Dy Permeation through an Alloy Diaphragm Using Electrochemical Implantation and Displantation

Abstract

The molten salt electrochemical process has been studied by Ito and co-workers including the present authors (1-12) and many other researchers (13-16). The present authors reported a unique phenomenon during the electrochemical formation of Dy-Ni alloys in molten LiCl-KCl-DyCl3: DyNi2 film with thickness of 60 µm was formed in 2 h at 700 K (1). The growth rate of DyNi2 was extremely high, compared with the conventional solid phase diffusion at temperatures lower than half of the melting temperature of DyNi2, i.e., 1531 K (17). In addition, the growth rate was found to be strongly affected by electrochemical parameters such as potential and current density. This phenomenon was termed “electrochemical implantation” (1), because it was different from the ordinary concepts of electrodeposition followed by solid phase diffusion. The authors also reported that anodic polarization of the formed DyNi2resulted in the rapid dissolution of Dy to form other Dy-Ni phases. The obtained phase and morphologies were dependent on the applied potential. This phenomenon was named “electrochemical displantation” (1).We proposed a new separation and recovery process for RE metals from scraps using molten salt and an alloy diaphragm (18-20). The new process is based on our previously discovered phenomena, i.e., “electrochemical implantation” and “electrochemical displantation” (1).This new process was first applied to chloride melts, and the separation of Dy from Nd and Pr were investigated using Cu, Ni and Zn cathodic electrodes in molten LiCl-KCl-DyCl3-NdCl3 (21-24) and LiCl-KCl-DyCl3-NdCl3-PrCl3 systems (25). The highest mass ratio of Dy/Nd+Pr in Dy-Nd-Pr-Ni alloy sample was found to be 50 at 0.65 V (vs. Li+/Li) for 1 h by ICP-AES. In this study, the investigation of Dy permeation through an alloy diaphragm using electrochemical implantation and displantation was investigated. The Dy permeation experiment was conducted with two kinds of electrolytic cell in molten LiCl-KCl systems at 723 K in order to confirm the theoretical feasibility of the present process.