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 α-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.