Metal Extraction and Recycling Division, CSIR-National Metallurgical Laboratory, Jamshedpur 831007, India; Academy of Scientific and Innovative Research (AcSIR), CSIR-NML, Jamshedpur 831007, India.
Metal Extraction and Recycling Division, CSIR-National Metallurgical Laboratory, Jamshedpur 831007, India.
Waste Manag. 2018 May;75:486-498. doi: 10.1016/j.wasman.2018.01.033. Epub 2018 Feb 1.
Increasing demands of rare earth (RE) metals for advanced technological applications coupled with the scarcity of primary resources have led to the development of processes to treat secondary resources like scraps or end of life products that are often rich in such metals. Spent NdFeB magnet may serve as a potential source of rare earths containing around ∼30% of neodymium and other rare earths. In the present investigation, a pyro-hydrometallurgical process has been developed to recover rare earth elements (Nd, Pr and Dy) from the spent wind turbine magnet. The spent magnet is demagnetized and roasted at 1123 K to convert rare earths and iron to their respective oxides. Roasting of the magnet not only provides selectivity, but enhances the leaching efficiency also. The leaching of the roasted sample with 0.5 M hydrochloric acid at 368 K, 100 g/L pulp density and 500 rpm for 300 min selectively recovers the rare earth elements almost quantitatively leaving iron oxide in the residue. Leaching of rare earth elements with hydrochloric acid follows the mixed controlled kinetic model with activation energy (E) of 30.1 kJ/mol in the temperature range 348-368 K. The leaching mechanism is further established by characterizing the leach residues obtained at different time intervals by scanning electron microscopy- energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction (XRD). Individual rare earth elements from the leach solution containing 16.8 g/L of Nd, 3.8 g/L Pr, 0.28 g/L of Dy and other minor impurity elements could be separated by solvent extraction. However, mixed rare earth oxide of 99% purity was produced by oxalate precipitation followed by roasting. The leach residue comprising of pure hematite has a potential to be used as pigment or can find other applications.
日益增长的对先进技术应用所需的稀土（RE）金属的需求，加上主要资源的稀缺，促使人们开发了处理二次资源的工艺，例如废料或报废产品，这些资源通常富含这些金属。废弃的钕铁硼磁铁可能是一种潜在的稀土来源，其中含有约 30%的钕和其他稀土元素。在本研究中，开发了一种火法-湿法冶金工艺，从报废风力涡轮机磁铁中回收稀土元素（Nd、Pr 和 Dy）。将废弃的磁铁退磁并在 1123 K 下进行焙烧，以使稀土和铁转化为各自的氧化物。焙烧不仅提供了选择性，而且还提高了浸出效率。在 368 K、100 g/L 矿浆密度和 500 rpm 的条件下，用 0.5 M 盐酸浸出焙烧后的样品 300 min，可选择性地几乎定量回收稀土元素，而将氧化铁留在残渣中。用盐酸浸出稀土元素遵循混合控制动力学模型，在 348-368 K 的温度范围内，活化能（E）为 30.1 kJ/mol。通过在不同时间间隔用扫描电子显微镜-能量色散 X 射线光谱（SEM-EDS）和 X 射线衍射（XRD）对浸出残渣进行表征，进一步确定了浸出机理。从含有 16.8 g/L Nd、3.8 g/L Pr、0.28 g/L Dy 和其他少量杂质元素的浸出液中，可以通过溶剂萃取分离出个别稀土元素。然而，通过草酸盐沉淀和随后的焙烧可以生产出 99%纯度的混合稀土氧化物。包含纯赤铁矿的浸出残渣具有作为颜料的潜力，或者可以找到其他应用。
