Visual and in situ Raman spectroscopic observations of the liquid-liquid immiscibility in aqueous uranyl sulfate solutions at temperatures up to 420 °c
|dc.identifier.citation||Wang, X. and Wan, Y. and Hu, W. and Chou, I. and Cai, S. and Lin, N. and Zhu, Q. et al. 2016. Visual and in situ Raman spectroscopic observations of the liquid-liquid immiscibility in aqueous uranyl sulfate solutions at temperatures up to 420 °c. Journal of Supercritical Fluids. 112: pp. 95-102.|
The phase behaviors of aqueous UO2SO4 solutions were investigated in situ with a microscope and a Raman spectrometer at temperatures from 25 to 420 °C. Results show that aqueous UO2SO4 solution separated into UO2SO4-rich (Urich) and UO2SO4-poor (Upoor) liquid phases coexisted with a vapor phase at =285.8 ± 0.5 °C. Both visual and Raman spectroscopic investigations suggest that a reversible strong UO2 2+-SO4 2- association was responsible for the liquid-liquid immiscibility in aqueous UO2SO4 solutions. Main evidences were summarized as: (1) the liquid-liquid phase separation temperature decreases with increasing UO2SO4 concentration up to 0.54 mol/kg, and then increased at greater concentrations, characterizing a lower critical solution temperature (LCST) at 285.8 °C ± 0.5 °C. LCST is commonly accepted as a diagnostic feature of polymer solutions; (2) analyses of the shapes of the Raman spectra of v1(UO2 2+) and v1(SO4 2-) bands show that the UO2 2+-SO4 2- association becomes stronger at elevated temperatures, especially in the immiscible Urich phase; and (3) with increasing temperature, the Urich phase becomes more concentrated, whereas the Upoor phase becomes more dilute, indicating that the hydration of UO2 2+ and SO4 2- cannot be maintained in the Urich phase. Destruction of the hydration spheres of UO2 2+ and SO4 2- further favors the ion association in the Urich phase. These results are important for describing similar sulfate solutions at elevated temperatures, especially under supercritical conditions.
|dc.title||Visual and in situ Raman spectroscopic observations of the liquid-liquid immiscibility in aqueous uranyl sulfate solutions at temperatures up to 420 °c|
|dcterms.source.title||Journal of Supercritical Fluids|
|curtin.department||Department of Applied Geology|