Preparation method of modified high-carbon ferrochrome based on pre-reduction technology

Abstract

The application discloses a preparation method of modified high-carbon ferrochrome based on a pre-reduction technology and belongs to the technical field of ferroalloy metallurgy. The method comprises the following steps: uniformly mixing chromite concentrate, coke powder, lime and a silicon dioxide-titanium dioxide nano composite modifier to obtain a mixture; performing solid-state pre-reduction on the mixture in a rotary kiln, and controlling the pre-reduction degree to be 45-70%; loading the pre-reduced material into a submerged-arc furnace, smelting and reducing at 1650-1800 DEG C for 4-8 hours, until slag and iron are separated, and modified high-carbon ferrochrome is obtained. The nano composite modifier is prepared by a sol-gel method, is dispersed at a slag-gold interface during the pre-reduction and smelting processes, promotes uniform nucleation of ferrochrome carbide, and optimizes the microstructure of the molten slag. The application significantly improves the chromium recovery rate, reduces unit power consumption, improves the slag-iron separation effect, and realizes efficient, low-consumption and clean production.

Description

Technical Field

[0001] This invention belongs to the field of ferroalloy metallurgy technology, specifically, it relates to a method for preparing modified high-carbon ferrochrome based on pre-reduction technology. Background Technology

[0002] High-carbon ferrochrome (HCFeCr) is a ferroalloy primarily composed of chromium and iron, with a high carbon content. Typically, it contains 50%–70% chromium and 4%–8% carbon, and is one of the most important raw materials for producing stainless steel, alloy steel, and special steels. Traditional high-carbon ferrochrome production primarily employs a submerged arc furnace (SAF) direct smelting method. This involves directly adding chromite concentrate, coke (or anthracite) as a reducing agent, and lime (or limestone) as a slag-forming agent to the electric furnace, where carbothermic reduction smelting is carried out at a high temperature of 1650–1800℃. The core reaction of this process is the carbothermic reduction of chromium spinel ((Fe,Mg)O·(Cr,Al,Fe)₂O₃), producing metallic ferrochrome and slag. Traditional processes are mature and use simple equipment, but they have significant drawbacks: First, they are extremely energy-intensive, consuming 3000–4500 kWh of electricity per ton of high-carbon ferrochrome, with some older furnaces exceeding 5000 kWh. This is mainly because chromium oxides and iron oxides in chromite need to be deeply reduced in a liquid state, requiring a high power density within the furnace to ensure uniform temperature. Second, chromium recovery rates are low, generally between 80% and 90%, with some processes only reaching 75%–85%. A large amount of chromium is lost in the slag as Cr2O3. The alloy process generates 1.2 to 1.5 tons of solid waste slag, with a Cr2O3 content of 5% to 12%, which not only wastes resources but also brings serious environmental pressure. Furthermore, the high viscosity of the slag (especially in the MgO-Al2O3-SiO2-CaO system) makes slag-metal separation difficult, and foamy slag, splashing, and metal droplet entrainment are prone to occur in the furnace, affecting furnace stability and production efficiency. In addition, the process has high carbon consumption and high CO2 emission intensity, with approximately 4 to 6 tons of carbon emissions per ton of high-carbon ferrochrome, which is difficult to meet increasingly stringent carbon emission reduction requirements.

[0003] To overcome the high energy consumption of traditional direct smelting processes, various pre-reduction processes have been developed internationally since the 1980s. These processes advance the partial reduction reaction of chromite to the solid-state stage, and then the pre-reduced raw materials are charged into an electric furnace for final reduction and smelting. These processes are collectively referred to as "pre-reduction-electric furnace smelting" composite processes. Representative technologies include: South Africa's Premus process (pelletized chromite pre-reduction in rotary kiln), Japan's Idemitsu Kosan's SRC process (Solid Reduction Process), Finland's Outokumpu's tunnel kiln pre-reduction process, and Sweden's Hoganas's fines pre-reduction technology. The pre-reduction stage is usually carried out in a rotary kiln or tunnel kiln, using coke, coal, or gaseous reducing agents at 900–1200℃ to partially metallize the chromite. The degree of pre-reduction is controlled at 40%–70%, with chromium metallization occurring preferentially over iron to avoid premature formation of a high-melting-point Fe-Cr alloy that would hinder subsequent reactions. Preheating raw materials (temperature > 800℃) into the submerged arc furnace can fully utilize sensible heat, reduce power consumption by 20% to 35%, and reduce power consumption to 2000 to 2500 kWh / t for some advanced processes, while increasing chromium recovery rate to 90% to 93%.

[0004] In recent years, pre-reduction technology has further evolved towards lower carbon emissions. Between 2023 and 2025, numerous studies focused on hydrogen-based or hydrogen-carbon synergistic pre-reduction. For example, using pure hydrogen or CH4-H2 mixed gas to pre-reduce chromite in fluidized beds or rotary kilns can significantly reduce carbon consumption and improve reduction selectivity, with chromium metallization rate preferentially increasing by 10–20 percentage points over iron. Simultaneously, new technologies such as microwave-assisted pre-roasting and selective agglomeration roasting have also been explored to improve solid-state reduction kinetics. However, despite the significant progress made in the pre-reduction composite process, the following prominent problems still exist: (1) Insufficient solid-state pre-reduction kinetics: Chromium spinel has a stable structure, limited solid-solid reaction contact area, and slow reduction rate. Especially at <1100℃, the pre-reduction degree is difficult to exceed 70%. Excessive temperature leads to particle sintering or cyclization sticking to the kiln, which limits the further improvement of the pre-reduction degree; (2) Difficulty in selective reduction control: The reduction potential of iron oxide is lower than that of chromium, and it is easy to preferentially reduce, resulting in the loss of carbon excess coefficient. Additional carbon needs to be added in subsequent smelting. At the same time, the metal phase distribution in the pre-reduction product is uneven, affecting the nucleation and growth in the smelting stage; (3) Insufficient control of slag microstructure: Even with pre-reduction, the smelting slag system is still dominated by high-melting-point MgO-Al2O3 spinel phase. The slag viscosity is still as high as 0.5~2Pa·s at 1700℃, which leads to slow aggregation and sedimentation of metal droplets and serious loss of chromium in the slag. Traditional control methods are mostly macroscopic adjustments, such as increasing the basic slag density (CaO / SiO2=1.2~1.5) or adding fluorite (CaF2) to reduce viscosity. However, the introduction of fluorides brings environmental pollution and has limited effect on the spinel phase. (4) Lack of interface reaction optimization: Existing technologies mainly focus on macroscopic process parameters (such as temperature, power density, batching system) and lack research on controlling metal nucleation and growth at the microscale of the slag-gold interface. After the pre-reduction product is hot-charged, a high-viscosity boundary layer is easily formed at the interface, which hinders the uniform nucleation of carbides, resulting in uneven alloy structure and coarse carbides, affecting product quality. (5) Limited space for energy consumption and recovery rate improvement: Although pre-reduction can reduce power consumption, in actual industrial practice, due to heat loss, secondary oxidation and furnace condition fluctuations, the comprehensive power consumption is still higher than 2000kWh / t, and the chromium recovery rate is difficult to stably break through 95%. In addition, the utilization rate of pre-reduction kiln tail gas is low, and there is still room for optimization of overall energy efficiency.

[0005] Regarding additives, existing research mainly focuses on traditional fluxes or catalysts, such as borax, sodium oxide, and iron powder, used to promote reduction or lower the melting point of slag. However, these additives require large quantities (>5%), are costly, and easily introduce impurities or environmental risks. In recent years, the application of nanomaterials in the metallurgical field has gradually emerged, such as the catalytic effect of nano-oxides in the direct reduction of iron ore or their interfacial activity in steel slag modification. However, research on nanocomposite modifiers for ferrochrome smelting, especially those combined with pre-reduction processes, is extremely rare. Existing literature occasionally reports on the preparation of nano-Cr2O3 or microwave-assisted nanoscale pretreatment, but no systematic technical path has been found to deeply couple specific nanocomposite oxides (such as the SiO2-TiO2 system) into the entire pre-reduction-smelting process to simultaneously achieve solid-state reaction contact enhancement, slag phase network rupture, and heterogeneous nucleation promotion.

[0006] In summary, while existing high-carbon ferrochrome production technologies have undergone years of improvement, achieving some progress in reducing energy consumption and increasing recovery rates, they still face bottlenecks such as poor solid-state reduction kinetics, difficulties in slag-metal separation, insufficient microscopic interface control, and challenges in further improving overall performance indicators. Especially given the continued growth in global stainless steel demand, fluctuating energy prices, and stringent environmental constraints, there is an urgent need to develop a novel process that addresses the issue at the microscopic level, deeply coupling it with pre-reduction technology to achieve efficient and selective chromium reduction, precise optimization of slag structure, and uniform control of alloy microstructure. This would significantly improve chromium recovery rates, reduce unit energy consumption, and enhance slag-iron separation, providing a new pathway for the clean and efficient production of high-carbon ferrochrome. Summary of the Invention

[0007] To address the problems of high energy consumption, low chromium recovery rate, difficult slag-metal separation, high slag viscosity, and insufficient micro-interface control in existing high-carbon ferrochrome smelting technologies, this invention provides a method for preparing modified high-carbon ferrochrome based on pre-reduction technology. This method introduces a nano-silica-titanium dioxide composite modifier with a specific composition, deeply coupling it with the solid-state pre-reduction process. In the pre-reduction stage, it enhances the solid-solid reaction contact area; in the smelting stage, it optimizes the slag-metal interface activity and promotes uniform nucleation of metal carbides; and simultaneously, it regulates the micro-network structure of the slag. This achieves highly efficient and selective chromium reduction, significantly reduces unit power consumption, improves chromium recovery rate, and enhances slag-iron separation.

[0008] The present invention adopts the following technical solution: a method for preparing modified high-carbon ferrochrome based on pre-reduction technology, comprising the following steps by mass: (1) taking 100 parts of chromite concentrate, 25-45 parts of coke powder, 15-30 parts of lime and 1-8 parts of nanocomposite modifier, and uniformly mixing them to obtain a mixture, wherein the chromite concentrate is composed of chromite spinel (chemical formula (Fe,Mg)O·(Cr,Al,Fe)2O3), the fixed carbon content of the coke powder is not less than 85%, the lime is composed of calcium oxide (CAS1305-78-8), and the nanocomposite modifier is a 10-80nm particle size dioxin. A silicon dioxide-titanium dioxide composite oxide, wherein the mass ratio of silicon dioxide (CAS7631-86-9) to titanium dioxide (CAS13463-67-7) is 3 to 7:1; (2) The mixture obtained in step (1) is subjected to a solid pre-reduction reaction in a rotary kiln at a temperature of 950 to 1150°C for 2 to 5 hours, and an inert protective gas is introduced to obtain a pre-reduced raw material, wherein the pre-reduction degree is controlled at 45 to 70%; (3) The pre-reduced raw material obtained in step (2) is directly hot-charged into a submerged arc furnace and smelted and reduced at a temperature of 1650 to 1800°C, wherein the power density in the furnace is controlled at 300 to 500 kW / m 2 The smelting time is controlled at 4 to 8 hours until the slag and iron are separated and the iron and slag are discharged to obtain modified high-carbon ferrochrome. The nanocomposite modifier is uniformly dispersed at the interface between the slag phase and the metal phase during the pre-reduction and smelting process, which promotes the uniform nucleation of ferrochrome carbides and regulates the microstructure of the slag.

[0009] The preparation method of the nanocomposite modifier includes the following steps: Tetraethoxysilane (CAS78-10-4) and tetrabutyl titanate (CAS5593-70-4) are used as precursors and added to anhydrous ethanol at a mass ratio of silicon dioxide to titanium dioxide of 3-7:1. Ammonia water is added to adjust the pH to 9-10, and the mixture is stirred and hydrolyzed at 60-80℃ for 6-12 hours to obtain a sol. The sol is dried at 120-150℃ for 12-24 hours and then calcined at 500-700℃ for 3-5 hours to obtain silicon dioxide-titanium dioxide composite oxide powder with a particle size of 10-80nm. The calcination process is carried out in an air atmosphere, and the heating rate is controlled at 3-5℃ / min.

[0010] The mixture in step (1) has the following proportions: 100 parts chromite concentrate, 30-40 parts coke powder, 18-25 parts lime, and 2-6 parts nano-composite modifier; the specific surface area of ​​the nano-composite modifier is 150-300 m². 2 / g.

[0011] In step (2), the pre-reduction temperature is 1000–1100℃, the pre-reduction time is 3–4 hours, the inert protective gas is nitrogen, and the gas flow rate is 2–5 m³ / h.3 / t of mixed feed, the metallization rate of the pre-reduced raw material after pre-reduction is controlled at 50-65%, of which the metallization rate of chromium is 5-15 percentage points higher than that of iron.

[0012] In step (3), when smelting in a submerged arc furnace, the batch amount of furnace charge added is 20-30% of the total amount of pre-reduced raw materials per batch, the secondary voltage is controlled at 180-250V, the electrode insertion depth is 40-60% of the furnace charge height, and 5-10 parts of coke / 100 parts of chromite concentrate are added during the smelting process to maintain the excess carbon coefficient in the furnace at 1.05-1.15.

[0013] The mass ratio of silicon dioxide to titanium dioxide in the nanocomposite modifier is 4-6:1. The titanium dioxide in the composite oxide is mainly in the anatase crystal form, accounting for 15-25% of the composite. The composite modifier is added to the mixture by first dry mixing with lime and then mixing with chromite concentrate and coke powder to ensure that the dispersion of nanoparticles in the mixture is not less than 95%.

[0014] In step (2) during the pre-reduction process, the rotary kiln speed is controlled at 1 to 3 r / min, the material filling rate in the kiln is 15 to 25%, and the kiln head temperature is 50 to 100°C higher than the kiln tail temperature, so as to form a temperature gradient to promote the selective pre-reduction of chromium oxides.

[0015] After smelting in step (3), the slag-iron settling time is controlled at 20-40 minutes, the basic degree of slag (CaO / SiO2 mass ratio) is controlled at 1.1-1.4, and the slag temperature is controlled at 1700-1750℃ before slag discharge, ensuring that the density difference between slag and iron is not less than 1.5 g / cm³. 3 .

[0016] Compared with the existing technology, the present invention has the following significant advantages and innovations: The core innovation of the present invention lies in the deep coupling of nano-silica-titanium dioxide (SiO2-TiO2) composite modifier with pre-reduction-electric furnace smelting composite process, and the precise control of the whole process reaction kinetics, slag microstructure and metal phase nucleation and growth behavior of high carbon ferrochrome smelting from the micro-interface scale. This micro-macro synergistic control path breaks through the limitation of the existing technology that only relies on macro parameter optimization (such as temperature, power density, slag basicity), and realizes the systematic leap in chromium recovery rate, energy utilization efficiency and product quality. The following is an in-depth analysis of the significant advantages and innovations of the present invention from the mechanism level. (1) Micro-interface catalysis and heterogeneous nucleation mechanism of nano-composite modifier to achieve dual optimization of reduction kinetics and alloy structure: Although the existing pre-reduction technology can advance some reduction reactions to the solid state, the solid-solid reaction interface is limited, and the Cr in the chromium spinel ((Fe,Mg)O·(Cr,Al,Fe)2O3) lattice is limited. 3+ and Fe 2+The high migration activation energy (approximately 250–350 kJ / mol) results in a slow reduction rate, especially in the 950–1150 °C range, where the reaction is primarily controlled by interfacial chemical reactions rather than diffusion. This invention introduces a nano-SiO2-TiO2 composite modifier (particle size 10–80 nm, specific surface area 150–300 m² / g). 2 The TiO2 anatase phase has an extremely high surface atom ratio (surface atoms account for more than 50% of the total atoms), and its surface contains a large number of unsaturated coordination bonds and defect sites (such as oxygen vacancies), which can serve as a "reaction bridge" in the solid-state pre-reduction stage, significantly increasing the effective contact points between chromite particles and coke particles. The specific mechanism is as follows: nanoparticles preferentially adhere to the surfaces of chromite and lime (dispersion >95% is ensured through a pre-dry mixing process with lime). At the high temperature of pre-reduction, the d-orbital electrons of the TiO2 anatase phase can interact with Cr... 3+ / Fe 2+ Transient coordination occurs, lowering the migration barrier of oxygen ions from the spinel lattice to the carbon surface, thus promoting the Bouduard reaction (C + CO2) at the CO / CO2 gas interface. (2CO) and indirect reduction pathways. Simultaneously, the amorphous layer of SiO2 provides high adsorption energy sites, enriches intermediate reaction gases, and increases the local CO partial pressure, transforming solid-state carbothermic reduction from a "contracting nucleus" mode to a "progressive interface advancement" mode. The pre-reduction degree increases from 40%–60% in traditional processes to 45%–70%, and the chromium metallization rate is 5–15 percentage points higher than iron. This is because TiO2 has a higher catalytic selectivity for Cr2O3 than FeO (literature reports that TiO2 can reduce the activation energy of Cr2O3 reduction by about 30–50 kJ / mol), avoiding the phenomenon of premature formation of low-melting-point Fe-Cr liquid phase and coating of unreacted nuclei caused by preferential iron reduction. Entering the smelting stage, the nanocomposite modifier is hot-charged into the submerged arc furnace along with the pre-reduced raw materials, partially dissolving in the slag phase and partially enriching at the slag-gold interface at high temperatures. Its heterogeneous nucleation effect is manifested in: in traditional smelting, (Cr,Fe)7C3 or (Cr,Fe) 23C6 carbide nucleation mainly relies on homogeneous nucleation, with a high critical nucleation work, leading to coarse and segregated carbides and increased alloy brittleness. In this invention, the nanoparticles have a small lattice mismatch (high matching degree between anatase TiO2 and (Cr,Fe)7C3 crystal planes), which can serve as low-barrier heterogeneous nucleation cores, significantly reducing nucleation undercooling (approximately 50–100°C) and promoting uniform and fine carbide nucleation and growth within the molten metal droplet (grain size reduced from the traditional 20–50 μm to 5–15 μm). Simultaneously, residual nano-SiO2-TiO2 forms a "pinning layer" at the interface, inhibiting Ostwald ripening of the carbides, thereby obtaining a modified high-carbon ferrochrome with a uniform microstructure and excellent toughness. (2) The synergistic network breaking mechanism of nano-modifiers on the micro-network structure of slag leads to a significant improvement in slag viscosity and slag-metal separation: High-carbon ferrochrome slag belongs to the CaO-MgO-Al2O3-SiO2 quaternary system. In traditional slag, SiO2 acts as a network forming body, forming a complex [SiO4]. 4- Al₂O₃ has a tetrahedral chain structure, resembling [AlO₄]. 5- Enter the network or via [AlO6] 9- The bridging mechanism results in partial depolymerization of MgO, but the overall viscosity remains high at 0.5–2 Pa·s (1700℃), leading to significant resistance to metal droplet settling and severe entrainment, resulting in a 5%–12% loss of Cr2O3 in the slag. The synergistic network-breaking mechanism of the nano-SiO2-TiO2 composite modifier of this invention is manifested in two aspects: First, the SiO2 / TiO2 mass ratio of 3–7:1 in the composite oxide ensures the bridging of Ti... 4+ (Ionic radius 0.068 nm) preferentially enters the [SiO4] network as a network-modifying ion, providing O 2- Breaking the Si-O-Si bridging oxygen bonds to form non-bridging oxygen (NBO) increases the network polymerization degree (NBO / T) from the traditional 1.2–1.5 to 1.8–2.2, and exponentially reduces viscosity (according to the Arrhenius equation η=Aexp(E)). a / RT), E a The viscosity decreases by approximately 20–40 kJ / mol. Secondly, the TiO2 anatase phase partially transforms into a low-melting-point titanate phase (such as CaTiO3, melting point ~1970℃ but forming a eutectic in the slag) in the high-temperature slag, further disrupting the Al-O-Al and Mg-Al spinel high-melting-point clusters (melting point >2000℃), causing the slag to transform from a "rigid network" to a "flexible chain + ion cluster" structure, resulting in a 20%–40% reduction in viscosity. Furthermore, the enrichment of nanoparticles at the slag-gold interface forms a surface-active layer, reducing the slag-gold interfacial tension (from ~1.2 N / m to ~0.8 N / m), promoting the rapid aggregation and sedimentation of fine metal droplets (<50 μm), and increasing the slag-iron density difference to >1.5 g / cm³. 3The settling time was shortened to 20-40 min, and the slag-gold separation effect was improved from "good" to "excellent". This mechanism is consistent with recent literature, confirming that the TiO2-SiO2 composite phase has a better network breaking efficiency than single oxide in silicate melt, and the interface effect is further amplified at the nanoscale, avoiding the fluorine pollution caused by traditional fluorite (CaF2). (3) Selective pre-reduction and thermal charging synergy thermodynamic-kinetic coupling mechanism to achieve efficient energy utilization and minimize chromium loss: In the traditional process, the Gibbs free energy change (ΔG) of iron oxide reduction is lower than that of chromium, resulting in preferential reduction of iron and the formation of a high melting point Fe-Cr alloy shell to hinder chromium diffusion. This invention achieves preferential metallization of chromium through the rotary kiln temperature gradient (kiln head height 50-100℃) and nano-modifier catalysis: oxygen vacancies on the TiO2 surface promote the selective breaking of Cr-O bonds, and the partial pressure of CO in the local reaction atmosphere increases, making the effective ΔG Cr Below ΔG Fe The chromium metallization rate is 5-15 percentage points higher than that of iron, avoiding the shell layer's diffusion inhibition phenomenon. Pre-reduction of raw materials via hot charging (>800℃) fully utilizes sensible heat (approximately 15%-20% of total energy consumption) and suppresses secondary oxidation under an inert atmosphere (traditional cold charging oxidation results in 2%-5% chromium loss). Combined with the reduced smelting load due to nano-modification (high pre-reduction degree, reduced final reduction power consumption), unit power consumption is reduced to 2100-2400 kWh / t, a 40%-50% reduction compared to traditional direct smelting and a 20%-30% reduction compared to conventional pre-reduction processes. Chromium recovery is consistently >95%, and Cr2O3 in the slag is <2%, mainly attributed to the blockage of microscopic loss channels (interfacial entrainment, volatilization, and dissolution loss) by the nano-modifier. (4) System integration advantages of process stability and environmental friendliness: The present invention has a wide parameter window (the index can be maintained at ±50℃ for pre-reduction temperature and ±2 parts for modifier addition), thanks to the buffering effect of nano-modifier: its high thermal stability (no sintering when calcined to 700℃) and interface adaptive dispersion alleviate the impact of furnace condition fluctuations on reaction uniformity. At the same time, it completely eliminates harmful additives such as fluorides and borax, and the tailings are easy to utilize (low Cr2O3, can be used as cement additive), and the CO2 emission intensity is reduced by about 30%, which meets the "dual carbon" target. (5) Overall innovation of technical path: Although existing technologies (such as WO2015015250A1 patent) have explored pre-reduction enhancement, they all remain at the level of macroscopic thermodynamic optimization or single gas reducing agent, lacking microscopic scale intervention. The present invention is the first to deeply embed a specific ratio of nano-SiO2-TiO2 composite prepared by sol-gel method into the entire process of ferrochrome, realizing the synergistic effect of "catalysis-nucleation-network breaking", forming a brand-new technical path. Experimental verification shows that the comprehensive indicators (recovery rate, power consumption, and product quality) are 10% to 20% higher than those reported in the latest literature, providing an industrially feasible innovative solution for the clean and efficient production of high-carbon ferrochrome.

[0017] In summary, this invention, through microscopic mechanism innovation driven by nano-modifiers, systematically solves the bottlenecks of existing technologies, realizes the green transformation and upgrading of high-carbon ferrochrome smelting, and has significant economic, social and environmental benefits. Attached Figure Description

[0018] Figure 1 This is a scanning electron microscope image of the silica-titanium dioxide nanocomposite oxide powder prepared in Example 1.

[0019] Figure 2 This is the infrared spectrum of the silica-titanium dioxide nanocomposite oxide powder prepared in Example 1.

[0020] Figure 3 This is a photograph of the modified high-carbon ferrochrome alloy prepared in Example 1. Detailed Implementation

[0021] The present invention will now be described in detail through specific embodiments. However, these illustrative embodiments are for purposes and uses only to illustrate the invention and do not constitute any limitation on the actual scope of protection of the invention, nor are they intended to restrict the scope of protection of the invention to these embodiments. For parameter ranges not mentioned, intermediate values ​​are selected. Also, for mass ratios not explicitly stated or mentioned, the mass ratio after addition generally refers to the mass ratio. Furthermore, in the present invention, the unit of mass is grams (g).

[0022] Example 1.

[0023] The preparation method of modified high-carbon ferrochrome based on pre-reduction technology includes the following steps: (1) Preparation of nanocomposite modifier: Tetraethoxysilane (TEOS, CAS78-10-4, purity 99.9%) and tetrabutyl titanate (TBOT, CAS5593-70-4, purity 99.0%) are used as precursors. The materials are prepared according to the mass ratio of silicon dioxide (SiO2) to titanium dioxide (TiO2) of 5:1 (the conversion rate of the precursors needs to be considered when calculating the amount added, SiO2 is derived from TEOS, and TiO2 is derived from TBOT). The precursors are added to anhydrous ethanol, and ammonia (25% concentration) is added to adjust the pH to 9.5. The hydrolysis reaction is carried out at 500 rpm for 8 hours under a constant temperature water bath at 70℃ to obtain a milky white sol. The sol is dried in a 135℃ forced-air drying oven for 18 hours to obtain a dry gel. The material was then placed in a muffle furnace and heated to 600°C at a rate of 4°C / min in air atmosphere. It was then held at that temperature for 4 hours, allowed to cool naturally, and then ground to obtain particles with an average diameter of approximately 45 nm and a specific surface area of ​​220 m². 2 / g of silica-titanium dioxide nanocomposite oxide powder (such as Figure 1 and Figure 2(as shown), where TiO2 is mainly anatase crystal. (2) Batching and mixing: Take 1000g of chromite concentrate (composition: Cr2O3 42%, FeO 18%, MgO 10%, Al2O3 14%, SiO2 4%; particle size -100 mesh accounts for 85%), 350g of coke powder (fixed carbon 88%, particle size -200 mesh accounts for 92%), 220g of lime (CaO content 92%, particle size -150 mesh accounts for 88%) and 40g of nanocomposite modifier prepared in step (1) (i.e. 4 parts / 100 parts of chromite). Mixing method: First, dry mix 40g of nanocomposite modifier and 220g of lime in a high-speed mixer for 10 minutes to make the nanoparticles adhere to the surface of the lime particles; then add chromite concentrate and coke powder, and continue mixing for 20 minutes to ensure that the dispersion of nanoparticles in the mixture reaches 98%. (3) Solid-state pre-reduction: The above mixture is loaded into a high-temperature tubular furnace simulating a rotary kiln. The rotation speed inside the kiln is controlled at 2 r / min, and the material filling rate is 20%. Nitrogen gas is introduced as a protective gas, and the flow rate is controlled at 3.5 m³ / min. 3 / t of mixed material (the laboratory flow rate is approximately 3.5L / min based on the proportional conversion). Set the kiln tail temperature to 1000℃ and the kiln head temperature to 1100℃ to form a temperature gradient. Conduct a solid pre-reduction reaction for 3.5 hours at an average temperature of 1050℃. Pre-reduction results: The pre-reduced raw material was obtained. After testing, the pre-reduction degree was 62% and the metallization rate was 58%, of which the metallization rate of chromium was 63% and the metallization rate of iron was 51% (chromium was 12 percentage points higher than iron). (4) Smelting reduction: The pre-reduced raw material obtained in step (3) was added to a 100kVA DC submerged arc furnace in batches while maintaining a temperature above 800℃ (hot charging). The batch addition amount of the furnace charge was 25% of the total amount. The secondary voltage was controlled at 220V, the electrode insertion depth was 50% of the furnace charge height, and the power density in the furnace was controlled at 400kW / m. 2 During the smelting process, 70g of coke (i.e., 7 parts / 100 parts chromite base) was added according to the furnace condition to maintain a carbon excess coefficient of 1.10. Smelting parameters: The smelting temperature was controlled at 1720℃ and the smelting time was 6 hours. (5) Iron tapping and slag tapping: After the smelting was completed, the heating was stopped and the slag and iron were allowed to stand and separate in the furnace for 30 minutes. The basic degree of slag (CaO / SiO2) was adjusted to 1.25. The slag was tapped first and then the iron was tapped at 1720℃. The density difference between slag and iron was measured to be 1.8g / cm³. 3 The final product is a modified high-carbon ferrochrome alloy, such as... Figure 3 As shown.

[0024] Examples 1-12 and Comparative Examples 1-12 were designed to verify the range of process parameters and the role of each component in this invention. Specific parameters for each example and comparative example are detailed in the table below. All units of mass are grams (g). Unless otherwise stated, the operating procedures are the same as in Example 1.

[0025] Table 1: Preparation parameters of nanocomposite modifiers (corresponding to step 1 and claim 2)

[0026]

[0027] Note: No modifier was added to Comparative Example 1; Comparative Example 2 used a physical mixture of micron-sized SiO2 and TiO2; the proportions in Comparative Example 3 were out of range; and the calcination temperature in Comparative Example 10 was too high, resulting in sintering.

[0028] Table 2: Ingredients and mixing parameters (corresponding to step 1 and claims 1, 3, 6)

[0029]

[0030] Note: Comparative Example 11 had a severe shortage of coke; Comparative Example 9 did not use stepwise mixing, resulting in poor dispersibility of the modifier.

[0031] Table 3: Pre-reduction process parameters (corresponding to step 2 and claims 2, 4, 7)

[0032]

[0033] Note: Comparative Example 4 had an excessively low pre-reduction temperature; Comparative Example 5 used a traditional cold-charge direct melting process; Comparative Example 12 used air, which resulted in severe secondary oxidation.

[0034] Table 4: Smelting reduction process parameters (corresponding to step 3 and claims 3, 5, 8)

[0035]

[0036] Note: Comparative Example 5 had no pre-reduction, resulting in a long smelting time and high coke consumption; Comparative Example 6 had pre-reduction but used cold charging, leading to low thermal efficiency; Comparative Example 7 had excessively low slag density, affecting slag-metal separation; Comparative Example 8 had insufficient power density.

[0037] Test Methods and Result Analysis: Performance indicators were tested on the modified high-carbon ferrochrome prepared in the above examples and comparative examples, as well as the smelting process. Unit power consumption (kWh / t): The electrical energy consumption for smelting one ton of qualified high-carbon ferrochrome. Product carbon content (%): Determined using an infrared carbon-sulfur analyzer. Chromium content in slag (%): The Cr2O3 content in the final slag was analyzed using X-ray fluorescence spectrometry (XRF). Slag-metal separation effect: Evaluated by observing the cross-section and measuring the density of slag-iron inclusions (Excellent / Good / Poor).

[0038] Table 5: Performance Test Results of Examples and Comparative Examples

[0039]

[0040] Results Analysis and Mechanism Elucidation: The Role of Nano-Modifiers (Example 1 and Comparative Examples 1 and 2): Example 1, with the addition of a nano-composite modifier, achieved a chromium recovery rate as high as 95.8%, while Comparative Example 1, without the addition, only achieved 82.4%. Comparative Example 2, using physically mixed micron-sized powders, also showed significantly less effect than Example 1. This indicates that the nano-modifier of the present invention is not a simple addition of components, but rather possesses a high specific surface area (220 m²). 2 / g) acted as a heterogeneous nucleation core at high temperatures, reducing the nucleation work of Cr-Fe-C formation; simultaneously, the nanoparticles dispersed at the slag-metal interface reduced the slag viscosity through the "pinning effect" and altered the microstructure of the slag (SiO2-TiO2 synergistic fractured silicon-oxygen tetrahedral network), promoting the aggregation and sedimentation of fine metal droplets, thereby significantly reducing chromium loss in the slag. Effects of proportion and dispersibility (Examples 1 and Comparative Examples 3 and 9): In Comparative Example 3, the modifier proportion was inappropriate (too high SiO2), failing to form an effective low-melting-point composite oxide phase, leading to a decrease in effectiveness. Comparative Example 9 did not employ the pre-dry mixing process with lime, resulting in nanoparticle agglomeration, reduced effective active area, and a chromium recovery rate decreased to 89.4%. Importance of pre-reduction and hot charging (Examples 1 and Comparative Examples 4, 5, 6, and 12): Comparative Example 5 used a traditional cold-charging direct refining process, with power consumption as high as 4200 kWh / t and low recovery rate. Comparative Example 4 had an excessively low pre-reduction temperature and insufficient metallization rate, resulting in a high subsequent smelting load. Comparative Example 6, although pre-reduction was performed, used cold charging, leading to significant heat loss. Comparative Example 12 used air instead of nitrogen, causing the pre-reduced metal to oxidize again, resulting in the worst effect. Example 1's hot charging process fully utilized sensible heat and, combined with a high metallization rate, achieved minimal energy consumption. Influence of process parameters (Examples 1 and Comparative Examples 7, 8, 11): Comparative Example 7 had an excessively low slag base, high slag viscosity, and poor slag-metal separation; Comparative Example 8 had insufficient power density, uneven temperature field inside the furnace, and incomplete reaction; Comparative Example 11 had insufficient reducing agent (coke), resulting in carbon deficiency and inability to fully reduce chromium oxides, causing severe deterioration of all indicators. Examples 1-12, by adjusting parameters within the scope of the claims, all achieved excellent smelting indicators, demonstrating the tolerance and stability of the process window of this invention. Regarding the calcination of the nano-modifier (Examples 1 and Comparative Example 10): In Comparative Example 10, the calcination temperature of the modifier was too high, leading to the sintering and growth of nanoparticles and a sharp decrease in specific surface area (down to 15m²). 2 ( / g), losing the nano-effect, its effect is close to that of physically mixed micron powder. In summary, this invention, through the integrated innovation of nano-modification pre-reduction technology, controls reaction kinetics at the microscale and optimizes energy utilization at the macroscale, significantly improving the production indicators of high-carbon ferrochrome.

[0041] The above description, in conjunction with specific embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the scope of protection defined by the claims submitted herein.

Claims

1. A method for preparing modified high-carbon ferrochrome based on pre-reduction technology, characterized in that, The mixture comprises the following steps by weight: (1) 100 parts of chromite concentrate, 25-45 parts of coke powder, 15-30 parts of lime and 1-8 parts of nano-composite modifier are uniformly mixed to obtain a mixture, wherein the chromite concentrate is composed of chromite spinel, the fixed carbon content of the coke powder is not less than 85%, the lime is composed of calcium oxide, and the nano-composite modifier is a silicon dioxide-titanium dioxide composite oxide with a particle size of 10-80 nm. The mass ratio of titanium is 3-7:1; (2) The mixture described in step (1) is subjected to a solid pre-reduction reaction in a rotary kiln at a temperature of 950-1150℃ for 2-5 hours, and an inert protective gas is introduced to obtain the pre-reduced raw material, wherein the pre-reduction degree is controlled at 45-70%; (3) The pre-reduced raw material described in step (2) is directly hot-charged into a submerged arc furnace and smelted and reduced at a temperature of 1650-1800℃, with the power density in the furnace controlled at 300-500kW / m 2 The smelting time is controlled at 4 to 8 hours until the slag and iron are separated and the iron and slag are discharged to obtain modified high-carbon ferrochrome. The nanocomposite modifier is uniformly dispersed at the interface between the slag phase and the metal phase during the pre-reduction and smelting process, which promotes the uniform nucleation of ferrochrome carbides and regulates the microstructure of the slag.

2. The method for preparing modified high-carbon ferrochrome based on pre-reduction technology according to claim 1, characterized in that: The preparation method of the nanocomposite modifier includes the following steps: tetraethoxysilane and tetrabutyl titanate are used as precursors and added to anhydrous ethanol at a mass ratio of silicon dioxide to titanium dioxide of 3-7:

1. Ammonia water is added to adjust the pH to 9-10, and the mixture is stirred and hydrolyzed at 60-80°C for 6-12 hours to obtain a sol. The sol is dried at 120-150°C for 12-24 hours and then calcined at 500-700°C for 3-5 hours to obtain silicon dioxide-titanium dioxide composite oxide powder with a particle size of 10-80 nm. The calcination process is carried out in an air atmosphere, and the heating rate is controlled at 3-5°C / min.

3. The method for preparing modified high-carbon ferrochrome based on pre-reduction technology according to claim 1, characterized in that: The mixture in step (1) has the following proportions: 100 parts chromite concentrate, 30-40 parts coke powder, 18-25 parts lime, and 2-6 parts nano-composite modifier; the specific surface area of ​​the nano-composite modifier is 150-300 m². 2 / g.

4. The method for preparing modified high-carbon ferrochrome based on pre-reduction technology according to claim 1, characterized in that: In step (2), the pre-reduction temperature is 1000–1100℃, the pre-reduction time is 3–4 hours, the inert protective gas is nitrogen, and the gas flow rate is 2–5 m³ / s. 3 / t of mixed feed, the metallization rate of the pre-reduced raw material after pre-reduction is controlled at 50-65%, of which the metallization rate of chromium is 5-15 percentage points higher than that of iron.

5. The method for preparing modified high-carbon ferrochrome based on pre-reduction technology according to claim 1, characterized in that: In step (3), when smelting in a submerged arc furnace, the batch amount of furnace charge added is 20-30% of the total amount of pre-reduced raw materials per batch, the secondary voltage is controlled at 180-250V, the electrode insertion depth is 40-60% of the furnace charge height, and 5-10 parts of coke / 100 parts of chromite concentrate are added during the smelting process to maintain the excess carbon coefficient in the furnace at 1.05-1.

15.

6. The method for preparing modified high-carbon ferrochrome based on pre-reduction technology according to claim 1, characterized in that: The mass ratio of silicon dioxide to titanium dioxide in the nanocomposite modifier is 4-6:

1. The titanium dioxide in the composite oxide is mainly in the anatase crystal form, accounting for 15-25% of the composite. The composite modifier is added to the mixture by first dry mixing with lime and then mixing with chromite concentrate and coke powder to ensure that the dispersion of nanoparticles in the mixture is not less than 95%.

7. The method for preparing modified high-carbon ferrochrome based on pre-reduction technology according to claim 1, characterized in that: In step (2) during the pre-reduction process, the rotary kiln speed is controlled at 1 to 3 r / min, the material filling rate in the kiln is 15 to 25%, and the kiln head temperature is 50 to 100°C higher than the kiln tail temperature, so as to form a temperature gradient to promote the selective pre-reduction of chromium oxides.

8. The method for preparing modified high-carbon ferrochrome based on pre-reduction technology according to claim 1, characterized in that: After smelting in step (3), the slag-iron settling time is controlled at 20-40 minutes, the basic slag density is controlled at 1.1-1.4, and the slag temperature is controlled at 1700-1750℃ before slag discharge, ensuring that the density difference between slag and iron is not less than 1.5 g / cm³. 3 .

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