Method for enriching rare earth based on neodymium iron boron waste

Abstract

The invention provides a method for enriching rare earth based on neodymium iron boron waste, and belongs to the technical field of magnetic materials, the method comprises the following steps: oxidizing roasting and crushing the neodymium iron boron waste to obtain neodymium iron boron powder, and the oxidizing roasting process comprises the following steps: keeping the temperature at 300-500 DEG C for 1.0-2.0 hours, and then keeping the temperature at 600-900 DEG C for 2.0-3.5 hours; the neodymium iron boron powder is granulated, a pressing technology is not adopted in the granulating process, and the particle size ranges from 100 micrometers to 500 micrometers; the granulated material is reduced, and ferric oxide is reduced into iron elementary substance; and carrying out carbonyl synthesis on the reduced material to generate pentacarbonyl iron liquid and obtain a rare earth enriched material at the same time. According to the method, on the basis of not adding an activating agent, the extraction rate of iron is 93% or above, and rare earth elements in the synthetic residues are enriched to 85% or above.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetic materials, and in particular relates to a method for enriching rare earths based on NdFeB waste. Background Art

[0002] Neodymium iron boron (NdFeB) permanent magnets have experienced rapid development in recent years due to their light weight, compact size, strong magnetism, high magnetic energy level, readily available raw materials, and low price. They are widely used in electronics, electrical machinery, medical equipment, aerospace, and other fields. The production process of NdFeB magnets produces NdFeB scrap, which accounts for approximately 30% of the raw material mass. This scrap contains approximately 30% rare earth elements (90% neodymium, the remainder praseodymium, and some also containing gadolinium, terbium, dysprosium, and holmium), and approximately 60% to 70% iron. Its recycling value has been increasingly recognized in recent years. Hydrometallurgical techniques are commonly used to recycle NdFeB scrap, including hydrochloric acid solution, total solvent extraction, and sulfate double salt extraction. However, these methods have the disadvantages of easily causing secondary pollution, low metal recovery efficiency, and low metal purity.

[0003] In the prior art, Chinese invention patent publication number CN112553482A discloses a method for efficiently extracting iron and enriching rare earth elements from NdFeB waste. This method combines a traditional sponge iron production process with a carbonyl iron synthesis and decomposition process. While producing the carbonyl iron product, it also enriches the rare and precious metals in the raw material, comprehensively recovering the valuable metals in the raw material. However, this solution still has corresponding technical problems, namely, the iron extraction rate and the degree of rare earth oxide enrichment are relatively low. The main reason is that the high iron content in the NdFeB waste causes the material to collapse during the carbonyl synthesis process, making it impossible to effectively remove some carbonyl iron. The iron element remaining in the rare earth oxides will form insoluble compounds, affecting the subsequent rare earth extraction efficiency. Secondly, the presence of rare earth oxides reduces the reaction activity of the carbonyl synthesis. This technology requires the addition of sulfate to activate the reaction process. However, the addition of sulfate causes new impurities in the material after carbonylation iron extraction, which increases the difficulty and cost of subsequent processing. Summary of the Invention

[0004] To address these issues, the present invention provides a method for enriching rare earth elements from NdFeB waste. Through an oxidative roasting process, the formation of a rare earth oxide microstructure is promoted, facilitating subsequent sintering with the ash of the reducing agent into a skeletal structure, facilitating the separation of carbonyl iron. Without the need for additional activators, the method achieves an iron extraction rate exceeding 93%, and enriches the rare earth elements in the synthetic residue to over 85%.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows: The invention provides a method for enriching rare earths based on NdFeB waste. The method comprises: performing oxidation roasting and crushing on the NdFeB waste to obtain NdFeB powder, wherein the oxidation roasting process comprises maintaining the temperature at 300-500°C for 1.0-2.0 hours and then maintaining the temperature at 600-900°C for 2.0-3.5 hours; granulating the NdFeB powder, wherein the granulation process does not adopt a pressing process and the particle size is 100-500 μm; reducing the granulated material to reduce iron oxide to elemental iron; and performing carbonyl synthesis on the reduced material to generate pentacarbonyl iron liquid, and simultaneously obtaining a rare earth-enriched material.

[0006] Furthermore, the mass percentage of iron in the NdFeB waste is 60%-70%.

[0007] Furthermore, the calcined NdFeB waste is crushed to 100-800 meshes.

[0008] Further, the temperature is raised to 300°C-500°C and maintained for 1.0h-2.0h, and then the temperature is raised to 600°C-900°C at a rate of 5°C / min-10°C / min and maintained for 2.0h-3.5h.

[0009] Furthermore, the granulation process is: mixing the NdFeB powder with a binder, agglomerating the NdFeB powder into balls, and the amount of the binder added is 3%-7% of the mass of the NdFeB powder.

[0010] Furthermore, a rotary drum granulator is used for granulation, the binder is added by spraying, the rotation speed is 12 r / min-18 r / min, and the inclination angle of the rotary drum granulator is 6°-7°.

[0011] Furthermore, the reduction process is as follows: reducing coal is used as a reducing agent, the ratio of the added amount of the reducing coal to the mass of the material satisfies 1:(1-4), and the reduction temperature is maintained at 800°C-1200°C for 2h-6h.

[0012] Furthermore, before reduction, at least half of the total amount of reduced coal is mixed with the granular material at a stirring speed of 10 r / min-20 r / min for 5 min-10 min; then the remaining reduced coal and the granular material are added to the reduction furnace for reduction reaction.

[0013] Furthermore, the average particle size of the reduced coal is less than 1 mm.

[0014] Furthermore, the process of carbonyl synthesis is as follows: reaction temperature is 100°C-200°C, and reaction pressure is 5MPa-20MPa.

[0015] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include: the present invention targets the characteristic of high iron content in NdFeB waste. First, the roasting process adopts a two-stage heating process. Specifically, the present invention adopts an oxidative roasting process. The elements in the NdFeB waste are oxidized in an oxidizing atmosphere, and the volume expands, causing the NdFeB waste to crack or disintegrate. The oxidation process of the NdFeB waste is controlled to achieve the formation of rare earth oxide microstructures during the oxidative roasting process. The formation of rare earth oxide microstructures is very important. Oxide microstructures with a certain size have the characteristics of low density, many pores and large surface roughness, which are similar to dendritic structures, making it easier for the subsequently generated carbonyl iron to separate from the channels of the interconnected microstructures formed by the oxides. However, the size of the oxide microstructure should not be too large or too small. If it is too large, the rare earth oxide will have sintering problems, resulting in reduced activity and decreased density of the microstructure itself; if it is too small, microchannels cannot be formed to separate the iron element. Based on the above considerations, the present invention adopts a two-stage heating process. In the first stage of the roasting process, the temperature is relatively low and maintained for a preset time. On the one hand, volatiles are removed to improve the cleanliness of the material. On the other hand, low-temperature oxidation roasting is beneficial to the formation and growth of the rare earth oxide microstructure and avoids sintering. If the roasting temperature is too high, the oxidation speed of the NdFeB waste is fast and the disintegration effect is large, which affects the formation and growth of the oxide microstructure, resulting in the generation amount, size and activity of the oxide microstructure failing to meet the requirements. The size of the rare earth oxide microstructure prepared by the invention through the two-stage roasting process is 500nm-1000nm. If the low-temperature oxidation roasting time is short, the nucleation rate of the rare earth oxide microstructure is low, the rare earth oxide microstructure formed subsequently is too small, and effective connection cannot be formed, the porosity is too low, and it cannot meet the requirements. If the low-temperature oxidation roasting time is long, the rare earth oxide microstructure size is large, and it is easy to burn out during the second roasting process, resulting in reduced porosity and activity; the second roasting process uses a higher temperature to improve the disintegration effect of the alloy structure, form porous oxides, increase the surface area to improve the reaction activity; it should be clarified that there is an influence between the first roasting process and the second roasting process. The first stage of the roasting process is intended to form a certain number and size of oxide microstructures, while the second stage of the roasting process, on the one hand, promotes the continued growth of the oxide microstructure, and on the other hand, affects the activity of the generated oxide microstructure (burning probability). At the same time, the second stage of the roasting process is intended to deeply disintegrate the NdFeB waste into a porous oxide structure, and a significant impact on the activity of the oxide microstructure should be avoided. Secondly, the NdFeB powder does not use a pressing process during the granulation process. Since the present application adopts a two-stage roasting process, a rare earth oxide microstructure is formed inside the powder. The use of a pressing process has a certain impact on the microstructure, and the density of the NdFeB particles after pressing increases, further hindering the separation of carbonyl iron.Finally, the granulated NdFeB powder was limited. The particle size affects the gas-solid reaction process during the subsequent reduction process. Although small NdFeB powder has a large specific surface area, it can easily lead to the local reduction atmosphere being unable to effectively contact the oxidized NdFeB powder to reduce the iron oxides, and local overheating during the reduction process can cause burning. On the other hand, although oversized NdFeB powder avoids the above problems, the iron content in the NdFeB scrap in this application is 60%-70%, which is extremely high. This can easily cause carbonyl iron to destroy the porous skeleton structure formed by the rare earth oxide microstructure during the flow process. Therefore, the above process needs to be strictly controlled. This process ensures the subsequent reaction activity while avoiding the addition of additional substances. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 This is an SEM image of the waste material after calcination provided in Example 1 of the present invention; Figure 2 The SEM image of the oxide microstructure provided in Example 1 of the present invention; Figure 3 This is an SEM image of the microstructure of carbonylation slag after carbonylation of the material provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0018] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] An embodiment of the present invention provides a method for enriching rare earths based on NdFeB waste, comprising: S1. Oxidatively calcining and crushing NdFeB waste to obtain NdFeB powder, wherein the oxidative calcination process is to maintain the temperature at 300° C.-500° C. for 1.0 h-2.0 h, and then maintain the temperature at 600° C.-900° C. for 2.0 h-3.5 h; Preferably, the temperature is maintained at 350-450°C for 1.0-2.0h, at 400°C for 1.5h, at 350-450°C for 1.5h, or at 400°C for 1.0-2.0h; then maintained at 650°C, 700°C, 750°C, 800°C, or 850°C for 2.0-3.5h, or maintained at 650°C, 700°C, 750°C, 800°C, or 850°C for 2.5-3.0h; S2. Granulating the NdFeB powder without using a pressing process, and the particle size is 100-500 μm; the particle size is preferably 200 μm, 300 μm or 400 μm; S3, reducing the granulated material to reduce the iron oxide to elemental iron; S4. Perform carbonyl synthesis on the reduced material to generate pentacarbonyl iron liquid and simultaneously obtain rare earth-enriched material.

[0020] The present invention aims at the characteristic of high iron content in NdFeB waste. First, the roasting process adopts a two-stage heating process. Specifically, the present invention adopts an oxidation roasting process. The elements in the NdFeB waste are oxidized in an oxidizing atmosphere, and the volume expands, causing the NdFeB waste to crack or disintegrate. The oxidation process of the NdFeB waste is controlled to achieve the formation of rare earth oxide microstructures during the oxidation roasting process. The formation of rare earth oxide microstructures is very important. Oxide microstructures with a certain size have the characteristics of low density, many pores and large surface roughness, similar to a dendritic structure, which facilitates the subsequent separation of carbonyl iron from the channels of the interconnected microstructures formed by the oxides, but the size of the oxide microstructures is not easy to be too large or too small. If the temperature is too large, the rare earth oxide will have the problem of sintering, which will reduce the activity and the density of the microstructure itself; if it is too small, it will not be able to form microchannels to separate the iron elements. Based on the above considerations, the present invention adopts a two-stage heating process. In the first stage of the roasting process, the temperature is low and maintained for a preset time. On the one hand, volatiles are removed to improve the cleanliness of the material. On the other hand, low-temperature oxidation roasting is beneficial to the formation and growth of the rare earth oxide microstructure, avoiding sintering. If the roasting temperature is too high, the oxidation speed of the NdFeB waste is fast, and the disintegration effect is large, which affects the formation and growth of the oxide microstructure, resulting in the generation amount, size and activity of the oxide microstructure cannot meet the requirements. The present invention adopts a two-stage roasting process. The size of the prepared rare earth oxide microstructure is 500nm-1000nm. If the low-temperature oxidation roasting time is short, the nucleation rate of the rare earth oxide microstructure is low, and the rare earth oxide microstructure formed subsequently is too small, unable to form an effective connection, and the porosity is too low to meet the requirements. If the low-temperature oxidation roasting time is long, the rare earth oxide microstructure size is larger, and it is easy to burn out during the second roasting process, resulting in reduced porosity and activity; the second roasting process uses a higher temperature to improve the disintegration effect of the alloy structure, forming porous oxides, increasing the surface area to improve the reaction activity; It should be made clear that there is an influence between the first roasting process and the second roasting process. The first roasting process The process is designed to form oxide microstructures of a certain number and size, and the second-stage roasting process, on the one hand, promotes the continued growth of the oxide microstructure, and on the other hand, affects the activity of the generated oxide microstructure (inducing the probability of burnout). At the same time, the second-stage roasting process is designed to deeply disintegrate the NdFeB waste into a porous oxide structure, and should avoid having a significant impact on the activity of the oxide microstructure. Secondly, the NdFeB powder does not use a pressing process during the granulation process. Since this application uses a two-stage roasting process, a rare earth oxide microstructure is formed inside the powder. The use of a pressing process has a certain impact on the microstructure, and the density of the NdFeB particles after pressing increases, further hindering the separation of carbonyl iron.Finally, the granulated NdFeB powder was limited. The particle size affects the gas-solid reaction process during the subsequent reduction process. Although small NdFeB powder has a large specific surface area, it can easily lead to the local reduction atmosphere being unable to effectively contact the oxidized NdFeB powder to reduce the iron oxides, and local overheating during the reduction process can cause burning. On the other hand, although oversized NdFeB powder avoids the above problems, the iron content in the NdFeB scrap in this application is 60%-70%, which is extremely high. This can easily cause carbonyl iron to destroy the porous skeleton structure formed by the rare earth oxide microstructure during the flow process. Therefore, the above process needs to be strictly controlled. This process ensures the subsequent reaction activity while avoiding the addition of additional substances.

[0021] It is understandable that carbonyl iron is in liquid state, and a certain amount of rare earth oxides are inevitably present in the carbonyl iron extracted in the prior art, and the inclusion of rare earth oxides affects the quality of carbonyl iron. The size of the rare earth oxide microstructure prepared by the present invention is 500nm-1000nm. The formed rare earth oxide microstructure has a certain strength and is interconnected to form a porous structure, which facilitates the outflow of carbonyl iron while avoiding the involvement of rare earth oxides in carbonyl iron as much as possible. Compared with the prior art, the inclusion of rare earth oxides can be reduced to less than 0.5%, which is 90% lower than the prior art.

[0022] It should be noted that due to the low content of the rare earth oxide microstructure in this application, it is still difficult to achieve the outflow of carbonyl iron by forming a framework structure composed solely of rare earth oxide microstructures, or the iron extraction efficiency is only about 90%. Therefore, it is necessary to combine it with the inorganic matter after the reduction coal is burned out to form a porous skeleton structure. It should be clarified that although the extraction rate is not much improved compared with the existing technology, the present application achieves a significant improvement in the extraction efficiency of iron without the addition of additional activators.

[0023] In the NdFeB scrap of the embodiment of the present invention, the mass percentage of iron is 60%-70%, preferably, the mass percentage of iron is 65%. For illustration, the composition of the NdFeB scrap selected in the embodiment of the present invention is shown in Table 1.

[0024] Table 1 Chemical composition of NdFeB waste

[0025] Others mainly include substances that do not participate in the reaction, such as Ca, Mg, and Si.

[0026] Preferably, the calcined NdFeB waste is crushed to 100-800 meshes, and preferably, the calcined NdFeB waste is crushed to 200 meshes, 300 meshes, 400 meshes, 500 meshes, 600 meshes or 700 meshes.

[0027] Preferably, the temperature is increased to 300°C-500°C at a rate of 10°C / min-25°C / min and maintained for 1.0h-2.0h. Preferably, the temperature is increased at a rate of 15°C / min or 20°C / min, and the temperature is increased to 350°C, 400°C or 450°C, and maintained for 1.5h; then the temperature is increased to 600°C-900°C at a rate of 5°C / min-10°C / min and maintained for 2.0h-3.5h. Preferably, the temperature is increased to 650°C, 700°C, 750°C, 800°C or 850°C at a rate of 6°C / min, 7°C / min, 8°C / min or 9°C / min and maintained for 2.5h-3.0h.

[0028] The early heating speed is fast to shorten the time of heating to the preset temperature and improve the processing efficiency. Secondly, it is kept at 300℃-500℃ for a certain time to allow the rare earth oxide to form a growth core. At this time, the material has not yet disintegrated. Then it is heated at a lower speed, that is, at a heating speed of 5℃ / min-10℃ / min to 600℃-900℃ and kept for 2.0h-3.5h. The lower heating speed promotes the growth of the rare earth oxide microstructure. Secondly, at this temperature, the material gradually disintegrates in the oxidizing atmosphere, forming tiny cracks, and the material gradually oxidizes from the outside to the inside. It is necessary to strictly control the second holding temperature and processing time to achieve a balance between disintegration and activity. The rare earth oxide microstructure still has a tendency to grow at high temperature. However, overburning is easily caused during the growth process, which causes the microstructure to sinter (burn out), reduce its activity, and is not conducive to the subsequent reduction and carbonyl reaction process. Therefore, the second insulation temperature and insulation time are limited to balance the growth and burn-out of the rare earth oxide microstructure. The accelerated oxidation rate will also affect the morphology of the rare earth oxide microstructure. For example, the active oxide microstructure has a low density and is not easily affected in the material disintegration process. The rare earth oxide after burn-out forms a dense ceramic phase, which causes the dense ceramic phase to break during the disintegration process, thereby affecting the channels formed by the interconnected rare earth oxide microstructures. Therefore, the insulation temperature and insulation time of this application are finally limited after taking the above-mentioned influences into consideration.

[0029] The granulation process is as follows: mixing the NdFeB powder with a binder, agglomerating the NdFeB powder into balls, and adding the binder in an amount of 3%-7% of the mass of the NdFeB powder. Preferably, the adding amount of the binder is 4%, 5% or 6% of the mass of the NdFeB powder.

[0030] The binders used in the embodiments of the present invention include carboxymethyl cellulose, pulp waste liquid, acrylamide, Peridot, and Alcotac (a graft copolymer of acrylamide and acrylic acid monomers). The binders not only provide adhesion between the powders but also decompose into nanocarbons during the reduction process. The nanocarbons facilitate penetrating the porous framework constructed by the rare earth oxides, reacting with the iron oxide and reducing it.

[0031] Specifically, a rotary drum granulator is used for granulation, and the binder is added by spraying. The rotation speed is 12r / min-18r / min, and the inclination angle of the rotary drum granulator is 6°-7°. Preferably, the rotation speed is 13r / min, 14r / min, 15r / min, 16r / min or 17r / min. The higher the rotation speed, the greater the centrifugal force of the material, the tighter the particles but the smaller the particle size; the lower the rotation speed, the larger the particle size. The larger the inclination angle, the shorter the residence time of the material, the faster the rolling speed of the particles, and the smaller the particle size; the smaller the inclination angle, the longer the residence time, which is conducive to the formation of large particles. The average particle size of the particles prepared by the above process of the present invention is 100µm-500µm, and the D30 particle size is not less than 85% of the average particle size, and the maximum crushing force of at least 80% of the particles is 5N-10N. It should be made clear that the above indicators are very critical for subsequent reactions. The particles should not be large in size and high in density, otherwise the reduction and subsequent carbonyl synthesis will be difficult, and the degree of separation of elemental iron will be low; secondly, the particles should not be small in size, as small size will lead to local overheating of the reaction, causing the porous skeleton structure constructed by rare earth oxides to sinter, affecting the reduction of iron oxide and carbonyl synthesis reactions; finally, the particles need to meet a certain strength to avoid collapse, which will lead to a decrease in subsequent reduction strength and carbonyl synthesis efficiency.

[0032] The reduction process involves using reducing coal as a reducing agent, with the ratio of the added reducing coal to the material mass satisfying 1:(1-4), and maintaining the reduction temperature at 800°C-1200°C for 2-6 hours. The reducing coal used in this embodiment of the present invention is a commercially available desulfurization product. When the reducing coal is oxidized, the inorganic substances generated combine with the rare earth oxide to form a channel for the carbonyl iron to flow out.

[0033] Preferably, the ratio of the amount of the reducing coal added to the material mass satisfies 1:2 or 1:3, and the reduction temperature is 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C or 1150°C and maintained for 3h, 4h or 5h.

[0034] Before reduction, at least half of the total amount of reduced coal added is mixed with the granular material, stirring at a speed of 10-20 rpm for 5-10 minutes. The remaining reduced coal is then added to the reduction furnace along with the granular material for reduction reaction. Preferably, before reduction, 50-80% of the total amount of reduced coal added is mixed with the granular material. First, the reducing coal particles may be crushed during the stirring and mixing process. Adding all of the reduced coal will increase the proportion of small-sized reducing coal, increasing the unevenness of the mixed material. Second, the inorganic matter and rare earth oxides after the oxidized reducing coal jointly construct a channel for the liquid carbonyl iron to flow. Appropriate small-sized reducing coal particles help to form a porous skeleton structure, while too much small-sized reducing coal will prevent the carbonyl iron from separating from the material. The remaining reducing coal is added by using two hoppers, one for the remaining reducing coal and the other for the mixture of reducing coal and granular material. The two hoppers add material to the reactor simultaneously.

[0035] Preferably, the stirring speed is 12 r / min, 15 r / min, 17 r / min or 18 r / min; and the stirring time is 6 min, 7 min, 8 min or 9 min.

[0036] The average particle size of the reduced coal is less than 1 mm. Preferably, the D5 of the reduced coal is less than 0.2 mm.

[0037] Preferably, the ash mass ratio of the reduced coal is 12%-19%.

[0038] The process of carbonyl synthesis is: reaction temperature 100℃-200℃, reaction pressure 5MPa-20MPa.

[0039] Preferably, the reaction temperature is 120°C, 140°C, 160°C or 180°C, and the reaction pressure is 10 MPa or 15 MPa.

[0040] In order to better illustrate the embodiments of the present invention, the present invention is further described in detail below through specific examples.

[0041] Example 1

[0042] The embodiment of the present invention provides a method for enriching rare earths based on NdFeB waste, comprising the following steps: S1. Oxidation roasting and crushing of NdFeB waste to obtain NdFeB powder. The oxidation roasting process is: heating to 400℃ and holding for 1.5h, then heating to 800℃ at a rate of 8℃ / min and holding for 3.0h. After roasting, the material is as follows: Figure 1 As shown, the oxide microstructure formed is as Figure 2As shown, it can be seen that rare earth oxide microstructures of a certain size are formed.

[0043] S2. Granulating the NdFeB powder. The granulation process does not use a pressing process. Instead, a rotary drum granulator is used for granulation. The binder is added by spraying. The rotation speed is 15 r / min and the rotary drum granulator is tilted at 6°. The average particle size is 200 μm. After drying, the D30 particle size is statistically determined to be 180 μm, and the maximum crushing force for more than 80% of the particles is 7 N.

[0044] S3. The granulated material is reduced to reduce the iron oxide to elemental iron.

[0045] Half of the total reduced coal was mixed with the granular material at a stirring speed of 15 rpm for 8 minutes. The remaining reduced coal and granular material were then added to the reduction furnace for a reduction reaction. The reduced coal was used as a reducing agent, with a mass-to-material ratio of 1:2. The reduction temperature was set at 1000°C for 4 hours. The average particle size of the reduced coal was 0.8 mm, and the D5 particle size was 0.18 mm.

[0046] S4, the reduced material is subjected to carbonyl synthesis to generate pentacarbonyl iron liquid and rare earth enriched material. The carbonyl synthesis process is as follows: reaction temperature 130 ° C, reaction pressure 12 MPa. The final carbonyl slag is as follows Figure 3 shown.

[0047] Example 2

[0048] The embodiment of the present invention provides a method for enriching rare earths based on NdFeB waste, comprising the following steps: S1. NdFeB waste is oxidatively roasted and crushed to obtain NdFeB powder. The oxidative roasting process is to raise the temperature to 300°C and hold for 1 hour, then raise the temperature to 600°C at a rate of 5°C / min and hold for 2 hours. The size of the rare earth oxide microstructure is 1000 nm.

[0049] S2. Granulate the NdFeB powder. The granulation process does not adopt a pressing process. A rotary drum granulator is used for granulation. The binder is added by spraying. The rotation speed is 12 r / min and the rotary drum granulator has an inclination angle of 6°. The average particle size is 500 μm. After drying, the D30 particle size is 432 μm, and the maximum crushing force of more than 80% of the particles is 5N.

[0050] S3. The granulated material is reduced to reduce the iron oxide to elemental iron.

[0051] Half of the total reduced coal was mixed with the granular material at a stirring speed of 10 rpm for 5 minutes. The remaining reduced coal and granular material were then added to the reduction furnace for a reduction reaction. The reduced coal was used as a reducing agent, with a mass-to-material ratio of 1:1. The reduction temperature was maintained at 800°C for 2 hours. The average particle size of the reduced coal was 0.8 mm, and the D5 particle size was 0.18 mm.

[0052] S4. Perform carbonyl synthesis on the reduced material to generate iron pentacarbonyl liquid and simultaneously obtain rare earth-enriched material. The carbonyl synthesis process is as follows: reaction temperature 100° C., reaction pressure 5 MPa.

[0053] Example 3

[0054] The embodiment of the present invention provides a method for enriching rare earths based on NdFeB waste, comprising the following steps: S1. NdFeB waste is oxidatively roasted and crushed to obtain NdFeB powder. The oxidative roasting process is to raise the temperature to 500°C and hold for 2.0 hours, then raise the temperature to 900°C at a rate of 10°C / min and hold for 3.5 hours. The size of the rare earth oxide microstructure is 500 nm.

[0055] S2. Granulating the NdFeB powder. The granulation process does not use a pressing process. Instead, a rotary drum granulator is used for granulation. The binder is added by spraying. The rotation speed is 18 r / min, the rotary drum granulator is tilted at 7°, and the average particle size is 100 μm. After drying, the D30 particle size is statistically determined to be 91 μm, and the maximum crushing force of more than 80% of the particles is 10 N.

[0056] S3. The granulated material is reduced to reduce the iron oxide to elemental iron.

[0057] Half of the total reduced coal was mixed with the granular material at a stirring speed of 20 rpm for 10 minutes. The remaining reduced coal and granular material were then added to the reduction furnace for a reduction reaction. The reduced coal was used as a reducing agent, with a mass-to-material ratio of 1:4. The reduction temperature was set at 1200°C for 5 hours. The average particle size of the reduced coal was 0.8 mm, and the D5 particle size was 0.18 mm.

[0058] S4. The reduced material is subjected to carbonyl synthesis to generate iron pentacarbonyl liquid and a rare earth-enriched material. The carbonyl synthesis process is as follows: a reaction temperature of 200° C. and a reaction pressure of 20 MPa.

[0059] Example 4

[0060] Unlike Example 1, this example mixed the reduced coal with the granular material at a stirring speed of 15 rpm for 8 minutes. The remaining reduced coal and granular material were then added to the reduction furnace for a reduction reaction. The reduced coal served as the reducing agent, with a mass-to-material ratio of 1:2. The reduction temperature was set at 1000°C for 4 hours. The average particle size of the reduced coal was 0.8 mm, and the D5 particle size was 0.18 mm.

[0061] Comparative Example 1 Different from Example 1, in step S1 of this comparative example, a one-step calcination method is adopted, that is, the temperature is raised to 800° C. at a rate of 8° C. / min and maintained for 4.5 hours.

[0062] Comparative Example 2 Different from Example 1, in step S1 of this comparative example, the temperature was raised to 400° C. and maintained for 0.5 h, and then raised to 800° C. at a rate of 8° C. / min and maintained for 3.0 h.

[0063] Comparative Example 3 Different from Example 1, in step S1 of this comparative example, the temperature was raised to 400° C. and maintained for 2.5 h, and then raised to 800° C. at a rate of 8° C. / min and maintained for 3.0 h.

[0064] Comparative Example 4 Different from Example 1, in step S1 of this comparative example, the temperature was raised to 400° C. and maintained for 1.5 h, and then the temperature was raised to 800° C. at a rate of 15° C. / min and maintained for 3.0 h.

[0065] Comparative Example 5 Different from Example 1, in step S1 of this comparative example, the temperature was raised to 400° C. and maintained for 1.5 h, and then the temperature was raised to 800° C. at a rate of 8° C. / min and maintained for 4 h.

[0066] Comparative Example 6 Different from Example 1, in step S2 of this comparative example, the rotation speed is 10 r / min, the inclination angle of the drum granulator is 6°, the average particle size is 600 μm, and the maximum crushing force for more than 80% of the particles is 3N.

[0067] Comparative Example 7 Different from Example 1, in step S2 of this comparative example, the rotation speed is 20 r / min, the inclination angle of the drum granulator is 6°, the average particle size is 85 μm, and the maximum crushing force for more than 80% of the particles is 12 N.

[0068] Comparative Example 8 Different from Example 1, in step S3 of this comparative example, the average particle size of the reduced coal is 1 mm, and the particle size of D5 is 0.3 mm.

[0069] In order to characterize the effectiveness of the technical solution, the following indicators are used for judgment: (1) Analyze the carbonylation slag to obtain the composition of the carbonylation material and process the carbonylation slag by chemical analysis.

[0070] (2) Calculate the deironing efficiency by: , is the deironing efficiency, is the mass percentage of iron in the material, It is the mass percentage of iron in carbonylation slag.

[0071] (3) Use chemical analysis to determine the content of rare earth oxides in the extracted iron.

[0072] The measurement results are shown in Table 1.

[0073] Table 1 Test results of various embodiments and comparative examples

[0074] It can be seen from Example 1 and Comparative Example 1 that the porous skeleton structure is partially burned to death through the one-step calcination process, thereby resulting in a high residual Fe content; it can be seen from Example 1, Comparative Examples 2 and 3 that in the roasting process, as in Comparative Example 2, if the low-temperature roasting time is short, fewer rare earth oxide microstructures are formed, and fewer flow channels for the subsequent formation of carbonyl iron are formed, resulting in some elemental iron remaining. If the low-temperature roasting time is long, more rare earth oxide microstructures are formed. Even if some rare earth oxide microstructures are fixed by high-temperature roasting and subsequent connection with reducing coal, some free rare earth oxide microstructures still exist, which causes the carbonyl iron to be involved in the outflow process. Since carbonyl iron is a high-value product, if too much rare earth oxide is involved, the quality of the carbonyl iron will be reduced. As can be seen from Example 1 and Comparative Examples 4 and 5, if the heating rate is too fast, the growth time of the rare earth oxide microstructure is short and the structure size is too small. On the one hand, it is impossible to form a path for the effective circulation of carbonyl iron. On the other hand, there is a possibility of being drawn into the liquid carbonyl iron. In Comparative Example 5, due to the long roasting time, part of the rare earth oxide microstructure is sintered, thereby increasing the reduction and carbonylation of iron, that is, there is a large amount of iron in the carbonyl slag. As can be seen from Example 1 and Comparative Examples 6 and 7, the granulation process has a certain impact on the extraction process. The main reasons are that the particles should not be large and dense, otherwise the reduction and subsequent carbonyl synthesis will be difficult and the degree of separation of elemental iron will be low; secondly, the particle size should not be small, as a small size will lead to local overheating of the reaction, causing the porous skeleton structure constructed by the rare earth oxide to sinter, affecting the reduction of iron oxide and the carbonyl synthesis reaction; finally, the particles need to meet a certain strength to avoid collapse, which will lead to a decrease in subsequent reduction strength and carbonyl synthesis efficiency. Therefore, the iron extraction efficiency in Comparative Examples 6 and 7 is significantly lower than that in Example 1. By comparing Example 1 and Comparative Example 8, it can be seen that reducing coal also promotes the extraction of iron. Since the ash of the reduced coal is connected with the oxide microstructure after reduction, a porous skeleton structure is formed, which facilitates the outflow of liquid carbonyl iron. The skeleton formed by the ash is relatively strong, which avoids the collapse of the skeleton structure during the carbonyl reaction.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for enriching rare earths based on NdFeB waste, characterized in that: include: The NdFeB waste is subjected to oxidation roasting and crushing to obtain NdFeB powder, wherein the oxidation roasting process is to maintain it at 300°C-500°C for 1.0h-2.0h, and then maintain it at 600°C-900°C for 2.0h-3.5h; The NdFeB powder is granulated without using a pressing process, and the particle size is 100 μm-500 μm; The granulated material is reduced to reduce the iron oxide to elemental iron; The reduced material is subjected to carbonyl synthesis to generate pentacarbonyl iron liquid and simultaneously obtain rare earth enriched material.

2. The method according to claim 1, characterized in that The mass percentage of iron in the NdFeB waste is 60%-70%.

3. The method according to claim 1, characterized in that The calcined NdFeB waste is crushed to 100-800 mesh.

4. The method according to claim 1, wherein Raise the temperature to 300-500°C and maintain for 1.0-2.0 hours, then raise the temperature to 600-900°C at a rate of 5-10°C / min and maintain for 2.0-3.5 hours.

5. The method according to claim 1, wherein The granulation process is as follows: mixing the NdFeB powder with a binder, agglomerating the NdFeB powder into balls, and adding the binder in an amount of 3% to 7% of the mass of the NdFeB powder.

6. The method according to claim 5, characterized in that A rotary drum granulator is used for granulation, and the binder is added by spraying. The rotation speed is 12r / min-18r / min, and the inclination angle of the rotary drum granulator is 6°-7°.

7. The method according to claim 1, characterized in that The reduction process is as follows: reducing coal is used as a reducing agent, the ratio of the added amount of the reducing coal to the mass of the material satisfies 1:(1-4), and the reduction temperature is maintained at 800°C-1200°C for 2h-6h.

8. The method according to claim 1, characterized in that Before reduction, mix at least half of the total amount of reduced coal with the granular material at a stirring speed of 10r / min-20r / min for 5min-10min; The remaining reduced coal is then added to the reduction furnace together with the granular material to carry out a reduction reaction.

9. The method according to claim 8, characterized in that The average particle size of the reduced coal is less than 1 mm.

10. The method according to claim 1, characterized in that The process of carbonyl synthesis is: reaction temperature 100℃-200℃, reaction pressure 5MPa-20MPa.

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