Oxidative roasting of Nd–Fe‒B permanent magnets prior to leaching improves the selectivity in the recovery of rare-earth elements over iron. However, the dissolution rate of oxidatively roasted Nd–Fe‒B permanent magnets in acidic solutions is very slow, often longer than 24 h. Upon roasting in air at temperatures above 500 °C, the neodymium metal is not converted to Nd₂O₃, but rather to the ternary NdFeO₃ phase. NdFeO₃ is much more difficult to dissolve than Nd₂O₃. In this work, the formation of NdFeO₃ was avoided by roasting Nd–Fe‒B permanent magnet production scrap in argon atmosphere, having an oxygen content of \( p_{{{\text{O}}_{2} }} \, \le \,10^{ - 20} \;{\text{atm}}, \) with the addition of 5 wt% of carbon as an iron reducing agent. For all the non-oxidizing iron roasting conditions investigated, the iron in the Nd–Fe‒B scrap formed a cobalt-containing metallic phase, clearly distinct from the rare-earth phase at microscopic level. The thermal treatment was optimized to obtain a clear phase separation of metallic iron and rare-earth phase also at the macroscopic level, to enable easy mechanical removal of iron prior to the leaching step. The sample roasted at the optimum conditions (i.e., 5 wt% carbon, no flux, no quenching step, roasting temperature of 1400 °C and roasting time of 2 h) was leached in the water-containing ionic liquid betainium bis(trifluoromethylsulfonyl)imide, [Hbet][Tf₂N]. A leaching time of only 20 min was sufficient to completely dissolve the rare-earth elements. The rare-earth elements/iron ratio in the leachate was about 50 times higher than the initial rare-earth elements/iron ratio in the Nd–Fe‒B scrap. Therefore, roasting in argon with addition of a small amount of carbon is an efficient process step to avoid the formation of NdFeO₃ and to separate the rare-earth elements from the iron, resulting in selective leaching for the recovery of rare-earth elements from Nd–Fe‒B permanent magnets.

中文翻译：

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Nd-Fe‒B永磁体的选择性焙烧作为离子液体强化浸出的预处理步骤

浸出前对Nd-Fe toB永磁体进行氧化焙烧可提高稀土元素对铁的回收率。但是，氧化焙烧的Nd-Fe‒B永磁体在酸性溶液中的溶解速度非常慢，通常会超过24小时。在高于500°C的温度下在空气中烘烤时，钕金属不会转化为Nd ₂ O ₃，而是会转化为三元NdFeO ₃相。NdFeO ₃比Nd ₂ O ₃难溶解得多。在这项工作中，通过在氩气中焙烧Nd-Fe‒B永磁生产废料来避免NdFeO ₃的形成，氧含量为\（p _ {{{{text {O}} _ {2}}} \，\ le \，10 ^ {-20} \; {\ text {atm}}，\）加上5 wt％的碳作为铁还原剂。在所研究的所有非氧化性铁焙烧条件下，Nd-Fe‒B废料中的铁形成了含钴的金属相，在微观上明显不同于稀土相。对热处理进行了优化，以便在宏观水平也获得金属铁和稀土相的清晰相分离，从而能够在浸出步骤之前轻松地机械去除铁。在最佳条件下（即碳含量为5 wt％，无助熔剂，无淬火步骤，焙烧温度为1400°C和焙烧时间为2 h）焙烧的样品浸入含水离子液体双（三氟甲基磺酰基）酰亚胺中，[Hbet] [Tf ₂N]。仅20分钟的浸提时间就足以完全溶解稀土元素。渗滤液中的稀土元素/铁比约为Nd-Fe‒B废料中的初始稀土元素/铁比的50倍。因此，在氩气中加入少量碳进行焙烧是避免NdFeO ₃形成并从铁中分离稀土元素的有效工艺步骤，从而有选择地进行浸提以从中回收稀土元素。钕铁硼永磁体。