A composite steel dephosphorization agent based on red mud modification and a preparation and application method thereof

Abstract

The present application belongs to the technical field of steelmaking auxiliary materials, and particularly relates to a composite steelmaking dephosphorization agent based on modified red mud and a preparation and application method thereof. The composite steelmaking dephosphorization agent comprises, by mass percentage, modified red mud 40-60%, CaO 20-30%, Fe2O3 10-15%, fluorite 5-10%, and a binder 1-5%. The modified red mud is used as a core raw material, the activity of the red mud is improved through acid leaching activation, the red mud is precisely and deeply activated and modified through gradient acid concentration, and CaO, Fe2O3, fluorite and the binder are compounded to form a composite active system with a synergistic dephosphorization effect. The problems of large composition fluctuation and poor activity of the red mud are solved, and high-value utilization of large quantities of solid waste is realized.

Description

Technical Field

[0001] This invention belongs to the field of steelmaking auxiliary materials technology, and particularly relates to a composite steelmaking dephosphorizing agent based on red mud modification and its preparation and application methods. Background Technology

[0002] Red mud is a large amount of solid waste generated during the production of alumina in the aluminum industry. Its emissions are directly linked to alumina production; typically, 2-3 tons of red mud are produced for every ton of alumina produced. As the world's largest alumina producer, my country's annual alumina production has exceeded 80 million tons, corresponding to annual red mud emissions of over 150 million tons, accounting for approximately 60% of global production. For a long time, red mud has mainly been disposed of through open-air stockpiling or dammed storage, with a cumulative stockpile exceeding 700 million tons, occupying over 120,000 mu (approximately 8,667 hectares) of land. Nearly 40% of these red mud storage sites are located in ecologically fragile or densely populated areas, posing significant environmental risks.

[0003] Red mud stockpiling not only causes a serious waste of land resources, but the heavy metal ions and highly alkaline substances it contains can easily enter the surrounding environment through rainwater runoff, surface runoff, or groundwater infiltration, causing soil compaction and salinization, leading to reduced crop yields in the region. Simultaneously, toxic and harmful elements such as fluorine, chromium, and lead in red mud can pollute groundwater and surface water. In some affected areas, the pH value of groundwater exceeds 10, and the heavy metal content exceeds the standard by 3-10 times, directly threatening the drinking water safety of surrounding residents. Even more serious is the fact that the current utilization rate of red mud resources in my country is less than 5%. With the continuous expansion of alumina production capacity, the pressure of red mud stockpiling will further intensify, becoming one of the core bottlenecks restricting the green and sustainable development of the aluminum industry.

[0004] Dephosphorization is one of the core processes in steelmaking to ensure steel quality and meet the performance requirements of high-end steel. Phosphorus, as a harmful element in steel, significantly reduces the low-temperature toughness, plasticity, and weldability of steel. Especially for high-end products such as high-speed railway steel, marine engineering steel, and ultra-low carbon automotive steel, the phosphorus content must be strictly controlled below 0.005%, which places extremely high demands on the precision and efficiency of the dephosphorization process.

[0005] Traditional steelmaking dephosphorizing agents use CaO and fluorite (CaF2) as core components, combined with oxidants such as Fe2O3 to assist in dephosphorization. However, this technology has many insurmountable drawbacks: First, the dephosphorization efficiency is limited, with a conventional dephosphorization rate of only about 80%, which is insufficient to meet the requirements of high-end steel for extremely low phosphorus content, requiring additional refining processes and significantly extending the production cycle. Second, fluorite is expensive and scarce, with its unit price increasing by more than 350% in recent years. Fluorite alone accounts for more than 60% of the cost of dephosphorizing agents, significantly increasing steelmaking production costs. Third, the fluorine in fluorite reacts violently with magnesium, calcium, and other components in the furnace lining, accelerating furnace lining corrosion, shortening converter lifespan, and increasing equipment maintenance and replacement costs. At the same time, fluoride emissions can also cause secondary environmental pollution.

[0006] While current mainstream lime-based dephosphorizing agents avoid the use of fluorite, they still face significant problems: the dephosphorization reaction requires high temperatures above 1600℃ and high alkalinity conditions (CaO / SiO2) ≥ 2.8, resulting in harsh reaction kinetics and energy consumption accounting for about 15% of the total energy consumption in steelmaking; moreover, the dephosphorization efficiency is only increased to 85%, and the amount of dephosphorizing agent used needs to be significantly increased to achieve the target phosphorus content, leading to a surge in steelmaking slag emissions, with the amount of steel slag generated per ton of steel increasing from 0.1 tons to 0.18 tons. Steel slag stockpiling also occupies land and causes environmental problems, further exacerbating the pressure on solid waste disposal.

[0007] Existing technologies have attempted to use red mud directly as a dephosphorizing agent raw material or to use red mud for steelmaking dephosphorization after simple physical mixing. For example, patent application number CN201710122907.9 discloses a method for producing converter dephosphorizing agent from alumina tailings (red mud), which involves magnetically separating red mud and then adding calcium aluminate and calcium carbonate for mixing and molding. However, this method only involves physical mixing and does not perform deep activation and modification of the red mud. The active components such as iron, aluminum, and calcium oxides inside the red mud are not fully dissociated, making it difficult to form a composite active phase with synergistic dephosphorization effect. Patent application number CN201410176170.5 discloses a method for recycling and reusing high-iron red mud as a steelmaking slag-forming agent, which involves mixing air-dried and finely ground red mud with lime in a certain proportion for slag formation. However, this method is only a simple physical mixing method, resulting in low utilization of the effective components of the red mud and the dephosphorization effect being easily affected by fluctuations in the original composition. Patent application CN201410036893.5 discloses a dephosphorizing agent for converter steelmaking using red mud from the aluminum industry as a base. This involves mixing dried red mud with lime, iron concentrate, and lightly calcined dolomite, followed by roasting and pressing. However, this method has limited applicability, only capable of treating molten iron with low to medium phosphorus content, and its dephosphorization effect on high-phosphorus molten iron is difficult to meet standards. Patent application CN202410261749.5 discloses a smelting method using red mud as a slag-forming material for dephosphorization in converter steelmaking. This involves ball milling, roasting reduction, and magnetic separation followed by mixing with iron oxide scale and dust to form pellets. However, this method lacks specificity in dephosphorization, as it does not add fluxing or activating modifiers, resulting in low and unstable dephosphorization efficiency under low alkalinity conditions.

[0008] In summary, existing technologies for applying red mud to dephosphorization generally suffer from the following technical defects: First, the composition of red mud fluctuates greatly: the composition of red mud produced from different bauxite deposits and different production processes (Bayer process, sintering process, combined process) varies significantly. The Fe2O3 content can fluctuate from 20% to 45%, the Al2O3 content from 10% to 25%, and the CaO content from 5% to 18%. This unstable composition makes it difficult to accurately control the dephosphorization effect, and the phosphorus content in molten steel can fluctuate from 0.008% to 0.012%, which cannot meet the quality requirements of high-end steel. The requirements are as follows: First, the active components of red mud have poor dispersibility: Red mud particles tend to agglomerate and form a dense structure, with active components such as CaO and Fe2O3 encapsulated inside the particles. The contact area with the molten steel is only 15%-20% of the theoretical value, making it impossible to fully react with phosphorus in the molten steel. Second, the basicity and dephosphorization activity of red mud are insufficient: The basicity (CaO / SiO2) of red mud is only 0.5-1.2, which is far lower than the high basicity of more than 2.5 required for the dephosphorization reaction. It is difficult to effectively absorb phosphorus in the molten steel to form stable phosphate compounds, and the dephosphorization rate is only 60%-70%.

[0009] Some studies have improved the activity of red mud through modification methods, such as strong alkali leaching, high-temperature calcination, and mechanical activation. However, there are still many obstacles to its industrialization: the strong alkali leaching process requires a large amount of sodium hydroxide, with 0.15 tons of sodium hydroxide needed per ton of modified red mud, which is costly and generates alkaline wastewater, causing secondary pollution; the high-temperature calcination process is energy-intensive, requiring more than 0.22 tons of standard coal per ton of modified red mud, which does not conform to the concept of green production; although mechanical activation can improve particle dispersibility, the modification effect is short-lived, the product stability is poor, and the activity is easily reduced by more than 30% during transportation and storage, which cannot meet the long-term needs of industrial production.

[0010] The goal is to develop a composite steelmaking dephosphorizing agent based on red mud modification. This agent activates the active components in red mud through a low-cost modification process and enhances dephosphorization performance by compounding functional additives. It has significant economic value, environmental benefits, and industry-driving effects. Summary of the Invention

[0011] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a composite steelmaking dephosphorizing agent based on red mud modification and its preparation and application method. By activating red mud to improve its activity, and combining it with CaO, Fe2O3 and fluorite, the dephosphorizing effect is enhanced, while realizing the high-value utilization of red mud.

[0012] To achieve the above objectives, the present invention provides the following technical solution: A composite steelmaking dephosphorizing agent based on red mud modification, comprising, by mass percentage: Modified red mud 40%–60%; CaO 20%–30%; Fe2O3 10%–15%; fluorite 5%–10%; binder 1%–5%.

[0013] Modified red mud is the core raw material. CaO provides an alkaline environment, promoting the combination of phosphorus oxides and CaO to form stable Ca3(PO4)2. Fe2O3 acts as an oxidant, oxidizing phosphorus in molten steel to P2O5. Fluorite lowers the melting point of slag, improves fluidity, and promotes dephosphorization. The binder improves formability and prevents pulverization.

[0014] The method for preparing the modified red mud includes the following steps: 1) Red mud is soaked in hydrochloric acid with a concentration of 10wt% to 12wt%, the solid-liquid mass ratio is (0.6 to 1): (4 to 5), the soaking temperature is 50 to 70℃, and the soaking time is 1.2 to 1.8 hours; 2) Then soak in hydrofluoric acid with a concentration of 18wt% to 20wt%, with a solid-liquid mass ratio of (0.8 to 1.3):(4 to 5), a soaking temperature of 50 to 70℃, and a soaking time of 2 to 2.5 hours; The above acid leaching treatment can precisely control the removal rate of inert impurities. By leaching red mud with hydrochloric acid and hydrofluoric acid, inert impurities such as Al2O3 and SiO2 are removed (reaction formula: Al2O3+6HCl=2AlCl3+3H2O; SiO2+4HF=SiF4+2H2O), while active components such as Fe2O3 and CaO are enriched, thereby improving the reactivity of red mud.

[0015] To address the difference in dissolution kinetics between Al2O3 and SiO2 in red mud, an acid leaching strategy was adopted: 10wt% to 12wt% hydrochloric acid was used to leach out the easily reactive Al2O3 first, achieving a removal rate of over 85%; subsequently, 18wt% to 20wt% hydrofluoric acid was used to remove SiO2, achieving a removal rate of over 90%, thereby increasing the total content of active ingredients from 42% in the original red mud to over 60%.

[0016] 3) After filtering and washing until neutral, dry to obtain modified red mud.

[0017] Compared with the unmodified red mud, the Fe2O3 content in the modified red mud increased to 45wt%, while the Al2O3 content decreased to 5wt%.

[0018] The red mud in step 1) has a particle size of 75μm to 150μm; the red mud contains, by mass percentage: Fe2O3 30% to 40%, Al2O3 15% to 20%, SiO2 12% to 18%, CaO 8% to 12%, Na2O 2% to 6%, K2O 0.5% to 2%, TiO2 2% to 6%, with the remainder being impurities.

[0019] The drying temperature in step 3) is 100-120℃, and the drying time is 2-3 hours.

[0020] The adhesive is water glass with a modulus of 2.8 to 3.5.

[0021] A method for preparing a composite steelmaking dephosphorizing agent based on red mud modification includes the following steps: 1) Ingredient mixing: Take the modified red mud, CaO (analytical grade), Fe2O3 (analytical grade), fluorite (CaF2 content ≥95wt%), and binder according to the mass ratio mentioned above, put them into a ball mill and mix for 30 minutes until they are evenly mixed to obtain a mixture; 2) Molding: The mixture is pressed into shape to obtain a dephosphorizing agent blank; 3) Place the dephosphorizing agent blank in a forced-air drying oven to dry and remove moisture to obtain a composite steelmaking dephosphorizing agent.

[0022] In step 1), the mixing is carried out using a ball mill, and the mixing time is 20 to 40 minutes.

[0023] In step 2), the mixture is added to a tablet press and compressed into granules with a diameter of 4-6 mm and a thickness of 2-4 mm under a pressure of 12-20 MPa, with a compressive strength ≥10 MPa.

[0024] In step 3), the drying temperature is 100-120℃ and the drying time is 3-5 hours.

[0025] A method for applying a composite steelmaking dephosphorizing agent based on red mud modification is proposed. In molten steel with an initial [P] content of 0.07% to 0.12%, the composite dephosphorizing agent is added during the oxygen blowing process in a converter when the carbon content of the molten steel drops to 0.8 wt% to 0.9 wt%. This stage is the optimal thermodynamic window for the dephosphorization reaction, which can maximize the reactivity of the dephosphorizing agent with phosphorus in the molten steel and avoid adding it too early, which would lead to the ineffective consumption of the dephosphorizing agent, or adding it too late, which would miss the optimal period for the dephosphorization reaction.

[0026] The amount of composite dephosphorizing agent added is 15-16 kg / ton of steel. This amount is calculated based on the initial phosphorus content of the molten steel, the converter smelting capacity, and the proportion of effective components of the dephosphorizing agent. This ensures sufficient material supply for the dephosphorization reaction while avoiding excessive addition that could lead to raw material waste and unnecessary fluctuations in the composition of the molten steel.

[0027] The temperature of the molten steel is 1400-1430℃. This temperature range can simultaneously take into account the thermodynamic and kinetic conditions of the dephosphorization reaction. It will not cause the stability of the dephosphorization slag system to decrease due to excessively high temperature, nor will it slow down the reaction rate due to excessively low temperature, thus ensuring that the dephosphorization reaction proceeds efficiently and in an orderly manner.

[0028] The oxygen blowing reaction lasts for 16–18 minutes, followed by a 1–3 minute settling period before tapping the steel. The 16–18 minutes of oxygen blowing reaction ensures that the dephosphorizing agent reacts fully with the phosphorus in the molten steel, while the subsequent 1–3 minute settling time facilitates the complete separation of the dephosphorizing slag from the molten steel, preventing phosphorus in the slag from seeping back into the molten steel, and ultimately ensuring that the phosphorus content in the molten steel meets the quality requirements.

[0029] Compared with the prior art, the beneficial effects of the present invention are: 1. The composite steelmaking dephosphorizing agent of this invention uses modified red mud as the core raw material. It enhances the activity of the red mud through acid leaching activation, employs a gradient acid concentration for precise deep activation and modification, selectively removes inert impurities such as Al2O3 and SiO2, enriches active components such as Fe2O3 and CaO, and combines CaO, Fe2O3, fluorite, and a binder to form a composite active system with synergistic dephosphorizing effects. This solves the problems of large fluctuations in red mud composition and poor activity, enabling the high-value utilization of bulk solid waste.

[0030] 2. The preparation process of this invention is simple and the product has good stability.

[0031] 3. This composite steelmaking dephosphorizing agent is used in the dephosphorization stage of steelmaking, achieving a dephosphorization rate of over 90%. After treatment, the phosphorus content of the molten steel is stably controlled at 0.007wt%~0.008wt%, meeting the quality requirements of high-end steel. It replaces most of the fluorite in traditional dephosphorizing agents, reducing fluoride emissions by over 90%; it replaces approximately 30% of lime, reducing the amount of steelmaking slag and producing no alkaline wastewater. Detailed Implementation

[0032] The present invention will now be described in detail, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0033] Example 1:

[0034] Composite steelmaking dephosphorizing agent, by mass percentage, includes: The mixture consists of 50% modified red mud, 25% CaO (analytical grade), 12% Fe2O3 (analytical grade), 8% fluorite (CaF2 content ≥95%), and 5% water glass (modulus 3.2).

[0035] The modified red mud preparation adopts a gradient acid concentration strategy: 11wt% hydrochloric acid is used to leach easily reactive Al2O3 first, with a removal rate of over 85%; then 18wt% hydrofluoric acid is used to remove SiO2, with a removal rate of over 90%, increasing the total content of active ingredients from 42% in the original red mud to over 60%.

[0036] A method for preparing a composite steelmaking dephosphorizing agent includes the following steps: (1) Red mud modification: Take the original red mud from the aluminum plant (the contents of each substance in the red mud are: Fe2O3 35wt%, Al2O3 18wt%, SiO2 15wt%, CaO 10wt%, Na2O 4wt%, K2O 1wt%, TiO2 3wt%, and the remainder is impurities) and crush it to 150 mesh. Add 11wt% hydrochloric acid solution (solid-liquid ratio 1:4) and stir and soak at 60℃ for 1.5 hours. Then replace it with 18wt% hydrofluoric acid solution (solid-liquid ratio 0.9:4). Before and after the replacement, it needs to be filtered and washed. Continue to stir and soak at 60℃ for 2 hours. After filtration, wash with deionized water until the pH of the filtrate is 7. Dry at 110℃ for 2.5 hours to obtain modified red mud (Fe2O3 45wt%, Al2O3 4.8wt%, SiO2 1.2wt%).

[0037] The red mud in step 1) has a particle size of 75μm to 150μm; the red mud contains, by mass percentage: Fe2O3 30% to 40%, Al2O3 15% to 20%, SiO2 12% to 18%, CaO 8% to 12%, Na2O 2% to 6%, K2O 0.5% to 2%, TiO2 2% to 6%, with the remainder being impurities.

[0038] (2) Mixing of ingredients: Weigh each component according to the above proportions, put them into a ball mill and mix for 30 minutes to obtain a uniform mixture.

[0039] (3) Molding: The mixture is added to the tablet press and pressed into granules with a diameter of 5 mm and a thickness of 3 mm under a pressure of 15 MPa, with a compressive strength of 12 MPa.

[0040] (4) Drying: The shaped granules are placed in a forced-air drying oven and dried at 110°C for 4 hours to obtain a composite steelmaking dephosphorizing agent.

[0041] Application of composite steelmaking dephosphorizing agent The composite dephosphorizing agent was applied to the dephosphorization stage of converter steelmaking. The initial [P] content of the molten steel was 0.08%. The composite dephosphorizing agent was added at a dosage of 15.5 kg / ton of steel when the carbon content of the molten steel dropped to 0.8 wt%. The steel temperature was controlled at 1420℃, and after 17 minutes of oxygen blowing reaction, the steel was allowed to stand for 2 minutes before tapping. The final [P] content of the molten steel dropped to 0.008%, achieving a dephosphorization rate of 90%.

[0042] Example 2

[0043] Composite steelmaking dephosphorizing agent, by mass percentage, includes: Modified red mud 45%, CaO (analytical grade) 28%, Fe2O3 (analytical grade) 12%, fluorite (CaF2 content ≥95%) 10%, water glass (modulus 3.2) 5%.

[0044] The modified red mud preparation adopts a gradient acid concentration strategy: 12wt% hydrochloric acid is used to leach easily reactive Al2O3 first, with a removal rate of over 85%; then 19wt% hydrofluoric acid is used to remove SiO2, with a removal rate of over 91%, increasing the total content of active ingredients from 42% in the original red mud to over 61%.

[0045] A method for preparing a composite steelmaking dephosphorizing agent includes the following steps: (1) Red mud modification: Take the original red mud from the aluminum plant (the contents of each substance in the red mud are: Fe2O3 36wt%, Al2O3 17wt%, SiO2 15wt%, CaO 10wt%, CaO 10wt%, Na2O3 wt%, K2O 1wt%, TiO2 3.5wt%, and the balance is impurities) and crush it to 120 mesh. Add 12wt% hydrochloric acid solution (solid-liquid ratio 1:4.5), stir and soak at 60℃ for 1.8 hours; then replace it with 19wt% hydrofluoric acid solution (solid-liquid ratio 1:5). Before and after the replacement, it needs to be filtered and washed, and continue to be stirred and soaked at 60℃ for 2 hours; after filtration, wash with deionized water until the pH of the filtrate is 7, and dry at 110℃ for 2.5 hours to obtain modified red mud (Fe2O3 44wt%, Al2O3 4.5wt%, SiO2 1.3wt%).

[0046] (2) Mixing of ingredients: Weigh each component according to the above proportions, put them into a ball mill and mix for 30 minutes to obtain a uniform mixture.

[0047] (3) Molding: The mixture is added to the tablet press and pressed into granules with a diameter of 5 mm and a thickness of 3 mm under a pressure of 16 MPa, with a compressive strength of 11.5 MPa.

[0048] (4) Drying: The shaped granules are placed in a forced-air drying oven and dried at 110°C for 4 hours to obtain a composite steelmaking dephosphorizing agent.

[0049] Application of composite steelmaking dephosphorizing agent A composite dephosphorizing agent was applied to the dephosphorization stage of converter steelmaking. The initial [P] content of the molten steel was 0.09%. When the carbon content of the molten steel dropped to 0.8 wt%, the composite steelmaking dephosphorizing agent was added at a dosage of 15 kg / ton of steel. The steel temperature was controlled at 1410℃, and after oxygen blowing for 16 minutes, the steel was allowed to stand for 2 minutes before tapping. The final [P] content of the molten steel dropped to 0.008%, and the dephosphorization rate reached 91.1%.

[0050] Example 3

[0051] Composite steelmaking dephosphorizing agent, by mass percentage, includes: Modified red mud 55%, CaO (analytical grade) 20%, Fe2O3 (analytical grade) 12%, fluorite (CaF2 content ≥95%) 8%, water glass (modulus 3.2) 5%.

[0052] The modified red mud preparation adopts a gradient acid concentration strategy: 12wt% hydrochloric acid is used to leach easily reactive Al2O3 first, with a removal rate of over 85%; then 19wt% hydrofluoric acid is used to remove SiO2, with a removal rate of over 93%, increasing the total content of active ingredients from 42% in the original red mud to over 63%.

[0053] A method for preparing a composite steelmaking dephosphorizing agent includes the following steps: (1) Red mud modification: Take the original red mud from the aluminum plant (the contents of each substance in the red mud are: Fe2O3 37wt%, Al2O3 18wt%, SiO2 16wt%, CaO 11wt%, Na2O3 wt%, K2O 1.5wt%, TiO2 3wt%, and the remainder is impurities) and crush it to 200 mesh. Add 12wt% hydrochloric acid solution (solid-liquid ratio 1:5) and stir and soak at 60℃ for 1.6 hours. Then replace it with 19wt% hydrofluoric acid solution (solid-liquid ratio 1.2:5). Before and after the replacement, it needs to be filtered and washed. Continue to stir and soak at 60℃ for 2.2 hours. After filtration, wash with deionized water until the pH of the filtrate is 7. Dry at 110℃ for 2.5 hours to obtain modified red mud (Fe2O3 46wt%, Al2O3 4.2wt%, SiO2 1.0wt%).

[0054] (2) Mixing of ingredients: Weigh each component according to the above proportions, put them into a ball mill and mix for 30 minutes to obtain a uniform mixture.

[0055] (3) Molding: The mixture is added to the tablet press and pressed into granules with a diameter of 5 mm and a thickness of 3 mm under a pressure of 18 MPa, with a compressive strength of 12.5 MPa.

[0056] (4) Drying: The shaped granules are placed in a forced-air drying oven and dried at 110°C for 4 hours to obtain a composite steelmaking dephosphorizing agent.

[0057] Application of composite steelmaking dephosphorizing agent The composite dephosphorizing agent was applied to the dephosphorization stage of converter steelmaking. The initial [P] content of the molten steel was 0.08%. When the carbon content of the molten steel dropped to 0.8 wt%, the composite steelmaking dephosphorizing agent was added at a dosage of 16 kg / ton of steel. The molten steel temperature was controlled at 1430℃, and after oxygen blowing for 18 minutes, the steel was allowed to stand for 2 minutes before tapping. Finally, the [P] content of the molten steel dropped to 0.007%, and the dephosphorization rate reached 91.25%.

[0058] Comparative Example 1. Composition and preparation of dephosphorizing agent The raw red mud was 50% unmodified, and the remaining components were the same as in Example 1 (CaO 25wt%, Fe2O3 12wt%, fluorite 8wt%, water glass 5wt%). The preparation process skipped the red mud modification step, and the raw red mud was directly crushed to 150 mesh, mixed with other components, shaped, and dried to obtain the comparative dephosphorizing agent.

[0059] 2. Application method of dephosphorizing agent The application conditions are exactly the same as in Example 1: the initial [P] of 0.08% molten steel is added when the carbon content drops to 0.8wt%, the addition amount is 15.5kg / ton of steel, the molten steel temperature is 1420℃, the oxygen blowing reaction is carried out for 17min, and the steel is allowed to stand for 2min before being tapped.

[0060] 3. Application Effect The final [P] content in the molten steel dropped to 0.022%, and the dephosphorization rate was only 72.5%, far lower than the dephosphorization effect in Example 1. A large number of inert impurities (Al2O3, SiO2) in the unmodified red mud were not removed, and the proportion of active components was low, resulting in insufficient dephosphorization reaction activity and inability to effectively capture phosphorus in the molten steel.

[0061] This invention uses modified red mud as the core raw material, combined with calcium oxide, iron oxide, fluorite, and a binder. The red mud's activity is enhanced through acid leaching, and the synergistic effect of each component strengthens the dephosphorization effect. The preparation method includes red mud modification, batching and mixing, molding, and drying. The process is simple and can be applied to the dephosphorization stage of steelmaking, achieving a dephosphorization rate of over 90%. Furthermore, it realizes the high-value utilization of industrial waste red mud, demonstrating significant economic and environmental benefits.

Claims

1. A composite steelmaking dephosphorizing agent based on red mud modification, characterized in that, Included by weight percentage: Modified red mud 40%–60%; CaO 20%–30%; Fe2O3 10%–15%; fluorite 5%–10%; binder 1%–5%.

2. The composite steelmaking dephosphorizing agent based on red mud modification according to claim 1, characterized in that, The method for preparing the modified red mud includes the following steps: 1) Red mud is soaked in hydrochloric acid with a concentration of 10wt% to 12wt%, the solid-liquid mass ratio is (0.6 to 1): (4 to 5), the soaking temperature is 50 to 70℃, and the soaking time is 1.2 to 1.8 hours; 2) Then soak in hydrofluoric acid with a concentration of 18wt% to 20wt%, with a solid-liquid mass ratio of (0.8 to 1.3):(4 to 5), a soaking temperature of 50 to 70℃, and a soaking time of 2 to 2.5 hours; 3) After filtering and washing until neutral, dry to obtain modified red mud.

3. The composite steelmaking dephosphorizing agent based on red mud modification according to claim 2, characterized in that, The red mud in step 1) has a particle size of 75μm to 150μm; the red mud contains, by mass percentage: Fe2O3 30% to 40%, Al2O3 15% to 20%, SiO2 12% to 18%, CaO 8% to 12%, Na2O 2% to 6%, K2O 0.5% to 2%, TiO2 2% to 6%, with the remainder being impurities.

4. The composite steelmaking dephosphorizing agent based on red mud modification according to claim 1, characterized in that, The drying temperature in step 3) is 100-120℃, and the drying time is 2-3 hours.

5. The composite steelmaking dephosphorizing agent based on red mud modification according to claim 1, characterized in that, The adhesive is water glass with a modulus of 2.8 to 3.

5.

6. A method for preparing a composite steelmaking dephosphorizing agent based on red mud modification as described in any one of claims 1-5, characterized in that, Includes the following steps: 1) Ingredient mixing: Take the modified red mud, CaO, Fe2O3, fluorite and binder according to the mass ratio mentioned above, mix them evenly to obtain the mixture; 2) Molding: The mixture is pressed into shape to obtain a dephosphorizing agent preform; 3) Dry the dephosphorizing agent billet to obtain the composite steelmaking dephosphorizing agent.

7. The preparation method of a composite steelmaking dephosphorizing agent based on red mud modification according to claim 6, characterized in that, In step 1), the mixing is carried out using a ball mill, and the mixing time is 20 to 40 minutes.

8. The preparation method of a composite steelmaking dephosphorizing agent based on red mud modification according to claim 6, characterized in that, In step 2), the mixture is added to a tablet press and compressed into granules with a diameter of 4-6 mm and a thickness of 2-4 mm under a pressure of 12-20 MPa, with a compressive strength ≥10 MPa.

9. The preparation method of a composite steelmaking dephosphorizing agent based on red mud modification according to claim 6, characterized in that, In step 3), the drying temperature is 100-120℃ and the drying time is 3-5 hours.

10. A method for applying the composite steelmaking dephosphorizing agent based on red mud modification as described in any one of claims 1-5, characterized in that, For molten steel with an initial [P] content of 0.07% to 0.12%, during the oxygen blowing process in the converter, when the carbon content of the molten steel drops to 0.8wt% to 0.9wt%, a composite dephosphorizing agent is added at a rate of 15 to 16 kg / ton of steel. The molten steel temperature is 1400 to 1430℃, the oxygen blowing reaction lasts for 16 to 18 minutes, and the steel is tapped after standing for 1 to 3 minutes after the oxygen blowing is completed.