Thermodynamic Model of the H2O–H2SO4–UO2SO4 System Incorporating Novel Experimental Data on Water Activity

Activity of water in aqueous solutions containing sulfuric acid and uranyl sulfate has been determined at 298.15, 310.65, and 323.15 K by means of the apparatus AQUALAB 4TE. The data obtained, along with literature information about activity of water and solid–liquid equilibria in the H2O–UO2SO4 and H2O–H2SO4–UO2SO4 systems, were used to develop a thermodynamic model of the ternary system mentioned. The resulting model, employing Pitzer–Simonson–Clegg (PSC) equations to represent the properties of a liquid phase, is valid within a wide range of temperatures and concentrations. Apart from introducing novel experimental data and a thermodynamic model, the reported study discusses advantages and disadvantages of the PSC-based thermodynamic descriptions of the H2O–H2SO4 subsystem presented in the literature.