CN110157916A - A low-cost method for preparing high-performance anisotropic NdFeB magnetic powder using NdFeB oil-based slice sludge - Google Patents

Abstract

The invention discloses a low-cost method for preparing high-performance anisotropic NdFeB magnetic powder by using NdFeB oil-based slice oil sludge, which belongs to the technical field of rare earth permanent magnet waste recycling and reuse. First of all, the cutting fluid and impurities in the oil sludge are removed by physical and chemical separation methods, and the content of carbon, hydrogen, oxygen and other impurities in the oil sludge is reduced to achieve the purpose of purification. A stable reaction system is constructed by adding metal calcium (Ca) as a reducing agent and supplemented with one or several buffers: potassium chloride and calcium chloride. On the basis of greatly reducing the amount of calcium metal, this reaction system is not only more conducive to the full progress of the reaction, but also greatly improves the grain size and distribution of the recovered magnetic powder, and improves the single crystal ratio and orientation degree of the recovered magnetic powder; in addition, During the reaction, the reactants are pressed into blocks, which is conducive to the full and uniform reaction of the reactants; the reduced products are ground into powder, and the mixture such as ice water is used to remove calcium, which reduces the degree of oxidation of the recovered magnetic powder and improves the speed of calcium removal. and efficiency. The invention has the characteristics of economy, high efficiency, environmental protection and the like.

Description

A low-cost preparation of high-performance anisotropic NdFeB oil-based slice sludge NdFeB magnetic powder method

technical field

The invention relates to reclaiming NdFeB oil-based slice oil sludge to prepare regenerated magnetic powder, and belongs to the technical field of rare earth permanent magnet waste recycling and reuse.

technical background

Sintered NdFeB permanent magnet materials have been widely used in various industries. my country is a major producer of NdFeB, supplying more than 90% of the world's NdFeB. In the production process of sintered NdFeB, about 40wt.% of the total weight of raw materials will produce NdFeB waste, and about 30wt.% of the waste is produced in the machining stage in the form of sludge waste, which contains high-rich rare earth elements and other valuable elements. In recent years, due to the increasing shortage of rare earth resources and the rising price of rare earth and metals, the production cost of sintered NdFeB magnets has increased significantly. In order to save resources and achieve sustainable development, it is imperative to recycle NdFeB sludge.

At present, the industry mainly adopts the traditional wet method to recover NdFeB oil sludge, mainly including: acid-soluble precipitation method, double salt conversion method, hydrochloric acid optimal solution method, etc. The final products obtained by these recovery methods are rare earth oxides or chlorides. Converting to NdFeB magnets also needs to go through multiple processes such as electrolysis, smelting, hydrogen explosion, and jet milling. On the whole, the traditional wet recycling method has a long recycling cycle, serious energy consumption, and discharges a large amount of waste liquid and waste gas to pollute the environment.

In order to simplify the recycling process, improve recycling efficiency and economy, and reduce the impact of recycling on the environment, researchers have developed a variety of methods for recycling NdFeB sludge, in order to directly convert sludge waste into sintered or bonded NdFeB. raw powder. Chinese patent (Application No. 201410101544.7) discloses a method for recovering valuable elements in NdFeB oil sludge by co-precipitation and diffusion reduction technology to obtain NdFeB magnetic powder. The performance is poor, and a large amount of metallic calcium is used in the reduction diffusion process, and the cost is high. Chinese patent (Application No. 201510101336.1) also successfully recovered NdFeB magnetic powder from sludge waste by using the reduction diffusion method, but it added additional raw materials such as NdO and FeB during the reduction diffusion process, resulting in an increase in the amount of reducing agent used. Helps reduce recycling costs. Chinese patent (application number 201811437315.7) discloses a method for recovering NdFeB casing sludge waste using Ca-chloride reduction and diffusion technology. In this method, it first uses blast drying to purify the sludge, although this method is effective The sludge is purified, but the oxygen content in the sludge is increased, which increases the amount of calcium added in the subsequent reduction and diffusion, which is not conducive to the reduction of recovery costs. In short, the current efficient recovery methods of NdFeB oil sludge generally have the following problems: 1) The amount of reducing agent Ca used is too large, resulting in high recovery costs. In the above recovery methods, the optimum amount of Ca used is generally more than 50wt.% of the sludge raw material. Not only the recovery price is high, but also the excessive Ga will greatly increase the oxygen content of the reduced powder in the subsequent calcium washing process and reduce the magnetic properties. Therefore, it is necessary to establish corresponding pretreatment methods according to the characteristics of sludge waste produced by different processing methods to minimize the oxygen content in order to reduce the amount of calcium reducing agent; 2) The magnetic properties and orientation of the recovered magnetic powder are not high. Magnetic powder has appropriate grain size and distribution, low oxygen content and non-magnetic impurities, and is an important means to improve magnetic properties and orientation degree. In the present invention, by studying and understanding the reaction process and mechanism, and carefully controlling the amount and proportion of the buffering agent in the reaction, a single-phase NdFeB recovery powder with narrow grain distribution and high single crystal content was successfully obtained, and the powder has a good degree of orientation , with high magnetic performance, which provides the possibility for the subsequent preparation of sintered magnets or bonded magnets.

The invention provides a recovery technology of oil-based sliced NdFeB oil sludge. The oil-based slice sludge is produced during the processing of the oil-based slicer. In order to prevent the magnet from being oxidized during the process, a large amount of oil-based cutting fluid, anti-rust agent and other organic substances are used in the process, resulting in a large amount of organic impurities in the sludge, thus Lead to higher carbon, hydrogen and oxygen content. For this kind of oil sludge, there is no corresponding short-process and low-cost recovery technology. On the basis of referring to the existing recycling methods, we invented a low-cost and high-efficiency recycling method for oil-based chip sludge, and successfully obtained high-performance recycled NdFeB magnetic powder with strong anisotropy.

Contents of the invention

The present invention selects oil-based slicing oil sludge as the recycling object, and by analyzing the machine processing technology of the oil sludge and the characteristics of the NdFeB oil sludge waste, a short-flow process based on purification pretreatment-calcium reduction and diffusion is invented, and high magnetic performance, isotropic Single-phase NdFeB powder with strong anisotropy. Firstly, through physical and chemical separation (including static deposition, air drying, magnetic separation, ultrasonic, acid-soluble cleaning, etc.) to remove the cutting fluid and impurities in the sludge, reduce the content of carbon, hydrogen, oxygen and other impurities in the sludge, and achieve the purpose of purification. A stable reaction system was constructed by adding metallic calcium (Ca) as a reducing agent and supplemented with two buffers: potassium chloride (KCl) and calcium chloride (CaCl ₂ ). This reaction system is not only conducive to the full progress of the reaction, but also improves the properties of the recovered magnetic powder, such as grain size, dispersion, and orientation, and increases the proportion of single crystals of the recovered magnetic powder; It is conducive to the full and uniform reaction of the reactants; the reduction product is ground into powder, and the mixture such as ice water is used to remove calcium, which reduces the degree of oxidation of the recovered magnetic powder and improves the speed and efficiency of calcium removal. The invention has the characteristics of economy (reduced calcium usage), high efficiency (short recovery process and good performance of regenerated magnetic powder), environmental protection (no waste gas, waste liquid and waste residue generated in the recovery process), and the like.

The process path of the present invention will be realized through the following steps, and specially designed and solved for the above-mentioned difficult problems.

A low-cost method for preparing high-performance anisotropic NdFeB magnetic powder using NdFeB oil-based slice sludge, characterized in that it comprises the following steps:

(1) Pretreatment of NdFeB oil-based slice sludge: the cutting fluid in the NdFeB oil-based slice sludge is separated from the NdFeB solid waste by physical or chemical methods, and the cutting fluid and impurities in the sludge are removed;

Preferably, the NdFeB oil-based slice sludge is deposited and centrifuged to remove the enriched cutting fluid in the upper layer, and then the sludge obtained is ultrasonically stirred and cleaned with a composite cleaning solution, an acidic solution, ethanol or acetone, and dried in a vacuum environment. After the above-mentioned composite cleaning solution and acidic solution are used for ultrasonic cleaning, distilled water is used to remove the residual cleaning solution, and finally dried to obtain NdFeB pretreated sludge; the oxygen content of the pretreated sludge is lower than 5wt.%, and the hydrogen content is lower than 0.5wt.%. The carbon content is lower than 0.3wt.%, and the composite emulsion is selected from one of the following: OP (emulsifier)+NaOH, OP+HCl, OP+NH ₄ Cl, OP+NaHCO ₃ , OP+Na ₂ CO ₃ Mixed water or alcohol solutions.

(2) Reduction diffusion: The pretreated oil sludge, metal calcium, and reaction buffer obtained in step (1) are mixed according to a certain proportion. 9.1wt.%～16.2wt.%, the total proportion of the reaction buffer is 30wt.%, wherein, the reaction buffer is selected from one or more of anhydrous CaCl ₂ , anhydrous KCl, anhydrous CaO, wherein, The optimal material ratio is pretreated oil sludge: calcium: calcium chloride: potassium chloride = 57.4: 12.6: 15: 15; the uniformly mixed reactants are pressed into blocks under a pressure of 20MPa ~ 70MPa, and the reactants are placed in Place in a stainless steel crucible in a tube furnace protected by argon gas, wash the furnace twice with argon gas, then flush it with argon gas, heat it to 850°C-1200°C for reduction and diffusion, and keep it warm for 90min-210min;

(3) Decalcification: prepare the ice-water mixture in advance, and place a magnet under the outside of the container, use a mortar to grind the product obtained in step (2) into powder, place it in the prepared ice-water mixture, soak 10min-20min, during this process, use a magnet to hold the powder to prevent it from floating, then remove the external magnet, continue soaking for 10min-20min, ultrasonically clean for 5min-10min, change the water, then ultrasonically clean for 5min-10min, change the water; repeat The above steps are 8 to 12 times, then the powder is washed with distilled water until the pH value of the solution is 7-8, and finally washed once with alcohol, the cleaned powder is dried in a vacuum environment, and then stored in a glove box to obtain Recover the magnetic powder; use a rolling ball mill to improve the particle size distribution and orientation of the reduced powder, wherein the mass ratio of the ball to material is 10-20:1, and the ball milling time is 0.5h-2.5h.

The ratio and dosage of the composite cleaning solution in step (1), in the composite cleaning solution, the concentration of OP is 3wt.% to 15wt.%, and the concentration of NaOH, HCl, NH ₄ Cl, NaHCO ₃ , or Na ₂ CO ₃ The concentration is 1wt.%-10wt.%. The acid solution used is HCl, HNO ₃ , H ₂ SO ₄ or acetic acid solution, and the concentration is 0.05wt.%-10wt.%. In each cleaning, the ratio of oil sludge to cleaning liquid is: 800ml-1500ml cleaning liquid is used for every 100g of oil sludge. The cleaning time by ultrasonic stirring is 1 min to 30 min each time.

The invention uses NdFeB oil-based slicing oil sludge waste as raw material, and directly adopts Ca reduction and diffusion technology to recycle after pretreatment to obtain high-performance regenerated NdFeB magnetic powder. The recovery process is short, efficient, environmentally friendly and Realize the recycling of resources; use metal calcium, potassium chloride, and calcium chloride to form a unique reaction system. The new reaction system can not only promote the reaction, but also significantly improve the dispersion and orientation of the reduced magnetic powder. In the reduction diffusion, The usage of calcium is effectively reduced, no extra rare earth elements are added, and the recycling method is simplified. Taken together, the amount of calcium used in reduction and diffusion is reduced by pretreatment of oil sludge, and the ratio of potassium chloride to calcium chloride in the reactant is adjusted to improve the orientation and magnetic properties of the reduced magnetic powder. The entire recovery method reaches It achieves the purpose of recycling with short process, low cost and high performance.

Description of drawings

Fig. 1. Room temperature magnetization of purified oil sludge and regenerated magnetic powder at 3T (embodiment 5).

Fig. 2. XRD spectrum of regenerated magnetic powder (embodiment 5).

Detailed ways

The present invention will be further described below in conjunction with the examples, but the present invention is not limited to the following examples.

In the composite cleaning solution, the concentration of OP is 3wt.% to 15wt.%, and the concentration of NaOH, HCl, NH ₄ Cl, NaHCO ₃ , or Na ₂ CO ₃ is 1wt.% to 10wt.%. The acidic solution used is HCl, HNO ₃ , H ₂ SO ₄ or acetic acid solution, the concentration is 0.05wt.%-10wt.%. In each cleaning, the ratio of oil sludge to cleaning liquid is: 800ml-1500ml cleaning liquid is used for every 100g of oil sludge. The cleaning time by ultrasonic stirring is 1 min to 30 min each time.

Example 1

Take 30g of NdFeB oil-based slice sludge, through sedimentation, centrifugation, and remove cutting fluid, first use OP-NH ₄ Cl aqueous solution to ultrasonically clean twice, distilled water twice, then dilute acetic acid solution once, distilled water twice, Finally, it was washed with acetone and dried under vacuum to obtain pretreated sludge. Take 5g of pretreated oil sludge, mix with 0.8g metallic calcium and 2.62g anhydrous calcium chloride, place it in a cemented carbide mold, and press it into a block on a cold press to obtain a reaction block; place the reaction block on a stainless steel Put the crucible in a tube furnace, raise the temperature to 1050°C in an argon atmosphere, and keep it warm for 120 minutes to obtain a reduced block; grind the reduced block into powder, and carry out the process in a container with an external magnet and a mixture of ice and water Remove calcium, soak for 10 minutes, remove the magnet, soak for 10 minutes, change water, ultrasonic cleaning for 7 minutes, change water, ultrasonic cleaning for 7 minutes, repeat the operation 9 times, and finally wash with absolute ethanol once, dry in a vacuum environment, and obtain M _3T = 135emu/g, recycled magnetic powder with orientation degree 1.2.

Example 2

Take 30g of NdFeB oil-based slice sludge, through sedimentation, centrifugation, and remove cutting fluid, first use OP-NaHCO ₃ aqueous solution to ultrasonically clean twice, distilled water twice, then dilute nitric acid solution once, distilled water twice, and finally Wash once with acetone and dry under vacuum to obtain pretreated sludge. Take 5g of pretreated oil sludge, mix with 1g of calcium metal, and 2.62g of anhydrous calcium chloride, place it in a cemented carbide mold, and press it into a block on a cold press to obtain a reaction block; put the reaction block in a stainless steel crucible In the process, put the crucible in a tube furnace, raise the temperature to 1050°C in an argon atmosphere, and keep it warm for 120 minutes to obtain a reduced block; grind the reduced block into powder, and remove it in a container with an external magnet and equipped with an ice-water mixture. Calcium, after soaking for 10 minutes, remove the magnet, soak for 10 minutes, change water, ultrasonic cleaning for 7 minutes, change water, ultrasonic cleaning for 7 minutes, repeat the operation 9 times, and finally wash with absolute ethanol once, and dry in a vacuum environment to obtain M _3T =142emu/g, recovered magnetic powder with an orientation degree of 1.7.

Example 3

Take 30g of NdFeB oil-based slice sludge, through sedimentation, centrifugation, and remove cutting fluid, first use OP-Na ₂ CO ₃ aqueous solution to ultrasonically clean twice, distilled water twice, then dilute sulfuric acid solution once, distilled water twice , and finally wash it with acetone, and dry it in a vacuum environment to obtain pretreated sludge. Take 5g of pretreated oil sludge, mix with 1.1g metallic calcium and 2.62g anhydrous calcium chloride, place it in a cemented carbide mold, and press it into a block on a cold press to obtain a reaction block; place the reaction block on a stainless steel Put the crucible in a tube furnace, raise the temperature to 1050°C in an argon atmosphere, and keep it warm for 120 minutes to obtain a reduced block; grind the reduced block into powder, and carry out the process in a container with an external magnet and a mixture of ice and water Remove calcium, soak for 10 minutes, remove the magnet, soak for 10 minutes, change water, ultrasonic cleaning for 7 minutes, change water, ultrasonic cleaning for 7 minutes, repeat the operation 9 times, and finally wash with absolute ethanol once, dry in a vacuum environment, and obtain M _3T = 148emu/g, recycled magnetic powder with orientation degree 2.1.

Example 4

Take 30g of NdFeB oil-based slice sludge, through sedimentation, centrifugation, and remove cutting fluid, first use OP-HCl aqueous solution to ultrasonically clean twice, distilled water twice, then dilute hydrochloric acid solution once, distilled water twice, and finally use Wash it with alcohol and dry it under vacuum to get pre-treated sludge. Take 5g of pretreated oil sludge, mix with 1.5g metallic calcium and 2.62g anhydrous calcium chloride, place it in a hard alloy mold, and press it into a block on a cold press to obtain a reaction block; place the reaction block on a stainless steel Put the crucible in a tube furnace, raise the temperature to 1050°C in an argon atmosphere, and keep it warm for 120 minutes to obtain a reduced block; grind the reduced block into powder, and carry out the process in a container with an external magnet and a mixture of ice and water Remove calcium, soak for 10 minutes, remove the magnet, soak for 10 minutes, change water, ultrasonic cleaning for 7 minutes, change water, ultrasonic cleaning for 7 minutes, repeat the operation 9 times, and finally wash with absolute ethanol once, dry in a vacuum environment, and obtain M _3T = 147emu/g, recycled magnetic powder with a degree of orientation of 1.9.

Example 5

Take 30g of NdFeB oil-based slice sludge, through sedimentation, centrifugation, and remove cutting fluid, first use OP-NaOH alcohol solution to ultrasonically clean twice, distilled water twice, and finally wash once with acetone, dry in vacuum environment, and obtain Deal with sludge. Take 5g of pretreated oil sludge, mix with 1.1g metallic calcium, 1.31g anhydrous potassium chloride, and 1.31g anhydrous calcium chloride, place it in a cemented carbide mold, and press it into a block on a cold press to obtain a reaction block ;Put the reaction block in a stainless steel crucible, place the crucible in a tube furnace, heat up to 1050°C under an argon atmosphere, and keep it warm for 120 minutes to obtain a reduced block; grind the reduced block into powder, place it in an external magnet and Carry out decalcification in a container filled with ice-water mixture, soak for 10 minutes, remove the magnet, soak for 10 minutes, change water, ultrasonic cleaning for 7 minutes, change water, ultrasonic cleaning for 7 minutes, repeat the operation 9 times, and finally wash with absolute ethanol once, put Dry in a vacuum environment to obtain recovered magnetic powder with M _3T =157emu/g and degree of orientation 15. The room temperature magnetization of purified oil sludge and regenerated magnetic powder at 3T is shown in Figure (1), and the phase of regenerated magnetic powder is shown in Figure (2).

Example 6

Take 30g of NdFeB oil-based slice sludge, through sedimentation, centrifugation, and remove cutting fluid, first use OP-NaOH aqueous solution to ultrasonically clean twice, distilled water twice, then dilute hydrochloric acid solution once, distilled water twice, and finally use Wash it with alcohol and dry it under vacuum to get pre-treated sludge. Take 5g of pretreated oil sludge, mix with 1.1g metallic calcium, and 2.62g anhydrous potassium chloride, place it in a cemented carbide mold, and press it into a block on a cold press to obtain a reaction block; place the reaction block on a stainless steel Put the crucible in a tube furnace, heat up to 1050°C under an argon atmosphere, and keep it warm for 150 minutes to obtain a reduced block; grind the reduced block into powder, and carry out the process in a container with an external magnet and a mixture of ice and water. Remove calcium, soak for 10 minutes, remove the magnet, soak for 10 minutes, change water, ultrasonic cleaning for 7 minutes, change water, ultrasonic cleaning for 7 minutes, repeat the operation 9 times, and finally wash with absolute ethanol once, dry in a vacuum environment, and obtain M _3T = 150emu/g, recycled magnetic powder with orientation degree 7.

Example 7

Take 30g of NdFeB oil-based slice sludge, through sedimentation, centrifugation, and remove cutting fluid, first use OP-NH ₄ Cl aqueous solution to ultrasonically clean twice, distilled water twice, then dilute hydrochloric acid solution once, distilled water twice, Finally, it was washed with acetone and dried under vacuum to obtain pretreated sludge. Take 5g of pretreated oil sludge, mix with 1.1g metallic calcium, 0.65g anhydrous potassium chloride, and 1.96g anhydrous calcium chloride, place it in a cemented carbide mold, and press it into a block on a cold press to obtain a reaction block ;Put the reaction block in a stainless steel crucible, place the crucible in a tube furnace, heat up to 1050°C under an argon atmosphere, and keep it warm for 120 minutes to obtain a reduced block; grind the reduced block into powder, place it in an external magnet and Carry out decalcification in a container filled with ice-water mixture, soak for 10 minutes, remove the magnet, soak for 10 minutes, change water, ultrasonic cleaning for 7 minutes, change water, ultrasonic cleaning for 7 minutes, repeat the operation 9 times, and finally wash with absolute ethanol once, put Dry in a vacuum environment to obtain recovered magnetic powder with M _3T =153 emu/g and degree of orientation 4.5.

Example 8

Take 30g of NdFeB oil-based slice sludge, through sedimentation, centrifugation, and remove cutting fluid, first use OP-NaOH alcohol solution to ultrasonically clean twice, distilled water twice, and finally use alcohol to wash once, dry in a vacuum environment, and obtain Deal with sludge. Take 5g of pretreated oil sludge, mix with 1.1g metallic calcium, 1.96g anhydrous potassium chloride, and 0.65g anhydrous calcium chloride, place it in a hard alloy mold, and press it into a block on a cold press to obtain a reaction block ;Put the reaction block in a stainless steel crucible, place the crucible in a tube furnace, heat up to 1050°C under an argon atmosphere, and keep it warm for 120 minutes to obtain a reduced block; grind the reduced block into powder, place it in an external magnet and Carry out decalcification in a container filled with ice-water mixture, soak for 10 minutes, remove the magnet, soak for 10 minutes, change water, ultrasonic cleaning for 7 minutes, change water, ultrasonic cleaning for 7 minutes, repeat the operation 9 times, and finally wash with absolute ethanol once, put Dry in a vacuum environment to obtain recovered magnetic powder with M _3T =150 emu/g and degree of orientation 2.2.

Example 9

Take 30g of NdFeB oil-based slice sludge, through sedimentation, centrifugation, and remove cutting fluid, first use OP-NaOH alcohol solution to ultrasonically clean twice, distilled water twice, then use dilute hydrochloric acid solution twice, distilled water twice, Finally, it is cleaned with alcohol and dried in a vacuum environment to obtain pre-treated sludge. Take 5g of pretreated oil sludge, mix with 1.1g metallic calcium and 2.62g anhydrous calcium oxide, place it in a cemented carbide mold, and press it into a block on a cold press to obtain a reaction block; put the reaction block in a stainless steel crucible In the process, put the crucible in a tube furnace, raise the temperature to 950°C in an argon atmosphere, and keep it warm for 120 minutes to obtain the reduced block; grind the reduced block into powder, and remove it in a container with an external magnet and equipped with ice-water mixture. Calcium, after soaking for 10 minutes, remove the magnet, soak for 10 minutes, change water, ultrasonic cleaning for 7 minutes, change water, ultrasonic cleaning for 7 minutes, repeat the operation 9 times, and finally wash with absolute ethanol once, and dry in a vacuum environment to obtain M _3T =150emu/g, recycled magnetic powder with an orientation degree of 1.5.

Claims (2)

1. a kind of method using neodymium iron boron oil base slice greasy filth preparation high-performance anisotropy NdFeB magnetic powder of low cost, It is characterized in that, comprising the following steps:

(1) pretreatment neodymium iron boron oil base is sliced greasy filth: the cutting fluid that neodymium iron boron oil base is sliced in greasy filth is led to neodymium iron boron solid waste It crosses and is either physically or chemically separated, remove the cutting fluid and impurity of greasy filth；

It is preferred that neodymium iron boron oil base is sliced sludge deposition, centrifugation, the cutting fluid of removal upper layer enrichment, then successively using compound Cleaning solution, acid solution, ethyl alcohol or acetone carry out the greasy filth that ultrasonic agitation cleaning obtains, and dry under vacuum conditions, above-mentioned Residual cleaning liquid is removed using distilled water is all made of after composite cleaning liquid, acid solution ultrasonic cleaning, is finally dried to obtain neodymium iron Boron pre-processes greasy filth；The pretreatment greasy filth oxygen content is lower than 5wt.%, and hydrogen content is lower than 0.5wt.%, and carbon content is lower than 0.3wt.%, multiple emulsion one kind chosen from the followings: OP (emulsifier)+NaOH, OP+HCl, OP+NH₄Cl、OP+ NaHCO₃、OP+Na₂CO₃Mixed aqueous solutions or alcoholic solution；

(2) vat blue RS: step (1) is obtained into pretreatment greasy filth, calcium metal, reaction buffer and is matched according to a certain percentage Material, it is pretreatment greasy filth accounting 53.8wt.%~60.9wt.%, reducing agent calcium metal accounting 9.1wt.%~16.2wt.%, anti- Answering the total accounting of buffer is 30wt.%；Wherein, reaction buffer is selected from anhydrous CaCl₂, anhydrous K Cl, one of anhydrous CaO Or it is several；Wherein, optimal material proportion is pretreatment greasy filth: calcium: calcium chloride: potassium chloride=57.4:12.6:15:15；It will mixing Uniform reactant is pressed into block under 20MPa~70MPa pressure, and reactant is placed in stainless steel crucible, argon is placed in In the tube furnace of gas shielded, using twice of ar purging, argon gas is then poured, is heated to being restored at 850 DEG C~1200 DEG C Diffusion keeps the temperature 90min~210min；

(3) deliming: ready mixture of ice and water in advance, and one piece of magnet is placed in container outer lower side, step (2) is obtained Product using mortar grinder at powder, be placed in ready mixture of ice and water, impregnate 10min~20min, in the process Powder, which is sucked, using magnet prevents from floating, and then removes external magnet afterwards, continues to impregnate 10min~20min, is cleaned by ultrasonic 5min ~10min changes water, then is cleaned by ultrasonic 5min~10min, changes water；It repeats the above steps 8~12 times, then wash with distilled water Powder to solution ph is 7-8, is finally used alcohol washes 1 time, and the powder after cleaning is placed in drying under vacuum environment, is then put It is placed in glove box and saves, recycling magnetic powder can be obtained；Improve the size distribution and the degree of orientation of reduced powder using rolling ball milling, Wherein ball material mass ratio is 10~20:1, and Ball-milling Time is ball milling 0.5h~2.5h.

2. according to the method for claim 1, which is characterized in that the proportion and dosage of the middle composite cleaning liquid of step (1) are closed System, in composite cleaning liquid, the concentration 3wt.%~15wt.%, NaOH, HCl, NH of OP₄Cl、NaHCO₃Or Na₂CO₃Concentration For 1wt.%~10wt.%；Used acid solution is HCl, HNO₃、H₂SO₄Or acetic acid solution, concentration be 0.05wt.%~ 10wt.%.In each cleaning, the ratio of greasy filth and cleaning solution are as follows: every 100g greasy filth uses 800ml~1500ml cleaning solution. The time of ultrasonic agitation cleaning is 1min~30min every time.