Red mud (medium-grade hematite) resource regeneration two-step reduction process system

Abstract

The invention discloses a red mud (medium-grade hematite) resource regeneration two-step reduction process system, and relates to the fields of environmental protection, new materials and the like. Aiming at the problems of complex chemical composition, economic and large-scale bottleneck, secondary pollution, insufficient technical maturity and the like in the comprehensive utilization of the existing red mud (middle-grade hematite), the method comprises the steps of red mud (middle-grade hematite) raw material pretreatment, pelletizing, drying, heat storage type external heat reduction process, sectional cooling, magnetic separation, subsequent treatment and the like. By means of the process system, 90%-100% of red mud (middle-grade hematite) recycling, efficient iron recycling and residue recycling can be achieved, economic benefits are remarkable, the treatment efficiency is improved, and external heating fuel self-supply can be achieved after equipment normally operates. The method effectively solves the problem of comprehensive utilization of the red mud (middle-grade hematite), and has a good application prospect.

Description

Technical Field

[0001] This invention relates to environmental protection, new materials, high-temperature melting reduction technology, and resource utilization technology systems, specifically to a two-step reduction process system for the resource recycling of red mud (medium-grade hematite). Background Technology

[0002] The production of alumina generates a large amount of red mud (medium-grade hematite), a highly alkaline solid waste. As a major alumina producer, my country's alumina output reached 85.81 million tons in 2024, corresponding to approximately 120 million tons of red mud (medium-grade hematite). The accumulated stockpile exceeds 1.6 billion tons, covering an area of ​​120,000 mu (approximately 8,667 hectares), accounting for one-third of the world's total stockpile. However, its comprehensive utilization rate is only 12%. This massive production of red mud (medium-grade hematite) and its extremely low utilization rate make the treatment and utilization of red mud (medium-grade hematite) a critical issue that urgently needs to be addressed.

[0003] The chemical composition of red mud (medium-grade hematite) is highly complex, which is one of the key factors leading to poor adaptability of related processes. Its iron content fluctuates wildly, ranging from 15% to 52%, making the development of a universally applicable process extremely difficult. For example, magnetic separation is a suitable method for high-iron red mud (medium-grade hematite), but for low-iron red mud (medium-grade hematite), the efficiency of magnetic separation is less than 50%, making it difficult to effectively extract iron. Furthermore, the mineral phases in red mud (medium-grade hematite) are very densely interbedded; for instance, hematite encasing nepheline is common. Conventional physical separation methods are inefficient in such cases, resulting in an iron concentrate grade of only 38.5%, far below the standard of 58%.

[0004] From the perspective of economic efficiency and large-scale development, there are also many bottlenecks. The cost of iron ore beneficiation processes is quite high, with traditional acid leaching costing $137 per ton, and additional neutralization of alkaline residue is required, which undoubtedly increases processing costs and environmental risks. In terms of building material applications, red mud (medium-grade hematite) is also greatly limited. For example, red mud (medium-grade hematite) ceramsite is prone to cracking due to alkaline precipitation, resulting in a market acceptance of less than 10%, making it difficult to apply on a large scale in the construction industry.

[0005] The treatment of red mud (medium-grade hematite) also carries a serious risk of secondary pollution. Wet storage can easily lead to dam failures, as seen in the 2010 Hungarian incident, and also cause groundwater pollution, with wastewater pH reaching 12-13, posing a significant threat to soil and water resources. Dry storage, on the other hand, generates severe dust pollution and requires a protective membrane with a thickness of ≥1.5mm to prevent harmful substances in the red mud (medium-grade hematite) from seeping into the soil and groundwater.

[0006] Furthermore, the current technology for processing red mud (medium-grade hematite) is not mature enough. Most technologies are still in the laboratory stage. For example, although biological dealkali treatment technology can reduce acid consumption by 60%, its annual processing capacity is only 100,000 tons, which is far from meeting the needs of large-scale processing of red mud (medium-grade hematite). Moreover, a national standard system for red mud (medium-grade hematite) processing is lacking. A nationwide road-use standard has not yet been established, and only Guangxi, Shandong, and other places allow the use of red mud (medium-grade hematite) based materials. This also limits the promotion and large-scale development of the resource utilization of red mud (medium-grade hematite). Summary of the Invention

[0007] The purpose of this invention is to provide a two-step reduction process system for the resource-based regeneration of red mud (medium-grade hematite). To achieve the above objective, this invention is implemented through the following technical solution: a two-step reduction process system for the resource-based regeneration of red mud (medium-grade hematite), comprising the step of drying the red mud (medium-grade hematite) raw material to <10% when the moisture content is ≥10% using a drying device after it arrives at the plant. The drying device can be selected according to the quantity and characteristics of the red mud (medium-grade hematite). For example, when the quantity of red mud (medium-grade hematite) is large and the moisture content is high and the texture is relatively uniform, a large continuous dryer can be selected, which has the characteristics of large processing capacity and high drying efficiency; if the quantity of red mud (medium-grade hematite) is relatively small and the composition is relatively complex, an intermittent drying device can be selected, which is convenient for flexibly adjusting the drying parameters according to the actual situation. The drying process requires ensuring uniform heating of the red mud (medium-grade hematite). Optimizing the internal structure of the drying equipment, such as by incorporating appropriate stirring or airflow distribution devices, ensures sufficient contact between the red mud (medium-grade hematite) and hot air during drying, preventing localized overheating or undried conditions and guaranteeing the stable operation of subsequent processes. Localized overheating of the red mud (medium-grade hematite) may cause changes in some components, affecting the subsequent reduction reaction. Conversely, undried red mud (medium-grade hematite) contains excessive moisture, leading to adhesion problems in subsequent pelletizing and other processes, affecting pellet quality. Pre-drying the red mud (medium-grade hematite) to control moisture content within a suitable range effectively avoids various adverse effects caused by moisture issues in subsequent processes. This provides a stable and high-quality raw material base for subsequent pelletizing and reduction processes, ensuring the smooth operation of the entire process and serving as a crucial preliminary step for the efficient resource utilization of red mud (medium-grade hematite).

[0008] Further, a catalyst and 5%-10% reducing agent are added. The ratio of catalyst to reducing agent is precisely adjusted according to the specific composition and properties of the red mud (medium-grade hematite). For example, when the red mud (medium-grade hematite) has a high iron content but the mineral phases are tightly intercalated, the proportion of catalyst added is appropriately increased to enhance the catalytic effect on the reduction reaction of iron oxides. If the red mud (medium-grade hematite) contains a lot of alkaline substances, affecting the reduction reaction, the proportion of reducing agent can be adjusted appropriately. After addition, the mixture is thoroughly stirred using specialized stirring equipment. The stirring time, speed, and other parameters are set according to the actual situation to ensure that the catalyst and reducing agent are fully and evenly mixed with the red mud (medium-grade hematite). Too short a stirring time may result in insufficient mixing, affecting the subsequent reaction effect; too fast a stirring speed may damage the original structure of the red mud (medium-grade hematite), which is not conducive to subsequent pelletizing. Subsequently, a disc pelletizer or a double-roller pelletizer is used for pelletizing. During the pelletizing process, the particle size, density, and other parameters of the pellets are controlled within the specified range. Suitable pellet size ensures good permeability during subsequent reduction processes, facilitating the full progress of the reduction reaction; suitable density ensures the pellets are not easily broken during transportation and subsequent processing. By precisely adjusting the ratio of catalyst and reducing agent and thoroughly mixing them, both catalyst and reducing agent can fully exert their effects, effectively promoting the reduction reaction of iron oxides and other elements in the subsequent red mud (medium-grade hematite). Employing appropriate pelletizing methods and controlling pellet parameters provides pellets with good reactivity and physical properties for the subsequent reduction process, helping to improve the recovery efficiency of elements such as iron, and is a key step in achieving efficient resource utilization of red mud (medium-grade hematite).

[0009] Furthermore, after pelleting, the raw material is dried again, with the moisture content strictly controlled to ≤3% using a precise drying control system. Temperature, time, and other parameters during the drying process are adjusted appropriately based on the characteristics of the red mud (medium-grade hematite) and the condition of the pellets to ensure uniform moisture removal without affecting pellet quality. For example, for pellets made from red mud (medium-grade hematite) with a specific composition, if their binding properties are strong, the drying temperature should not be too high to prevent the surface from drying too quickly while internal moisture remains, leading to pellet cracking. If the pellets are more porous, the drying time can be appropriately extended to ensure sufficient moisture removal. Precise control of the drying process ensures that the pellets maintain good physical structure and properties in subsequent reduction processes. Strictly controlling the moisture content of the raw material after pelleting prevents moisture from having adverse effects during subsequent high-temperature reduction processes, such as affecting the reducing atmosphere or causing pellet cracking. Precise control of drying parameters ensures uniform moisture removal without affecting pellet quality, creating favorable conditions for subsequent reduction reactions, improving the recovery of elements such as iron, and ensuring the stability and efficiency of the entire process.

[0010] Furthermore, the regenerative external heat reduction process employs regenerative combustion technology. This technology, through a special regenerator structure design, maximizes the recovery of waste heat from flue gas, strictly controlling the exhaust temperature below 150℃. The unique regenerator structure efficiently absorbs and stores waste heat from the flue gas, releasing it in subsequent processes to heat materials, significantly improving energy efficiency. Simultaneously, it enables the combustion of low-calorific-value fuels, utilizing CO-containing waste gas generated in the reduction atmosphere as fuel, fully utilizing previously potentially emitted waste gas, further reducing energy consumption and costs. The primary reduction stage employs flame-insulated heating to ensure the reducing agent is fully utilized in the reduction reaction of iron oxides. Flame-insulated heating allows for sufficient contact and uniform reaction between the reducing agent and iron oxides, minimizing the generation of secondary oxidation. Unreacted reducing agent exists in the tail gas as CO. This tail gas is collected above the inlet of the red mud (medium-grade hematite) pellets. The preheating effect of the flue gas passing through the red mud (medium-grade hematite) pellet bed keeps the temperature of the collected CO-containing tail gas below 150 degrees Celsius. The high-temperature tail gas, after filtration and dust removal, is used as fuel for the regenerative combustion system for primary reduction heat source. During normal operation, no additional fuel such as natural gas is required for roasting. By strictly controlling core technical parameters such as primary reduction temperature and time, agglomeration and vitrification of the red mud (medium-grade hematite) after the reduction reaction are prevented. Precise temperature and time control ensures that iron oxides and other components react fully under suitable conditions, avoiding product quality problems caused by improper reaction conditions. The regenerative external heat reduction process achieves high energy efficiency and cost reduction by recovering waste heat from the flue gas and utilizing low-calorific-value fuels and CO-containing waste gas. The flame-insulated heating method ensures the sufficiency and uniformity of the reduction reaction, and the strict control of the primary reduction parameters prevents the occurrence of undesirable product conditions. It effectively improves the recovery efficiency of elements such as iron and product quality, while reducing energy consumption and environmental pollution. This is one of the core advantages of this process system.

[0011] Furthermore, segmented cooling technology cools the product in stages according to a specific temperature gradient, precisely controlling the cooling rate and medium flow rate at each stage. For example, a slower cooling rate and a larger medium flow rate are used in the high-temperature stage to ensure uniform cooling of the product's internal structure; the cooling rate can be appropriately accelerated in the low-temperature stage. The heat generated during cooling is used to dry the raw materials through specialized heat exchange equipment, achieving efficient heat recovery and utilization, further reducing production energy consumption. By recovering heat from the cooling process for raw material drying, energy is fully utilized, reducing additional energy consumption. Segmented cooling technology, through precise control of the cooling process, ensures product quality and avoids product defects caused by improper cooling. Simultaneously, it achieves efficient heat recovery and utilization, reducing energy consumption in the production process and improving the energy efficiency of the entire process system, demonstrating the significant advantages of the process system in energy conservation and environmental protection.

[0012] Furthermore, the product after the first reduction is subjected to magnetic separation using a 1200 Gauss magnetic separator to separate magnetic and non-magnetic materials based on their magnetic differences. High-performance magnetic separators can more accurately separate materials based on magnetic differences, improving separation efficiency and purity. The magnetic material is then melted in an electric arc furnace. A reducing agent is added to the slag for a second-stage reduction to further improve iron recovery and reduce the iron content in the slag. The electric arc furnace parameters are precisely set according to the reduction requirements. The lower layer of melt is low-carbon iron, which meets the standards for direct sale. The upper layer of high-temperature slag mainly consists of alumina and silica eutectics, which can be further processed. Precisely setting the electric arc furnace parameters ensures the quality and quantity of low-carbon iron. The non-magnetic material is first screened. Small particles are directly stored in the warehouse as raw materials for cement building materials. Larger particles (≥5mm) undergo Al separation. Carbon particles are screened out using specialized Al separation equipment and stored in the reducing agent warehouse. The remaining tailings are stored in the warehouse as raw materials for cement building materials. This precise separation and utilization of different components enabled the effective use of various elements in red mud (medium-grade hematite). Through magnetic separation, two-stage reduction, and further processing of non-magnetic materials, the separation and effective utilization of different components in red mud (medium-grade hematite) were achieved. This yielded a low-carbon iron product that met standards, while also converting some components of the non-magnetic materials into usable raw materials. This improved the resource utilization rate of red mud (medium-grade hematite), reduced waste generation, and demonstrated the significant value of the process system in comprehensive resource utilization.

[0013] Furthermore, this process achieves an iron recovery rate of ≥95% from red mud (medium-grade hematite), and the resulting reduced iron meets or exceeds the requirements of grade H88, adhering to standard YB / T4170-2008. Precise control of all parameters throughout the process ensures both high iron recovery and high-quality reduced iron. This precise control of parameters from raw material pretreatment to final product output, such as drying moisture content, reducing agent ratio, reduction temperature, and time, guarantees efficient reduction of iron from red mud (medium-grade hematite) and the production of high-quality reduced iron. The high iron recovery rate from red mud (medium-grade hematite) and the high-quality reduced iron product are significant achievements of this process system. A high recovery rate signifies efficient utilization of iron resources in red mud (medium-grade hematite), reducing waste; the high-quality reduced iron product meets relevant standards, possesses high market value, and brings significant economic benefits to the process system while also satisfying market demand for high-quality steel raw materials.

[0014] Furthermore, every 1 ton of high-iron red mud (medium-grade hematite) (Fe2O3 content 50%) can produce 500 kg of direct reduced iron (DRE). At a price of 2.4 yuan / kg, the sales revenue can reach 1200 yuan. This economic benefit is achieved through process optimization and precise control of each stage. By optimizing and precisely controlling each stage, including raw material processing, reduction reaction, and product separation, efficient DRE production from high-iron red mud (medium-grade hematite) has been achieved, resulting in considerable sales revenue. This economic benefit demonstrates the economic feasibility and profitability of this process system in practical applications. Through process optimization and control, valuable products and economic benefits can be obtained from red mud (medium-grade hematite), providing strong economic support for the commercial promotion of red mud (medium-grade hematite) resource utilization and promoting the sustainable development of the red mud (medium-grade hematite) resource utilization industry.

[0015] Furthermore, employing a vertical kiln process, the processing capacity can reach 1 million tons / year. The new multi-stage heat exchange device within the kiln increases the waste heat recovery rate of flue gas to 90%. Through the rational design of the vertical kiln structure and heat exchange device, efficient processing and waste heat recovery are achieved. The vertical kiln process features large processing capacity and continuous production, meeting the needs of large-scale red mud (medium-grade hematite) processing. The new multi-stage heat exchange device within the kiln efficiently recovers waste heat from the flue gas, improving energy utilization efficiency and reducing production costs. The high processing capacity and efficient waste heat recovery capability of the vertical kiln process give this system a high-efficiency and energy-saving advantage when processing red mud (medium-grade hematite). It can rapidly process large quantities of red mud (medium-grade hematite) while simultaneously recovering and utilizing waste heat from the flue gas, reducing energy consumption, lowering production costs, and improving the overall economic and environmental benefits of the process system, making it suitable for large-scale industrial applications.

[0016] Furthermore, once the equipment is operating normally, it can achieve self-sufficiency in external heat fuel, eliminating the need for additional consumption of natural gas or other fuels. Through the synergistic effect of the regenerative external heat reduction process and segmented cooling technology, it achieves efficient energy utilization and self-sufficiency. The regenerative external heat reduction process recovers and utilizes waste heat from flue gas and CO-containing waste gas as fuel, while the segmented cooling technology recovers heat for raw material drying. The synergy of these two technologies allows the process system to provide the necessary heat during operation, reducing dependence on external fuels such as natural gas. Achieving self-sufficiency in external heat fuel not only reduces production costs but also reduces the consumption of fossil fuels and environmental pollution. This demonstrates the innovation and sustainability of the process system in energy utilization, aligns with current energy conservation and environmental protection requirements, and provides an economical and environmentally friendly solution for the resource utilization of red mud (medium-grade hematite).

[0017] This invention provides a two-step reduction process system for the resource-based regeneration of red mud (medium-grade hematite), which has the following beneficial effects: 1. Firstly, regarding raw material pretreatment, when the moisture content of the red mud (medium-grade hematite) raw material arrives at the plant and is ≥10%, a drying device is used to dry the moisture to <10%. The appropriate type of drying equipment can be selected based on the quantity and characteristics of the red mud (medium-grade hematite). The drying process ensures uniform heating of the red mud (medium-grade hematite), avoiding localized overheating or undried conditions. This lays a solid foundation for the stable operation of subsequent processes. By precisely controlling the moisture content of the red mud (medium-grade hematite), subsequent processes such as pelletizing can proceed more smoothly, improving the stability and reliability of the entire process flow.

[0018] In the pelletizing process, 5%-10% of reducing agent and catalyst are added, and the proportions are precisely adjusted according to the specific composition and properties of the red mud (medium-grade hematite). The mixture is thoroughly stirred using specialized equipment to ensure complete and uniform mixing of the catalyst and reducing agent with the red mud (medium-grade hematite). Subsequently, a disc pelletizer or a double-roller pelletizer is used to pelletize the materials, while controlling the particle size, density, and other parameters of the pellets within specified ranges. This precise batching and pelletizing method allows the red mud (medium-grade hematite) to react more effectively in the subsequent reduction process, improving the recovery efficiency of elements such as iron.

[0019] After pelleting, the raw materials undergo a second drying process. A precise drying control system strictly controls the moisture content to ≤3%. Furthermore, parameters such as temperature and time are adjusted during the drying process based on the characteristics of the red mud (medium-grade hematite) and the condition of the pellets to ensure uniform moisture removal without affecting pellet quality. This step further guarantees the dryness of the raw materials, which is beneficial for improving the efficiency of the reduction reaction, while avoiding the adverse effects of excessive or insufficient moisture on pellet quality.

[0020] The regenerative external heat reduction process offers numerous advantages. This process employs regenerative combustion technology, utilizing a unique regenerative structure design to maximize the recovery of waste heat from the flue gas, strictly controlling the exhaust temperature below 150°C. Simultaneously, it enables the combustion of low-calorific-value fuels, using the CO-containing waste gas generated during the reduction atmosphere as fuel. The primary reduction stage employs flame-insulated heating to ensure the reducing agent is fully utilized in the reduction reaction of iron oxides. Unreacted reducing agent exists as CO in the exhaust gas, collected at the red mud (medium-grade hematite) inlet. The preheating effect of the flue gas passing through the red mud (medium-grade hematite) inlet maintains the temperature of the collected CO-containing exhaust gas below 150°C. The filtered and dust-removed high-temperature exhaust gas serves as the fuel for the regenerative combustion system, acting as the heat source for the primary reduction. During normal operation, no additional fuels such as natural gas are required for roasting. By strictly controlling core technical parameters such as the primary reduction temperature and time, the process prevents the red mud (medium-grade hematite) from agglomerating or vitrifying after the reduction reaction. This process not only achieves energy conservation and emission reduction and lowers production costs, but also increases the output of elemental iron, improves economic efficiency, and ensures the quality of reduced iron.

[0021] Segmented cooling technology cools the product in stages according to a specific temperature gradient. During the cooling process, the cooling rate and medium flow rate are precisely controlled at each stage. The heat generated during cooling is used to dry the raw materials through specialized heat exchange equipment, achieving efficient heat recovery and utilization, further reducing production energy consumption. This heat recovery and utilization method improves energy utilization efficiency, reduces the overall energy consumption of the process, and meets the requirements of energy conservation and environmental protection.

[0022] The product after the first reduction is subjected to magnetic separation using high-performance magnetic separation equipment. Magnetic and non-magnetic materials are separated based on their magnetic differences. The magnetic material undergoes a two-stage reduction process using an electric arc furnace. The parameters of the electric arc furnace are precisely set according to the reduction requirements. The lower layer of molten material is low-carbon iron, meeting the standards for direct sale. The upper layer of high-temperature slag mainly consists of alumina and silica eutectic compounds, which can be further processed. The non-magnetic material is first screened. Small particles are directly used as raw materials for cement and building materials and stored in a warehouse. Larger particles (≥5mm) undergo Al separation. Carbon particles are screened out using specialized Al separation equipment and stored in a reducing agent warehouse. The remaining tailings are stored in a warehouse as raw materials for cement and building materials. This precise separation and utilization of different components achieves full-component utilization of red mud (medium-grade hematite), improving resource utilization and facilitating subsequent deep processing.

[0023] This process achieves an iron recovery rate of ≥95% from red mud (medium-grade hematite), and the resulting reduced iron meets or exceeds the requirements of grade H88, adhering to standard YB / T4170-2008. By precisely controlling each parameter throughout the entire process, the iron recovery rate and the quality of the reduced iron are guaranteed. The high recovery rate and high-quality reduced iron make this invention highly economically competitive and also meet market demand for high-quality reduced iron.

[0024] From an economic perspective, 1 ton of high-iron red mud (medium-grade hematite) (Fe2O3 content ≈ 50%) can produce 500 kg of direct reduced iron. At 2.4 yuan / kg, the sales revenue can reach 1200 yuan. There is also revenue generated from the sale of carbon-containing waste and high-alumina aluminum-silicon eutectic. Good economic benefits can be achieved through the optimization of the process flow and precise control of each link.

[0025] In terms of processing capacity and energy utilization, the vertical kiln process is adopted, with a single kiln capacity reaching 1 million tons, resulting in a large throughput. The new multi-stage heat exchange device within the kiln increases the waste heat recovery rate of flue gas to 90%. Through the rational design of the vertical kiln structure and heat exchange device, efficient processing and waste heat recovery are achieved. After normal operation, the equipment can achieve self-sufficiency in external heat fuel, eliminating the need for additional consumption of natural gas or other fuels. Through the synergistic effect of regenerative external heat reduction technology and segmented cooling technology, efficient energy utilization and self-sufficiency are achieved. High processing capacity improves production efficiency, while energy self-sufficiency and efficient utilization significantly reduce production costs, meeting the requirements of sustainable development.

[0026] In summary, the two-step reduction process system for the resource-based regeneration of red mud (medium-grade hematite) of this invention effectively solves many problems in the treatment and resource utilization of red mud (medium-grade hematite) through a series of innovative technologies and process steps. It has significant technical advantages, economic benefits, and environmental benefits. If all red mud (medium-grade hematite) with an iron content of 45% or more in the country were treated using this process, it would not only significantly reduce dependence on imported foreign ores but also increase the annual economic benefits of aluminum-containing resources by trillions of yuan, benefiting the country and its people, and has broad application prospects. Attached Figure Description

[0027] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0028] Figure 1 This is the overall flowchart of the present invention. Detailed Implementation

[0029] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses consistent with some aspects of this disclosure as detailed in the appended claims.

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0031] How to use This process system is suitable for the resource utilization of red mud (medium-grade hematite) generated during alumina production. Through nine core steps, it achieves efficient recovery of metal elements and full utilization of all components in the red mud (medium-grade hematite). Specific usage methods are as follows: Red mud (medium-grade hematite) pre-drying: After the red mud (medium-grade hematite) raw material arrives at the plant, its moisture content is tested. If the moisture content is ≥10%, a drying equipment matching the quantity and characteristics of the red mud (medium-grade hematite) is selected (e.g., a continuous dryer is selected for large quantities, and an intermittent dryer is selected for small quantities) to dry the moisture content to <10%. During the drying process, the equipment parameters need to be controlled to ensure that the red mud (medium-grade hematite) is heated evenly, avoiding local overheating or undried phenomena, so as to provide raw materials with suitable moisture content for subsequent processes.

[0032] Catalyst and reducing agent addition and pelletizing: Add catalyst and 5%-10% reducing agent to the pre-dried red mud (medium-grade hematite) (the ratio is precisely adjusted according to the specific composition and properties of the red mud (medium-grade hematite)). Mix thoroughly using specialized stirring equipment (stirring time, speed, and other parameters are set according to the actual characteristics of the red mud (medium-grade hematite)). After mixing, prepare pellets using a disc pelletizer or a double-roller pelletizer. During the process, strictly control the particle size, density, and other parameters of the pellets within the specified range to ensure that the pellet structure is stable and suitable for subsequent reduction reactions.

[0033] Secondary drying after pelletizing: The formed pellets undergo secondary drying, with the moisture content strictly controlled to ≤3% through a precision drying control system. During drying, parameters such as temperature and time are adjusted according to the characteristics of the red mud (medium-grade hematite) and the actual condition of the pellets to ensure uniform removal of moisture without damaging the quality of the pellets (such as avoiding surface cracking or internal moisture residue due to excessively high temperatures).

[0034] Regenerative External Heat Reduction: This reduction process employs regenerative combustion technology, utilizing a special regenerator structure to recover waste heat from flue gas, controlling the exhaust temperature below 150℃. It simultaneously burns low-calorific-value fuels and recycles the CO-containing waste gas generated during the reduction process as fuel. The primary reduction stage uses flame-insulated heating to ensure the reducing agent precisely targets iron oxides. Unreacted CO tail gas is collected from the red mud (medium-grade hematite) inlet, preheated (temperature ≤150℃), filtered for dust removal, and used as the fuel heat source for the regenerative combustion system. No additional fuel such as natural gas is required during normal operation. Strict control of the temperature and time parameters of the primary reduction prevents agglomeration or vitrification of the red mud (medium-grade hematite) after reduction.

[0035] Segmented cooling: The product after primary reduction is cooled in stages according to a specific temperature gradient, with precise control over the cooling rate and medium flow rate at each stage. The heat generated during cooling is used for raw material drying through heat exchange equipment, achieving efficient heat recovery and further reducing energy consumption in the production process.

[0036] Magnetic separation and product separation: The product after the first reduction is subjected to magnetic separation. High-performance magnetic separation equipment is used to separate magnetic and non-magnetic materials according to their magnetic differences. The magnetic material enters the electric arc furnace for a second-stage reduction (the electric arc furnace parameters are precisely set according to the reduction requirements). The lower layer of melt is low-carbon iron (which can be sold directly), and the upper layer of high-temperature slag (mainly composed of eutectic compounds such as alumina and silicon dioxide) is further processed. The non-magnetic material is first processed by screening equipment. Small particles (<5mm) are directly used as raw materials for cement building materials and stored in the warehouse. Large particles (≥5mm) are then subjected to Al separation (carbon particles are screened out using special equipment and stored in the reducing agent warehouse). The remaining tailings are used as a carbon-containing tailings warehouse.

[0037] Iron recovery and product quality control: By precisely controlling the parameters of the entire process (covering drying, reduction, magnetic separation and other links), we ensure that the iron recovery rate of red mud (medium-grade hematite) is ≥85%, and the reduced iron obtained meets the requirements of grade H88 or higher (implementation standard YB / T4170-2008), ensuring that the quality of iron products meets market standards.

[0038] Economic Benefit Guarantee: Based on the synergistic optimization of the above process steps, 1 ton of high-iron red mud (medium-grade hematite) (Fe2O3 content ≈ 50%) can produce 500 kg of direct reduced iron. Calculated at 2.4 yuan / kg, the sales revenue can reach 1200 yuan. There is also revenue generated from the sale of carbon-containing waste and high-alumina aluminum-silicon eutectic. Good economic benefits are achieved through the optimization of the process flow and precise control of each link.

[0039] High-efficiency processing and energy self-sufficiency: Utilizing a vertical kiln process, the processing capacity can reach 15-20 tons / hour; through a new multi-stage heat exchange device within the kiln, the waste heat recovery rate of flue gas is increased to 90%. After the equipment is in normal operation, relying on the synergy of regenerative external heat reduction process and segmented cooling technology, the self-supply of external heat fuel is achieved (without the need for additional consumption of natural gas or other fuels), ensuring efficient energy utilization and continuous production.

[0040] Example 1: Complete process flow for high-red mud (medium-grade hematite) processing scenarios A large alumina plant produces a large amount of red mud (medium-grade hematite) daily, with unstable moisture content. After the red mud (medium-grade hematite) raw material is transported to the processing workshop, its moisture content is first tested. If it exceeds 10%, a continuous drying system matched to the daily processing capacity of the red mud (medium-grade hematite) is activated. Through uniform material distribution and a hot air circulation system, the moisture content is reduced to below 10%. Subsequently, based on the composition test results of the red mud (medium-grade hematite), a catalyst and reducing agent are added in proportion (the reducing agent ratio is controlled at 5%-10%), and thoroughly mixed using high-speed stirring equipment to ensure that the catalyst is evenly adhered to the surface of the red mud (medium-grade hematite) particles. The mixed material is then pelletized by a disc pelletizer. By adjusting the pelletizer's speed and scraper position, the pellet size and density are controlled to be uniform. After pelletizing, the material enters a secondary drying stage, using a segmented temperature-controlled drying system to strictly control the moisture content below 3%, preventing the pellets from cracking or pulverizing due to uneven moisture content.

[0041] The pellets enter the regenerative external heat reduction process. The regenerative combustion system recovers waste heat from the flue gas through a honeycomb-shaped regenerator, stabilizing the exhaust temperature below 150℃. The primary reduction uses a flame-insulated heating method, ensuring full contact and reaction between the reducing agent and iron oxides. Unreacted CO tail gas is preheated at the inlet of red mud (medium-grade hematite) to recover heat, then filtered for dust removal and recycled as fuel, eliminating the need for additional natural gas or other fuels. Temperature and time parameters are monitored in real time during the reduction process to ensure the pellets do not agglomerate or vitrify. The reduction product is processed by a segmented cooling system. Slow cooling is used at high temperatures to ensure uniform internal structure, while the cooling rate is accelerated at low temperatures. The heat released during cooling is used for raw material drying through heat exchange equipment.

[0042] The cooled product undergoes magnetic separation. The magnetic material (mainly containing iron) enters an electric arc furnace for two-stage reduction. The furnace parameters are precisely set according to the reduction requirements of iron oxides, ultimately yielding a low-carbon iron product. The non-magnetic material is classified by screening equipment. Small particles are directly used as raw materials for cement building materials, while larger particles are further separated to remove carbon particles, which are then recycled to a reducing agent warehouse. The remaining tailings are used as raw materials for ceramic production. The entire process achieves full utilization of both metallic and non-metallic components in red mud (medium-grade hematite), and the efficient processing capacity of the vertical kiln ensures stable processing of large-scale red mud (medium-grade hematite).

[0043] Example 2: Rapid processing mode for low-moisture red mud (medium-grade hematite) Red mud (medium-grade hematite) stored in a certain red mud (medium-grade hematite) stockpile had a moisture content of less than 10% upon arrival at the plant due to good prior storage conditions. The pre-drying step was skipped, and the process proceeded directly to the catalyst and reducing agent addition stage. Based on the compositional characteristics of the red mud (medium-grade hematite), the ratio of catalyst to reducing agent was adjusted (reducing agent content was between 5% and 10%). Pelletizing was performed using a double-roller briquetting machine, and the pressure regulation function of the briquetting machine was used to control the pellet density, ensuring the pellets were compact and not easily broken. After pelletizing, a primary drying stage was adopted, using a low-temperature, slow drying method to precisely control the moisture content to below 3%, avoiding damage to the pellet structure from high temperatures.

[0044] The subsequent reduction process employs a regenerative external heat reduction system. The heat storage medium uses materials with high specific heat capacity to efficiently recover waste heat from the flue gas and maintain the exhaust temperature below 150℃. In the primary reduction stage, flame-insulated heating directs the reducing agent to act on iron oxides. Unreacted CO tail gas is preheated through the red mud (medium-grade hematite) inlet and then recycled, requiring no external fuel supplementation. During the reduction process, precise temperature and time control prevents abnormal conditions in the pellets. The reduction product is processed by a segmented cooling system. The high-temperature section uses natural convection cooling, while the low-temperature section combines forced air cooling. The cooling heat is used for raw material drying.

[0045] The magnetic separation process utilizes permanent magnet separators to efficiently separate magnetic materials (iron-based components) from non-magnetic materials (aluminum, titanium, and other compounds). The magnetic materials undergo secondary reduction in an electric arc furnace, producing low-carbon iron that meets standards. The non-magnetic materials are screened; smaller particles are used directly as building material raw materials, while larger particles are separated to remove carbon particles for reuse. The tailings are used in ceramic production. This method simplifies pretreatment steps, enabling rapid and efficient processing of low-moisture red mud (medium-grade hematite) while ensuring resource recovery.

[0046] Example 3: Customized treatment of complex red mud (medium-grade hematite) The red mud (medium-grade hematite) produced in a certain red mud (medium-grade hematite) mining area has a complex composition, with large fluctuations in iron content and dense mineral phase dissemination. Upon arrival at the plant, the raw materials are first tested for moisture and composition. If the moisture content exceeds the standard, intermittent drying equipment is used to reduce the moisture content to below 10% through precise temperature control. Based on the iron content and mineral dissemination characteristics of the red mud (medium-grade hematite), a customized ratio of catalyst and reducing agent is determined (reducing agent accounts for 5%-10%), and the mixing time is extended using multi-stage stirring equipment to ensure sufficient contact between the reducing agent and the iron oxides encapsulated in the minerals. In the pelletizing process, a disc pelletizer is used. By adjusting the disc inclination angle and feeding speed, pellets with uniform particle size and good air permeability are prepared.

[0047] After pelleting, the material enters a secondary drying stage. The drying curve is adjusted according to the pellet characteristics to strictly control the moisture content to below 3%. In the regenerative external heat reduction process, the regenerator structure is optimized for complex red mud (medium-grade hematite) to maximize the recovery of waste heat from the flue gas and control the exhaust temperature below 150℃. The primary reduction uses a flame-insulated heating method. By adjusting the flame distribution, the reducing agent preferentially acts on the difficult-to-reduce iron oxide inclusions. Unreacted CO tail gas is preheated and recycled, requiring no additional fuel. During the reduction process, temperature and time parameters are dynamically monitored to avoid agglomeration or vitrification problems.

[0048] The reduction product is processed by a segmented cooling system. The high-temperature section uses a combination of water and air cooling, while the low-temperature section recovers heat through heat exchange equipment for raw material drying. The magnetic separation stage uses a high-gradient magnetic separator to precisely separate magnetic materials (mainly containing iron) from non-magnetic materials (containing aluminum, titanium, etc.). The magnetic material enters an electric arc furnace for secondary reduction, producing low-carbon iron products. The non-magnetic material undergoes multi-stage screening; small particles are directly used as building material raw materials, larger particles are separated to remove carbon particles for reuse, and the remaining tailings are sold as carbon-containing tailings. This embodiment solves the resource utilization problem of complex red mud (medium-grade hematite) through customized process parameters, achieving efficient utilization of all components.

[0049] Example 4 Taking 50% TFe as an example, ferric oxide contains 73.5% in red mud (medium-grade hematite). After processing by this device, 500KG of iron can be recovered. The oxygen in the ferric oxide reacts with the reducing agent to produce carbon monoxide. The carbon monoxide is then burned to produce carbon dioxide crystals and emitted. The remaining 26% of the residue becomes about 170KG of eutectic material containing alumina and silicon dioxide. The rest, along with about 200KG of unreacted residual carbon, can be used as raw material for the deep processing of aluminum-magnesium alloys or as raw material for ceramic factories, and can be turned into combustible fuel (calorific value of about 3000Kcal / KG) for cement plants or coal-fired power plants, thus achieving 100% resource utilization.

[0050] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A two-step reduction process system for the resource-based regeneration of red mud (medium-grade hematite), characterized in that: After the red mud (medium-grade hematite) raw material arrives at the plant, if the moisture content is ≥10%, a drying device is first used to dry the moisture content to <10%. The drying device can be selected according to the quantity and characteristics of the red mud (medium-grade hematite). The drying process must ensure that the red mud (medium-grade hematite) is heated evenly to avoid local overheating or undried conditions, so as to ensure the stable progress of subsequent processes.

2. The two-step reduction process system for the resource recycling and regeneration of red mud (medium-grade hematite) according to claim 1, characterized in that: Add 5%-10% of the catalyst and reducing agent. The ratio of catalyst to reducing agent is precisely adjusted according to the specific composition and properties of the red mud (medium-grade hematite). After addition, the mixture is thoroughly stirred using specialized stirring equipment. The stirring time, speed, and other parameters are set according to the actual situation to ensure that the catalyst and reducing agent are fully and evenly mixed with the red mud (medium-grade hematite). Then, a disc pelletizer or a double roller pelletizer is used to pelletize the mixture. During the pelletizing process, the particle size, density, and other parameters of the pellets are controlled within the specified range.

3. The two-step reduction process system for the resource recycling and regeneration of red mud (medium-grade hematite) according to claim 2, characterized in that: After pelleting, the raw material is dried again. The moisture content is strictly controlled to ≤3% through a precise drying control system. The temperature, time and other parameters during the drying process are reasonably adjusted according to the characteristics of red mud (medium-grade hematite) and the condition of the pellets to ensure that the moisture is removed evenly and does not affect the quality of the pellets.

4. The two-step reduction process system for the resource recycling and regeneration of red mud (medium-grade hematite) according to claim 3, characterized in that: The regenerative external heat reduction process employs regenerative combustion technology. This technology maximizes the recovery of waste heat from flue gas through a special regenerative structure design, strictly controlling the exhaust temperature below 150°C. Simultaneously, it enables the combustion of low-calorific-value fuels, using CO-containing waste gas generated in the reduction atmosphere as fuel. The primary reduction stage employs flame-insulated heating to ensure the reducing agent is fully utilized in the reduction reaction of iron oxides. Unreacted reducing agent exists in the exhaust gas as CO. The exhaust gas is collected from the pellet inlet of the vertical primary reducer. Utilizing the preheating effect of the flue gas passing through the pellet bed on the red mud (medium-grade hematite) raw material, the temperature of the collected CO-containing exhaust gas is kept below 150°C. The high-temperature exhaust gas after filtration and dust removal serves as fuel for the regenerative combustion system, acting as the heat source for primary reduction. During normal operation, no additional fuels such as natural gas are required for heating. By strictly controlling core technical parameters such as primary reduction temperature and time, it prevents the red mud (medium-grade hematite) from agglomerating or vitrifying after the reduction reaction.

5. The two-step reduction process system for the resource recycling and regeneration of red mud (medium-grade hematite) according to claim 4, characterized in that: Segmented cooling technology cools products in stages according to a specific temperature gradient. During the cooling process, the cooling rate and medium flow rate of each stage are precisely controlled. The heat generated during cooling is used to dry the raw materials through specialized heat exchange equipment, achieving efficient heat recovery and utilization, and further reducing production energy consumption.

6. The two-step melting reduction process system for the resource recycling of red mud (medium-grade hematite) according to claim 5, characterized in that: A 1200 Gauss magnetic separator is used to separate the product after the first reduction. Magnetic and non-magnetic materials are separated based on their magnetic differences. The magnetic material is then subjected to two-stage reduction by electric arc furnace melting. The lower layer of melt is low-carbon iron (iron content > 98%), which meets the standards for direct sale. The upper layer of high-temperature slag is mainly composed of eutectic compounds such as alumina and silicon dioxide, which can be further processed. The non-magnetic material is first screened by screening equipment. Small particles are directly used as raw materials for cement building materials and stored in the carbon tailings silo. Large particles (≥ 5 mm) are then separated by an Al-X-ray intelligent separator. After the carbon particles are screened out by a special Al separation equipment, the large carbon particles are stored in the reducing agent warehouse, and the remaining tailings are stored in the carbon tailings silo.

7. The two-step reduction process system for the resource recycling and regeneration of red mud (medium-grade hematite) according to claim 6, characterized in that: This process achieves an iron recovery rate of ≥95% from red mud (medium-grade hematite), and the resulting reduced iron is not lower than the H88 grade requirement. The standard implemented is YB / T4170-2008. By precisely controlling each parameter of the entire process, the iron recovery rate and the quality of the reduced iron (Fe≥98%) are guaranteed.

8. The two-step reduction process system for the resource recycling and regeneration of red mud (medium-grade hematite) according to any one of claims 1-7, characterized in that: Processing high-iron red mud (medium-grade hematite): 1 ton of high-iron red mud (medium-grade hematite) (Fe2O3 content ≈ 50%) can produce 500 kg of direct reduced iron. Calculated at 2.4 yuan / kg, the sales revenue can reach 1200 yuan. There is also revenue generated from the sale of carbon-containing waste and high-alumina aluminum-silicon eutectic. Good economic benefits can be achieved through the optimization of the process flow and precise control of each link.

9. The two-step reduction process system for the resource-based regeneration of red mud (medium-grade hematite) according to any one of claims 1-7, characterized in that: The vertical kiln process has a large capacity, with a single kiln producing up to 1 million tons per year. The new multi-stage heat exchange device inside the kiln increases the waste heat recovery rate of flue gas to 90%. Through the rational design of the vertical kiln structure and heat exchange device, efficient processing and waste heat recovery are achieved.

10. The two-step reduction process system for the resource recycling and regeneration of red mud (medium-grade hematite) according to any one of claims 1-7, characterized in that: Once the equipment is in normal operation, it can achieve self-sufficiency in external heat fuel without the need for additional consumption of natural gas or other fuels. Through the synergistic effect of the regenerative external heat reduction process and the segmented cooling technology, it achieves efficient energy utilization and self-sufficiency.

Images