Extractive separation of trivalent lanthanide metals with a combination of Di(2-ethylhexyl)phosphoric acid and 1,10-phenanthroline

The equilibrium extraction behavior of a series of trivalent lanthanide ions (Ln³⁺) using a chloroform-Kerosine solution containing Di(2-ethylhexyl)phosphoric acid, combined with an adductant, 1,10-phenanthroline monohydrate (phen), was studied. The enhancement of the extraction by addition of such a neutral adductant is explained in terms of the extraction of the quaternary complex, M(HX₂)₃(phen)₂, in addition to the neutral complex, M(HX₂)₃, into the organic phase. The stoichiometry, extraction constants and separation factors of these systems were determined. The extraction constants of these systems partially follow the order of the atomic numbers. The synergistic extraction constants increased in the other Gd > Er > Ho > Eu > Cc > La > Pr and the highest separation factor was observed for Er-Ho (2.09). pH₁₂ values were also obtained. In this synergistic extraction system, both the extraction equilibrium constants and the separation factors were found to be greater than those of commercial extractants.