Continuous preparation method of high-quality premelting type calcium aluminate based on secondary aluminum ash

Abstract

The invention belongs to the technical field of recycling of secondary aluminum ash, and particularly discloses a continuous preparation method of high-quality pre-melting type calcium aluminate based on secondary aluminum ash, which comprises the following steps: carrying out homogenization pretreatment on a mixture prepared from the secondary aluminum ash, a calcium oxide-rich raw material and a cosolvent according to a certain proportion; and then the homogenized mixture is subjected to continuous high-temperature melting under the oxygen-enriched condition to form liquid calcium aluminate, and finally continuous cooling forming is conducted, so that full-quantification and harmless treatment and resource utilization of the secondary aluminum ash hazardous waste are achieved, online regulation and control of the raw material proportion in the homogenized mixture are combined, and the production efficiency is improved. And finally, online adjustment and continuous production of components of the high-quality pre-melting type calcium aluminate product superior to various performance technical indexes of the standard YB / T4265 are realized, and stability control and diversity of the product are facilitated, so that the market requirements can be quickly met.

Description

Technical Field

[0001] This invention relates to the field of secondary aluminum ash recycling technology, and in particular to a continuous method for preparing high-quality pre-melted calcium aluminate based on secondary aluminum ash. Background Technology

[0002] Secondary aluminum ash, commonly known as black ash, is the residue produced after the primary extraction and recovery of aluminum resources from aluminum slag. It is mainly composed of aluminum, aluminum oxides, nitrides, and molten salts. Therefore, secondary aluminum ash possesses the dual characteristics of causing environmental harm and resource waste: on the one hand, it contains a large amount of aluminum compounds, which have high industrial recycling and reuse value; on the other hand, it often contains heavy metals such as nitrides, Cr, Cd, and Pb, as well as harmful ions such as F-, Cl-, and CN-. Under large-scale accumulation, it easily forms irritating and flammable gases such as NH3 and CH4 from atmospheric moisture. Large-scale landfilling of aluminum slag not only pollutes the soil but also leads to groundwater pollution due to the migration of heavy metals and harmful ions. Therefore, the National Hazardous Waste List (2021 Edition) and the newly issued National Hazardous Waste List (2025 Edition) issued by the Ministry of Ecology and Environment, the National Development and Reform Commission and other departments both list secondary aluminum ash as HW48 hazardous waste, specifically including: ① Waste code: 321-024-48, aluminum ash slag generated on the surface of the melt during the transfer, refining, alloying and casting processes of electrolytic aluminum liquid, as well as salt slag and secondary aluminum ash generated during the aluminum recycling process; ② Waste code: 321-026-48, aluminum ash slag generated on the surface of the melt during the remelting, refining, alloying and casting processes of waste aluminum and aluminum ingots, as well as salt slag and secondary aluminum ash generated during the aluminum recycling process.

[0003] my country is a major producer and consumer of aluminum. In 2024, the national primary aluminum output was 44.005 million tons, the total output of processed aluminum products was 49 million tons, and the output of recycled aluminum was approximately 10.55 million tons. Assuming that 1 ton of primary aluminum produces 8-15 kg of electrolytic aluminum ash, 1 ton of aluminum product processing (including smelting, alloy preparation, and ingot casting) produces 20-50 kg of aluminum ash slag, and 1 ton of aluminum alloy recycling produces approximately 80-200 kg of aluminum ash slag, the annual discharge of various types of aluminum ash slag in my country is estimated to be over 4 million tons. However, my country still faces challenges in managing aluminum ash, including overstocking at storage facilities, lack of local hazardous waste treatment capacity, difficulties in inter-provincial transfer, and significant challenges in collective disposal. In recent years, with the development of a resource-saving and environmentally friendly society and the gradual increase in environmental protection efforts, there is an urgent need to explore and develop high-value, harmless, and clean resource utilization technologies for hazardous waste aluminum ash slag.

[0004] After years of exploration and research, the current processing technologies for secondary aluminum ash mainly include: wet processing, pyrometallurgical processing, and combined wet-pyrometallurgical processing.

[0005] Patent publication number CN115028151B discloses a method for the comprehensive utilization of secondary aluminum ash. The process steps include: mixing and reacting secondary aluminum ash, a catalyst, and a solvent, followed by separation to obtain ammonia, high-alumina material, and desalination filtrate; evaporating and crystallizing the desalination filtrate to obtain an aluminum refining agent; mixing and reacting the high-alumina material with an acid solution, followed by solid-liquid separation to obtain an acid hydrolysate and a filter cake; drying the filter cake to obtain inert high-alumina material; mixing the acid hydrolysate with a separating agent, followed by solid-liquid separation to obtain aluminum salt crystals and filtrate. This method achieves full utilization of resources in aluminum ash, converting nitrogen in the ash into ammonia water, soluble salts into aluminum refining agent products, soluble aluminum into aluminum salt crystal products, and inert aluminum into inert high-alumina material products. Therefore, this method is a combined wet and pyrometallurgical process. Because the desalination filtrate needs to be evaporated and crystallized, and the filter cake needs to be dried, the energy consumption is large. Furthermore, acid hydrolysis is required after solid-liquid separation, resulting in a long processing procedure, high investment, and the generation of a large amount of waste acid hydrolysis liquid. In addition, the heavy metal oxides inside the secondary aluminum ash are not centrally treated, which can easily cause secondary pollution.

[0006] Patent publication number CN117623349B discloses a method for recycling secondary aluminum ash and its application. This method mainly includes the following three steps: S1, pre-treating the secondary aluminum ash with heated water washing, then mixing it with ammonium sulfate, calcining and leaching it to obtain a leachate, then cooling and crystallizing the leachate, separating the solid, and calcining it to obtain alumina; S2, hydroxylating the alumina to obtain hydroxylated alumina; S3, blending the hydroxylated alumina with carboxymethyl cellulose and reacting it with ultrasonic heating to obtain modified alumina. Therefore, this method is a wet process. Because this method requires pre-treatment with water washing, ammonium sulfate mixing and calcination, water leaching, calcination, hydroxylation, and ultrasonic heating to prepare modified alumina, the preparation process is lengthy, requires significant investment, and easily discharges large amounts of reaction waste liquid and residue, causing secondary pollution to the environment.

[0007] Patent publication number CN113913619A discloses a method for efficient nitrogen removal from secondary aluminum ash and preparation of pre-melted calcium aluminate refining agent. This method involves mixing secondary aluminum ash with quicklime and soda ash, then oxidizing aluminum nitride to aluminum oxide and ammonia through high-temperature treatment in air. The mixture is then melted to obtain calcium aluminate melt, which is poured and cooled to obtain the pre-melted calcium aluminate refining agent. This indicates that the method is a pyrometallurgical process. However, since secondary aluminum ash contains 1-6% metallic aluminum and aluminum compounds such as AlN and AlF, combustion requires oxygen. This method only involves nitrogen and sulfur removal from the secondary aluminum ash in air, which can easily lead to inefficient reactions and high impurity content in the calcium aluminate product. Furthermore, this method involves intermittent pouring of liquid calcium aluminate, which cannot achieve continuous production, resulting in unstable product quality and low production efficiency.

[0008] Patent publication number CN114853460B discloses a method for simultaneously preparing calcium aluminate from secondary aluminate ash using a sintering machine. This method involves mixing secondary aluminate ash with calcium-containing raw materials, recycled ore, and fuel to form granules. The resulting granules are then fed onto a sintering machine for ignition and sintering. The resulting sintered ore is cooled and crushed to obtain the sintered calcium aluminate product. Therefore, this method is a pyrometallurgical process, specifically a sintering process. It is difficult to remove Fe2O3 and heavy metal oxides from the secondary aluminate ash, easily leading to a high impurity content in the sintered calcium aluminate product.

[0009] In summary, the existing secondary aluminum ash resource utilization process is lengthy, easily causes secondary environmental pollution, is difficult to remove heavy metals from products, has high impurity content in pre-melted calcium aluminate products, and has high production costs due to intermittent production. These problems urgently need to be solved. Summary of the Invention

[0010] To address the aforementioned technical problems, this invention provides a continuous method for preparing high-quality pre-melted calcium aluminate based on secondary aluminum ash.

[0011] To achieve the above objectives, the present invention is implemented according to the following technical solution: A continuous preparation method for high-quality pre-melted calcium aluminate based on secondary aluminum ash includes the following steps: S1. Homogenization pretreatment: Secondary aluminum ash, calcium oxide-rich raw materials, and flux are mixed in a certain proportion and mechanically stirred under closed conditions to obtain a homogenized mixture. The mass percentages of secondary aluminum ash, calcium oxide-rich raw materials, and flux in the homogenized mixture are 38-56 wt%, 40-60 wt%, and 1-4 wt%, respectively. S2. Continuous high-temperature melting: First, the homogenized mixture is continuously added to the continuous high-temperature melting furnace under closed conditions through a hydraulic feeding system. Then, under oxygen-enriched air conditions, the heat released by the combustion of natural gas is adjusted by adjusting the direction of the combustion nozzle to make the homogenized mixture evenly heated. When the temperature reaches 1580±35℃, a high-temperature melting reaction occurs to form liquid calcium aluminate. Finally, the liquid calcium aluminate is discharged out of the continuous high-temperature melting furnace through overflow, realizing continuous production. S3. Continuous cooling and molding: Liquid calcium aluminate is poured onto a chain plate machine or grate cooler with a cooling tank to achieve continuous production of pre-melted calcium aluminate products.

[0012] Further, preferably, the secondary aluminum ash is the aluminum ash residue generated on the surface of the melt during the transfer, alloying, and casting processes of electrolytic aluminum liquid, or the aluminum ash residue generated on the surface of the melt during the remelting, alloying, and casting processes of waste aluminum and aluminum ingots, after mechanical ball milling to extract and recover metallic aluminum. The secondary aluminum ash contains more than 72 wt% aluminum and aluminum compounds, and has a maximum particle size of less than 2 mm. The aluminum compounds are mainly composed of Al2O3, AlN, and AlF.

[0013] Furthermore, the calcium oxide-rich raw material is one or both of quicklime and limestone.

[0014] Furthermore, the flux is one or more of sodium oxide, potassium oxide, sodium carbonate, and potassium carbonate.

[0015] Preferably, in step S2, the oxygen-enriched air is air with an oxygen content of 50-70%.

[0016] Furthermore, the inner cavity of the continuous high-temperature melting furnace has a rectangular cross-section, and the inner wall of the furnace is provided with a furnace body refractory material layer. One side of the continuous high-temperature melting furnace has a feeding port for adding homogenized mixture, and the upper part of the other side has an overflow trough. A sunken heavy metal collection trough is provided at the bottom of the continuous high-temperature melting furnace on one side of the overflow trough. The upper part of the high-temperature melting furnace is provided with a combustion nozzle and a negative pressure exhaust device. Under oxygen-enriched air conditions (i.e., air with an oxygen content of 55%), the heat released by the combustion of natural gas is uniformly heated by adjusting the direction of the combustion nozzle. Once the temperature reaches 1570-1580℃, the furnace... The upper homogenized mixture undergoes a high-temperature melting reaction to form liquid calcium aluminate. Under high temperature, a sintered layer is formed between the low-temperature homogenized mixture entering from the feed port and the upper liquid calcium aluminate. Simultaneously, the liquid calcium aluminate is continuously discharged from the high-temperature melting furnace through the overflow tank, achieving continuous production. Fluorides, chlorides, sulfides, and nitrides generated during the high-temperature melting reaction are collected and treated in stages by the environmental protection system. Heavy metal oxides such as lead oxide, cadmium oxide, chromium oxide, and mercury oxide generated during the reaction accumulate in the bottom collection tank under the action of gravity and density difference, achieving the harmless treatment of secondary aluminum ash hazardous waste.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) By mixing and feeding materials under closed conditions, the present invention can avoid the reaction between secondary aluminum ash hazardous waste and moisture in the air to form corrosive ammonia gas. At the same time, under oxygen-rich conditions, the homogenized mixture composed of secondary aluminum ash, calcium oxide-rich raw materials and flux can undergo a high-temperature melting reaction, with a reaction temperature of up to 1580±35℃, so that the calcium aluminate obtained by the reaction is in a liquid state in the furnace. (2) The present invention is equipped with a negative pressure exhaust device at the top of the continuous high temperature melting furnace, and a heavy metal collection tank is also provided at the bottom of the overflow tank area. The fluorides, chlorides, sulfides and nitrides generated during the high temperature melting reaction are collected in a unified manner to the environmental protection system for step-by-step treatment. The heavy metal oxides such as lead oxide, cadmium oxide, chromium oxide and mercury oxide generated during the reaction are collected in the bottom collection tank under the action of gravity and density difference, and transferred to a qualified professional institution for centralized treatment, thus realizing the full-quantification and harmless treatment of secondary aluminum ash hazardous waste. (3) The present invention can continuously feed a homogenized mixture consisting of secondary aluminum ash, calcium oxide-rich raw materials and flux into a continuous high-temperature melting furnace under closed conditions. Combined with continuous cooling and forming equipment, it can promote the continuous production of pre-melted calcium aluminate products for steelmaking, facilitate the control of product performance stability, and realize the resource utilization of secondary aluminum ash hazardous waste. (4) The pre-melted calcium aluminate product prepared by the present invention meets the performance technical indicators of standard YB / T4265 (name: pre-melted calcium aluminate for steelmaking). Moreover, due to the high temperature of the high-temperature melting reaction, about 1580±35℃, the content of impurity elements such as S, P, N and F in the pre-melted calcium aluminate product can be greatly reduced, which is beneficial to the improvement of the refining quality of downstream special steel. (5) The present invention can control the composition of liquid calcium aluminate by adjusting the proportion of raw materials in the homogenized mixture, thereby realizing the online adjustment and continuous production of pre-melted calcium aluminate products for steelmaking, which is conducive to product diversity and can quickly adapt to market demand. Attached Figure Description

[0018] Figure 1 This is a flowchart of the continuous preparation method of high-quality pre-melted calcium aluminate based on secondary aluminum ash according to the present invention.

[0019] Figure 2 This is a schematic diagram of a continuous high-temperature melting furnace.

[0020] Figure 3 This is a physical image of a pre-melted calcium aluminate product according to an embodiment of the present invention.

[0021] Figure 4 This is a curve showing the relationship between the Al2O3 content in the pre-melted calcium aluminate product and the ratio of secondary aluminum ash to calcium oxide-rich raw materials according to an embodiment of the present invention.

[0022] The attached diagram is labeled as follows: 1. Furnace body refractory material layer; 2. Homogenized mixture; 3. Liquid calcium aluminate; 4. Combustion spray; 5. Sintered layer; 6. Overflow trough; 7. Negative pressure exhaust device; 8. Heavy metal collection trough. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0024] according to Figure 1 The flowchart shown illustrates the continuous preparation method of high-quality pre-melted calcium aluminate based on secondary aluminum ash. The following detailed examples illustrate this method.

[0025] Example 1: S1. Homogenization pretreatment: Secondary aluminum ash, calcium oxide-rich raw materials, and flux are mixed in a certain proportion and mechanically stirred under sealed conditions to obtain a homogenized mixture. The mass percentages of secondary aluminum ash, calcium oxide-rich raw materials, and flux in the homogenized mixture are 38wt%, 60wt%, and 2wt%, respectively, and the ratio of secondary aluminum ash to calcium oxide-rich raw materials is 0.63.

[0026] S2, Continuous High-Temperature Melting: The homogenized mixture is continuously fed into a continuous high-temperature melting furnace under closed conditions via a hydraulic feeding system, such as... Figure 2 As shown in the illustration, this embodiment exemplarily demonstrates a continuous high-temperature melting furnace. The inner cavity of the continuous high-temperature melting furnace has a rectangular cross-section with a length of 5-8m. The inner cavity wall of the continuous high-temperature melting furnace is provided with a furnace body refractory material layer 1. One side of the continuous high-temperature melting furnace is provided with a feeding port 2 for adding homogenized mixture, with a width of 0.5-1.5m. The upper part of the other side is provided with an overflow trough 6, with a width of 1m. The bottom of the continuous high-temperature melting furnace on one side of the overflow trough 6 is provided with a sunken heavy metal collection trough 8, with a width of 0.5-1.5m. The upper part of the high-temperature melting furnace is provided with a combustion nozzle 4 and a negative pressure air extraction device 7. Then, under oxygen-enriched air conditions (i.e., air with an oxygen content of 55%), natural gas is released by combustion by adjusting the direction of the combustion nozzle. The heat ensures that the homogenized mixture is heated evenly. When the temperature reaches 1570-1580℃, the homogenized mixture in the upper part of the furnace undergoes a high-temperature melting reaction to form liquid calcium aluminate. Under the action of high temperature, a sintered layer 5 is formed between the low-temperature homogenized mixture entering from the feeding port 2 and the upper liquid calcium aluminate. At the same time, the liquid calcium aluminate 3 is continuously discharged out of the high-temperature melting furnace through the overflow tank, realizing continuous production. The fluorides, chlorides, sulfides and nitrides generated during the high-temperature melting reaction are collected and treated in stages by the environmental protection system. Heavy metal oxides such as lead oxide, cadmium oxide, chromium oxide and mercury oxide generated during the reaction accumulate in the bottom collection tank 8 under the action of gravity and density difference, realizing the harmless treatment of secondary aluminum ash hazardous waste.

[0027] S3. Continuous Cooling and Molding: The liquid calcium aluminate 3 discharged from the overflow tank 6 is poured onto a chain conveyor or grate cooler equipped with a cooling tank to achieve continuous production of pre-melted calcium aluminate products. In some embodiments, the cooling tank is shaped like an inverted trapezoid or cone, with a depth ranging from 25-45 mm and a volume ranging from 35-50 mL. A physical image of the pre-melted calcium aluminate product obtained in this embodiment is shown below. Figure 3 As shown.

[0028] Example 2: S1, Homogenization pretreatment: Secondary aluminum ash, calcium oxide-rich raw materials, and flux are mixed in a certain proportion and mechanically stirred under sealed conditions to obtain a homogenized mixture. The mass percentages of secondary aluminum ash, calcium oxide-rich raw materials, and flux in the homogenized mixture are 45wt%, 52wt%, and 3wt%, respectively, and the ratio of secondary aluminum ash to calcium oxide-rich raw materials is 0.83.

[0029] S2, Continuous High-Temperature Melting: The homogenized mixture is continuously fed into a continuous high-temperature melting furnace under closed conditions via a hydraulic feeding system, such as... Figure 2 As shown in the illustration, this embodiment exemplarily demonstrates a continuous high-temperature melting furnace. The inner cavity of the continuous high-temperature melting furnace has a rectangular cross-section with a length of 5-8m. The inner cavity wall of the continuous high-temperature melting furnace is provided with a furnace body refractory material layer 1. One side of the continuous high-temperature melting furnace is provided with a feeding port 2 for adding homogenized mixture, with a width of 0.5-1.5m. The upper part of the other side is provided with an overflow trough 6, with a width of 1m. The bottom of the continuous high-temperature melting furnace on one side of the overflow trough 6 is provided with a sunken heavy metal collection trough 8, with a width of 0.5-1.5m. The upper part of the high-temperature melting furnace is provided with a combustion nozzle 4 and a negative pressure air extraction device 7. Then, under oxygen-enriched air conditions (i.e., air with an oxygen content of 58%), natural gas is released by combustion by adjusting the direction of the combustion nozzle. The heat ensures that the homogenized mixture is heated evenly. When the temperature reaches 1585-1595℃, the homogenized mixture in the upper part of the furnace undergoes a high-temperature melting reaction to form liquid calcium aluminate. Under the action of high temperature, a sintered layer 5 is formed between the low-temperature homogenized mixture entering from the feeding port 2 and the upper liquid calcium aluminate. At the same time, the liquid calcium aluminate 3 is continuously discharged out of the high-temperature melting furnace through the overflow trough, realizing continuous production. The fluorides, chlorides, sulfides and nitrides generated during the high-temperature melting reaction are collected and treated in stages by the environmental protection system. Heavy metal oxides such as lead oxide, cadmium oxide, chromium oxide and mercury oxide generated during the reaction accumulate in the bottom collection tank 8 under the action of gravity and density difference, realizing the harmless treatment of secondary aluminum ash hazardous waste.

[0030] S3. Continuous cooling and molding: The liquid calcium aluminate 3 discharged from the overflow tank 6 is poured onto a chain plate machine or grate cooler with a cooling tank to realize the continuous production of pre-melted calcium aluminate products. In some embodiments, the shape of the cooling tank is an inverted trapezoid or cone shape with a larger top and a smaller bottom, with a depth range of 25-45mm and a volume range of 35-50 mL.

[0031] Example 3: S1. Homogenization pretreatment: Secondary aluminum ash, calcium oxide-rich raw materials, and flux are mixed in a certain proportion and mechanically stirred under sealed conditions to obtain a homogenized mixture. The mass percentages of secondary aluminum ash, calcium oxide-rich raw materials, and flux in the homogenized mixture are 48wt%, 49wt%, and 3wt%, respectively, and the ratio of secondary aluminum ash to calcium oxide-rich raw materials is 0.97.

[0032] S2, Continuous High-Temperature Melting: The homogenized mixture is continuously fed into a continuous high-temperature melting furnace under closed conditions via a hydraulic feeding system, such as... Figure 2 As shown in the illustration, this embodiment exemplarily demonstrates a continuous high-temperature melting furnace. The inner cavity of the continuous high-temperature melting furnace has a rectangular cross-section with a length of 5-8m. The inner cavity wall of the continuous high-temperature melting furnace is provided with a furnace body refractory material layer 1. One side of the continuous high-temperature melting furnace is provided with a feeding port 2 for adding homogenized mixture, with a width of 0.5-1.5m. The upper part of the other side is provided with an overflow trough 6, with a width of 1m. The bottom of the continuous high-temperature melting furnace on one side of the overflow trough 6 is provided with a sunken heavy metal collection trough 8, with a width of 0.5-1.5m. The upper part of the high-temperature melting furnace is provided with a combustion nozzle 4 and a negative pressure air extraction device 7. Then, under oxygen-enriched air conditions (i.e., air with an oxygen content of 63%), natural gas is released by combustion by adjusting the direction of the combustion nozzle. The heat ensures that the homogenized mixture is heated evenly. When the temperature reaches 1585-1595℃, the homogenized mixture in the upper part of the furnace undergoes a high-temperature melting reaction to form liquid calcium aluminate. Under the action of high temperature, a sintered layer 5 is formed between the low-temperature homogenized mixture entering from the feeding port 2 and the upper liquid calcium aluminate. At the same time, the liquid calcium aluminate 3 is continuously discharged out of the high-temperature melting furnace through the overflow trough, realizing continuous production. The fluorides, chlorides, sulfides and nitrides generated during the high-temperature melting reaction are collected and treated in stages by the environmental protection system. Heavy metal oxides such as lead oxide, cadmium oxide, chromium oxide and mercury oxide generated during the reaction accumulate in the bottom collection tank 8 under the action of gravity and density difference, realizing the harmless treatment of secondary aluminum ash hazardous waste.

[0033] S3. Continuous cooling and molding: The liquid calcium aluminate 3 discharged from the overflow tank 6 is poured onto a chain plate machine or grate cooler with a cooling tank to realize the continuous production of pre-melted calcium aluminate products. In some embodiments, the shape of the cooling tank is an inverted trapezoid or cone shape with a larger top and a smaller bottom, with a depth range of 25-45mm and a volume range of 35-50 mL.

[0034] Example 4: S1, Homogenization pretreatment: Secondary aluminum ash, calcium oxide-rich raw materials, and flux are mixed in a certain proportion and mechanically stirred under closed conditions to obtain a homogenized mixture. The mass percentages of secondary aluminum ash, calcium oxide-rich raw materials, and flux in the homogenized mixture are 53wt%, 44wt%, and 3wt%, respectively, and the ratio of secondary aluminum ash to calcium oxide-rich raw materials is 1.2.

[0035] S2, Continuous High-Temperature Melting: The homogenized mixture is continuously fed into a continuous high-temperature melting furnace under closed conditions via a hydraulic feeding system, such as... Figure 2 As shown in the illustration, this embodiment exemplarily demonstrates a continuous high-temperature melting furnace. The furnace has a rectangular cross-section with an inner length of 5-8m. The inner wall of the furnace is provided with a furnace body refractory material layer 1. One side of the furnace has a feeding port 2 for adding homogenized mixture, with a width of 0.5-1.5m; the other side has an overflow trough 6 with a width of 1m. At the bottom of the furnace on one side of the overflow trough 6, a sunken heavy metal collection trough 8 with a width of 0.5-1.5m is provided. The upper part of the furnace is equipped with a combustion nozzle 4 and a negative pressure exhaust device 7. Then, under oxygen-enriched air conditions (i.e., air with an oxygen content of 68%), natural gas is released through combustion by adjusting the direction of the combustion nozzle. The heat ensures that the homogenized mixture is heated evenly. When the temperature reaches 1595-1605℃, the homogenized mixture in the upper part of the furnace undergoes a high-temperature melting reaction to form liquid calcium aluminate. Under the action of high temperature, a sintered layer 5 is formed between the low-temperature homogenized mixture entering through the feeding port 2 and the upper liquid calcium aluminate. At the same time, the liquid calcium aluminate 3 is continuously discharged out of the high-temperature melting furnace through the overflow tank, realizing continuous production. The fluorides, chlorides, sulfides and nitrides generated during the high-temperature melting reaction are collected and treated in stages by the environmental protection system. Heavy metal oxides such as lead oxide, cadmium oxide, chromium oxide and mercury oxide generated during the reaction accumulate in the bottom collection tank 8 under the action of gravity and density difference, realizing the harmless treatment of secondary aluminum ash hazardous waste.

[0036] S3. Continuous cooling and molding: The liquid calcium aluminate 3 discharged from the overflow tank 6 is poured onto a chain plate machine or grate cooler with a cooling tank to realize the continuous production of pre-melted calcium aluminate products. In some embodiments, the shape of the cooling tank is an inverted trapezoid or cone shape with a larger top and a smaller bottom, with a depth range of 25-45mm and a volume range of 35-50 mL.

[0037] Example 5: S1, Homogenization pretreatment: Secondary aluminum ash, calcium oxide-rich raw materials, and flux are mixed in a certain proportion and mechanically stirred under closed conditions to obtain a homogenized mixture. The mass percentages of secondary aluminum ash, calcium oxide-rich raw materials, and flux in the homogenized mixture are 56wt%, 40wt%, and 4wt%, respectively, and the ratio of secondary aluminum ash to calcium oxide-rich raw materials is 1.4.

[0038] S2, Continuous High-Temperature Melting: The homogenized mixture is continuously fed into a continuous high-temperature melting furnace under closed conditions via a hydraulic feeding system, such as... Figure 2As shown in the illustration, this embodiment exemplarily demonstrates a continuous high-temperature melting furnace. The inner cavity of the continuous high-temperature melting furnace has a rectangular cross-section with a length of 5-8m. The inner cavity wall of the continuous high-temperature melting furnace is provided with a furnace body refractory material layer 1. One side of the continuous high-temperature melting furnace is provided with a feeding port 2 for adding homogenized mixture, with a width of 0.5-1.5m. The upper part of the other side is provided with an overflow trough 6, with a width of 1m. The bottom of the continuous high-temperature melting furnace on one side of the overflow trough 6 is provided with a sunken heavy metal collection trough 8, with a width of 0.5-1.5m. The upper part of the high-temperature melting furnace is provided with a combustion nozzle 4 and a negative pressure air extraction device 7. Then, under oxygen-enriched air conditions (i.e., air with an oxygen content of 70%), natural gas is released by combustion by adjusting the direction of the combustion nozzle. The heat ensures that the homogenized mixture is heated evenly. When the temperature reaches 1605-1615℃, the homogenized mixture in the upper part of the furnace undergoes a high-temperature melting reaction to form liquid calcium aluminate. Under the action of high temperature, a sintering layer 5 is formed between the low-temperature homogenized mixture entering from the feeding port 2 and the upper liquid calcium aluminate. At the same time, the liquid calcium aluminate 3 is continuously discharged out of the high-temperature melting furnace through the overflow tank, realizing continuous production. The fluorides, chlorides, sulfides and nitrides generated during the high-temperature melting reaction are collected and treated in stages by the environmental protection system. Heavy metal oxides such as lead oxide, cadmium oxide, chromium oxide and mercury oxide generated during the reaction accumulate in the bottom collection tank 8 under the action of gravity and density difference, realizing the harmless treatment of secondary aluminum ash hazardous waste.

[0039] S3. Continuous cooling and molding: The liquid calcium aluminate 3 discharged from the overflow tank 6 is poured onto a chain plate machine or grate cooler with a cooling tank to realize the continuous production of pre-melted calcium aluminate products. In some embodiments, the shape of the cooling tank is an inverted trapezoid or cone shape with a larger top and a smaller bottom, with a depth range of 25-45mm and a volume range of 35-50 mL.

[0040] Comparative Example 1 Except for the cosolvent mass percentage being 0.5 wt% in step S1, the remaining steps are consistent with those in Example 1.

[0041] Comparative Example 2 Except for the oxygen content of 45% in the oxygen-enriched air in step S2, the other steps are the same as in Example 2.

[0042] Comparative Example 3 Except for the target temperature of 1500-1510°C for the high-temperature melting reaction in step S2, the other steps are consistent with those in Example 3.

[0043] The pre-melted calcium aluminate prepared in Examples 1-5 and Comparative Examples 1-3 were subjected to compositional analysis, and the results are shown in Table 1.

[0044] Table 1 ; As shown in Table 1, when the mass percentage of the flux added in step S1 is low (0.5 wt%), the melting reaction of the homogenized mixture composed of secondary aluminum ash, calcium oxide-rich raw materials, and flux will not be smooth. Consequently, the content of impurities such as fluoride, SO3, P2O5, and heavy metal oxides in the pre-melted calcium aluminate product exceeds the upper limit, which is not conducive to improving product quality. Compared with Example 1, the mass contents of fluoride, SO3, P2O5, and heavy metal oxides in the pre-melted calcium aluminate product of Comparative Example 1 increased from 0.6 wt%, 0.04 wt%, 0.03 wt%, and 0.002% to 1.0 wt%, 0.09 wt%, 0.08 wt%, and 0.007%, respectively. When the oxygen content in the oxygen-enriched air in step S2 is low (45%), the high-temperature melting reaction in the furnace will be in a complete state, thus reducing the actual temperature of the high-temperature melting reaction. Compared with Example 2, the high-temperature melting reaction temperature in Comparative Example 2 drops from approximately 1585-1595℃ to 1530-1540℃. This will lead to an increase in the viscosity of the liquid calcium aluminate in the furnace, resulting in the floating of Fe2O3, fluorides, SO3, P2O5, and heavy metals within the liquid calcium aluminate. Oxides are difficult to remove by settling, which is not conducive to improving the quality of pre-melted calcium aluminate products and the harmless treatment of secondary aluminum ash hazardous waste. Compared with Example 2, the mass contents of Fe2O3, fluoride, SO3 and P2O5 in the pre-melted calcium aluminate product of Comparative Example 2 increased from 1.0wt%, 0.7wt%, 0.05wt%, 0.04wt% and 0.003% to 1.6wt%, 1.1wt%, 0.09wt%, 0.08wt% and 0.008%, respectively.

[0045] When the melting reaction temperature in step S2 is low (1510-1520℃), the viscosity of the liquid calcium aluminate in the melting furnace will increase, which will make it difficult to remove Fe2O3, fluoride, SO3, and P2O5 floating and heavy metal oxides sinking in the liquid calcium aluminate. This is not conducive to improving the quality of the pre-melted calcium aluminate product and the harmless treatment of secondary aluminum ash hazardous waste. Compared with Example 3, the mass content of Fe2O3, fluoride, SO3, and P2O5 in the pre-melted calcium aluminate product of Comparative Example 3 increased from 1.0wt%, 0.8wt%, 0.06wt%, 0.06wt%, and 0.003% to 1.7wt%, 1.2wt%, 0.1wt%, 0.08wt%, and 0.01%, respectively.

[0046] Furthermore, combining the results of Examples 1-5, by Figure 4It can be seen that the Al2O3 content in pre-melted calcium aluminate products is directly proportional to the ratio of secondary aluminum ash to calcium oxide-rich raw materials. In other words, the composition of liquid calcium aluminate can be controlled by adjusting the proportion of raw materials in the homogenized mixture, thereby achieving online adjustment and continuous production of pre-melted calcium aluminate products.

[0047] In summary, the continuous preparation method of high-quality pre-melted calcium aluminate based on secondary aluminum ash provided by this invention realizes the harmless treatment and resource utilization of hazardous waste such as secondary aluminum ash, and ultimately achieves online adjustment and continuous production of high-quality pre-melted calcium aluminate products with performance and technical indicators superior to those of standard YB / T4265 (name: pre-melted calcium aluminate for steelmaking).

[0048] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. A continuous preparation method for high-quality pre-melted calcium aluminate based on secondary aluminum ash, characterized in that, Includes the following steps: S1. Homogenization pretreatment: Secondary aluminum ash, calcium oxide-rich raw materials, and flux are mixed in a certain proportion and mechanically stirred under closed conditions to obtain a homogenized mixture. The mass percentages of secondary aluminum ash, calcium oxide-rich raw materials, and flux in the homogenized mixture are 38-56 wt%, 40-60 wt%, and 1-4 wt%, respectively. S2. Continuous high-temperature melting: First, the homogenized mixture is continuously added to the continuous high-temperature melting furnace under closed conditions through a hydraulic feeding system. Then, under oxygen-enriched air conditions, the heat released by the combustion of natural gas is adjusted by adjusting the direction of the combustion nozzle to make the homogenized mixture evenly heated. When the temperature reaches 1580±35℃, a high-temperature melting reaction occurs to form liquid calcium aluminate. Finally, the liquid calcium aluminate is discharged out of the continuous high-temperature melting furnace through overflow, realizing continuous production. S3. Continuous cooling and molding: Liquid calcium aluminate is poured onto a chain plate machine or grate cooler with a cooling tank to achieve continuous production of pre-melted calcium aluminate products.

2. The continuous preparation method of high-quality pre-melted calcium aluminate based on secondary aluminum ash according to claim 1, characterized in that: The secondary aluminum ash contains more than 72 wt% aluminum and aluminum compounds, with a maximum particle size of less than 2 mm. The aluminum compounds are mainly composed of Al2O3, AlN, and AlF.

3. The continuous preparation method of high-quality pre-melted calcium aluminate based on secondary aluminum ash according to claim 1, characterized in that: The calcium oxide-rich raw material is one or both of quicklime and limestone.

4. The continuous preparation method of high-quality pre-melted calcium aluminate based on secondary aluminum ash according to claim 3, characterized in that: The flux is one or more of sodium oxide, potassium oxide, sodium carbonate, and potassium carbonate.

5. The continuous preparation method of high-quality pre-melted calcium aluminate based on secondary aluminum ash according to claim 1, characterized in that: In step S2, the oxygen-enriched air is air with an oxygen content of 50-70%.

6. The continuous preparation method of high-quality pre-melted calcium aluminate based on secondary aluminum ash according to claim 1, characterized in that: The inner cavity of the continuous high-temperature melting furnace has a rectangular cross-section. The inner cavity wall of the continuous high-temperature melting furnace is provided with a furnace body refractory material layer. One side of the continuous high-temperature melting furnace is provided with a feeding port for adding homogenized mixture, and the upper part of the other side is provided with an overflow trough. The bottom of the continuous high-temperature melting furnace on one side of the overflow trough is provided with a sunken heavy metal collection trough. The upper part of the high-temperature melting furnace is provided with a combustion nozzle and a negative pressure exhaust device.

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