Experimental Data and Thermodynamic Model in the Salt–Water Ternary System (NaBO2 + Na2B4O7 + H2O) at T = 298.15 K and p = 0.1 MPa

Solubilities, refractive indices, densities, and pH for the ternary system (NaBO2 + Na2B4O7 + H2O) at 298.15 K were measured by the dissolution equilibrium method. The phase diagram of the ternary system was established and calculated. In the phase diagram of the ternary system of (NaBO2 + Na2B4O7 + H2O), there is one invariant point, two crystallization regions corresponding to the sodium metaborate tetrahydrate (NaBO2·4H2O), and borax (Na2B4O7·10H2O). The solubility calculation of the ternary system was carried out with three models on the basis of the Pitzer and Harvie–Weare (HW) model. The first model (model I) assumes that there is only two boron ions B(OH)4– and B4O5(OH)42– in the solution. The second model (model II) assumes that there are four forms for boron corresponding to B(OH)3, B(OH)4–, B3O3(OH)4–, and B4O5(OH)42– in the solution. The third model was extended from model II by adding OH– in the solution. The calculated pH data for the solution with model III are in accordance with the experim...