A method for recovering silicon carbide powder based on wire cutting sludge and silicon carbide powder

Abstract

The application discloses a method for recovering silicon carbide powder based on wire-cut sludge and the silicon carbide powder, and relates to the technical field of semiconductors. The silicon carbide powder is prepared after the wire-cut sludge is pretreated, step-by-step cleaned, purified, crushed and post-treated. The three-stage process of step-by-step cleaning, high-temperature purification and crushing treatment is innovatively adopted to realize closed-loop recovery of SiC in the wire-cut sludge. Through selective oxidation of the step-by-step cleaning and the high-temperature purification, the removal rate of metal impurities is greatly improved. The mechanical force chemical method is adopted in the crushing treatment to reconstruct the SiC crystal lattice, so that the problem of waste particle defects is solved, and high-sintering-activity nano powder is obtained. The heavy metals are converted into recyclable chlorides, and the pollution problem of the wire-cut sludge is efficiently solved. The raw material is the wire-cut sludge, the raw material cost is effectively controlled, the profit space of per ton of SiC powder is increased, and the environmental influence is reduced.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more specifically, to a method for recovering silicon carbide powder from wire-cut sludge and silicon carbide powder. Background Technology

[0002] Silicon carbide (SiC), as an important third-generation semiconductor material, has broad application prospects in power electronics, radio frequency devices, and other fields due to its excellent physicochemical properties. Traditional SiC powder preparation processes mainly employ the Acheson method, which involves heating quartz sand and petroleum coke to above 2500℃ in a resistance furnace for a carbothermic reduction reaction, or using chemical vapor deposition to react silicon-containing and carbon-containing gases at high temperatures to generate SiC. These traditional methods have significant drawbacks: the Acheson method requires a large amount of electrical energy to maintain the ultra-high temperature reaction environment, and the purification costs of raw materials such as quartz sand and petroleum coke are high; the resulting product usually contains unreacted raw materials and impurity phases, requiring multiple acid washing processes to achieve high purity, which not only increases production costs but also generates a large amount of acidic waste liquid. Meanwhile, the photovoltaic and semiconductor wafer manufacturing processes generate a large amount of wire cutting sludge, which mainly contains SiC cutting abrasive, silicon powder, metal fragments, and organic cutting fluid residues.

[0003] The aforementioned wire cutting sludge is classified as hazardous solid waste. The current disposal method is solidification and landfill, which not only occupies a large amount of land resources, but also allows heavy metal ions and organic cutting fluids to easily leach into the soil and groundwater through rainwater, posing a persistent environmental risk. This treatment method neither meets the requirements of a circular economy nor complies with increasingly stringent environmental management regulations for hazardous waste.

[0004] How to recover the effective components from wire cutting sludge and make reasonable use of them while reducing environmental impact is one of the technical challenges that urgently needs to be solved in this field.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for recovering silicon carbide powder based on wire-cut sludge and silicon carbide powder, so as to solve or improve the above-mentioned technical problems.

[0007] This invention is implemented as follows: In a first aspect, the present invention provides a method for recovering silicon carbide powder based on wire-cut sludge, comprising the following steps: The pretreated raw materials are subjected to step washing to obtain the washed product; The cleaning product was purified by placing it in an oxidizing gas atmosphere at a temperature of 800℃-950℃ to obtain a purified product. The purified product is then pulverized and post-treated to obtain silicon carbide powder.

[0008] In an optional implementation, the step cleaning includes primary pickling, secondary pickling, and tertiary rinsing; The reagents for primary pickling include an HCl solution with a mass concentration of 8wt%-12wt%; The reagents for secondary pickling include HF solution with a mass concentration of 3wt%-8wt% and HNO3 solution with a mass concentration of 3wt%-8wt%. The reagents for the third-stage rinsing are selected from at least one of ultrapure water, deionized water, and distilled water; And / or, after the step washing, a filter press dewatering process is also included; the moisture content of the filter cake after filter press dewatering is ≤15%, and the residual chloride ion content is ≤100ppm.

[0009] In an optional embodiment, the oxidizing gas includes chlorine and argon in a volume ratio of 1:(2-4); And / or, the purification process takes 2-4 hours.

[0010] In an optional embodiment, the purified product has a SiC purity of ≥99.95% and a residual total amount of the metal elements Fe and Al of ≤50ppm.

[0011] In an optional embodiment, the pulverization process includes the following steps: The purified product was placed in an air jet mill and pulverized at 0.6 MPa-1.0 MPa until the D50 was 3 μm-6 μm to obtain the pulverized product. An alcohol solution and grinding balls were added to the pulverized product, and the product was wet-milled for 5.5-7.0 hours at a speed of 400-600 rpm to obtain the wet-milled product. After adding a dispersant to the wet milling product, the product was sieved to obtain a sieved product with a D50 of 120nm-180nm.

[0012] In an optional embodiment, the grinding process has at least one of the following characteristics: Feature 1: The alcohol solution is selected from at least one of ethanol, propanol, and isopropanol; Feature 2: The grinding balls are made of at least one of zirconium oxide and silicon carbide; Feature 3: The average particle size of the grinding balls is 0.25mm-0.35mm; Feature 4: The ball-to-material ratio in the grinding process is (7-10):1; Feature 5: The temperature during the grinding process is ≤40℃.

[0013] In an optional embodiment, the mass concentration of the dispersant is 0.3wt%-0.7wt%; And / or, the dispersant is selected from at least one of sodium dodecylbenzenesulfonate, ammonium polyacrylate and polyvinylpyrrolidone.

[0014] In an optional embodiment, the pretreatment of the raw materials includes centrifugal dehydration, drying and sieving. The raw material is wire cutting sludge, which includes 40wt%-60wt% SiC, 15wt%-25wt% silicon powder, 5wt%-10wt% metal impurities and 20wt%-30wt% cutting fluid. Centrifugal dehydration treatment includes dehydrating the raw material at a speed of 2800rpm-3500rpm until the filter cake moisture content is ≤30%, thus obtaining the filter cake; The filter cake was subjected to a first drying treatment at a temperature of 110℃-130℃ for 3.5h-4.5h to obtain the first dried product. The first dried product was sieved under conditions of an amplitude of 2mm-3mm and a sieve mesh size of 180-200 mesh to obtain pretreated raw materials.

[0015] In an optional embodiment, the post-processing includes: subjecting the sieved product after pulverization to a second drying process under the conditions of an inlet temperature of 200℃-240℃, an outlet temperature of 85℃-95℃, and an atomization pressure of 0.25MPa-0.4MPa, to obtain a second dried product. And / or, the second dried product is packaged under a vacuum of ≤-0.1MPa and an inert atmosphere.

[0016] Secondly, the present invention provides a silicon carbide powder, which is prepared by any of the methods described in the foregoing embodiments.

[0017] The present invention has the following beneficial effects: This invention innovatively employs a three-stage process—stepped washing, high-temperature purification, and pulverization—to achieve closed-loop recovery of SiC from wire-cut sludge. Specifically, the selective oxidation through stepped washing and high-temperature purification significantly improves the removal rate of metallic impurities (such as Fe and Al). The pulverization process uses a mechanochemical method to reconstruct the SiC lattice, solving the problem of particle defects in the waste material and obtaining highly sinterable active nanoparticles. Heavy metals are converted into recyclable chlorides (such as FeCl3 for wastewater treatment), effectively solving the pollution problem of wire-cut sludge. Using wire-cut sludge as raw material effectively controls raw material costs, increases the profit margin per ton of SiC powder, and reduces environmental impact. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0019] In a first aspect, the present invention provides a method for recovering silicon carbide powder based on wire-cut sludge, comprising the following steps: The pretreated raw materials are subjected to step washing to obtain the washed product; The cleaning product was purified by placing it in an oxidizing gas atmosphere at a temperature of 800℃-950℃ to obtain a purified product. The purified product is then pulverized and post-treated to obtain silicon carbide powder.

[0020] This invention innovatively employs a three-stage process—step-by-step cleaning, high-temperature purification, and pulverization—to achieve closed-loop recovery of SiC from line-cut sludge, reducing raw material costs by 30%. Specifically, the selective oxidation through step-by-step cleaning and high-temperature purification achieves a removal rate of >99.9% for metallic impurities (such as Fe and Al). The pulverization process utilizes a mechanochemical method to reconstruct the SiC lattice, resolving particle defects in the waste material and obtaining highly sinterable active nanoparticles with a D50 ≤ 200 nm. Heavy metals are converted into recyclable chlorides (such as FeCl3 for wastewater treatment), effectively solving the pollution problem of line-cut sludge and reducing environmental impact.

[0021] Furthermore, the purification temperature is 900℃. If the temperature is <800℃, the metal chloride will not volatilize sufficiently; if the temperature is >1000℃, it will lead to oxidation of the SiC surface.

[0022] Specifically, the purification process employs a heating procedure. When the temperature is below 300℃, argon gas is introduced to purge oxygen from the equipment. Once the temperature reaches 600℃, chlorine gas is introduced to prevent the oxidation of silicon carbide. The purified tail gas is then sprayed with a NaOH solution to reduce the amount of unreacted chlorine. The NaOH concentration is 22wt%-28wt%.

[0023] In an optional embodiment, the pretreatment of the raw materials includes centrifugal dehydration, drying and sieving. The raw material is wire cutting sludge, comprising 40wt%-60wt% SiC, 15wt%-25wt% silicon powder, 5wt%-10wt% metallic impurities, and 20wt%-30wt% cutting fluid. The cutting fluid is stored in a corrosion-resistant tank for later use; the metallic impurities include 6.5wt% Fe and 1.2wt% Al.

[0024] It should be noted that, in the specific embodiments of the present invention, the wire-cut sludge is specifically produced by a photovoltaic / semiconductor plant, and its composition may vary depending on the production batch and demand of the product.

[0025] The centrifugal dewatering process includes dewatering the raw material at a speed of 2800 rpm-3500 rpm until the filter cake moisture content is ≤30%, thus obtaining a filter cake. The centrifugal dewatering equipment is a screw centrifuge, and centrifugation is carried out until the filter cake is in block form with no dripping liquid. After testing, the filter cake moisture content is ≤30%. In other embodiments of the present invention, the centrifugal dewatering equipment can be reasonably selected according to actual needs.

[0026] Furthermore, the centrifugal dehydration process was carried out at a speed of 3000 rpm for 20 minutes.

[0027] The filter cake is subjected to a first drying treatment at a temperature of 110℃-130℃ for 3.5h-4.5h to obtain a first dried product. The first drying treatment is a hot air drying process using a disc dryer. During the first drying treatment, a moisture analyzer is used to monitor the moisture content of the product in real time, and the moisture content of the final first dried product is ≤5%. In other embodiments of the present invention, the hot air drying equipment can be reasonably selected according to actual needs.

[0028] Furthermore, the temperature of the first drying treatment was 120±5℃ and the time was 4.0h.

[0029] The first dried product is sieved under conditions of an amplitude of 2mm-3mm and a sieve mesh size of 180-200 mesh to obtain pretreated raw materials. The sieving equipment is an ultrasonic vibrating screen, used to remove metal fragments with an average particle size >75μm. In other embodiments of the present invention, the sieving equipment can be reasonably selected according to actual needs.

[0030] Furthermore, the sieving process was carried out for 10 minutes under the conditions of an amplitude of 2 mm and a screen mesh of 200 mesh.

[0031] In an optional implementation, the step cleaning includes primary pickling, secondary pickling, and tertiary rinsing; The primary pickling reagent includes an HCl solution with a mass concentration of 8wt%-12wt%. The primary pickling is carried out at a constant temperature of 60±2℃, assisted by stirring, to remove free Fe / Ni impurities. The reaction equipment is selected appropriately according to needs; in this embodiment, a reaction vessel is used. The stirring speed is 180rpm-250rpm, and the time is 1.5h-2.5h.

[0032] Furthermore, the HCl solution had a mass concentration of 10 wt%, the stirring speed was 200 rpm, and the time was 2.0 h; the removal rate of free Fe / Ni impurities was greater than 95%.

[0033] The secondary pickling reagents include an HF solution with a mass concentration of 3wt%-8wt% and an HNO3 solution with a mass concentration of 3wt%-8wt%. The secondary pickling is carried out at a constant temperature of 40±2℃, supplemented by ultrasonic treatment, to remove silicon oxides and metals such as Fe and Al. The reaction equipment is selected appropriately according to needs; in this embodiment, an ultrasonic reaction tank made of titanium alloy is used. The ultrasonic treatment power is 750W-900W, and the time is 0.8h-1.5h. Furthermore, the mass concentration of HF must be strictly controlled to ≤5wt% to prevent excessive corrosion of SiC. When the corrosion rate of SiC >0.1μm / h, the process must be stopped.

[0034] Furthermore, the reagents for secondary pickling include a 5 wt% HF solution and a 5 wt% HNO3 solution, and the ultrasonic treatment power is 800 W for 1.0 h; the removal rate of silicon oxide and metals Fe and Al is >98%.

[0035] The reagents for the three-stage rinsing are selected from at least one of ultrapure water, deionized water, and distilled water; it is treated by countercurrent rinsing and three-stage series rinsing tanks; the solid-liquid ratio is controlled at 1:(4-6), the pH is 6.5-7.0, and the rinsing is repeated 3-5 times; after the three-stage rinsing, the resistivity of SiC powder is ≤10μs / cm.

[0036] It should be noted that real-time monitoring of the pH / conductivity of SiC powder during the stepped cleaning process and the recycling of rinsing water help reduce wastewater discharge.

[0037] Furthermore, the solid-liquid ratio of the three-stage rinsing is 1:5, and the equipment used is selected reasonably according to actual needs.

[0038] And / or, after the step washing, a filter press dewatering process is also included; the moisture content of the filter cake after filter press dewatering is ≤15%, and the residual chloride ion content is ≤100ppm.

[0039] The equipment for dewatering by pressure filtration is a fully automatic plate and frame filter press, using a diaphragm filter with a pressure of 0.5MPa-0.7MPa. Specifically, the pressure of the diaphragm filter is 0.6MPa.

[0040] In an optional embodiment, the oxidizing gas includes chlorine and argon in a volume ratio of 1:(2-4); And / or, the purification process takes 2-4 hours.

[0041] In an optional embodiment, the chlorine flow rate is 1.8 L / (min·kg) - 2.5 L / (min·kg), and argon is used as a carrier gas to prevent deflagration. Further, the chlorine flow rate is 2.0 L / (min·kg).

[0042] Insufficient purification reaction time will result in high Fe residue; excessive time will increase energy consumption.

[0043] The purification reaction equipment is a tubular furnace made of quartz. The diameter of the quartz reaction tube is 180mm-200mm, and it is connected to a condensation recovery system for removing impurities (Si) and recovering Fe, facilitating the collection of FeCl3 / SiCl4. The relevant chemical equations are: 2Fe(s) + 3Cl2(g) → 2FeCl3(g), Si(impurity, s) + 2Cl2(g) → SiCl4(g); the metallic impurities are volatilized and removed after forming gaseous chlorides with a boiling point <400℃.

[0044] In an optional embodiment, the purified product has a SiC purity of ≥99.95% and a residual total amount of the metal elements Fe and Al of ≤50ppm.

[0045] In an optional embodiment, the pulverization process includes the following steps: The purified product was placed in an air jet mill and pulverized at 0.6 MPa-1.0 MPa until the D50 was 3 μm-6 μm, thus obtaining the pulverized product. The air jet mill is used to break up the agglomerated purified product. The ceramic-lined air jet mill is used for deagglomeration and particle size pre-control, as detailed below: Deagglomeration refers to the process of dispersing soft agglomerates (particle size 50μm-200μm) formed by the high surface activity of SiC powder after acid washing and chlorine purification. Air jet mills utilize high-speed airflow to cause particles to collide with each other, breaking up agglomerates to D50≈5μm without the need for mechanical grinding media, thus avoiding the decrease in grinding efficiency caused by large particle agglomeration in subsequent wet grinding.

[0046] Particle size pre-control refers to reducing the feed particle size from 200μm (after sieving) to 5μm, which can reduce the ball-to-material ratio and grinding time of wet grinding by 30%-50%, significantly reducing energy consumption and media wear.

[0047] An alcohol solution and grinding balls are added to the pulverized product, and wet milling is performed at a speed of 400-600 rpm for 5.5-7.0 hours to obtain the wet-milled product. This wet milling process, aided by chemical reagents, is a mechanical grinding process, using a mechanochemical method to reconstruct the SiC lattice. The equipment is selected appropriately according to actual needs; in this embodiment, a planetary ball mill equipped with a cooling jacket is used.

[0048] It should be noted that the mechanochemical method for lattice reconstruction refers to the following: SiC coarse powder (D50≈5μm) purified by chlorine gas is mixed with ethanol medium and a dispersant (such as ammonium polyacrylate), and then placed in a planetary ball mill and ground for 6 hours at 500 rpm using zirconia balls (Φ0.3mm). During this process, the local high temperature and pressure generated by mechanical collisions induce plastic deformation and dynamic recrystallization of the SiC particles, reconstructing the high-density dislocations (>10) in the original lattice. 12 cm -2 Through dislocation slip and climb rearrangement, subgrain boundaries are formed and eventually evolve into dislocation-free nanocrystals (D50≈150nm). At the same time, ammonium polyacrylate molecules are chemically bonded to the SiC surface through carboxylate groups to form a stable coating layer, which prevents nanoparticle aggregation and passivates surface active sites.

[0049] Furthermore, the wet milling process was carried out at a speed of 500 rpm for 6 hours.

[0050] After adding a dispersant to the wet-milled product, it is sieved to obtain a sieved product with a D50 of 120nm-180nm. The dispersant helps prevent the agglomeration of the wet-milled product and increases the Zeta potential to >40mV. The dispersant is added using an online dispersant injection system. In other embodiments of the invention, other suitable methods are used to add the dispersant.

[0051] It should be noted that the screening process uses a nanoscale centrifugal classifier to remove large particles with a diameter >500nm. Specifically, in the embodiments of this invention, a three-channel dynamic separator is used to achieve separation of product particles with a diameter D50 of 150±10nm.

[0052] In an optional embodiment, the grinding process has at least one of the following characteristics: Feature 1: The alcohol solution is selected from at least one of ethanol, propanol and isopropanol; further, it is ethanol.

[0053] Feature 2: The grinding ball is made of at least one of zirconium oxide and silicon carbide; more specifically, zirconium oxide.

[0054] Feature 3: The average particle size of the grinding balls is 0.25mm-0.35mm; further, it is 0.3mm.

[0055] Feature 4: The ball-to-material ratio in the grinding process is (7-10):1; further, it is 8:1.

[0056] Feature 5: The temperature during the grinding process is ≤40℃.

[0057] In an optional embodiment, the mass concentration of the dispersant is 0.3wt%-0.7wt%; more specifically, 0.3wt%.

[0058] And / or, the dispersant is selected from at least one of sodium dodecylbenzenesulfonate, ammonium polyacrylate, and polyvinylpyrrolidone. More specifically, it is ammonium polyacrylate.

[0059] In an optional embodiment, the post-processing includes: subjecting the sieved product after pulverization to a second drying process under conditions of an inlet temperature of 200℃-240℃, an outlet temperature of 85℃-95℃, and an atomization pressure of 0.25MPa-0.4MPa to obtain a second dried product; the moisture content of the second dried product is ≤1%, and the drying equipment used is a centrifugal spray drying tower. In other embodiments of the present invention, the appropriate equipment can be selected according to actual needs.

[0060] And / or, the second dried product is packaged under a vacuum of ≤-0.1 MPa and an inert atmosphere. The gas providing the inert atmosphere is selected from at least one of argon, nitrogen, and helium.

[0061] In optional embodiments, the present invention does not particularly limit the specifications and materials of the packaging bags used for packaging. Specifically, in the embodiments of the present invention, the packaging bags used are 25kg in size and made of aluminum foil; automatic weighing packaging is adopted.

[0062] In summary, the present invention provides a method for recovering silicon carbide powder based on wire-cut sludge, comprising the following steps: (1) Raw material preparation and pretreatment The raw materials for wire cutting sludge are obtained from photovoltaic / semiconductor plants, including 40wt%-60wt% SiC, 15wt%-25wt% silicon powder, 5wt%-10wt% metal impurities, and 20wt%-30wt% cutting fluid; among which, the metal impurities include 6.5wt% Fe and 1.2wt% Al.

[0063] The pretreatment of raw materials includes centrifugal dehydration, drying and sieving. The centrifugal dehydration process includes dehydrating the raw material at a speed of 2800 rpm to 3500 rpm until the filter cake moisture content is ≤30%, thus obtaining the filter cake. The filter cake was subjected to a first drying treatment at a temperature of 110℃-130℃ for 3.5h-4.5h to obtain the first dried product. The first dried product was sieved under conditions of an amplitude of 2mm-3mm and a sieve mesh size of 180-200 mesh to obtain pretreated raw materials.

[0064] (2) Step cleaning The pretreated raw material obtained in step (1) is subjected to step cleaning to obtain the cleaning product; Step cleaning includes primary pickling, secondary pickling, and tertiary rinsing; The primary pickling reagent includes an HCl solution with a mass concentration of 8wt%-12wt%. The primary pickling is carried out in a constant temperature environment of 60±2℃, with the assistance of stirring at a speed of 180rpm-250rpm for 1.5h-2.5h.

[0065] The reagents for secondary pickling include HF solution with a mass concentration of 3wt%-8wt% and HNO3 solution with a mass concentration of 3wt%-8wt%. Secondary pickling is carried out in a constant temperature environment of 40±2℃, supplemented by ultrasonic treatment with a power of 750W-900W and a time of 0.8h-1.5h.

[0066] The reagents for the three-stage rinsing are selected from at least one of ultrapure water, deionized water, and distilled water; the process involves countercurrent rinsing and a three-stage series rinsing tank; the solid-liquid ratio is controlled at 1:(4-6), the pH at 6.5-7.0, and the rinsing is repeated 3-5 times to obtain the cleaned product. After the three-stage rinsing, the resistivity of the SiC powder is ≤10μs / cm.

[0067] (3) Purification treatment The cleaning product obtained in step (2) is placed in an oxidizing gas atmosphere at a temperature of 800℃-950℃ for purification treatment to obtain a purified product. The oxidizing gases include chlorine and argon in a volume ratio of 1:(2-4), wherein the flow rate of chlorine is 1.8 L / (min·kg)-2.5 L / (min·kg); the purification process takes 2-4 hours.

[0068] The purified product has a SiC purity of ≥99.95% and a residual total amount of the metal elements Fe and Al of ≤50ppm.

[0069] (4) Crushing process The purified product obtained in step (3) is subjected to pulverization, which includes the following steps: The purified product was placed in an air jet mill and pulverized at 0.6 MPa-1.0 MPa until the D50 was 3 μm-6 μm to obtain the pulverized product. An alcohol solution and grinding balls are added to the pulverized product, and the product is wet-milled for 5.5-7.0 hours at a speed of 400-600 rpm to obtain a wet-milled product. The alcohol solution is selected from at least one of ethanol, propanol, and isopropanol. The grinding balls are made of at least one of zirconium oxide and silicon carbide. The average particle size of the grinding balls is 0.25-0.35 mm. The ball-to-material ratio in the grinding process is (7-10):1. The temperature in the grinding process is ≤40℃.

[0070] After adding a dispersant to the wet-milled product, the product is sieved to obtain a sieved product with a D50 of 120nm-180nm. The mass concentration of the dispersant is 0.3wt%-0.7wt%; the dispersant is selected from at least one of sodium dodecylbenzenesulfonate, ammonium polyacrylate, and polyvinylpyrrolidone.

[0071] (5) Post-processing The sieved product obtained in step (4) is post-processed to obtain silicon carbide powder.

[0072] The post-processing includes: subjecting the pulverized and sieved product to a second drying process under the conditions of an inlet temperature of 200℃-240℃, an outlet temperature of 85℃-95℃, and an atomization pressure of 0.25MPa-0.4MPa to obtain a second dried product. The second dried product is packaged under a vacuum of ≤-0.1 MPa and an inert atmosphere. The gas providing the inert atmosphere is selected from at least one of argon, nitrogen, and helium.

[0073] Secondly, the present invention provides a silicon carbide powder, which is prepared by any of the methods described in the foregoing embodiments.

[0074] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0075] Example 1 This embodiment provides a method for recovering silicon carbide powder based on wire-cut sludge, including the following steps: (1) Raw material preparation and pretreatment The raw materials for wire cutting sludge are obtained from photovoltaic / semiconductor plants, including 40wt%-60wt% SiC, 15wt%-25wt% silicon powder, 5wt%-10wt% metal impurities, and 20wt%-30wt% cutting fluid; among which, the metal impurities include 6.5wt% Fe and 1.2wt% Al.

[0076] The pretreatment of raw materials includes centrifugal dehydration, drying and sieving. The centrifugal dehydration process includes dehydrating the raw material at a speed of 3000 rpm for 20 minutes until the filter cake moisture content is ≤30%, thus obtaining the filter cake; the equipment is a screw centrifuge.

[0077] The filter cake was subjected to a first drying treatment at a temperature of 120±5℃ for 4.0h to obtain a first dried product; the moisture content of the first dried product was ≤5%; the equipment was a disc dryer.

[0078] The first dried product was sieved under conditions of 2 mm amplitude and 200 mesh to obtain pretreated raw materials. The equipment was an ultrasonic vibrating screen.

[0079] (2) Step cleaning The pretreated raw material obtained in step (1) is subjected to step cleaning to obtain the cleaning product; Step cleaning includes primary pickling, secondary pickling, and tertiary rinsing; The primary pickling reagent includes a 10wt% HCl solution; the primary pickling is carried out in a constant temperature environment of 60±2℃, with the assistance of stirring at a speed of 200rpm for 2.0h.

[0080] The reagents for secondary pickling include 5wt% HF solution and 5wt% HNO3 solution. Secondary pickling is carried out in a constant temperature environment of 40±2℃, supplemented by ultrasonic treatment with a power of 800W for 1.0h.

[0081] The reagent used for the three-stage rinsing was deionized water; it was treated using countercurrent rinsing and a three-stage series rinsing tank; the solid-liquid ratio was controlled at 1:5, the pH at 6.5-7.0, and the rinsing was repeated three times to obtain the cleaned product. After the three-stage rinsing, the resistivity of the SiC powder was ≤10μs / cm.

[0082] The Fe content in the cleaning product was 0.25 wt%.

[0083] (3) Purification treatment The cleaning product obtained in step (2) was placed in an oxidizing gas atmosphere at a temperature of 900℃ for purification treatment to obtain a purified product; the equipment was a tube furnace, the reaction tube was made of quartz material and the tube diameter was 200mm.

[0084] The oxidizing gases include chlorine and argon in a volume ratio of 1:3, with a chlorine flow rate of 2.0 L / (min·kg); the purification process takes 3 hours.

[0085] The purified product has a SiC purity of ≥99.95% and a residual total amount of the metal elements Fe and Al of ≤50ppm.

[0086] (4) Crushing process The purified product obtained in step (3) is subjected to pulverization, which includes the following steps: The purified product was placed in an air jet mill and pulverized at 0.8 MPa until the D50 was 5 μm to obtain the pulverized product. An alcohol solution and grinding balls were added to the pulverized product, and the mixture was wet-milled for 6.0 h at a speed of 500 rpm to obtain a wet-milled product. The alcohol solution was ethanol; the grinding balls were made of zirconium oxide; the average particle size of the grinding balls was 0.3 mm; and the temperature of the grinding process was ≤40℃.

[0087] After adding a dispersant to the wet-milled product, the product was sieved to obtain a sieved product with a D50 of 150 ± 10 nm. The mass concentration of the dispersant was 0.5 wt%; the dispersant was ammonium polyacrylate.

[0088] (5) Post-processing The sieved product obtained in step (4) is post-processed to obtain silicon carbide powder.

[0089] The post-processing includes: subjecting the sieved product after pulverization to a second drying process under the conditions of an inlet temperature of 220°C, an outlet temperature of 90°C, and an atomization pressure of 0.3 MPa to obtain a second dried product; The second dried product was packaged under a vacuum of ≤-0.1 MPa and an inert atmosphere. The inert gas provided was nitrogen.

[0090] Comparative Example 1 This comparative example provides a method for recovering silicon carbide powder based on wire-cut sludge, including the following steps: (1) Raw material preparation and pretreatment Natural quartz sand (SiO2≥99.2%) is coarsely crushed to a particle size <5mm using a crusher; petroleum coke (fixed carbon≥95%) is pulverized to <3mm using a hammer crusher. Weigh the SiO2 and C materials according to a mass ratio of 1:1.5 and put them into a twin-screw mixer. Add 3wt% wood chips as a pore-forming agent and dry mix for 2 hours until uniform to obtain a mixture. Control the moisture content of the mixture to 5%-8%; if the moisture content is insufficient, spray water mist to adjust it.

[0091] (2) Charging of the resistance furnace A 20cm thick coke layer is laid at the bottom of the rectangular graphite furnace body as a conductive bed; a graphite electrode with a diameter of 30cm is inserted vertically; the mixture obtained in step (1) is filled in layers, and compacted once every 30cm thick layer is filled, with a 50cm diameter cavity reserved in the center as the reaction core area. The top layer is covered with a 20cm coke insulation layer, and the sides of the furnace are sealed with refractory clay.

[0092] (3) High-temperature synthesis reaction The electrodes were subjected to 10kV / 50kA AC current and heated to 1400℃ at a rate of 50℃ / h (time taken 28h). When kept at a constant temperature of 1400-2000℃ for 12 hours, the following reaction occurs: SiO2 + 3C → SiC + 2CO↑; Continue to increase the temperature to 2500℃ at a rate of 30℃ / h and maintain it for 48h to ensure the reaction is complete; The total power consumption at this stage is approximately 6500 kWh / ton of product.

[0093] (4) Cooling and furnace opening After power failure, allow it to cool naturally for 72 hours until the temperature is below 50℃; Remove the side fire-resistant walls and use an excavator to remove the outer layer of unreacted material (approximately 40% of the total). The silicon carbide crystal block (with a radial columnar crystal structure) in the central reaction zone is manually chiseled out.

[0094] (5) Crushing and grading The silicon carbide crystal block obtained in step (4) is coarsely crushed by a crusher to particles with an average particle size of <2cm; then, it is conveyed to a double roll crusher for further crushing to an average particle size of <5mm; and then wet-milled using a ball mill (water-to-material ratio 2:1) for 24 hours, with D50≈5μm; A hydrocyclone was used to remove coarse particles with an average particle size >10μm to prepare a slurry.

[0095] (6) Chemical purification The slurry obtained in step (5) was transferred to an acid-resistant reactor, and a mixture of 20 wt% hydrofluoric acid (HF) and 15 wt% nitric acid (HNO3) was added; the mixture was stirred and acid-washed at 80°C for 6 hours to dissolve the metal oxides and free silicon. SiO2 + 6HF → H2SiF6 + 2H2O; Then, a filter press is used for dehydration, and the filtrate is washed with deionized water until the conductivity of the filtrate is <50μS / cm.

[0096] (7) Drying and sieving The filter cake obtained in step (6) is sent to a spray drying tower (inlet air temperature 250℃) for drying to produce powder with a moisture content of <0.5%; The powder is processed using an ultrasonic vibrating screen (400 mesh) to remove hard agglomerates; Then, a magnetic separator (magnetic field strength 1.2T) is used to remove iron impurities.

[0097] (8) Quality inspection and packaging The product obtained in step (7) is subjected to quality testing, and qualified products are packaged.

[0098] Analysis example This analysis compares Example 1 and Comparative Example 1, focusing on metal removal rate, overall energy consumption, and wastewater discharge volume. The results are summarized in Table 1. Specifically, the metal removal rate is calculated as follows: (1 - Con...) 处理后金属含量 / Con 处理前金属含量 The metal (Fe, Al) content was determined using an inductively coupled plasma optical emission spectrometer (ICP-OES). The calculation formula for the metal removal rate and the test method for the metal content in the following experimental examples are the same as those in the analytical examples, and will not be repeated hereafter.

[0099] Table 1 Analysis Results

[0100] Experimental Example 1 This experiment was conducted to investigate the effect of different reagents on the metal removal rate during the step cleaning process. The implementation method was the same as in Example 1, except that the reagents used in the first and second acid washing processes were different or the acid washing procedures in the step cleaning were different. The Fe removal rate, Al removal rate, SiC loss rate and acid consumption were summarized, and the relevant results are shown in Table 2.

[0101] The SiC loss rate was detected by thermogravimetric analysis (TGA); the acid consumption was calculated by dividing the total amount of acid used in each pickling cycle recorded by an electromagnetic flowmeter by the mass of the material being treated.

[0102] Table 2. Investigation of Stepwise Cleaning Reagents and Procedures

[0103] Note: "Single-stage" refers to a pickling process performed only once; "Level 1 and Level 2" refer to two pickling processes performed.

[0104] As can be seen from the data in Table 2, the step-by-step cleaning (from HCl in the first-stage pickling to the HF / HNO3 mixed reagent in the second-stage pickling) achieved a metal removal rate of >99% while ensuring a low SiC loss rate (<1.5%). The introduction of HNO3 in the mixed reagent significantly improved the Al removal rate.

[0105] Experimental Example 2 This experiment was conducted to investigate the effects of temperature and gas ratio during the purification process. The implementation method was the same as in Example 1, except for the difference in temperature or gas ratio. The results of Fe residue, SiC purity and energy consumption were summarized and are shown in Table 3.

[0106] Fe residue: After acid washing, the sample was treated with chlorine gas, and the Fe and Al residues in the solid were determined by ICP-MS (inductively coupled plasma mass spectrometry), with a detection limit of 0.1 ppm.

[0107] SiC purity: The test method used was GD-MS (glow emission mass spectrometry). The specific purity test data is presented using Example 1 as an example. See Table 4 for details.

[0108] Energy consumption: The heating power of the tubular furnace is monitored using a power recorder, and the electrical energy consumed per kilogram of material (kWh / kg) is calculated by integration.

[0109] Table 3. Investigation of purification treatment temperature and gas.

[0110] As can be seen from the data in Table 3, when the purification temperature is 900℃ and the volume ratio of chlorine to argon is 1:3, the total residual amount of Fe and Al is <50ppm and the energy consumption is controllable. When the temperature is greater than 950℃, the energy consumption increases dramatically and the purity improvement is limited.

[0111] Table 4 Purity data for Example 1

[0112] Experimental Example 3 This experiment was used to investigate the effect of time on the purification process. The implementation method was the same as in Example 1, except for the time. The Fe residue, Al residue and SiC yield were summarized and the relevant results are shown in Table 5.

[0113] Fe residue and Al residue: same as in test example 2.

[0114] SiC yield: Weigh the solid mass before and after chlorine treatment, and calculate the yield after deducting volatiles (FeCl3, SiCl4, etc.); SiC yield = mass after treatment / mass before treatment × 100%.

[0115] Table 5. Investigation of purification processing time

[0116] As can be seen from Table 5, the purification process reaches its peak marginal benefit when the purification time is 3 hours, and the yield decreases significantly when the reaction time is extended further.

[0117] Test Example 4 This experiment was conducted to investigate the effects of rotational speed and time on the properties of the wet-milled product during the wet milling process. The implementation method was the same as in Example 1, except for the difference in rotational speed or time. The results of D50, specific surface area and agglomeration index of the wet-milled product were summarized and are shown in Table 6.

[0118] Among them, D50 (median particle size) was calculated using a laser particle size analyzer (Malvern Mastersizer 3000), wet dispersion (ethanol medium, ultrasonication for 1 min), and Mie scattering model.

[0119] Specific surface area: BET method (nitrogen adsorption, Micromeritics ASAP 2460), the sample was tested after degassing at 200℃ for 4 h.

[0120] Agglomeration index: Calculated as D50 (laser particle size) / DBET, where DBET = 6 / (ρ×SBET), and ρ is the density of SiC (3.21 g / cm³). 3 A reunification index greater than 1.2 indicates the presence of significant reunification.

[0121] Table 6. Investigation of wet milling speed and time

[0122] The aggregation index is calculated as laser particle size D50 / BET equivalent particle size. An aggregation index greater than 1.2 indicates significant aggregation.

[0123] As can be seen from the data in Table 6, the optimal balance between particle size and dispersibility can be achieved when the wet milling speed is 500 rpm and the time is 6 h; when the speed is ≥600 rpm, although the particle size is finer, agglomeration is intensified.

[0124] Experimental Example 5 This experiment was conducted to investigate the effect of the type of dispersant. The implementation method was the same as in Example 1, except for the type of dispersant. The zeta potential, sedimentation rate and viscosity were summarized and the results are shown in Table 7.

[0125] Among them, Zeta potential: The sample was diluted to 0.1 wt% and the pH was 6.5 using a Zeta potential analyzer (Malvern Zetasizer Nano ZS) and measured by electrophoretic light scattering.

[0126] Sedimentation rate: After the suspension (solid content 5 wt%) is allowed to stand for 24 hours, the supernatant is taken, dried and weighed, and the sedimentation rate is calculated as (initial solid mass - supernatant solid mass) / initial solid mass × 100%.

[0127] Viscosity: Rotational viscometer (Brookfield DV2T), using UL adapter, shear rate 100 s. -1 , constant temperature of 25℃.

[0128] Table 7. Investigation of Dispersant Types

[0129] As can be seen from the data in Table 7, the dispersant ammonium polyacrylate can achieve low viscosity and high stability dispersion through electrostatic repulsion (high negative potential).

[0130] In summary, the embodiments of this invention innovatively employ a three-stage process of stepped washing, high-temperature purification, and pulverization to achieve closed-loop recovery of SiC from line-cut sludge. Specifically, the selective oxidation through stepped washing and high-temperature purification significantly improves the removal rate of metallic impurities (such as Fe and Al). The pulverization process uses a mechanochemical method to reconstruct the SiC lattice, solving the problem of particle defects in the waste material and obtaining highly sinterable active nanoparticles. Heavy metals are converted into recyclable chlorides (such as FeCl3 for wastewater treatment), effectively solving the pollution problem of line-cut sludge. Using line-cut sludge as raw material effectively controls raw material costs, increases the profit margin per ton of SiC powder, and reduces environmental impact.

[0131] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for recovering silicon carbide powder based on wire-cut sludge, characterized in that, Includes the following steps: The pretreated raw materials are subjected to step washing to obtain the washed product; The cleaning product was purified by placing it in an oxidizing gas atmosphere at a temperature of 800℃-950℃ to obtain a purified product. The purified product is then subjected to pulverization and post-treatment to obtain silicon carbide powder.

2. The method according to claim 1, characterized in that, The stepped cleaning process includes primary acid washing, secondary acid washing, and tertiary rinsing. The reagent for primary pickling includes an HCl solution with a mass concentration of 8wt%-12wt%. The reagents for the secondary pickling include an HF solution with a mass concentration of 3wt%-8wt% and an HNO3 solution with a mass concentration of 3wt%-8wt%. The reagents used for the three-stage rinsing are selected from at least one of ultrapure water, deionized water, and distilled water; And / or, the step cleaning process further includes pressure filtration and dewatering; the moisture content of the filter cake after pressure filtration and dewatering is ≤15%, and the residual chloride ion content is ≤100ppm.

3. The method according to claim 1, characterized in that, The oxidizing gas includes chlorine and argon in a volume ratio of 1:(2-4); And / or, the purification process takes 2-4 hours.

4. The method according to claim 1, characterized in that, The purified product has a SiC purity of ≥99.95% and a residual total amount of the metal elements Fe and Al of ≤50ppm.

5. The method according to claim 1, characterized in that, The pulverization process includes the following steps: The purified product was placed in an air jet mill and pulverized at 0.6 MPa-1.0 MPa until the D50 was 3 μm-6 μm to obtain the pulverized product. An alcohol solution and grinding balls are added to the pulverized product, and the product is wet-milled for 5.5-7.0 hours at a speed of 400-600 rpm to obtain the wet-milled product. After adding a dispersant to the wet milling product, the product is sieved to obtain a sieved product with a D50 of 120nm-180nm.

6. The method according to claim 5, characterized in that, The grinding process has at least one of the following characteristics: Feature 1: The alcohol solution is selected from at least one of ethanol, propanol, and isopropanol; Feature 2: The grinding balls are made of at least one material selected from zirconium oxide and silicon carbide; Feature 3: The average particle size of the grinding balls is 0.25mm-0.35mm; Feature 4: The ball-to-material ratio in the grinding process is (7-10):1; Feature 5: The temperature during the grinding process is ≤40℃.

7. The method according to claim 5, characterized in that, The mass concentration of the dispersant is 0.3wt%-0.7wt%; And / or, the dispersant is selected from at least one of sodium dodecylbenzenesulfonate, ammonium polyacrylate, and polyvinylpyrrolidone.

8. The method according to claim 1, characterized in that, The pretreatment of raw materials includes centrifugal dehydration, drying and sieving. The raw material is wire cutting sludge, which includes 40wt%-60wt% SiC, 15wt%-25wt% silicon powder, 5wt%-10wt% metal impurities and 20wt%-30wt% cutting fluid. The centrifugal dehydration process includes dehydrating the raw material at a speed of 2800 rpm-3500 rpm until the filter cake moisture content is ≤30%, thus obtaining a filter cake. The filter cake is subjected to a first drying treatment at a temperature of 110℃-130℃ for 3.5h-4.5h to obtain a first dried product. The first dried product is sieved under conditions of amplitude of 2mm-3mm and sieve mesh of 180-200 mesh to obtain pretreated raw material.

9. The method according to claim 1, characterized in that, The post-processing includes: subjecting the sieved product after pulverization to a second drying process under conditions of an inlet temperature of 200℃-240℃, an outlet temperature of 85℃-95℃, and an atomization pressure of 0.25MPa-0.4MPa, to obtain a second dried product. And / or, the second dried product is packaged under a vacuum of ≤-0.1MPa and an inert atmosphere.

10. A silicon carbide powder, characterized in that, It is prepared by the method described in any one of claims 1-9.

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