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The extraction behavior of rare earth (RE) species was investigated on benzoyltrifluoroacetone (Hbfa) /triethyl-pentyl-phosphonium bis(trifluoromethyl-sulfonyl)amide ([P2225][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 (β) 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 (logβ) of [Nd(bfa)3] and [Dy(bfa)3] were estimated to be 7.58 and 7.93, respectively. The value of logβ(Dy) was larger than that of logβ(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 Å or 2.407 Å, respectively. This result suggested that the Dy3+ion would be combined more strongly with the [bfa]−anion than the Nd3+ion. [ABSTRACT FROM PUBLISHER]

The extraction behavior of rare earth (RE) elements usingN,N,N′,N′-tetraoctyl diglycolamide (TODGA) in an ionic liquid (IL) system was investigated by slope analyses. Metallic salts of Pr(III), Nd(III), and Dy(III) with bis(trifluoromethylsulfonyl)amide (TFSA) were synthesized and studied for their extraction mechanism. The selected concentration of TODGA was diluted with triethylpentylphosphonium bis(trifluoromethylsulfonyl)amide ([P2225][TFSA]) to prepare an extracting phase for the slope analyses. The stoichiometry of RE(III) was determined in order to estimate the extracted species. Furthermore, the complexation state of the extracted species was evaluated by spectroscopic analyses, including Fourier-transform infrared (FT-IR) spectroscopy, Raman spectroscopy, and ultraviolet–visible (UV–Vis) spectroscopy. The FT-IR and Raman spectra were estimated using density functional theory (DFT) calculations. Thorough analysis of the FT-IR spectrum was carried out in order to assign the TODGA group that mainly coordinated the metal ion. The solvation of the [TFSA]−anion in the coordination sphere of [Nd(TODGA)(2–3)]3+was investigated by Raman spectroscopic analysis. The coordination ability of TODGA was investigated from the peak shift of the hypersensitive transition (4I9/2→2G7/2) in UV–Vis spectroscopic measurements. From electrochemical analysis, the extracted [Nd(TODGA)3]3+complex in [P2225][TFSA] was found to be reduced as per the following reaction: [Nd(TODGA)3]3++ 3e−→ Nd(0) + 3[TODGA] at −3.0 V, and the diffusion coefficient of [Nd(TODGA)3]3+was calculated to be 1.6 × 10−11m2s−1at 373 K. The direct electrodeposition of the extracted [Nd(TODGA)3]3+in [P2225][TFSA] at 373 K allowed us to conclude that the middle layer of Nd electrodeposits was the metallic state, while a part of the top surface was the oxidation state by XPS analysis. [ABSTRACT FROM PUBLISHER]