Solid–Liquid Equilibrium in the Ternary Systems NaCl–Na 2 SeO 3 –H 2 O and Na 2 SO 4 –Na 2 SeO 3 –H 2 O at 268.15 and 288.15 K

The solid–liquid equilibria of the binary system Na2SeO3–H2O and the ternary systems NaCl–Na2SeO3–H2O and Na2SO4–Na2SeO3–H2O at 268.15 and 288.15 K were investigated by isothermal dissolution equilibrium method. The results indicate that for the ternary system NaCl–Na2SeO3–H2O at 268.15 K, the equilibrium phase diagram contains two invariant points, three univariable curves, and five crystallization regions comprising NaCl·2H2O, NaCl·2H2O + NaCl, NaCl, NaCl + Na2SeO3·5H2O and Na2SeO3·5H2O. By 288.15 K, the phase diagram undergoes a transition from five to three crystallization regions, with the NaCl·2H2O crystallization region disappearing. The equilibrium phase diagram at 268.15 K for the ternary system Na2SO4–Na2SeO3–H2O comprises two invariant points, three univariant curves, and five crystallization regions. The invariant points are characterized by the equilibrium solid phase ice + Na2SO4·10H2O and Na2SO4·10H2O + Na2SeO3·5H2O. When heated to 288.15 K, the ice regions in the equilibrium phase diagram of the ternary system disappeared, but five crystal regions were still displayed. As temperature increases, the crystalline forms of salts in the equilibrium phase diagram change.