Solid-liquid phase equilibrium and phase diagram of the ternary system (NaNO3 + CsNO3 + H2O) and its application for cesium nitrate separation

Abstract

In order to separate cesium nitrate from the eluant mixture sodium nitrate solution, the phase equilibrium of the ternary system (NaNO3 + CsNO3 + H2O) at 338.15 K and 0.1 MPa was investigated using the isothermal equilibrium solution method, and the solubilities and physicochemical properties (density and refractive index) of the system were determined, experimentally. According to the experimental data, the phase diagram and physicochemical properties versus the composition diagram of the ternary system at 338.15 K were established for the first time. There is one invariant point (NaNO3 + CsNO3), two univariant curves, and two crystallizing regions corresponding to NaNO3 and CsNO3. The phase diagram belongs to a simple-type ternary system, and neither double salt nor solid solution was formed. Based on the phase diagrams of this system at 298.15 and 338.15 K, the cycle separation process for CsNO3 recovery from the eluant of sodium nitrate mixture solution was evolved. It is worth noting that 90.29 % CsNO3 can be separated from the mixed solution after three cycles. It is significant for the green recovery of cesium nitrate from the eluent solution containing sodium nitrate effectively.