environmental Science at the University of Oklahoma, her master’s and bachelor’s degrees in Environmental Science at Jilin University, China.

Abstract: Iron-based materials used in water treatment and groundwater remediation—especially micro- and nano-sized zerovalent iron (nZVI)—can be more effective when modified with lower-valent forms of sulfur (i.e., “sulfidated”). Controlled sulfidation for this purpose (using sulfide, dithionite, etc.) is the main topic of this review. Material characterization shows that varying sulfidation protocols (e.g., concerted or sequential) and key operational variables (e.g., S/Fe ratio and sulfidation duration) result in materials with structures and morphologies ranging from core-shell to multiphase. A meta-analysis of available kinetic data for dechlorination under anoxic conditions, shows that sulfidation usually increases dechlorination rates, and simultaneously hydrogen production is suppressed. Therefore, sulfidation can greatly improve the efficiency of utilization of reducing equivalents for contaminant removal. This benefit is most likely due to inhibited corrosion as a result of sulfidation. Sulfidation may also favor desirable pathways of contaminant removal, such as (i) dechlorination by reductive elimination rather than hydrogenolysis and (ii) sequestration of metals as sulfides that could be resistant to reoxidation. These net effects of sulfidation on contaminant removal by iron-based materials may substantially improve its practical utility for water treatment and remediation of contaminated groundwater.