Speciation of U(IV) sulfate in aqueous solution – spectroscopic characterization and thermodynamic modelling

For a high level radioactive waste disposal as well as former uranium mining sites after sealing U(IV) is expected to be the stable oxidation state due to reducing conditions. Thermodynamic data on U(IV) in aqueous solution is needed for a reliable safety assessment but still sparse by reason of its low solubility and a lack of appropriate measuring systems. By employing a combination of absorption- and fluorescence spectroscopy to study U(IV) sulfate complexation in acidic aqueous solution we gained complex formation constants, extinction coefficients and single component absorption spectra of U4+, UOH3+, U(SO4)2+ and U(SO4)2.