1 / 11

Marine Geochemistry of Uranium

Marine Geochemistry of Uranium. J. Kirk Cochran School of Marine & Atmospheric Sciences Stony Brook University (SUNY) Stony Brook, NY 11794-5000. U in Seawater. Concentration- ~3.3 m g/L, 2.45 dpm 238 U/L at 35 per mil salinity

Download Presentation

Marine Geochemistry of Uranium

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Marine Geochemistry of Uranium J. Kirk Cochran School of Marine & Atmospheric Sciences Stony Brook University (SUNY) Stony Brook, NY 11794-5000

  2. U in Seawater • Concentration- ~3.3 mg/L, 2.45 dpm 238U/L at 35 per mil salinity • 234U/238U activity ratio = 1.144 ± 0.002 (due to preferential chemical weathering of 234U from continents) • Present as U6+, speciated as UO2(CO3)34- • Long residence time in seawater (~450,000 y)

  3. U vs Salinity Pates & Muir (2007)

  4. U Speciation • In solution, U6+ as UO2(CO3)34- (Langmuir, 1978) • In special environments (anoxic basins, reducing marine sediments), reduction can occur, leading to rapid removal of U4+ from solution • But, even in such environments, U in solution is U6+

  5. Where in the oceans is U6+ reduced? An anoxic basin U4+ U6+ and Total U U in the Cariaco Basin water column (Anderson, 1987) U in anoxic basin sediment pore water (Barnes and Cochran, 1990)

  6. U in nearshore sediments • Separation of oxidation states by ion exchange chromatography • Samples of sediment pore water (anoxic) have U in solution as U6+ • But total U concentrations in pore waters are less than predicted from salinity, indicating removal Cochran et al. (1986)

  7. U Removal in Nearshore Sediments • Uranium removal rate correlates with sulfate reduction rate in nearshore (estuarine) sediments • U can be reduced by sulfate- reducing bacteria Barnes & Cochran (1993)

  8. The Oceanic U Balance • Dominant input is from rivers • Dominant sink are sediments (suboxic, anoxic) • Removal associated with alteration of oceanic crust (low T weathering of marine basalts, high T alteration associated with hydrothermal circulation) Barnes and Cochran (1990)

  9. Large Scale Removal of U from Aqueous Solution (Seawater?) • Zero valent iron (ZVI, Fe0) • Used to remediate groundwater contaminants, for example • Fe is oxidized as contaminant is reduced • For U: Fe0 + UO22+→ Fe2+ + UO2; DG° = -164 kJ mol-1 IN OUT Luna-Velasco et al. (2010)

  10. U6+ U4+ Flow U6+ U4+ U6+ U4+ Luna-Velasco et al. (2010)

  11. References • Anderson, R.F. (1987) Redox behavior of uranium in an anoxic marine basin. Uranium 3, 145-164. • Barnes, C. and J.K. Cochran (1990) Uranium removal in oceanic sediments and the oceanic U balance. Earth and Planetary Science Letters 97, 94-101. • Barnes, C. and J.K. Cochran (1993) Uranium geochemistry in estuarine sediments: Controls on removal and release processes. Geochimica et Cosmochimica Acta 57, 555-569. • Langmuir, D. (1978) Uranium solution-mineral equilibria at low temperatures with applications to sedimentary ore deposits. Geochimica et Cosmochimica Acta 42, 547-569. • Cochran, J.K. (1993) The oceanic chemistry of the U- and Th-series nuclides. In: Uranium Series Disequlibirium, (eds. M. Ivanovich & R.S. Harmon), 2d edition, Clarendon Press, Oxford, UK. • Cochran, J.K., A.E. Carey, E.R. Sholkovitz and L.D. Surprenant (1986) The geochemistry of uranium and thorium in coastal marine sediments ands sediment porewaters. Geochimica et Cosmochimica Acta 50, 663-680. • Luna-Velasco, A., R. Sierra-Alvarez, B. Castro and J. A. Field (2010) Removal of nitrate and hexavalent uranium from groundwater by sequential treatment in bioreactors packed with elemental sulfur and zero-valent iron. Biotechnology and Bioengineering, doi: 10.1002/bit.22881.

More Related