Measurement and Modeling of the Solubility of NH4VO3 in the Na2HPO4–H2O and (NH4)2HPO4–H2O Systems

The solubilities of ammonium metavanadate (NH4VO3) in (NH4)2HPO4–H2O and Na2HPO4–H2O systems were measured in the temperature range from 298.15 to 338.15 K by the isothermal dissolution method. The experimental data indicate that the solubility of NH4VO3 increases with the addition of Na2HPO4, while it first decreases and then increases with the addition of (NH4)2HPO4. The common ion effect and chemical equilibrium were used to explain the solubility tendencies. Two models, the Bromley–Zemaitis model and Pitzer model, were selected to correlate the solubilities of NH4VO3 in the above systems. The parameters of the new model referring to four ion–ion pairs and one ion–molecule pair were obtained via the regression of the experimental data, and the results agreed well with the experimental values. The new chemical model was then applied to analyze the main vanadium-bearing species distribution in the systems mentioned above. All of this work will develop the thermodynamics for an industrial application in the precipitation of NH4VO3.