A method for preparing high-performance recycled magnet by recovering neodymium-iron-boron scrap

Abstract

Disclosed in the present invention is a method for preparing a high-performance recycled magnet by recovering neodymium-iron-boron scrap: (1) pretreating neodymium-iron-boron scrap, sampling, detecting the components of the scrap by ICP, and classifying the components of the scrap and converting into an atomic percentage general formula as follows: Rer0Gag0Bb0Mm0Fef0, wherein r0, g0, b0, m0, and f0 respectively represent atomic percentage contents of Re, Ga, B, M, and Fe elements in the neodymium-iron-boron scrap; (2) designing the composition of a target neodymium-iron-boron magnet as Rer1Gag1Bb1Mm1Fef1, wherein x1=b1 / f1, x1 ranges from 0.062 to 0.072, y1=r1 / f1, y1 ranges from 0.17 to 0.21, z1=g1, and z1 ranges from 0.05% to 0.5%; and feeding on the basis of the composition difference between the neodymium-iron-boron scrap and the target neodymium-iron-boron magnet; and (3) melting the neodymium-iron-boron scrap and supplemented raw materials, and obtaining a high-performance recycled magnet by means of a conventional process. In the present invention, the target magnet is designed to have low boron and high gallium, so that a Re6Fe13Ga phase exists in the magnet, weakening adverse effects caused by high carbon, and obtaining a high-performance neodymium-iron-boron magnet having performance close to or even higher than that of an original magnet, thereby improving the production quality of the neodymium-iron-boron magnet.

Description

A method for preparing high-performance regenerated magnets using neodymium iron boron waste recycling Technical Field

[0001] This invention belongs to the field of sintered NdFeB magnets, specifically relating to a method for preparing high-performance regenerated magnets using NdFeB waste recycling. Background Technology

[0002] Neodymium iron boron (NdFeB) magnets are high-performance magnetic materials widely used in various electronic devices, such as electric vehicles, wind turbines, and maglev trains. With technological advancements and increasingly stringent environmental requirements, the performance demands on NdFeB magnets are also rising. Simultaneously, the production process of NdFeB magnets generates a large amount of waste, making the effective recycling of this waste to reduce resource waste and environmental pollution a pressing issue. In the field of magnetic material manufacturing technology, sintered NdFeB waste is typically recycled using a smelting and separation method to recover rare earth elements. This involves crushing and burning the waste, then chemically separating the desired rare earth oxides, followed by electrolytic reduction to obtain rare earth metals. These rare earth metals are then smelted, powdered, shaped, and sintered to produce NdFeB magnets. Alternatively, a crushing and additive method can be used to recycle NdFeB waste, as illustrated in CN112331474A, where the waste is hydrogen-crushed into powder and then blended with normal NdFeB powder to produce NdFeB magnets.

[0003] While existing technologies, such as smelting and separation, can produce high-performance magnets, they require complex smelting and separation processes, are lengthy and costly, and have low recycling rates, failing to recover elements other than rare earth elements, leading to resource waste and environmental pollution. The crushing and addition method has shorter process steps, but waste materials easily introduce impurities, causing magnet defects and affecting magnet strength. Furthermore, the magnetic properties of the waste are uncontrollable; a few poorly performing pieces of waste may affect the magnetic properties of the entire batch, failing to meet market demand for high-performance magnets.

[0004] Therefore, developing an efficient, environmentally friendly, and economical technology for recycling NdFeB waste is a pressing issue that needs to be addressed in this field. Technical issues

[0005] To address the aforementioned technical problems, this invention provides a method for preparing high-performance regenerated magnets using neodymium iron boron waste. Technical solutions

[0006] The technical solution adopted in this invention is:

[0007] A method for preparing high-performance regenerated magnets using neodymium iron boron waste, the method comprising the following steps:

[0008] (1) Waste composition analysis: After pretreatment, NdFeB waste was sampled and its composition was analyzed by ICP. The waste composition was classified and converted into atomic percentage formula as follows: Re r0 Ga g0 B b0 M m0 Fe f0 All rare earth elements are counted as Re; Al, Cu, Nb, Zr, Ti, and Mn are counted as M; elements other than Re, Ga, B, and M are counted as Fe. r0, g0, b0, m0, and f0 represent the atomic percentage content of Re, Ga, B, M, and Fe elements in NdFeB waste, respectively, and f0 = 100% - r0 - g0 - b0 - m0.

[0009] (2) Composition design: The composition of the target neodymium iron boron magnet is Re. r1 Ga g1 B b1 M m1 Fe f1

[0010] r1, g1, b1, m1, and f1 represent the atomic percentage content of Re, Ga, B, M, and Fe elements in the target NdFeB magnet, respectively.

[0011] Where x1 = b1 / f1, the range of x1 is limited to 0.062~0.072;

[0012] y1 = r1 / f1, limiting the range of y1 to 0.17~0.21;

[0013] z1 = g1, and the range of z1 is limited to 0.05%~0.5%;

[0014] f1=100%-r1-g1-b1-m1

[0015] Feeding is carried out according to the compositional differences between the NdFeB waste and the target NdFeB magnet;

[0016] (3) Add neodymium iron boron waste and supplementary raw materials to a vacuum induction furnace to smelt and obtain neodymium iron boron alloy, and then produce high-performance regenerated magnets according to conventional processes.

[0017] In step (3), the neodymium iron boron alloy is subjected to hydrogen crushing and air jet milling; the resulting powder is oriented and then subjected to vacuum sintering and tempering to obtain a high-performance regenerated magnet.

[0018] The orientation molding is generally performed under a magnetic field of ≥1.2T;

[0019] The vacuum sintering is generally carried out in a vacuum sintering furnace at a temperature of 1000~1110℃ for 3~15 hours.

[0020] The tempering process includes a two-stage tempering process, wherein the first-stage tempering process is tempering at a temperature of 880~920℃ for 1~6 hours, and the second-stage tempering process is tempering at a temperature of 420~500℃ for 2~8 hours.

[0021] In step (1), x0=b0 / f0, y0=r0 / f0, z0=g0.

[0022] In this invention, all rare earth elements are included in Re, and the rare earth elements include: Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0023] In step (1), the pretreatment steps of NdFeB waste are: high temperature demagnetization, degreasing, cleaning, vibrating grinding, and sieving to remove visible impurities. The waste is then sorted and sampled. The sample can be a single sample or a mixed sample.

[0024] In this invention, Re6Fe is used in the design. 13 Ga phase is used to mitigate the adverse effects of high carbon content in NdFeB waste recycled magnets, but to generate sufficient Re6Fe... 13 For the Ga phase, b1:f1 must satisfy ≤0.072; otherwise, Re2Fe will be generated preferentially. 14 Phase B consumes almost all of the Fe, leaving insufficient Fe, therefore Re6Fe 13 Ga phase is difficult to form or forms in very small quantities, thus hindering the utilization of Re6Fe. 13 The Ga phase mitigates the adverse effects of carbon. Considering other magnetic properties, a b1 / f1 ratio of 0.062 to 0.072 is reasonable, meaning x1 should be in the range of 0.062 to 0.072. When the target magnet's Hcj requirement is higher or the carbon content in the NdFeB waste is higher, the value of x1 should be appropriately reduced.

[0025] Neodymium iron boron magnets are mainly composed of the main phase Re2Fe 14 Composed of a boron phase and a Re-rich phase at grain boundaries, the presence of a sufficiently rich Re phase is necessary for decoupling and for the magnet to possess high magnetic properties. The main phase, Re₂Fe, is formed. 14The B phase requires a ratio of r1:f1 = 1:7, approximately 0.14. To obtain sufficient Re-rich phase at grain boundaries, this ratio needs to be ≥0.14. Considering high overall magnetic performance and cost-effectiveness, this ratio is typically 0.14~0.17 in conventional processes. However, for the high-carbon characteristics of NdFeB waste recycled magnets, this invention adjusts this ratio to 0.17~0.21, meaning y1 ranges from 0.17 to 0.21. The higher the carbon content, the higher the value of y1 should be. Increasing the value of y1 is equivalent to increasing the Re element content in the magnet, which is beneficial for improving the magnetic performance Hcj. However, a higher y1 value requires increasing the amount of rare earth elements added, increasing production costs. When y1 reaches a certain value, the beneficial effect on Hcj tends to level off or even decrease, while the adverse effect on Br becomes more pronounced. Therefore, the design of y1 must comprehensively consider the balance between cost and magnet performance. Furthermore, a small amount of Re element will be lost during production; therefore, the designed y1 value can be appropriately higher than the actual value.

[0026] Re6Fe 13 The formation of the Ga phase requires Ga elements, which in turn generate Re6Fe. 13 The Ga phase requires an atomic percentage content of ≥0.05% Ga. Higher Ga content increases cost, but with sufficient Re and Fe, the resulting Re6Fe phase can be produced. 13 The higher the Ga phase content, the better it is for the Hcj of the magnet. Considering both overall magnetic performance and cost-effectiveness, the Ga content should be controlled between 0.05% and 0.5%, meaning the range of z1 is 0.05% to 0.5%. The value of z1 is related to the x1 value, which is related to the carbon content of the NdFeB waste and the Hcj of the target magnet. The higher the x1 value, the lower the z1 value should be. If z0 < z1 or Ga is not detected in the NdFeB waste, Ga needs to be added during smelting. The amount of Ga to be added needs to be calculated using the difference between z1 and z0; otherwise, Ga is not needed.

[0027] In step (2), the materials need to be fed according to the compositional differences between the NdFeB waste and the target NdFeB magnet. However, since the composition of NdFeB waste is diverse and uncontrollable, it is unknown which element is more or less according to the composition design. Generally speaking, when feeding materials, it is necessary to first determine which element is more, and then supplement other elements based on this element.

[0028] Therefore, the specific steps for calculating material input are generally as follows:

[0029] The difference between x0 and x1 is used to evaluate the boron content in NdFeB waste. x0 = b0 / f0 is the boron-to-iron mass ratio in the NdFeB waste, and x1 = b1 / f1 is the boron-to-iron mass ratio of the target NdFeB magnet. If the difference is positive, it means that the B in the waste is more than x0-x1 than the Fe, and vice versa.

[0030] The difference between y0 and y1 is used to evaluate the Re content in the NdFeB waste. y0 = r0 / f0, which is the mass ratio of Re element to Fe in the NdFeB waste. y1 = r1 / f1, which is the mass ratio of Re element to Fe in the target NdFeB magnet. If the difference is positive, it means that Re is more than Fe by y0 - y1; otherwise, it is less by y1 - y0.

[0031] Compare x0 - x1, (y0 - y1) / 2 and 0, and take the maximum value as k. The purpose of finding the maximum value is to determine which of B, Re, and Fe is relatively the most, and for the element that is the most, the other two types of elements are supplemented according to the relative difference. Since the content of Re in the NdFeB magnet is approximately twice that of B, it is more reasonable to use (y0 - y1) / 2 to compare with x0 - x1 to determine the relative amount.

[0032] Boron is supplemented according to the waste weight × 0.138 × (k + x1 - x0). It should be noted that in actual production, ferroboron is generally used, and the addition amount of ferroboron needs to be calculated according to the boron content in ferroboron; rare earth is supplemented according to the waste weight × (4k + 2y1 - 2y0), and different types of rare earth raw materials can be selected according to the target magnetic properties requirements; pure iron is supplemented according to the waste weight × 8k; when z0 < z1, Ga metal is supplemented according to the waste weight × 1.1 × (z1 - z0).

[0033] It should be noted that there are multiple rare earth elements, and there are molecular weight differences among different rare earth elements. Therefore, when supplementing rare earth according to the waste weight × (4k + 2y1 - 2y0), if different rare earth elements are selected for feeding, there may be differences in atomic percentages, but in practice, the impact on the atomic percentages of rare earth elements in the final recycled magnet is not significant and is within the target requirements range.

[0034] The main difficulties in the recovery and preparation of NdFeB by the waste melting method in the prior art are uncontrollable composition and high carbon content. The rare earth carbide deteriorates the grain boundary structure, thus affecting the magnetic properties. The sintered NdFeB magnet prepared by the present invention can achieve controllable composition to a certain extent; by designing the target magnet to have low boron and high gallium and combining with appropriate preparation processes, there is Re6Fe 13 Ga phase in the magnet. This phase is distributed along the grain boundary and has the function of repairing the lattice structure and weakening the adverse effects brought by high carbon, enabling the NdFeB magnet to have the high performance of a normal NdFeB magnet, and even the Hcj is higher than that of the original magnet. The technical solution has been verified to be feasible and has been applied to large-scale production to meet the market demand. Beneficial effects

[0035] The beneficial effects of the present invention are as follows:

[0036] 1. This technology solves the problem of obtaining stable, high-performance NdFeB magnets in existing technologies. By remelting waste materials and rationally adjusting the waste composition, the magnets, despite having a high carbon content, still achieve high performance. This is because the magnets have a high rare-earth content, and even after combining with impurities such as carbon and oxygen, there is still a sufficient amount of rare-earth phase; the low-boron, high-gallium composition design introduces Re6 (FeCo). 13 Ga phase is used to repair grain boundary structure and weaken the adverse effects of rare earth carbide relative to grain boundaries.

[0037] 2. This invention solves the problems of relatively long and expensive recycling processes in existing technologies. Compared with long-distance rare earth recycling, the recycling process of this invention does not require smelting and separation; high-performance NdFeB magnets can be obtained directly through remelting, which greatly shortens the recycling process and reduces recycling costs.

[0038] 3. This invention solves the problems of low recycling rates in existing technologies, which lead to ineffective resource utilization, resource waste, and environmental pollution. Through the recycling of NdFeB waste, all elements in the waste are fully utilized, and the pollution caused by the waste is reduced, thus contributing to sustainable development.

[0039] 4. This invention solves the problem of improving the production quality of NdFeB magnets in existing technologies. By adjusting the waste composition and remelting process, this invention can obtain high-performance NdFeB magnets with properties close to or even higher than the original magnets, thereby improving the production quality of NdFeB magnets. The best embodiment of the present invention

[0040] The technical solution of the present invention will be further described below with reference to specific embodiments. The embodiments described below are exemplary and are only used to better understand the present invention, and should not be construed as limiting the present invention. Example 1

[0041] Take 500 kg of N42 material scrap. The original blank has magnetic properties of Br = 13.2 kGs and Hcj = 12.5 kOe. Clean it with degreasing agent and water, grind the sawdust with diamond abrasive, and then sieve it to remove visible impurities. Take a sample for ICP analysis and find that Pr 6.9 Nd 21 Ce 2.5 Cu 0.1 Al 0.3 Ga 0.1 Zr 0.2 B 0.95 Co 0.5 Fe bal (Mass fraction), converted to the atomic percentage formula Re r0 Ga g0 B b0 M m0 Fef0 , it is obtained that r0 = 13.86%, g0 = 0.09%, b0 = 5.73%, m0 = 0.97%, f0 = 79.35%, and the carbon content is 1200 ppm. The target grade is N42M, and the target magnetic property is above 13 kGs + 14 kOe. Considering the above factors comprehensively, x1 = b1 / f1 takes the value of 0.07, y1 = r1 / f1 takes the value of 0.19, and z1 = g1 takes the value of 0.3%; it is calculated that b0 / f0 - x1 = 0.00226, (r0 / f0 - y1) / 2 = -0.00766. k is the maximum value of b0 / f0 - x1, (r0 / f0 - y1) / 2, and 0, then k = b0 / f0 - x1 = 0.00226. Since 0.138(k + x1 - b0 / f0) = 0, boron supplementation is not required; (4k + 2y1 - 2y0)×500 = 19.84, and 19.84 kg of PrNd metal needs to be supplemented (the PrNd alloy is an alloy with a Pr:Nd mass ratio of 25:75, and other rare earth elements or PrNd alloys with other mass ratios can also be supplemented. Although there are differences in the molecular weights of rare earth elements, the impact on the atomic percentage content results of the overall rare earth elements is not significant, the same below); because g0 < z1, 1.1 kg of metal Ga needs to be supplemented (the calculation formula is (0.3% - 0.09%)×1.1×500 = 1.05 ≈ 1.135 kg). The amount of iron supplementation is the weight of the waste multiplied by 8k, and it is calculated that 8×0.00226×500 = 9.04 kg, so 9.04 kg of iron is supplemented. The neodymium iron boron waste and the supplementary raw materials are put into a vacuum melting furnace to melt the neodymium iron boron alloy; the hydrogen breaking + jet milling process is used to make powder, and the average particle size of the powder is 3.2 μm; under the protection of closed nitrogen, a magnetic field of 1.5 T is applied for orientation and forming; sintering is carried out at 1080 °C for 8 hours in a vacuum sintering furnace, and the tempering process is 900 °C×4 hours + 460 °C×6 hours, and air-cooled to room temperature to obtain the neodymium iron boron blank. The composition of the blank is tested and converted into the general formula of atomic percentage as Re 14.9 Ga 0.3 B 5.51 M 0.93 Fe 78.36 . During the production process, a small amount of Re element will be burned out, the same below. r / f = 0.190, b / f = 0.070, g1 = 0.294%, and the actual composition is very close to the designed composition. A cylinder with a diameter of 10×10 is taken to test the magnetic properties. The results show that Br is 13 kGs and Hcj is 15.8 kOe. Without adding heavy rare earths, Hcj has a significant increase, greatly improving the high-temperature resistance of the magnet, making it possible to apply the recycled neodymium iron boron magnet to the high-end market. Example 2

[0042] Take 500 kg of the material skin of N38 material. The original magnetic properties of the blank are Br = 12.4 kGs and Hcj = 12.1 kOe. The pretreatment is the same as in Example 1; samples are taken for ICP composition analysis to obtain: Pr 5.9 Nd 18 Ce8Cu 0.1 Al 0.5 Ga 0.2 Zr 0.2 B 0.85 Co 0.5 Fe bal (mass fraction). Converted to the general formula of atomic percentage Re r0 Ga g0 B b0 M m0 Fe f0 , and it is obtained that r0 = 14.79%, g0 = 0.19%, b0 = 5.2%, m0 = 1.47%, f0 = 78.35%, and the carbon content is 1100 ppm. The target grade is N38M, and the target magnetic properties are above 12.4 kGs + 14 kOe. Considering the above factors comprehensively, x1 = b1 / f1 takes the value of 0.069, y1 = r1 / f1 takes the value of 0.2, and z1 = g1 takes the value of 0.25%; it is calculated that b0 / f0 - x1 = -0.00269, (r0 / f0 - y1) / 2 = -0.00563. k is the maximum value of b0 / f0 - x1, (r0 / f0 - y1) / 2, and 0, then k = 0. Because 0.138(k + x1 - x0)×500 = 0.185, 0.185 kg of boron needs to be supplemented. Note: In the operation, it is necessary to convert according to the purity of ferroboron to the weight of ferroboron. The influence of the increased Fe on the composition is very small and can be ignored. The same applies hereinafter. (4k + 2y1 - 2y0)×500 = 11.26, 11.26 kg of PrNd metal needs to be supplemented; because g0 < z1, 0.33 kg of metal Ga needs to be supplemented (the calculation formula is (0.25% - 0.19%)×1.1×500 ≈ 0.33 kg). k = 0, and no iron needs to be supplemented. The subsequent process is the same as in Example 1. The composition of the test blank is measured and converted into the general formula of atomic percentage, which is Re 15.5 Ga 0.25 B 5.36 M 1.46 Fe 77.43 . r1 / f1 = 0.20, b1 / f1 = 0.069, g1 = 0.25%, and the actual composition is very close to the designed composition. Take a cylinder with a diameter of 10×10 to test the magnetic properties. The results show that Br = 12.4 kGs and Hcj = 14.5 kOe. Without adding heavy rare earths, Hcj has a significant increase and basically meets the design value. Example 3

[0043] Take 500 kg of the material skin of N35H material. The original magnetic properties of the blank are Br = 12.1 kGs and Hcj = 17.3 kOe. The pretreatment is the same as in Example 1; samples are taken for ICP composition analysis and obtained: Pr 7.9 Nd 24 Cu 0.1 Ga 0.2 Zr 0.2 B 0.88 Co 0.5 Fe bal (mass fraction). Converted to the general formula of atomic percentage Re r0 Ga g0 B b0 M m0 Fe f0 , it is obtained that r0 = 14.78%, g0 = 0.19%, b0 = 5.41%, m0 = 0.25%, f0 = 79.37%, and the carbon content is 1000 ppm. The target grade is N35H, and the target magnetic properties are above 12 kGs + 18 kOe. Considering the above factors comprehensively, x1 = b1 / f1 takes the value of 0.069, y1 = r1 / f1 takes the value of 0.175, and z1 = g1 takes the value of 0.33%; it is calculated that b0 / f0 - x1 = -0.00083, (r0 / f0 - y1) / 2 = 0.00566. k is the maximum value of b0 / f0 - x1, (r0 / f0 - y1) / 2, and 0, then k = 0.00566. Because 0.138(k + x1 - x0)×500 = 0.45, so 0.45 kg of boron needs to be supplemented. 4k + 2y1 - 2y0 = 0, so no Re needs to be supplemented. Because g0 < z1, 0.766 kg of metallic Ga needs to be supplemented (the calculation formula is (0.33% - 0.19%)×1.1×500 ≈ 0.766 kg). The amount of iron to be supplemented is the weight of the waste multiplied by 8k, and it is calculated that 8×0.00566×500 = 22.65 kg, so 22.65 kg of iron is supplemented. The subsequent process is the same as in Example 1. The composition of the blank is tested and converted into the general formula of atomic percentage, which is Re 13.82 Ga 0.32 B 5.63 M 0.24 Fe 79.99 . r1 / f1 = 0.173, b1 / f1 = 0.07, g1 = 0.32%, and the actual composition is close to the designed composition. Take a cylinder with a diameter of 10×10 to test the magnetic properties. The results show that Br = 12 kGs and Hcj = 18.4 kOe. In this embodiment of the process, no new rare earth raw materials are put in. Therefore, when the total mass of rare earth elements does not change, the Hcj of the regenerated magnet increases by 1.1 kOe, and the magnetic properties are improved. In this embodiment, the value of y1 is relatively low, and the increase range of Hcj is limited, but the magnetic properties of the obtained regenerated magnet still meet the design requirements.

Claims

1. A method for preparing high-performance regenerated magnets using neodymium iron boron waste, characterized in that... The method includes the following steps: (1) Waste composition analysis: After pretreatment, NdFeB waste was sampled and its composition was analyzed by ICP. The waste composition was classified and converted into atomic percentage formula as follows: Re r0 Ga g0 B b0 M m0 Fe f0 All rare earth elements are counted as Re; Al, Cu, Nb, Zr, Ti, and Mn are counted as M; elements other than Re, Ga, B, and M are counted as Fe. r0, g0, b0, m0, and f0 represent the atomic percentage content of Re, Ga, B, M, and Fe elements in NdFeB waste, respectively, and f0 = 100% - r0 - g0 - b0 - m0. (2) Composition design: The composition of the target neodymium iron boron magnet is Re. r1 Ga g1 B b1 M m1 Fe f1 r1, g1, b1, m1, and f1 respectively represent the atomic percentage contents of Re, Ga, B, M, and Fe elements in the target NdFeB magnet. Where x1 = b1 / f1, and the range of x1 is limited to 0.062 - 0.

072. y1 = r1 / f1, and the range of y1 is limited to 0.17 - 0.

21. z1 = g1, and the range of z1 is limited to 0.05% - 0.5%. f1 = 100% - r1 - g1 - b1 - m1. Charging is carried out according to the compositional differences between the NdFeB waste and the target NdFeB magnet. (3) Add the NdFeB waste and the supplemented raw materials into a vacuum induction furnace for smelting to obtain an NdFeB alloy, and prepare a high-performance recycled magnet according to the conventional process.

2. The method as described in claim 1, characterized in that... In the step (1), all rare earth elements are counted as Re, and the rare earth elements include: Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu.

3. The method as described in claim 1, characterized in that... In the step (3), the NdFeB alloy is subjected to hydrogen crushing and jet milling to form powder; the obtained powder is subjected to orientation forming, and then vacuum sintering and tempering treatments are carried out to prepare a high-performance recycled magnet.

4. The method as described in claim 3, characterized in that... The orientation forming is carried out under a magnetic field ≥ 1.2 T; the vacuum sintering is carried out in a vacuum sintering furnace at a temperature of 1000 - 1110 °C for 3 - 15 hours; the tempering treatment includes a two-stage tempering treatment, where the first-stage tempering treatment is carried out at a temperature of 880 - 920 °C for 1 - 6 hours, and the second-stage tempering treatment is carried out at a temperature of 420 - 500 °C for 2 - 8 hours.

5. The method as described in claim 1, characterized in that... In the step (2), the charging calculation steps are as follows: Use the difference between x0 and x1 to evaluate the boron content in the NdFeB waste. x0 = b0 / f0 is the mass ratio of boron to iron in the NdFeB waste, and x1 = b1 / f1 is the mass ratio of boron to iron in the target NdFeB magnet. If the difference is positive, it means that B in the waste is more than Fe by x0 - x1, and vice versa, it is less by x1 - x0. Use the difference between y0 and y1 to evaluate the Re content in the NdFeB waste. y0 = r0 / f0 is the mass ratio of the Re element to iron in the NdFeB waste, and y1 = r1 / f1 is the mass ratio of the Re element to iron in the target NdFeB magnet. If the difference is positive, it means that Re is more than Fe by y0 - y1, and vice versa, it is less by y1 - y0. Compare x0 - x1, (y0 - y1) / 2, and 0, and take the maximum value as k. Supplement boron by waste weight × 0.138 × (k + x1 - x0); supplement rare earth by waste weight × (4k + 2y1 - 2y0); supplement pure iron by waste weight × 8k; when z0 < z1, supplement Ga metal by waste weight × 1.1 × (z1 - z0).

6. The method as described in claim 1, characterized in that... In the step (1), the pretreatment steps of the NdFeB waste are: high-temperature demagnetization, degreasing, cleaning, vibration milling, and sieving to remove visible impurities, and the obtained waste is classified and sampled.