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The solubilities, refractive indices and pH values in the brine system Li2SO4‒LiBO2‒Li2B4O7‒H2O at 323.15 K were obtained by isothermal dissolution method. The dry-salt phase diagram is composed of one invariant point, three univariant curves, and three crystallization regions of Li2SO4⋅H2O, LiBO2⋅2H2O and Li2B4O7⋅3H2O. A comparison of the phase diagrams of this system at 288.15 K, 308.15 K and 323.15 K shows that area of Li2SO4⋅H2O crystallization zone increases whereas the areas of crystallization zone of lithium metaborate salt and Li2B4O7⋅3H2O changed intricately with temperature increasing. The refractive indices and pH values in the system change regularly with the lithium metaborate concentration of equilibrium solution changing. The calculated refractive indices with empirical formula are in agreement with the experimental values. Combining the equilibrium constants for different boron species, the distributions of six boron species in the mixed solution in the system were calculated with total boron concentration and pH values. The main boron species in the mixed solution of the quaternary system are B(OH)3, B(OH)4‒, B4O5(OH)42‒ and B3O3(OH)4‒. The mole fractions of the four boron species are mainly affected by the concentration of boron concentration. [ABSTRACT FROM AUTHOR]

[Display omitted] • The solubilities in systems Na 2 SO 4 –NaBO 2 –H 2 O and NaCl–Na 2 SO 4 –NaBO 2 –H 2 O were studied. • The Pitzer thermodynamic model of the two systems was constructed. • The calculated solubility data agree well with the experimental values. 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. [ABSTRACT FROM AUTHOR]