Solubility Measurement and Thermodynamic Model of Solid–Liquid Phase Equilibrium in the Ternary System CaCl ₂ -H ₃ BO ₃ -H ₂ O at T = (288.15 and 308.15) K and P = 0.1 MPa

The solid and liquid equilibria in the ternary CaCl2-H3BO3-H2O system at 288.15 and 308.15 K were investigated using the dissolution equilibrium method. The phase diagrams of this system at two temperatures consist of two single-salt crystallization regions corresponding to CaCl2·6H2O and H3BO3 at 288.15 K, CaCl2·4H2O and H3BO3 at 308.15 K, two univariant solubility curves, and one invariant point. A comparison of the phase diagrams at four temperatures shows that the solubilities of H3BO3 and calcium chloride salts increase as the temperature increases. The concentrations of different boron species were calculated with the pH data and the concentration of total boron in the solution. The predominant boron species in the solution is H3BO3 with the mole fraction no less than 0.99. Combining the Pitzer binary parameters of CaCl2, the temperature dependence equations for Pitzer parameters and dissolution equilibrium constant of H3BO3 from 288.15 to 323.15 K were obtained by fitting the solubilities in the ternary system on the basis of Pitzer model. The calculated solubility data at the four temperatures with the Pitzer model agree with the experimental data.