CN117187600A - A method for recovering all rare earth elements from rare earth magnetic material waste - Google Patents

Abstract

The invention provides a method for recycling all rare earth elements in rare earth magnetic material waste, which comprises the following steps of firstly crushing, burning and oxidizing the rare earth magnetic material waste to obtain sufficient oxide; and then mixing the sufficient oxide obtained in the steps with carbon, reducing the mixture through heat treatment, cooling the mixture, and separating the mixture to obtain the metal material and the rare earth oxide. The invention firstly carries out impurity removal, crushing and oxidation treatment on materials, converts rare earth metals, iron and other metals into oxides, reduces the iron, copper and other oxides into metals through a carbon reduction body, ensures that the metals are in a liquid state, ensures that the oxides are in a solid state, and is poured into a mold, and after cooling, the metals and the oxides are effectively separated through a physical method. The invention can realize the full recycling of metals in the rare earth magnetic material waste, has simple and convenient operation, continuous and controllable process, low cost, no need of acid and alkali, no waste water, no toxic gas discharge and no waste, and is suitable for continuous operation.

Description

A method for recovering all rare earth elements from rare earth magnetic material waste

Technical field

The invention belongs to the technical field of rare earth magnetic material waste recycling and relates to a method for recovering all rare earth elements in rare earth magnetic material waste.

Background technique

NdFeB permanent magnet materials have been widely used in defense industry, aerospace, medical equipment, computers, electronics, robots and new energy automobile industries due to their superior magnetic properties.

Today, more than 300,000 tons of R-Fe-B series permanent magnets are produced globally every year. Waste materials such as magnet chips, cutting chips, grinding chips, and ultrafine powder will be generated during the manufacturing process, accounting for 25 to 35% of the input materials. . And as time goes by, permanent magnets as components of various products will gradually expire and be scrapped, such as the more common R-Fe-B series permanent magnets in electric machinery, medical equipment, toys, packaging, hardware machinery, aerospace and other fields. Magnets include permanent magnet motors, speakers, magnetic separators, computer disk drives, magnetic resonance imaging equipment instruments, etc. Similar technical solutions for recycling are also disclosed in the prior art. For example, CN97120123.4 discloses a method for recycling rare earth compounds. A method for recycling rare earth compounds includes the following steps: (1) Preliminary treatment of recycled raw materials ; (2) Leaching of acid solutions of rare earth compounds; (3) Filtration; (4) Precipitation of solutions containing rare earth metal ions; (5) Drying and burning of precipitates. However, in the method used in this technical solution, acid needs to be used more than twice, clean water needs to be used, and drying and roasting need to be done more than twice, which requires a large amount of acid consumption, and the acidic solution needs to be processed, which requires a large amount of consumption. Not only does the process require a long process, but the rare earth yield is not high. At the same time, large amounts of iron contained in magnetic waste are discharged as salt solutions or piled up as other solid waste. Small amounts of other metals such as copper, aluminum, cobalt, niobium, etc. are also treated as waste and cannot be recycled. For another example, CN201580016947.4 also discloses a method for recovering rare earth elements. Specifically, it discloses that after oxidizing treatment objects containing at least rare earth elements and iron group elements, the treatment environment is transferred to the presence of carbon for heat treatment. , thereby separating and recovering rare earth elements as oxides from iron group elements. However, this method also has the following shortcomings: ① Due to the use of vacuum or inactive atmosphere, the equipment structure is complex and expensive, and the reaction with gas release is evacuated, and the vacuum degree is difficult to reach the target value, and the running time will be long. ② Carbon and oxide materials are placed in layers, resulting in poor contact between carbon and iron oxides. Calculations and practice have proven that the reaction products between carbon and iron oxide or ferric oxide are mainly carbon monoxide - a solid-solid reaction, contact Failure to do so will seriously affect the reaction speed and extent, and may cause the iron oxide content to be too high. ③Resources have not been fully utilized, and the utilization of iron group metals and other small amounts of metals has not been realized. ④The operation convenience is poor.

Therefore, how to provide a more appropriate method for low-cost and green recycling of various elements, especially rare earth elements, has become an important technical issue at the moment, and it is also one of the issues that many front-line researchers in the industry urgently need to solve. .

Contents of the invention

In view of this, the technical problem to be solved by the present invention is to provide a method for recovering all rare earth elements in rare earth magnetic material waste. This is a method for processing rare earth magnetic material waste that fully utilizes the metal in the rare earth magnetic material waste and realizes the full recycling of the metal in the rare earth magnetic material. The present invention can recover rare earth oxides and other metals from the rare earth magnetic material waste. The method has simple operation, low cost, no acid-base continuous cycle, no waste, is suitable for continuous operation, and is more suitable for the promotion and application of large-scale industrial production.

The invention provides a method for recovering all rare earth elements in rare earth magnetic material waste, which includes the following steps:

1) After crushing, burning and oxidizing the rare earth magnetic material waste, sufficient oxides are obtained;

2) Mix the sufficient oxides obtained in the above steps with carbon, reduce them through heat treatment, then cool them, and then separate them to obtain metal materials and rare earth oxides.

Preferably, the particle size of the crushed rare earth magnetic material waste is less than or equal to 0.061mm;

The combustion oxidation method carries out combustion oxidation in an oxygen-containing atmosphere;

The oxygen volume content of the oxygen-containing atmosphere is 4% to 21%.

Preferably, the temperature of the combustion oxidation is greater than or equal to 500°C;

The combustion and oxidation time is 12 to 24 hours.

Preferably, the rare earth magnetic material waste contains one or more rare earths selected from the group consisting of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium and yttrium. element;

The mass ratio of the sufficient oxide to carbon is, based on the Fe element in the sufficient oxide, the mass ratio of Fe to carbon is (2.4-2.8): 1;

The carbon includes one or more of blast furnace coke, pitch coke and charcoal.

Preferably, the carbon includes waste rare earth molten salt electrolysis anodes and/or waste graphite tanks;

The temperature of the heat treatment reduction is greater than or equal to 710°C;

The heat treatment reduction time is 4 to 6 hours.

Preferably, the separation method includes peeling;

After the cooling, in the obtained material, the rare earth oxide is located in the upper layer of the material;

The rare earth oxide has a loose mass structure.

Preferably, the rare earth oxide also includes one or more of carbon, aluminum oxide, titanium oxide, niobium oxide and iron oxide;

The mass content of the aluminum oxide in the rare earth oxide is 0.1% to 0.5%.

Preferably, the mass content of the titanium oxide in the rare earth oxide is 0.03% to 0.10%;

The mass content of the niobium oxide in the rare earth oxide is 0.03% to 0.3%;

The mass content of the iron oxide in the rare earth oxide is 0.3% to 10%.

Preferably, the metal material includes an alloy of iron group elements;

The metal material also includes one or more of rare earth elements, aluminum elements and carbon elements.

Preferably, the mass content of the rare earth elements in the metal material is 90% to 99.5%;

The mass content of the aluminum element in the metal material is 0.03% to 0.10%;

The mass content of the carbon element in the metal material is 0.005% to 0.1%.

The invention provides a method for recovering all rare earth elements in rare earth magnetic material waste, which includes the following steps: first, the rare earth magnetic material waste is crushed, burned and oxidized to obtain sufficient oxides; and then the sufficient oxides obtained in the above steps are mixed with carbon After mixing, reduction through heat treatment, cooling, and separation, metal materials and rare earth oxides are obtained. Compared with the existing technology, the present invention creatively designs a recycling method with specific process routes and process parameters. This method fully utilizes the metal in the rare earth magnetic material waste and realizes the full recycling of the metal in the rare earth magnetic material. Methods for processing rare earth magnetic material waste. The invention can recover rare earth oxides and other metals from rare earth magnetic material waste. The method has simple operation, low cost, no acid and alkali continuous circulation, no waste, and is suitable for continuous operation.

This invention first removes impurities, crushes and oxidizes the materials, converts rare earth metals, iron and other metals into oxides, and reduces the oxides of iron, copper, etc. into metals through carbon reducers. The metals are in a liquid state and the oxides are in a liquid state. In solid state, it is poured into a mold, and after cooling, the metal and oxide are effectively separated by physical methods. The present invention can realize full recycling of metals in rare earth magnetic material waste through this recycling process, and the operation is simple and convenient, the process is continuously controllable, low cost, does not require the use of acids and bases, does not produce waste water, does not emit toxic gases, and has no waste. It has very little environmental pollution, is suitable for continuous operation, and is more suitable for the promotion and application of large-scale industrial production.

Experimental results show that using the method for recovering all rare earth elements from rare earth material waste provided by the present invention, the yield is greater than 92.5%, which is greater than 90% of the industry, and the recovery path is simple, no waste is generated, and the cost is low.

Detailed ways

In order to further understand the present invention, the preferred embodiments of the present invention are described below in conjunction with the examples. However, it should be understood that these descriptions are only to further illustrate the features and advantages of the present invention and are not intended to limit the claims of the invention.

All raw materials of the present invention have no particular restrictions on their sources. They can be purchased in the market or prepared according to conventional methods well known to those skilled in the art.

There is no particular limit on the purity of all the raw materials in the present invention. The present invention preferably adopts industrial purity or conventional purity used in the field of NdFeB magnet recycling.

The invention provides a method for recovering all rare earth elements in rare earth magnetic material waste, which includes the following steps:

1) After crushing, burning and oxidizing the rare earth magnetic material waste, sufficient oxides are obtained;

2) Mix the sufficient oxides obtained in the above steps with carbon, reduce them through heat treatment, then cool them, and then separate them to obtain metal materials and rare earth oxides.

In the present invention, all rare earth elements preferably refer to the recovery of all rare earth elements in the rare earth magnetic material waste, including light rare earths and/or heavy rare earths. This recycling method belongs to the fire recycling method.

In the present invention, the rare earth magnetic material waste is first crushed, burned and oxidized to obtain sufficient oxides.

In the present invention, the particle size of the pulverized rare earth magnetic material waste is preferably less than or equal to 0.061 mm, more preferably less than or equal to 0.06 mm, and less than or equal to 0.059 mm.

In the present invention, the combustion oxidation method is preferably carried out in an oxygen-containing atmosphere.

In the present invention, the oxygen volume content of the oxygen-containing atmosphere is preferably 4% to 21%, more preferably 8% to 17%, and more preferably 11% to 13%.

In the present invention, the temperature of the combustion oxidation is preferably greater than or equal to 500°C, more preferably greater than or equal to 600°C, and even more preferably greater than or equal to 800°C. Specifically, it can be 500-1450°C, or 600-1350°C, or 700-1250°C, or 800-1150°C.

In the present invention, the combustion and oxidation time is preferably 12 to 24 hours, more preferably 14 to 22 hours, and more preferably 16 to 20 hours.

In the present invention, the rare earth magnetic material waste preferably contains one of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium and yttrium or A variety of rare earth elements are more preferably one of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium and yttrium.

Finally, in the present invention, the sufficient oxide obtained in the above steps is mixed with carbon, reduced through heat treatment, then cooled, and separated to obtain metal materials and rare earth oxides.

In the present invention, the mass ratio of the sufficient oxide to carbon is, based on the Fe element in the sufficient oxide, the mass ratio of Fe to carbon is preferably (2.4-2.8):1, more preferably (2.45-2.75 ): 1, more preferably (2.5-2.7): 1, more preferably (2.55-2.65): 1.

In the present invention, the carbon preferably includes one or more of blast furnace coke, pitch coke and charcoal, more preferably blast furnace coke, pitch coke or charcoal.

In the present invention, the carbon preferably includes waste rare earth molten salt electrolysis anodes and/or waste graphite tanks, and more preferably is waste rare earth molten salt electrolysis anodes or waste graphite tanks.

In the present invention, the temperature of the heat treatment reduction is preferably equal to or greater than 710°C, more preferably equal to or greater than 750°C, and greater than or equal to 800°C. Specifically, it can be 710-1450°C, or 800-1200°C, or 900-1100°C.

In the present invention, the heat treatment reduction time is preferably 4 to 6 hours, more preferably 4.4 to 5.6 hours, and more preferably 4.8 to 5.2 hours.

In the present invention, the separation method preferably includes peeling off.

In the present invention, in the material obtained after the cooling, the rare earth oxide is preferably located in the upper layer of the material.

In the present invention, the rare earth oxide preferably has a loose mass structure.

In the present invention, the rare earth oxide preferably includes one or more of carbon, aluminum oxide, titanium oxide, niobium oxide and iron oxide, and more preferably carbon, aluminum oxide, titanium oxide substance, niobium oxide or iron oxide. Specifically, the iron oxide preferably includes ferric oxide and ferric tetroxide, wherein ferric oxide is ≤10% and ferric oxide is >90%.

In the present invention, the mass content of the aluminum oxide in the rare earth oxide is preferably 0.1% to 0.5%, more preferably 0.15% to 0.45%, more preferably 0.2% to 0.4%, and more preferably 0.25% to 0.25%. 0.35%.

In the present invention, the mass content of the titanium oxide in the rare earth oxide is preferably 0.03% to 0.10%, more preferably 0.04% to 0.09%, more preferably 0.05% to 0.08%, and more preferably 0.06% to 0.06%. 0.07%.

In the present invention, the mass content of the niobium oxide in the rare earth oxide is preferably 0.03% to 0.3%, more preferably 0.08% to 0.25%, and more preferably 0.13% to 0.2%.

In the present invention, the mass content of the iron oxide in the rare earth oxide is preferably 0.3% to 10%, more preferably 2% to 8%, and more preferably 4% to 6%.

In the present invention, the metal material preferably includes an iron group element alloy.

In the present invention, the metal material preferably includes one or more of rare earth elements, aluminum elements and carbon elements, more preferably rare earth elements, aluminum elements or carbon elements.

In the present invention, the mass content of the rare earth element in the metal material is preferably 90% to 99.5%, more preferably 92% to 98%, and more preferably 94% to 96%.

In the present invention, the mass content of the aluminum element in the metal material is preferably 0.03% to 0.10%, more preferably 0.04% to 0.09%, more preferably 0.05% to 0.08%, and more preferably 0.06% to 0.07% .

In the present invention, the mass content of the carbon element in the metal material is preferably 0.005% to 0.1%, more preferably 0.01% to 0.08%, and more preferably 0.03% to 0.06%.

The present invention is a complete and refined overall technical solution, which can better improve recycling efficiency and process continuity, reduce recycling costs and environmental impact. The above-mentioned recovery method of all rare earth elements in rare earth magnetic material waste can specifically include the following steps:

A method for recovering all rare earth elements in rare earth magnetic material waste, including the following steps:

Step (1): Add the crushed material to the rotary kiln for full oxidation;

Step (2): Mix the fully oxidized material and an appropriate amount of carbon powder evenly, and put it into the heating device;

Step (3): The heating device is heated, the carbon particles and the oxides of the iron group elements are fully reduced, and the oxides of the iron group elements are reduced to iron group metals;

Step (4): Pour the material reacted in step (3) into the mold, and the mold is cooled by water cooling. Cool to below 100℃;

Step (5): Separate the cooled material in step (4) to obtain rare earth oxides, trace amounts of one or more of aluminum oxides, titanium oxides, niobium oxides, and iron group element alloys . Among them, iron group element alloys can be sold directly to steelmaking companies. Specifically, the iron group element alloy is at the bottom, and the rare earth oxide is relatively loose and can be separated by peeling off.

Specifically, the first choice for carbon is rare earth molten salt electrolysis waste anodes or waste graphite tanks.

Specifically, the carbon can also be equipped with blast furnace coke, pitch coke or charcoal.

Specifically, the particle size of the processed material after crushing in step (1) is less than 0.061 mm (250 mesh).

Specifically, the treated materials containing at least rare earth elements and iron group elements are materials that have removed oil stains and reduced impurities to appropriate levels.

Specifically, the oxidation device can be selected from an atmosphere protected rotary kiln, an atmosphere furnace or a tunnel kiln.

Specifically, the smelting device can be selected from medium frequency furnaces, power frequency furnaces, and high frequency induction furnaces.

Specifically, the magnetic material waste includes one or more rare earth elements among lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium and yttrium.

Specifically, the particle size of the processed material after the reduced oxide is crushed is less than 0.061 mm (250 mesh).

The above content of the present invention provides a method for recovering all rare earth elements in rare earth magnetic material waste. The recycling method with specific process routes and process parameters designed by the present invention is a method for processing rare earth magnetic material waste that fully utilizes the metal in the rare earth magnetic material waste and realizes the full recovery and utilization of the metal in the rare earth magnetic material. The invention can recover rare earth oxides and other metals from rare earth magnetic material waste. The method has simple operation, low cost, no acid and alkali continuous circulation, no waste, and is suitable for continuous operation.

This invention first removes impurities, crushes and oxidizes the materials, converts rare earth metals, iron and other metals into oxides, and reduces the oxides of iron, copper, etc. into metals through carbon reducers. The metals are in a liquid state and the oxides are in a liquid state. In solid state, it is poured into a mold, and after cooling, the metal and oxide are effectively separated by physical methods. The present invention can realize full recycling of metals in rare earth magnetic material waste through this recycling process, and the operation is simple and convenient, the process is continuously controllable, low cost, does not require the use of acids and bases, does not produce waste water, does not emit toxic gases, and has no waste. It has very little environmental pollution, is suitable for continuous operation, and is more suitable for the promotion and application of large-scale industrial production.

Experimental results show that using the method for recovering all rare earth elements from rare earth material waste provided by the present invention, the yield is greater than 92.5%, which is greater than 90% of the industry, and the recovery path is simple, no waste is generated, and the cost is low.

In order to further illustrate the present invention, a method for recovering all rare earth elements from rare earth magnetic material waste provided by the present invention is described in detail below with reference to the examples. However, it should be understood that these examples are implemented based on the technical solution of the present invention. Detailed embodiments and specific operating procedures are given only to further illustrate the features and advantages of the present invention, but are not intended to limit the claims of the present invention, and the protection scope of the present invention is not limited to the following examples.

Example 1

The R-Fe-B ultrafine powder is burned in a rotary kiln and kept at 800°C for 120 minutes. The material is oxidized into oxides, of which the mass of iron oxides accounts for 49.3%. Mix the oxidized material and carbon powder (ash content less than 1%) evenly. The mass ratio of carbon to iron oxide is 1:6.0. Add the mixed materials into the intermediate frequency furnace, raise the temperature in the atmospheric environment, and treat it at 1350°C for 30 minutes. Pour the material into the casting ladle and quickly cool it to below 200°C. After cooling to room temperature, the metal blocks and metal particles are separated from other materials.

In Example 1 of the present invention, 102kg of oxide was put in, and after reduction, 35.76kg of metal and 48.93kg of oxide were obtained. The yield of rare earth elements is 95.15%.

The content of rare earth elements in metals was measured using ICP-AES, the content of iron in oxides was measured using the GB/T 12690.6-2017 standard method, and C was measured using a carbon-sulfur meter.

See Table 1. Table 1 is an analysis of the main element contents in the rare earth oxides and metal alloys in Example 1 of the present invention.

Table 1

project Fe Pr Nd Gd Al C Phase A 99.5 0.01 0.01 0 0.42 0.25 Phase B 2.22 19.41 77.62 0.483 0.076 0.01

Example 2

For R-Fe-B irregular block materials, first use a high-speed crusher to break into materials smaller than 0.061mm, and then use a rotary kiln for combustion treatment. The materials are kept at 800°C for 120 minutes. The materials are oxidized into oxides, among which the mass of iron oxides Accounting for 69.89%. Take 20kg of the oxidized material and mix it with 2.33Kg of graphite powder, then add it to the intermediate frequency furnace in three batches and smelt for 210 minutes. Pour the smelted material into the pouring mold (the mold needs to be water-cooled), and then separate the metal block from other materials after cooling to close to room temperature.

In Example 2 of the present invention, 12.9 kg of metal and 8.02 kg of oxide were obtained after smelting. The rare earth element yield is 93.5%.

See Table 2. Table 2 is an analysis of the main element contents in the rare earth oxides and metal alloys in Example 2 of the present invention.

Table 2

project Fe Pr Nd Ce Gd Al C Phase A 99.5 0.01 0.01 0.01 0 0.02 0.237 Phase B 3.52 16.41 51.21 28.2 0.483 0.196 0.035

Example 3

For R-Fe-B grinding powder, non-metallic oxides are first selected through a magnetic separator, and then burned in a rotary kiln. The material is kept at 850°C for 120 minutes, and the material is oxidized into oxides, of which the mass of iron oxides accounts for 69.5%. . Mix 20kg of deoxidized material with 2.0 graphite powder, add it to a 50kg intermediate frequency furnace in three batches, and smelt for 180 minutes. Then pour the material into a ladle (water cooling). After cooling to near room temperature, separate the metal blocks, metal particles and other materials. .

In Example 3 of the present invention, 12.54kg of metal and 8.52kg of oxide were obtained after smelting. The yield of rare earth elements is 92.57%.

See Table 3. Table 3 is an analysis of the main element contents in the rare earth oxides and metal alloys in Example 3 of the present invention.

table 3

project Fe Pr Nd Ce Gd Si C Phase A 99.5 0.01 0.01 0.01 0 0.032 0.178 Phase B 4.57 16.40 51.22 26.7 0.483 0.046 0.055

The above is a detailed introduction to the method for recovering all rare earth elements in rare earth magnetic material waste provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above examples is only for assistance. An understanding of the methods and core concepts of the invention, including the best mode, and also enables any person skilled in the art to practice the invention, including making and using any devices or systems and performing any combined methods. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims, and may include other embodiments that occur to those skilled in the art. These other embodiments shall also be included within the scope of the claims if they have structural elements that do not differ from the literal expressions of the claims, or if they include equivalent structural elements with insubstantial differences from the literal expressions of the claims.

Claims (10)

1. A method for recovering all rare earth elements from rare earth magnetic material waste, which is characterized by comprising the following steps: 1) After crushing, burning and oxidizing the rare earth magnetic material waste, sufficient oxides are obtained; 2) Mix the sufficient oxides obtained in the above steps with carbon, reduce them through heat treatment, then cool them, and then separate them to obtain metal materials and rare earth oxides. 2. The recycling method according to claim 1, characterized in that the particle size of the crushed rare earth magnetic material waste is less than or equal to 0.061 mm; The combustion oxidation method carries out combustion oxidation in an oxygen-containing atmosphere; The oxygen volume content of the oxygen-containing atmosphere is 4% to 21%. 3. The recycling method according to claim 1, characterized in that the temperature of the combustion and oxidation is greater than or equal to 500°C; The combustion and oxidation time is 12 to 24 hours. 4. The recycling method according to claim 1, characterized in that the rare earth magnetic material waste contains lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, one or more rare earth elements from the group consisting of lutetium, scandium and yttrium; The mass ratio of the sufficient oxide to carbon is, based on the Fe element in the sufficient oxide, the mass ratio of Fe to carbon is (2.4-2.8): 1; The carbon includes one or more of blast furnace coke, pitch coke and charcoal. 5. The recycling method according to claim 1, wherein the carbon includes waste rare earth molten salt electrolysis anodes and/or waste graphite tanks; The temperature of the heat treatment reduction is greater than or equal to 710°C; The heat treatment reduction time is 4 to 6 hours. 6. The recycling method according to claim 1, characterized in that the separation method includes stripping; After the cooling, in the obtained material, the rare earth oxide is located in the upper layer of the material; The rare earth oxide has a loose mass structure. 7. The recycling method according to claim 1, wherein the rare earth oxide further includes one or more of carbon, aluminum oxide, titanium oxide, niobium oxide and iron oxide; The mass content of the aluminum oxide in the rare earth oxide is 0.1% to 0.5%. 8. The recycling method according to claim 7, characterized in that the mass content of the titanium oxide in the rare earth oxide is 0.03% to 0.10%; The mass content of the niobium oxide in the rare earth oxide is 0.03% to 0.3%; The mass content of the iron oxide in the rare earth oxide is 0.3% to 10%. 9. The recycling method according to claim 1, wherein the metal material includes an alloy of iron group elements; The metal material also includes one or more of rare earth elements, aluminum elements and carbon elements. 10. The recycling method according to claim 9, characterized in that the mass content of the rare earth elements in the metal material is 90% to 99.5%; The mass content of the aluminum element in the metal material is 0.03% to 0.10%; The mass content of the carbon element in the metal material is 0.005% to 0.1%.