All-waste sintered regenerated neodymium-iron-boron magnet and preparation method thereof

Abstract

The invention provides an all-waste regenerated sintered neodymium-iron-boron magnet and a preparation method thereof. The method comprises the following steps: 1) classifying pretreated waste magnets to obtain a low-rare-earth-content magnet and a high-rare-earth-content magnet; (2) carrying out coarse crushing treatment on the low-rare-earth-content magnet, and then carrying out hydrogen crushing and jet milling treatment to obtain low-rare-earth-content magnet regenerated powder; (3) the high-rare-earth-content magnet is subjected to smelting and rapid hardening treatment to obtain a casting piece, then hydrogen decrepitation and jet milling treatment are conducted, and high-rare-earth-content magnet regenerated powder is obtained; (4) the low-rare-earth-content magnet regeneration powder and the high-rare-earth-content magnet regeneration powder are mixed in proportion, and mixed powder is obtained; 5, the mixed powder is subjected to compression molding, sintering and heat treatment.The utilization rate of rare earth secondary resources can be increased, dependence on rare earth primary resources and pollution of waste magnets to the environment are reduced, and green circulation and recycling of the rare earth secondary resources such as magnets in scrapped products and part of waste in the production process are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of neodymium-iron-boron magnetic materials, and particularly relates to a fully waste sintered recycled neodymium-iron-boron magnet and a preparation method thereof. Background Art

[0002] The reserves of rare earth resources have been decreasing year by year, and a large amount of high-quality rare earth waste has been generated during the production and consumption processes of the rare earth industry. The abundance values of these high-abundance rare earth wastes can even reach dozens or hundreds of times that of the original ore level. The content of rare earth elements in waste magnets accounts for about 30%, and the content of impurities therein is relatively low. It can maintain the original structure of the magnet and is a high-quality secondary resource. The precise and efficient recovery of waste magnets can save a large amount of mineral resources and reduce the environmental burden. Therefore, in the context of the shortage of rare earth resources, it is of great practical significance to recycle and utilize the recycled resources mainly composed of waste neodymium-iron-boron magnets and recycle them into neodymium-iron-boron sintered magnets according to their properties.

[0003] CN 112289533 B discloses a recycled neodymium-iron-boron magnetic material and a preparation method thereof. The preparation method is to mix the recycled waste neodymium-iron-boron after hydrogen breaking and jet milling with new materials and sinter to prepare finished neodymium-iron-boron. CN111968816 B discloses a recycled sintered neodymium-iron-boron magnetic steel and a preparation method thereof. During the preparation process, residual powder is collected and an appropriate amount of rare earth metal powder is added for proportioning, pressing, sintering and other processes. In the results disclosed by the above inventions, new materials are needed as supplements. Therefore, it is necessary to provide a new recycling process for neodymium-iron-boron magnets and recycled magnets to improve the utilization rate of rare earth secondary resources, reduce the dependence on rare earth primary resources and the environmental pollution caused by waste magnets. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a method for recycling and remanufacturing waste magnets using waste magnets as raw materials and optimizing the preparation process. The present invention improves the recycling process of neodymium-iron-boron magnets and the formula of recycled magnets, improves the utilization rate of rare earth secondary resources, reduces the dependence on rare earth primary resources and the environmental pollution caused by waste magnets, and realizes the green cycle and recycling of rare earth secondary resources such as magnets in waste products and some waste materials in the production process.

[0005] In a first aspect, the present invention provides a preparation method for a fully waste sintered recycled neodymium-iron-boron magnet, including: 1) Classify the pretreated waste magnets to obtain low-rare-earth magnets and high-rare-earth magnets.

[0006] 2) Coarsely crush the low-rare-earth magnets, then perform hydrogen breaking and jet milling to obtain low-rare-earth magnet recycled powder.

[0007] 3) The high rare earth content magnet is melted and rapidly solidified to obtain a casting sheet, and then subjected to hydrogen crushing and air flow milling treatment to obtain a high rare earth content magnet regenerated powder.

[0008] 4) The low rare earth content magnet regeneration powder and the high rare earth content magnet regeneration powder are mixed in proportion to obtain a mixed powder.

[0009] 5) Pressing, sintering and heat treating the mixed powder. The present invention provides a method for recycling waste magnets by using waste magnets as raw materials and shortening the preparation process. The NdFeB magnet regeneration process of the present invention is completely derived from waste magnets, and no other raw materials are introduced. In the regeneration and preparation method of all-waste sintered NdFeB magnets provided by the present invention, waste magnets are subjected to two specific paths to obtain regenerated powder, and different types of regenerated magnets are produced by adjusting the composition ratio. Compared with the traditional preparation process of sintered NdFeB magnets starting from metal or alloy raw materials, the present invention reduces the smelting and rapid solidification process, thereby saving manufacturing costs. In addition, the method not only saves material costs, but also does not require the introduction of external raw materials, thereby reducing production energy consumption. According to the powder making method and ratio of the present invention, magnets with specific properties can also be produced in a targeted manner.

[0010] Preferably, in step 1), the waste magnets are selected from permanent magnets disassembled from waste motors, scrapped wind power equipment, new energy vehicles and other equipment at the end of their life cycle, and waste materials and unqualified products in the production process.

[0011] Preferably, in step 1), the pretreatment includes demagnetization, surface pretreatment, cleaning and component detection. In the embodiment of the present invention, the waste magnets include waste motors, scrapped wind power equipment, permanent magnets disassembled from new energy vehicles, waste materials in the production process, and unqualified products, but do not include powdered materials, sludge materials, etc. generated during the production and processing of sintered NdFeB magnets. The metal raw materials used in the embodiment of the present invention are all derived from waste magnets, and no other metal raw materials are needed. The waste NdFeB magnets are classified and sorted according to whether they are magnetic and the surface state (including the type of coating, whether they are oxidized, whether they are cleaned, etc.).

[0012] Preferably, in step 1), the demagnetization includes thermal demagnetization treatment, preferably performed in a vacuum or inert gas atmosphere, and the non-magnetic sample is not demagnetized.

[0013] Preferably, in step 1), the surface pretreatment includes chemical immersion or mechanical grinding to remove the surface coating, and sandblasting, shot peening or pickling to remove the surface oxide scale; the waste magnets with nickel plating on the surface are preferably sieved to remove the coating after hydrogen crushing. In the embodiment of the present invention, the waste magnets are classified according to the surface state, and different surface treatment methods can be selected according to the type and surface state of the surface coating. If there is no coating or oxide layer on the surface, no surface pretreatment is performed.

[0014] Preferably, in step 1), the cleaning includes cleaning the magnet with deionized water and absolute ethanol and drying it to obtain a magnet with a clean surface. After cleaning, the substrate is silver-gray or gray. In the embodiments of the present invention, there are dust, oil and other pollution sources on the surface of the magnet after pretreatment. The used magnet is cleaned with deionized water or absolute ethanol, and compressed gas is used to blow dry it to prevent oxidation on the surface.

[0015] Preferably, in step 1), the pretreated used magnet is subjected to component detection by spectral rapid sorting technology; classification is carried out according to the detection results, and classification is carried out according to the rare earth element content and rare earth element types.

[0016] As a preference, in step 1), the total rare earth amount of the low-rare-earth magnet is less than 31 wt.%, preferably 28.5 - 30 wt.%; the total rare earth amount of the high-rare-earth magnet is higher than 31 wt.%, preferably 32.5 - 34.5 wt.%. In the embodiments of the present invention, two specific powder-making processes are respectively used for different magnets; the hydrogen crushing powder-making process is applicable to low-rare-earth magnets, and the remelting powder-making process is applicable to high-rare-earth magnets.

[0017] Preferably, in step 2), the coarse crushing treatment includes coarsely crushing the low-rare-earth magnet to a particle size less than 30 mm under the protection of an inert gas atmosphere.

[0018] More preferably, in step 2), the hydrogen absorption temperature for hydrogen crushing is 20 - 280°C; the average particle size X50 of the powder after air jet milling is 2 - 5.5 μm.

[0019] Preferably, in step 3), the melting and rapid solidification includes remelting and rapidly solidifying the high-rare-earth magnet to obtain a cast sheet, and the refining temperature for the melting and rapid solidification is 1450 - 1480°C.

[0020] More preferably, in step 3), the hydrogen absorption temperature for hydrogen crushing is 20 - 280°C; the average particle size X50 of the powder after air jet milling is 2 - 5.5 μm.

[0021] As a preference, it further includes adding a lubricant and an antioxidant to the regenerated powder of the high-rare-earth magnet and the regenerated powder of the low-rare-earth magnet. In the present invention, the additives added to the regenerated powder can be of common types in the art. In the embodiments of the present invention, conventional commercially available products are used, and the dosages are conventional dosages. The present invention does not make specific limitations thereto.

[0022] Further preferably, the total rare earth content of the low-rare-earth-content magnet recycled powder is not less than 28%, preferably 28.5 - 30 wt.%; the total rare earth content of the high-rare-earth-content magnet recycled powder is not less than 31.5%, preferably 32.5 - 34.5 wt.%.

[0023] Further preferably, in step 4), the mass ratio of the low-rare-earth-content magnet recycled powder to the high-rare-earth-content magnet recycled powder is 9:1 - 1:9, preferably 6:4 - 4:6.

[0024] Preferably, in step 5), the pressing and forming includes orientation pressing under a magnetic field of 1.7 - 1.9 T, and the oxygen content in the system is lower than 50 ppm during the pressing process.

[0025] Preferably, in step 5), the isostatic pressing treatment is carried out with a holding pressure of 200 - 225 MPa and a holding time of 120 - 240 s.

[0026] Further preferably, in step 5), the sintering temperature is 1020 - 1010 °C and the time is 1 - 6 h.

[0027] Preferably, in step 5), the heat treatment includes: primary heat treatment at a temperature of 800 - 950 °C for 2 - 6 h, and secondary heat treatment at a temperature of 400 - 600 °C for 2 - 6 h.

[0028] In the present invention, the sintered magnet is heat-treated in a vacuum environment. After the end of the holding process of the primary heat treatment, it is rapidly cooled to room temperature in an argon atmosphere, and then the secondary heat treatment is carried out, and then it is rapidly cooled to room temperature in an argon atmosphere. Under the preferred heat treatment conditions, the thin-layer grain boundary phase in the magnet can be better distributed, and the coercivity of the magnet can be improved.

[0029] A method for recycling and reusing waste magnets provided by the present invention, which uses waste magnets as raw materials and shortens the preparation process, realizes green, efficient, energy-saving and circular recycling and utilization. This method enables the green recycling and utilization of rare earth secondary resources such as magnets in waste products and some waste materials in the production process. In the preparation process of the recycled sintered NdFeB magnet, the raw materials used completely come from waste magnets and no other raw materials are introduced. Compared with the traditional preparation process of sintered NdFeB magnets starting from metal or alloy raw materials, the present invention reduces a part of the melting and rapid solidification processes, thereby saving the manufacturing cost. In addition, this preparation method does not require the introduction of additional metal raw materials, saves the material cost, and reduces the production energy consumption. According to different powder-making methods, the present invention can also produce recycled magnets with different properties targeted.

[0030] In the second aspect, the present invention provides a fully waste-material sintered recycled NdFeB magnet obtained by the preparation method of the above-mentioned fully waste-material sintered recycled NdFeB magnet.

[0031] The beneficial effects of the present invention are at least as follows: The present invention provides a method for recycling and remanufacturing waste magnets that uses waste magnets as raw materials and shortens the preparation process. This method for recycling waste magnets and preparing recycled magnets has the characteristics of simplicity, greenness, environmental friendliness, and high efficiency. The present invention does not introduce other metal materials as raw materials, reducing the raw material cost. At the same time, by adjusting the magnetic powder ratio with different rare earth contents, the performance range of the recycled magnets is expanded, and the comprehensive utilization rate of waste sintered NdFeB magnets is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0033] Figure 1 It is a schematic diagram of the preparation process of a fully waste recycled sintered NdFeB magnet provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0035] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0036] For those technical or conditions not specified in the embodiments of the present invention, they shall be in accordance with the technologies or conditions described in the literature in the field or in accordance with the product specifications. For the devices, equipment, reagents, etc. not specified by the manufacturer, they are all conventional products that can be obtained through regular channels. The additives and raw materials involved are all commercially available products.

[0037] In the embodiments of the present invention, the waste magnets used are selected from permanent magnets disassembled from equipment such as waste motors, scrapped wind power equipment, and new energy vehicles at the end of their life cycles, waste material heads and unqualified products during the production process.

[0038] Example 1 This example provides a method for recycling and preparing a fully waste recycled sintered neodymium iron boron magnet, and the steps are as follows: The waste magnets used as raw materials are waste magnets with low rare earth content and waste magnets with high rare earth content. Demagnetize the waste magnets, and after sorting, clean and polish the surface to obtain magnets with a smooth surface.

[0039] Among them, the total rare earth content of the low rare earth content magnet is not less than 30 wt.%. The total rare earth content of the high rare earth content magnet is not less than 32.50 wt.%.

[0040] Coarsely crush the low rare earth content magnet under a nitrogen protection atmosphere to a particle size less than 30 mm. Then add it to a hydrogen crushing furnace, heat it to 180°C in a vacuum environment and keep it warm. After closing the vacuum system, fill it with hydrogen to start hydrogen absorption. After hydrogen absorption saturation, evacuate and heat it to 550°C and dehydrogenate for 4 h. After dehydrogenation, rapidly cool it. The cooled material is transferred to an oxygen-excluding storage tank under inert gas protection. Add antioxidant and lubricant respectively according to the mass ratio of one-thousandth and five-ten-thousandths to the powder, and mix evenly for use. Control the oxygen content of the jet mill system to below 20 ppm, transfer the hydrogen-crushed coarse powder of the low rare earth content waste magnet to the jet mill, control the rotation speed of the jet mill, and obtain a powder with an average particle size of 3.3 μm. Store the powder in an oxygen-excluding storage tank, add antioxidant and lubricant respectively according to the mass ratio of one-thousandth and five-ten-thousandths to the powder, and mix evenly for use.

[0041] Put the high rare earth content magnet into a melting and rapid solidification furnace, heat it until it is completely melted and carry out homogenization refining. During the refining process, the temperature of the molten liquid metal is maintained at about 1460°C. After the refining is completed, pour the molten metal into a water-cooled copper roller through a transfer ladle to obtain a flaky ingot. Remelt and cast the high rare earth content waste magnet sheet, transfer it to a hydrogen crushing furnace, evacuate to below 0.01 Pa, after closing the vacuum system, fill it with hydrogen at room temperature until hydrogen absorption saturation. After hydrogen absorption saturation, keep the furnace pressure below 0.01 Pa, heat it to 550°C and keep it warm for 4 h for dehydrogenation process. After dehydrogenation, transfer the material to an air-excluding storage tank under inert gas protection, add antioxidant and lubricant respectively according to the mass ratio of one-thousandth and five-ten-thousandths to the powder, and mix evenly for use. Control the oxygen content of the jet mill system to below 20 ppm, and transfer the hydrogen-crushed coarse powder of the low rare earth content waste magnet to the jet mill. Store the powder in a storage tank, add antioxidant and lubricant respectively according to the mass ratio of one-thousandth and five-ten-thousandths to the powder, and mix evenly for use.

[0042] Weigh the two powders in proportion under inert gas protection and transfer them to the same material tank. The material ratio (low rare earth content: high rare earth content) is 7:3, and mix evenly.

[0043] The mixed powder is subjected to orientation pressing under a nitrogen protection and a magnetic field of 1.8 T. During the pressing process, the oxygen content in the system is lower than 50 ppm. To increase the density of the green compact, the green compact is subjected to isostatic pressing at a pressure of 220 MPa for 180 s.

[0044] The green compact is unpacked in a glove box under an inert gas protection and transferred to a sintering furnace, where it is sintered in a vacuum environment at a sintering temperature of 1080 °C for 3 h. It is rapidly cooled to room temperature under an argon atmosphere.

[0045] The sintered magnet is heat-treated in a vacuum environment. The first-stage heat treatment temperature is 900 °C, and it is held for 3 h. After the holding process ends, it is rapidly cooled to room temperature under an argon atmosphere. Subsequently, a second-stage heat treatment is carried out at a temperature of 500 °C for 4 h, and then it is rapidly cooled to room temperature under an argon atmosphere.

[0046] Example 2-4 The method of Example 1 is adopted, with the difference that the material ratio (low rare earth content: high rare earth content) of 7:3 is changed to 6:4, 5:5, and 4:6 respectively.

[0047] Comparative Example 1-4 The waste magnet used in this comparative example is the same as the waste magnet in Example 1.

[0048] The waste magnet is added to a hydrogen crushing furnace and heated to 180 °C in a vacuum environment and held. After closing the vacuum system, hydrogen is filled to start hydrogen absorption. After hydrogen absorption saturation, it is evacuated and heated to 550 °C for 4 h of dehydrogenation. After dehydrogenation ends, it is rapidly cooled. The cooled material is transferred to an oxygen-excluding storage tank under an inert gas protection. Antioxidants and lubricants are added at a mass ratio of one-thousandth and five-ten-thousandths to the powder respectively, and they are mixed evenly for use. The oxygen content of the jet mill system is controlled below 20 ppm. The hydrogen-crushed coarse powder of the waste magnet with low rare earth content is transferred to the jet mill, and the rotation speed of the jet mill is controlled to obtain a powder with an average particle size of 3.3 μm. The powder is stored in an oxygen-excluding storage tank, and antioxidants and lubricants are added at a mass ratio of one-thousandth and five-ten-thousandths to the powder respectively, and they are mixed evenly for use. The low rare earth content magnet and the high rare earth content magnet are separately pulverized to finally obtain two kinds of powders. The material ratios (powder mixing) of the low rare earth content magnet and the high rare earth content magnet in Comparative Examples 1-4 are 7:3, 6:4, 5:5, and 4:6 respectively.

[0049] The preparation process after obtaining the powder is the same as the preparation process in Example 1.

[0050] Table 1 Performance of the recycled magnets prepared in Examples 1-4 and Comparative Examples 1-4

[0051] Examples 5 - 8 This example provides a method for recycling and preparing a fully waste - recycled sintered Nd - Fe - B magnet, and the steps are as follows: The waste magnets used as raw materials are waste magnets with low rare - earth content and waste magnets with high rare - earth content. Demagnetize the waste magnets, and after sorting, clean and polish the surface to obtain magnets with a smooth surface.

[0052] After testing, the magnets meet the following performance: Among them, the total rare - earth content of the waste magnets with low rare - earth content is not less than 30 wt.%. The total rare - earth content of the waste magnets with high rare - earth content is not less than 32.50 wt.%.

[0053] Coarsely crush the waste magnets with low rare - earth content to a particle size of less than 30 mm under a nitrogen - protection atmosphere. Then add them to a hydrogen - crushing furnace, heat to 180°C in a vacuum environment and hold for a certain time. After closing the vacuum system, fill with hydrogen to start hydrogen absorption. After hydrogen - absorption saturation, evacuate the vacuum and heat to 550°C for 4 h for dehydrogenation. After dehydrogenation, rapidly cool. The cooled material is transferred to an oxygen - excluded storage tank under inert - gas protection. Add antioxidant and lubricant respectively at a mass ratio of one - thousandth and five - thousandths to the powder, mix evenly and set aside. Control the oxygen content in the jet - mill system to below 20 ppm. Transfer the hydrogen - crushed coarse powder of the waste magnets with low rare - earth content to the jet - mill, control the rotation speed of the jet - mill to obtain a powder with an average particle size of 3.3 μm. Store the powder in an oxygen - excluded storage tank, add antioxidant and lubricant respectively at a mass ratio of one - thousandth and five - thousandths to the powder, mix evenly and set aside.

[0054] Put the waste magnets with high rare - earth content into a melting and rapid - solidification furnace, heat until completely melted and carry out homogenization refining. During the refining process, keep the temperature of the molten liquid metal at about 1460°C. After refining, pour the molten metal into a water - cooled copper roll through a transfer ladle to obtain flaky ingots. Remelt and cast the waste magnets with high rare - earth content into flakes, transfer them to a hydrogen - crushing furnace, evacuate the vacuum to below 0.01 Pa, then fill with hydrogen at room temperature after closing the vacuum system until hydrogen - absorption saturation. After hydrogen - absorption saturation, keep the furnace pressure below 0.01 Pa, heat to 550°C and hold for 4 h for dehydrogenation process. After dehydrogenation, transfer the material to an air - excluded storage tank under inert - gas protection. Add antioxidant and lubricant respectively at a mass ratio of one - thousandth and five - thousandths to the powder, mix evenly and set aside. Control the oxygen content in the jet - mill system to below 20 ppm. Transfer the hydrogen - crushed coarse powder of the waste magnets with low rare - earth content to the jet - mill. Store the powder in a storage tank, add antioxidant and lubricant respectively at a mass ratio of one - thousandth and five - thousandths to the powder, mix evenly and set aside.

[0055] Weigh two kinds of powders in proportion under the protection of inert gas and transfer them to the same material tank. The material ratios of the low-rare-earth-content magnets and high-rare-earth-content magnets in Examples 5-8 are 7:3, 6:4, 5:5, and 4:6 respectively, and mix them evenly.

[0056] Under the protection of nitrogen gas, the mixed powders are subjected to orientation pressing under a magnetic field of 1.8 T. During the pressing process, the oxygen content in the system is lower than 50 ppm. To improve the density of the green compact, isostatic pressing treatment is carried out on the green compact, with a holding pressure of 220 MPa and a holding time of 180 s.

[0057] Remove the packaging of the green compact in a glove box protected by inert gas, transfer it to a sintering furnace, and sinter it in a vacuum environment at a sintering temperature of 1080 °C for 3 h. Rapidly cool it to room temperature under an argon atmosphere.

[0058] The sintered magnets are heat-treated in a vacuum environment. The primary heat treatment temperature is 880 °C, and the holding time is 3 h. After the holding process ends, rapidly cool it to room temperature under an argon atmosphere. Subsequently, secondary heat treatment is carried out at a temperature of 480 °C for 4 h, and then rapidly cool it to room temperature under an argon atmosphere.

[0059] Comparative Examples 5-8 The waste magnets used in the comparative examples are the same as those in Example 1.

[0060] Add the waste magnets to a hydrogen crushing furnace, heat them to 180 °C in a vacuum environment and hold the temperature. After closing the vacuum system, fill it with hydrogen to start hydrogen absorption. After hydrogen absorption saturation, evacuate the vacuum and heat it to 550 °C for 4 h of dehydrogenation. After dehydrogenation ends, rapidly cool it. The cooled material is transferred to an oxygen-excluding storage tank under the protection of inert gas. Add antioxidant and lubricant respectively at a mass ratio of one-thousandth and five-thousandths of the powder mass, and mix them evenly for use. Control the oxygen content in the jet mill system to below 20 ppm. Transfer the hydrogen-crushed coarse powder of the low-rare-earth-content waste magnets to the jet mill, control the rotation speed of the jet mill, and obtain a powder with an average particle size of 3.3 μm. Store the powder in an oxygen-excluding storage tank, add antioxidant and lubricant respectively at a mass ratio of one-thousandth and five-thousandths of the powder mass, and mix them evenly for use. The low-rare-earth-content magnets and high-rare-earth-content magnets are separately pulverized. The material ratios (powder mixing) of the low-rare-earth-content magnets and high-rare-earth-content magnets in Comparative Examples 5-8 are 7:3, 6:4, 5:5, and 4:6 respectively.

[0061] The preparation process after obtaining the powder is the same as that in Example 1.

[0062] Table 2 Performance of the recycled magnets prepared in Examples 5-8 and Comparative Examples 5-8

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A preparation method of a fully waste sintered recycled neodymium iron boron magnet, characterized in that, Comprising: 1) Classify the pre-treated waste magnets to obtain low-rare-earth magnets and high-rare-earth magnets; 2) Coarsely crush the low-rare-earth magnets, then perform hydrogen crushing and jet milling to obtain low-rare-earth magnet recycled powder; 3) Melt and rapidly solidify the high-rare-earth magnets to obtain cast sheets, then perform hydrogen crushing and jet milling to obtain high-rare-earth magnet recycled powder; 4) Mix and proportion the low-rare-earth magnet recycled powder and the high-rare-earth magnet recycled powder to obtain a mixed powder; 5) Compress, sinter and heat-treat the mixed powder.

2. The preparation method of the all-waste sintered recycled neodymium iron boron magnet according to claim 1, characterized in that, In step 1), the waste magnets are selected from permanent magnets disassembled from equipment such as waste motors, scrapped wind power equipment, and new energy vehicles at the end of their life cycles, waste scraps and unqualified products during the production process.

3. The preparation method of the all-waste sintered recycled neodymium iron boron magnet according to claim 1 or 2, characterized in that, In step 1), the total rare-earth content of the low-rare-earth magnets is less than 31 wt.%; the total rare-earth content of the high-rare-earth magnets is more than 31 wt.%.

4. The preparation method of the all-waste sintered recycled neodymium iron boron magnet according to any one of claims 1-3, characterized in that, In step 2), the coarse crushing treatment includes coarsely crushing the low-rare-earth magnets to a particle size less than 30 mm under the protection of an inert gas atmosphere; In step 2), the hydrogen absorption temperature for hydrogen crushing is 20~280 °C; the average particle size X50 of the powder after jet milling is 2~5.5 μm.

5. The preparation method of the all-waste sintered recycled NdFeB magnet according to any one of claims 1-4, characterized in that, In step 3), the melt and rapid solidification includes remelting and rapidly solidifying the high-rare-earth magnets to obtain cast sheets, and the refining temperature for the melt and rapid solidification is 1450~1480 °C.

6. The preparation method of the all-waste sintered recycled neodymium-iron-boron magnet according to any one of claims 1-5, characterized in that, In step 3), the hydrogen absorption temperature for hydrogen crushing is 20~280 °C; the average particle size X50 of the powder after jet milling is 2~5.5 μm.

7. The preparation method of the all-waste sintered recycled NdFeB magnet according to any one of claims 1-6, characterized in that, In step 4), the mass ratio of the low-rare-earth magnet recycled powder to the high-rare-earth magnet recycled powder is 9:1~1:9, preferably 6:4~4:

6.

8. The preparation method of the all-waste sintered recycled NdFeB magnet according to any one of claims 1-7, characterized in that, In step 5), the compression molding includes orientation pressing under a magnetic field of 1.7~1.9 T, and the oxygen content in the system is less than 50 ppm during the pressing process; In step 5), the isostatic pressing treatment is carried out with a holding pressure of 200~225 MPa and a holding time of 120~240 s.

9. The preparation method of the all-waste sintered recycled neodymium-iron-boron magnet according to any one of claims 1-8, characterized in that, In step 5), the sintering temperature is 1020~1010 °C and the time is 1~6 h; In step 5), the heat treatment includes: performing primary heat treatment at a temperature of 800~950 °C for 2~6 h, and performing secondary heat treatment at a temperature of 400~600 °C for 2~6 h.

10. The all-waste sintered recycled Nd-Fe-B magnet obtained by the preparation method of the all-waste sintered recycled Nd-Fe-B magnet according to any one of claims 1-9.

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