Solubility Isotherm Determination of the H3BO3 + RbCl + H2O and H3BO3 + NH4Cl + H2O Systems at T = 273.15, 298.15, 323.15, 348.15, and 363.15 K and Thermodynamic Modeling

Highly concentrated boron is widespread in salt lake brine and nuclear wastewater. Treatment of these aqueous solutions involves the solubility of extensive boron-containing minerals. Recently, we concentrated on the temperature-dependent solubility of the H3BO3 + salt + water system. Here, we systematically determined the ternary solubility isotherms in the H3BO3 + RbCl + H2O and H3BO3 + NH4Cl + H2O systems at T = (273.15, 298.15, 323.15, 348.15 and 363.15) K, using an isothermal equilibrium method. The results showed that both ternary systems belonged to a simple eutectic case. The solubility isotherms consisted of the solubility branches of H3BO3(cr) and RbCl(cr) or NH4Cl(cr). Using a revised Pitzer–Simonson–Clegg (rPSC) model implemented in the ISLEC software, these ternary solubility data were represented by fitting the interaction parameters between H3BO3 and RbCl and H3BO3 and NH4Cl. With the help of these models, polythermal phase diagrams of the two ternary systems are predicted.