Method for utilizing disassembled neodymium-iron-boron waste
By performing thermal demagnetization, surface treatment, and grain boundary diffusion on dismantled NdFeB waste materials, the problems of cumbersome processes, high costs, and significant pollution in existing technologies have been solved, achieving efficient and low-cost magnet performance restoration and regeneration.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- 中稀(广西)金源稀土新材料有限公司
- Filing Date
- 2022-09-23
- Publication Date
- 2026-06-26
AI Technical Summary
Existing technologies for processing NdFeB waste are cumbersome, costly, polluting, and have low yields. Furthermore, the regeneration process requires the addition of rare earth elements, which reduces the performance of the magnets.
The process involves repairing dismantled NdFeB waste through steps such as thermal demagnetization, surface treatment, machining, grain boundary diffusion, and heat treatment. The magnet surface is covered with reducing metals or their hydrides and heat-treated under vacuum or protective gas. Grain boundary diffusion is then performed using a mixture of heavy rare earth elements and BFe.
It achieves the restoration of magnet performance, simplifies the process, reduces environmental pollution and processing losses, improves the coercivity and heat resistance of magnets, and reduces costs.
Smart Images
Figure BDA0003861445410000061
Abstract
Description
Technical Field
[0001] This invention belongs to the field of NdFeB waste recycling technology, and specifically relates to a method for utilizing NdFeB waste from dismantled machines. Background Technology
[0002] Sintered NdFeB is a third-generation rare-earth permanent magnet material. It is the most widely used magnetic material with the highest comprehensive magnetic properties today, and is widely used in IT electronics, industrial motors and new energy industries.
[0003] Sintered NdFeB magnets can be used for extended periods under normal operating conditions. However, due to equipment upgrades and replacements, these sintered NdFeB magnets used in equipment are often rendered unusable, resulting in a large amount of NdFeB waste. Sintered NdFeB contains reactive rare earth elements, making it prone to surface damage, oxidation, and corrosion over long-term use. Therefore, NdFeB waste removed from scrapped equipment is generally not suitable for direct use.
[0004] Rare earth elements in sintered NdFeB have significant recycling value. Early NdFeB recovery primarily employed a hydrochloric acid-based resolution process. This process first uses a strong acid to completely dissolve the NdFeB matrix, then removes iron impurities by controlling valence state and pH value. Subsequently, high-purity rare earth oxides are obtained through extraction, precipitation, and calcination. Furthermore, single rare earth metals can be prepared via electrolytic reduction and recycled as raw materials for NdFeB. This process yields high-purity rare earth elements without compromising material performance. However, its drawbacks are also obvious, including a cumbersome process flow, high acid and alkali consumption, high processing costs, significant pollution, and low yield.
[0005] HD method for preparing regenerated magnets is a newly developed high-efficiency recycling technology for NdFeB waste. For example, patent number CN201710160868.1 discloses a method for producing high-performance NdFeB using sintered NdFeB waste, which specifically includes the following steps: Step (1) Pre-treating the sintered NdFeB waste to make magnet blocks; Step (2) Performing the hydrogen explosion treatment on the magnet blocks to make coarse powder; Step (3) Mechanically crushing the coarse powder, adding solid additives, and then grinding it into fine powder with an average particle size of 2.8-3.2μm by air jet milling, adding liquid lubricant to the fine powder, and adding DyH3 to the fine powder according to the weight ratio of DyH3 added; Step (4) After the fine powder with added DyH3 is passivated, pressing it into a compact and performing isostatic pressing treatment; Step (5) Sintering and tempering. The drawbacks of this process are also obvious. Because the rare earth elements in the waste are oxidized, the regeneration process requires the replenishment of a large amount of rare earth elements, increasing processing costs and significantly reducing magnet performance. Furthermore, the yield rate in magnet remanufacturing is only 60-70%, which further increases material consumption and costs. Summary of the Invention
[0006] In view of the shortcomings of the prior art, the present invention proposes a method for utilizing NdFeB waste from dismantled machinery.
[0007] Specifically, this is achieved through the following technical solutions:
[0008] A method for utilizing dismantled NdFeB waste involves sequentially performing thermal demagnetization and surface treatment on the dismantled NdFeB waste, then repairing the magnet surface with a reducing agent, followed by machining to the required size, and finally performing grain boundary diffusion and heat treatment to restore its serviceability.
[0009] Specifically, the method for utilizing the aforementioned dismantled NdFeB waste includes the following steps:
[0010] (1) Place the dismantled neodymium iron boron waste magnets at a temperature of 350-600℃ and demagnetize them for 1-5 hours under the protection of any gas such as air, argon or nitrogen to obtain a non-magnetic matrix.
[0011] (2) Remove the coating, rust and surface inclusions on the substrate surface by pickling, mechanical grinding or grinding. Then, clean NdFeB substrate is obtained by air purging and drying in a drying oven.
[0012] (3) Cover the magnet surface with reducing metal or its hydride powder, and then treat it at 675-850°C for 3-5 hours in a vacuum sintering furnace under vacuum conditions or protective gas protection.
[0013] (4) The magnet is machined to the required size and then heat-treated in a vacuum sintering furnace to restore its performance.
[0014] The aforementioned dismantled NdFeB waste refers to intact block-shaped NdFeB magnets removed from motors, magnetic separators, or other NdFeB devices.
[0015] The reducing metal is any one of Ca, Mg, Zn, Al, or the lanthanides.
[0016] The protective gas is either nitrogen or argon.
[0017] The heat treatment includes a two-stage tempering process, first sintering at 850–1020°C for 6–12 hours, and then sintering at 470–530°C for 1–5 hours.
[0018] The aforementioned grain boundary diffusion refers to attaching a mixture of heavy rare earth elements, BFe, and n-hexane to the surface of a magnet by any of the following methods: physical adhesion, spraying, and coating; the heavy rare earth elements are Dy, Tb, or their compounds; and the ratio of n-hexane, rare earth metal, and BFe in the mixture is 50:45:5 to 5:47:3.
[0019] The method for utilizing the dismantled NdFeB waste may further include performing surface treatment and magnetization on the recycled magnets.
[0020] Beneficial effects:
[0021] This invention primarily employs surface repair methods, including simple surface treatment, surface reduction, and grain boundary diffusion, to restore the magnet's performance and meet the requirements for continued service. This process is simple and efficient, eliminating the need for separation, purification, or pulverization remanufacturing, significantly shortening the process and avoiding environmental pollution and processing losses associated with regeneration. Therefore, it features environmental friendliness, energy efficiency, high cost, and low cost.
[0022] This invention uses various reducing metals or their compounds to repair the surface of waste magnets. In particular, a mixture of BFe and heavy rare earth elements is used as a penetrant, which significantly improves the coercivity and heat resistance of the magnets, while basically not damaging the remanence of the magnets. This invention meets the application requirements of magnet reuse processes where magnets are thinned and the working load line is reduced, thus requiring a simultaneous increase in the coercivity of the magnets. It has good practical effects. Detailed Implementation
[0023] The specific embodiments of the present invention will be described in further detail below, but the present invention is not limited to these embodiments. Any improvements or substitutions based on the basic spirit of these embodiments shall still fall within the scope of protection claimed by the claims of the present invention.
[0024] Example 1
[0025] A method for utilizing dismantled NdFeB waste includes the following steps:
[0026] (1) Place the dismantled neodymium iron boron waste magnets at 350°C and demagnetize them in air atmosphere for 5 hours to obtain a non-magnetic matrix;
[0027] (2) The coating, rust and inclusions on the substrate surface are removed by mechanical grinding through material self-grinding, and the impurities adhering to the surface are removed by airflow sweeping. Then, the substrate is dried at 100°C in a drying oven to obtain a clean NdFeB substrate.
[0028] (3) CaH2 powder is covered on the surface of the magnet and treated at 675°C for 3 hours in a vacuum sintering furnace under vacuum conditions to obtain a surface-repaired magnet.
[0029] (4) The magnet is machined to the required size and coated with a blend of dysprosium fluoride, ferroboron and n-hexane by spraying. The ratio of n-hexane:dysprosium fluoride:ferroboron in the blend is 50:45:5. Then it is treated in a vacuum sintering furnace at 950°C for 12 hours and then at 470°C for 5 hours to obtain a regenerated magnet.
[0030] Example 2
[0031] A method for utilizing dismantled NdFeB waste includes the following steps:
[0032] (1) The dismantled neodymium iron boron waste magnets were placed at 600℃ and demagnetized for 1 hour under argon atmosphere protection to obtain a non-magnetic matrix.
[0033] (2) The coating, rust and inclusions on the substrate surface are dissolved by using nitric acid-assisted ultrasonic cleaning. After washing the surface with running water, it is dried in a drying oven at 100°C to obtain a clean NdFeB substrate.
[0034] (3) NdHx powder is covered on the surface of the magnet and treated at 850°C for 5 hours in a vacuum sintering furnace under vacuum conditions to obtain a surface-repaired magnet.
[0035] (4) The magnet is machined to the required size and then coated with a blend of terbium hydride, ferroboron and n-hexane. The ratio of n-hexane:terbium hydride:ferroboron in the blend is 50:47:3. The magnet is then treated in a vacuum sintering furnace at 850°C for 6 hours and then at 530°C for 1 hour to obtain a regenerated magnet.
[0036] Example 3
[0037] A method for utilizing dismantled NdFeB waste includes the following steps:
[0038] (1) The dismantled neodymium iron boron waste magnets were placed at 550°C and demagnetized for 2 hours under nitrogen atmosphere protection to obtain a non-magnetic matrix.
[0039] (2) The coating, rust and inclusions on the substrate surface are removed by mechanical grinding. After washing the surface with running water, it is dried in a drying oven at 100°C to obtain a clean NdFeB substrate.
[0040] (3) PrHx powder is applied to the surface of the magnet and then treated at 800°C for 4 hours in a vacuum sintering furnace under vacuum conditions to obtain a surface-repaired magnet.
[0041] (4) The magnet is machined to the required size and then coated with a blend of dysprosium hydride, terbium hydride, ferroboron and n-hexane. The ratio of n-hexane:dysprosium hydride, terbium hydride:ferroboron in the blend is 50:23:23:4. Then it is treated in a vacuum sintering furnace at 900°C for 10 hours and then at 500°C for 2 hours to obtain a regenerated magnet.
[0042] The original properties of the NdFeB waste materials from Examples 1-3 and dismantled machines were tested and are shown in Table 1:
[0043] Table 1
[0044]
Claims
1. A method for utilizing dismantled NdFeB waste, characterized in that, After undergoing thermal demagnetization and surface treatment, the surface of the dismantled NdFeB magnets is repaired using reducing metals or their hydrides. Following machining to the required dimensions, the magnets then undergo grain boundary diffusion and heat treatment. The process includes the following steps: (1) Place the dismantled neodymium iron boron waste magnets at a temperature of 350-600℃ and demagnetize them for 1-5 hours under the protection of any gas such as air, argon or nitrogen to obtain a non-magnetic matrix. (2) Remove the coating, rust and surface inclusions on the substrate surface by pickling, mechanical grinding or grinding. Then, clean NdFeB substrate is obtained by air purging and drying in a drying oven. (3) Cover the magnet surface with reducing metal or its hydride powder, and then treat it at 675-850°C for 3-5 hours in a vacuum sintering furnace under vacuum conditions or protective gas protection. (4) The magnet is machined to the required size, and a mixture of heavy rare earth elements and BFe and n-hexane is attached to the surface of the magnet by any of the following methods: physical adhesion, spraying and coating. Then, it is heat-treated in a vacuum sintering furnace. The reducing metal is any one of Ca, Mg, Zn, and Al.
2. The method for utilizing dismantled NdFeB waste as described in claim 1, characterized in that, The protective gas is either nitrogen or argon.
3. The method for utilizing dismantled NdFeB waste as described in claim 1, characterized in that, The heat treatment includes a two-stage tempering process, first sintering at 850–1020°C for 6–12 hours, and then sintering at 470–530°C for 1–5 hours.
4. The method for utilizing dismantled NdFeB waste as described in claim 1, characterized in that, The heavy rare earth elements are Dy, Tb, or their compounds.
5. The method for utilizing dismantled NdFeB waste as described in claim 1, characterized in that, The ratio of n-hexane, rare earth metals and BFe in the mixture is 50:45:5 to 5:47:3.