Selective separation of samarium(III) by synergistic extraction with β-diketone and methylphenylphenanthroline carboxamide

The complex for Pr(III) was very stable (the stability constant, β¯, denoted as [LnA3B]o[LnA3]o−1[B]o−1, was 108.3). It suggests that LnA3 can form two 5-membered rings with MePhPTA, and the size of Pr(III) matches to the distance between the donor atoms in MePhPTA. Although the stability constant decreased with increasing Ln atomic number, the synergistic extraction constant (Kex31 = [LnA3B]o[H+]3[Ln3+]−1[HA]o−3[B]o−1) was the largest for Sm(III). Since the constant, Kex31, is given by Kex31=Kex30×β¯ where Kex30 = [LnA3]o[H+]3[Ln3+]−1[HA]o−3, the largest Kex31 of Sm(III) is attributable to the difference of the degree of the variation of Kex30 between the light and the heavy Lns(III); the increment of extraction constant of LnA3 (log Kex30) for light Lns is larger than the decrement of the stability constant of LnA3B (log⁡β¯), while the increment of log Kex30 of post-Sm lessens than the decrement of log⁡β¯. From these results, it is concluded that selective separation of a particular Ln(III) among all Lns(III) is possible using synergistic extraction with a suitable combination of a multidentate β-diketone and a Lewis base.