Permeation Tendency of Rare-earth Elements through a Ni-based Alloy Diaphragm in LiCl–KCl Eutectic Melts (Supporting Information)

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 °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.

本研究通过在450°C的LiCl-KCl共晶熔体中使用稀土(Ni)合金膜，考察了La、Ce、Pr、Nd、Gd和Tb的渗透趋势。该实验作为一项针对Nd-Fe-B永磁体新型回收工艺的研究的一部分而进行，鉴于废弃的磁体可能含有La、Ce、Pr、Gd和Tb等稀土杂质。渗透实验在两种条件下进行，这些条件预计能够实现Nd和Dy的选择性渗透，这一结论基于我们之前的研究，该研究证实了Nd和Dy的选择性渗透。结果发现，Gd和Tb的渗透趋势与Dy相似，而Ce和Pr的行为则类似于Nd。在所有实验条件下，La的渗透几乎可以忽略不计。这些趋势基于所施加电位和RENi2/RENi3（RE = Ce、Pr、Nd、Gd、Tb和Dy）以及La7Ni16/LaNi3的平衡电位进行讨论。渗透实验后合金膜的横截面通过扫描电子显微镜/能谱仪进行了分析。在合金膜中检测到了相对较高的Gd、Tb和Dy浓度，而La、Ce、Pr和Nd的浓度在两次实验中均较低。