Solid-Liquid Phase Equilibrium for the Ternary System NaVO3-KVO3-H2O at 298.15 K

The stable phase equilibrium of the ternary system NaVO3-KVO3-H2O at 298.15 K was investigated using the isothermal solution equilibrium method and the Schreinemaker wet residue method. The equilibrium liquid phase solubility data and physical property data [density (rho), refractive index (n(D)), pH] were determined, and X-ray diffraction was utilized to verify the material composition of the equilibrium solid phase. Phase diagrams and physical property-composition diagrams were constructed based on the equilibrium solubility data and physical property data. The results show that the ternary system has a complex salt generation process with two invariant points, three univariate curves, and three crystalline phase regions corresponding to NaVO3<middle dot>2H(2)O, KVO3, and Na2mKn(VO3)(2m+n), respectively. The solid phase precipitated from a saturated NaVO3 solution at 298.15 K is NaVO3<middle dot>2H(2)O, as confirmed by a comparison of experimental results and the literature. The chemical composition of the complex salt generated from the NaVO3-KVO3-H2O ternary system follows the general formula of the Na2mKn(VO3)(2m+n) complex salt proposed by Druzynski's group, thereby validating the reliability of the present experiment. This study provides new experimental data for the preparation and separation of metavanadate.