Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

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 are 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 Pitzer and Harvie-Weare (HW) model. The first model (model I) is to assume that there is only two boron ions B(OH)4- and B4O5(OH)42- in the solution. The second model (model II) is to assume 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 with adding OH- in the solution. The calculated pH data for the solution with model III are in accordance with the experimental values. The results show that model III are more reliable. The results of solubility calculation for the system containing borate in this study are essential for the development of universal thermodynamic models for brine systems containing borate.