Permeation Tendency of Rare-earth Elements through a Ni-based Alloy Diaphragm in LiCl-KCl Eutectic Melts

The permeation tendency of La, Ce, Pr, Nd, Gd, and Tb was examined using a rare earth (RE)-Ni alloy diaphragm in LiCl-KCl eutectic melts at 450 degrees C. This experiment was conducted as a part of an ongoing study on a new recycling process for Nd-Fe-B permanent magnets, because wasted magnets may contain La, Ce, Pr, Gd, and Tb as RE impurities. The permeation experiments were performed under two conditions that were expected to enable the selective permeation of Nd and Dy, respectively, which were determined on the basis of our previous studies confirming the selective permeation of Nd and Dy. As a result, Gd and Tb showed a similar permeation tendency to Dy, whereas Ce and Pr behaved like Nd. Under both experimental conditions, La hardly permeated. These tendencies are discussed on the basis of the applied potential and the equilibrium potential for RENi2/RENi3 (RE = Ce, Pr, Nd, Gd, Tb, and Dy) and La7Ni16/LaNi3. The cross sections of the alloy diaphragm after the permeation experiments were analyzed via scanning electron microscopy/energy-dispersive X-ray spectroscopy. Relatively high concentrations of Gd, Tb, and Dy were detected in the alloy diaphragm, whereas the concentrations of La, Ce, Pr, and Nd were low in both experiments.