Chapter 12 - Analysis of Uranium-Contaminated Zero Valent Iron Media Sampled from Permeable Reactive Barriers Installed at U.S. Department of Energy Sites in Oak Ridge, Tennessee, and Durango, Colorado

Abstract

This chapter presents a study in which permeable reactive barriers, composed of zero valent iron (ZVI), were installed and operated at U.S. Department of Energy sites located at the Y-12 Plant in Oak Ridge, Tennessee, and at the uranium mill tails repository near Durango, Colorado. The ZVI medium was intended to remove select toxic solutes, especially uranium (U), from contaminated groundwater. Core samples from these barrier installations were sampled after prolonged exposure to contaminated groundwater. Core samples were protected from exposure to the ambient atmosphere by packaging them in argon-purged containers for shipment to an off-site laboratory. The aim was to protect media from exposure to oxygen, which could alter the valence state of the treatment medium itself and of the metal deposits therein. Samples were then subjected to a battery of analytical techniques, including X-ray photoelectron spectroscopy (XPS), a surface-sensitive technique that can be used to determine the average valence state of elements. One of the major findings of this study was that ZVI media had extensive surface deposition of various mineral phases including amorphous iron sulfide and iron oxyhydroxide, and crystalline calcite and gypsum. U was present within the media at somewhat modest levels and the U on the ZVI surface was at least partially oxidized.