Nucleation Behaviors of Nd and Dy in TFSA-Based Ionic Liquids

The nucleation behavior of [Nd(III)(TFSA)5]2- and [Dy(III)(TFSA)5]2- in the TFSA-based ionic liquid (IL), triethyl-pentyl-phosphonium bis(trifluoromethyl-sulfonyl)amide, [P2225][TFSA], was investigated in this study. The initial process of Nd and Dy electrodeposition was evaluated by chronoamperometry, indicating that the initial nucleation and the growth of Nd and Dy on the electrode surface occurred via instantaneous nucleation at -3.40 and -3.60 V, respectively. As the overpotential induced more negative, the nucleation mechanism altered from instantaneous to progressive. The number density of Nd and Dy nuclei tended to decrease as the overpotential gradually increased in this system. Moreover, the potentiostatic electrodeposition of Nd and Dy metals was examined at 393 K. The surface morphology of the electrodeposits was consistent with the chronoamperometric results. From the EDX and the XPS analyses, we ascertained that the main electrodeposits were rare earth metals with a small quantity of light elements. The series of results enabled us to conclude that the greater part of the electrodeposited Nd and Dy metals was obtained from TFSA-based IL bath by potentiostatic electrodeposition with elevating temperatures, and the control of the water content of the electrolyte was an important factor for the recovery of metallic Nd and Dy with high purity

Purification of Rare Earth Amide Salts by Hydrometallurgy and Electrodeposition of Rare Earth Metals Using Ionic Liquids

This paper reports a novel bench-scale hydrometallurgical procedure and electrodeposition using triethyl-pentyl-phosphonium bis(trifluoromethyl-sulfonyl)amide ([P2225][TFSA]) ionic liquids (ILs) for the recovery of rare earth (RE) metals from spent Nd-Fe-B magnets. The hydrometallurgical treatments were carried out at bench scale to produce RE amide salts of high purity. In the leaching process employing 1.7 kg of oxidized Nd-Fe-B fine powder and 14.2 L of an acid medium of 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide (H[TFSA]), selective leaching of RE ions (85.7±5.8% Nd) was performed at bench scale. Then, Fe (<99.9%) was successfully separated from RE ions in the deironization process. The total amount of the recovered amide salts through the evaporation treatment using a spray dryer was 3.57 kg. From the CV/EQCM measurements for Nd(III) at 373 K, a clear cathodic peak with the mass increased, and the ηρ decreased was observed at −2.79 V. Considering our previous investigations, the reduction of Nd(III)/Nd(0) was indicated as [Nd(III)(TFSA)5]2− + 3e− → Nd(0) + 5[TFSA]−. In addition, the Mapp value in the range of −2.49 V ~ −2.94 V was 46.8 g mol−1, which was close to the theoretical value for the electrodeposition reaction of Nd(III)/Nd(0), 48.1 g mol−1. Moreover, the electrodeposition of Nd(0) was carried out under the condition of −3.20 V versus Fc/Fc+ at 373 K. The electrodeposits were identified with the metallic Nd in the middle layer investigated by X-ray diffraction and X-ray photoelectron spectroscopy. Finally, we demonstrated that the novel recovery process consisted of hydrometallurgy and electrodeposition using ILs was effective by calculating material flow

Analysis of Thermodynamic Properties for Rare Earth Complexes in Ionic Liquids by Raman Spectroscopy and DFT Calculation

The coordination states of the divalent and trivalent rare earth complexes in ionic liquid, triethyl-pentyl-phosphonium bis(trifluoromethyl-sulfonyl) amide [P2225][TFSA] were investigated by Raman spectroscopy and DFT calculation. The concentration dependences of the deconvoluted Raman spectra were investigated for 0.23-0.45 mol kg-1 RE(III), RE=Nd and Dy, and the mixed sample of RE(II)/RE(III)=1/3 at the molar ratio in [P2225][TFSA]. According to the conventional analysis, the solvation number; n of rare earth complexes in [P2225][TFSA] were determined to be n=4.06 for Nd(II), 5.01 for Nd(III), 4.12 for Dy(II) and 5.00 for Dy(III). Thermodynamic properties such as ΔisoG, ΔisoH and ΔisoS for the isomerism of [TFSA]- from trans- to cis-isomer in bulk and the first solvation sphere of the centered [RE3+] cation in [P2225][TFSA] were evaluated from the temperature dependence in the range of 298-398K. ΔisoG(bulk), ΔisoH(bulk) and TΔisoS(bulk) at 298 K were -1.06, 6.86, and 7.92 kJ mol-1, respectively. The trans-[TFSA]-was dominant in the enthalpy due to the positive value of ΔisoH(bulk) and TΔisoS(bulk) was slightly larger than ΔisoH(bulk), so that cis-[TFSA]- was revealed to be an entropy-controlled in [P2225][TFSA]. On the other hand, in the first solvation sphere of [RE3+] cation, ΔisoH (Nd)(-47.39 kJ mol-1) increased to the negative value remarkably and implied that the cis-[TFSA]- isomers were stabilized for enthalpy. ΔisoH(Nd) contributed to the remarkable decrease in the ΔisoG(Nd) and this result clearly indicated that the cis-[TFSA]- bound to Nd3+ cation was preferred and the coordination state of [Dy(III)(cis-TFSA)5]2- was stable in [P2225][TFSA] The optimized geometries and the bonding energies of [RE(II)(cis-TFSA)4]2- and [RE(III)(cis-TFSA)5]2- clusters were also investigated from DFT calculation with ADF package. The bonding energy; ΔEb was calculated from ΔEb= Etot(cluster) - Etot(RE2,3+) - nEtot([TFSA]-). ΔEb([Nd(II)(cis-TFSA)4]2-), ΔEb([Nd(III)(cis-TFSA)5]2-), ΔEb([Dy(II)(cis-TFSA)4]2-) and ΔEb([Dy(III)(cis-TFSA)5]2-) were -2241.6, -4362.3, -2135.4 and -4284.2 kJmol-1, respectively. This result was revealed that [RE(III)(cis-TFSA)5]2-cluster formed stronger coordination bonds than [Dy(II)(cis-TFSA)4]2- cluster. The average atomic charges and the bond distances of these clusters were consistent with the thermodynamic properties

Phase Equilibrium Relations of Semiclathrate Hydrates Based on Tetra- n-butylphosphonium Formate, Acetate, and Lactate

Phase equilibrium (temperature-composition) relations of tetra-n-butylphosphonium formate (TBP-For), acetate (TBP-Ace), and lactate (TBP-Lac) semiclathrate hydrate systems have been measured. The highest equilibrium temperatures of TBP-For, TBP-Ace, and TBP-Lac semiclathrate hydrates were 280.9, 284.6, and 283.8 K at the atmospheric pressure, respectively, where the composition of tetra-n-butylphosphonium carboxylate was approximately 0.035 ± 0.001 (mole fraction) in every system. The dissociation enthalpies of tetra-n-butylphosphonium carboxylate semiclathrate hydrates were measured by differential scanning calorimetry. The dissociation enthalpies of TBP-For, TBP-Ace, and TBP-Lac semiclathrate hydrates were (187 ± 3), (193 ± 3), and (177 ± 3) J·g-1, respectively.Jin Shimada, Masami Shimada, Takeshi Sugahara, et al. Phase Equilibrium Relations of Semiclathrate Hydrates Based on Tetra-n-butylphosphonium Formate, Acetate, and Lactate. Journal of Chemical & Engineering Data, 63 (9), 3615-3620, September 13, © 2018 American Chemical Society. https://doi.org/10.1021/acs.jced.8b0048