Method for preparing high-coercivity magnetic powder from neodymium-iron-boron recycled material

Abstract

The application discloses a method for preparing high-coercivity magnetic powder from neodymium-iron-boron recovery liquid, and belongs to the technical field of rare earth permanent magnet material recycling and reuse, and comprises the following steps: S1, carrying out acid solution reaction on retired fluoride grain boundary diffusion neodymium-iron-boron magnets after crushing treatment, and filtering to obtain a recovery liquid containing RE 3+ and F ‑ ; S2, adding a zirconium-based cellulose fluoride ion shielding agent into the recovery liquid to obtain a defluorination liquid; S3, adding a bifunctional chitosan crystal growth regulator into the defluorination liquid, and then co-precipitating with an ammonium oxalate solution to obtain a precursor; S4, calcining and reducing diffusion alloying; and S5, hydrogen crushing and airflow mill grading. The application solves the problem that fluorine ions combine with rare earth ions to form rare earth fluoride precipitation in the short-process recovery of retired fluoride grain boundary diffusion neodymium-iron-boron magnets by means of the zirconium-based cellulose fluoride ion shielding agent and the bifunctional chitosan crystal growth regulator.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet material recycling technology, specifically relating to a method for preparing high coercivity magnetic powder from neodymium iron boron recycled slurry. Background Technology

[0002] Sintered NdFeB permanent magnets are widely used in new energy vehicle drive motors and wind turbines. To improve the intrinsic coercivity of the magnets, the industry generally adopts a grain boundary diffusion process of heavy rare earth fluorides using dysprosium fluoride (DyF3) or terbium fluoride (TbF3) as the diffusion source. This process causes some fluorine atoms to remain in the grain boundary phase of the magnet in the form of rare earth fluoride oxides.

[0003] As the first batch of magnets using the aforementioned grain boundary diffusion process enters their decommissioning period, their secondary recycling has created an industrial demand. Currently, the most promising recycling route for industrialization is the short-process "acid dissolution—oxalic acid co-precipitation—calcination reduction—hydrogenation—air jet milling," a process that has been thoroughly validated in fluorine-free primary waste. However, when this short process is directly applied to decommissioned magnets containing fluorine, the following technical problem arises: residual fluorine in the magnet's grain boundary phase is dissolved in hydrochloric acid and enters the feed solution, forming fluoride ions (F). - In the subsequent oxalate coprecipitation process, it competes with oxalate ions for rare earth ions (RE ions). 3+ The combination of these elements leads to the precipitation of REF3 under co-precipitation conditions at pH 2.5-3.5. The extremely fine nano-sized REF3 particles can penetrate the filter cloth and be lost with the filtrate, causing the primary rare earth recovery rate to drop from over 90% in the original waste system to 75-85%. The relatively larger REF3 particles remain in the precursor filter cake and are transformed into fluorine oxide impurities during subsequent calcination, degrading the coercivity of the regenerated magnetic powder.

[0004] To address the aforementioned problems, existing technologies typically involve adding a strong alkali such as sodium hydroxide to the feed solution to preprecipitate fluoride ions before co-precipitation. However, this method inevitably introduces a large amount of cationic impurities such as sodium ions into the feed solution, deteriorating the purity of the precursor. How to block the competitive binding of fluoride ions to rare earth ions without introducing new cationic impurities is a pressing technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing high coercivity magnetic powder from NdFeB recycled slurry, in order to solve the problem that during the short-process recycling of decommissioned NdFeB magnets with fluoride grain boundary diffusion, fluoride ions compete with oxalate ions in the oxalic acid co-precipitation step to combine with rare earth ions to form rare earth fluorides, resulting in a decrease in rare earth yield.

[0006] The technical solution adopted in this invention is as follows: A method for preparing high coercivity magnetic powder from NdFeB recycled slurry, comprising the following steps:

[0007] S1. Preparation of decommissioned fluoride-diffused NdFeB magnet solution: Decommissioned fluoride-diffused NdFeB magnets are crushed and then placed in 6 mol / L hydrochloric acid at 60-70℃ for acid dissolution. After filtration, the pH of the filtrate is adjusted to 1.5-2.0 to obtain a solution containing RE. 3+ With F - The recovered liquid material;

[0008] S2, Fluoride Ion Overall Shielding: Add zirconium-based cellulose fluoride ion shielding agent to the recovered liquid obtained in step S1, stir and react for 1-3 hours at 30-50℃ and pH 1.5-2.0, filter and separate the zirconium-based cellulose fluoride ion shielding agent loaded with fluoride ions to obtain defluorination liquid;

[0009] S3. Precipitation of precursor by co-precipitation with fine crystal plane control: Add bifunctional chitosan crystal growth regulator to the defluorinated solution obtained in step S2, stir evenly, adjust the pH to 2.5-3.5 with ammonia water, add ammonium oxalate solution dropwise at 50-65℃ until the co-precipitation reaction is completed, filter, wash with deionized water at 60-70℃, and vacuum dry to obtain the precursor.

[0010] S4. Calcination and Reduction Diffusion Alloying: The precursor obtained in step S3 is calcined at 800℃ under a hydrogen / argon mixed atmosphere, according to the target Nd2Fe... 14 B. FeB alloy powder and metallic calcium powder are added in stoichiometric ratio, and after uniform mixing, a reduction diffusion reaction is carried out at 1080℃ under argon protection. The resulting alloy body is washed with water to remove CaO byproducts, filtered and vacuum dried to obtain NdFeB alloy powder.

[0011] S5. Hydrogen crushing and air jet milling classification: The NdFeB alloy powder obtained in step S4 is placed in a hydrogen crushing chamber, and high-purity hydrogen gas of 0.1-0.5 MPa is introduced. The temperature is raised to 550°C at a heating rate not exceeding 5°C / min, and held at 550°C for 2 hours. The hydrogen is removed by vacuum to obtain hydrogen crushing coarse powder. The hydrogen crushing coarse powder is then ultra-finely crushed and classified by air jet milling under argon protection to obtain high coercivity NdFeB magnetic powder with a particle size D50 of 3 μm.

[0012] Furthermore, in step S2, the amount of zirconium-based cellulose fluoride ion shielding agent added is 5-15 g / L; in step S3, the amount of bifunctionalized chitosan crystal growth regulator added is 1-3 g / L.

[0013] Furthermore, the preparation method of the zirconium-based cellulose fluoride ion shielding agent includes the following steps:

[0014] A1. Disperse sodium carboxymethyl cellulose in anhydrous N,N-dimethylformamide, add urea and stir to dissolve, cool in an ice bath to 0-5°C under nitrogen protection, slowly add phosphorus oxychloride, then heat to 80°C to react, cool and filter, wash first with anhydrous ethanol, then wash with deionized water until the filtrate is neutral, and vacuum dry to obtain intermediate A1.

[0015] A2. Disperse intermediate A1 obtained in step A1 in a mixed solvent of isopropanol / deionized water, add 4 mol / L sodium hydroxide solution, activate and stir at 40°C, then slowly add 70% (w / w) aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride, react at 60°C, cool, adjust pH to 7.0 with 1 mol / L hydrochloric acid, filter, wash alternately with deionized water and anhydrous ethanol, and vacuum dry to obtain intermediate A2;

[0016] A3. Dissolve zirconium oxychloride octahydrate in deionized water, adjust the pH to 2.0 with 1 mol / L hydrochloric acid, add intermediate A2 obtained in step A2, stir and react at 60℃, filter, wash first with pH 2.0 hydrochloric acid solution, then wash with deionized water until neutral, and vacuum dry to obtain zirconium-based cellulose fluoride ion shielding agent.

[0017] Furthermore, the preparation method of the bifunctionalized chitosan crystal growth regulator includes the following steps:

[0018] B1. Chitosan with a degree of deacetylation of not less than 85% was dissolved in a 1% (w / w) aqueous solution of acetic acid, and then diluted with methanol to obtain a chitosan solution. Separately, succinic anhydride was dissolved in methanol and added dropwise to the above chitosan solution at 40°C. The reaction was carried out at 40°C. After the reaction was completed, the pH was adjusted to 10.0 with 1 mol / L sodium hydroxide to precipitate a solid. The solid was filtered, washed alternately with deionized water and anhydrous ethanol, and dried under vacuum to obtain intermediate B1.

[0019] B2. Disperse intermediate B1 obtained in step B1 in a mixed solvent of isopropanol / deionized water, add sodium hydroxide pre-dissolved in deionized water, activate and stir at 60°C, then slowly add 70% (w / w) aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride, react at 65°C, cool, neutralize to pH 7.0 with 1 mol / L hydrochloric acid, dialyze with deionized water, freeze-dry the inner liquid to obtain a bifunctional chitosan crystal growth regulator.

[0020] Furthermore, in step S1, the decommissioned fluoride grain boundary diffused NdFeB magnets are crushed to a particle size of less than 5 mm, the acid dissolution reaction time is 3-5 h, and the solid-liquid ratio is 1:5 to 1:8 (mass-volume ratio, kg:L).

[0021] Furthermore, the zirconium-based cellulose fluoride ion shielding agent loaded with fluoride ions separated by filtration in step S2 is desorbed with 1 mol / L sodium hydroxide solution at 40°C for 2 hours, and then regenerated with pH 2.0 hydrochloric acid solution for recycling.

[0022] Furthermore, in step S3, the concentration of ammonium oxalate solution is 0.5 mol / L, filtration is performed using a Buchner funnel, and the solution is washed four times with a liquid-to-solid ratio of not less than 10:1; in step S5, the material of the hydrogen crushing chamber is Inconel 625 alloy.

[0023] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0024] 1. This invention solves the problem of rare earth fluoride precipitation during the short-process recycling of decommissioned fluoride-diffused NdFeB magnets by synergistic use of zirconium-based cellulose fluoride ion shielding agent and bifunctionalized chitosan crystal growth regulator. This increases the original rare earth primary recovery rate of 75-85% to more than 90%, reducing the loss of rare earth resources during the recycling process.

[0025] 2. Both functional substances used in this invention are based on natural polymers, and no cationic impurities such as sodium ions are introduced throughout the process. The zirconium-based cellulose fluoride ion shielding agent can be recycled through simple desorption after use, thus fully preserving the inherent advantages of the short-process technology in terms of economy and environmental friendliness, and avoiding the impurity pollution problem of the alkaline pre-defluorination route. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a flowchart of a method for preparing highly coercive magnetic powder from NdFeB recycled slurry in this embodiment. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, and not all embodiments. The components of the embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0030] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0031] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0032] Example 1: This example provides a method for preparing high coercivity magnetic powder from NdFeB recycled slurry, including the following steps:

[0033] S1. Preparation of decommissioned fluoride-diffused NdFeB magnet solution: 1.0 kg of decommissioned fluoride-diffused NdFeB magnets were crushed to a particle size of less than 5 mm using a jaw crusher. The resulting solution was placed in 6.0 L of 6 mol / L hydrochloric acid and mechanically stirred at 65 °C for 4 h for acid dissolution (solid-to-liquid ratio 1:6, kg:L). After the reaction, the insoluble residue was removed by filtration with qualitative filter paper. The pH of the filtrate was adjusted to 1.8 with concentrated ammonia to obtain a solution containing RE. 3+ With F - The recovered liquid material;

[0034] S2, Fluoride Ion Overall Shielding: Zirconium-based cellulose fluoride ion shielding agent is added to the recovered liquid obtained in step S1, and the reaction is carried out at 40℃ with mechanical stirring at 300 r / min for 2 h (the pH is kept constant at 1.8 during stirring). After the reaction is completed, the fluoride-loaded zirconium-based cellulose fluoride ion shielding agent is separated by suction filtration through a Buchner funnel to obtain a defluorinated liquid. The separated fluoride-loaded zirconium-based cellulose fluoride ion shielding agent is desorbed with 1 mol / L sodium hydroxide solution at 40℃ for 2 h. After desorption, it is regenerated with pH 2.0 hydrochloric acid solution and recycled.

[0035] S3. Precursor preparation by co-precipitation with fine crystal plane control: Add a bifunctional chitosan crystal growth regulator to the defluorinated solution obtained in step S2, and mechanically stir at 300 r / min for 20 min to uniformly disperse the regulator in the solution. Then adjust the pH to 3.0 with concentrated ammonia, raise the temperature to 60℃, and add 0.5 mol / L ammonium oxalate solution dropwise at a rate of 5 mL / min using a peristaltic pump until the coprecipitation reaction is complete. Continue to mature and stir for 1 h, filter through a Buchner funnel, wash 4 times with deionized water at 65℃ (liquid-solid ratio 10:1), and vacuum dry at 80℃ for 12 h to obtain the precursor.

[0036] S4. Calcination and Reduction Diffusion Alloying: The precursor obtained in step S3 is loaded into an alumina boat and placed in a tube furnace. A hydrogen / argon mixture (volume ratio 5:95, flow rate 500 mL / min) is introduced, and the temperature is increased to 800℃ at a rate of 3℃ / min. The temperature is held for 2 hours to complete the oxalate decomposition. After cooling to room temperature, the precursor is removed, and the actual mass of the oxide and iron is calculated. Based on the actual mass and the target Nd2Fe... 14 The stoichiometric ratio of B (atomic ratio Nd:Fe:B = 2:14:1) was increased by adding FeB alloy powder (containing 19.8 wt% B) and metallic calcium powder (purity 99.5%, the amount added is 110% of the stoichiometric ratio required for the theoretical reduction of RE2O3). The mixture was then mixed in a planetary ball mill at 200 r / min for 30 min. The uniformly mixed powder was placed in an alumina crucible and heated to 1080 °C at 5 °C / min under argon protection in a tube furnace for 4 h to carry out a reduction diffusion alloying reaction. After the furnace cooled to room temperature, the alloy was removed and placed in deionized water. It was then wet-milled and washed at 150 r / min for 2 h to fully remove CaO byproducts. After filtration through a Buchner funnel, it was vacuum-dried at 80 °C for 12 h to obtain NdFeB alloy powder.

[0037] S5. Hydrogenation and Airflow Mill Classification: The NdFeB alloy powder obtained in step S4 is loaded into an Inconel 625 alloy hydrogenation chamber. First, a vacuum is drawn to below 10 Pa, then high-purity hydrogen (99.999% purity) is introduced to a pressure of 0.3 MPa. The temperature is increased to 550°C at a rate of 3°C / min and held at 550°C for 2 hours. After holding, a vacuum is drawn to remove hydrogen to below 10 Pa, and the powder is cooled to room temperature to obtain coarse hydrogenated powder. This coarse powder is transferred to an airflow mill. Under argon protection and with high-purity nitrogen as the working medium, the classifier rotates at 10000 r / min for ultrafine grinding and classification to obtain high-coercivity NdFeB magnetic powder with a particle size D50 of 3 μm. The process is as follows: Figure 1 As shown.

[0038] In step S2, the amount of zirconium-based cellulose fluoride ion shielding agent added is 10 g / L; in step S3, the amount of bifunctionalized chitosan crystal growth regulator added is 2 g / L.

[0039] The preparation method of the zirconium-based cellulose fluoride ion shielding agent includes the following steps:

[0040] A1. 10.0 g of sodium carboxymethyl cellulose was dispersed in 200 mL of anhydrous N,N-dimethylformamide, and 20.0 g of urea was added and stirred to dissolve. The mixture was cooled to 0-5 °C in an ice bath under nitrogen protection. 10.0 mL of phosphorus oxychloride was slowly added dropwise over 1 h. The temperature was then increased to 80 °C at a rate of 1 °C / min and reacted for 6 h. After cooling, the mixture was filtered and washed three times with anhydrous ethanol (100 mL each time) and then with deionized water until the filtrate was neutral. The filtrate was dried under vacuum at 60 °C for 12 h to obtain intermediate A1.

[0041] A2. Disperse 5.0 g of intermediate A1 obtained in step A1 in 100 mL of isopropanol / deionized water mixed solvent (volume ratio 60:40), add 10 mL of 4 mol / L sodium hydroxide solution, activate and stir at 40 °C for 30 min, then slowly add 15 mL of 70% (w / w) 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution over 1 h, react at 60 °C for 8 h, cool, adjust pH to 7.0 with 1 mol / L hydrochloric acid, filter, wash three times alternately with deionized water and anhydrous ethanol, and vacuum dry at 50 °C for 12 h to obtain intermediate A2;

[0042] A3. Dissolve 3.22g of zirconium oxychloride octahydrate in 100mL of deionized water, adjust the pH to 2.0 with 1mol / L hydrochloric acid, add 4.0g of intermediate A2 obtained in step A2, stir and react at 60℃ for 6h, filter, wash 3 times (50mL each time) with pH2.0 hydrochloric acid solution, then wash with deionized water until neutral, and vacuum dry at 60℃ for 12h to obtain zirconium-based cellulose fluoride ion shielding agent.

[0043] The preparation method of the bifunctionalized chitosan crystal growth regulator includes the following steps:

[0044] B1. Dissolve 10.0g of chitosan with a degree of deacetylation of not less than 85% in 200mL of 1% acetic acid aqueous solution, and then dilute with 200mL of methanol to obtain a chitosan solution. Separately, dissolve 12.0g of succinic anhydride in 80mL of methanol and add it dropwise to the above chitosan solution at 40℃ for 1h. React at 40℃ for 8h. Adjust the pH to 10.0 with 1mol / L sodium hydroxide to precipitate a solid. Filter the solid and wash it three times alternately with deionized water and anhydrous ethanol. Dry it under vacuum at 50℃ for 12h to obtain intermediate B1.

[0045] B2. Disperse 5.0g of intermediate B1 obtained in step B1 in 100mL of isopropanol / deionized water mixed solvent (volume ratio 70:30), add 3.0g of sodium hydroxide pre-dissolved in 10mL of deionized water, activate and stir at 60℃ for 30min, then slowly add 12mL of 70% 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution over 1h, react at 65℃ for 8h, cool and neutralize to pH 7.0 with 1mol / L hydrochloric acid, transfer to a dialysis bag with a molecular weight cutoff of 3,500 Da, dialyze with deionized water for 72h, changing the solution 8 times during the process, and freeze-dry the inner solution at -50℃ and 10Pa for 24h to obtain the bifunctional chitosan crystal growth regulator.

[0046] Example 2: This example differs from Example 1 in that the amount of zirconium-based cellulose fluoride ion shielding agent added in step S2 is 5 g / L; and the amount of bifunctionalized chitosan crystal growth regulator added in step S3 is 1 g / L. The rest are the same.

[0047] Example 3: This example differs from Example 1 in that the amount of zirconium-based cellulose fluoride ion shielding agent added in step S2 is 15 g / L; and the amount of bifunctionalized chitosan crystal growth regulator added in step S3 is 3 g / L. The rest are the same.

[0048] Comparative Example 1: This comparative example is based on Example 1, but differs from Example 1 in that sodium carboxymethyl cellulose without any modification is used instead of zirconium-based cellulose fluoride ion shielding agent. That is, sodium carboxymethyl cellulose without modification is added directly to the recovered liquid obtained in step S1 at the same amount (10 g / L) as the zirconium-based cellulose fluoride ion shielding agent in step S2 of Example 1. The remaining reaction conditions and subsequent steps are the same as in Example 1.

[0049] Comparative Example 2: This comparative example differs from Example 1 in that the zirconium-based cellulose fluoride ion shielding agent in this comparative example only completes steps A1 and A2 to prepare intermediate A2, without performing step A3; that is, intermediate A2 is directly used as the shielding agent. The rest is the same as in Example 1.

[0050] Comparative Example 3: This comparative example is based on Example 1, but differs from Example 1 in that the zirconium-based cellulose fluoride ion shielding agent in this comparative example only completes steps A1 and A3, omitting step A2. The rest is the same as in Example 1.

[0051] Comparative Example 4: This comparative example is based on Example 1, but differs from Example 1 in that unmodified chitosan is used instead of the bifunctionalized chitosan crystal growth regulator. That is, unmodified chitosan is added directly to the defluorination solution obtained in step S2 at the same amount (2 g / L) of the bifunctionalized chitosan crystal growth regulator in step S3 of Example 1. The remaining reaction conditions and subsequent steps are the same as in Example 1.

[0052] Comparative Example 5: This comparative example differs from Example 1 in that the bifunctionalized chitosan crystal growth regulator in this comparative example only completes step B1 to prepare intermediate B1, without performing step B2. The rest is the same as in Example 1.

[0053] Comparative Example 6: This comparative example differs from Example 1 in that the preparation of the bifunctional chitosan crystal growth regulator in this comparative example does not involve step B1; instead, chitosan with a degree of deacetylation of not less than 85% is directly modified according to step B2. The rest of the process is the same as in Example 1.

[0054] Comparative Example 7: This comparative example is based on Example 1, but differs from Example 1 in that the fluoride ion shielding process in step S2 is omitted in this comparative example. The recovered liquid obtained in step S1 is directly introduced into step S3 for co-precipitation reaction. The amount of bifunctional chitosan crystal growth regulator added in step S3 and other reaction conditions are the same as in Example 1.

[0055] Comparative Example 8: This comparative example differs from Example 1 in that the addition of the bifunctional chitosan crystal growth regulator in the co-precipitation process of fine crystal plane control in step S3 is omitted. That is, after step S2, the co-precipitation reaction is carried out directly according to the pH adjustment, temperature control, and ammonium oxalate addition conditions of step S3 in Example 1. The rest is the same as in Example 1.

[0056] Comparative Example 9: This comparative example differs from Example 1 in that it uses an alkaline pre-defluorination scheme as a control, and does not use zirconium-based cellulose fluoride ion shielding agent or bifunctional chitosan crystal growth regulator. In step S2, 1 mol / L sodium hydroxide solution is added to the recovered liquid obtained in step S1 to preprecipitate fluoride ions by neutralization (the amount of sodium hydroxide added is based on adjusting the pH of the liquid to 5.0). After stirring for 2 hours, the precipitate is separated by filtration, and then the pH of the filtrate is adjusted back to 3.0 using 6 mol / L hydrochloric acid. In step S3, a coprecipitation reaction is directly carried out using 0.5 mol / L ammonium oxalate solution, without adding the bifunctional chitosan crystal growth regulator. The rest of the process is the same as in Example 1.

[0057] Comparative Example 10: This comparative example serves as a blank control. Zirconium-based cellulose fluoride ion shielding agent and bifunctionalized chitosan crystal growth regulator are not used; that is, the overall fluoride ion shielding process in step S2 is omitted. The recovered liquid obtained in step S1 directly enters the co-precipitation process. The co-precipitation reaction is carried out according to the pH adjustment, temperature control, and ammonium oxalate addition conditions in step S3 of Example 1. No regulator is added during the co-precipitation process. The rest is consistent with Example 1.

[0058] Experimental Example 1: The defluorination solutions, coprecipitation filtrates and precursor products obtained from Examples 1-3 and Comparative Examples 1-10 were subjected to fluoride ion control effect, coprecipitation process efficiency and quantitative characterization of rare earth fluoride (REF3) impurity phase. The results are shown in Table 1.

[0059] The residual F⁻ concentration in the defluorination feed solution and coprecipitate filtrate was determined using the fluoride ion selective electrode method. The rare earth yield was determined by inductively coupled plasma optical emission spectrometry (ICP-OES) to determine the residual rare earth concentration in the filtrate, which was calculated based on the initial total rare earth content of the feed solution according to mass balance. The precursor particle size D50 was determined using a laser particle size analyzer. The precursor fluorine content was determined by high-temperature hydrolysis-ion chromatography, with a sample weight of 0.2 g. The precursor impurity phase content was quantified using the Rietveld full-spectrum fitting method, expressed as a mass fraction (wt%), with a detection limit of 0.05 wt%. Each sample was prepared independently in triplicate, and each indicator in each batch was tested in parallel three times.

[0060] Table 1. Test results of each group of samples:

[0061]

[0062] Experimental Example 2: The magnetic powders obtained in Examples 1-3 and Comparative Examples 1-10 were then oriented, pressed, sintered, and tempered to form standard NdFeB magnets. The magnetic properties and sodium impurity content were characterized, and the results are shown in Table 2.

[0063] Intrinsic coercivity Hcj, remanence Br, and maximum energy product (BH)max were measured at room temperature using a pulsed hysteresis loop analyzer. The sodium content of the magnet was determined by inductively coupled plasma mass spectrometry (ICP-MS), with a sample weight of 0.1 g. Each group of samples was prepared independently in 3 batches, and the magnetic properties of 5 samples were measured in each batch. The sodium impurity content of each batch was measured in parallel 3 times.

[0064] Table 2. Detection results of magnetic properties and sodium impurity content of regenerated magnets in each group:

[0065]

[0066] Experimental Example 3: The zirconium-based cellulose fluoride ion shielding agent used in Example 1 was subjected to a ten-cycle reuse test according to the desorption and regeneration method described in the instruction manual to verify its reuse performance. The results are shown in Table 3.

[0067] Each cycle was carried out under the conditions of step S2 in Example 1 (dosage 10 g / L, feed solution F). - Initial concentration 8.5 × 10 -3 After the reaction, the solid-phase shielding agent loaded with fluoride ions was separated by filtration. It was then desorbed with 1 mol / L sodium hydroxide solution at 40℃ for 2 h. After desorption, it was regenerated with pH 2.0 hydrochloric acid solution and then added to the next round of shielding reaction. The F content in the defluorination solution was measured after each cycle. - Residual concentration and shielding agent mass loss rate.

[0068] Table 3. Test results of the recyclability of zirconium-based cellulose fluoride ion shielding agent:

[0069]

[0070] Based on the data in Tables 1, 2, and 3, it can be concluded that this invention, through the synergistic effect of zirconium-based cellulose fluoride ion shielding agent and bifunctionalized chitosan crystal growth regulator, solves the problem of rare earth fluoride precipitation caused by fluoride ions combining with rare earth ions during the short-process recovery of decommissioned fluoride-diffused NdFeB magnets. This increases the primary rare earth yield to over 90%, and reduces the content of rare earth fluoride impurities in the precursor to below 0.1 wt%. Simultaneously, the entire process does not introduce cationic impurities such as sodium ions, and the shielding agent can be recycled and reused, fully preserving the economic and environmental advantages of the short-process technology. Compared with existing technologies, it has significant comprehensive competitiveness and possesses complete conditions for industrial application.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing high coercivity magnetic powder from NdFeB recycled slurry, characterized in that, Includes the following steps: S1. Preparation of decommissioned fluoride-diffused NdFeB magnet solution: Decommissioned fluoride-diffused NdFeB magnets are crushed and then placed in 6 mol / L hydrochloric acid at 60-70℃ for acid dissolution. After filtration, the pH of the filtrate is adjusted to 1.5-2.0 to obtain a solution containing RE. 3+ With F - The recovered liquid material; S2, Fluoride Ion Overall Shielding: Add zirconium-based cellulose fluoride ion shielding agent to the recovered liquid obtained in step S1, stir and react for 1-3 hours at 30-50℃ and pH 1.5-2.0, filter and separate the zirconium-based cellulose fluoride ion shielding agent loaded with fluoride ions to obtain defluorination liquid; S3. Precipitation of precursor by co-precipitation with fine crystal plane control: Add bifunctional chitosan crystal growth regulator to the defluorinated solution obtained in step S2, stir evenly, adjust the pH to 2.5-3.5 with ammonia water, add ammonium oxalate solution dropwise at 50-65℃ until the co-precipitation reaction is completed, filter, wash with deionized water at 60-70℃, and vacuum dry to obtain the precursor. S4. Calcination and Reduction Diffusion Alloying: The precursor obtained in step S3 is calcined at 800℃ under a hydrogen / argon mixed atmosphere, according to the target Nd2Fe... 14 B. FeB alloy powder and metallic calcium powder are added in stoichiometric ratio, and after uniform mixing, a reduction diffusion reaction is carried out at 1080℃ under argon protection. The resulting alloy body is washed with water to remove CaO byproducts, filtered and vacuum dried to obtain NdFeB alloy powder. S5. Hydrogen crushing and air jet milling classification: The NdFeB alloy powder obtained in step S4 is placed in a hydrogen crushing chamber, and high-purity hydrogen gas of 0.1-0.5MPa is introduced. The temperature is raised to 550℃ at a heating rate not exceeding 5℃ / min, and held at 550℃ for 2 hours. The hydrogen is removed by vacuum to obtain hydrogen crushing coarse powder. The hydrogen crushing coarse powder is then ultra-finely crushed and classified by air jet milling under argon protection to obtain high coercivity NdFeB magnetic powder with a particle size D50 of 3μm. The preparation method of the zirconium-based cellulose fluoride ion shielding agent includes the following steps: A1. Disperse sodium carboxymethyl cellulose in anhydrous N,N-dimethylformamide, add urea and stir to dissolve, cool in an ice bath to 0-5°C under nitrogen protection, slowly add phosphorus oxychloride, then heat to 80°C to react, cool and filter, wash first with anhydrous ethanol, then wash with deionized water until the filtrate is neutral, and vacuum dry to obtain intermediate A1. A2. Disperse intermediate A1 obtained in step A1 in a mixed solvent of isopropanol / deionized water, add 4 mol / L sodium hydroxide solution, activate and stir at 40°C, then slowly add 70% (w / w) aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride, react at 60°C, cool, adjust pH to 7.0 with 1 mol / L hydrochloric acid, filter, wash alternately with deionized water and anhydrous ethanol, and vacuum dry to obtain intermediate A2; A3. Dissolve zirconium oxychloride octahydrate in deionized water, adjust the pH to 2.0 with 1 mol / L hydrochloric acid, add intermediate A2 obtained in step A2, stir and react at 60℃, filter, wash first with pH 2.0 hydrochloric acid solution, then wash with deionized water until neutral, and vacuum dry to obtain zirconium-based cellulose fluoride ion shielding agent. The preparation method of the bifunctionalized chitosan crystal growth regulator includes the following steps: B1. Chitosan with a degree of deacetylation of not less than 85% was dissolved in a 1% (w / w) aqueous solution of acetic acid, and then diluted with methanol to obtain a chitosan solution. Separately, succinic anhydride was dissolved in methanol and added dropwise to the above chitosan solution at 40°C. The reaction was carried out at 40°C. After the reaction was completed, the pH was adjusted to 10.0 with 1 mol / L sodium hydroxide to precipitate a solid. The solid was filtered, washed alternately with deionized water and anhydrous ethanol, and dried under vacuum to obtain intermediate B1. B2. Disperse intermediate B1 obtained in step B1 in a mixed solvent of isopropanol / deionized water, add sodium hydroxide pre-dissolved in deionized water, activate and stir at 60°C, then slowly add 70% (w / w) aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride, react at 65°C, cool, neutralize to pH 7.0 with 1 mol / L hydrochloric acid, dialyze with deionized water, freeze-dry the inner liquid to obtain a bifunctional chitosan crystal growth regulator.

2. The method for preparing high coercivity magnetic powder from NdFeB recycled slurry according to claim 1, characterized in that, In step S2, the amount of zirconium-based cellulose fluoride ion shielding agent added is 5-15 g / L; in step S3, the amount of bifunctionalized chitosan crystal growth regulator added is 1-3 g / L.

3. The method for preparing high coercivity magnetic powder from NdFeB recycled slurry according to claim 1, characterized in that, In step S1, the decommissioned fluoride grain boundary diffused NdFeB magnets are crushed to a particle size of less than 5 mm, the acid dissolution reaction time is 3-5 h, and the solid-liquid ratio is 1:5 to 1:8; the solid-liquid ratio is the ratio of the mass of the solid to the volume of the liquid, and the units are kg and L, respectively.

4. The method for preparing high coercivity magnetic powder from NdFeB recycled slurry according to claim 1, characterized in that, The zirconium-based cellulose fluoride ion shielding agent loaded with fluoride ions separated by filtration in step S2 is desorbed at 40°C for 2 h with 1 mol / L sodium hydroxide solution. After desorption, it is regenerated with pH 2.0 hydrochloric acid solution and then recycled.

5. The method for preparing high coercivity magnetic powder from NdFeB recycled slurry according to claim 1, characterized in that, In step S3, the concentration of ammonium oxalate solution is 0.5 mol / L, filtration is performed using a Buchner funnel, and the solution is washed 4 times with a liquid-to-solid ratio of not less than 10:

1. In step S5, the hydrogen crushing chamber is made of Inconel 625 alloy.

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