Thermodynamic model for uranium release from hanford site tank residual waste.

A thermodynamic model of U solid-phase solubility and paragenesis was developed for Hanford Site tank residual waste that will remain in place after tank closure. The model was developed using a combination of waste composition data, waste leach test data, and thermodynamic modeling of the leach test data. The testing and analyses were conducted using actual Hanford Site tank residual waste. Positive identification of U phases by X-ray diffraction was generally not possible either because solids in the waste were amorphous or their concentrations were not detectable by XRD for both as-received and leached residual waste. Three leachant solutions were used in the studies: deionized water, CaCO3 saturated solution, and Ca(OH)2 saturated solution. Analysis of calculated saturation indices indicate that NaUO2PO4·xH2O and Na2U2O7(am) are present in the residual wastes initially. Leaching of the residual wastes with deionized water or CaCO3 saturated solution results in preferential dissolution Na2U2O7(am) and formation of schoepite. Leaching of the residual wastes with Ca(OH)2 saturated solution appears to result in transformation of both NaUO2PO4·xH2O and Na2U2O7(am) to CaUO4. Upon the basis of these results, the paragenetic sequence of secondary phases expected to occur as leaching of residual waste progresses for two tank closure scenarios was identified.

[1]  Akira Kitamura,et al.  Solubility of U(YI) in Highly Basic Solutions , 1998 .

[2]  Nancy J. Hess,et al.  Thermodynamics of the U(VI)-Ca2+-Cl −-OH −-H2O system: Solubility product of becquerelite , 2002 .

[3]  P. A. Williams,et al.  The aqueous chemistry of uranium minerals. Part 2. Minerals of the liebigite group , 1980, Mineralogical Magazine.

[4]  A. Navrotsky,et al.  Thermodynamic properties of soddyite from solubility and calorimetry measurements , 2007 .

[5]  P. Burns,et al.  Solubility measurements of the uranyl oxide hydrate phases metaschoepite, compreignacite, Na–compreignacite, becquerelite, and clarkeite , 2008 .

[6]  F. Glasser,et al.  Reactions between cement components and U(VI) oxide , 1995 .

[7]  E. Wieland,et al.  Uranium(VI) Uptake by Synthetic Calcium Silicate Hydrates , 2008 .

[8]  E. Curti.  Coprecipitation of radionuclides with calcite: estimation of partition coefficients based on a review of laboratory investigations and geochemical data , 1999 .

[9]  A. Navrotsky,et al.  Thermodynamic properties of autunite, uranyl hydrogen phosphate, and uranyl orthophosphate from solubility and calorimetric measurements. , 2009, Environmental science & technology.

[10]  R. Reeder,et al.  Uranyl Incorporation into Calcite and Aragonite: XAFS and Luminescence Studies , 2000 .

[11]  M. ATKINS,et al.  Influence of Cement on the Near Field Environment and its Specific Interactions with Uranium and Iodine , 1988 .

[12]  S. Brooks,et al.  Determination of the formation constants of ternary complexes of uranyl and carbonate with alkaline earth metals (Mg2+, Ca2+, Sr2+, and Ba2+) using anion exchange method. , 2006, Environmental science & technology.

[13]  B. Arey,et al.  Residual waste from Hanford tanks 241-C-203 and 241-C-204. 1. Solids characterization. , 2006, Environmental science & technology.

[14]  Sue B. Clark,et al.  The Gibbs free energies and enthalpies of formation of U6+ phases: An empirical method of prediction , 1999 .

[15]  Andrew R. Felmy,et al.  The solubility product of NaUO2PO4·xH2O determined in phosphate and carbonate solutions , 2005 .

[16]  K. M. Beck,et al.  Coprecipitation of Uranium(VI) with Calcite: XAFS, micro-XAS, and luminescence characterization , 2001 .

[17]  L. Benninger,et al.  THE COPRECIPITATION OF PU AND OTHER RADIONUCLIDES WITH CACO3 , 1993 .