Selective Permeation of Neodymium Through an Alloy Diaphragm in Molten Chloride Systems

Abstract

As part of an ongoing study of a new recycling process for Nd-Fe-B permanent magnets, selective permeation of Nd through an RE-Ni (RE=Nd and Dy) alloy diaphragm was investigated in LiCl-KCl eutectic melts containing NdCl3 and DyCl3 or LaCl3 at 450°C. Selective permeation of Nd was achieved by controlling the potential of the alloy diaphragm, which functions as a bipolar electrode. Interestingly, EDX analysis revealed that the molar ratio of Nd/Dy in the alloy diaphragm was less than 0.05, which is two orders of magnitude lower than that of the permeated amount. These results suggest that the transportation rate of Nd atoms in the alloy diaphragm was extremely high compared to that of Dy. In order to obtain further insight into the transportation mechanism of RE atoms in the alloy diaphragm, STEM observations were also carried out. The results suggested that the transportation of RE atoms cannot be explained by simple grain boundary diffusion.

Electrochemical Formation of Elemental Boron in LiCl–KCl–KBF4 at 723 K

“…Finally, the RE element is recovered as a metal or alloy by electrodeposition on a cathode in the catholyte. [6][7][8] By using a phenomenon in which a specific RE elements can be alloyed and dealloyed rapidly with iron-group (IG) metals by electrochemical methods in molten salts, the RE-IG alloy is used as the alloy diaphragm and acts as a bipolar electrode. Selective RE permeation through the alloy diaphragm proceeds via three steps: (a) reduction and alloying of RE ions on the anolyte side of the diaphragm, (b) transportation of RE atoms in the diaphragm, and (c) oxidation and dissolution of RE elements on the catholyte side of the diaphragm.…”

“…9,10 Because the reaction rate in each step is dependent on the type of RE elements and the electrolytic conditions, Nd and Dy can be separated and recovered from waste magnets. 7 Generally, only RE elements are dissolved from the magnet in our process, as mentioned above. However, B and Fe contained in the Nd-Fe-B magnet may accidentally dissolve from the magnet as well.…”