Method for reducing high-grade iron powder from low-grade red mud powder and fly ash and application

Abstract

The invention relates to the technical field of metal refining and powder metallurgy, and discloses a method for reducing high-grade iron powder through low-grade red mud powder and fly ash and application of the method. The method comprises the following steps that S1, the red mud powder and the fly ash are selected as raw materials, the mass fraction of iron in the red mud powder ranges from 10% to 30%, and the fly ash contains iron oxide; the mass ratio of the red mud powder to the fly ash is (100: 10)-(100: 90); s2, the red mud powder and the fly ash are evenly mixed according to the mass ratio, and pellets with the diameter being 5-16 mm are formed through pelletizing; and S3, the pellets are fed into a high-temperature reduction furnace. By adopting an accurate drying process, an atmosphere control technology and a particle size optimization and compaction technology, water content control, oxidation reaction inhibition and improvement of particle size uniformity and density consistency of the iron powder are realized, the stability, purity and fluidity of the iron powder are remarkably improved, oxidation loss in production and transportation is reduced, and the production cost is reduced. And high quality and reliability of a final product are ensured.

Description

Technical Field

[0001] The invention relates to the technical field of metal refining and powder metallurgy, and specifically to a method and application of reducing high-grade iron powder with low-grade red mud powder and fly ash. Background Art

[0002] Red mud is an inevitable solid waste produced during the production of alumina. It is mainly composed of iron oxide, bauxite and other impurities. For every ton of alumina produced, about 1 to 2 tons of red mud will be produced. Due to its high iron content and appearance similar to red soil, the treatment and resource utilization of red mud has always been a problem that plagues alumina production plants. At present, there are two main ways to comprehensively utilize red mud: one is to extract useful components and recover valuable metals; the other is to use it as a raw material for bulk materials.

[0003] In the prior art, direct reduction iron extraction methods have always been the main way to recover iron resources in red mud, but these methods face many problems. The iron grade and iron metal recovery rate of previous reduction methods are generally low, and it is usually difficult to reach more than 94%. Although there has been certain research progress in the traditional coal-based reduction method and red mud treatment process, there are still a series of problems such as high energy consumption, high cost, narrow application range of iron-containing raw materials and fuels, complex process flow, large investment, and low resource utilization. These technologies are difficult to meet the actual needs of improving recovery rates, reducing energy consumption and costs, resulting in the failure to fully utilize red mud resources. A large amount of red mud is still abandoned in slag yards, occupying land, causing environmental pollution and waste of metal resources. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method and application of reducing low-grade red mud powder and fly ash to high-grade iron powder, which solves the problems in the prior art that iron powder is easily oxidized, has inaccurate moisture content control, and has uneven density during production, drying, compaction, and packaging.

[0005] To achieve the above objectives, the present invention is implemented by the following technical scheme: a method and application of reducing high-grade iron powder with low-grade red mud powder and fly ash, comprising the following steps:

[0006] S1: selecting red mud powder and fly ash as raw materials, the mass fraction of iron in the red mud powder is between 10% and 30%, the fly ash contains iron oxides, and the mass ratio of the red mud powder to the fly ash is 100:10 to 100:90;

[0007] S2: uniformly mixing the red mud powder and the fly ash according to the mass ratio, and forming pellets with a diameter of 5 to 16 mm by balling;

[0008] S3: Feed the pellets into a high-temperature reduction furnace, reduce them using a reducing gas, control the temperature at 850°C to 1000°C, and control the reduction time at 40 to 120 minutes. The reducing gas is a coal gas rich in carbon monoxide, and the volume fraction of CO / CO2 in the coal gas ≥ 2, and the CO concentration is 80% to 90%.

[0009] S4: Cool the reduced pellets using low-temperature coal gas, control the cooling temperature below 100°C, and the cooling time is 40 to 120 minutes. The volume fraction of CO / CO2 in the low-temperature coal gas ≥ 2.

[0010] S5: Crush and grind the cooled pellets until the particle size is less than 75μm. In the particle size distribution of the iron powder after grinding, the particles exceeding 75μm do not exceed 5%.

[0011] S6: Conduct magnetic separation on the iron powder after grinding using a high-gradient magnetic separation device with a magnetic field intensity of 4000 Oe to 8000 Oe to separate metallic iron from impurities and obtain high-grade reduced iron powder. The mass fraction of metallic iron in the reduced iron powder ≥ 94%, and the carbon content in the reduced iron powder ≤ 1.00%.

[0012] Preferably, the volume fraction of CO / CO2 in the low-temperature coal gas is maintained above 2.0.

[0013] Preferably, the volume fraction of CO / CO2 in the reducing gas is greater than 2, and the reduction reaction temperature is controlled between 900°C ± 10°C.

[0014] Preferably, the ratio of red mud powder to fly ash is 30:70 to 80:20.

[0015] Preferably, the carbon monoxide concentration in the reducing gas is 80% to 90%.

[0016] Preferably, in the particle size distribution of the iron powder after grinding, the particles exceeding 75μm < 5%.

[0017] Preferably, the recovery rate of the metallic iron powder ≥ 90%.

[0018] Preferably, the metallization rate of the reduced iron powder ≥ 95%.

[0019] Preferably, the Fe mass fraction of the reduced iron powder ≥ 94%, and the carbon content is ≤ 1.00%.

[0020] The present invention also provides an application of the method for reducing high-grade reduced iron powder from low-grade red mud powder and fly ash in the production of smelting low-carbon steel or high-quality steel.

[0021] The present invention provides a method and application for reducing high-grade reduced iron powder from low-grade red mud powder and fly ash.

[0022] It has the following beneficial effects:

[0023] 1. The present invention adopts the atmosphere control technology of refined iron powder. By adjusting the gas composition in the package, the oxidation reaction of metallic iron powder is effectively inhibited. Compared with the protection method that simply relies on packaging materials in the prior art, the present invention adds atmosphere adjustment in the packaging stage, significantly improving the stability of iron powder and reducing the quality loss during transportation.

[0024] 2. The present invention effectively reduces the moisture content of iron powder by optimizing the drying process and controlling temperature and humidity. Compared with the traditional simple drying method, the present invention can control the moisture content below 5% within a shorter time, avoiding the oxidation problem caused by moisture, and at the same time ensuring the fluidity and compactness of the product.

[0025] 3. The present invention uses the particle size control technology in the refining process to effectively reduce the oxidation rate of fine iron powder particles. Compared with the process that fails to effectively control the particle size in the prior art, the present invention improves the purity and performance of iron powder by precisely controlling the particle size, avoiding the instability of product quality caused by the rapid oxidation of fine particles.

[0026] 4. The present invention adopts an efficient compaction technology to optimize the particle density of metallic iron powder. Compared with the iron powder compaction method with uneven density in the traditional technology, the present invention can ensure that the density of each batch of iron powder is consistent, significantly improving the fluidity and operability after packaging, and further enhancing the application scope and market competitiveness of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a method step diagram of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0029] Please refer to the attached Figure 1 , the embodiments of the present invention provide a method and application for reducing low-grade red mud powder and fly ash to high-grade reduced iron powder, including the following steps:

[0030] S1: Select red mud powder and fly ash as raw materials. The mass fraction of iron in the red mud powder is between 10% and 30%, and the fly ash contains iron oxides. The mass ratio of the red mud powder to the fly ash is 30:70 to 70:30;

[0031] In this embodiment, the raw material selection steps include screening, component analysis, ratio calculation and pretreatment of red mud powder and fly ash.

[0032] Red mud powder is the residue after extracting alumina from bauxite by the Bayer process. It is a powdery solid, mainly containing components such as Fe2O3, SiO2, and Al2O3. Fly ash comes from the flue gas dust collection system of coal-fired power plants and is also powdery particles, containing components such as Fe2O3, SiO2, and CaO.

[0033] To ensure the reduction reaction efficiency, the following limitations are set for the mass fraction of iron elements in the raw materials:

[0034] The mass fraction of Fe in red mud powder is 10% - 30%;

[0035] The content of Fe2O3 in fly ash is controlled at 5% - 25%.

[0036] The above ranges can achieve stable production of high-grade reduced iron powder through experimental verification.

[0037] Red mud powder and fly ash are mixed in a mass ratio of R m The mixing ratio range is:

[0038] 30% ≤ R m ≤ 70%;

[0039] where R m represents the percentage of the mass of red mud powder in the total mass of the mixture. The mass ratio of fly ash is (100% - R m ).

[0040] To achieve the best reaction conditions, the raw material ratio is designed through an iron element mass balance model. Let:

[0041] M r be the mass of red mud powder, unit: kg;

[0042] M f be the mass of fly ash, unit: kg;

[0043] C r be the content of Fe2O3 in red mud powder (mass fraction), unit: %;

[0044] C f be the content of Fe2O3 in fly ash, unit: %.

[0045] The total content of Fe2O3 in the pellet mixture is:

[0046]

[0047] To ensure stable reduction yield, the condition needs to be met:

[0048] C total ≥20%;

[0049] In the above formula, if C total ≥20%, the final yield of metallic iron is insufficient and the reduction conditions are not met.

[0050] Furthermore, to achieve controllable pelletizing characteristics, it is required that the average particle sizes of red mud powder and fly ash are less than 75 μm respectively. The particle size measurement method uses a laser particle size analyzer, and the result should meet the standard of D90 ≤ 75 μm.

[0051] In actual operation, red mud powder and fly ash enter the automatic batching machine through the conveying system respectively, and the weighing system controls the raw material ratio and adjusts it according to the set R m value. The mixture after proportioning enters the high-speed mixer through the belt conveyor device, and after being stirred evenly, it is output to the next pelletizing section.

[0052] During the mixing process of red mud powder and fly ash, it is necessary to ensure that the mixing uniformity coefficient K mix is greater than 0.85, which is defined as follows:

[0053]

[0054] where: σ is the standard deviation of the Fe2O3 content in the mixed sample; μ is the average value of the Fe2O3 content in the mixed sample.

[0055] This parameter is obtained by testing the Fe2O3 content distribution of the sample by ICP-OES.

[0056] The raw material mixing system in this step includes a red mud powder storage bin, a fly ash storage bin, an electronic batching scale, a high-speed mixer and a transfer conveyor belt. The above devices are connected in sequence to form a continuous mixing structure to ensure that the materials are not discrete and do not bridge.

[0057] During the implementation process, if the iron content of the red mud powder is too low, the system compensates by increasing the batch of materials with a higher mass fraction of metallic iron in the reduced iron powder in the fly ash. The batching system is embedded with a PID control module to achieve dynamic adjustment of the proportioning accuracy of ±1%.

[0058] Through the above structure and process, the raw material selection and proportioning steps are completed, providing a premixed material with a unified particle size and uniform composition for subsequent pelletizing and reduction reactions.

[0059] S2: Uniformly mix red mud powder and fly ash according to the above mass ratio, and form pellets with a diameter of 5 - 16 mm through pelletizing;

[0060] In step S2, first, the mixture of red mud powder and fly ash that has completed proportioning and drying is pelletized. The purpose of this step is to form the material into pellets with good reduction performance and a stable structure for subsequent high-temperature reduction reactions.

[0061] Specifically, the mixed powder is fed into the pelletizing equipment through a conveying system. The equipment includes a disk pelletizer or a drum pelletizer, and the pelletizer is equipped with a stirring device for uniformly stirring the mixture. To improve the agglomeration of the material, an appropriate amount of water and binder are added to the mixture. The water addition amount is generally controlled between 8% and 12%, and the specific ratio is determined by the hygroscopicity of the material and the agglomeration requirements.

[0062] During the pelletizing process, the binder added is a natural or synthetic polymer substance. Common binders include kaolin, starch, polyvinyl alcohol, etc. The mass fraction of the binder is controlled between 1% and 3% to ensure the stability of the pellets. For different material addition amounts, the choice of binder will be adjusted. Through experimental optimization, it is ensured that the binder does not affect the effect of the reduction reaction.

[0063] During the pelletizing process, by controlling the rotation speed and inclination angle of the pelletizer, the rolling mode of the material is adjusted. The pellet diameter in this step needs to be controlled between 5 and 16 mm. For this purpose, the rotation speed is controlled at 60 - 100 r / min, and the inclination angle is set at 40° to 50° to ensure that the material can roll sufficiently to form uniform pellets.

[0064] After pelletizing, the pellets need to be dried and preheated. The preheating temperature is set at 150°C to 200°C, and the preheating time is about 30 to 60 minutes. Through the preheating process, the moisture evaporates, and the binder further combines with the material to ensure the stability of the pellet structure.

[0065] Mathematical model and physical connection relationship

[0066] To optimize the pelletizing process, the following mathematical model can be used to determine the optimal water and binder dosages. Set the key parameters in the model:

[0067] W: Water addition amount, unit: %;

[0068] C: Binder addition amount, unit: %;

[0069] D: Pellet diameter, unit: mm;

[0070] K ball : Pelletizing efficiency coefficient, defined as a function of the ratio of the minimum binder dosage required for pellet formation to the material.

[0071] The pelletizing efficiency coefficient K in the model ballIt is closely related to the particle size distribution of moisture, binder, and raw materials. Based on experimental data, the following relationship is established:

[0072]

[0073] where α is an empirical constant, usually ranging from 0.2 to 0.3, and is adjusted according to the characteristics of different materials.

[0074] This model helps optimize the addition amounts of water and binder, ensuring the best balance between pellet strength and reduction reaction performance. By adjusting C and W, the physical properties of the pellets can be precisely controlled, avoiding the decline in reduction reaction effectiveness caused by excessive binder or excessive moisture.

[0075] In terms of physical structure, the pelletizing system includes the following components:

[0076] A mixture of red mud powder and fly ash is fed into the stirrer through a conveyor belt;

[0077] The stirrer is connected to the conveying systems of water and binder and is used to uniformly stir the materials;

[0078] The stirred materials are fed into a pelletizer, and the pelletizer includes a rotating disk or a drum and is connected to an electric drive system;

[0079] The output materials of the pelletizer are fed into a preheating furnace through a conveyor belt for drying and preheating treatment.

[0080] The above components work together through an automatic control system and a sensor network, thus ensuring the high efficiency and consistency of the pelletizing process.

[0081] By implementing this step, it can be ensured that the materials after pelletizing have a good spherical structure and stable granularity. This structural characteristic is crucial for the high efficiency of subsequent reduction reactions. The uniformity of the pellets improves the speed and efficiency of the reduction reaction and reduces energy waste during the high-temperature reduction process.

[0082] By optimizing the addition amounts of binder and moisture, the mechanical strength and compressive capacity of the pellets can be significantly improved, avoiding fragmentation or cracking during the high-temperature reduction process. In addition, the preheating process effectively removes the excess moisture, preventing the interference of moisture during the reduction process and ensuring the smooth progress of the reaction.

[0083] This step not only ensures the high quality and high stability of the pellets but also provides an ideal material form and consistent reaction conditions for subsequent high-temperature reduction reactions.

[0084] S3: Feed the pellets into a high-temperature reduction furnace and reduce them using a reducing gas. Control the temperature at 850°C to 1000°C and the reduction time at 40 to 120 minutes. The reducing gas is coal gas rich in carbon monoxide, and the volume fraction of CO / CO2 in the coal gas ≥ 2, and the CO concentration is 80% to 90%.

[0085] In step S3, a high-temperature reduction reaction is carried out to achieve the goal of reducing iron oxides in red mud powder and fly ash to metallic iron. This step uses a fixed-bed furnace or a rotary furnace for the reaction, and the specific selection depends on the reaction scale and the required reaction conditions.

[0086] First, the mixed and pelletized material is fed into a reduction furnace for a high-temperature reduction reaction. This process is carried out in a reducing atmosphere, and generally carbon monoxide (CO) or hydrogen (H2) is used as the reducing gas. The reduction temperature is controlled between 850°C and 1050°C. The specific temperature range is optimized and adjusted according to parameters such as the mass fraction of metallic iron in the reduced iron powder in the material, the particle size, and the gas flow rate in the atmosphere.

[0087] During the reaction process, the reducing gas used reacts with the pellet material, and iron oxides (Fe2O3) are reduced to metallic iron, while carbon dioxide (CO2) or water vapor (H2O) is released.

[0088] During this process, controlling the flow rate of the reaction gas and the atmosphere composition is crucial for the reduction efficiency. Set the relationship between the gas flow rate F (unit: m 3 / h) and the furnace temperature T:

[0089] F = k1·T + k2;

[0090] Among them, k1 and k2 are empirical constants obtained by fitting according to experimental data, and the specific values depend on the furnace atmosphere, raw material characteristics, and reaction scale.

[0091] The duration (t reaction ) of the high-temperature reduction reaction is also a key parameter, usually between 2 and 4 hours. This time is adjusted according to the pellet diameter, temperature, and gas flow velocity. The specific calculation process is as follows:

[0092]

[0093] Among them, D is the pellet diameter (unit: mm), v gas is the flow velocity of the reducing gas (unit: m / s), and β is an empirical constant, usually taking a value of 0.5.

[0094] During the reaction process, the temperature in the furnace needs to be evenly distributed to ensure that the material stays in the high-temperature zone for enough time. The temperature in the furnace is monitored in real time by a thermocouple, and the control system adjusts the fuel input according to the feedback signal to maintain a stable temperature.

[0095] After the reduction reaction, the reaction gas is separated from the material. The unreacted gas can be recovered by a recovery device and reused in the reaction, thereby reducing energy consumption. After the waste gas is cooled to an appropriate temperature by a gas cooler, it is sent to a dust removal system for treatment.

[0096] The reduction reaction system includes the following key components:

[0097] A reduction furnace, which includes multiple temperature control zones inside and is equipped with thermocouples and burners;

[0098] A reduction gas source, usually a gas cylinder or a gas generator, which provides high-purity carbon monoxide (CO) or hydrogen (H2);

[0099] A material input system, which feeds the pelletized material into the reduction furnace through a conveyor belt;

[0100] An exhaust gas recovery system, which realizes the treatment of exhaust gas through a cooler, a gas separation device and a recovery device;

[0101] A temperature monitoring and gas flow control system, which adjusts the reaction conditions in real time to ensure the stability of the reaction temperature and the atmosphere flow.

[0102] Through the high-temperature reduction reaction, the iron oxides in the red mud powder and fly ash can be efficiently converted into metallic iron, and a high reduction efficiency can be achieved in this process. Controlling the temperature and reaction time has a direct impact on the reduction effect. By adjusting the gas flow and reaction time, the yield and quality of metallic iron can be further optimized.

[0103] In addition, through the design of the exhaust gas recovery system, the energy utilization rate can be improved, the exhaust gas emissions can be reduced, and it has good environmental friendliness and economy. The optimized reaction conditions can achieve precise control of the reduction process, making the reaction process more efficient and stable, and further improving the operability and reliability of the overall process.

[0104] S4: Cool the reduced pellets with low-temperature gas, control the cooling temperature below 100 °C, and the cooling time is 40 to 120 minutes. The volume fraction of CO / CO2 in the low-temperature gas ≥ 2;

[0105] In step S4, magnetic separation is carried out on the product after high-temperature reduction to effectively separate metallic iron from non-magnetic mineral components. This step realizes the efficient extraction of the metallic iron component in the product by establishing a magnetic response model, combining magnetic field strength control and particle size distribution analysis.

[0106] First, establish a magnetic separation model to describe the relationship between magnetic separation efficiency and particle size and magnetic field strength. Let:

[0107] M eη is the extraction rate of metallic iron in the reducing agent per unit mass, with the unit of %.

[0108] H is the magnetic field strength of the magnetic separation equipment, with the unit of Gauss (Gs).

[0109] d is the average particle size of the metal particles in the reduction product, with the unit of μm.

[0110] η is the magnetic separation efficiency coefficient, with the unit of %.

[0111] Define the following empirical formula to guide the setting of magnetic separation parameters:

[0112]

[0113] Among them, k is an empirical constant, usually determined by experimental fitting, and the value range is 10 - 20.

[0114] The above formula shows that the greater the magnetic field strength or the coarser the metal particles, the more obvious the magnetic separation effect. According to this relationship, select a magnetic field strength of 6000 - 12000 Gs to adapt to reduction products with different particle size distributions.

[0115] The reduction product is crushed by a crusher to a particle size less than 1 mm and then enters the magnetic separation equipment to ensure the full effect of the magnetic field on the particles. The magnetic separation equipment includes:

[0116] A feeding system, connected to the high-temperature reduction product conveyor belt;

[0117] A magnetic separation drum section, provided with high-strength permanent magnets;

[0118] A non-magnetic collector, connected to the bottom of the magnetic separation drum;

[0119] A magnetic component conveyor, used to send the iron-rich material to the subsequent processing section.

[0120] Each component is connected by a chain structure or a vibrating conveying device to form a continuous operation system. The rotation speed of the magnetic separation drum is controlled at 30 - 50 rpm to ensure the full effect of the material in the magnetic field. The magnetic field direction is perpendicular to the material movement direction to enhance the separation accuracy.

[0121] To improve the magnetic separation accuracy, the magnetic separation process can be divided into two treatments: primary and secondary. The primary magnetic separation mainly removes obvious magnetic and non-magnetic substances; the secondary magnetic separation is used to further improve the mass fraction of metallic iron in the reduced iron powder. After two-stage magnetic separation, the recovery rate of metallic iron reaches more than 85%, and the residual iron content in the non-magnetic substance is controlled below 1%.

[0122] Furthermore, to verify the relationship between the magnetic separation accuracy and the particle size of the material, the following evaluation function can be constructed:

[0123]

[0124] Among them, Q is the magnetic separation purity coefficient, C m is the mass fraction of metallic iron in the magnetic product, C f is the theoretical content of metallic iron in the raw material, R m is the recovery rate of the magnetic product.

[0125] By comparing the Q values under different magnetic field intensities, the magnetic field parameters and the magnetic separation rhythm are further optimized.

[0126] The magnetic separation system is equipped with a dust removal device and a cooling fan to ensure the stable operation of the equipment and the safety of the operating environment. The entire system is integrated into an automatic control module, and the magnetic field switch, the roller speed, and the material flow are coordinately controlled through a PLC control program.

[0127] After magnetic separation, the iron-rich material obtained enters the cooling device, and the temperature of the material is reduced to room temperature through a cooling water jacket or an air-cooling method, and then enters the subsequent storage or processing link. The non-magnetic substances are sent to the tailings yard or further resource utilization unit through a belt conveyor device.

[0128] Through the above implementation structure and process control, the metal components in the reduction product can be efficiently separated, and the recovery and utilization of iron resources in red mud can be realized.

[0129] S5: Crush and grind the cooled pellets until the particle size is less than 75 μm. In the particle size distribution of the iron powder after grinding, the particles exceeding 75 μm do not exceed 5%.

[0130] The refining and treatment in step S5 mainly include further processing the reduction product after magnetic separation, removing impurities through heat treatment and chemical reactions, and finally obtaining a metal iron product with a higher purity. The core technical elements involved in this step include refining temperature control, atmosphere regulation, and reaction time optimization, etc.

[0131] First, establish a refining process model, assuming that the purity of metallic iron is P Fe , and the content of impurities is P imp . The mass fraction of metallic iron in the reduced iron powder is represented by the following reaction equation:

[0132]

[0133] Among them, m Fe is the mass of metallic iron, m imp is the mass of impurities.

[0134] Secondly, set the heat treatment temperature in the refining process as T ref , and the reaction time as t ref , and calculate the purity growth rate of metallic iron according to the following formula:

[0135] ΔPFe =k·T ref ·t ref ;

[0136] Wherein, k is the reaction rate constant, which depends on the initial purity of metallic iron and the type of impurities, and is usually obtained by fitting experimental data. The refining temperature T ref is preferably controlled between 1100 °C and 1300 °C to promote the further purification of metallic iron.

[0137] During the reaction process, an atmosphere control system is used to provide an oxygen-rich or hydrogen-rich atmosphere to promote the oxidation reaction of impurities. The atmosphere composition and temperature act together to further improve the refining effect. For oxide impurities (such as silicon, aluminum, etc.), their oxidation reactions at high temperatures can be represented by the following equations:

[0138] SiO2 + 2CO → Si + 2CO2;

[0139] For other impurities such as sulfur and phosphorus, by adjusting the hydrogen ratio in the atmosphere, the content of these impurities can be effectively reduced.

[0140] During this process, the relationship between the atmosphere flow rate (F gas ) and the concentration of reducing components (such as CO or H2) in the atmosphere is described by the following formula:

[0141] F gas =α·C gas ·A

[0142] Wherein, C gas is the gas concentration (such as CO or H2), A is the reaction area, and α is an empirical constant.

[0143] During the refining process, an atmosphere reflux device is used to recycle the treated gas, reducing resource waste and improving energy efficiency. The reflux gas is cooled by a condenser, and after removing the impurities therein, it is re-introduced into the reaction furnace.

[0144] Furthermore, an on-line analysis system is set up in the refining stage to monitor the purity of metallic iron, the impurity content, and the atmosphere composition in real time. The temperature, atmosphere flow rate, reaction time and other parameters are dynamically adjusted through the PLC control system to ensure that the purity of each batch of metallic iron meets the requirements.

[0145] In terms of physical structure, the refining equipment mainly includes:

[0146] A reaction furnace, which is internally provided with an adjustable temperature control system and an atmosphere control device;

[0147] An atmosphere control device, including gas cylinders, flow meters and pipeline systems, which is connected to the reaction furnace;

[0148] A cooling system, connected to the condenser through cooling pipes, recovers the atmosphere used during the reaction;

[0149] A gas reflux device is used to recover the gas and reintroduce it into the reaction furnace.

[0150] These components are interconnected through a heat exchange system, pipes, and a control module to form an efficient circulating refining system.

[0151] Through this refining process, the mass fraction of metallic iron in the finally obtained reduced iron powder can reach over 94%, and the impurity content is reduced to no more than 5%. In addition, this refining process can also effectively remove volatile heavy metals and other harmful substances, meeting environmental protection standards.

[0152] S6: Perform magnetic separation on the ground iron powder using a high-gradient magnetic separation device with a magnetic field strength of 4000 Oe to 8000 Oe to separate metallic iron from impurities and obtain high-grade reduced iron powder. The mass fraction of metallic iron in the reduced iron powder is greater than or equal to 94%, and the carbon content in the reduced iron powder is ≤ 1.00%;

[0153] In step S6, after the refined iron powder undergoes refining, cooling, and drying, it enters the post-treatment and packaging stage. The goal of this step is to ensure the stability of metallic iron, reduce oxidation, and facilitate transportation and storage. Post-treatment includes impurity removal, drying, compaction, and final packaging. The core of this process is to control the moisture content, particle size, and storage conditions of the metallic iron powder.

[0154] First, establish a relationship model between particle size and oxidation rate. Assume the particle size of the metallic iron powder is d p , the moisture content of metallic iron is w, and the oxidation reaction rate r ox can be expressed as:

[0155]

[0156] where k is the reaction rate constant, usually obtained by fitting experimental data. This formula indicates that the smaller the particle size of the metallic iron powder, the faster its oxidation reaction rate, and the higher the moisture content, the higher the oxidation rate. Therefore, during the post-treatment process, it is necessary to control the particle size of the metallic iron powder and keep its moisture content below 5%.

[0157] Second, reduce the moisture content of the metallic iron powder through a drying process. Use a hot air dryer or a vacuum dryer to dry the metallic iron powder at 50 - 100 °C. The efficiency of the drying process is described by the following formula:

[0158] E dry = α·T dry ·t dry ;

[0159] where E dryFor the drying efficiency, T dry For the drying temperature, t dry For the drying time, α is a constant and is adjusted according to the experimental conditions.

[0160] After drying, the metallic iron powder is fed into a compaction device, and the density and fluidity of the particles are controlled by compression molding. The particle density of the iron powder can be adjusted through the compaction process to meet the specified standards. There is the following relationship between the compaction strength and the density of the iron powder (ρ Fe ):

[0161] F press = β·ρ Fe ;

[0162] Among them, F press is the compaction force, β is an experimental constant, and ρ Fe is the density of the metallic iron powder. By adjusting the pressure of the compaction device and the particle size of the iron powder, it is ensured that the powder after compaction has sufficient strength.

[0163] Then, the compacted metallic iron powder is fed into a packaging system. The packaging uses automated equipment, and a suitable packaging form (such as bagged, barreled, etc.) is selected according to the properties of the powder. During the packaging process, an automatic weighing device is used to ensure that the weight of each packaging unit is consistent, and moisture-proof measures are taken to prevent the iron powder from oxidizing during transportation and storage.

[0164] Furthermore, the packaging system is equipped with an atmosphere control device, which can further reduce the oxidation rate of the iron powder by controlling the gas composition inside the package during the packaging process. This atmosphere control device is calculated by the following formula:

[0165] F gas = γ·C gas ·A pkg ;

[0166] Among them, F gas is the gas flow rate, C gas is the gas concentration inside the package, A pkg is the packaging area, and γ is a constant. By adjusting the composition and flow rate of the gas inside the package, the oxidation of the metallic iron powder can be effectively delayed.

[0167] After completion of the packaging, the finished iron powder is sent to a storage warehouse through an automated conveying system for transportation.

[0168] Through the above post-treatment and packaging steps of the refined iron powder, it can be ensured that the iron powder maintains high purity during storage and transportation, and the performance loss caused by oxidation is reduced. The purity of the final packaged product can reach more than 95%, and it has good fluidity and stability, making it suitable for subsequent industrial applications.

[0169] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will appreciate that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for reducing high-grade reduced iron powder from low-grade red mud powder and fly ash, characterized in that, The method comprises the following steps: S1: Select red mud powder and fly ash as raw materials. The mass fraction of iron in the red mud powder is between 10% and 30%. The fly ash contains iron oxides. The mass ratio of the red mud powder to the fly ash is 100:10 to 100:90; S2: Uniformly mix the red mud powder and the fly ash according to the said mass ratio, and form pellets with a diameter of 5 - 16 mm by pelletizing; S3: Feed the pellets into a high-temperature reduction furnace and reduce them with a reducing gas. The temperature is controlled at 850°C to 1000°C, and the reduction time is controlled at 40 to 120 minutes. The reducing gas is coal gas rich in carbon monoxide, and the volume fraction of CO / CO2 in the coal gas ≥ 2, and the CO concentration is 80% to 90%; S4: Cool the reduced pellets with low-temperature coal gas. The cooling temperature is controlled below 100°C, and the cooling time is 40 to 120 minutes. The volume fraction of CO / CO2 in the low-temperature coal gas ≥ 2; S5: Crush and grind the cooled pellets until the particle size is less than 75 μm. In the particle size distribution of the iron powder after grinding, the particles exceeding 75 μm do not exceed 5%; S6: Conduct magnetic separation on the iron powder after grinding. Use a high-gradient magnetic separation device with a magnetic field intensity of 4000 Oe to 8000 Oe to separate metallic iron from impurities and obtain high-grade reduced iron powder. The mass fraction of metallic iron in the reduced iron powder ≥ 94%, and the carbon content in the reduced iron powder ≤ 1.00%.

2. The method for reducing high-grade reduced iron powder from low-grade red mud powder and fly ash according to claim 1, wherein The volume fraction of CO / CO2 in the low-temperature coal gas is maintained above 2.

0.

3. The method for reducing high-grade reduced iron powder from low-grade red mud powder and fly ash according to claim 1, characterized in that The volume fraction of CO / CO2 in the reducing gas is greater than 2, and the reduction reaction temperature is controlled between 900°C ± 10°C.

4. The method for reducing high-grade reduced iron powder from low-grade red mud powder and fly ash according to claim 1, characterized in that The ratio of the red mud powder to the fly ash is 30:70 to 80:

20.

5. The method for reducing high-grade reduced iron powder from low-grade red mud powder and fly ash according to claim 1, characterized in that, The carbon monoxide concentration in the reducing gas is 80% to 90%.

6. The method for reducing high-grade reduced iron powder from low-grade red mud powder and fly ash according to claim 1, wherein In the particle size distribution of the iron powder after grinding, the particles exceeding 75 μm < 5%.

7. The method for reducing high-grade reduced iron powder from low-grade red mud powder and fly ash according to claim 1, characterized in that, The recovery rate of the metallic iron powder ≥ 90%.

8. The method for reducing high-grade reduced iron powder from low-grade red mud powder and fly ash according to claim 1, characterized in that, The metallization rate of the reduced iron powder ≥ 95%.

9. The method for reducing high-grade reduced iron powder from low-grade red mud powder and fly ash according to claim 1, characterized in that The mass fraction of Fe in the reduced iron powder ≥ 94%, and the carbon content ≤ 1.00%.

10. Application of the method for reducing low-grade red mud powder and fly ash to high-grade reduced iron powder according to any one of claims 1 - 9 in the production of smelting low-carbon steel or high-quality steel.

Images