Solubilization behaviors of interfacial lutetium-extractant complex in a solvent extraction system

Abstract Knowledge of the solubilization behaviors of rare-earth-extractant complex is mandatory for full comprehension of interfacial phenomenon and intermediate state of rare earth (RE) ion transport from water to oil during solvent extraction. The lutetium with 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester (P507) extraction system was explored as a case study for the solubilization behaviors in this paper. With a quantitative analysis of a white crud obtained in the practical process, the results demonstrate that the insoluble REL 3 (L = the anion of P507) complex enriches at the oil/water interface and forms the network polymers. Besides, with the increase of RE loading ratios in the oil phase, the interfacial tension increases while the free ligand in the bulk phase decreases, which results in the flocculation of REL 3 complex and the formation of polymers at the interface. Furthermore, the properties of the oil phase and the interface reveal that the free ligand can solubilize the REL 3 complex along with the transfer of water from microemulsion to aqueous phase. In addition, the change of aqueous acidity can regulate the solubilization behaviors of the interfacial complex to improve RE extraction efficiency. These fundamental studies will hopefully provide new insights into the solubilization of metal-extractant complex and a technical guidance to the transfer of RE from water to oil.