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

Abstract

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.