This title appears in the Scientific Report :
2013
Solid solution formation and uptake of Radium in the presence of barite
Solid solution formation and uptake of Radium in the presence of barite
The phase relations in the BaSO4-RaSO4-H2O system may determine the solubility of radium in natural waters due to the formation of a solid solution. In the near-field of nuclear waste repositories for spent fuel, radium may enter a system in which barite is in equilibrium with the aqueous solution....
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Personal Name(s): | Brandt, Felix (Corresponding author) |
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Klinkenberg, Martina / Vinograd, Victor / Rozov, Konstantin / Bosbach, Dirk | |
Contributing Institute: |
Nukleare Entsorgung; IEK-6 |
Imprint: |
2013
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Conference: | Goldschmidt Conference 2013, Firenze (Italy), 2013-08-25 - 2013-08-30 |
Document Type: |
Conference Presentation |
Research Program: |
Slow processes in close-to-equilibrium conditions for radionuclides in water/solid systems of relevance to nuclear waste management Safety Research for Nuclear Waste Disposal |
Publikationsportal JuSER |
The phase relations in the BaSO4-RaSO4-H2O system may determine the solubility of radium in natural waters due to the formation of a solid solution. In the near-field of nuclear waste repositories for spent fuel, radium may enter a system in which barite is in equilibrium with the aqueous solution. Thermodynamically, a RaxBa1-xSO4 solid solution is expected to form as solubility controlling phase rather than RaSO4. However, due to a lack of reliable data, the solid solution system RaSO4-BaSO4-H2O is currently not considered in long term safety assessments for nuclear waste repositories. The solubility product of the pure RaSO4 endmember is poorly constrained between pKRaSO4 = 10.26 to 10.41 by only very few experimental data [1,2]. Published interaction parameters WBaRa of the RaSO4-BaSO4-H2O system varies varies in different studies [3, 4] between 0.9 and 3.9 - 6.5 kJ/mol.
In this study we have combined experimental data, atomistic calculations and thermodynamic modeling to study in detail how a radium containing solution will equilibrate with solid BaSO4 under repository relevant conditions. Batch sorption experiments at close to equilibrium conditions indicate the formation of a RaxBa1-xSO4 solid. Our first principles calculations based on the single defect method [5] indicate a value of WBaRa = 2.5 ± 1.0 kJ/mol, implying a non-ideal solid solution. Thermodynamic assessment calculations indicate that the final experimental Ra(aq) concentration at room temperature and 90 °C can be matched with
WBaRa ≈ 1.5 kJ/mol and pKRaSO4 ≈ 10.41.
[1] Lind, S. C., et al (1918). J Am Chem Soc 40, 465-472. [2] Paige, C. R. et al.(1998). Geochim. Cosmochim. Acta 62, 15-23. [3] Zhu, C., 2004. Geochim. Cosmochim. Acta 68, 3327-3337. [4] Curti, E., et al. (2010). Geochim. Cosmochim. Acta 74, 3553-3570. [5] Sluiter & Kawazoe (2002) Europhys Lett. 57, 526-532. |