PVTx Measurements and Partial Molar Volumes for Aqueous Li2SO4 Solutions at Temperatures from 297 to 573 K and at Pressures Up to 40 MPa

Densities of four aqueous Li2SO4 solutions (0.0944, 0.2798, 0.6115, 0.8850 mol· kg−1 ) have been measured in the liquid phase with a constant-volume piezometer immersed in a precision liquid thermostat. Measurements were made for ten isotherms between 297 and 573 K. The range of pressure was from 3.9 to 40 MPa. The total uncertainty of density, pressure, temperature, and concentration measurements were estimated to be less than 0.06%, 0.05%, 10 mK, and 0.014%, respectively. The reliability and accuracy of the experimental method was confirmed with measurements on pure water for two isobars at 10 and 38 MPa. Experimental and calculated (IAPWS formulation) densities for pure water show excellent agreement within their experimental uncertainties (average absolute deviation within 0.02 to 0.05%). Saturated liquid densities were determined by extrapolating experimental P-r data to the vapor pressure at fixed temperature and composition using an iInterpolating equation. Apparent and partial molar volumes were derived using measured densities for aqueous solutions and pure water. Derived apparent molar volumes were extrapolated to zero concentration to yield partial molar volumes of electrolyte (Li2SO4) at infinite dilution. The temperature, pressure, and concentration dependences of partial and apparent molar volumes were studied. A polynomial type of equation of state for specific volume was obtained as a function of temperature, pressure, and composition by a least-squares method using the experimental data. The average absolute deviation (AAD) between measured and calculated values from this polynomial equation for density was 0.02%. Measured values