A method for recycling low-cost neodymium-iron-boron magnetic sludge

Abstract

The application provides a low-cost method for recycling neodymium-iron-boron magnetic sludge, which comprises the following steps: adding a reducing agent, a diffusion medium and an optional rare earth supplement into pretreated neodymium-iron-boron sludge to form raw materials, and then sequentially performing high-energy ball milling treatment, annealing treatment and cleaning treatment on the raw materials to obtain regenerated neodymium-iron-boron magnetic powder; the reducing agent comprises lanthanum hydride and / or cerium hydride; the diffusion medium comprises one or more of CaCl2 and KCl; and the rare earth supplement is REH x Lanthanum hydride and / or cerium hydride are used as the reducing agent, and the annealing temperature is reduced through high-energy ball milling treatment, so that a neodymium-iron-boron single phase can be obtained; the recycling method has the advantages of low annealing treatment temperature and the like, and the cost of recycling the neodymium-iron-boron sludge is effectively reduced.

Description

Technical Field

[0001] This application relates to the technical field of industrial waste recycling and reuse, and in particular to a low-cost method for recycling neodymium iron boron magnetic mud. Background Technology

[0002] Sintered NdFeB permanent magnets, due to their excellent comprehensive magnetic properties such as extremely high energy product, coercivity, and remanence, have become indispensable key functional materials in modern high-tech industries, widely used in new energy vehicle drive motors, wind turbines, industrial robots, and electronic information, among many other fields. As the largest application product of rare earth elements, its global production has continued to grow significantly, reflecting the strong demand brought about by the clean energy transition and the development of high-end manufacturing. However, its production process generates industrial solid waste accounting for approximately 30% of the total raw materials, of which about 77% is oily sludge waste with a special form and high processing difficulty. This type of waste has a complex composition, rich in about 30 wt.% rare earth elements, and is a secondary resource with high recycling value. Failure to achieve efficient recycling and reuse will not only result in a serious waste of precious strategic rare earth resources but also exacerbate environmental burdens and restrict the sustainable development of the industrial chain. Therefore, conducting research on green and efficient recycling technologies for sintered NdFeB oily sludge waste is of great strategic significance for ensuring national rare earth resource security and promoting the development of a circular economy.

[0003] Currently, recycling technologies for sintered NdFeB sludge waste can be broadly categorized into two types based on their principles and objectives: extraction-based recycling and in-situ regeneration-based recycling. Extraction-based recycling, represented by hydrometallurgical methods, is a traditional process. Its technical route typically involves extracting single rare earth metals from the sludge waste through processes such as acid dissolution, extraction separation, precipitation, and electrolysis, followed by the reprocessing of sintered NdFeB magnets using powder metallurgy. The other type is in-situ regeneration-based recycling, represented by the calcothermal reduction diffusion method. This technology aims to remove harmful impurities (such as oxygen) from the sludge waste, directly obtaining recycled NdFeB magnetic powder for magnet production. In comparison, the calcothermal reduction diffusion method, as an emerging process, exhibits significant advantages in terms of shorter process flow and synergistic recovery of all elements.

[0004] While existing recycling technologies offer pathways for the resource utilization of NdFeB waste, several significant limitations and challenges remain. Hydrometallurgical processes are lengthy and complex, involving the use of large quantities of chemical reagents, which can easily generate secondary pollution and are not environmentally friendly; their economic efficiency and resource efficiency also need improvement. As for the more promising calcothermic reduction diffusion method, it faces challenges due to the relatively excessive market capacity for lanthanum and cerium, and the high price of metallic calcium as a reducing agent. This significantly increases the cost of recycling NdFeB sludge, severely restricting the large-scale industrial application and economic feasibility of this technology. Summary of the Invention

[0005] To address the problems existing in the background technology, this application provides a low-cost method for recycling NdFeB magnetic sludge, which solves the problem of high cost in the process of recycling NdFeB sludge.

[0006] The specific details of the invention are as follows: This application provides a low-cost method for recycling neodymium iron boron magnetic mud, the method comprising the following steps: A reducing agent, a diffusion medium, and optional rare earth supplements are added to pretreated NdFeB sludge to form a raw material. The raw material is then subjected to high-energy ball milling, annealing, and cleaning treatment in sequence to obtain regenerated NdFeB magnetic powder. The reducing agent includes: lanthanum hydride and / or cerium hydride; The diffusion medium includes: CaCl2 and / or KCl; The rare earth supplement is REH. x .

[0007] Optionally, by weight, the raw materials include 65-90 parts of the pretreated NdFeB sludge, 15-35 parts of the reducing agent, 1-10 parts of the diffusion medium, and 0-5 parts of the rare earth supplement.

[0008] Optionally, the rare earth metal in the recycled NdFeB magnetic powder is 25wt.%~32wt.%.

[0009] Optionally, the high-energy ball mill has a voltage of 50~110 V, a milling time of 1~10 h, and a ball-to-material ratio of 1:10~1:30.

[0010] Optionally, the annealing process includes: The raw material is subjected to high-energy ball milling and then annealed in a high vacuum environment. The annealing temperature is 800 ℃~1100 ℃, the heating rate is 5 ℃ / min~10 ℃ / min, and the holding time is 1 h~5 h.

[0011] Optionally, the NdFeB sludge is pretreated by sequentially placing it in anhydrous ethanol, NaOH-anhydrous ethanol solution, and anhydrous ethanol, and then dried to obtain the pretreated NdFeB sludge; the NaOH-anhydrous ethanol solution includes an emulsifier.

[0012] Optionally, the solid-liquid ratio of the NdFeB sludge to the anhydrous ethanol is 1:5 to 1:10, and the solid-liquid ratio of the NdFeB sludge to the NaOH-anhydrous ethanol solution is 1:2 to 1:8.

[0013] Optionally, in the NaOH-anhydrous ethanol solution, the concentration of NaOH is 0.3 wt.% to 2 wt.%, and the concentration of the emulsifier is 1 wt.% to 5 wt.%.

[0014] Optionally, the oxygen content in the pretreated NdFeB sludge is 20,000 ppm to 60,000 ppm.

[0015] Optionally, the cleaning process includes: The annealed raw material was sequentially washed in an ice water compound, an acidic aqueous solution, and anhydrous ethanol until the pH of the solution was neutral. The solid-liquid ratio of the annealed raw material to the acidic aqueous solution was 1:30 to 1:60, and the concentration of acid in the acidic aqueous solution was 0.5 wt.% to 2 wt.%.

[0016] Compared with the prior art, this application has the following advantages: This application provides a low-cost method for recycling NdFeB magnetic sludge. The method involves adding a reducing agent, a diffusion medium, and optional rare earth supplements to pretreated NdFeB sludge to form a raw material. The raw material is then subjected to annealing and washing processes to obtain regenerated NdFeB magnetic powder. The reducing agent includes lanthanum hydride and / or cerium hydride; the diffusion medium includes CaCl2 and / or KCl; and the rare earth supplement is REH2O. x By using lanthanum hydride and / or cerium hydride as reducing agents and supplementing with high-energy ball milling to lower the annealing temperature, the reduction effect of NdFeB sludge can be achieved, ultimately obtaining NdFeB single-phase sludge. This recovery method not only solves the problem of overcapacity of cerium and lanthanum rare earth elements, but also, compared to conventional methods using calcium as a reducing agent for NdFeB sludge recovery, offers advantages such as lower annealing temperature and shorter processing time; furthermore, it effectively reduces the cost of NdFeB sludge recovery, making it more suitable for large-scale industrial production and providing a new approach for future sludge recovery. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 The image shown is a SEM image of the recycled NdFeB magnetic powder provided in Embodiment 1 of this application; Figure 2 The XRD patterns of the recycled NdFeB magnetic powder and the original sludge provided in Example 1 and the comparative example of this application are shown. Figure 3The VSM diagram of the regenerated NdFeB magnetic powder provided in Embodiment 1 of this application is shown. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its application or use. Based on the embodiments of this application, any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the protection scope of this application. Furthermore, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this application.

[0020] Specific experimental steps or conditions are not specified in the embodiments; they can be performed according to the conventional experimental steps or conditions described in the prior art. Reagents and other instruments used, unless otherwise specified, are all commercially available conventional reagent products. Furthermore, the accompanying drawings are merely illustrative diagrams of the embodiments of this application and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore, repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0021] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of this application specification.

[0022] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0023] This application provides a low-cost method for recovering NdFeB magnetic sludge. The method uses lanthanum hydride and / or cerium hydride as reducing agents, and achieves the reduction and recovery of NdFeB sludge through reduction diffusion under vacuum heating conditions; rare earth hydrides (such as LaH2O) are also used. x In the crystal structure of La x+ With H -Due to their ionic bonding, rare earth hydride crystals exhibit superior lattice vibration and ion migration capabilities compared to metallic calcium or metallic lanthanum / cerium under the same temperature conditions. Therefore, rare earth hydrides can induce reduction reactions of oxidized metals in NdFeB sludge under milder vacuum heat treatment conditions. This means that at the same reaction temperature, the reaction rate is faster when using lanthanum hydride or cerium hydride as reducing agents. On the other hand, the H2 generated by the decomposition of rare earth hydrides forms microbubble flows inside the reactants. The disturbance of the airflow reduces the agglomeration of NdFeB sludge at high temperatures, thereby improving the reduction reaction efficiency of NdFeB sludge.

[0024] Furthermore, the mining process of rare earth minerals reveals their symbiotic relationship; lanthanum and cerium are not mined independently but are byproducts of the separation process in rare earth deposits such as bastnaesite, resulting in marginal costs approaching zero. This avoids the additional capital and energy investment required for the entire limestone calcination-molten salt electrolysis process necessary for calcium extraction. Moreover, the waste heat and byproduct steam from La electrolysis in the combined plant can be reused, making the use of lanthanum hydride / cerium hydride as a reducing agent even more economically viable.

[0025] The specific embodiments of the present invention are described below: This application provides a low-cost method for recycling neodymium iron boron magnetic mud, the method comprising the following steps: A reducing agent, a diffusion medium, and optional rare earth supplements are added to pretreated NdFeB sludge to form a raw material. The raw material is then subjected to high-energy ball milling, annealing, and cleaning to obtain regenerated NdFeB magnetic powder. The reducing agent includes: lanthanum hydride and / or cerium hydride; The diffusion medium includes: CaCl2 and / or KCl; The rare earth supplement is REH. x .

[0026] This application uses lanthanum hydride and / or cerium hydride as reducing agents to reduce these oxides to metallic elements or low-valence available states through electron transfer, laying the foundation for the subsequent reconstruction of the NdFeB phase and avoiding the degradation of product performance caused by the residual rare earth elements in oxide form.

[0027] The diffusion medium includes CaCl2 and / or KCl; the raw material form of NdFeB sludge (mostly fine particles and flocculents) has the problem of uneven composition. The function of the above diffusion medium is to promote the uniform distribution of each element (Nd, Fe, B, etc.) by reducing atomic diffusion resistance or providing diffusion channels, so as to ensure that the reduction product forms a stable crystal structure.

[0028] It should also be noted that when selecting rare earth supplements, since neodymium is lost the most and accounts for the largest proportion in neodymium iron boron sludge, neodymium hydride can be preferred as a rare earth supplement.

[0029] It should also be noted that the reducing agent used in this application is cerium hydride or lanthanum hydride. Therefore, the recovered NdFeB sludge is particularly suitable for NdFeB sludge produced from cerium-containing magnets.

[0030] During the pretreatment of NdFeB sludge, a small amount of rare earth elements are lost due to purification, or during the reduction process, rare earth elements may volatilize (e.g., Nd has a low boiling point and is easily lost at high temperatures), or react with impurities (e.g., with Cl in the dispersant). - The formation of NdOCl leads to insufficient rare earth content; while sintered NdFeB magnets have extremely high requirements for the content of rare earth (such as Nd) (the rare earth content accounts for about 26-32 wt.%). Rare earth supplements can accurately replenish the missing rare earth elements and ensure that the final magnetic powder composition meets the standards for magnet preparation.

[0031] In this embodiment, by using lanthanum hydride and / or cerium hydride as reducing agents, no new impurities are introduced during the reduction and recovery of NdFeB sludge. Furthermore, the annealing temperature is lowered through high-energy ball milling, allowing for the acquisition of NdFeB single-phase sludge. This recovery method, using lanthanum hydride and / or cerium hydride as reducing agents, can help address the problem of overcapacity in cerium and lanthanum rare earth elements. Simultaneously, compared to conventional methods using calcium as a reducing agent for the reduction and recovery of NdFeB sludge, this method offers advantages such as lower annealing temperature and shorter processing time. It also effectively reduces the preparation cost of recovered NdFeB sludge, making it more suitable for large-scale industrial production and providing new ideas for future sludge recovery.

[0032] In some embodiments, by weight, the raw materials comprise 65-90 parts of the pretreated NdFeB sludge, 15-35 parts of the reducing agent, 1-10 parts of the diffusion medium, and 0-5 parts of the rare earth supplement.

[0033] It should be noted that the pretreated NdFeB sludge is 65 to 90 parts. For example, the pretreated NdFeB sludge can be any one or any two of the following values: 65 parts, 68 parts, 70 parts, 72 parts, 75 parts, 77 parts, 79 parts, 80 parts, 82 parts, 85 parts, 88 parts, and 90 parts.

[0034] It should be noted that the reducing agent is 15-35 parts. For example, the reducing agent can be any one or any combination of 15, 18, 20, 22, 25, 27, 29, 30, 32, 33, and 35 parts. A reducing agent of 20-35 parts is beneficial for completely reducing oxides in the crude oil sludge, ensuring key properties of the magnet such as remanence and coercivity, while controlling costs and avoiding byproduct residues that could affect product purity.

[0035] It should be noted that the diffusion medium is 1 to 10 parts. For example, the diffusion medium can be any combination of 1, 2, 3, 5, 7, 9, and 10 parts. The diffusion medium needs to form a liquid phase at a certain temperature to encapsulate the metal particles and reduce atomic diffusion resistance. With a diffusion medium of 1 to 10 parts, the liquid phase can uniformly encapsulate the sludge particles, forming a uniform Nd₂Fe₂. 14 Phase B ensures that the diffusion medium can be easily cleaned to completely remove residual medium, thus guaranteeing the mechanical strength and magnetic properties of the magnet.

[0036] It should be noted that the rare earth supplement is 0 to 5 parts. For example, the rare earth supplement is 0, 1, 2, 3, 4, or 5 parts. If the sludge undergoes multiple pretreatments (such as acid washing to remove impurities) or long-term storage, resulting in the loss of rare earth due to volatilization and dissolution, the rare earth supplement is set at 0 to 5 parts. This is based on the maximum rare earth loss rate to ensure that the rare earth is not excessive, which would generate Nd-rich impurity phases (such as Nd4Fe2B2), thereby reducing the coercivity of the magnet. At the same time, excessive rare earth will significantly increase the raw material cost.

[0037] In this embodiment, the mass fraction range of the above-mentioned materials takes into account the characteristics of sludge, reaction requirements, product objectives, cost control, etc., and ultimately achieves stable production of regenerated magnetic powder that meets the standards for preparing magnets at the lowest cost.

[0038] In some embodiments, the rare earth metals in the recycled NdFeB magnetic powder are 25 wt.% to 32 wt.%.

[0039] It should be noted that the mass of rare earth metals in the recycled NdFeB magnetic powder is 25 wt.% to 32 wt.%, for example, it can be one or any two of the following: 25 wt.%, 26 wt.%, 27 wt.%, 28 wt.%, 29 wt.%, 30 wt.%, 31 wt.%, 32 wt.%.

[0040] In this embodiment, the rare earth metal in the recycled NdFeB magnetic powder is 25wt.%~32wt.%, which can accurately match the rare earth content requirements of the main phase of the sintered NdFeB magnet, ensuring the magnetic properties and structural stability of the recycled magnet from the source of composition.

[0041] In some embodiments, the high-energy ball mill uses a voltage of 50~110 V, a milling time of 1~10 h, and a ball-to-material ratio of 1:10~1:30.

[0042] It should be noted that the voltage of the high-energy ball mill can be any value within the range of 50V, 60V, 70V, 80V, 90V, 100V, 101V, 102V, 105V, 106V, 108V, and 110V. The ball milling time can be any value within the range of 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, and 10 h. The ball-to-material ratio can be any value within the range of 1:10, 1:15, 1:20, 1:25, and 1:30.

[0043] In this embodiment, the voltage of the high-energy ball mill is 50~110 V. High-energy ball milling can reduce the temperature of subsequent annealing by introducing crystal defects and refining the particle size. In this case, defects provide atomic diffusion paths, and fine particles reduce the recrystallization barrier and improve the reduction reaction rate.

[0044] In some embodiments, the annealing process includes: The raw material is subjected to high-energy ball milling and then annealed in a high vacuum environment. The annealing temperature is 800 ℃~1100 ℃, the heating rate is 5 ℃ / min~10 ℃ / min, and the holding time is 1 h~5 h.

[0045] It should be noted that the annealing temperature is 800℃~1100℃. For example, the annealing temperature can be any value within the range of 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, and 1100℃. The reduction in annealing temperature is also due to the use of lanthanum hydride and / or cerium hydride as reducing agents, which effectively lowers the reaction initiation threshold. Furthermore, the generated byproducts (such as La2O3) have a loose structure and do not hinder the normal progress of the reduction reaction. In contrast, using the traditional calcium reduction method, the generated byproduct CaO (melting point 2614℃) easily forms a dense oxide layer on the product surface. The encapsulation effect of CaO hinders the contact between Ca and unreacted sludge, requiring extended holding time or increased temperature to break down the barrier.

[0046] It should be noted that the heating rate is 5℃ / min to 10℃ / min. For example, the heating rate can be any one or any two of the following: 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, and 10℃ / min. A heating rate of 5℃ / min to 10℃ / min can avoid local overheating and component segregation, ensuring the uniformity of the reaction.

[0047] It should be noted that the holding time is 1 to 5 hours. For example, the holding time can be any one or a combination of 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, and 5 hours. The holding time of 1 to 5 hours ensures that the reaction proceeds fully and achieves element diffusion and phase equilibrium.

[0048] In this embodiment, the above-mentioned annealing conditions not only ensure that the oxidized metal in the raw material is efficiently reduced to the target metal phase, but also avoid side reactions and performance degradation by precisely controlling the reaction process. In the end, regenerated NdFeB magnetic powder with "high metallization rate, uniform composition and can be directly used for magnet preparation" is produced, laying the foundation for the high-performance regeneration of subsequent magnets.

[0049] In some embodiments, the neodymium iron boron sludge is pretreated by sequentially placing it in anhydrous ethanol, NaOH-anhydrous ethanol solution, and anhydrous ethanol, and then dried to obtain the pretreated neodymium iron boron sludge. The NaOH-anhydrous ethanol solution includes an emulsifier, which includes OP emulsifier (the main component of which is alkylphenol polyoxyethylene ether).

[0050] In practice, the NdFeB sludge is first placed in anhydrous ethanol and stirred continuously for 10-20 minutes. After magnetic separation, the waste liquid is poured out, and then alkaline washing is performed. The alkaline washing step uses a NaOH-anhydrous ethanol solution, and the aforementioned emulsifier is added during this process. The NdFeB sludge is stirred continuously in the NaOH-anhydrous ethanol solution for 10-20 minutes, and this step is repeated twice. After magnetic separation, the waste liquid is poured out, and then anhydrous ethanol is added again and stirred continuously for 10-20 minutes. After magnetic separation, the waste liquid is poured out, and the washed NdFeB sludge is immediately placed in a vacuum environment to dry, obtaining pretreated NdFeB sludge.

[0051] It should be noted that the core component of NdFeB sludge is NdFeB magnetic powder particles. However, due to the mixing of cutting oil, lubricating oil, rust-preventive oil, etc. during the production / recycling process, these greases will coat the magnetic powder particles and hinder subsequent reactions (such as uneven particle dispersion during ball milling and obstructed contact between the reducing agent and oxide during reduction). Treatment with anhydrous ethanol can perform preliminary degreasing and pre-cleaning.

[0052] It should be noted that NaOH, anhydrous ethanol, and emulsifier work synergistically to solve the problems of removing stubborn grease and achieving cleanliness of the magnetic powder surface. NaOH can saponify stubborn grease and neutralize acidic impurities, the emulsifier can enhance degreasing efficiency and prevent impurities from re-adhering, and anhydrous ethanol can prevent the magnetic powder from oxidizing, facilitating subsequent drying.

[0053] It should be noted that anhydrous ethanol can be used for a second rinsing process to remove residual impurities.

[0054] In this embodiment, the pretreatment process uses a combination of physical dissolution (anhydrous ethanol), chemical saponification (NaOH), interfacial emulsification (emulsifier), and drying to remove impurities and avoid interference with the subsequent reduction reaction. This exposes metal / oxide active sites on the surface of the NdFeB magnetic powder particles, creating conditions for particle refinement during subsequent high-temperature ball milling and for the contact reaction between the reducing agent and oxides during reduction, ultimately improving the rare earth recovery rate and the performance of the regenerated magnet.

[0055] In some embodiments, the solid-liquid ratio of the NdFeB sludge to the anhydrous ethanol is 1:5 to 1:10, and the solid-liquid ratio of the NdFeB sludge to the NaOH-anhydrous ethanol solution is 1:2 to 1:8.

[0056] It should be noted that the solid-liquid ratio of NdFeB sludge to anhydrous ethanol is 1:5 to 1:10. For example, the solid-liquid ratio of NdFeB sludge to anhydrous ethanol can be any one of 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10, or any combination thereof. The anhydrous ethanol here refers to the anhydrous ethanol added during the first pretreatment, i.e., the anhydrous ethanol used before the NaOH-anhydrous ethanol solution step.

[0057] It should be noted that the solid-liquid ratio of NdFeB sludge to NaOH-anhydrous ethanol solution is 1:2 to 1:8. For example, the solid-liquid ratio of NdFeB sludge to NaOH-anhydrous ethanol solution is one or any two of the following: 1:2, 1:3, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:7, 1:8.

[0058] In this embodiment, the solid-liquid ratio of NdFeB sludge to anhydrous ethanol is 1:5 to 1:10, which fully wets the sludge and dissolves free oils. At the same time, the amount of anhydrous ethanol is controlled to reduce drying energy consumption and cost. The solid-liquid ratio of NdFeB sludge to NaOH-anhydrous ethanol solution is 1:2 to 1:8, which can maintain the effective concentration of NaOH, enhance the saponification / neutralization reaction, reduce alkali adsorption, and reduce the burden of subsequent rinsing.

[0059] In some embodiments, the concentration of NaOH in the NaOH-anhydrous ethanol solution is 0.3 wt.% to 2 wt.%, and the concentration of the emulsifier is 1 wt.% to 5 wt.%.

[0060] It should be noted that the concentration of NaOH is 0.3 wt.% to 2 wt.%. For example, the concentration of NaOH can be one or any two of the following: 0.3 wt.%, 0.5 wt.%, 0.8 wt.%, 1.0 wt.%, 1.2 wt.%, 1.5 wt.%, 1.6 wt.%, 1.8 wt.%, and 2 wt.%.

[0061] It should be noted that the concentration of the emulsifier is 1 wt.% to 5 wt.%. For example, the concentration of the emulsifier can be one or any two of the following: 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, 5 wt.%.

[0062] In this embodiment, the concentration of NaOH is 0.3wt.%~2wt.%, which can saponify stubborn greases and neutralize acidic impurities; avoid corroding Nd elements and reduce the burden of subsequent rinsing; the concentration of emulsifier is 1wt.%~5wt.%, which reduces the interfacial tension between oil and ethanol, stabilizes the emulsion, avoids secondary adhesion of grease, and controls costs and residues.

[0063] In some embodiments, the oxygen content in the pretreated NdFeB sludge is 20,000 ppm to 60,000 ppm.

[0064] It should be noted that the oxygen content in the pretreated NdFeB sludge is between 20,000 ppm and 60,000 ppm. For example, the oxygen content in the pretreated NdFeB sludge can be one or any two of the following values: 20,000 ppm, 22,000 ppm, 25,000 ppm, 28,000 ppm, 30,000 ppm, 32,000 ppm, 35,000 ppm, 40,000 ppm, 50,000 ppm, and 60,000 ppm.

[0065] In this embodiment, the oxygen content in the pretreated NdFeB sludge is 20,000ppm-60,000ppm, which avoids the increased difficulty of reduction and the deterioration of magnetic properties caused by excessive oxygen content, and also avoids the increase in process cost due to excessive oxygen control.

[0066] In some embodiments, the cleaning process includes: The annealed raw material was sequentially washed in an ice water compound, an acidic aqueous solution, and anhydrous ethanol until the pH of the solution was neutral. The solid-liquid ratio of the annealed raw material to the acidic aqueous solution was 1:30 to 1:60, and the concentration of acid in the acidic aqueous solution was 0.5 wt.% to 2 wt.%.

[0067] It should be noted that the solid-liquid ratio of the annealed raw material to the acidic aqueous solution is 1:30 to 1:60. For example, the solid-liquid ratio of the annealed raw material to the acidic aqueous solution can be one or any two of the following: 1:30, 1:35, 1:40, 1:45, 1:50, 1:55, and 1:60.

[0068] It should be noted that the concentration of the acid is 0.5 wt.% to 2 wt.%, for example, the concentration of the acid can be one or any two of the following: 0.5 wt.%, 0.8 wt.%, 1.0 wt.%, 1.2 wt.%, 1.3 wt.%, 1.5 wt.%, 1.6 wt.%, 1.8 wt.%, 2 wt.%.

[0069] It should be noted that the acid in the above-mentioned acidic aqueous solution can be acetic acid, hydrochloric acid, etc., but considering safety issues, this application prefers an aqueous solution of acetic acid.

[0070] In practice, prepare an ice-water compound in advance, grind the annealed raw material into powder and sieve it through a 200-mesh sieve. Slowly pour the powder into a beaker containing the ice-water compound in small amounts several times, and ultrasonically clean it for 20-30 minutes. Place a magnet close to the beaker, and after magnetic separation, pour out the waste liquid. Then add an acetic acid aqueous solution and ultrasonically clean it for 40-60 minutes. After magnetic separation, pour out the waste liquid. Rinse with deionized water 4-6 times until the solution pH is neutral. Finally, add anhydrous ethanol solution and clean for 10-15 minutes. Pour out the waste liquid and immediately place it in a vacuum environment to dry, obtaining regenerated NdFeB magnetic powder.

[0071] The Nd and Fe in the annealed raw materials are both highly reactive metals (especially Nd, which readily reacts with air / O2 and water to form oxides at room temperature). The low-temperature environment (around 0°C) of the ice-water compound significantly reduces the reaction rate between the metals and water / air, preventing secondary oxidation of the annealed metal phase and reducing the loss of magnetic elements. Simultaneously, it rapidly dissolves and fixes impurities. Although ice water is low in temperature, it can still effectively dissolve salts and small molecule impurities. Furthermore, the low temperature prevents impurities from undergoing "dissolution-reprecipitation" due to temperature fluctuations, preventing them from re-adhering to the sludge surface. Acidic aqueous solution washing can selectively remove "insoluble oxide impurities," restoring the purity of the metal phase. Water washing to pH neutrality thoroughly deacidifies and removes residues, preventing subsequent hidden damage.

[0072] In this embodiment, the purity is improved by first solidifying impurities at low temperature to prevent oxidation, then removing insoluble oxides in an acidic environment, and finally deacidifying to maintain neutrality. This process maximizes the retention of the main phase and avoids the damage of impurities to the crystal structure and magnetic properties of the magnet. At the same time, stability is ensured by preventing secondary oxidation or corrosion of the reduction products through a low-temperature and neutral environment, thus ensuring that subsequent processes can proceed stably and ultimately producing regenerated NdFeB magnetic powder that meets the performance requirements.

[0073] To enable those skilled in the art to better understand this application, the following embodiments will be used to provide a detailed description of a low-cost method for recycling neodymium iron boron magnetic mud.

[0074] The present application will be described in detail below through embodiments.

[0075] Example 1 The sludge was pretreated by taking 6.62g of pretreated NdFeB sludge, 2.65g of reducing agent cerium hydride, 0.40g of diffusion medium CaCl2, and 0.33g of rare earth supplement NdFeB, and mixing them to form raw materials. The raw materials were placed in a stainless steel ball mill jar filled with argon and ball-milled at 110V for 4 hours. The ball-milled raw materials were placed in a cemented carbide container and pressed into blocks by a cold press at a pressure of 15MPa. The blocks were placed in a stainless steel crucible, and the crucible was placed in a tube furnace and evacuated to a vacuum state. The furnace was heated to 900℃ at a heating rate of 10℃ / min for annealing and held at that temperature for 180min. After the process was completed, the tube furnace was cooled to room temperature and then cleaned to obtain regenerated NdFeB magnetic powder.

[0076] Example 2 The difference between Example 2 and Example 1 is as follows: The reducing agent was adjusted to a mixture of 2.65 g of cerium hydride and lanthanum hydride, with a mass ratio of cerium hydride to lanthanum hydride of 8:2.

[0077] The other steps and dosages are the same as in Example 1, to obtain recycled NdFeB magnetic powder.

[0078] Example 3 The difference between Example 3 and Example 1 is as follows: The masses of the pretreated NdFeB sludge, reducing agent, diffusion medium, and rare earth supplement were adjusted to 6.80 g, 2.38 g, 0.48 g, and 0.34 g, respectively.

[0079] The other steps and dosages are the same as in Example 1, to obtain recycled NdFeB magnetic powder.

[0080] The oxygen content in the pretreated NdFeB sludge obtained in Examples 1-3 during the pretreatment step was between 20,000 ppm and 60,000 ppm, and the mass of rare earth metals in the regenerated NdFeB magnetic powder obtained in Examples 1-3 was between 25 wt.% and 32 wt.%.

[0081] Comparative Example 1 Regenerated NdFeB magnetic powder was prepared using the same process as in Example 1, except that the reducing agent in the annealing process was metallic cerium.

[0082] Comparative Example 2 Regenerated NdFeB magnetic powder was prepared using the same process as in Example 1, except that the reducing agent in the annealing process was lanthanum metal.

[0083] Comparative Example 3 Regenerated NdFeB magnetic powder was prepared using the same process as in Example 1, except that high-energy ball milling was not performed before annealing.

[0084] The regenerated powders obtained in Example 1 and the comparative example were characterized, and the results are as follows: Figure 1 The microstructure of the regenerated magnetic powder obtained by annealing cerium hydride in oil sludge is shown.

[0085] Figure 2 The XRD patterns of the recycled NdFeB magnetic powder and the original sludge provided in Example 1 and the comparative example of this application are shown; Figure 2 As shown, Example 1 (i.e. Figure 2 The regenerated NdFeB magnetic powder obtained by (labeled as cerium hydride) exhibits a sharper peak shape and higher peak intensity, indicating that a single-phase NdFeB has been synthesized. In contrast, Comparative Example 1, using metallic cerium as a reducing agent (i.e., Figure 2 The XRD results obtained (labeled as metallic cerium) showed that when the reducing agent was metallic cerium, NdFeB single-phase could not be obtained; furthermore, Comparative Example 3, without high-energy ball milling at a lower annealing temperature (i.e., Figure 2 The XRD results obtained (marked as 900℃ without ball milling) show that the NdFeB single phase of this application could not be obtained when the processing conditions were 900℃ without high-energy ball milling.

[0086] in accordance with Figure 2 The results show that NdFeB single-phase NdFeB can only be obtained using the preparation method of this application when the reducing agent is cerium hydride and / or lanthanum hydride, i.e., hydrides. Furthermore, high-energy ball milling can reduce the annealing temperature.

[0087] It should be noted that the XRD patterns obtained in Examples 2 and 3 are similar to those in Example 1 and will not be shown again; when using lanthanum metal as a reducing agent in Comparative Example 2, the XRD pattern obtained is similar to that obtained in Comparative Example 1 using cerium metal as a reducing agent and will not be shown again.

[0088] Figure 3 This indicates that Example 1 yielded recycled NdFeB magnetic powder M. 3T The value was 160.1 emu / g. The regenerated NdFeB magnetic powder obtained in the other examples and... Figure 3 Similarly, M 3T All values ​​were between 130 and 160.1 emu / g, and will not be repeated here.

[0089] In summary, this application uses lanthanum hydride and / or cerium hydride as reducing agents to recover sintered NdFeB sludge, which can achieve significant results. After high-energy ball milling, NdFeB single phase can be obtained at a relatively low temperature.

[0090] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0091] For the sake of simplicity, the method embodiments are described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to this application. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and components involved are not necessarily essential to this application.

[0092] The above provides a detailed description of a low-cost method for recycling neodymium iron boron magnetic mud. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and its core ideas. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A low-cost method for recycling neodymium iron boron magnetic mud, characterized in that, The method includes the following steps: A reducing agent, a diffusion medium, and rare earth supplements are added to pretreated NdFeB sludge to form a raw material. The raw material is then subjected to high-energy ball milling, annealing, and cleaning treatment in sequence to obtain regenerated NdFeB magnetic powder. The reducing agent includes: lanthanum hydride and / or cerium hydride; The diffusion medium includes: CaCl2 and / or KCl; The rare earth supplement is REH. x .

2. The method according to claim 1, characterized in that, By weight, the raw materials comprise 65-90 parts of the pretreated NdFeB sludge, 15-35 parts of the reducing agent, 1-10 parts of the diffusion medium, and 1-5 parts of the rare earth supplement.

3. The method according to claim 1, characterized in that, The rare earth metal in the recycled NdFeB magnetic powder is 25wt.%~32wt.%.

4. The method according to claim 1, characterized in that, The high-energy ball mill operates at a voltage of 50-110 V, a milling time of 1-10 h, and a ball-to-material ratio of 1:10-1:

30.

5. The method according to claim 1, characterized in that, The annealing process includes: The raw material is subjected to high-energy ball milling and then annealed in a high-vacuum environment. The annealing temperature is 800 ℃~1100 ℃, the heating rate is 5℃ / min~10℃ / min, and the holding time is 1 h~5 h.

6. The method according to claim 1, characterized in that, The neodymium iron boron sludge was pretreated by sequentially placing it in anhydrous ethanol, NaOH-anhydrous ethanol solution, and anhydrous ethanol, and then dried to obtain the pretreated neodymium iron boron sludge; the NaOH-anhydrous ethanol solution contained an emulsifier.

7. The method according to claim 6, characterized in that, The solid-liquid ratio of the NdFeB sludge to the anhydrous ethanol is 1:5 to 1:10, and the solid-liquid ratio of the NdFeB sludge to the NaOH-anhydrous ethanol solution is 1:2 to 1:

8.

8. The method according to claim 7, characterized in that, In the NaOH-anhydrous ethanol solution, the concentration of NaOH is 0.3 wt.% to 2 wt.%, and the concentration of the emulsifier is 1 wt.% to 5 wt.%.

9. The method according to any one of claims 6 to 8, characterized in that, The oxygen content in the pretreated NdFeB sludge is 20,000 ppm to 60,000 ppm.

10. The method according to claim 1, characterized in that, The cleaning process includes: The annealed raw material was sequentially washed in an ice-water mixture, an acidic aqueous solution, and anhydrous ethanol until the pH of the solution was neutral. The solid-liquid ratio of the annealed raw material to the acidic aqueous solution was 1:30 to 1:60, and the concentration of acid in the acidic aqueous solution was 0.5 wt.% to 2 wt.%.

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