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℃焙烧获得，适合Nd的选择性浸出。虽然600℃的焙烧仍不足以完全氧化，但720℃的焙烧使NdFeO形成。这些特性与焙烧条件一起影响浸出行为。在600℃焙烧的粒径为32μm的NdFeB粉末样品中，表现出最高的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。采用控制相系统，通过将颗粒尺寸减小至16μm，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℃焙烧条件的浸出效率最低。副产物Fe3O也表现出良好的抗浸出性，浸出3-4小时后，其浸出效率仅为5-6%。