Resource utilization method for producing chromium-containing steel by converter steelmaking and cooperating with chromium slag

Abstract

The invention discloses a resource utilization method of chromium-containing steel produced by converter steelmaking and chromium slag, which utilizes components beneficial to steelmaking slag melting and alloying in the chromium slag, adopts an innovative process technology to produce the chromium slag into composite pellets, and is mainly used as a slag melting agent in the converter steelmaking process. And the function of directly alloying pellets is achieved, a slagging agent and part of ferrochrome in the converter steelmaking process are replaced, the converter steelmaking technology can be optimized, the steelmaking cost can be reduced, and the chromium slag hazardous waste can be used as a steelmaking raw material for resource utilization.

Description

Technical Field

[0001] The invention relates to a method for resource utilization of chromium slag in converter steelmaking production of chromium-containing steel. Background Art

[0002] Chromium slag refers to the residue produced during the chromium salt production process after chromite, soda ash and calcium filler are mixed in a certain proportion, calcined at high temperature, and sodium chromate is leached with water. The harmful components in chromium slag are mainly hexavalent chromium (Cr 6+ ) ions, which are harmful to the human digestive tract, respiratory tract, skin, and mucous membranes, and can even cause cancer. Therefore, chromium slag is listed as a national hazardous waste. The composition of chromium slag stored in a certain place is shown in the table below: ; Literature review (1) Xiao Yu and Jiang Dachun published a paper titled “Research on the Technology of Co-disposal of Chromium Slag by Using Metallurgical Sintering Furnace and Blast Furnace” in the 35th volume of Chongqing University Journal in 2012. The paper states: “In view of the imperfect current chromium slag treatment methods, a technology and process method for co-disposal of chromium slag by using sintering furnace and blast furnace has been developed. Without changing the sintering furnace and blast furnace processes, the reducing atmosphere microenvironment of numerous small ball cores is used to achieve complete detoxification and resource utilization of chromium slag”; (2) Wang Zhen, Yuan Shouqian, Ren Yujun et al. published a paper titled “Research on the Technology of Co-disposal of Chromium Slag by Using Metallurgical Sintering Furnace and Blast Furnace” in the 35th volume of Chongqing University Journal in 2012. The paper states: “In view of the imperfect current chromium slag treatment methods, a technology and process method for co-disposal of chromium slag by using sintering furnace and blast furnace has been developed. Without changing the sintering furnace and blast furnace processes, the reducing atmosphere microenvironment of numerous small ball cores is used to achieve complete detoxification and resource utilization of chromium slag”; (3) Wang Zhen, Yuan Shouqian, Ren Yujun et al. published a paper titled “Research on the Technology of Co-disposal of Chromium Slag by Using Metallurgical Sintering Furnace and Blast Furnace” in the 1st issue of Ferroalloys in 2016. A paper titled "Experimental Ratios for Smelting Ferrochrome Using Calcium-Free Chromium Slag" was published in the journal. The paper states, "Gansu Jinshi Chemical Co., Ltd. is a chemical company that produces chromium salts as its main product and a variety of by-products simultaneously. It is also the first chemical company in China to use a calcium-free roasting process to produce chromium salts. In production practice, a method has been successfully found to simultaneously treat the fine slag produced by this process, using blue carbon as a reducing agent and vanadium slag and silica as fluxes to reduce the chromium slag to produce chromium-containing cast iron. This method has, to a certain extent, solved the problem of fine slag treatment and achieved good economic benefits." The above literature introduction shows that the above literature does not mention the process technology for utilizing converter steelmaking in conjunction with the resource utilization of chromium slag.

[0003] The long-flow converter steelmaking process is currently the mainstream steelmaking process. Its basic process uses 65% to 100% molten iron and 0% to 35% scrap steel. High-velocity oxygen jets are used to blow oxygen into the surface of the molten iron and scrap bath, oxidizing and removing harmful elements such as Si, Mn, P, C, and S from the molten iron. The physical heat of the molten iron and the chemical heat generated during the oxygen blowing process are then used to achieve thermal and material balance during the blowing process. To remove harmful elements from the molten steel and systematically optimize the converter steelmaking process, slag-forming materials such as lime, dolomite, and fluorite are added during the converter steelmaking process. Therefore, converter steelmaking is a high-temperature process primarily based on alkaline materials, with continuous redox reactions occurring between the slag and the molten iron. The temperature in the oxygen jet reaction zone ranges from 2250°C to 3500°C.

[0004] During the converter blowing process, while blowing in oxygen, slag auxiliary materials are added in batches. In order to promote the melting of slag auxiliary materials, fluxes are also added during the converter steelmaking process. Common fluxes include bauxite, iron bauxite, iron oxide scale, manganese ore, sintered pellets, sintered ore, red mud pellets and fluorite. The converter blowing is divided into three stages, namely 1 to 3 minutes before the converter starts blowing, which is the stage when Si, Mn and P in the molten pool undergo oxidation reactions, which is called the silicon-manganese oxidation period; after most of the silicon-manganese in the molten pool is oxidized to form oxides that enter the slag, the carbon in the molten pool begins to undergo oxidation reactions to generate CO or CO2 gas, of which the amount of CO produced accounts for more than 90% of the carbon-oxygen reaction. The decarburization reaction mainly relies on the alkaline slag to continuously transfer O to the molten pool. 2- After the decarburization reaction is complete, the generated CO enters the furnace gas and is recovered by the gas recovery system. This phase is called the carbon-oxygen reaction period. After the majority of the decarburization reaction is complete, the converter steelmaking process enters the stage of adjusting the temperature and final composition. After the composition and temperature adjustments are completed, the blowing process is essentially complete. This phase is called the refining period. After the converter steelmaking refining period, the steelmaking process of deoxidation and alloying begins.

[0005] Literature review: (1) Sun Yijie and Xiong Yincheng published a paper titled "Development and Application of Composite Slagging Agent for Steelmaking" in the 5th issue of "Steelmaking" in 2001. The paper states that "the composite slagging agent is composed of converter sludge, iron oxide scale and a certain proportion of catalyst as the main raw materials, so it takes into account the advantages of both iron oxide scale and fluorite as two fluxes." (2) An Zhiping, Dong Weimin and Wang Haixia published a paper titled "Experimental Research and Application of Bauxite Slagging Process" in the 4th issue of "Henan Metallurgy" in 2008. The paper states that "using bauxite as a flux for slagging can replace fluorite, and its slagging effect can fully meet the process requirements of slagging in the converter process. Using bauxite for slagging improves the kinetic conditions of the molten pool reaction, reduces the "three sticking" accidents of the converter, and the dephosphorization and desulfurization capabilities of the slag are equivalent to those when using fluorite for slagging." According to the above-mentioned published documents, there is currently no process for resource utilization of chromium slag as a converter slagging agent.

[0006] Direct alloying of steel involves directly using alloying element oxides as the alloying material. By adding a reducing agent or using deoxidizing elements in the steel to reduce the alloying elements, the alloying elements are then introduced into the molten steel to achieve the desired alloying effect. Direct alloying eliminates the need for ferroalloy production, reducing the cost of steel alloying. Furthermore, the direct alloying process utilizes lower-grade waste slag and alloying element oxides, thereby reducing mineral resource consumption and playing a significant role in the comprehensive utilization of mineral resources. Direct alloying of steel has evolved from the initial direct alloying of manganese ore to include niobium, chromium, molybdenum, tungsten, vanadium, and rare earth elements. Driven by the strategic demands of environmental protection and sustainable economic development, direct alloying steelmaking processes are gaining increasing attention, widespread recognition, and application in steelmaking.

[0007] References (1) Di Lin, Wang Ping, and Fu Jie published a paper titled "Research and Application Status of Direct Alloying Steelmaking Process" in the 3rd issue of Special Steel in 2000. The paper states that "the direct alloying steelmaking process of manganese ore and chromium ore has been successfully applied in production. The direct alloying steelmaking process of manganese ore has been relatively mature in converter production. Chromium ore can replace ferrochrome in the smelting of stainless steel and achieve significant economic benefits. The research and promotion of the direct alloying steelmaking process of niobium ore is of great significance to the comprehensive utilization of niobium resources in my country. . The direct alloying steelmaking process meets the current requirements of comprehensive resource utilization and environmental protection. It is a promising process and needs further development and application. " (2) Zhang Fengshan and Ni Hongwei published a paper entitled "Research on the Direct Reduction and Alloying of Chromium Ore to Smelt Stainless Steel" in the third issue of "Special Steel" magazine in 2001. The paper states that "under high temperature and a certain reducing agent, the reduction rate and degree of chromium ore mainly depend on the structure and composition of the chromium ore, the composition of the slag, the temperature and the distribution of the charge, etc."

[0008] According to the above literature, there is no technology for using chromium slag in direct alloying process as described in the literature. Summary of the Invention

[0009] The purpose of the present invention is to provide a method for resource utilization of chromium slag in converter steelmaking production of chromium-containing steel. The method can realize resource utilization of valuable elements in chromium slag. While resource utilization, the harmless treatment of chromium slag is achieved, and the cost of hazardous waste treatment is greatly reduced.

[0010] The technical solution adopted by the present invention is a method for producing chromium-containing steel by converter steelmaking and utilizing chromium slag as a resource, which is implemented according to the following steps: 1) After dehydration and drying, the chromium slag is processed into 70-200 mesh and transported to the high-pressure dry powder pelletizing machine production line for standby use; 2) Process the secondary aluminum ash produced by the aluminum plant, in which the total amount of Al+AlN+Al2O3 is greater than 70%, into 50-70 mesh, and transport it to the high-pressure dry powder pelletizing machine production line for standby use; 3) Purchase waste coal tar as a binder and transport it to the pelletizing production line for use; 4) First, the chromium slag and the secondary aluminum ash are mixed in a ratio of 90% by mass to 10% by mass to form a mixture, and then the waste coal tar is added as a binder in a ratio of 10% by weight of the mixture, and a high-pressure dry powder pelletizing machine is used to produce pellets of 30 to 50 mm, wherein the main component of the pellets W[Fe2O3+Al2O3]%>60%; if W[Fe2O3+Al2O3]%<60%, the amount of secondary aluminum ash added is increased for adjustment, and the amount of waste coal tar used remains unchanged; 5) The above pellets are transported to the converter production line and used as slagging agent in the converter steelmaking process; 6) When the converter starts blowing, the above pellets are added at the same time as lime and dolomite. The amount of pellets added is 3.5 to 4.5 kg per ton of steel. The converter smelting process remains unchanged.

[0011] The present invention has discovered the following scientific phenomena through research: 1. The total content of Fe2O3 and Al2O3 components in the chromium slag, which have the effect of fluxing and slagging, is above 66%. When used as a slagging agent for converters, the slagging effect combines the advantages of both iron oxide slagging and bauxite slagging, and can replace the slagging agent in the converter steelmaking process for resource utilization; 2. The melting point of sodium chromate in chromium slag is 792°C, and calcium chromate dehydrates at 200°C. These two substances can dissociate into ions under the converter steelmaking conditions of about 1200°C, providing the basic conditions for the harmless transformation of chromium slag in the converter steelmaking process. From the theoretical perspective of thermodynamic conditions, it can be seen that after chromium slag is added to the converter, it dissociates under the thermodynamic conditions of converter steelmaking. The reaction equation is as follows: Na2CrO4→Cr 3+ +Na + +O 2- CaCrO4→Cr 3+ +Ca 2+ +O 2- 3. After the chromium slag dissociates into ions, the high-valent chromium at the steel-slag interface and in the steel-slag will be reduced to metallic chromium or trivalent chromium by Si, C, P, Fe, etc. in the molten pool. The metallic chromium enters the molten pool, and the trivalent chromium exists in the slag. This is the inventor's unique research result and the main theoretical basis for the harmless transformation of chromium slag. The main chemical reactions are as follows: Cr 6+ +3O 2- +3[C]→Cr+3{CO} Cr 6+ +O 2- +[Si]→Cr+SiO2 Cr 6+ +O 2- +[P]→Cr+P2O5 Cr 6+ +O 2- +[Si]→Cr+SiO2 4. The inventors have discovered that the chromium oxide that has not been reduced to metallic chromium will first precipitate during the solidification process of the slag according to the solidification characteristics of the slag. Magnesium-chromium spinel and iron-chromium spinel phases will be preferentially generated in the steel slag. Since the steel slag is overburned silicate cement clinker, the trivalent chromium will be harmlessly converted after entering the slag. Its safety is currently the most effective process mode to ensure that the main reactions are: Cr2O3+FeO→Cr2O3·FeO (melting point 2150℃) Cr2O3+MgO→MgO·Cr2O3 (melting point 2180℃) The inventors have discovered that the reduction reaction that can occur in large quantities after the chromate in the chromium slag dissociates is as follows: (Cr2O3)+3C=2[Cr]+3CO ΔG=785128-522.79TJ / mol According to the above thermodynamic data, chromium oxide can be reduced to a metallic state by carbon at around 800°C. This process is an endothermic reaction that can reduce the molten pool temperature in the converter smelting process. It is the basic process principle for the harmless conversion of chromium slag in the steelmaking process.

[0012] Based on the above research findings, the inventors adopted the following process to recycle chromium slag. 1. Using chromium slag as the primary raw material, 10% aluminum ash is added to the chromium slag and mixed evenly (the mass ratio of chromium slag to aluminum ash is 90%:10%). Coal tar is used as a binder to produce pellets from this mixture, which are used as a slagging agent in the early stages of converter blowing. 2. The pellets are added to the converter simultaneously with the addition of lime and magnesia flux, with the addition amount controlled at 3.5-4.5 kg per ton of steel. The rest of the converter smelting process remains unchanged.

[0013] The innovative points of the present invention are as follows: 1. The inventors added aluminum ash to the chromium slag and used it as a slagging agent for the converter. Since the Fe2O3 and Al2O3 content of the above mixture exceeds 60%, the slagging effect has the advantages of both iron oxide slagging and bauxite slagging, creating conditions for the resource utilization of chromium slag; 2. In order to recover the metallic chromium in the chromium slag and balance the heat of chemical reaction, the inventors used waste coal tar as a binder to make balls of the above mixture and use it as slagging agent pellets for the converter. After the above pellets are added to the converter, the C and H elements produced by the thermal cracking of the coal tar react with the chromium oxide in the chromium slag to reduce the chromium oxide to metallic chromium and enter the converter iron liquid, and the gas produced by the reaction escapes, which can alleviate the safety risks of slag overflow and splashing in the early stage of converter smelting.

[0014] Compared with traditional chromium slag detoxification processes, this invention can realize resource utilization of valuable elements in chromium slag. Simultaneously with resource utilization, it achieves harmless treatment of chromium slag, significantly reducing hazardous waste disposal costs. Converter steelmaking can save an equivalent amount of traditional steelmaking slag-removing agents annually, resulting in significant environmental benefits. DETAILED DESCRIPTION

[0015] The implementation of the present invention is described by taking a 150-ton converter production line as an example: A method for producing chromium-containing steel by converter steelmaking and utilizing chromium slag as a resource is implemented according to the following steps: 1) After dehydration and drying, the chromium slag is processed into 70-200 mesh and transported to the high-pressure dry powder pelletizing machine production line for standby use; 2) Process the secondary aluminum ash produced by the aluminum plant, in which the total amount of Al+AlN+Al2O3 is greater than 70%, into 50-70 mesh, and transport it to the high-pressure dry powder pelletizing machine production line for standby use; 3) Purchase waste coal tar as a binder and transport it to the pelletizing production line for use; 4) First, the chromium slag and the secondary aluminum ash are mixed in a ratio of 90% by mass to 10% by mass to form a mixture, and then the waste coal tar is added as a binder in a ratio of 10% by weight of the mixture, and a high-pressure dry powder pelletizing machine is used to produce pellets of 30 to 50 mm, wherein the main component of the pellets W[Fe2O3+Al2O3]%>60%; if W[Fe2O3+Al2O3]%<60%, the amount of secondary aluminum ash added is increased for adjustment, and the amount of waste coal tar used remains unchanged; 5) The above pellets are transported to the converter production line and used as slagging agent in the converter steelmaking process; 6) When the converter starts blowing, the above pellets are added at the same time as lime and dolomite. The amount of pellets added is 3.5 to 4.5 kg per ton of steel. The converter smelting process remains unchanged.

Claims

1. A method for producing chromium-containing steel by converter steelmaking and utilizing chromium slag as a resource, characterized in that Follow these steps to implement: 1) After dehydration and drying, the chromium slag is processed into 70-200 mesh and transported to the high-pressure dry powder pelletizing machine production line for standby use; 2) Process the secondary aluminum ash produced by the aluminum plant, in which the total amount of Al+AlN+Al2O3 is greater than 70%, into 50-70 mesh, and transport it to the high-pressure dry powder pelletizing machine production line for standby use; 3) Purchase waste coal tar as a binder and transport it to the pelletizing production line for use; 4) First, the chromium slag and the secondary aluminum ash are mixed in a ratio of 90% by mass to 10% by mass to form a mixture, and then the waste coal tar is added as a binder in a ratio of 10% by weight of the mixture, and a high-pressure dry powder pelletizing machine is used to produce pellets of 30 to 50 mm, wherein the main component of the pellets W[Fe2O3+Al2O3]%>60%; if W[Fe2O3+Al2O3]%<60%, the amount of secondary aluminum ash added is increased for adjustment, and the amount of waste coal tar used remains unchanged; 5) The above pellets are transported to the converter production line and used as slagging agent in the converter steelmaking process; 6) When the converter starts blowing, the above pellets are added at the same time as lime and dolomite. The amount of pellets added is 3.5 to 4.5 kg per ton of steel. The converter smelting process remains unchanged.