Prediction of Diffusion Behaviors Between Liquid Magnesium and Neodymium-Iron-Boron Magnets

The extraction behavior of the rare earth metal Nd from Nd-Fe-B alloy was investigated using Mg, a typical low-melting-point element. Among the alloy components, Nd has a selective affinity with Mg; thus, Nd was successfully diffused into the Mg at a temperature of 1023 K. This is significantly above the Mg melting point. The Nd diffusion sequence during the solid (Nd-Fe-B) liquid (Mg) reaction was examined using scanning and transmission electron microscopy, while energy dispersive spectroscopy and X-ray diffractometry were used for the phase characterization. As the liquid Mg encountered the solid Nd-Fe-B, the Nd began to diffuse into the Mg; this was followed by the formation of Nd-Mg compounds within the alpha-Mg matrix. In addition, the Nd-deficient solid was converted to Fe2B. The Mg infiltration sequence and the reaction mechanism between the phases were also examined. This investigation presents a proposed pyro-metallurgical method for recycling critical rare earths in an energy-conserving and environmentally friendly manner, as an alternative to the conventionally used hydro-metallurgy.