Method for removing polyphenylene sulfide from waste injection molded neodymium iron boron magnet

Abstract

The application discloses a method for removing polyphenylene sulfide in waste injection molding Nd-Fe-B magnets, and belongs to the field of material recycling. A large amount of polyphenylene sulfide exists in waste injection molding Nd-Fe-B magnets, is thermoplastic, is very stable, and is insoluble in any solvent below 200 DEG C. The application aims to provide a method for removing polyphenylene sulfide in waste injection molding magnets without destroying Nd-Fe-B phases. The technical scheme is that polyphenylene sulfide can be oxidized into polyphenylene sulfide sulfone by hydrogen peroxide, waste injection molding Nd-Fe-B magnetic powder is mechanically stirred in a hydrogen peroxide solution for a period of time, and then the oxidized waste magnetic powder is washed by using anhydrous ethanol through ultrasonic cleaning, so as to achieve the purpose of magnetic powder recycling. The application is a method for removing polyphenylene sulfide in waste injection molding magnets, which is easy to operate, low in cost, green and environment-friendly, and improves the magnetic performance of waste magnetic powder.

Description

TECHNICAL FIELD

[0001] The application discloses a method for removing polyphenylene sulfide from waste injection molded Nd-Fe-B magnet, and belongs to the field of material recycling. BACKGROUND

[0002] With the rapid development of new energy vehicles, wind power generation, electronic equipment, medical devices, aviation industry, national defense and military industry, permanent magnet motor and other industries, the consumption of rare earth permanent magnet materials is increasing year by year, especially the third generation of rare earth permanent magnet material neodymium iron boron with high magnetic energy product. Neodymium iron boron mainly has sintered and bonded neodymium iron boron. Bonded neodymium iron boron has surpassed its deficiency in magnetic properties due to its characteristics such as being able to be made into various different shapes, not needing to be reprocessed after forming, high utilization rate of raw materials (waste can be recycled), and is widely used in the fields of electronics and medicine. There are four main forming methods for bonded magnets: mold pressing forming, injection molding, extrusion forming and calendering. Among them, mold pressing forming and injection molding are more commonly used. In mold pressing forming bonded magnets, thermosetting epoxy resin adhesives are used the most. Injection molding has been favored by many magnetic material manufacturers in recent years because it can produce products with more complex shapes, and the dimensional tolerance of the products after forming is easy to control, making the products more advantageous in assembly. Polyphenylene sulfide is a thermoplastic resin, which is commonly used in injection molded neodymium iron boron magnets due to its characteristics of high temperature resistance and good chemical stability.

[0003] A large amount of corner waste and defective products are produced in each process during the production of bonded Nd-Fe-B permanent magnets. With the development of rare earth industry and the progress of society, resource comprehensive utilization and environmental protection have attracted widespread attention. In order to improve the secondary utilization rate of rare earth resources, the recycling of rare earth permanent magnet waste is imperative. In the past decade, there have been a large number of studies on the recycling of sintered Nd-Fe-B magnets, but the recycling of bonded Nd-Fe-B magnets has received little attention. The recycling of waste bonded Nd-Fe-B magnets is not only to remove a small amount of oil and oxides on the surface, but also to remove the resin and additives inside the magnet, so the traditional wet recycling and pyrometallurgical recycling processes for recycling sintered Nd-Fe-B waste are not suitable for recycling bonded Nd-Fe-B magnets. In patents CN 106001541 A, CN 105772734 A, CN 104668567 A, CN 108188151 A and CN 108188152 A, the molded bonded magnets are recycled, and the removed resin is thermosetting epoxy resin. Patents CN 106001541 A, CN 105772734 A and CN 104668567 A all use physical methods such as swelling and similar solubility to remove organic matter; patents CN 108188151 A and CN 108188152 A use the principle that ammonia can open the ring of epoxy resin to remove organic matter. The binder in injection molded magnets is thermoplastic resin polyphenylene sulfide, which has excellent chemical stability and is insoluble in any solvent below 200℃, so it cannot be removed by physical methods such as swelling or chemical methods such as ring opening. Therefore, a green and environmentally friendly method for removing polyphenylene sulfide from injection molded Nd-Fe-B magnets while retaining the Nd-Fe-B phase is needed. SUMMARY

[0004] The purpose of the present application is to propose a short process, green and environmentally friendly process for removing the binder polyphenylene sulfide from waste injection molded Nd-Fe-B magnets while retaining the Nd-Fe-B phase, thereby obtaining regenerated Nd-Fe-B magnetic powder for effective recycling.

[0005] The method for removing polyphenylene sulfide from waste injection molded Nd-Fe-B magnets according to the present application is carried out in the following steps:

[0006] First, the waste injection molded Nd-Fe-B magnets are crushed and passed through a 60-200 mesh sieve to obtain raw waste magnetic powder A;

[0007] Second, the magnetic powder A obtained in the first step is mixed with hydrogen peroxide solution at a mass ratio of 1:30-1:50 in a three-necked flask, and mechanically stirred for 1-16 h to obtain magnetic powder B;

[0008] Thirdly, the magnetic powder B obtained in the second step is taken out, anhydrous ethanol is used to cover the magnetic powder B and ultrasonic oscillation is performed for 5-15 min, and the magnetic powder C is obtained by washing 2-4 times, centrifuging and discarding the supernatant.

[0009] Fourthly, the magnetic powder C obtained in the third step is taken out, vacuum drying is performed for 2-4 h at a drying temperature of 20-40 DEG C, and the regenerated neodymium-iron-boron magnetic powder from which the polyphenylene sulfide is removed is obtained.

[0010] The temperature of mechanical stirring is preferably 20-100 DEG C.

[0011] The mass concentration of the hydrogen peroxide solution is preferably 25-30 wt%, and the amount of addition is 1 / 3 to 2 / 3 of the volume of the three-necked bottle.

[0012] The centrifugal rate is preferably 6000-8000 r / min, and the centrifugal time is preferably 3-5 min.

[0013] Compared with the prior art, the present application has the following beneficial effects:

[0014] Since the chemical stability of the thermoplastic resin polyphenylene sulfide is good, and the polyphenylene sulfide is insoluble in any solvent below 200 DEG C, the physical swelling and chemical ring-opening methods in the prior art are not applicable. The present application finds that the polyphenylene sulfide can be oxidized to polyphenylene sulfide sulfone by using hydrogen peroxide through the reaction of various solutions with injection-molded neodymium-iron-boron magnets, and the reaction process is shown in the accompanying drawings. Figure 1 The oxidized polyphenylene sulfide is more easily dissolved in ethanol and thus removed, and the neodymium-iron-boron phase in the magnetic powder is retained, so that the recycled neodymium-iron-boron magnetic powder is obtained, and the magnetic performance is improved. Meanwhile, the hydrogen peroxide used in the implementation process of the present application is not polluting to the environment, has the advantages of simple operation, green environmental protection and low cost, and is easy to realize industrialization. Therefore, the present application has a broad application prospect in the field of resource recycling magnetic materials. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 Chemical formula of the reaction of polyphenylene sulfide with hydrogen peroxide

[0016] Figure 2 The left drawing is the SEM result of the waste injection-molded neodymium-iron-boron magnetic powder in Example 3, and the right drawing is the SEM result of the recycled injection-molded neodymium-iron-boron magnetic powder. DETAILED DESCRIPTION

[0017] The present application will be further described below in combination with examples and drawings.

[0018] Example 1

[0019] A method for removing polyphenylene sulfide in waste injection-molded neodymium-iron-boron magnets is performed according to the following steps:

[0020] First step, the waste injection Nd-Fe-B magnet was crushed and passed through a 60 mesh sieve to obtain raw waste magnetic powder A;

[0021] Second step, the magnetic powder A obtained in the first step was poured into a three-necked bottle with a hydrogen peroxide solution with a mass concentration of 25wt.% at a mass ratio of 1:30. Mechanical stirring was carried out at 80°C for 1h to obtain magnetic powder B;

[0022] Third step, the magnetic powder B obtained in the second step was taken out, anhydrous ethanol was used to cover the magnetic powder B and ultrasonic oscillation was carried out for 5min, and the magnetic powder C was obtained after washing twice and centrifugation at a speed of 6000r / min for 3min.

[0023] Fourth step, the magnetic powder C obtained in the third step was taken out and vacuum dried for 2h at a drying temperature of 25°C to obtain the regenerated Nd-Fe-B magnetic powder with polyphenylene sulfide removed.

[0024] The magnetic properties of the waste injection Nd-Fe-B magnetic powder obtained in this embodiment and the recycled injection Nd-Fe-B magnetic powder were compared as shown in Table 1.

[0025] Table 1 Comparison of magnetic properties of waste injection Nd-Fe-B magnetic powder and recycled injection Nd-Fe-B magnetic powder

[0026] H cj (kOe) M r (emu / g)]]> M S (emu / g)]]> Waste injection molded NdFeB magnetic powder 8.11 73.92 113.56 Recycled injection molded NdFeB magnetic powder 8.02 75.21 116.34

[0027] Example 2

[0028] A method for removing polyphenylene sulfide from waste injection Nd-Fe-B magnets was carried out in the following steps:

[0029] First step, the waste injection Nd-Fe-B magnet was crushed and passed through a 100 mesh sieve to obtain raw waste magnetic powder A;

[0030] Second step, the magnetic powder A obtained in the first step was poured into a three-necked bottle with a hydrogen peroxide solution with a mass concentration of 28wt.% at a mass ratio of 1:40. Mechanical stirring was carried out at 50°C for 2h to obtain magnetic powder B;

[0031] Third step, the magnetic powder B obtained in the second step was taken out, anhydrous ethanol was used to cover the magnetic powder B and ultrasonic oscillation was carried out for 10min, and the magnetic powder C was obtained after washing three times and centrifugation at a speed of 7000r / min for 4min.

[0032] Fourth step, the magnetic powder C obtained in the third step was taken out and vacuum dried for 3h at a drying temperature of 25°C to obtain the regenerated Nd-Fe-B magnetic powder with polyphenylene sulfide removed.

[0033] The magnetic properties of the waste injection Nd-Fe-B magnetic powder obtained in this embodiment and the recycled injection Nd-Fe-B magnetic powder were compared as shown in Table 2.

[0034] Table 2 Comparison of magnetic properties of waste injection Nd-Fe-B magnetic powder and recycled injection Nd-Fe-B magnetic powder

[0035] H cj (kOe) M r (emu / g)]]> M S (emu / g)]]> Waste injection molded NdFeB magnetic powder 8.11 73.92 113.56 Recycled injection molded NdFeB magnetic powder 8.09 76.61 117.01

[0036] Example 3

[0037] A method for removing polyphenylene sulfide from waste injection molded Nd-Fe-B magnets, comprising the following steps:

[0038] Firstly, waste injection molded Nd-Fe-B magnets were crushed and passed through a 200-mesh sieve to obtain raw waste magnetic powder A;

[0039] Secondly, magnetic powder A obtained in the first step was poured into a three-necked flask with hydrogen peroxide solution with a mass concentration of 28 wt.%, at a mass ratio of 1:50. Mechanical stirring was carried out at 20°C for 16h to obtain magnetic powder B;

[0040] Thirdly, magnetic powder B obtained in the second step was taken out, covered with anhydrous ethanol and ultrasonically shaken for 15min, and washed 4 times. The supernatant was discarded after centrifugation at 8000r / min for 5min to obtain magnetic powder C;

[0041] Fourthly, magnetic powder C obtained in the third step was taken out and vacuum dried for 4h at a drying temperature of 20°C to obtain regenerated Nd-Fe-B magnetic powder with polyphenylene sulfide removed.

[0042] The magnetic properties of waste injection molded Nd-Fe-B magnetic powder obtained in this example and recycled injection molded Nd-Fe-B magnetic powder were compared as shown in Table 3, and the SEM morphology results are shown in Figure 2 .

[0043] Table 3 Comparison of magnetic properties of waste injection molded Nd-Fe-B magnetic powder and recycled injection molded Nd-Fe-B magnetic powder

[0044] H cj (kOe) M r (emu / g)]]> M S (emu / g)]]> Waste injection molded NdFeB magnetic powder 8.11 76.08 113.56 Recycled injection molded NdFeB magnetic powder 8.21 79.19 121.17

Claims

1. A method for removing polyphenylene sulfide from scrap injection molded neodymium-iron-boron magnets, characterized in that, The following steps are taken: First, the waste injection molding Nd-Fe-B magnet is crushed and passed through a 60-200 mesh sieve to obtain raw waste magnetic powder A; Second, the magnetic powder A obtained in the first step is mixed with hydrogen peroxide solution at a mass ratio of 1:30-1:50 in a three-necked flask, and mechanically stirred for 1-16 hours to obtain magnetic powder B; the mass concentration of the hydrogen peroxide solution is 25wt.%-30wt.%; Third, the magnetic powder B obtained in the second step is taken out, covered with anhydrous ethanol, and ultrasonically shaken for 5-15 minutes, washed 2-4 times, and after centrifugation, the supernatant is discarded to obtain magnetic powder C; Fourth, the magnetic powder C obtained in the third step is taken out, vacuum dried for 2-4 hours at a drying temperature of 20℃-40℃ to obtain regenerated Nd-Fe-B magnetic powder from which polyphenylene sulfide has been removed.

2. The method according to claim 1, characterized in that The temperature of mechanical stirring is 20℃-100℃.

3. The method of claim 1, wherein, The centrifugal rate is 6000-8000r / min, and the centrifugal time is 3-5min.

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