Solid-liquid equilibrium for the ternary systems (Na2CO3 + NaCl + H2O) and (Na2CO3 + Na2SO4 + H2O) at 313.15 K and atmospheric pressure

Highlights: • Phase diagram for the system (Na₂CO₃ + NaCl + H₂O), (Na₂CO₃ + Na₂SO₄ + H₂O) at 313.15 K. • Diagrams of η, ρ, pH, n_D and solubility vs composition are constructed. • Comparison with Literature Data of the solubility of two ternary systems. -- Abstract: The stable (solid + liquid) phase equilibrium and physico-chemical properties of the ternary systems (Na₂CO₃ + NaCl + H₂O) and (Na₂CO₃ + Na₂SO₄ + H₂O) at T = 313.15 K have determined by the method of isothermal solution saturation. The solid phases formed in the systems studied were determined by the Schreinemaker wet residue method. According to the experimental data, the phase diagrams and the diagrams of physico-chemical properties versus composition were plotted. It was found that there is one invariant point, two univariant curves and three fields of crystallization in the ternary systems (Na₂CO₃ + NaCl + H₂O) at T = 313.15 K. The three crystallization regions correspond to NaCl (I), Na₂CO₃·H₂O (II), the mixed of (NaCl + Na₂CO₃·H₂O) (III). Field EFUC (IV) corresponds to unsaturated solution. Based on the phase diagrams obtained, we analyzed each invariant point. When Na₂CO₃ and NaCl were analyzed as (15.80, 17.04) wt%, respectively, the ternary system (Na₂CO₃ + NaCl + H₂O) reached saturation at T = 313.15 K. The phase diagram of the ternary system at 313.15 K includes two invariant points, three invariant curves, and three fields of crystallization of single salts corresponding to Na₂CO₃, Na₂CO₃·2Na₂SO₄, Na₂SO₄. The two invariant points are cosaturated with two salts, that is (Na₂CO₃·H₂O + Na₂CO₃·2Na₂SO₄) and (Na₂SO₄ + Na₂CO₃·2Na₂SO₄), respectively. In the phase diagram of the two ternary systems at 313.15 K, the crystallization region of Na₂SO₄ was significantly larger than the crystallization region of Na₂CO₃·H₂O and NaCl. The quaternary phase equilibrium in Na⁺//C1⁻, CO₃²⁻, SO₄²⁻-H₂O system at 313.15 K was also researched by means the through and intermediate translation techniques together. Thus, knowledge of (solid + liquid) equilibrium, especially the crystalline fields at T = 313.15 K, would be extremely valuable to design and optimize solvent extraction process of Na₂SO₄ and other crystallization processes involving the two ternary systems in the industrial production.