Pyrometallurgical recovery of rare-earth elements from NdFeB wastes is affected by the quality of the raw materials, and mixed rare-earth products add little value. Therefore, this study investigates NaBF4 fluoride roasting for the recovery of rare-earth elements and its underlying mechanisms. Reasonable roasting temperatures were determined based on thermodynamic calculations, and single-factor experiments were conducted. When roasted at 600 °C for 30 min with 65 % NaBF4, the fluorination rate of rare-earth elements reached 95.83 %. The composition of the clinker mesophase after roasting under different conditions was analyzed. At high temperatures, oxygen heteroatoms entered the crystal lattice of the rare-earth fluorides, which were subsequently removed during acid leaching, thereby reducing the recovery rate. A three-factor, three-level Box–Behnken test was conducted using the response surface methodology to analyze the effects of various factors and their interactions on the fluorination rate. Thus, an experimental basis for the recovery of rare-earth elements from NdFeB by fluoridation roasting was established. The roasting temperature had the greatest effect on the fluorination rate, followed by the roasting time and amount of NaBF4. The model predicted an optimal fluorination rate of 98.63 % when the material was roasted at 573 °C for 25 min with 59 % NaBF4. The clinker was acid-leached under optimal conditions (2.5 h at 80 °C with 9 M HCl and a liquid–solid ratio of 4 mL/g), and the Purity of fluorinated rare earths reached 99.39%. These results provide theoretical and experimental support for the application of pyrometallurgy in the recovery of rare-earth elements from NdFeB wastes.

中文翻译：

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NaBF4氟化法从钕铁硼废料中回收稀土元素的机理及实验研究


从钕铁硼废料中火法冶金回收稀土元素受原料质量的影响，混合稀土产品几乎没有价值。因此，本研究研究了 NaBF4 氟化物焙烧对稀土元素回收的作用及其潜在机制。根据热力学计算确定合理的焙烧温度，并进行单因素实验。当在 600 °C 下用 65 % 的 NaBF4 烘烤 30 分钟时，稀土元素的氟化率达到 95.83 %。分析了不同条件下烘烤后熟料中间相的组成。在高温下，氧杂原子进入稀土氟化物的晶格，随后在酸浸过程中被去除，从而降低了回收率。使用响应面方法进行了三因素、三水平 Box-Behnken 检验，以分析各种因素及其相互作用对氟化速率的影响。从而建立了通过氟化焙烧从钕铁硼中回收稀土元素的实验基础。焙烧温度对氟化速率的影响最大，其次是焙烧时间和 NaBF4 含量。该模型预测，当材料在 573 °C 下用 59 % NaBF4 烘烤 25 min 时，最佳氟化率为 98.63 %。熟料在最佳条件下（80 °C，9 M HCl，液固比4 mL/g，2.5 h）进行酸浸，氟化稀土纯度达到99.39%。这些结果为火法冶金技术在钕铁硼废料稀土元素回收中的应用提供了理论和实验支持。