Accurate smelting method of high-purity raw material low-carbon silicon-manganese alloy

Abstract

The application belongs to the technical field of metallurgy, and discloses a high-purity raw material low-carbon silicon-manganese alloy precise smelting method. The method adds 0.1%-0.3% of nano CaO-Al2O3 composite catalyst in electrolytic manganese, silica and semi-coke raw materials, and then smelts in stages in an inert atmosphere ore-heating electric furnace after mixing and briquetting; the catalyst forms CaAl2O4 active phase at 1550-1650 DEG C, selectively adsorbs and activates SiO2, and reduces the reduction activation energy of SiO2 by 46.4%, while Fe2O3 is inhibited from reduction due to difficult adsorption. The application breaks through the inherent constraints of thermodynamics and kinetics in traditional silicon-manganese alloy smelting by constructing a nano catalyst-selective reduction technology paradigm, significantly reduces energy consumption and carbon emissions, and simultaneously realizes the multiple goals of low carbonization, high purification and greenization without sacrificing production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology and relates to a method for the precise smelting of high-purity raw material low-carbon silicon-manganese alloy. Background Technology

[0002] As an indispensable composite deoxidizer and alloying additive in the steelmaking process, the quality of silicon-manganese alloy directly affects the purity, mechanical properties, and processing stability of high-end steel. With the continuous improvement of material performance requirements in my country's high-end equipment manufacturing, new energy vehicle, and special alloy industries, the market demand for high-purity, low-carbon silicon-manganese alloys is becoming increasingly urgent.

[0003] For a long time, the electric furnace smelting process using semi-coke as a reducing agent has been widely used in industry to prepare silicon-manganese alloys. This process, relying on the high fixed carbon content and low cost of semi-coke, effectively achieved the large-scale reduction of manganese and silicon oxides during a specific historical period, forming a relatively mature production system. Semi-coke undergoes a carbothermic reduction reaction with MnO in silica and manganese ore at high temperatures to generate the target product, Mn-Si alloy.

[0004] Semi-coke itself contains high levels of volatile matter and ash, and its reduction process relies on excessive carbon, resulting in a generally high carbon content in the final alloy, making it difficult to meet the composition requirements of low-carbon or even ultra-low-carbon alloys. On the other hand, traditional manganese ore raw materials often contain iron oxides such as Fe2O3, which are easily reduced into the alloy phase under high-temperature and strong reducing atmosphere. However, existing processes lack a selective inhibition mechanism for iron impurities, resulting in persistently high iron content in the product, which seriously restricts further improvement in alloy purity.

[0005] The semi-coke reduction system is essentially a non-selective, strongly reducing environment. Its thermodynamic driving force acts simultaneously on multiple oxides such as SiO2, MnO, and Fe2O3, making it difficult to precisely control the target reaction pathway. If one attempts to control carbon residue by reducing the carbon content, it will lead to insufficient SiO2 reduction and a significant decrease in alloy yield. If one maintains a high carbon ratio to ensure reduction efficiency, it will inevitably exacerbate carbon contamination and iron co-reduction problems, creating a dilemma where reducing carbon content results in a loss of yield, while maintaining yield increases impurities. Summary of the Invention

[0006] To achieve the aforementioned objectives, this invention provides a method for the precise smelting of high-purity, low-carbon silicon-manganese alloys. This method introduces a nano-calcium-based composite catalyst into a traditional electric furnace smelting system, constructing a reaction interface with selective catalytic reduction capabilities. This fundamentally alters the reaction kinetics of SiO2 and Fe2O3 during the high-temperature reduction process, thereby simultaneously achieving a significant reduction in residual carbon and suppression of iron impurities while ensuring high yields of manganese and silicon.

[0007] The method for precise smelting of high-purity raw material low-carbon silicon-manganese alloy according to the present invention specifically includes the following steps:

[0008] First, prepare the raw materials according to the following mass percentages: 92.5%-94.0% electrolytic manganese, 5.0%-6.5% silica, 0.8%-1.2% semi-coke, and 0.1%-0.3% nano-CaO-Al2O3 composite catalyst. Specifically, the electrolytic manganese has a total impurity element content of less than 0.05% and an iron content of less than 0.005%; the silica has a SiO2 content higher than 99.0% and a total Al2O3 and CaO content of less than 0.5%; the semi-coke has a fixed carbon content higher than 82%, volatile matter of less than 8%, and ash content of less than 5%; the nano-CaO-Al2O3 composite catalyst is composed of CaO and Al2O3 in a molar ratio of 3:1, with an average particle size of 50-100 nm and a specific surface area of ​​45-60 m². 2 / g, pore volume 0.18-0.25cm 3 / g.

[0009] Next, the above raw materials are mixed evenly in a mixer for 15-20 minutes at a speed of 30-40 rpm to ensure that the nano-catalyst particles are monodisperse in the material without agglomeration. The mixed material is then briquetteed to a density of 2.8-3.2 g / cm³. 3 The cylindrical briquettes have a diameter of 80-100mm and a height of 60-80mm to enhance the permeability and heat transfer efficiency of the material in the electric furnace.

[0010] Subsequently, the briquettes are loaded into a three-phase AC submerged arc furnace for smelting. The submerged arc furnace operates at a voltage of 180-220V and a current of 25-35kA. The furnace atmosphere is an inert gas protective environment, with the oxygen partial pressure controlled at 10. -6 -10 - 8 Within the Pa range. The smelting process is divided into three stages: the first stage is the preheating stage, where the furnace temperature is raised from room temperature to 1200℃ at a rate of 8-12℃ / min for 90-110min; the second stage is the catalytic reduction stage, where the furnace temperature is raised to 1550-1650℃ and maintained within this temperature range for 120-150min, which is the core period for the selective catalytic effect of the nanocatalyst; the third stage is the alloy clarification and slag-metal separation stage, where the furnace temperature is raised to 1700-1750℃ and held for 30-45min to allow the molten alloy to settle fully and achieve complete separation of the slag phase and the metal phase.

[0011] During the catalytic reduction stage, the nano-CaO-Al2O3 composite catalyst forms a spinel-structured CaAl2O4 active phase at high temperature, and the exposed Ca on its surface... 2+ -O2- The coordinating unsaturated sites exhibit strong adsorption capacity for SiO2 molecules. After adsorption, the Si-O bonds of SiO2 undergo polarization stretching, with the bond length increasing from 0.161 nm to 0.178 nm and the bond energy decreasing from 452 kJ / mol to 380 kJ / mol, thus significantly reducing the activation energy of the subsequent carbothermic reduction reaction. Experimental measurements show that, in the presence of a catalyst, the apparent activation energy of the SiO2 + 2C → Si + 2CO reaction decreases from 280 kJ / mol in the uncatalyzed state to 150 kJ / mol, a reduction of 46.4%. Meanwhile, Fe2O3, lacking effective chemical affinity with the catalyst surface, cannot form a stable adsorption configuration; its reduction reaction Fe2O3 + 3C → 2Fe + 3CO maintains an activation energy above 310 kJ / mol, and the reaction rate constant at 1600 °C is only 1 / 20 of that of the uncatalyzed SiO2 reduction reaction. Therefore, under the same thermodynamic conditions, SiO2 is preferentially reduced, while Fe2O3 remains essentially unreduced and is effectively eliminated from the slag phase.

[0012] In a preferred embodiment of the present invention, the nano-CaO-Al2O3 composite catalyst is prepared by a co-precipitation-calcination method. The specific steps are as follows: calcium nitrate and aluminum nitrate are dissolved in deionized water at a molar ratio of Ca:Al = 3:1 to prepare a mixed solution with a total metal ion concentration of 1.0 mol / L; under stirring conditions, ammonia water with a concentration of 2.0 mol / L is added dropwise at a rate of 2 mL / min to adjust the pH value to 9.5-10.0, generating a white flocculent coprecipitate; the precipitate is centrifuged, washed until pH=7, and then dried at 80℃ for 12 hours; finally, it is calcined at 900℃ for 2 hours to obtain the nano-CaO-Al2O3 composite catalyst.

[0013] As another preferred embodiment of the present invention, the furnace lining of the electric submerged arc furnace is made of magnesium-chromium refractory material with a Cr2O3 content of 18%-22%, an MgO content of 75%-80%, and a thermal conductivity of 3.5-4.2 W / (m·K). It can work stably for a long time at 1750℃ without reacting significantly with the slag, thus avoiding the introduction of additional impurities.

[0014] Compared with the prior art, the beneficial effects of the present invention are:

[0015] The technical solution of this invention, by introducing a nanoscale calcium-based composite catalyst, controls the selectivity of the reduction reaction at the atomic level, thus solving the fundamental contradiction in the traditional semi-coke reduction process: reducing carbon content results in decreased yield, while maintaining yield increases impurities. Its core lies in utilizing the catalyst's differentiated adsorption and activation capabilities for different oxides to construct an asymmetric reaction energy barrier distribution, ensuring that the target reaction (SiO2 reduction) has an absolute kinetic advantage, while the side reaction (Fe2O3 reduction) is effectively suppressed. This mechanism does not rely on external energy input or complex post-processing steps; it achieves synergistic optimization of low carbon, high purity, and high yield within the existing electric furnace smelting framework simply through fine-tuning of the raw material formulation and process parameters. Detailed Implementation

[0016] This invention provides a method for the precise smelting of high-purity low-carbon silicon-manganese alloys. By introducing a nano-calcium-based composite catalyst into a traditional electric furnace smelting system, a reaction interface with selective catalytic reduction function is constructed. This fundamentally alters the reaction kinetics of silicon dioxide and ferric oxide during high-temperature reduction, thereby simultaneously achieving a significant reduction in residual carbon and suppression of iron impurities while ensuring high yields of manganese and silicon. The technical solution employed in this invention, without altering the existing electric furnace structure, achieves atomic-level precise control of the reduction reaction pathway through systematic optimization of raw material ratios, catalyst characteristics, and thermal regime.

[0017] The technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples, so as to ensure that those skilled in the art can fully understand and implement the present invention.

[0018] Example 1: Nanocatalyst addition amount 0.2%; catalytic reduction temperature 1600℃; electrolytic manganese 93.2%, silica 5.8%, semi-coke 1.0%; briquetted density 3.0 g / cm³ 3 Staged smelting (preheating for 100 min, catalytic reduction for 135 min, and clarification for 40 min);

[0019] Preparation process: raw material pretreatment → precise batching → mixing and briquetting → preheating in an inert atmosphere furnace → catalytic reduction → clarification and separation → alloy casting → finished product.

[0020] Example 2: The amount of nano-catalyst added was 0.1%, and the rest of the formulation and process were the same as in Example 1;

[0021] Preparation process: Same as in Example 1 (catalyst dosage adjusted).

[0022] Example 3: The amount of nano-catalyst added was 0.3%, and the rest of the formulation and process were the same as in Example 1;

[0023] Preparation process: Same as in Example 1 (catalyst dosage adjusted).

[0024] Example 4: Catalytic reduction temperature 1550℃, other formulations and processes are the same as in Example 1;

[0025] Preparation process: Same as in Example 1 (melting temperature adjusted).

[0026] Example 5: Catalytic reduction temperature 1650℃, other formulations and processes are the same as in Example 1;

[0027] Preparation process: Same as in Example 1 (melting temperature adjusted).

[0028] Example 6: Semi-coke ratio 0.8%, other formulations and processes are the same as in Example 1;

[0029] Preparation process: Same as in Example 1 (adjustment of reducing agent dosage).

[0030] Example 7: Semi-coke ratio 1.2%, other formulations and processes are the same as in Example 1;

[0031] Preparation process: Same as in Example 1 (adjustment of reducing agent dosage).

[0032] Example 8: Compacted block density 2.8 g / cm³ 3 The remaining formulas and processes are the same as in Example 1;

[0033] Preparation process: Same as in Example 1 (adjustment of briquetting parameters).

[0034] Comparative Example 1: No nano-CaO-Al2O3 catalyst; other formulations and processes are the same as in Example 1;

[0035] Preparation process: raw material pretreatment → batching and mixing → briquetting → smelting → casting → finished product.

[0036] Comparative Example 2: Conventional single-temperature melting (1700℃ constant temperature for 240 min); no catalyst; other formulations are the same as in Example 1;

[0037] Preparation process: Raw material mixing → direct high-temperature melting → casting → finished product.

[0038] Test method:

[0039] Composition and purity testing: Carbon content was measured using a high-frequency infrared carbon-sulfur analyzer; Iron, silicon, and manganese content were measured using an inductively coupled plasma atomic emission spectrometer; Elemental yield was calculated.

[0040] Energy consumption and low-carbon testing: Statistics on semi-coke consumption; monitoring of electricity consumption in the smelting process; calculation of the carbon emission reduction rate.

[0041] Process stability testing: Detecting the air permeability and heat transfer efficiency of the briquettes; verifying the slag-gold separation effect of staged smelting; evaluating the activity stability of the catalyst.

[0042] The test data comparisons are shown in Table 1 and Table 2.

[0043] Table 1. Comparison of Carbon Content, Iron Content, Silicon Yield, and Manganese Yield

[0044] ;

[0045] Table 2 Comparison of the reduction rate of semi-coke and the reduction rate of energy consumption

[0046] ;

[0047] Examples 1-8 showed carbon content ≤0.12% and iron content ≤0.024%, which were far superior to the comparative examples. Comparative example 1 failed due to the lack of a catalyst and selective reduction failed. Comparative example 2 had high impurities and high energy consumption due to the traditional process. This confirms that nano-catalyst + staged smelting is the key to low carbon and high purity.

[0048] Increasing the catalyst addition (Examples 2→1→3) reduces the carbon and iron content and improves the yield; the catalytic reduction temperature is suitable for all ranges from 1550-1650℃, with higher temperatures being more conducive to catalytic activity; reducing the semi-coke ratio still ensures the yield, demonstrating the energy-saving advantage of the catalyst.

[0049] The alloy used in this example has high purity, meeting the needs of high-end steel; the amount of semi-coke used is reduced by 15-20%, and energy consumption is reduced by 8-12%, making it low-carbon and environmentally friendly; the yield is ≥98.5%, with high resource utilization; the process is compatible with existing electric furnaces, requiring no equipment modification and is easy to scale up.

[0050] Compared to the catalyst-free process (Comparative Example 1), the carbon content of the example was reduced by 67%, the iron content by 93%, and the silicon yield was increased by 4%. Compared to the traditional process (Comparative Example 2), the carbon content was reduced by 69%, the iron content by 94%, and the energy consumption was reduced by 25%, solving the industry problem of difficulty in achieving both carbon reduction and high yield and low impurities in the traditional process.

[0051] In summary, the method described in this invention, through the synergy of selective catalysis and staged melting, can achieve low-carbon, high-purity, and high-efficiency smelting with different parameter combinations, and is suitable for high-end silicon-manganese alloy production scenarios.

[0052] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for precise smelting of high-purity, low-carbon silicon-manganese alloy, characterized in that, Includes the following steps: Weigh out the following components by mass percentage: 92.5%-94.0% electrolytic manganese, 5.0%-6.5% silica, 0.8%-1.2% semi-coke, and 0.1%-0.3% nano-CaO-Al2O3 composite catalyst; the total impurity element content of the electrolytic manganese is less than 0.05%, and the iron content is less than 0.005%; the SiO2 content of the silica is higher than 99.0%, and the total content of Al2O3 and CaO is less than 0.5%; the fixed carbon content of the semi-coke is higher than 82%, the volatile matter is less than 8%, and the ash content is less than 5%; the nano-CaO-Al2O3 composite catalyst is composed of CaO and Al2O3 in a molar ratio of 3:1, with an average particle size of 50-100 nm and a specific surface area of ​​45-60 m². 2 / g, pore volume 0.18-0.25cm 3 / g; After the above raw materials are mixed evenly, they are pressed into cylindrical blocks. The compressed briquettes are loaded into a three-phase AC submerged arc furnace for smelting. The smelting process includes the following steps: The preheating stage involves raising the furnace temperature to 1200℃ and holding it at that temperature for 90-110 minutes. The catalytic reduction stage involves raising the furnace temperature to 1550-1650℃ and maintaining that temperature for 120-150 minutes. And the clarification and separation stage, in which the furnace temperature is raised to 1700-1750℃ and held for 30-45 minutes; During the catalytic reduction stage, the nano-CaO-Al2O3 composite catalyst forms a spinel-structured CaAl2O4 active phase in situ, selectively adsorbing and activating SiO2, reducing its carbothermic reduction activation energy, and simultaneously inhibiting the reduction of Fe2O3. This results in a silicon-manganese alloy with a carbon content of 0.08%-0.12%, an iron content of 0.015%-0.025%, a silicon yield higher than 98.5%, and a manganese yield higher than 99.0%.

2. The method for precise smelting of high-purity raw material low-carbon silicon-manganese alloy according to claim 1, characterized in that, The electrolytic manganese is crushed to a particle size of 5-10 mm, then iron inclusions are removed by a magnetic separation device, followed by ultrasonic cleaning and vacuum drying at 105°C.

3. The method for precise smelting of high-purity raw material low-carbon silicon-manganese alloy according to claim 1, characterized in that, The silica, after sieving, has a particle size of 3-8 mm, and the semi-coke, after crushing and air classification, has a particle size of 1-3 mm.

4. The method for precise smelting of high-purity raw material low-carbon silicon-manganese alloy according to claim 1, characterized in that, The nano-CaO-Al2O3 composite catalyst was activated by passing high-purity nitrogen gas at 200°C for 1 hour before use to remove physically adsorbed water and activate surface active sites.

5. The method for precise smelting of high-purity raw material low-carbon silicon-manganese alloy according to claim 1, characterized in that, The raw materials are mixed using a three-dimensional motion mixer with a mixing time of 15-20 minutes and a rotation speed of 30-40 rpm. The uniformity of C, Si, and Mn element distribution is monitored in real time using an online near-infrared spectrometer to ensure that the spectral signal fluctuation amplitude is less than ±2%.

6. The method for precise smelting of high-purity raw material low-carbon silicon-manganese alloy according to claim 1, characterized in that, The briquetting pressure is 150-180 MPa, the holding time is 30 seconds, and the density of each briquette is measured online using a gamma-ray densitometer, discarding those with a density exceeding 2.8-3.2 g / cm³. 3 Non-conforming products within the specified range.

7. The method for precise smelting of high-purity raw material low-carbon silicon-manganese alloy according to claim 1, characterized in that, The atmosphere inside the furnace of the electric submerged arc furnace is established by evacuating and then filling it with high-purity argon. After repeating the evacuation and filling process three times, the positive pressure inside the furnace is maintained at 500 Pa, and the oxygen partial pressure is monitored in real time by a zirconium oxygen sensor.

8. The method for precise smelting of high-purity raw material low-carbon silicon-manganese alloy according to claim 1, characterized in that, The furnace lining of the electric arc furnace is made of magnesium-chromium refractory material, with a Cr2O3 content of 18%-22%, an MgO content of 75%-80%, a thermal conductivity of 3.5-4.2 W / (m·K), a lining thickness of 400 mm, and an internal cooling water jacket to maintain the furnace shell temperature below 80°C.