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An innovative process using only water and sodium chloride for recovering rare earth elements from Nd-Fe-B permanent magnets comprised in WEEE Nicolas Maât, Virginie Nachbaur, Rodrigue Lardé, Jean Juraszek, and Jean-Marie Le Breton ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b01226 • Publication Date (Web): 09 Sep 2016 Downloaded from http://pubs.acs.org on September 10, 2016

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ACS Sustainable Chemistry & Engineering

An innovative process using only water and sodium chloride for recovering rare earth elements from Nd-Fe-B permanent magnets comprised in WEEE

Nicolas Maât, Virginie Nachbaur, Rodrigue Lardé, Jean Juraszek, Jean-Marie Le Breton* Groupe de Physique des Matériaux, UMR 6634 CNRS, Université de Rouen Normandie, INSA Rouen 76800 Saint Etienne du Rouvray *correspondingauthor ([email protected])

Keywords: : recycling, Nd-Fe-B, hydrothermal treatment, rare earth, permanent magnet

Abstract We developed a new and environmentally friendly approach for recycling Ni-Cu coated NdFe-B permanent magnets included in computer hard disks drives collected as WEEE. In a closed reactor, the coated magnets are heated at 250°C in water mixed with sodium chloride for up to 18 hours. 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 Nd2Fe14BHx. The volume expansion of the intergranular phase, in relation with the formation of Nd(OH)3, together with the lattice expansion of the Nd2Fe14BHx phase causes the disintegration of the magnets. Finally, Nd2Fe14BHx is oxidized by water into Fe3O4 and Nd(OH)3. The Nd(OH)3 crystals can be isolated from the Fe3O4crystals by magnetic separation. This process is thus an easy way to extract rare earths from permanent magnets comprised in WEEE. It uses green chemistry design principles, and can be applied to large amounts of magnetic wastes.

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Introduction Rare earths are chemical elements used in a large quantity of devices and applications1,2. Rare earth elements are of significant interest, as these chemical elements are pivotal for the development of emerging clean energy technologies3and are vital to the economic well-being of the industrialized countries4. Due to their importance for industrial development and their supplying limits5, the European Union classified these compounds the present as strategic and critical materials in 2011. Substitution of these elements is currently investigated in many laboratories6–9, but an alternative way has emerged: recycling10. The substantial use of these materials by the industrialized countries, and the ecological and economical issues linked to rare earths mining have motivated the exploitation of ”urban mines”. In these mines, the Waste of Electrical and Electronic Equipment (WEEE) represents the domestic waste of electrical and technological applications. Their collection and sorting are regulated by European directives, which impose recycling it. For example, in 2018, 70% of the personal computers shall be recycled11. In the present study we focus on Neodymium-Iron-Boron permanent magnets comprised in hard disk drives. Since their discovery in 198412, Nd-Fe-B sintered magnets are the most powerful magnets used in industry and applications13. These materials are composed of a magnetic phase with the Nd2Fe14B stoichiometry, and a non-stoichiometric intergranular phase denoted as Nd-rich. The Nd2Fe14B phase is ferromagnetic at temperatures lower than 585K12 being thus responsible for the very good intrinsic magnetic properties of the magnet. It crystallizes in a tetragonal structure (a = 0.880 nm, c = 1.221 nm)12. This ferromagnetic phase is surrounded by Nd-rich intergranular regions which disconnect the magnetic Nd2Fe14B grains, and thus contributes to the good coercivity of the magnet14–18. The Nd-rich boundary phase may have various stoichiometries, like Nd4Fe, and may contain other phases stabilized by additions14,16,18. This region can also contain Nd oxides. A B-rich minor phase with the Nd1+εFe4B4 stoichiometry is sometimes observed19,20. Different methods are used for the production of magnets with a high degree of texture: for instance, alignment of microcrystalline powder in a magnetic field and subsequent sintering, dieupsetting of isotropic hot-pressed nanocrystalline magnet powders or pre-alignment of HDDR powders followed by hot-pressing21,22. To improve the physical properties of Nd-Fe-B magnets, Cobalt, Dysprosium or Praseodymium can be added23,24. Those elements are used to increase the magnetic properties or the working temperature range. Dysprosium particularly increases the coercivity of the material.


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Environmental conditions such as humidity and temperature are very harmful for magnetic properties of sintered magnets, due to the sensitivity of neodymium to both hydrogen and oxygen25. This is why, for applications and devices, magnets are electrochemically coated with metallic films in order to prevent corrosion. Different metals may be used, the more common being nickel, copper, aluminum and zinc, or a combination of these metals, for example nickel-copper-nickel multilayered coatings21. Numerous laboratory processes have been developed to remove the metallic protective layer and to recover the rare earths comprised in permanent magnet26–31. Hydrometallurgy is usually the most cited: sulfuric or hydrochloric acids are used to dissolve the alloy, and then rare earths are precipitated as salts by adding oxalic acid or soda32,33. Such methods produce large quantities of waste and cause environmental issues. To achieve rare-earth extraction, organic solvents can also be used34–36, or molten metals like silver or magnesium37,38. Many reviews describe precisely the recent developments related to this topic26,30,31. We developed a new and environmentally friendly approach for recycling rare earth permanent magnets. Such a process is easy to set up, and can be applied to large amounts of magnetic waste. Only water and sodium chloride are used. The reaction takes place at low temperature, 250°C for example, and only in two steps. First, hydrothermal treatment of the magnets is performed, leading to the formation of both neodymium hydroxide crystals and iron oxide crystals. Then, rare earth hydroxide crystals are isolated from iron oxide crystals by magnetic separation. Permanent magnets can be processed directly after dismantling the electronic products, because with this new approach, metallic coating is removed during the treatment and can be recovered separately from rare earth and metal salts after sieving. Furthermore, water can be used again to recycle other magnets, which is an environmental and economical benefit. The hydrothermal treatment is currently the object of many investigations for organic compounds recycling, but up to now it has still not been employed for metallic alloy recycling. This method provides an easy way to extract rare earths from permanent magnets comprised in WEEE, employing green chemistry design principles.

Experimental The samples for the recycling process are Ni-Cu coated Nd-Fe-B permanent magnets included in computer hard disk drives collected as WEEE. The average weight of a magnet is about 10 grams. As



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described above, several additives may be used to increase magnetic properties of permanent magnets. Material compositions depend on both age and brand of the hard disk drive. The average composition of the Nd-Fe-B magnets deduced from the measurements performed on all the investigated samples is given in Table 1.

Experimental process. The reaction takes place in a Teflon lined bomb provided by Parr Instruments (figure 1). This reactor is filled with 30 mL of distilled water. One Nd-Fe-B permanent magnet is put into the reactor, and 0.01g of NaCl is added. In this study, NaCl is used as a catalyst to improve water oxidative power. The reactor has a complete volume of 50mL. The reactor is closed and heated at 250°C for various reaction times, up to 18 hours. The temperature is chosen in relation with the water ionization constant. The minimum is reached for 250°C. At the end of the reaction the reactor is cooled in ambient air and the remaining powder is washed several times with distilled water and finally dried under vacuum. Nd-Fe-B magnets dismantled from hard disk drives were treated for 4, 8 and 18 hours in the apparatus described above. The nomenclature of the investigated samples is given in Table 2. Moreover, magnetic separation has been performed on the powder obtained after 18 hours, in order to separate magnetic and non-magnetic particles, the magnetic particles being removed from the sample. The corresponding sample is denoted as sample E.

Characterization X-ray powder diffraction (XRD) analysis was performed under Bragg-Brentano geometry, on a D8 Diffractometer (Bruker AXS), using Co Kα radiation (λKα1 = 0.178897 nm and λKα2 = 0.179285 nm). Diffraction intensity was measured with a 2θ step of 0.01°. Powders were observed by scanning electron microscopy (SEM), using a Zeiss 1530 electron microscope, equipped with electron dispersive X-ray spectroscopy (EDX). SEM observations and EDX measurements were performed at 5 and 20 kV, respectively.

Results and discussion


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After the treatment, and for all heating times, we observed that the metallic coating has been totally removed from the magnet by the hydrothermal process and is retrieved at the bottom of the reactor in the form of flakes with a size of a few millimeters. After 4 hours (sample B), the magnet remains as a bulk piece of sintered material. Some powder, which has been removed from the magnet, is recovered at the bottom of the reactor. After 8 hours (sample C), the magnet is pulverized and the major part of the sample has become powder. After heating for 18 hours (sample D), the magnet is entirely pulverized and only powder remains (Figure 2). After washing and drying, powders C and D contain dark grey particles and several shiny particles. The shiny particles, which have a bigger size than the dark grey particles, are very probably small pieces of the metallic coating that has been removed from the magnet by the hydrothermal process. In figure 3 are presented the XRD patterns of sample C before (figure a) and after (figure b) sieving with a screen mesh of 250 µm. The sieved powder reveals the absence of shiny particles. In the XRD pattern of the unsieved sample, one can clearly observe peaks corresponding to Ni-Cu. After sieving, these peaks are no longer visible. This shows that the shiny particles correspond to the Ni-Cu coating that was removed from the powder. This indicates that sieving allows the removal of the coating pieces from the powder recovered after the treatment. The complete interpretation of the XRD pattern of sample C is presented in section “Structural identification and degradation mechanism”.

Influence of the reaction time on the morphology In figure 4 are shown the SEM micrographs of sample A. The surface of the magnet reveals Nd2Fe14B grains (in grey contrast) of about 10 µm in size, and Nd-rich intergranular regions. These observations are consistent with the literature12,15,16,18,39, in agreement with the conventional microstructure of Nd-Fe-B permanent magnets. In figure 5 are shown SEM micrographs of the surface of the magnet treated for 4 hours (sample B) and of the powder that has been removed from the magnet. The image shows intergranular cracks on the surface of the magnet, evidencing the loosening of the Nd2Fe14B grains due to the hydrothermal treatment. The powder that has been removed from the magnet is composed of Nd-Fe-B grains with a size of about 10 µm, and small grains which seem to correspond to the Nd-rich degraded regions with a size less than 1 µm. One can notice that the degraded Nd-rich



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particles result from the boundary zone inflation, which leads both to the loosening of the Nd-Fe-B grains and to the self-pulverization of the magnet. In figure 6 are shown SEM micrographs of sample C. The images show that the powdered magnet is composed of Nd2Fe14B grains with a size of about 10 µm, and small grains corresponding to the Nd-rich degraded regions with a size less than 1 µm (figures 6a and 6b). The powdered magnet thus appears to be similar in size as the powder that has been removed from the magnet after a 4 hour treatment. A more detailed view of the surface of a Nd2Fe14B grain reveals the presence of nanosized grains (figure 6c). The SEM observations show that the Nd-rich phase has been degraded by the hydrothermal process; this degradation is observable after 4 hours, and leads to the loosening of the Nd2Fe14B grains from the magnet. Increasing the treatment time to 8 hours leads to the pulverization of the magnet into a powder, with a particle size corresponding to the initial grain size of the magnet. The powder that results from the pulverization of the magnet is thus composed of the Nd-Fe-B grains of the initial magnet, but a nanosized texture is observed on the surface. On the pictures associated with sample D (figure 7), the crystallographic grains are completely dissociated, and the powder contains octahedral and needle shaped crystals. If the treatment time is increased at the same temperature, these crystals grow and reach the micrometric scale. As clearly shown by EDX composition measurements, the octahedral crystals are iron oxides, and needle-shaped crystals are neodymium oxides (Figure 8). These characterizations are correlated to the structural analysis in the following section. SEM observations of sample E (Figure 9) reveal the presence of needle-shaped crystals only. This indicates that the octahedral crystals have been removed from the sample after magnetic separation, thus showing that the octahedral crystals are magnetic. In agreement with EDX analysis, sample E contains neodymium oxides only. The magnetic iron oxides have been removed from the sample by magnetic separation so that only rare earth compounds remain in the solution. To characterize the phases formed at the different stages of the treatment, we performed XRD analysis.

Structural identification and degradation mechanism


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For the XRD analysis, sample A has been hand-crushed in a mortar. The powder removed from sample B has been sieved with a 250 µm mesh before the analysis. Sample C and D have also been sieved. The XRD patterns of samples A, B, C, D and E are shown in figure 10. The XRD pattern of sample A shows all the peaks of the Nd2Fe14B phase, in agreement with JCPDS file 00-039-0473. One can notice that the main peak of the minor Nd-rich phase (Nd oxides) is observed as well in the figure (JCPDS file 03-065-3184). In the XRD pattern of the powder recovered in sample B, all the peaks of the Nd2Fe14B phase are observed. The coating reacts with the solution, leading to its removal from the magnet as pieces each about a millimeter in size, which can be recovered by sieving. Then, the Nd-rich boundary zone starts to react with water, leading to the pulverization of the magnet. However, a close inspection of the pattern shows that the Nd2Fe14B peaks are shifted to low angles. This is related to the increase of the lattice parameters of the Nd2Fe14B phase after the treatment. This modification can be observed more precisely in figure 11. The XRD pattern of sample C reveals that the peaks of the Nd2Fe14B phase are shifted to lower angles, as compared with those of sample B. This indicates that the expansion of the lattice parameters of the Nd2Fe14B phase continues between 4 and 8 hours of treatment. In table 3 are summarized the lattice parameters of the Nd2Fe14B phase calculated from the measured peak positions of each sample. The lattice parameters of the Nd2Fe14B phase in sample A correspond to the Nd2Fe14B stoichiometric composition. For samples B and C, an important increase of the lattice parameters is observed. For sample B, the measured parameters correspond to the Nd2Fe14BH1,86 phase (JCPDS file 01-086-0277). For sample C, the measured parameters correspond to the Nd2Fe14BH3,31 phase (JCPDS file 01-086-0276). These results show that the observed volume expansion is due to the hydrogenation of the Nd2Fe14B phase. The peaks of the Nd(OH)3 phase (JCPDS file 01-070-0215) are also observed, with a higher intensity for sample C than for sample B. This suggests a more important oxidation of the neodymium located in the boundary zone in sample C than in sample B. This is consistent with the fact that the major part of sample C is recovered as a powder. These results indicate that during the treatment of the sintered magnet, the coating is removed first. Then the Nd-rich phase reacts with water, leading to the formation of Nd(OH)3 and to an inflation of the intergranular regions. This inflation leads to the pulverization of the magnet.



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After degradation of the Nd-rich zone, the Nd2Fe14B grains are oxidized by water, which cause grain swelling. This inflation is a consequence of the dissociation of the Nd2Fe14B phase into iron and neodymium oxides. By reacting with water, neodymium crystallizes in an hexagonal structure as Nd(OH)3 and iron in a cubic structure as Fe3O4 (JCPDS file 03-065-3107). At the end of the reaction, (sample D), only magnetite Fe3O4 and Neodymium hydroxide Nd(OH)3 remain, which means that the Nd2Fe14B phase is totally dissociated. By correlating these results with previous SEM observations, we can claim that octahedral crystals are magnetite and needle-shaped crystals are rare earth hydroxides. It is worth mentioning that octahedral magnetite is often observed in solvothermal synthesis, and has been reported first by Hirano et al.40 Octahedral magnetite is the kinetically most favorable shape with low activation energy barrier in such conditions41. Formation of needle-shaped neodymium hydroxides has already been observed by Bian et al.42 by hydrolysis of Nd-Fe-B-C alloys. By increasing the reaction time, iron and neodymium crystals can mature, with an increased grain size and an improved crystallinity. After 8 hours of reaction, crystals have a nanometric size, while after 18 hours of treatment a micrometric size is reached. The magnetic separation of the iron and neodymium crystals is thus possible. Such a magnetic separation of rare earth hydroxides and iron compounds has been demonstrated by Bian et al.42, who reach a rare earth hydroxide purity of 99.7%. In the present investigation, the XRD analysis shows, in agreement with SEM observations, that the major part of the powder recovered after magnetic separation (sample E) is composed of Nd(OH)3. The powder recovered after 8 hours of hydrothermal reaction (sample C) has been annealed under vacuum at various temperatures, in the 200-300°C range. The X-ray diffraction patterns of the annealed powders are shown in figure 12. Before annealing, the powder is composed of an inflated Nd2Fe14B crystallographic phase, as seen previously. After annealing, one can see in the figure that the diffraction peaks have been shifted to high angles, up to positions that correspond to those of the Nd2Fe14B phase. This modification can be observed more precisely in figure 13. This shows that the inflation/deflation process is reversible, and corresponds to a hydrogenation/dehydrogenation process of the Nd2Fe14B phase. This phenomenon has already been observed and studied, and reported dehydrogenation temperatures are consistent with our results43. One can notice that the peaks of the Nd2O3 neodymium oxide (JCPDS file 03-065-3184) are observed in the patterns of the annealed samples, showing that this phase is formed upon annealing. Conversion of rare earth hydroxides in rare earth oxides is interesting from an economical point of view, because rare earth oxides are more valuable than the rare earth hydroxides. Indeed, rare earth oxides are widely applied


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in various domains, and are also used as raw materials to produce rare earth metals by electrolysis30,34. Taking these considerations into account, we assume the following mechanism to explain NdFe-B magnets degradation under hydrothermal conditions. The hypothesis proposed in this study is supported by literature results25,44. The disintegration of the magnets in humid environment starts with the reaction of the Ndrich phase with water, leading to Nd(OH)3 and hydrogen. Yan et al. suggested an anodic reaction between the Nd-rich phase and water, with a simultaneous cathodic reduction of water on the Nd2Fe14B matrix phase25. Then, atomic hydrogen is absorbed by Nd2Fe14B leading to the formation of the Nd2Fe14BHx phase. The lattice expansion of the Nd2Fe14B phase and the volume expansion on formation of Nd(OH)3 leads to the disintegration of the magnets. Yan et al.25 also suggested the formation of NdH2+x as an intermediate product of the reaction of the Nd-rich zone with hydrogen. This compound has not been observed in our study. In a second step, the Nd2Fe14BHx is oxidized by water into Fe3O4 and Nd(OH)3. The dissociation of the Nd2Fe14B phase upon oxidation, into iron and neodymium oxides has been the subject of numerous publications45. Iron and neodymium oxides were observed as dissociation products. In our investigation, the formation of Fe3O4 and Nd(OH)3 compounds instead of Nd2O3 and Fe is due to the presence of water in the hydrothermal reactor. Here, the last step of the process, magnetic separation, has been performed only to demonstrate the feasibility of the method. The low quality of our magnetic separator (a magnet and a vial), and the weak quantities used in the experiments do not permit, for the moment, to estimate precisely the yield of the process. The purpose of the article is to explain the mechanism wich occured during the hydrothermal treatment, because the pulverization of an alloy with an hydrothermal treatment is a very innovative concept. Improvement of the magnetic separation is in progress, but more experiments are required. Inductively Coupled Plasma (ICP) measurements were performed on the rare earth hydroxides fraction (sample E). The following elements were quantified: neodymium, dysprosium, praseodymium and iron. More than 95% of the sample is constituted of mixed rare earths. The main impurity is iron. This product contains at least neodymium, dysprosium and praseodymium. ICP measurements realized on the solvent recovered at the end of the reaction demonstrate that neither rare earth nor iron has been dissolved into the solvent. All the elements are recovered as crystals.



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Rare earths are recovered together, but we did not collect evidence of the presence of cobalt or boron in one or other fraction. In this process, NaCl is essential. Two experiments were realized in the same conditions of temperature and pressure, but only with distilled water, with a reaction time of 100 hours. The samples are, first, a Nd-Fe-B magnet with his metallic coating, and the second is a Nd-Fe-B magnet without magnetic coating. In both experiments, at the end of the process, the samples are recovered as bulk materials. The metallic coating is not damaged by the process, and only the color of the NdFe-B material (initilally grey) changes into black. So, without NaCl, the reaction does not take place, or is so slow that we can not observe it. If the concentration of NaCl is increased, the reaction time slightly decreased. But, with an high concentration of NaCl, final products need to be carefully washed, because NaCl crystals are present in the powder at the end of the process. NaCl can be replaced by well-known oxidative salts, like sodium sulfite and metabisulfite. Indeed, the same results are observed when Na2S2O5 or Na2S2O4 are added in the reactor. The reaction time remains the same, and the same compounds are recovered at the end of the process : Fe3O4 and Nd(OH)3. Coated Nd-Fe-B magnets can be treated after disassembling of WEEE without any preparation step. The hydrothermal way is thus a promising and low-cost path to recycle Nd-Fe-B magnets. Moreover, because water can be used several times for recycling other magnets, and because only one chemical reagent is used, NaCl for instance, in very low concentrations, this method has a very low environmental impact. So, it can be set up easily and applied to large amounts of magnetic waste. This hydrothermal treatment is a new and environmentally friendly approach for recycling rare earth permanent magnets.

Acknowledgments This work is part of the project ANR-13-ECOT-0006-06 "EXTRADE”. The BRGM (Bureau de Recherches Géologiques et Minières) is gratefully acknowledged for having provided the samples. The authors are thankful to Cyril Aymonier (ICMCB Bordeaux, France) for ICP measurements.


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(23) Kusunoki, M.; Yoshikawa, M.; Minowa, T.; Honshima, M. Binary Alloy Method for the Production of Nd Fe Co B Permanent Magnets, 3rd IUMRS Int. Conf. Adv. Mater., pp. 10131016,. 1994. (24) Ohashi, K.; Yokoyama, T.; Tawara, Y. Effects of Rare Earth Oxide Addition on NdFeB Magnets. IEEE Transl. J. Magn. Jpn.1988, 3 (2), 145–151. (25) Yan, G.; Williams, A. J.; Farr, J. P. G.; Harris, I. R. The effect of density on the corrosion of NdFeB magnets.J. Alloys Compd.1999, 292 (1–2), 266–274. (26) Tanaka, M.; Oki, T.; Koyama, K.; Narita, H.; Oishi, T. Chapter 255 - Recycling of Rare Earths from Scrap. In Handbook on the Physics and Chemistry of Rare Earths; Pecharsky, J.-C. G. B. and V. K., Ed.; Including Actinides; Elsevier, 2013; Vol. 43, pp 159–211. (27) Elwert, T.; Goldmann, D.; Schmidt, F.; Stollmaier, R. Hydrometallurgical recycling of sintered NdFeB magnets. World Met.2013, 66, 209–219. (28) Rademaker, J. H.; Kleijn, R.; Yang, Y. Recycling as a Strategy against Rare Earth Element Criticality: A Systemic Evaluation of the Potential Yield of NdFeB Magnet Recycling. Environ. Sci. Technol.2013, 47 (18), 10129–10136. (29) Sprecher, B.; Kleijn, R.; Kramer, G. J. Recycling potential of neodymium: the case of computer hard disk drives. Environ. Sci. Technol.2014, 48 (16), 9506–9513. (30) Binnemans, K.; Jones, P. T.; Blanpain, B.; Van Gerven, T.; Yang, Y.; Walton, A.; Buchert, M. Recycling of rare earths: a critical review. J. Clean. Prod.2013, 51, 1–22. (31) Firdaus, M.; Rhamdhani, M. A.; Durandet, Y.; Rankin, W. J.; McGregor, K. Review of HighTemperature Recovery of Rare Earth (Nd/Dy) from Magnet Waste. J. Sustain. Metall.2016, just accepted. (32) Lyman, J. W.; Palmer, G. R. Neodymium and iron recovery from NdFeB permanent magnet scrap. 1992. (33) Lyman, J. W.; Palmer, G. R. Recycling of neodymium iron boron magnet scrap. 1993. (34) Nash, K. L. Chapter 121 Separation chemistry for lanthanides and trivalent actinides. In Handbook on the Physics and Chemistry of Rare Earths; Karl A. Gschneidner, J., LeRoy Eyring, G. R.Choppin and G. H.Lander, Ed.; Lanthanides/Actinides: Chemistry; Elsevier, 1994; Vol. 18, pp 197–238. (35) Lenz, T. G.; Smutz, M. The extraction of neodymium and samarium by di(2-ethylhexyl) phosphoric acid from aqueous chloride, perchlorate and nitrate systems. J. Inorg. Nucl. Chem.1968, 30 (2), 621–637. (36) Naganawa, H.; Shimojo, K.; Mitamura, H. A New Green Extractant of the DiglycolAmic Acid Type for Lanthanides.Solvent Extr. Res. Dev. Jpn.2007, 14, 151–159. (37) O. Takeda, T. H. O. Phase equilibrium of the system Ag–Fe–Nd, and Nd extraction from magnet scraps using molten silver. J. Alloys Compd.2004, 379, 305–313. (38) Nagai, T.; Uzawa, T. Recovery of Rare Earth Metals from Wasted Magnet. In Rare Metal Technology 2014; Neelameggham, N. R., Alam, S., Oosterhof, H., Jha, A., Wang, S., Eds.; John Wiley & Sons, Inc., 2014; pp 99–101. (39) Shinba, Y.; Konno, T. J.; Ishikawa, K.; Hiraga, K.; Sagawa, M. Transmission electron microscopy study on Nd-rich phase and grain boundary structure of Nd–Fe–B sintered magnets. J. Appl. Phys.2005, 97 (5), 53504. (40) Hirano, S.; Somiya, S. Hydrothermal crystal growth of magnetite in the presence of hydrogen. J. Cryst. Growth1976, 35 (3), 273–278. (41) Zhang, L.; Li, Q.; Liu, S.; Ang, M.; Tade, M. O.; Gu, H.-C. Synthesis of pyramidal, cubical and truncated octahedral magnetite nanocrystals by controlling reaction heating rate.Adv. Powder Technol.2011, 22 (4), 532–536. (42) Bian, Y.; Guo, S.; Jiang, L.; Liu, J.; Tang, K.; Ding, W. Recovery of Rare Earth Elements from NdFeB Magnet by VIM-HMS Method. ACS Sustain. Chem. Eng.2016, 4 (3), 810–818. (43) Cadogan, J. M.; Coey, J. M. D. Hydrogen absorption and desorption in Nd2Fe14B. Appl. Phys. Lett.1986, 48 (6), 442–444.


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(44) Le Breton, J.; Teillet, J. Oxidation of (Nd, Dy) FeB permanent magnets investigated by 57 Fe Mossbauer spectroscopy. Magn. IEEE Trans. On1990, 26 (5), 2652–2654. (45) Edgley, D. S.; Le Breton, J. M.; Steyaert, S.; Ahmed, F. M.; Harris, I. R.; Teillet, J. Characterisation of high temperature oxidation of Nd-Fe-B magnets. J. Magn. Magn. Mater.1997, 173 (1–2), 29– 42.



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Tables

Table 1: Composition of Nd-Fe-B magnets comprised in hard disks drives collected as WEEE (mass %) Nd

Fe

B

Dy

Pr

Ni

Cu

27.15

64.22

1.15

1.46

3.97

1.04

0.85

D

E

18 hours

18 hours

Sample name Reaction time (temperature = 250°C)

Table 2: Operating conditions for samples A B C Before hydrothermal treatment: reference sample

4 hours

8 hours

Magnetic separation

X

Table 3: Nd2Fe14B lattice parameters calculated from XRD patterns. a(nm, ±0.0005)

c(nm±0.0005)

Volume (nm3)

Sample A

0.879

1.220

942.62

Sample B

0.886

1.229

964.76

Sample C

0.890

1.233

976.66


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Figure captions

Figure 1: Crystallization bomb and Teflon reactor used for hydrothermal process Figure 2: Left: permanents magnets after dismantling. Right: powder recovered at the end of the process, denoted as sample D. Figure 3: XRD patterns of the powder recovered after 8h of hydrothermal treatment at 250°C, denoted as sample C, (a) before and (b) after sieving. Figure 4- SEM cross section micrographs of a fractured Nd-Fe-B magnet before hydrothermal treatment (sample A). Figure 5- SEM micrographs of a Nd-Fe-B magnet after a reaction time of 4 h (sample B): (a) cross section of the surface of the magnet at the end of the process, and (b) image of the powder recovered at the bottom of the reactor. Figure 6: SEM micrographs of the powder recovered after a reaction time of 8hours (sample C). Figure 7: SEM micrographs of the recovered powder after a reaction time of 18H (sample D). Figure 8: EDX measurements realized on sample D: (a) octahedral crystals analysis (position 1 shown in figure 7), (b) needle-shaped crystals analysis (position 2 in figure 7). Figure 9: SEM micrograph of the recovered powder after magnetic separation (sample E). Figure 10: XRD patterns of samples A,B,C,D and E. Figure 11: Magnification of a section of the XRD analysis performed on samples A, B and C, on the range from 47 to 53°, revealing the shift of the Nd2Fe14B peaks as the treatment time increases. Figure 12: XRD patterns of the powder recovered after 8 hours of hydrothermal treatment (sample C), before and after subsequent annealing for one hour under vacuum at the indicated temperatures. Figure 13: Magnification of a section of the XRD analysis performed on annealed samples, on the range from 47 to 53°, revealing the shift of the Nd2Fe14B peaks as the treatment temperature increases.



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An innovative process using only water and sodium chloride for recovering rare earth elements from Nd-Fe-B permanent magnets comprised in WEEE

Nicolas Maât, Virginie Nachbaur, Rodrigue Lardé, Jean Juraszek, Jean-Marie Le Breton

Thanks to hydrothermal treatment, a rare earth alloy (here a Nd-Fe-B magnet) is powdered and Nd and Fe elements can be recovered separately to be reused: Nd in needle-shaped crystals and Fe in octahedral crystals.


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Figure 1: Crystallization bomb and Teflon reactor used for hydrothermal process



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Figure 2: Left: permanents magnets after dismantling. Right: powder recovered at the end of the process, denoted as sample D.


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Figure 3: XRD patterns of the powder recovered after 8h of hydrothermal treatment at 250°C, denoted as sample C, (a) before and (b) after sieving.



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Figure 4- SEM cross section micrographs of a fractured Nd-Fe-B magnet before hydrothermal treatment (sample A).


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Figure 5- SEM micrographs of a Nd-Fe-B magnet after a reaction time of 4 h (sample B): (a) cross section of the surface of the magnet at the end of the process, and (b) image of the powder recovered at the bottom of the reactor.



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a

b

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c

Figure 6: SEM micrographs of the powder recovered after a reaction time of 8hours (sample C).


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Figure 7: SEM micrographs of the recovered powder after a reaction time of 18H (sample D).



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Figure 8: EDX measurements realized on sample D: (a) octahedral crystals analysis (position 1 shown in figure 7), (b) needle-shaped crystals analysis (position 2 in figure 7).


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Figure 9: SEM micrograph of the recovered powder after magnetic separation (sample E).



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Figure 10 : XRD patterns of samples A,B,C,D and E.


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Figure 11: Magnification of a section of the XRD analysis performed on samples A, B and C, on the range from 47 to 53°, revealing the shift of the Nd2Fe14B peaks as the treatment time increases.



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Figure 12: XRD patterns of the powder recovered after 8 hours of hydrothermal treatment (sample C), before and after subsequent annealing for one hour under vacuum at the indicated temperatures.


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Figure 13: Magnification of a section of the XRD analysis performed on annealed samples, on the range from 47 to 53°, revealing the shift of the Nd2Fe14B peaks as the treatment temperature increases.


An Innovative Process Using Only Water and ... - ACS Publications

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