Rare earth reduction regulation and recovery method for high-cerium-content sintered neodymium-iron-boron waste

Abstract

The invention discloses a rare earth reduction regulation and recovery method for high-cerium-content sintered neodymium-iron-boron waste, and belongs to the field of neodymium-iron-boron waste recovery. Performing hydrogen explosion on the magnet subjected to surface treatment to obtain hydrogen explosion coarse powder; carrying out jet milling on the hydrogen explosion powder to obtain jet milled powder; fully mixing the airflow fine powder with a small amount of light rare earth element supplements, and carrying out orientation compression, sintering and tempering to obtain a single-phase sintered regenerated magnet; and carrying out grain boundary diffusion on the obtained regenerated sintered magnet by using a diffusion source containing a small amount of medium rare earth Nd, Pr or alloy thereof to obtain the high-performance regenerated magnet. According to the method, a small amount of light rare earth is added to inhibit the second phase, and then high-performance regeneration of the magnet waste is achieved through grain boundary diffusion of reduced rare earth elements such as Nd and Pr and alloy. The regenerated magnet prepared by the method is lower in total rare earth content, higher in light rare earth content, and better in residual magnetism, coercive force and comprehensive magnetic energy product.

Description

Technical Field

[0001] The invention relates to the field of NdFeB waste recycling, and in particular to a method for preparing high-performance regenerated magnets based on rare earth reduction regulation of high-cerium content sintered NdFeB waste. Background Art

[0002] NdFeB magnets have been widely used in many fields such as electronic information, household appliances, and aerospace due to their excellent comprehensive magnetic properties. They play an important role in green new energy fields such as new energy vehicles and wind power generation. With the rapid development of these fields, the output of NdFeB permanent magnet materials has also increased, and the adverse effects of production waste and scrapped magnets on the environment have also attracted widespread attention from the society. On the one hand, in the production process of NdFeB magnets, especially in the machining process, about 30% of scraps and cutting waste will be generated. On the other hand, every year a large number of magnets are scrapped due to exceeding their service life. These are valuable secondary resources of rare earths and have important recycling value.

[0003] At present, the main recycling method for sintered NdFeB solid waste is the "magnet-magnet" powder metallurgy method, which recycles and powders through surface treatment, hydrogen crushing, and airflow milling to obtain NdFeB single crystal powder, which is used for sintering (CN117334428A, CN115954202A). During the recycling process, the original composition, size, and surface contamination degree of the waste are different, which on the one hand makes the loss of rare earth elements after surface treatment and hydrogen explosion very different, and on the other hand, it will also bring about an increase in oxygen content, which directly affects the sintering and performance of subsequent regenerated magnets. Therefore, the regeneration process will be based on the composition of the original magnet, comprehensively consider the loss of each rare earth element and the oxygen content, and supplement the rare earth elements. The supplement amount is usually more than 100% of the total loss amount, so as to obtain a regenerated magnet with a higher magnetic property recovery rate (CN113436878A). However, a large amount of rare earth supplementation will bring about a significant decrease in remanence, especially for sintered NdFeB waste with high cerium content (cerium content accounts for more than 30% of the total rare earth mass).

[0004] At present, the output of high-cerium content sintered NdFeB magnets has reached nearly 1 / 3 of NdFeB sintered magnets and continues to increase. The physical phase and microstructure of Ce-containing sintered NdFeB magnets are closely related to the Ce content. They usually contain a certain amount of CeFe2 phase, which not only affects the magnetic properties, but also affects the distribution of other rare earth elements such as Pr. This also causes a relatively large loss of Ce and Pr elements in the waste powder making process. In addition, the high activity of the cerium element itself and the higher oxygen content in high-Ce magnets than in ordinary magnets have led to a significant increase in the oxygen content in the recycled magnetic powder. Therefore, the recycling research of this type of waste usually adds excessive amounts of rare earth elements such as Nd, Pr and their alloys with better intrinsic properties to restore the magnetic properties. Due to the increase in rare earth content, the remanence of the recycled magnet is reduced, and the cost is greatly increased.

[0005] Therefore, the present invention proposes a method for preparing high-performance regenerated magnets by reducing and regulating the amount of rare earths. First, a small amount of light rare earth elements such as La are introduced to suppress the CeFe2 phase and improve the remanence of the regenerated magnet; then, based on the lost rare earth elements such as Nd and Pr, a small amount of nano-micron hydride or its low-melting point alloy is used for grain boundary diffusion to improve the coercive force of the magnet while maintaining high remanence. Compared with the traditional component addition method for preparing regenerated magnets, the total rare earth content in the present invention is lower and the light rare earth content is higher, but the remanence, coercive force and comprehensive magnetic energy product are all better. Therefore, it is a method for recycling high-cerium content sintered NdFeB waste with great application prospects. Summary of the invention

[0006] The present invention provides a new method for preparing high-performance regenerated magnets by reducing the amount of rare earths in sintered NdFeB waste with high cerium content (the cerium content accounts for more than 30-80wt.% of the total rare earth mass). The second phase is firstly suppressed by adding a small amount of light rare earth, and then the grain boundary diffusion of rare earth elements such as Nd and Pr and alloys is reduced to achieve high-performance regeneration of the waste on the basis of reducing the amount of rare earth addition.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] (1) Surface treatment of high cerium content sintered NdFeB waste: first, soak the waste in 3-7% NaOH solution, wash it with alkali under ultrasonic environment until there is no oil stain on the surface of the waste, and then ultrasonically clean it in 0.3-0.7% dilute nitric acid until there is no oxide layer and rust on the surface of the waste;

[0009] (2) placing the waste obtained in step (1) in a hydrogen environment and performing hydrogen explosion treatment to obtain regenerated hydrogen explosion powder;

[0010] (3) subjecting the hydrogen explosion powder obtained in step (2) to a jet milling treatment to obtain jet milled powder;

[0011] (4) Analyze and test the composition of the jet mill powder. According to the content of light rare earth Ce, add one or more alloy powders containing La, Y, Ga, etc. to the jet mill powder to adjust the ratio of (La / Y / Ga):Ce in the jet mill powder to 1:9-2:8. In addition, according to the total loss of other rare earth elements Nd and Pr, rare earth micron powder with a content lower than that can be added and mixed evenly.

[0012] (5) subjecting the mixed powder finally obtained in step (4) to oriented pressing, sintering, tempering, and cooling to obtain a regenerated sintered NdFeB magnet;

[0013] (6) Rare earth compound micro-nano powder (NdH x , PrH x , (Nd / Pr)Cu, (Nd / Pr)Al, etc.) and polyvinyl butyral (PVB) binder are dissolved in anhydrous ethanol to form a uniform suspension;

[0014] (7) placing the regenerated sintered NdFeB magnet obtained in step (5) on a heating table and heating it to 70-80° C., then using a spray gun to evenly spray the suspension prepared in step (6) on the surface of the regenerated sintered NdFeB magnet to form a uniform diffusion source coating, and then heating the magnet for 1-2 minutes to evaporate the anhydrous ethanol;

[0015] (8) The sprayed regenerated sintered NdFeB magnet is placed in a vacuum tube furnace for grain boundary diffusion treatment.

[0016] Furthermore, the specific operation of hydrogen explosion of the waste in step (2) is: placing the waste in a hydrogen explosion furnace chamber at a temperature of 200-260°C and a hydrogen pressure of 1 MPa to absorb hydrogen for 3 hours, and at 550°C and 1×10 -3 Pa was dehydrogenated for 5 h to obtain the waste hydrogen explosion coarse powder.

[0017] Furthermore, the sintered NdFeB waste contains rare earth element Ce, and its content is 30-80% of the total rare earth mass.

[0018] Furthermore, the average particle size of the jet milled powder obtained in step (3) is 3-6 μm.

[0019] Furthermore, the alloy powder containing one or more of La, Y, Ga, etc. in step (4) is one or more of the hydrides of La, Y, Ga; the rare earth supplement is a hydride of Nd or Pr with a particle size of 3 to 6 μm, so that the total amount of added Nd and / or Pr is 0 to 50% of the total loss.

[0020] Furthermore, in step (5), under argon protection, the sintering temperature is 1040-1060°C, the sintering time is 3-5h, and the tempering treatment is divided into two stages, the primary treatment temperature is 820-870°C, the tempering time is 3-6h, and the secondary treatment temperature is 440-480°C, and the tempering time is 3-6h.

[0021] Furthermore, the weight gain ratio of the magnet after spraying in step (7) is 0.5 to 1 wt.%.

[0022] Furthermore, the specific operation steps of the magnet in the vacuum tube furnace in step (8) are as follows: placing the sprayed regenerated sintered NdFeB magnet into the vacuum tube furnace, evacuating the vacuum tube furnace to 10 -3 Pa; then the magnet is subjected to a two-stage heat treatment, wherein the first stage heat treatment is: temperature 860-900°C, heat preservation for 3-10 hours; the second stage heat treatment is: temperature 500°C, heat preservation for 3 hours.

[0023] The advantage of the present invention is that high-performance regeneration of sintered NdFeB waste with high cerium content is achieved through the reduction and regulation of light and medium rare earths. DETAILED DESCRIPTION

[0024] In order to explain the technical content and the effect achieved by the present invention in detail, a flake waste material with a total rare earth (TRE) content of 29.72wt.%, Ce / TRE=30.75% is taken as an example for detailed description. The waste material has a size of about 25*80*(0.5-1.5)mm, and a large amount of oil stains and rust marks are adhered to its surface.

[0025] The room temperature magnetic properties and rare earth contents of the original magnet and the regenerated magnet obtained in each example are respectively listed in Table 1 and Table 2. In order to illustrate the loss of rare earth content, the rare earth content of the jet milled powder is also listed in Table 2.

[0026] Example 1

[0027] (1) The surface of the Ce-containing sintered NdFeB waste was first treated by immersing the waste in a 5% NaOH solution, alkali washing for 20 minutes twice under an ultrasonic environment, and then ultrasonically cleaning it in 0.5% dilute nitric acid for 10 seconds to obtain a waste with a clean surface;

[0028] (2) The waste obtained in (1) was placed in a hydrogen explosion furnace chamber and hydrogen was absorbed for 3 h at a temperature of 250 °C and a hydrogen pressure of 1 MPa. -3 Pa was dehydrogenated for 5 h to obtain the waste hydrogen explosion coarse powder.

[0029] (3) The hydrogen explosion powder obtained in step (2) is subjected to air jet milling treatment under nitrogen protection, and is ground at a speed of 4400 r / min for 2 h to obtain regenerated air jet milled powder with a particle size of 3-6 μm;

[0030] (4) According to the composition test results, the total loss of rare earth is 2.02wt.%, of which Ce loss is 0.64wt.%, Nd loss is 0.46wt.%, and Pr loss is 0.92wt.%. First, LaHx micron powder is added to the regenerated air flow mill so that La:Ce in the regenerated magnet is 1:9;

[0031] (5) sintering the mixed powder of step (4) at 1050° C. for 3 h, and then performing a two-stage tempering treatment, wherein the first-stage treatment temperature is 850° C. and the tempering time is 3 h; and the second-stage treatment temperature is 465° C. and the tempering time is 3 h;

[0032] (6)NdH x Micron powder and PVB binder are dissolved in anhydrous ethanol to form a uniform suspension, in which NdH x The mass ratio of micron powder to binder is 1:0.02;

[0033] (7) placing the regenerated sintered NdFeB magnet obtained in step (5) on a heating table and heating it to 70-80° C., then using a spray gun to evenly spray the suspension prepared in step (6) on the surface of the NdFeB magnet at a weight gain ratio of 1 wt.%, to form a uniform diffusion source coating, and then heating the magnet for 1-2 min to evaporate the anhydrous ethanol;

[0034] (8) Place the sprayed regenerated sintered NdFeB magnet into a vacuum tube furnace and evacuate the vacuum tube furnace to 10 -3 Pa; then the magnet is subjected to two-stage heat treatment, wherein the first stage heat treatment is: temperature 880°C, heat preservation 6h; the second stage heat treatment is: temperature 500°C, heat preservation 3h, to obtain a regenerated magnet.

[0035] Example 2

[0036] (1) The surface of the Ce-containing sintered NdFeB waste was first treated by immersing the waste in a 5% NaOH solution, alkali washing for 20 minutes twice under an ultrasonic environment, and then ultrasonically cleaning it in 0.5% dilute nitric acid for 10 seconds to obtain a waste with a clean surface;

[0037] (2) The waste obtained in (1) was placed in a hydrogen explosion furnace chamber and hydrogen was absorbed for 3 h at a temperature of 250 °C and a hydrogen pressure of 1 MPa. -3 Pa was dehydrogenated for 5 h to obtain the waste hydrogen explosion coarse powder.

[0038] (3) The hydrogen explosion powder obtained in step (2) is subjected to air flow milling treatment under nitrogen protection, and ground at a speed of 4400 r / min for 2 h to obtain regenerated air flow milled powder with a particle size of 3-6 μm;

[0039] (4) According to the composition test results, the total loss of rare earth is 2.02wt.%, of which Ce loss is 0.64wt.%, Nd loss is 0.46wt.%, and Pr loss is 0.92wt.%. First, LaHx micron powder is added to the regenerated airflow mill so that La:Ce in the regenerated magnet is 1:9; then NdHx is added according to the total loss of Nd and Pr elements in the hydrogen explosion-airflow mill recovery process. x Micron powder, the addition amount is 50% of the total loss of Nd and Pr elements;

[0040] (5) The mixed powder of step (4) was sintered at 1050° C. for 3 h, and then subjected to two-stage tempering treatment: the first-stage treatment temperature was 850° C. and the tempering time was 3 h; the second-stage treatment temperature was 465° C. and the tempering time was 3 h;

[0041] (6)NdH x Micron powder and PVB binder are dissolved in anhydrous ethanol to form a uniform suspension, in which NdH x The mass ratio of micron powder to binder is 1:0.02;

[0042] (7) placing the regenerated sintered NdFeB magnet on a heating table and heating it to 70-80° C., then using a spray gun to evenly spray the suspension prepared in step (6) on the surface of the NdFeB magnet at a weight gain ratio of 0.5 wt.%, to form a uniform diffusion source coating, and then heating the magnet for 1-2 min to evaporate the anhydrous ethanol;

[0043] (8) Place the sprayed regenerated sintered NdFeB magnet into a vacuum tube furnace and evacuate the vacuum tube furnace to 10 -3 Pa; then the magnet is subjected to two-stage heat treatment, wherein the first stage heat treatment is: temperature 880°C, heat preservation 6h; the second stage heat treatment is: temperature 500°C, heat preservation 3h, to obtain a regenerated magnet.

[0044] Example 3

[0045] (1) The surface of the Ce-containing sintered NdFeB waste was first treated by immersing the waste in a 5% NaOH solution, alkali washing for 20 minutes twice under an ultrasonic environment, and then ultrasonically cleaning it in 0.5% dilute nitric acid for 10 seconds to obtain a waste with a clean surface;

[0046] (2) The waste obtained in (1) was placed in a hydrogen explosion furnace chamber and hydrogen was absorbed for 3 h at a temperature of 250 °C and a hydrogen pressure of 1 MPa. -3 Pa dehydrogenation for 5h to obtain waste hydrogen explosion coarse powder;

[0047] (3) The hydrogen explosion powder obtained in step (2) is subjected to air jet milling treatment under nitrogen protection, and is ground at a speed of 4400 r / min for 2 h to obtain regenerated air jet milled powder with a particle size of 3-6 μm;

[0048] (4) According to the composition test results, the total loss of rare earth is 2.02wt.%, of which Ce loss is 0.64wt.%, Nd loss is 0.46wt.%, and Pr loss is 0.92wt.%. First, LaHx micron powder is added to the regenerated airflow mill powder to make La:Ce=1:9 in the regenerated magnet. Then, NdHx is added according to the total loss of Nd and Pr elements in the hydrogen explosion-airflow mill recovery process. x Micron powder, the addition amount is 50% of the total loss of Nd and Pr elements;

[0049] (5) sintering the mixed powder of step (4) at 1050° C. for 3 h, and then performing a two-stage tempering treatment, wherein the first-stage treatment temperature is 850° C. and the tempering time is 3 h; and the second-stage treatment temperature is 465° C. and the tempering time is 3 h;

[0050] (6)NdH x Micron powder and PVB binder are dissolved in anhydrous ethanol to form a uniform suspension, in which NdH x The mass ratio of micron powder to binder is 1:0.02;

[0051] (7) placing the regenerated sintered NdFeB magnet on a heating table and heating it to 70-80° C., then using a spray gun to evenly spray the suspension prepared in step (6) on the surface of the NdFeB magnet with a weight gain ratio of 1 wt.%, to form a uniform diffusion source coating, and then heating the magnet for 1-2 minutes to evaporate the anhydrous ethanol;

[0052] (8) Place the sprayed regenerated sintered NdFeB magnet into a vacuum tube furnace and evacuate the vacuum tube furnace to 10 -3 Pa; then the magnet is subjected to two-stage heat treatment, wherein the first stage heat treatment is: temperature 880°C, heat preservation 6h; the second stage heat treatment is: temperature 500°C, heat preservation 3h, to obtain a regenerated magnet.

[0053] Comparative Example

[0054] (1) The surface of the Ce-containing sintered NdFeB waste was first treated by immersing the waste in a 5% NaOH solution, alkali washing for 20 minutes twice under an ultrasonic environment, and then ultrasonically cleaning it in 0.5% dilute nitric acid for 10 seconds to obtain a waste with a clean surface;

[0055] (2) The waste obtained in (1) was placed in a hydrogen explosion furnace chamber and hydrogen was absorbed for 3 h at a temperature of 250 °C and a hydrogen pressure of 1 MPa. -3 Pa was dehydrogenated for 5 h to obtain the waste hydrogen explosion coarse powder.

[0056] (3) The hydrogen explosion powder obtained in step (2) is subjected to air jet milling treatment under nitrogen protection, and is ground at a speed of 4400 r / min for 2 h to obtain regenerated air jet milled powder with a particle size of 3-6 μm;

[0057] (4) According to the composition test results, the total loss of rare earth is 2.02wt.%, of which Ce loss is 0.64wt.%, Nd loss is 0.46wt.%, and Pr loss is 0.92wt.%. According to the loss of rare earth elements in the hydrogen explosion-jet mill recovery process, corresponding supplements are made, and the added amount is 110% of the loss of each rare earth element;

[0058] (5) After the jet milled powder and the rare earth supplement are evenly mixed, they are sintered at 1050°C for 3 hours, and then subjected to two-stage tempering treatment: the first-stage treatment temperature is 850°C and the tempering time is 3 hours; the second-stage treatment temperature is 495°C and the tempering time is 3 hours. The properties and composition of the sintered magnets are shown in Appendix 1 and 2.

[0059] Table 1. Room temperature magnetic properties of different magnets

[0060]

[0061]

[0062] Appendix 2. Rare earth content of different magnets*

[0063]

[0064] * Note: To illustrate the loss of rare earth content, the rare earth content of the jet milled powder is also listed in the table.

Claims

1. A rare earth reduction, regulation and recovery method based on high cerium content sintered NdFeB waste, characterized in that: The following steps are involved: (1) For the surface treatment of high cerium content sintered NdFeB waste, first soak the waste in 3-7% NaOH solution, wash it 1-3 times in ultrasonic environment, each time for 10-30 minutes, until there is no oil stain on the surface of the waste, and then ultrasonically clean it in 0.3-1.0% dilute nitric acid for 5-30 seconds, until there is no oxide layer and rust on the surface of the waste; (2) placing the waste obtained in step (1) in a hydrogen environment and performing hydrogen explosion treatment to obtain regenerated hydrogen explosion powder; (3) subjecting the hydrogen explosion powder obtained in step (2) to a jet milling treatment to obtain jet milled powder; (4) Conducting component testing on the jet milled powder, and adding one or more alloy powders containing La, Y, Ga, etc. to the jet milled powder according to the results, adjusting the ratio of (La / Y / Ga):Ce in the jet milled powder to 1:9-2:8; in addition, selectively adding rare earth supplement powder according to the total loss of Nd and Pr elements, and mixing them evenly; (5) subjecting the mixed powder finally obtained in step (4) to oriented pressing, sintering, tempering and cooling to obtain a regenerated sintered NdFeB magnet; (6) dissolving a rare earth compound or its alloy powder and a polyvinyl butyral (PVB) binder in anhydrous ethanol to form a uniform suspension; (7) placing the regenerated sintered NdFeB magnet obtained in step (5) on a heating table and heating it to 70-80° C., then using a spray gun to evenly spray the suspension prepared in step (6) on the surface of the regenerated sintered NdFeB magnet to form a uniform diffusion source coating, and then heating the magnet for 1-2 minutes to evaporate the anhydrous ethanol; (8) The sprayed regenerated sintered NdFeB magnet is placed in a vacuum tube furnace for grain boundary diffusion treatment.

2. The method according to claim 1, characterized in that Step (1) The sintered NdFeB waste contains the rare earth element Ce, and its content accounts for 30-80% of the total rare earth content.

3. The method according to claim 1, characterized in that The specific operation of hydrogen explosion of the waste in step (2) is as follows: placing the waste in a hydrogen explosion furnace chamber at a temperature of 200-260°C and a hydrogen pressure of 1 MPa to absorb hydrogen for 3 hours, and then heating the waste at 550°C and 1×10 -3 Pa is dehydrogenated for 5 hours to obtain the waste hydrogen explosion coarse powder; the particle size of the jet mill powder obtained in step (3) is 3-6μm.

4. The method according to claim 1, characterized in that The alloy powder containing one or more of La, Y, Ga, etc. in step (4) is one or more of the hydrides of La, Y, Ga; the rare earth supplement is the hydride of Nd or Pr, with a particle size of 3 to 6 μm, so that the total amount of added Nd and / or Pr is 0 to 50% of the total loss.

5. The method according to claim 1, characterized in that In step (5), under argon protection, the sintering temperature is 1040-1060°C, the sintering time is 3-5h, and the tempering treatment is divided into two stages, the primary treatment temperature is 820-870°C, the tempering time is 3-6h, and the secondary treatment temperature is 440-480°C, and the time is 3-6h.

6. The method according to claim 1, characterized in that In step (6), the rare earth compound is NdH x , PrH x Nano-micron powder or low melting point alloy powder, such as (Nd / Pr)Cu, (Nd / Pr)Al and other alloy powders.

7. The method according to claim 1, characterized in that The weight gain ratio of the magnet after spraying in step (7) is 0.5 to 1 wt.%.

8. The method according to claim 1, characterized in that The specific operation steps of the magnet in the vacuum tube furnace in step (8) are as follows: placing the sprayed regenerated sintered NdFeB magnet into the vacuum tube furnace, evacuating to 10 -3 Pa; then the magnet is subjected to a two-stage heat treatment, wherein the first stage heat treatment is: temperature 860-900°C, heat preservation for 3-10 hours; the second stage heat treatment is: temperature 460-510°C, heat preservation for 3 hours.

9. A regenerative magnet prepared according to the method of any one of claims 1 to 8.

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