Method for preparing reduced iron powder using slag

Abstract

The present invention discloses a method for preparing reducing iron powder by using slag, and the method comprises the following steps: a) crushing and screening the slag to obtain slag particles with uniform particle size; b) mixing the crushed slag with an appropriate amount of aluminum powder, and controlling the amount of aluminum powder to reduce production costs; c) contacting the mixed slag and aluminum powder mixture with supercritical CO2 fluid and carbon monoxide or methane, and pretreating the slag under supercritical conditions to activate iron oxides in the slag; by combining supercritical fluid technology with SHS reaction, molten salt electrolysis and subsequent separation technology, not only can the advantages of each process be brought into play, but also the disadvantages of a single process can be overcome through interaction, so as to form an efficient, low-cost and environmentally friendly iron powder production process. The optimized integration of this process not only improves the reduction efficiency and product purity, but also significantly reduces production costs and energy consumption, and reduces environmental pollution, and has broad industrial application prospects.

Description

Technical Field

[0001] The invention belongs to the field of metal material preparation, and in particular relates to a method for preparing reduced iron powder by utilizing slag. Background Art

[0002] In the metal smelting and material processing industries, iron powder, as an important raw material, is widely used in powder metallurgy, magnetic materials, coatings, chemical catalysts and other fields. Traditional iron powder preparation methods mainly include carbon thermal reduction and hydrogen reduction. Although these methods have been widely used in industrial production, they also have some significant disadvantages and limitations.

[0003] Disadvantages of traditional preparation methods:

[0004] Carbothermal reduction method: This method uses coke or coal as a reducing agent to generate iron powder by reducing iron oxides at high temperature. Although this method is low-cost, a large amount of coke or coal is consumed during the reduction process, resulting in high energy consumption. In addition, a large amount of greenhouse gases such as carbon dioxide will be produced during the carbothermal reduction process, causing serious environmental pollution problems. Due to the high reaction temperature and long reaction time during the process, the purity of the iron powder of the final product is often not high, usually between 85% and 88%, which is difficult to meet the market demand for high-purity iron powder.

[0005] Hydrogen reduction method: The hydrogen reduction method uses hydrogen to reduce iron oxides at high temperatures to generate iron powder. This method has certain advantages in reducing carbon dioxide emissions, but the preparation and storage costs of hydrogen are high, and there are high safety risks during the reduction process. At the same time, the hydrogen reduction method has high energy consumption and the overall production cost is relatively expensive, making it difficult to be widely used in large-scale industrial production. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing reduced iron powder using slag. The method of the present invention combines supercritical fluid technology with SHS reaction, molten salt electrolysis and subsequent separation technology, which can not only give full play to the advantages of each process, but also overcome the shortcomings of a single process through interaction, thereby forming an efficient, low-cost and environmentally friendly iron powder production process. The optimized integration of this process not only improves the reduction efficiency and product purity, but also significantly reduces production costs and energy consumption, and reduces environmental pollution, and has broad industrial application prospects.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A method for preparing reduced iron powder using slag, the method comprising the following steps:

[0009] a) crushing and screening the slag to obtain slag particles with uniform particle size;

[0010] b) Mix the crushed slag with an appropriate amount of aluminum powder and control the amount of aluminum powder to reduce production costs;

[0011] c) contacting the mixed slag and aluminum powder mixture with supercritical CO2 fluid and carbon monoxide or methane to pretreat the slag under supercritical conditions to activate iron oxides in the slag;

[0012] d) in the same reactor, a self-propagating high temperature synthesis reaction is triggered by an external ignition source, during which metallic iron and aluminum oxide are produced;

[0013] e) after the self-propagating high temperature synthesis reaction is completed, injecting molten salt into the reactor to fully mix the reaction product with the molten salt to form an electrolyte solution;

[0014] f) electrolytic purification in molten salt to further purify metallic iron through electrochemical reaction;

[0015] g) After electrolysis, the reduced iron, alumina and other impurities are separated by a combination of sedimentation and magnetic separation;

[0016] h) Filtering and purifying the molten salt to remove impurities and recycling it for the next round of electrolysis process.

[0017] Wherein, the electrolysis step in step f) comprises:

[0018] f1) A cathode and an anode are arranged in a molten salt electrolytic cell, and a reduction reaction of iron ions occurs on the cathode to generate pure iron;

[0019] f2) An oxidation reaction occurs at the anode to produce aluminum oxide or oxygen, which is separated from the molten salt.

[0020] Wherein, the method of step g) comprises the following steps:

[0021] g1) allowing the molten salt and the reaction product in the reactor to stand and slightly stir, so that the reduced iron particles settle to the bottom of the reactor, and using the built-in magnetic field to initially attract the iron particles;

[0022] g2) introducing the mixture of molten salt and iron particles deposited at the bottom into a magnetic separation channel, separating high-purity iron powder through a magnetic field, and separating non-magnetic alumina and impurities at the same time;

[0023] g3) Collect the separated iron powder and send the molten salt and suspended impurities to the impurity treatment system for further recovery.

[0024] The amount of aluminum powder added in step b) is controlled within a range of 3% to 5% of the total mass of the slag to maximize cost-effectiveness.

[0025] Wherein, the supercritical conditions in step c) include a supercritical CO2 environment with a temperature of 31°C to 100°C and a pressure of 7.38 MPa to 25 MPa, combined with carbon monoxide or methane as a reducing agent; the CO volume fraction is 15% to 25%; and the CH4 volume fraction is 10% to 20%.

[0026] The self-propagating high temperature synthesis reaction in step d) is triggered by an electric heating wire ignition source, and no additional external heating is required during the reaction.

[0027] Wherein, the purification treatment of the molten salt in step h) includes high-temperature filtration and chemical purification to remove solid impurities and soluble impurities to ensure the purity of the molten salt.

[0028] Wherein, the particle size of the particles after crushing in step a) is 1 mm to 10 mm.

[0029] The molten salt is kept in liquid state by cyclic heating during use, and is continuously circulated and used after purification after each electrolysis.

[0030] Wherein, the cathode in step f1) is made of a high temperature resistant and corrosion resistant material, including graphite or platinum.

[0031] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0032] 1. In this method, multiple processes are combined to form an optimized overall process. Each process not only plays its own advantages, but also overcomes the shortcomings of using it alone through interaction, thereby improving the efficiency and effect of the entire system:

[0033] Supercritical CO2 has high diffusivity and solubility, which can significantly enhance the contact efficiency between the reducing agent (CO or CH4) and the iron oxide. In this process, the iron oxide is partially reduced or activated, making it easier to reduce in the subsequent SHS reaction. At the same time, since the iron oxide has been partially reduced in supercritical CO2, the amount of aluminum powder required for the SHS reaction can be significantly reduced. This not only reduces the cost of raw materials, but also reduces the excess heat generation during the reaction process, avoiding side reactions that may be caused by excessive heat.

[0034] The traditional SHS reaction relies on a large amount of aluminum powder to provide sufficient heat, while the supercritical fluid pretreatment makes the iron oxide easier to reduce, thereby reducing the heat requirement. The uniform diffusion characteristics of the supercritical fluid environment ensure the uniform distribution of the reactants, overcoming the problem of incomplete reaction or inconsistent product quality caused by uneven distribution of reactants in the traditional SHS reaction.

[0035] The mixture of reduced iron and alumina produced after the SHS reaction is mixed with molten salt at high temperature to form a stable electrolyte solution. This solution can not only maintain the high fluidity of the reactants, but also provide a suitable environment for electrolytic purification. At the same time, the introduction of molten salt not only keeps the reaction products in liquid state, facilitating subsequent electrolytic separation, but also further improves the purity of iron powder through the ion exchange process.

[0036] The products of traditional SHS reactions usually contain more impurities, but the molten salt electrolysis process can effectively remove these impurities and improve the purity of iron powder. The solid products (such as alumina) after the SHS reaction are usually difficult to separate, but in molten salt, these products can be converted into other separable compounds through electrolysis or separated by sedimentation, which simplifies the separation process.

[0037] Electrolysis in molten salt keeps the reduced iron and impurities (such as aluminum oxide) in a dispersed state. Through sedimentation separation, the iron particles settle to the bottom due to their high density and are then further purified by magnetic separation. The electrolysis process first purifies the iron powder, sedimentation separation removes most of the impurities, and magnetic separation further improves the purity of the iron powder. The combination of multiple steps makes the separation process more thorough and efficient.

[0038] After traditional molten salt electrolysis, some impurities may still exist, but the combination of sedimentation and magnetic separation can further purify the product, overcoming the disadvantage of incomplete impurity removal in the single electrolysis method. At high temperatures, molten salt may adsorb or dissolve impurities, but through subsequent sedimentation and magnetic separation, these impurities are effectively removed, allowing the molten salt to be purified and recycled.

[0039] The optimization of each process combines to form an efficient and low-cost iron powder production process. The combination of supercritical fluid pretreatment and SHS reaction reduces energy requirements and raw material consumption, while the combination of molten salt electrolysis and subsequent separation steps further improves the purity and yield of the product.

[0040] The combination of multiple processes makes the reduction process cleaner, reduces the emission of waste gas and waste residue, and reduces resource waste and environmental pollution by reusing molten salt.

[0041] Traditional methods usually have high energy consumption, low efficiency, and low product quality. By using supercritical conditions, the energy consumption of the process is reduced; through precise multi-step separation, the production of high-purity products is ensured.

[0042] The combination of various processes makes the process smoother, improves the degree of automation, reduces the difficulty of operation, and reduces dependence on manual operation.

[0043] This method combines multiple processes such as supercritical fluid pretreatment, self-propagating high-temperature synthesis reaction, molten salt electrolysis, and subsequent sedimentation and magnetic separation, which not only brings out the advantages of each process, but also overcomes the shortcomings when used alone. This multi-process synergy improves the reduction efficiency and product purity, reduces production costs and environmental impact, and simplifies the operation process. Overall, this method constructs an efficient, low-cost and environmentally friendly iron powder production process with broad industrial application prospects.

[0044] 2. Compared with the traditional iron powder reduction process, this process has higher efficiency and lower cost:

[0045] Traditional iron powder reduction processes usually rely on high-temperature reduction (such as coke reduction), which requires maintaining high temperature for a long time, and the reduction efficiency is limited by the diffusion rate of the reactants.

[0046] This process uses the high diffusivity of supercritical CO2 fluid and carbon monoxide or methane to achieve rapid pretreatment at lower temperatures and high pressures. The high solubility and diffusivity of supercritical fluids allow the reduction reaction of iron oxide particles to proceed more evenly and efficiently, thereby accelerating the reduction process and reducing pretreatment time. The use of supercritical fluids not only improves the reduction efficiency, but also reduces the energy consumption required to maintain high temperatures, thereby saving costs.

[0047] Traditional iron powder production processes usually require a continuous external heat source (such as an electric furnace or a coal-fired furnace) to maintain a high-temperature reaction, which results in a large amount of energy consumption. At the same time, the reduction process of the traditional process is often slow and inefficient. Once the self-propagating high-temperature synthesis (SHS) reaction is triggered, it can be self-sustaining without the need for an additional external heating source. The violent exothermic reaction between aluminum powder and iron oxide can complete the reduction in a very short time to produce high-purity metallic iron. Because the SHS reaction is self-sustaining and efficient, the energy utilization rate of the entire reaction process is extremely high, which significantly reduces energy consumption, and the reaction time is greatly shortened, further reducing operating costs.

[0048] In traditional reduction methods, the purity of iron powder is often affected by impurities in the slag, requiring additional purification steps (such as re-smelting or chemical purification). These steps are not only time-consuming and energy-consuming, but also prone to produce a large amount of waste, increasing processing costs. Molten salt electrolytic purification can further purify iron powder to a high purity under well-controlled conditions, and by-products (such as alumina) can be effectively recovered through the electrolytic process. The recycling of molten salt also reduces raw material consumption and waste disposal costs. Through the electrolytic purification process, high-purity reduced iron powder can be efficiently produced, and the recovery of by-products and the reuse of molten salts further reduce material costs and environmental protection treatment costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0051] See also Figure 1 A method for preparing reduced iron powder using slag comprises the following steps:

[0052] 1. Slag crushing and screening (step a)

[0053] The collected slag is initially crushed, and the large pieces of slag are crushed into smaller particles using a jaw crusher or a hammer crusher. Subsequently, these particles are screened to ensure that their particle size is between 1mm and 10mm. Slag particles with uniform particle size are obtained through crushing and screening to ensure good reaction contact area and uniform reaction rate in the subsequent reaction process.

[0054] 2. Mixing slag with aluminum powder (step b)

[0055] Mix the crushed slag with aluminum powder at a ratio of 3% to 5% of the total slag mass. Use a ball mill or mixer to ensure that the aluminum powder is evenly distributed in the slag particles. In the subsequent reaction, the aluminum powder will act as a reducing agent, and the reaction is as follows:

[0056] Heat;

[0057] The reaction products are metallic iron and aluminum oxide. The amount of aluminum powder is controlled to achieve self-sustaining reaction and reduce production costs at the same time.

[0058] 3. Supercritical fluid pretreatment (step c)

[0059] The mixed slag and aluminum powder mixture is placed in a supercritical fluid reactor and supercritical CO2 and carbon monoxide (CO) or methane (CH4) are injected. The reaction temperature is maintained between 31°C and 100°C and the pressure is between 7.38 MPa and 25 MPa to achieve supercritical conditions; the volume fraction of CO is 15% to 25%; the volume fraction of CH4 is 10% to 20%.

[0060] Chemical reaction:

[0061] Carbon monoxide as reducing agent: ;

[0062] Methane as reducing agent: ;

[0063] Under supercritical conditions, the high solubility and diffusivity of CO2 are utilized to make the reduction reaction more uniform, reduce the difficulty of reducing iron oxides and increase the reaction rate.

[0064] 4. Self-propagating high temperature synthesis (SHS) (step d)

[0065] The SHS reaction is triggered by an electric heating wire ignition source. During the reaction, aluminum powder and iron oxide react violently exothermically without the need for additional external heating.

[0066] Chemical reaction: ;

[0067] Ignition temperature: above 660°C (melting point of aluminum); Reaction time: from a few seconds to a few minutes; The strong exothermic reaction between aluminum powder and iron oxide is used to efficiently reduce iron oxide in a short time and generate aluminum oxide at the same time.

[0068] 5. Formation of molten salt electrolyte solution (step e)

[0069] During the SHS reaction, a molten salt (such as a mixture of calcium chloride, sodium chloride or potassium chloride) preheated to a liquid state is gradually injected into the reactor to ensure that the molten salt is fully mixed with the reaction products to form an electrolyte solution.

[0070] Temperature control: The temperature of the molten salt is controlled at 800°C to 900°C to ensure that it is in a liquid state. This forms a stable electrolyte environment, which is convenient for the subsequent electrolytic purification process.

[0071] 6. Molten salt electrolysis purification (step f)

[0072] A cathode and an anode are set in the electrolytic cell, and a voltage of 3V to 5V is applied to perform electrolytic purification.

[0073] Electrochemical reaction:

[0074] Cathodic reaction (reduction of iron): ;

[0075] Anodic reaction (alumina formation): ;

[0076] Current density: 0.1 A / cm2 to 0.5 A / cm2. Electrolysis time: 1 hour to 3 hours. The cathode is made of high temperature and corrosion resistant materials, including graphite or platinum. The electrolysis process further purifies the metallic iron, while producing aluminum oxide as a by-product.

[0077] 7. Comprehensive sedimentation and magnetic separation (step g)

[0078] g1) Sedimentation and stirring: The electrolyzed molten salt and the reaction products are allowed to stand and slightly stirred to allow the reduced iron particles to settle to the bottom of the reactor, while the embedded magnetic field is used to attract the iron particles. Specific: After the molten salt electrolysis or reduction reaction is completed, it is kept in a liquid state. The molten salt mixture is stirred moderately to ensure that the smaller iron particles are fully in contact with the molten salt and settle, while preventing local crystallization caused by temperature reduction. After stopping stirring, the molten salt mixture is allowed to stand for a period of time (30 minutes to 1 hour), and gravity is used to gradually settle the denser iron particles to the bottom, while lighter impurities such as alumina are suspended in the upper layer. After standing, the settled iron particles and part of the molten salt mixture are collected through the bottom discharge system.

[0079] g2) Magnetic separation: The molten salt and iron particle mixture after sedimentation is introduced into the magnetic separation channel, and the magnetic field is used to separate high-purity iron powder, and non-magnetic aluminum oxide and other impurities are separated at the same time. Specific: Prepare a high-efficiency magnetic separator, adjust the magnetic field strength to suit the magnetic characteristics of the iron powder, and ensure that only the magnetic iron particles are adsorbed and separated. Pump the molten salt and iron powder mixture collected from the sedimentation separation process into the magnetic separation channel. The magnetic separator uses a magnetic field to separate the magnetic iron particles from the non-magnetic impurities, and the iron powder is adsorbed on the magnetic surface of the magnetic separation equipment. Non-magnetic impurities (such as aluminum oxide) are separated during the magnetic separation process and discharged through the outlet and enter the impurity recovery system. Clean the iron powder on the magnetic separator regularly and collect it in a special container for further processing or output as a final product.

[0080] g3) Iron powder collection: The separated iron powder is collected from the magnetic separation channel, and the molten salt and suspended impurities are sent to the impurity treatment system for further recovery.

[0081] Magnetic field strength: According to the magnetic characteristics of the iron powder, the magnetic field strength is adjusted to ensure the separation effect. Sedimentation time: 30 minutes to 1 hour to ensure that the iron particles are fully settled. Achieve efficient iron powder separation and recover alumina and other by-products. Specific: The collected iron powder is washed to remove residual molten salt, and then dried to obtain pure iron powder. The dried iron powder is screened and graded according to the particle size to ensure that the product meets specific quality and specification requirements.

[0082] 8. Purification and recycling of molten salt (step h)

[0083] High temperature filtration: Solid impurities in molten salt are removed by high temperature filtration system.

[0084] Chemical purification: Chemical purifiers are used to remove dissolved impurities and metal ions to ensure the purity of the molten salt.

[0085] Cycle Heating: The purified molten salt is kept in liquid form by heating and stored in a molten salt tank, ready for the next round of use.

[0086] Ensure the purity and recycling capacity of molten salt, reduce material consumption and environmental pollution.

[0087] This method realizes an efficient process for preparing high-purity reduced iron powder from slag through multi-step integration. Each step is optimized to ensure the control of reaction conditions and the maximum utilization of resources, reduce production costs, improve process efficiency, and ensure the high purity and environmental friendliness of the final product through advanced separation and purification technologies.

[0088] Specifically, the steps of molten salt purification are:

[0089] 8.1 High temperature filtration

[0090] Solid impurities in the molten salt, including unreacted oxide particles, by-products produced during the reaction and other solid impurities, are removed to keep the molten salt in a liquid state.

[0091] Use a high temperature resistant filtering device (such as a ceramic filter or a metal filter) for filtering, and the pore size of the filter should be small enough to intercept the tiny solid particles in the molten salt.

[0092] The molten salt is passed through a filter, where solid impurities are retained by the filter while the clean molten salt continues to flow into the next processing step.

[0093] Clean or replace filters regularly to prevent clogging and ensure filtering effectiveness.

[0094] 8.2 Chemical purification

[0095] Remove the dissolved metal impurities and other soluble impurities in the molten salt to ensure the purity of the molten salt so that it can be recycled again. Add an appropriate amount of chemical purifiers (such as sodium carbonate, calcium hydroxide or other suitable chemical agents) to the filtered molten salt. These purifiers react with impurities to form insoluble precipitates. Under appropriate temperature and stirring conditions, the purifiers and impurities react fully. The precipitate generated by the reaction will gradually settle to the bottom.

[0096] The molten salt is left to stand and the precipitate is allowed to settle to the bottom of the reactor. The precipitate is then discharged through a bottom discharge system or separated by further filtration.

[0097] The purified molten salt can be reheated to the use temperature and recycled in the next round of electrolysis or reduction reaction.

[0098] 8.3 Reheating and Storage of Molten Salt

[0099] Keep the molten salt in a high-temperature liquid state so that it does not need to be melted again in the next round of use, thus saving energy. The purified molten salt is heated to a use temperature of 800°C to 900°C using a heating device to ensure that it remains in a liquid state.

[0100] The heated molten salt is stored in a high temperature resistant molten salt tank to prevent heat loss. The storage tank should have good thermal insulation to maintain the molten salt temperature.

[0101] A molten salt circulation system is established so that the purified molten salt can enter the reactor or electrolytic cell for use at any time, ensuring the continuity and efficiency of the process.

[0102] The test results of preparing reducing iron powder from slag according to the method of the present invention are as follows:

[0103]

[0104] Analysis and Conclusion

[0105] Iron powder purity and yield:

[0106] Experiment 4 (3% aluminum powder, 15% CO, 10% CH4, 90°C supercritical conditions, NaCl / KCl mixed molten salt) showed the highest iron powder purity and high yield, 99% and 93%, respectively. Despite the low aluminum content, the reduction process was ensured to proceed adequately by increasing the concentrations of CO and CH4.

[0107] Experiment 1 (5% aluminum powder, 25% CO, no CH4, 80°C supercritical conditions, NaCl molten salt) also showed high iron powder purity and yield, 98% and 92%, respectively. This shows that the aluminum powder content can be effectively reduced while maintaining high yield at higher CO concentrations.

[0108] The iron powder purity and yield of the conventional method 1 and the conventional method 2 are significantly lower than those of the test of the present invention, with the purity being 85% to 88% and the yield being 70% to 75%. This shows the disadvantages of the conventional method in terms of iron powder purity and yield.

[0109] Energy consumption:

[0110] Experiment 2 (3% aluminum powder, 20% CO, no CH4, 60°C supercritical conditions, KCl molten salt) showed the lowest energy consumption. Although the aluminum content was the lowest and the energy consumption was correspondingly lower, the purity and yield of the iron powder were also relatively lower, at 96% and 88%, respectively.

[0111] The energy consumption was the highest in Runs 4 and 3, mainly due to the operation at higher supercritical conditions and electrolysis voltages. However, the iron powder purity and yield of these runs were higher, so the higher energy consumption was acceptable when pursuing high quality products.

[0112] The energy consumption of the conventional method 1 and the conventional method 2 is very high, but the final product quality and yield are far inferior to those of the experiment of the present invention, and the energy efficiency is relatively low.

[0113] 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 and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing reduced iron powder using slag, characterized in that: The method comprises the following steps: a) crushing and screening the slag to obtain slag particles with uniform particle size; b) Mix the crushed slag with an appropriate amount of aluminum powder and control the amount of aluminum powder to reduce production costs; c) contacting the mixed slag and aluminum powder mixture with supercritical CO2 fluid and carbon monoxide or methane to pretreat the slag under supercritical conditions to activate iron oxides in the slag; d) in the same reactor, a self-propagating high temperature synthesis reaction is triggered by an external ignition source, during which metallic iron and aluminum oxide are produced; e) after the self-propagating high temperature synthesis reaction is completed, injecting molten salt into the reactor so that the reaction product and the molten salt are fully mixed to form an electrolyte solution; f) electrolytic purification in molten salt to further purify metallic iron through electrochemical reaction; g) After electrolysis, the reduced iron, alumina and other impurities are separated by a combination of sedimentation and magnetic separation; h) Filtering and purifying the molten salt to remove impurities and recycling it for the next round of electrolysis process.

2. The method for preparing reduced iron powder using slag according to claim 1, characterized in that: The electrolysis step in step f) comprises: f1) A cathode and an anode are arranged in a molten salt electrolytic cell, and a reduction reaction of iron ions occurs at the cathode to generate pure iron; f2) An oxidation reaction occurs at the anode to produce aluminum oxide or oxygen, which is separated from the molten salt.

3. The method for preparing reduced iron powder using slag according to claim 1, characterized in that: The method of step g) comprises the following steps: g1) allowing the molten salt and the reaction product in the reactor to stand and slightly stir, so that the reduced iron particles settle to the bottom of the reactor, and using the built-in magnetic field to initially attract the iron particles; g2) introducing the mixture of molten salt and iron particles deposited at the bottom into a magnetic separation channel, separating high-purity iron powder through a magnetic field, and separating non-magnetic alumina and impurities at the same time; g3) Collect the separated iron powder and send the molten salt and suspended impurities to the impurity treatment system for further recovery.

4. The method for preparing reduced iron powder using slag according to claim 1, characterized in that: The amount of aluminum powder added in step b) is controlled to be 3% to 5% of the total mass of the slag to maximize cost-effectiveness.

5. The method for preparing reduced iron powder using slag according to claim 1, characterized in that: The supercritical conditions in step c) include a supercritical CO2 environment with a temperature of 31°C to 100°C and a pressure of 7.38 MPa to 25 MPa, combined with carbon monoxide or methane as a reducing agent; the CO volume fraction is 15% to 25%; the CH4 volume fraction is 10% to 20%.

6. The method for preparing reduced iron powder using slag according to claim 1, characterized in that: The self-propagating high temperature synthesis reaction in step d) is triggered by an electric heating wire ignition source, and no additional external heating is required during the reaction.

7. The method for preparing reduced iron powder using slag according to claim 1, characterized in that: The purification treatment of the molten salt in step h) includes high-temperature filtration and chemical purification to remove solid impurities and soluble impurities to ensure the purity of the molten salt.

8. The method for preparing reduced iron powder using slag according to claim 1, characterized in that: The particle size of the pulverized particles in step a) is 1 mm to 10 mm.

9. The method for preparing reduced iron powder using slag according to claim 1, characterized in that: The molten salt is kept in liquid state by cyclic heating during use, and is continuously circulated for use after purification treatment after each electrolysis.

10. The method for preparing reduced iron powder using slag according to claim 2, characterized in that: The cathode in step f1) is made of a material that is resistant to high temperatures and corrosion, including graphite or platinum.

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