An Innovative Process Using Only Water and Sodium Chloride for Recovering Rare Earth Elements from Nd–Fe–B Permanent Magnets Found in the Waste of Electrical and Electronic Equipment

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• 作者：Nicolas Maât ; Virginie Nachbaur ; Rodrigue Lardé ; Jean Juraszek ; Jean-Marie Le Breton
• 刊名：ACS Sustainable Chemistry & Engineering
• 出版年：2016
• 出版时间：December 5, 2016
• 年：2016
• 卷：4
• 期：12
• 页码：6455-6462
• 全文大小：558K
• ISSN：2168-0485

文摘

We developed a new and environmentally friendly approach for recycling Ni–Cu-coated Nd–Fe–B permanent magnets included in computer hard disk drives collected as the waste of electrical and electronic equipment (WEEE). In a closed reactor, the coated magnets are heated at 250 °C in water mixed with sodium chloride for up to 18 h. First, the hydrothermal treatment induces the removal of the metallic coating that can be recovered by sieving. Then, the Nd-rich phase reacts with water, leading to the formation of Nd(OH)₃. Atomic hydrogen is absorbed by the Nd₂Fe₁₄B phase, leading to the formation of Nd₂Fe₁₄BH_x. The volume expansion of the intergranular phase, in relation to the formation of Nd(OH)₃, together with the lattice expansion of the Nd₂Fe₁₄BH_x phase causes the disintegration of the magnets. Finally, Nd₂Fe₁₄BH_x is oxidized by water into Fe₃O₄ and Nd(OH)₃. The Nd(OH)₃ crystals can be isolated from the Fe₃O₄ crystals by magnetic separation. This process is thus an easy way to extract rare earths from permanent magnets found in WEEE. It uses green chemistry design principles and can be applied to large amounts of magnetic wastes.