Thermodynamic modeling of the solvent extraction equilibrium for the recovery of vanadium (V) from acidic sulfate solutions using Di-(2-ethylhexyl) phosphoric acid

A study of the reaction mechanism and thermodynamic modeling of pentavalent vanadium V(V) extraction from NaVO3-H2SO4-H2O solutions using Di-(2-ethylhexyl) phosphoric acid (D2EHPA or HA) extractant was carried out. The effects of initial pH of the solution, extractant concentration, and temperature on the extraction of V(V) were examined. The stoichiometry of the extraction reaction was determined using the slope analysis method. The extracted species was shown to be VO2A. A thermodynamic modeling approach was proposed for the prediction of equilibrium concentrations and pH of the system based on the known initial concentrations and process temperature. In the presented approach, the non-ideality of both aqueous and organic phases was taken into account. The activity coefficients of all organic components were calculated using UNIQUAC-NRF model, while the Electrolyte-UNIQUAC-NRF model was employed to calculate the activity coefficients of ions in aqueous phase. The equilibrium constant of the extraction reaction and the unknown parameters of the models were adjusted through the regression of experimental data at 25 °C, 35 °C, and 45 °C. Adjusted parameters were used for the prediction of equilibrium vanadium concentration in organic phase and equilibrium pH of the aqueous phase. Both of regressed and predicted values were in very good agreement with the experimental data. Moreover, calculated standard molar enthalpy of the reaction indicated the endothermicity of extraction reaction between VO2+ and D2EHPA.