A method for preparing recycled NdFeB magnetic powder and its application in the preparation of sintered magnets

Abstract

This invention provides a regenerated NdFeB magnetic powder, its preparation method, and its application in the preparation of sintered magnets. The regenerated NdFeB magnetic powder is prepared primarily from sintered NdFeB processing sludge through pretreatment, reduction heat treatment, crushing and pulverization, and powder screening. The reduction heat treatment is a two-stage process. In the first stage, flowing hydrogen is used as a reducing agent to reduce the oxygen content in the sludge and decrease the consumption of reducing agent in the second stage. In the second stage, at least one of the rare earth elements La, Ce, and Sm is used as a reducing agent. Even if these reducing agents are not completely removed in subsequent processing steps, they will not significantly affect the performance of the regenerated magnetic powder and the regenerated magnet. The preparation method of the regenerated NdFeB magnetic powder provided by this invention avoids contact with solvents such as water, methanol, and ethanol. The sintered magnets prepared from this regenerated NdFeB magnetic powder exhibit excellent performance.

Description

Technical Field

[0001] This invention belongs to the field of magnetic materials - rare earth permanent magnet waste recycling technology, specifically involving a method for preparing recycled NdFeB magnetic powder from mud-like waste generated during the cutting and processing of sintered NdFeB magnets, and the application of the recycled NdFeB magnetic powder in the preparation of recycled sintered magnets. Background Technology

[0002] Sintered NdFeB magnets are currently the most produced and widely used NdFeB permanent magnet material. In recent years, the demands for thinner, lighter, and more integrated electronic devices have become increasingly stringent in high-tech fields, especially microelectronics. This requires increasingly smaller magnetic components, necessitating extensive machining to shape and size the blanks. Approximately 30 wt.% of the original magnet's mass is used for machining the outer magnets, generating magnetic shavings. These shavings mix with protective agents and coolants used in the machining process to form a mud-like waste. This mud-like waste contains 25 wt.%–28 wt.% rare earth elements, making it highly valuable for recycling. Therefore, the recycling of NdFeB mud-like waste has received increasing attention in recent years.

[0003] Currently, the industrial-scale recycling of sintered NdFeB sludge waste still relies on traditional hydrometallurgical or pyrometallurgical methods to recover the high-value rare earth elements. Obtaining NdFeB magnetic powder requires a series of steps including electrolysis, smelting, and hydrogen explosion, resulting in a lengthy and energy-intensive process. The high pollution associated with electrolysis is also difficult to avoid. Whether considering mitigating the environmental problems that may result from rare earth mining or from the perspective of strategic rare earth resource reserves, it is crucial to prioritize the research and development of new processes for recovering rare earth resources from NdFeB sludge waste.

[0004] Invention patent 202210424762.9 discloses a method for pretreatment, calcium reduction, and calcium washing of processed sludge to achieve batch regeneration of processed sludge. While this method can recycle and reuse NdFeB processed sludge in batches, the reducing agent used is metallic calcium or calcium hydride. For NdFeB magnetic powder or sintered NdFeB magnets, calcium is a harmful impurity, and thorough calcium removal is necessary after the reduction reaction. The calcium removal process requires ammonium chloride / methanol solution, which consumes a large amount of organic reagents. Furthermore, the rare earth elements contained in the reduced magnetic sludge can partially react with methanol, affecting the rare earth element recovery rate. Invention patent 201910563818.7 discloses a similar recovery method, which uses an ice-water mixture to wash calcium. Although this can lower the material temperature and reduce the reaction between rare earth elements and water, the localized high temperature caused by the calcium-water reaction still leads to the reaction of rare earth elements with water, consuming some rare earth elements. Invention patents 201510100851.8 and 201811437315.7, among others, disclose methods for reducing crude oil mud with calcium.

[0005] Currently, among the methods for recycling NdFeB sludge waste, the calcium reduction-diffusion method has significantly shortened the reaction process and improved recycling efficiency. However, it still suffers from problems such as high calcium consumption, uneven particle size of regenerated magnetic powder, small recovery volume, and long production cycle. Therefore, it is necessary to develop a method for recycling NdFeB sludge waste to prepare large quantities of regenerated magnetic powder with uniform particle size. Summary of the Invention

[0006] To address the problems of existing technologies, this invention provides a method for preparing recycled NdFeB magnetic powder, using sintered NdFeB processing sludge as the main raw material, and obtaining it through steps such as pretreatment, reduction heat treatment, crushing and powdering, and magnetic separation. This invention also provides a method for preparing recycled NdFeB sintered magnets, using the aforementioned recycled NdFeB magnetic powder as the main raw material, and obtaining it through steps such as powder mixing, molding, sintering, and heat treatment.

[0007] A method for preparing recycled NdFeB magnetic powder, characterized by the following steps:

[0008] (1) Raw material preparation: Collect and obtain the sludge F0 generated during the processing of sintered NdFeB magnets.

[0009] (2) Oil sludge pretreatment: The collected processed oil sludge F0 is pretreated by physical and chemical methods to remove organic and inorganic impurities contained in the oil sludge and obtain dry oil sludge F1 with an O content of less than 1 wt.%.

[0010] (3) Reduction heat treatment: The pretreated dry sludge F1 is subjected to two-stage reduction heat treatment to obtain sludge F2.

[0011] The first stage of the two-stage reduction heat treatment uses flowing hydrogen as a reducing agent and inert gases such as argon as carrier gases, with a reduction temperature of 600–800°C. The second stage of the two-stage reduction heat treatment uses micron-sized powders of La and / or Ce and / or Sm as a reducing agent, with a reduction temperature of 800–1100°C.

[0012] The amount of hydrogen used is in moles; 1 mol of oxygen atoms in the dried sludge corresponds to 0.5 to 0.8 mol of hydrogen.

[0013] The amount of the metal reducing agent is measured in moles. 1 mol of oxygen atoms in the dried sludge corresponds to 0.4–0.6 mol of metallic La, 0.30–0.45 mol of metallic Ce, or 0.4–0.6 mol of metallic Sm. The amounts of the combined reducing agents can be combined according to the aforementioned amounts.

[0014] (4) Crushing and grinding: The oil sludge F2 after reduction heat treatment is crushed and ground in two stages. The first stage is hydrogen absorption crushing and the second stage is air jet mill crushing. After crushing and grinding, powder F3 is obtained.

[0015] (5) Powder screening: Using the classifying wheel and cyclone separator of the air jet mill, some large particles with a particle size of more than 10 μm and small particles with a particle size of less than 1 μm in powder F3 are removed to obtain regenerated NdFeB magnetic powder F4.

[0016] Furthermore, the oil sludge F0 refers to the mud-like waste generated during the cutting and machining process of sintered NdFeB magnets, the main component of which is RE. a Fe b M c B d X e In the formula, RE represents one or more rare earth metals; M represents one or more of Co, Cu, Al, Ga, Zr, Nb, and Ti; B represents boron; X represents O, N, C, S, etc.; a, b, c, d, and e represent the mass fractions of the corresponding elements, and 25≤a≤33, 55≤b≤70, 0≤c≤3, 0.85≤d≤0.95, and 3≤e≤6.

[0017] Furthermore, the main phase composition of the processed sludge F0 is RE2Fe. 14 B, as well as rare earth oxides, nitrides, carbides, etc.

[0018] Furthermore, the physical and chemical methods in the sludge pretreatment step include magnetic separation, ultrasonic water washing, ultrasonic acid washing, ultrasonic alkali washing, centrifugal dehydration, centrifugal removal of organic solvents, and drying.

[0019] Furthermore, during the reduction heat treatment process, the material is stirred by methods such as stirring and turning the reaction vessel to promote the full reduction of the entire sludge.

[0020] Furthermore, the hydrogen gas in the first-stage reduction heat treatment can be recycled, and during the circulation process, a solid desiccant is used to absorb water and dry the hydrogen gas.

[0021] Furthermore, the O content in the regenerated NdFeB magnetic powder F4 is less than 0.2 wt.%, the proportion of large particles with a particle size of 10 μm or more is less than 5%, and the proportion of small particles with a particle size of less than 1 μm is less than 4%.

[0022] A method for preparing a recycled NdFeB sintered magnet, using the aforementioned recycled NdFeB magnetic powder as the main raw material, is obtained through steps such as powder mixing, molding, sintering and heat treatment.

[0023] The beneficial effects of the present invention include: (1) using flowing hydrogen as a reducing agent for the first-stage reduction heat treatment, reducing the iron oxides and other oxides in the sludge that can be reduced by hydrogen, reducing the oxygen content in the sludge, and reducing the consumption of reducing agent in the second-stage reduction heat treatment process; (2) using micron-sized powders of La and / or Ce and / or Sm as a reducing agent in the second-stage reduction heat treatment process. La, Ce, and Sm are rare earth elements, and even if they are not completely removed, they will not significantly affect the performance of the regenerated magnetic powder and the regenerated magnet; (3) crushing, pulverizing, and sieving the material after reduction heat treatment. The La, Ce, and Sm oxides generated during the reduction heat treatment process are separated out due to their small particle size, and the unreacted La, Ce, and Sm are further crushed into fine powder and removed. The resulting regenerated NdFeB magnetic powder has low oxygen content and uniform particle size. (4) using the technology of the present invention, the magnetic powder obtained by reduction heat treatment no longer comes into contact with solvents such as water, methanol, and ethanol. Detailed Implementation

[0024] This invention provides a method for preparing recycled NdFeB magnetic powder. The method uses mud-like waste generated during the machining of sintered NdFeB magnets as the main raw material, and obtains the powder through pretreatment, reduction heat treatment, crushing and pulverizing, and powder screening steps. The resulting recycled NdFeB magnetic powder has the characteristics of low O content and uniform particle size distribution, with an O content of less than 0.2 wt.%, a large particle size of more than 10 μm accounting for less than 5%, and a small particle size of less than 1 μm accounting for less than 4%.

[0025] A method for preparing recycled NdFeB magnetic powder includes the following steps:

[0026] (1) Raw material preparation: Collect and obtain the sludge F0 generated during the processing of sintered NdFeB magnets.

[0027] The oil sludge F0 refers to the mud-like waste generated during the machining process of sintered NdFeB magnets. Generally, any oil sludge generated during the machining process of sintered NdFeB magnets can be used as a raw material for this method to prepare recycled NdFeB magnetic powder. However, the composition and phase composition of different types of magnetic sludge vary greatly. In order to obtain high-performance recycled NdFeB magnetic powder, this preparation method limits the composition of the oil sludge, specifying that the main component of oil sludge F0 is RE. a Fe b M c B d X e Its main phase composition is RE2Fe 14B, as well as rare earth oxides, nitrides, carbides, etc. In the formula, RE represents one or more rare earth metals; M represents one or more of Co, Cu, Al, Ga, Zr, Nb, Ti; Fe represents iron; B represents boron; X represents O, N, C, S, etc.; a, b, c, d, e are the mass fractions of the corresponding elements, and 25≤a≤33, 55≤b≤70, 0≤c≤3, 0.85≤d≤0.95, 3≤e≤6.

[0028] (2) Oil sludge pretreatment: The collected processed oil sludge F0 is pretreated by physical and chemical methods to remove organic and inorganic impurities contained in the oil sludge and obtain dry oil sludge F1 with an O content of less than 1 wt.%.

[0029] The main purpose of the sludge pretreatment is to reduce the content of organic and inorganic impurities in the sludge. Common physical or chemical methods such as magnetic separation, ultrasonic water washing, ultrasonic acid washing, ultrasonic alkali washing, centrifugal dehydration, centrifugal removal of organic solvents, and drying are all acceptable. To improve the pretreatment effect, these methods can be used multiple times or in combination. To facilitate the calculation of the amount of reducing agent required for reduction heat treatment, it is necessary to test the O content of the dried sludge after pretreatment.

[0030] (3) Reduction heat treatment: The pretreated dry sludge F1 is subjected to two-stage reduction heat treatment to obtain sludge F2.

[0031] The first-stage reduction heat treatment uses flowing hydrogen as the reducing agent and inert gases such as argon as the carrier gas. The reduction temperature is 600–800℃, mainly used to reduce iron oxides and other oxides in crude oil sludge that can be reduced by hydrogen. The amount of hydrogen used is measured in moles; 1 mol of oxygen atoms in the dried sludge corresponds to 0.5–0.8 mol of hydrogen. The water and unreacted hydrogen produced by the hydrogen reduction reaction flow through a solid desiccant zone under the influence of the carrier gas. The solid desiccant absorbs and dries the carrier gas and unreacted hydrogen, and the dried hydrogen can be recycled.

[0032] The second-stage reduction heat treatment uses micron-sized La and / or Ce and / or Sm powders as reducing agents, with a reduction temperature of 800–1100℃. It is mainly used to reduce rare earth oxides and unreduced iron oxides in crude oil sludge. The amount of reducing agent is measured in moles; 1 mol of oxygen atoms in dried oil sludge corresponds to 0.4–0.6 mol of metallic La, 0.30–0.45 mol of metallic Ce, or 0.4–0.6 mol of metallic Sm. The amounts of combined reducing agents can be configured according to the aforementioned amounts. Using La, Ce, and Sm instead of Ca in the existing process as reducing agents, and leveraging the strong reducing properties of La, Ce, and Sm to reduce rare earth oxides in the oil sludge, avoids contact between magnetic powder and liquid reagents during the Ca washing process after the reduction reaction. This reduces reagent consumption and also minimizes the reaction between the magnetic powder and reagents. Furthermore, since La, Ce, and Sm are all rare earth elements, utilizing their strong reducing properties to reduce rare earth oxides in the oil sludge avoids the negative impact of small amounts of residual Ca on the performance of the magnetic powder and magnets. Using micron-sized powder as a reducing agent increases the surface area of ​​the reducing agent, promoting rapid and sufficient contact between the reducing agent and the oil sludge, and shortening the reduction heat treatment time.

[0033] Oxygen in oil sludge mainly exists in the form of oxides. Oxygen in rare earth oxides accounts for approximately 50-70% of the total oxygen content, while oxygen in oxides of iron and other substances accounts for approximately 30-50%. Because hydrogen is readily available and relatively inexpensive, its reducing properties can be used to reduce oxides such as iron oxides, which can be reduced by hydrogen, thus reducing the consumption of reducing agent during the second-stage reduction heat treatment. Compared to oil sludge that has not undergone the first-stage reduction heat treatment with hydrogen, the amount of reducing agent consumed during the second-stage reduction heat treatment can be reduced by 25-45%. To ensure complete reduction of the oil sludge, the material is stirred and the reaction vessel is rotated during the reduction heat treatment process.

[0034] The high temperature during the reduction heat treatment process can also promote the decomposition of organic matter contained in the sludge, removing it in the form of carbon oxides and nitrogen oxides.

[0035] (4) Crushing and grinding: The oil sludge F2 after reduction heat treatment is crushed and ground in two stages. The first stage is hydrogen absorption crushing and the second stage is air jet mill crushing. After crushing and grinding, powder F3 is obtained.

[0036] The main purpose of crushing and grinding is to break the adhesion between powder particles caused during the reduction heat treatment process; at the same time, by taking advantage of the characteristic of rare earth elements to become brittle after absorbing hydrogen, the reducing agent introduced during the second-stage reduction heat treatment is crushed into tiny particles and removed by subsequent screening steps.

[0037] (5) Powder screening: Using the classifying wheel and cyclone separator of the air jet mill, some large particles with a particle size of more than 10 μm and small particles with a particle size of less than 1 μm in powder F3 are removed to obtain regenerated NdFeB magnetic powder F4.

[0038] The regenerated magnetic powder prepared by the aforementioned method for preparing regenerated NdFeB magnetic powder has the characteristics of concentrated particle size distribution and low C / N / O content. The O content in the magnetic powder is less than 0.2 wt.%, the proportion of large particles with a particle size of more than 10 μm is less than 5%, and the proportion of small particles with a particle size of less than 1 μm is less than 4%.

[0039] The method for preparing recycled NdFeB sintered magnets uses the aforementioned recycled NdFeB magnetic powder as the main raw material, and proceeds through steps such as powder mixing, molding, sintering, and heat treatment. The powder mixing step can involve mixing the recycled magnetic powder itself, primarily to further improve powder uniformity, or it can involve mixing the recycled magnetic powder with other magnetic powders, primarily to obtain recycled magnets with various properties. The molding, sintering, and heat treatment steps are common processes in the rare earth permanent magnet industry. Appropriate process parameters can be selected based on the size and performance requirements of the recycled magnet; these will not be listed individually here.

[0040] The present invention will be further described in detail below with reference to the embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0041] Example 1

[0042] Regenerated NdFeB magnetic powder is prepared by the following steps:

[0043] (1) Raw material preparation: The sludge generated during the processing of sintered NdFeB magnet slices was collected and tested. Its main components were (PrNdDyTb). 27.22 Fe 65.02 (CoCuAlGaZr) 2.24 B 0.89 (ONCS) 4.63 (wt.%), its main phase composition is RE2Fe 14 B, as well as rare earth oxides, nitrides, carbides, etc.

[0044] (2) Oil sludge pretreatment: The collected processing oil sludge was pretreated by ultrasonic water washing → magnetic separation → centrifugal drying → ultrasonic alcohol cleaning → magnetic separation → centrifugal drying → ultrasonic acid washing → magnetic separation → centrifugal drying → ultrasonic water washing → magnetic separation → centrifugal drying → ultrasonic alcohol cleaning → magnetic separation → centrifugal drying → vacuum drying to remove organic and inorganic impurities in the oil sludge and obtain dry oil sludge with an O content of 0.98 wt.%.

[0045] (3) Reduction heat treatment: The pretreated dry sludge is subjected to two-stage reduction heat treatment to obtain low-oxygen magnetic powder.

[0046] The first-stage reduction heat treatment uses flowing hydrogen as a reducing agent at a reduction temperature of 600℃. The amount of hydrogen used, measured in moles, is 0.5 times the oxygen atom content in the dry sludge, i.e., 1 mol of oxygen atoms corresponds to 0.5 mol of hydrogen. During the reduction heat treatment, the material is continuously stirred using a stirring fork.

[0047] The second-stage reduction heat treatment used metallic La powder with an average particle size of 3 μm as a reducing agent at a reduction temperature of 1100℃. The amount of metallic La used, measured in moles, was 0.4 times the oxygen atom content in the dried sludge, i.e., 1 mol of oxygen atoms corresponded to 0.4 mol of metallic La. The material was continuously stirred using a stirring fork during the reduction heat treatment.

[0048] (4) Crushing and grinding: The low-oxygen magnetic powder after reduction heat treatment is crushed and ground in two stages. The first stage is hydrogen absorption crushing and the second stage is air jet milling. Crushed magnetic powder is obtained after crushing and grinding.

[0049] (5) Powder screening: Using the classifying wheel and cyclone separator of the air jet mill, some large particles with a particle size of more than 10 μm and small particles with a particle size of less than 1 μm are removed from the crushed magnetic powder to obtain regenerated NdFeB magnetic powder.

[0050] Regenerated NdFeB sintered magnets are prepared by the following steps:

[0051] Using the aforementioned recycled NdFeB magnetic powder as the main raw material, NdFeB powder is mixed in at a ratio of 2g NdFeB to 98g of recycled magnetic powder, and then processed through steps such as molding, sintering and heat treatment.

[0052] Example 2

[0053] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Example 1, except that the amount of hydrogen used in the first-stage reduction heat treatment was changed: the amount of hydrogen used, measured in moles, was 0.8 times the oxygen atom content in the dried sludge, that is, 1 mol of oxygen atoms corresponds to 0.8 mol of hydrogen.

[0054] Example 3

[0055] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Example 1, except that the amount of metallic La powder used in the second-stage reduction heat treatment was changed: the amount of metallic La, measured in moles, was 0.6 times the oxygen atom content in the dried sludge, that is, 1 mol of oxygen atoms corresponded to 0.6 mol of metallic La.

[0056] Example 4

[0057] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Example 2, except that the amount of metallic La powder used in the second-stage reduction heat treatment was changed: the amount of metallic La, measured in moles, was 0.6 times the oxygen atom content in the dried sludge, that is, 1 mol of oxygen atoms corresponds to 0.6 mol of metallic La.

[0058] Comparative Example 1

[0059] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Example 3, except that the first-stage reduction heat treatment using hydrogen as a reducing agent was not performed.

[0060] Comparative Example 2

[0061] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Comparative Example 1, the only difference being that the amount of metal reducing agent used was twice that in Comparative Example 1.

[0062] Comparative Example 3

[0063] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Comparative Example 1, except that the metal reducing agent was changed from metal Ce to metal Ca, and after reduction heat treatment, the magnets were washed twice with water to remove calcium.

[0064] Comparative Example 4

[0065] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Comparative Example 2, except that the metal reducing agent was changed from metal Ce to metal Ca, and after reduction heat treatment, the magnets were washed twice with water to remove calcium.

[0066] Comparative Example 5

[0067] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Comparative Example 4, the only difference being that the number of water washing and calcium removal cycles was 4.

[0068] The relevant indicators of the regenerated NdFeB magnetic powder and regenerated magnets obtained in Examples 1-4 and Comparative Examples 1-5 were compared and tested, and the results are shown in Table 1.

[0069] Table 1. Relevant indicators of the regenerated NdFeB magnetic powder and regenerated magnets obtained in Examples 1-4 and Comparative Examples 1-5.

[0070]

[0071] As can be seen from Table 1: (1) Using flowing hydrogen as a reducing agent for the first-stage reduction heat treatment can reduce the iron oxides and other oxides in the sludge that can be reduced by hydrogen, thereby reducing the consumption of reducing agent in the second-stage reduction heat treatment process; (2) Using micronized La metal powder as a reducing agent in the second-stage reduction heat treatment process can easily remove the reduction products and leave no metal reducing agent residue.

[0072] Example 5

[0073] Regenerated NdFeB magnetic powder is prepared by the following steps:

[0074] (1) Raw material preparation: The sludge generated during the processing of sintered NdFeB magnet slices was collected and tested to determine its composition as (PrNdDyGdHo). 26.85 Fe 63.85 (CoCuAlGaNb) 2.84 B 0.88 (ONCS) 5.58 (wt.%), its main phase composition is RE2Fe 14 B, as well as rare earth oxides, nitrides, carbides, etc.

[0075] (2) Oil sludge pretreatment: The collected processed oil sludge was pretreated by ultrasonic water washing → magnetic separation → centrifugal drying → ultrasonic alcohol cleaning → magnetic separation → centrifugal drying → ultrasonic acid washing → magnetic separation → centrifugal drying → ultrasonic water washing → magnetic separation → centrifugal drying → ultrasonic alcohol cleaning → magnetic separation → centrifugal drying → vacuum drying to remove organic and inorganic impurities in the oil sludge and obtain dry oil sludge with an O content of 0.89 wt.%.

[0076] (3) Reduction heat treatment: The pretreated dry sludge is subjected to two-stage reduction heat treatment to obtain low-oxygen magnetic powder.

[0077] The first-stage reduction heat treatment uses flowing hydrogen as a reducing agent at a reduction temperature of 700℃. The amount of hydrogen used, measured in moles, is 0.5 times the oxygen atom content in the dried sludge, i.e., 1 mol of oxygen atoms corresponds to 0.5 mol of hydrogen. During the reduction heat treatment, the material is continuously stirred using a stirring fork.

[0078] The second-stage reduction heat treatment used Sm metal powder with an average particle size of 3 μm as a reducing agent at a reduction temperature of 950℃. The amount of Sm metal used, measured in moles, was 0.4 times the oxygen atom content in the dried sludge, i.e., 1 mol of oxygen atoms corresponded to 0.4 mol of Sm metal. The material was continuously stirred using a stirring fork during the reduction heat treatment.

[0079] (4) Crushing and grinding: The low-oxygen magnetic powder after reduction heat treatment is crushed and ground in two stages. The first stage is hydrogen absorption crushing and the second stage is air jet milling. Crushed magnetic powder is obtained after crushing and grinding.

[0080] (5) Powder screening: Using the classifying wheel and cyclone separator of the air jet mill, some large particles with a particle size of more than 10 μm and small particles with a particle size of less than 1 μm are removed from the crushed magnetic powder to obtain regenerated NdFeB magnetic powder.

[0081] Regenerated NdFeB sintered magnets are prepared by the following steps:

[0082] Using the aforementioned recycled NdFeB magnetic powder as the main raw material, the mixture is prepared by adding 50g of recycled magnetic powder to 50g of NdFeB. 33 Fe 66.1 B 0.9 The proportion of magnetic powder (wt.%) is used to mix the powders, which are then processed through steps such as molding, sintering, and heat treatment.

[0083] Example 6

[0084] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Example 5, except that the amount of hydrogen used in the first-stage reduction heat treatment was changed: the amount of hydrogen used, measured in moles, was 0.8 times the oxygen atom content in the dried sludge, that is, 1 mol of oxygen atoms corresponds to 0.8 mol of hydrogen.

[0085] Example 7

[0086] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Example 5, except that the amount of Sm powder used in the second-stage reduction heat treatment was changed: the amount of Sm powder used, measured in moles, was 0.6 times the oxygen atom content in the dried sludge, that is, 1 mol of oxygen atoms corresponds to 0.6 mol of Sm powder.

[0087] Example 8

[0088] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Example 6, except that the amount of Sm powder used in the second-stage reduction heat treatment was changed: the amount of Sm powder used, measured in moles, was 0.6 times the oxygen atom content in the dried sludge, that is, 1 mol of oxygen atoms corresponds to 0.6 mol of Sm powder.

[0089] Comparative Example 6

[0090] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Example 7, except that the first-stage reduction heat treatment using hydrogen as a reducing agent was not performed.

[0091] Comparative Example 7

[0092] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Comparative Example 6, the only difference being that the amount of metal reducing agent used was twice that in Comparative Example 6.

[0093] Comparative Example 8

[0094] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Comparative Example 6, except that the metal reducing agent was changed from metal Sm to metal Ca, and after reduction heat treatment, they were washed twice with water to remove calcium.

[0095] Comparative Example 9

[0096] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Comparative Example 7, except that the metal reducing agent was changed from metal Sm to metal Ca, and after reduction heat treatment, they were washed twice with water to remove calcium.

[0097] Comparative Example 10

[0098] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Comparative Example 9, the only difference being that the number of times calcium was removed by washing with water was 4.

[0099] The relevant indicators of the regenerated NdFeB magnetic powder and regenerated magnets obtained in Examples 5-8 and Comparative Examples 6-10 were compared and tested, and the results are shown in Table 2.

[0100] Table 2. Relevant indicators of the regenerated NdFeB magnetic powder and regenerated magnets obtained in Examples 5-8 and Comparative Examples 6-10.

[0101]

[0102] As can be seen from Table 2: (1) Using flowing hydrogen as a reducing agent for the first-stage reduction heat treatment can reduce the iron oxides and other oxides in the sludge that can be reduced by hydrogen, thereby reducing the consumption of reducing agent in the second-stage reduction heat treatment process; (2) Using micronized powder of metal Sm as a reducing agent in the second-stage reduction heat treatment process can easily remove the reduction products and leave no metal reducing agent residue.

[0103] Example 9

[0104] Regenerated NdFeB magnetic powder is prepared by the following steps:

[0105] (1) Raw material preparation: The sludge generated during the processing of sintered NdFeB magnet slices was collected and tested to determine its composition as (PrNdGdHo). 27.85 Fe 65.92 (CoCuAlGaNb) 2.21 B 0.88 (ONCS) 3.14 (wt.%), its main phase composition is RE2Fe 14 B, as well as rare earth oxides, nitrides, carbides, etc.

[0106] (2) Oil sludge pretreatment: The collected processed oil sludge was pretreated by ultrasonic water washing → magnetic separation → centrifugal drying → ultrasonic alcohol cleaning → magnetic separation → centrifugal drying → ultrasonic acid washing → magnetic separation → centrifugal drying → ultrasonic water washing → magnetic separation → centrifugal drying → ultrasonic alcohol cleaning → magnetic separation → centrifugal drying → vacuum drying to remove organic and inorganic impurities in the oil sludge and obtain dry oil sludge with an O content of 0.94 wt.%.

[0107] (3) Reduction heat treatment: The dried sludge is subjected to two-stage reduction heat treatment to obtain low-oxygen magnetic powder.

[0108] The first-stage reduction heat treatment uses flowing hydrogen as a reducing agent at a reduction temperature of 800℃. The amount of hydrogen used, measured in moles, is 0.5 times the oxygen atom content in the dry sludge, i.e., 1 mol of oxygen atoms corresponds to 0.5 mol of hydrogen. During the reduction heat treatment, the material is continuously stirred using a stirring fork.

[0109] The second-stage reduction heat treatment used Ce powder with an average particle size of 3.5 μm as a reducing agent at a reduction temperature of 800 °C. The amount of Ce powder used, measured in moles, was 0.3 times the oxygen atom content in the dried sludge, i.e., 1 mol of oxygen atoms corresponded to 0.3 mol of Ce powder. The material was continuously stirred using a stirring fork during the reduction heat treatment.

[0110] (4) Crushing and grinding: The low-oxygen magnetic powder after reduction heat treatment is crushed and ground in two stages. The first stage is hydrogen absorption crushing and the second stage is air jet milling. Crushed magnetic powder is obtained after crushing and grinding.

[0111] (5) Powder screening: Using the classifying wheel and cyclone separator of the air jet mill, some large particles with a particle size of more than 10 μm and small particles with a particle size of less than 1 μm are removed from the crushed magnetic powder to obtain regenerated NdFeB magnetic powder.

[0112] Regenerated NdFeB sintered magnets are prepared by the following steps:

[0113] Using the aforementioned recycled NdFeB magnetic powder as the main raw material, the powder is mixed with 3g of dysprosium hydride at a ratio of 97g of recycled magnetic powder, and then processed through steps such as molding, sintering and heat treatment.

[0114] Example 10

[0115] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Example 9, except that the amount of hydrogen used in the first-stage reduction heat treatment was changed: the amount of hydrogen used, measured in moles, was 0.8 times the oxygen atom content in the dried sludge, that is, 1 mol of oxygen atoms corresponds to 0.8 mol of hydrogen.

[0116] Example 11

[0117] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Example 9, except that the amount of metallic Ce powder used in the second-stage reduction heat treatment was changed: the amount of metallic Ce, measured in moles, was 0.45 times the oxygen atom content in the dried sludge, that is, 1 mol of oxygen atoms corresponded to 0.45 mol of metallic Ce.

[0118] Example 12

[0119] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Example 10, except that the amount of metallic Ce powder used in the second-stage reduction heat treatment was changed: the amount of metallic Ce, measured in moles, was 0.45 times the oxygen atom content in the dried sludge, i.e., 1 mol of oxygen atoms corresponded to 0.45 mol of metallic Ce.

[0120] Comparative Example 11

[0121] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Example 11, except that the first-stage reduction heat treatment using hydrogen as a reducing agent was not performed.

[0122] Comparative Example 12

[0123] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Comparative Example 11, the only difference being that the amount of metal reducing agent used was twice that in Comparative Example 11.

[0124] Comparative Example 13

[0125] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Comparative Example 11, except that the metal reducing agent was changed from metal Ce to metal Ca, and after reduction heat treatment, the magnets were washed twice with water to remove calcium.

[0126] Comparative Example 14

[0127] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Comparative Example 12, except that the metal reducing agent was changed from metal Ce to metal Ca, and after reduction heat treatment, the magnets were washed twice with water to remove calcium.

[0128] Comparative Example 15

[0129] Regenerated magnetic powder and regenerated magnets were prepared using the same process as in Comparative Example 14, the only difference being that the number of water washing and calcium removal cycles was 4.

[0130] The relevant indicators of the regenerated NdFeB magnetic powder and regenerated magnets obtained in Examples 9-12 and Comparative Examples 11-15 were compared and tested, and the results are shown in Table 3.

[0131] Table 3. Relevant indicators of the regenerated NdFeB magnetic powder and regenerated magnets obtained in Examples 9-12 and Comparative Examples 11-15.

[0132]

[0133] As can be seen from Table 3: (1) Using flowing hydrogen as a reducing agent for the first-stage reduction heat treatment can reduce the iron oxides and other oxides in the sludge that can be reduced by hydrogen, thereby reducing the consumption of reducing agent in the second-stage reduction heat treatment process; (2) Using micronized Ce metal powder as a reducing agent in the second-stage reduction heat treatment process can easily remove the reduction products and leave no metal reducing agent residue.

[0134] The embodiments described above provide a detailed explanation of the technical solution of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, or similar substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing recycled NdFeB magnetic powder, characterized in that: Includes the following steps: (1) Raw material preparation: Collect and obtain the sludge F0 generated during the processing of sintered NdFeB magnets; (2) Oil sludge pretreatment: The collected oil sludge F0 is pretreated by physical and chemical methods to remove organic and inorganic impurities contained in the oil sludge and obtain dry oil sludge F1 with an O content of less than 1 wt.%; (3) Reduction heat treatment: The pretreated dried sludge F1 is subjected to two-stage reduction heat treatment to obtain sludge F2; The two-stage reduction heat treatment includes a first-stage reduction heat treatment and a second-stage reduction heat treatment. The first-stage reduction heat treatment uses flowing hydrogen as a reducing agent and an inert gas as a carrier gas, with a reduction temperature of 600~800℃; the second-stage reduction heat treatment uses micron-sized powders of La and / or Ce and / or Sm as a metal reducing agent, with a reduction temperature of 800~1100℃. The hydrogen gas in the first-stage reduction heat treatment is recycled, and a solid desiccant is used to absorb water and dry the hydrogen gas during the circulation process. The amount of hydrogen used is in moles, with 1 mol of oxygen atoms in the dried sludge corresponding to 0.5 to 0.8 mol of hydrogen. In the second-stage reduction heat treatment, the amount of metal reducing agent used is in moles. 1 mol of oxygen atoms in the dried sludge corresponds to 0.4~0.6 mol of metal La, or 0.30~0.45 mol of metal Ce, or 0.4~0.6 mol of metal Sm. (4) Crushing and grinding: The oil sludge F2 after reduction heat treatment is crushed and ground in two stages. The first stage is hydrogen absorption crushing and the second stage is air jet mill crushing. After crushing and grinding, powder F3 is obtained. (5) Powder screening: Using the classifying wheel and cyclone separator of the air jet mill, some large particles with a particle size of more than 10 μm and small particles with a particle size of less than 1 μm in powder F3 are removed to obtain regenerated NdFeB magnetic powder F4.

2. The preparation method according to claim 1, characterized in that: The oil sludge F0 refers to the mud-like waste generated during the cutting and machining process of sintered NdFeB magnets, whose main component is RE. a Fe b M c B d X e In the formula, RE is one or more rare earth metals; M is one or more of Co, Cu, Al, Ga, Zr, Nb, and Ti; B is boron; X is O, N, C, or S; a, b, c, d, and e are the mass fractions of the corresponding elements, and 25≤a≤33, 55≤b≤70, 0≤c≤3, 0.85≤d≤0.95, and 3≤e≤6.

3. The preparation method according to claim 2, characterized in that: The main phase composition of the sludge F0 is RE2Fe. 14 B, as well as rare earth oxides, nitrides, and carbides.

4. The preparation method according to claim 1, characterized in that: In the sludge pretreatment step, the physical and chemical methods include magnetic separation, ultrasonic water washing, ultrasonic acid washing, ultrasonic alkali washing, centrifugal dehydration, centrifugal removal of organic solvents, and drying.

5. The preparation method according to claim 1, characterized in that: In the reduction heat treatment step, the material is stirred by stirring and / or turning the reaction vessel to promote the full reduction of the entire sludge.

6. A type of recycled NdFeB magnetic powder, characterized in that: It is prepared by the preparation method as described in any one of claims 1 to 5.

7. A recycled NdFeB sintered magnet, characterized in that: It is prepared using the recycled NdFeB magnetic powder as described in claim 6 as the raw material.

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