EQUATION-OF-STATE REPRESENTATION OF PHASE-EQUILIBRIA AND VOLUMETRIC PROPERTIES OF THE SYSTEM NACL-H2O ABOVE 573-K

A comprehensive equation of state has been developed for the system NaCl-H2O at high temperatures and pressures. The equation consists of a reference part and a perturbation contribution. The reference part represents the properties of a mixture of hard-sphere ion pairs and dipolar solvent molecules. The perturbation part arises from all other interactions and comprises a virial-type expansion truncated after the fifth virial coefficient. Mixing rules for the perturbation part are guided by the composition dependence of virial coefficients and contain empirically determined terms for unlike-molecule interactions. The equation has been fitted to extensive experimental data in the temperature range 573-773 K and to more limited data above 773 K. In both temperature regions, the equation reproduces vapor-liquid equilibria, volumetric properties, and solubilities of solid NaCl essentially within experimental uncertainty. It is valid at temperatures between 573 K and ca. 1200 K and pressures up to 5 kbar.