1999 Progress Report: Improving the Performance of Permeable Reactive Barriers: Enhancing Reactivity and Longevity through Understanding of Surface OxidesEPA Grant Number: R827117
Title: Improving the Performance of Permeable Reactive Barriers: Enhancing Reactivity and Longevity through Understanding of Surface Oxides
Investigators: Tratnyek, Paul G. , Westall, John C.
Institution: Oregon Graduate Institute of Science & Technology , Oregon State University
EPA Project Officer: Lasat, Mitch
Project Period: October 1, 1998 through September 30, 2001 (Extended to November 30, 2002)
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
Project Amount: $374,252
RFA: Exploratory Research - Environmental Engineering (1998) RFA Text | Recipients Lists
Research Category: Sustainability , Land and Waste Management , Engineering and Environmental Chemistry
Recent work on the remediation of contaminants with permeable reactive barriers (PRBs) containing zero-valent iron (ZVI) has shown that remediation performance is strongly affected by the layers of precipitates that form on the iron surface over time. The goal of this study is to explore the extent to which long-term performance of PRBs can be predicted and enhanced through a mechanistic understanding of the role of precipitates in the treatment zone. The approach includes electrochemical experiments with oxide film electrodes, column and batch experiments that combine solution phase chemistry with surface analysis, and modeling to integrate experimental results with theory.
An electrochemical cell is being used to study the rates of reduction of carbon tetrachloride (CT) and nitrobenzene (NB) by Fe(II) sites in a Fe(III)-oxide film. Fe(III)-oxide films were prepared on gold electrodes, and the Fe(II) sites were introduced into the film by controlled electrochemical reduction of a small fraction of the Fe(III) in the film. The fundamental mechanism of reduction and the factors affecting the overall reduction rate are being investigated by varying the Fe(II) content in the iron oxide, controlling the mass transport of chemicals to the oxide surface, and varying the thickness of the oxide coating.
Batch experiments are being performed with a granular iron from a variety of sources and with model contaminants of various chemical types (including several colorimetric indicators as well as CT, NB, and trichloroethene). The granular iron also is being analyzed using a variety of surface analysis techniques (e.g., x-ray photoelectron spectroscopy). The results of these analyses will be correlated to obtain a better understanding of the factors that control the reactivity of aqueous contaminants with iron metal.
The electrochemical experiments will be extended to cover a range of types of iron oxides. The batch experiments will be extended to cover an even greater range of model contaminants. The preliminary conclusions drawn from the electrochemical and batch experiments will be used to design column experiments that will be initiated during Year 2. The column design process will be integrated with the model development process.