Ultra-short process engineering recovery technology of sintered neodymium-iron-boron oil sludge

Abstract

This invention discloses an ultra-short-process engineered method for recycling sintered NdFeB sludge to prepare regenerated sintered magnets, belonging to the field of green regeneration technology for rare earth permanent magnets. The technology mainly includes steps such as batch purification, powder mixing, briquetting, and sintering of the sludge. First, the sintered NdFeB machined sludge is purified to remove impurities and oxides, and then vacuum-dried to obtain a purified powder with low oxygen content. Then, rare earth additives are added in a certain proportion and incorporated back into the original NdFeB air-jet milled powder or other specific NdFeB powder. After orientation, molding, and sintering, regenerated magnets are prepared. Using this technology, the sludge waste has a high recycling rate. By controlling the recycling ratio and rare earth content, the performance of the regenerated magnets not only meets the requirements for industrial use but also enables the regeneration of multiple grades, significantly reducing production costs. The method is simple, and the generated waste liquid can be recovered through traditional distillation, resulting in low energy and environmental impact and high economic efficiency.

Description

Technical Field:

[0001] This invention belongs to the field of ultra-short process recycling and reuse of various sintered NdFeB sludge, and involves an engineering recycling technology method for preparing high-performance regenerated sintered magnets at low cost using various sintered NdFeB sludge. Background Technology

[0002] Sintered NdFeB permanent magnets hold a pivotal position in the field of magnetic materials due to their excellent magnetic and mechanical properties. With technological advancements and increasing industrialization, the production volume of sintered NdFeB permanent magnets has been increasing year by year. The production conditions for sintered NdFeB permanent magnets are subject to certain limitations, resulting in most of them being rectangular in shape. Furthermore, due to the numerous stringent requirements for their applications, especially regarding the external shape of the magnets, multiple processing steps are unavoidable before application. The production and processing of sintered NdFeB magnets generate approximately 20-60 wt.% sludge waste. This waste contains about 25 wt.%-30 wt.% rare earth resources, as well as other valuable alloying elements such as Co, Cu, Al, and Ga, representing a valuable secondary resource. The engineering-based recycling of NdFeB oil sludge waste with an ultra-short process for all elements can not only promote the rapid and high-quality development of the rare earth industry, but also meet the requirements of the national high-quality development strategy goals such as green, low-carbon, and carbon neutrality.

[0003] Currently, the industrial recycling of NdFeB waste both domestically and internationally mainly utilizes hydrometallurgical or pyrometallurgical processes. Hydrometallurgical processes primarily separate and extract rare earth elements from sintered NdFeB sludge waste; however, this method involves a long recovery process, generates significant pollutants, and incurs high environmental costs, failing to meet current requirements for green environmental protection, energy conservation, and sustainable development. While pyrometallurgical processes generally have a lower overall environmental impact, they require higher-quality waste materials and are more suitable for recovering rare earth elements or rare earth alloys from blocky NdFeB waste with low oxidation levels and relatively few impurities. They have significant limitations with sludge waste containing high oxygen content. Furthermore, the rare earth recovery rate and purity vary considerably among different pyrometallurgical processes; methods such as chloride and molten salt recovery are costly and remain in the laboratory stage.

[0004] In recent years, the direct recycling of NdFeB sludge waste into regenerated magnetic powder through sludge purification and calcium reduction diffusion technology has greatly shortened the process flow. However, the calcium reduction diffusion method for recycling NdFeB sludge waste still suffers from problems such as small processing capacity, inability to mass-produce, and poor magnetic properties of the regenerated magnetic powder and regenerated sintered magnets. For example, invention patent CN201710762926.8 discloses a method for preparing regenerated sintered NdFeB magnets from NdFeB sludge waste through specific double-sided grinding. This method prepares regenerated sintered magnets by purifying the sludge and doping it with nano-rare earth hydride powder, but the magnetic properties are poor, making industrial production and application impossible. Invention patent CN201811437315.7 discloses a method for preparing regenerated sintered magnets from sludge waste through purification, calcium reduction diffusion, and rare earth alloy doping. This method involves a complex sludge purification process with many steps, a long purification time, and a small amount of sludge to be processed. Furthermore, the magnetic properties of the regenerated sintered magnets prepared are also poor, indicating significant room for improvement.

[0005] To address the above problems, this invention provides a method for batch production of high-performance regenerated sintered magnets from sintered NdFeB sludge. This method is applicable to sintered NdFeB sludge produced by various processing methods, and features a short purification process, ease of operation, large processing capacity, and the ability to recover and reuse the generated waste liquid after distillation. It also boasts low energy and environmental impact and high economic efficiency. More importantly, the regenerated magnets meet the performance requirements for industrial use and can be regenerated in multiple grades; it is also easy to produce on a large scale and industrially. Summary of the Invention

[0006] This invention mainly includes steps such as batch purification, powder mixing, briquetting, and sintering of sludge. First, the sludge is poured into a cleaning agent and stirred to remove organic matter and other impurities. Then, the cleaning agent is changed to further purify the sludge through stirring. Next, it is placed in a vacuum drying oven to dry. Finally, rare earth additives are added in a certain proportion, and the mixture is then incorporated back into the original NdFeB air-jet mill powder or other specific NdFeB powders before sintering. This technology, on the one hand, enables the ultra-short process recycling and reuse of all elements in sintered NdFeB sludge, significantly reducing environmental pollution and resource waste caused by sludge recycling. On the other hand, the technology can process sintered NdFeB sludge at an industrial level, with a high recovery rate of regenerated magnet performance, making mass production feasible. Furthermore, the treated waste liquid can be recycled using traditional physical methods.

[0007] (1) Add the obtained sludge to a specific cleaning agent and stir. After stirring for a period of time, use magnetic separation to separate the non-magnetic material from the magnetic powder. Change the cleaning agent and repeat stirring, cleaning and magnetic separation of the obtained magnetic powder to obtain cleaner magnetic powder and non-magnetic material. Repeat the above process of changing the cleaning agent, stirring and magnetic separation multiple times. The non-magnetic material is in the cleaning agent solution. The two cleaning agents can be the same or different.

[0008] Preferably, the cleaning agent is selected from any one or a combination of at least two of the following: an aqueous solution of OP emulsifier, an ethanol solution of OP emulsifier, a methanol solution of OP, and an acetone solution of OP. The centrifuged sludge is cleaned 2-3 times, each time for 15-20 minutes.

[0009] Similarly, used cleaning agents are recycled and reused using traditional distillation processes.

[0010] (2) The magnetic powder obtained in step (1) is added to a hydrochloric acid solution of a certain concentration and stirred and cleaned for a period of time to remove most of the oxides, thereby reducing the overall oxygen content of the magnetic powder and obtaining purified magnetic powder; the hydrochloric acid solution is an aqueous hydrochloric acid solution or an ethanol hydrochloric acid solution; the hydrochloric acid solution is used for repeated treatment multiple times; the mass percentage concentration of hydrochloric acid is between 0.5-2wt.%, and the stirring and cleaning time is between 10-30min.

[0011] (3) The purified magnetic powder obtained in step (2) is remixed into a mixed powder containing the original NdFeB powder and a specific rare earth additive; after mixing by a mixer, a uniformly distributed regenerated mixed NdFeB powder is obtained; the original NdFeB powder is selected from: air jet mill powder of the corresponding NdFeB magnet that produced the sludge in step (1); the specific additive is one or more of the following specific additives: (Re)nFe14B, (Re)nX, n can take any positive value (preferably 4), X is a metal or non-metal element, preferably Re = Nd; the mass percentage of purified magnetic powder in the regenerated mixed NdFeB powder, i.e., the remixing ratio, is greater than 0 and less than 60%, and then the overall rare earth content is adjusted by adjusting the ratio of the original NdFeB powder and the specific rare earth additive, so that the rare earth content in the regenerated mixed NdFeB powder is 30-35 wt.%.

[0012] Additional additives such as lubricants and antioxidants can be added to the recycled mixed NdFeB powder;

[0013] (5) The uniformly mixed NdFeB powder obtained in step (4) is subjected to orientation molding and isostatic pressing in sequence.

[0014] The magnets were then subjected to sintering and heat treatment in sequence to obtain regenerated sintered magnets.

[0015] Step (5) Sintering process: sintering temperature is between 1020-1100℃, and sintering time is 2-5h.

[0016] The heat treatment process involves a primary heat treatment temperature between 880-980℃ and a heat treatment time of 2-8 hours, and a secondary heat treatment temperature between 420-560℃ and a heat treatment time of 2-7 hours.

[0017] On the one hand, this invention enables the recycling and reuse of all elements of sintered NdFeB sludge in an ultra-short process, greatly reducing environmental pollution and resource waste caused by sludge recycling; on the other hand, the technology can process sintered NdFeB sludge at an industrial level, making it feasible for mass production, and the treated waste liquid can be recycled using traditional physical methods. Attached Figure Description

[0018] Figure 1 It is derived from Example 2, where the purified sludge content is fixed at 50 wt.%, and the ratio of the original NdFeB air jet mill powder and rare earth additives is adjusted to obtain a regenerated mixed NdFeB powder with a rare earth content of 30.5 wt.%. After sintering and heat treatment, the demagnetization curve of the regenerated magnet is obtained. Detailed Implementation

[0019] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the following embodiments.

[0020] Example 1

[0021] According to the test results, the oil-based chip sludge waste contains Nd2Fe. 14 The mixture contained substances such as boron (B) and Nd₂O₃, with a rare earth content of 27.2 wt.%, no heavy rare earth elements, an oxygen content of 4.73 wt.%, and a saturation magnetization of 98.2 emu / g. 500g of the sludge was poured into a three-necked flask containing a cleaning agent consisting of 5L anhydrous ethanol and 30ml Op-10 emulsifier. The flask was continuously stirred for 20 minutes, and this process was repeated twice. Then, 5L of a 0.5 vol.% hydrochloric acid-ethanol solution was added and stirred for 5 minutes, repeating this process three times. The resulting purified sludge (i.e., purified magnetic powder, the same in the following examples) had an oxygen content of approximately 0.7 wt.% and a rare earth content of 26.6 wt.%. The purified sludge (i.e., purified magnetic powder, the same in the following examples) was then fixed at 50 wt.%, and the composition was adjusted by using neodymium iron boron air jet milling and specific rare earth additives such as Nd₄Fe₂O₃. 14 The proportion of B is used to change the overall rare earth content of the mixed magnetic powder used to prepare the regenerated magnet, wherein the rare earth content of the original NdFeB air jet mill powder is 30 wt.% and the rare earth content of the specific rare earth additive is 41.5 wt.%.

[0022] This embodiment utilizes this method to prepare three types of regenerated sintered magnets.

[0023] The first type consists of 50 wt.% purified sludge (i.e., purified magnetic powder, the same in the following examples), 36 wt.% neodymium iron boron air jet milling, and 14 wt.% specific rare earth additives, thereby obtaining regenerated mixed magnetic powder with a rare earth content of 30 wt.%.

[0024] The second type is a regenerated mixed magnetic powder with a rare earth content of 30.5 wt.% obtained by adding 50 wt.% purified sludge (i.e., purified magnetic powder, the same in the following examples) to neodymium iron boron air jet milling 30 wt.% and specific rare earth additives 18 wt.%.

[0025] The third type consists of 50 wt.% purified sludge (i.e., purified magnetic powder, the same in the following examples), 25 wt.% neodymium iron boron air jet milling, and 25 wt.% specific rare earth additives, to obtain regenerated mixed magnetic powder with a rare earth content of 31 wt.%.

[0026] Then, the powder is mixed, sintered, and heat-treated. Next, the sintering process of the NdFeB magnet is carried out, with the heat treatment conditions being sintering at 1080℃ / 3h, first-stage heat treatment at 900℃ / 3h, and second-stage heat treatment at 500℃ / 3h. The magnetic properties of the resulting regenerated sintered magnets are shown in the table below.

[0027] Example 2

[0028] The purified sludge was derived from multi-wire cutting sludge. Tests revealed that the sludge contained Nd₂Fe₂. 14 The material contains boron (B) and Nd₂O₃, with a rare earth content of 27.5 wt.% and 0.5-1 wt.% heavy rare earth elements, an oxygen content of 4.23 wt.%, and a saturation magnetization of 122.2 emu / g. The sludge was cleaned three times with hydrochloric acid-ethanol solution, resulting in purified sludge with an oxygen content of approximately 0.68 wt.% and a rare earth content of 26.5 wt.%. The original NdFeB air-milled powder contained 29.5 wt.% rare earth elements, and the specific rare earth additive contained 41.5 wt.% rare earth elements. The powder was then mixed, sintered, and heat-treated for reference. This embodiment utilizes this method to prepare three types of regenerated sintered magnets. The first type consists of 50 wt.% purified sludge, 36 wt.% NdFeB air-milled powder, and 14 wt.% specific rare earth additives, resulting in regenerated mixed magnetic powder with a rare earth content of 30 wt.%.

[0029] The second type is a regenerated mixed magnetic powder with a rare earth content of 30.5 wt.% obtained by adding 50 wt.% purified sludge, 30 wt.% neodymium iron boron air jet milling, and 18 wt.% specific rare earth additives.

[0030] The third type consists of 50 wt.% purified sludge, 24 wt.% neodymium iron boron air jet milling, and 26 wt.% specific rare earth additives, resulting in regenerated mixed magnetic powder with a rare earth content of 31 wt.%.

[0031] Example 3

[0032] The purified sludge was derived from double-sided mill sludge. This sludge waste had a rare earth content of 27.8 wt.%, contained 1-2 wt.% heavy rare earth elements, had an oxygen content of 3.23 wt.%, and a saturation magnetization of 110.2 emu / g. The purified sludge obtained after hydrochloric acid and ethanol treatment had an oxygen content of 0.72 wt.% and a rare earth content of 26.8 wt.%. The purified sludge content was then fixed at 50 wt.%, and the overall rare earth content of the mixed magnetic powder used to prepare the regenerated magnet was changed by adjusting the ratio of NdFeB air jet mill powder and specific rare earth additives. The NdFeB air jet mill powder had a rare earth content of 30 wt.%, and the specific rare earth additives had a rare earth content of 41.5 wt.%. The powder was then mixed, sintered, and heat-treated.

[0033] This embodiment utilizes this method to prepare three types of regenerated sintered magnets for reference.

[0034] The first type consists of 50 wt.% purified sludge, 36 wt.% neodymium iron boron air jet milling, and 14 wt.% specific rare earth additives, resulting in regenerated mixed magnetic powder with a rare earth content of 30 wt.%.

[0035] The second type is a regenerated mixed magnetic powder with a rare earth content of 30.5 wt.% obtained by adding 50 wt.% purified sludge, 30 wt.% neodymium iron boron air jet milling, and 18 wt.% specific rare earth additives.

[0036] The third type consists of 50 wt.% purified sludge, 23 wt.% neodymium iron boron air jet milling, and 27 wt.% specific rare earth additives, resulting in regenerated mixed magnetic powder with a rare earth content of 31 wt.%.

[0037] Table 1. Overview of Magnetic Properties and Performance Recovery Rate of Regenerated Magnets

[0038]

Claims

1. A short-process engineered recycling method for sintered NdFeB sludge, characterized in that, Includes the following steps: (1) Add the obtained sludge to a specific cleaning agent and stir. After stirring for a period of time, use an electromagnet to perform magnetic separation to separate the neodymium iron boron magnetic powder from the non-magnetic impurities. Change the cleaning agent and repeat stirring, cleaning, magnetic separation to obtain cleaner magnetic powder and non-magnetic substances. Repeat the above process of changing the cleaning agent, stirring, and magnetic separation multiple times. (2) The magnetic powder obtained in step (1) is added to an acidic solution of a certain concentration and stirred and washed for a period of time to remove most of the oxides, thereby reducing the overall oxygen content of the magnetic powder and obtaining purified magnetic powder; the acidic solution is hydrochloric acid ethanol solution. The sludge was repeatedly treated with hydrochloric acid solution; the hydrochloric acid concentration was between 0.5% and 2% by mass, and the stirring and washing time was between 10 and 30 minutes. The number of acid treatments and purification effects for different types of sludge are as follows: In the initial state, the X50 of untreated sludge was between 4.8 and 5.1 μm, the rare earth content was between 27.1 and 27.5 wt.%, the oxygen content was between 4.5 and 4.9 wt.%, the carbon content was between 1.45 and 1.7 wt.%, and the magnetic properties were between 97 and 99 emu / g. After one alkali treatment and three acid treatments, the X50 was between 2.9 and 3.2 μm, the rare earth content was between 26.3 and 26.8 wt.%, the oxygen content was between 0.5 and 0.6 wt.%, the carbon content was between 0.1 and 0.2 wt.%, and the magnetic properties were between 130 and 135 emu / g. (3) The purified magnetic powder obtained in step (2) is remixed into a mixed powder with similar particle size and containing original NdFeB powder and specific rare earth additives. The particle size of the powder and the rare earth additives is adjusted by adjusting the air jet mill process. After mixing by a mixer, a uniformly distributed regenerated mixed NdFeB powder is obtained. The original NdFeB powder is selected from: the air jet mill powder corresponding to the NdFeB magnets that produced the sludge in step (1). The specific additives are one or more of the following specific rare earth additives: (Re)nFe14B, (Re)nX, where n can take any positive value and X is a metal or non-metal element. (4) After the uniformly mixed NdFeB powder obtained in step (3) is subjected to orientation pressing and isostatic pressing in sequence, it is then subjected to sintering and heat treatment in sequence to obtain a regenerated sintered magnet; Step (1) The cleaning agent is selected from any one or at least a combination of two or more of the following: aqueous solution of OP emulsifier, ethanol solution of OP emulsifier, methanol solution of OP, and acetone solution of OP. Step (3) The mass percentage of purified magnetic powder in the regenerated mixed NdFeB powder, i.e. the re-doping ratio, is greater than 0 and less than 60%. Then, by adjusting the ratio of the original NdFeB powder and specific rare earth additives, the overall rare earth content is adjusted so that the rare earth content in the regenerated mixed NdFeB powder is 30-35 wt.%.

2. The method according to claim 1, characterized in that, In step (3), n is 4 and Re = Nd.

3. The method according to claim 1, characterized in that, Step (1) The used cleaning agent is recycled and reused through a traditional distillation process.

4. The method according to claim 1, characterized in that, In step (3), additional lubricants and antioxidants are added to the regenerated mixed NdFeB powder.

5. The method according to claim 1, characterized in that, Step (4) Sintering process: sintering temperature between 1020-1100℃, sintering time between 2-5h; The heat treatment process involves a primary heat treatment temperature between 880-980℃ and a heat treatment time of 2-8 hours, and a secondary heat treatment temperature between 420-560℃ and a heat treatment time of 2-7 hours.

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