CAREER: Formation and Reactivity of Nanoscale Corrosion Products - An Integrated Research and Education Plan

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

0348125 Vikesland The career development plan has been broken down into two primary components: a research plan describing experiments to examine the formation and reactivity of nanoscale corrosion products and a teaching plan that is designed to reinvigorate the pedagogical environment of the Introduction to Environmental Engineering class at Virginia Tech. The objective of this project is to evaluate the role that nanoscale corrosion products play in determining the reactivity of the granular iron based treatment schemes used for the remediation of organohalide contaminated subsurface environments. The results from the proposed studies will be used in the development of an improved conceptual model of the phenomena responsible for contaminant remediation within granular iron systems. Using Iron Corrosion to Remediate Contaminated Groundwater The discovery that chlorinated solvents readily react with reduced iron has led to rapid acceptance of in situ iron Permeable Reactive Barriers (PRBs) as the cleanup method of choice for many contaminated sites. Although the exact mechanisms involved have not been fully elucidated, field demonstrations indicate that the reactions can be rapid under environmentally relevant conditions. At the current time, over eighty field-scale PRBs employing iron as a reactive material for treatment of contaminated groundwater have been installed. Questions remain, however, concerning the relative reactivities of the numerous types of iron used in these walls. A key variable that dictates the applicability of iron PRBs as a remediation technique is the organohalide degradation rate. These rates are a function not only of the identity and concentration of the organohalide undergoing remediation (i.e., chlorinated alkanes vs. chlorinated alkenes, but also of the groundwater composition (i.e., pH, ionic content), the quantity of iron present, and its structural makeup. The quantity, or concentration, of iron is important because contaminant reduction requires either direct electron-transfer between the contaminant and the iron surface or indirect electron-transfer via surface evolved reactive intermediates (e.g., H2). Observed reaction rates, as evinced by pseudo-first-order rate coefficients (kobs values), typically scale linearly with iron concentration, a result indicative of surface mediated reactions. The type or composition of the iron metal used for organohalide remediation also significantly affects iron reactivity. Observed differences in the reactivity of various types of iron were historically attributed primarily to variability in their surface areas. Recent reports have suggested, but never experimentally documented, that this additional variability results from fundamental differences in the composition of the iron substrates.