JP2011037675A - Method for producing silicon carbide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce silicon carbide usable as a grinding material, abrasive grains, or an abrasive material by making it possible to recover SiC and Si from a solution or a waste liquid to such a degree as to eliminate wastewater pollution. <P>SOLUTION: Provided is a method for producing silicon carbide comprising the step of subjecting a solution or waste liquid at least containing fine SiC particles and/or fine Si particles to solid/liquid separation by using a separation aid at least containing a carbon powder and a silicon oxide powder to obtain a solid component, the step of mixing the solid component with optionally an additive containing a carbon powder and/or a silicon oxide powder, and the step of reacting the solid component or the solid component mixed with the additive by heating to a temperature which is higher than 1,850°C and lower than 2,400°C in a non-oxidizing atmosphere, to produce silicon carbide. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention includes: (a) a solution containing unnecessary SiC fine particles produced as a by-product with a particle size equal to or smaller than the target particle size in the classification step when producing SiC fine powder; and (b) grinding a single crystal or polycrystalline Si ingot or molded product. (C) Slurry containing SiC and Si fine particles generated when wafers and flakes are produced by cutting a single crystal or polycrystalline silicon with a wire saw using SiC as abrasive grains. The present invention relates to a method for recovering and regenerating SiC, Si, or a mixed fine powder thereof, which has been conventionally difficult and unnecessary from waste liquids.

In recent years, silicon carbide powder has been frequently used as a raw material for single crystal or polycrystalline substrates such as silicon, quartz, SiC, GaAs, and GaN, or for cutting, grinding, polishing, and further forming glass and ceramics. This silicon carbide powder is usually produced by a batch reaction by the conventional Atchison method. The Atchison method is a U-type furnace that is open to the atmosphere. A graphite electrode is passed through the center in the longitudinal direction, and a mixture of several millimeters to several centimeters of silica sand and carbon is piled up around the electrode in a bowl shape. The SiC is manufactured by flowing and heating. This reaction (SiO ₂ + 3C → SiC + 2CO) is an endothermic reaction, and since only the graphite electrode is a heating element and has a high temperature, the reaction reacts well around the electrode and mainly produces α-SiC as a high-temperature stable crystal. A remote portion is unreacted or a large amount of a mixture of β-SiC and α-SiC, which is a low-temperature stable crystal whose use is relatively limited, is generated. Since the furnace is open to the atmosphere, the thermal efficiency is poor, and the surrounding environment is likely to be polluted with dust or CO gas generated by the reaction. After the reaction, the in-furnace hardened and hardened material is roughly crushed, and only the desired α-SiC portion is selected and further pulverized. The remaining unreacted material and the mixture of β-SiC and α-SiC are returned to the reaction raw material again as unnecessary products. The finely pulverized product is further adjusted to an optimum particle size and particle size distribution according to the application by wet classification using water or the like and dry classification using air or nitrogen according to various applications. The SiC fine powder thus obtained is currently used in a large amount as the above-mentioned cutting, grinding and polishing abrasive grains, abrasives, or as raw material powder for SiC molded bodies.

  By the way, as described above, in the production of (a) SiC fine powder, an optimum average particle size and particle size distribution are required depending on the purpose of use and application. Therefore, a classification step for separating desired particle size and unnecessary particle size is indispensable. In this classification, a moisture classification method that enables precise classification at a relatively low cost is common, but a large amount of unnecessary SiC fine powder aqueous solution that is not in demand is generated. Further, even in the case of dry classification, unnecessary fine powder was generated in the same manner, and it was difficult to process them. In addition, (b) a large amount of waste liquid containing Si facet particles was generated when grinding an ingot or molded product of single crystal or polycrystalline silicon, and disposal of the waste was also a problem. On the other hand, in (c) wire saws, a slurry in which various additives such as SiC fine powder and ethylene glycol, surfactants, rust preventives, etc. are added in water or oil solvent is used to cut silicon ingots. To do. When this slurry is cut into a large amount of single crystal or polycrystalline silicon, the optimum SiC particle size and particle size distribution are initially caused by wear and cracking of SiC fine powder, etc. As the cutting ability decreases, the silicon fine powder of the face accumulates and the viscosity of the slurry rises, making it impossible to circulate and replace the slurry. The waste slurry that has become unusable contains not only water or oil solvents, but also consumed SiC and finely divided SiC powder and various additives, and can be simply discarded from the standpoint of drainage pollution. The disposal was a big problem.

  The treatment of the aqueous solutions and waste liquids in the above (a) and (b) is currently a solid liquid because it is super fine even if SiC or Si fine powder is recovered from the solution or waste liquid with a centrifuge or a filter and used effectively. It is extremely difficult to completely separate the waste, industrial waste or incineration without cease, or after drying by heating with a large amount of heat, the dry residue SiC or Si is returned to the deoxidizer of the blast furnace or the raw material of the Atchison furnace with low economic value It is only used for.

Regarding the mixed fine powder of SiC and Si in the wire saw slurry waste liquid of (c) above, several recovery and effective utilization methods have been proposed so far, such as Patent Documents 1 and 2. In these methods, a sufficient amount of carbon, such as petroleum coke or carbon black, that can convert the contained Si fine powder into SiC is added to the waste slurry, and dried, or solid sludge obtained by centrifugation or filtration is used. By heating as it is, the Si of the facet is collected and utilized as SiC (Si + C → SiC).
However, various problems occur when these proposed methods are carried out, and the obtained SiC is too fine and has a low utility value. In other words, when petroleum coke is used for carbon by the above method, the specific surface area of carbon is too small, and SiC and Si fine powder cannot be sufficiently adsorbed, and a lot of fine powder leaks into the filtrate even after centrifugation or filtration. , SiC and Si solids are not sufficiently recovered, and the filtrate becomes turbid and causes a problem in wastewater treatment. In addition, when carbon black is used for carbon, because of the fine particle size, the viscosity of the waste liquid is increased and centrifugal separation and filtration operations become difficult, which is not practical. On the other hand, it is not economical to heat and dry a solution or waste liquid as it is without solid-liquid separation because a large amount of heat is required. The SiC fine powder remaining and recovered in the waste slurry is in a state of sag and fine grain as described above and cannot be used for advanced applications such as a wire saw. The fine Si powder collected together with SiC reacts with carbon by heating to produce new SiC, but the recovered Si used as a raw material is a fine powder because of the wire saw face and has a wide particle size distribution. Is very fine and has a wide particle size distribution. Like recovered SiC, it has a required particle size and is not suitable for wire saws that require a sharp particle size distribution. These improvements have been desired.

Japanese Patent Laid-Open No. 11-116227 JP 2002-255532 A

  The present invention includes, for example, (a) a solution containing unnecessary SiC fine particles generated as a by-product with a particle size equal to or smaller than a target particle size in a classification step when producing SiC fine particles, and (b) a single crystal or polycrystalline Si ingot or molded product. Waste liquid containing Si facet fine particles when grinding, (c) SiC and Si fine particles generated when wafers and flakes are produced by cutting single crystal or polycrystalline silicon with wire saw using SiC as abrasive grains The slurry waste solution, etc., and SiC and Si in the waste solution are recovered almost completely without drainage pollution, and used as a high-purity, high-value-added abrasive, abrasive, and abrasive for wire saws, lapping, polishing, etc. It provides a method of playing.

In the present invention, a solution or waste liquid containing at least SiC fine particles and / or Si fine particles such as (a), (b) and (c) is subjected to solid-liquid separation using a separation aid containing at least carbon powder and silicon oxide powder. To obtain a solid content, mixing the solid content with an additive containing carbon powder and / or silicon oxide powder, if necessary, and mixing with the solid content or additive to obtain silicon carbide. And a step of heating and reacting the solid content in a non-oxidizing atmosphere at a temperature higher than 1850 ° C. and lower than 2400 ° C. Thereby, SiC and Si in the above solution and waste liquid can be recovered without drainage pollution, and can be regenerated into a high-value-added abrasive, abrasive, or abrasive having an optimum particle size and particle size distribution.
That is, the present invention recovers and regenerates SiC fine powder and / or Si fine powder in the above-mentioned solution and waste liquid, and combines the solution and / or waste liquid with at least carbon powder and silicon oxide powder to assist the separation in solid-liquid separation. As a material, it is further used as a reaction raw material for SiC particle size enlargement, and if necessary mixed with an additive containing carbon powder and / or silicon oxide powder, then exceeds 1850 ° C. and 2400 ° C. in a non-oxidizing atmosphere. Heat reaction to less than In addition, the solid content is recovered by solid-liquid separation, SiC fine powder is generated by reaction with Si fine powder and carbon powder, and the residual SiC fine powder that is consumed and circulated is enlarged and grown (grain growth). ) To obtain the optimum particle size and particle size distribution according to the application.

  As described above, in the conventional method, since only carbon is added to the waste liquid, when the added carbon has a large particle size or a small specific surface area, fine SiC or Si leaks during solid-liquid separation such as centrifugation or filtration. Recovery is insufficient. On the other hand, in the case of fine particles of carbon, if a necessary amount of carbon is added to the solution or waste liquid, it becomes a grease or dumpling, and the operation of solid-liquid separation becomes impossible. Moreover, in these methods, the recovered SiC and the SiC of the reaction product of Si and carbon have a fine particle size, and the addition of carbon alone makes it difficult to enlarge the particle, and a particle size of the required size can be obtained. Absent. In contrast, in the present invention, since carbon and silicon oxide function as a separation aid and SiC reaction raw material, both the consumed and finely-divided SiC particles are larger than both the facet Si and the carbon of the reaction product SiC. Thus, particles having a desired size can be obtained.

The method of the present invention will be described in detail below.
First, a solution or waste liquid containing at least silicon carbide fine particles and / or silicon fine particles is subjected to solid-liquid separation using a separation aid containing at least carbon powder and silicon oxide powder to obtain a solid content.
The solution or waste liquid containing at least silicon carbide fine particles and / or silicon fine particles includes, for example, (a) a wet classification process such as a moisture class when producing SiC fine particles, and unnecessary SiC fine particles that are generated as a by-product at a target particle size or less. A solution containing unnecessary SiC fine powder produced as a by-product in a dry classification process such as sieve classification, or (b) Si facet fine particles when grinding a single crystal or polycrystalline Si ingot or molded product. Examples of the waste liquid contained include: (c) SiC fine particles generated when SiC and abrasive grains are cut with a wire saw to produce wafers and flakes, and a slurry waste liquid containing Si fine particles.
The average particle size of the silicon carbide fine particles contained in the solution or the waste liquid is generally 20 μm or less, and an appropriate particle size is used depending on the application, and is usually 1 to 20 μm. When the average particle size is less than 1 μm, the cutting speed is lowered, the productivity is deteriorated, and it is difficult to regenerate the desired particle size, grinding and polishing ability. On the other hand, if it exceeds 20 μm, many grinding scratches and cutting loss are likely to occur.
In addition, the average particle diameter described in this specification is based on a laser diffraction / scattering method.
A preferred concentration of the total amount of silicon carbide fine particles and silicon fine particles in the solution or waste liquid is 5 to 70%. If it is too dilute, the efficiency of solid-liquid separation may deteriorate, and if it is too concentrated, the fluidity may be poor and handling may be difficult. Prior to solid-liquid separation, concentration or dilution may be performed to adjust to a preferred concentration.

The separation aid used in the present invention contains at least carbon powder and silicon oxide powder.
Carbon powder contained in the separation aid, preferably having a specific surface area of ^{1m 2} / ^g~700m 2 / g using the BET method. This is because SiC and Si fine powder are sufficiently adsorbed on carbon, solid-liquid separation is improved, operation is easy, and high recovery is possible. If the specific surface area is too small, the adsorption ability of the solid fine particles may be inferior as a separation aid. Conversely, if the specific surface area is too large, the viscosity increases and the solid-liquid separation operation may be difficult. The average particle diameter of the carbon powder used for the separation aid preferably gives the specific surface area, and is, for example, 0.1 μm to 1 mm.
Examples of the type of carbon used for the separation aid include charcoal, coke, and activated carbon.

The silicon oxide powder used for the separation aid preferably has an average particle size of 1 mm or less in consideration of the SiC-forming reaction in a later step.
The preferable mass ratio of the carbon powder and the silicon oxide powder contained in the separation aid is preferably 0.6 or more for the carbon powder / silicon oxide powder in view of the conversion to SiC in the subsequent process.

The separation aid may further contain an organic polymer flocculant in order to facilitate solid-liquid separation. As the organic polymer flocculant, for example, polyacrylamide, polyethyleneamine, polyethyleneimine, etc. are thermally decomposed to become carbon, and those which remain as impurities, such as inorganic flocculants, are preferable. More effective recovery of silicon fine particles and / or silicon fine particles is possible.
The content of the polymer flocculant contained in the separation aid is preferably 0 to 10% by mass with respect to the total amount of carbon powder and silicon oxide powder contained in the separation aid in consideration of aggregation efficiency and economy. .

  The amount of separation aid used is the total amount of silicon carbide fine particles and silicon fine particles contained in the solution or waste liquid, considering the filtration efficiency and economic efficiency with respect to the total mass of silicon carbide fine particles and silicon fine particles in the solution or waste liquid. It is preferably 0.1 to 10 mol per 0.0 mol.

  Solid-liquid separation can be performed using a known method, and examples thereof include filtration, use of a filter press and a centrifuge.

Next, the solid component separated by solid-liquid separation is mixed with an additive containing at least carbon powder and / or silicon oxide powder as necessary. The term “as needed” means that the amount added as a separation aid is mixed with an additive when the particle size is insufficient for increasing the particle size.
The carbon powder added to the solid as necessary functions as a part of the reaction raw material of SiC or as a reaction field, and determines the reaction rate and the yield of produced SiC. Therefore, if the particle size is too large, the reaction rate becomes slow and the yield of produced SiC decreases, which is not economical. The average particle diameter of the carbon powder added to the solid as necessary is preferably 1 mm or less, more preferably 0.1 μm to 100 μm.
Charcoal, coke, activated carbon, etc. are mentioned as a kind of carbon added to solid content as needed.

  The particle size of silicon oxide powder added to the solid content as needed is different from the carbon powder added as needed to the solid content, and hardly affects the yield of generated SiC, but if it is too large, the reaction The speed is slow and this is not a good idea. The average particle size of the silicon oxide powder added to the solid as necessary is preferably 1 mm or less.

  Whether carbon powder, silicon oxide powder, or both ratios are added to the solids as necessary depends on the degree of SiC enlargement and the ratio involved in the reaction between the two. Can be selected.

The total of the carbon powder and silicon oxide powder contained in the separation aid and the carbon powder and silicon oxide powder contained in the additive that is added as necessary remains in the waste liquid as well as the carbon in the additive. It becomes a reaction raw material of SiC that has been produced or newly produced SiC. That is, it works as a raw material for grain enlargement (grain growth) for finely-grained or just remaining SiC grains, and as a reaction raw material for newly produced SiC. Accordingly, the total amount of carbon and silicon oxide added varies depending on the composition of the solid obtained by solid-liquid separation.
The total amount of carbon powder and silicon oxide powder contained in the separation aid and the additive is preferably 0.1 to 50 mol per 1.0 mol of the total amount of silicon carbide fine particles and silicon fine particles contained in the solution or waste liquid. It is. If it is less than 0.1 mol, enlargement of the particle size of the remaining SiC is insufficient, or the particle size of newly produced SiC becomes extremely small. Moreover, when it exceeds 50 mol, it will become excess with respect to the quantity required for reaction, and an extra removal process may be needed after reaction, and a particle size may become large and may be unpreferable.

Next, in order to obtain silicon carbide, the solid content after solid-liquid separation or the solid content after mixing with an additive as necessary is heated and reacted in a non-oxidizing atmosphere.
The heating reaction is preferably performed at a temperature gradient for crystal rearrangement to α-silicon carbide after the silicon carbide precursor and / or β-silicon carbide is generated.
Intermediates produced by reducing silicon oxide with carbon are SiO and Si as shown in the following formulas (1) and (2).
SiO ₂ + C = SiO + CO (1)
SiO + C = Si + CO (2)
The intermediate reaction SiO and Si produced by reducing silicon oxide with carbon, which is a reaction raw material for SiC, or Si fine powder such as facets in the recovered solution and waste liquid is easily evaporated. Therefore, in order to obtain SiC in a high yield in the heating reaction, the silicon oxide is carbonized at a temperature of 1100 to 1850 ° C. quickly, preferably without causing rapid evaporation in the form of SiO or Si as much as possible without first raising the temperature at the beginning of the reaction. The temperature gradient is such that the silicon carbide precursor and / or β-silicon carbide is produced by complete reaction with C, and is further raised to a high temperature of more than 1850 ° C. and less than 2400 ° C. to cause crystal dislocation to α-silicon carbide. Is preferred. Whether it is a silicon carbide precursor or β-silicon carbide at once, the vapor pressure is extremely low if it is a SiC compound, and it does not decompose unless it exceeds 2400 ° C, so there is almost no loss, and the final maximum temperature is 1850 ° C or less. This is because it may be difficult to completely convert the reactant into α-silicon carbide.
Examples of the non-oxidizing atmosphere include a gas atmosphere selected from nitrogen, argon, and the like.
The silicon carbide precursor is, for example, an organic silicon compound in which a part of the remaining organic matter in the waste liquid or an added organic polymer flocculant has reacted. Further, the crystal dislocation from the silicon carbide precursor or β-silicon carbide to α-silicon carbide is, for example,
This can be confirmed by analysis using an X-ray diffractometer.

As a method of giving a temperature gradient to the heating reaction, for example, there is a method of moving from a low temperature region to a high temperature region in an apparatus that cuts the temperature region in the same reaction furnace or a plurality of reaction furnaces having different temperatures.
Preferably, a pusher or a rotary sealed reactor that moves a certain distance every certain time may be used. Massive productivity and the above optimal temperature gradient, less dust generation, good thermal efficiency, and easy recovery of by-product gas as a closed reactor that moves a certain distance every fixed time, such as temperature This is because a controlled pusher reactor and rotary reactor are optimal.

  The silicon carbide powder obtained by heating reaction preferably has an average particle size of 1 to 200 μm. If necessary, it may be pulverized using a pulverizer. This silicon carbide powder can be reused for abrasives, abrasive grains, and abrasives.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these at all.
Example 1
After crushing α-SiC produced by the Atchison method to an average particle size of 10 μm, the coarse and fine portions were cut with a moisture grade. The rough part was again turned into a pulverized raw material. After thoroughly mixing 1000 kg of an aqueous solution (solid content: 40%) of a fine portion having an average particle size of 2 μm or less, 48 kg of charcoal powder having an average particle size of 80 μm and a specific surface area of 393 m ² / g, and 70 kg of silica powder having an average particle size of 120 μm The solution was filtered with an Excel filter. Solid-liquid separation was good, and the filtrate was transparent with no mixing of fine powder. The collected solid was dried. Thereafter, the solid content in the container under the Ar gas flow in the pusher furnace in which the first zone was controlled at 1400 ° C., the second zone at 1600 ° C., the third zone at 1800 ° C., and the fourth zone at 2300 ° C. Each zone was heated and reacted while moving through each zone.
In addition, there was almost no evaporation of Si or SiO in the first to third zones, β-SiC was generated almost 100% of the theoretical value, and crystals were completely transferred to α-SiC in the fourth zone. Further, excess carbon was removed at 750 ° C. in the atmosphere. As a result, α-SiC in the finer portion having an average particle diameter of 2 μm or less was recovered and regenerated as α-SiC having an average particle diameter of 9.5 μm by enlarging unnecessary SiC fine powder (grain growth). This thing was suitable as an abrasive grain for wire saws.

Comparative Example 1
After crushing α-SiC produced by the Atchison method to an average particle size of 10 μm, the coarse and fine portions were cut with a moisture grade. The rough part was again turned into a pulverized raw material. After thoroughly mixing 1000 kg (solid content: 40%) of an aqueous solution of finely divided portions having an average particle size of 2 μm or less and 48 kg of oil coke having an average particle size of 110 μm and a specific surface area of 0.5 m ² / g, the mixture was filtered through an Excel filter. However, the filter cloth was clogged, and it took a long time for solid-liquid separation, and the filtrate became turbid, and fine powder of solids escaped into the filtrate.

Comparative Example 2
After crushing α-SiC produced by the Atchison method to an average particle size of 10 μm, the coarse and fine portions were cut with a moisture grade. The rough part was again turned into a crushed raw material. After thoroughly mixing 1000 kg of an aqueous solution (solid content: 40%) of a finely divided portion having an average particle diameter of 2 μm or less and 48 kg of acetylene black having a specific surface area of 750 m ² / g, the mixture was filtered through an Excel filter. However, the viscosity of the solution increased and liquid could not be sent with a pump, and solid-liquid separation operation was impossible.

Example 2
A wire saw waste liquid of 35% by mass of solid component and 65% by mass of solution component, wherein the solid component is composed of 30% by mass of α-SiC, 4.1% by mass of Si, and 0.9% by mass of Fe. Prepared a wire saw waste liquid which is a mixture of ethylene glycol, surfactant and water. To this 1000 kg of wire saw waste liquid, 20 kg of coke having a specific surface area of 50 m ² / g pulverized to an average particle diameter of 15 μm, 20 kg of silica powder having an average particle diameter of 50 μm, and 500 g of polyacrylamide as a polymer flocculant were added and mixed. Solid-liquid separation. Solid-liquid separation was easy, and the filtrate was clear and colorless. The solid matter thus separated was further mixed with 56 kg of the above coke and 30 kg of silica powder. This material is dried and placed in a container in a rotary furnace in which the first zone is controlled to 1850 ° C. (approximately 100% β-SiC is formed in this zone), the second zone is controlled to 1950 ° C., and the third zone is controlled to 2200 ° C. The solid content was moved every 20 minutes, and heated and reacted under Ar gas flow. The obtained recovered and reclaimed product was 100% α-SiC and had an average particle size of 8 μm, which could be regenerated to be almost the same as the average particle size of 8.5 μm of the SiC abrasive grains before use. In addition, SiC in the waste liquid before reproduction | regeneration was quite unsatisfactory with the average particle diameter of 3 micrometers.

Comparative Example 3
Recovery and regeneration were attempted under exactly the same conditions as in Example 2 except that no silica was added. The grain size of finely divided SiC cannot be enlarged (granular growth), and the average grain diameter remains almost 3 μm, and new SiC produced by the reaction between the faceted Si fine powder and coke has an average grain diameter of 1 μm. The particle size distribution with a peak was wide. This product was unsuitable for advanced applications such as wire saws.

Example 3
1000 kg of waste aqueous solution containing Si facet particles when cylindrically grinding a single crystal Si ingot (facet, 25.3 mass% of Si fine particles with an average particle size of 1.1 μm, containing a trace amount of amine-based rust preventive material) 150 kg of activated carbon having an average particle diameter of 32 μm and a specific surface area of 695 m ² / g and 25 kg of quartz powder having an average particle diameter of 170 μm were added and mixed well, followed by solid-liquid separation with an automatic filter press. The solid liquid separated well, and the filtrate was colorless and transparent and could be drained as it was. The recovered solid content was dried and the temperature was controlled at 1300 ° C. in the first zone, 1500 ° C. in the second zone, 1700 ° C. in the third zone, and 2250 ° C. in the fourth zone in the same pusher reactor as in Example 1. The solid content in the container under the flow of Ar gas was heated and reacted while moving through each zone every 40 minutes. In addition, there was almost no evaporation of Si or SiO in the first to third zones, β-SiC was generated almost 100% of the theoretical value, and α-SiC was completely formed in the fourth zone. Further, excess carbon was removed at 750 ° C. in the atmosphere. As a result, fine Si facets having an average particle diameter of 1.1 μm were recovered as α-SiC having an average particle diameter of 7.5 μm and turned into effective resources. This product had a high value suitable for lapping abrasive grains and SiC forming raw materials.

Comparative Example 4
To 1000 kg of the same waste aqueous solution used in Example 3, 149 kg of talc having an average particle size of 53 μm was added as a separation aid, and after mixing well, solid-liquid separation was performed with an automatic filter press. However, the filtration rate was very slow and the filtrate was turbid and the recovery of Si was incomplete, and the solid content was an unusable waste.

Claims (8)

Separating a solution or waste liquid containing at least silicon carbide fine particles and / or silicon fine particles by solid-liquid separation using a separation aid containing at least carbon powder and silicon oxide powder;
Mixing the solid content with an additive containing at least carbon powder and / or silicon oxide powder as required;
In order to obtain silicon carbide, production of silicon carbide comprising at least a step of heating and reacting the solid content or the solid content mixed with the additive in a non-oxidizing atmosphere at a temperature higher than 1850 ° C. and lower than 2400 ° C. Method.   The method for producing silicon carbide according to claim 1, wherein the silicon carbide obtained by the heating reaction has an average particle diameter of 1 to 200 μm. The method for producing silicon carbide according to claim 1 or ² , wherein the carbon powder contained in the separation aid has a specific surface area of 1 to 700 m ² / g based on the BET method.   The carbonization according to any one of claims 1 to 3, wherein the heating reaction step has a temperature gradient for crystal rearrangement to α-silicon carbide after the silicon carbide precursor and / or β-silicon carbide is formed. A method for producing silicon.   The method for producing silicon carbide according to any one of claims 1 to 4, wherein the heating reaction step uses a pusher or a rotary sealed reaction furnace that moves a certain distance every certain time.   The total amount of carbon powder and silicon oxide powder contained in the separation aid and the additive is 0.1 to 50 mol per 1.0 mol of silicon carbide fine particles and silicon fine particles contained in the solution or waste liquid. The method for producing silicon carbide according to any one of claims 1 to 5.   The method for producing silicon carbide according to claim 1, wherein the carbon powder contained in the additive has an average particle size of 100 μm or less. The method for producing silicon carbide according to claim 1, wherein the separation aid further contains an organic polymer flocculant.