A process for treating alumina red mud using a cement rotary kiln

Abstract

This invention relates to the fields of industrial solid waste resource utilization and metallurgical technology, specifically disclosing a process for treating alumina red mud using a cement rotary kiln. The process includes the following steps: red mud pretreatment, cement rotary kiln modification and calcination, calcination product cooling, and multi-resource separation and extraction. By specifically modifying the cement rotary kiln structure, precisely controlling the atmosphere, and providing a complete process, the process achieves the resource utilization of high-speed rail red mud. Compared with existing red mud treatment and resource utilization technologies, this method has breakthrough advantages in solid waste treatment, resource recovery, cost and energy consumption, environmental protection and emission reduction, and industrial application.

Description

Technical Field

[0001] This invention belongs to the field of industrial solid waste resource utilization and metallurgical technology, specifically relating to a process method for treating alumina red mud using a cement rotary kiln. Background Technology

[0002] Red mud is a typical bulk industrial solid waste generated during alumina production. my country's alumina industry discharges over 100 million tons of red mud annually, with a cumulative stockpile exceeding 600 million tons. The large-scale stockpiling of red mud not only occupies significant land resources, but its alkaline soluble substances are also easily leached and seeped in by rainwater, causing a series of ecological and environmental problems such as soil salinization and groundwater pollution, becoming a key bottleneck restricting the green and low-carbon development of the alumina industry. High-iron red mud, in particular, has a total iron (TFe) content of 20%–60% and an alumina (Al2O3) content of 20%–30%, and is also associated with valuable elements such as titanium and sodium, possessing extremely high resource utilization value. However, its valuable resources have long been inefficiently recovered, resulting in serious resource waste, and there is an urgent need to develop large-scale, high-value-added resource disposal technologies.

[0003] Currently, there is a great deal of research both domestically and internationally on the resource utilization of high-speed railway red mud and related processes for direct iron reduction. However, existing technologies and related patent solutions all have obvious technical defects and application limitations, and a mature technology system that can be industrialized and promoted on a large scale has not yet been formed. They cannot simultaneously meet the industrialization needs of solid waste co-processing, efficient resource recovery, energy saving and cost reduction, and environmental protection and emission reduction. The specific problems are as follows:

[0004] The co-processing capacity of solid waste is weak and the range of raw material compatibility is narrow: Existing related patents, such as CN120505469A, can only process solid waste that is a combination of red mud and secondary aluminum ash. Some patents are only designed for single solid wastes such as metallurgical dust, iron ore or tailings. They cannot achieve co-processing of high-iron red mud and dust-like solid wastes from the entire metallurgical process. In addition, they have poor compatibility with raw material composition and it is difficult to process high-iron red mud with TFe≥30% and Al2O3≥20% on a large scale. The comprehensive utilization rate of solid waste is low.

[0005] Low resource recovery efficiency and insufficient product added value: Most red mud treatment patents, such as CN118460809A, can only recover iron from red mud and produce iron briquettes as a single product. They cannot achieve the extraction of all components, including iron, aluminum, titanium, and alkali. Moreover, the iron resource recovery efficiency and product grade are low. At the same time, valuable elements such as aluminum, titanium, and sodium in red mud are not effectively recovered, resulting in insufficient resource utilization and product added value that is far from meeting industrialization expectations.

[0006] High equipment and energy costs hinder industrialization and economic viability: For example, the plasma torch hydrogen reduction process used in patent CN117337336A requires large equipment investment and high operating energy consumption; some technologies also require the construction of new dedicated reduction kilns, failing to leverage the thermal advantages of existing mature industrial equipment, resulting in high equipment investment costs. At the same time, the lack of energy-saving designs such as flue gas waste heat recovery and CO2 recycling leads to high energy consumption per ton of product, which restricts the industrialization of the technology.

[0007] The lack of environmental protection and emission reduction design leads to a high risk of secondary pollution: Some patents, such as CN118910350A, only focus on improving the metallization rate of iron, neglecting the removal of impurities such as sulfur and phosphorus, resulting in insufficient control of pollutant emissions during the production process; the hydrogen reduction process used in patent CN117377779A has a large carbon emission and has not been designed for low carbonization; and the traditional method of co-processing red mud in cement kilns carries the risk of alkali discharge due to the loss of sodium-based substances, and the CO2 in the flue gas is not effectively utilized, which can easily cause secondary ecological and environmental problems.

[0008] Poor industrial adaptability and insufficient scale and stability of treatment: Existing red mud treatment technologies mostly use equipment such as electric rotary kilns and fluidized beds. The former requires a large-capacity power station, while the latter is prone to adhesion and flow loss problems, both of which have technical pain points for industrial operation. Conventional cement rotary kilns lack targeted structural modifications, atmosphere control, and sorting process designs for red mud treatment, making it impossible to achieve efficient resource utilization of red mud and difficult to form a large-scale treatment capacity, which is far from meeting the daily red mud treatment needs of thousands of tons in industrial production.

[0009] As a mature thermal equipment in industrial production, cement rotary kilns have inherent advantages such as large processing capacity, high thermal efficiency, mature industrial application, and strong operational stability. If targeted structural modifications, precise atmosphere control, and supporting process design can be implemented to break through the bottlenecks in the existing technology for red mud treatment, it is expected to realize the large-scale, high-value-added resource utilization of high-speed railway red mud.

[0010] Based on this, the present invention leverages the equipment advantages of cement rotary kilns to develop a targeted modification and process method to solve many defects in existing technologies. Summary of the Invention

[0011] The purpose of this invention is to provide a process for treating alumina red mud using a cement rotary kiln, so as to solve the problems mentioned in the background art.

[0012] To achieve the above objectives, the present invention provides the following technical solution:

[0013] A process for treating alumina red mud using a cement rotary kiln includes the following steps:

[0014] S1. Red mud pretreatment: Select high-iron red mud with a total iron (TFe) content ≥30% and an alumina content ≥20%, mix it with sodium-based additives and reducing agents at a mass ratio of 78.3~87:9~10:3, and then dry, crush and screen it to obtain pretreated material with a moisture content ≤10% and a particle size ≤5mm. The total amount of additives added is 20%~30% of the red mud mass.

[0015] S2. Cement Rotary Kiln Modification and Calcination: The structure and supporting systems of the cement rotary kiln are modified, while the pulverized coal injection system at the kiln tail is retained. By adjusting the pulverized coal injection rate and combustion air volume, a reducing atmosphere is maintained in the area above 750°C in the rear half of the kiln, and an oxidizing atmosphere is maintained in the area below 750°C in the front half of the kiln. The pretreated material from step S1 is fed into the modified cement rotary kiln and calcined at 900~1200°C for 45~60 minutes.

[0016] S3. Cooling of calcined products: The sintered products are cooled to room temperature by a circulating water quenching system.

[0017] S4. Multi-resource separation and extraction:

[0018] S41. The cooled product is processed to 350 mesh by a wet mill and then magnetically separated under a magnetic field of 3500~4500 Gauss to obtain metallic iron powder with a grade of ≥90%.

[0019] S42. When the concentration of sodium aluminate solution in the magnetic separation circulating water is close to saturation, CO2 in the purified flue gas is introduced to carry out carbonization reaction. The reaction product is separated into solid and liquid by thickener and filter press to obtain crude corundum raw material. The crude product is dried to obtain corundum raw material product.

[0020] S43. The filtrate after solid-liquid separation in S42 is purified, concentrated, and crystallized to obtain sodium carbonate product;

[0021] S44. Titanium concentrate powder is obtained by gravity separation of magnetic separation tailings, wherein the TiO2 content is ≥45%;

[0022] S45. The flue gas generated by the cement rotary kiln is used for power generation by the waste heat boiler, and then purified by the desulfurization, denitrification and dust removal system. The separated CO2 is used for the carbonization reaction of S42, and the remaining flue gas is discharged.

[0023] Preferably, the modification of the cement rotary kiln in step S2 includes the following: modifying the first 6-8 meters of the kiln body at the feed end into a three-lobe structure; dismantling or modifying the decomposition furnace and cyclone preheater into a flue, with pretreated materials being conveyed into the kiln from the bottom of the C5 preheater; dismantling the original cooling grate cooler and replacing it with a circulating water quench system; and equipping it with a wet process tower mill, magnetic separation system, carbonization reactor, and flue gas combustion power generation system.

[0024] Preferably, the reducing agent is one or more of lignite, coke powder, or biomass fuel; and the sodium-based additive is at least one of sodium carbonate and sodium hydroxide.

[0025] The cement rotary kiln selected is a type with a daily cement clinker production capacity of 4,000 tons or more. After modification with this process, its daily high-iron red mud processing capacity is ≥6,000 tons. For cement clinker rotary kilns with different production capacities below 4,000 tons per day, the daily high-iron red mud processing capacity after modification with this process is 1.5 times its original daily cement clinker production capacity. For non-cement calcining / roasting rotary kilns, after modification according to the kiln structure and supporting system modification plan of this process, they are used for high-iron red mud processing in this process, and the processing efficiency is consistent with the matching principle of the modified cement rotary kiln's production capacity.

[0026] Preferably, in step S4, the iron recovery rate is ≥88%, the aluminum recovery rate is ≥88%, the titanium recovery rate is ≥84%, and the sodium recovery rate is ≥93%; the purity of the corundum raw material product is ≥89%, the grade of the sodium carbonate product is ≥94.6%, and the TiO2 content in the titanium concentrate powder is ≥45.8%.

[0027] Preferably, in step S2, the material filling rate in the cement rotary kiln is above 17%, and the kiln rotation speed is controlled at 1.45~1.5 r / min.

[0028] Preferably, in step S2, the flue gas gas power generation system and the existing waste heat power generation system of the cement plant operate in parallel, the existing flue gas purification system of the cement plant is reused, and the newly added desulfurization and denitrification device adopts the SCR process.

[0029] Preferably, 5% to 10% of metallurgical dust and sludge are added to the pretreated material in step S1. The metallurgical dust and sludge is one or more of the dust and slurry solid wastes collected by the dust removal system of each process in the entire metallurgical production process, including sintering, blast furnace, steelmaking, steel rolling and other processes.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] This invention discloses a process for treating alumina red mud using a cement rotary kiln. Through targeted structural modifications to the cement rotary kiln, precise atmosphere control, and a complete process system, it achieves the resource utilization of high-speed rail red mud. Compared with existing red mud treatment and resource utilization technologies, it has breakthrough advantages in solid waste treatment, resource recovery, cost and energy consumption, environmental protection and emission reduction, and industrial application, as detailed below:

[0032] This process can efficiently treat high-iron red mud with a total iron (TFe) content of ≥30% and an alumina (Al2O3) content of ≥20%. Furthermore, 5% to 10% metallurgical dust can be added to the pretreated material, enabling the co-treatment of high-iron red mud with dust and sludge solid waste from the entire metallurgical process, including sintering, blast furnace, and steelmaking. This process overcomes the limitations of existing technologies that can only treat red mud, metallurgical dust, or iron ore tailings. The comprehensive utilization rate of solid waste reaches 100%, making it suitable for the actual needs of simultaneous treatment of multiple solid wastes in industrial production.

[0033] This process achieves efficient recovery of all valuable elements such as iron, aluminum, titanium, and sodium from red mud, with an iron recovery rate of ≥88%, a metallic iron powder grade of ≥90%, a titanium recovery rate of ≥84%, a TiO2 content in titanium concentrate of ≥45.8%, an aluminum recovery rate of ≥88%, a corundum raw material purity of ≥89%, a sodium recovery rate of ≥93%, and a sodium carbonate product grade of ≥94.6%. Compared with existing technologies that can only produce iron briquettes, this process increases the added value of resources by more than 40%, while producing a variety of high-value-added products such as high-grade metallic iron powder, corundum raw materials, titanium concentrate, and sodium carbonate, thus maximizing the utilization of red mud resources.

[0034] This process relies on the existing mature cement rotary kiln for targeted modification, eliminating the need to build a new dedicated reduction kiln and reducing equipment investment costs by 30%-50%. Simultaneously, it is equipped with a flue gas gas power generation system that operates in parallel with the existing waste heat power generation system, realizing secondary power generation from flue gas waste heat. Furthermore, it utilizes CO2 in the purified flue gas to complete the carbonization reaction, achieving CO2 self-circulation. The energy consumption per ton of product is reduced by 25% compared to traditional coal-based direct reduction technology and by more than 60% compared to plasma torch hydrogen reduction technology, significantly reducing the production and operation costs of red mud resource utilization.

[0035] This process achieves highly efficient removal of impurities and pollutants during resource recovery, with sulfur removal rates ≥95% and phosphorus removal rates ≥87%. After purification by the desulfurization, denitrification, and dust removal system, the pollutant emission concentration of the cement rotary kiln flue gas is far below the national emission standards. The efficient recovery of sodium resources is achieved through the recycling of sodium-based additives, reducing the risk of alkaline discharge by 80% compared to the traditional cement kiln co-processing of red mud. At the same time, the CO2 conversion rate in the carbonization reaction is ≥90%, achieving CO2 solidification and utilization, reducing carbon emissions by 70% compared to the hydrogen reduction process. This reduces secondary pollution in the red mud treatment process from the source, achieving the dual benefits of solid waste disposal and low-carbon emission reduction.

[0036] This process develops a standardized retrofit plan for cement rotary kilns. After retrofitting, rotary kilns with a daily cement clinker production capacity of over 4,000 tons can process red mud at a capacity of ≥6,000 tons per day. For other cement rotary kilns, the processing capacity after retrofitting is 1.5 times the original cement production capacity. Furthermore, non-cement calcining / roasting rotary kilns can also be retrofitted and applied according to this plan, with a processing scale far exceeding 1 million tons / year, meeting the needs of large-scale industrial production. After retrofitting, the inherent advantage of cement rotary kilns with a thermal efficiency of ≥75% is retained, while avoiding the industrial pain points of electric rotary kilns, such as the need for large-capacity power stations and the tendency of fluidized beds to stick and lose flow. At the same time, the entire process and equipment are designed based on mature industrial technologies, with strong operational stability, making it easy to promote and apply in the alumina, cement, and metallurgical industries.

[0037] This process establishes a system in which calcined products are rapidly cooled, ground, and magnetically separated to achieve slag-iron separation. Magnetic separation circulating water enables the liquid-phase extraction of aluminum and sodium resources. The flue gas serves both as waste heat power generation and as a CO2 feedstock for the carbonization reaction. No excess waste residue, wastewater, or waste gas is generated, achieving dual recycling of energy and resources, which aligns with the industrial development concepts of green, low-carbon, and circular economy. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] The following describes the specific implementation of the present invention in further detail with reference to the experimental raw materials of high-speed rail red mud and the process parameters of cement rotary kiln modification. The scope of protection of the present invention is not limited to the specific embodiments. All embodiments are based on the modification of a Φ4.8×72m cement clinker rotary kiln. The core product is metallic iron powder with a grade of ≥90%. After the modification, the daily red mud processing capacity reaches more than 6,000 tons.

[0041] Example 1

[0042] Using high-iron red mud from an aluminum company as raw material, the main chemical composition of the raw ore is: Fe2O3 = 60.01% (equivalent to TFe≈42%), Al2O3 = 19.8%, TiO2 = 3.55%, Na2O = 2.03%, SiO2 = 4.7%, P = 0.040%. An experiment was conducted on the separation process in a cement rotary kiln sintering process. The specific steps are as follows:

[0043] Red mud pretreatment: The high-iron red mud is mixed with sodium-based additives (sodium carbonate purity 98%) and lignite reducing agent (fixed carbon 65%, particle size ≤3mm) at a dry basis mass ratio of 87:10:3. The mixture is then continuously dried at 120℃ using a hot air dryer until the moisture content reaches 8%. After primary crushing by a jaw crusher and secondary crushing by a cone crusher, the material is sieved through a 10-mesh vibrating screen to a particle size ≤5mm to obtain the pretreated material. A total of 6500 tons of this pretreated material (including 6000 tons of red mud and 500 tons of additives) is processed daily. The mixing equipment uses a twin-shaft mixer with a mixing speed of 35 r / min and a mixing time of 18 min, achieving a material mixing uniformity ≥95%.

[0044] Cement rotary kiln modification and calcination: The first 7 meters of the Φ4.8×72m cement clinker rotary kiln were modified into a three-blade structure (blade angle 120°, blade height 1 / 4 of the kiln's inner diameter). The decomposition furnace and cyclone preheater were removed and replaced with equal-diameter flues. Pretreated materials were continuously fed from the bottom of the C5 preheater at a rate of 55t / h via a quantitative screw conveyor. The kiln tail pulverized coal injection system was retained, and the pulverized coal injection rate was adjusted to 37.5t / h to ensure that the atmosphere at 750℃ in the rear half of the kiln was zero, and the oxygen content in the area above 750℃ was ≤0.5% for a reducing atmosphere; the oxygen content in the area below 750℃ in the rear half of the kiln was ≥10% for an oxidizing atmosphere. The kiln rotation speed was 1.5r / min, the material filling rate in the kiln was 18%, the sintering temperature in the kiln was 950℃~980℃, the total material residence time was 50 minutes, and the flue gas emission was 120,000 Nm³ / h.

[0045] After the sintered product is discharged from the kiln tail, it is sent to the circulating water quenching system (circulating water flow rate 90m³ / h, cooling rate 120℃ / min) to cool to room temperature. The bulk density of the product after cooling is 1.8t / m³.

[0046] Separation and extraction of iron, aluminum, silicon, alkali, and titanium:

[0047] (1) The cooled product is fed into a wet mill and ground to 350 mesh (residue rate ≤1%) with water at a solid-liquid ratio of 1:2.5. The ground slurry is then fed into a permanent magnet drum separator and magnetically separated under a magnetic field of 3500-4500 Gauss to obtain metallic iron powder with a grade of 91.3% and an iron recovery rate of 89.5%.

[0048] (2) The magnetic separation circulating water is collected in the storage tank. When the concentration of sodium aluminate solution in the tank reaches 190 g / L (close to saturation), it is sent to the bubble carbonization reactor (effective volume 50 m³) at a rate of 40 m³ / h by a centrifugal pump. At normal temperature and pressure, CO2 with a purity ≥90% in the purified flue gas is introduced at a rate of 0.8 m³ / h. The carbonization reaction time is 75 min, and the pH value at the end of the reaction is controlled at 8.5-9.0. The reaction product is first sent to a high-efficiency thickener to concentrate to a solid content of 35% (underflow concentration), and then sent to a plate and frame filter press to filter under a pressure of 0.4 MPa to obtain a crude corundum raw material. The crude product is dried in a hot air dryer at 108℃ for 3 h until the moisture content is ≤0.5% to obtain the corundum raw material product. The aluminum recovery rate is 89.3%, the silicon recovery rate is 84.3%, and the purity of the corundum raw material product is 89.2%.

[0049] (3) The filtrate after the above pressure filtration is a crude sodium carbonate solution. It is first filtered through a precision filter (filtration accuracy 5μm) to remove suspended impurities, and then sent to a vacuum concentration tank. It is concentrated to a sodium carbonate concentration of 300g / L under a vacuum of -0.085MPa and a temperature of 65℃. Then it is sent to a cooling crystallizer and cooled to 28℃ for crystallization at a cooling rate of 6℃ / h. After crystallization, it is separated by centrifugation (speed 3000r / min) and dried by hot air (80℃, 2h) to obtain sodium carbonate product with a grade of 94.8% and a sodium recovery rate of 93.7%.

[0050] (4) After magnetic separation, the tailings are subjected to gravity separation and dewatering to obtain titanium concentrate powder, in which the titanium dioxide content is 46.3%, the titanium recovery rate is 85.2%, and the tailings treatment volume is 1800t / d;

[0051] (5) Waste heat recovery system: In addition to the existing waste heat power generation boiler system, a dual-pressure waste heat boiler (evaporation capacity 25t / h) waste heat power generation system is added. The temperature of the flue gas drops to 380℃ after passing through the waste heat boiler. Dust removal of the flue gas adopts bag filter (outlet particulate matter ≤10mg / Nm³), desulfurization adopts wet limestone-gypsum method (SO2≤50mg / Nm³), and denitrification adopts SCR process (reaction temperature 320℃, vanadium-titanium catalyst, NOx≤100mg / Nm³). The existing flue gas purification system is reused. After purification, CO2 in the flue gas is separated and extracted by membrane separation device (purity ≥90%) for carbonization reaction. The CO2 separation and recovery rate is 92%.

[0052] Overall process indicators: Total iron recovery rate of 89.5%, comprehensive grade of metallic iron powder ≥91%; Ti recovery rate of 85.2%, aluminum recovery rate of 89.3%, silicon recovery rate of 84.3%; significant impurity removal effect, S removal rate of 95.38%, P removal rate of 87.50%; daily processing capacity of 6,000 tons of red mud, daily production of approximately 2,478 tons of metallic iron powder with a grade of ≥91%, 1,333 tons of corundum raw materials, 390 tons of titanium concentrate powder, 1,100 tons of sodium carbonate, and 360,000 kWh of waste heat from flue gas power generation (approximately 130 million kWh of electricity generation per year). The total water consumption is 3.5 t / t of red mud, and the electricity consumption is 85 kWh / t of red mud.

[0053] Example 2

[0054] Using a certain high-speed iron red mud (TFe=52.3%, Al2O3=16.5%, TiO2=4.2%, SiO2=3.89%, P=0.035%) as raw material, a large-scale process test of cement rotary kiln was carried out. The specific steps are as follows:

[0055] Red mud pretreatment: The high-iron red mud is mixed evenly with sodium-based additives (sodium hydroxide purity 99% + sodium carbonate purity 98%, mass ratio 1:1) and lignite reducing agent (fixed carbon 68%, particle size ≤3mm) at a dry basis mass ratio of 87:10:3. The mixture is then dried to a moisture content of 8% using a drum dryer at 120℃. After crushing by a jaw crusher and impact crusher, the material is sieved through a 10-mesh vibrating screen to a particle size ≤5mm to obtain the pretreated material. A total of 6500 tons of this pretreated material (including 6000 tons of red mud + 500 tons of additives) is processed daily. The mixing speed of the twin-shaft mixer is 38 r / min, and the mixing time is 16 min, achieving a material mixing uniformity ≥96%.

[0056] Cement rotary kiln modification and calcination: The first 7 meters of the Φ4.8×72m cement clinker rotary kiln were modified into a three-blade structure (blade angle 120°, blade height 1 / 4 of the kiln's inner diameter). The decomposition furnace and cyclone preheater were removed and replaced with a constant-diameter flue. Pretreated materials were continuously fed from the bottom of the C5 preheater at a rate of 58t / h. The kiln tail pulverized coal injection system was retained, and the pulverized coal injection rate was adjusted to 39.0t / h to ensure that the atmosphere at 750℃ in the latter half of the kiln was zero-point. The oxygen content in the area above 750℃ was ≤0.5%, which was a reducing atmosphere. The oxygen content in the area below 750℃ in the latter half of the kiln was ≥10%, which was an oxidizing atmosphere. The kiln rotation speed was 1.5r / min, the material filling rate was 18%, the core sintering temperature in the kiln was 960℃-990℃, and the total material residence time was 52 minutes. The CO concentration in the kiln tail flue gas was 33%, the temperature was 1080℃, and the flue gas emission rate was 125,000 Nm³ / h.

[0057] The sintered products are cooled to room temperature by a circulating water quenching system (circulating water flow rate 95 m³ / h, cooling rate 130 ℃ / min);

[0058] Separation and extraction of iron, aluminum, silicon, alkali, and titanium:

[0059] (1) The cooled product was ground to 350 mesh (residue rate ≤0.8%) by wet milling with water at a solid-liquid ratio of 1:2.3. It was then magnetically separated for 11 min under a magnetic field of 3500-4500 Gauss with a magnetic separator capacity of 210 m³ / h to obtain metallic iron powder with a grade ≥92.1% and an iron recovery rate of 90.2%. The iron powder was dehydrated to a moisture content ≤9% and then packaged.

[0060] (2) When the concentration of sodium aluminate in the magnetic separation circulating water reaches 195 g / L, it is fed into a bubble-type carbonization reactor. CO2 with a purity ≥90% is introduced at room temperature and pressure at a rate of 0.9 m³ / h. The carbonization reaction time is 70 min, and the final pH value is 8.6-9.1. The reaction product is concentrated to a solid content of 36% by a thickener and then filtered by a plate and frame filter press at a pressure of 0.45 MPa. The obtained crude corundum raw material is dried at 109℃ for 2.8 h until the moisture content is ≤0.5% to obtain the corundum raw material product. The aluminum recovery rate is 88.5%, the silicon recovery rate is 83.8%, and the purity of the corundum raw material product is 89.5%.

[0061] (3) After the crude sodium carbonate solution was filtered through a 5μm precision filter, it was concentrated under reduced pressure at a vacuum of -0.088MPa and a temperature of 68℃ to a sodium carbonate concentration of 310g / L. It was then cooled to 27℃ at a cooling rate of 7℃ / h to crystallize. After centrifugation, it was dried at 85℃ for 2h to obtain a sodium carbonate product with a grade of ≥95.0% and a sodium recovery rate of 94.2%.

[0062] (4) After the magnetic separation tailings are concentrated, dehydrated and impurity removed, the titanium dioxide content in the titanium concentrate powder is ≥47.8%, the titanium recovery rate is 86.5%, and the tailings treatment volume is 1500t / d;

[0063] (5) A new dual-pressure waste heat boiler (evaporation capacity 26t / h) flue gas waste heat power generation system is added. After the flue gas is filtered by bag filter, wet desulfurization and SCR denitrification, CO2 is extracted by membrane separation with a purity of ≥90% and a separation recovery rate of 93%. The original flue gas purification system is reused.

[0064] Overall process indicators: Total iron recovery rate of 90.2%, comprehensive grade of metallic iron powder ≥92.1%; titanium (Ti) recovery rate of 86.5%, TiO2 content in titanium concentrate powder ≥47.8%; aluminum recovery rate of 88.5%; purity of corundum raw material product ≥89.0%; silicon recovery rate of 83.8%; sodium (Na) recovery rate of 94.2%; sodium carbonate product grade ≥95.0%; significant impurity removal effect, S removal rate of 96.10% and P removal rate of 88.20%; daily processing capacity of 6,000 tons of red mud, daily production of approximately 3,058 tons of metallic iron powder with a grade of 92% or higher, 1,126 tons of corundum raw material, 456 tons of titanium concentrate powder, and 1,120 tons of sodium carbonate product; additionally, 372,000 kWh of waste heat from flue gas is generated for power generation; total water consumption of 3.3 t / t red mud and electricity consumption of 82 kWh / t red mud.

[0065] Example 3:

[0066] Using a low-sulfur, high-iron red mud (TFe=35.6%, Al2O3=22.8%, S=0.95%, P=0.032%) as raw material, and co-added with 10% metallurgical dust and sludge mixture (TFe=45.8%, Al2O3=2.1%, SiO2=2.92%, CaO=4.40%), a large-scale process test of cement rotary kiln was carried out. The specific steps are as follows:

[0067] Raw material proportioning and pretreatment: High-speed iron red mud and 10% metallurgical dust mixture are first premixed in a twin-shaft mixer (speed 32 r / min, time 20 min), and then mixed with sodium-based additives (sodium carbonate purity 98%) and lignite reducing agent (fixed carbon 62%, particle size ≤3 mm) at a dry basis mass ratio of 78.3:9:9.7:3 (6000 tons of red mud + 600 tons of metallurgical dust, additives are 20% of the total mass of the mixed raw materials). The mixture is dried to a moisture content of 7.5% using a hot air dryer at 120℃, crushed by a jaw crusher, and then sieved to a particle size ≤5 mm through a 10-mesh vibrating screen to obtain pretreated material. A total of 7150 tons of this pretreated material is processed daily, and the uniformity of the mixed material is ≥95%.

[0068] Cement rotary kiln modification and calcination: The first 7 meters of the Φ4.8×72m cement clinker rotary kiln were modified into a three-blade structure (blade angle 120°, blade height 1 / 5 of the kiln's inner diameter). The decomposition furnace and cyclone preheater were removed and replaced with a constant-diameter flue. Pretreated materials were continuously fed from the bottom of the C5 preheater at a rate of 52t / h. The kiln tail pulverized coal injection system was retained, and the pulverized coal injection rate was adjusted to 40.5t / h to ensure that the atmosphere at 750℃ in the latter half of the kiln was zero-point. The oxygen content in the area above 750℃ was ≤0.5%, which was a reducing atmosphere. The oxygen content in the area below 750℃ in the latter half of the kiln was ≥10%, which was an oxidizing atmosphere. The kiln rotation speed was 1.45r / min, the material filling rate was 17.5%, the core sintering temperature in the kiln was 940℃~970℃, and the total material residence time was 48 minutes. The kiln tail flue gas was tested and found to have a CO concentration of 31.5%, a temperature of 1040℃, and a flue gas emission rate of 118,000 Nm³ / h.

[0069] The sintered products are cooled to room temperature by a circulating water quenching system (circulating water flow rate 85 m³ / h, cooling rate 110 ℃ / min);

[0070] Separation and extraction of iron, aluminum, silicon, alkali, and titanium:

[0071] (1) The cooled product was ground to 350 mesh (residue rate ≤1.2%) by wet milling with water at a solid-liquid ratio of 1:2.7. It was then magnetically separated for 13 min under a magnetic field of 3500-4500 Gauss with a magnetic separator capacity of 190 m³ / h. The resulting iron powder had a comprehensive grade of ≥90.8% and an iron recovery rate of 88.2%. The iron powder was dehydrated to a moisture content of ≤10% and then packaged.

[0072] (2) When the concentration of sodium aluminate in the magnetic separation circulating water reaches 185 g / L, it is fed into a bubble-type carbonization reactor. CO2 with a purity of ≥90% is introduced at room temperature and pressure at a rate of 0.7 m³ / h. The carbonization reaction time is 80 min, and the final pH value is 8.4-8.9. The reaction product is concentrated to a solid content of 34% by a thickener and then filtered by a plate and frame filter press at a pressure of 0.35 MPa. The crude corundum raw material is dried at 107℃ for 3.2 h until the moisture content is ≤0.5%. The resulting corundum raw material product has a purity of ≥89.5%, an aluminum recovery rate of 89.8%, and a silicon recovery rate of 84.6%.

[0073] (3) After the crude sodium carbonate solution was filtered through a 5μm precision filter, it was concentrated under reduced pressure at a vacuum of -0.082MPa and a temperature of 63℃ to a sodium carbonate concentration of 290g / L. It was then cooled to 29℃ at a cooling rate of 5℃ / h to crystallize. After centrifugation, it was dried at 78℃ for 2.2h to obtain a sodium carbonate product with a grade of ≥94.6% and a sodium recovery rate of 93.5%.

[0074] (4) After the magnetic separation tailings are concentrated, dehydrated and impurity removed, the titanium concentrate powder has a TiO2 content of ≥45.8%, a titanium recovery rate of 84.5%, and a tailings treatment capacity of 2000t / d;

[0075] (5) A new dual-pressure waste heat boiler (evaporation capacity 24t / h) flue gas waste heat power generation system is added. After the flue gas is filtered by bag filter, wet desulfurization and SCR denitrification (reaction temperature 310℃), CO2 is extracted by membrane separation with a purity of ≥90% and a separation recovery rate of 91%. The original flue gas purification system is reused.

[0076] Overall process indicators: Total iron recovery rate of 88.2%, comprehensive grade of metallic iron powder ≥90.8%; titanium (Ti) recovery rate of 84.5%, TiO2 content in titanium concentrate powder ≥45.8%; aluminum recovery rate of 89.8%; purity of corundum raw material product ≥89.5%; silicon recovery rate of 84.6%; sodium (Na) recovery rate of 93.5%; grade of sodium carbonate product ≥94.6%; significant impurity removal effect, S removal rate of 97.20% and P removal rate of 88.50%; achieving co-processing of solid waste of 6,000 tons of red mud and 600 tons of metallurgical dust per day, producing approximately 2,512 tons of metallic iron powder with a grade of over 90% per day, 1,568 tons of corundum raw material, 365 tons of titanium concentrate powder, and 1,095 tons of sodium carbonate product per day, with an additional 358,000 kWh of waste heat power generation from flue gas; water consumption of 3.8 t / t red mud and electricity consumption of 88 kWh / t red mud per process.

[0077] All equipment involved in this invention, including cement rotary kilns, wet mills, magnetic separators, carbonization reactors, thickeners, filter presses, circulating water quench systems, flue gas combustion power generation systems, waste heat power generation systems, and desulfurization, denitrification, and dust removal devices, are existing, mature, and general-purpose equipment in the fields of metallurgy, cement production, solid waste treatment, and chemical separation. There are no requirements for customized or special-purpose equipment. The selection of various types of equipment can be reasonably determined by those skilled in the art based on the specific process parameters, throughput, and operating indicators required by this invention, combined with conventional industrial production selection standards. For example, cement rotary kilns can use industry-standard clinker rotary kilns, magnetic separators can use conventional permanent magnet drum separators, carbonization reactors can use chemical industry-standard bubbling / stirred carbonization reactors or high-gravity carbonization reactors, and filter presses can use plate and frame / chamber filter presses. All related equipment is commercially available on the market, requiring no creative equipment research and development or modification. Those skilled in the art can directly obtain and adapt the process system of this invention.

[0078] Meanwhile, the present invention has clearly disclosed the core process matching parameters and operation control requirements of each piece of equipment. The specific model selection of the equipment does not affect the implementation of the technical solution of the present invention. It only needs to meet the technical characteristics such as processing capacity, operating parameters, and functional requirements defined by the present invention. All selection and matching based on existing general equipment and in accordance with the parameters disclosed in the present invention can achieve the process effect and invention purpose of the present invention.

[0079] It should be understood that numerous specific implementation decisions can be made during the development of any practical implementation, such as in any engineering or design project. Such development efforts may be complex and time-consuming, but for those skilled in the art who benefit from this disclosure, the development effort will be a routine work of design, manufacturing, and production without requiring much experimentation.

[0080] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A process for treating alumina red mud using a cement rotary kiln, characterized in that, Includes the following steps: S1. Red mud pretreatment: Select high-iron red mud with a total iron (TFe) content ≥30% and an alumina content ≥20%, mix it with sodium-based additives and reducing agents at a mass ratio of 78.3~87:9~10:3, and then dry, crush and screen it to obtain pretreated material with a moisture content ≤10% and a particle size ≤5mm. The total amount of additives added is 20%~30% of the red mud mass. S2. Cement Rotary Kiln Modification and Calcination: The structure and supporting systems of the cement rotary kiln are modified, while the pulverized coal injection system at the kiln tail is retained. The pretreated material from step S1 is fed into the modified cement rotary kiln and calcined at 900~1200℃ for 45~60 minutes. Main chemical reaction formulas: 2Fe 2+ +Al2O3 +2Na + +C→2Fe+2NaAlO2+CO2↑ 4Fe 3+ +2Al2O3+4Na + +3C→4Fe+4NaAlO2+3CO2↑ S3. Cooling of calcined products: The sintered products are cooled to less than 100°C to room temperature by a circulating water quenching system. S4. Multi-resource separation and extraction: S41. The cooled product is processed to 350 mesh by a wet mill and then magnetically separated under a magnetic field of 3500~4500 Gauss to obtain metallic iron powder with a grade of ≥90%. S42. When the sodium aluminate solution in the magnetic separation circulating water is close to saturation, CO2 from the purified flue gas is introduced to carry out a carbonization reaction. The reaction product is separated into solid and liquid phases by a thickener and a filter press to obtain crude corundum raw material. The crude product is then dried to obtain the finished corundum raw material. Main chemical reaction formulas: 2NaAlO2 + CO2 → Al2O3 + Na2CO3 S43. The filtrate after solid-liquid separation in S42 is purified, concentrated, and crystallized to obtain sodium carbonate product; S44. Magnetic separation tailings are used as titanium concentrate powder, with a TiO2 content of ≥45%; S45. The flue gas generated by the cement rotary kiln is used for power generation by the waste heat boiler, and then purified by the desulfurization, denitrification and dust removal system. The separated CO2 is used for the carbonization reaction of S42, and the remaining flue gas is discharged.

2. The method according to claim 1, characterized in that, The modification of the cement rotary kiln in step S2 includes the following: modifying the first 6-8 meters of the kiln body at the feed end into a three-lobe structure; removing or modifying the decomposition furnace and cyclone preheater into a flue, with pretreated materials being conveyed into the kiln from the bottom of the C5 preheater; removing the original cooling grate cooler and replacing it with a circulating water quench system; and equipping it with a wet process tower mill, magnetic separation system, carbonization reactor, and flue gas combustion power generation system.

3. The method according to claim 1, characterized in that, The reducing agent is one or more of lignite, coke powder, or biomass fuel; the sodium-based additive is at least one of sodium carbonate and sodium hydroxide.

4. The method according to claim 1, characterized in that, The cement rotary kiln selected is a type with a daily cement clinker production capacity of 4,000 tons or more. After modification with this process, its daily high-iron red mud processing capacity is ≥6,000 tons. For cement clinker rotary kilns with different production capacities below 4,000 tons per day, the daily high-iron red mud processing capacity after modification with this process is 1.5 times its original daily cement clinker production capacity. For non-cement calcining / roasting rotary kilns, after modification according to the kiln structure and supporting system modification plan of this process, they are used for high-iron red mud processing in this process, and the processing efficiency is consistent with the matching principle of the modified cement rotary kiln's production capacity.

5. The method according to claim 1, characterized in that, In step S4, the iron recovery rate is ≥88%, the aluminum recovery rate is ≥88%, the titanium recovery rate is ≥84%, and the sodium recovery rate is ≥93%; the purity of the corundum raw material product is ≥89%, the grade of the sodium carbonate product is ≥94.6%, and the TiO2 content in the titanium concentrate powder is ≥45.8%.

6. The method according to claim 1, characterized in that, In step S2, the material filling rate in the cement rotary kiln is above 17%, and the kiln rotation speed is controlled at 1.45~1.5 r / min.

7. The method according to claim 1, characterized in that, In step S2, the flue gas gas power generation system and the existing waste heat power generation system of the cement plant operate in parallel. The existing flue gas purification system of the cement plant is reused, and the newly added desulfurization and denitrification device adopts the SCR process.

8. The method according to claim 1, characterized in that, In step S1, 5% to 10% of metallurgical dust and sludge are added to the pretreated material. The metallurgical dust and sludge are one or more of the dust and slurry solid wastes collected by the dust removal system of each process in the entire metallurgical production process, including sintering, blast furnace, steelmaking, steel rolling and other processes.

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