Phase Equilibria\nof Aqueous Ternary Systems Li₂SO₄ + Na₂SO₄ + H₂O and Na₂SO₄ +\nK₂SO₄ +\nH₂O at 303.2 K

Abstract

The phase equilibria of ternary systems Li₂SO₄ + Na₂SO₄ + H₂O and\nNa₂SO₄ + K₂SO₄ + H₂O at\n303.2 K were investigated by using the isothermal dissolution method.\nThe solubility, density, and refractive index of the systems were\nmeasured. There are two ternary invariant points and three crystallization\nregions corresponding to Li₂SO₄·3Na₂SO₄·12H₂O, Li₂SO₄·H₂O, and Na₂SO₄·10H₂O in the system Li₂SO₄ + Na₂SO₄ + H₂O at 303.2 K. There are two ternary\ninvariant points and three crystallization regions corresponding to\nNa₂SO₄·10H₂O, Na₂SO₄·3K₂SO₄, and K₂SO₄ in the system Na₂SO₄ + K₂SO₄ + H₂O at 303.2 K. By comparing the\nphase diagrams of the ternary system Li₂SO₄ +\nNa₂SO₄ + H₂O at different temperatures,\none can find that the existence form of double salt changes from Li₂SO₄·3Na₂SO₄·12H₂O to Li₂SO₄·Na₂SO₄. By comparing the phase diagrams of the ternary system Na₂SO₄ + K₂SO₄ + H₂O at different temperatures, the double salt Na₂SO₄·3K₂SO₄ was not found at 273.2\nK, while it was formed at 303.2 and 313.2 K. Meanwhile, the thermodynamic\ndata of these two systems at 303.2 K were fitted by the Pitzer–Simonson–Clegg\nmodel, and the calculated values agree well with the experimental\nvalues.