A method for preparing steel refining slag by synergistically using aluminum dross and regenerated fluoride

Abstract

This invention discloses a method for preparing steelmaking refining slag using aluminum ash and recycled fluorides, belonging to the field of metallurgical solid waste resource utilization technology. Existing processes are divided into two categories that are mutually exclusive: one involves binary calcination of aluminum ash and calcium, requiring the addition of fluorite on-site, which cannot handle fluorine-containing hazardous waste; the other involves separate melting and regenerating cryolite, which easily generates large amounts of fluorine-containing dust in the furnace. This invention uses aluminum ash, recycled fluorine-containing solid waste, and calcium raw materials as ternary core components, which can be supplemented with silicon, magnesium, barium, and manganese as fine-tuning auxiliary materials. After mixing all materials, the mixture is calcined at a constant temperature of 800–1300°C in air, resulting in a solid-phase reaction that generates a composite aluminum-fluorine-calcium salt. Under the same smelting conditions and basic batching, the amount of auxiliary slag-forming materials required for complete slag formation in this product is significantly lower than that required for physically mixing uncalcined materials, which can greatly reduce the amount of fluorite purchased and used by steel plants, and simultaneously and harmlessly dispose of two types of aluminum industry solid waste. The process involves two implementation routes: direct calcination of powder and pre-pressed ball calcination. Existing calcium aluminate production lines can be put into operation simply by adjusting the ingredients, resulting in low industrialization transformation costs.

Description

Technical Field

[0001] This invention relates to a method for processing auxiliary materials in the refining of LF furnace steel, and also to the field of harmless and resource-based utilization of industrial solid waste in the aluminum electrolysis and aluminum processing industries. Background Technology

[0002] The LF refining furnace is a core piece of equipment for steel deoxidation, desulfurization, and composition fine-tuning. The melting rate and high-temperature fluidity of the refining slag directly determine the refining efficiency. Currently, steel mills commonly use fluorite as a flux. Fluorite is a restricted mineral, and its purchase price fluctuates greatly. At 1600℃, fluorite decomposes to produce fluorinated fumes, resulting in high dust removal and defluorination costs for enterprises.

[0003] Aluminum ash is a solid waste byproduct of aluminum smelting and electrolytic aluminum production, containing alumina and aluminum nitride. When stored in the open, it releases ammonia gas when exposed to rainwater. Recycled cryolite and fluorine-containing waste residue from aluminum electrolysis contain soluble fluorine, which can easily cause fluoride pollution of water and soil when stored, and have extremely low resource utilization value when conventionally landfilled. Recycled cryolite has a low melting point, but when added to molten steel for rapid pyrolysis, it produces ultrafine dust, and the flue gas emissions are difficult to meet standards, making it unsuitable as a raw material for slag formation.

[0004] Existing publicly available technologies fall into two categories, and neither category offers any combined insights: Category 1: Calcium aluminate is prepared by binary high-temperature calcination of aluminum ash and calcium raw materials. No recycled cryolite is added during the sintering stage. Only fluorite is added on-site. It is impossible to simultaneously dispose of fluorine-containing hazardous waste, and the slag-forming efficiency is limited.

[0005] The second type: ice crystal is melted and recycled separately to make blocks. The entire process does not involve simultaneous high-temperature reaction with aluminum ash or calcium raw materials. Using it alone results in severe smoke and dust pollution.

[0006] The industry has long adopted the approach of "separate production and on-site physical mixing," and there is no solution for simultaneous high-temperature co-firing of aluminum ash, recycled fluorine-containing solid waste, and calcium raw materials, which presents a clear technological gap. Summary of the Invention

[0007] The invention addresses the challenge of addressing the multiple requirements of reducing fluorite content, co-processing solid waste, and minimizing fluorine dust from smelting, which are currently addressed by existing calcium aluminate sintering and recycled cryolite melting methods. This invention provides a simultaneous high-temperature co-firing process using ternary raw materials. The calcination process induces a solid-phase reaction to generate a composite aluminum-fluorine-calcium salt, reducing the amount of slag-forming auxiliary materials required with the same raw material ratio. Existing calcium aluminate production lines can achieve mass production without modifying the main equipment, requiring only adjustments to the feed formulation.

[0008] Complete technical solution A method for synergistically preparing steelmaking refining slag using aluminum ash and recycled fluorides, wherein the raw materials are divided into ternary core components and optional functional modifiers; the ternary core components are aluminum ash, recycled fluorine-containing solid waste, and calcareous raw materials; the functional modifiers are selected from one or more siliceous, magnesium, barium, and manganese materials; complete preparation steps: S1. Raw material pretreatment: Various solid raw materials are crushed, ball-milled and sieved separately to unify the particle size for easy mixing and solid-phase reaction; S2. Ingredient mixing: Based on 100 parts by weight of aluminum ash, add 15-45 parts of recycled fluorine-containing solid waste and 20-60 parts of calcium raw materials according to the ratio, and add 0-30 parts of functional regulator as needed. Stir thoroughly to obtain a homogeneous mixed dry powder. S3. High-temperature calcination: The mixed powder is fed into a rotary kiln or box furnace and kept at a constant temperature of 800-1300℃ for 30-180 minutes in an air environment. The system undergoes a solid-phase reaction to generate a new composite aluminum fluorine calcium salt phase. S4. Cooling and Shaping: The high-temperature clinker is naturally cooled, crushed and screened to the particle size used by the steel plant to obtain the finished refining slag.

[0009] Preferred process: After mixing dry powder in S2, a high-pressure pressing and dense pelletizing process is added before calcination. This ensures sufficient particle contact, complete solid-phase reaction, and regular agglomeration of the finished product, eliminating the need for secondary processing.

[0010] Auxiliary material description: Silicon, magnesium, barium, and manganese regulators only slightly adjust the viscosity of the slag and desulfurization performance. The core reaction system of ternary aluminum ash-calcium-regenerated fluoride remains unchanged. Adding only these auxiliary materials cannot circumvent the protection scope of this invention.

[0011] The ternary raw materials of this invention undergo a solid-phase reaction in an air atmosphere at 800–1300°C, where alumina, calcium oxide and regenerated fluoride react to form a stable composite aluminum-fluorine-calcium salt phase. Those skilled in the art can qualitatively identify this characteristic new phase by X-ray diffraction (XRD) detection, and distinguish the product of this invention from the phase structure of a physical mixture of single calcium aluminate and pure cryolite.

[0012] Performance evaluation criteria: Using a fixed and identical original batch, the only distinction is whether it is calcined at a high temperature of 800-1300℃. Under the same LF smelting conditions and the same slag basicity, the total amount of external auxiliary slag-forming materials required for complete slag formation of molten steel and the amount of fluorine-containing dust generated in the smelting flue gas are used as comparative evaluation indicators. The finished product obtained by the ternary high-temperature co-firing of this invention requires a significantly lower amount of auxiliary materials to complete the slag formation of molten steel than the same proportion of uncalcined physical mixtures, and the amount of fluorine-containing dust released during the smelting process is significantly lower.

[0013] Beneficial effects 1. Compared with the binary aluminum ash calcium sintering process: the sintering stage directly introduces recycled fluorine-containing solid waste to participate in the solid-phase reaction, which can significantly reduce the amount of fluorite added at the smelting site, and simultaneously achieve the co-treatment of aluminum ash and recycled fluorine-containing hazardous waste, avoiding the water, soil and air pollution risks caused by the separate storage of the two types of solid waste. 2. Compared with the physical mixing and slag-making process of melting cryolite alone: ​​aluminum ash, calcium raw materials and recycled fluoride react simultaneously at high temperature and solid phase, and fluorine elements combine into the composite aluminum fluorine calcium salt lattice system. This avoids the rapid decomposition of single cryolite when heated in the furnace and releasing a large amount of ultrafine fluorine-containing dust. The emission level of fluorine pollutants in smelting flue gas is significantly reduced, and the operating load of dust removal and defluorination environmental protection equipment in steel plants is reduced. 3. Core Innovation: For the first time, two independent industry production processes are integrated into a ternary raw material co-firing route. By relying on the solid-phase reaction of roasting to form a stable composite aluminum-fluorine-calcium salt, a synergistic fluxing effect is achieved. It is impossible to achieve multiple advantages such as reducing fluorite, synergistic disposal of dual solid wastes, and reducing fluorine dust by using any one of the existing processes alone. 4. Industrialization advantages: Existing calcium aluminate production lines do not require replacement or modification of the main calcination equipment; only the raw material ratio needs to be adjusted to switch to producing this product, resulting in low investment in new equipment and modifications. 5. Environmental benefits: Centralized processing of two types of industrial hazardous waste generated from aluminum smelting and electrolytic aluminum significantly reduces the cost of transporting and landfilling solid waste for enterprises, aligning with the green, low-carbon, and circular metallurgical policy orientation of the steel and aluminum industries. Detailed Implementation

[0014] All examples and comparative examples have the same raw material ratios. The only variable is whether the calcination is carried out at a high temperature of 800-1300℃. The evaluation indicators are the amount of auxiliary materials used for complete slag formation under the same working conditions and the level of fluorine dust release in flue gas.

[0015] Example 1 (Preferred pre-compression ball process, no regulator) Raw material weight proportions: 100 parts aluminum ash, 25 parts recycled cryolite, and 40 parts quicklime; mixed evenly and pressed into high-pressure balls, calcined at 1150℃ for 60 minutes, cooled and sieved to obtain the finished refined slag. Under the same LF furnace smelting conditions, the amount of external auxiliary slag-forming materials required for this finished product to complete the slag formation of molten steel is far lower than that of the same proportion of mixture that is only physically mixed and not calcined at high temperature, resulting in a significant reduction in the emission of fluorine-containing dust generated during smelting.

[0016] Example 2 (dry powder direct calcination process, without regulators) Raw material weight parts: 100 parts aluminum ash, 35 parts fluorine-containing waste residue from aluminum smelting, and 50 parts limestone; the powder is directly calcined at 1200℃ for 90 minutes, then cooled and briquetteed again. The fluxing effect is better than that of uncalcined materials, and less fluorine-containing dust is released from the smelting flue gas.

[0017] Example 3 (Expanded Scheme with Added Silicon-Magnesium Modifier) Raw material weight parts: 100 parts aluminum ash, 25 parts recycled cryolite, 40 parts quicklime, 8 parts quartz sand, and 5 parts magnesia sand; briquetting and calcination at 1150℃; the amount of auxiliary materials required for slag melting is basically the same as in Example 1, with only a slight optimization of slag viscosity; the ternary core reaction system remains unchanged, and the fluorine volatilization inhibition effect is similar.

[0018] Comparative Example 1 (Benchmarked against physical hybrid cold pressing process) The proportions are the same as in Example 1, except that the mixture is cold-pressed without roasting. Under the same working conditions, more external slag-forming auxiliary materials are required to achieve complete slag formation of molten steel. The amount of fluorine-containing dust released in the flue gas during the smelting process is large, and the environmental protection treatment pressure is higher.

[0019] Comparative Example 2 (Compared to binary aluminum-gray sintering process) 100 parts aluminum ash and 40 parts limestone were used, without the addition of recycled cryolite. The product, calcium aluminate, was roasted at 1150℃. The fluxing capacity was insufficient, and fluorite still needed to be added during smelting. The fluorine waste could not be disposed of, and the pressure on flue gas fluorine emission control was even greater. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the process flow of a preferred embodiment of the present invention, which includes two preparation routes: direct calcination of dry powder and pre-pressed ball calcination.

Claims

1. A method for synergistically preparing steelmaking refining slag using aluminum ash and recycled fluoride, characterized in that, The raw materials comprise a ternary core component and optional functional modifiers; the ternary core component is aluminum ash, recycled fluorine-containing solid waste, and calcareous raw materials; the optional functional modifiers are selected from one or more of siliceous materials, magnesium materials, barium materials, and manganese materials; the preparation steps are as follows: S1. Raw material pretreatment: Aluminum ash, recycled fluorine-containing solid waste, calcium raw materials and optional functional regulators are crushed, ground and screened to the target particle size respectively. S2. Ingredient mixing: Based on 100 parts by weight of aluminum ash, mix all raw materials and stir to obtain a uniform dry powder; S3. High-temperature calcination: The mixed dry powder is fed into the calcination equipment and calcined at a constant temperature of 800-1300℃ in air atmosphere. The material undergoes a solid-phase reaction to generate a new composite aluminum-fluorine-calcium salt phase. S4. Cooling and Shaping: The roasted clinker is naturally cooled, then crushed and screened to obtain the finished steelmaking refining slag.

2. The method for preparing steelmaking refining slag by synergistic use of aluminum ash and recycled fluoride according to claim 1, characterized in that: After obtaining the mixed dry powder in step S2 and before high-temperature calcination in step S3, a high-pressure pressing and densification process for green pellets is added. After the green pellets are formed, they are sent to the calcination equipment for constant temperature treatment.

3. The method for preparing steelmaking refining slag by synergistic use of aluminum ash and recycled fluoride according to claim 1, characterized in that: The recycled fluorine-containing solid waste is selected from at least one of recycled cryolite and fluorine-containing waste residue from aluminum smelting; the calcium raw material is one or a combination of quicklime and limestone.

4. The method for preparing steelmaking refining slag by synergistic use of aluminum ash and recycled fluoride according to claim 1, characterized in that, The raw material ratio is based on 100 parts by weight of aluminum ash: 15-45 parts of recycled fluorine-containing solid waste, 20-60 parts of calcium-based raw materials, and 0-30 parts of total functional regulators.

5. The method for preparing steelmaking refining slag by synergistic use of aluminum ash and recycled fluoride according to claim 4, characterized in that: The siliceous material is quartz sand or silica fume; the magnesian material is magnesium oxide or magnesia sand; the barium material is barium oxide or barium carbonate; and the manganese material is manganese oxide or manganese ore powder.

6. The method for preparing steelmaking refining slag by synergistic use of aluminum ash and recycled fluoride according to claim 1, characterized in that: The roasting and heat preservation time should be controlled between 30 and 180 minutes.

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