Uranium in geologic fluids: Estimates of standard partial molal properties, oxidation potentials, and hydrolysis constants at high temperatures and pressures

Details Uranium in geologic fluids: Estimates of standard partial molal properties, oxidation potentials, and hydrolysis constants at high temperatures and pressures Uranium in geologic fluids: Estimates of standard partial molal properties, oxidation potentials, and hydrolysis constants at high temperatures and pressures

Oct 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997gecoa..61.4245s&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 61, Issue 20, pp.4245-4266

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9

Scientific paper

Theoretical methods are used with the available experimental data to provide estimates of parameters for the revised-HKF equations of state for aqueous uranium species. These parameters are used with standard state thermodynamic data at 25°C and 1 bar to calculate equilibrium constants for redox reactions among the four most common oxidation states of uranium (U(III), U(IV), U(V), and U(VI)), and their hydrolysis reactions at temperatures to 1000°C and pressures to 5 kb. A total of nineteen aqueous uranium species are included. The predicted equilibrium constants are used to construct oxidation potential-pH diagrams at elevated temperatures and pressures and to calculate the solubilities of uraninite as functions of temperature and pH, which are compared to experimental data. Oxidation potential-pH diagrams illustrate the relative stabilities of aqueous uranium species and indicate that U (IV) and U(VI) species predominate in aqueous solution in the U---O---H system. Increasing temperature stabilizes U (VI) and U (III) species relative to U (IV) species, but U (IV) species dominate at oxidation states consistent with mineral-buffer assemblages and near-neutral pH. At low pH, U(VI) is stabilized relative to U (IV) suggesting that uranium transport in hydrothermal systems requires either acidic solutions or potent complexes of U(IV).

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