Thermodynamic characterization of boltwoodite and uranophane: Enthalpy of formation and aqueous solubility |
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| Authors: | Tatiana Y. Shvareva Drew Gorman-Lewis Peter C. Burns Jeremy B. Fein |
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| Affiliation: | a Peter A. Rock Thermochemistry Laboratory, University of California, Davis, One Shields Avenue, Davis, CA 95616, United States
b University of Notre Dame, Department of Civil Engineering and Geological Sciences, 156 Fitzpatrick Hall, Notre Dame, IN 46556, United States |
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| Abstract: | Boltwoodite and uranophane are uranyl silicates common in oxidized zones of uranium ore deposits. An understanding of processes that impact uranium transport in the environment, especially pertaining to the distribution of uranium between solid phases and aqueous solutions, ultimately requires determination of thermodynamic parameters for such crystalline materials. We measured formation enthalpies of synthetic boltwoodites, K(UO2)(HSiO4)·H2O and Na(UO2)(HSiO4)·H2O, and uranophane, Ca(UO2)2(HSiO4)2·5H2O, by high temperature oxide melt solution calorimetry. We also studied the aqueous solubility of these phases from both saturated and undersaturated conditions at a variety of pH. The combined data permit the determination of standard enthalpies, entropies and Gibbs free energies of formation for each phase and analysis of its potential geological impact from a thermodynamic point of view. |
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