Method for preparing composite reducing agent for industrial silicon from different caking coals by natural fermentation of coffee wastewater

Abstract

The present application relates to a kind of coffee wastewater natural fermentation different binding coal preparation industrial silicon composite reducing agent method, belong to carbonaceous reducing agent pellet preparation technical field.The present application mixes coffee wastewater and different binding coal powder after wet grinding, grinding is mixed uniformly to obtain mixture A;Mixture A is placed in the closed environment of temperature 18~33 ℃ Natural fermentation 10~30d obtains fermentation carbon material B, and fermentation carbon material B is dried after grinding to obtain fermentation carbon material powder;Coffee shell powder is added to NaOH solution and soaked activation treatment, solid-liquid separation obtains coffee shell binder;Fermentation carbon material powder, waste biomass, coffee shell binder, water are mixed uniformly to obtain fermentation carbon material mixture;Fermentation carbon material mixture is formed by cold pressing, and drying obtains cylindrical blank;Cylindrical blank is placed in argon atmosphere and is microwave calcined, and furnace cooling is cooled to room temperature to obtain industrial silicon composite reducing agent pellet.The composite reducing agent can reduce 7~10% of burn loss rate, and the silicon yield is increased by 2~4%.

Description

Technical Field

[0001] This invention relates to a method for preparing a composite reducing agent for industrial silicon by natural fermentation of coffee wastewater with different caking coals, belonging to the field of carbonaceous reducing agent pellet preparation technology. Background Technology

[0002] Currently, my country's industrial silicon smelting mainly uses a mixture of two or more raw materials, such as coal, petroleum coke, semi-coke, semi-coke, charcoal, and wood blocks, in a certain proportion as carbonaceous raw materials. Depending on the composition of the carbonaceous reducing agent used, industrial silicon production can be divided into all-coal processes and semi-coal / semi-coke processes. The semi-coal / semi-coke process uses a large proportion of charcoal and petroleum coke. Although charcoal has high porosity and good reactivity, its production consumes a large amount of forest resources, severely damaging the ecological environment. Petroleum coke also suffers from severe high-temperature graphitization, high electrical conductivity, low resistivity, poor reactivity, and severe crusting on the furnace surface, affecting the permeability of the furnace charge, causing severe sparking, and making furnace conditions difficult to control. Therefore, the future development direction is to focus on all-coal. However, high-temperature pyrolysis of coal affects the permeability of the furnace charge, reducing the utilization rate of carbon raw materials, resulting in poor reactivity, and also causing ash and coking on the heated surface of the furnace, increasing slag, and easily leading to furnace bottom rise. Therefore, researching and developing new all-coal carbonaceous reducing agents for industrial silicon has practical significance and economic value.

[0003] Currently, carbonaceous reducing agents made from a mixture of charcoal, petroleum coke, and bituminous coal are used to reduce silica. For example, patent CN115072724A designs a method where biomass carbon, semi-coke, petroleum coke, coke-based reducing agents, bonded washed coal, and unbonded washed coal are thoroughly mixed according to a mass ratio and then fed into a submerged arc furnace for industrial silicon smelting. CN113636560A describes a reducing agent obtained by mixing 40-45 parts charcoal powder, 20-25 parts washed coal powder, 8-12 parts petroleum coke powder, 3-6 parts microsilica powder, 4-5 parts pre-impregnated adhesive, 6-8 parts composite binder, and 4-5 parts NaOH solution. However, this mixing technology may still have problems such as low reducing agent activity, poor furnace permeability, and additional energy consumption. CN105329897A also discloses the preparation of a composite carbonaceous reducing agent. The method involves mixing a mixture of prepared petroleum coke, anthracite / bituminous coal, and carbon powder to obtain a mixture. An organic binder, additives, and water are added to the mixture and stirred until homogeneous. The mixture is then formed into pellets, dried, and the composite reducing agent is obtained. However, this method focuses on the particle size and proportion of the materials and is mainly aimed at the formulation of the reducing agent. The reactivity of the reducing agent is relatively low.

[0004] Coal has a high resistivity, a suitable caking index, and is not easily graphitized, making it a viable alternative to charcoal as a reducing agent in the production of industrial silicon. However, using only whole coal as a reducing agent in industrial silicon smelting, without any charcoal or wood blocks, and employing high current and low voltage conditions to stabilize furnace conditions, accelerate and complete the reaction, effectively increasing output and reducing energy consumption, results in untreated coal containing a high ash content. This affects the permeability of the furnace charge, leading to poor reactivity and low raw material utilization. Furthermore, non-caking and slightly caking coals, due to their weak caking properties and high coke content, also have low utilization rates, resulting in raw material waste. Summary of the Invention

[0005] To address the problems in the preparation of all-coal carbonaceous reducing agents in existing technologies, this invention proposes a method for preparing a composite reducing agent for industrial silicon through natural fermentation of coffee wastewater with different caking coals. Using different caking coals as all-coal reducing agents, coffee wastewater and different caking coals are wet-milled and mixed for fermentation. This allows the organic matter in the coffee wastewater to be affinity-modified and modified onto the composite caking coal. Simultaneously, alkali metals and alkali metal additives in the coffee wastewater, such as K and Na, can be adsorbed into the composite caking coal, significantly improving its porosity and chemical reactivity. Finally, waste coffee shell powder is soaked and activated using NaOH solution. This process modifies the internal organic structure of coffee shell powder, enhancing its adhesiveness and creating a coffee shell binder. This binder is then used to bond fermented carbon material powder and waste biomass. Microwave roasting releases volatile components, increasing the porosity of the pellets and creating a porous structure, thus improving their chemical reactivity. The bio-oil in the waste biomass diffuses internally and externally, further enhancing the pellets' bonding performance and reducing binder costs. Simultaneously, roasting densifies the pellets, increasing their strength. Therefore, this process can reduce energy consumption in industrial silicon smelting and production, effectively minimizing environmental pollution.

[0006] A method for preparing a composite reducing agent for industrial silicon through natural fermentation of coffee wastewater with coals of different caking properties, characterized by the following specific steps:

[0007] (1) Coffee wastewater and different caking coal powders are mixed and then wet-milled to obtain mixture A; the different caking coal powders contain non-caking coal or weakly caking coal, as well as one or more of medium-weakly caking coal, medium-strongly caking coal, and highly caking coal; the caking index n of non-caking coal is 0≤n<1, the caking index n of weakly caking coal is 1≤n≤20, the caking index n of medium-weakly caking coal is 20<n≤50, the caking index n of medium-strongly caking coal is 50<n≤65, and the caking index n of highly caking coal is 65<n≤95;

[0008] (2) Mixture A is placed in a closed environment at a temperature of 18-33℃ and fermented naturally for 10-30 days to obtain fermented carbon material B. After drying, fermented carbon material B is ground to obtain fermented carbon material powder.

[0009] (3) The coffee shell powder was added to NaOH solution for soaking and activation treatment, and the solid and liquid were separated to obtain the coffee shell binder; the fermented carbon material powder, waste biomass, coffee shell binder and water were mixed to obtain the fermented carbon material mixture;

[0010] (4) The mixture of fermented carbon materials is cold-pressed and dried to obtain a cylindrical blank;

[0011] (5) The cylindrical blank is placed in an argon atmosphere for microwave calcination and then cooled to room temperature in the furnace to obtain composite reducing agent pellets for industrial silicon.

[0012] In step (1), the fixed carbon content of non-caking coal is not less than 57 wt.%, the fixed carbon content of weakly caking coal is not less than 57 wt.%, the fixed carbon content of medium-weakly caking coal is 55-75 wt.%, the fixed carbon content of medium-strongly caking coal is 55-75 wt.%, and the fixed carbon content of highly caking coal is 55-75 wt.%.

[0013] In step (1), at least 50% of the different bonding coal powders have a particle size of less than 0.15 mm and a particle size of no more than 0.063 mm.

[0014] Based on the total mass of mixture A as 100%, coffee wastewater accounts for 20-35 wt.%, and non-caking or weakly caking coal accounts for 45-55 wt.%.

[0015] In step (2), the carbon material powder fermented in the process contains 35-45 wt.% particles with a diameter not greater than 0.063 mm.

[0016] In step (3), the particle size of the coffee shell powder is less than 0.15 mm; the mass concentration of the NaOH solution is 4-8%, and the soaking and activation treatment time is 20-60 min.

[0017] By mass percentage, waste biomass accounts for 3-5 wt.% of the fermented carbon material mixture in step (3), coffee shell binder accounts for 2-4%, water accounts for 5-10%, and the remainder is fermented carbon material powder; the waste biomass is one or more of the following: walnut shells, pine nut shells, coconut shells, peanut shells, rice husks, coffee shells, sunflower seed shells, corn cobs, and sugarcane bagasse.

[0018] The cold pressing pressure in step (4) is 10-20 MPa, the diameter of the cylindrical blank is 55-65 mm, and the height is 70-100 mm.

[0019] The microwave roasting temperature in step (5) is 500-650℃, the time is 2-4h, and the microwave power is 3-5kW.

[0020] The fixed carbon content of the composite reducing agent pellets for industrial silicon in step (4) is greater than 65 wt.%, the ash content is less than 4 wt.%, the bonding index is higher than 65, the reactivity is greater than 90%, and the cold strength of the pellets is greater than 7500 N.

[0021] The coffee wastewater is a residual liquid generated during the coffee making process. It contains high levels of organic matter (such as COD and BOD) and polyphenols (such as tannins, caffeic acid, and caffeine). The coffee wastewater also contains alkali metals such as K, Ca, and Na, with K, Ca, and Na concentrations of 60–100 mg / L, 10–20 mg / L, and 6–15 mg / L, respectively.

[0022] The principle of natural fermentation of coffee wastewater with different types of caking coal: Wet milling ensures sufficient contact between the composite caking coal and the coffee wastewater, allowing the wastewater to better penetrate the pores of the composite caking coal and increasing the reaction contact area. In a closed environment, the organic matter in the coffee wastewater produces highly selective biocatalytic enzymes during natural fermentation. These enzymes adhere to the surface and pores of the composite caking coal particles, and the potassium (K) in the coffee wastewater... + Ca 2+ Na + When cations migrate to the active sites of these catalytic enzyme molecules, they alter the carbon material structure and graphitization characteristics of the molecules.

[0023] Microwave-roasted modified composite carbon material raw materials: After microwave roasting, the macromolecular structure and oxygen-containing functional groups in the fermented carbon material decompose and become easier to detach. The carbon skeleton loses a large number of methylene and methyl groups, and the hydrogen bond breaking generates a large number of active H molecules. These active H molecules migrate outward to the surface and pores of the composite bridging coal particles and react with the organic matter attached to coffee wastewater, further catalyzing and promoting pyrolysis, and improving the chemical reactivity of the composite bridging coal. In addition, as the temperature rises, coffee wastewater and waste biomass will produce a large amount of CH4 and H2. The gaseous products will escape outward, causing a large number of micropores to form on the surface of the composite bridging coal particles. At the same time, molten or gaseous alkali metal molecules such as K, Ca, and Na in coffee wastewater and waste biomass continue to diffuse inward, further promoting the cracking of fixed carbon in the composite bridging coal and reducing the activation energy required for its cracking reaction. Meanwhile, the bio-oil from the cracking of waste biomass will bind the composite carbon reducing agent pellets, improving the performance of the carbon material pellets.

[0024] The beneficial effects of this invention are:

[0025] (1) The present invention uses different caking coals as whole coal reducing agents and prepares a porous, highly active, highly adhesive composite carbonaceous reducing agent by adding coffee wastewater for natural fermentation. It has a high fixed carbon content, high chemical reactivity, low ash content, and high adhesiveness, and can be applied to industrial silicon smelting production.

[0026] (2) In this invention, coffee wastewater is mixed with different types of caking coal and wet-milled. During the grinding process, coffee wastewater can effectively penetrate and promote the mixing of composite caking coal, increase the contact area and improve the porosity, so that the mixed carbon material has high reactivity and can improve the reaction efficiency of industrial silicon smelting.

[0027] (3) After the coffee shells are soaked in NaOH solution, -OH penetrates into the crystalline region of the coffee shell fibers, weakening the hydrogen bonds between cellulose and hemicellulose and the saponification of ester bonds between xylan hemicellulose and other components, causing the organic components to swell, increasing the porosity, and forming a hydrogel. With coffee shell adhesive as the adhesive, the alkali metal in the coffee shell can effectively enhance the reaction activity of the pellets in silicon smelting and accelerate the reaction rate.

[0028] (4) In this invention, coffee shell binder is used to bind fermented carbon material powder and waste biomass, and microwave roasting is used to release its volatile components, which can increase the porosity inside the pellets, form a porous structure, and improve the chemical reactivity of the pellets; the bio-oil in the waste biomass diffuses inside and outside, which promotes the binding performance of the pellets and saves the cost of binder. At the same time, roasting makes the pellets denser, thereby improving the strength of the pellets.

[0029] (5) The composite reducing agent pellets for industrial silicon of the present invention can improve the silicon reduction rate, reduce the slag content, increase the silicon yield, reduce the raw material cost of industrial silicon smelting, and effectively solve the problem of excessive energy consumption. It can significantly reduce the electricity consumption per ton of silicon, increase the active power, reduce carbon emissions, reduce production costs, and achieve low carbon and energy saving. Detailed Implementation

[0030] 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.

[0031] In this embodiment of the invention, coffee wastewater is a residual liquid generated during the coffee making process. Coffee wastewater contains high levels of organic matter (such as COD and BOD) and polyphenols (such as tannins, caffeic acid, and caffeine). Coffee wastewater also contains alkali metals such as K, Ca, and Na, with K, Ca, and Na contents of 69.7 mg / L, 12.8 mg / L, and 8.6 mg / L, respectively.

[0032] Example 1: A method for preparing a composite reducing agent for industrial silicon by natural fermentation of coffee wastewater with different caking coals, the specific steps of which are as follows:

[0033] (1) Coffee wastewater, weakly caking coal and medium-strongly caking coal are mixed and wet-milled to obtain mixed powder A; the weakly caking coal has a fixed carbon content of 63.3 wt.%, a caking index of 14, and 52% of the particles are less than 0.15 mm and no more than 0.063 mm; the medium-strongly caking coal has a fixed carbon content of 70.2 wt.%, a caking index of 63, and 53% of the particles are less than 0.15 mm and no more than 0.063 mm; based on a total mass of 100 wt.% for mixed powder A, the content of coffee wastewater in mixed powder A is 31 wt.%, the content of weakly caking coal is 49 wt.%, and the content of medium-strongly caking coal is 20 wt.%.

[0034] (2) Mixture A was placed in a closed environment at 29°C and allowed to ferment naturally for 21 days to obtain fermented carbon material B. Fermented carbon material B was placed in a drying oven at 105°C and dried for 20 hours before being ground to obtain fermented carbon material powder. The fermented carbon material powder contained 43 wt.% of particles with a diameter not greater than 0.063 mm.

[0035] (3) Coffee shell powder (particle size less than 0.15 mm) was added to a 6 wt.% NaOH solution and soaked for 30 min to activate it. The solid and liquid were separated to obtain coffee shell binder. Fermented carbon material powder, waste biomass (pine nut shells), coffee shell binder and water were mixed to obtain fermented carbon material mixture. Based on the mass of fermented carbon material mixture as 100%, waste biomass (pine nut shells) accounted for 4%, coffee shell binder accounted for 4%, water accounted for 8%, and the remainder was fermented carbon material powder.

[0036] (4) The fermented carbon material mixture is cold-pressed at 17MPa and dried to obtain a cylindrical blank; the cylindrical blank has a diameter of 55mm and a height of 85mm;

[0037] (5) The cylindrical blank is placed in an argon atmosphere (argon flow rate is 2L / min) for microwave calcination, and then cooled to room temperature in the furnace to obtain a porous whole coal industrial silicon composite reducing agent; wherein the microwave calcination temperature is 600℃, the time is 3h, and the microwave power is 4kW.

[0038] In this embodiment, the composite reducing agent pellets for industrial silicon have a fixed carbon content of 68.3 wt.%, an ash content of 3.5 wt.%, a reactivity of 92.3%, a bonding index of 67, and a cold strength of 7846 N.

[0039] 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 carbonaceous reducing agent and added to a submerged arc furnace for smelting. After smelting, 8.85g 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.%.

[0040] Example 2: A method for preparing a composite reducing agent for industrial silicon by natural fermentation of coffee wastewater with different caking coals, the specific steps of which are as follows:

[0041] (1) Coffee wastewater, non-caking coal and strongly caking coal are mixed and wet-milled to obtain mixed powder A; the non-caking coal has a fixed carbon content of 58.9 wt.%, a caking index of 0, and 54% of the particles are less than 0.15 mm and no more than 0.063 mm; the strongly caking coal has a fixed carbon content of 72.3 wt.%, a caking index of 82, and 52% of the particles are less than 0.15 mm and no more than 0.063 mm; based on a total mass of 100 wt.% for mixed powder A, the content of coffee wastewater in mixed powder A is 33 wt.%, the content of non-caking coal is 50 wt.%, and the content of strongly caking coal is 17 wt.%.

[0042] (2) Mixture A was placed in a closed environment at 26°C and allowed to ferment naturally for 22 days to obtain fermented carbon material B. Fermented carbon material B was placed in a drying oven at 110°C and dried for 20 hours before being ground to obtain fermented carbon material powder. The fermented carbon material powder contained 45 wt.% of particles with a diameter not greater than 0.063 mm.

[0043] (3) Coffee shell powder (particle size less than 0.15 mm) was added to a 4 wt.% NaOH solution and soaked for 50 min to activate it. The solid and liquid were separated to obtain coffee shell binder. Fermented carbon material powder, waste biomass (walnut shells), coffee shell binder and water were mixed to obtain fermented carbon material mixture. Based on the mass of fermented carbon material mixture as 100%, waste biomass (walnut shells) accounted for 3%, coffee shell binder accounted for 4%, water accounted for 9%, and the remainder was fermented carbon material powder.

[0044] (4) The fermented carbon material mixture is cold-pressed at 15MPa and dried to obtain a cylindrical blank; the cylindrical blank has a diameter of 60mm and a height of 95mm;

[0045] (5) The cylindrical blank is placed in an argon atmosphere (argon flow rate of 2.5L / min) for microwave calcination and cooled to room temperature in the furnace to obtain a porous whole coal industrial silicon composite reducing agent; wherein the microwave calcination temperature is 550℃, the time is 2h, and the microwave power is 5kW.

[0046] In this embodiment, the composite reducing agent pellets for industrial silicon have a fixed carbon content of 69.5 wt.%, an ash content of 3.2 wt.%, a reactivity of 94.3%, a bonding index of 72, and a cold strength of 7923 N.

[0047] 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 carbonaceous reducing agent and added to a submerged arc furnace for smelting. After smelting, 9.03g 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.%.

[0048] Example 3: A method for preparing a composite reducing agent for industrial silicon by natural fermentation of coffee wastewater with different caking coals, the specific steps of which are as follows:

[0049] (1) Coffee wastewater, weakly caking coal and strongly caking coal are mixed and wet-milled to obtain mixed powder A; the weakly caking coal has a fixed carbon content of 60.8 wt.%, a caking index of 11, and 51% of the particles are less than 0.15 mm and no more than 0.063 mm; the strongly caking coal has a fixed carbon content of 73.4 wt.%, a caking index of 80, and 54% of the particles are less than 0.15 mm and no more than 0.063 mm; based on a total mass of 100 wt.% for mixed powder A, the content of coffee wastewater in mixed powder A is 29 wt.%, the content of weakly caking coal is 51 wt.%, and the content of strongly caking coal is 20 wt.%.

[0050] (2) Mixture A was placed in a closed environment at 31°C and allowed to ferment naturally for 15 days to obtain fermented carbon material B. Fermented carbon material B was placed in a drying oven at 100°C and dried for 20 hours before being ground to obtain fermented carbon material powder. The fermented carbon material powder contained 41 wt.% of particles with a diameter not greater than 0.063 mm.

[0051] (3) Coffee shell powder (particle size less than 0.15 mm) was added to an 8 wt.% NaOH solution and soaked for 20 min to activate it. The solid and liquid were separated to obtain coffee shell binder. Fermented carbon material powder, waste biomass (peanut shells), coffee shell binder and water were mixed to obtain fermented carbon material mixture. Based on the mass of fermented carbon material mixture as 100%, waste biomass (peanut shells) accounted for 5%, coffee shell binder accounted for 3%, water accounted for 10%, and the remainder was fermented carbon material powder.

[0052] (4) The fermented carbon material mixture is cold-pressed at 13MPa and dried to obtain a cylindrical blank; the cylindrical blank has a diameter of 62mm and a height of 84mm;

[0053] (5) The cylindrical blank is placed in an argon atmosphere (argon flow rate is 3L / min) for microwave calcination, and then cooled to room temperature in the furnace to obtain a porous whole coal industrial silicon composite reducing agent; wherein the microwave calcination temperature is 620℃, the time is 4h, and the microwave power is 3kW.

[0054] In this embodiment, the composite reducing agent pellets for industrial silicon have a fixed carbon content of 69.5 wt.%, an ash content of 3.2 wt.%, a reactivity of 94.3%, a bonding index of 72, and a cold strength of 7923 N.

[0055] 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 carbonaceous reducing agent and added to a submerged arc furnace for smelting. After smelting, 9.03g 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.%.

[0056] Example 4: A method for preparing a composite reducing agent for industrial silicon by natural fermentation of coffee wastewater with different caking coals, the specific steps of which are as follows:

[0057] (1) Coffee wastewater, weakly caking coal, moderately weakly caking coal, and moderately strongly caking coal are mixed and wet-milled to obtain mixed powder A. The weakly caking coal has a fixed carbon content of 59.8 wt.%, a caking index of 10, and 51% of the particles are less than 0.15 mm and no more than 0.063 mm. The moderately weakly caking coal has a fixed carbon content of 68.4 wt.%, a caking index of 45, and 53% of the particles are less than 0.15 mm and no more than 0.063 mm. The moderately strongly caking coal has a fixed carbon content of 71.6 wt.%, a caking index of 59, and 52% of the particles are less than 0.15 mm and no more than 0.063 mm. Based on a total mass of 100 wt.% for mixed powder A, the content of coffee wastewater in mixed powder A is 29 wt.%, the content of weakly caking coal is 45 wt.%, the content of moderately weakly caking coal is 10 wt.%, and the content of moderately strongly caking coal is 16 wt.%.

[0058] (2) Mixture A was placed in a closed environment at 33°C and allowed to ferment naturally for 13 days to obtain fermented carbon material B. Fermented carbon material B was placed in a drying oven at 105°C and dried for 20 hours before being ground to obtain fermented carbon material powder. The fermented carbon material powder contained 38 wt.% of particles with a diameter not greater than 0.063 mm.

[0059] (3) Coffee shell powder (particle size less than 0.15 mm) was added to a 5 wt.% NaOH solution and soaked for 40 min to activate it. The solid and liquid were separated to obtain coffee shell binder. Fermented carbon material powder, waste biomass (sunflower seed shells), coffee shell binder and water were mixed to obtain fermented carbon material mixture. Based on the mass of fermented carbon material mixture as 100%, waste biomass (sunflower seed shells) accounted for 4%, coffee shell binder accounted for 4%, water accounted for 10%, and the remainder was fermented carbon material powder.

[0060] (4) The fermented carbon material mixture is cold-pressed at 17MPa and dried to obtain a cylindrical blank; the cylindrical blank has a diameter of 63mm and a height of 88mm;

[0061] (5) The cylindrical blank was placed in an argon atmosphere (argon flow rate of 3.5 L / min) for microwave calcination and cooled to room temperature with the furnace to obtain a porous whole coal industrial silicon composite reducing agent; wherein the microwave calcination temperature was 640℃, the time was 4h, and the microwave power was 5kW.

[0062] In this embodiment, the composite reducing agent pellets for industrial silicon have a fixed carbon content of 68.6 wt.%, an ash content of 3.3 wt.%, a reactivity of 91.9%, a bonding index of 69, and a cold strength of 7821 N.

[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 10.1g of the above-mentioned composite carbonaceous reducing agent and added to a submerged arc furnace for smelting. After smelting, 8.95g 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 5: A method for preparing a composite reducing agent for industrial silicon by natural fermentation of coffee wastewater with different caking coals, the specific steps of which are as follows:

[0065] (1) Coffee wastewater, weakly caking coal, medium-weakly caking coal and highly caking coal are mixed and wet-milled to obtain mixed powder A; the weakly caking coal has a fixed carbon content of 58.6 wt.%, a caking index of 16, and 52% of the particles are less than 0.15 mm and no more than 0.063 mm; the medium-weakly caking coal has a fixed carbon content of 67.5 wt.%, a caking index of 48, and 55% of the particles are less than 0.15 mm and no more than 0.063 mm; the highly caking coal has a fixed carbon content of 70.6 wt.%, a caking index of 87, and 54% of the particles are less than 0.15 mm and no more than 0.063 mm; based on a total mass of 100 wt.% for mixed powder A, the content of coffee wastewater in mixed powder A is 28 wt.%, the content of weakly caking coal is 47 wt.%, the content of medium-weakly caking coal is 10 wt.%, and the content of highly caking coal is 15 wt.%.

[0066] (2) Mixture A was placed in a closed environment at 27°C and allowed to ferment naturally for 24 days to obtain fermented carbon material B. Fermented carbon material B was placed in a drying oven at 110°C and dried for 18 hours before being ground to obtain fermented carbon material powder. The fermented carbon material powder contained 45 wt.% of particles with a diameter not greater than 0.063 mm.

[0067] (3) Coffee shell powder (particle size less than 0.15 mm) was added to a 7 wt.% NaOH solution and soaked for 60 min to activate it. The solid and liquid were separated to obtain coffee shell binder. Fermented carbon material powder, waste biomass (a mixture of coconut shell and rice husk in a mass ratio of 1:1), coffee shell binder and water were mixed to obtain fermented carbon material mixture. Based on the mass of fermented carbon material mixture as 100%, waste biomass (a mixture of coconut shell and rice husk) accounted for 5%, coffee shell binder accounted for 4%, water accounted for 11%, and the remainder was fermented carbon material powder.

[0068] (4) The fermented carbon material mixture is cold-pressed at 13MPa and dried to obtain a cylindrical blank; the cylindrical blank has a diameter of 59mm and a height of 78mm;

[0069] (5) The cylindrical blank is placed in an argon atmosphere (argon flow rate of 2.5L / min) for microwave calcination and cooled to room temperature in the furnace to obtain a porous whole coal industrial silicon composite reducing agent; wherein the microwave calcination temperature is 540℃, the time is 3h, and the microwave power is 3kW.

[0070] In this embodiment, the composite reducing agent pellets for industrial silicon have a fixed carbon content of 70.9 wt.%, an ash content of 3.1 wt.%, a reactivity of 93.4%, a binding index of 72, and a cold strength of 8019 N.

[0071] 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 carbonaceous reducing agent and added to a submerged arc furnace for smelting. After smelting, 8.84g 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.%.

[0072] Example 6: A method for preparing a composite reducing agent for industrial silicon by natural fermentation of coffee wastewater with different caking coals, the specific steps of which are as follows:

[0073] (1) Coffee wastewater, non-caking coal, medium-strong caking coal and high-caking coal are mixed and wet-milled to obtain mixed powder A; the non-caking coal has a fixed carbon content of 58.9 wt.%, a caking index of 0.5, and 51% of the particles are less than 0.15 mm and no more than 0.063 mm; the medium-strong caking coal has a fixed carbon content of 68.3 wt.%, a caking index of 62, and 52% of the particles are less than 0.15 mm and no more than 0.063 mm; the high-caking coal has a fixed carbon content of 72.8 wt.%, a caking index of 84, and 51% of the particles are less than 0.15 mm and no more than 0.063 mm; based on a total mass of 100 wt.% of mixed powder A, the content of coffee wastewater in mixed powder A is 34 wt.%, the content of non-caking coal is 46 wt.%, the content of medium-strong caking coal is 7 wt.%, and the content of high-caking coal is 13 wt.%.

[0074] (2) Mixture A was placed in a closed environment at 25°C and allowed to ferment naturally for 26 days to obtain fermented carbon material B. Fermented carbon material B was placed in a drying oven at 110°C and dried for 25 hours before being ground to obtain fermented carbon material powder. The fermented carbon material powder contained 40 wt.% of particles with a diameter not greater than 0.063 mm.

[0075] (3) Coffee shell powder (particle size less than 0.15 mm) was added to a 6 wt.% NaOH solution and soaked for 40 min to activate it. The solid and liquid were separated to obtain coffee shell binder. Fermented carbon material powder, waste biomass (a mixture of corn shells, walnut shells and coffee shells in a mass ratio of 1:1:2), coffee shell binder and water were mixed to obtain fermented carbon material mixture. Based on the mass of fermented carbon material mixture as 100%, waste biomass (a mixture of corn shells, walnut shells and coffee shells) accounted for 5%, coffee shell binder accounted for 4%, water accounted for 11%, and the remainder was fermented carbon material powder.

[0076] (4) The fermented carbon material mixture is cold-pressed at 17MPa and dried to obtain a cylindrical blank; the cylindrical blank has a diameter of 60mm and a height of 86mm;

[0077] (5) The cylindrical billet was placed in an argon atmosphere (argon flow rate of 3L / min) for microwave calcination and cooled to room temperature in the furnace to obtain a porous whole coal industrial silicon composite reducing agent; wherein the microwave calcination temperature was 650℃, the time was 3h, and the microwave power was 4kW.

[0078] In this embodiment, the composite reducing agent pellets for industrial silicon have a fixed carbon content of 73.1 wt.%, an ash content of 2.9 wt.%, a reactivity of 95.4%, a bonding index of 75, and a cold strength of 7864 N.

[0079] 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 carbonaceous reducing agent and added to a submerged arc furnace for smelting. After smelting, 9.16g 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.%.

[0080] Example 7: A method for preparing a composite reducing agent for industrial silicon by natural fermentation of coffee wastewater with different caking coals, the specific steps of which are as follows:

[0081] (1) Coffee wastewater, non-caking coal, medium-weak caking coal, medium-strong caking coal, and high-caking coal are mixed and wet-milled to obtain mixed powder A. The non-caking coal has a fixed carbon content of 57.9 wt.%, a caking index of 0, and 52% of the particles have a particle size less than 0.15 mm and no greater than 0.063 mm. The medium-weak caking coal has a fixed carbon content of 63.4 wt.%, a caking index of 48, and 51% of the particles have a particle size less than 0.15 mm and no greater than 0.063 mm. The medium-strong caking coal has a fixed carbon content of 69.7 wt.%, a caking index of 6... 1. Particles with a diameter less than 0.15 mm and no greater than 0.063 mm account for 52%; the fixed carbon content of high-caking coal is 73.2 wt.%, the caking index is 89, and particles with a diameter less than 0.15 mm and no greater than 0.063 mm account for 51%; based on the total mass of mixed powder A as 100 wt.%, the content of coffee wastewater in mixed powder A is 31 wt.%, the content of non-caking coal is 45 wt.%, the content of medium-weak caking coal is 6 wt.%, the content of medium-strong caking coal is 6 wt.%, and the content of high-caking coal is 12 wt.%.

[0082] (2) Mixture A was placed in a closed environment at 27°C and allowed to ferment naturally for 30 days to obtain fermented carbon material B. Fermented carbon material B was placed in a drying oven at 105°C and dried for 20 hours before being ground to obtain fermented carbon material powder. The fermented carbon material powder contained 43 wt.% of particles with a diameter not greater than 0.063 mm.

[0083] (3) Coffee shell powder (particle size less than 0.15 mm) was added to a 6 wt.% NaOH solution and soaked for 30 min to activate it. The solid and liquid were separated to obtain coffee shell binder. Fermented carbon material powder, waste biomass (a mixture of sugarcane bagasse, peanut shells, rice husks and coffee shells in a mass ratio of 1:2:1:2), coffee shell binder and water were mixed to obtain fermented carbon material mixture. Based on the mass of fermented carbon material mixture as 100%, waste biomass (a mixture of sugarcane bagasse, peanut shells, rice husks and coffee shells) accounted for 5%, coffee shell binder accounted for 4%, water accounted for 10%, and the remainder was fermented carbon material powder.

[0084] (4) The fermented carbon material mixture is cold-pressed at 11 MPa and dried to obtain a cylindrical blank; the cylindrical blank has a diameter of 65 mm and a height of 98 mm;

[0085] (5) The cylindrical billet was placed in an argon atmosphere (argon flow rate of 3L / min) for microwave calcination and cooled to room temperature in the furnace to obtain a porous whole coal industrial silicon composite reducing agent; wherein the microwave calcination temperature was 630℃, the time was 2.5h, and the microwave power was 5kW.

[0086] In this embodiment, the composite reducing agent pellets for industrial silicon have a fixed carbon content of 73.9 wt.%, an ash content of 2.8 wt.%, a reactivity of 94.7%, a bonding index of 76, and a cold strength of 7929 N.

[0087] 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 carbonaceous reducing agent and added to a submerged arc furnace for smelting. After smelting, 9.21g 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.%.

[0088] 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 preparing a composite reducing agent for industrial silicon through natural fermentation of coffee wastewater and different types of caking coal, characterized in that, The specific steps are as follows: (1) Coffee wastewater and different caking coal powders are mixed and then wet-milled to obtain mixture A; the different caking coal powders contain non-caking coal or weakly caking coal, as well as one or more of medium-weakly caking coal, medium-strongly caking coal, and highly caking coal; the caking index n of non-caking coal is 0≤n<1, the caking index n of weakly caking coal is 1≤n≤20, the caking index n of medium-weakly caking coal is 20<n≤50, the caking index n of medium-strongly caking coal is 50<n≤65, and the caking index n of highly caking coal is 65<n≤95; based on the total mass of mixture A as 100%, coffee wastewater accounts for 20~35wt.%, and non-caking coal or weakly caking coal accounts for 45~55wt.%; (2) Mixture A is placed in a closed environment at a temperature of 18~33℃ and fermented naturally for 10~30 days to obtain fermented carbon material B. Fermented carbon material B is dried and ground to obtain fermented carbon material powder. (3) The coffee shell powder is added to NaOH solution for soaking and activation treatment, and the solid and liquid are separated to obtain coffee shell binder; the fermented carbon material powder, waste biomass, coffee shell binder and water are mixed to obtain fermented carbon material mixture; (4) The mixture of fermented carbon materials is cold-pressed and dried to obtain a cylindrical blank; (5) The cylindrical blank is placed in an argon atmosphere for microwave calcination and then cooled to room temperature in the furnace to obtain composite reducing agent pellets for industrial silicon.

2. The method for preparing a composite reducing agent for industrial silicon by natural fermentation of coffee wastewater with different caking coals according to claim 1, characterized in that: Step (1) The fixed carbon content of non-caking coal is not less than 57 wt.%, the fixed carbon content of weakly caking coal is not less than 57 wt.%, the fixed carbon content of medium-weakly caking coal is 55~75 wt.%, the fixed carbon content of medium-strongly caking coal is 55~75 wt.%, and the fixed carbon content of highly caking coal is 55~75 wt.%.

3. The method for preparing a composite reducing agent for industrial silicon by natural fermentation of coffee wastewater with different caking coals according to claim 1, characterized in that: Step (1) The particle size of different bonding coal powders is less than 0.15 mm and the particle size is not greater than 0.063 mm, which is not less than 50%.

4. The method for preparing a composite reducing agent for industrial silicon by natural fermentation of coffee wastewater with different caking coals according to claim 1, characterized in that: In step (2), the particle size of the fermented carbon material powder is no greater than 0.063 mm, accounting for 35~45 wt.%.

5. The method for preparing a composite reducing agent for industrial silicon by natural fermentation of coffee wastewater with different caking coals according to claim 1, characterized in that: Step (3) The particle size of the coffee shell powder is less than 0.15 mm; the mass concentration of the NaOH solution is 4~8%, and the soaking and activation treatment time is 20~60 min.

6. The method for preparing a composite reducing agent for industrial silicon by natural fermentation of coffee wastewater with different caking coals according to claim 1, characterized in that: In terms of mass percentage, waste biomass accounts for 3-5 wt.% of the fermented carbon material mixture in step (3), coffee shell binder accounts for 2-4%, water accounts for 5-10%, and the remainder is fermented carbon material powder; the waste biomass is one or more of the following: walnut shell, pine nut shell, coconut shell, peanut shell, rice husk, coffee shell, sunflower seed shell, corn cob, and sugarcane bagasse.

7. The method for preparing a composite reducing agent for industrial silicon by natural fermentation of coffee wastewater with different caking coals according to claim 1, characterized in that: Step (4) The cold pressing pressure is 10~20MPa, the diameter of the cylindrical blank is 55~65mm, and the height is 70~100mm.

8. The method for preparing a composite reducing agent for industrial silicon by natural fermentation of coffee wastewater with different caking coals according to claim 1, characterized in that: Step (5) The microwave roasting temperature is 500~650℃, the time is 2~4h, and the microwave power is 3~5kW.

9. The method for preparing a composite reducing agent for industrial silicon by natural fermentation of coffee wastewater with different caking coals according to claim 1, characterized in that: Step (4) The fixed carbon content of the composite reducing agent pellets for industrial silicon is greater than 65 wt.%, the ash content is less than 4 wt.%, the bonding index is higher than 65, the reactivity is greater than 90%, and the cold strength of the pellets is greater than 7500 N.