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 Na 2 SeO 3 –H 2 O and 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 were investigated by isothermal dissolution equilibrium method. The results indicate that for the ternary system NaCl–Na 2 SeO 3 –H 2 O at 268.15 K, the equilibrium phase diagram contains two invariant points, three univariable curves, and five crystallization regions comprising NaCl·2H 2 O, NaCl·2H 2 O + NaCl, NaCl, NaCl + Na 2 SeO 3 ·5H 2 O and Na 2 SeO 3 ·5H 2 O. By 288.15 K, the phase diagram undergoes a transition from five to three crystallization regions, with the NaCl·2H 2 O crystallization region disappearing. The equilibrium phase diagram at 268.15 K for the ternary system Na 2 SO 4 –Na 2 SeO 3 –H 2 O comprises two invariant points, three univariant curves, and five crystallization regions. The invariant points are characterized by the equilibrium solid phase ice + Na 2 SO 4 ·10H 2 O and Na 2 SO 4 ·10H 2 O + Na 2 SeO 3 ·5H 2 O. 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.