The increased demand for rare earth elements in advanced technological applications and supply shortages call for metal recovery from secondary sources. Permanent magnet (Nd2Fe14B or NdFeB) may serve as a potential secondary source due to its high rare earth (Nd+Pr+Dy: ∼30 %) content and its vast application. The present study utilizes a chloridizing roasting (CaCl2.2 H2O) pre-treatment process followed by water leaching, acid leaching (0.5 M HCl, S/L =1/10 g/ml, 90 °C, 3 h), oxalic acid precipitation and calcination (850 °C, 2 h) to obtain mixed rare earth oxides. The process was optimized based on temperature (400–700 °C), dosage (CaCl2.2H2O: NdFeB=0.5:1–2.5:1), and time (30–120 min) on the rare earth dissolution. The theoretical activation energy for the chloridizing roasting process is estimated as 22.3 (OFW) and 16.7 kJ/mol (KAS), while the experimental activation energy for Nd and Dy dissolution was determined to ∼29.3 and ∼17.7 kJ/mol, respectively depicting product layer diffusion-controlled kinetics. Higher dosages of CaCl2.2H2O (1.5:1 and 2:1) favored NdOCl formation, thereby, higher dissolution; however, further higher dosage (2.5:1) leads to reduced Nd dissolution due to higher CaO formation and acid consumption by Ca during leaching. Incomplete oxidation at lower temperatures (400 °C) and iron dissolution impair the Nd dissolution and selectivity. Excessive oxidation at >700 °C favors the formation of NdFeO3, decreasing Nd dissolution. The maximum dissolution of Nd was ∼89 %, while for Dy, it was ∼88 % at optimum conditions of 600 °C, 90 min, 2:1. Water leaching post-roasting leads to ∼87 % Ca removal and the precipitation efficiency of rare earth oxalates was 99 %. The overall extraction for rare earth elements was ∼89 %, and 1 kg of NdFeB powder can yield ∼285 g of rare earth oxides (∼239 g Nd2O3, ∼14 g Dy2O3) with 96 % purity. Further, this study demonstrates that using CaCl2.2 H2O as a solid chlorinating agent in chlorination roasting enhances recovery rates of mixed rare earth oxides while providing a safer and more environment-friendly alternative for industrial applications.

中文翻译：

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废钕铁硼磁体的氯化焙烧研究用于回收稀土值


先进技术应用中对稀土元素的需求增加和供应短缺要求从二次来源回收金属。永磁体（Nd2Fe14B 或 NdFeB）由于其高稀土含量 （Nd+Pr+Dy： ∼30 %） 及其广泛的应用，可以作为潜在的二次来源。本研究采用氯化焙烧 （CaCl2.2 H2O） 预处理工艺，然后进行水浸、酸浸（0.5 M HCl，S/L =1/10 g/ml，90 °C，3 h）、草酸沉淀和煅烧（850 °C，2 h）得到混合稀土氧化物。根据温度 （400–700 °C）、用量 （CaCl2.2H2O： NdFeB=0.5：1–2.5：1） 和时间 （30–120 min） 对稀土溶解进行优化。氯化焙烧过程的理论活化能估计为 22.3 （OFW） 和 16.7 kJ/mol （KAS），而 Nd 和 Dy 溶解的实验活化能分别为 ∼29.3 和 ∼17.7 kJ/mol，描绘了产物层扩散控制的动力学。较高剂量的 CaCl2.2H2O （1.5：1 和 2：1） 有利于 NdOCl 的形成，因此，更高的溶解度;然而，由于浸出过程中 CaO 的形成和 Ca 的酸消耗较高，进一步升高的剂量 （2.5：1） 会导致 Nd 溶解减少。在较低温度 （400 °C） 下的不完全氧化和铁溶解会损害 Nd 的溶解和选择性。>700 °C 的过度氧化有利于 NdFeO3 的形成，从而减少 Nd 的溶解。Nd 的最大溶出度为 ∼89 %，而 Dy 的最大溶出度为 ∼88 %，在 600 °C、90 分钟、2：1 的最佳条件下。焙烧后水浸出导致 ∼87% 的 Ca 去除，稀土草酸盐的沉淀效率为 99%。 稀土元素的总提取率为 ∼89 %，1 公斤钕铁硼粉末可产生约 285 克纯度为 96% 的稀土氧化物（∼239 g Nd2O3，∼14 g Dy2O3）。此外，本研究表明，在氯化焙烧中使用 CaCl2.2 H2O 作为固体氯化剂可以提高混合稀土氧化物的回收率，同时为工业应用提供更安全、更环保的替代方案。