In this study, deep eutectic solvents (DESs) were employed as environmentally friendly alternatives of inorganic acid to selectively leach REEs from waste NdFeB magnets. Three DESs were tested, effective for light REE leaching, and preliminary experiments were conducted to study the selective leaching of REEs, using synthetic materials, NdO, Fe, FeO, and FeO. The findings suggest that neodymium and iron should exist as NdO and FeO, respectively, for selective leaching. To enhance the selective leaching of the NdFeB magnet, three pretreatment methods were applied: oxidative roasting, NaOH digestion, and NaOH digestion-oxidative roasting. During the oxidative roasting, NdFeO was formed, and it hindered REE leaching, achieving the highest REE leaching efficiency of 22.5% in the guanidine hydrochloride (GUC)-lactic acid (LA) DES. To counteract NdFeO formation, the NaOH digestion was introduced, yielding Nd(OH) and FeO. These were then converted to NdO and FeO through oxidative roasting. With the NaOH-digested product, selective REE leaching was achieved solely with the ethylene glycol (EG)-maleic acid (MA) DES, while it was feasible in all three DESs with the NaOH digestion-oxidative roasting. The EG-MA DES displayed the highest selectivity, with a leaching efficiency of 97.3% Nd and 0.8% Fe. Additionally, the solvent could be reused at least twice, and the leaching efficiencies of 97% for Nd and 0.7% for Fe were maintained. This selective leaching technique benefits from using environmentally friendly solvents compared to the traditional inorganic acid leaching and demonstrates high REE selectivity and solvent reusability, suggesting a novel method for REE recovery via DESs.

中文翻译：

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预处理方法对低共熔溶剂选择性浸出NdFeB永磁体稀土元素的影响


在这项研究中，采用低共熔溶剂 (DES) 作为无机酸的环保替代品，从废 NdFeB 磁体中选择性浸出稀土元素。测试了三种对轻质稀土元素浸出有效的 DES，并进行了初步实验，以研究使用合成材料 NdO、Fe、FeO 和 FeO 选择性浸出稀土元素。研究结果表明，为了选择性浸出，钕和铁应分别以 NdO 和 FeO 的形式存在。为了增强NdFeB磁体的选择性浸出，采用了三种预处理方法：氧化焙烧、NaOH消解和NaOH消解-氧化焙烧。在氧化焙烧过程中，NdFeO的形成阻碍了稀土元素的浸出，在盐酸胍（GUC）-乳酸（LA）DES中实现了最高的稀土元素浸出效率，达到22.5%。为了抵消 NdFeO 的形成，引入了 NaOH 消化，产生 Nd(OH) 和 FeO。然后通过氧化焙烧将它们转化为 NdO 和 FeO。对于 NaOH 消化产物，仅使用乙二醇 (EG)-马来酸 (MA) DES 即可实现选择性 REE 浸出，而在所有三种 DES 中，使用 NaOH 消化氧化焙烧都是可行的。 EG-MA DES 显示出最高的选择性，Nd 浸出率为 97.3%，Fe 浸出率为 0.8%。此外，溶剂可重复使用至少两次，并且Nd的浸出率保持在97%，Fe的浸出率保持在0.7%。与传统的无机酸浸出相比，这种选择性浸出技术受益于使用环保溶剂，并表现出高稀土元素选择性和溶剂可重复使用性，提出了一种通过 DES 回收稀土元素的新方法。