Enhancement of Orthophosphoric Acid Extraction by the Synergic Effect of Tributyl Phosphate and Methyl Isobutyl Ketone in the Quaternary System H2O–H3PO4–TBP–MIBK at 298.2 K

A systematic experimental study of the isoplethic sections for the quaternary system H₂O–H₃PO₄–TBP–MIBK was carried out at 298.2 K under atmospheric pressure in order to evaluate the synergic effect of tributyl phosphate (TBP) and methyl isobutyl ketone (MIBK) as a mixed solvent for orthophosphoric acid (H₃PO₄) extraction. Liquid–liquid equilibria diagrams were fully established for the following TBP/MIBK mass-percent ratios: 0/100, 30/70, 50/50, 80/20, and 100/0. The reliability of the LLE measurements was confirmed by the Othmer-Tobias and Hand equations. The results show that the quaternary system is type II and that the demixing area expands with an increasing TBP content. Moreover, the mixed solvent enhances MIBK selectivity for acid concentrations below 50 wt %, while the 80/20 weight ratio shows the optimal selectivity for acid concentrations below 25 wt %. Furthermore, these experimental results were compared to the values predicted by the NRTL model. It can be seen that the interaction parameters of the NRTL model used provide good results with a root-mean-square deviation (RMSD) of 0.0135.