Mean activity coefficients of {yNaCl + (1−y)Na2B4O7}(aq) systems at 288.2 K and 318.2 K for ionic strengths in the range 0.01–0.50 mol·kg−1, and phase equilibria

•The activity coefficients of the NaCl in the NaCl–Na2B4O7–H2O solutions at 288.2 K and 318.2 K were determined by cell potential method.•Single salt parameters of Na2B4O7 and mixed ion parameters of the ternary system NaCl–Na2B4O7–H2O were fitted using the Pitzer model.•Other thermodynamic properties of NaCl–Na2B4O7–H2O solution were calculated.•The solubility data of NaCl–Na2B4O7–H2O at 288.2 K and 318.2 K were calculated, and the results were more in line with the experimental values.•Design of a preliminary boron extraction process from brine of Zabuye Salt Lake using phase diagrams. Zabuye Salt Lake is rich in boron resources, and the separation and precipitation process of boron from the brines can be developed by investigating the activity coefficients and phase equilibria of the ternary subsystem {yNaCl + (1−y)Na2B4O7}(aq) at 288.2 K and 318.2 K. In this work, the mean activity coefficients of NaCl in {yNaCl + (1−y)Na2B4O7}(aq) systems were determined by using the cell potentials and Nernst equation. The unreported single salt parameters βNa2B4O5(OH)40, βNa2B4O5(OH)41 and CNa2B4O5(OH)4Φ of Na2B4O7 and the mixed salt parameters θCl,B4O5(OH)4 and ψNa,Cl,B4O5(OH)4 were determined by using activity coefficients and the Pitzer model. The obtained parameters are used to calculate other thermodynamic properties. Furthermore, phase equilibria of the ternary subsystem {yNaCl + (1−y)Na2B4O7}(aq) at 288.2 K and 318.2 K are measured experimentally. Subsequently, the solubility data of the ternary subsystem {yNaCl + (1−y)Na2B4O7}(aq) were theoretically predicted by the Pitzer model. The calculated results agree well with the experimental results, indicating that the obtained parameters are reliable. These key thermodynamic data for the development of boron-rich brine resources were provided. Based on the phase diagram of the ternary system, a separation process for borates was designed in this work.