Method for preparing molten iron and pure semi-steel by three removal process-based vanadium extraction

Abstract

This invention discloses a method for vanadium extraction from molten iron and preparation of pure semi-steel based on a three-stage descaling process, belonging to the field of metallurgical technology. The method comprises the following sequential steps: vanadium-containing molten iron → deep Si removal → vanadium extraction → vanadium slag removal → P removal → S removal → pure semi-steel; the entire process is completed in the same dedicated molten iron ladle within the three-stage descaling station of the molten iron pretreatment, without passing through a separate vanadium extraction converter. Specifically, after deep Si removal, the Si content in the molten iron is ≤0.15%; the final vanadium extraction temperature is controlled at 1360~1450℃, and the molten iron temperature after vanadium slag removal is controlled at 1350~1430℃; the final pure semi-steel has the following chemical composition by mass percentage: C≥3.2%, Mn≤0.10%, P≤0.010%, S≤0.005%, and the vanadium slag has the following chemical composition by mass percentage: V₂O₅15~25%, SiO₂≤20%, CaO≤2.5%. This invention deeply integrates the vanadium extraction process with the three-stage devanadium removal process, eliminating the need for a separate vanadium extraction converter. It has advantages such as low equipment investment, high vanadium slag grade, high semi-steel purity, optimized heat utilization, and a short process flow.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a method for vanadium extraction and preparation of pure semi-steel through molten iron pretreatment, and more particularly to a method for completing vanadium extraction and preparation of pure semi-steel in the same molten iron ladle based on a three-stage molten iron removal process (removal of Si, P, and S). Background Technology

[0002] Vanadium, an important strategic metal, is widely used in steel, aerospace, energy storage batteries, and chemical catalysts. Vanadium primarily originates from vanadium-titanium magnetite, accounting for approximately 85% of global resources. After smelting vanadium-containing iron from vanadium-titanium magnetite in a blast furnace, existing vanadium extraction techniques mainly include the converter double-stage extraction process and the ladle extraction process.

[0003] The converter duplex vanadium extraction process is currently the most mature and widely used vanadium extraction technology. Its process flow is as follows: vanadium-titanium magnetite ore → blast furnace smelting (to obtain vanadium-containing molten iron) → vanadium extraction converter smelting (to obtain vanadium slag and semi-steel) → semi-steel → converter smelting. The vanadium slag, as the main raw material for vanadium extraction, enters the next process, using sodium roasting-water leaching or calcification roasting-acid / alkali leaching to obtain flake vanadium (high-purity V₂O₅). The semi-steel is then further smelted in a conventional converter to produce qualified molten steel. The converter duplex vanadium extraction process has the advantages of high vanadium slag grade, high production efficiency, and significant economic benefits, thus becoming a landmark core technology for large vanadium-titanium magnetite smelting enterprises in China, such as Panzhihua Iron and Steel Group and Chengde Iron and Steel Group.

[0004] However, there are many technical challenges and difficulties in the double-tank vanadium extraction process: (1) The temperature control of the vanadium extraction converter is difficult. If the temperature is too high, carbon will be oxidized in large quantities, and the vanadium slag grade will decrease. If the temperature is too low, the slag fluidity will be poor and the slag-iron separation will be difficult. (2) The vanadium extraction converter needs to be designed with a suitable oxygen lance and oxygen supply system to quickly form a highly oxidizing atmosphere and promote the oxidation of vanadium. (3) The vanadium extraction converter is corroded by highly oxidizing slag, and the furnace lining life is short. (4) It is difficult to remove harmful elements P and S in the decarburization converter after vanadium extraction, and the purity of the molten steel is low. (5) The heat of the decarburization converter after vanadium extraction is low and the endpoint hit rate is low, which is not conducive to the production of high-quality steel grades. (6) The double-tank vanadium extraction process usually adopts a mode of one vanadium extraction converter corresponding to two conventional steelmaking converters, or one vanadium extraction converter corresponding to one conventional steelmaking converter. The initial investment is high and the converter utilization coefficient is low.

[0005] The vanadium extraction process using a ladle shaker involves adding molten iron and a certain amount of oxidant (such as iron ore or steel mill scale) to a horizontally reciprocating ladle and then shaking it. The selective oxidation of vanadium is achieved through the reaction of the oxidant with the molten iron. However, this method has a long processing cycle, low efficiency, and is rarely used.

[0006] In recent years, researchers have proposed various improvement schemes. Chinese patent application CN116287531A discloses a vanadium-containing molten iron converter smelting process. This process involves pre-treating and desulfurizing vanadium-titanium molten iron before placing it in a vanadium-extraction converter for vanadium extraction and dephosphorization. The semi-steel is then subjected to high-carbon smelting in a steelmaking converter, resulting in pure molten steel with high carbon, high manganese, low nitrogen, low phosphorus, and low oxygen content. Through the design of the vanadium-containing molten iron process flow, the coordination of each step is achieved, effectively avoiding problems such as insufficient heat source, high oxidizing properties, and difficulty in controlling phosphorus in the final molten steel. However, this process is essentially still a duplex process, and the addition of lime during dephosphorization in the vanadium-extraction converter inevitably increases the CaO content in the vanadium slag, affecting vanadium flake extraction.

[0007] Chinese patent application CN120311044A discloses a method for vanadium extraction using a top-blown nitrogen-oxygen mixed gas. Addressing issues in existing vanadium extraction processes such as excessively rapid molten pool temperature rise, insufficient stirring, and limited vanadium oxidation rate, the method improves vanadium recovery and reduces residual vanadium content in semi-finished steel by precisely controlling the nitrogen-oxygen mixed blowing ratio, rationally allocating blowing time, and combining heat balance calculations and endpoint control. This ensures steel quality and meets the requirements of subsequent steelmaking processes. However, this process is essentially still a duplex process, and cannot solve the problems of short converter life, high initial investment, and low converter utilization coefficient in vanadium extraction.

[0008] Chinese patent application CN115821070A discloses a method for vanadium extraction from molten iron through oxidation. In this method, a mixture of carbon dioxide and oxygen is top-blown and bottom-blown, utilizing the weak oxidizing properties of carbon dioxide to replace some of the oxygen in the reaction. This achieves vanadium extraction while preserving carbon without the addition of a coolant. However, this process is essentially still a duplex process and its complex flow cannot fundamentally resolve the inherent limitations of the duplex method.

[0009] Chinese patent application CN117802328A discloses a vacuum method for extracting vanadium from vanadium-containing molten iron. The method involves rotating a ladle containing vanadium-containing molten iron to a vacuum treatment position. Under vacuum, the vanadium-containing molten iron completes a reciprocating circulation from the ladle to the vacuum chamber. During this circulation, iron oxide pellets are added through a vacuum hopper. This reciprocating circulation process provides favorable kinetic conditions, reducing the vanadium content in the molten iron to extremely low levels. Simultaneously, the resulting vanadium slag has a lower TFe content than the vanadium slag produced by converter treatment, and a higher V2O5 content than the vanadium slag produced by converter vanadium extraction. However, the vacuum device requires a large initial investment, and the resulting semi-steel has high levels of harmful elements P and S, resulting in low steel purity.

[0010] The three-stage hot metal removal process is a core step in the pretreatment of molten hot metal in iron and steel metallurgy. Broadly speaking, it includes the removal of Si, P, and S from molten hot metal. This process enables the economical and stable production of high-end steel with ultra-low P and ultra-low S content, significantly improving steelmaking quality and the ability to develop various product varieties. The three-stage hot metal removal process is based on thermodynamic principles of sequential control, process isolation of conflicting environments, and professional and efficient reaction intensification. It restructures the steelmaking process, doubling the efficiency of converter steelmaking, laying the foundation for clean steel production, opening the door to high-end products, and improving the technical and economic indicators and green and low-carbon level of the entire steel manufacturing process.

[0011] However, there are no reports in the existing technology of deeply integrating and synergistically optimizing the vanadium extraction process and the three-stage devanadium removal process in the same molten iron ladle. Therefore, developing a short-process, high-efficiency, and low-cost method that can complete vanadium extraction and obtain pure semi-steel at the same station without the need for a separate vanadium extraction converter has significant industrial application value. Summary of the Invention

[0012] The technical problem this invention aims to solve is to provide a method for vanadium extraction from molten iron and the preparation of pure semi-steel based on a three-stage desulfurization process. This method deeply integrates and synergistically optimizes the three-stage desulfurization process (Si removal, P removal, and S removal) of molten iron pretreatment with the vanadium extraction process. After blast furnace smelting, vanadium-containing molten iron does not need to enter a separate vanadium extraction converter. Instead, the oxidation sequence and thermodynamic conditions are precisely controlled within the same molten iron ladle used in the three-stage desulfurization process, sequentially completing deep Si removal, vanadium extraction, vanadium slag removal, P removal, and S removal, ultimately yielding pure semi-steel. This invention aims to solve the problems of high equipment investment, low converter utilization, short furnace lining life, high P / S content in semi-steel, and insufficient heat in existing double-stage converter vanadium extraction methods. It also addresses the low efficiency of existing ladle methods and the high investment costs of vacuum methods. This method features a short process flow, high vanadium extraction efficiency, simplified steelmaking tasks, and optimal heat and material utilization throughout the entire process.

[0013] To achieve the above objectives, the present invention adopts the following technical solution: The method for vanadium extraction from molten iron and preparation of pure semi-steel based on the three-stage descaling process is characterized by the following production process: vanadium-containing molten iron → deep Si descaling → vanadium extraction → vanadium slag removal → P descaling → S descaling → pure semi-steel; the method is completed in the three-stage descaling station of molten iron pretreatment, without passing through a separate vanadium extraction converter. The following steps are performed sequentially: S1, Vanadium-containing molten iron preparation: Vanadium-titanium magnetite ore is beneficiated to obtain vanadium-titanium iron concentrate, which is then sintered / pelletized and smelted in a blast furnace to obtain vanadium-containing molten iron. The vanadium-containing molten iron is transported to the molten iron pretreatment desulfurization station using special molten iron ladle cars; the vanadium-containing molten iron contains V ≥ 0.15% and (Si+Ti) ≤ 1.0%; S2, Deep Si Removal Step: Vanadium-containing molten iron is placed in a special molten iron ladle. A desiccating agent is sprayed from the top of the ladle to below the surface of the molten iron using a spray gun. Simultaneously, N2 is sprayed to assist in stirring. After desiccation, the molten iron ladle is tilted to a certain angle using a ladle tilting car, ensuring that the molten iron does not overflow. The desiccated slag is then removed to a slag pan using a slag remover, ensuring that the Si content in the molten iron is ≤ 0.15%. S3, Vanadium extraction step: After deep deSi removal and slag removal, vanadium is extracted by blowing oxygen with a water-cooled oxygen lance in the same special molten iron ladle, and a coolant is added to control the temperature. The final temperature of vanadium extraction is controlled at 1360~1450℃. S4, Vanadium slag removal step: After vanadium extraction, the molten iron ladle is tilted to a certain angle using a ladle tilting car, ensuring that the molten iron does not overflow. The slag remover is then started to remove the vanadium slag into a special vanadium slag pan. After removing the vanadium slag, the temperature of the molten iron is controlled at 1350~1430℃. S5, De-P step: After removing the vanadium slag, de-P is removed in the same dedicated molten iron ladle using the spray method. Lime powder is sprayed from the top to below the molten iron surface through the spray gun and top coolant is added. At the same time, oxygen is blown by a water-cooled oxygen gun to remove P. After the de-P is removed, the de-P slag is removed. S6, Desulfurization step: After desulfurization, desulfurization is carried out in the same special molten iron ladle using a spraying method. The magnesium / calcium composite powder is sprayed from the top to below the surface of the molten iron through a spray gun using a carrier gas. The magnesium / calcium composite powder is composed of magnesium powder 15%~25%, CaO 60%~80%, and the remainder is composed of SiO2, Al2O3, FeO, a small amount of flux and unavoidable impurities, with a total content ≤10%. After desulfurization, the desulfurization slag is removed, and finally pure semi-steel is obtained. The chemical composition of the pure semi-steel, by mass percentage, is: C ≥ 3.2%, Mn ≤ 0.10%, P ≤ 0.010%, S ≤ 0.005%; The chemical composition of the vanadium slag by mass percentage is: V2O5 15~25%, SiO2 ≤20%, CaO ≤2.5%.

[0014] Furthermore, in step S2, the desilicated agent used for deep desilicated processing is composed of sintered ore powder, lime powder, and fluorite powder in a specific ratio; the sintered ore powder, by mass percentage, comprises: TFe 50%~60%, CaO 8%~12%, SiO2 4%~7%, MgO 2%~5%, and Al2O3 1.5%~3%. 、 In addition to the unavoidable impurities, the mass percentage of each component of the deSi agent is as follows: 40-50% sintered ore powder, 30-45% lime powder, and 15-20% fluorite powder.

[0015] Furthermore, in step S3, the water-cooled oxygen gun uses a 3-hole nozzle, and the oxygen flow rate is controlled at 25-50 Nm³. 3 / min; the water-cooled oxygen lance is 1000~2000mm above the molten iron surface when blowing oxygen in a special molten iron ladle.

[0016] Furthermore, in steps S3 and / or S5, the top-applied coolant is one or a combination of several of the following: iron oxide pellets, composite cold-fixed pellets, oxide pellets, and iron ore, and the total iron content (TFe) in the coolant is ≥50%.

[0017] Furthermore, in step S5, the water-cooled oxygen gun used for P removal employs a 3-hole nozzle, with the oxygen flow rate controlled at 25-50 Nm³. 3 / min.

[0018] Furthermore, the blow gun used in steps S2, S5, and S6 employs a two-hole nozzle, and the outer side of the blow gun body is covered with refractory material.

[0019] Furthermore, the special molten iron ladle is constructed using aluminum-silicon carbide-titanium bricks, whose chemical composition by mass percentage is: Al2O3 55%–75%, SiC 15%–30%, TiO2 3%–10%, C 2%–5%, with the remainder being unavoidable impurities such as SiO2 and Fe2O3, and the total impurity content ≤5%.

[0020] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. Simplified equipment and reduced investment: Compared with the double-tank converter method for vanadium extraction, there is no need to equip a dedicated vanadium extraction converter, reducing equipment investment and improving the utilization rate of conventional steelmaking converters; compared with the ladle method for vanadium extraction, the processing cycle is shorter, the molten iron ladle has a longer lifespan, and the efficiency is higher.

[0021] 2. High-quality vanadium slag with low impurities: Deep desiccation and removal of the desiccated slag before vanadium extraction prevent SiO2 from contaminating the vanadium slag; removal of the vanadium slag before P and S removal prevents CaO from lime powder and magnesium / calcium composite powder from contaminating the vanadium slag. The obtained vanadium slag has a V2O5 grade of 15-25%, SiO2 ≤ 20%, and CaO ≤ 2.5%, significantly reducing the energy consumption and cost of subsequent V2O5 extraction.

[0022] 3. High purity of semi-steel and simplified steelmaking process: The obtained pure semi-steel contains P≤0.010% and S≤0.005%, which is significantly lower than the traditional duplex vanadium extraction process. Subsequent steelmaking tasks are simplified to decarburization and heating, enabling slag-less smelting, shortening the smelting cycle, and improving steel yield and stability.

[0023] 4. Optimized heat utilization and energy saving: The exothermic deSi and vanadium extraction processes and the temperature-controlled deP and deS processes are completed sequentially in the same molten iron ladle, avoiding the heat waste caused by process separation in the traditional duplex vanadium extraction process, solving the contradiction of insufficient heat in semi-steel, optimizing heat distribution throughout the process and reducing process temperature drop.

[0024] 5. Flexible operation and strong adaptability: By adjusting the type and amount of coolant, it can adapt to vanadium-containing molten iron with different Si and V contents. The vanadium extraction endpoint temperature has a wide controllable range (1360-1450℃) and good process stability. Attached Figure Description

[0025] Figure 1 This is a process flow diagram of the present invention.

[0026] Figure 2 This is a flowchart of the Si removal process in this invention.

[0027] Figure 3 This is a flowchart of the vanadium extraction process in this invention.

[0028] Figure 4 This is a flowchart of the dephosphorization process in this invention.

[0029] Figure 5 This is a flow chart of the desulfurization process in this invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the following embodiments are for illustrative purposes only and are not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0031] Example 1 This embodiment was implemented in a 60-ton dedicated molten iron ladle at a certain factory, using the vanadium extraction and pure semi-steel preparation method based on the three-stage desulfurization process described in this invention.

[0032] The chemical composition of vanadium-containing molten iron is shown in Table 1: Table 1 Chemical composition of vanadium-containing molten iron in Example 1 (mass percentage, %) Testing revealed that the vanadium-containing molten iron in this embodiment contained 0.189% V and 0.268% (Si+Ti), meeting the requirements for entry into the plant of V≥0.15% and (Si+Ti)≤1.0%, thus demonstrating economic viability in vanadium extraction.

[0033] The specific implementation steps are as follows: S1, Vanadium-containing molten iron preparation: Vanadium-titanium magnetite ore is beneficiated to obtain vanadium-titanium iron concentrate, which is then sintered / pelletized and smelted in a blast furnace to obtain the aforementioned vanadium-containing molten iron. This molten iron is transported to the pretreatment desulfurization station using dedicated molten iron ladle cars. The dedicated molten iron ladle is constructed of aluminum-silicon carbide-titanium bricks, whose chemical composition, by mass percentage, is: Al2O3 69%, SiC 19%, TiO2 7%, C 2.2%, with the remainder being unavoidable impurities such as SiO2 and Fe2O3, and the total impurity content ≤5%.

[0034] In this embodiment, the 60-ton special molten iron ladle is constructed with aluminum-silicon carbide-titanium bricks. The high Al2O3 content significantly improves the strength of the bricks at both room temperature and high temperature. The high SiC content greatly enhances the molten iron ladle's resistance to slag and iron erosion, thermal conductivity, and thermal shock resistance. The addition of 7% TiO2 significantly improves the molten iron ladle's impermeability, increasing its lifespan to 382 cycles.

[0035] S2, deep Si removal: such as Figure 1 and Figure 2 As shown, vanadium-containing molten iron is poured into a special molten iron ladle, where desilicate powder is sprayed from the top down to below the surface of the molten iron using a blowtorch, while simultaneously spraying N2 to assist stirring. The desilicate powder is composed of sintered ore powder, lime powder, and fluorite powder in a specific mass percentage. In this embodiment, the proportions of each component are: sintered ore powder 50%, lime powder 30%, and fluorite powder 20%. After desilicated iron, the molten iron ladle is tilted to 10 degrees using a ladle tilting car (ensuring no overflow of molten iron), and the desilicated slag is removed to a slag pan using a slag remover. Testing shows that the Si content in the molten iron after deep desilicated iron is 0.08%, meeting the requirement of Si ≤ 0.15%.

[0036] S3, Vanadium extraction: such as... Figure 1 and Figure 3 As shown, after deep desilting and slag removal, vanadium extraction is performed using a water-cooled oxygen lance in the same dedicated molten iron ladle. The water-cooled oxygen lance uses a 3-hole nozzle, and the oxygen flow rate is controlled at 23 Nm³. 3 The oxygen blowing rate was [per minute], with the water-cooled oxygen lance positioned 1000 mm above the molten iron surface. Simultaneously, a top coolant was added to control the temperature. In this embodiment, the coolant was iron oxide pellets (made primarily from rolled steel scale), with a total iron content (TFe) of 58%, and an addition amount of 720 kg. The final vanadium extraction temperature was controlled at 1373℃. After vanadium extraction, the carbon content in the semi-steel was 3.56%.

[0037] S4, Vanadium Slag Removal: After vanadium extraction, the molten iron ladle is tilted to 10 degrees using a ladle tilting car (ensuring no overflow of molten iron). The slag remover is then used to remove the vanadium slag into a dedicated vanadium slag pan, which is then transported by slag cart to a centralized vanadium slag storage point. The temperature of the molten iron after removing the vanadium slag is 1355℃. The chemical composition of the vanadium slag obtained in this embodiment is shown in Table 2.

[0038] Table 2 Chemical composition of vanadium slag in Example 1 (mass percentage, %) S5, remove P: such as Figure 1 and Figure 4 As shown, after vanadium slag removal, phosphorus (P) removal was performed using a spraying method in the same dedicated molten iron ladle. Lime powder was sprayed from the top to below the molten iron surface using a spray gun, while a water-cooled oxygen lance was used for oxygen blowing, and a coolant was added to control the temperature. After P removal, the molten iron ladle was tilted to 10 degrees using a ladle tilting car, and the slag removal machine was started to remove the P-removed slag into a slag pot. Testing revealed that the carbon (C) content in the semi-steel after P removal was 3.27%, and the phosphorus (P) content was 0.005%.

[0039] S6, removing S: such as Figure 1 and Figure 5 As shown, after phosphorus removal and slag removal, sulfur removal was performed using a spray method in the same dedicated molten iron ladle. Using nitrogen (N2) as the carrier gas, magnesium / calcium composite powder was sprayed from the top to below the molten iron surface through a spray gun. After desuling, the desuling slag was removed, ultimately yielding pure semi-steel. Testing revealed that the sulfur content in the pure semi-steel was 0.003%. The complete chemical composition of the pure semi-steel is shown in Table 3.

[0040] Table 3 Chemical composition of pure semi-steel in Example 1 (mass percentage, %) In this embodiment, the blow gun used in steps S2, S5, and S6 has a two-hole nozzle, and the outside of the blow gun body is covered with refractory material.

[0041] This embodiment successfully achieved vanadium extraction from molten iron and the preparation of pure semi-steel based on a three-stage desulfurization process in a 60-ton dedicated molten iron ladle. The obtained vanadium slag had a V₂O₅ grade of 15.3%, a SiO₂ content of 12.22%, and a CaO content of 0.8%, meeting the quality requirements for vanadium slag. The obtained pure semi-steel had C ≥ 3.2%, P ≤ 0.010%, and S ≤ 0.005%, providing high-quality raw materials for subsequent converter smelting. The dedicated molten iron ladle had a service life of 382 cycles.

[0042] Example 2 This embodiment was implemented in a 100-ton special molten iron ladle in a certain factory. The chemical composition of the vanadium-containing molten iron is shown in Table 4.

[0043] Table 4 Chemical composition of vanadium-containing molten iron in Example 2 (mass percentage, %) The specific implementation steps are as follows: S1: The vanadium-containing molten iron has a V content of 0.20% and a (Si+Ti) content of 0.51%, which meets the requirements. The special molten iron ladle is constructed using the same aluminum-silicon carbide-titanium brick material as in Example 1. In this example, the lifespan of the 100-ton special molten iron ladle is increased to 350 cycles.

[0044] S2: The Si content in the molten iron after deep deSi removal is 0.11%. The mass percentages of sinter powder, lime powder, and fluorite powder in the deSi removal agent are 40%, 45%, and 15%, respectively. The tilting angle of the molten iron ladle is 25 degrees.

[0045] S3: Vanadium extraction is performed using a water-cooled oxygen lance, with the oxygen flow rate controlled at 35 Nm. 3 The extraction speed was [speed] / min, and the gun height was 1500 mm. The coolant was a combination of iron oxide pellets and oxide pellets, with 750 kg of iron oxide pellets (TFe=58%) and 500 kg of oxide pellets (TFe=55%) added. The final vanadium extraction temperature was controlled at 1395℃. The carbon content of the semi-steel after vanadium extraction was 3.72%.

[0046] S4: The temperature of the molten iron after removing the vanadium slag is 1366℃. The vanadium slag contains 19.8% V2O5, 15.33% SiO2, and 1.5% CaO.

[0047] S5: After P removal, the C content in the semi-steel is 3.70% and the P content is 0.007%.

[0048] S6: The S content in the semi-steel after desulfurization is 0.005%. The final pure semi-steel contains C ≥ 3.2%, Mn ≤ 0.10%, P ≤ 0.010%, and S ≤ 0.005%.

[0049] In this embodiment, the blow gun used in steps S2, S5, and S6 has a two-hole nozzle, and the outside of the blow gun body is covered with refractory material.

[0050] Example 3 This embodiment was implemented in a 150-ton special molten iron ladle in a certain factory. The chemical composition of the vanadium-containing molten iron is shown in Table 5.

[0051] Table 5 Chemical composition of vanadium-containing molten iron in Example 3 (mass percentage, %) The specific implementation steps are as follows: S1: The vanadium-containing molten iron has a V content of 0.28% and a (Si+Ti) content of 0.76%, which meets the requirements. The special molten iron ladle is constructed using the same aluminum-silicon carbide-titanium brick material as in Example 1. In this example, the lifespan of the 150-ton special molten iron ladle is increased to 323 cycles.

[0052] S2: The Si content in the molten iron after deep deSi removal is 0.15%. The mass percentages of sinter powder, lime powder, and fluorite powder in the deSi removal agent are 45%, 35%, and 20%, respectively. The tilting angle of the molten iron ladle is 35 degrees.

[0053] S3: Vanadium extraction oxygen flow rate controlled at 40 Nm 3The extraction speed was [speed] / min, and the gun height was 1800 mm. The coolant consisted of a combination of four components: iron oxide pellets, composite chilled pellets, oxide pellets, and iron ore. The addition amounts were: iron oxide pellets (TFe=58%) 600 kg, composite chilled pellets (TFe=50%) 550 kg, oxide pellets (TFe=55%) 550 kg, and iron ore (TFe=50%) 800 kg. The final vanadium extraction temperature was controlled at 1420℃. The carbon content of the semi-steel after vanadium extraction was 3.85%.

[0054] S4: The temperature of the molten iron after removing the vanadium slag is 1391℃. The vanadium slag contains 24% V2O5, 18.67% SiO2, and 2.1% CaO.

[0055] S5: After P removal, the C content in the semi-steel is 3.82% and the P content is 0.009%.

[0056] S6: The S content in the semi-steel after desulfurization is 0.002%. The final pure semi-steel contains C ≥ 3.2%, Mn ≤ 0.10%, P ≤ 0.010%, and S ≤ 0.005%.

[0057] In this embodiment, the blow gun used in steps S2, S5, and S6 has a two-hole nozzle, and the outside of the blow gun body is covered with refractory material.

[0058] Comparative Example 1 Under similar molten iron conditions, the method of this invention (three-stage vanadium extraction process) was compared with the traditional converter double-stage vanadium extraction method. The composition of the molten iron is shown in Table 6.

[0059] Table 6 Comparison of chemical composition of molten iron in Comparative Example 1 (mass percentage, %) The chemical composition of vanadium slag obtained by the two methods is compared in Table 7.

[0060] Table 7 Comparison of chemical composition of vanadium slag in Comparative Example 1 (mass percentage, %) The chemical composition and temperature comparison of the semi-steel obtained by the two methods are shown in Table 8.

[0061] Table 8 Comparison of chemical composition (%) and temperature of semi-steel in Comparative Example 1 As can be seen from the above comparison, the SiO2 and CaO content in the vanadium slag obtained by the method of the present invention is significantly lower than that of the traditional duplex method, and the V2O5 grade is higher; the P and S content in the obtained pure semi-steel is greatly reduced, and the semi-steel temperature is higher.

[0062] Comparative Example 2 Under similar molten iron conditions, the method of this invention (three-stage vanadium extraction process) was compared with the traditional converter double-stage vanadium extraction method. The composition of the molten iron is shown in Table 9.

[0063] Table 9 Comparison of chemical composition of molten iron in Comparative Example 2 (mass percentage, %) The chemical composition of vanadium slag obtained by the two methods is compared in Table 10.

[0064] Table 10 Comparison of chemical composition of vanadium slag in Comparative Example 2 (mass percentage, %) The chemical composition and temperature comparison of the semi-steel obtained by the two methods are shown in Table 11.

[0065] Table 11 Comparison of chemical composition and temperature of semi-steel in Comparative Example 2 Comparative Example 3 Under similar molten iron conditions, the method of this invention (three-stage vanadium extraction process) and the traditional converter double-stage vanadium extraction method were compared. The composition of the molten iron is shown in Table 12.

[0066] Table 12 Comparison of chemical composition of molten iron in Comparative Example 3 (mass percentage, %) The chemical composition of vanadium slag obtained by the two methods is compared in Table 13.

[0067] Table 13 Comparison of chemical composition of vanadium slag in Comparative Example 3 (mass percentage, %) The chemical composition and temperature comparison of the semi-steel obtained by the two methods are shown in Table 14.

[0068] Table 14 Comparison of chemical composition (%) and temperature of semi-steel in Comparative Example 3 The results of the above comparative examples 1-3 show that, compared with the converter double-stage vanadium extraction method, the method of the present invention has significant advantages in terms of vanadium slag grade (higher V2O5, lower SiO2 and CaO), semi-steel purity (significantly reduced P and S content), and semi-steel temperature (higher).

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for vanadium extraction from molten iron and preparation of pure semi-steel based on a three-stage desulfurization process, characterized in that, The production process is as follows: vanadium-containing molten iron → deep Si removal → vanadium extraction → vanadium slag removal → P removal → S removal → pure semi-steel; the method is completed in the three-stage descaling station of molten iron pretreatment, without going through a separate vanadium extraction converter; The following steps are performed sequentially: S1, Preparation of vanadium-containing molten iron: V ≥ 0.15%, (Si + Ti) ≤ 1.0% in vanadium-containing molten iron; S2, Deep Si Removal Step: Vanadium-containing molten iron is placed in a special molten iron ladle, and Si removal powder is sprayed from the top to below the surface of the molten iron through a spray gun. At the same time, N2 is sprayed to assist in stirring. After Si removal is completed, the Si removal slag is removed, so that Si in the molten iron is ≤0.15%. S3, Vanadium extraction step: After deep deSi removal and slag removal, vanadium is extracted by blowing oxygen with a water-cooled oxygen lance in the same special molten iron ladle, and a coolant is added to control the temperature. The final temperature of vanadium extraction is controlled at 1360~1450℃. S4, Vanadium slag removal step: After vanadium extraction is completed, remove the vanadium slag. After removing the vanadium slag, control the temperature of the molten iron at 1350~1430℃. S5, Dephosphorization step: After removing the vanadium slag, dephosphorize using the spraying method in the same dedicated molten iron ladle. Lime powder is sprayed from the top to below the surface of the molten iron through a spray gun. At the same time, oxygen is blown by a water-cooled oxygen gun, and a coolant is added to control the temperature. After dephosphorization until P in the semi-steel is ≤0.010%, stop the oxygen blowing and powder spraying, and remove the dephosphorized slag. S6, Desulfurization step: After desulfurization and slag removal, desulfurization is carried out in the same special molten iron ladle using the spray method. With N2 as the carrier gas, magnesium / calcium composite powder is sprayed from the top to below the surface of the molten iron through the spray gun. After desulfurization until S in the semi-steel is ≤0.005%, the powder spraying is stopped, the desulfurization slag is removed, and finally pure semi-steel is obtained. The chemical composition of the pure semi-steel, by mass percentage, is: C ≥ 3.2%, Mn ≤ 0.10%, P ≤ 0.010%, S ≤ 0.005%; The chemical composition of the vanadium slag by mass percentage is: V2O5 15~25%, SiO2 ≤20%, CaO ≤2.5%.

2. The method according to claim 1, characterized in that, In step S2, the deSi agent used for deep deSi removal consists of the following components by mass percentage: 40-50% sintered ore powder, 30-45% lime powder, and 15-20% fluorite powder.

3. The method according to claim 1, characterized in that, In step S3, the water-cooled oxygen gun uses a 3-hole nozzle, and the oxygen flow rate is controlled at 25-50 Nm. 3 / min.

4. The method according to claim 1, characterized in that, In step S3, the water-cooled oxygen lance is 1000-2000 mm above the molten iron surface when blowing oxygen in the special molten iron ladle.

5. The method according to claim 1, characterized in that, In steps S3 and / or S5, the top-applied coolant is one or a combination of several of the following: iron oxide pellets, composite cold-fixed pellets, oxide pellets, and iron ore, and the total iron content (TFe) in the coolant is ≥50%.

6. The method according to claim 1, characterized in that, The blow guns used in steps S2, S5, and S6 have two-hole nozzles and are covered with refractory material on the outside of the blow gun body.

7. The method according to claim 1, characterized in that, In step S5, the water-cooled oxygen lance used for dephosphorization employs a 3-hole nozzle, with the oxygen flow rate controlled at 25-50 Nm³. 3 / min.

8. The method according to claim 1, characterized in that, The special molten iron ladle is constructed using aluminum-silicon carbide-titanium bricks.

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