Selective leaching behavior of the spent NdFeB magnets was investigated to find out how controlled phase system through the roasting conditions gave an impact on the performance of the selective leaching. The pre-formed NdO by the selective oxidation made it possible to prevent the formation of NdFeO at high roasting temperature. This resulted in the ideal NdO and FeO phase system, which was obtained by roasting at 660 °C, suitable for the selective leaching of Nd. While the roasting at 600 °C was still not enough to get full oxidation, the roasting at 720 °C made the NdFeO formed. These characteristics with the roasting conditions affected leaching behavior. The NdFeB powder sample of 32 μm particle diameter, roasted at 600 °C showed the highest Nd leaching efficiency as well as the highest Fe leaching efficiency, which seemed to be ascribed to the existence of the metallic Fe. The poor leaching efficiency for the large powder size after roasting was ascribed to the poor diffusion characteristic of the HSO solution. With the controlled phase system, the 100% leaching efficiency of Nd could be obtained by reducing the particle size to 16 μm. The formation of NdFeO as a co-product, which had resistance to the reaction with the leaching agent, could prevent the dissolution of NdO around the NdFeO layer. Thus, the 720 °C roasting condition showed the lowest leaching efficiency. The co-product FeO also showed good resistance to leaching so its leaching efficiency was just 5–6% after the leaching time of 3–4 h.

中文翻译：

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选择性氧化和焙烧工艺相结合处理的废 NdFeB 磁体中 Nd 的选择性浸出行为


研究了废 NdFeB 磁体的选择性浸出行为，以了解通过焙烧条件控制的相系统如何影响选择性浸出的性能。通过选择性氧化预先形成的 NdO 可以防止在高焙烧温度下形成 NdFeO。这产生了理想的 NdO 和 FeO 相体系，该体系通过 660 °C 焙烧获得，适合 Nd 的选择性浸出。虽然 600°C 的焙烧仍不足以完全氧化，但 720°C 的焙烧使得 NdFeO 形成。这些特性与焙烧条件一起影响浸出行为。在 600 °C 下焙烧的粒径为 32 μm 的 NdFeB 粉末样品显示出最高的 Nd 浸出效率以及最高的 Fe 浸出效率，这似乎归因于金属 Fe 的存在。焙烧后大粉末的浸出效率差是由于 H2SO4 溶液的扩散特性差。通过控制相系统，通过将颗粒尺寸减小至 16 μm，可以获得 100% 的 Nd 浸出效率。 NdFeO作为副产物的形成，具有抵抗与浸出剂反应的能力，可以阻止NdFeO层周围NdO的溶解。因此，720°C 的焙烧条件显示出最低的浸出效率。副产品 Fe3O 也表现出良好的耐浸出性，因此在浸出时间为 3-4 小时后，其浸出效率仅为 5-6%。