Solid Liquid Phase Equilibria in the Ternary System NaCl–Na₂SeO₃–H₂O and Na₂SO₄–Na₂SeO₃–H₂O at 298.15, 323.15 K

At temperatures of 298 and 323 K, the solubility data for both solid and liquid phases across various systems was measured utilizing the isothermal dissolution equilibrium method at equilibrium. This investigation encompasses the binary system Na2SeO3–H2O as well as the ternary systems NaCl–Na2SeO3–H2O and Na2SO4–Na2SeO3–H2O. The research findings indicate that at both 298 and 323 K, the ternary system NaCl–Na2SeO3–H2O exhibits one invariant point, two univariant curves, and three crystallization regions. These correspond to NaCl, Na2SeO3, and a combination of them, respectively. In the context of the ternary system Na2SO4–Na2SeO3–H2O, there are significant differences in the equilibrium phase diagram at two different temperatures. At 298 K, the phase diagram comprises two invariant points, three univariant curves, and five crystallization regions, which correspond to Na2SO4·10H2O, Na2SO4, Na2SeO3, Na2SO4·10H2O and Na2SO4, Na2SO4 and Na2SeO3. At 323 K, the most notable distinction is the decrease in the number of invariant points from two to one, while the number of univariant curves is exactly two; the number of crystalline regions is reduced from five to three, consisting only of Na2SO4, Na2SeO3, Na2SO4 and Na2SeO3.