The acid-soluble residue from end-of-life NdFeB magnet waste is often introduced into the ferrous metallurgical process to recover iron oxide as a value added product, but this approach has a low economic value. In this work, a ferrous chloride solution from NdFeB magnet waste containing rare earth elements, which was obtained after the leaching and impurity removal process from the acid-soluble residue, was used as the raw material. The crystallization mechanism and reaction kinetics in the oxidation precipitation process were studied to prepare high-purity iron oxide. The results showed that the growth of γ-FeOOH flakes with smooth surfaces and uniform morphologies could be explained by Ostwald's ripening theory. The apparent activation energy of the oxidative precipitation reaction of ferrous iron was 56.8 kJ/mol, indicating a chemically controlled reactions. Under the optimal oxidative precipitation conditions, the precipitation efficiency of ferrous ions and rare earth elements was 98.8 % and < 1 %, respectively. The precipitated product was well-crystallized γ-FeOOH with an aggregated flake morphology. It was roasted at 700 °C for 2 h to obtain an iron oxide product with a purity of 99.6 %. This study could provide technical support for the valuable utilization of acid-soluble residues from NdFeB magnet waste and to propose new methods for the utilization of other iron wastes and residues.

中文翻译：

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从报废的 NdFeB 磁废料中制备高纯度氧化铁


报废钕铁硼磁废料中的酸溶性残留物通常被引入黑色冶金工艺中，以回收氧化铁作为增值产品，但这种方法的经济价值较低。本工作以含稀土元素的钕铁硼磁渣为原料，从酸溶性残渣中经浸出除杂过程得到的含稀土元素的氯化亚铁溶液。研究了氧化沉淀过程中的结晶机理和反应动力学，制备了高纯度的氧化铁。结果表明，具有光滑表面和均匀形态的 γ-FeOOH 薄片的生长可以用 Ostwald 的成熟理论来解释。亚铁氧化沉淀反应的表观活化能为 56.8 kJ/mol，表明发生了化学控制的反应。在最佳氧化沉淀条件下，亚铁离子和稀土元素的沉淀效率分别为 98.8 % 和 < 1 %。沉淀产物为结晶良好的 γ-FeOOH，具有聚集的片状形态。在 700 °C 下烘烤 2 小时，得到纯度为 99.6 % 的氧化铁产品。本研究可为钕铁硼磁渣中酸溶性残渣的有价值利用提供技术支持，并为其他铁废料和残渣的利用提出新方法。