The research presents an effective approach to achieve the selective separation of rare earth elements (REEs) from waste Nd-Fe-B magnets. Investigations show that the use of a two-stage roasting process can significantly reduce the amount of ammonium sulfate required and improve the separation efficiencies of REEs. During the first low-temperature roasting stage, almost 80% of REEs can be transformed into RE₂(SO₄)₃ or NH₄RE(SO₄)₂ at 400 °C within 1 h, whilst simultaneously iron and other impurities are converted into insoluble metal ammonium sulfates. These intermediate products can then be subjected to a further roasting procedure at 750 °C for 2 h, leading to an extraction of REEs of up to 96%. In contrast, the extraction of the related impurities: Fe, Al, Cu and Co is only 0.008%, 0.27%, 1.64% and 3.48%, respectively. Through the analysis and characterization of the calcine and leach residue, it was found that the decomposition of NH₄RE(SO₄)₂ and the reaction of Fe₂(SO₄)₃ and RE₂O₃ together improve the extraction of REEs during the second roasting stage. After separation of REEs, the main phase present in the leach residue is hematite, which can be recycled as a feedstock material for iron or steelmaking processes. Moreover, waste gases from this process – like NH₃, SO₂, and SO₃ - can also be recovered and reused in the preparation of (NH₄)₂SO₄, which significantly reduces the costs of the recycling operations. Overall, this newly developed process has considerable environmental and economic advantages for the recovery of valuable metals from waste Nd-Fe-B magnets.

该研究提出了一种从废弃 Nd-Fe-B 磁体中选择性分离稀土元素 (REE) 的有效方法。研究表明，采用两段焙烧工艺可以显着降低硫酸铵的用量，提高稀土元素的分离效率。在第一个低温焙烧阶段，几乎 80% 的 REE 可以转化为 RE ₂ (SO ₄ ) ₃或 NH ₄ RE(SO ₄ ) ₂在 400 °C 下 1 小时内，同时铁和其他杂质转化为不溶性金属硫酸铵。然后，可以将这些中间产物在750°C的温度下进一步烘烤2小时，从而使REE的提取率高达96％。相比之下，相关杂质Fe、Al、Cu和Co的提取率分别仅为0.008%、0.27%、1.64%和3.48%。通过对煅烧残渣和浸出残渣的分析表征，发现NH ₄ RE(SO ₄ ) ₂的分解和Fe ₂ (SO ₄ ) ₃与RE ₂ O _{3 的反应}共同提高了第二焙烧阶段稀土元素的提取。稀土元素分离后，浸出残渣中的主要相是赤铁矿，可作为炼铁或炼钢工艺的原料回收。此外，该过程产生的废气（如 NH ₃、SO ₂和 SO ₃）也可以回收并重新用于 (NH ₄ ) ₂ SO ₄的制备，这显着降低了回收操作的成本。总体而言，这种新开发的工艺在从废弃 Nd-Fe-B 磁体中回收有价值的金属方面具有相当大的环境和经济优势。