A method for removing nylon from waste injection-molded bonded NdFeB magnetic powder using potassium permanganate chemical reaction method

Abstract

A method for recovering injection-molded bonded NdFeB magnetic powder by removing organic matter from waste polyamide bonded NdFeB magnetic powder using a potassium permanganate chemical reaction method relates to the technical field of material recovery. The mixed solvent used is composed of potassium permanganate, sodium lauryl sulfate, sodium hydroxide and deionized water, wherein the concentration range of potassium permanganate is 0.02-0.05 mol / L, the concentration range of sodium lauryl sulfate is: 0.01-0.03 mol / L, and the amount of sodium hydroxide is maintained at a solution pH value between 7-10. The invention has the advantages that the polyamide binder in waste injection-molded bonded NdFeB magnetic powder is effectively removed by adjusting the solution pH through a potassium permanganate-sodium lauryl sulfate (SDS) mixed solvent system and an alkaline medium, and a solution formula and a treatment method that are less destructive to NdFeB magnetic powder are provided, and the recovery process is simple, easy to operate, highly safe, low cost, and the binder removal effect is remarkable.

Description

Technical Field

[0001] The invention discloses a method for removing nylon from waste injection-molded bonded NdFeB magnetic powder by utilizing a potassium permanganate chemical reaction method, and belongs to the technical field of NdFeB material recovery. Background Art

[0002] With the rapid development and continuous advancement of modern technology, rare earth permanent magnet materials have undergone significant iterations and upgrades, evolving from the initial samarium-cobalt 1:5 type (first generation) and samarium-cobalt 2:17 type (second generation) to the third generation of neodymium iron boron permanent magnets, which boast the highest overall performance. Based on differences in production and manufacturing techniques, neodymium iron boron permanent magnets can be subdivided into three categories: sintered, bonded, and hot-pressed. Current research on neodymium iron boron recycling focuses primarily on the recycling of sintered magnets. Compared to sintered magnets, bonded neodymium iron boron offers superior performance uniformity, a simplified production process, lower costs, high-precision dimensional control, robust processing capabilities, and the ability to meet precision manufacturing requirements. These advantages perfectly align with the trend toward smaller, lighter, and thinner electronic products. Consequently, they have found widespread application in computers, mobile devices, office automation equipment, new energy vehicles, and various household appliances. However, with the scrapping of related products and the generation of scrap during the processing process, waste is inevitable, which not only leads to the waste of rare earth resources, but also causes pollution problems. In view of this, in order to promote the recycling of rare earth resources, strengthen environmental protection and reduce production costs, research on the field of bonded NdFeB recovery has far-reaching significance and value.

[0003] Bonded NdFeB magnets are primarily composed of NdFeB magnetic powder, a binder, and a series of additives (such as coupling agents, lubricants, and antioxidants). Different molding processes utilize different binders. For example, molded bonded magnets often use a specific ratio of epoxy resin, its curing agent, and a coupling agent. Calendered bonded magnets generally use ethylene or nitrile rubber as a binder. Injection molded magnets tend to use thermoplastic polyamide (nylon) as a binder.

[0004] Given that different bonded NdFeB magnets use different types and contents of binders, as shown in Table 1, their recycling strategies are also completely different. A major challenge in the recycling of bonded magnets is how to effectively remove the difficult-to-degrade polymer binder while minimizing damage to the magnetic powder. Currently, there have been preliminary studies on the recycling of molded bonded magnets (such as welding machine magnets using epoxy resin): Sun Shuo, Zhang Yu, Zhu Peihong and others from Beijing University of Technology used sodium hypochlorite and sodium hydroxide in patents CN 113351613 A and CN113351614A to chemically react with the cyano functional groups and epoxy groups in the cured epoxy resin at room temperature and pressure, respectively, to destroy the structure of the binder, thereby achieving effective stripping of organic matter from waste MQ bonded NdFeB magnetic powder. However, given that the polyamide nylon binder used in injection-molded bonded magnets has a structure and properties completely different from those of epoxy resin and polyphenylene sulfide binders, and accounts for a large proportion, existing technical methods cannot decompose the nylon binder at room temperature and pressure, thereby achieving the recycling and reuse of NdFeB.

[0005] Table 1 Common processes and binder compositions for bonded NdFeB magnets

[0006]

[0007]

[0008] At present, the research on the recovery of waste injection molded bonded NdFeB magnets is still in a state of scarcity at home and abroad. The binder of injection molded magnets is mainly composed of polyamide, and existing research mainly focuses on the decomposition of polyamide fibers. It has not studied whether it is applicable to the decomposition of the binder in waste injection molded bonded NdFeB magnetic powder, and whether it affects the main phase of NdFeB. For example, in patent CN107056624 B, nylon 66 particles are subjected to alcoholysis reaction with alcohol and an acidic catalyst, followed by extraction and distillation with an organic solvent to obtain a refined fraction of hexamethylenediamine. However, if the acidic catalyst used in this method is applied to the recovery of waste injection molded bonded NdFeB, it will corrode the NdFeB magnetic powder, thereby affecting the magnetic properties of the recovered powder. See also patent CN 114874489A, which obtains a nylon solution by filtering after reacting polyamide crushed material with an ionic liquid, then pouring the nylon solution into deionized water to precipitate nylon, and obtaining regenerated nylon powder after washing and drying. However, ionic liquids, composed of cations and highly electronegative anions, are highly corrosive to NdFeB. Furthermore, the relatively high cost of ionic liquids could be a potential barrier to the large-scale industrialization of waste injection molded NdFeB magnet recycling projects.

[0009] In summary, there is an urgent need to develop an effective method for recycling injection molded bonded magnets, especially a recycling technology for polyamide bonded NdFeB magnets. Summary of the Invention

[0010] The purpose of the present invention is to develop a solution formula and treatment method that can effectively remove the polyamide binder in waste injection-molded bonded NdFeB magnetic powder while causing less damage to the NdFeB magnetic powder.

[0011] The present invention provides a mixed solvent formula for removing nylon binder from waste injection-molded bonded NdFeB magnetic powder. The mixed solvent consists of potassium permanganate, sodium lauryl sulfate, sodium hydroxide and deionized water. The concentration range of potassium permanganate is 0.02-0.05 mol / L, the concentration range of sodium lauryl sulfate is 0.01-0.03 mol / L, and the amount of sodium hydroxide is such that the pH value of the solution is maintained between 7 and 10.

[0012] The method for removing polyamide binder from waste injection-molded bonded NdFeB magnetic powder and recovering NdFeB magnetic powder provided by the present invention comprises the following steps:

[0013] (1) Crushing of waste magnets:

[0014] The bonded NdFeB magnet waste is placed in a jaw crusher for crushing, and then sieved to obtain magnetic powder A with a particle size of less than 150 μm.

[0015] (2) Mixed solvent configuration:

[0016] Weigh a certain amount of potassium permanganate and sodium dodecyl sulfate (SDS) into deionized water and stir to dissolve to form a mixed solvent. The concentration of potassium permanganate should be between 0.02-0.05 mol / L, and the concentration of sodium dodecyl sulfate should be between 0.01-0.03 mol / L. Then, add an appropriate amount of NaOH to adjust the solution pH to 7-10.

[0017] (3) Binder decomposition:

[0018] Pour magnetic powder A into the mixed solvent with a solid-liquid ratio of 1g:1mL-1g:80mL, introduce flowing argon atmosphere for protection, and stir at the same time. The stirring speed of the stirring paddle is constant at 80-150r / min to avoid magnetic powder agglomeration or solution splashing. React under this condition for 2-4h.

[0019] (4) Separation of binder and magnetic powder:

[0020] After the reaction is completed, the reaction mixture is centrifuged at 1500-2000 r / min for 2-3 times, each time for 5-10 minutes. The supernatant is discarded to obtain magnetic powder B.

[0021] (5) Recovering magnetic powder cleaning:

[0022] Pour magnetic powder B and deionized water into a container at a mass-to-volume ratio of 1g:20mL-1g:50mL, and ultrasonically clean the powder 2-5 times, each time for 5-20 minutes. Then, ultrasonically clean the powder 2-5 times with ethanol to remove the residual solvent to obtain magnetic powder C. The mass-to-volume ratio of magnetic powder B to ethanol is 1g:20mL-1g:50mL.

[0023] (6) Magnetic powder drying:

[0024] The magnetic powder C is dried in a vacuum drying oven at an absolute vacuum degree of 0.01 Pa-0.001 Pa at room temperature to a constant weight to obtain the regenerated NdFeB magnetic powder D with the binder removed.

[0025] This method uses an alkaline mixed solvent system consisting of potassium permanganate, sodium lauryl sulfate, and sodium hydroxide to decompose the polyamide binder at room temperature and pressure. This method significantly removes the binder and effectively protects the NdFeB magnetic powder. The recovered magnetic powder's magnetic properties, including saturation magnetization (Ms), residual magnetization (Br), and coercivity (Hcj), approach those of the original powder. The potassium permanganate oxidation reaction for polyamide is as follows:

[0026]

[0027] Reaction principle:

[0028] Under alkaline conditions, potassium permanganate (KMnO4) attacks and breaks the amide bonds in the polyamide molecular chain, forming functional groups such as amino and carboxyl groups, which causes the polyamide to decompose and separate from the waste bonded magnetic powder, thereby realizing the recovery of NdFeB magnetic powder.

[0029] The advantages of the present invention are:

[0030] 1. This method does not require extreme reaction conditions and can effectively remove the polyamide binder at room temperature and pressure. It also causes minimal damage to NdFeB at room temperature and pressure, making it easy to implement and control in both the laboratory and industrial production. Furthermore, compared with traditional chemical or physical treatment methods, potassium permanganate oxidation has a lower environmental pollution risk and does not produce a large amount of harmful byproducts during the reaction.

[0031] 2. Use sodium hydroxide to adjust the pH value to between 7 and 10. In an alkaline environment, the oxidizing property of potassium permanganate is reduced, and the reduction product is K2MnO4. This does not produce MnO2 that would interfere with the separation of magnetic powder and binder. Simultaneously, the reduced oxidizing property also reduces the destructive effect on NdFeB. Furthermore, when processing waste injection-molded bonded NdFeB magnets, the method has strong selectivity for the amide bonds of polyamide. This means that this method can precisely remove the target polymer with minimal impact on the magnet itself, thus ensuring the performance and quality of the recovered magnetic powder.

[0032] 3. The sodium lauryl sulfate (SDS) used in the present invention mainly exists as a surfactant and plays a dispersing and emulsifying role in the reaction system. It can help potassium permanganate to be better dispersed in the solution, increase its contact area with polyamide, and thus promote the oxidation reaction. At the same time, SDS may also suppress the self-decomposition of potassium permanganate to a certain extent, thereby improving reaction efficiency. And by using SDS to assist in the decomposition of the binder, the consumption of potassium permanganate can be reduced, further reducing the influence of the oxidant on the oxidative corrosion of the NdFeB magnetic powder.

[0033] 4. The regenerated injection-molded magnetic powder obtained by the present invention has significantly improved magnetic properties. While the saturation magnetization and residual magnetization are significantly increased, the coercivity is also maintained at a high level (the coercivity recovery rate is over 90%). At the same time, considering the better plasticity and toughness of injection-molded bonded magnetic powder, it is easy to process and shape into injection-molded bonded magnets and is less prone to cracking and breakage, which has a better production prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 : SEM image in Example 1.

[0035] Figure 2 : VSM diagram in Example 1. DETAILED DESCRIPTION

[0036] Example 1

[0037] The method provided in this embodiment for removing nylon binder from waste injection-molded bonded NdFeB magnetic powder to recover NdFeB magnetic powder comprises the following steps:

[0038] (1) Crushing of waste magnets:

[0039] The bonded NdFeB magnet waste is placed in a jaw crusher for crushing, and then sieved to obtain magnetic powder A with a particle size of less than 150 μm.

[0040] (2) Mixed solvent configuration:

[0041] Weigh 3.16g of potassium permanganate and 3.456g of sodium dodecyl sulfate (SDS) into deionized water and stir to dissolve to form a mixed solvent. The concentration of potassium permanganate is 0.05 mol / L, and the concentration of sodium dodecyl sulfate is 0.03 mol / L. Add an appropriate amount of sodium hydroxide to adjust the solution pH to 10.

[0042] (3) Binder decomposition:

[0043] Pour 10 g of magnetic powder A into 400 mL of mixed solvent (solid-liquid ratio is 1 g:40 mL) and introduce flowing argon atmosphere for protection while stirring. The stirring speed is constant at 150 r / min to avoid magnetic powder agglomeration or solution splashing. React under this condition for 3 h.

[0044] (4) Separation of binder and magnetic powder:

[0045] After the reaction is completed, the reaction product is centrifuged at 2000 r / min for two times, each time for 10 minutes. The supernatant is discarded to obtain magnetic powder B.

[0046] (5) Recovering magnetic powder cleaning:

[0047] Magnetic powder B and deionized water were poured into a container at a mass-to-volume ratio of 1 g:40 mL, and ultrasonically cleaned three times for 10 min each time. Magnetic powder C was then ultrasonically cleaned three times with ethanol to remove residual solvent. The mass-to-volume ratio of magnetic powder B to ethanol was 1 g:40 mL.

[0048] (6) Magnetic powder drying:

[0049] The magnetic powder C was dried in a vacuum drying oven at an absolute vacuum of less than 0.01 Pa at room temperature to a constant weight to obtain the regenerated NdFeB magnetic powder D with the binder removed. The SEM test was performed on the powder as shown in the attached figure. Figure 1 As shown in the figure, it can be seen that the surface of the recovered magnetic powder obtained after treatment is smooth and almost free of binder, indicating that the binder between the magnetic powders is effectively dissolved. Then a VSM test was performed on it and the hysteresis loop under this embodiment was obtained as shown in the attached figure. Figure 2 shown.

[0050] The carbon and oxygen content comparison of the recycled bonded NdFeB magnetic powder obtained by this embodiment and the waste bonded NdFeB magnetic powder is shown in Table 2.

[0051] Table 2 Comparison of carbon and oxygen content between recycled bonded NdFeB magnetic powder and waste bonded NdFeB magnetic powder

[0052] Carbon content oxygen content Waste bonded NdFeB magnetic powder 5.907087％ 0.607045％ Recycling bonded NdFeB magnetic powder 0.053216％ 0.104443％

[0053] The magnetic properties of the recycled bonded NdFeB magnetic powder obtained in this embodiment are compared with those of the waste bonded NdFeB magnetic powder as shown in Table 3.

[0054] Table 3 Comparison of magnetic properties of recycled bonded NdFeB magnetic powder and waste bonded NdFeB magnetic powder

[0055] Ms(emu / g) Mr(emu / g) Hcj(kOe) Waste bonded NdFeB magnetic powder 117.47 79.69 8.72 Recycling bonded NdFeB magnetic powder 127.33 86.76 8.49

[0056] Example 2

[0057] The method provided in this embodiment for removing nylon binder from waste injection-molded bonded NdFeB magnetic powder to recover NdFeB magnetic powder comprises the following steps:

[0058] (1) Crushing of waste magnets:

[0059] The bonded NdFeB magnet waste is placed in a jaw crusher for crushing, and then sieved to obtain magnetic powder A with a particle size of less than 150 μm.

[0060] (2) Mixed solvent configuration:

[0061] Weigh 1.106g of potassium permanganate and 3.024g of sodium dodecyl sulfate (SDS) into deionized water and stir to dissolve to create a mixed solvent. The concentration of potassium permanganate is 0.02 mol / L, and the concentration of sodium dodecyl sulfate is 0.03 mol / L. Add an appropriate amount of sodium hydroxide to adjust the solution's pH to 7.

[0062] (3) Binder decomposition:

[0063] Pour 10 g of magnetic powder A into 350 mL of mixed solvent with a solid-liquid ratio of 1 g:35 mL. Pass flowing argon atmosphere for protection while stirring. The stirring speed is constant at 150 r / min to avoid magnetic powder agglomeration or solution splashing. React under this condition for 3 h.

[0064] (4) Separation of binder and magnetic powder:

[0065] After the reaction is completed, the reaction product is centrifuged at 2000 r / min for two times, each time for 10 minutes. The supernatant is discarded to obtain magnetic powder B.

[0066] (5) Recovering magnetic powder cleaning:

[0067] Magnetic powder B and deionized water were poured into a container at a mass-to-volume ratio of 1 g:50 mL, and ultrasonically cleaned twice for 10 min each time. Magnetic powder C was then ultrasonically cleaned three times with ethanol to remove residual solvent. The mass-to-volume ratio of magnetic powder B to ethanol was 1 g:50 mL.

[0068] (6) Magnetic powder drying:

[0069] The magnetic powder C was dried in a vacuum drying oven at an absolute vacuum degree of less than 0.01 Pa at room temperature to a constant weight to obtain the regenerated NdFeB magnetic powder D with the binder removed.

[0070] The carbon and oxygen content comparison of the recycled bonded NdFeB magnetic powder obtained by this embodiment and the waste bonded NdFeB magnetic powder is shown in Table 4.

[0071] Table 4 Comparison of carbon and oxygen content between recycled bonded NdFeB magnetic powder and waste bonded NdFeB magnetic powder

[0072] Carbon content oxygen content Waste bonded NdFeB magnetic powder 5.907087％ 0.607045％ Recycling bonded NdFeB magnetic powder 0.101066％ 0.579689％

[0073] Example 3

[0074] The method provided in this embodiment for removing nylon binder from waste injection-molded bonded NdFeB magnetic powder to recover NdFeB magnetic powder comprises the following steps:

[0075] (1) Crushing of waste magnets:

[0076] The bonded NdFeB magnet waste is placed in a jaw crusher for crushing, and then sieved to obtain magnetic powder A with a particle size of less than 150 μm.

[0077] (2) Mixed solvent configuration:

[0078] Weigh 3.95g of potassium permanganate and 1.44g of sodium dodecyl sulfate (SDS) into deionized water and stir to dissolve to create a mixed solvent. The concentration of potassium permanganate is 0.05 mol / L, and the concentration of sodium dodecyl sulfate is 0.01 mol / L. Add an appropriate amount of sodium hydroxide to adjust the solution's pH to 8.

[0079] (3) Binder decomposition:

[0080] Pour 10 g of magnetic powder A into 500 mL of mixed solvent with a solid-liquid ratio of 1 g:50 mL. Pass a flowing argon atmosphere for protection while stirring. The stirring blade speed is constant at 150 r / min to avoid magnetic powder agglomeration or solution splashing. React under this condition for 3 h.

[0081] (4) Separation of binder and magnetic powder:

[0082] After the reaction is completed, the reaction product is centrifuged at 1500 r / min for two times, each time for 10 minutes. The supernatant is discarded to obtain magnetic powder B.

[0083] (5) Recovering magnetic powder cleaning:

[0084] Magnetic powder B and deionized water were poured into a container at a mass-to-volume ratio of 1 g:20 mL, and ultrasonically cleaned twice for 10 min each time. Magnetic powder C was then ultrasonically cleaned three times with ethanol to remove residual solvent. The mass-to-volume ratio of magnetic powder B to ethanol was 1 g:30 mL.

[0085] (6) Magnetic powder drying:

[0086] The magnetic powder C was dried in a vacuum drying oven at an absolute vacuum degree of less than 0.01 Pa at room temperature to a constant weight to obtain the regenerated NdFeB magnetic powder D with the binder removed.

[0087] The carbon and oxygen content comparison of the recycled bonded NdFeB magnetic powder obtained by this embodiment and the waste bonded NdFeB magnetic powder is shown in Table 5.

[0088] Table 5 Comparison of carbon and oxygen content between recycled bonded NdFeB magnetic powder and waste bonded NdFeB magnetic powder

[0089] Carbon content oxygen content Waste bonded NdFeB magnetic powder 5.907087％ 0.607045％ Recycling bonded NdFeB magnetic powder 0.083423％ 0.293659％

[0090] Example 4

[0091] The method provided in this embodiment for removing nylon binder from waste injection-molded bonded NdFeB magnetic powder to recover NdFeB magnetic powder comprises the following steps:

[0092] (1) Crushing of waste magnets:

[0093] The bonded NdFeB magnet waste was placed in a jaw crusher for crushing and sieved to obtain magnetic powder A with a particle size of 150 μm.

[0094] (2) Mixed solvent configuration:

[0095] Weigh 0.948g of potassium permanganate and 0.864g of sodium dodecyl sulfate (SDS) into deionized water and stir to dissolve to form a mixed solvent. The concentration of potassium permanganate is 0.02 mol / L, and the concentration of sodium dodecyl sulfate is 0.01 mol / L. Add an appropriate amount of sodium hydroxide to adjust the solution pH to 8.

[0096] (3) Binder decomposition:

[0097] Pour 5 g of magnetic powder A into 300 mL of mixed solvent with a solid-liquid ratio of 1 g:60 mL. Pass a flowing argon atmosphere for protection while stirring. The stirring speed is constant at 150 r / min to avoid magnetic powder agglomeration or solution splashing. React under this condition for 3 h.

[0098] (4) Separation of binder and magnetic powder:

[0099] After the reaction is completed, the reaction product is centrifuged at 1500 r / min for two times, each time for 15 minutes. The supernatant is discarded to obtain magnetic powder B.

[0100] (5) Recovering magnetic powder cleaning:

[0101] Magnetic powder B and deionized water were poured into a container at a mass-to-volume ratio of 1 g:30 mL, and ultrasonically cleaned four times for 15 min each time. Magnetic powder C was then ultrasonically cleaned twice with ethanol to remove residual solvent. The mass-to-volume ratio of magnetic powder B to ethanol was 1 g:25 mL.

[0102] (6) Magnetic powder drying:

[0103] The magnetic powder C was dried in a vacuum drying oven at an absolute vacuum degree of less than 0.01 Pa at room temperature to a constant weight to obtain the regenerated NdFeB magnetic powder D with the binder removed.

[0104] The carbon and oxygen content comparison of the recycled bonded NdFeB magnetic powder obtained by this embodiment and the waste bonded NdFeB magnetic powder is shown in Table 6.

[0105] Table 6 Comparison of carbon and oxygen content between recycled bonded NdFeB magnetic powder and waste bonded NdFeB magnetic powder

[0106] Carbon content oxygen content Waste bonded NdFeB magnetic powder 5.907087％ 0.607045％ Recycling bonded NdFeB magnetic powder 0.099641％ 0.508327％

[0107] Example 5

[0108] The method provided in this embodiment for removing nylon binder from waste injection-molded bonded NdFeB magnetic powder to recover NdFeB magnetic powder comprises the following steps:

[0109] (1) Crushing of waste magnets:

[0110] The bonded NdFeB magnet waste is placed in a jaw crusher for crushing, and then sieved to obtain magnetic powder A with a particle size of less than 150 μm.

[0111] (2) Mixed solvent configuration:

[0112] Weigh 3.16g of potassium permanganate and 2.304g of sodium dodecyl sulfate (SDS) into deionized water and stir to dissolve to create a mixed solvent. The concentration of potassium permanganate is 0.05 mol / L, and the concentration of sodium dodecyl sulfate is 0.02 mol / L. Add an appropriate amount of sodium hydroxide to adjust the solution's pH to 9.

[0113] (3) Binder decomposition:

[0114] Pour 5 g of magnetic powder A into 400 mL of mixed solvent with a solid-liquid ratio of 1 g:80 mL. Pass a flowing argon atmosphere for protection while stirring. The stirring speed is constant at 150 r / min to avoid magnetic powder agglomeration or solution splashing. React under this condition for 2 h.

[0115] (4) Separation of binder and magnetic powder:

[0116] After the reaction is completed, the reaction product is centrifuged at 1000 r / min for two times, each time for 10 minutes. The supernatant is discarded to obtain magnetic powder B.

[0117] (5) Recovering magnetic powder cleaning:

[0118] Magnetic powder B and deionized water were poured into a container at a mass-to-volume ratio of 1 g:25 mL, and ultrasonically cleaned twice for 10 min each time. Magnetic powder C was then ultrasonically cleaned twice with ethanol to remove residual solvent. The mass-to-volume ratio of magnetic powder B to ethanol was 1 g:20 mL.

[0119] (6) Magnetic powder drying:

[0120] The magnetic powder C was dried in a vacuum drying oven at an absolute vacuum degree of less than 0.01 Pa at room temperature to a constant weight to obtain the regenerated NdFeB magnetic powder D with the binder removed.

[0121] The carbon and oxygen content comparison of the recycled bonded NdFeB magnetic powder obtained by this embodiment and the waste bonded NdFeB magnetic powder is shown in Table 7.

[0122] Table 7 Comparison of carbon and oxygen content between recycled bonded NdFeB magnetic powder and waste bonded NdFeB magnetic powder

[0123] Carbon content oxygen content Waste bonded NdFeB magnetic powder 5.907087％ 0.607045％ Recycling bonded NdFeB magnetic powder 0.064996％ 0.233543％

[0124] The magnetic properties of the recycled bonded NdFeB magnetic powder obtained in this embodiment and the waste bonded NdFeB magnetic powder are compared as shown in Table 8.

[0125] Table 8 Comparison of magnetic properties of recycled bonded NdFeB magnetic powder and waste bonded NdFeB magnetic powder

[0126] Ms(emu / g) Mr(emu / g) Hcj(kOe) Waste bonded NdFeB magnetic powder 117.47 79.69 8.72 Recycling bonded NdFeB magnetic powder 126.13 85.32 8.42

[0127] Example 6

[0128] The method provided in this embodiment for removing nylon binder from waste injection-molded bonded NdFeB magnetic powder to recover NdFeB magnetic powder comprises the following steps:

[0129] (1) Crushing of waste magnets:

[0130] The bonded NdFeB magnet waste is placed in a jaw crusher for crushing, and then sieved to obtain magnetic powder A with a particle size of less than 150 μm.

[0131] (2) Mixed solvent configuration:

[0132] Weigh 0.948g of potassium permanganate and 1.728g of sodium dodecyl sulfate (SDS) into deionized water and stir to dissolve to form a mixed solvent. The concentration of potassium permanganate is 0.03 mol / L, and the concentration of sodium dodecyl sulfate is 0.03 mol / L. Add an appropriate amount of sodium hydroxide to adjust the solution pH to 8.

[0133] (3) Binder decomposition:

[0134] Pour 10 g of magnetic powder A into 200 mL of mixed solvent with a solid-liquid ratio of 1 g:20 mL. Pass a flowing argon atmosphere for protection while stirring. The stirring speed is constant at 150 r / min to avoid magnetic powder agglomeration or solution splashing. React under this condition for 3 h.

[0135] (4) Separation of binder and magnetic powder:

[0136] After the reaction is completed, the reaction product is centrifuged at 2000 r / min for two times, each time for 10 minutes. The supernatant is discarded to obtain magnetic powder B.

[0137] (5) Recovering magnetic powder cleaning:

[0138] Magnetic powder B and deionized water were poured into a container at a mass-to-volume ratio of 1 g:30 mL, and ultrasonically cleaned three times for 15 min each time. Magnetic powder C was then ultrasonically cleaned twice with ethanol to remove residual solvent. The mass-to-volume ratio of magnetic powder B to ethanol was 1 g:50 mL.

[0139] (6) Magnetic powder drying:

[0140] The magnetic powder C was dried in a vacuum drying oven at an absolute vacuum degree of less than 0.01 Pa at room temperature to a constant weight to obtain the regenerated NdFeB magnetic powder D with the binder removed.

[0141] The carbon and oxygen content comparison of the recycled bonded NdFeB magnetic powder obtained by this embodiment and the waste bonded NdFeB magnetic powder is shown in Table 9.

[0142] Table 9 Comparison of carbon and oxygen content between recycled bonded NdFeB magnetic powder and waste bonded NdFeB magnetic powder

[0143] Carbon content oxygen content Waste bonded NdFeB magnetic powder 5.907087％ 0.607045％ Recycling bonded NdFeB magnetic powder 0.403562％ 0.862514％

[0144] Example 7

[0145] The method provided in this embodiment for removing nylon binder from waste injection-molded bonded NdFeB magnetic powder to recover NdFeB magnetic powder comprises the following steps:

[0146] (1) Crushing of waste magnets:

[0147] The bonded NdFeB magnet waste is placed in a jaw crusher for crushing, and then sieved to obtain magnetic powder A with a particle size of less than 150 μm.

[0148] (2) Mixed solvent configuration:

[0149] Weigh 1.264g of potassium permanganate and 0.576g of sodium dodecyl sulfate (SDS) into deionized water and stir to dissolve to create a mixed solvent. The concentration of potassium permanganate is 0.04 mol / L, and the concentration of sodium dodecyl sulfate is 0.01 mol / L. Add an appropriate amount of sodium hydroxide to adjust the solution's pH to 7.

[0150] (3) Binder decomposition:

[0151] Pour 5 g of magnetic powder A into 200 mL of mixed solvent with a solid-liquid ratio of 1 g:40 mL. Pass a flowing argon atmosphere for protection while stirring. The stirring speed is constant at 150 r / min to avoid magnetic powder agglomeration or solution splashing. React under this condition for 3 h.

[0152] (4) Separation of binder and magnetic powder:

[0153] After the reaction is completed, the reaction product is centrifuged at 2000 r / min for two times, each time for 10 minutes. The supernatant is discarded to obtain magnetic powder B.

[0154] (5) Recovering magnetic powder cleaning:

[0155] Magnetic powder B and deionized water were poured into a container at a mass-to-volume ratio of 1 g:20 mL, and ultrasonically cleaned 5 times for 10 min each time. Magnetic powder C was then ultrasonically cleaned twice with ethanol to remove residual solvent. The mass-to-volume ratio of magnetic powder B to ethanol was 1 g:20 mL.

[0156] (6) Magnetic powder drying:

[0157] The magnetic powder C was dried in a vacuum drying oven at an absolute vacuum degree of less than 0.01 Pa at room temperature to a constant weight to obtain the regenerated NdFeB magnetic powder D with the binder removed.

[0158] The carbon and oxygen content comparison of the recycled bonded NdFeB magnetic powder obtained by this embodiment and the waste bonded NdFeB magnetic powder is shown in Table 10.

[0159] Table 10 Comparison of carbon and oxygen content between recycled bonded NdFeB magnetic powder and waste bonded NdFeB magnetic powder

[0160] Carbon content oxygen content Waste bonded NdFeB magnetic powder 5.907087％ 0.607045％ Recycling bonded NdFeB magnetic powder 0.095678％ 0.402658％

[0161] Example 8

[0162] The method provided in this embodiment for removing nylon binder from waste injection-molded bonded NdFeB magnetic powder to recover NdFeB magnetic powder comprises the following steps:

[0163] (1) Crushing of waste magnets:

[0164] The bonded NdFeB magnet waste is placed in a jaw crusher for crushing, and then sieved to obtain magnetic powder A with a particle size of less than 150 μm.

[0165] (2) Mixed solvent configuration:

[0166] Weigh 0.237g of potassium permanganate and 0.288g of sodium dodecyl sulfate (SDS) into deionized water and stir to dissolve to create a mixed solvent. The concentration of potassium permanganate is 0.03 mol / L, and the concentration of sodium dodecyl sulfate is 0.02 mol / L. Add an appropriate amount of sodium hydroxide to adjust the solution's pH to 8.

[0167] (3) Binder decomposition:

[0168] Pour 50 g of magnetic powder A into 50 mL of mixed solvent with a solid-liquid ratio of 1 g:1 mL. Pass flowing argon atmosphere for protection while stirring. The stirring blade speed is constant at 150 r / min to avoid magnetic powder agglomeration or solution splashing. React under this condition for 3 h.

[0169] (4) Separation of binder and magnetic powder:

[0170] After the reaction is completed, the reaction product is centrifuged at 2000 r / min for two times, each time for 10 minutes. The supernatant is discarded to obtain magnetic powder B.

[0171] (5) Recovering magnetic powder cleaning:

[0172] Magnetic powder B and deionized water were poured into a container at a mass-to-volume ratio of 1 g:50 mL, and ultrasonically cleaned three times for 15 min each time. Magnetic powder C was then ultrasonically cleaned four times with ethanol to remove residual solvent. The mass-to-volume ratio of magnetic powder B to ethanol was 1 g:40 mL.

[0173] (6) Magnetic powder drying:

[0174] The magnetic powder C was dried in a vacuum drying oven at an absolute vacuum degree of less than 0.01 Pa at room temperature to a constant weight to obtain the regenerated NdFeB magnetic powder D with the binder removed.

[0175] The carbon and oxygen content comparison of the recycled bonded NdFeB magnetic powder obtained by this embodiment and the waste bonded NdFeB magnetic powder is shown in Table 11.

[0176] Table 11 Comparison of carbon and oxygen content between recycled bonded NdFeB magnetic powder and waste bonded NdFeB magnetic powder

[0177] Carbon content oxygen content Waste bonded NdFeB magnetic powder 5.907087％ 0.607045％ Recycling bonded NdFeB magnetic powder 1.925314％ 0.104443％

Claims

1. A method for removing nylon from waste injection-molded bonded NdFeB magnetic powder using potassium permanganate chemical reaction method, characterized in that: Provided is a mixed solvent for removing nylon binder from waste injection-molded bonded NdFeB magnetic powder. The mixed solvent consists of potassium permanganate, sodium lauryl sulfate, sodium hydroxide, and deionized water. The concentration of potassium permanganate is in the range of 0.02-0.05 mol / L, the concentration of sodium lauryl sulfate is in the range of 0.01-0.03 mol / L, and the amount of sodium hydroxide used is such that the pH value of the solution is maintained between 7 and 10.

2. The method according to claim 1, characterized in that The following steps are involved: (1) Crushing of waste magnets: The bonded NdFeB magnet waste is put into a jaw crusher for crushing, and then sieved to obtain magnetic powder A with a particle size of less than 150 μm; (2) Mixed solvent configuration: Weigh potassium permanganate and sodium lauryl sulfate and add them to deionized water, stirring to promote dissolution to obtain a mixed solvent, wherein the concentration of potassium permanganate is in the range of 0.02-0.05 mol / L and the concentration of sodium lauryl sulfate is in the range of 0.01-0.03 mol / L; then add NaOH to adjust the pH of the solution to 7-10; (3) Binder decomposition: Pour magnetic powder A into the mixed solvent with a solid-liquid ratio of 1g:1mL-1g:80mL, introduce flowing argon atmosphere for protection, and stir at the same time. The stirring speed is constant at 80-150r / min to avoid magnetic powder agglomeration or solution splashing. React under this condition for 2-4h; (4) Separation of binder and magnetic powder: After the reaction is completed, the reactants are centrifuged at a speed of 1500-2000 r / min for 2-3 times, each time for 5-10 minutes; the supernatant is discarded to obtain magnetic powder B; (5) Recovering magnetic powder cleaning: Pour magnetic powder B and deionized water into a container at a mass volume ratio of 1g:20mL-1g:50mL, and ultrasonically clean them 2-5 times, each time for 5-20 minutes; then ultrasonically clean them with ethanol 2-5 times to remove the residual solvent to obtain magnetic powder C; (6) Magnetic powder drying: The magnetic powder C is dried in a vacuum drying oven at an absolute vacuum degree of 0.01 Pa-0.001 Pa at room temperature to a constant weight to obtain the regenerated NdFeB magnetic powder D with the binder removed.

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