Thermodynamics of formation of coffinite, USiO4

Xiaofeng Guo, Stéphanie Szenknect, Adel Mesbah, Sabrina Labs, Nicolas Clavier, Christophe Poinssot, Sergey V. Ushakov, Hildegard Curtius, Dirk Bosbach, Rodney C. Ewing, Peter C. Burns, Nicolas Dacheux, Alexandra Navrotsky

Research output: Contribution to journalArticlepeer-review

54 Scopus citations

Abstract

Coffinite, USiO4, is an important U(IV) mineral, but its thermodynamic properties are not well-constrained. In this work, two different coffinite samples were synthesized under hydrothermal conditions and purified from a mixture of products. The enthalpy of formation was obtained by high-temperature oxide melt solution calorimetry. Coffinite is energetically metastable with respect to a mixture of UO2 (uraninite) and SiO2 (quartz) by 25.6 ± 3.9 kJ/mol. Its standard enthalpy of formation from the elements at 25 ° C is -1,970.0 ± 4.2 kJ/mol. Decomposition of the two samples was characterized by X-ray diffraction and by thermogravimetry and differential scanning calorimetry coupled with mass spectrometric analysis of evolved gases. Coffinite slowly decomposes to U3O8 and SiO2starting around 450 °C in air and thus has poor thermal stability in the ambient environment. The energetic metastability explains why coffinite cannot be synthesized directly from uraninite and quartz but can be made by low-temperature precipitation in aqueous and hydrothermal environments. These thermochemical constraints are in accord with observations of the occurrence of coffinite in nature and are relevant to spent nuclear fuel corrosion.

Original languageEnglish (US)
Pages (from-to)6551-6555
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume112
Issue number21
DOIs
StatePublished - May 26 2015
Externally publishedYes

Keywords

  • Calorimetry
  • Coffinite
  • U(IV) minerals
  • USiO
  • Uranium

ASJC Scopus subject areas

  • General

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