Evaluation of the Extraction Properties and Stability of Extracted Rare Earth Complexes in Ionic Liquid Extraction System Using beta-Diketone

摘要

The extraction behavior of rare earth (RE) species was investigated on benzoyltrifluoroacetone (Hbfa) /triethyl- pentyl- phosphonium bis(trifluoromethyl- sulfonyl) amide ([P-2225][TFSA]) system in this study. The stoichiometry of the extracted complex shown RE: ligands = 1: 3 by slope analysis regardless of the kinds of acid media in the aqueous phase. The extraction mechanism in this system was revealed as [RE3+] aq + 3[Hbfa] IL [RE(bfa)(3)] IL + 3[H+] aqand [TFSA]-anion did not participate in the extraction mechanism. The result of Raman spectroscopy also supported the stoichiometry of the extracted complex. Moreover, the chelate formation constant (beta) of [Nd(bfa)(3)] and [Dy(bfa)(3)] was also evaluated by the direct measurement of [bfa]-anion by ion chromatography. The hypersensitive peak (4I9/2. 2G7/2*) in the UV-Vis-NIR spectrum also confirmed the formation of [Nd(bfa)(3)]. The average chelate formation constants (log beta) of [Nd(bfa)(3)] and [Dy(bfa)(3)] were estimated to be 7.58 and 7.93, respectively. The value of log (Dy) was larger than that of log beta(Nd); thus, this result indicates that [Dy(bfa) 3] was more stable than [Nd(bfa)(3)]. Furthermore, the optimized structure of the extracted complexes -[Nd(bfa) 3(H2O) 3] and [Dy(bfa) 3(H2O)(2)] -were also evaluated by the density functional theory (DFT) calculation. On the optimized geometries, the average bond length of the centered Nd3+ ion or Dy3+ ion against the O atom in the 1-carbonyl group was 2.728 or 2.407, respectively. This result suggested that the Dy3+ ion would be combined more strongly with the [bfa]-anion than the Nd3+ ion.