Solubility measurement and thermodynamic modeling of solid–liquid equilibria in quaternary system NaCl–Na2SO4–NaBO2–H2O at 323.15 K

The solubilities and refractive indices in the systems Na 2 SO 4 –NaBO 2 –H 2 O and NaCl–Na 2 SO 4 –NaBO 2 –H 2 O at 323.15 K were studied by the isothermal dissolution method. The phase diagram of the ternary system is composed of two single-salt crystallizations for Na 2 SO 4 and NaBO 2 ·4H 2 O. A comparison of the diagrams of system Na 2 SO 4 –NaBO 2 –H 2 O from 288.15 K to 323.15 K shows that the crystallization region of NaBO 2 ·4H 2 O changes greatly as the temperature increasing, and the solid phase of mirabilite at 288.15 K and 298.15 K transforms into the nardite at 308.15 K and 323.15 K. The dry-salt diagram of the quaternary system consists of four salt crystallization fields for NaCl , NaBO 2 ·4H 2 O, NaCl·NaBO 2 ·2H 2 O and Na 2 SO 4 , five univariant solubility curves and two invariant points. On the basis of the Pitzer model, the lacking Pitzer parameters and dissolution equilibrium constants of the solid phases in this quaternary system were fitted with the solubilities and other thermodynamic properties in this study and literature. The calculated solubilities in the two systems are in good agreement with the experimental data.