A method for improving the resistivity of composite semi-coke reducing agent for industrial silicon

Abstract

This invention relates to a method for improving the resistivity of a composite semi-coke reducing agent for industrial silicon, belonging to the technical field of composite reducing agents for industrial silicon. The invention involves crushing and grinding vacuum-dried bituminous coal and vacuum-dried petroleum coke to a particle size of 3-8 cm to obtain microspherical bituminous coal particles and microspherical petroleum coke particles. These particles are then uniformly mixed to obtain a microspherical mixture. Water is added to the microspherical mixture, and the mixture is further ground to obtain mixture A. A silicon slag modifier is added to mixture A and ground uniformly to obtain mixture B. Mixture B is then microwave-modified under a protective atmosphere and cooled to room temperature to obtain modified mixture C. Modified mixture C is then placed under a protective atmosphere and activated with hydrogen gas at 550-850°C for 45-90 minutes, and cooled to room temperature to obtain a high-resistivity composite semi-coke reducing agent for industrial silicon. The composite semi-coke reducing agent of this invention has a high fixed carbon content, low price, high resistivity, good reactivity, and good compressive strength.

Description

Technical Field

[0001] This invention relates to a method for improving the resistivity of composite semi-coke reducing agents for industrial silicon, belonging to the technical field of composite reducing agents for industrial silicon. Background Technology

[0002] For a long time, charcoal has been the primary reducing agent used in industrial silicon production. However, charcoal production consumes a large amount of forest resources, and the tight supply and rising prices of charcoal have severely impacted the economic benefits of industrial silicon companies. To address the shortage and high cost of reducing agents in the industrial silicon industry, two main solutions exist: finding substitutes for charcoal and reducing the amount of charcoal used in the smelting process. Regarding substitutes, petroleum coke and bituminous coal are primarily used as reducing agents. To reduce charcoal usage, a mixed reducing agent composed of charcoal, petroleum coke, and bituminous coal is used, with petroleum coke and bituminous coal partially replacing charcoal. Both solutions primarily focus on the application research of petroleum coke and bituminous coal.

[0003] Petroleum coke is cheaper than charcoal and has the lowest ash content among various carbonaceous raw materials, with a fixed carbon content exceeding 90%. However, petroleum coke undergoes severe graphitization at high temperatures, rapidly transforming into a large-grained graphite structure with excessively low resistivity and poor reactivity. While using petroleum coke exclusively as a reducing agent can smelt industrial silicon, the poor permeability of the furnace charge, the tendency for sintering at the furnace throat, and the difficulty in processing increase the smelting difficulty and power consumption. Using bituminous coal as a reducing agent offers strong reactivity, with its chemical activity almost five times that of petroleum coke, and it is cheaper. However, compared to charcoal, bituminous coal has a lower resistivity. Furthermore, using large quantities of bituminous coal can lead to surface sintering, poor furnace charge permeability, and a high ash content, which reduces the quality of the silicon product.

[0004] Replacing or partially replacing charcoal with bituminous coal and petroleum coke in the smelting of industrial silicon can reduce the cost of industrial silicon production. Patent CN103626183A discloses a carbonaceous reducing agent for industrial silicon production, composed of petroleum coke and modified petroleum coke particles. This reducing agent has a dry basis fixed carbon content ≥76%, residual ash content ≤1%, volatile matter 10%–16%, and moisture content ≤8%, which can extend the furnace life by about double. However, the petroleum coke in this reducing agent has low reactivity, and the resistivity is not improved. Patent CN103626183A also discloses the preparation of a composite carbonaceous reducing agent. A mixture of prepared petroleum coke, bituminous coal, and charcoal powder is uniformly mixed to obtain a mixture. An organic binder, additives, and water are added to the mixture and stirred until uniform. The mixture is then formed into pellets, dried, and the composite reducing agent is obtained. However, this method mainly focuses on the particle size and proportion of the materials, primarily addressing the reducing agent formulation issue, and the reducing agent's reactivity remains low. Patent CN115072724A designs a method for thoroughly mixing biomass carbon, semi-coke, petroleum coke, coke-based reducing agents, caking washed coal, and uncaking washed coal according to a mass ratio, and then feeding the mixture into a submerged arc furnace for industrial silicon smelting. However, this mixing technology still suffers from problems such as low reducing agent activity, poor furnace charge permeability, and additional energy consumption. Patent CN117448566A discloses a composite carbonaceous reducing agent pellet for industrial silicon and its preparation method, which uses different caking coals in combination with water, binders, waste biomass, and alkali metal additives to coat charcoal powder and petroleum coke layer by layer. However, this method mainly focuses on the efficient utilization of powder and low-rank coal resources in the reducing agent and does not fundamentally improve resistivity and reactivity.

[0005] In the industrial silicon smelting process, the reducing agent needs to have a high resistivity. However, when using a composite reducing agent with high levels of coke and coal, the electrodes rise, failing to penetrate deeply and stably into the furnace bottom. This results in a high surface temperature and a low bottom temperature, making it difficult for molten silicon to flow out, causing the furnace bottom to rise further, severely impacting industrial silicon production and the company's economic benefits. Current industrial technologies cannot fundamentally solve the problem of the lower resistivity of bituminous coal and petroleum coke compared to charcoal. Summary of the Invention

[0006] To address the issue that the resistivity of reducing agents for industrial silicon prepared from bituminous coal and petroleum coke is lower than that of charcoal, this invention proposes a method to improve the resistivity of a composite semi-coke reducing agent for industrial silicon. This method utilizes a silicon slag modifier to modify microspherical bituminous coal particles and microspherical petroleum coke particles, and then activates them with hydrogen to prepare a high-resistivity composite semi-coke reducing agent for industrial silicon. This agent has high fixed carbon content, low price, high resistivity, good reactivity, and good compressive strength. Simultaneously, silicon is recovered from the silicon slag. The product's performance is similar to that of charcoal, and it can directly replace charcoal as a carbonaceous reducing agent for industrial silicon smelting.

[0007] A method for improving the resistivity of composite semi-coke reducing agents used in industrial silicon includes the following steps:

[0008] (1) Vacuum-dried bituminous coal and vacuum-dried petroleum coke are crushed and ground to a particle size of 3-8 cm to obtain micro-spherical bituminous coal particles and micro-spherical petroleum coke particles. The micro-spherical bituminous coal particles and micro-spherical petroleum coke particles are mixed evenly to obtain a micro-spherical mixture. Water is added to the micro-spherical mixture and mixed and ground to obtain mixture A.

[0009] (2) Add the silicon slag modifier to mixture A and grind it evenly to obtain mixture B;

[0010] (3) Place the mixture B under a protective atmosphere for microwave carbonization modification, and cool it to room temperature to obtain the modified mixture C;

[0011] (4) The modified mixture C is placed in a protective atmosphere and activator hydrogen is introduced. It is activated at a temperature of 550-850℃ for 45-90 min and then cooled to room temperature to obtain a high resistivity composite semi-coke reducing agent for industrial silicon.

[0012] In step (1), the fixed carbon content of the bituminous coal is 55-70 wt.%, the reactivity at 1100℃ is 70-88%, and the resistivity at 900℃ is 2500-4000 μΩ·m; the fixed carbon content of the petroleum coke is 80-94 wt.%, the reactivity at 1100℃ is 40-52%, and the resistivity at 900℃ is 950-1250 μΩ·m.

[0013] In step (1), the microsphere mixture contains 30-60 wt% microsphere bituminous coal particles and 60-70 wt% microsphere petroleum coke particles; the mass ratio of water to the microsphere mixture is 2-5:100; and the particle size of mixture A is 1-3 mm.

[0014] The silicon slag modifier in step (2) is an industrial waste slag separated from the electric furnace of a silicon plant. It is collected after being slowly cooled in the air and then pre-roasted at a temperature of 800-1300℃ for 2-10 hours to obtain the silicon slag modifier.

[0015] The silicon slag modifier in step (2) contains Si, SiC, Ca2Al2SiO7 and unavoidable impurities. By mass percentage, the silicon slag modifier contains 15-25% Si, 10-20% Ca, 5-10% Al, 0.5-2% Fe, and <0.05% P.

[0016] In step (2), the silica slag modifier in mixture B accounts for 2-5 wt%, and the particle size of mixture B is 0.5-1.5 mm.

[0017] The protective gas in step (3) is helium, argon or nitrogen, the microwave carbonization modification temperature is 500-1100℃, the time is 1-3h, and the microwave power is 2-5kW.

[0018] The protective gas in step (4) is helium, argon or nitrogen, and the rate of introduction of the activator hydrogen is 2 to 5 mL / min.

[0019] The fixed carbon content of the composite semi-coke reducing agent for industrial silicon in step (4) is ≥75%, the reactivity at 1100℃ is ≥90%, the resistivity at 900℃ is ≥5000μΩ·m, and the compressive strength is ≥11Mpa.

[0020] The principle behind the improvement of resistivity of petroleum coke and bituminous coal by silicon slag modifier: The high content of Ca, Al, Fe and other substances with high resistivity in silicon slag modifier can improve the overall resistivity when mixed with petroleum coke and bituminous coal. At the same time, SiC and Ca2Al2SiO7 in the modifier significantly enhance the thermal vibration of free electrons in petroleum coke and bituminous coal during microwave heating carbonization, thereby increasing the resistivity of petroleum coke and bituminous coal. This results in a composite semi-coke reducing agent with high resistivity. When applied to industrial silicon smelting, it can expand the crucible (molten pool) area in the furnace, causing the high-temperature zone to shift downward, reducing the material surface temperature, and reducing heat loss.

[0021] The principle behind hydrogen activator enhancing the activity of composite semi-coke reducing agents: During the hydrogenation pyrolysis of the reducing agent, hydrogen mainly participates in the pyrolysis process through hydrogen abstraction reactions of free radicals. The hydrogen in the gas is primarily coupled with free radicals generated by the dissociation of hydrogen induced by active free radicals. Some non-volatile free radicals can abstract hydrogen from the gas to generate CH, C-(H)2, and C-(H)3 substances, subsequently undergoing C-C bond cleavage to form CH4. For different free radicals, the smaller the structure, the stronger the hydrogen abstraction ability. Simultaneously, hydrogen adsorption and activation on the oxide surface involves heterolytic cleavage to generate protons (OH) and MH. - The modes of homolytic cleavage to generate protons and reduce oxides, the active center of hydrogenase, construct Lewis base-transition metal catalysts, and utilize the nucleophilicity of LB sites for bifunctional catalytic activation of hydrogen.

[0022] The beneficial effects of this invention are:

[0023] (1) The present invention uses wet grinding with water to mix bituminous coal, petroleum coke and silicon slag modifier, which promotes the mixing of mixed carbon materials and increases the contact area. At the same time, microwave carbonization treatment causes the water in the mixed carbon materials to evaporate, increases the porosity, and makes the mixed carbon materials have high reactivity, which can improve the reaction efficiency of industrial silicon smelting.

[0024] (2) The addition of petroleum coke to the composite reducing agent of the present invention can significantly improve the compressive strength. Therefore, the composite semi-coke reducing agent composed of a large proportion of petroleum coke and bituminous coal has high compressive strength. At the same time, microwave heating carbonization treatment not only promotes the improvement of the resistivity of the composite reducing agent by the silicon slag modifier, but also densifies the reducing agent to further improve the compressive strength.

[0025] (3) This invention uses silicon slag modifier to modify the resistivity of the composite reducing agent composed of petroleum coke and bituminous coal, which greatly improves the overall resistivity of the composite reducing agent. Compared with the simple high coke and high coal reducing agent, the composite reducing agent has a higher resistivity, which is close to that of charcoal. It can replace or partially replace charcoal in the production of industrial silicon in industrial silicon smelting.

[0026] (4) This invention uses hydrogen activator to activate composite reducing agent, so that it has high porosity and reduction activity, which can improve silica reduction rate, reduce slag content, and increase silicon yield. It effectively solves the problem of excessive energy consumption, significantly reduces the electricity consumption per ton of silicon, and increases active power. Moreover, the activator hydrogen is environmentally friendly and pollution-free.

[0027] (5) This invention enables high-quality and efficient recycling and comprehensive utilization of industrial silicon slag, namely, re-smelting and recovering metallic silicon from the silicon slag in the composite reducing agent, and can solve the environmental problems and treatment cost problems caused by industrial waste residue, further reducing the cost of raw materials for industrial silicon smelting. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0029] Example 1: A method for improving the resistivity of composite semi-coke reducing agent for industrial silicon, the specific steps of which are as follows:

[0030] (1) Bituminous coal and petroleum coke that have been vacuum dried at 100℃ for 12h are crushed and ground to a particle size of 3-4cm to obtain microspherical bituminous coal particles and microspherical petroleum coke particles. The microspherical bituminous coal particles and microspherical petroleum coke particles are mixed evenly to obtain a microspherical mixture. Water is added to the microspherical mixture and ground to obtain a mixture A with an average particle size of 2mm. The fixed carbon content of the bituminous coal is 62.3wt.%, the reactivity at 1100℃ is 79.4%, and the resistivity at 900℃ is 3256μΩ·m. The fixed carbon content of the petroleum coke is 87.6wt.%, the reactivity at 1100℃ is 46.8%, and the resistivity at 900℃ is 1107μΩ·m. The microspherical mixture contains 50wt% microspherical bituminous coal particles and 50wt% microspherical petroleum coke particles. The mass ratio of water to the microspherical mixture is 3:100.

[0031] (2) The silicon slag modifier was added to mixture A and ground evenly to obtain mixture B with an average particle size of 1 mm (the silicon slag modifier in mixture B accounts for 4 wt%). The silicon slag modifier was an industrial waste residue separated from the electric furnace of a silicon plant in Yunnan. It was collected after being slowly cooled in the air and then pre-calcined at 1050℃ for 6 hours to obtain the silicon slag modifier. The silicon slag modifier contained Si, SiC, Ca2Al2SiO7 and unavoidable impurities. By mass percentage, the silicon slag modifier contained 20.1% Si, 15.4% Ca, 7.3% Al, 1.2% Fe and 0.011% P.

[0032] (3) Mixture B was placed in an argon atmosphere for microwave carbonization modification and cooled to room temperature to obtain modified mixture C; wherein the microwave carbonization modification temperature was 800℃, the time was 2h, and the microwave power was 3.5kW.

[0033] (4) The modified mixture C was placed in an argon atmosphere and activator hydrogen gas (3.5 mL / min) was introduced. It was activated at 700℃ for 65 min and cooled to room temperature to obtain a high resistivity composite semi-coke reducing agent for industrial silicon.

[0034] The composite semi-coke reducing agent for industrial silicon prepared in this embodiment has high porosity, resistivity, compressive strength and reactivity; the fixed carbon content is 79.7 wt.%, the reactivity (1100℃) is 91.2%, the resistivity (900℃) is 5103 μΩ·m and the compressive strength is 11.8 MPa;

[0035] 20.0g of silica (99.5% SiO2, 0.05% Al2O3, 0.03% Fe2O3, 0.05% CaO) was crushed into blocks with a particle size of 25-100mm. After washing and sieving, it was mixed evenly with 10.1g of the above-mentioned composite semi-coke reducing agent and added to a 12.5MVA submerged arc furnace for smelting. After smelting, 8.87g of industrial silicon product was obtained. The composition of the industrial silicon product obtained after smelting was Si>99.6Wt.%, Fe≤0.19Wt.%, Al≤0.09Wt.%, Ca≤0.05Wt.%.

[0036] Example 2: A method for improving the resistivity of composite semi-coke reducing agent for industrial silicon, the specific steps of which are as follows:

[0037] (1) Bituminous coal and petroleum coke, which were vacuum dried at 105℃ for 12h, were crushed and ground to a particle size of 7-8cm to obtain microspherical bituminous coal particles and microspherical petroleum coke particles. The microspherical bituminous coal particles and microspherical petroleum coke particles were mixed evenly to obtain a microspherical mixture. Water was added to the microspherical mixture and ground to obtain a mixture A with an average particle size of 3mm. The fixed carbon content of the bituminous coal was 65.4wt.%, the reactivity (1100℃) was 83.1%, and the resistivity (900℃) was 2837μΩ·m. The fixed carbon content of the petroleum coke was 90.3wt.%, the reactivity (1100℃) was 43.6%, and the resistivity (900℃) was 1196μΩ·m. The microspherical mixture contained 60wt% microspherical bituminous coal particles and 40wt% microspherical petroleum coke particles. The mass ratio of water to the microspherical mixture was 2:100.

[0038] (2) The silicon slag modifier was added to mixture A and ground evenly to obtain mixture B with an average particle size of 1 mm (the silicon slag modifier in mixture B accounts for 3 wt%). The silicon slag modifier was an industrial waste residue separated from the electric furnace of a silicon plant in Yunnan. It was collected after being slowly cooled in the air and then pre-calcined at 1200℃ for 8 hours to obtain the silicon slag modifier. The silicon slag modifier contained Si, SiC, Ca2Al2SiO7 and unavoidable impurities. By mass percentage, the silicon slag modifier contained 22.1% Si, 14.8% Ca, 7.1% Al, 0.8% Fe and 0.013% P.

[0039] (3) Place the mixture B under a nitrogen atmosphere for microwave carbonization modification, and cool it to room temperature to obtain the modified mixture C; wherein the microwave carbonization modification temperature is 500℃, the time is 3h, and the microwave power is 5kW.

[0040] (4) The modified mixture C was placed in a nitrogen atmosphere and activator hydrogen gas (4 mL / min) was introduced. It was activated at 750℃ for 60 min and cooled to room temperature to obtain a high resistivity composite semi-coke reducing agent for industrial silicon.

[0041] The composite semi-coke reducing agent for industrial silicon prepared in this embodiment has high porosity, resistivity, compressive strength and reactivity; the fixed carbon content is 82.8 wt.%, the reactivity (1100℃) is 90.9%, the resistivity (900℃) is 5076 μΩ·m and the compressive strength is 11.4 MPa.

[0042] 20.0g of silica (99.5% SiO2, 0.05% Al2O3, 0.03% Fe2O3, 0.05% CaO) was crushed into blocks with a particle size of 25-100mm. After washing and sieving, it was mixed evenly with 10.0g of the above-mentioned composite semi-coke reducing agent and added to a 12.5MVA submerged arc furnace for smelting. After smelting, 8.98g of industrial silicon product was obtained. The composition of the industrial silicon product obtained after smelting was Si>99.6Wt.%, Fe≤0.19Wt.%, Al≤0.09Wt.%, Ca≤0.05Wt.%.

[0043] Example 3: A method for improving the resistivity of composite semi-coke reducing agent for industrial silicon, the specific steps of which are as follows:

[0044] (1) Bituminous coal and petroleum coke, which were vacuum dried at 110℃ for 12h, were crushed and ground to a particle size of 6-7cm to obtain microspherical bituminous coal particles and microspherical petroleum coke particles. The microspherical bituminous coal particles and microspherical petroleum coke particles were mixed evenly to obtain a microspherical mixture. Water was added to the microspherical mixture and ground to obtain a mixture A with an average particle size of 3mm. The fixed carbon content of the bituminous coal was 58.7wt.%, the reactivity (1100℃) was 74.5%, and the resistivity (900℃) was 2679μΩ·m. The fixed carbon content of the petroleum coke was 91.7wt.%, the reactivity (1100℃) was 50.1%, and the resistivity (900℃) was 1247μΩ·m. The microspherical mixture contained 55wt% microspherical bituminous coal particles and 45wt% microspherical petroleum coke particles. The mass ratio of water to the microspherical mixture was 4:100.

[0045] (2) The silicon slag modifier was added to mixture A and ground evenly to obtain mixture B with an average particle size of 1.5 mm (the silicon slag modifier in mixture B accounts for 5 wt%). The silicon slag modifier was an industrial waste residue separated from the electric furnace of a silicon plant in Yunnan. It was collected after being slowly cooled in the air and then pre-calcined at 1300℃ for 2 hours to obtain the silicon slag modifier. The silicon slag modifier contained Si, SiC, Ca2Al2SiO7 and unavoidable impurities. By mass percentage, the silicon slag modifier contained 19.4% Si, 16.1% Ca, 8.7% Al, 1.5% Fe and 0.31% P.

[0046] (3) Place the mixture B under a helium atmosphere for microwave carbonization modification, and cool it to room temperature to obtain the modified mixture C; wherein the microwave carbonization modification temperature is 1000℃, the time is 1h, and the microwave power is 2kW.

[0047] (4) The modified mixture C was placed in a helium atmosphere and activator hydrogen gas (3 mL / min) was introduced. It was activated at 800℃ for 50 min and cooled to room temperature to obtain a high resistivity composite semi-coke reducing agent for industrial silicon.

[0048] The composite semi-coke reducing agent for industrial silicon prepared in this embodiment has high porosity, resistivity, compressive strength and reactivity; the fixed carbon content is 80.9 wt.%, the reactivity (1100℃) is 91.5%, the resistivity (900℃) is 5049 μΩ·m and the compressive strength is 12.2 MPa;

[0049] 20.0g of silica (99.5% SiO2, 0.05% Al2O3, 0.03% Fe2O3, 0.05% CaO) was crushed into blocks with a particle size of 25-100mm. After washing and sieving, it was mixed evenly with 10.0g of the above-mentioned composite semi-coke reducing agent and added to a 12.5MVA submerged arc furnace for smelting. After smelting, 8.94g of industrial silicon product was obtained. The composition of the industrial silicon product obtained after smelting was Si>99.6Wt.%, Fe≤0.19Wt.%, Al≤0.09Wt.%, Ca≤0.05Wt.%.

[0050] Example 4: A method for improving the resistivity of composite semi-coke reducing agent for industrial silicon, the specific steps of which are as follows:

[0051] (1) Bituminous coal and petroleum coke, which were vacuum dried at 110℃ for 12h, were crushed and ground to a particle size of 3-4cm to obtain microspherical bituminous coal particles and microspherical petroleum coke particles. The microspherical bituminous coal particles and microspherical petroleum coke particles were mixed evenly to obtain a microspherical mixture. Water was added to the microspherical mixture and ground to obtain a mixture A with an average particle size of 1mm. The fixed carbon content of the bituminous coal was 56.9wt.%, the reactivity (1100℃) was 72.4%, and the resistivity (900℃) was 2597μΩ·m. The fixed carbon content of the petroleum coke was 92.4wt.%, the reactivity (1100℃) was 51.2%, and the resistivity (900℃) was 1019μΩ·m. The microspherical mixture contained 40wt% microspherical bituminous coal particles and 60wt% microspherical petroleum coke particles. The mass ratio of water to the microspherical mixture was 5:100.

[0052] (2) The silicon slag modifier was added to mixture A and ground evenly to obtain mixture B with an average particle size of 0.5 mm (the silicon slag modifier in mixture B accounts for 2 wt%). The silicon slag modifier was an industrial waste residue separated from the electric furnace of a silicon plant in Yunnan. It was collected after being slowly cooled in the air and then pre-calcined at 800℃ for 10 h to obtain the silicon slag modifier. The silicon slag modifier contained Si, SiC, Ca2Al2SiO7 and unavoidable impurities. By mass percentage, the silicon slag modifier contained 24.1% Si, 12.7% Ca, 6.4% Al, 0.7% Fe and 0.008% P.

[0053] (3) Place the mixture B under an argon atmosphere for microwave carbonization modification, and cool it to room temperature to obtain the modified mixture C; wherein the microwave carbonization modification temperature is 1100℃, the time is 1.5h, and the microwave power is 2kW.

[0054] (4) The modified mixture C was placed in an argon atmosphere and activator hydrogen gas (2 mL / min) was introduced. It was activated at 850℃ for 45 min and cooled to room temperature to obtain a high resistivity composite semi-coke reducing agent for industrial silicon.

[0055] The composite semi-coke reducing agent for industrial silicon prepared in this embodiment has high porosity, resistivity, compressive strength and reactivity; the fixed carbon content is 81.4 wt.%, the reactivity (1100℃) is 92.1%, the resistivity (900℃) is 5027 μΩ·m and the compressive strength is 12.4 MPa.

[0056] 20.0g of silica (99.5% SiO2, 0.05% Al2O3, 0.03% Fe2O3, 0.05% CaO) was crushed into blocks with a particle size of 25-100mm. After washing and sieving, it was mixed evenly with 10.0g of the above-mentioned composite semi-coke reducing agent and added to a 12.5MVA submerged arc furnace for smelting. After smelting, 8.87g of industrial silicon product was obtained. The composition of the industrial silicon product obtained after smelting was Si>99.6Wt.%, Fe≤0.19Wt.%, Al≤0.09Wt.%, Ca≤0.05Wt.%.

[0057] Example 5: A method for improving the resistivity of composite semi-coke reducing agent for industrial silicon, the specific steps of which are as follows:

[0058] (1) Bituminous coal and petroleum coke, which were vacuum dried at 100℃ for 12h, were crushed and ground to a particle size of 4-5cm to obtain microspherical bituminous coal particles and microspherical petroleum coke particles. The microspherical bituminous coal particles and microspherical petroleum coke particles were mixed evenly to obtain a microspherical mixture. Water was added to the microspherical mixture and ground to obtain a mixture A with an average particle size of 2mm. The fixed carbon content of the bituminous coal was 68.2wt.%, the reactivity (1100℃) was 85.7%, and the resistivity (900℃) was 3829μΩ·m. The fixed carbon content of the petroleum coke was 82.9wt.%, the reactivity (1100℃) was 42.7%, and the resistivity (900℃) was 976μΩ·m. The microspherical mixture contained 45wt% microspherical bituminous coal particles and 55wt% microspherical petroleum coke particles. The mass ratio of water to the microspherical mixture was 4:100.

[0059] (2) The silicon slag modifier was added to mixture A and ground evenly to obtain mixture B with an average particle size of 1.5 mm (the silicon slag modifier in mixture B accounts for 3 wt%). The silicon slag modifier was an industrial waste residue separated from the electric furnace of a silicon plant in Yunnan. It was collected after being slowly cooled in the air and then pre-calcined at 850℃ for 9 hours to obtain the silicon slag modifier. The silicon slag modifier contained Si, SiC, Ca2Al2SiO7 and unavoidable impurities. By mass percentage, the silicon slag modifier contained 21.7% Si, 16.2% Ca, 8.6% Al, 1.7% Fe and 0.21% P.

[0060] (3) Mixture B was placed in a nitrogen atmosphere for microwave carbonization modification and cooled to room temperature to obtain modified mixture C; wherein the microwave carbonization modification temperature was 600℃, the time was 2.5h, and the microwave power was 4kW.

[0061] (4) The modified mixture C was placed in a nitrogen atmosphere and activator hydrogen gas (2.5 mL / min) was introduced. It was activated at 800℃ for 70 min and cooled to room temperature to obtain a high resistivity composite semi-coke reducing agent for industrial silicon.

[0062] The composite semi-coke reducing agent for industrial silicon prepared in this embodiment has high porosity, resistivity, compressive strength and reactivity; the fixed carbon content is 78.4 t.%, the reactivity (1100℃) is 91.7%, the resistivity (900℃) is 5197 μΩ·m and the compressive strength is 12.1 MPa;

[0063] 20.0g of silica (99.5% SiO2, 0.05% Al2O3, 0.03% Fe2O3, 0.05% CaO) was crushed into blocks with a particle size of 25-100mm. After washing and sieving, it was mixed evenly with 10.0g of the above-mentioned composite semi-coke reducing agent and added to a 12.5MVA submerged arc furnace for smelting. After smelting, 9.11g of industrial silicon product was obtained. The composition of the industrial silicon product obtained after smelting was Si>99.6Wt.%, Fe≤0.19Wt.%, Al≤0.09Wt.%, Ca≤0.05Wt.%.

[0064] Example 6: A method for improving the resistivity of composite semi-coke reducing agent for industrial silicon, the specific steps of which are as follows:

[0065] (1) Bituminous coal and petroleum coke, which were vacuum dried at 105℃ for 12h, were crushed and ground to a particle size of 7-8cm to obtain microspherical bituminous coal particles and microspherical petroleum coke particles. The microspherical bituminous coal particles and microspherical petroleum coke particles were mixed evenly to obtain a microspherical mixture. Water was added to the microspherical mixture and ground to obtain a mixture A with an average particle size of 2.5mm. The fixed carbon content of the bituminous coal was 59.4wt.%, the reactivity (1100℃) was 77.6%, and the resistivity (900℃) was 3161μΩ·m. The fixed carbon content of the petroleum coke was 85.7wt.%, the reactivity (1100℃) was 44.2%, and the resistivity (900℃) was 1042μΩ·m. The microspherical mixture contained 55wt% microspherical bituminous coal particles and 45wt% microspherical petroleum coke particles. The mass ratio of water to the microspherical mixture was 3:100.

[0066] (2) The silicon slag modifier was added to mixture A and ground evenly to obtain mixture B with an average particle size of 1 mm (the silicon slag modifier in mixture B accounts for 5 wt%). The silicon slag modifier was an industrial waste residue separated from the electric furnace of a silicon plant in Yunnan. It was collected after being slowly cooled in the air and then pre-calcined at 900℃ for 7 h to obtain the silicon slag modifier. The silicon slag modifier contained Si, SiC, Ca2Al2SiO7 and unavoidable impurities. By mass percentage, the silicon slag modifier contained 23.2% Si, 13.8% Ca, 9.0% Al, 1.1% Fe and 0.005% P.

[0067] (3) Place the mixture B under a helium atmosphere for microwave carbonization modification, and cool it to room temperature to obtain the modified mixture C; wherein the microwave carbonization modification temperature is 700℃, the time is 2.5h, and the microwave power is 3kW.

[0068] (4) The modified mixture C was placed in a helium atmosphere and activator hydrogen gas (5 mL / min) was introduced. It was activated at 550℃ for 90 min and cooled to room temperature to obtain a high resistivity composite semi-coke reducing agent for industrial silicon.

[0069] The composite semi-coke reducing agent for industrial silicon prepared in this embodiment has high porosity, resistivity, compressive strength and reactivity; the fixed carbon content is 77.9 wt.%, the reactivity (1100℃) is 90.6%, the resistivity (900℃) is 5246 μΩ·m and the compressive strength is 11.9 MPa;

[0070] 20.0g of silica (99.5% SiO2, 0.05% Al2O3, 0.03% Fe2O3, 0.05% CaO) was crushed into blocks with a particle size of 25-100mm. After washing and sieving, it was mixed evenly with 10.0g of the above-mentioned composite semi-coke reducing agent and added to a 12.5MVA submerged arc furnace for smelting. After smelting, 9.19g of industrial silicon product was obtained. The composition of the industrial silicon product obtained after smelting was Si>99.6Wt.%, Fe≤0.19Wt.%, Al≤0.09Wt.%, Ca≤0.05Wt.%.

[0071] Example 7: A method for improving the resistivity of composite semi-coke reducing agent for industrial silicon, the specific steps of which are as follows:

[0072] (1) Bituminous coal and petroleum coke, which were vacuum dried at 110℃ for 12h, were crushed and ground to a particle size of 7-8cm to obtain microspherical bituminous coal particles and microspherical petroleum coke particles. The microspherical bituminous coal particles and microspherical petroleum coke particles were mixed evenly to obtain a microspherical mixture. Water was added to the microspherical mixture and ground to obtain a mixture A with an average particle size of 3mm. The fixed carbon content of the bituminous coal was 69.1wt.%, the reactivity (1100℃) was 86.8%, and the resistivity (900℃) was 3592μΩ·m. The fixed carbon content of the petroleum coke was 80.9wt.%, the reactivity (1100℃) was 41.3%, and the resistivity (900℃) was 999μΩ·m. The microspherical mixture contained 30wt% microspherical bituminous coal particles and 70wt% microspherical petroleum coke particles. The mass ratio of water to the microspherical mixture was 4:100.

[0073] (2) The silicon slag modifier was added to mixture A and ground evenly to obtain mixture B with an average particle size of 1.5 mm (the silicon slag modifier in mixture B accounts for 4 wt%). The silicon slag modifier was an industrial waste residue separated from the electric furnace of a silicon plant in Yunnan. It was collected after being slowly cooled in the air and then pre-calcined at 1250℃ for 5 h to obtain the silicon slag modifier. The silicon slag modifier contained Si, SiC, Ca2Al2SiO7 and unavoidable impurities. By mass percentage, the silicon slag modifier contained 20.7% Si, 15.1% Ca, 7.2% Al, 1.0% Fe and 0.020% P.

[0074] (3) Place the mixture B under a nitrogen atmosphere for microwave carbonization modification, and cool it to room temperature to obtain the modified mixture C; wherein the microwave carbonization modification temperature is 900℃, the time is 3h, and the microwave power is 4kW.

[0075] (4) The modified mixture C was placed in a nitrogen atmosphere and activator hydrogen gas (4.5 mL / min) was introduced. It was activated at 650℃ for 80 min and cooled to room temperature to obtain a high resistivity composite semi-coke reducing agent for industrial silicon.

[0076] The composite semi-coke reducing agent for industrial silicon prepared in this embodiment has high porosity, resistivity, compressive strength and reactivity; the fixed carbon content is 80.5 wt.%, the reactivity (1100℃) is 90.8%, the resistivity (900℃) is 5129 μΩ·m and the compressive strength is 11.6 MPa;

[0077] 20.0g of silica (99.5% SiO2, 0.05% Al2O3, 0.03% Fe2O3, 0.05% CaO) was crushed into blocks with a particle size of 25-100mm. After washing and sieving, it was mixed evenly with 10.0g of the above-mentioned composite semi-coke reducing agent and added to a 12.5MVA submerged arc furnace for smelting. After smelting, 9.05g of industrial silicon product was obtained. The composition of the industrial silicon product obtained after smelting was Si>99.6Wt.%, Fe≤0.19Wt.%, Al≤0.09Wt.%, Ca≤0.05Wt.%.

[0078] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for improving the resistivity of a composite semi-coke reducing agent for industrial silicon, characterized in that, The specific steps are as follows: (1) Vacuum-dried bituminous coal and vacuum-dried petroleum coke are crushed and ground to a particle size of 3-8 cm to obtain microspherical bituminous coal particles and microspherical petroleum coke particles. The microspherical bituminous coal particles and microspherical petroleum coke particles are mixed evenly to obtain a microspherical mixture. Water is added to the microspherical mixture and mixed and ground to obtain mixture A. The microspherical mixture contains 30-60 wt% microspherical bituminous coal particles and 60-70 wt% microspherical petroleum coke particles. (2) Add the silicon slag modifier to mixture A and grind it evenly to obtain mixture B; the silicon slag modifier contains Si, SiC, Ca2Al2SiO7 and unavoidable impurities. By mass percentage, the silicon slag modifier contains 15~25% Si, 10~20% Ca, 5~10% Al, 0.5~2% Fe and <0.05% P. (3) Place the mixture B under a protective atmosphere for microwave carbonization modification, and cool it to room temperature to obtain the modified mixture C; (4) The modified mixture C is placed in a protective atmosphere and activator hydrogen is introduced. It is activated at a temperature of 550~850℃ for 45~90min and cooled to room temperature to obtain a high resistivity composite semi-coke reducing agent for industrial silicon.

2. The method for improving the resistivity of composite semi-coke reducing agent for industrial silicon according to claim 1, characterized in that: Step (1) The fixed carbon content of the bituminous coal is 55~70 wt.%, the reactivity at 1100℃ is 70~88%, and the resistivity at 900℃ is 2500~4000 Ω·cm. The fixed carbon content of petroleum coke is 80-94 wt.%, its reactivity at 1100℃ is 40-52%, and its resistivity at 900℃ is 950-1250 Ω·cm. .

3. The method for improving the resistivity of composite semi-coke reducing agent for industrial silicon according to claim 1, characterized in that: Step (1): The mass ratio of water to microsphere mixture is 2~5:100; the particle size of mixture A is 1~3mm.

4. The method for improving the resistivity of composite semi-coke reducing agent for industrial silicon according to claim 1, characterized in that: In step (2), the silica slag modifier in mixture B accounts for 2~5wt%, and the particle size of mixture B is 0.5~1.5mm.

5. The method for improving the resistivity of composite semi-coke reducing agent for industrial silicon according to claim 1, characterized in that: Step (3) The protective gas is helium, argon or nitrogen, the microwave carbonization modification temperature is 500~1100℃, the time is 1~3h, and the microwave power is 2~5kW.

6. The method for improving the resistivity of composite semi-coke reducing agent for industrial silicon according to claim 1, characterized in that: Step (4) The protective gas is helium, argon or nitrogen, and the activator hydrogen is introduced at a rate of 2~5 mL / min.

7. The method for improving the resistivity of composite semi-coke reducing agent for industrial silicon according to claim 1, characterized in that: Step (4) The fixed carbon content of the composite semi-coke reducing agent for industrial silicon is ≥75wt.%, the reactivity at 1100℃ is ≥90%, and the resistivity at 900℃ is ≥5000. Compressive strength ≥11 MPa.