Investigation of Dy Permeation through Dy Alloy Diaphragm Using Molten Salt Electrolysis

Abstract

We have been developing a new process for the separation and recovery of rare earth metals using molten salt electrolysis and an alloy diaphragm. The diaphragm functions as a bipolar electrode and enables selective permeation of rare earth ions via the following steps: (1) Rare earth ions are produced by anodic dissolution of wastes containing rare earth metals in the anode room. (2) The rare earth ions are electrochemically reduced at the surface of the alloy diaphragm to form rare earth alloy. (3) The rare earth metals in the alloy diffuse to the other side surface of the alloy diaphragm and are dissolved into the cathode room as rare earth ions by anodic oxidation. (4) The rare earth ions in the cathode room are recovered as rare earth metals or alloys on a transition metal electrode. In this study, the permeation experiment was conducted with a new electrolytic cell. The current density due to alloy formation and anodic oxidation of Dy were measured individually using two potentio/galvanostats, and the results were discussed. DyCl3 was added to LiCl-KCl eutectic melts and Dy was permeated through a DyNi2 diaphragm film by potentiostatic electrolysis. The permeation rate (i.e. current density) was 280 A/m-2and the current efficiency was 98 % (max).