Masahiko Matsumiya

By Masahiko Matsumiya

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.

Part of the book: Electroplating of Nanostructures

By Masahiko Matsumiya

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.

Part of the book: Ionic Liquids