Thermodynamics of uranyl minerals: Enthalpies of formation of rutherfordine, UO2CO3, andersonite, Na2CaUO2(CO3)3 (H2O)5, and grimselite, K3NaUO 2(CO3)3H2O

Karrie Ann Kubatko, Katheryn B. Helean, Alexandra Navrotsky, Peter C. Burns

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30 Scopus citations

Abstract

Enthalpies of formation of rutherfordine, UO2CO3, andersonite, Na2CaUO2(CO3)3 (H2O)5, and grimselite, K3NaUO 2(CO3)3(H2O), have been determined using high-temperature oxide melt solution calorimetry. The enthalpy of formation of rutherfordine from the binary oxides, ΔHr-ox, is -99.1 ± 4.2 kJ/mol for the reaction UO3 (xl, 298 K) + CO2 (g, 298 K) = UO2CO3 (xl, 298 K). The ΔHr-ox for andersonite is - 710.4 ± 9.1 kJ/mol for the reaction Na2O (xl, 298 K) + CaO (xl, 298 K) + UO3 (xl, 298 K) + 3CO2 (g, 298 K) + 5H2O (1, 298 K) = Na2CaUO2(CO3)3 (H2O)6 (xl, 298 K). The ΔHr-ox for grimselite is -989.3 ± 14.0 kJ/mol for the reaction 1.5 K2O (xl, 298 K) + 0.5Na2O (xl, 298 K) + UO3 (xl, 298 K) + 3CO2 (g, 298 K) + H2O (1, 298 K) = K3NaUO2(CO3)3 H2O (xl, 298 K). The standard enthalpies of formation from the elements, ΔHfo, are -1716.4 ± 4.2, -5593.6 ± 9. 1, and -4431.6 ± 15.3 kJ/mol for rutherfordine, andersonite, and grimselite, respectively. Energetic trends of uranyl carbonate formation from the binary oxides and ternary carbonates are dominated by the acid-base character of the binary oxides. However, even relative to mixtures Of UO2CO3, K2CO3, and Na2CO3 or CaCO3, andersonite and grimselite are energetically stable by 111.7 ± 10.2 and 139.6 ± 16.1 kJ/mol, respectively, suggesting additional favorable interactions arising from hydration and/or changes in cation environments. These enthalpy values are discussed in comparison with earlier estimates.

Original languageEnglish (US)
Pages (from-to)1284-1290
Number of pages7
JournalAmerican Mineralogist
Volume90
Issue number8-9
DOIs
StatePublished - Aug 2005
Externally publishedYes

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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