The electrochemical formation of Dy–Ni alloys was investigated in molten CaCl2–DyCl3 (1.0 mol%) at 1123 K. Cyclic voltammetry indicated the formation of Dy–Ni alloys at more negative than 1.0 V vs. Ca2+/Ca. Higher cathodic currents were observed from approximately 0.6 V, which indicated the formation of Dy–Ni alloys having higher Dy concentration. An open-circuit potentiometry was carried out with Mo and Ni electrodes before and after the addition of DyCl3. After the potentiostatic electrolysis of Mo electrode at −0.50 V for 30 s in molten CaCl2–DyCl3, only one potential plateau appeared at 0.33 V, which was interpreted as the equilibrium potential of Dy3+/Dy. In contrast, four potential plateaus were observed at 0.49, 0.62, 0.87, and 1.04 V for Ni electrode after the potentiostatic electrolysis at 0.25 V for 15 min. According to energy-dispersive X-ray spectroscopy and X-ray diffraction of the electrolyzed samples, the four potential plateaus correspond to the two-phase coexisting states of (DyNi + DyNi2), (DyNi2 + DyNi3), (DyNi3 + DyNi5), and (DyNi5 + Ni). Standard Gibbs energies of formation were calculated for Dy–Ni alloys.

The electrochemical formation of Neodymium–Nickel (Nd–Ni) alloys was investigated in a molten CaCl2–NdCl3 (1.0 mol%) system at 1123 K. Cyclic voltammograms for Molybdenum (Mo) and Ni electrodes showed the electrodeposition/dissolution of metallic Nd and the formation/dissolution of Nd–Ni alloys, respectively. The equilibrium potential of Nd3+/Nd was determined at 0.27 V (vs. Ca2+/Ca) by open-circuit potentiometry for a Mo electrode. The potentials of 0.48, 0.68, and 0.95 V, corresponding to the two-phase coexisting states of (NdNi2 + NdNi3), (NdNi3 + NdNi5), and (NdNi5 + Ni), respectively, were confirmed using energy-dispersive X-ray spectroscopy and X-ray diffraction of the Ni electrode electrolyzed samples. The optimum electrolysis conditions for the Nd and Dysprosium (Dy) separation were discussed, and the standard Gibbs energies of formation were calculated for Nd–Ni alloys.

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Here we study the recovery process of rare earth metals from Nd magnet scraps via electrolysis in a molten salt and with an alloy diaphragm. In the present study, the electrochemical formation of Dy-Fe and Nd-Fe alloys, which was an important step of the recovery process, was investigated in molten CaCl2-LiCl systems at 873 K. Two Dy-Fe alloy samples were prepared by potentiostatic electrolysis of Fe plate electrodes at 0.30 V (vs. Li+/Li) and 0.50 V for 1 h in CaCl2-LiCl-DyCl3 (0.50 mol% added). The formation of DyFe5 was suggested by X-ray diffraction (XRD). Potentiostatic electrolysis was also conducted at 0.30 V and 0.50 V for 1 h using Fe plate electrodes in CaCl2-LiCl-NdCl3 (0.50 mol% added). XRD analysis suggested the formation of Nd2Fe17 for both samples. The equilibrium potentials for (DyFe5+Fe) and (Nd2Fe17+Fe) coexisting phases were indicated.