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

Quantitative first and second formation constants of aqueous uranyl sulfate complexes were obtained from Raman spectra of solutions in fused silica capillary cells at 25 MPa, at temperatures ranging from 25 to 375 °C. Temperature-dependent values of the symmetric O-U-O vibrational frequencies of UO(aq), UOSO(aq), and UO(SO)(aq) were determined from the high-temperature spectra. Temperature-independent Raman scattering coefficients of UO(aq) were calculated directly from uranyl triflate spectra from 25 to 300 °C, while those of UOSO(aq) and UO(SO)(aq) were derived from spectroscopic data at 25 °C and concentrations calculated using the formation constants of Tian and Rao ( 2009 , 41 , 569 - 574 ), together with the Specific Ion Interaction Theory (SIT) activity coefficient model.