REDUCTIVE PRECIPITATION OF URANIUM(VI) BY ZERO-VALENT IRON

This study was undertaken to determine the effectiveness of zero-valen t iron (Fe-0) and several adsorbent materials in removing uranium (U) from contaminated groundwater and to investigate the rates and mechani sms that are involved in the reactions. Fe-0 filings were used as redu ctants, and the adsorbents included peat materials, iron oxides, and a carbon-based sorbent (Cercona Bone-Char). Results indicate that Fe-0 filings are much more effective than the adsorbents in removing uranyl (UO22+) from the aqueous solution. Nearly 100% of U was removed throu gh reactions with Fe-0 at an initial concentration up to 76 mM (or 18 000 mg of U/L). Results from the batch adsorption and desorption and f rom spectroscopic studies indicate that reductive precipitation of U o n Fe-0 is the major reaction pathway. Only a small percentage (<4%) of UO22+ appeared to be adsorbed on the corrosion products of Fe-0 and c ould be desorbed by leaching with a carbonate solution. The study also showed that the reduced U(IV) species on Fe-0 surfaces could be reoxi dized and potentially remobilized when the reduced system becomes more oxidized. Results of this research support the application of the per meable reactive barrier technology using Fe-0 as a reactive media to i ntercept U and other groundwater contaminants migrating to the tributa ries of Bear Creek at the U.S. Department of Energy's Y-12 Plant locat ed in Oak Ridge, TN.