Process for extracting iron by deeply reducing red mud

Abstract

The invention provides a process for extracting iron by deeply reducing red mud, which comprises the following steps: molding and drying the red mud, mixing with a carbon-containing material, loading into a vertical furnace reduction chamber with a vertical multi-cavity structure, alternately arranging the reduction chamber and a heating chamber, and transferring heat between the reduction chamber and the heating chamber through a high-temperature-resistant material, so that the reduction chamber is not in contact with flue gas or air; gas or liquid fuel is combusted in the heating chamber through a heat accumulating type combustion device, and generated high-temperature flue gas flows vertically or horizontally and is led out from the side face or the bottom of the heating chamber; the reduction chamber is divided into a drying section, a preheating section, a reduction section and a cooling section from top to bottom, reducing gas is introduced into the bottom of the reduction chamber, and a reduction reaction is carried out under the micro-positive pressure of 10-500 Pa; after being indirectly cooled by the cooling section, the reduced material is continuously discharged through an airtight discharge valve; and the reduced pellets are separated through magnetic separation, and unreacted carbon is recycled. The method has the beneficial effects that the fuel consumption is reduced, the energy consumption per ton of iron is less than 330 kgce, the metallization ratio of iron in the red mud is improved to be higher than 94%, and the pollutant emission is greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of metallurgical solid waste resource utilization, and particularly to a process for extracting iron from deeply reduced red mud. Background Art

[0002] In the metallurgical industry, the treatment of red mud has always been an important and challenging issue. As an industrial waste residue generated during the extraction of alumina from bauxite, red mud has a large output and contains various valuable metals. If not properly treated, it will not only occupy a large amount of land, but also may cause serious pollution to soil, water sources and the air. Extracting iron from red mud can not only realize the recycling of resources, reduce environmental pollution, but also provide a certain amount of raw material supplement for the steel industry, which has important economic and environmental significance.

[0003] Some early methods adopted simple chemical leaching methods, attempting to separate iron oxide from red mud. However, this method has many drawbacks: on the one hand, a large amount of chemical reagents are required in the chemical leaching process, which not only has a high cost, but also the subsequent treatment of these chemical reagents has become a difficult problem and is prone to cause secondary pollution to the environment; on the other hand, the reduction efficiency of chemical leaching method for iron oxide is low, and it is difficult to deeply reduce it to elemental iron, resulting in a low recovery rate of iron resources.

[0004] Later, some high-temperature reduction processes emerged, such as using a traditional rotary kiln for high-temperature reduction. Although the rotary kiln can achieve the reduction of iron oxide to a certain extent, this equipment has the problem of low thermal efficiency. Due to the structural characteristics of the rotary kiln, a large amount of heat is dissipated to the surrounding environment through the kiln body during the heating process, resulting in waste of energy. At the same time, the movement and reaction process of materials in the rotary kiln are difficult to accurately control, making the reduction effect of iron oxide unstable and the metallization rate difficult to reach a high level. Moreover, during the reduction process of the traditional rotary kiln, the temperature of the finally discharged flue gas is relatively high, usually far higher than 150°C - 160°C, which not only increases energy consumption, but also places higher requirements on the subsequent flue gas treatment equipment and increases the treatment cost. For the related patents of the rotary kiln reduction roasting process, such as the invention patent with the patent application number CN201210294361.2 and the name of a method for comprehensive utilization of high-iron red mud for iron smelting and aluminum extraction, it needs to be carried out under high-temperature conditions of 1200 - 1400°C. During this process, the thermal efficiency is low, and the metallization rate of iron oxide is not high, and the energy consumption per ton of red mud reaches 800 - 1200 kWh. High energy consumption and low efficiency have become the main bottlenecks of this process.

[0005] There are also some attempts to use a fixed-bed reactor for reduction, but the fixed-bed reactor has deficiencies in continuous production. It is difficult to achieve continuous feeding and discharging of materials, resulting in low production efficiency and unable to meet the needs of large-scale industrial production.

[0006] At present, a variety of process technologies have been developed for iron extraction from red mud, but each has its limitations:

[0007] The magnetic separation method is a relatively direct method. For example, in the invention patent with the patent application number CN202010694246.9 and the name "Method for the comprehensive utilization of red mud by reducing roasting, separating and recovering iron and synchronously activating silicon and aluminum", however, the direct magnetic separation recovery rate of this method is only 25%, the grade of the obtained iron concentrate is ≤60%, and it contains a large amount of Al2O3 impurities, which makes the iron concentrate unable to be directly used for blast furnace smelting, restricting its application value.

[0008] The electric furnace reduction iron extraction process, such as the invention patent with the patent application number CN202411432869.3 and the name "Process for extracting iron from red mud by electric furnace reduction", adds red mud as a dephosphorizer in converter steelmaking, uses Al2O3 and Na2O in red mud to improve the dephosphorization efficiency, and directly reduces high-iron red mud to extract iron by injecting carbon powder into the electric furnace. The recovery rate of metallic iron can reach 80%. However, this process has the problem of high equipment investment, and the slag phase separation is difficult, increasing the production cost and difficulty.

[0009] The electromagnetic magnetization pre-reduction roasting technology, such as the invention patent with the patent application number 202411838921.5 and the name "Method for treating red mud", reduces the smelting temperature through electromagnetic magnetization pre-reduction roasting, combines magnetic separation to enrich iron concentrate powder, the tail slag can be used for building materials, and aluminum can be further extracted from the magnetic separation tailings. However, this technology has a large equipment investment, high process complexity, and is relatively sensitive to fluctuations in the composition of red mud, making it difficult to operate stably in actual production.

[0010] The acid leaching hydrothermal reaction process, such as the invention patent with the patent application number 201810706581.9 and the name "Method for low-cost and high-efficiency separation of iron-containing substances from red mud", pretreats red mud with dilute acid (HCl / H2SO4), combines hydrothermal reaction (150 - 200 °C) and microwave heating, and then recovers iron concentrate through magnetic separation. However, this process has the problems of high acid consumption and energy consumption, the equipment faces a large corrosion risk, and the wastewater treatment cost is also high, resulting in greater environmental protection pressure.

[0011] In summary, the existing iron extraction processes from red mud have deficiencies to varying degrees in terms of recovery rate, energy consumption, continuous production, cost, environmental protection, and process stability. There is an urgent need for a more efficient, energy-saving, environmentally friendly, and stable process for deeply reducing red mud to extract iron. Summary of the Invention

[0012] The present invention proposes a process for extracting iron from deeply reduced red mud and its installation structure, which solves the above problems in the prior art.

[0013] The technical solution of the present invention is realized as follows:

[0014] A process for extracting iron from red mud by deep reduction, comprising the following steps:

[0015] The red mud is formed and dried, and the obtained pellets are mixed with carbon-containing materials to obtain the material to be reduced;

[0016] The material to be reduced is charged into the reduction chamber of a vertical multi-chamber structure, and the material moves downward by gravity. The reduction chambers and heating chambers in the vertical furnace are arranged alternately, and heat is transferred between the reduction chamber and the heating chamber through high-temperature resistant materials, so that the reduction chamber is not in contact with flue gas or air;

[0017] In the heating chamber, gaseous or liquid fuel is burned by a regenerative combustion device, and the generated high-temperature flue gas flows vertically or horizontally and is led out from the side or bottom of the heating chamber, and the flue gas discharge temperature < 160 °C;

[0018] The reduction chamber is divided into a drying section, a preheating section, a reduction section and a cooling section from top to bottom. A reducing gas is introduced into the bottom of the reduction chamber, and the reduction reaction is carried out under a slightly positive pressure of 10 - 500 Pa; A certain amount of reducing gas can be introduced into the bottom of the reduction chamber for deep reduction;

[0019] The reduced material is indirectly cooled in the cooling section and continuously discharged through an airtight discharge valve;

[0020] The reduced pellets are separated by magnetic separation, and the unreacted carbon is recycled.

[0021] Furthermore, the process for extracting iron from red mud by deep reduction according to the present invention further comprises the following steps:

[0022] The reduced pellets are crushed and separated by magnetic separation to obtain iron concentrate powder or molten iron is produced through a smelting and separation process.

[0023] Preferably, the particle size of the pellets is 5 - 30 mm.

[0024] Preferably, the pellets and the carbon-containing materials are mixed in a mass ratio of 1:0.1 - 1:1.

[0025] Preferably, the fuel burned by the regenerative combustion device is gaseous or liquid fuel, and the calorific value is 10.7 - 37 MJ / Nm 3 or 2.1 - 50 MJ / kg.

[0026] Preferably, the reduction chamber is divided into a drying section at 100 - 300 °C, a preheating section at 300 - 700 °C, a reduction section at 700 - 1100 °C and a cooling section at 1100 - 100 °C from top to bottom.

[0027] Preferably, the reducing gas introduced into the bottom of the reduction chamber is CO, H2 or a mixture of both.

[0028] Preferably, the liquid fuel burned by the regenerative combustion device includes heavy oil, diesel oil or micro-nano coal water slurry.

[0029] Preferably, the reduction reaction temperature is 800 - 1200 °C.

[0030] Preferably, the carbon-containing material is one or more of coal, biomass, and industrial carbon-containing solid waste.

[0031] The beneficial effects of the present invention are as follows:

[0032] 1. The heating chamber and the reduction chamber are separated, effectively avoiding the ineffective transfer and dissipation of heat in traditional equipment and improving the heat utilization efficiency;

[0033] 2. During the heating process, a regenerative combustion device is adopted. The heat storage body stores heat during the combustion stage and transfers the stored heat to the combustion-supporting air during the smoke exhaust stage, enabling the combustion-supporting air to be preheated to a relatively high temperature, thus greatly improving the combustion efficiency and reducing fuel consumption;

[0034] 3. The material moves downward by gravity, ensuring the continuity of production and overcoming the deficiencies of existing fixed-bed reactors in continuous production;

[0035] 4. The inside of the reduction chamber is reasonably divided into a drying section, a preheating section, a reduction section, and a cooling section from top to bottom. The sectional design enables the material to undergo more reasonable physical and chemical reactions at different stages; in the preheating section, the material can use the waste heat generated by reduction for preliminary heating, reducing the heat required for subsequent reduction and further reducing energy consumption; in the reduction section, by precisely controlling conditions such as temperature and the concentration of reducing gas, the efficient reduction of iron oxide to elemental iron is achieved; the cooling section cools the reduced product, facilitating subsequent discharging and collection;

[0036] 5. Continuous discharging is carried out through the airtight discharging valve at the bottom of the cooling section, ensuring safety while improving production efficiency and realizing continuous and automated production of the entire reduction process. Description of the Drawings

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0038] Figure 1 It is a flow chart of a process for deeply reducing red mud to extract iron according to the present invention. Detailed Embodiments

[0039] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0040] As Figure 1 shown, a process for extracting iron from deep-reduced red mud according to the present invention includes the following steps:

[0041] Form and dry the red mud to obtain pellets, and mix the pellets with a carbon-containing material to obtain a material to be reduced;

[0042] Load the material to be reduced into the reduction chamber of a vertical multi-chamber structure. The material moves downward by gravity. The reduction chambers and heating chambers in the vertical furnace are arranged alternately. The reduction chambers and heating chambers transfer heat through high-temperature resistant materials, so that the reduction chambers are not in contact with flue gas or air;

[0043] In the heating chamber, burn gaseous or liquid fuel through a regenerative combustion device. The generated high-temperature flue gas flows vertically or horizontally and is led out from the side or bottom of the heating chamber. The flue gas discharge temperature < 160°C;

[0044] The reduction chamber is divided into a drying section, a preheating section, a reduction section, and a cooling section from top to bottom. Introduce a reducing gas into the bottom of the reduction chamber and carry out a reduction reaction under a slightly positive pressure of 10 - 500 Pa;

[0045] The reduced material is indirectly cooled in the cooling section and continuously discharged through an airtight discharge valve;

[0046] Magnetically separate the reduced pellets, and recycle the unreacted carbon.

[0047] Among them, the slightly positive pressure in the reduction chamber is 10 - 500 Pa, specifically, it can be 10 Pa, 50 Pa, 100 Pa, 200 Pa, 300 Pa, 400 Pa, or 500 Pa, etc.; in the present invention, the slightly positive pressure is a key process parameter for the operation of the reduction chamber and has the following functions:

[0048] Maintain a reducing atmosphere and prevent the infiltration of external air: (1) Isolate oxygen to avoid metal oxidation: Reducing gases such as CO and H2 are introduced into the reduction chamber. If it is in a negative pressure or atmospheric pressure environment, external air (containing O2 and H2O) may infiltrate through the furnace body gaps, resulting in the re-oxidation of the reduced metallic iron and reducing the metallization rate and iron recovery rate; (2) Slightly positive pressure makes the pressure inside the furnace slightly higher than the external atmospheric pressure, forming a "pressure barrier" to prevent air from entering, ensuring that the reduction reaction proceeds in an oxygen-free environment and guaranteeing the efficient conversion of Fe2O3 into metallic iron; (3) Stabilize the composition of the reducing gas; Maintaining a slightly positive pressure can prevent external moisture (H2O) from entering the furnace, reduce the interference of the water-gas reaction on the concentration of the reducing gas, ensure the effective partial pressure of reducing agents such as CO and H2, and enhance the reaction rate.

[0049] Promote the uniform distribution of reducing gases and strengthen the gas-solid reaction: (1) Optimize gas flow and material contact: The reducing gas is introduced from the bottom, and the slightly positive pressure pushes the gas to uniformly penetrate the material layer (red mud pellets and carbon-containing materials) from bottom to top, increasing the gas-solid contact area and time, and making the reduction reaction more complete; (2) If the pressure is too low (such as atmospheric pressure), the gas may short-circuit or stagnate, resulting in incomplete local reduction; if the pressure is too high, it may increase the gas compression energy consumption and the requirements for equipment sealing; (3) Suppress harmful side reactions: In a positive pressure environment, reaction products such as CO2 and H2O are discharged in time to avoid their accumulation in the furnace, which may lead to reverse reactions (such as the indirect oxidation of iron), ensuring that the thermodynamic equilibrium shifts towards the direction of generating metallic iron.

[0050] Prevent the intrusion of external impurities and ensure the purity of materials: (1) Isolate pollutants such as dust and moisture: In an industrial environment, external dust (containing impurities such as SiO2 and CaO) or moisture may enter through the furnace body gaps, contaminating the materials or changing the slag phase composition (such as increasing the impurity content of the tail slag); (2) The slightly positive pressure forms an "air curtain" to prevent external pollutants from entering, ensuring the stable content of Al2O3 in the tail slag and meeting the requirements for the raw material purity in the subsequent aluminum extraction process.

[0051] Cooperate with the sealing device to achieve continuous and stable production: (1) Ensure the tightness of the discharging system: An airtight discharging device is adopted at the bottom of the cooling section. The slightly positive pressure and the sealing device work together to avoid gas leakage or external air backflow during discharging, ensuring small pressure fluctuations during continuous feeding of the shaft furnace and maintaining process stability;

[0052] Reduce equipment wear and maintenance costs: The stable slightly positive pressure avoids frequent damage to the seals caused by pressure fluctuations, extends the equipment life, and reduces the maintenance costs in industrial production.

[0053] The existing rotary kiln process: mostly operates under negative pressure, is prone to inhaling air, leading to iron oxidation, and the metallization rate is only 60% - 70%; the present invention has a slightly positive pressure design, precisely isolates oxygen through pressure control, and cooperates with the efficient utilization of reducing gas, raising the metallization rate to > 94%, significantly superior to the prior art.

[0054] The core function of the slightly positive pressure is to create a stable reducing environment through pressure regulation, prevent oxidation, promote reactions, ensure purity, and achieve continuous production. It is the key process parameter for the high metallization rate and low energy consumption (one of the key process parameters of the energy consumption per ton of iron), directly supporting the high efficiency and reliability of the deep reduction of red mud to extract iron.

[0055] For the process of extracting iron from deep-reduced red mud described in the present invention, the heating chamber and the reduction chamber are distributed separately, effectively avoiding the ineffective transfer and dissipation of heat in traditional equipment and improving the heat utilization efficiency.

[0056] During the heating process, a regenerative combustion device is adopted. The heat storage body stores heat during the combustion stage and transfers the stored heat to the combustion-supporting air during the smoke exhaust stage, enabling the combustion-supporting air to be preheated to a relatively high temperature, thus greatly improving the combustion efficiency, reducing fuel consumption, and reducing the energy consumption per ton of iron to 330 kgce.

[0057] The materials move downward by gravity, ensuring the continuity of production and overcoming the deficiencies of existing fixed-bed reactors in continuous production.

[0058] Inside the reduction chamber, it is reasonably divided into a drying section, a preheating section, a reduction section, and a cooling section from top to bottom. The sectional design enables the materials to undergo more reasonable physical and chemical reactions at different stages; in the preheating section, the materials can use the waste heat generated by reduction for preliminary heating, reducing the heat required for subsequent reduction and further reducing energy consumption; in the reduction section, through precise control of conditions such as temperature and reducing gas concentration, the efficient reduction of iron oxide to elemental iron is achieved; the cooling section cools the reduced products, facilitating subsequent discharging and collection.

[0059] Continuous discharging through an airtight discharging valve further improves production efficiency and realizes continuous and automated production of the entire reduction process.

[0060] Among them, the process of extracting iron from deep-reduced red mud described in the present invention further includes the following steps:

[0061] The reduced pellets are separated by crushing and magnetic separation to obtain iron concentrate powder or molten iron is produced through smelting and separation processes. At the same time, the purity of the reduced iron concentrate powder or molten iron is greater than TFe95%.

[0062] Among them, the pellets and carbon-containing materials are mixed at a mass ratio of 1:0.1 to 1:1, specifically, it can be 1:0.2, 1:0.4, 1:0.5, 1:0.7, 1:0.9 or 1:1, which can achieve the best balance of cost, efficiency and stability while ensuring the sufficiency of the reduction reaction: this ratio range corresponds to a carbon-iron molar ratio of 0.8 to 2.0:1, which can not only ensure sufficient reduction gases such as CO and H2, promote the efficient conversion of Fe2O3 and make the metallization rate > 94%, but also avoid the waste of reducing agent caused by excessive carbon (reducing carbon consumption by 30% compared with the traditional process); from the perspective of economy and adaptability, this ratio is compatible with coal with a fixed carbon content of 40% - 60%, biomass with a fixed carbon content of 12% - 30% and industrial carbon-containing solid waste. By adjusting the ratio, the cost of the reducing agent can be reduced by 40% - 60% compared with using coke; from the perspective of process synergy, the uniformly mixed materials form a reduction reaction gradient in the shaft furnace, that is, the volatile matter is removed in the preheating section, the carbothermal reaction occurs in the reduction section, and the temperature is reduced in the cooling section. The unreacted carbon can be recycled after magnetic separation, and the recovery rate > 90%. This ratio design takes into account the thermodynamic requirements of the reduction reaction, the economy of the reducing agent and the anti-fluctuation ability of the process, and is one of the key control parameters to achieve "the energy consumption per ton of iron < 330 kgce and the reduction of red mud > 60%".

[0063] Among them, the gas or liquid fuel burned by the regenerative combustion device has a calorific value of 10.7 - 37 MJ / Nm 3 or 2.1 - 50 MJ / kg, which can achieve multiple advantages in terms of fuel adaptability, thermal efficiency improvement and cost control: from the perspective of fuel compatibility, this calorific value range covers coal (calorific value about 12 - 29 MJ / kg), biomass (such as wood chips, calorific value about 12 - 19 MJ / kg), industrial waste liquid (such as waste oil, calorific value about 33 - 38 MJ / kg) and traditional fuels (such as natural gas, calorific value about 36 MJ / kg). It can utilize cheap industrial solid waste or low-grade fuels (the cost is reduced by 30 - 50% compared with high-quality fuels). At the same time, the combustion efficiency of low-calorific value fuels can be increased to more than 99% through regenerators, avoiding problems such as incomplete combustion caused by too low calorific value, such as black smoke emission and insufficient heat; from the perspective of thermal efficiency and energy consumption, the regenerative device recovers the waste heat of the flue gas to preheat the combustion-supporting air to 1000°C. Even when using low-calorific value fuels, the temperature requirement of 1000 - 1100°C in the reduction section can be met through the full utilization of heat, and the energy consumption per ton of iron is reduced by more than 50% compared with the rotary kiln process (to below 330 kgce).

[0064] Among them, the reduction chamber is divided into a drying section at 100 - 300°C, a preheating section at 300 - 700°C, a reduction section at 700 - 1100°C and a cooling section at 1100 - 100°C from top to bottom.

[0065] The drying section is located at the top of the reduction chamber. During the falling process, the materials to be reduced are further dried by the high-temperature reducing gas rising from the reduction section. The preheating section exchanges heat with the high-temperature reducing gas rising from the reduction section and is preheated. The drying section and the preheating section recover the heat of the high-temperature reducing gas, reducing the waste of heat brought out by the reducing gas. The height design of the preheating section needs to be optimized according to the material characteristics and processing capacity to ensure that the material can be fully preheated to the appropriate temperature, which can generally raise the material temperature to 500-700℃.

[0066] The reduction section is located in the middle and lower part of the furnace body and is the key area for the reduction of ferric oxide. In this area, the carbon-containing material and the reducing gas hydrogen, carbon monoxide or a mixture of the two gases introduced from the bottom react with the preheated material to be reduced at high temperature to reduce ferric oxide to elemental iron.

[0067] The cooling section is located at the bottom of the reduction chamber, where the product after roasting and reduction is cooled. The cooling section uses indirect cooling to cool the product.

[0068] The reducing gas introduced into the bottom of the reduction chamber is CO, H2 or a mixture of the two. The gas flow rate is adjusted according to the metallization rate of ferric oxide.

[0069] Among them, the liquid fuel burned by the heat storage combustion device includes heavy oil, diesel or micro-nano water-coal slurry.

[0070] The temperature of the reduction section is strictly controlled at 800-1100°C, which can ensure high reduction efficiency and metallization rate, and achieve an optimal balance between reaction efficiency, energy consumption and process stability in the process of iron extraction from red mud: this temperature range covers the thermodynamic window for efficient reaction of ferric oxide with reducing gases such as carbon, carbon monoxide and hydrogen, ensuring that Fe2O3 is quickly converted into metallic iron with a metallization rate of >94%, while avoiding slagging and material discharge difficulties in the furnace due to excessively high temperatures such as exceeding 1100°C; the temperature range of 800-1100°C is suitable for cheap carbon-containing materials such as coal and biomass. The reduction characteristics, combined with the waste heat recovery technology of the regenerative combustion device, reduce the energy consumption per ton of iron to below 330kgce, which is significantly lower than traditional processes such as rotary kilns; the temperature is greater than 800℃ to ensure the necessary reduction speed, and the upper limit of 1100℃ avoids the melting and agglomeration of impurities in the red mud, maintains the stable permeability of the materials in the furnace, and ensures that the gas-solid reaction proceeds evenly; in addition, this temperature range is compatible with the segmented control of the vertical furnace reduction section, so that the materials are fully dehydrated in the preheating section, efficiently react in the reduction section, and have a cooling effect in the cooling section, ultimately ensuring that the metallization rate is greater than 94%, creating ideal conditions for subsequent magnetic separation and tailings resource utilization. This temperature design shows significant advantages in energy saving, high efficiency, and stability by accurately matching the reduction reaction kinetics and thermodynamic requirements, and is one of the core control parameters of the red mud deep reduction iron extraction process.

[0071] Among them, the carbon-containing material is one or more of coal, biomass, and industrial carbon-containing solid waste, with a fixed carbon content ≥ 15% and a particle size of 5 - 20 mm. In the process for extracting iron from deeply reduced red mud of the present invention, coke is not used, but one or more of coal, biomass, and industrial carbon-containing solid waste are used, which is low-cost and environmentally friendly.

[0072] Among them, between the reduction chamber and the heating chamber, there is a high-temperature resistant heat-conducting material, such as high-aluminum refractory bricks with Al2O3 ≥ 65% and a thermal conductivity of the high-aluminum refractory bricks > 1.0 W / (m·K).

[0073] Among them, the regenerative combustion device includes a ceramic regenerator with a heat exchange efficiency ≥ 90%. The regenerative combustion device is a key part to achieve efficient combustion and energy conservation. There is a regenerator inside the regenerative combustion device, which is usually made of a ceramic material with high temperature resistance and good heat storage performance. During the combustion process, when the high-temperature flue gas is discharged, a large amount of heat carried by it is absorbed and stored by the regenerator. When the combustion-supporting air enters, the regenerator transfers the stored heat to the combustion-supporting air, so that the combustion-supporting air can be preheated to a high temperature above 1000°C. Such high-temperature combustion-supporting air enters the heating chamber to participate in combustion, which can greatly improve the combustion efficiency and reduce fuel consumption. For example, in the traditional combustion mode, more natural gas and other fuels need to be consumed to reach a certain temperature, while after using this regenerative combustion device, the fuel consumption can be significantly reduced. At the same time, the regenerative combustion device is connected to the heating chamber through a reasonable pipeline layout to ensure that the combustion-supporting air and fuel can enter the heating chamber evenly and stably.

[0074] Example 1:

[0075] The red mud is formed and dried. The pellet has a particle size of 5 mm. The prepared pellet and the carbon-containing material are mixed at a mass ratio of 1:0.2 to obtain the material to be reduced;

[0076] The material to be reduced is loaded into the reduction chamber of a vertical multi-chamber structure shaft furnace. The material moves downward by gravity. In the shaft furnace, the reduction chamber and the heating chamber are arranged alternately. The reduction chamber and the heating chamber transfer heat through a high-temperature resistant material, so that the reduction chamber is not in contact with flue gas or air;

[0077] In the heating chamber, through the regenerative combustion device, a gaseous fuel with a calorific value of 8.4 MJ / Nm 3 is burned. The generated high-temperature flue gas flows vertically or horizontally and is led out from the side or bottom of the heating chamber. The flue gas emission temperature < 160°C;

[0078] The reduction chamber is divided into a drying section at 300°C, a preheating section at 700°C, a reduction section at 1100°C, and a cooling section at 100°C from top to bottom. A reducing gas H2 is introduced into the bottom of the reduction chamber, and the reduction reaction is carried out under a slightly positive pressure of 100 Pa;

[0079] After the reduced material is cooled by the jacket water in the cooling section, it is continuously discharged through the airtight discharging device;

[0080] The reduced pellets are separated by magnetic separation, and the unreacted carbon is recycled;

[0081] The reduced pellets are separated by crushing and magnetic separation to obtain iron powder or molten iron is produced through the smelting and separation process. The magnetic separation tailings or the smelting and separation tailings are fully recycled as raw materials for extracting Al2O3.

[0082] Example 2:

[0083] The red mud pellets are dried. The particle size of the pellets is 30 mm, and the compressive strength of the pellets is ≥1 kN. The prepared pellets are mixed with the carbon-containing material in a mass ratio of 1:0.6 to obtain the material to be reduced;

[0084] The material to be reduced is loaded into the reduction chamber of the vertical multi-chamber structure shaft furnace. The material moves downward by gravity. In the shaft furnace, the reduction chambers and the heating chambers are arranged alternately. The reduction chambers and the heating chambers are separated by high-temperature resistant materials so that the reduction chambers are not in contact with flue gas or air;

[0085] In the heating chamber, a gas with a calorific value of 3.3 MJ / kg is burned through a regenerative combustion device. The generated high-temperature flue gas flows vertically or horizontally and is led out from the side or bottom of the heating chamber. The flue gas discharge temperature <160 °C;

[0086] The reduction chamber is divided into a drying section at 300 °C, a preheating section at 600 °C, a reduction section at 1000 °C, and a cooling section at 150 °C from top to bottom. Reduction gas CO is introduced into the bottom of the reduction chamber, and the reduction reaction is carried out under a slightly positive pressure of 500 Pa;

[0087] After the reduced material is cooled by the jacket water in the cooling section, it is continuously discharged through the airtight discharge valve;

[0088] The reduced pellets are separated by magnetic separation, and the unreacted carbon is recycled;

[0089] The reduced pellets are separated by crushing and magnetic separation to obtain iron concentrate powder or molten iron is produced through smelting and separation.

[0090] Comparative example:

[0091] The red mud pellets are dried. The particle size of the pellets is 5 mm. The prepared pellets are mixed with coal in a mass ratio of 1:1 to obtain the material to be reduced;

[0092] The material to be reduced is loaded into the rotary kiln, and reduction roasting is carried out at 1200 °C. The material to be reduced stays in the rotary kiln for 6 hours, the temperature out of the kiln is 1000 °C, then it is cooled down to below 70 °C, and then sent to the magnetic separation process.

[0093] The technical effects of the examples and the comparative example are as follows in the table:

[0094] Example 1 Example 2 Comparative example Metallization rate 96.2％ 95.8％ 90％ Energy consumption per ton of iron (kgce) 310 329 800

[0095] In the process for extracting iron from deeply reduced red mud according to the present invention, the metallization rate of Fe2O3 is greater than 94%, the extraction rate of iron is greater than 95%, and the reduction of red mud is greater than 60%; the thermal efficiency > 80%, and the energy consumption per ton of iron is less than 330 kgce; and it can be produced on a large scale, realizing the full recycling of solid waste.

[0096] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A process for extracting iron from red mud by deep reduction, characterized in that, It includes the following steps: The red mud is formed and dried, and the obtained pellets are mixed with carbon-containing materials to obtain the material to be reduced; The material to be reduced is loaded into the reduction chamber of a vertical multi-chamber structure, and the material moves downward by gravity. The reduction chambers and heating chambers in the shaft furnace are arranged alternately. Heat is transferred between the reduction chamber and the heating chamber through high-temperature resistant materials, so that the reduction chamber is not in contact with flue gas or air; In the heating chamber, gas or liquid fuel is burned through a regenerative combustion device, and the generated high-temperature flue gas flows vertically or horizontally and is led out from the side or bottom of the heating chamber. The flue gas discharge temperature < 160°C; The reduction chamber is divided into a drying section, a preheating section, a reduction section and a cooling section from top to bottom. A reducing gas is introduced into the bottom of the reduction chamber, and the reduction reaction is carried out under a slightly positive pressure of 10 - 500 Pa; The reduced material is indirectly cooled in the cooling section and continuously discharged through an airtight discharge valve; The reduced pellets are separated by magnetic separation, and the unreacted carbon is recycled; 2. The process for extracting iron from red mud by deep reduction according to claim 1, characterized in that It also includes the following steps: The reduced pellets are separated by crushing and magnetic separation to obtain iron concentrate powder or molten iron is produced through a smelting and separation process; 3. The process for extracting iron from red mud by deep reduction according to claim 1, characterized in that, The particle size of the pellets is 5 - 30 mm; 4. The process for extracting iron from red mud by deep reduction according to claim 1, characterized in that, The pellets and the carbon-containing materials are mixed at a mass ratio of 1:0.1 - 1:1; 5. The process for extracting iron from red mud by deep reduction according to claim 1, characterized in that, The fuel burned by the regenerative combustion device is gaseous or liquid fuel, with a calorific value of 10.7 - 37 MJ / Nm 3 or 2.1 - 50 MJ / kg.

6. The process for extracting iron from red mud by deep reduction according to claim 1, wherein The reduction chamber is divided into a drying section at 100 - 300°C, a preheating section at 300 - 700°C, a reduction section at 700 - 1100°C and a cooling section at 1100 - 100°C from top to bottom; 7. The process for extracting iron from red mud by deep reduction according to claim 1, characterized in that, The reducing gas introduced into the bottom of the reduction chamber is CO, H2 or a mixture of both; 8. The process for extracting iron from red mud by deep reduction according to claim 1, characterized in that The liquid fuel burned by the regenerative combustion device includes heavy oil, diesel or micro-nano coal water slurry; 9. The process for extracting iron from red mud by deep reduction according to claim 1, characterized in that, The reduction reaction temperature is 800 - 1200°C; 10. The process for extracting iron from red mud by deep reduction according to claim 1, characterized in that, The carbon-containing material is one or more of coal, biomass, and industrial carbon-containing solid waste.

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