Method for preparing iron-chromium-cobalt alloy from cobalt slag and ferrochrome slag

Abstract

The invention discloses a method for preparing an iron-chromium-cobalt alloy by using cobalt slag and ferrochrome slag, and belongs to the technical field of metallurgy and comprehensive utilization of resources. According to the method, zinc hydrometallurgy byproduct cobalt slag and ferrochrome alloy smelting byproduct ferrochrome slag serve as main raw materials, aluminum blocks and lime are matched, after drying, crushing, fine grinding and mixing are conducted, an aluminothermy self-propagating reduction reaction is triggered through electric auxiliary heating, high-temperature smelting is conducted at the temperature larger than or equal to 1500 DEG C, and finally the ferrochrome cobalt alloy is obtained through slag-metal separation and casting forming. According to the method, high-valued utilization of the dangerous waste residues is achieved, the process is simple, cost is low, energy consumption is low, the obtained alloy is low in carbon content and excellent in magnetic performance (residual magnetism is not smaller than 1.365 T, coercive force is not smaller than 48.63 kA / m, and magnetic energy product is not smaller than 48.26 kJ / m < 3 >), and the method is suitable for the field of permanent magnet materials and related high-end manufacturing.

Description

Technical Field

[0001] This invention belongs to the field of metallurgy and comprehensive resource utilization technology, specifically relating to a method for preparing permanent magnet alloys using industrial waste slag, and more particularly to a method for preparing iron-chromium-cobalt (Fe-Cr-Co) alloys using cobalt slag and ferrochrome slag as the main raw materials. Background Technology

[0002] Cobalt is an important strategic metal, widely used in batteries, alloys, catalysts, and other fields. my country's cobalt resources are relatively scarce. High-cobalt slag produced in the by-process recovery system of hydrometallurgical zinc smelting often contains 10%–15% cobalt, representing an important secondary cobalt resource. Currently, this type of cobalt-containing waste slag is mostly treated as hazardous waste and stockpiled or subjected to simple disposal, which not only wastes cobalt resources but also causes serious environmental pollution due to the leaching of heavy metals.

[0003] Ferrochrome slag is the main solid waste generated during the smelting of ferrochrome alloys. Approximately 1.1 to 1.6 tons of ferrochrome slag are produced for every ton of ferrochrome alloy produced. This slag often contains a certain amount of valuable metals such as chromium and iron, but its utilization rate is low under current technology. It is mostly disposed of by open-air stockpiling or landfilling. Long-term stockpiling can lead to harmful elements such as chromium seeping into the soil and groundwater, causing serious damage to the ecological environment.

[0004] Fe-Cr-Co permanent magnet alloys are amplitude-modulated decomposition permanent magnet materials with high ductility, high-temperature stability, and excellent magnetic properties. They are widely used in hysteresis motors, high-speed motors, anti-theft devices, and other equipment. Traditional Fe-Cr-Co alloy preparation often uses pure metals or concentrates as raw materials, which involves long processes, high energy consumption, high costs, and requires high purity of raw materials.

[0005] Currently, common methods for treating metal-containing waste residues such as cobalt slag and ferrochrome slag include hydrometallurgical processes and pyrometallurgical processes. However, these methods suffer from problems such as complex processes, low metal recovery rates, high risks of secondary pollution, and high costs. Achieving efficient, clean, and high-value utilization of these waste residues remains a pressing technical challenge for the metallurgical and environmental protection fields. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide a method for preparing iron-chromium-cobalt alloys using cobalt slag and ferrochrome slag. This method uses cobalt slag and ferrochrome slag as the main raw materials, resulting in low production costs and producing Fe-Cr-Co alloys with excellent magnetic properties. This method helps alleviate the scarcity of metal resources in my country. The synergistic preparation of iron-chromium-cobalt alloys using these two slags also enables the rational treatment of hazardous solid waste, yielding significant environmental, economic, and social benefits.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: A method for preparing iron-chromium-cobalt alloy using cobalt slag and ferrochrome slag includes the following steps: Step 1: Take aluminum blocks, cobalt slag, ferrochrome slag and lime as raw materials, dry and dehydrate them at 120℃, and set them aside for later use; Step 2: Crush the cobalt slag and ferrochrome slag obtained in Step 1 into particles with a diameter of less than 10 mm. Step 3: The lime obtained in Step 1, as well as the cobalt slag and ferrochrome slag particles crushed in Step 2, are ball-milled separately using a planetary ball mill and then passed through a 100-mesh sieve. Step 4: Put all the raw materials that have been sieved in step 3 into a mixer and mix them thoroughly to obtain a mixture for later use; Step 5: Spread the aluminum block and the mixture evenly on the bottom of the crucible of the electromagnetic induction furnace. Use electric auxiliary heating to promote the aluminothermic self-propagating reduction reaction. After the material is completely melted, continue to supply power to maintain the system temperature at no less than 1500℃ to allow for a full reaction. After the reaction is completed, pour out the slag on the top of the crucible, and then pour the refined molten metal into the cast iron ingot mold. After cooling, demold to obtain the iron-chromium-cobalt alloy.

[0008] Furthermore, the cobalt slag is the slag obtained after impurity removal during the wet zinc smelting process, and the ferrochrome slag is the slag produced during the smelting of ferrochrome alloys.

[0009] Furthermore, in step one, the amounts of each raw material, by weight percentage, are: cobalt slag 30%–35%, ferrochrome slag 25%–30%, aluminum blocks 20%–25%, and lime 10%–15%.

[0010] Furthermore, by weight percentage, the main components of cobalt slag are: Fe2O3 10-15%, SO3 20-25%, Co2O3 25-30%, ZnO 5-10%, MnO 5-10%, CaO 2-3%, and unavoidable impurities.

[0011] Furthermore, by weight percentage, the main components of ferrochrome slag are: SiO2 28-30%, Fe2O3 5-8%, MgO 25-28%, TiO2 3-5%, Cr2O3 10-13%, Al2O3 25-28%, and unavoidable impurities.

[0012] Furthermore, in step five, the system temperature is maintained above 1500°C for at least 30 minutes.

[0013] Furthermore, the magnetic properties of the obtained iron-chromium-cobalt alloy satisfy the following requirements: remanence not less than 1.365T, coercivity not less than 48.63kA / m, and magnetic energy product not less than 48.26kJ / m. 3 .

[0014] The principle of this invention is explained below. Cobalt slag mainly consists of Fe2O3, Co2O3, ZnO, MnO, CaO, etc., while ferrochrome slag mainly consists of SiO2, Fe2O3, MgO, Co2O3, Al2O3, etc. This invention uses electric auxiliary heating to promote the aluminothermic self-propagating reduction reaction. After the material is completely melted, power is continuously supplied to maintain the system temperature above 1500℃ for 30 minutes. At this high temperature, aluminum acts as a reducing agent and reacts with Fe2O3, Co2O3, and Cr2O3 in the slag. Fe₂O₃ + Al = Fe + Al₂O₃; Co₂O₃ + Al = Co + Al₂O₃; Cr₂O₃ + Al = Cr + Al₂O₃; The reaction releases a large amount of heat, maintaining a high system temperature and promoting metal reduction and alloying. During cooling, liquid iron and the reduced cobalt and chromium solidify into an iron-chromium-cobalt alloy. The addition of lime adjusts the slag basicity and combines with the reaction product Al2O3 to form the low-melting-point compound CaO•Al2O3, improving slag fluidity and facilitating slag-metal separation. MgO, however, cannot be reduced and enters the slag.

[0015] Next, the functions of each raw material in this invention will be explained: Cobalt slag and ferrochrome slag are the main sources of metals, providing alloying elements such as Fe, Co, and Cr. Aluminum block: as a reducing agent, it reduces metal oxides in the slag and releases heat of reaction; Lime: Adjusts the composition and alkalinity of slag, promotes slag fluidity, and facilitates the separation of molten metal from slag.

[0016] Beneficial effects: (1) This invention uses ferrochrome slag and cobalt slag as the main raw materials and aluminum as the reducing agent. It achieves alloying by utilizing the large amount of chemical heat spontaneously released through the aluminothermic self-propagating reduction reaction, which greatly reduces energy consumption and production costs. This process realizes the direct reduction and alloying of valuable metals in waste slag, which not only effectively utilizes waste resources, but also significantly shortens the smelting process, reduces material loss, and improves the recovery rate of alloying elements. It is a highly efficient new technology that conforms to the development direction of green metallurgy.

[0017] (2) By precisely controlling the aluminothermic self-propagating reduction reaction, this invention achieves selective reduction of cobalt in cobalt slag and iron and chromium in ferrochrome slag, and synthesizes Fe-Cr-Co alloys that can be directly applied to end products in one step.

[0018] (3) The CaO added in this invention can effectively adjust the slag basicity and form low-melting-point compounds (such as CaO•Al2O3) with the Al2O3 generated in the reaction, which significantly improves the fluidity of the slag at high temperatures. This not only facilitates the aggregation, growth and sedimentation of metal droplets and promotes slag-metal separation, but also enhances heat and mass transfer efficiency, making the aluminothermic reduction reaction more thorough, thereby improving the purity of the alloy and the element yield.

[0019] (4) In this invention, an aluminothermic self-propagating reduction reaction is initiated by electric auxiliary heating, without the addition of any carbonaceous reducing agent or carbon-containing materials, thus fundamentally preventing carbon elements from being reduced into the alloy melt. This feature significantly reduces the carbon content in the finished alloy, which not only helps to improve the magnetic properties of the alloy (such as increasing coercivity and energy product), but also enhances the corrosion resistance of the alloy in harsh environments and extends the service life of the material.

[0020] (5) The technical principle of this invention is based on the reduction reaction of aluminum to metal oxides at high temperature: 2[Al] + 3MeO → 3[Me] + Al2O3 By pouring out some of the slag, the reaction equilibrium can be shifted to the right, making the reduction more thorough and thus increasing the alloy yield and metal recovery rate.

[0021] (6) The iron-chromium-cobalt alloy prepared by this invention has excellent comprehensive properties, with a remanence of over 1.365T, a coercivity of over 48.63 kA / m, and a magnetic energy product of 48.26 kJ / m. 3 In addition to the above, it also has good corrosion resistance and can be widely used in many high-end fields such as petrochemicals, aerospace, and machinery manufacturing. Detailed Implementation

[0022] In the specific implementation of this invention, to achieve efficient utilization of cobalt slag and ferrochrome slag and to prepare a high-performance iron-chromium-cobalt alloy, the specific operations of each process step are described in detail below. This method sequentially includes key processes such as raw material pretreatment, crushing, ball milling, mixing, and aluminothermic self-propagating reduction. These steps work synergistically to ensure the uniformity of the alloy's composition and its overall performance. Step 1: Raw material preparation and pretreatment: Aluminum blocks, cobalt slag, ferrochrome slag, and lime are dried and dehydrated at 120℃ to remove moisture from the raw materials and prevent the generation of water vapor during the high-temperature reaction, which would affect the stability and safety of the reaction. The weight percentages of each raw material are as follows: cobalt slag 30%–35%, ferrochrome slag 25%–30%, aluminum blocks 20%–25%, and lime 10%–15%. Step 2, Crushing treatment: Crush the cobalt slag and ferrochrome slag into particles with a diameter of less than 10mm to increase the specific surface area of ​​the raw materials, which is beneficial for subsequent ball milling and uniform mixing. Step 3: Ball milling and sieving: The crushed cobalt slag, ferrochrome slag and lime are ball milled separately using a planetary ball mill and then sieved through a 100-mesh sieve to obtain fine powder with uniform particle size, ensuring that the components are fully contacted and reacted completely during the mixing and reaction process. Step 4: Mixing: Place the sieved raw materials into a mixer and mix them thoroughly to obtain a uniform mixture, so as to ensure that the aluminothermic reduction reaction can proceed synchronously and uniformly. Step 5: Preparation of iron-chromium-cobalt alloy: Aluminum blocks and mixtures are evenly spread at the bottom of the crucible of an electromagnetic induction furnace. An aluminothermic self-propagating reduction reaction is initiated by electric auxiliary heating. The high temperature is maintained by the large amount of chemical heat released by the reaction itself. After the materials are completely melted, the power supply is continuously supplied to maintain the system temperature at no less than 1500℃ for 30 minutes to promote the full reduction of metal oxides and the fusion of alloying elements. After the reaction is completed, the upper slag is poured out to achieve slag-metal separation. The molten metal is then poured into a cast iron ingot mold, cooled, and demolded to obtain an iron-chromium-cobalt alloy with uniform composition and dense structure.

[0023] It should be noted that the cobalt slag is the slag obtained after impurity removal during the hydrometallurgical zinc smelting process, while the ferrochrome slag is the slag produced during the smelting of ferrochrome alloys. By weight percentage, the main components of the cobalt slag are: Fe₂O₃ 10–15%, SO₃ 20–25%, Co₂O₃ 25–30%, ZnO 5–10%, MnO 5–10%, CaO 2–3%, and unavoidable impurities. The main components of the ferrochrome slag are: SiO₂ 28–30%, Fe₂O₃ 5–8%, MgO 25–28%, TiO₂ 3–5%, Cr₂O₃ 10–13%, Al₂O₃ 25–28%, and unavoidable impurities.

[0024] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments and comparative examples. 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 protection scope of the present invention.

[0025] Example 1 A method for preparing iron-chromium-cobalt alloy using cobalt slag and ferrochrome slag, the specific steps of which are as follows: Step 1: Take 30% cobalt slag, 30% ferrochrome slag, 25% aluminum blocks, and 15% lime by weight, and set aside. Step 2: Crush the cobalt slag and ferrochrome slag into particles smaller than 10mm; Step 3: The cobalt slag, ferrochrome slag and lime obtained in Step 1 are ball-milled separately using a ball mill and then passed through a 100-mesh sieve. Step 4: Place the sieved raw materials into a three-dimensional mixer and mix for 10 hours to obtain a mixture for later use. Step 5: Add aluminum blocks and mixture evenly to the bottom of the crucible of the electromagnetic induction furnace. Use electric auxiliary heating to promote the aluminothermic self-propagating reduction reaction. After the material is completely melted, continue to supply power to maintain the system temperature at 1600℃ for 30 minutes. After pouring out the upper layer of slag in the crucible (slag-metal separation), pour the refined molten metal into the cast iron ingot mold. After cooling, demold to obtain the iron-chromium-cobalt alloy.

[0026] Example 2 A method for preparing iron-chromium-cobalt alloy using cobalt slag and ferrochrome slag, the specific steps of which are as follows: Step 1: Take 33% cobalt slag, 28% ferrochrome slag, 24% aluminum blocks, and 15% lime by weight, and set aside. Step 2: Crush the cobalt slag and ferrochrome slag into particles smaller than 10mm; Step 3: The cobalt slag, ferrochrome slag and lime obtained in Step 1 are ball-milled separately using a ball mill and then passed through a 100-mesh sieve. Step 4: Place the sieved raw materials into a three-dimensional mixer and mix for 10 hours to obtain a mixture for later use. Step 5: Add aluminum blocks and mixture evenly to the bottom of the crucible of the electromagnetic induction furnace. Use electric auxiliary heating to promote the aluminothermic self-propagating reduction reaction. After the material is completely melted, continue to supply power to maintain the system temperature at 1550℃ for 30 minutes. After pouring out the upper layer of slag in the crucible (slag-metal separation), pour the refined molten metal into the cast iron ingot mold. After cooling, demold to obtain the iron-chromium-cobalt alloy.

[0027] Comparative Example 1 A method for preparing iron-chromium-cobalt alloy using cobalt slag and ferrochrome slag, the specific steps of which are as follows: Step 1: Take 35% cobalt slag, 32% ferrochrome slag, 25% aluminum blocks, and 8% lime by weight, and set aside. Step 2: Crush the cobalt slag and ferrochrome slag into particles smaller than 10mm; Step 3: The cobalt slag, ferrochrome slag and lime obtained in Step 1 are ball-milled separately using a ball mill and then passed through a 100-mesh sieve. Step 4: Place the sieved raw materials into a three-dimensional mixer and mix for 10 hours to obtain a mixture for later use. Step 5: Add aluminum blocks and mixture evenly to the bottom of the crucible of the electromagnetic induction furnace. Use electric auxiliary heating to promote the aluminothermic self-propagating reduction reaction. After the material is completely melted, continue to supply power to maintain the system temperature above 1500℃ for 30 minutes. After pouring out the upper layer of slag in the crucible (slag-metal separation), pour the refined molten metal into the cast iron ingot mold. After cooling, demold to obtain the iron-chromium-cobalt alloy.

[0028] The alloys obtained in Examples 1-2 and Comparative Example 1 were subjected to magnetic property testing on an ATM-3 automatic magnetic property tester. The results are shown in Table 1.

[0029] Table 1 Test results of Examples 1-2 and Comparative Example 1 As shown in Table 1, the alloys prepared in Examples 1 and 2 exhibit excellent magnetic properties, with remanence exceeding 1.36 T, coercivity higher than 48.6 kA / m, and magnetic energy product greater than 48.5 kJ / m. 3 This is thanks to its comprehensive process control: a reasonable raw material ratio (15% lime) ensures that the slag has appropriate alkalinity and good fluidity, promoting the complete aluminothermic reduction reaction and allowing cobalt in the cobalt slag and iron and chromium in the ferrochrome slag to be fully reduced and alloyed; sufficient reaction temperature and time ensure good fusion of the molten metal and effective separation of slag and metal. In contrast, the alloy of Comparative Example 1 showed a significant decrease in various magnetic properties. The reason for this is not only that the lime content was too low (8%), resulting in insufficient slag alkalinity and poor fluidity, affecting reaction kinetics and metal particle aggregation; the deeper reason is that the raw material ratio itself deviated from the optimized range, with a high total amount of ferrochrome slag and cobalt slag (67% in total), while the lime content was relatively insufficient. This imbalance in the formula led to an increase in the amount and deterioration of the slag phase generated during the reaction, further hindering heat transfer and metal reduction, ultimately resulting in a decrease in metal yield and deterioration of alloy performance. It can be seen that the superior performance of this invention is the result of the combined effects of precise raw material ratio, efficient start-up and maintenance of the aluminothermic self-propagating reaction, and high-temperature smelting environment. Among them, the amount of lime (10%~15%) is one of the key parameters for adjusting the entire reaction system and ensuring the smooth operation of the process. It must be controlled in coordination with the proportion of other raw materials in order to achieve the dual goals of waste slag resource utilization and high-performance alloy preparation.

[0030] This method achieves integrated preparation from hazardous waste slag to high-performance alloys through a complete process chain of "waste slag pretreatment—material control—aluminothermic self-propagating reduction—slag-metal separation". First, the cobalt slag and ferrochrome slag are dried, crushed, and finely ground, which not only removes moisture that affects reaction safety but also significantly improves the reactivity of the raw materials, laying the foundation for subsequent efficient reduction. Second, precise control of the raw material ratio (30%-35% cobalt slag, 25%-30% ferrochrome slag, 20%-25% aluminum blocks, and 10%-15% lime) is crucial. This ensures that the amount of aluminum in the reducing agent is sufficient to fully reduce the target metal oxide, while the amount of lime added optimizes the slag composition. During the reaction stage, an electrically assisted heating method reliably initiates the aluminothermic self-propagating reduction reaction, and a continuous power supply maintains a high temperature above 1500℃. This ensures the full progress and propagation of the strongly exothermic reaction, and the continuous high temperature provides the necessary thermodynamic conditions for the complete reduction of the metal oxide, the mutual solubility and diffusion of alloying elements, and the good flow of the molten slag. Finally, by pouring out the upper slag, a clean slag-gold separation is achieved, allowing direct casting to obtain alloy ingots with uniform composition. Throughout the process, each step is interconnected: pretreatment ensures the quality of the raw materials, batch control lays the foundation for the reaction, aluminothermic reduction and high-temperature smelting achieve the core material transformation, and slag-gold separation directly determines the purity and performance of the final product.

[0031] The present invention has provided a detailed description of a method for preparing iron-chromium-cobalt alloy using cobalt slag and ferrochrome slag. Specific examples have been used to illustrate the principles and specific implementation methods of the invention. These embodiments are only used to help understand the method and core ideas of the present invention. It should be noted that any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention by those skilled in the art fall within the protection scope of the present invention.

Claims

1. A method for preparing iron-chromium-cobalt alloy using cobalt slag and ferrochrome slag, characterized in that, Includes the following steps: Step 1: Take aluminum blocks, cobalt slag, ferrochrome slag and lime as raw materials, dry and dehydrate them at 120℃, and set them aside for later use; Step 2: Crush the cobalt slag and ferrochrome slag obtained in Step 1 into particles with a diameter of less than 10mm. Step 3: The lime obtained in Step 1, as well as the cobalt slag and ferrochrome slag particles crushed in Step 2, are ball-milled separately using a planetary ball mill and then passed through a 100-mesh sieve. Step 4: Put all the raw materials that have been sieved in step 3 into a mixer and mix them thoroughly to obtain a mixture for later use; Step 5: Spread the aluminum block and the mixture evenly on the bottom of the crucible of the electromagnetic induction furnace. Use electric auxiliary heating to promote the aluminothermic self-propagating reduction reaction. After the material is completely melted, continue to supply power to maintain the system temperature at no less than 1500℃ to allow for a full reaction. After the reaction is completed, pour out the slag on the top of the crucible, and then pour the refined molten metal into the cast iron ingot mold. After cooling, demold to obtain the iron-chromium-cobalt alloy.

2. The method according to claim 1, characterized in that, The cobalt slag is the slag obtained after impurity removal during the wet zinc smelting process, and the ferrochrome slag is the slag produced during the smelting of ferrochrome alloys.

3. The method according to claim 1, characterized in that, In step one, the amount of each raw material used, by weight percentage, is as follows: cobalt slag 30%–35%, ferrochrome slag 25%–30%, aluminum blocks 20%–25%, and lime 10%–15%.

4. The method according to claim 1, characterized in that, By weight percentage, the main components of cobalt slag are: Fe2O3 10-15%, SO3 20-25%, Co2O3 25-30%, ZnO 5-10%, MnO 5-10%, CaO 2-3%, and unavoidable impurities.

5. The method according to claim 1, characterized in that, By weight percentage, the main components of ferrochrome slag are: SiO2 28-30%, Fe2O3 5-8%, MgO 25-28%, TiO2 3-5%, Cr2O3 10-13%, Al2O3 25-28%, and unavoidable impurities.

6. The method according to claim 1, characterized in that, In step five, the system temperature should be maintained above 1500℃ for at least 30 minutes.

7. The method according to claim 1, characterized in that, The magnetic properties of the obtained iron-chromium-cobalt alloy meet the following requirements: remanence not less than 1.365T, coercivity not less than 48.63kA / m, and magnetic energy product not less than 48.26kJ / m. 3 .

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