A controlled-oxygen flash roasting recycling process for NdFeB waste

Abstract

This invention relates to the field of rare earth resource recycling technology, specifically to a controlled-oxygen flash roasting recycling process for NdFeB waste. The process includes the following steps: material and carrier gas preparation, controlled-oxygen flash roasting, and product collection and separation. This invention achieves, for the first time, the direct separation of rare earth elements and iron from NdFeB in a pure pyrometallurgical process, producing rare earth oxides and metallic iron powder, eliminating the need for leaching and thus preventing acidic wastewater at the source. Furthermore, utilizing the suspension reaction of the flash furnace and the instantaneous heat transfer from the preheated carrier gas, selective oxidation is completed within 10-120 seconds, far exceeding the efficiency of traditional roasting. Simultaneously, the reaction temperature is lower, requiring only 450-650℃, and no acid or alkali reagents are needed, significantly reducing operating costs. During the reaction, because iron remains in a metallic state and has a significant magnetic difference from rare earth oxides, efficient separation can be achieved through simple weak magnetic separation.

Description

Technical Field

[0001] This invention relates to the field of rare earth resource recycling technology, specifically to a recycling process for neodymium iron boron waste using oxygen-controlled flash roasting. Background Technology

[0002] Recovering rare earth elements and iron from NdFeB waste is crucial for achieving resource recycling. Existing technologies mostly employ hydrometallurgy, which involves long processes and heavy pollution. In the pyrometallurgical process, the traditional roasting-leaching method is usually carried out at high temperatures, resulting in the simultaneous and complete oxidation of rare earth elements and iron. This not only leads to high energy consumption but also requires subsequent acid leaching for separation, failing to fully utilize the advantages of the short pyrometallurgical process.

[0003] The key to achieving efficient separation of rare earth elements and iron lies in utilizing the differences in their chemical properties. Thermodynamically, rare earth elements are more easily oxidized than iron. Theoretically, by precisely controlling the oxygen partial pressure and temperature of the system, selective oxidation of rare earth elements can be achieved, while iron remains unoxidized. However, in traditional static or moving bed calcination equipment, the gas-solid mass and heat transfer efficiency is low, and it is difficult to precisely control the micro-zone atmosphere, resulting in low selective oxidation efficiency and hindering industrial applications.

[0004] Flash roasting technology offers a solution to this problem. It disperses materials in a suspended state within the reaction space, creating excellent gas-solid contact conditions. However, traditional flash furnaces are mainly used for the oxidative roasting of sulfide ores, and their atmosphere is oxygen-rich air, which is not suitable for the precisely controlled oxygen environment required by this technology.

[0005] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a controlled-oxygen flash roasting recycling process for NdFeB waste. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a controlled-oxygen flash roasting recycling process for neodymium iron boron waste.

[0007] A controlled-oxygen flash roasting recycling process for NdFeB waste includes the following steps: S1. Material and carrier gas preparation: crush and grind the NdFeB waste into fine powder of 100-400 mesh to obtain waste powder. Preheat the nitrogen-oxygen mixture with an oxygen concentration of 0.5%~5% by volume to 400℃~600℃ to obtain preheated low oxygen carrier gas. S2. Controlled oxygen flash roasting: Waste powder is mixed with preheated low-oxygen carrier gas in the waste bin, and then injected into the reaction tower through the Venturi feed nozzle at the top of the flash furnace; the auxiliary heating system is controlled to heat the main body temperature of the reaction tower to 450℃~650℃; under these conditions, the rare earth elements are instantaneously and selectively oxidized, while the iron element is retained in the metallic state, resulting in a gas-solid mixture; S3. Product collection and separation: The gas-solid mixture obtained from the reaction is collected by a cyclone dust collector to obtain a roasted product composed of rare earth oxides and metallic iron; the roasted product is separated by magnetic separation to obtain rare earth oxide-rich and metallic iron powder.

[0008] Furthermore, in step S2, the residence time of the material in the reaction tower is 10s to 120s.

[0009] Furthermore, in step S3, a weak magnetic field magnetic separator is used for magnetic separation, with a magnetic field strength of 0.05~0.3T.

[0010] Furthermore, the method is based on a NdFeB waste recycling system, which includes a waste silo and feeder, a low-oxygen nitrogen-oxygen mixture preparation and preheating system, a Venturi feed nozzle, a reaction tower, an auxiliary heating system, a settling chamber, a cyclone dust collector, and a tail gas treatment and circulation system. The waste silo is connected to the feeder and the low-oxygen nitrogen-oxygen mixed gas preparation and preheating system, respectively, and is connected to the Venturi feed nozzle. The Venturi feed nozzle is connected to the reaction tower. An auxiliary heating system is installed inside the reaction tower. The lower part of the reaction tower is a settling chamber. A cyclone dust collector is installed at the bottom of the reaction tower. The lower part of the reaction tower is connected to the tail gas treatment and circulation system. The output end of the tail gas treatment and circulation system is connected to the low-oxygen nitrogen-oxygen mixed gas preparation and preheating system.

[0011] Furthermore, the exhaust gas treatment and recirculation system can send a portion of the purified exhaust gas back to the low-oxygen nitrogen-oxygen mixture preparation and preheating system to reduce gas consumption.

[0012] The present invention has the following advantages: 1. This invention is the first to achieve direct separation of rare earth elements and iron from neodymium iron boron in a pure pyrometallurgical process, producing rare earth oxides and metallic iron powder without leaching, thus eliminating acidic wastewater at the source.

[0013] 2. This invention utilizes the suspension reaction of the flash furnace and the instantaneous heat transfer brought by the preheated carrier gas to complete selective oxidation within 10-120 seconds, with an efficiency far exceeding that of traditional roasting.

[0014] 3. The reaction temperature of this invention is lower, requiring only 450-650℃, and it does not require the consumption of chemical reagents such as acids and alkalis, thus significantly reducing operating costs.

[0015] 4. In the reaction process of this invention, since iron remains in a metallic state, its magnetic properties differ greatly from those of rare earth oxides, and efficient separation can be achieved through simple weak magnetic separation. Attached Figure Description

[0016] Figure 1 This is a flow chart of the oxygen-controlled flash roasting recovery process of NdFeB waste according to the present invention.

[0017] Figure 2 This is a schematic diagram of the neodymium iron boron waste recycling system of the present invention. Detailed Implementation

[0018] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this invention. Example

[0019] A controlled-oxygen flash roasting recycling process for NdFeB waste, such as Figure 1 As shown, it includes the following steps: S1. Material and Carrier Gas Preparation: The waste NdFeB material with the following composition (wt%) is used: Nd 26.0%, Pr 5.5%, Fe 65.1%, B 1.0%, and other 2.4%. The waste NdFeB material is crushed and ground into 100-mesh fine powder to obtain waste powder. A nitrogen-oxygen mixture with an oxygen concentration of 0.5% by volume is preheated to 400°C to obtain a preheated low-oxygen carrier gas. S2. Controlled oxygen flash roasting: Waste powder is mixed with preheated low-oxygen carrier gas in the waste bin and then injected into the reaction tower through the Venturi feed nozzle at the top of the flash furnace; the auxiliary heating system is controlled to heat the main body temperature of the reaction tower to 450°C, and the residence time of the material in the reaction tower is 10s. Under these conditions, the rare earth elements are instantaneously and selectively oxidized, while the iron element is retained in the metallic state, resulting in a gas-solid mixture. S3. Product collection and separation: The gas-solid mixture obtained from the reaction is collected by a cyclone dust collector to obtain a roasted product composed of rare earth oxides and metallic iron; the roasted product is separated by magnetic separation using a weak magnetic field separator with a magnetic field strength of 0.05~0.3T to obtain rare earth oxide-rich and metallic iron powder.

[0020] The method is based on a neodymium iron boron waste recycling system, such as... Figure 2 As shown, the system includes a waste silo and feeder, a low-oxygen nitrogen-oxygen mixture preparation and preheating system, a venturi feed nozzle, a reaction tower, an auxiliary heating system, a settling chamber, a cyclone dust collector, and a tail gas treatment and circulation system. The waste silo is connected to the feeder and the low-oxygen nitrogen-oxygen mixed gas preparation and preheating system, respectively, and is connected to the Venturi feed nozzle. The Venturi feed nozzle is connected to the reaction tower. An auxiliary heating system is installed inside the reaction tower. The lower part of the reaction tower is a settling chamber. A cyclone dust collector is installed at the bottom of the reaction tower. The lower part of the reaction tower is connected to the tail gas treatment and circulation system. The output end of the tail gas treatment and circulation system is connected to the low-oxygen nitrogen-oxygen mixed gas preparation and preheating system. The exhaust gas treatment and recirculation system can send part of the purified exhaust gas back to the low-oxygen nitrogen-oxygen mixture preparation and preheating system to reduce gas consumption. Example

[0021] A controlled-oxygen flash roasting recycling process for NdFeB waste, such as Figure 1 As shown, it includes the following steps: S1. Material and Carrier Gas Preparation: The composition (wt%) of Nd26.0%, Pr5.5%, Fe65.1%, B1.0%, and other 2.4% NdFeB waste is used. The NdFeB waste is crushed and ground into 300-mesh fine powder to obtain waste powder. A nitrogen-oxygen mixture with an oxygen concentration of 1.0% by volume is preheated to 500℃ to obtain preheated low-oxygen carrier gas. S2. Controlled-Oxygen Flash Calcination: Waste powder is mixed with preheated low-oxygen carrier gas in the waste bin and then injected into the reaction tower through the Venturi feed nozzle at the top of the flash furnace. The auxiliary heating system is controlled to heat the main body of the reaction tower to 550°C. The residence time of the material in the reaction tower is 60s. Under these conditions, the rare earth elements are instantaneously and selectively oxidized, while the iron element is retained in the metallic state, resulting in a gas-solid mixture. S3. Product collection and separation: The gas-solid mixture obtained from the reaction is collected by a cyclone dust collector to obtain a roasted product composed of rare earth oxides and metallic iron; the roasted product is separated by magnetic separation using a weak magnetic field separator with a magnetic field strength of 0.05~0.3T to obtain rare earth oxide-rich and metallic iron powder.

[0022] The method is based on a neodymium iron boron waste recycling system, such as... Figure 2 As shown, the system includes a waste silo and feeder, a low-oxygen nitrogen-oxygen mixture preparation and preheating system, a venturi feed nozzle, a reaction tower, an auxiliary heating system, a settling chamber, a cyclone dust collector, and a tail gas treatment and circulation system. The waste silo is connected to the feeder and the low-oxygen nitrogen-oxygen mixed gas preparation and preheating system, respectively, and is connected to the Venturi feed nozzle. The Venturi feed nozzle is connected to the reaction tower. An auxiliary heating system is installed inside the reaction tower. The lower part of the reaction tower is a settling chamber. A cyclone dust collector is installed at the bottom of the reaction tower. The lower part of the reaction tower is connected to the tail gas treatment and circulation system. The output end of the tail gas treatment and circulation system is connected to the low-oxygen nitrogen-oxygen mixed gas preparation and preheating system. The exhaust gas treatment and recirculation system can send part of the purified exhaust gas back to the low-oxygen nitrogen-oxygen mixture preparation and preheating system to reduce gas consumption. Example

[0023] A controlled-oxygen flash roasting recycling process for NdFeB waste, such as Figure 1 As shown, it includes the following steps: S1. Material and Carrier Gas Preparation: The waste NdFeB material with the following composition (wt%) is used: Nd 26.0%, Pr 5.5%, Fe 65.1%, B 1.0%, and other 2.4%. The waste NdFeB material is crushed and ground into a 400-mesh fine powder to obtain waste powder. A nitrogen-oxygen mixture with an oxygen concentration of 5% by volume is preheated to 600°C to obtain a preheated low-oxygen carrier gas. S2. Controlled oxygen flash roasting: Waste powder is mixed with preheated low-oxygen carrier gas in the waste bin and then injected into the reaction tower through the Venturi feed nozzle at the top of the flash furnace; the auxiliary heating system is controlled to heat the main body temperature of the reaction tower to 650°C and the residence time of the material in the reaction tower is 120s. Under these conditions, the rare earth elements are instantaneously and selectively oxidized, while the iron element is retained in the metallic state, resulting in a gas-solid mixture. S3. Product collection and separation: The gas-solid mixture obtained from the reaction is collected by a cyclone dust collector to obtain a roasted product composed of rare earth oxides and metallic iron; the roasted product is separated by magnetic separation using a weak magnetic field separator with a magnetic field strength of 0.05~0.3T to obtain rare earth oxide-rich and metallic iron powder.

[0024] The method is based on a neodymium iron boron waste recycling system, such as... Figure 2 As shown, the system includes a waste silo and feeder, a low-oxygen nitrogen-oxygen mixture preparation and preheating system, a venturi feed nozzle, a reaction tower, an auxiliary heating system, a settling chamber, a cyclone dust collector, and a tail gas treatment and circulation system. The waste silo is connected to the feeder and the low-oxygen nitrogen-oxygen mixed gas preparation and preheating system, respectively, and is connected to the Venturi feed nozzle. The Venturi feed nozzle is connected to the reaction tower. An auxiliary heating system is installed inside the reaction tower. The lower part of the reaction tower is a settling chamber. A cyclone dust collector is installed at the bottom of the reaction tower. The lower part of the reaction tower is connected to the tail gas treatment and circulation system. The output end of the tail gas treatment and circulation system is connected to the low-oxygen nitrogen-oxygen mixed gas preparation and preheating system. The exhaust gas treatment and recirculation system can send part of the purified exhaust gas back to the low-oxygen nitrogen-oxygen mixture preparation and preheating system to reduce gas consumption.

[0025] The rare earth oxidation rate, iron metallic state retention rate, iron grade of iron powder, iron recovery rate, and rare earth content in rare earth-rich oxides of Examples 1-3 were tested, and the results are shown in Table 1.

[0026] Table 1 (Unit: %) Example 1 ＞99 95.2 92.8 93.1 46.3 Example 2 ＞99 97.5 93.8 95.2 48.5 Example 3 ＞99 94.1 92.5 92.0 45.2 As shown in Table 1, the rare earth content in the "rare earth-rich oxide" of this invention is 40%~50%, which is consistent with the material balance and reaction mechanism of the process. This is mainly because the total rare earth content of the raw material itself is limited, and during the roasting process, rare earth reacts with elements such as boron to form stable borates. This product is an ideal precursor for hydrometallurgical processes, achieving efficient enrichment of rare earth and removal of iron, resulting in significant overall economic benefits.

[0027] Furthermore, the data from the above embodiments demonstrate that the method and system of the present invention can successfully achieve efficient and clean separation of rare earth elements and iron from NdFeB waste, making it an innovative technology with great industrial application prospects.

[0028] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims. Parts not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A controlled-oxygen flash roasting recycling process for NdFeB waste, characterized in that, Specifically, the following steps are included: S1. Material and carrier gas preparation: crush and grind the NdFeB waste into fine powder of 100-400 mesh to obtain waste powder. Preheat the nitrogen-oxygen mixture with an oxygen concentration of 0.5%~5% by volume to 400℃~600℃ to obtain preheated low oxygen carrier gas. S2. Controlled oxygen flash roasting: Waste powder is mixed with preheated low-oxygen carrier gas in the waste bin, and then injected into the reaction tower through the Venturi feed nozzle at the top of the flash furnace; the auxiliary heating system is controlled to heat the main body temperature of the reaction tower to 450℃~650℃; under these conditions, the rare earth elements are instantaneously and selectively oxidized, while the iron element is retained in the metallic state, resulting in a gas-solid mixture; S3. Product collection and separation: The gas-solid mixture obtained from the reaction is collected by a cyclone dust collector to obtain a roasted product composed of rare earth oxides and metallic iron; the roasted product is separated by magnetic separation to obtain rare earth oxide-rich and metallic iron powder.

2. The oxygen-controlled flash roasting recovery process for NdFeB waste according to claim 1, characterized in that, In step S2, the residence time of the material in the reaction tower is 10s to 120s.

3. The oxygen-controlled flash roasting recovery process for NdFeB waste according to claim 1, characterized in that, In step S3, a weak magnetic field magnetic separator is used for magnetic separation, with a magnetic field strength of 0.05~0.3T.

4. The oxygen-controlled flash roasting recovery process for NdFeB waste according to claim 1, characterized in that, The method is based on a neodymium iron boron waste recycling system, which includes a waste silo and feeder, a low-oxygen nitrogen-oxygen mixture preparation and preheating system, a venturi feed nozzle, a reaction tower, an auxiliary heating system, a settling chamber, a cyclone dust collector, and a tail gas treatment and circulation system. The waste silo is connected to the feeder and the low-oxygen nitrogen-oxygen mixed gas preparation and preheating system, respectively, and is connected to the Venturi feed nozzle. The Venturi feed nozzle is connected to the reaction tower. An auxiliary heating system is installed inside the reaction tower. The lower part of the reaction tower is a settling chamber. A cyclone dust collector is installed at the bottom of the reaction tower. The lower part of the reaction tower is connected to the tail gas treatment and circulation system. The output end of the tail gas treatment and circulation system is connected to the low-oxygen nitrogen-oxygen mixed gas preparation and preheating system.

5. The oxygen-controlled flash roasting recovery process for NdFeB waste according to claim 4, characterized in that, The exhaust gas treatment and recirculation system can send a portion of the purified exhaust gas back to the low-oxygen nitrogen-oxygen mixture preparation and preheating system to reduce gas consumption.

Images