Visual and in situ Raman spectroscopic observations of the liquid–liquid immiscibility in aqueous uranyl sulfate solutions at temperatures up to 420°C

Abstract

spectroscopic observations of the liquid-liquid immiscibility in aqueous uranyl sulfate solutions at temperatures up to 420 circ C, The Journal of Supercritical Fluids http://dx.doi.org/10. 1016/j.supflu.2016.03.005 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Challenging the thorium-immobility paradigm

“…A related consideration is the reported occurrence of liquid-liquid immiscibility observed in multiple sulfate-bearing systems (e.g. UO 2 , Li, Mg 28–30 ) at elevated temperatures (>285.8 °C, >336.5 °C, and >259.5 °C, respectively) 31 , which may serve to provide a source of excess sulfate for complexation. In these studies, aqueous sulfate solutions were observed to separate into a high density, sulfate-rich (up to 70% of total sulfate) phase and a low-density sulfate-depleted aqueous phase.…”

Investigation of Uranyl Sulfate Complexation under Hydrothermal Conditions by Quantitative Raman Spectroscopy and Density Functional Theory

“…23,76,77 The slight temperature dependence of ṽ1(UO 2 2+ ) is consistent with the only other hightemperature Raman studies in the literature. 28,78 Extrapolation of the band position of UO 2 2+ (aq) up to 375 °C using the welldefined linear behavior of the O−U−O vibrational stretch from 25 to 300 °C was assumed to result in minimal error.…”

“…The value of the scattering coefficient of UO 2 2+ (aq) relative to CF 3 SO 3 − (aq) varied little with temperature, and the use of the average value of 2.43 ± 0.06 over all temperatures introduces negligible uncertainty, especially at high temperatures where UO 2 2+ (aq) is either a minor species or undetectable in solution. 28 4.2. Raman Spectra and Scattering Coefficients of UO 2 SO 4 0 (aq) and UO 2 (SO 4 ) 2 2− (aq).…”

“…Wang et al 28 reported an additional Raman band at 1002 cm −1 in UO 2 SO 4 solutions, which was not included in these fits. This band may be present with a low intensity, but it was not apparent in our spectra, possibly due to the significant overlap with other Raman peaks in the sulfate region, or possibly because it is a broad, nonsymmetric vibrational mode that was not observed in the reduced isotropic spectra.…”

“…The development of high-pressure fused silica capillary cells by I. M. Chou and co-workers has proved to be a particularly effective tool for obtaining Raman spectra for concentrated aqueous sulfate systems under hydrothermal conditions. A recently reported study by Wang et al 28 used this method to observe the liquid−liquid phase behavior and semiquantitative vibrational spectra of uranyl sulfate under hydrothermal conditions at steam saturation pressure. In the present study, the capillary cell methods reported by Applegarth et al 39 were used to measure the Raman spectra of uranyl sulfate over a wide range of temperatures and solution compositions, in order to determine complexation constants for reactions 1 and 2, at a constant pressure of 25 MPa.…”