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

Abstract

The invention belongs to the technical field of metallurgy, and discloses an accurate smelting method for a high-purity raw material low-carbon silicon-manganese alloy. The method comprises the following steps: adding 0.1%-0.3% of a nano CaO-Al2O3 composite catalyst into electrolytic manganese, silica and semi-coke raw materials, mixing and briquetting, and performing staged smelting in an inert atmosphere ore-smelting electric furnace; the catalyst forms a CaAl2O4 active phase at 1550-1650 DEG C, and selectively adsorbs and activates SiO2, so that the reduction activation energy is reduced by 46.4%, and the reduction of Fe2O3 is inhibited due to difficult adsorption. According to the method, by constructing a nano catalyst-selective reduction technology normal form, the inherent constraints of thermodynamics and dynamics in traditional silicon-manganese alloy smelting are broken through, energy consumption and carbon emission are remarkably reduced, and multiple targets of low carbonization, high purification and greenization are synchronously achieved on the premise that the production efficiency is not sacrificed.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgy, and relates to a high-purity raw material low-carbon silicon-manganese alloy precise smelting method. BACKGROUND

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

[0003] For a long time, the electric furnace smelting process using semicoke as a reducing agent has been widely used in industry to prepare silicon-manganese alloy. This process relies on the high fixed carbon content and low cost advantage of semicoke, effectively realizes the large-scale reduction of manganese and silicon oxides at a certain historical stage, and forms a relatively mature production system. Semicoke reacts with SiO2 and MnO in manganese ore through carbothermal reduction at high temperature to generate the target product Mn-Si alloy.

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

[0005] The semicoke reduction system is essentially a non-selective strong reduction environment, and its thermodynamic driving force acts on SiO2, MnO and Fe2O3 and other oxides, making it difficult to precisely control the target reaction path. If the carbon content is reduced to control carbon residues, SiO2 reduction will not be sufficient, and the alloy yield will be significantly reduced. If the carbon content is maintained to ensure the reduction efficiency, carbon pollution and iron co-reduction problems will be inevitably aggravated, forming a dilemma of reducing carbon at the expense of yield and preserving yield at the expense of impurities. SUMMARY

[0006] To achieve the above-mentioned application purposes, the application provides a high-purity raw material low-carbon silicon-manganese alloy precise smelting method. This method introduces a nano calcium-based composite catalyst into the traditional electric furnace smelting system to construct a reaction interface with selective catalytic reduction function, fundamentally changing the reaction kinetics path of SiO2 and Fe2O3 in the high-temperature reduction process, thereby simultaneously achieving significant reduction of carbon residues and source inhibition of iron impurities while ensuring high yield of manganese and silicon elements.

[0007] The high-purity raw material low-carbon silicon-manganese alloy precise smelting method comprises the following steps: Firstly, the raw materials are prepared according to the mass percentage: electrolytic manganese 92.5%-94.0%, silica 5.0%-6.5%, low-quality coke 0.8%-1.2%, and nano CaO-Al2O3 composite catalyst 0.1%-0.3%. The total content of impurity elements in the electrolytic manganese is less than 0.05%, and the content of iron is less than 0.005%; the content of SiO2 in the silica is higher than 99.0%, and the total content of Al2O3 and CaO is less than 0.5%; the content of fixed carbon in the low-quality coke is higher than 82%, the content of volatile matter is less than 8%, and the content of ash is less than 5%; the nano CaO-Al2O3 composite catalyst is composed of CaO and Al2O3 with a molar ratio of 3:1, the average particle size is 50-100 nm, the specific surface area is 45-60 m 2 / g, and the pore volume is 0.18-0.25 cm 3 / g.

[0008] Secondly, the above raw materials are uniformly mixed in a mixer for 15-20 min at a speed of 30-40 rpm, so that the nano catalyst particles are in a monodisperse state in the material without agglomeration. The mixed material is formed into a cylindrical briquette with a density of 2.8-3.2 g / cm 3 , a diameter of 80-100 mm, and a height of 60-80 mm to enhance the gas permeability and heat transfer efficiency of the material in the electric furnace.

[0009] Subsequently, the briquette is loaded into a three-phase alternating-current electric arc furnace for smelting. The working voltage of the electric arc furnace is 180-220 V, the current intensity is 25-35 kA, the atmosphere in the hearth is an inert gas protection environment, and the oxygen partial pressure is controlled in the range of 10 -6 -10 - 8 Pa. The smelting process is divided into three stages: the first stage is a preheating stage, the furnace temperature is raised from room temperature to 1200 DEG C at a rate of 8-12 DEG C / min, and the duration is 90-110 min; the second stage is a catalytic reduction stage, the furnace temperature is raised to 1550-1650 DEG C, and maintained for 120-150 min in this temperature range, which is the core period of the selective catalytic action of the nano catalyst; the third stage is an alloy refining and slag-metal separation stage, the furnace temperature is raised to 1700-1750 DEG C, and the holding time is 30-45 min, so that the molten alloy is fully settled to realize the complete separation of the slag phase and the metal phase.

[0010] In the catalytic reduction stage, the nano CaO-Al2O3 composite catalyst forms a CaAl2O4 active phase with a spinel structure at high temperature, and the Ca 2+ -O 2-The coordination unsaturated sites have strong adsorption capacity to SiO2 molecules. After the adsorption of SiO2, the Si-O bond of SiO2 is polarized and stretched, the bond length is increased from 0.161 nm to 0.178 nm, and the bond energy is decreased from 452 kJ / mol to 380 kJ / mol, thereby significantly reducing the activation energy of the subsequent carbothermic reduction reaction. Experimental measurement shows that in the presence of the catalyst, the apparent activation energy of the reaction of SiO2+2C→Si+2CO is reduced from 280 kJ / mol in the uncatalyzed state to 150 kJ / mol, with a reduction of 46.4%. At the same time, Fe2O3 cannot form a stable adsorption configuration due to the lack of effective chemical affinity with the surface of the catalyst, and the activation energy of the reduction reaction of Fe2O3+3C→2Fe+3CO is maintained at more than 310 kJ / mol, and the reaction rate constant at 1600 DEG C is only 1 / 20 of the uncatalyzed SiO2 reduction reaction. Therefore, under the same thermodynamic conditions, SiO2 is preferentially reduced, and Fe2O3 is basically in the unreduced state and is effectively excluded into the slag phase.

[0011] As a preferred embodiment of the present application, 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 according to the 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, 2 mL / min of ammonia water with a concentration of 2.0 mol / L is added dropwise to adjust the pH value to 9.5-10.0 to generate white flocculent co-precipitate; the precipitate is centrifuged and washed to pH=7, and then dried at 80 DEG C for 12 hours; finally, the nano CaO-Al2O3 composite catalyst is obtained by calcining at 900 DEG C for 2 hours.

[0012] As another preferred embodiment of the present application, the furnace lining of the ore smelting electric furnace adopts magnesia-chrome refractory material, the content of Cr2O3 is 18%-22%, the content of MgO is 75%-80%, and the thermal conductivity is 3.5-4.2 W / (m·K), which can work stably at 1750 DEG C for a long time without significant reaction with the molten slag, thereby avoiding the introduction of additional impurities.

[0013] Compared with the prior art, the present application has the following beneficial effects: The technical scheme of the present application solves the fundamental contradiction in the traditional reduction process of coking coal, that is, reducing carbon reduces yield, and preserving yield increases impurities, by introducing a nano-scale calcium-based composite catalyst to regulate the selectivity of the reduction reaction at the atomic level. The core lies in using the differential adsorption and activation ability of the catalyst for different oxides to construct an asymmetric reaction energy barrier distribution, so that the target reaction (reduction of SiO2) occupies an absolute advantage in kinetics, while the side reaction (reduction of Fe2O3) is effectively suppressed. This mechanism does not depend on external energy input or complex post-processing procedures, but only through the fine-tuning of raw material formula and process parameters, the synergistic optimization of low carbon, high purity and high yield can be realized within the existing electric furnace smelting framework. DETAILED DESCRIPTION

[0014] The present application provides a precise smelting method of high-purity raw material low-carbon silicon-manganese alloy, which introduces a nano calcium-based composite catalyst into the traditional electric furnace smelting system, constructs a reaction interface with selective catalytic reduction function, fundamentally changes the reaction kinetics path of silicon dioxide and iron trioxide in the high-temperature reduction process, and simultaneously realizes the significant reduction of carbon residue and the source inhibition of iron impurities while ensuring the high yield of manganese and silicon elements. The technical scheme adopted by the present application realizes the atomic-level precise regulation of the reduction reaction path by optimizing the raw material ratio, catalyst characteristics and thermal system without changing the existing electric furnace main structure.

[0015] The technical scheme of the present application will be described in detail below in combination with specific examples and comparative examples to ensure that those skilled in the art can fully understand and implement the present application.

[0016] Example 1: The addition amount of nano catalyst is 0.2%; the catalytic reduction temperature is 1600℃; the electrolytic manganese is 93.2%, the silica is 5.8%, and the coking coal is 1.0%; the briquette density is 3.0g / cm 3 ; the smelting is carried out in stages (preheating for 100min, catalytic reduction for 135min, and clarification for 40min); Preparation process: raw material pretreatment → precise batching → mixed briquetting → preheating in inert atmosphere furnace → catalytic reduction → clarification separation → alloy casting → finished product.

[0017] Example 2: The addition amount of nano catalyst is 0.1%, and the rest of the formula and process are the same as example 1; Preparation process: same as example 1 (catalyst dosage adjustment).

[0018] Example 3: The addition amount of nano catalyst is 0.3%, and the rest of the formula and process are the same as example 1; Preparation process: same as example 1 (catalyst dosage adjustment).

[0019] Example 4: Catalytic reduction temperature 1550℃, other formulations and processes are the same as in Example 1; Preparation process: Same as in Example 1 (melting temperature adjusted).

[0020] Example 5: Catalytic reduction temperature 1650℃, other formulations and processes are the same as in Example 1; Preparation process: Same as in Example 1 (melting temperature adjusted).

[0021] Example 6: Semi-coke ratio 0.8%, other formulations and processes are the same as in Example 1; Preparation process: Same as in Example 1 (adjustment of reducing agent dosage).

[0022] Example 7: Semi-coke ratio 1.2%, other formulations and processes are the same as in Example 1; Preparation process: Same as in Example 1 (adjustment of reducing agent dosage).

[0023] Example 8: Compacted block density 2.8 g / cm³ 3 The remaining formulas and processes are the same as in Example 1; Preparation process: Same as in Example 1 (adjustment of briquetting parameters).

[0024] Comparative Example 1: No nano-CaO-Al2O3 catalyst; other formulations and processes are the same as in Example 1; Preparation process: raw material pretreatment → batching and mixing → briquetting → smelting → casting → finished product.

[0025] Comparative Example 2: Conventional single-temperature melting (1700℃ constant temperature for 240 min); no catalyst; other formulations are the same as in Example 1; Preparation process: Raw material mixing → direct high-temperature melting → casting → finished product.

[0026] Test method: 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.

[0027] 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.

[0028] 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.

[0029] The test data comparisons are shown in Table 1 and Table 2.

[0030] Table 1. Comparison of Carbon Content, Iron Content, Silicon Yield, and Manganese Yield ; Table 2 Comparison of the reduction rate of semi-coke and the reduction rate of energy consumption ; 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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 high-purity raw material low-carbon silicon-manganese alloy precision smelting method, characterized by, The method comprises the following steps: electrolytic manganese 92.5%-94.0%, silica 5.0%-6.5%, coke 0.8%-1.2%, and nano CaO-Al2O3 composite catalyst 0.1%-0.3% are weighed according to mass percentage; the above raw materials are uniformly mixed and then pressed into a cylindrical briquette; the briquette is loaded into a three-phase alternating current submerged arc furnace for smelting, and the smelting process comprises the following steps in sequence: a preheating stage of increasing the furnace temperature to 1200℃ and maintaining for 90-110 min; a catalytic reduction stage of increasing the furnace temperature to 1550-1650℃ and maintaining for 120-150 min; and a clarification and separation stage of increasing the furnace temperature to 1700-1750℃ and maintaining for 30-45 min.

2. The high purity feedstock low carbon silicon-manganese alloy precision smelting method according to claim 1, characterized in that, the iron content of the electrolytic manganese is less than 0.005%; the SiO2 content of the silica is higher than 99.0%; the fixed carbon content of the coke is higher than 82%; the nano CaO-Al2O3 composite catalyst is composed of CaO and Al2O3 with a molar ratio of 3:

1.

3. The high purity feedstock low carbon silicon-manganese alloy precision smelting method according to claim 1, characterized in that, In the catalytic reduction stage, the nano CaO-Al2O3 composite catalyst forms a spinel structure CaAl2O4 active phase in situ, selectively adsorbs and activates SiO2, reduces the carbon thermal reduction reaction activation energy, and inhibits the reduction of Fe2O3, so that the carbon content of the obtained silicon-manganese alloy is 0.08%-0.12%, the iron content is 0.015%-0.025%, the silicon yield is higher than 98.5%, and the manganese yield is higher than 99.0%.

4. The high purity feedstock low carbon silicon-manganese alloy precision smelting method according to claim 1, characterized in that, After the electrolytic manganese is crushed to a particle size of 5-10 mm, the iron inclusions are removed by a magnetic separation device, and the electrolytic manganese is subjected to ultrasonic cleaning and 105℃ vacuum drying treatment.

5. The high purity feedstock low carbon silicon-manganese alloy precision smelting method according to claim 1 or 2, characterized in that, After the silica is sieved, the particle size is 3-8 mm, and after the coke is crushed and classified by airflow, the particle size is 1-3 mm.

6. The high purity feedstock low carbon silicon-manganese alloy precision smelting process of claim 1, wherein, Before use, the nano CaO-Al2O3 composite catalyst is activated at 200℃ for 1 hour by passing high-purity nitrogen to remove physically adsorbed water and activate the surface active sites.

7. 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 by a three-dimensional motion mixer for 15-20 min at a speed of 30-40 rpm, and the uniformity of C, Si, and Mn element distribution is monitored in real time by an online near-infrared spectrometer to ensure that the spectral signal fluctuation amplitude is less than ±2%.

8. The high purity feedstock low carbon silicon-manganese alloy precision smelting process of claim 1, wherein, The briquette forming pressure is 150-180 MPa, the pressure maintaining time is 30 seconds, and the density of each briquette is detected on line by a gamma ray density meter, and the briquettes with density exceeding 2.8-3.2 g / cm 3 are rejected.

9. The method of claim 1, wherein the high purity feedstock low carbon silicon-manganese alloy is precision smelted by the steps of: The atmosphere in the hearth of the submerged arc furnace is established by vacuumizing and then filling high-purity argon, and after repeating the vacuumizing and filling for 3 times, the positive pressure in the furnace is maintained at 500 Pa, and the oxygen partial pressure is monitored in real time by a zirconium oxygen sensor. ​ 10. The method of claim 1, wherein the high purity feedstock low carbon silicon-manganese alloy is precision smelted. The furnace lining of the submerged arc furnace is made of magnesia-chrome refractory material, the Cr2O3 content is 18%-22%, the MgO content is 75%-80%, the thermal conductivity is 3.5-4.2 W / (m·K), the thickness of the furnace lining is 400 mm, and a cooling water jacket is arranged inside to maintain the furnace shell temperature below 80℃.