Rotary kiln suitable for recycling neodymium iron boron waste and recycling method

Abstract

The invention discloses a rotary kiln suitable for recycling neodymium iron boron waste and a recycling method, and belongs to the field of rare earth recycling. The rotary kiln comprises a kiln head, a kiln middle section and a kiln tail which are sequentially connected; the kiln head is positioned at the front end of the rotary kiln; the kiln middle section is positioned between the kiln head and the kiln tail; the kiln tail is positioned at the rear end of the rotary kiln; the kiln head is provided with a feeding hole; the kiln middle section is sequentially provided with a pyrolysis area and a cooling area; the pyrolysis area is located at the front end of the kiln middle section and used for conducting pyrolysis treatment on neodymium iron boron waste. The cooling area is positioned behind the pyrolysis area and is used for cooling the pyrolyzed waste materials; the kiln tail is sequentially provided with a discharging port, a screen and an air suction port. The rotary kiln provided by the invention is combined with the neodymium iron boron waste material recovery method provided by the invention, so that the roasting effect on the neodymium iron boron waste material can be effectively improved under the condition of low energy consumption, and finally, the rare earth recovery rate is greatly increased.

Description

Technical Field

[0001] The present application belongs to the field of rare earth recycling, and specifically relates to a rotary kiln and a recycling method suitable for recycling NdFeB waste. Background Art

[0002] With the rapid development of science and technology, NdFeB magnets are widely used in electronic devices such as mobile phones, headphones, and computer hard drives due to their excellent magnetic properties. However, the accelerated replacement of electronic products has led to an increase in the amount of NdFeB magnets discarded year by year. At the same time, a large amount of waste will be generated during the production and processing of NdFeB magnets. These wastes are rich in rare earth elements and have great recycling value. As an important rare earth functional material, the demand for NdFeB magnets continues to increase with the rapid development of new energy vehicles, wind power generation, electronic information and other industries. China is the world's largest producer of NdFeB, with an output of 170,000 tons in 2018, accounting for nearly 90% of the world's total output. However, about 30% of waste will be generated during the production process, plus a large number of magnets that are scrapped every year due to reaching their service life. These wastes contain 20%-30% of rare earth elements, which are valuable secondary resources. Recycling NdFeB waste will not only help alleviate the shortage of rare earth resources in my country, but also effectively reduce environmental pollution and resource waste, and promote the sustainable development of the rare earth industry. At present, there are various methods for recycling NdFeB waste, mainly including hydrometallurgy, electrochemical method and pyrometallurgy, each of which has its advantages and disadvantages. Wet recovery processes such as hydrochloric acid full dissolution method, hydrochloric acid excellent dissolution method, sulfuric acid double salt precipitation method, etc., although they have strong adaptability to raw materials and high purity of rare earth products, have a long process and are not environmentally friendly; pyrometallurgical recovery processes such as oxidation method, chlorination method, liquid alloy extraction method, etc., have a short process and are relatively friendly to the environment, but usually obtain mixed rare earth compounds with low product purity.

[0003] In addition, the oxidation roasting process of NdFeB waste is a self-heating oxidation reaction, which can easily lead to a rapid increase in local temperature in the kiln, material agglomeration, and affect the full oxidation of rare earth elements and the final leaching rate. Therefore, taking appropriate heat dissipation measures and strengthening temperature control to prevent local overheating and sintering is crucial to improving the recovery rate of rare earth elements. Summary of the invention

[0004] In order to solve at least one of the above technical problems, a method for recovering rare earths with simple operation, high rare earth leaching rate, low cost and convenient use is developed. The present application provides a rotary kiln and a recovery method suitable for recovering NdFeB waste.

[0005] In a first aspect, the present application provides a rotary kiln suitable for recycling NdFeB waste, comprising a kiln head 1, a kiln middle section 2 and a kiln tail 3 connected in sequence;

[0006] The kiln head 1 is located at the front end of the rotary kiln;

[0007] The kiln middle section 2 is located between the kiln head 1 and the kiln tail 3;

[0008] The kiln tail 3 is located at the rear end of the rotary kiln;

[0009] The kiln head 1 is provided with a feed inlet 4;

[0010] The kiln middle section 2 is provided with a pyrolysis zone 5 and a cooling zone 6 in sequence;

[0011] The pyrolysis zone 5 is located at the front end of the kiln middle section 2 and is used for pyrolysis treatment of NdFeB waste;

[0012] The cooling zone 6 is located after the pyrolysis zone 5 and is used to cool the waste after the pyrolysis treatment;

[0013] The kiln tail 3 is provided with a screen 7, an air exhaust port 8 and a material discharge port 9 in sequence.

[0014] By adopting the above technical solutions, the rotary kiln can realize the continuous feeding, pyrolysis, cooling and separation of NdFeB waste, simplifying the operation process and improving production efficiency. The division of each functional area enables each processing step to be carried out under optimal conditions, thereby improving the recovery rate and purity of rare earth elements.

[0015] Optionally, the rotary kiln has an inclination angle of 2-5° to the horizontal plane, and the kiln head 1 is higher than the kiln tail 3.

[0016] By adopting the above technical solutions, the inclined design enables the materials to move smoothly under the action of gravity, reducing the demand for mechanical power and energy consumption. At the same time, the materials stay in the kiln for a longer time, which helps to improve the effect of pyrolysis and cooling, and ensure the full release and recovery of rare earth elements.

[0017] Optionally, baffles 10 are provided in both the pyrolysis zone 5 and the cooling zone 6; the number of groups of the baffles 10 is 3-5; and the height of the baffles is 0.1 m-0.2 m.

[0018] By adopting the above technical solution, the design of the baffle increases the residence time of the material in the kiln, making the material more uniform during pyrolysis and cooling. The height of the baffle is moderate, which will not hinder the flow of materials and can effectively prevent excessive aggregation of materials, thereby improving the leaching rate and recovery efficiency of rare earth elements.

[0019] Optionally, the baffle 10 is a spiral auger-like structure.

[0020] By adopting the above technical solution, the spiral auger-shaped baffle further enhances the stirring and dispersion effect of the material, making the material more uniform during the pyrolysis and cooling process. This structural design helps to increase the leaching rate of rare earth elements, while reducing the possibility of material agglomeration and improving the treatment effect.

[0021] Optionally, the baffles 10 arranged in the pyrolysis zone 5 and the cooling zone 6 have an angle of 30-50° and 40-70° with the vertical direction of the rotary kiln cylinder, respectively.

[0022] By adopting the above technical solution, different baffle angle designs meet the processing requirements of the two different stages of pyrolysis and cooling. The baffle angle in the pyrolysis zone is gentle, which helps the material to be heated evenly at high temperatures; the baffle angle in the cooling zone is steeper, which helps the material to cool quickly. This design optimizes the processing process and improves the recovery rate of rare earth elements and product quality.

[0023] In a second aspect, the present application provides a method for recycling NdFeB waste, using the rotary kiln provided by the present application; the method comprises the following steps:

[0024] S1. Add steel balls to the crushed NdFeB waste to obtain a mixture;

[0025] S2, pouring the mixture obtained in step S1 into the rotary kiln feed port 4 for mixing, then passing the mixture through the pyrolysis zone 5 for pyrolysis reaction, and then passing through the cooling zone 6 for cooling to obtain a cooled mixture;

[0026] S3, the mixture in step S2 is separated through the sieve 7, and the separated materials are then passed through the discharge port 9 to collect the steel balls and the roasted products.

[0027] By adopting the above technical scheme, the present application proposes a method for recycling NdFeB waste, and the specific steps are as follows: first, the NdFeB waste is crushed, and then steel balls with a certain diameter ratio are added. The mixed materials are poured into a rotary kiln. The steel balls play a key role in this process. They can not only absorb part of the self-heating heat generated by the NdFeB waste during the oxidation roasting process, effectively control the temperature in the kiln, and prevent the material from agglomerating and insufficiently oxidized due to excessive temperature, but also continue to play a grinding role in the whole process of oxidation roasting, which helps to further crush large particles of NdFeB waste, increase the specific surface area of ​​the material, and improve the leaching rate of rare earth elements. The design of the screen allows the steel balls and rare earth elements to be effectively separated, simplifying the subsequent processing steps. In addition, the addition of steel balls improves the fluidity of the material, making the material more evenly distributed in the rotary kiln, and further improving the effect of pyrolysis and cooling. After the material is fully cooled by the baffle of the rotary kiln cooling section, the material and the steel balls are separated by the screen set at the tail of the rotary kiln. The separated steel balls are cooled by water and returned to the kiln head for reuse. This method optimizes the structure of the rotary kiln, adds steel balls with dual functions of heat storage and grinding, and controls the temperature of the reaction zone, thereby achieving efficient oxidation of NdFeB waste and significantly improving the leaching rate of rare earth elements. This method is simple to operate and easy to use, and greatly reduces the recycling cost of NdFeB waste. It solves the problems of complex operation, low rare earth leaching rate and high cost of traditional recycling methods, and achieves efficient and low-cost recycling of NdFeB waste.

[0028] Optionally, the diameter of the steel ball in step S1 is 20-40 mm.

[0029] By adopting the above technical solution, selecting steel balls of appropriate diameter can significantly improve the treatment effect of NdFeB waste. Steel balls of 20-40mm can not only effectively absorb the additional self-heating heat generated by part of the NdFeB waste during the oxidation roasting process in addition to the heat required for roasting, and prevent the material from agglomerating and insufficient oxidation due to excessive temperature, but also continue to play a grinding role in the whole roasting process, further crushing large particles of NdFeB waste, increasing the specific surface area of ​​the material, and improving the leaching rate of rare earth elements. In addition, steel balls of this diameter can better disperse the material during the mixing process, improve the fluidity of the material, make the material more evenly distributed in the rotary kiln, and further improve the effect of pyrolysis and cooling. Through these measures, the efficient treatment of NdFeB waste and the high leaching rate of rare earth elements are ensured, while the operation process is simplified and the recycling cost is reduced.

[0030] Optionally, the steel balls in step S1 are steel balls of three different particle sizes; the diameters of the three steel balls of different particle sizes are 20 mm, 30 mm, and 40 mm respectively; and the mass percentages are 0-60%: 0-40%: 0-30%.

[0031] By adopting the above technical solution, the combined use of steel balls of different particle sizes can significantly improve the treatment effect of NdFeB waste. 20mm steel balls can penetrate into the tiny gaps of the material for fine grinding; 30mm steel balls can grind and disperse on a medium scale; 40mm steel balls provide sufficient impact force to further crush large particles of NdFeB waste. This combination of multi-particle size steel balls can not only effectively absorb the additional self-heating heat generated by part of the NdFeB waste during the oxidation roasting process in addition to the heat required for roasting, and prevent the phenomenon of insufficient oxidation of materials due to excessive temperature caused by agglomeration of materials, but also continue to play a grinding role in the entire roasting process, increase the specific surface area of ​​the material, and improve the leaching rate of rare earth elements. In addition, steel balls of different particle sizes cooperate with each other during the mixing process, which enhances the dispersion and fluidity of the material, makes the material more evenly distributed in the rotary kiln, and further improves the effect of pyrolysis and cooling. The design of the screen enables the steel balls and roasting products to be effectively separated, simplifying the subsequent processing steps. The separated steel balls are cooled by water and then returned to the kiln head for reuse. These measures ensure the efficient oxidation of NdFeB waste and the high leaching rate of rare earth elements, simplify the operation process, reduce the recycling cost, solve the problems of complex operation, low rare earth leaching rate and high cost of traditional recycling methods, and realize the efficient and low-cost recycling of NdFeB waste.

[0032] Optionally, the pore size of the sieve 7 is 16 mm.

[0033] By adopting the above technical solution, the appropriate mesh aperture size can effectively separate the steel balls and rare earth elements, preventing the fine rare earth particles from being blocked by the mesh. This design ensures the complete recovery of the roasting product.

[0034] Optionally, in step S1, the mixing mass ratio of the NdFeB waste and the steel balls is 1:1-5.

[0035] By adopting the above technical solution, a reasonable mixing ratio of waste materials and steel balls can ensure uniform distribution and adequate treatment of the materials in the rotary kiln. The mixture under this ratio shows good fluidity and dispersibility during pyrolysis and cooling, which improves the leaching rate and recovery efficiency of rare earth elements.

[0036] The present invention includes at least one of the following beneficial technical effects.

[0037] 1. The rotary kiln can realize the continuous feeding, pyrolysis, cooling and separation of NdFeB waste, simplifying the operation process and improving production efficiency. The division of each functional area enables each processing step to be carried out under the best conditions, thereby improving the recovery rate and purity of rare earth elements.

[0038] 2. The design of the baffle increases the residence time of the material in the kiln, making the material more uniform during pyrolysis and cooling. The height of the baffle is moderate, which will not hinder the flow of materials, but can effectively prevent excessive aggregation of materials, thereby improving the leaching rate and recovery efficiency of rare earth elements.

[0039] 3. The present application proposes a method for recycling NdFeB waste, and the specific steps are as follows: first, the NdFeB waste is crushed, and then steel balls of a certain diameter ratio are added to mix evenly. The mixed materials are poured into a rotary kiln. The steel balls play a key role in this process. They can not only absorb the additional self-heating heat generated by part of the NdFeB waste during the oxidation roasting process in addition to the heat required for roasting, but also effectively control the temperature in the kiln, prevent the material from agglomerating and insufficiently oxidized due to excessive temperature, but also continue to play a grinding role in the whole process of oxidation roasting, which helps to further grind large particles of NdFeB waste, increase the specific surface area of ​​the material, and improve the leaching rate of rare earth elements. The design of the screen allows the steel balls and rare earth elements to be effectively separated, simplifying the subsequent processing steps. In addition, the addition of steel balls improves the fluidity of the material, makes the material more evenly distributed in the rotary kiln, and further improves the effect of pyrolysis and cooling. After the material is fully cooled by the baffle of the rotary kiln cooling section, the material and the steel balls are separated by the screen set at the tail of the rotary kiln. The separated steel balls are returned to the kiln head for reuse after being cooled by water, thus realizing the recycling of the steel balls. This method optimizes the inclination angle of the rotary kiln, the height, number and spiral inclination of the baffles in the kiln, and regulates the temperature of the reaction zone, thereby realizing efficient oxidation of NdFeB waste and significantly improving the leaching rate of rare earth elements. This method is simple to operate and easy to use, and greatly reduces the recycling cost of NdFeB waste, solves the problems of complex operation, low rare earth leaching rate and high cost of traditional recycling methods, and realizes efficient and low-cost recycling of NdFeB waste.

[0040] 4. Selecting steel balls with appropriate diameters can significantly improve the treatment effect of NdFeB waste. Steel balls of 20-40mm can not only effectively absorb part of the self-heating heat generated by NdFeB waste during the oxidation roasting process, and prevent the material from agglomerating and insufficient oxidation due to excessive temperature, but also continue to play a grinding role in the entire roasting process, further crushing large particles of NdFeB waste, increasing the specific surface area of ​​the material, and improving the leaching rate of rare earth elements. In addition, steel balls of this diameter can better disperse the material during the mixing process, improve the fluidity of the material, make the material more evenly distributed in the rotary kiln, and further improve the pyrolysis and cooling effects. Through these measures, the efficient treatment of NdFeB waste and the high leaching rate of rare earth elements are ensured, while the operation process is simplified and the recycling cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1This is a structural diagram of a rotary kiln. In the figure, 1 is the kiln head; 2 is the middle section of the kiln; 3 is the kiln tail; 4 is the feed inlet; 5 is the pyrolysis zone; 6 is the cooling zone; 7 is the screen; 8 is the exhaust port; 9 is the discharge port; and 10 is the baffle. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and advantages of the present application more clear, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.

[0043] With the rapid development of science and technology, NdFeB magnets are widely used in electronic devices such as mobile phones, headphones, and computer hard drives due to their excellent magnetic properties. However, the accelerated replacement of electronic products has led to an increase in the amount of NdFeB magnets discarded year by year. At the same time, a large amount of waste will be generated during the production and processing of NdFeB magnets. These wastes are rich in rare earth elements and have great recycling value. As an important rare earth functional material, the demand for NdFeB magnets continues to increase with the rapid development of new energy vehicles, wind power generation, electronic information and other industries. China is the world's largest producer of NdFeB, with an output of 170,000 tons in 2018, accounting for nearly 90% of the world's total output. However, about 30% of waste will be generated during the production process, plus a large number of magnets that are scrapped every year due to reaching their service life. These wastes contain 20%-30% of rare earth elements, which are valuable secondary resources. Recycling NdFeB waste will not only help alleviate the shortage of rare earth resources in my country, but also effectively reduce environmental pollution and resource waste, and promote the sustainable development of the rare earth industry. At present, there are various methods for recycling NdFeB waste, mainly including hydrometallurgy, electrochemical method and pyrometallurgy, each of which has its advantages and disadvantages. Wet recovery processes such as hydrochloric acid full dissolution method, hydrochloric acid excellent dissolution method, sulfuric acid double salt precipitation method, etc., although they have strong adaptability to raw materials and high purity of rare earth products, have a long process and are not environmentally friendly; pyrometallurgical recovery processes such as oxidation method, chlorination method, liquid alloy extraction method, etc., have a short process and are relatively friendly to the environment, but usually obtain mixed rare earth compounds with low product purity.

[0044] In addition, the oxidation roasting process of NdFeB waste is a self-heating oxidation reaction, which causes the local temperature in the kiln to rise rapidly, the material to agglomerate, and affects the full oxidation and final leaching rate of rare earth elements. Therefore, taking appropriate heat dissipation measures and strengthening temperature control to prevent local overheating are crucial to improving the recovery rate of rare earth elements. Therefore, in order to solve at least one of the above technical problems, the inventors of the present application have developed a method for recovering rare earths that is simple to operate, has a high rare earth leaching rate, is low in cost, and is easy to use. In the present application, a rotary kiln and a recovery method suitable for recovering NdFeB waste are provided.

[0045] In a first aspect, the present application provides a rotary kiln suitable for recycling NdFeB waste, comprising a kiln head 1, a kiln middle section 2 and a kiln tail 3 connected in sequence;

[0046] The kiln head 1 is located at the front end of the rotary kiln;

[0047] The kiln middle section 2 is located between the kiln head 1 and the kiln tail 3;

[0048] The kiln tail 3 is located at the rear end of the rotary kiln;

[0049] The kiln head 1 is provided with a feed inlet 4;

[0050] The middle section 2 of the kiln is provided with a pyrolysis zone 5 and a cooling zone 6 in sequence;

[0051] The pyrolysis zone 5 is located at the front end of the kiln middle section 2 and is used for pyrolysis treatment of NdFeB waste;

[0052] The cooling zone 6 is located after the pyrolysis zone 5 and is used to cool the waste after the pyrolysis treatment;

[0053] The kiln tail 3 is provided with a screen 7, an exhaust port 8 and a discharge port 9 in sequence. Based on the above, the present application can realize the continuous feeding, pyrolysis, cooling and separation of NdFeB waste by the rotary kiln, simplify the operation process and improve the production efficiency. The division of each functional area enables each processing step to be carried out under the best conditions, thereby improving the recovery rate and purity of rare earth elements.

[0054] In some embodiments, the rotary kiln has an inclination angle of 2-5° with the horizontal plane, and the kiln head 1 is higher than the kiln tail 3. The inclined design allows the material to move smoothly under the action of gravity, reducing the demand for mechanical power and reducing energy consumption. At the same time, the material stays in the kiln for a longer time, which helps to improve the effect of pyrolysis and cooling, ensure the full oxidation of NdFeB waste, and improve the leaching rate of rare earth elements.

[0055] In some embodiments, baffles 10 are provided in both the pyrolysis zone 5 and the cooling zone 6; the number of baffles 10 is 3-5; and the height of the baffles is 0.1m-0.2m. The design of the baffles increases the residence time of the material in the kiln, making the material more uniform during the pyrolysis and cooling process. The height of the baffles is moderate, which will not hinder the flow of the material, and can effectively prevent the material from overheating and agglomeration, thereby improving the leaching rate and recovery efficiency of rare earth elements.

[0056] In some embodiments, the baffle 10 is a spiral auger-shaped structure. The spiral auger-shaped baffle further enhances the stirring and dispersion effect of the material, making the material more uniform during the pyrolysis and cooling process. This structural design helps to increase the leaching rate of rare earth elements, while reducing the possibility of material agglomeration and improving the treatment effect.

[0057] In some embodiments, the baffles 10 disposed in the pyrolysis zone 5 and the cooling zone 6 are at an angle of 30-50° and 40-70° to the vertical direction of the rotary kiln cylinder, respectively. Different baffle angle designs meet the processing requirements of the two different stages of pyrolysis and cooling. The baffle angle in the pyrolysis zone is relatively gentle, which helps the material to be heated evenly at high temperatures; the baffle angle in the cooling zone is relatively steep, which helps the material to cool quickly. This design optimizes the processing process and improves the recovery rate of rare earth elements and product quality.

[0058] In a second aspect, the present application provides a method for recycling NdFeB waste, using the rotary kiln provided by the present application; the method comprises the following steps:

[0059] S1, adding steel balls to the ground NdFeB waste and mixing evenly to obtain a mixture;

[0060] S2, pouring the mixture obtained in step S1 into the rotary kiln feed port 4 for mixing, then passing the mixture through the pyrolysis zone 5 for pyrolysis reaction, and then passing through the cooling zone 6 for cooling to obtain a cooled mixture;

[0061] S3, the mixture of step S2 is separated through the screen 7, and the separated material is passed through the discharge port 9 to collect steel balls and rare earth elements. The present application proposes a method for recycling NdFeB waste, and the specific steps are as follows: first, the NdFeB waste is crushed, and then steel balls with a certain diameter ratio are added and poured into the rotary kiln. The steel balls play a key role in this process. They can not only absorb the extra self-heating heat generated by part of the NdFeB waste in the oxidation roasting process except the heat required for roasting, but also effectively control the temperature in the kiln, prevent the phenomenon of insufficient oxidation due to material agglomeration caused by excessive temperature, and can also continue to play a grinding role in the whole process of oxidation roasting, which helps to further crush large particles of NdFeB waste, increase the specific surface area of ​​the material, and improve the leaching rate of rare earth elements. The design of the screen allows steel balls and rare earth elements to be effectively separated, simplifying the subsequent processing steps. In addition, the addition of steel balls improves the fluidity of the material, makes the material more evenly distributed in the rotary kiln, and further improves the effect of pyrolysis and cooling. After the material is fully cooled by the baffle of the rotary kiln cooling section, the material and the steel balls are separated by the screen set at the tail of the rotary kiln. The separated steel balls are returned to the kiln head for reuse after water cooling, thus realizing the recycling of the steel balls. This method optimizes the inclination angle of the rotary kiln, the height, number and spiral inclination of the baffles in the kiln, and accurately controls the temperature of the reaction zone, thereby realizing efficient oxidation of NdFeB waste and significantly improving the leaching rate of rare earth elements. This method is simple to operate and easy to use, and greatly reduces the recycling cost of NdFeB waste, solves the problems of complex operation, low rare earth leaching rate and high cost of traditional recycling methods, and realizes efficient and low-cost recycling of NdFeB waste.

[0062] In some embodiments, the diameter of the steel ball in step S1 is 20-40 mm; the mass percentage is 0-60%: 0-40%: 0-30%. Selecting a steel ball of appropriate diameter can significantly improve the treatment effect of NdFeB waste. The 20-40 mm steel ball can not only effectively absorb the additional self-heating heat generated by part of the NdFeB waste during the oxidation roasting process in addition to the heat required for roasting, and prevent the phenomenon of insufficient oxidation of the material due to excessive temperature agglomeration, but also continue to play a grinding role in the whole roasting process, further crushing the large particles of NdFeB waste, increasing the specific surface area of ​​the material, and improving the leaching rate of rare earth elements. In addition, the steel ball of this diameter can be better dispersed in the material during the mixing process, improve the fluidity of the material, make the material more evenly distributed in the rotary kiln, and further improve the effect of pyrolysis and cooling. Through these measures, the efficient oxidation of NdFeB waste and the high leaching rate of rare earth elements are ensured, while simplifying the operation process and reducing the recycling cost.

[0063] In some embodiments, the steel balls in step S1 are three kinds of steel balls with different particle sizes; the diameters of the three kinds of steel balls with different particle sizes are 20mm, 30mm, and 40mm respectively. The combined use of steel balls with different particle sizes can significantly improve the treatment effect of NdFeB waste. The 20mm steel balls can penetrate into the tiny gaps of the material for fine grinding; the 30mm steel balls are ground and dispersed on a medium scale; the 40mm steel balls provide sufficient impact force to further crush the large particles of NdFeB waste. The combined use of this multi-particle size steel ball can not only effectively absorb the additional self-heating heat generated by part of the NdFeB waste in the oxidation roasting process in addition to the heat required for roasting, prevent the phenomenon of insufficient oxidation of materials due to excessive temperature agglomeration, but also continue to play a grinding role in the whole roasting process, increase the specific surface area of ​​the material, and improve the leaching rate of rare earth elements. In addition, the steel balls of different particle sizes cooperate with each other during the mixing process, enhance the dispersibility and fluidity of the material, make the material more evenly distributed in the rotary kiln, and further improve the effect of pyrolysis and cooling. The design of the screen enables the steel balls and rare earth elements to be effectively separated, simplifying the subsequent processing steps. The separated steel balls are returned to the kiln head for reuse after being cooled by water, realizing the recycling of the steel balls. Through these measures, the efficient treatment of NdFeB waste and the high leaching rate of rare earth elements are ensured, while the operation process is simplified, the recycling cost is reduced, and the problems of complex operation, low rare earth leaching rate and high cost of traditional recycling methods are solved, realizing the efficient and low-cost recycling of NdFeB waste.

[0064] In some embodiments, the aperture size of the screen 7 is 16 mm. The appropriate screen aperture size can effectively separate the steel balls and rare earth elements and prevent the fine rare earth particles from being blocked by the screen. This design ensures the complete recovery of rare earth elements and improves the recovery rate and purity.

[0065] In some embodiments, the mixing mass ratio of the NdFeB waste and the steel balls in step S1 is 1:1-5. A reasonable mixing ratio of the waste and the steel balls can ensure uniform distribution and sufficient treatment of the materials in the rotary kiln. The mixture at this ratio exhibits good fluidity and dispersibility during pyrolysis and cooling, thereby improving the leaching rate and recovery efficiency of the rare earth elements. Specific embodiments

[0067] The scheme of the present application is described below in conjunction with the following specific examples. Unless otherwise specified, the raw materials used in the following examples are all from common commercial products, and the devices or equipment used are all purchased from conventional market sales channels.

[0068] Example 1

[0069] The present embodiment provides a method for recycling NdFeB waste, wherein crushed NdFeB waste is added to steel balls with a diameter of 20 mm, the mass ratio of steel balls to materials is 1:1, the mixture is evenly mixed, and poured into the inlet of a rotary kiln with an inclination angle of 2°. Under the action of gravity, the rotary kiln rotates, and the mixture of the material and the steel balls passes through a pyrolysis section of a rotary kiln equipped with three baffles with a height of 0.1 m and an inclination angle of 30° alternately installed. The steel balls absorb a portion of the heat generated by the combustion of the NdFeB waste, and the material reacts fully. Subsequently, the mixture of the material and the steel balls passes through a cooling section of a rotary kiln equipped with three baffles with a height of 0.1 m and an inclination angle of 40° alternately installed, and is fully cooled. The material and the steel balls are separated at the tail of the rotary kiln, and the leaching rate of rare earth elements is calculated.

[0070] The rotary kiln used in this embodiment includes a kiln head 1, a kiln middle section 2 and a kiln tail 3 connected in sequence;

[0071] The kiln head 1 is located at the front end of the rotary kiln;

[0072] The kiln middle section 2 is located between the kiln head 1 and the kiln tail 3;

[0073] The kiln tail 3 is located at the rear end of the rotary kiln;

[0074] The kiln head 1 is provided with a feed inlet 4;

[0075] The middle section 2 of the kiln is provided with a pyrolysis zone 5 and a cooling zone 6 in sequence;

[0076] The pyrolysis zone 5 is located at the front end of the kiln middle section 2 and is used for pyrolysis treatment of NdFeB waste;

[0077] The cooling zone 6 is located after the pyrolysis zone 5 and is used to cool the waste after the pyrolysis treatment;

[0078] The kiln tail 3 is provided with a screen 7, an air exhaust port 8 and a material discharge port 9 in sequence. The pyrolysis zone 5 and the cooling zone 6 are both provided with a baffle 10 of a spiral auger-like structure.

[0079] The present application is based on the above rotary kiln, which can realize the continuous feeding, pyrolysis, cooling and separation of NdFeB waste, simplifies the operation process and improves production efficiency. The division of each functional area enables each processing step to be carried out under optimal conditions, thereby improving the recovery rate and purity of rare earth elements. The leaching rate of rare earth elements in this embodiment is 94.9%.

[0080] Example 2

[0081] The difference between this embodiment and embodiment 1 is that the diameter of the steel balls used in the rotary kiln in this embodiment is 30 mm. The leaching rate of rare earth elements in this embodiment is 95.6%.

[0082] Example 3

[0083] The difference between this embodiment and embodiment 1 is that the diameter of the steel balls used in the rotary kiln in this embodiment is 40 mm. The leaching rate of rare earth elements in this embodiment is 95.3%.

[0084] Example 4

[0085] The difference between this embodiment and embodiment 1 is that this embodiment is as follows: the ground NdFeB waste is added to steel balls of different particle sizes, the mass percentages of 20mm, 30mm and 40mm steel balls are 40%, 30% and 30% respectively, the mass ratio of steel balls to materials is 1:1, the mixture is evenly mixed, and poured into the inlet of the rotary kiln with an inclination angle of 2°. Under the action of gravity, the rotary kiln rotates, and the material and steel ball mixture passes through the pyrolysis section of the rotary kiln equipped with 3 baffles with a height of 0.1m and an inclination angle of 30°. The steel balls absorb the additional heat generated by the combustion of the NdFeB waste in addition to the heat required for roasting, and the material reacts fully. Subsequently, the material and steel ball mixture passes through the cooling section of the rotary kiln equipped with 3 baffles with a height of 0.1m and an inclination angle of 40°, and is fully cooled. The material and steel balls are separated at the tail of the rotary kiln, and the leaching rate of rare earth elements is 98.1%.

[0086] In Table 1, the mass percentages of 20 mm, 30 mm, and 40 mm steel balls are represented by G1, G2, and G3, respectively;

[0087] In Table 1, the mass ratio of steel ball to material is represented by Z1;

[0088] In Table 1, the inclination angle (°) of the rotary kiln is represented by H1;

[0089] In Table 1, the number of baffles in the pyrolysis section of the rotary kiln is represented by R1, the baffle inclination angle (°) is represented by R2, and the baffle height is represented by R3;

[0090] In Table 1, the number of baffles in the cooling stage of the rotary kiln is represented by L1, the baffle inclination angle (°) is represented by L2, and the baffle height is represented by L3.

[0091] Table 1 - The differences between Example 5-57 and Example 4 and the rare earth element leaching rates of Example 1-57 are shown in Table 1.

[0092] Table 1-

[0093]

[0094]

[0095]

[0096] Result analysis: According to the above data, the influence of different parameter combinations on the leaching rate can be summarized. In the experimental design in this embodiment, the main variables include the raw material particle size distribution (G1, G2, G3), the mass ratio of steel balls to materials (Z1), the inclination angle of the rotary kiln (H1), the number and height of the baffles in the pyrolysis section and the cooling section (R1, R2, R3 and L1, L2, L3). From the leaching rate, it can be seen that when the raw material particle size is relatively uniform and the mass ratio of steel balls to materials is appropriate, the leaching rate is higher. For example, in Examples 4 to 6, 13 to 15, etc., in these embodiments, the proportions of G1, G2, and G3 are 40%, 30%, and 30%, respectively, the mass ratio of steel balls to materials is 1:1 or 1:3, the inclination angle of the rotary kiln is 2° or 3°, and the number of baffles in the pyrolysis section is 3, the baffle height is 0.1 meter, and the baffle inclination angle is 30°, the number of baffles in the cooling section is 3, the baffle height is 0.1 meter, and the baffle inclination angle is 40°, and the leaching rate reaches more than 98%.

[0097] In addition, with the increase of the rotary kiln inclination angle and the increase of the number of baffles, the leaching rate also increased, which shows that the appropriate mechanical structure helps to improve the processing efficiency. For example, in Examples 5 and 6, the number of baffles in the pyrolysis section increased to 4 and 5, the baffle height increased to 0.15 meters and 0.2 meters, respectively, the baffle inclination angles were 40° and 50°, the number of baffles in the cooling section increased to 4 and 5, the baffle height increased to 0.15 meters and 0.2 meters, respectively, the baffle inclination angles were 55° and 70°, and the leaching rates reached 98.5% and 98.6%, respectively.

[0098] However, when a certain particle size ratio is too high, such as when the G1 ratio in Examples 19 and 55 reaches 80%, the leaching rate is relatively low, probably because too fine particles are not conducive to effective physical mixing and chemical reaction. For example, in Example 19, the G1 ratio is 80%, G2 and G3 are 0% and 20% respectively, and the leaching rate is 97.1%; in Example 55, the G1 ratio is 80%, G2 and G3 are 0% and 20% respectively, and the leaching rate is 97.0%. In summary, optimizing the raw material particle size distribution and reasonably setting the rotary kiln inclination angle and baffle parameters are key factors in improving the leaching rate.

[0099] Comparative Example 1

[0100] The difference between this comparative example and Example 1 is that no steel balls are added in this comparative example. Other conditions are the same as those in Example 1. Result: The leaching rate of rare earth elements is 85.4%. The reason is that without steel balls, the grinding effect of the material in the rotary kiln is poor, and the large particles of NdFeB waste are not fully crushed, resulting in a reduction in the specific surface area of ​​the material, which affects the leaching rate of rare earth elements.

[0101] Comparative Example 2

[0102] The difference between this comparative example and Example 1 is that the inclination angle of the rotary kiln in this comparative example is 1°. Other conditions are the same as those in Example 1. Result: The leaching rate of rare earth elements is 88.2%. The reason is that the smaller inclination angle slows down the movement speed of the material in the kiln. Although it increases the residence time of the material, it may also cause excessive aggregation of the material in certain areas, affecting the uniform distribution of the material and the pyrolysis effect, thereby reducing the leaching rate.

[0103] Comparative Example 3

[0104] The difference between this comparative example and Example 1 is that the pyrolysis section in this comparative example is not provided with a baffle. Other conditions are the same as those in Example 1. Result: The rare earth element leaching rate is 86.9%. The reason is that the lack of a baffle shortens the residence time of the material during the pyrolysis process, and the material cannot be fully heated, resulting in incomplete pyrolysis, thereby affecting the leaching rate of the rare earth elements.

[0105] Comparative Example 4

[0106] The difference between this comparative example and Example 1 is that the cooling section in this comparative example is not provided with a baffle. Other conditions are the same as those in Example 1. Result: The rare earth element leaching rate is 89.5%. The reason is that the lack of a baffle in the cooling section speeds up the cooling speed of the material. Although the production efficiency is improved to a certain extent, the excessively fast cooling speed may cause stress concentration inside the material, affecting the leaching effect of the rare earth elements.

[0107] Result analysis: Combined with the experimental test results of Examples 1-57 and Comparative Examples 1-4, it can be seen that the rotary kiln provided by the present application is capable of realizing continuous feeding, pyrolysis, cooling and separation of NdFeB waste, simplifying the operation process and improving production efficiency. In addition, the division of each functional area enables each processing step to be carried out under optimal conditions, thereby improving the recovery rate of rare earth elements. The design of the baffle increases the residence time of the material in the kiln, making the material more uniform during the pyrolysis and cooling process. The height of the baffle is moderate, which will not hinder the flow of the material, but can effectively prevent the material from excessively agglomerating, thereby improving the leaching rate and recovery efficiency of rare earth elements. Steel balls play a key role in the oxidation roasting process. They can not only absorb some of the extra self-heating heat generated by NdFeB waste in the oxidation roasting process in addition to the heat required for roasting, effectively control the temperature in the kiln, and prevent the material from agglomerating and insufficient oxidation due to excessive temperature, but also continue to play a grinding role in the whole process of oxidation roasting, which helps to further crush large particles of NdFeB waste, increase the specific surface area of ​​the material, and improve the leaching rate of rare earth elements. The design of the screen allows the steel balls and rare earth elements to be effectively separated, simplifying the subsequent processing steps. The addition of steel balls improves the fluidity of the material, making the material more evenly distributed in the rotary kiln, and further improving the effect of pyrolysis and cooling. By optimizing the inclination angle of the rotary kiln, the height, number and spiral inclination of the baffles in the kiln, the temperature of the reaction zone is precisely controlled, and the efficient oxidation of NdFeB waste is achieved, which significantly improves the leaching rate of rare earth elements. The method is simple to operate and easy to use, and greatly reduces the recycling cost of NdFeB waste. It solves the problems of complex operation, low rare earth leaching rate and high cost of traditional recycling methods, and realizes efficient and low-cost recycling of NdFeB waste. Selecting steel balls with appropriate diameters can significantly improve the treatment effect of NdFeB waste. Steel balls with a diameter of 20-40 mm can not only effectively absorb the additional self-heating heat generated by part of the NdFeB waste in the oxidation roasting process in addition to the heat required for roasting, and prevent the phenomenon of insufficient oxidation caused by excessive temperature due to material agglomeration, but also continue to play a grinding role in the whole roasting process, further crushing large particles of NdFeB waste, increasing the specific surface area of ​​the material, and improving the leaching rate of rare earth elements. In addition, steel balls with this diameter can be better dispersed in the material during the mixing process, improve the fluidity of the material, make the material more evenly distributed in the rotary kiln, and further improve the effect of pyrolysis and cooling. Through these measures, the efficient treatment of NdFeB waste and the high leaching rate of rare earth elements are ensured, while the operation process is simplified and the recycling cost is reduced. Optimizing the design and operating parameters of the rotary kiln, especially the addition of steel balls and the design of the baffles, is of great significance for improving the treatment effect of NdFeB waste and the leaching rate of rare earth elements.

[0108] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the principles of the present application should be included in the protection scope of the present application.

Claims

1. A rotary kiln suitable for recycling NdFeB waste, characterized in that: It comprises a kiln head (1), a kiln middle section (2) and a kiln tail (3) which are connected in sequence; The kiln head (1) is located at the front end of the rotary kiln; The kiln middle section (2) is located between the kiln head (1) and the kiln tail (3); The kiln tail (3) is located at the rear end of the rotary kiln; The kiln head (1) is provided with a feed inlet (4); The middle section (2) of the kiln is provided with a pyrolysis zone (5) and a cooling zone (6) in sequence; The pyrolysis zone (5) is located at the front end of the kiln middle section (2) and is used to perform pyrolysis treatment on NdFeB waste; The cooling zone (6) is located after the pyrolysis zone (5) and is used to cool the waste material after the pyrolysis treatment; The kiln tail (3) is provided with a screen (7), an air exhaust port (8) and a material discharge port (9) in sequence.

2. The rotary kiln according to claim 1, characterized in that: The rotary kiln has an inclination angle of 2-5° with respect to the horizontal plane, and the kiln head (1) is higher than the kiln tail (3).

3. The rotary kiln according to claim 1, characterized in that: Baffles (10) are provided in both the pyrolysis zone (5) and the cooling zone (6); the number of groups of the baffles (10) is 3-5; and the height of the baffles is 0.1m-0.2m.

4. The rotary kiln according to claim 3, characterized in that: The baffle (10) is a spiral auger-shaped structure.

5. The rotary kiln according to claim 4, characterized in that: The baffles (10) arranged in the pyrolysis zone (5) and the cooling zone (6) have angles of 30-50° and 40-70° with the vertical direction of the rotary kiln cylinder, respectively.

6. A method for recycling NdFeB waste, characterized in that: Using the rotary kiln according to any one of claims 1 to 5; the method comprises the following steps: S1. Add steel balls to the crushed NdFeB waste to obtain a mixture; S2, pouring the mixed material obtained in step S1 into the feed port (4) of the rotary kiln for mixing, then passing the mixed material through the pyrolysis zone (5) for pyrolysis reaction, and then passing through the cooling zone (6) for cooling to obtain a cooled mixture; S3, passing the mixture in step S2 through the sieve (7) for separation, and then passing the separated materials through the discharge port (9) to collect the steel balls and the roasted products.

7. The recycling method according to claim 6, characterized in that: The diameter of the steel ball in step S1 is 20-40 mm.

8. The recycling method according to claim 7, characterized in that: The steel balls in step S1 are three kinds of steel balls with different particle sizes; the diameters of the three kinds of steel balls with different particle sizes are 20 mm, 30 mm, and 40 mm respectively; and the mass percentages are 0-60%: 0-40%: 0-30%.

9. The recycling method according to claim 6, characterized in that: The aperture size of the sieve (7) is 16 mm.

10. The recycling method according to claim 6, characterized in that: In step S1, the mixing mass ratio of the NdFeB waste and the steel balls is 1:1-5.

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