A method for efficient recovery of sintered cerium-containing permanent magnet waste

Abstract

The application relates to the technical field of waste recycling, in particular to a method for efficiently recycling sintered cerium-containing permanent magnet waste, which comprises the following steps: firstly, classifying the waste and treating the waste by microwave-plasma cooperation; secondly, coarsely crushing and compound hydrogen crushing; thirdly, preparing multi-element alloyed nano powder containing special additives; fourthly, adding an antioxidant and performing airflow grinding and molecular self-assembly powder mixing; and finally, performing magnetic field assisted forming and gradient sintering to prepare high-performance permanent magnets. The application can efficiently utilize rare earth resources and reduce waste; the application has strong environmental protection and can reduce pollution; the prepared permanent magnets have excellent performance, excellent and stable magnetic energy product and other indexes; the application can also process various waste, has wide adaptability and can reduce enterprise cost.

Description

Technical Field

[0001] This invention relates to the field of waste recycling technology, specifically a method for the efficient recycling of sintered cerium-containing permanent magnet waste. Background Technology

[0002] Rare earth permanent magnet materials, especially sintered cerium-containing permanent magnets, play an indispensable role in many key areas of modern industry due to their excellent magnetic properties, such as drive motors for new energy vehicles, core components of wind power generation equipment, and micro-motors for electronic devices. With the booming development of these industries, the demand for sintered cerium-containing permanent magnets continues to rise, leading to a daily increase in the amount of waste and scrapped products generated during the production process. Failure to properly handle this waste will not only result in a significant waste of rare earth resources but also cause serious environmental problems.

[0003] Currently, methods for processing sintered cerium-containing permanent magnet waste have many drawbacks. Traditional pyrometallurgical processes require high-temperature smelting, which is not only energy-intensive but also results in low recovery rates due to the volatilization and loss of rare earth elements such as cerium during the smelting process. Furthermore, high-temperature treatment can introduce impurities, affecting the performance of recycled materials. While hydrometallurgical processes can avoid the problems caused by high temperatures to some extent, the process is complex, requires the use of large amounts of chemical reagents, and can easily cause environmental pollution. Moreover, both pyrometallurgical and hydrometallurgical methods struggle to precisely control the microstructure and magnetic properties of recycled materials, leading to unstable product quality that fails to meet the demands of the high-end market.

[0004] Furthermore, existing waste recycling methods often overlook the diversity of waste materials. Waste generated at different production stages varies greatly in surface condition, composition, and structure. For example, waste generated during sintering may have a severe oxide layer on its surface; machining waste may be contaminated with oil; and electroplating waste may have a coating. Failure to address these differences will affect the effectiveness of subsequent recycling processes.

[0005] Against the backdrop of increasingly fierce global competition for rare earth resources and ever-stricter environmental protection requirements, the development of an efficient, environmentally friendly method for recycling sintered cerium-containing permanent magnet waste, capable of precisely controlling the performance of recycled materials, is urgently needed. This will not only help alleviate the shortage of rare earth resources and reduce enterprise production costs, but also reduce environmental pollution and promote the sustainable development of related industries. This patent is based on this situation and aims to fill the gap in existing technology, providing an innovative solution for the recycling and utilization of sintered cerium-containing permanent magnet waste. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the shortcomings of existing technologies, this invention provides a method for the efficient recycling of sintered cerium-containing permanent magnet waste.

[0008] (II) Technical Solution

[0009] A method for efficient recycling of sintered cerium-containing permanent magnet waste includes the following key steps:

[0010] Waste classification and pretreatment enhancement: Sintered unqualified magnetic blocks are classified as Class I waste, and the oxide layer is removed by chamfering; Machining waste is classified as Class II waste, and is treated by low-temperature degreasing and chamfering; Electroplating unqualified products and scrapped products are classified as Class III waste, and are treated by high-temperature baking to remove the plating and chamfering; All three types of waste undergo water washing, ultrasonic vibration, magnetic separation, drying and air cooling.

[0011] Composite hydrogen crushing: First, the pretreated waste is mixed and coarsely crushed to a particle size of less than 25mm, and argon gas is introduced for protection; in the hydrogen crushing process, a step-by-step hydrogen treatment process is adopted. The first step is to absorb hydrogen at a hydrogen absorption pressure of 0.08-0.12MPa for 1-3 hours, and the second step is to increase the pressure to 0.15-0.2MPa to absorb hydrogen for 1-2 hours.

[0012] Preparation of multi-element alloyed nanopowder: The auxiliary materials are weighed and placed in a high-temperature and high-pressure alloying nano furnace, and electric arc melting is carried out under a hydrogen-argon mixed gas atmosphere. The auxiliary alloy MMxT1-x nanopowder is prepared by evaporation and condensation, and then passivated in a nitrogen-argon mixed glove box. The particle size D50 of the nanopowder is 30-150nm.

[0013] Intelligent airflow mill classification: A novel antioxidant with a content of 0.3-0.5‰ is added to the coarse powder from hydrogen crushing. The structural formula of the novel antioxidant is as follows:

[0014]

[0015] Mix for 1.5-2.5 hours; use an intelligent airflow mill system to automatically adjust the speed of the sorting wheel and the pressure of the mill chamber to make the average particle size D50 3.2-4.5μm, and the ratio of particle size D90 to D10 less than 4.2;

[0016] Molecular self-assembly powder mixing: Add 3-5% of the total mass of multi-element alloyed nanopowder to the waste fine powder, and then add 0.6-0.8‰ of the total mass of the mixed fine powder as a self-assembly lubricant; in a three-dimensional mixer, first mix the powder at a low speed of 150-200 r / min, and then mix the powder at a high speed of 300-400 r / min.

[0017] Magnetic field-assisted forming and gradient sintering: After powder mixing, a 2-3T pulsed magnetic field is applied in a magnetic field orientation press to assist orientation and molding, followed by densification treatment in a cold isostatic press; the green body is then subjected to gradient sintering in a vacuum sintering furnace.

[0018] Preferably, the chamfering and descaling time is more than 30 minutes; the temperature selected for low-temperature degreasing of the second type of waste is 200℃.

[0019] Preferably, in the auxiliary alloy MMxT1-x, MM is a mixed rare earth alloy containing La, Ce, Pr, and Nd, and T is one or more non-rare earth metals such as Al, Cu, Ga, and Co., where x is the mass percentage of the mixed rare earth MM in the auxiliary alloy multiplied by 100, and 50.0 ≤ x < 100.0.

[0020] Preferably, during high-speed mixing of the self-assembled lubricant, the chemical bond energy formed between the end groups of the hyperbranched polymer molecules and the active sites on the powder surface is 20-30 kJ / mol.

[0021] Preferably, during magnetic field-assisted molding, the pulse frequency of the pulsed magnetic field is 50-100Hz and the pulse width is 5-10ms.

[0022] Preferably, during the gradient sintering process, the vacuum level inside the vacuum sintering furnace is maintained at 3-5×10-3 Pa throughout the entire process.

[0023] Preferably, the maximum energy product of the permanent magnet is 35MGOe≤(BH)max≤55MGOe, the remanence range is 12-15kGs, and the coercivity range is 13-15kOe.

[0024] Preferably, the regenerated cerium-containing rare earth permanent magnets prepared by this method have uniform internal grain size, with an average grain size of 5-10 μm.

[0025] Preferably, the gradient sintering is performed in a high vacuum environment, with the first vacuum heat treatment temperature being 960–1030°C and the treatment time being 4–6 hours; the second heat treatment temperature being 780–880°C and the treatment time being 2–3 hours; and the third heat treatment temperature being 460–550°C and the treatment time being 3–6 hours.

[0026] (III) Beneficial Technical Effects

[0027] Compared with existing technologies, the beneficial effects of this invention are:

[0028] 1. Through precise waste sorting and advanced pretreatment technology, rare earth elements in waste can be fully recovered, significantly improving the utilization rate of rare earth resources. Compared with traditional methods, it reduces the loss of rare earth elements during the recycling process, effectively alleviates the problem of rare earth resource shortage, and provides strong support for the sustainable development of related industries.

[0029] 2. It eliminates the high-energy-consuming and high-polluting steps in traditional processes; compared with traditional surface treatment methods, microwave-plasma synergistic processing technology does not require the use of a large number of chemical reagents, reducing the generation of wastewater, waste gas and waste residue; moreover, the entire recycling process has low energy consumption, which is in line with the current green and environmentally friendly development concept.

[0030] 3. The method of this patent can precisely control the microstructure and magnetic properties of regenerated permanent magnets; the addition of multi-element alloyed nanopowder, combined with molecular self-assembly powder mixing and gradient sintering process, makes the key performance indicators of regenerated permanent magnets, such as maximum energy product, remanence and coercivity, excellent and with high performance stability; its maximum energy product can be stably maintained between 35-55 MGOe, which can meet the performance requirements of permanent magnets in different fields, especially the strict requirements of high-end manufacturing industry for high-performance permanent magnets.

[0031] 4. This invention is highly adaptable and can handle cerium-containing permanent magnet waste from different sources and in different states. Waste generated during sintering, machining, or electroplating can be efficiently recycled and reused through targeted processing, greatly expanding the application scope of waste recycling, reducing production costs for enterprises, and improving economic benefits. Attached Figure Description

[0032] Figure 1 This is a flowchart of a method for efficient recycling of sintered cerium-containing permanent magnet waste proposed in this invention;

[0033] Figure 2 This is a graph comparing the maximum magnetic energy product of the embodiment and the comparative example;

[0034] Figure 3 This is a line graph comparing the remanence and coercivity of the embodiment and the comparative example;

[0035] Figure 4 This is a columnar comparison diagram of the average grain size of the embodiments and comparative examples;

[0036] Figure 5 This is the nuclear magnetic resonance spectrum of a novel antioxidant. Detailed Implementation

[0037] Example 1

[0038] Raw material preparation: Collect cerium-containing permanent magnet waste generated from sintering, machining, and electroplating processes, and label them as Category I, Category II, and Category III waste, respectively. Prepare raw materials such as mixed rare earth alloys (MM), non-rare earth metals (Al, Cu), antioxidants, and self-assembling lubricants based on hyperbranched polymers.

[0039] Waste sorting and pretreatment enhancement: Three types of waste were placed separately. The first type of waste was chamfered for 45 minutes to remove the oxide layer; the second type of waste underwent low-temperature degreasing at 200℃ for 2 hours and chamfering for 40 minutes; the third type of waste underwent baking at 850℃ for 2 hours and chamfering for 35 minutes. All waste was sequentially subjected to ultrasonic vibration (40kHz / 15min), magnetic separation (1.2T magnetic field strength), drying at 80℃, and air cooling (25℃ airflow).

[0040] Composite hydrogen crushing: The pretreated waste materials are mixed and coarsely crushed to a particle size of less than 20 mm using a crusher. Composite hydrogen crushing is then carried out under argon protection. In the first step, hydrogen is absorbed at a hydrogen absorption pressure of 0.1 MPa for 2 hours. In the second step, the pressure is increased to 0.18 MPa, and hydrogen absorption continues for 1.5 hours. The dehydrogenation temperature is controlled at 500℃, and the vacuum degree is 1.5 Pa at the end of dehydrogenation, yielding coarse powder.

[0041] Preparation of multi-element alloyed nanopowder: according to MM 70 (AlCu) 25 The ingredients were proportioned and placed in a high-temperature, high-pressure alloying nano-furnace. Arc melting was carried out at 1600℃ and 6MPa pressure under a hydrogen-argon mixed gas atmosphere for 3 hours. After evaporation and condensation, the mixture was passivated in a nitrogen-argon mixed glove box (nitrogen:argon = 1:3) to obtain nanoparticles with a particle size D50 of 100nm.

[0042] Intelligent airflow mill classification: An antioxidant at a ratio of 0.4‰ was added to the coarse powder after hydrogen crushing, and the mixture was stirred for 2 hours. Using an intelligent airflow mill system, based on real-time laser particle size monitoring feedback, the sorting wheel speed was adjusted to 4000 rpm and the mill chamber pressure to 0.6 MPa, so that the average particle size D50 of the magnetic powder was 4 μm, and the ratio of particle size D90 to D10 was 4.

[0043] Molecular self-assembly powder mixing: 4% of the total mass of multi-element alloyed nanopowder was added to the waste fine powder, followed by 0.7‰ of the total mass of the mixed fine powder. In a three-dimensional mixer, the powder was first mixed at a low speed of 180 r / min for 1.5 hours, and then at a high speed of 350 r / min for 2.5 hours.

[0044] Magnetic field-assisted forming and gradient sintering: After powder mixing, a 2.5T pulsed magnetic field is applied in a magnetic field orientation press to assist orientation and molding. The pulse frequency is 80Hz and the pulse width is 8ms. Then, it undergoes densification treatment in a cold isostatic press. The green body is then subjected to gradient sintering in a vacuum sintering furnace. The first stage is heated to 980℃ for 4 hours; the second stage is cooled to 840℃ for 2.5 hours; and the third stage is heated to 500℃ for 5 hours, yielding a recycled cerium-containing rare earth permanent magnet.

[0045] Performance testing: The performance test results of this permanent magnet show that its maximum magnetic energy product reaches 45 MGOe, remanence is 13.5 kGs, coercivity is 14 kOe, and average grain size is 8 μm.

[0046] Example 2

[0047] Raw material preparation: Similar to Example 1, prepare cerium-containing permanent magnet waste from different sources, as well as raw materials such as MM and non-rare earth metals (Ga, Co).

[0048] Waste sorting and pretreatment enhancement: Category I waste was chamfered for 50 minutes to remove the oxide layer; Category II waste was degreased at 200℃ for 2 hours and chamfered for 50 minutes; Category III waste was baked at 850℃ for 2 hours to remove plating and chamfered for 40 minutes. All waste was subjected to ultrasonic oscillation (40kHz / 15min), magnetic separation (1.2T magnetic field strength), drying at 80℃, and air cooling (25℃ airflow) in sequence.

[0049] Composite hydrogen crushing: coarsely crushed to a particle size of less than 22 mm, under argon protection, the first step is to absorb hydrogen at a hydrogen absorption pressure of 0.09 MPa for 2.5 hours, the second step is to increase the pressure to 0.16 MPa and absorb hydrogen for 1.2 hours, the dehydrogenation temperature is 490℃, and the vacuum degree is 1.8 Pa at the end of dehydrogenation to obtain coarse powder.

[0050] Preparation of multi-element alloyed nanopowder: according to MM 80 (GaCo) 17 The ingredients were proportioned and smelted in a high-temperature, high-pressure alloying nano-furnace under the same atmosphere and conditions for 3.5 hours. After passivation, nanoparticles with a particle size D50 of 120 nm were obtained.

[0051] Intelligent airflow mill classification: Add 0.4‰ antioxidant and mix for 2.2 hours. Adjust the sorting wheel speed of the intelligent airflow mill to 4100 rpm and the mill chamber pressure to 0.65 MPa, so that the average particle size D50 of the magnetic powder is 4.2 μm and the particle size D90 to D10 ratio is 4.1.

[0052] Molecular self-assembly powder mixing: The amount of nanoparticles added is 4.5% of the total powder mass, and 0.7‰ self-assembly lubricant is added. Mix the powder at a low speed of 190r / min for 1.8 hours and at a high speed of 380r / min for 2.2 hours.

[0053] Magnetic field-assisted forming and gradient sintering: Orientation pressing and cold isostatic pressing are performed under the assistance of a 2.8T pulsed magnetic field (pulse frequency 90Hz, pulse width 9ms). The green body is heated to 990℃ in a vacuum sintering furnace for 4.5 hours in the first stage; cooled to 850℃ for 2.8 hours in the second stage; and heated to 510℃ for 5.5 hours in the third stage to produce a permanent magnet.

[0054] Performance testing: The performance test results of this permanent magnet show that its maximum magnetic energy product is as high as 48 MGOe, remanence reaches 14 kGs, coercivity is 14.2 kOe, and average grain size is 7 μm.

[0055] Example 3

[0056] Raw material preparation: Collect waste materials and prepare raw materials such as MM and non-rare earth metals (Al, Cu, Ti).

[0057] Waste sorting and pretreatment enhancement: Category I waste was chamfered for 50 minutes to remove the oxide layer; Category II waste was degreased at 200℃ for 2.5 hours and chamfered for 45 minutes; Category III waste was baked at 860℃ for 2.2 hours to remove plating and chamfered for 40 minutes. All waste was subjected to ultrasonic oscillation (45kHz / 20min), magnetic separation (1.8T magnetic field strength), drying at 85℃, and air cooling (20℃ airflow) in sequence.

[0058] Composite hydrogen crushing: coarsely crushed to a particle size of less than 23 mm, under argon protection, the first step is to absorb hydrogen at a hydrogen absorption pressure of 0.11 MPa for 1.8 hours, the second step is to increase the pressure to 0.17 MPa and absorb hydrogen for 1.3 hours, the dehydrogenation temperature is 510℃, and the vacuum degree is 1.6 Pa at the end of dehydrogenation to obtain coarse powder.

[0059] Preparation of multi-element alloyed nanopowder: according to MM 65 (AlCuTi) 32 The ingredients were proportioned and smelted in a high-temperature, high-pressure alloying nano-furnace for 4 hours to obtain nanoparticles with a particle size D50 of 80 nm, which were then passivated.

[0060] Intelligent airflow mill classification: Add 0.35‰ antioxidant and mix for 2.3 hours. Adjust the sorting wheel speed of the intelligent airflow mill to 3900 rpm and the mill chamber pressure to 0.55 MPa, so that the average particle size D50 of the magnetic powder is 3.8 μm and the particle size D90 to D10 ratio is 3.9.

[0061] Molecular self-assembly powder mixing: The amount of nanoparticles added is 3.5% of the total powder mass, and 0.65‰ self-assembly lubricant is added. Mix the powder at a low speed of 170r / min for 1.6 hours and at a high speed of 360r / min for 2.3 hours.

[0062] Magnetic field-assisted forming and gradient sintering: Orientation pressing and cold isostatic pressing are performed under the assistance of a 2.6T pulsed magnetic field (pulse frequency 70Hz, pulse width 7ms). The green body is placed in a vacuum sintering furnace, heated to 970℃ in the first stage for 4.2 hours; cooled to 830℃ in the second stage for 2.3 hours; and heated to 490℃ in the third stage for 4.8 hours to obtain permanent magnets.

[0063] Performance testing: The performance test results of this permanent magnet show that its maximum magnetic energy product is 42 MGOe, remanence reaches 13 kGs, coercivity is 13.5 kOe, and average grain size is 9 μm.

[0064] Comparative Example

[0065] Raw material preparation: Select cerium-containing permanent magnet waste materials from the same source and in the same quantity as in Example 1, and prepare conventional additives and lubricants.

[0066] Processing Procedure: Traditional sorting methods are employed, involving only simple surface cleaning and mechanical polishing. Hydrogen decomposition utilizes conventional single-step hydrogen absorption at a pressure of 0.098 MPa for 3 hours and a dehydrogenation temperature of 550℃. The air jet mill uses standard equipment without intelligent control. Powder mixing uses a standard lubricant and is performed in a conventional mixer at a single speed of 200 rpm for 3 hours. The molding and sintering processes follow traditional methods, without magnetic field assistance or gradient sintering.

[0067] Performance testing: The performance test results of this permanent magnet show that its maximum magnetic energy product is 30 MGOe, remanence is 11 kGs, coercivity is 12 kOe, and average grain size is 12 μm.

[0068] Comparison table of key performance indicators between the examples and comparative examples:

[0069]

[0070]

[0071] Conclusion: This table compares the differences between the embodiments and the comparative examples in key performance indicators of permanent magnets. The embodiments significantly outperform the comparative examples in terms of maximum energy product, remanence, and coercivity, and also have a smaller average grain size, indicating that the recycling method of this patent can effectively improve the performance of permanent magnets.

[0072] Comparison table of process parameters and costs between the examples and comparative examples:

[0073] project Example 1 Example 2 Example 3 Comparative Example Microwave power (W) 400 500 450 - Plasma discharge frequency (kHz) 30 35 32 - Hydrogen absorption pressure (MPa) 0.1 / 0.18 0.09 / 0.16 0.11 / 0.17 0.098 Dehydrogenation temperature (°C) 500 490 510 550 Production cost (RMB / kg) 80 82 78 90

[0074] Conclusion: This table illustrates the differences between the embodiments and the comparative examples in terms of process parameters and production costs. The embodiments employ innovative process parameters and have lower production costs than the comparative examples, demonstrating the advantages of this patented method in process optimization and cost control.

[0075] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for efficient recycling of sintered cerium-containing permanent magnet waste, characterized in that, This includes the following key steps: Waste sorting and pretreatment enhancement: Sintered unqualified magnetic blocks are classified as the first category of cerium-containing permanent magnet waste, and the oxide layer is removed by chamfering; The cerium-containing permanent magnet waste from machining is classified as Category II, and undergoes low-temperature degreasing and chamfering treatment; the substandard electroplated products and scrapped products are classified as Category III, and undergo high-temperature baking to remove the plating and chamfering treatment; all three categories of cerium-containing permanent magnet waste undergo water washing, ultrasonic vibration, magnetic separation, drying and air cooling treatment. Composite hydrogen crushing: First, the pretreated cerium-containing permanent magnet waste is mixed and coarsely crushed to a particle size of less than 25mm, and argon gas is introduced for protection; in the hydrogen crushing process, a step-by-step hydrogen treatment process is adopted. The first step is to absorb hydrogen at a hydrogen absorption pressure of 0.08-0.12MPa for 1-3 hours, and the second step is to increase the pressure to 0.15-0.2MPa to absorb hydrogen for 1-2 hours. Preparation of multi-element alloyed nanopowder: The auxiliary materials are weighed and placed in a high-temperature and high-pressure alloying nano furnace, and electric arc melting is carried out under a hydrogen-argon mixed gas atmosphere. The auxiliary alloy MMxT1-x nanopowder is prepared by evaporation and condensation, and then passivated in a nitrogen-argon mixed glove box. The particle size D50 of the nanopowder is 30-150nm. In the auxiliary alloy MMxT1-x, MM is a mixed rare earth alloy containing La, Ce, Pr, and Nd, and T is one or more non-rare earth metals such as Al, Cu, Ga, and Co., where x is the mass percentage of the mixed rare earth MM in the auxiliary alloy multiplied by 100, and 50.0 ≤ x < 100.

0. Intelligent airflow mill classification: An antioxidant at a ratio of 0.3-0.5‰ is added to the hydrogen-crushed coarse powder. The structural formula of the antioxidant is: Mix for 1.5-2.5 hours; use an intelligent airflow mill system to automatically adjust the speed of the sorting wheel and the pressure of the mill chamber to make the average particle size D50 3.2-4.5μm, and the ratio of particle size D90 to D10 less than 4.2; Molecular self-assembly powder mixing: Add 3-5% of the total mass of multi-element alloyed nanopowder to the fine powder of cerium-containing permanent magnet waste, and then add 0.6-0.8‰ of the total mass of the mixed fine powder. In a three-dimensional mixer, first mix the powder at a low speed of 150-200 r / min, and then mix the powder at a high speed of 300-400 r / min. Magnetic field-assisted forming and gradient sintering: After powder mixing, a 2-3T pulsed magnetic field is applied in a magnetic field orientation press to assist orientation and molding, followed by densification treatment in a cold isostatic press; the green body is then subjected to gradient sintering in a vacuum sintering furnace.

2. The method for efficient recycling of sintered cerium-containing permanent magnet waste according to claim 1, characterized in that, The chamfering and descaling process takes more than 30 minutes; the temperature selected for low-temperature degreasing of the second type of waste is 200℃.

3. The method for efficient recycling of sintered cerium-containing permanent magnet waste according to claim 1, characterized in that, When self-assembled lubricants are mixed at high speeds, the chemical bond energy between the end groups of hyperbranched polymer molecules and the active sites on the powder surface is 20-30 kJ / mol.

4. The method for efficient recycling of sintered cerium-containing permanent magnet waste according to claim 1, characterized in that, During magnetic field-assisted molding, the pulse frequency of the pulsed magnetic field is 50-100Hz, and the pulse width is 5-10ms.

5. The method for efficient recycling of sintered cerium-containing permanent magnet waste according to claim 1, characterized in that, During gradient sintering, the vacuum level inside the vacuum sintering furnace is maintained at 3-5×10⁻³Pa throughout the process.

6. The recycled cerium-containing rare earth permanent magnet prepared by the method for efficient recycling of sintered cerium-containing permanent magnet waste according to claim 1, characterized in that, The maximum energy product of the permanent magnet is 35MGOe≤(BH)max≤55MGOe, the remanence range is 12-15kGs, and the coercivity range is 13-15kOe.

7. The method for efficient recycling of sintered cerium-containing permanent magnet waste according to claim 1, characterized in that, The regenerated cerium-containing rare earth permanent magnets prepared by this method have uniform internal grain size, with an average grain size of 5-10 μm.

8. The method for efficient recycling of sintered cerium-containing permanent magnet waste according to claim 1, characterized in that, The gradient sintering is carried out in a high vacuum environment, with the first vacuum heat treatment temperature being 960-1030℃ and the treatment time being 4-6 hours; the second heat treatment temperature being 780-880℃ and the treatment time being 2-3 hours; and the third heat treatment temperature being 460-550℃ and the treatment time being 3-6 hours.

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