Process for producing converter slagging agent by using electrolytic aluminum iron removal slag

Abstract

The invention relates to a process for producing a converter slagging agent by using electrolytic aluminum iron removal slag, the slagging agent required by converter steelmaking is produced by using the iron removal slag generated in the electrolytic aluminum industry and adding part of active substances, and the slagging agent is used in the earlier stage and the middle stage of converter steelmaking, so that the converter slagging speed is increased, the converter slagging effect can be maintained, and the converter slagging agent can be used in the converter steelmaking process. And meanwhile, the process effect of later-stage slag splashing furnace protection of the converter can be optimized, a process method with high competitiveness is developed for large-scale treatment of hazardous waste generated in the electrolytic aluminum industry in the steel industry in China, and the technical advantage of cross innovation in different technical fields is manifested.

Description

Technical Field

[0001] The invention relates to a process for producing a converter slagging agent by utilizing electrolytic aluminum iron removal slag. Background Art

[0002] During the electrolytic aluminum production process, the conductive steel claws of the anodes operate in a high-temperature environment for a period of time. The heated iron on the claws' surfaces reacts with oxygen in the ambient air to form iron oxide scale. This iron oxide scale falls into the electrolytic cell, significantly negatively impacting the aluminum electrolysis process. Therefore, the surface of the aluminum anodes must be regularly cleaned of the iron oxide scale. During this cleaning process, the electrolyte and aluminum oxide adhering to the anode surface also flake off and mix with the iron oxide scale, becoming a waste product in the aluminum electrolysis industry known as iron removal slag.

[0003] The iron removal slag produced by the electrolytic aluminum industry contains soluble fluorides, nitrides, carbides, etc., and is therefore a reactive and toxic hazardous waste. The composition of the iron removal slag produced by a certain enterprise is shown in Table 1 below: ; Literature review (1) Ma Jianli, Shang Xiaofu, Ma Yunpeng, et al. published a paper titled "Development Direction of Hazardous Waste Treatment Technology in Electrolytic Aluminum Industry" in the 36th volume of the journal "Chemical Environmental Protection" in 2016. In the middle of the paper, there is a sentence "Resources and environment are the key to sustainable development. The carbonaceous materials and fluorides contained in the hazardous wastes generated by the electrolytic aluminum industry are secondary resources that can be recycled. From the development history of related treatment technologies at home and abroad, it can be seen that realizing the resource treatment of electrolytic aluminum waste tank linings is an inevitable choice in today's world facing the dual pressure of resources and environment. Classification treatment and flotation-leaching process can well achieve the goal of turning hazardous wastes from electrolytic aluminum industry into treasure, and is the best process choice for this type of hazardous waste treatment technology. In addition, due to the advantages of wet method in resource utilization of hazardous wastes from electrolytic aluminum industry, it will inevitably become the future of related treatment technologies. Development direction. "; (2) Gao Yu published a paper entitled "Current Status and Development Trend of Hazardous Waste Disposal Technology in Electrolytic Aluminum Industry" in the 4th issue of "Nonferrous Metallurgy Design and Research" in 2019, in which there is a statement that "At present, the domestic electrolytic aluminum hazardous waste, overhaul slag, waste cathode and waste tank lining are mainly treated by storage and harmless wet treatment technology. The wet treatment process is insufficient in resource utilization after harmless treatment, or the added value of the resource-based terminal products is low. The harmless tailings of overhaul slag are mainly calcium fluoride, and the fluorine resources have not been effectively mined and utilized. The highly graphitized carbon components in the waste cathode become ordinary carbon powder, which has not been mined and utilized."; (3) Yang Xuechun published a paper entitled "A Brief Analysis of the Treatment Methods of Overhaul Waste Slag of Electrolytic Aluminum Plants" in the 3rd issue of "Nonferrous Metallurgy Design and Research" in 2007, in which there is a statement that "The recycling and utilization of electrolytic tank overhaul waste slag, Domestically, this process is still at the theoretical research stage and has not yet been put into practical production. There are two basic theories for treating electrolytic cell overhaul slag in my country. One involves using a rotary kiln to burn the carbon in the slag. The fluorine released into the flue gas is then adsorbed by alumina. The remaining solid slag can be used as a raw material for the cement and refractory industries or for road paving. The other involves acid hydrolysis, where concentrated sulfuric acid is added to the electrolytic cell overhaul slag. After further treatment, products such as hydrofluoric acid, graphite powder, sodium aluminate, aluminum hydroxide, and fluoride salts can be obtained. While both methods achieve the goal of detoxifying electrolytic cell overhaul slag, their feasibility and economic benefits remain to be further verified.

[0004] According to the above literature, the iron removal slag produced by the electrolytic aluminum industry is a hazardous waste with complex components, and there is currently no clear process technology for its resource utilization.

[0005] The process of converter steelmaking is to blow high-speed industrial pure oxygen onto the surface of molten iron in the converter, and to add slag-forming materials to form slag.

[0006] The principle of the converter steelmaking process is to blow oxygen into the converter, causing oxidation reactions with carbon, phosphorus, sulfur, silicon, manganese and other elements in the molten iron. The formed oxides enter the slag or furnace gas, thereby reducing the content of carbon, phosphorus, sulfur, silicon, hydrogen, nitrogen and other elements that have a negative impact on the performance of steel.

[0007] During the initial stages of converter steelmaking, oxygen is blown to oxidize most of the silicon, manganese, and phosphorus in the molten iron, converting these elements into oxides. These react with added calcareous fluxes (lime, limestone, etc.) and magnesian fluxes (dolomite lumps, light-burned dolomite, magnesium balls, magnesite, etc.) to form slag, which coats the surface of the molten iron. Through interfacial reactions between the slag and the molten iron, as well as various complex chemical reactions within the emulsion of the molten iron and slag, harmful substances in the molten iron and steelmaking raw materials are further reduced to below the composition range required for the desired steel grade. Rapid slag dissolution is crucial to the overall performance of the converter steelmaking process.

[0008] To promote rapid dissolution of the calcium and magnesium fluxes added to the converter, various types of slagging agents are used in the converter steelmaking process. The most common are fluorite, iron ore, manganese ore, and ferrous bauxite. The primary purpose of using slagging agents is to promote the dissolution of lime and improve smelting conditions. The basic principle is to utilize certain oxides added to calcium oxide to react with it, thereby lowering its melting point. The range of melting point reduction achieved by adding 1% of a certain substance to CaO is shown in Table 2 below.

[0009] ; Literature review (1) Huang Zhiyong, Yuan Tingwei, Yan Genfa, et al. published a paper titled "Experimental Study on the Application of MnO-based Fluorine-free Composite Slag-forming Agent in Shagang Converter Smelting" in the Journal of Anhui Metallurgical Technology Vocational College, No. 1, 2006. The paper states: "Fluorine-free composite slag-forming agents include borate or B2O3-based; CaO-Fe2O3-based, Al2O3-based, TiO2-based, MnO-based and other series. Due to considerations of resources, price, slag-forming speed, slag fluidity and other factors, among the various fluorine-free composite slag-forming agents mentioned above, only the MnO-based and CaO-Fe2O3-based ones are satisfactory." The article does not mention the use of electrolytic aluminum slag for iron removal and slag slag reduction; (2) Yang Zhizheng, Cao Tongyou, Qu Tie, et al. published a paper titled "Characteristics and Applications of Fluorine-free Flux in Combined Blown Converter Slag" in the Journal of Wuhan Engineering Vocational and Technical College, No. 3, 2011. The article states, "Efficient, clean, and economical converter smelting is the direction of development in steelmaking technology. Fluorite, the primary slag flux currently used in converter smelting, accelerates slagging, reduces splashing, and prevents gun sticking. However, the CaF2 in fluorite is partially retained in the molten converter slag, while some volatilizes into the converter flue gas as fluorides. Most of this then dissolves into water during the flue gas purification process, polluting the air and water and seriously endangering the health of on-site operators and related personnel. It also corrodes production equipment, causing premature aging. Currently, steel companies are the primary emitters of fluoride pollutants. Therefore, replacing fluorite with other materials as a converter slag flux, or using other methods to promote rapid slag melting, has become a pressing issue in the converter smelting process." The article also fails to mention the process of producing converter slag-removing agents from iron-removing slag produced by the electrolytic aluminum industry.

[0010] In summary, there is currently no introduction to a process method for utilizing electrolytic aluminum deironing slag as a converter slagging agent for resource utilization. Summary of the Invention

[0011] The purpose of the present invention is to provide a process for producing a converter slag-forming agent using electrolytic aluminum deironing slag, which can be used as a resource on a large scale to utilize the deironing slag produced by the electrolytic aluminum industry. The processing cost is low, the deironing slag is completely harmlessly converted, and no new solid waste is generated during the resource utilization process.

[0012] The technical solution adopted by the present invention is a process for producing a converter slag agent using electrolytic aluminum iron removal slag, which is implemented according to the following production steps: 1) First, use the ball mill to crush the iron removal slag to less than 1 cm, and then transport it to the high-pressure dry powder briquetting machine production line for use; 2) The aluminum ash produced by the electrolytic aluminum enterprise is processed into a particle size of less than 1mm using a ball mill. After the metallic aluminum in the aluminum ash is selected, the aluminum ash is transported to the pelletizing production line for use; 3) The coal tar produced in the process of producing anode carbon blocks and cathode carbon blocks in electrolytic aluminum enterprises is transported to the pelletizing production line for use; 4) The iron removal slag and aluminum ash described in step 1) and step 2) are mixed in a weight ratio of 70%:30%, and coal tar is added to the mixed powder material as a binder during the mixing process, wherein the amount of coal tar is 5% to 10% by weight of the iron removal slag and aluminum ash mixture. After stirring evenly, a high-pressure dry powder briquetting machine is used to press the mixture into pellets with a particle size of 20 to 50 mm, wherein the composition range of the pellets is as follows: TC <10%, SiO2 ≤8%, Al2O3>15%, Na>2%, F≤15%, TFe>10%, and H2O≤5%; 5) The above pellets are transported to the converter steelmaking production line for standby use; 6) In the converter steelmaking process, the above pellets are used as slagging agents in the early and middle stages of smelting, with the amount used per ton of steel being 0.5kg to 1.5kg. The use process is the same as the process of using fluorite or bauxite for slagging in converter steelmaking.

[0013] The inventor discovered the following scientific phenomena through experiments and research: 1. The inventors discovered that the fluorides in the iron removal slag are sodium fluoroaluminate, sodium fluoride, etc., which have a lower melting point than the calcium fluoride used in the converter. During the converter steelmaking process, they can quickly dissociate into fluoride ions, which can help the calcium flux and magnesium flux of the converter. They can be used as a resource substitute for fluorite in the converter steelmaking process. 2. After the slag is removed during the converter steelmaking process, the soluble fluorides in the iron slag are transformed harmlessly. The principle of harmless transformation is as follows: A: Dissolution of soluble fluorides in converter high temperature slag: 2Na3AlF6+6(O)→3Na2O+Al2O3+12F - 2NaF+(O)→Na2O +2F - B: The most basic harmless transformation of F ions dissolved in converter slag during solidification: Ca 2+ +2F - =CaF2 Mg 2+ +2F - =MgF2 3. The inventors have discovered that adjusting the fluxing components in the iron removal slag can achieve a synergistic effect of fluxing effects and optimize the converter steelmaking process. The synergistic effect is best achieved by adding alumina components. 4. The inventors have found that after adding alumina, the converter slag is quickly deslagging, and the alumina combines with the magnesium oxide in the steel slag to form magnesium-aluminum spinel, which is beneficial to the slag splashing and furnace protection effect in the later stage of the converter, and is conducive to improving the competitiveness of the product; 5. The inventors have discovered that the low-melting-point liquid slag formed by sodium salt, alumina and silica can exist stably in the high-alkalinity slag of the converter, which is beneficial to reducing the dry-out of the converter slag and improving the dephosphorization capacity of the converter.

[0014] The innovative features of the present invention are as follows: 1. Based on the above scientific discoveries, the inventors proposed crushing the iron removal slag to a particle size of less than 1mm, adding coal tar as a binder, and adding hazardous waste aluminum ash generated by electrolytic aluminum enterprises. The pellets were pressed into pellets using a high-pressure dry powder briquetting machine, and then used as a slagging agent in the converter steelmaking process to recycle the iron removal slag. This solved the problem of resource utilization of iron removal slag. 2. When the slagging agent pellets produced with coal tar as a binder are added to the converter, the pellets are heated and the coal tar in the pellets undergoes a chemical cracking reaction, which can promote the rapid cracking of the pellets into multiple small particles, participate in the fluxing reaction, and increase the reaction rate; 3. The C and H elements produced by thermal cracking of coal tar can react with Fe2O3 in the iron removal slag to generate low-valent FeO, which increases the slag reduction rate; 4. The use of Na element in iron removal slag can significantly improve the dephosphorization capacity in the converter steelmaking process and improve the performance of the product.

[0015] The beneficial effects of the present invention are as follows: 1. By utilizing the present invention, the iron removal slag generated by the electrolytic aluminum industry can be utilized on a large scale as a resource, with low processing cost, thorough harmless transformation of the iron removal slag, and no new solid waste generated during the resource utilization process, which has significant environmental advantages; 2. Since the sodium salt, aluminum oxide, ferric oxide, and fluorine element in the iron removal slag are all slag-forming and fluxing components, the slag-forming agent composition of the present invention is easy to control, and the requirements for a single component are not high, so the change in the composition of the iron removal slag during the resource utilization process has little effect on the slag-forming effect of converter steelmaking, which is beneficial to the large-scale resource utilization of iron removal slag; 3. By utilizing the process method of the present invention, not only the harmless transformation of the iron removal slag is achieved, but also the converter slag-forming process and the slag splashing furnace protection process are optimized, which is beneficial to the promotion and implementation of the slag-forming agent in steel mills. DETAILED DESCRIPTION

[0016] The embodiments of the present invention are described by taking an electrolytic aluminum production line with an annual output of 1.6 million tons and a converter steelmaking production line with an annual output of 15 million tons in Northwest China as examples.

[0017] A process for producing a converter slag-removing agent using electrolytic aluminum iron removal slag is implemented according to the following production steps: 1) First, use the ball mill to crush the iron removal slag to less than 1 cm, and then transport it to the high-pressure dry powder briquetting machine production line for use; 2) The aluminum ash produced by the electrolytic aluminum enterprise is processed into a particle size of less than 1mm using a ball mill. After the metallic aluminum in the aluminum ash is selected, the aluminum ash is transported to the pelletizing production line for use; 3) The coal tar produced in the process of producing anode carbon blocks and cathode carbon blocks in electrolytic aluminum enterprises is transported to the pelletizing production line for use; 4) The iron removal slag and aluminum ash described in step 1) and step 2) are mixed in a weight ratio of 70%:30%, and coal tar is added to the mixed powder material as a binder during the mixing process, wherein the amount of coal tar is 5% to 10% by weight of the iron removal slag and aluminum ash mixture. After stirring evenly, a high-pressure dry powder briquetting machine is used to press the mixture into pellets with a particle size of 20 to 50 mm, wherein the composition range of the pellets is as follows: TC <10%, SiO2 ≤8%, Al2O3>15%, Na>2%, F≤15%, TFe>10%, and H2O≤5%; 5) The above pellets are transported to the converter steelmaking production line for standby use; 6) In the converter steelmaking process, the above pellets are used as slagging agents in the early and middle stages of smelting, with the amount used per ton of steel being 0.5kg to 1.5kg. The use process is the same as the process of using fluorite or bauxite for slagging in converter steelmaking.

Claims

1. A process for producing converter slag-removing agent using electrolytic aluminum iron removal slag, characterized in that Follow the production steps below: 1) First, use the ball mill to crush the iron removal slag to less than 1 cm, and then transport it to the high-pressure dry powder briquetting machine production line for use; 2) The aluminum ash produced by the electrolytic aluminum enterprise is processed into a particle size of less than 1mm using a ball mill. After the metallic aluminum in the aluminum ash is selected, the aluminum ash is transported to the pelletizing production line for use; 3) The coal tar produced in the process of producing anode carbon blocks and cathode carbon blocks in electrolytic aluminum enterprises is transported to the pelletizing production line for use; 4) The iron removal slag and aluminum ash described in step 1) and step 2) are mixed in a weight ratio of 70%:30%, and coal tar is added to the mixed powder material as a binder during the mixing process, wherein the amount of coal tar is 5% to 10% by weight of the iron removal slag and aluminum ash mixture. After stirring evenly, a high-pressure dry powder briquetting machine is used to press the mixture into pellets with a particle size of 20 to 50 mm, wherein the composition range of the pellets is as follows: TC <10%, SiO2 ≤8%, Al2O3>15%, Na>2%, F≤15%, TFe>10%, and H2O≤5%; 5) The above pellets are transported to the converter steelmaking production line for standby use; 6) In the converter steelmaking process, the above pellets are used as slagging agents in the early and middle stages of smelting, with the amount used per ton of steel being 0.5kg to 1.5kg. The use process is the same as the process of using fluorite or bauxite for slagging in converter steelmaking.