A hydrogenation-disproportionation process for reclaiming bulk neodymium-iron-boron magnets

Abstract

The application discloses a hydrogenation-diffusion method for recycling block neodymium-iron-boron magnets, and pre-treatment, hydrogenation, diffusion and post-treatment processes are sequentially carried out in a closed reaction system, and oxygen-free transmission is realized among units of the system. The method comprises the following steps: in the pre-treatment device, low-temperature hydrogen reduction, mechanical stripping and vacuum thermal activation are sequentially performed to form a hydrogen adsorption active interface; in the high-pressure hydrogenation furnace, hydrogenation treatment is carried out by adopting three-stage temperature-pressure synergistic regulation to realize hydrogen body phase penetration and Nd2Fe 14 BH x phase domain generation; in the diffusion furnace, the hydrogenation product is sequentially sent into a preheating activation area, a main diffusion area and a cooling transition area to complete phase directional separation and nano structure freezing in a hydrogen-argon mixed atmosphere; and in the inert atmosphere post-treatment unit, crushing and grading are carried out in a high-purity argon environment to obtain regenerated magnetic powder. The application effectively solves the technical problems of uneven hydrogenation of large-size block magnets, generation of impurities in the diffusion process and out-of-control oxidation in the post-treatment.

Description

Technical Field

[0001] This invention relates to the field of rare earth permanent magnet material recycling technology, and in particular to a hydrogenation-disproportionation method for recycling bulk NdFeB magnets. Background Technology

[0002] In the production and application of NdFeB permanent magnet materials, sintered NdFeB is widely used in industries such as new energy vehicles due to its excellent magnetic properties. However, sintered NdFeB magnets are highly brittle during machining, and a large number of waste block NdFeB magnets are generated at the end of their service life, requiring urgent disposal. Given the increasing scarcity of rare earth resources and the ever-increasing environmental protection requirements, how to efficiently recycle and utilize NdFeB waste, especially block NdFeB magnets, has become a hot topic and a challenge in this field.

[0003] Currently, the main technological approaches for recycling and reusing NdFeB waste are as follows: First, chemical extraction is used to extract rare earth elements and other valuable metals from the waste. However, this process suffers from low recovery rates, complex separation procedures, and difficulty in guaranteeing product purity. Furthermore, it involves the use of large amounts of acids and alkalis, resulting in a heavy environmental burden. Second, the waste is hydrogen-blasted and mixed with NdFeB powder of the same composition, then refined through air jet milling, pressed into shape, and sintered to prepare regenerated magnets. While this short-process recycling method can recycle the waste, the magnetic properties of the regenerated magnets often show a significant decrease, especially in remanence and coercivity. Third, the HDDR process is used to prepare anisotropic magnetic powder. Although this process can obtain magnetic powder with a certain degree of orientation, existing HDDR technologies are mostly designed for alloy ingots with specific compositions. For blocky processing waste with electroplated layers, oxide films, and complex compositions, direct application presents problems such as uneven hydrogenation initiation, incomplete reaction, and difficulty in controlling the microstructure.

[0004] In existing hydrogenation technologies, conventional hydrogenation processes typically employ single-temperature and single-pressure conditions. For large-sized, blocky waste materials, hydrogen atoms struggle to uniformly penetrate from the surface to the core, easily leading to both surface over-hydrogenation and incomplete core reaction. This results in subsequent processes failing to achieve a uniform microstructure. In the disproportionation stage, traditional processes often use single-temperature disproportionation reactions, limiting their ability to control the directional separation of rare-earth-rich and iron-rich phases. This can easily generate non-magnetic impurities, affecting the magnetic properties of the regenerated magnetic powder. Furthermore, in the post-processing crushing and classification stages, existing technologies largely lack strict atmospheric control. Fresh surfaces exposed to air are highly susceptible to oxidation, leading to high oxygen content in the regenerated magnetic powder, which in turn affects the densification and magnetic property recovery of the sintered magnets.

[0005] In view of the above-mentioned technological status, there is an urgent need in this field to develop a recycling method that can effectively solve key problems such as uneven hydrogenation of bulk NdFeB magnets, generation of impurity phases during disproportionation, and runaway oxidation during post-processing, so as to achieve efficient utilization of rare earth resources in waste and effective restoration of the magnetic properties of regenerated magnets. Summary of the Invention

[0006] To address the aforementioned shortcomings, this invention proposes a hydrogenation-disproportionation method for recycling bulk NdFeB magnets, which effectively solves the technical problems of uneven hydrogenation of large-sized bulk magnets, impurity phase generation during disproportionation, and uncontrolled oxidation during post-processing.

[0007] This invention provides the following technical solution: a hydrogenation-disproportionation method for recovering block NdFeB magnets, wherein the pretreatment, hydrogenation, disproportionation and posttreatment processes are carried out sequentially in a closed reaction system. The closed reaction system includes a pretreatment device, a high-pressure hydrogenation furnace, a disproportionation furnace and an inert atmosphere posttreatment unit, and each unit is connected by a vacuum-sealed channel or an inert gas-protected gas lock chamber to realize oxygen-free transport of block magnets and their derived intermediate products throughout the process. The method includes the following steps: S1. In the pretreatment device, the bulk NdFeB magnet is subjected to low-temperature hydrogen reduction, mechanical stripping and vacuum thermal activation in sequence to remove the surface electroplating layer and oxide film and form a hydrogen adsorption active interface, thereby improving the initial adsorption rate of hydrogen atoms and improving the uniformity of hydrogenation initiation. S2. In the high-pressure hydrogenation furnace, based on the hydrogen adsorption active interface formed in step S1, hydrogenation is carried out using a three-stage temperature-pressure coordinated control method to achieve hydrogen penetration along grain boundaries and dislocations in the bulk phase and Nd2Fe. 14 BH x Phase-wide generation ensures that hydrogen reaches the predetermined penetration depth within the bulk material to avoid incomplete core reactions; S3. In the disproportionation furnace, the product after full hydrogenation in step S2 is sequentially fed into the preheating activation zone, the main disproportionation zone and the cooling transition zone. Phase-oriented separation and nanostructure freezing are completed under the H2-Ar mixed atmosphere to suppress the generation of non-magnetic impurity phases and stabilize the rare earth-rich nanoscale structure. S4. In the inert atmosphere post-treatment unit, the disproportionation product obtained after step S3 is crushed and classified in a high-purity Ar environment to obtain regenerated magnetic powder. In particular, steps S1 to S4 utilize a closed reaction system to achieve oxygen-free transport throughout the entire process, allowing the process effects of each step to be superimposed and collectively ensure the particle size D of the regenerated magnetic powder. 50 It has a diameter of 3–5 μm, an oxygen content of ≤0.15 wt%, and magnetic properties close to those of the original magnet.

[0008] As an improvement, in step S1, hydrogen gas with a purity of ≥99.99% is introduced into the low-temperature hydrogen reduction process, and the temperature is controlled at 150–250℃ to weaken the bonding force between the electroplated layer and the substrate, thereby facilitating the subsequent mechanical peeling and removal of the electroplated layer, and providing a clean surface for the formation of a hydrogen adsorption active interface by vacuum thermal activation.

[0009] As an improvement, in step S1, vacuum thermal activation is performed at a vacuum level better than 10. -2 The process is carried out under Pa conditions, with a thermal activation temperature of 300–450°C and a holding time of 1–2 hours, in order to remove residual oxygen / hydroxyl radicals and form a hydrogen adsorption active interface after mechanical stripping to remove the electroplated layer.

[0010] As an improvement, the specific process for the three-stage temperature-pressure coordinated control in step S2 is as follows: First stage: Keeping the temperature in the first temperature range of 60–70℃ and the first hydrogen pressure range of 0.02–0.05MPa, so that hydrogen atoms are preferentially adsorbed at the grain boundaries and dislocations of the hydrogen adsorption active interface formed in step S1, forming an initial adsorption layer. The second stage involves heating to the second temperature range of 80–90℃ and pressurizing to the second hydrogen pressure range of 0.08–0.15MPa at a heating rate of 2–5℃ / min and a pressurization rate of 0.01–0.02MPa / min, followed by holding at the temperature to allow hydrogen atoms to diffuse into the bulk along grain boundaries and dislocations, thus achieving bulk infiltration. The third stage: Continue heating at the same rate to the third temperature range (95–100℃) and pressurize to the third hydrogen pressure range (0.2–0.3 MPa), then hold at this temperature to allow hydrogen atoms to permeate into the bulk core, completing the Nd2Fe synthesis. 14 BH x Global generation and embrittlement of phases.

[0011] As an improvement, the disproportionation reaction in step S3 is carried out under a 5% H2-Ar mixed atmosphere and a total pressure of 0.10±0.005MPa to maintain the stability of the hydrogen partial pressure. Combined with the zoned temperature control of the preheating activation zone, the main disproportionation zone and the cooling transition zone, the directional separation of the R-rich phase and the α-Fe phase and the freezing of the nanostructure are achieved.

[0012] As an improvement, in step S3, the temperature of the preheating activation zone is controlled at 520–560℃ to induce the initiation of the disproportionation reaction; after preheating activation, the hydrogenation product is sent to the main disproportionation zone, where the temperature is controlled at 820–850℃ to achieve the directional separation of the R-rich phase and the α-Fe phase; after the main disproportionation, the product is sent to the cooling transition zone, where it is cooled to 400℃ using a programmed cooling method at a rate of 2–10℃ / min to freeze the nanostructure and suppress grain coarsening.

[0013] As an improvement, the high-purity Ar environment in step S4 requires a dew point ≤ -40℃ and an O2 content < 1ppm to block the oxygen intrusion path during the crushing and classification process.

[0014] As an improvement, in step S4, the disproportionation product is subjected to coarse crushing, fine crushing, and air classification in sequence. The coarse crushing is carried out by jaw crushing, and the fine crushing is carried out by ball milling, so that the particle size of the regenerated magnetic powder reaches D. 50 The size is 3–5 μm and the oxygen content is ≤0.15 wt%.

[0015] Compared with the prior art, the advantages of the present invention are as follows: This method constructs a closed reaction system comprising a pretreatment device, a high-pressure hydrogenation furnace, a disproportionation furnace, and an inert atmosphere post-treatment unit. It employs a vacuum-sealed channel or an inert gas-protected gas lock chamber to achieve oxygen-free transfer between units, ensuring that the block magnet and its derivative intermediates remain in an oxygen-free environment throughout the entire process. This fundamentally avoids oxidative pollution caused by material transfer between processes, laying a reliable foundation for the superposition of process effects in subsequent steps.

[0016] In the pretreatment step, the bulk NdFeB magnets are subjected to low-temperature hydrogen reduction, mechanical stripping, and vacuum thermal activation in sequence. Hydrogen gas with a purity of not less than 99.99% is used at 150 to 250°C to weaken the adhesion between the electroplated layer and the substrate, facilitating the thorough removal of the surface electroplated layer and oxide film by mechanical stripping. Subsequently, the magnets are subjected to a vacuum degree better than 10... -2 Vacuum thermal activation at 300 to 450°C for 1 to 2 hours effectively removes residual oxygen and hydroxide ions, forming a clean and highly active hydrogen adsorption interface. This pretreatment process not only eliminates surface barriers that hinder hydrogen permeation but also significantly improves the initial adsorption rate of hydrogen atoms, enhances the uniformity of hydrogenation initiation, and provides an ideal reaction interface for subsequent hydrogenation treatment.

[0017] In the hydrogenation process, based on the hydrogen adsorption active interface formed during pretreatment, a three-stage temperature-pressure coordinated control method is used for hydrogenation. The first stage involves holding at 60-70℃ and 0.02-0.05 MPa to allow hydrogen atoms to preferentially adsorb at grain boundaries and dislocations on the active interface, forming an initial adsorption layer. The second stage involves heating at a rate of 2-5℃ per minute and pressurizing at a rate of 0.01-0.02 MPa per minute, increasing the temperature to 80-90℃ and pressurizing to 0.08-0.15 MPa, followed by holding to allow hydrogen atoms to diffuse along grain boundaries and dislocations into the bulk, achieving bulk penetration. The third stage continues heating at the same rate to 95-100℃ and pressurizing to 0.2-0.3 MPa, followed by holding to allow hydrogen atoms to penetrate into the core of the bulk, completing the Nd₂Fe₂ process. 14 BH xPhase formation and embrittlement are achieved throughout the entire process. This three-stage progressive control process ensures that hydrogen reaches the predetermined penetration depth within the bulk magnet, effectively avoiding the problem of incomplete core reaction and realizing uniform hydrogenation of the bulk magnet.

[0018] In the disproportionation process, the fully hydrogenated product is sequentially fed into a preheating activation zone, a main disproportionation zone, and a cooling transition zone. The disproportionation reaction is carried out under a 5% hydrogen-argon mixed atmosphere and a total pressure of 0.10 ± 0.005 MPa. The temperature in the preheating activation zone is controlled at 520–560 °C to induce the disproportionation reaction. After preheating activation, the product is fed into the main disproportionation zone, where the temperature is controlled at 820–850 °C to achieve directional separation of the R-rich phase and the α-Fe phase under a stable hydrogen partial pressure. After main disproportionation, the product is fed into the cooling transition zone, where it is cooled to 400 °C at a rate of 2–10 °C per minute for nanostructure freezing, effectively suppressing grain coarsening. This zoned temperature control process, combined with stable hydrogen partial pressure conditions, achieves directional phase separation and nanostructure freezing, effectively suppressing the formation of non-magnetic impurity phases and stabilizing the nanoscale structure of the rare-earth-rich phase.

[0019] In the post-processing step, the disproportionation products are subjected to coarse crushing, fine crushing, and airflow classification in a high-purity argon environment with a dew point not exceeding -40°C and an oxygen content less than 1 ppm. Through multi-stage pulverization, the particle size of the regenerated magnetic powder is brought to D. 50 The particle size is 3 to 5 μm, and the oxygen content is controlled to within 0.15 wt% under complete oxygen-free protection. This high-purity argon environment effectively blocks the oxygen intrusion path during the crushing and classification process, avoids oxidation of fresh surfaces, and ensures the chemical stability of the magnetic powder.

[0020] Through the synergistic effect of the pretreatment, hydrogenation, disproportionation, and posttreatment steps in the closed reaction system, the combined process effects under oxygen-free transport throughout the entire process are achieved. The final obtained regenerated magnetic powder particle size D... 50 With a particle size of 3 to 5 μm and an oxygen content not exceeding 0.15 wt%, the magnetic properties are close to those of the original magnets. The method of this invention effectively solves key technical problems such as uneven hydrogenation of large-sized bulk magnets, impurity phase generation during the disproportionation process, and uncontrolled oxidation in post-processing. It realizes the efficient recycling and high-value reuse of bulk NdFeB magnets, and has significant advantages such as strong process continuity, stable product quality, and high resource utilization. Attached Figure Description

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Figure 1 This is a flowchart of a hydrogenation-disproportionation method for recycling bulk NdFeB magnets. Detailed Implementation

[0022] like Figure 1A hydrogenation-disproportionation method for recycling bulk NdFeB magnets, wherein the pretreatment, hydrogenation, disproportionation and posttreatment processes are carried out sequentially in a closed reaction system. The closed reaction system includes a pretreatment device, a high-pressure hydrogenation furnace, a disproportionation furnace and an inert atmosphere posttreatment unit, and each unit is connected by a vacuum-sealed channel or an inert gas-protected gas lock chamber to achieve oxygen-free transport of bulk magnets and their derivative intermediates throughout the process. The method includes the following steps: S1. In the pretreatment device, the bulk NdFeB magnet is subjected to low-temperature hydrogen reduction, mechanical stripping and vacuum thermal activation in sequence to remove the surface electroplating layer and oxide film and form a hydrogen adsorption active interface, thereby improving the initial adsorption rate of hydrogen atoms and improving the uniformity of hydrogenation initiation. S2. In the high-pressure hydrogenation furnace, based on the hydrogen adsorption active interface formed in step S1, hydrogenation is carried out using a three-stage temperature-pressure coordinated control method to achieve hydrogen penetration along grain boundaries and dislocations in the bulk phase and Nd2Fe. 14 BH x Phase-wide generation ensures that hydrogen reaches the predetermined penetration depth within the bulk material to avoid incomplete core reactions; S3. In the disproportionation furnace, the product after full hydrogenation in step S2 is sequentially fed into the preheating activation zone, the main disproportionation zone and the cooling transition zone. Phase-oriented separation and nanostructure freezing are completed under the H2-Ar mixed atmosphere to suppress the generation of non-magnetic impurity phases and stabilize the rare earth-rich nanoscale structure. S4. In the inert atmosphere post-treatment unit, the disproportionation product obtained after step S3 is crushed and classified in a high-purity Ar environment to obtain regenerated magnetic powder. In particular, steps S1 to S4 utilize a closed reaction system to achieve oxygen-free transport throughout the entire process, allowing the process effects of each step to be superimposed and collectively ensure the particle size D of the regenerated magnetic powder. 50 It has a diameter of 3–5 μm, an oxygen content of ≤0.15 wt%, and magnetic properties close to those of the original magnet.

[0023] The vacuum-sealed channel ensures the material remains in an oxygen-free negative pressure environment throughout the process, eliminating any possibility of air infiltration. The airlock chamber employs a double-door interlock design: after the inlet door is closed, high-purity Ar is introduced to 0.105 MPa, and the pressure is maintained for 5 minutes. After testing, O2 is measured to be <0.5 ppm, and then the outlet door is opened. The entire ventilation process takes <90 seconds, and the total amount of oxygen intrusion is <0.03 mL. Both connection methods ensure that the cumulative oxygen exposure during material transfer between units is <5 × 10¹² molecules / cm³. 2 This is far below the Nd surface oxide monolayer coverage threshold (2.5 × 10¹⁵ molecules / cm²). 2 Therefore, it can ensure that no oxidation events occur throughout the entire process from raw material feeding to regenerated magnetic powder packaging, providing hardware assurance for a final oxygen content of ≤0.15wt%.

[0024] In step S1, the low-temperature hydrogen reduction process introduces hydrogen gas with a purity ≥99.99% and controls the temperature at 150–250℃ to weaken the bonding force between the electroplated layer and the substrate. This facilitates subsequent mechanical stripping and removal of the electroplated layer and provides a clean surface for the formation of a hydrogen adsorption active interface during vacuum thermal activation. Using ≥99.99% high-purity hydrogen gas avoids the competitive adsorption of impurities such as N2 and O2 on the surface of the electroplated layer (typically a Ni-Cu-Ni multilayer structure) or the formation of nitride / oxide barrier layers. The temperature range of 150–250℃ precisely matches the hydride formation and decomposition equilibrium of the Ni-H system (Ni+xH2⇌NiH). x (x=0.01–0.05), which causes the Ni layer to undergo controllable volume expansion, accumulates micro-stress at the Ni / substrate interface, weakens the bonding strength of the electroplated layer, reduces the mechanical peeling force, and provides a clean and pollution-free active interface for subsequent vacuum thermal activation and hydrogenation.

[0025] In step S1, the mechanical stripping process is carried out under the protection of high-purity argon gas, using flexible mechanical grinding (or ultrasonic-assisted vibration scraping) to strip the magnet surface. Due to the weakening effect of hydrogen gas in the early stage, the bubbling and loose Ni-Cu-Ni electroplating layer and the outer loose oxide scale are easily and completely peeled off. At the same time, the oxygen-free environment throughout the process completely eliminates the secondary oxidation of the fresh NdFeB substrate.

[0026] In step S1, vacuum thermal activation is performed at a vacuum level better than 10. -2 The process is carried out under Pa conditions, with a thermal activation temperature of 300–450℃ and a holding time of 1–2 hours. This is to remove residual oxygen / hydroxyl radicals and form a hydrogen adsorption active interface after mechanical stripping to remove the electroplated layer, thereby improving the desorption rate of H2O, O2, and hydrocarbon contaminants adsorbed on the magnet surface and exposing a clean Nd-Fe-B alloy surface. This temperature range is sufficient to stimulate surface atomic migration, forming a high density of hydrogen adsorption vacancies, while avoiding the melting of low-melting-point phases caused by exceeding the NdFeB eutectic point. Holding for 1–2 hours ensures sufficient surface reconstruction, and the surface hydrogen wetting angle decreases after activation, increasing the initial hydrogen adsorption rate. The optimized electronic structure is conducive to hydrogen molecule dissociation, providing a highly active interface basis for subsequent hydrogenation reactions.

[0027] In step S2, the specific process of three-stage temperature-pressure coordinated control is as follows: First stage: Keeping the temperature in the first temperature range of 60–70℃ and the first hydrogen pressure range of 0.02–0.05MPa, so that hydrogen atoms are preferentially adsorbed at the grain boundaries and dislocations of the hydrogen adsorption active interface formed in step S1, forming an initial adsorption layer. The second stage involves heating to the second temperature range of 80–90℃ and pressurizing to the second hydrogen pressure range of 0.08–0.15MPa at a heating rate of 2–5℃ / min and a pressurization rate of 0.01–0.02MPa / min, followed by holding at the temperature to allow hydrogen atoms to diffuse into the bulk along grain boundaries and dislocations, thus achieving bulk infiltration. The third stage: Continue heating at the same rate to the third temperature range (95–100℃) and pressurize to the third hydrogen pressure range (0.2–0.3 MPa), then hold at this temperature to allow hydrogen atoms to permeate into the bulk core, completing the Nd2Fe synthesis. 14 BH x Global generation and embrittlement of phases.

[0028] By setting mild conditions of 60–70℃ and 0.02–0.05 MPa in the first stage, hydrogen molecules undergo controllable dissociation and physical / chemical adsorption at the activation interface, avoiding localized temperature runaway caused by hydrogen absorption exothermics, thus establishing a stable initial hydrogen concentration gradient. Based on this, the second stage raises the temperature to 80–90℃ and simultaneously increases the pressure to 0.08–0.15 MPa, which not only increases the diffusion coefficient of hydrogen atoms at grain boundaries and dislocation defects but also enhances the driving force for their migration to the bulk core, increasing the hydrogen penetration depth from the surface to the entire thickness direction. The third stage further raises the temperature to 95–100℃ and 0.2–0.3 MPa, promoting the full occupation of Nd₂Fe₂. 14 B lattice interstitial positions and induces anisotropic expansion of the unit cell, Nd2Fe 14 BH x When the intensity of the phase diffraction peak reaches its maximum value, the full width at half maximum (FWHM) decreases, indicating that the integrity of the main phase crystallization is improved. At the same time, the macroscopic embrittlement strain energy of the material accumulates to a critical value, and the bulk spontaneously disintegrates into fragments. This also reduces the size dispersion of the fragments, verifying the decisive role of the synergistic effect of the three-stage parameters on the reaction uniformity and controllable embrittlement.

[0029] In step S2, the holding time for each stage is 1–3 hours, and the pressure increase rate between adjacent stages is controlled at 0.01–0.02 MPa / min, and the heating rate is controlled at 2–5 °C / min. In this invention, the 1–3 hour holding time ensures that the reaction in each stage reaches approximately dynamic equilibrium: the first stage is the adsorption start-up and shutdown period, during which the hydrogen surface coverage rate increases significantly; the second stage is the bulk phase penetration period, during which the hydrogen concentration profile changes from an exponential decay at the surface to an approximately linear distribution; and the third stage is the main phase formation period, during which Nd₂Fe₂... 14 BH xThe phase content increases. The pressure increase rate is controlled at 0.01–0.02 MPa / min to match the hydrogen pressure change with the hydrogen diffusion response time inside the material (τ≈d² / D, where d is the characteristic thickness and D is the diffusion coefficient), avoiding local oversaturation microcracks caused by the pressure front leading the hydrogen concentration front; the heating rate of 2–5 °C / min keeps the temperature difference between the inside and outside of the thick block small, eliminating the risk of thermal stress concentration; the synergy of the two significantly improves the stability of the hydrogenation process.

[0030] In step S3, the disproportionation reaction is carried out under a 5% H2-Ar mixed atmosphere and a total pressure of 0.10±0.005MPa to maintain a stable hydrogen partial pressure. Combined with zoned temperature control in the preheating activation zone, main disproportionation zone, and cooling transition zone, the directional separation of the R-rich phase and α-Fe phase and the freezing of the nanostructure are achieved. By limiting the H2 volume fraction to 5%, the required hydrogen partial pressure for the disproportionation reaction is ensured, while Ar is used as a thermodynamically inert dilution gas to effectively suppress reverse hydrogenation or metastable hydride residues caused by hydrogen supersaturation. Under this atmosphere, the disproportionation onset temperature is delayed compared to the pure hydrogen atmosphere, but the width of the main reaction peak temperature region is narrowed, and the reaction selectivity is improved. By strictly controlling the total pressure at 0.10±0.005MPa, on the one hand, the pressure feedback closed-loop system eliminates the gas flow disturbance between batches, reducing the fluctuation range of the actual hydrogen partial pressure in each functional zone; on the other hand, it keeps the Gibbs free energy change (ΔG) of the disproportionation reaction in the optimal range, thereby ensuring that the separation kinetics of the R-rich phase and α-Fe phase are highly reproducible. The coefficient of variation of the two-phase separation degree decreased.

[0031] In step S3, the temperature of the preheating activation zone is controlled at 520–560℃ to induce the disproportionation reaction. After preheating activation, the hydrogenated product is sent to the main disproportionation zone, where the temperature is controlled at 820–850℃ to achieve the directional separation of the R-rich phase and the α-Fe phase. After main disproportionation, the product is sent to the cooling transition zone, where it is programmed to cool to 400℃ at a rate of 2–10℃ / min to freeze the nanostructure and inhibit grain coarsening. The zoned temperature-controlled disproportionation is achieved through the preheating activation zone. A stable initiation reaction, precise provision of thermodynamic driving force for phase decomposition in the main disproportionation region, and programmed cooling in the cooling transition region suppressing the agglomeration of rare earth-rich phases ensure that the average particle size of the R-rich phase in the disproportionation product remains stable at 28±3 nm, and the content of non-magnetic impurities (such as NdO and Fe2O3) is <0.12 wt%. By setting a temperature range of 520–560 °C in the preheating activation region, sufficient thermal activation energy is provided below the main disproportionation energy barrier, enabling controllable dehydrogenation and lattice relaxation on the surface of the hydrogenated product. Within this range, Nd2Fe... 14 BH xThe reversible broadening of the phase peaks indicates that the lattice has begun to loosen but phase decomposition has not yet occurred, providing a homogenized starting state for the subsequent main reaction. After the main disproportionation region is raised to 820–850℃, the system crosses the activation energy threshold of the disproportionation reaction, the R-rich phase precipitates, the nucleation rate of the α-Fe phase increases, and the energy difference between the two phase interfaces decreases, driving the R-rich phase to orientedly segregate along the α-Fe grain boundary. The cooling transition region is programmed to cool down to 400℃ at a rate of 1.5℃ / min, allowing the system to quickly pass through the sensitive temperature range of R-rich phase aggregation kinetics (550–450℃), suppressing the Ostwald ripening effect. In step S4, the high-purity Ar environment requires a dew point ≤ -40℃ and an O2 content < 1ppm to block the oxygen intrusion path during the crushing and classification process, thereby fundamentally eliminating the participation of H2O in Nd oxidation.

[0032] In step S4, the disproportionation product undergoes a three-stage progressive treatment: coarse crushing (jaw crusher, feed size ≤2.5mm, output size 100–500μm), fine crushing (planetary ball mill, Al2O3 tank, ZrO2 ball-to-material ratio 10:1, rotation speed 300rpm, time 8min), and air classification (classifier wheel rotation speed 8000rpm, feed rate 1.2kg / h). This process avoids localized temperature rise oxidation and lattice damage caused by single high-intensity grinding, and achieves a narrow particle size distribution through precise airflow field control, ensuring that the regenerated magnetic powder reaches the D particle size standard. 50 The particle size is 3–5 μm, and the oxygen content is ≤0.15 wt%. Preferably, the oxygen content of the regenerated magnetic powder is controlled at 0.13–0.15 wt%. 50 The particle size is 3.8 μm, and the particle size distribution span is D. 90 / D 10 ≤2.1, thus providing a precursor with both high chemical activity and good flowability for subsequent remolding.

[0033] The raw material for the block NdFeB magnets is N42 grade sintered magnets (size 20mm×15mm×10mm, surface electroplated with Ni-Cu-Ni, remanence Br=1.32T, coercivity Hcj=1120kA / m, maximum energy product (BH)max=332kJ / m³); high-purity hydrogen (purity ≥99.99%) and high-purity argon (purity ≥99.999%, dew point ≤-40℃, O2<0.5ppm) are both provided by the gas company; the vacuum heat treatment equipment is a Q150T ES type sputtering coating machine with a vacuum heating table; the high-pressure hydrogenation furnace is a GSL-1700X-HVC type hydrogen atmosphere furnace (maximum working pressure 0.5MPa, pressure control accuracy ±0.002MPa); the disproportionation furnace is a three-zone tube furnace (quartz tube inner diameter 80mm, independent temperature control in each zone, accuracy ±1℃); Example 1 Twenty N42 grade block NdFeB magnets, each measuring 20mm × 15mm × 10mm and weighing a total of 245.6g, were used as raw materials. The magnets had a nickel plating and a natural oxide film on their surface. The block magnets were placed in a pretreatment device within a closed reaction system. First, a low-temperature hydrogen reduction process was performed, introducing 99.99% pure hydrogen gas and heating to 200℃ for 2 hours to weaken the adhesion between the electroplated layer and the substrate. Subsequently, under an inert atmosphere, mechanical peeling was performed using diamond cutting tools to completely remove the surface electroplated layer. After mechanical peeling, the magnets were transferred to a vacuum thermal activation zone at a vacuum level of 5 × 10⁻⁶. -3 Vacuum thermal activation was performed by holding the magnet at 380℃ for 1.5 hours under vacuum conditions to remove residual oxygen and hydroxide ions from the surface after stripping, forming a clean and highly active hydrogen adsorption interface. The magnet surface after pretreatment exhibited a uniform gray-black metallic luster, and energy dispersive spectroscopy showed that the surface nickel content was less than 0.1 at%, indicating that the electroplated layer had been completely removed.

[0034] The pre-treated and activated magnet is transferred to a high-pressure hydrogenation furnace through a vacuum-sealed channel. Hydrogenation is then performed in a closed system using a three-stage temperature-pressure coordinated control method. The first stage involves holding the magnet at 65°C in the first temperature range and 0.035 MPa in the first hydrogen pressure range for 2 hours. This allows hydrogen atoms to preferentially adsorb at the grain boundaries and dislocations of the hydrogen adsorption active interface formed during pretreatment, creating an initial adsorption layer. The second stage involves increasing the temperature to 85°C in the second temperature range and increasing the pressure to 0.12 MPa in the second hydrogen pressure range at a rate of 3°C per minute and 0.015 MPa per minute, then holding for 2 hours. This allows hydrogen atoms to diffuse along the grain boundaries and dislocations into the bulk, achieving bulk penetration. The third stage continues with increasing the temperature to 98°C in the third temperature range and increasing the pressure to 0.25 MPa in the third hydrogen pressure range, then holding for 2 hours. This allows hydrogen atoms to penetrate into the core of the bulk, completing the Nd₂Fe₂ process. 14 BH x Phase formation and embrittlement. After hydrogenation, the product is a loose, black, blocky substance that easily disintegrates into fragments with an average size of 2.1 mm. X-ray diffraction analysis shows that Nd₂Fe₂... 14 BH x The diffraction peak intensity of the phase reached its maximum value, with the number of hydrogen atoms x being approximately 1.2, and no residual α-Fe or neodymium oxide peaks appeared, indicating that the hydrogenation reaction was complete and uniform.

[0035] The hydrogenation products were transferred to a disproportionation furnace via a gas-lock chamber and subjected to disproportionation reaction under a 5% hydrogen-argon mixed atmosphere and a total pressure of 0.100±0.002MPa. The hydrogenation products sequentially passed through a preheating activation zone, a main disproportionation zone, and a cooling transition zone. The preheating activation zone was controlled at 540℃ for 15 minutes to induce the disproportionation reaction. After preheating activation, the products were fed into the main disproportionation zone, where the temperature was controlled at 835℃ for 45 minutes to achieve directional separation of the rare-earth-rich phase and the α-Fe phase under a stable hydrogen partial pressure. After main disproportionation, the products were fed into the cooling transition zone, where they were cooled to 400℃ at a programmed cooling rate of 1.5℃ per minute for 10 minutes to freeze the nanostructure and effectively suppress grain coarsening.

[0036] The disproportionated products were transferred to an inert atmosphere post-treatment unit via a gas lock chamber. In a high-purity argon environment with a dew point no higher than -42°C and an oxygen content lower than 0.3 ppm, coarse crushing, fine crushing, and air classification were performed sequentially. The coarse crushing process achieved an output particle size of 320 micrometers. Subsequently, the product was finely crushed by ball milling for 8 minutes. Finally, a precise classification was performed using an air classifier with a classifying wheel speed of 8000 rpm to obtain regenerated magnetic powder. Analysis of the obtained regenerated magnetic powder showed that its particle size D50 was 3.8 micrometers, with uniform particle size distribution and a D90 to D10 ratio of 2.09; the oxygen content was 0.142 wt%, lower than the control target of 0.15 wt%; X-ray diffraction revealed that the main phase was Nd₂Fe. 14 B and α-Fe, the rare earth-rich phase, are distributed in an amorphous state. High-resolution transmission electron microscopy (HRTEM) observation shows that the average particle size of the rare earth-rich phase is 28.2 nm, with a standard deviation of ±2.7 nm, and the nanoscale structure is uniform and stable. Inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis shows that the elemental composition of the regenerated magnetic powder deviates from that of the original magnet by less than 0.5 at%, and the composition remains well maintained. This embodiment successfully realizes the closed-loop hydrogenation-disproportionation regeneration of bulk NdFeB magnets. The resulting regenerated magnetic powder has a narrow particle size distribution, low oxygen content, and nanoscale rare earth-rich phase structure, fully meeting the precursor requirements for high-performance regenerated magnets.

[0037] Example 2 Under the same preparation conditions as in Example 1, only the first temperature range defined in this application was adjusted from 60–70°C to the lower limit of 60°C, and the first hydrogen pressure range was adjusted from 0.02–0.05 MPa to the lower limit of 0.02 MPa, to obtain the hydrogenated product. The results show that this product can still achieve complete pulverization of the entire magnet, with an average fragment size of 2.3 mm. XRD detection of Nd₂Fe 14 BH xCompared to Example 1, the adsorption efficiency was reduced by 8.3%, but still remained above 90.2%, verifying that the lower limit of the parameters in the first stage could still meet the requirements of the adsorption start-stop function. This demonstrates that the technical solution of the present invention has good feasibility and stability within the range of 60–70℃ and 0.02–0.05MPa.

[0038] Example 3 Under the same preparation conditions as in Example 1, only the third hydrogen pressure range defined in this application was adjusted from 0.2–0.3 MPa to the upper limit of 0.3 MPa to obtain the hydrogenated product. The results showed that the average size of the product fragments was 1.9 mm, and the Nd2Fe... 14 BH x The phase content reached 99.1%, but was accompanied by trace amounts of NdH2 impurity phase (XRD peak intensity accounted for 0.8%), indicating that 0.3 MPa is within the safe upper limit of hydrogenation reaction, and the generation of the main phase in the whole domain can still be achieved, which verifies the rationality and boundary inclusiveness of the hydrogen pressure range in this application.

[0039] Example 4 With all other preparation conditions the same as in Example 1, only the temperature of the main disproportionation region specified in this application was adjusted from 820–850℃ to the upper limit of 850℃ to obtain the disproportionation product. The results showed that the average particle size of the R-rich phase in the product increased to 32.5 nm, and a small amount of R-rich phase aggregates (particle size > 50 nm) appeared. However, the R-rich phase and the α-Fe phase remained spatially separated, and the content of non-magnetic impurities was 0.11 wt%. This verified that 850℃ is still within the effective temperature control window of the main disproportionation reaction, supporting the adequacy of the temperature range in this application.

[0040] Example 5 With all other preparation conditions the same as in Example 1, only the airflow stager speed defined in this application was changed from the corresponding D. 50 =3–5μm standard settings adjusted to make D 50 Regenerated magnetic powder was prepared by achieving a critical value of 3.0 μm. The results show that the powder has a D... 50 =3.0μm, D 90 / D 10 =2.21, oxygen content is 0.148wt%, SEM shows that the particles have good sphericity and no obvious agglomeration, which verifies the feasibility of the particle size range and the process robustness of this application.

[0041] Example 6 With all other preparation conditions the same as in Example 1, only the vacuum thermal activation temperature specified in this application was adjusted from 300–450℃ to the lower limit of 300℃ to obtain the activated magnet. The results show that the initial hydrogen adsorption rate on the magnet surface is reduced by 24% compared to Example 1, and the time required for the third stage of hydrogenation is extended to 2.5 hours to achieve the same Nd₂Fe₂. 14 BH x The phase content is reduced, but full-domain hydrogenation and complete pulverization can still be achieved in the end, which verifies that 300℃ as the lower limit is still technically feasible and supports the wide range of temperature range in this application.

[0042] Example 7 With all other preparation conditions the same as in Example 1, only the low-temperature hydrogen reduction temperature specified in this application was adjusted from 150–250°C to the upper limit of 250°C to obtain the pretreated magnet. The results showed that the integrity rate of the electroplated layer on the magnet was still 98.7%, but slight oxidation appeared on the substrate surface (XPS detection of Nd...). 3+ The percentage increased to 1.2%, and the mechanical peeling force further decreased to 1.1 N / mm, indicating that 250℃ is at the upper limit of the safety of the reduction process, and still meets the technical effect of the example, verifying the rationality of the temperature range.

[0043] Example 8 With all other preparation conditions the same as in Example 1, only the heating rate specified in this application was adjusted from 2–5 °C / min to the lower limit of 2 °C / min to obtain the hydrogenated product. The results showed that the hydrogenation uniformity of the product was improved, and the standard deviation of the hydrogen concentration profile of the entire magnet was reduced by 12%, but the single batch processing cycle was extended by 37%, verifying that although 2 °C / min is not preferred, it is still within the feasible range, supporting the full disclosure of the heating rate range in this application.

[0044] Example 9 Under the same preparation conditions as in Example 1, only the dew point of the high-purity Ar environment specified in this application was adjusted from ≤-40℃ to -40℃ (i.e., the upper limit) to obtain regenerated magnetic powder. The results showed that the oxygen content of the powder was 0.149wt%, which was within the allowable error range (±0.005wt%) compared with Example 1 (0.142wt%). The Nd loss rate detected by ICP-OES increased by 0.03at%, which was still within an acceptable level. This verifies that the dew point of -40℃ as a boundary value can still ensure that the oxygen content meets the standard, supporting the rigor of the dew point index in this application.

[0045] Example 10 Under the same preparation conditions as in Example 1, only the O2 content after gas exchange in the airlock chamber, as specified in this application, was adjusted from <1 ppm to 0.9 ppm to obtain regenerated magnetic powder. The results showed that the oxygen content of this powder was 0.145 wt%, an increase of 0.003 wt% compared to Example 1. XPS surface analysis showed Nd... 3+ The percentage increased from 5.3% to 5.7%, proving that the oxygen content of 0.9 ppm is still within the safe threshold, and verifying the effectiveness of the connection method in this application for oxygen blocking.

[0046] Comparative Example 1 is a blank control group. Step S1 low-temperature hydrogen reduction and mechanical stripping are skipped, and hydrogenation is performed directly after vacuum thermal activation. Comparative Example 2 is the parameter over-limit group, and the temperature of the third stage of hydrogenation is set to 105℃; Comparative Example 3 is commercially available recycled magnetic powder (HG-Dy series from a certain company, nominally D...). 50 =4.2μm, oxygen content ≤0.18wt%). Comparative Example 4 is the closest to the prior art group, adopting the single-stage hydrogenation (90℃ / 0.2MPa) + crushing process under conventional air environment disclosed in CN103276232A; Comparative Example 5 is the missing functional group, with the high-purity Ar protection in step S4 omitted, and the samples were pulverized and classified in ordinary dry air. All samples were prepared into Φ10mm×5mm cylindrical blanks using the same sintering process (vacuum sintering, 1080℃×2h, followed by tempering at 900℃×1h), and their magnetic properties were tested.

[0047] Table 1 Comparison of the properties of regenerated magnetic powder and comparative sintered magnets The results are shown in Table 1. Magnet B obtained in Example 1. r H cj and (BH) max The coercivity recovery rate was restored to 97.0%, 97.8%, and 97.6% of the original material, respectively, significantly better than all comparative examples. It exhibited the lowest oxygen content and the finest and narrowest R-rich phase particle size and distribution, confirming that this invention, through a four-pronged mechanism of pretreatment removal, three-stage hydrogenation permeation, zoned temperature-controlled disproportionation, and inert powder preservation, synergistically solved the three major technical bottlenecks of uneven hydrogenation in bulk materials, uncontrolled phase separation, and oxidation degradation. Particularly noteworthy is that the coercivity recovery rate of Example 1 was higher than the remanence recovery rate, indicating that the nanoscale R-rich phase structure effectively enhanced the grain boundary antimagnetic domain pinning ability. This coercivity surpassing phenomenon is an unexpected technical effect brought about by this invention.

[0048] Example 11 In this application embodiment, the test samples included regenerated magnetic powders prepared according to each embodiment of Examples 1 to Comparative Examples 4, and magnets were prepared under the same sintering conditions to test their practical application performance in the stator core of a permanent magnet synchronous motor (PMSM). The test was conducted according to GB / T32569–2016 "Technical Conditions for Permanent Magnet Synchronous Motors," with continuous operation for 100 hours at rated load (15kW), rated speed 3000 r / min, and ambient temperature 40℃. The results showed that the motor prepared using the magnetic powder from Example 1 achieved an efficiency of 95.3%, a temperature rise of only 18.2K, and a vibration value <1.2 mm / s; while the motor using the magnetic powder from Comparative Example 4 had an efficiency of 92.1%, a temperature rise of 31.5K, and a vibration value of 2.8 mm / s. All magnets prepared in Examples 1 to 10 met the industrial application thresholds of motor efficiency ≥94.0%, temperature rise ≤25K, and vibration ≤2.0 mm / s, verifying that the technical solution of this invention can stably produce regenerated magnetic powder that meets the requirements of practical applications under different parameter combinations. Experimental results show that the regenerated magnetic powder prepared in this invention exhibits good magnetic property stability and thermal reliability in permanent magnet synchronous motors.

[0049] The above description only illustrates the preferred embodiments of the present invention and should not be construed as limiting the scope of the claims. The present invention is not limited to the above embodiments, and variations in its specific structure are permitted. All modifications made within the scope of the independent claims of this invention are also within the scope of protection of this invention.

Claims

1. A hydrogenation-disproportionation method for recycling bulk NdFeB magnets, characterized in that, The pretreatment, hydrogenation, disproportionation and posttreatment processes are carried out sequentially in a closed reaction system. The closed reaction system includes a pretreatment device, a high-pressure hydrogenation furnace, a disproportionation furnace and an inert atmosphere posttreatment unit. Each unit is connected by a vacuum-sealed channel or an inert gas-protected gas lock chamber to achieve oxygen-free transport of the block magnet and its derivative intermediates throughout the entire process. The method includes the following steps: S1. In the pretreatment device, the blocky NdFeB magnet is subjected to low-temperature hydrogen reduction, mechanical stripping and vacuum thermal activation in sequence to remove the surface electroplating layer and oxide film and form a hydrogen adsorption active interface, thereby improving the initial adsorption rate of hydrogen atoms and improving the uniformity of hydrogenation initiation. S2. In the high-pressure hydrogenation furnace, based on the hydrogen adsorption active interface formed in step S1, hydrogenation is carried out using a three-stage temperature-pressure coordinated control to achieve hydrogen penetration along grain boundaries and dislocations in the bulk phase and Nd2Fe. 14 BH x Phase-wide generation ensures that hydrogen reaches the predetermined penetration depth within the bulk material to avoid incomplete core reactions; S3. In the disproportionation furnace, the product after being fully hydrogenated in step S2 is sequentially fed into the preheating activation zone, the main disproportionation zone and the cooling transition zone. Phase-oriented separation and nanostructure freezing are completed under the H2-Ar mixed atmosphere to suppress the generation of non-magnetic impurity phases and stabilize the rare earth-rich nanoscale structure. S4. In the inert atmosphere post-treatment unit, the disproportionation product obtained after step S3 is crushed and classified in a high-purity Ar environment to obtain regenerated magnetic powder. In this process, steps S1 to S4 utilize a closed reaction system to achieve oxygen-free transport throughout the entire process, allowing the effects of each step to be superimposed and collectively ensuring the particle size D of the regenerated magnetic powder. 50 It has a diameter of 3–5 μm, an oxygen content of ≤0.15 wt%, and magnetic properties close to those of the original magnet.

2. The hydrogenation-disproportionation method for recycling bulk NdFeB magnets according to claim 1, characterized in that, In the low-temperature hydrogen reduction process described in step S1, hydrogen gas with a purity of ≥99.99% is introduced and the temperature is controlled at 150–250℃ to weaken the bonding force between the electroplated layer and the substrate, thereby facilitating the subsequent mechanical peeling and removal of the electroplated layer, and providing a clean surface for the formation of a hydrogen adsorption active interface through vacuum thermal activation.

3. The hydrogenation-disproportionation method for recycling bulk NdFeB magnets according to claim 1, characterized in that, The vacuum thermal activation described in step S1 is performed at a vacuum level better than 10. -2 The process is carried out under Pa conditions, with a thermal activation temperature of 300–450°C and a holding time of 1–2 hours, in order to remove residual oxygen / hydroxyl radicals and form a hydrogen adsorption active interface after mechanical stripping to remove the electroplated layer.

4. The hydrogenation-disproportionation method for recycling bulk NdFeB magnets according to claim 1, characterized in that, In step S2, the specific process of the three-stage temperature-pressure coordinated control is as follows: First stage: Keeping the temperature in the first temperature range of 60–70℃ and the first hydrogen pressure range of 0.02–0.05MPa, so that hydrogen atoms are preferentially adsorbed at the grain boundaries and dislocations of the hydrogen adsorption active interface formed in step S1, forming an initial adsorption layer. The second stage involves heating to the second temperature range of 80–90℃ and pressurizing to the second hydrogen pressure range of 0.08–0.15MPa at a heating rate of 2–5℃ / min and a pressurization rate of 0.01–0.02MPa / min, followed by holding at the temperature to allow hydrogen atoms to diffuse into the bulk along grain boundaries and dislocations, thus achieving bulk infiltration. The third stage: Continue heating at the same rate to the third temperature range (95–100℃) and pressurize to the third hydrogen pressure range (0.2–0.3 MPa), then hold at this temperature to allow hydrogen atoms to permeate into the bulk core, completing the Nd2Fe synthesis. 14 BH x Global generation and embrittlement of phases.

5. The hydrogenation-disproportionation method for recycling bulk NdFeB magnets according to claim 1, characterized in that, The disproportionation reaction described in step S3 is carried out under a 5% H2-Ar mixed atmosphere and a total pressure of 0.10±0.005MPa to maintain the stability of the hydrogen partial pressure. Combined with the zoned temperature control of the preheating activation zone, the main disproportionation zone and the cooling transition zone, the directional separation of the R-rich phase and the α-Fe phase and the freezing of the nanostructure are achieved.

6. The hydrogenation-disproportionation method for recycling bulk NdFeB magnets according to claim 5, characterized in that, In step S3, the temperature of the preheating activation zone is controlled at 520–560℃ to induce the initiation of the disproportionation reaction; after preheating activation, the hydrogenation product is sent to the main disproportionation zone, where the temperature is controlled at 820–850℃ to achieve the directional separation of the R-rich phase and the α-Fe phase. After primary disproportionation, the product is sent to a cooling transition zone and cooled to 400°C using a programmed cooling rate of 2–10°C / min for nanostructure freezing to suppress grain coarsening.

7. The hydrogenation-disproportionation method for recycling bulk NdFeB magnets according to claim 1, characterized in that, The high-purity Ar environment described in step S4 requires a dew point ≤ -40℃ and an O2 content < 1ppm to block the oxygen intrusion path during the crushing and classification process.

8. The hydrogenation-disproportionation method for recycling bulk NdFeB magnets according to claim 1, characterized in that, In step S4, the disproportionation product is subjected to coarse crushing, fine crushing, and air classification in sequence. The coarse crushing is carried out by jaw crushing, and the fine crushing is carried out by ball milling, so that the particle size of the regenerated magnetic powder reaches D. 50 The size is 3–5 μm and the oxygen content is ≤0.15 wt%.

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