Siberian Federal University

The data of phase equilibria and phase diagrams have an important significance to guide the development and utilization of brine-mineral resources, design process of obtain, separation and purification of inorganic salts, and provide a theoretical basis for understanding the recovery of rare earth elements, whether from the environment or the economy. Therefore, the phase diagram determination of the corresponding systems is essential for establishment of the optimal temperature-concentration conditions of the process of crystallization. The efficiency of the investigation of the solid-liquid equilibria in quinary system CO(NH2)2 – NH4Cl – (NH4)2SO4 – NH4H2PO4 – H2O at 25 °C by the optimized sections method was shown. The method is allowed to determine the compositions of equilibrium solid phases without isolating them from liquid in the systems differently complexity. As a result of the formation of one complex salt NH4Cl·CO(NH2)2 between urea and ammonium chloride the quinary system has two invariant regions – eutonic and peritonic. In this study, the specifics of predicting the compositions of two invariant points, experimental determination of the compositions on the hyperplanes of invariant regions for computation of the compositions of equilibrium liquid and solid phases were considered. The efficiency of the algorithm for predicting the compositions of invariant points in the system was proved. The methodology of experimental design in studies of univariant curves and salt crystallization surfaces was described. According to the experimental data the phase diagram projection on the salt base of the system was constructed