Takashi Nagai

Abstract:

Rare Earth (RE) metals are used as various functional materials, including permanent magnets, hydrogen storage alloys and luminescent materials. The consumption of neodymium (Nd) and dysprosium (Dy) is increasing dramatically because of an exceptionally high demand for Nd-Fe-B-(Dy) magnets and a significant amount of the magnets is wasted. Therefore it is important to develop a recovery process of the elements from the wasted magnets. In order to design a recovery process, the thermodynamic information of Nd and Dy in iron (Fe) -based alloys is necessary. The thermodynamic information was measured by double Knudsen cell mass spectrometry at high temperature. The Gibbs energies of formation of the intermetallic compounds between Nd and Fe, and Dy and Fe were estimated. The activity of Nd in Fe/Nd2Fe17 equilibrium at 1473 K is calculated to be 0.15, that of Dy in Fe/Dy2Fe17 equilibrium to be 0.0057 with the estimated data. Using this difference, a new recovery process was designed. In the recovery process, Nd is extracted from the magnets containing Nd and Dy by silver (Ag) at high temperature. Nd is separated as Ag-Nd alloy form magnet, which is Fe-based alloy with Dy. Nd and Dy are recovered and separated at once. The process was demonstrated in this study. Wasted magnet and Ag in a graphite crucible were charged and heated in inert Ar atmosphere in an electric resistance furnace. Nd can be extracted about 80 mass% by Ag rapidly, although only 20 mass % Dy was extracted in the same experimental condition. And Nd was recovered from Nd-Ag alloy by hydrochloric acid leaching.