Solid–Liquid Phase Equilibria in the Ternary Aqueous Systems (NaB5O8 + KB5O8 + H2O) and (LiB5O8 + KB5O8 + H2O) at 298.15 K and 101.325 kPa

Abstract

Solid–liquid phase equilibria of the ternary systems (NaB5O8 + KB5O8 + H2O) and (LiB5O8 + KB5O8 + H2O) at T = 298.15 K and p = 101.325 kPa were investigated, using a combination of the methods of isothermal dissolution equilibrium and the wet-residue solid phase (Schreinemarker’s rule). From the experimental results, the phase diagrams and the diagrams of physicochemical properties versus composition were drawn for each system. The phase diagrams of the systems (NaB5O8 + KB5O8 + H2O) and (LiB5O8 + KB5O8 + H2O) at 298.15 K contain one invariant point, two univariant curves and two crystallization regions. The area of the crystallization region of KB5O8·4H2O is much larger than that of NaB5O8·5H2O in the former system and that of LiB5O8·5H2O in the later system. Owing to the different solubilities of the salts in the aqueous systems, the solubility of KB5O8 in the solution decreased obviously with increasing concentration of NaB5O8 or LiB5O8 in either ternary system, indicating that both NaB5O8 or LiB5O8 have a relatively strong effect on the solubility of KB5O8. It was found that both systems belong to the simple eutectic type, and neither double salts nor solid solutions were formed. The distribution behaviors of densities and refractive indices in the two ternary systems at 298.15 K are similar and change regularly with increasing KB5O8 concentration in each system. The density and refractive index calculated on the basis of empirical equations of salt–water electrolytes agree well with the experimental values.