Method for preparing sintered neodymium-iron-boron magnet through graded recovery of neodymium-iron-boron oil sludge waste

Abstract

The invention discloses a method for preparing a sintered neodymium-iron-boron magnet by graded recovery of neodymium-iron-boron oil sludge waste, which comprises the following steps of: 1, wet-grinding, screening, centrifuging and drying the oil sludge waste to obtain coarse oil sludge and fine oil sludge; 2, carrying out vacuum degreasing and hydrogen reduction on the coarse and fine oil sludge to obtain a coarse and fine hydrogen reduction phase; 3, performing element adjustment on the hydrogen reduction phases of the coarse powder and the fine powder, mixing with a reducing agent and fused salt, and performing reduction diffusion reaction to obtain recycled magnetic powder and rare earth-rich magnetic powder; and step 4, mixing the recycled magnetic powder and the rare earth-rich magnetic powder, and carrying out orientation compression and sintering to obtain the recycled magnet. According to the method, the oil sludge waste is subjected to wet grinding and screening to complete impurity removal, crushing and grading, the same technology is adopted, the recycled magnetic powder and the rare earth-rich magnetic powder are synchronously prepared, the rare earth-rich magnetic powder replaces a traditional rare earth-rich phase and is directly mixed with the recycled magnetic powder to be sintered, the recycled neodymium-iron-boron magnet is obtained, and the method is suitable for the technical field of rare earth permanent magnet waste recycling and reusing.

Description

Technical Field

[0001] The invention belongs to the technical field of recycling and reusing rare earth permanent magnet waste, and in particular relates to a method for preparing sintered NdFeB magnets by graded recycling of NdFeB oil sludge waste. Background Art

[0002] The non-renewable nature of rare earths is the driving force for the development of the rare earth recycling industry and the research and development of key technologies for recycled products. Among them, sintered NdFeB is the most widely used rare earth permanent magnet material, with advantages such as high remanence, high coercivity, and high magnetic energy product, becoming a key basic material for modern society, high-tech industries, and national defense technology. With the annual increase in the output of sintered NdFeB and the development demand for thinner and more integrated electronic devices, a large amount of waste is generated during its processing, especially oil sludge waste, which accounts for about 30% of the total weight of NdFeB magnets, and the pressure to be processed and the waste of resources are huge.

[0003] Due to the serious pollution and oxidation of NdFeB oil sludge waste, hydrometallurgical technology is currently mainly used for recycling, generally including roasting, acid dissolution, extraction, precipitation and burning, which are complicated, polluting and wasteful of iron resources. The NdFeB oil sludge waste recycling technology developed based on calcium thermal reduction can overcome the above shortcomings, but this method is limited by existing processes and technologies, and is heavily dependent on the quality of the oil sludge waste and the long process of processing the oil sludge waste; at the same time, when preparing sintered NdFeB, it is necessary to add additional rare earth-rich raw materials (neodymium hydride or rare earth-rich alloys prepared by smelting) to supplement rare earth elements. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the above-mentioned prior art and provide a method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste. The method wet-grinds and screens the NdFeB oil sludge waste to remove impurities, crush and grade the NdFeB oil sludge waste, then obtains graded recovered magnetic powder and rare earth-rich magnetic powder through hydrogen reduction and reduction diffusion reaction, and finally obtains recovered NdFeB magnets by mixed sintering of the recovered magnetic powder and the rare earth-rich magnetic powder, thus solving the problems of high quality requirements of the oil sludge waste or long pretreatment process and additional addition of rare earth-rich raw materials in the prior art of NdFeB oil sludge waste recovery technology.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste, characterized in that the method comprises the following steps: Step 1, wet-grinding the NdFeB oil sludge waste, and then sieving, centrifuging and drying in sequence to obtain coarse powder oil sludge and fine powder oil sludge; Step 2: Degreasing the coarse powder sludge and the fine powder sludge obtained in step 1 in a vacuum environment and reducing them in a hydrogen atmosphere in turn to obtain a coarse powder hydrogen-reduced phase and a fine powder hydrogen-reduced phase; Step 3: adjusting the element ratio of the coarse powder hydrogen reduction phase and the fine powder hydrogen reduction phase obtained in step 2, and then mixing them with a reducing agent and a molten salt to perform a reduction diffusion reaction to obtain recovered magnetic powder and rare earth-rich magnetic powder; the element ratio is adjusted to adjust the ratio of Fe, RE, and B elements; RE represents a rare earth element; Step 4: Mix the recovered magnetic powder obtained in step 3 with the rare earth-rich magnetic powder, orient and press them in a magnetic field, and then sinter them to obtain a recovered NdFeB magnet.

[0006] The above-mentioned method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste is characterized in that the wet grinding in step one is a low-temperature ball milling process with the addition of an organic solvent, the temperature of the low-temperature ball milling process is not higher than 25°C, the organic solvent is one or more of ethanol, acetone and n-hexane, the mass ratio of the NdFeB oil sludge waste, the organic solvent and the grinding balls in the ball mill is 1:0.7~1.2:10~15, the rotation speed of the ball mill is 300r / min~400r / min, and the time of the ball mill is 12h~36h.

[0007] The present invention simultaneously performs impurity removal and crushing of NdFeB oil sludge waste by adopting a wet grinding process, and the addition of an organic solvent is conducive to dissolving organic impurities wrapped on the surface of oil sludge particles, and the ball milling process can accelerate the dissolution of organic impurities in the organic solvent, and then the organic impurities and the organic solvent are removed after centrifugation and drying, which can effectively remove impurities and reduce the content of C, H and O elements; by controlling the temperature of the low-temperature ball milling process to be no higher than 25°C, further oxidation of NdFeB oil sludge waste and volatilization of the organic solvent can be prevented; by controlling the mass ratio of NdFeB oil sludge waste, the organic solvent and the grinding balls in the ball milling, the impurity removal and ball milling efficiency can be effectively improved, and the problem of poor dispersibility of magnetic oil sludge particles and insufficient dissolution of impurities in the organic solvent due to too little organic solvent, thereby reducing the impurity removal effect, or too much organic solvent, resulting in reduced ball milling efficiency and waste of resources, can be avoided.

[0008] The above-mentioned method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste is characterized in that the coarse powder oil sludge in step one is the screened material screened with a 400-600 mesh sieve, and the fine powder oil sludge is the screened material screened with a sieve of 1000 mesh or above.

[0009] The present invention adopts 400-600 mesh screens and 1000 mesh screens or above for screening, and the obtained coarse powder sludge and fine powder sludge particle sizes can make subsequent hydrogen reduction, reduction diffusion and sintering reactions proceed smoothly, and avoids that the particle size of the coarse powder sludge or the fine powder sludge is too large, which causes insufficient subsequent reaction, and the prepared recovered magnetic powder or rare earth-rich magnetic powder particles are too large, resulting in difficulty in uniform mixing of the recovered magnetic powder or rare earth-rich magnetic powder during sintering, and further resulting in difficulty in forming uniform neodymium-rich phase grain boundaries during the sintering process, and reducing the density of the recovered neodymium iron boron magnet or generating holes; and avoids that the particle size of the coarse powder sludge or the fine powder sludge is too small, which causes aggravated sludge oxidation and increased ball milling burden.

[0010] In addition, the coarse powder sludge and fine powder sludge obtained by screening with 400-600 mesh sieves and 1000 mesh and above sieves can control the average particle size of the recovered magnetic powder to 3µm-6µm. Magnetic powder of this particle size can be directly sintered without going through ball milling or air flow milling processes, avoiding problems such as complex morphology, uneven size, and many surface defects of magnetic powder particles caused by ball milling or air flow milling.

[0011] The above-mentioned method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste is characterized in that the degreasing temperature under the vacuum environment in step 2 is 200°C~300°C, and the insulation time is 1h~2h; the reduction temperature under the hydrogen atmosphere is 750°C~850°C, and the insulation time is 1.5h~3h.

[0012] The present invention can effectively remove high-boiling-point organic impurities remaining on the surfaces of coarse powder sludge and fine powder sludge by controlling the vacuum degreasing temperature and time, and further reduce the contents of C, H and O, thereby avoiding the formation of coke or carbide due to the vacuum degreasing temperature being too high and the time being too long, or insufficient removal of high-boiling-point organic impurities due to the vacuum degreasing temperature being too low and the time being too short; and can effectively reduce the Fe element in the coarse powder sludge and fine powder sludge to Fe elemental substance by controlling the hydrogen reduction temperature and the heat preservation time, thereby avoiding serious aggregation and growth of metal particles due to the temperature being too high and the time being too long, or insufficient hydrogen reduction due to the temperature being too low and the time being too short, thereby increasing the amount of the reducing agent used in the reduction diffusion reaction.

[0013] The above-mentioned method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste is characterized in that the element ratio in step three is adjusted to add one or more of rare earth compounds, iron compounds and boron compounds, the rare earth compounds include salts and oxides containing rare earth elements, the iron compounds include iron powder and iron oxides, and the boron compounds include boric acid and boron oxides.

[0014] The above-mentioned method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste is characterized in that the rare earth compound added to the coarse powder hydrogen reduction phase is a salt and oxide containing Nd, and the molar ratio of Fe, RE, and B elements after the element ratio of the coarse powder hydrogen reduction phase is adjusted is 14:2.15~2.25:1.00~1.05; the rare earth compound added to the fine powder hydrogen reduction phase is one or more of salts and oxides containing Nd, Pr, Dy, Tb, Ce, and Sm, and the molar ratio of Fe, RE, and B elements after the element ratio of the fine powder hydrogen reduction phase is adjusted is 14:4.2~6.2:1.00~1.05.

[0015] The present invention is based on RE2Fe 14 The atomic ratio of each element in the B compound is used to adjust the elemental composition of the coarse powder hydrogen reduction phase and the fine powder hydrogen reduction phase, in order to make the coarse powder hydrogen reduction phase and the fine powder hydrogen reduction phase form Nd2Fe 14 Recycled magnetic powder with B as the main phase and Nd2 (Nd, Pr, Dy, Tb, Ce, Sm) 2~4 Fe 14 B rare earth-rich magnetic powder, the rare earth-rich magnetic powder contains one or more of the elements Nd, Pr, Dy, Tb, Ce, Sm; by regulating the type of rare earth compound added to the fine powder hydrogen reduction phase, different rare earth elements can be introduced to adjust the magnetic properties of the recovered NdFeB magnet.

[0016] The above-mentioned method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste is characterized in that the reducing agent in step three is Ca and / or CaH2, and the mass of the reducing agent is 35%~60% of the mass of the coarse powder hydrogen reduction phase or the fine powder hydrogen reduction phase after adjusting the element ratio; the molten salt is one or more of potassium chloride, sodium chloride and calcium chloride, and the mass of the molten salt is 5%~20% of the mass of the reducing agent.

[0017] The above-mentioned method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste is characterized in that the reduction diffusion reaction temperature T1 of the coarse powder hydrogen reduction phase in step 3 is 950°C~1050°C, and the reaction time t1 is 3h~6h; the reduction diffusion reaction temperature T2 of the fine powder hydrogen reduction phase is , T2 is in °C, reaction time t2 is , the unit of t2 is h.

[0018] The present invention adjusts the reduction diffusion reaction temperature and reaction time according to the RE content in the rare earth-rich magnetic powder to avoid excessive temperature and long time leading to the growth of rare earth-rich magnetic powder particles, sintering and excessive volatilization of rare earth, or insufficient reaction and residual impurities due to too low temperature and short time.

[0019] The above-mentioned method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste is characterized in that the mass ratio of the recovered magnetic powder and the rare earth-rich magnetic powder mixed in step 4 is 1:0.2~0.7.

[0020] The above-mentioned method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste is characterized in that the sintering system described in step 4 is: heating to 200°C~300°C and keeping warm for 1h~2h, heating to 600°C~800°C and keeping warm for 2h~3h, heating to 1040°C~1100°C and keeping warm for 3h~4h, then keeping warm at 890°C~930°C for 3h, and finally keeping warm at 500°C~550°C for 3h.

[0021] The invention performs degreasing by keeping a mixture of recycled magnetic powder and rare earth-rich magnetic powder at 200-300°C for 1-2 hours, dehydrogenating by keeping a mixture at 600-800°C for 1.5-3 hours, sintering by keeping a mixture at 1040-1100°C for 3-4 hours, and then performing secondary aging treatment by keeping a mixture at 890-930°C for 3 hours and at 500-550°C for 3 hours.

[0022] Compared with the prior art, the present invention has the following advantages: 1. The present invention wet-grinds and sieves the NdFeB oil sludge waste to remove impurities, crush and grade the NdFeB oil sludge waste, then obtains graded recovered magnetic powder and rare earth-rich magnetic powder through hydrogen reduction and reduction diffusion reaction, and finally obtains recovered NdFeB magnets with good performance by mixed sintering of the recovered magnetic powder and the rare earth-rich magnetic powder.

[0023] 2. The present invention removes most of the impurities in the NdFeB sludge waste by adopting a wet grinding process, and combines a subsequent vacuum degreasing process to ensure that the impurities are fully removed, thereby avoiding the lengthy and cumbersome impurity removal operation in the prior art, simplifying the process flow, and avoiding the introduction of new impurities.

[0024] 3. The present invention uses coarse and fine powder sludge after wet grinding and screening as raw materials, adopts the same process route, and simultaneously prepares recycled magnetic powder and rare earth-rich magnetic powder. The rare earth-rich magnetic powder can replace the neodymium hydride or rare earth-rich alloy added when preparing sintered NdFeB in the prior art, and the preparation of the rare earth-rich magnetic powder does not add additional processes and additional equipment, thereby achieving high resource utilization and single process route recycling of NdFeB oil sludge waste, and reducing production costs.

[0025] 4. The present invention adopts wet grinding and screening to control the particle size of the oil sludge to prepare coarse magnetic powder and rare earth-rich magnetic powder with a particle size suitable for sintering. There is no need for secondary ball milling or air flow milling, thus avoiding the problems of complex morphology, uneven size, and many surface defects of magnetic powder particles caused by ball milling or air flow milling, and also avoiding the risk of oxidation during ball milling or air flow milling.

[0026] 5. The present invention controls the impurity removal rate and the particle size of the recovered magnetic powder by adjusting the wet grinding parameters, and regulates the rare earth type and rare earth content in the rare earth-rich magnetic powder by adding rare earth compounds, thereby preparing a series of recovered magnets with different properties. The overall process has strong controllability and applicability.

[0027] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention is a preparation flow chart of the method.

[0029] Figure 2 This is a microscopic structure diagram of the coarse powder sludge obtained in step 1 of Example 1 of the present invention.

[0030] Figure 3 This is a microscopic structure diagram of the fine powder sludge obtained in step 1 of Example 1 of the present invention.

[0031] Figure 4 This is the XRD diagram of the recovered magnetic powder and rare earth-rich magnetic powder obtained in step 3 of Example 1 of the present invention.

[0032] Figure 5 This is a microstructure diagram of the recovered magnetic powder obtained in step three of Example 1 of the present invention.

[0033] Figure 6 This is a diagram showing the magnetic measurement results of the NdFeB oil sludge waste in Example 1 of the present invention and the recovered magnetic powder obtained in step 3.

[0034] Figure 7 This is a diagram of the magnetic measurement results of the recovered NdFeB magnet obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0035] The mass purity of the rare earth compound, iron compound and boron compound used in Examples 1 to 4 is all above 99%.

[0036] Example 1 like Figure 1 As shown, the method of this embodiment includes the following steps: Step 1, adding ethanol to the NdFeB oil sludge waste material and ball milling at a speed of 350r / min for 30h, then sieving and centrifuging with 500-mesh and 1000-mesh stainless steel sieves respectively, and then vacuum drying at 60°C to obtain coarse powder oil sludge and fine powder oil sludge; the mass ratio of the NdFeB oil sludge waste material, ethanol and grinding balls in the ball mill is 1:1:10; Step 2: heating the coarse powder sludge and the fine powder sludge obtained in step 1 to 250° C. in a vacuum environment for 2 hours for degreasing, and then heating to 850° C. in a hydrogen atmosphere for 2 hours for reduction, and cooling to obtain a coarse powder hydrogen-reduced phase and a fine powder hydrogen-reduced phase; Step 3: Add Nd2O3 and B2O3 to the coarse powder hydrogen reduction phase obtained in step 2, adjust the molar ratio of Fe, RE, and B elements in the coarse powder hydrogen reduction phase to 14:2.25:1, uniformly mix with CaH2 and KCl, introduce argon gas at a flow rate of 0.1L / min, heat to 1050°C for reduction diffusion reaction for 4h, cool and use dilute acetic acid aqueous solution for ultrasonic washing and magnetic separation, wash with anhydrous ethanol and vacuum dry to obtain a phase of Nd2Fe 14 B's recovered magnetic powder; the mass of the CaH2 is 40% of the mass of the mixture formed by the coarse powder hydrogen reduction phase and Nd2O3 and B2O3, and the mass of the KCl is 8% of the mass of the CaH2; Nd2O3, Dy2O3 and B2O3 are added to the fine powder hydrogen reduction phase obtained in step 2, and the molar ratio of Fe, RE and B elements in the fine powder hydrogen reduction phase is adjusted to 14:5:1.02. After being uniformly mixed with CaH2 and KCl, argon gas is introduced at a flow rate of 0.1L / min, and the temperature is raised to 1050°C for reduction diffusion reaction for 3.5h. After cooling, ultrasonic washing and magnetic separation are performed with dilute acetic acid aqueous solution, and rare earth-rich magnetic powder is obtained after washing with anhydrous ethanol and vacuum drying; the mass of CaH2 is 50% of the mass of the mixture formed by the fine powder hydrogen reduction phase and Nd2O3, Dy2O3 and B2O3, and the mass of KCl is 10% of the mass of CaH2; Step 4: Mix the recovered magnetic powder and rare earth-rich magnetic powder obtained in step 3 in a mass ratio of 1:0.4, orient and press-form in a 2.2T magnetic field, place in a vacuum tube furnace, first keep at 250°C for 1h for degreasing, then heat to 600°C for 2h for dehydrogenation, then heat to 1070°C for 3h for sintering, finally keep at 900°C for 3h and 500°C for 3h for secondary aging treatment, and then cool to obtain a recovered NdFeB magnet.

[0037] In this embodiment, Nd2O3 may be replaced by a neodymium salt other than Nd2O3, B2O3 may be replaced by boric acid, and KCl may be replaced by NaCl and / or CaCl2.

[0038] The coarse powder sludge and fine powder sludge obtained in step 1 of this embodiment were subjected to microstructural analysis. Figure 2 and Figure 3 As shown, there is a significant difference in particle size between the coarse powder sludge and the fine powder sludge, and both have irregular morphology with clear particle surfaces and contours, indicating that wet grinding and screening can effectively remove impurities, crush and classify the sludge waste.

[0039] The coarse powder hydrogen reduction phase and the fine powder hydrogen reduction phase obtained in step 2 of this embodiment were subjected to component analysis, and the results are shown in Table 1, wherein RE (rare earth elements) and B elements are insufficient. According to the component analysis results, appropriate rare earth compounds and boron compounds are added to the coarse powder hydrogen reduction phase and the fine powder hydrogen reduction phase to adjust the element molar ratio of the coarse powder hydrogen reduction phase and the fine powder hydrogen reduction phase.

[0040] Table 1 Mass percentage (%) of the components of the coarse powder hydrogen reduction phase and the fine powder hydrogen reduction phase of Example 1

[0041] The recovered magnetic powder and rare earth-rich magnetic powder obtained in step 3 of this embodiment were subjected to XRD analysis, and the results were as follows: Figure 4 As shown, the phase composition of the recovered magnetic powder is Nd2Fe 14 B, the phase composition of rare earth-rich magnetic powder is Nd2Fe 14 B and Nd2H5; the microstructure of the recovered magnetic powder was analyzed, such as Figure 5 As shown in the figure, the recovered magnetic powder is spherical particles with a particle size of 3μm~6μm, and has good dispersion and uniformity; magnetic tests were carried out on NdFeB oil sludge waste and recovered magnetic powder, and the results are as follows Figure 6 As shown, compared with NdFeB oil sludge waste, the saturation magnetization intensity of the recovered magnetic powder treated by the method of this embodiment is significantly improved.

[0042] The recovered NdFeB magnets obtained in this example were subjected to magnetic testing, and the results were as follows: Figure 7 As shown, Br (remanence) is 11.26 kGs, Hcj (intrinsic coercive force) is 12.51 kOe, and (BH)max (maximum magnetic energy product) is 29.97 MGOe.

[0043] Example 2 The method of this embodiment includes the following steps: Step 1, adding a mixture of ethanol and acetone to the NdFeB oil sludge waste material and ball milling at a speed of 300 r / min for 12 hours, then sieving and centrifuging with 400 mesh and 1000 mesh stainless steel sieves respectively, and then vacuum drying at 50°C to obtain coarse powder oil sludge and fine powder oil sludge; the mass ratio of the NdFeB oil sludge waste material, the mixture of ethanol and acetone and the grinding balls in the ball mill is 1:0.7:10; Step 2: heating the coarse powder sludge and the fine powder sludge obtained in step 1 to 300° C. for 1 h in a vacuum environment for degreasing, and then heating to 800° C. for 2 h in a hydrogen atmosphere for reduction, and cooling to obtain a coarse powder hydrogen-reduced phase and a fine powder hydrogen-reduced phase; Step 3: Add Fe and B2O3 to the coarse powder hydrogen reduction phase obtained in step 2, adjust the molar ratio of Fe, RE, and B elements in the coarse powder hydrogen reduction phase to 14:2.15:1.03, uniformly mix with CaH2, KCl, and CaCl2, introduce argon gas at a flow rate of 0.1L / min, heat to 1000°C for reduction diffusion reaction for 4h, cool and use dilute acetic acid aqueous solution for ultrasonic washing and magnetic separation, wash with anhydrous ethanol, and vacuum dry to obtain a phase of Nd2Fe 14 B's recovered magnetic powder; the mass of the CaH2 is 35% of the mass of the mixture formed by the coarse powder hydrogen reduction phase and Fe and B2O3, and the total mass of the KCl and CaCl2 is 10% of the mass of the CaH2; Nd2O3, Dy2O3, Sm2O3 and B2O3 are added to the fine powder hydrogen reduction phase obtained in step 2, and the molar ratio of Fe, RE and B elements in the fine powder hydrogen reduction phase is adjusted to 14:5.5:1. After being uniformly mixed with CaH2, KCl and CaCl2, argon gas is introduced at a flow rate of 0.1L / min, and the temperature is raised to 970°C for reduction diffusion reaction for 3.7h. After cooling, ultrasonic washing and magnetic separation are carried out with dilute acetic acid aqueous solution, and rare earth-rich magnetic powder is obtained after washing with anhydrous ethanol and vacuum drying; the mass of the CaH2 is 50% of the mass of the mixture formed by the fine powder hydrogen reduction phase and Nd2O3, Dy2O3, Sm2O3 and B2O3, and the total mass of the KCl and CaCl2 is 15% of the mass of the CaH2; Step 4: Mix the recovered magnetic powder and rare earth-rich magnetic powder obtained in step 3 in a mass ratio of 1:0.4, orient and press-form in a 2.2T magnetic field, place in a vacuum tube furnace, first keep at 200°C for 2h for degreasing, then heat to 700°C for 2h for dehydrogenation, then heat to 1040°C for 3.5h for sintering, finally keep at 900°C for 3h and 550°C for 3h for secondary aging treatment and then cool to obtain a recovered NdFeB magnet.

[0044] The performance test of the recycled NdFeB magnet obtained in this example showed that Br was 10.54 kGs, Hcj was 11.86 kOe, and (BH)max was 26.72 MGOe.

[0045] Example 3 The method of this embodiment includes the following steps: Step 1, adding n-hexane to the NdFeB oil sludge waste material and ball milling at a speed of 350 r / min for 24 hours, then sieving and centrifuging with 400 mesh and 1000 mesh stainless steel sieves respectively, and then vacuum drying at 70°C to obtain coarse powder oil sludge and fine powder oil sludge; the mass ratio of the NdFeB oil sludge waste material, n-hexane and grinding balls in the ball mill is 1:1.2:12; Step 2: heating the coarse powder sludge and fine powder sludge obtained in step 1 to 300° C. for 2 h in a vacuum environment for degreasing, and then heating to 750° C. for 3 h in a hydrogen atmosphere for reduction, and cooling to obtain a coarse powder hydrogen-reduced phase and a fine powder hydrogen-reduced phase; Step 3: Add Fe, Nd2O3 and B2O3 to the coarse powder hydrogen reduction phase obtained in step 2, adjust the molar ratio of Fe, RE and B elements in the coarse powder hydrogen reduction phase to 14:2.23:1.05, evenly mix with Ca and KCl, introduce argon gas at a flow rate of 0.1L / min, heat to 1050°C for reduction diffusion reaction for 3h, cool and use dilute acetic acid aqueous solution for ultrasonic washing and magnetic separation, wash with anhydrous ethanol and vacuum dry to obtain a phase of Nd2Fe 14 B's recovered magnetic powder; the mass of Ca is 50% of the mass of the mixture formed by the coarse powder hydrogen reduction phase and Fe, Nd2O3, and B2O3, and the mass of KCl is 5% of the mass of Ca; Add Nd2O3, Dy2O3, CeO2 and B2O3 to the fine powder hydrogen reduction phase obtained in step 2, adjust the molar ratio of Fe, RE and B elements in the fine powder hydrogen reduction phase to 14:6.2:1, mix evenly with Ca and KCl, introduce argon gas at a flow rate of 0.1L / min, heat to 1000℃ for reduction diffusion reaction for 3h, cool and use dilute acetic acid aqueous solution for ultrasonic washing and magnetic separation, wash with anhydrous ethanol and vacuum dry to obtain rare earth-rich magnetic powder; the mass of Ca is 60% of the mass of the mixture formed by the fine powder hydrogen reduction phase and Nd2O3, Dy2O3, CeO2 and B2O3, and the mass of KCl is 20% of the mass of Ca; Step 4: Mix the recovered magnetic powder and rare earth-rich magnetic powder obtained in step 3 in a mass ratio of 1:0.2, orient and press-form in a 2.2T magnetic field, place in a vacuum tube furnace, first keep at 300°C for 1.5h for degreasing, then heat to 600°C for 3h for dehydrogenation, then heat to 1100°C for 3h for sintering, finally keep at 890°C for 3h and 520°C for 3h for secondary aging treatment, and then cool to obtain a recovered NdFeB magnet.

[0046] The performance of the recycled NdFeB magnet obtained in this example was tested, and the results showed that Br was 10.29 kGs, Hcj was 9.77 kOe, and (BH)max was 25.74 MGOe.

[0047] Example 4 The method of this embodiment includes the following steps: Step 1, adding ethanol to the NdFeB oil sludge waste material and ball milling at a speed of 400 r / min for 36 hours, then sieving and centrifuging with 600 mesh and 1000 mesh stainless steel sieves respectively, and then vacuum drying at 65°C to obtain coarse powder oil sludge and fine powder oil sludge; the mass ratio of the NdFeB oil sludge waste material, ethanol and grinding balls in the ball mill is 1:1:15; Step 2: heating the coarse powder sludge and the fine powder sludge obtained in step 1 to 200° C. in a vacuum environment for 1.5 h for degreasing, and then heating to 850° C. in a hydrogen atmosphere for 1.5 h for reduction, and cooling to obtain a coarse powder hydrogen-reduced phase and a fine powder hydrogen-reduced phase; Step 3: Add Nd2O3 and B2O3 to the coarse powder hydrogen reduction phase obtained in step 2, adjust the molar ratio of Fe, RE and B elements in the coarse powder hydrogen reduction phase to 14:2.2:1, uniformly mix with CaH2 and KCl, introduce argon gas at a flow rate of 0.1L / min, heat to 950°C for reduction diffusion reaction for 6h, cool and use dilute acetic acid aqueous solution for ultrasonic washing and magnetic separation, wash with anhydrous ethanol and vacuum dry to obtain a phase of Nd2Fe 14 B's recovered magnetic powder; the mass of the CaH2 is 60% of the mass of the mixture formed by the coarse powder hydrogen reduction phase and Nd2O3 and B2O3, and the mass of the KCl is 20% of the mass of the CaH2; Nd2O3, Tb2O3 and B2O3 are added to the fine powder hydrogen reduction phase obtained in step 2, and the molar ratio of Fe, RE and B elements in the fine powder hydrogen reduction phase is adjusted to 14:4.2:1.05. After being uniformly mixed with CaH2 and KCl, argon gas is introduced at a flow rate of 0.1L / min, and the temperature is raised to 950°C for reduction diffusion reaction for 5.5h. After cooling, ultrasonic washing and magnetic separation are performed with dilute acetic acid aqueous solution, and rare earth-rich magnetic powder is obtained after washing with anhydrous ethanol and vacuum drying; the mass of CaH2 is 45% of the mass of the mixture formed by the fine powder hydrogen reduction phase and Nd2O3, Tb2O3 and B2O3, and the mass of KCl is 10% of the mass of CaH2; Step 4: Mix the recovered magnetic powder and rare earth-rich magnetic powder obtained in step 3 in a mass ratio of 1:0.7, orient and press-form in a 2.2T magnetic field, place in a vacuum tube furnace, first keep at 250°C for 2h for degreasing, then heat to 800°C for 1.5h for dehydrogenation, then heat to 1070°C for 4h for sintering, finally keep at 930°C for 3h and 500°C for 3h for secondary aging treatment, and then cool to obtain a recovered NdFeB magnet.

[0048] The performance test of the recycled NdFeB magnet obtained in this example showed that Br was 10.61 kGs, Hcj was 11.44 kOe, and (BH)max was 27.58 MGOe.

[0049] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste, characterized in that: The method comprises the following steps: Step 1, wet-grinding the NdFeB oil sludge waste, and then sieving, centrifuging and drying in sequence to obtain coarse powder oil sludge and fine powder oil sludge; Step 2: Degreasing the coarse powder sludge and the fine powder sludge obtained in step 1 in a vacuum environment and reducing them in a hydrogen atmosphere in turn to obtain a coarse powder hydrogen-reduced phase and a fine powder hydrogen-reduced phase; Step 3: adjusting the element ratio of the coarse powder hydrogen reduction phase and the fine powder hydrogen reduction phase obtained in step 2, and then mixing them with a reducing agent and a molten salt to perform a reduction diffusion reaction to obtain recovered magnetic powder and rare earth-rich magnetic powder; the element ratio is adjusted to adjust the ratio of Fe, RE, and B elements; RE represents a rare earth element; Step 4: Mix the recovered magnetic powder obtained in step 3 with the rare earth-rich magnetic powder, orient and press them in a magnetic field, and then sinter them to obtain a recovered NdFeB magnet.

2. The method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste according to claim 1, characterized in that: The wet milling in step one is a low-temperature ball milling process with the addition of an organic solvent, the temperature of the low-temperature ball milling process is not higher than 25°C, the organic solvent is one or more of ethanol, acetone and n-hexane, the mass ratio of the NdFeB sludge waste, the organic solvent and the grinding balls in the ball mill is 1:0.7~1.2:10~15, the rotation speed of the ball mill is 300r / min~400r / min, and the ball milling time is 12h~36h.

3. The method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste according to claim 1, characterized in that: The coarse powder sludge in step 1 is the undersize after sieving with a 400-600 mesh sieve, and the fine powder sludge is the undersize after sieving with a sieve of 1000 mesh or more.

4. The method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste according to claim 1, characterized in that: In step 2, the temperature of degreasing under vacuum environment is 200°C~300°C, and the insulation time is 1h~2h; the temperature of reduction under hydrogen atmosphere is 750°C~850°C, and the insulation time is 1.5h~3h.

5. The method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste according to claim 1, characterized in that: The element ratio in step three is adjusted to add one or more of rare earth compounds, iron compounds and boron compounds. The rare earth compounds include salts and oxides containing rare earth elements, the iron compounds include iron powder and iron oxides, and the boron compounds include boric acid and boron oxide.

6. The method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste according to claim 5, characterized in that: The rare earth compound added to the coarse powder hydrogen reduction phase is a salt and oxide containing Nd, and after the element ratio of the coarse powder hydrogen reduction phase is adjusted, the molar ratio of Fe, RE, and B elements is 14:2.15~2.25:1.00~1.05; the rare earth compound added to the fine powder hydrogen reduction phase is one or more of the salts and oxides containing Nd, Pr, Dy, Tb, Ce, and Sm, and after the element ratio of the fine powder hydrogen reduction phase is adjusted, the molar ratio of Fe, RE, and B elements is 14:4.2~6.2:1.00~1.

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7. The method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste according to claim 1, characterized in that: In step three, the reducing agent is Ca and / or CaH2, and the mass of the reducing agent is 35% to 60% of the mass of the coarse powder hydrogen reduction phase or the fine powder hydrogen reduction phase after adjusting the element ratio; the molten salt is one or more of potassium chloride, sodium chloride and calcium chloride, and the mass of the molten salt is 5% to 20% of the mass of the reducing agent.

8. The method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste according to claim 1, characterized in that: The reduction diffusion reaction temperature T1 of the coarse powder hydrogen reduction phase in step 3 is 950°C~1050°C, and the reaction time t1 is 3h~6h; the reduction diffusion reaction temperature T2 of the fine powder hydrogen reduction phase is , T2 is in °C, reaction time t2 is , the unit of t2 is h.

9. The method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste according to claim 1, characterized in that: The mass ratio of the recovered magnetic powder to the rare earth-rich magnetic powder in step 4 is 1:0.2~0.

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10. The method for preparing sintered NdFeB magnets by graded recovery of NdFeB oil sludge waste according to claim 1, characterized in that: The sintering system in step 4 is: heating to 200℃~300℃ and keeping warm for 1h~2h, heating to 600℃~800℃ and keeping warm for 1.5h~3h, heating to 1040℃~1100℃ and keeping warm for 3h~4h, then keeping warm at 890℃~930℃ for 3h, and finally keeping warm at 500℃~550℃ for 3h.

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