Thermodynamic model for tungstic acid extraction from sodium tungstate in sulfuric acid medium by primary amine N1923 diluted in toluene

A thermodynamic model for the extraction of tungstic acid from sodium tungstate in sulfuric acid using the primary amine N1923 diluted in toluene has been developed. The liquid–liquid extraction equilibrium data were determined by performing a series of experiments at 293.15 K. The activity coefficients of the ions and molecules in the aqueous and organic phases were calculated using the Pitzer equations. Nonlinear regression, based on the balance equations of chemical, mass and charge equilibria and the experimental data, was used as the optimization method. Next, the thermodynamic equilibrium constant and the new Pitzer parameters for sodium tungstate electrolytes in the aqueous phase and the binary interactions between the species in the organic phase were obtained. The new model was used to predict the extraction efficiency from different initial conditions. Experiments were performed to verify the new model. The results indicated that the model could moderately predict this extraction system. Furthermore, the extraction reaction mechanism was investigated using the new model, and the scope of the new model is discussed.