A thermodynamic model for the NaVO3–H2O and NH4VO3–H2O systems in the temperature range from 272 to 350 K at atmospheric pressure

Thermodynamic data for the binary systems and have been reviewed and used to construct an internally consistent model for the calculation of macroscopic solution properties and phase equilibria at . The explicit consideration of association of to was found necessary which is also suggested by a wide array of previous experimental evidence from e.g., spectroscopy. The recognition of the minor species based on spectroscopic data had negligible effect on most computed properties but improved the fit to the enthalpy of dilution data in high dilutions without introducing any further adjustable parameters. The Pitzer ion-interaction approach was used to model the excess Gibbs free energy. The model reproduces the experimental equilibrium solubilities, freezing point depressions and enthalpies of dilution practically within their experimental uncertainties. The predictive capability of the model was tested with some data on these properties left out of the parameter optimization, with generally good results. The present model provides a theoretically founded quantitative summary of thermodynamic information available for these systems which can be utilized e.g., in models for industrial processes and readily extended if new data becomes available. The limitations and capabilities of the model are also discussed. • Thermodynamic data for the title systems were extensively reviewed and collected. • A model describing all equilibrium data within their uncertainties in a thermodynamically consistent manner is reported. • The model combines data from both spectroscopic methods and measurements of macroscopic properties. • The model successfully predicted a priori the enthalpy of dilution data for NH 4 VO 3 .