Development of Recycling Process for Rare Earth Magnets by Electrodeposition Using Ionic Liquids Media
Development of Recycling Process for Rare Earth Magnets by Electrodeposition Using Ionic Liquids Media
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DOI：
10.1149/05011.0549ecst
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发表时间：
2013-03
期刊：
影响因子：
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通讯作者：
M. Ishii;M. Matsumiya;S. Kawakami
中科院分区：
文献类型：
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作者：
M. Ishii;M. Matsumiya;S. Kawakami
稀土（RE）金属对于高科技至关重要，并且近年来此类元素的价格急剧上涨。特别是稀土金属被用作许多工业产品中具有高磁通密度的磁性材料。然而，其中许多没有被作为有用资源重新利用而被报废。因此，开发二次消费电子产品中稀土金属的回收工艺非常重要。为此，我们已经证明，从环境友好系统的角度来看，使用离子液体介质的新型稀土回收工艺是有效的。我们建议的稀土磁体回收流程如图1所示。这种回收工艺主要有两个优点。首先，由于化学和电化学过程非常简单，因此在回收过程中几乎不产生二次废物。此外，当在电沉积过程(I)和(II)之后可以重复使用电解质时，可以在使用离子液体介质的电化学过程中构建闭循环。其次，离子液体介质具有常温液态、不易燃、蒸气压可忽略不计、离子电导率高等优点。离子液体的这些特性使我们能够在低温下进行电沉积，并可以建立节能的回收系统。在这项研究中，稀土磁体的废料（例如VCM）被用作起始材料。稀土磁体通常保持高磁通密度（约400mT），因此通过以363K/h加热至居里温度（583K），稀土磁体被退磁。对于热处理后得到的RE磁体，退磁率超过99.9％。此外，稀土磁体的镀层表面膜一般由Ni-Cu-Ni三层组成。对于这样的涂膜，可以有效地应用化学蚀刻工艺。结果，Ni镀膜被选择性溶解，得到了去除Ni层的稀土合金。在这些过程之后，将稀土合金溶解在酰胺酸中，并进行金属 TFSA 盐的合成，因为有必要从水溶液转化为离子液体介质。当我们在 373K 下将稀土磁体溶解在 1M HTFSA 中 30 分钟时，溶解速率为 31.9 μg/s cm。 RE磁体的酰胺酸溶解组分在373K下蒸发，蒸发后的金属TFSA盐在373K下真空干燥72小时。通过ICP-AES评价可知，金属TFSA盐中的金属比率为Nd:Fe:B=2:14.0:0.89。该比例与Nd磁体中金属的比例一致。对于电化学过程，阳极溶解过程和电沉积过程（I）在离子液体介质中同时进行。这种用于回收铁族金属的电沉积工艺(I)已经以超过90%的高电流效率进行了回收。另外，在连续的电沉积过程(I)中没有发生离子液体的分解反应。最后，对于电沉积过程（II），应用胆碱基离子液体作为电解介质，并在-3.7V的恒电位条件下进行Nd的电沉积。经过该电沉积过程后，获得黑色电沉积物，并通过 XPS 分析顶面，如图 2 所示。 Nd3d5/2光谱的结合能为981.5eV，该结果表明电沉积物主要由Nd金属和部分Nd氧化物组成。目前正在进行通过深度分析对氧化态进行进一步分析。
Rare earth (RE) metals are essential for high technology and the price of such elements has drastically increased in recent. Particularly the RE metals are utilized as magnetic materials with high flux density for a lot of industrial products. However, many of them were scrapped without reusing as the useful resources. Therefore it is very important to develop the recycling process of RE metals from the secondary used consumer electronics. For this purpose, we have already demonstrated that a novel RE recycling process using the ionic liquids media was effective from a standpoint of environmentalfriendly system. Our suggested recycling process of RE magnets was shown in Fig.1. This recycling process has mainly two advantages. Firstly, there were almost no secondary wastes in the recycling process because the chemical and electrochemical processes are very simple. In addition, when it is possible to reuse of the electrolytes after the electrodeposition process (I) and (II), the closedcycle can construct in the electrochemical process using the ionic liquids media. Secondly, the ionic liquids media have attractive features such as liquid state at room temperature, non-flammability, negligible vapor pressure and high ionic conductivity. These features of the ionic liquids enabled us to perform the electrodeposition at low temperatures and saving-energy recycling system can be established. In this study, the waste of the RE magnets such as VCM was applied as the starting materials. The RE magnets generally remain high magnetic flux density (ca.400mT), so that the RE magnets were demagnetized by heating at 363K/h up to curie temperature (583K). For the obtained RE magnets after heating treatment, the demagnetization ratio was performed over 99.9%. Moreover, the coating surface film of RE magnets was generally composed of the Ni-Cu-Ni triple layers. For thus coating film, the chemical etching process can be effectively applied. As a result, Ni coating film was selectively dissolved and we obtained the RE alloys removed Ni layers. After these processes RE alloys were dissolved in amide-acid and the synthesis of the metallic TFSA-salts were executed, because it is necessary to convert from the aqueous solution to the ionic liquids media. When we dissolved RE magnets in 1M HTFSA at 373K for 30 min, the rate of dissolution was 31.9 μg/s cm. Amid-acid dissolved components of RE magnets was evaporated at 373K and the metallic TFSA-salts after evaporation was dried with vacuum at 373K for 72h. It was revealed that the ratio of metals in the metallic TFSA-salts was Nd:Fe:B=2:14.0:0.89 evaluated by ICP-AES. This ratio is consistent with the ratio of metals in Nd magnets. For the electrochemical process, the anodic dissolution process and the electrodeposition process (I) was simultaneously executed in ionic liquids media. This electrodeposition process (I) for the recovery of the iron group metals has already recovered at highly current efficiency more than 90%. In addition, no decomposition reaction of the ionic liquids occurred in the successive electrodeposition process (I). Finally, for the electrodeposition process (II), the choline-based ionic liquids was applied as the electrolytic media and the electrodeposition of Nd was performed on potentiostatic condition at -3.7V. After this electrodeposition process, the black-colored electrodeposites were obtained and the top surface was analyzed by XPS as shown in Fig.2. The binding energy of Nd3d5/2 spectrum was assigned at 981.5eV and this result revealed that the electrodeposites were composed of the mainly Nd metal and a part of Nd oxides. Further analysis of the oxidation state by the depth analysis is currently in progress.