• Resources Recycling
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• v.12 no.6
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• pp.57-63
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• 2003

In this study, the separation of neodymium was investigated from NdFeB permanent magnet scrap. Decomposition and leach-ing process of NdFeB permanent magnet scrap by oxidation roasting and sulfuric arid leaching were examined. Neodymium could be separated from iron by double salt precipitation using sodium sulfate. The optimum conditions established for decom-position and leaching are as follows: oxidation roasting temperature is $500^{\circ}C$ for sintered scrap and $700^{\circ}C$ for bonded scrap, concentration of sulfuric acid in leaching solution is 2.0 M, leaching temperature and time is $50^{\circ}C$ and 2 hrs, and pulp density is 15%. The leaching yield of neodymium and iron was 99.4% and 95.7% respectively. The optimum condition for separation of neodymium by double-salt precipitation was 2 equivalents of sodium sulfate and $50^{\circ}C$ The yield of neodymium was above 99.9%.

• Resources Recycling
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• v.13 no.6
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• pp.43-48
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• 2004

For the separation of neodymium from NdFeB permanent magnet scrap, the scrap was roasted for oxidizing, and leached with acetic acid followed by fractional crystallization for selective separation. From the analysis results of the leached solution, the optimum condition for the recovery of neodymium was found that leaching temperature, leaching time and pulp density are 80$^{\circ}C$, 3 hours, and 35%, respectively. At this optimum condition, more than 90% of neodymium could be recovered. Concentration of neodymium acetate in acetic acid. The optimum condition for the recovery of neodymium acetate crystal from the leached solution was that the initial leaching solution was evaporated until the remaining volume was about 1/5 of the initial volume. At this condition, 67.5% of neodymium was recovered from the leached solution. The neodymium remaining in the concentrated solution was recovered by reacting it with oxalic acid.

• Resources Recycling
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• v.27 no.1
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• pp.38-44
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• 2018

A large amount of Nd-Fe-B magnet scraps are generated during magnet manufacture process. In this study, selective chlorination of the rare earth elements by hydrogen chloride gas which obtained from the pyrolysis of polyvinyl chloride (PVC) was investigated. In thermogravimetric analysis, drastic weight loss was occurred at about 500 K and 710 K. At the isothermal experiments, the weight loss reaches about 30% above 673 K. XRD patterns characterized that after each experiments, ${\alpha}$-Fe, Nd oxychloride, Nd chloride, and Fe chlorides were formed, and the leaching residues remain only ${\alpha}$-Fe. The yields of Nd, Dy, and Fe for the isothermal experiment were increased with temperature and peaked at 873 K. As PVC ratio increased, the yields of Nd, Dy and Fe were also increased.

• Clean Technology
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• v.28 no.2
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• pp.110-116
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• 2022

In this study, iron oxide (FeO_x) nanoparticles were synthesized using iron (Fe) by-products recovered from NdFeB permanent magnet scraps, and the effect of heat-treatment temperature on the physical properties of the FeO_x nanoparticles was investigated. In order to prepare the FeO_x nanoparticles, 2.0 M ammonia (NH₄OH) solution was added to an iron by-product solution diluted to c.a. 10 wt% in D.I. water, which led to the precipitation of the iron oxide precursor. Then, the FeO_x nanoparticles were synthesized by heat-treatment at 300 ℃, 400 ℃, 500 ℃ and 600 ℃. After that, the physical properties of the FeO_x nanoparticles were investigated in order to understand the effect of the heat-treatment temperature. The results of the X-ray diffraction (XRD) analysis showed that the diffraction peak in accordance with the <104> direction increased as the heat-treatment increased, and a diffraction peak indicating the α-Fe₂O₃ crystal structure was detected at heat-treatment temperatures above 500 ℃. The BET specific surface area analysis revealed that the specific surface area decreased as the heat-treatment temperature increased to above 400 ℃. Observation with a high resolution transmission electron microscope (HRTEM) showed that rod-shaped nanoparticles were formed, and the size of the nanoparticles showed a tendency to increase as the heat-treatment temperature increased.

• Resources Recycling
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• v.13 no.5
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• pp.37-44
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• 2004

In this study, neodymium oxalate powders were prepared by injecting oxalic acid to the neodymium chloride solution resulted from the acid leaching solution of NdFeB magnet scrap. The effect of experimental conditions on the characteristics of neodymium oxalate powders were investigated. Neodymium oxalate was aggregated by primary particles formed by nucleation, and average size of aggregates was affected by experimental conditions. In a constant volume, increase of reactants affected the average size of aggregate formed by collision of primary particles. In a constant concentration of reactants, agitation speed decreased the size of aggregate due to breakage of particles attached on the surface of aggregate. The number of primary particles decreased with increasing reaction temperature, and the size of aggregates decreased due to the decrease of collision probability. From the results of decomposition behavior of neodymium oxalate, oxalate decomposed from $400^{\circ}C$, and neodymium oxide began to crystallize at above $620^{\circ}C$.

• Journal of Powder Materials
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• v.28 no.2
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• pp.91-96
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• 2021

Rare earth magnets with excellent magnetic properties are indispensable in the electric device, wind turbine, and e-mobility industries. The demand for the development of eco-friendly recycling techniques has increased to realize sustainable green technology, and the supply of rare earth resources, which are critical for the production of permanent magnets, are limited. Liquid metal extraction (LME), which is a type of pyrometallurgical recycling, is known to selectively extract the metal forms of rare earth elements. Although several studies have been carried out on the formation of intermetallic compounds and oxides, the effect of oxide formation on the extraction efficiency in the LME process remains unknown. In this study, microstructural and phase analyses are conducted to confirm the oxidation behavior of magnets pulverized by a jaw crusher. The LME process is performed with pulverized scrap, and extraction percentages are calculated to confirm the effect of the oxide phases on the extraction of Dy during the reaction. During the L ME process, Nd is completely extracted after 6 h, while Dy remains as Dy₂Fe₁₇ and Dy-oxide. Because the decomposition rate of Dy₂Fe₁₇ is faster than the reduction rate of Dy-oxide, the importance of controlling Dy-oxide on Dy extraction is confirmed.