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

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 Nd 2 Fe 14 B phase, leading to the formation of Nd 2 Fe 14 BH x . The volume expansion of the intergranular phase, in relation to the formation of Nd(OH) 3, together with the lattice expansion of the Nd 2 Fe 14 BH x phase causes the disintegration of the magnets. Finally, Nd 2 Fe 14 BH x is oxidized by water into Fe 3 O 4 and Nd(OH) 3 . The Nd(OH) 3 crystals can be isolated from the Fe 3 O 4 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.