A method for recycling NdFeB waste

Abstract

The invention discloses a method for recovering NdFeB waste, and the steps are as follows: (1) pre-treating and crushing NdFeB waste; (2) heat-treating the crushed magnetic powder under a reducing atmosphere; (3) using the heat-treated magnetic powder as an anode, a graphite rod or a Pt wire as a cathode, and an aqueous solution containing 0.5M NaCl and 1-3M NaH2PO4 and adjusting the pH to 4-5 using 1M H3PO4 as an electrolyte for anodic oxidation, and using 1M H3PO4 to maintain the pH stability of the electrolyte during the reaction; (4) filtering the electrolyte after the reaction, recovering the precipitate and washing it to neutrality. The method for recovering NdFeB waste provided by the invention has the characteristics of being green, simple, and low in cost. By treating the NdFeB waste, effective leaching and separation of neodymium is achieved, the working voltage is low, and it is safe and energy-saving. It effectively solves the problem that low-conductivity NdFeB waste is difficult to be anodic oxidized and has high energy consumption, has a high reaction speed, and can achieve large-scale industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of resource recovery and environmental protection, and specifically relates to a method for recovering NdFeB waste. The method can realize rapid separation and recovery of rare earth metals in NdFeB waste, and has high economic value and environmental benefits. Background Art

[0002] Compared with other permanent magnet materials, NdFeB permanent magnets have excellent magnetic properties such as high magnetic energy product and high coercive force. At the same time, they also take into account the qualities of high cost performance, small size, and corrosion resistance. They are widely used in modern industrial fields such as automobiles, motors, and wind power generation. NdFeB permanent magnets contain about 1% boron, about 60% iron, and about 30% rare earth elements. In the production and processing of NdFeB permanent magnets, the utilization rate of raw materials is only about 75%, which will produce a large amount of waste. The sintering process of NdFeB is long, and the product quality requirements are high, and the product is easy to oxidize and crack, which makes the product easy to scrap. Waste or waste products are inevitably generated in each link of the entire process. NdFeB waste is directly discharged into the environment without treatment, which will cause great damage to the environment. NdFeB waste contains a variety of heavy metal elements. Extensive landfill methods for solid waste disposal will lead to excessive heavy metals in soil and water. With the cycle of the ecosystem, heavy metals will eventually be enriched in humans, animals and soil, causing potential impacts on human health. At the same time, the valuable metals contained in NdFeB waste have extremely high economic value. Therefore, it is very necessary to comprehensively utilize NdFeB waste resources. At present, the recovery of rare earths in NdFeB waste has also become the focus of rare earth production companies.

[0003] The recycling of NdFeB waste is usually divided into two directions: one is to separate and extract various elements in NdFeB waste, especially rare earth elements, to prepare oxides or other compounds with a certain purity, which are used as raw materials in different fields; the other is to use waste to prepare NdFeB magnets or other products with certain functions, such as preparing regenerated sintered magnets, wave absorbing materials, etc. The extraction of waste elements can be divided into two types: wet recovery and pyrometallurgical recovery. The wet recovery process uses acid as a leaching agent to separate rare earth elements from rare earth and transition metal solutions through precipitation, solvent extraction, ion exchange or ionic liquid technologies, and obtains a single rare earth oxide after roasting. For example, CN111439773A discloses a method for recovering rare earth oxides from rare earth oxide waste residues, which completes the recovery of rare earth oxides through four steps of oxidative roasting and crushing and grinding, concentrated sulfuric acid dissolution, oxalic acid precipitation, precipitation incineration and solution treatment. The wet recycling process of NdFeB waste is relatively mature and is suitable for various sources and types of magnet waste. It mainly includes hydrochloric acid full dissolution method, hydrochloric acid excellent dissolution method, double salt precipitation method, and oxalate precipitation method. This method has strong adaptability to raw materials, high rare earth recovery rate and product purity, and high recovery rate, but the process is long, and the waste acid and waste liquid produced will also bring certain environmental problems. The pyrometallurgical recovery process uses sufficient reaction kinetic conditions at high temperature to change the element occurrence state in the material through metallurgical physical and chemical reactions, thereby extracting valuable metals. The pyrometallurgical process has become the main treatment method for rare earth recovery and utilization in foreign NdFeB waste in recent years because of its large processing capacity, short process and low pollution. However, the pyrometallurgical recovery rate is low, the energy consumption is high, and the material quality has high requirements. It is suitable for waste with a light degree of oxidation. Its products are basically mixed rare earth products, which need further separation and purification.

[0004] The recycling method of preparing NdFeB permanent magnets using waste materials has the advantages of being direct and efficient. For blocky waste materials with a low degree of oxidation, it can be used to prepare regenerated NdFeB permanent magnets, so that the characteristics of the complete grain boundary structure of NdFeB block waste materials can be fully utilized, and it is no longer necessary to go through the purification processes such as dissolution and separation, and it can be used to prepare magnets with a little treatment. For example, CN111370219A discloses a preparation process for the full-cycle recycling and production of new permanent magnets of NdFeB waste magnetic steel, and the preparation process includes: waste material treatment, hydrogen crushing, mixing, air flow milling, mixed powder cooling treatment, magnetic field forming, cold isostatic pressing, microwave sintering, magnetic field heat treatment and other steps. By optimizing the hydrogen crushing dehydrogenation process, the grain refinement technology of air flow milling and other processes, especially the cooling treatment adopted after the powder screening link and the microwave high temperature sintering + magnetic field aging heat treatment process adopted in the sintering link, not only the performance of the waste 38M magnetic steel is restored, but also the performance of the product is further improved. CN109192495B discloses a method for preparing a regenerated sintered NdFeB permanent magnet. The method comprises the following steps: mixing magnetic powder after surface pretreatment and crushing with heavy rare earth-rich powder in a certain mass ratio and subjecting to heat treatment, so that the heavy rare earth atoms diffuse into the surface layer of the magnetic powder to obtain modified magnetic powder; mixing high-abundance rare earth powder with modified magnetic powder in a mass ratio to obtain mixed magnetic powder; placing the mixed magnetic powder in a magnetic field with a magnetic field strength of more than 1.5T and subjecting the mixed magnetic powder to oriented pressing to prepare a compact; subjecting the compact to high-temperature sintering and tempering treatment to prepare a regenerated sintered NdFeB permanent magnet.

[0005] It can be seen that the above recovery methods all have certain limitations or certain requirements for NdFeB waste, and it is impossible to directly recycle and reuse the recovered NdFeB waste that has not been processed and classified. With the advancement of technology, it has been proposed that the use of electrochemical methods combined with extraction or other subsequent means can more effectively and environmentally friendly realize the extensive recovery of NdFeB waste. For example, CN115818692A discloses a method for separating rare earth salts from a mixed solution containing ferrous sulfate, using a mixed solution containing one or more of FeCl2, FeSO4, and Nd2(SO4)3, H3BO3 as a buffer, and HCl or H2SO4 to adjust the solution pH, and modulate to obtain an initial solution; using rare earth iron alloy waste as an anode for electrochemical leaching, recovering iron by electrodeposition, adding dilute H2SO4 during the electrochemical leaching process to keep the system pH≤2, filtering the mixed solution to remove solid insolubles, dripping dilute sulfuric acid to adjust the pH value pH≤2, and heating the neodymium element in a N2 atmosphere for crystallization recovery, but this method cannot achieve the separation of rare earth and iron during the leaching process. CN103540756A discloses a method for treating waste NdFeB materials to dissolve rare earths, which includes crushing the materials into powder, wetting, dispersing and slurrying with an electrolyte solution; then adding an oxidant to control the potential to +400-+800mV, and adding an inorganic acid to control the pH to 2.5-4.5; leaching for 30-80min at a temperature of 50-90°C; after leaching, solid-liquid separation and filter residue washing are performed; and the leachate after separating the solid leaching residue is purified, enriched and separated from the rare earths. CN112941321A discloses a method for strengthening the leaching reaction of NdFeB magnets by electrochemical anodic oxidation combined with an ionic flocculant, including: using NdFeB waste magnets as the anode of the electrolysis system, using an inert conductive material as the cathode, and performing electrolysis at room temperature, so that the rare earth and iron elements in the NdFeB waste magnets enter the solution, and the ionic flocculant moves rapidly under the electric field to promote the precipitation of metal elements and strengthen the leaching reaction. After the electrolysis is completed, the recovered product is obtained by filtration, and the electrolyte is reused in the electrolysis process. CN111154980A discloses a method for electrolytic regeneration of NdFeB waste solution, which first removes the anti-corrosion layer on the surface of the NdFeB disassembled waste, and then uses the magnetism of NdFeB to aggregate the waste into a whole and use it as the anode of the electrolysis system. During the electrolysis process, the anode dissolves, and rare earth and iron ions enter the solution. Among them, iron ions are precipitated at the cathode to become high-purity iron; rare earth elements are enriched in the electrolyte in an ionic state, and after the electrolysis is completed, the rare earth elements in the electrolyte are recovered by solvent extraction.

[0006] Electrochemical methods have great advantages over conventional wet and dry recycling methods, but they still cannot separate rare earth and iron at once, and the poor conductivity of NdFeB requires high voltage or high current density processing, which increases energy consumption. It can be seen that it is of great significance to develop a low-cost, environmentally friendly, simple and easy-to-operate electrochemical recycling method for NdFeB waste. Summary of the invention

[0007] In order to solve the defects in the prior art, the present invention provides a method for recycling NdFeB waste, which utilizes an electrochemical method to effectively recover the rare earth metal neodymium in NdFeB waste, and solves the problems of large acid and alkali consumption and serious environmental pollution in the existing wet method for recycling magnetic steel waste. The method of the present invention crushes the NdFeB waste that has been degreased, deoxidized and metal-plated to obtain a small-particle raw material, and then continues to perform reduction and demagnetization treatment on the raw material to reduce internal oxides and improve the conductivity of the particles. After that, the NdFeB waste is anodized in an electrolytic cell to oxidize the neodymium in the NdFeB waste within a specific voltage range and enter the electrolyte in the form of ions to form a precipitate. At this voltage, only a small amount of iron is present in the form of Fe 2+ The method for recovering NdFeB waste provided by the present invention is green, simple, and low-cost. By treating NdFeB waste, effective leaching and separation of neodymium is achieved. The working voltage is low, and it is safe and energy-saving. The problem of excessive internal resistance requiring high voltage or high current in conventional electrochemical separation is avoided. The method has a high reaction speed and can realize large-scale industrial production.

[0008] In order to achieve the above-mentioned invention object, the present application provides a method for recycling NdFeB waste, wherein the NdFeB waste includes but is not limited to NdFeB cutting waste, sintered blanks, unqualified products and NdFeB waste formed by pressing fragments, comprising the following steps:

[0009] (1) Pre-treating the NdFeB waste and then crushing it into magnetic powder with an average particle size in the range of 0.5 to 10 μm; the average particle size of the NdFeB waste is preferably 1 to 10 μm, such as 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, etc.; the smaller the particle size, the faster the reaction speed, but the energy required for crushing is higher. At the same time, the applicant found that when the particle size is too small, iron will react in large quantities in the electrolytic cell, resulting in an increase in anodization time and raw material demand.

[0010] (2) Place the magnetic powder in a heat treatment device, first continuously introduce argon for 5 minutes to remove the air in the device, and then continuously introduce hydrogen at a flow rate of 5 to 30 m / s. 3 / h, and heat up to 360-420℃, at which temperature the magnetism of NdFeB magnets will disappear, keep warm for 3-10h, and take out after cooling to room temperature; this step of treatment can simultaneously achieve the demagnetization of NdFeB waste and the reduction of internal oxides of NdFeB waste, thereby improving the conductivity of particles;

[0011] (3) The particles after heat treatment in step (2) are placed in a Pt bag at the anode of the electrolytic cell. The Pt bag is a metal bag made of Pt wire, and the pore size of the Pt bag is less than 0.5 μm. The purpose of adopting this setting is to facilitate the electrochemical treatment of the granular material without special molding treatment. On the other hand, since the pore size of the metal bag is smaller than the particle size of the magnetic powder, the magnetic powder cannot pass through the metal bag, thereby avoiding the contact between the magnetic powder and the cathode and the tank body during the reaction, which is beneficial to the anodic oxidation of the NdFeB waste. The cathode of the electrolytic cell is a graphite rod or a Pt wire, and the electrolyte is an aqueous solution containing 0.5M NaCl and 1-3M NaH2PO4, and the pH is adjusted to 4-5 using 1M H3PO4. When the pH is too low, Fe dissolves in large quantities and the filterability of the residue deteriorates. When the pH is high, the dissolution of rare earth neodymium slows down and the dissolution rate decreases. On the one hand, NaCl in the electrolyte acts as a conductive salt. On the other hand, the presence of Cl ions also helps the electrolytic dissolution of neodymium. NaH2PO4 can precipitate the neodymium ions leached from the electrolyte. Compared with neodymium phosphate, neodymium dihydrogen phosphate has a lower solubility. Most of the precipitates are neodymium dihydrogen phosphate, Fe 2+ No precipitation is produced; under continuous stirring conditions, the power is turned on to anodize the magnetic powder, and the stirring rate is between 200 and 1000 rpm, such as 950 rpm, 900 rpm, 850 rpm, 800 rpm, 750 rpm, 700 rpm, 600 rpm, 500 rpm, 400 rpm, 300 rpm, 200 rpm, etc., preferably 400 to 700 rpm. Within this preferred range, it is possible to ensure that the magnetic powder is fully mixed in the electrolyte, and to avoid the electrolyte overflowing out of the tank due to the vortex being too deep caused by the stirring speed being too fast; 1MH3PO4 is used during the reaction to maintain the pH stability of the electrolyte, because when the ferrous ions in the electrolyte are consumed, the cathode performs the reduction of hydrogen ions, resulting in an increase in the pH of the electrolyte, which is not conducive to the separation of neodymium. Therefore, the pH value should be adjusted downward regularly (or continuously) to maintain a stable electrolysis process. The temperature of the anodic oxidation reaction does not need to be specifically limited, and room temperature is sufficient. By anodic oxidation of the NdFeB waste material that has been specifically pretreated, neodymium is dissolved as an ion and precipitated as an anion in the electrolyte. The electrochemical treatment has simple raw materials, uses minimal chemical input, and does not produce any chemical waste output, especially no wastewater. At the same time, the electrolyte after separating and recovering neodymium can continue to be recycled. This method also allows the recovery of pure metallic iron deposited on the cathode. When the electrolytic cell is working, the anode magnetic powder is oxidized, causing the main phase Nd2Fe 14 B. A small amount of neodymium-rich phase and a small amount of Nd 1.1 The metal in the Fe4B4 phase is oxidized and leached, and the neodymium metal in the NdFeB waste is also oxidized and leached, and a small amount of metallic iron is oxidized and leached. Since the electrode potential of neodymium is lower, it is easier to lose electrons and be oxidized than metallic iron in the raw material. 3+enters the electrolyte in the form of H2PO 4- Combined to form a precipitate, the anode electrode reaction is as follows:

[0012] Nd-3e - →Nd 3+ ;

[0013] 2Nd2Fe 14 B+74H + →4Nd 3+ +28Fe 2+ +2B 3+ +37H2↑;

[0014] Fe-2e - →Fe 2+ ;

[0015] Nd 3+ +3H2PO4 - →Nd(H2PO4)3↓

[0016] Mainly composed of Nd2Fe 14 B is mainly anodic oxidation and neodymium metal oxidation, in addition, there is a small amount of iron oxidation, mainly Fe 2+ It exists in the electrolyte in the form of hydrogen ion reduction and iron reduction precipitation at the cathode. The reaction formula is as follows: Fe 2+ +2e - →Fe;

[0017] 2H + +2e - →H2↑

[0018] (4) After the reaction is completed, the electrolyte is filtered, the precipitate is recovered and washed to neutrality.

[0019] Furthermore, the pretreatment in step (1) includes mechanical grinding and / or chemical dissolution to remove the surface coating / plating, oxide layer and other contaminants of the NdFeB waste; the mechanical grinding includes at least one of ion grinding, high-pressure air flow milling, ball milling, polishing and sand blasting; the chemical dissolution is diluted acid ultrasonic treatment to remove the surface metal coating; the crushing method includes at least one of jaw crushing, hydrogen crushing, air flow milling and ball milling.

[0020] Furthermore, in step (3), the voltage of the electrolytic cell during the reaction is 0.5-1.5V vs. Ag / AgCl reference electrode, and the electrolysis time is 3-12h. If the anode voltage is too low, such as less than 0.5V, the rate of anodic oxidation leaching of neodymium and its compounds is too slow, and energy consumption increases. If the anode voltage is too high, such as exceeding 1.5V, a large amount of iron in the magnetic powder will be oxidized and enter the electrolyte, affecting the anodic oxidation leaching of neodymium, reducing the product purity and the recovery efficiency of neodymium.

[0021] Furthermore, in step (3), the pH of the system is 4 before the reaction, and the pH of the system is tested in real time during the reaction, so that the pH of the electrolyte is stabilized between 4 and 5.

[0022] Furthermore, in step (3), the electrolyte is an aqueous solution containing 0.5M NaCl, 3M NaH2PO4 and adjusted to pH 4 using 1MH3PO4, and the anodic oxidation voltage is 1-1.5V vs. Ag / AgCl reference electrode, and the time is 5-12h.

[0023] Furthermore, the filtration in step (4) is suction filtration, and the recovered neodymium is precipitated in the form of a compound in the filter residue and repeatedly rinsed with deionized water.

[0024] Furthermore, the washed precipitate is dried in an oven at 50 to 80° C. for 2 to 5 hours.

[0025] Furthermore, the method for recycling NdFeB waste comprises the following steps:

[0026] (1) Pre-treating the NdFeB waste to remove the coating / plating layer, oxide layer and other contaminants on the surface of the NdFeB waste; crushing it into magnetic powder with an average particle size of 1 to 10 μm by jaw crushing + ball milling;

[0027] (2) Place the magnetic powder in a heat treatment device, first continuously introduce argon for 5 minutes to remove the air in the device, and then continuously introduce hydrogen at a flow rate of 20 to 30 m / s. 3 / h, and heat to 380℃, keep warm for 5h, cool to room temperature and take out;

[0028] (3) placing the particles heat-treated in step (2) into an electrolytic cell anode Pt bag, wherein the Pt bag is a metal bag woven with Pt wire, the pore size of the Pt bag is less than 0.5 μm, the electrolytic cell cathode is a graphite rod or Pt wire, and the electrolyte is an aqueous solution containing 0.5 M NaCl and 3 M NaH2PO4 and adjusted to pH 4 using 1 M H3PO4; under continuous stirring, turning on the power supply, and anodizing the magnetic powder at a voltage of 1 to 1.5 V vs. Ag / AgCl, and using 1 M H3PO4 to maintain the pH of the electrolyte stable during the reaction;

[0029] (4) After the reaction is completed, the electrolyte is filtered to recover the filter residue, and the filter residue is repeatedly rinsed with deionized water until it is neutral. The washed precipitate is dried in an oven at 80° C. for 5 h.

[0030] Compared with the prior art, the technical solution of this application has the following beneficial effects:

[0031] 1. The present invention provides a new method for recycling NdFeB waste, which can be widely used in the recycling and treatment of NdFeB waste. It does not need to sort NdFeB waste, has strong adaptability to raw materials, and does not have the problems of large acid and alkali consumption and large amount of wastewater in traditional hydrometallurgical processes. By using NdFeB waste particles as anodes, controlling the material size through pre-treatment, improving the conductivity of particles through reduction heat treatment, and applying a voltage within a lower range in a specific electrolyte, the oxidation precipitation of neodymium can be achieved, which effectively solves the problem that low-conductivity NdFeB waste is difficult to be anodic oxidized and has high energy consumption. At the same time, the separation recovery rate of neodymium is high, and there is a good market prospect.

[0032] 2. The recovery method of the present invention has a short process flow, simple process conditions, low acid and alkali consumption, and no discharge of wastewater and iron-containing waste slag, which increases the recovery value of NdFeB waste, has considerable economic, social and environmental protection benefits, and meets the needs of large-scale commercial applications. DETAILED DESCRIPTION

[0033] In order to make the technical problems solved by the present invention, the technical solutions adopted and the technical effects achieved clearer, the technical solutions of the embodiments of the present invention are further described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0034] It should be noted that the reference to "embodiment" in this document means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0035] The experimental methods in the following examples are conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples are commercially available unless otherwise specified.

[0036] Example 1

[0037] A method for recycling NdFeB waste comprises the following steps:

[0038] (1) Use sandblasting + chemical dissolution to remove the coating / plating layer, oxide layer and other contaminants on the surface of NdFeB waste, and then use jaw crusher + ball milling to crush it into magnetic powder with an average particle size of 0.5-10μm;

[0039] (2) Place the magnetic powder in a heat treatment device, first continuously introduce argon for 5 minutes to remove the air in the device, and then continuously introduce hydrogen at a flow rate of 30 m / s. 3 / h, and heat to 420℃, keep warm for 10h, cool to room temperature and take out;

[0040] (3) placing the particles heat-treated in step (2) into a Pt bag at the anode of an electrolytic cell, wherein the Pt bag is a metal bag woven with Pt wires, the pore size of the Pt bag is less than 0.5 μm, the cathode of the electrolytic cell is a graphite rod, and the electrolyte is an aqueous solution containing 0.5 M NaCl and 2 M NaH2PO4 and adjusted to pH 4 using 1 M H3PO4; under continuous stirring, turning on the power supply, and anodizing the magnetic powder at a voltage of 1.5 V vs. Ag / AgCl for 5 h, and using 1 M H3PO4 to maintain the pH of the electrolyte between 4 and 5 during the reaction;

[0041] (4) After the reaction is completed, the electrolyte is filtered, the filter residue is recovered, and the filter residue is repeatedly rinsed with deionized water until it is neutral. The washed precipitate is dried in an oven at 80°C for 5 hours. The test found that the leaching rate of neodymium in NdFeB waste by this method is 97.4%, and the leaching rate of iron is 1.5%. The purity of neodymium in the product is high, and there is basically no iron.

[0042] Example 2

[0043] A method for recycling NdFeB waste comprises the following steps:

[0044] (1) Use polishing + chemical dissolution to remove the coating / plating layer, oxide layer and other contaminants on the surface of NdFeB waste, and then use hydrogen crushing + ball milling to crush it into magnetic powder with an average particle size of 1 to 5 μm;

[0045] (2) Place the magnetic powder in a heat treatment device, first continuously introduce argon for 5 minutes to remove the air in the device, and then continuously introduce hydrogen at a flow rate of 15m / s. 3 / h, and heat to 370℃, keep warm for 3h, cool to room temperature and take out;

[0046] (3) placing the particles heat-treated in step (2) into an electrolytic cell anode Pt bag, wherein the Pt bag is a metal bag woven with Pt wire, the pore size of the Pt bag is less than 0.5 μm, the electrolytic cell cathode is Pt wire, and the electrolyte is an aqueous solution containing 0.5 M NaCl and 1 M NaH2PO4 and adjusted to pH 5 using 1 M H3PO4; under continuous stirring, turning on the power supply, and anodizing the magnetic powder at a voltage of 1.0 V vs. Ag / AgCl for 10 h, and using 1 M H3PO4 to maintain the pH of the electrolyte between 4 and 5 during the reaction;

[0047] (4) After the reaction is completed, the electrolyte is filtered, the filter residue is recovered, and the filter residue is repeatedly rinsed with deionized water until it is neutral. The washed precipitate is dried in an oven at 50°C for 2 hours. The test found that the leaching rate of neodymium in NdFeB waste by this method is 96.3%, and the leaching rate of iron is 0.9%. The purity of neodymium in the product is high, and there is basically no iron.

[0048] Example 3

[0049] A method for recycling NdFeB waste comprises the following steps:

[0050] (1) Using ion milling + chemical dissolution to remove the coating / plating layer, oxide layer and other contaminants on the surface of NdFeB waste, and then using hydrogen crushing + air flow milling to crush it into magnetic powder with an average particle size of 0.5 to 3 μm;

[0051] (2) Place the magnetic powder in a heat treatment device, first introduce argon gas for 5 minutes to remove the air in the device, and then continue to introduce hydrogen at a flow rate of 5m / s. 3 / h, and heat to 360℃, keep warm for 8h, cool to room temperature and take out;

[0052] (3) placing the particles heat-treated in step (2) into an electrolytic cell anode Pt bag, wherein the Pt bag is a metal bag woven with Pt wire, the pore size of the Pt bag is less than 0.5 μm, the electrolytic cell cathode is Pt wire, and the electrolyte is an aqueous solution containing 0.5 M NaCl and 3 M NaH2PO4 and adjusted to a pH of 4.5 using 1 M H3PO4; under continuous stirring, turning on the power supply, anodizing the magnetic powder at a voltage of 0.5 V vs. Ag / AgCl for 12 h, and using 1 M H3PO4 to maintain the pH of the electrolyte between 4 and 5 during the reaction;

[0053] (4) After the reaction is completed, the electrolyte is filtered and the residue is recovered. The residue is repeatedly rinsed with deionized water until it is neutral. The washed precipitate is dried in an oven at 60°C for 4 hours. The test found that the leaching rate of neodymium in NdFeB waste by this method is 95.2%, and the leaching rate of iron is 0.7%. The purity of neodymium in the product is high and there is no iron.

[0054] Comparative Example 1

[0055] A method for recycling NdFeB waste comprises the following steps:

[0056] (1) Use polishing + chemical dissolution to remove the coating / plating layer, oxide layer and other contaminants on the surface of NdFeB waste, and then use hydrogen crushing + ball milling to crush it into magnetic powder with an average particle size of 15 to 100 μm;

[0057] (2) Place the magnetic powder in a heat treatment device, first continuously introduce argon for 5 minutes to remove the air in the device, and then continuously introduce hydrogen at a flow rate of 15m / s. 3 / h, and heat to 370℃, keep warm for 3h, cool to room temperature and take out;

[0058] (3) placing the particles heat-treated in step (2) into an electrolytic cell anode Pt bag, wherein the Pt bag is a metal bag woven with Pt wire, the pore size of the Pt bag is less than 0.5 μm, the electrolytic cell cathode is Pt wire, and the electrolyte is a dilute sulfuric acid solution containing 0.5 M NaCl and 1 M sodium sulfate with a pH of 4; under continuous stirring, turning on the power supply, anodizing the magnetic powder at a voltage of 1.0 V vs. Ag / AgCl for 10 h, and using 1 M H3PO4 to maintain the pH of the electrolyte between 4 and 5 during the reaction;

[0059] (4) After the reaction is completed, the electrolyte is filtered and the residue is recovered. The residue is repeatedly rinsed with deionized water until it is neutral. The washed precipitate is dried in an oven at 50°C for 2 hours. The test found that the leaching rate of neodymium in NdFeB waste by this method is 79.6%, while the leaching rate of iron is 42.1%. The reaction produces more gas, the purity of neodymium in the product is not high, and there are many impurities.

[0060] Comparative Example 2

[0061] A method for recycling NdFeB waste comprises the following steps:

[0062] (1) Use polishing + chemical dissolution to remove the coating / plating layer, oxide layer and other contaminants on the surface of NdFeB waste, and then use hydrogen crushing + ball milling to crush it into magnetic powder with an average particle size of 1 to 5 μm;

[0063] (2) Place the magnetic powder in a heat treatment device and continue to introduce argon for 5 minutes to remove the air in the device. Then, continue to heat the device at a flow rate of 15m / s. 3 / h continuously introduce argon and raise the temperature to 370℃, keep it at that temperature for 3h, cool it to room temperature and take it out;

[0064] (3) placing the particles heat-treated in step (2) into an electrolytic cell anode Pt bag, wherein the Pt bag is a metal bag woven with Pt wire, the pore size of the Pt bag is less than 0.5 μm, the electrolytic cell cathode is Pt wire, and the electrolyte is an aqueous solution containing 0.5 M NaCl and 1 M NaH2PO4 and adjusted to pH 5 using 1 M H3PO4; under continuous stirring, turning on the power supply, anodizing the magnetic powder at a voltage of 1.0 V vs. Ag / AgCl for 10 h, and using 1 M H3PO4 to maintain the pH of the electrolyte between 4 and 5 during the reaction;

[0065] (4) After the reaction is completed, the electrolyte is filtered and the residue is recovered. The residue is repeatedly rinsed with deionized water until it is neutral. The washed precipitate is dried in an oven at 50°C for 2 hours. The test found that the leaching rate of neodymium in NdFeB waste by this method is 47.9%, while the leaching rate of iron is 11.3%. The purity of neodymium in the product is average.

[0066] Comparative Example 3

[0067] A method for recycling NdFeB waste comprises the following steps:

[0068] (1) Use polishing + chemical dissolution to remove the coating / plating layer, oxide layer and other contaminants on the surface of NdFeB waste, and then use hydrogen crushing + ball milling to crush it into magnetic powder with an average particle size of 1 to 5 μm;

[0069] (2) Place the magnetic powder in a heat treatment device, first continuously introduce argon for 5 minutes to remove the air in the device, and then continuously introduce hydrogen at a flow rate of 15m / s. 3 / h, and heat to 370℃, keep warm for 3h, cool to room temperature and take out;

[0070] (3) hot pressing the particles after the heat treatment in step (2) to form a thin plate with a thickness of 3 mm, which is used as the anode of an electrolytic cell, wherein the cathode of the electrolytic cell is a Pt wire, and the electrolyte is an aqueous solution containing 0.5M NaCl and 1M NaH2PO4 and adjusted to pH 4 using 1M H3PO4; under continuous stirring, the power is turned on, and the magnetic powder is anodized at a voltage of 1.0V vs.Ag / AgCl for 10 hours, and 1M H3PO4 is used to maintain the pH of the electrolyte between 4 and 5 during the reaction;

[0071] (4) After the reaction is completed, the electrolyte is filtered and the residue is recovered. The residue is repeatedly rinsed with deionized water until it is neutral. The washed precipitate is dried in an oven at 50°C for 2 hours. The test found that the leaching rate of neodymium in NdFeB waste by this method is 71.2%, and the leaching rate of iron is 15.4%. The purity of neodymium in the product is high, and there is basically no iron.

[0072] Comparative Example 4

[0073] A method for recycling NdFeB waste comprises the following steps:

[0074] (1) Use polishing + chemical dissolution to remove the coating / plating layer, oxide layer and other contaminants on the surface of NdFeB waste, and then use hydrogen crushing + ball milling to crush it into magnetic powder with an average particle size of 1 to 5 μm;

[0075] (2) Place the magnetic powder in a heat treatment device, first continuously introduce argon for 5 minutes to remove the air in the device, and then continuously introduce hydrogen at a flow rate of 15m / s. 3 / h, and heat to 370℃, keep warm for 3h, cool to room temperature and take out;

[0076] (3) placing the particles heat-treated in step (2) into an electrolytic cell anode Pt bag, wherein the Pt bag is a metal bag woven with Pt wire, the pore size of the Pt bag is less than 0.5 μm, the electrolytic cell cathode is Pt wire, and the electrolyte is an aqueous solution containing 0.5 M NaCl and 1 M NaH2PO4 and adjusted to pH 5 using 1 M H3PO4; under continuous stirring, turning on the power supply, and anodizing the magnetic powder at a voltage of 2.0 V vs. Ag / AgCl for 10 h, and using 1 M H3PO4 to maintain the pH of the electrolyte between 4 and 5 during the reaction;

[0077] (4) After the reaction is completed, the electrolyte is filtered and the residue is recovered. The residue is repeatedly rinsed with deionized water until it is neutral. The washed precipitate is dried in an oven at 50°C for 2 hours. The test found that the leaching rate of neodymium in NdFeB waste by this method is 90.1%, and the leaching rate of iron is 16.3%. The purity of neodymium in the product is average, and there is a small amount of iron compounds.

[0078] Comparative Example 5

[0079] A method for recycling NdFeB waste comprises the following steps:

[0080] (1) Use polishing + chemical dissolution to remove the coating / plating layer, oxide layer and other contaminants on the surface of NdFeB waste, and then use hydrogen crushing + ball milling to crush it into magnetic powder with an average particle size of 1 to 5 μm;

[0081] (2) Place the magnetic powder in a heat treatment device, first continuously introduce argon for 5 minutes to remove the air in the device, and then continuously introduce hydrogen at a flow rate of 15m / s. 3 / h, and heat to 370℃, keep warm for 3h, cool to room temperature and take out;

[0082] (3) placing the particles heat-treated in step (2) into an electrolytic cell anode Pt bag, wherein the Pt bag is a metal bag woven with Pt wire, the pore size of the Pt bag is less than 0.5 μm, the electrolytic cell cathode is Pt wire, and the electrolyte is an aqueous solution containing 0.5 M NaCl and 1 M NaH2PO4 and adjusted to pH 4 using 1 M H3PO4; under continuous stirring, turning on the power supply, and anodizing the magnetic powder at a voltage of 1.0 V vs. Ag / AgCl for 10 h;

[0083] (4) After the reaction is completed, the electrolyte is filtered, the filter residue is recovered, and the filter residue is repeatedly rinsed with deionized water until it is neutral. The washed precipitate is dried in an oven at 50°C for 2 hours. The test found that the leaching rate of neodymium in NdFeB waste by this method is 80.2%, and the leaching rate of iron is 4.8%. The purity of neodymium in the product is low, and a large amount of iron-containing compounds exist, which need to be purified again before use.

[0084] Comparative Example 6

[0085] A method for recycling NdFeB waste comprises the following steps:

[0086] (1) Using ion milling + chemical dissolution to remove the coating / plating layer, oxide layer and other contaminants on the surface of NdFeB waste, and then using hydrogen crushing + air flow milling to crush it into magnetic powder with an average particle size of 0.5 to 3 μm;

[0087] (2) Place the magnetic powder in a heat treatment device, first introduce argon gas for 5 minutes to remove the air in the device, and then continue to introduce hydrogen at a flow rate of 5m / s. 3 / h, and heat to 360℃, keep warm for 8h, cool to room temperature and take out;

[0088] (3) placing the particles heat-treated in step (2) into an electrolytic cell anode Pt bag, wherein the Pt bag is a metal bag woven with Pt wire, the pore size of the Pt bag is less than 0.5 μm, the electrolytic cell cathode is Pt wire, and the electrolyte is an aqueous solution containing 0.5 M NaCl and 3 M NaH2PO4 and adjusted to pH 4 using 1 M H2SO4; under continuous stirring, turning on the power supply, anodizing the magnetic powder at a voltage of 0.5 V vs. Ag / AgCl for 12 h, and using 1 M H2SO4 to maintain the pH of the electrolyte between 4 and 5 during the reaction;

[0089] (4) After the reaction is completed, the electrolyte is filtered and the residue is recovered. The residue is repeatedly rinsed with deionized water until it is neutral. The washed precipitate is dried in an oven at 60°C for 4 hours. The test found that the leaching rate of neodymium in NdFeB waste by this method is 93.1%, and the leaching rate of iron is 2.3%. The purity of neodymium in the product is high and there is no iron, but part of the neodymium exists in the form of neodymium sulfate. The product still needs to be further separated and purified before use.

[0090] From the test results in the above embodiments and comparative examples, it can be seen that the NdFeB waste recovery method in this application can realize the leaching recovery of rare earth neodymium in waste NdFeB materials, the leaching rate is high and the product purity can meet industrial needs, and it can be directly used as a raw material for subsequent processing, and iron has a small amount of leaching, and is recovered again on the cathode to achieve separation from neodymium. After cleaning, crushing and reduction treatment of the present application scheme, the oxidation leaching of neodymium can be achieved at a relatively low voltage, and at the same time, only a small amount of iron is precipitated. It can be seen that the treatment scheme of the present application can effectively realize the reduction of oxidized substances in NdFeB waste, maintain the good conductivity of anode particles, and the electrolysis efficiency is high. The recovery method of the present invention does not impose any restrictions on the composition, oxygen content, etc. of NdFeB waste, and the recovery method is widely applicable. Whether it is a permanent magnet deactivated and demagnetized or waste materials such as scraps generated during manufacturing, the compounds containing rare earth elements obtained can be effectively processed and recovered, and their purity is high.

[0091] The above is a detailed description of a method for recycling NdFeB waste. The above content is a further detailed description of the present invention in combination with a specific preferred embodiment. It cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, its architecture can be flexible and can derive a series of products. Just making a few simple deductions or substitutions should be regarded as belonging to the scope of patent protection determined by the submitted claims of the present invention.

Claims

1. A method for recycling NdFeB waste, characterized in that: The following steps are involved: (1) Pre-treating NdFeB waste and then crushing it into magnetic powder with an average particle size ranging from 0.5 to 10 μm; (2) Place the magnetic powder in a heat treatment device, first continuously introduce argon for 5 minutes to remove the air in the device, and then continuously introduce hydrogen at a flow rate of 5 to 30 m / s. 3 / h, and heat to 360-420℃, keep warm for 3-10h, cool to room temperature and take out; (3) placing the particles heat-treated in step (2) into a Pt bag at the anode of an electrolytic cell, wherein the Pt bag is a metal bag woven with Pt wire, the pore size of the Pt bag is less than 0.5 μm, the cathode of the electrolytic cell is a graphite rod or a Pt wire, and the electrolyte is an aqueous solution containing 0.5 M NaCl and 1 to 3 M NaH2PO4 and adjusted to a pH of 4 to 5 using 1 M H3PO4; under continuous stirring, turning on the power supply, anodizing the magnetic powder, and using 1 M H3PO4 to maintain the pH of the electrolyte stable during the reaction; (4) After the reaction is completed, the electrolyte is filtered, the precipitate is recovered and washed to neutrality.

2. The method for recycling NdFeB waste according to claim 1, characterized in that: The pretreatment in step (1) includes mechanical grinding and / or chemical dissolution to remove the surface coating / plating layer, oxide layer and other pollutants of the NdFeB waste; the crushing method includes at least one of jaw crushing, hydrogen crushing, air flow milling and ball milling.

3. The method for recycling NdFeB waste according to claim 1, characterized in that: NdFeB waste includes but is not limited to NdFeB cutting waste, sintered blanks, rejected products and NdFeB waste formed by pressing fragments.

4. The method for recycling NdFeB waste according to claim 1, characterized in that: In step (3), the voltage of the electrolytic cell during the reaction is 0.5-1.5 V vs. Ag / AgCl reference electrode, and the electrolysis time is 3-12 h.

5. The method for recycling NdFeB waste according to claim 1, characterized in that: In step (3), the pH of the system before the reaction is 4, and the pH of the system is tested in real time during the reaction so that the pH of the electrolyte is stabilized between 4 and 5.

6. The method for recycling NdFeB waste according to claim 1, characterized in that: In step (3), the electrolyte is an aqueous solution containing 0.5M NaCl and 3M NaH2PO4, the pH of which is adjusted to 4 using 1M H3PO4, and the voltage of the anodic oxidation is 1 to 1.5V vs. Ag / AgCl reference electrode, and the time is 5 to 12h.

7. The method for recycling NdFeB waste according to claim 1, characterized in that: The filtration in step (4) is suction filtration, and the recovered neodymium is precipitated in the form of a compound in the filter residue and is repeatedly rinsed with deionized water.

8. The method for recycling NdFeB waste according to claim 7, characterized in that: The washed precipitate is dried in an oven at 50-80°C for 2-5 hours.

9. The method for recycling NdFeB waste according to claim 2, characterized in that: The mechanical grinding includes at least one of ion grinding, high-pressure airflow grinding, ball grinding, polishing, and sandblasting; the chemical dissolution is diluted acid ultrasonic treatment to remove the surface metal coating.

10. The method for recycling NdFeB waste according to claim 1, characterized in that: The steps include: (1) Pre-treating the NdFeB waste to remove the coating / plating layer, oxide layer and other contaminants on the surface of the NdFeB waste; crushing it into magnetic powder with an average particle size of 1 to 10 μm by jaw crushing + ball milling; (2) Place the magnetic powder in a heat treatment device, first continuously introduce argon for 5 minutes to remove the air in the device, and then continuously introduce hydrogen at a flow rate of 20 to 30 m / s. 3 / h, and heat to 380℃, keep warm for 5h, cool to room temperature and take out; (3) placing the particles heat-treated in step (2) into an electrolytic cell anode Pt bag, wherein the Pt bag is a metal bag woven with Pt wire, the pore size of the Pt bag is less than 0.5 μm, the electrolytic cell cathode is a graphite rod or Pt wire, and the electrolyte is an aqueous solution containing 0.5 M NaCl and 3 M NaH2PO4 and adjusted to pH 4 using 1 M H3PO4; under continuous stirring, turning on the power supply, and anodizing the magnetic powder at a voltage of 1 to 1.5 V vs. Ag / AgCl, and using 1 M H3PO4 to maintain the pH of the electrolyte stable during the reaction; (4) After the reaction is completed, the electrolyte is filtered to recover the filter residue, and the filter residue is repeatedly rinsed with deionized water until it is neutral. The washed precipitate is dried in an oven at 80° C. for 5 h.