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Selective separation of rare earths from spent Nd-Fe-B magnets using two-stage ammonium sulfate roasting followed by water leaching
Hydrometallurgy ( IF 4.8 ) Pub Date : 2021-05-13 , DOI: 10.1016/j.hydromet.2021.105626
Fupeng Liu , Feixiong Chen , Longjun Wang , Shuaibing Ma , Xingbang Wan , Jinliang Wang

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.



中文翻译:

使用硫酸铵焙烧和水浸两阶段从废 Nd-Fe-B 磁体中选择性分离稀土

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。

更新日期:2021-05-30
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