PHASE BEHAVIOR AND IN-SITU DENSITY DETERMINATION IN CONCENTRATED SALT SOLUTIONS UNDER HYDROTHERMAL CONDITIONS

An optical cell was constructed to observe phase behavior in aqueous electrolyte solutions at temperatures up to 450°C and pressures up to 1200 bar. The goal was to map out the single-phase region for a certain concentrated, multicomponent waste solution, to explore the possibility of hydrothermal treatment. The cell was observed by an imaging system which could also be used to measure the refractive index of the fluid, allowing the density to be determined by means of the Lorentz-Lorenz relationship. The validity of the technique was verified for pure water and for NaCl-water systems. Data for a multicomponent system is presented as a family plot of density vs. pressure, for several different temperatures, with the lowest pressure on each plot corresponding to a phase boundary. Dara is also presented for the binary system NaNO₃-water.