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

Technical Report · Wed Jun 01 04:00:00 EDT 2005

DOI:https://doi.org/10.2172/885429· OSTI ID:885429

Felmy, Andrew R; Choppin, Gregory R

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.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA; Florida State University, Tallahassee, FL
• Sponsoring Organization: USDOE - Office of Science (SC)
• OSTI ID: 885429
• Report Number(s): EMSP-86753--2005
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
54 ENVIRONMENTAL SCIENCES
ACTINIDES
BISMUTH PHOSPHATES
CARBONATES
CHEMISTRY
LEACHING
PHOSPHATES
RADIOISOTOPES
SILICA
SOLUBILITY
TANKS
THERMODYNAMIC MODEL
THERMODYNAMICS
URANIUM
URANIUM CARBONATES
WASTES