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

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.