Pure and Applied Chemistry

Abstract: A comprehensive thermodynamic model, referred to as the mixed-solvent electrolyte (MSE) model, has been applied to calculate phase equilibria, speciation, and other thermodynamic properties of selected systems that are of interest for understanding the chemistry of salt lakes and natural waters. In particular, solubilities and chemical speciation have been analyzed for various boron-containing systems, which represent an important subset of solution chemistry for such applications. The model has been shown to reproduce the speciation, solubility, and vapor–liquid equilibrium (VLE) data in the boric acid + water system over wide ranges of temperature and concentration. Specifically, solubilities have been accurately represented in the full concentration range of the B₂O₃ + H₂O system (x_B2O3 = 0~1), which includes H₃BO₃. The accuracy of the model has also been demonstrated by calculating solubilities in various aqueous borate systems, i.e., M_nO + B₂O₃ + H₂O (where M = Li, Na, Ca, Mg), and their mixtures with a chloride salt or an acid (i.e., LiCl, NaCl, HCl). The model predicts the effects of chemical speciation, temperature, and concentrations of various acid, base, and salt components on the formation of competing solid phases.