LAUSR

Abstract Solid-liquid equilibrium (SLE) of Na + //Cl − , NO 3 − , SO 4 2− -H 2 O quaternary system at 373.15 K was determined via isothermal solubility equilibrium method. The dry-salt phase diagram and the tri-prism stereogram of this system were obtained found on the solubility data. Without any solid solutions or double salts, the phase diagram is the simplest one of the quaternary system, consisting of one invariant point, three univariant curves, three crystallization fields of single salts, three cocrystallization fields for two salts and one cocrystallization field for three salts. At the same time, the physicochemical properties (density and conductivity) of this system were measured in the experiment. Moreover, comparing with the equilibrium phase diagrams in the temperature range from 258.15 K to 373.15 K, it could be found that the crystallization field of the double salt D (NaNO 3 .Na 2 SO 4 .10H 2 O) reduces with the temperature increases, and disappears at 373.15 K. With the growing temperature, the crystallization field of Na 2 SO 4 enlarges while the crystallization fields of NaNO 3 and NaCl both reduce. All above the experimental results obtained can be applied to solve the salt separation of the relative brine system mainly containing the four aforementioned ions as well as conduct further theoretical studies.