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Thermodynamic characterization of synthetic autunite

  • Ewa A. Dzik , Haylie L. Lobeck , Lei Zhang and Peter C. Burns EMAIL logo
Published/Copyright: October 2, 2017
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American Mineralogist
From the journal American Mineralogist Volume 102 Issue 10

Abstract

Autunite, Ca[(UO2)(PO4)]2(H2O)11, is a common uranyl mineral found in oxidized portions of uranium deposits, as well as subsurface environments contaminated by uranium. Enthalpies of formation of autunite were obtained via high-temperature oxide melt calorimetry using a 3Na2O⋅4MoO3 solvent at 976 K. The synthetic analog of autunite was prepared using slow mixing by diffusion into an aqueous barrier solution at room temperature. Prior to calorimetric measurements, the material was characterized using powder X-ray diffraction (PXRD), inductively coupled plasma optical emission spectrometry (ICP-OES), thermogravimetric analysis (TGA), and Raman spectroscopy, to ensure purity. The calculated enthalpy of formation from binary oxides of autunite is −579.92 ± 21.68 kJ/mol; the enthalpy of formation from the elements is −8311.32 ± 21.79 kJ/mol. The measured drop solution enthalpy allowed calculation of the enthalpy of the reaction of dehydration of autunite to meta-autunite. The results demonstrate that autunite is a metastable phase and explain the observed rapid dehydration to meta-autunite, a lower hydrate, as well as the common occurrence of the latter mineral in nature.

Keywords: Autunite; calorimetry; uranium; enthalpy; thermodynamics; metaphase; Actinides in Geology; Energy and the Environment

Special collection papers can be found online at http://www.minsocam.org/MSA/AmMin/special-collections.html.

Acknowledgments

This work is supported by the Office of Basic Energy Sciences of the U.S. Department of Energy as part of the Materials Science of Actinides Energy Frontier Research Center (DE-SC0001089). The ICP-OES analyses were conducted at the Center for Environmental Science and Technology (CEST) at the University of Notre Dame. PXRD, TGA, Raman spectroscopy, and high-temperature calorimetry data were collected in the Materials Characterization Facility supported by the Center for Sustainable Energy at Notre Dame (ND Energy).

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Received: 2017-2-13
Accepted: 2017-6-8
Published Online: 2017-10-2
Published in Print: 2017-10-26

© 2017 by Walter de Gruyter Berlin/Boston

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https://doi.org/10.2138/am-2017-6109
Keywords for this article
Autunite; calorimetry; uranium; enthalpy; thermodynamics; metaphase; Actinides in Geology; Energy and the Environment

Articles in the same Issue

  1. Highlights and Breakthroughs
  2. Making a fine-scale ruler for oxide inclusions
  3. Special Collection: Biomaterials—Mineralogy Meets Medicine
  4. Substitution of sulfate in apatite
  5. Actinides in Geology, Energy, and the Environment
  6. Thermodynamic characterization of synthetic autunite
  7. Special Collection: Apatite: A Common Mineral, Uncommonly Versatile
  8. The crystal structure of turneaureite, Ca5(AsO4)3Cl, the arsenate analog of chlorapatite, and its relationships with the arsenate apatites johnbaumite and svabite
  9. Special Collection: From Magmas to Ore Deposits
  10. Cu-Mo partitioning between felsic melts and saline-aqueous fluids as a function of XNaCleq, fO2, and fS2
  11. Special Collection: Dynamics of Magmatic Processes
  12. Continuous mush disaggregation during the long-lasting Laki fissure eruption, Iceland
  14. A new hydrothermal moissanite cell apparatus for optical in-situ observations at high pressure and high temperature, with applications to bubble nucleation in silicate melts
  16. Experimental and thermodynamic investigations on the stability of Mg14Si5O24 anhydrous phase B with relevance to Mg2SiO4 forsterite, wadsleyite, and ringwoodite
  18. Model for the origin, ascent, and eruption of lunar picritic magmas
  20. Phase relations of Fe-Mg spinels including new high-pressure post-spinel phases and implications for natural samples
  22. A Raman calibration for the quantification of SO42− groups dissolved in silicate glasses: Application to natural melt inclusions
  24. The system fayalite-albite-anorthite and the syenite problem
  26. Kiglapait mineralogy V: Feldspars in a hot, dry magma
  28. Orientation of exsolution lamellae in mantle xenolith pyroxenes and implications for calculating exsolution pressures
  30. Spin state and electronic environment of iron in basaltic glass in the lower mantle
  32. A shallow origin of so-called ultrahigh-pressure chromitites, based on single-crystal X-ray structure analysis of the high-pressure Mg2Cr2O5 phase, with modified ludwigite-type structure
  34. Biologically mediated crystallization of buddingtonite in the Paleoproterozoic: Organic-igneous interactions from the Volyn pegmatite, Ukraine
  36. Mengxianminite (Ca2Sn2Mg3Al8[(BO3)(BeO4)O6]2) a new borate mineral from Xianghualing skarn, Hunan Province, China, with a highly unusual chemical combination (B + Be + Sn)
  37. Letter: Special Collection: Nanominerals and Mineral Nanoparticles
  38. Previously unknown mineral-nanomineral relationships with important environmental consequences: The case of chromium release from dissolving silicate minerals
  39. Letter: Special Collection: Nanominerals and Mineral Nanoparticles
  40. Protoenstatite: A new mineral in Oregon sunstones with “watermelon” colors
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