Effects of nitrate on the stability of uranium in a bioreduced region of the subsurface

Journal Article · Tue Jun 01 04:00:00 EDT 2010 · Environmental Science & Technology

DOI:https://doi.org/10.1021/es1000837· OSTI ID:985786

Wu, Weimin ^[1]; Carley, Jack M ^[2]; Green, Stefan ^[3]; Luo, Jian ^[4]; Kelly, Shelly D ^[5]; Van Nostrand, Joy ^[6]; Lowe, Kenneth Alan ^[2]; Mehlhorn, Tonia L ^[2]; Carroll, Sue L ^[2]; Boonchayanant, Dr Benjaporn ^[1]; Loeffler, Frank E ^[2]; Jardine, Philip M ^[2]; Criddle, Craig ^[2]

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1. Stanford University
2. ORNL
3. Florida State University, Tallahassee
4. Georgia Institute of Technology
5. Argonne National Laboratory (ANL)
6. University of Oklahoma, Norman

The effects of nitrate on the stability of reduced, immobilized uranium were evaluated in field experiments at a U.S. Department of Energy site in Oak Ridge, TN. Nitrate (2.0 mM) was injected into a reduced region of the subsurface containing high levels of previously immobilized U(IV). The nitrate was reduced to nitrite, ammonium, and nitrogen gas; sulfide levels decreased; and Fe(II) levels increased then deceased. Uranium remobilization occurred concomitant with nitrite formation, suggesting nitrate-dependent, iron-accelerated oxidation of U(IV). Bromide tracer results indicated changes in subsurface flowpaths likely due to gas formation and/or precipitate. Desorption-adsorption of uranium by the iron-rich sediment impacted uranium mobilization and sequestration. After rereduction of the subsurface through ethanol additions, background groundwater containing high levels of nitrate was allowed to enter the reduced test zone. Aqueous uranium concentrations increased then decreased. Clone library analyses of sediment samples revealed the presence of denitrifying bacteria that can oxidize elemental sulfur, H{sub 2}S, Fe(II), and U(IV) (e.g., Thiobacillus spp.), and a decrease in relative abundance of bacteria that can reduce Fe(III) and sulfate. XANES analyses of sediment samples confirmed changes in uranium oxidation state. Addition of ethanol restored reduced conditions and triggered a short-term increase in Fe(II) and aqueous uranium, likely due to reductive dissolution of Fe(III) oxides and release of sorbed U(VI). After two months of intermittent ethanol addition, sulfide levels increased, and aqueous uranium concentrations gradually decreased to <0.1 {mu}M.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 985786
• Journal Information: Environmental Science & Technology, Journal Name: Environmental Science & Technology Journal Issue: 13 Vol. 44; ISSN 1520-5851; ISSN 0013-936X
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
BIOREMEDIATION
CATALYTIC EFFECTS
DISSOLUTION
ETHANOL
NITRATES
OXIDATION
RADIONUCLIDE MIGRATION
STABILITY
URANIUM
VALENCE