The Aqueous Thermodynamics and Complexation Reactions of Anionic Silica and Uranium Species to High Concentration.

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Highly basic tank wastes contain several important radionuclides, including 90Sr, 99Tc, and 60Co, as well as actinide elements (i.e., isotopes of U, Pu, and Am). These highly basic tank wastes are known to have leaked into the vadose zone at the Hanford Site. In particular, wastes from the bismuth phosphate process contained very high concentrations of U as well as carbonate, phosphate, nitrate, and other components (AEC 1951) and these solutions have leaked into the subsurface at the Hanford site. The tanks containing the bismuth phosphate wastes were frequently saturated with respect to the solid phases of these components [e.g., ... continued below

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Felmy, Andrew R. & Choppin, Gregory R. June 1, 2005.

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Description

Highly basic tank wastes contain several important radionuclides, including 90Sr, 99Tc, and 60Co, as well as actinide elements (i.e., isotopes of U, Pu, and Am). These highly basic tank wastes are known to have leaked into the vadose zone at the Hanford Site. In particular, wastes from the bismuth phosphate process contained very high concentrations of U as well as carbonate, phosphate, nitrate, and other components (AEC 1951) and these solutions have leaked into the subsurface at the Hanford site. The tanks containing the bismuth phosphate wastes were frequently saturated with respect to the solid phases of these components [e.g., NaUO2PO4(c) and Na4UO2(CO3)3(c)]. These solids were referred to as ''hard sludge'' (Na4UO2(CO3)3(c)) and ?soft sludge? [NaUO2PO4(c)] because of their different crystal forms. The preliminary studies of the solubility of these solids in tank wastes (AEC 1951) indicate that aqueous U carbonate complexes dominate the solution chemistry of uranium even when the equilibrium solid was NaUO2PO4. Thus there was a need to develop an accurate thermodynamic model for the solubility of potentially important U(VI) phosphate and carbonate phases as well as to develop a model for the uranium carbonate complexes valid to high ionic strength. In this project we are examining the solubility of these important solid phases as well as the aqueous thermodynamics of U(VI) species under strongly basic conditions. Also included is a description of our efforts to include these thermodynamic models in the reactive transport and residual leaching models being used at the Hanford site and elsewhere.

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  • Report No.: EMSP-86753--2005
  • Grant Number: FG07-02ER15023
  • DOI: 10.2172/885429 | External Link
  • Office of Scientific & Technical Information Report Number: 885429
  • Archival Resource Key: ark:/67531/metadc891523

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  • June 1, 2005

Added to The UNT Digital Library

  • Sept. 23, 2016, 2:42 p.m.

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  • Nov. 4, 2016, 6:34 p.m.

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Felmy, Andrew R. & Choppin, Gregory R. The Aqueous Thermodynamics and Complexation Reactions of Anionic Silica and Uranium Species to High Concentration., report, June 1, 2005; Richland, Washington. (digital.library.unt.edu/ark:/67531/metadc891523/: accessed April 25, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.