Liquid-solid metastable equilibria of a quinary system Na⁺, K⁺//Cl^-, SO₄^2-, NO₃^--H₂O at 298 K

An experimental study on metastable equilibria of a quinary system Na⁺, K⁺//Cl^-, SO₄^2-, NO₃^--H₂O at 298 K was performed using an isothermal evaporation method. Metastable equilibrium solubilities were determined experimentally, and the metastable equilibrium phase diagram under the condition saturated with NaCl was plotted. The results show that there are four invariant points, nine univariant curves and six regions of crystallization: Na₂SO₄·NaNO₃·H₂O + NaCl, NaNO₃ + NaCl, 3K₂SO₄·Na₂SO₄ + NaCl, KNO₃ + NaCl, Na₂SO₄ + NaCl and KCl + NaCl. Some differences were found between the metastable diagram and the stable phase diagram at 298 K, and the crystallization regions of 3K₂SO₄·Na₂SO₄ become smaller.