Study of the solubility in Na–Ba–Cl–H2O, Na–Ba–H2PO2–H2O, Na–Cl–H2PO2–H2O, and Ba–Cl–H2PO2–H2O ternaries, and in Na+, Ba2+/Cl−, (H2PO2)−//H2O reciprocal quaternary system at 0 °C

The solubility and the physicochemical properties (density and conductivity) in the Na–Ba–Cl–H2O, Na–Ba–H2PO2–H2O, Na–Cl–H2PO2–H2O, and Ba–Cl–H2PO2–H2O ternaries, and in Na+, Ba2+/Cl−, (H2PO2)−//H2O reciprocal quaternary systems at 0 °C were investigated using the isothermal method.Two invariant point were determined in Na+, Ba2+/Cl−, (H2PO2)−//H2O reciprocal quaternary system.The composition of invariant point of the first (as a weight) was determined as fallowing; 15.03% mass NaCl, 12.36% mass BaCl2, 2.86% mass Ba(H2PO2)2, and 69.75% mass H2O. It was plotted that the liquid phase and the following three solid phases were in equilibrium at the invariant point at 0 °C. These are NaCl, BaCl2·H2O, Ba(H2PO2)2·H2O.As for the composition of the second invariant point (as a weight) was determined as follows: 1.06% mass NaCl, 43.98% mass NaH2PO2, 0.51% mass Ba(H2PO2)2, 54.45% mass H2O. It was determined that the liquid phase and the following three solid phases were in equilibrium at the invariant point at 0 °C. These are NaCl, NaH2PO2·H2O, Ba(H2PO2)2·H2O.According to results, the least soluble salt was Ba(H2PO2)2. The crystallization field of this salt, being the largest in comparison with those of other salts, occupied 82% of the general crystallization field.

► 5 ternary systems’ solubilities, phase equilibrium, conductivities, and densities have been studied experimentally.
► Reciprocal quaternary systems’ solubility and phase equilibrium have been studied.
► In all systems’ solid phase NaCl, Ba(H2PO2)2·H2O, BaCl2·2H2O, NaH2PO2·H2O have been found.
► It has been found that Ba(H2PO2)2 salt contains 82 wt.% of the general crystallization field.