Method for removing organic matters in waste bonded neodymium-iron-boron magnet

Abstract

The invention discloses a method for removing organic matters in a waste bonded neodymium-iron-boron magnet, which comprises the following steps: removing epoxy groups in the waste bonded neodymium-iron-boron magnet by using a chemical method, and gradually hydrolyzing epoxy resin in the waste bonded neodymium-iron-boron magnet into glycerol by using an alkaline substance sodium hydroxide. According to the method, a chemical reaction process is adopted, epoxy groups in epoxy resin are decomposed in a targeted mode, so that the purpose of removing organic matter in the waste bonded neodymium-iron-boron magnet is achieved, the organic matter in the waste bonded neodymium-iron-boron magnet is removed more thoroughly through the method, and no organic solvent polluting the environment exists. Compared with an existing method, the method is more efficient, more environmentally friendly and more economical; according to the method, the recycled neodymium-iron-boron magnetic powder is recycled, the recycled regenerated neodymium-iron-boron magnetic powder is obtained after recycling, the recycled neodymium-iron-boron magnetic powder and the original magnetic powder are proportioned to produce products again, and through the certain proportioning of the recycled magnetic powder and the original magnetic powder, the production cost of enterprises is reduced and the competitiveness of the enterprises is enhanced under the condition that the performance of the products is not affected.

Description

Technical Field

[0001] The invention belongs to the technical field of material recovery, and in particular relates to a method for removing organic matter from waste bonded NdFeB magnets. Background Art

[0002] Rare earth permanent magnet materials are important basic functional materials supporting modern society and are closely related to people's lives. Rare earth bonded magnets are widely used in electric vehicles, household appliances, hard disk storage and other fields due to their high magnetic properties, high dimensional accuracy, large shape freedom, low eddy current loss, and suitability for multi-pole magnetization. Under the background of global energy conservation and emission reduction, the development trend of miniaturization, lightweight and high speed of devices such as motors and sensors requires smaller bonded magnets and thinner annular magnetic ring walls, which also leads to a high defect rate of magnets, resulting in a large amount of resource waste and increased production costs for enterprises; the content of rare earth elements in NdFeB accounts for more than 30%, and rare earth elements are used in all aspects of industrial production. It is a strategic resource. Therefore, the reasonable recovery of rare earth resources in waste bonded magnets has put forward new requirements for my country to improve its energy structure, develop renewable resources, improve efficiency, save energy and reduce emissions, and also provides a broad market space for the development of low-carbon economic industries such as wind power generation, new energy vehicles, and energy-saving home appliances.

[0003] At present, there are many studies on the recycling of waste sintered NdFeB magnets at home and abroad. The organic matter in the waste sintered NdFeB magnets is the oil stains produced by oxidation or contamination of the surface during use, but these impurities only exist on the surface of the waste sintered NdFeB magnets. Therefore, the oxides or oil stains on the surface of the waste sintered NdFeB magnets can be removed by washing with some solvents or simple treatment. The recycling of waste sintered NdFeB magnets currently mainly includes: acid dissolution precipitation process, complex salt conversion process, hydrochloric acid optimal dissolution process, etc. Bonded NdFeB magnets are made by pre-mixing and granulating NdFeB magnetic powder and epoxy resin powder, and using powder metallurgy technology to press the powder into a magnet product of a certain size and shape. Therefore, the recycling of waste bonded NdFeB magnet powder is not just to remove oxides or oil stains on the surface of waste sintered NdFeB magnets as described in patents (CN104690270A) and patents (CN110218870A), but to remove organic matter in the magnets. The organic matter in bonded NdFeB magnets is mainly epoxy resin that shows a three-dimensional network cross-linked structure after curing, in which bisphenol A type epoxy resin is used as the main body, and dicyandiamide and silane coupling agents are used as other auxiliary agents. The changes in the structure of organic matter in bonded NdFeB magnets during high temperature curing are shown in the attached figure. Figure 1As shown, since the organic matter that is a three-dimensional cross-linked network structure after curing is very stable, it is difficult to remove it. At present, the patent (CN201610345151.X) removes organic matter in waste bonded NdFeB magnets by the principle of similar dissolution between solvents. The disadvantages of this process are: the process is complicated and the processing time is long, and only the epoxy resin with a short chain structure is removed, so the removal effect is not ideal. The patent (CN108188151A) uses ammonia water to react with the epoxy functional groups in the epoxy resin to open the ring, thereby removing organic matter in waste bonded NdFeB magnets. However, the curing process of the bonded magnet is essentially the reaction between the amino group in the curing agent dicyandiamide and the epoxy group in the epoxy resin, so the bonded NdFeB magnet after curing contains a large number of amino groups, so the method of removing organic matter in waste bonded NdFeB magnets using ammonia water is not thorough. Summary of the invention

[0004] The purpose of the present invention is to provide a method for removing organic matter from waste bonded NdFeB magnets, so as to solve the problem of removing waste bonded NdFeB magnets in the prior art.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for removing organic matter from waste bonded NdFeB magnets, characterized by following the steps:

[0007] Step 1: crushing the waste bonded NdFeB magnets, putting the crushed waste bonded NdFeB magnet powders into an 80-mesh sieve for sieving, and separating the particles to obtain NdFeB magnet powders;

[0008] Step 2: Prepare a sodium hydroxide (NaOH) / ethylene glycol mixed solution, wherein the mass ratio of sodium hydroxide to ethylene glycol is 1:9.26;

[0009] Step 3: Remove the solidified organic matter in the waste bonded NdFeB magnets; add the prepared sodium hydroxide / ethylene glycol mixed solution and NdFeB magnet powder into the reactor in a ratio of 1kg:2L, set the reactor temperature to 90°C, set the stirring paddle speed to 250r / min, and react for 4-6 hours. After the reaction is completed, pour out the supernatant to obtain magnetic powder A;

[0010] Step 4: Remove the decomposition products of the cured epoxy resin; pour the magnetic powder A and the anhydrous ethanol solution into a stainless steel container in a certain ratio, perform ultrasonic oscillation 3 times, each time for 10 minutes, pour out the supernatant after each ultrasonication, and add new anhydrous ethanol for ultrasonic cleaning; the magnetic powder needs to be stirred during the process, and after the cleaning is completed, magnetic powder B is obtained; the mass ratio of magnetic powder A to anhydrous ethanol is 1:1 to 1:2;

[0011] Step 5: Place magnetic powder B in an oven, set the temperature to 80°C, and dry for 60 minutes to obtain recycled NdFeB magnetic powder.

[0012] Furthermore, during step three, the pressure in the kettle is set to 0.2 MPa.

[0013] Further, the epoxy groups in the waste bonded NdFeB magnets are removed by chemical method, and the epoxy resin in the waste bonded NdFeB magnets is gradually hydrolyzed into glycerol by using alkaline substance sodium hydroxide. NaOH reacts with epoxy resin at high temperature, and the epoxy resin is decomposed into glycerol;

[0014] Step 1: Alkoxy groups attack the cross-linked part of dicyandiamide in the binder to depolymerize;

[0015] Step 2: Alkoxy groups attack the ether bonds in the main chain of bisphenol A epoxy resin, causing the main chain to break;

[0016] Step 3: Alkoxy attacks the ether bond at the other end of the main chain, which eventually causes the main chain of bisphenol A to gradually decrease and form small molecules of bisphenol A.

[0017] The technical solution of the present invention has the following beneficial effects:

[0018] 1. When the mixing amount of recycled magnetic powder is 40wt%, the magnetic properties of the regenerated magnet reach more than 97% of the original magnet, thus realizing the preparation and use of "all-waste regeneration" regenerated magnet;

[0019] 2. This method realizes the recycling and secondary utilization of rare earth permanent magnet resources. By adjusting the ratio of recycled magnetic powder to original magnetic powder, the production cost of the enterprise is reduced and the competitiveness of the enterprise is enhanced without affecting the product performance.

[0020] 3. This method uses a chemical reaction process to specifically decompose the epoxy groups in the epoxy resin to achieve the purpose of removing organic matter from waste bonded NdFeB magnets. Through this method, the organic matter in the waste bonded magnets is removed more thoroughly, and there is no organic solvent that pollutes the environment. Compared with the previous methods, this method is more efficient, environmentally friendly and economical. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below.

[0022] Figure 1 It is a process in which sodium hydroxide reacts with epoxy resin to decompose epoxy resin into glycerol. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0024] Embodiment 1:

[0025] A method for removing organic matter from waste bonded NdFeB magnets is carried out according to the following steps:

[0026] Step 1: crushing the waste bonded NdFeB magnets, putting the crushed waste bonded NdFeB magnet powders into an 80-mesh sieve for sieving, and separating the particles to obtain NdFeB magnet powders;

[0027] Step 2: Prepare a sodium hydroxide / ethylene glycol mixed solution, with the mass ratio of sodium hydroxide to ethylene glycol being 1:9.26; (When ethylene glycol and sodium hydroxide are mixed, a uniform solution can be formed. Ethylene glycol, as a solvent, helps dissolve sodium hydroxide, and the solubility of sodium hydroxide and the stability of the solution can be optimized by adjusting the ratio of ethylene glycol to water. Under certain specific conditions, such as high temperature or a specific ratio, the solubility of sodium hydroxide in ethylene glycol may be higher).

[0028] Step 3: Remove the solidified organic matter in the waste bonded NdFeB magnets; add the prepared sodium hydroxide / ethylene glycol mixed solution and NdFeB magnet powder into the reactor in a ratio of 1kg:2L, set the reactor temperature to 90°C, the pressure in the reactor to 0.2MPa, the stirring paddle speed to 250r / min, and the reaction time to 4 hours. After the reaction is completed, pour out the supernatant to obtain magnetic powder A;

[0029] Step 4: Remove the decomposition products of the cured epoxy resin; pour the magnetic powder A and the anhydrous ethanol solution into a stainless steel container in a certain ratio, perform ultrasonic oscillation 3 times, each time for 10 minutes, pour out the supernatant after each ultrasonication, and add new anhydrous ethanol for ultrasonic cleaning; the magnetic powder needs to be stirred during the process, and after the cleaning, magnetic powder B is obtained; the mass ratio of magnetic powder A to anhydrous ethanol is 1:2;

[0030] Step 5: Place magnetic powder B in an oven, set the temperature to 80°C, and dry for 60 minutes to obtain recycled NdFeB magnetic powder.

[0031] In the above steps: the original magnetic powder + other additives are prepared into products through a certain process method, and products with poor size or poor performance will be produced during the preparation process. Then the product is crushed into powder, and NdFeB magnetic powder is recovered from the crushed powder (other additives are removed), and the recovered NdFeB magnetic powder is mixed with the original magnetic powder in a certain ratio to produce products again.

[0032] When the recycled magnetic powder obtained in this embodiment is mixed with 20wt% and 40wt%, the magnetic properties of the regenerated magnet and the original magnet are compared, as shown in Table 1. (Note: 20wt% or 40wt% of the recycled NdFeB magnetic powder is mixed with the original magnetic powder to produce products again)

[0033] Table 1: Comparison of magnetic properties between regenerated magnets and original magnets when recycled magnetic powder is mixed with 20wt% and 40wt% of the powder:

[0034]

[0035] in conclusion:

[0036] 1. When the mixing amount of recycled magnetic powder is 40wt%, the magnetic properties of the regenerated magnet reach more than 97% of the original magnet, thus realizing the preparation and use of "all-waste regeneration" regenerated magnet;

[0037] 2. This method realizes the recycling and secondary utilization of rare earth permanent magnet resources. By adjusting the ratio of recycled magnetic powder to original magnetic powder, the production cost of the enterprise is reduced and the competitiveness of the enterprise is enhanced without affecting the product performance.

[0038] refer to Figure 1 middle:

[0039] The epoxy groups in the waste bonded NdFeB magnets are removed by chemical methods, and the epoxy resin in the waste bonded NdFeB magnets is gradually hydrolyzed into glycerol using alkaline sodium hydroxide. NaOH reacts with the epoxy resin at high temperature, and the epoxy resin is decomposed into glycerol;

[0040] Step 1: Alkoxy groups attack the cross-linked part of dicyandiamide in the binder to depolymerize;

[0041] Step 2: Alkoxy groups attack the ether bonds in the main chain of bisphenol A epoxy resin, causing the main chain to break;

[0042] Step 3: Alkoxy attacks the ether bond at the other end of the main chain, which eventually causes the main chain of bisphenol A to gradually decrease and form small molecules of bisphenol A.

[0043] The above embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention. The protection scope of the present invention is defined by the claims. Various modifications or equivalent substitutions may be made to the present invention within the essence and protection scope of the present invention. Such modifications or equivalent substitutions shall also be deemed to fall within the protection scope of the present invention.

[0044] In the description of the present invention, it should be noted that the terms "inside", "front", "back", "left", "right", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the circle, or are the orientation or positional relationship in which the product of the invention is usually placed when in use, and are only used to facilitate the description of the present invention and simplify the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, these terms indicating orientation or positional relationship cannot be understood as limiting the present invention.

[0045] In the description of the present invention, it is further explained that, unless otherwise clearly specified and limited, the terms "disposed" and "connected" should be understood in a broad sense. For example, these terms can indicate a fixed connection, a detachable connection, or an integral connection between elements; they can also indicate a mechanical connection, an electrical connection; they can also indicate a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of these terms in the present invention can be understood according to specific circumstances.

Claims

1. A method for removing organic matter from waste bonded NdFeB magnets, characterized in that: Follow the steps below; Step 1: crushing the waste bonded NdFeB magnets, putting the crushed waste bonded NdFeB magnet powders into an 80-mesh sieve for sieving, and separating the particles to obtain NdFeB magnet powders; Step 2: Prepare a sodium hydroxide (NaOH) / ethylene glycol mixed solution, wherein the mass ratio of sodium hydroxide to ethylene glycol is 1:9.26; Step 3: Remove the solidified organic matter in the waste bonded NdFeB magnets; add the prepared sodium hydroxide / ethylene glycol mixed solution and NdFeB magnet powder into the reactor in a ratio of 1kg:2L, set the reactor temperature to 90°C, set the stirring paddle speed to 250r / min, and react for 4-6 hours. After the reaction is completed, pour out the supernatant to obtain magnetic powder A; Step 4: Remove the decomposition products of the cured epoxy resin; pour the magnetic powder A and the anhydrous ethanol solution into a stainless steel container in a certain ratio, perform ultrasonic oscillation 3 times, each time for 10 minutes, pour out the supernatant after each ultrasonication, and add new anhydrous ethanol for ultrasonic cleaning; the magnetic powder needs to be stirred during the process, and after the cleaning is completed, magnetic powder B is obtained; the mass ratio of magnetic powder A to anhydrous ethanol is 1:1 to 1:2; Step 5: Place magnetic powder B in an oven, set the temperature to 80°C, and dry for 60 minutes to obtain recycled NdFeB magnetic powder.

2. A method for removing organic matter from waste bonded NdFeB magnets according to claim 1, characterized in that: During step 3, the pressure in the kettle was set to 0.2 MPa.

3. A method for removing organic matter from waste bonded NdFeB magnets according to claim 1, characterized in that: The epoxy groups in the waste bonded NdFeB magnets are removed by chemical methods, and the epoxy resin in the waste bonded NdFeB magnets is gradually hydrolyzed into glycerol using alkaline sodium hydroxide. NaOH reacts with the epoxy resin at high temperature, and the epoxy resin is decomposed into glycerol; Step 1: Alkoxy groups attack the cross-linked part of dicyandiamide in the binder to depolymerize; Step 2: Alkoxy groups attack the ether bonds in the main chain of bisphenol A epoxy resin, causing the main chain to break; Step 3: Alkoxy attacks the ether bond at the other end of the main chain, which eventually causes the main chain of bisphenol A to gradually decrease and form small molecules of bisphenol A.

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