A method for directional oxidation separation of neodymium iron boron waste

Abstract

The application discloses a directional oxidation separation method of neodymium iron boron waste, and belongs to the technical field of secondary resource recovery. The method comprises the following steps: uniformly mixing neodymium iron boron waste, superfine powder, a boron-containing compound and a carbon-containing substance to obtain mixed raw materials; pouring the mixed raw materials into a closed electric furnace, introducing inert gas into the electric furnace, and discharging air in the furnace; controlling the temperature rising rate of the electric furnace, and rising the temperature to a smelting temperature at different temperature rising rates in a low-temperature section, a medium-temperature section and a high-temperature section to realize pyrolysis, oil removal, oxidation treatment of the neodymium iron boron waste and smelting and separation of rare earth slag; and continuously or periodically discharging the rare earth slag and molten iron from a slag outlet and an iron outlet respectively to obtain the rare earth slag and the molten iron. The application can realize efficient separation of rare earth elements and valuable metals such as iron, cobalt and copper.

Description

Technical Field

[0001] This invention relates to the field of secondary resource recycling technology, specifically a method for the directional oxidation separation of neodymium iron boron waste. Background Technology

[0002] Neodymium iron boron (NdFeB) permanent magnets contain rare earth elements such as neodymium, dysprosium, terbium, and praseodymium, accounting for more than 30% of the total magnet content. Sintering is a typical NdFeB permanent magnet manufacturing process and is widely used. However, the manufacturing process generates a large amount of waste, such as cutting sludge, abrasive, and ultrafine powder. NdFeB waste recycling technologies mainly include direct recycling, calcium thermal reduction diffusion, selective oxidation, chlorination separation, liquid alloying, slag-metal separation, and oxidative roasting-hydrochloric acid dissolution. Direct recycling is suitable for NdFeB waste with few impurities and no contamination. After crushing and re-sintering, it is returned to the NdFeB manufacturing process for producing low-grade NdFeB magnets. However, NdFeB waste with more impurities, such as cutting sludge, abrasive, and ultrafine powder, requires chemical methods to change the state of the rare earth elements, recovering them as oxides or salts. The oxidative roasting-hydrochloric acid dissolution process is currently the most widely used method for recycling NdFeB waste, but it has problems such as complex process, difficulty in recovering some rare earth elements mixed in with hematite slag, and difficulty in effectively recovering valuable elements such as iron, cobalt, and copper.

[0003] The slag-metal separation method is a potential efficient way to recover NdFeB waste. The doctoral dissertation, "Research on a New Process for Recovering Rare Earth Elements from NdFeB Waste," reported a method for recovering NdFeB waste using oxidative roasting-carbothermic reduction-magnetic separation. This method involves completely oxidizing the NdFeB waste through oxidative roasting, followed by carbothermic reduction to obtain a mixture of rare earth slag and metallic iron. Magnetic separation is then used to separate the rare earth oxide slag and metallic iron, achieving directional separation of rare earth and iron. However, this method does not utilize the difference in oxidizability between rare earth and iron in the NdFeB waste. Even after all the iron is oxidized, carbothermic reduction is still required to recover the metallic iron. Furthermore, magnetic separation of rare earth slag and metallic iron makes complete separation of slag and iron difficult. The paper "Extraction of Rare Earth Elements from Permanent Magnet Scraps by FeO-B2O3 Flux Treatment" proposes first using FeO and B2O3 to create a FeO-B2O3 system additive, and then using this additive to oxidize and cut the NdFeB waste. The results show that FeO and B2O3 can fully oxidize rare earth metals, but this method lacks a way to lower the melting point of rare earth oxide slag and alloys. The rare earth oxide slag and alloys need to be thoroughly crushed after cooling and then separated by magnetic separation. Furthermore, the FeO-B2O3 system additives need to be obtained through pre-calcination, increasing production costs. Patent CN106119523A proposes using various NdFeB waste materials and controlling the proportions of different NdFeB waste materials. In a rotary kiln, the rare earth and iron in the NdFeB waste react with oxygen in the air, generating a large amount of heat and achieving self-heating calcination, thus achieving complete oxidation of the NdFeB waste and converting rare earth into oxides and iron into Fe2O3. This method confirms that the oxidation reaction of NdFeB waste is a strongly exothermic reaction that can generate a large amount of heat, but this method does not achieve selective oxidation; both rare earth and iron are completely oxidized, and separation of rare earth and iron is impossible. Patent CN 106498166 A proposes a method for the complete recovery of NdFeB waste. The NdFeB waste undergoes thermal degreasing, and rare earth elements are oxidized using B2O3 or Fe2O3 as oxidants at 1000℃~1400℃. The rare earth slag and iron-boron alloy are then separated by gravity separation under an inert atmosphere. This method uses solid-phase oxidants such as B2O3 or Fe2O3 to oxidize the NdFeB waste, achieving directional oxidation of rare earth elements. However, it requires grinding the mixture of rare earth slag and iron-boron alloy under an inert atmosphere before separating them by gravity separation, making the separation conditions harsh. Patent CN109457116A proposes a method for flash roasting and high-gravity slag gold fusion separation of NdFeB waste. By controlling the oxygen injection ratio in the gas, i.e., controlling the oxygen partial pressure inside the furnace, rare earth elements and a small amount of iron are oxidized. The flux used is one or more of SiO2, CaO, MgO, Al2O3, and B2O3.After roasting, the mixture passes through a layer of incandescent coke, where a small amount of iron is reduced to metallic iron and combines with carbon to form molten iron. The mixture of rare earth slag and molten iron is then separated using a high-gravity slag-metal separator. This method uses oxygen as an oxidant to achieve directional oxidation of rare earth elements and B2O3 as a flux to improve the viscosity of the rare earth slag. However, the mixture of rare earth slag and molten iron requires separation using a high-gravity slag-metal separator, resulting in high production costs.

[0004] Therefore, developing a new method for recycling NdFeB waste that is low-cost, has a short process, and can achieve efficient separation of rare earth elements has become an urgent technical challenge in this field. Summary of the Invention

[0005] To address the problems of complex recycling processes, demanding separation conditions, and low resource utilization in NdFeB waste, the present invention aims to provide a directional oxidation separation method for NdFeB waste, specifically including the following steps: (1) Mix NdFeB waste, ultrafine powder, boron-containing compounds and carbon-containing substances evenly to obtain mixed raw materials.

[0006] (2) Pour the mixed raw materials into a closed electric furnace, introduce inert gas into the furnace, and exhaust the air inside the furnace; control the heating rate of the electric furnace, and heat it to the melting temperature according to different heating rates in the low temperature section, medium temperature section and high temperature section.

[0007] (3) The rare earth slag and molten iron obtained after smelting are continuously or periodically discharged from the slag outlet and the iron outlet respectively to obtain rare earth slag and molten iron.

[0008] Preferably, the NdFeB waste in step (1) of the present invention includes one or more of the following: cut NdFeB waste, scrap, and scrapped NdFeB magnetic materials.

[0009] Preferably, the boron-containing compound in step (1) of the present invention includes one or more of boron oxide, boric acid, and iron borate.

[0010] Preferably, the carbon-containing material in step (1) of the present invention includes one or more of coke, coal, and graphite.

[0011] Preferably, in step (1) of the present invention, the mass ratio of neodymium iron boron waste, ultrafine powder, boron-containing compound and carbon-containing material is 100:0~100:10~70:0~10.

[0012] Preferably, the inert gas in step (2) of the present invention is one or more of argon and nitrogen.

[0013] Preferably, in step (2) of the present invention, the heating rate of the low temperature section is 10~14℃ / min, and the temperature is raised to 350~420℃.

[0014] Preferably, in step (2) of the present invention, the heating rate in the medium temperature range is 7~9℃ / min, and the temperature is raised to 980~1020℃.

[0015] Preferably, in step (2) of the present invention, the heating rate of the high-temperature section is 4~6℃ / min, and the temperature is raised to 1200~1450℃.

[0016] Preferably, in step (2) of the present invention, the melting temperature is 1200~1450℃ and the melting time is 50~70 min.

[0017] This invention provides a method for the directional oxidation separation of neodymium iron boron waste, which has the following beneficial effects: (1) This invention achieves the directional oxidation of rare earth elements and selective retention of iron by rationally combining boron-containing compounds and carbon-containing materials, fully utilizing the difference in oxidizing properties between rare earth elements and iron in NdFeB waste. This eliminates the need for additional complex oxidants and achieves the separation of rare earth elements and iron. It simplifies the separation process and reduces the complexity of the process.

[0018] (2) The present invention uses boron-containing compounds to play a fluxing role, without the need to add other fluxing agents such as SiO2 and CaO. It can significantly reduce the melting point and viscosity of rare earth oxide slag, so that the rare earth slag formed after smelting can achieve natural stratification with the molten iron. It does not require special devices such as super gravity melting separators and complex grinding equipment. It can be discharged separately through the slag outlet and iron outlet of the closed electric furnace. The operation is simple, greatly reducing equipment investment and production costs. At the same time, it avoids the problem that magnetic separation, gravity separation and other methods are difficult to achieve complete separation of slag and iron, and improves separation efficiency.

[0019] (3) By controlling the ratio of mixed raw materials, smelting temperature and heating rate, this invention achieves efficient recovery of rare earth elements in NdFeB waste, while also realizing the direct recovery and utilization of iron, and taking into account the synergistic recovery of valuable elements such as cobalt and copper. It solves the problems of incomplete rare earth recovery and waste of valuable elements in existing processes, improves the level of comprehensive resource utilization, and has a short process and low energy consumption, making it suitable for large-scale industrial production and having significant economic and environmental benefits. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the reaction process in Embodiment 1 of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The composition and content of the NdFeB cutting waste processed in this embodiment of the invention are shown in Table 1 below.

[0023] Table 1 The components and contents of the processed material in this embodiment of the invention are shown in Table 2 below.

[0024] Table 2 Example 1 A method for directional oxidation separation of NdFeB waste specifically includes the following steps: (1) The waste material from cutting NdFeB, ultrafine powder, boron oxide and graphite are mixed evenly in a mass ratio of 100:30:25:1.6 to obtain mixed raw materials.

[0025] (2) Pour the mixed raw materials into a sealed electric furnace, introduce argon into the furnace, and exhaust the air inside the furnace; control the heating rate of the electric furnace, and heat it to 1350℃ for 60 minutes at different heating rates in the low temperature section (10℃ / min to 400℃), medium temperature section (7℃ / min to 1000℃), and high temperature section (5℃ / min to 1350℃) to achieve thermal deoiling, oxidation treatment of NdFeB waste and rare earth slag melting.

[0026] (3) Rare earth slag and molten iron are periodically discharged from the slag outlet and the iron outlet respectively to obtain rare earth slag and molten iron.

[0027] The rare earth slag obtained in this embodiment contains 1.1% iron, 0.025% cobalt, and 0.022% copper. The rare earth content in the alloy after the molten iron is cooled is 0.05%. The rare earth recovery rate is 99.3%, the iron recovery rate is 98.6%, the cobalt recovery rate is 99.2%, and the copper recovery rate is 99.3%.

[0028] The reaction process diagram of this embodiment is shown below. Figure 1 As shown, in the low-temperature section, the present invention isolates oxygen by injecting inert gas, preventing the NdFeB waste from being oxidized, and removing organic matter in the NdFeB waste through pyrolysis and volatilization. In the medium-temperature section, the difference in oxidation degree between the NdFeB waste and the ultrafine powder is utilized. For example, in the NdFeB waste, rare earth elements and valuable components such as iron, cobalt, and copper mainly exist in elemental form and are only slightly oxidized, while in the ultrafine powder, rare earth elements and valuable components such as iron, cobalt, and copper mainly exist in oxide form and are completely oxidized. From a thermodynamic perspective, Nd, Pr, Al, and B react with Fe2O3, B2O3, CoO, and Cu2O to generate Nd2O3 and Pr6O. 11The Gibbs free energies of Al2O3 and B2O3 are all negative within the temperature range covered by the invention. The ultrafine powder acts as an oxidant in cutting NdFeB waste, achieving the self-oxidation of the NdFeB waste. By controlling the proportion of NdFeB waste, the Fe2O3, CoO, and Cu2O in the ultrafine powder are used to directionally oxidize the rare earth elements in the NdFeB waste, forming rare earth oxides and metals Fe, Co, and Cu. Within the temperature range involved in the invention, B2O3 reacts with Nd, Pr, and Al to generate Nd2O3 and Pr6O. 11 The Gibbs free energy of Al2O3 is negative, while the Gibbs free energy of B2O3 reacting with Fe, Co, and Cu to form FeO, Fe2O3, CoO, and Cu2O is positive. B2O3 can act as a selective oxidant for rare earth elements, oxidizing only rare earth elements and not Fe, Co, or Cu. Using boron-containing compounds as selective oxidants for rare earth elements allows for the selective oxidation of rare earth elements on the basis of auto-oxidation, without oxidizing Fe, Co, or Cu, thus achieving complete oxidation of rare earth elements. Furthermore, the heat generated from the oxidation of NdFeB waste is directly used for furnace charge heating, reducing production costs. In the high-temperature section, boron-containing compounds act as fluxes for rare earth oxides, lowering the melting point of the rare earth oxide slag and causing it to transform from a solid to a liquid state. This invention achieves deoiling, oxidation, and melting in a single furnace at a specified heating rate within a closed electric furnace, yielding rare earth-rich slag and alloys.

[0029] Example 2 A method for directional oxidation separation of NdFeB waste specifically includes the following steps: (1) Mix NdFeB cutting waste, ultrafine powder, boric acid and graphite in a mass ratio of 100:50:53:4.2 to obtain mixed raw materials.

[0030] (2) Pour the mixed raw materials into a sealed electric furnace, introduce argon into the furnace, and exhaust the air inside the furnace; control the heating rate of the electric furnace, and heat it to 1400℃ for 60 minutes at different heating rates in the low temperature section (12℃ / min to 380℃), medium temperature section (7℃ / min to 1020℃), and high temperature section (5℃ / min to 1400℃) to achieve thermal deoiling, oxidation treatment of NdFeB waste and rare earth slag melting.

[0031] (3) Rare earth slag and molten iron are periodically discharged from the slag outlet and the iron outlet respectively to obtain rare earth slag and molten iron.

[0032] The rare earth slag obtained in this embodiment contains 0.8% iron, 0.02% cobalt, and 0.02% copper. The rare earth content in the alloy after the molten iron is cooled is 0.06%. The rare earth recovery rate is 99.3%, the iron recovery rate is 98.8%, the cobalt recovery rate is 99.2%, and the copper recovery rate is 99.3%.

[0033] Example 3 A method for directional oxidation separation of NdFeB waste specifically includes the following steps: (1) Mix the raw material, boron oxide and graphite in a mass ratio of 100:26:1.4 to obtain a mixed raw material.

[0034] (2) Pour the mixed raw materials into a sealed electric furnace, introduce argon into the furnace, and exhaust the air inside the furnace; control the heating rate of the electric furnace, and heat it to 1300℃ for 60 minutes at different heating rates in the low temperature section (10℃ / min to 390℃), the medium temperature section (7℃ / min to 1000℃), and the high temperature section (5℃ / min to 1300℃) to achieve oxidation treatment of NdFeB waste and rare earth slag melting.

[0035] (3) Rare earth slag and molten iron are periodically discharged from the slag outlet and the iron outlet respectively to obtain rare earth slag and molten iron.

[0036] The rare earth slag obtained in this embodiment contains 1.2% iron, 0.021% cobalt, and 0.018% copper. The rare earth content in the alloy after the molten iron is cooled is 0.016%. The rare earth recovery rate is 99.6%, the iron recovery rate is 98.8%, the cobalt recovery rate is 99.2%, and the copper recovery rate is 99.3%.

[0037] Example 4 A method for directional oxidation separation of NdFeB waste specifically includes the following steps: (1) Mix the cutting NdFeB waste, ultrafine powder and boric acid in a mass ratio of 100:100:10 to obtain mixed raw materials.

[0038] (2) Pour the mixed raw materials into a sealed electric furnace, introduce argon into the furnace, and exhaust the air inside the furnace; control the heating rate of the electric furnace, and heat it to 1200℃ in sequence according to different heating rates in the low temperature section (14℃ / min to 350℃), medium temperature section (8℃ / min to 980℃), and high temperature section (4℃ / min to 1200℃) for 70 min, so as to achieve thermal deoiling, oxidation treatment of NdFeB waste and rare earth slag melting.

[0039] (3) Rare earth slag and molten iron are periodically discharged from the slag outlet and the iron outlet respectively to obtain rare earth slag and molten iron.

[0040] The rare earth slag obtained in this embodiment contains 1.8% iron, 0.025% cobalt, and 0.023% copper. The rare earth content in the alloy after the molten iron is cooled is 0.11%. The rare earth recovery rate is 98.5%, the iron recovery rate is 98.1%, the cobalt recovery rate is 99.0%, and the copper recovery rate is 99.1%.

[0041] Example 5 A method for directional oxidation separation of NdFeB waste specifically includes the following steps: (1) Mix NdFeB cutting waste, ultrafine powder, boron oxide and graphite in a mass ratio of 100:10:70:10 to obtain mixed raw materials.

[0042] (2) Pour the mixed raw materials into a sealed electric furnace, introduce argon gas into the electric furnace, and exhaust the air in the furnace; control the heating rate of the electric furnace, and heat it to 1300℃ for 50 min at different heating rates in the low temperature section (12℃ / min to 400℃), the medium temperature section (9℃ / min to 1020℃), and the high temperature section (6℃ / min to 1300℃) to achieve thermal deoiling, oxidation treatment of NdFeB waste and rare earth slag melting.

[0043] (3) Rare earth slag and molten iron are periodically discharged from the slag outlet and the iron outlet respectively to obtain rare earth slag and molten iron.

[0044] The rare earth slag obtained in this embodiment contains 1.2% iron, 0.024% cobalt, and 0.019% copper. The rare earth content in the alloy after the molten iron is cooled is 0.018%. The rare earth recovery rate is 99.6%, the iron recovery rate is 98.7%, the cobalt recovery rate is 99.3%, and the copper recovery rate is 99.4%.

[0045] Comparative Example 1 The difference between this comparative example and Example 1 is that the heating process does not use segmented control, but uses the same heating rate (14℃ / min) to heat to 1350℃. The remaining steps are the same as in Example 1.

[0046] The rare earth slag obtained in this comparative example contained 3.2% iron, 0.066% cobalt, and 0.067% copper, while the rare earth content in the alloy was 0.63%. The rare earth recovery rate was 96.92%, the iron recovery rate was 95.33%, the cobalt recovery rate was 96.86%, and the copper recovery rate was 97.65%.

[0047] The rapid heating rate caused the boron oxide melt to overheat instantaneously, generating a large number of bubbles that overflowed, reducing the amount of boron oxide in the system and resulting in a higher viscosity of the final slag. Consequently, the separation effect between the slag and the metal in this comparative example was poor.

[0048] Comparative Example 2 The difference between this comparative example and Example 1 is that the melting temperature is 1100°C, while the other steps are the same as in Example 1.

[0049] The rare earth slag obtained in this comparative example contained 9.8% iron, 0.034% cobalt, and 0.041% copper, while the rare earth content in the alloy was 2.3%. The rare earth recovery rate was 92.2%, the iron recovery rate was 88.2%, the cobalt recovery rate was 92.1%, and the copper recovery rate was 91.4%.

[0050] Due to the low melting temperature, the alloy was not completely melted, resulting in poor separation of metal and slag, which led to a low recovery rate of iron and rare earth elements in this comparative example.

[0051] Comparative Example 3 The difference between this comparative example and Example 1 is that the melting temperature is 1550°C, while the other steps are the same as in Example 1.

[0052] The rare earth slag obtained in this comparative example contains 2.8% iron, 0.024% cobalt, and 0.023% copper. The rare earth content in the alloy is 0.12%, with a rare earth recovery rate of 98.21%, an iron recovery rate of 96.2%, a cobalt recovery rate of 98.9%, and a copper recovery rate of 99.0%.

[0053] The excessively high smelting temperature led to an increase in the volatilization of boron oxide, an increase in slag viscosity, and a deterioration in the separation of slag and metal. This resulted in an increase in mechanically entrained small metal particles in the slag and a decrease in iron recovery rate.

[0054] In this invention, the boron-containing compound achieves a "dual-purpose" effect; the carbon-containing substance acts as a flux for the alloy, lowering its melting point and causing it to transform from a solid to a liquid state. Through the synergistic effect of mixing raw materials and the heating process, the existing forms of rare earth oxide slag and the alloy are altered, changing the separation conditions from solid-solid or solid-liquid separation to liquid-liquid separation. This strengthens the separation conditions of rare earth oxide slag and the alloy, achieving complete separation under natural gravity conditions without the need for magnetic separation or hypergravity enhancement methods. This invention uses a closed electric furnace to control the heating rate, resulting in low equipment investment costs. Furthermore, the closed electric furnace has good dust collection efficiency, leading to significant environmental benefits. Therefore, this invention has good economic, environmental, and social benefits.

[0055] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for directional oxidation separation of NdFeB waste, characterized in that, Specifically, the following steps are included: (1) Mix NdFeB waste, ultrafine powder, boron-containing compounds and carbon-containing substances evenly to obtain mixed raw materials; (2) Pour the mixed raw materials into a closed electric furnace, introduce inert gas into the furnace, and exhaust the air inside the furnace; control the heating rate of the electric furnace, and heat it to the melting temperature according to different heating rates in the low temperature section, medium temperature section and high temperature section for melting. (3) The rare earth slag and molten iron obtained after smelting are continuously or periodically discharged from the slag outlet and the iron outlet respectively to obtain rare earth slag and molten iron.

2. The method for directional oxidation separation of NdFeB waste according to claim 1, characterized in that, The NdFeB waste mentioned in step (1) includes one or more of the following: cut NdFeB waste, scrap, and scrapped NdFeB magnetic materials; the boron-containing compound includes one or more of the following: boron oxide, boric acid, and iron borate; and the carbon-containing substance includes one or more of the following: coke, coal, and graphite.

3. The method for directional oxidation separation of NdFeB waste according to claim 1, characterized in that, The mass ratio of NdFeB waste, ultrafine powder, boron-containing compound and carbon-containing material in step (1) is 100:0~100:10~70:0~10.

4. The method for directional oxidation separation of NdFeB waste according to claim 1, characterized in that, The inert gas mentioned in step (2) is one or more of argon and nitrogen.

5. The method for directional oxidation separation of NdFeB waste according to claim 1, characterized in that, The heating rate of the low-temperature section in step (2) is 10~14℃ / min, and the temperature is raised to 350~420℃.

6. The method for directional oxidation separation of NdFeB waste according to claim 1, characterized in that, The heating rate in the intermediate temperature range mentioned in step (2) is 7~9℃ / min, and the temperature is raised to 980~1020℃.

7. The method for directional oxidation separation of NdFeB waste according to claim 1, characterized in that, The heating rate of the high-temperature section in step (2) is 4~6℃ / min, and it is raised to 1200~1450℃.

8. The method for directional oxidation separation of NdFeB waste according to claim 1, characterized in that, The melting temperature in step (2) is 1200~1450℃ and the melting time is 50~70min.

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