This title appears in the Scientific Report :
2013
Please use the identifier:
http://dx.doi.org/10.1016/j.gca.2013.08.028 in citations.
Solid–aqueous equilibrium in the BaSO4–RaSO4–H2O system: First-principles calculations and a thermodynamic assessment
Solid–aqueous equilibrium in the BaSO4–RaSO4–H2O system: First-principles calculations and a thermodynamic assessment
Phase relations in the BaSO4–RaSO4–H2O system are important for understanding the role of barite-type minerals in controlling the concentration of Ra2+ in natural water reservoirs. These relations are extremely sensitive to the difference in the solubility products of the end-members and to the degr...
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Personal Name(s): | Vinograd, V. L. (Corresponding author) |
---|---|
Brandt, F. / Rozov, K. / Klinkenberg, M. / Refson, K. / Winkler, B. / Bosbach, D. | |
Contributing Institute: |
Nukleare Entsorgung; IEK-6 |
Published in: | Geochimica et cosmochimica acta, 122 (2013) S. 398 - 417 |
Imprint: |
New York, NY [u.a.]
Elsevier
2013
|
DOI: |
10.1016/j.gca.2013.08.028 |
Document Type: |
Journal Article |
Research Program: |
Safety Research for Nuclear Waste Disposal |
Publikationsportal JuSER |
Phase relations in the BaSO4–RaSO4–H2O system are important for understanding the role of barite-type minerals in controlling
the concentration of Ra2+ in natural water reservoirs. These relations are extremely sensitive to the difference in the
solubility products of the end-members and to the degree of non-ideality of the solid solution phase. Experimental constraints
to the standard entropy of RaSO4 and the regular interaction parameter of the barite–RaSO4 solid solution are ambiguous.
This study is focused on determination of these parameters from first principles. The phonon density of states of RaSO4 is
computed with the aid of the density functional perturbation theory. The regular interaction parameter in the BaSO4–RaSO4
solid solution, WBaRa, is interpreted as the slope of the enthalpy of mixing in the limit of infinite dilution (xRa = 0) and is
calculated from the change in the total energy of a 2 2 2 supercell of BaSO4 due to the insertion of a single substitutional
defect of Ra. The method is validated by computing W values for a wider range of binary solid solutions with barite and aragonite
structures. The computed value of WBaRa = 2.50 ± 1.00 kJ/mol implies that the solid–aqueous equilibrium in the
BaSO4–RaSO4–H2O system may have an alyotropic point in close proximity to the BaSO4 end-member. The assessment
of available data on re-crystallization of barite in Ra-bearing aqueous solutions suggests that the barite crystals may fully
equilibrate on the time scale of hundred days. |