Reductive Precipitation of Uranium(VI) by Zero-Valent Iron

Abstract

This study was undertaken to determine the effectiveness of zero-valent iron (Fe0) and several adsorbent materials in removing uranium (U) from contaminated groundwater and to investigate the rates and mechanisms that are involved in the reactions. Fe0 filings were used as reductants, and the adsorbents included peat materials, iron oxides, and a carbon-based sorbent (Cercona Bone-Char). Results indicate that Fe0 filings are much more effective than the adsorbents in removing uranyl (UO22+) from the aqueous solution. Nearly 100% of U was removed through reactions with Fe0 at an initial concentration up to 76 mM (or 18 000 mg of U/L). Results from the batch adsorption and desorption and from spectroscopic studies indicate that reductive precipitation of U on Fe0 is the major reaction pathway. Only a small percentage (<4%) of UO22+ appeared to be adsorbed on the corrosion products of Fe0 and could be desorbed by leaching with a carbonate solution. The study also showed that the reduced U(IV) species on Fe0 surfaces could be reoxidized and potentially remobilized when the reduced system becomes more oxidized. Results of this research support the application of the permeable reactive barrier technology using Fe0 as a reactive media to intercept U and other groundwater contaminants migrating to the tributaries of Bear Creek at the U.S. Department of Energy's Y-12 Plant located in Oak Ridge, TN.