Abstract
UV-visible absorption spectra of uranium(VI)-tributylphosphate (U(VI)-TBP) complex dissolved in supercritical CO 2 at 40–60°C and 100–250 kg cm −2 were recorded. Wavelengths and molar extinction coefficients for the absorption peaks of U(VI)-TBP were determined and confirmed to be in good agreement with those of UO 2(NO 3) 2(TBP) 2 complex dissolved in organic solvents such as n-hexane. The absorbance at a given wavelength was proportional to the concentration of U(VI) species in supercritical CO 2, indicating a feasibility of in-situ determination of U(VI) concentration in CO 2 phase. A lower detection limit of U(VI)-TBP complex was estimated to be ca. 1×10 −3M. The molar extinction coefficient of U(VI)-TBP in supercritical CO 2 decreased slightly with an increase of the density of CO 2 medium, suggesting that the solute–solvent interaction of U(VI)-TBP complex with CO 2 was affected by the density. On the basis of the spectra obtained, phase behavior and solubility of UO 2(NO 3) 2(TBP) 2+H(NO 3)(TBP)+TBP in supercritical CO 2 were elucidated.
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