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

Abstract

The present application relates to a kind of converter slagging agent production process using electrolytic aluminum iron slag removal, using the iron slag removal generated by electrolytic aluminum industry, add part of active substance, produce the converter steelmaking required slagging agent, use in the early stage and middle stage of converter steelmaking, not only improve the speed of converter slagging, and can maintain converter slagging effect, simultaneously can also optimize the process effect of converter later stage splashing slag protection furnace, for Chinese steel industry scale processing electrolytic aluminum industry generated hazardous waste develops a kind of extremely competitive process method, highlights the technical advantage of cross innovation in different technical fields.

Description

Technical Field

[0001] This invention relates to a process for producing converter slagging agent using iron removal slag from electrolytic aluminum. Background Technology

[0002] In the electrolytic aluminum production process, after the anode conductive steel claws operate in a high-temperature environment for a period of time, they heat up, and the red-hot iron on their surface reacts with oxygen in the ambient air to form iron oxide scale. This iron oxide scale falls into the electrolytic cell and has a significant negative impact on the electrolytic aluminum process. Therefore, the iron oxide scale on the surface of the electrolytic aluminum anode needs to be cleaned regularly. During the cleaning process, the electrolyte and aluminum oxide adhering to the anode surface also peel off and mix with the iron oxide scale, becoming a type of waste in the electrolytic aluminum industry, known as iron removal slag.

[0003] Iron removal slag produced in the electrolytic aluminum industry contains easily soluble fluorides, nitrides, and carbides, and is therefore classified as a reactive and toxic hazardous waste. The composition of iron removal slag produced by a certain enterprise is shown in Table 1 below: ; A review of literature (1) reveals that Ma Jianli, Shang Xiaofu, Ma Yunpeng, et al. published a paper entitled "Development Direction of Hazardous Waste Treatment Technology in Electrolytic Aluminum Industry" in the 36th volume of the journal "Chemical Industry and Environmental Protection" in 2016. The paper states that "resources and environment are key to sustainable development. The carbonaceous materials and fluorides contained in the hazardous waste generated by the electrolytic aluminum industry are recyclable secondary resources. From the development history of related treatment technologies both domestically and internationally, it can be seen that realizing the resource utilization of electrolytic aluminum waste tank liners is an inevitable choice for the world facing the dual pressures of resources and environment. Classification treatment and flotation-leaching processes can effectively achieve the goal of turning hazardous waste from the electrolytic aluminum industry into valuable resources, and are currently the best process choice for treating this type of hazardous waste. Furthermore, due to the advantages of wet processing in the resource utilization of hazardous waste from the electrolytic aluminum industry, it will inevitably become the future treatment technology for related materials." The content of the 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 fourth issue of the journal "Design and Research of Nonferrous Metallurgy" in 2019. In the middle, there is the content of "Currently, the domestic electrolytic aluminum hazardous waste overhaul slag, waste cathode and waste tank lining are mainly stored and harmlessly treated by wet treatment technology. The resource utilization of the wet treatment process after harmless treatment is insufficient, or the added value of the end product of resource utilization is low. The harmless tailings of overhaul slag are mainly calcium fluoride, among which fluorine resources have not been effectively explored and utilized. The highly graphitized carbon components in the waste cathode become ordinary carbon powder, which have not been explored and utilized either."; (3) Yang Xuechun published a paper entitled "A Brief Analysis of the Treatment Methods of Overhaul Waste Slag in Electrolytic Aluminum Plants" in the third issue of the journal "Design and Research of Nonferrous Metallurgy" in 2007. In the middle, there is the content of "Recycling and Utilization of Overhaul Waste Slag in Electrolytic Cells, Currently, domestic research on the treatment of electrolytic cell overhaul waste residue is still in the theoretical research stage and has not yet been put into actual production. There are basically two theories regarding the treatment of this waste residue in my country: one is to use a rotary kiln calcination method to burn the carbon in the waste residue, allowing the fluorine to enter the flue gas and be adsorbed by alumina. The remaining solid waste residue can be used as raw material for the cement and refractory materials industries or for road paving; the other is to use acid hydrolysis, adding concentrated sulfuric acid to the electrolytic cell overhaul waste residue, and further processing after the reaction yields products such as hydrofluoric acid, graphite powder, sodium aluminate, aluminum hydroxide, and fluoride salts. While both methods can achieve the goal of non-toxic treatment of electrolytic cell overhaul waste residue, whether they can be industrialized and what the economic benefits are remains to be further verified.

[0004] As can be seen from the literature above, the iron removal slag produced in 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 involves blowing high-speed industrial pure oxygen onto the surface of the molten iron added to the converter, while simultaneously adding slag-forming materials to create slag.

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

[0007] In the initial stage of converter steelmaking, oxygen blowing oxidizes most of the silicon, manganese, and phosphorus in the molten iron, converting these elements into oxides. These oxides react with added calcareous fluxes (lime, limestone, etc.) and magnesian fluxes (dolomite lumps, lightly calcined dolomite, magnesia balls, magnesite, etc.) to form slag, which covers the surface of the molten iron. Through the interfacial reaction between the slag and the molten iron, and various complex chemical reactions occurring in the emulsion where the molten iron and slag are emulsified, harmful substances in the molten iron and steelmaking raw materials are further reduced to below the composition range required for the steel grade. The rapid melting of the slag is crucial to the process outcome of converter steelmaking.

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

[0009] ; A review of literature (1) reveals that Huang Zhiyong, Yuan Tingwei, Yan Genfa, et al. published a paper entitled "Experimental Study on the Application of MnO-based Fluorine-free Composite Slag Forming Agent in the Converter Smelting of Shagang Steel" in the first issue of the "Journal of Anhui Metallurgical Technology Vocational College" in 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. Considering factors such as resources, price, slag forming speed, and slag fluidity, among the various fluorine-free composite slag forming agents mentioned above, only MnO-based and CaO-Fe2O3-based are satisfactory." The article does not mention the relevant content of using electrolytic aluminum to remove iron slag and slag; (2) Yang Zhizheng, Cao Tongyou, Qu Tie, et al. published a paper entitled "Characteristics and Application of Fluorine-Free Flux in Reblown Converter Slag" in the third issue of the Journal of Wuhan Engineering Vocational College in 2011. The article states that "High-efficiency, clean, and economical converter smelting is the direction of steelmaking technology development. Fluorite, as the main slag flux used in current converter smelting, has the functions of rapid slag formation, reducing splashing, and preventing lance sticking. However, some of the CaF2 in fluorite is retained in the molten converter slag, while some volatilizes into the converter flue gas as fluorides. Most of this then dissolves in water during the flue gas purification process, polluting the air and water, seriously endangering the health of on-site operators and related personnel, and simultaneously corroding production equipment, causing premature aging. Currently, steel enterprises are the main emitters of fluoride pollutants. Therefore, in the converter smelting process, using other materials to replace fluorite as a converter slag flux, or using other methods to promote rapid slag melting, has become one of the problems that must be solved." The article also fails to mention the process of producing converter slagging agents using iron-removing slag generated from the electrolytic aluminum industry.

[0010] In summary, there is currently no process method described for utilizing electrolytic aluminum slag as a slagging agent in converters for resource recovery. Summary of the Invention

[0011] The purpose of this invention is to provide a process for producing converter slagging agent using iron removal slag from electrolytic aluminum. This process enables large-scale resource utilization of iron removal slag generated in the electrolytic aluminum industry, with low processing costs, thorough harmless conversion of the iron removal slag, and no new solid waste generated during resource utilization.

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

[0013] The inventors discovered the following scientific phenomena through experimentation and research: 1. The inventors discovered that, apart from the fluorides in the iron slag, which are sodium fluoroaluminate, sodium fluoride, etc., with melting points lower than those of calcium fluoride used in converters, fluoride ions can be released relatively quickly during the converter steelmaking process. The calcium and magnesium fluxes used in the converter can be used as resource-based substitutes for fluorite in the converter steelmaking process. 2. After the slag-removal process in the converter steelmaking process is completed, the easily soluble fluorides in the iron slag can be harmlessly transformed. The principle of this harmless transformation is as follows: A: Melting of readily soluble fluorides in high-temperature steel slag from a converter: 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 discovered that adjusting the fluxing components in the iron removal slag can achieve a synergistic effect in fluxing, thereby optimizing the converter steelmaking process. The synergistic effect is best when alumina is added. 4. The inventors discovered that after adding alumina, the converter slag formation is rapid, 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 helps to improve the competitiveness of the product. 5. The inventors discovered that the low-melting-point liquid slag formed by sodium salt with alumina and silica can exist stably in the high-basicity steel slag of the converter, which is beneficial to reducing the re-drying of the converter steel slag and improving the dephosphorization capacity of the converter.

[0014] The innovative aspects of this invention are as follows: 1. Based on the above scientific findings, the inventor proposed to crush the iron removal slag to a particle size of less than 1mm, add coal tar as a binder, add aluminum ash, a hazardous waste generated by electrolytic aluminum enterprises, and press it into pellets using a high-pressure dry powder briquetting machine, so as to use it as a slag-reducing agent in the converter steelmaking process, thus solving the problem of resource utilization of iron removal slag. 2. When slag-reducing pellets made with coal tar as a binder are added to the converter, the coal tar in the pellets undergoes thermal decomposition, which promotes the rapid decomposition of the pellets into multiple small particles, which participate in the fluxing reaction and increase the reaction rate. 3. The C and H elements produced after thermal cracking of coal tar can react with Fe2O3 in the iron removal slag to generate low-valence FeO, which increases the slag-forming speed. 4. By utilizing the Na element in the iron slag, the dephosphorization capacity in the converter steelmaking process can be significantly improved, thereby enhancing the performance of the products.

[0015] The beneficial effects of this invention are as follows: 1. This invention enables large-scale resource utilization of iron removal slag produced in the electrolytic aluminum industry, resulting in low processing costs, thorough harmless conversion of the iron removal slag, and no new solid waste generated during resource utilization, demonstrating significant environmental advantages; 2. Since sodium salts, alumina, ferric oxide, and fluorine in the iron removal slag are all slag-forming fluxing components, the composition of the slag-forming agent in this invention is easy to control, and the requirements for individual components are not high. Therefore, changes in the composition of the iron removal slag during resource utilization have little impact on the slag-forming effect in converter steelmaking, which is conducive to the large-scale resource utilization of iron removal slag; 3. The process method of this invention not only achieves the harmless conversion of iron removal slag but also optimizes the converter slag-forming process and slag splashing furnace protection process, which is conducive to the promotion and implementation of slag-forming agents in steel plants. Detailed Implementation

[0016] The embodiments of the present invention are illustrated using a 1.6 million-ton-per-year electrolytic aluminum production line and a 15 million-ton-per-year converter steelmaking production line in Northwest China as examples.

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

Claims

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