Method for efficient and high-value utilization of waste quartz crucible

Abstract

The application discloses a kind of high-efficiency high-value utilization methods of waste quartz crucible, belong to the secondary resource efficient utilization and high-value spherical silicon powder preparation technical field.The method is with waste quartz crucible as raw material using closed circuit crushing process respectively to be coarsely crushed to 20~50mm, medium crushing to 5~15mm and fine grinding to <3mm, then after pickling impurity removal, ultrafine grinding classification and high-temperature spheroidization, obtain the purity of 4N grade above submicron spherical silicon powder;The waste quartz crucible has the composite structure of brittle crystallization layer and ductile body.Based on the physicochemical properties of waste quartz crucible, through whole-process collaborative control, realize the advantages of low energy consumption, less impurities introduction in crushing and fine grinding process, mild conditions, less pollution in pickling impurity removal process, fine particle size, narrow interval in ultrafine grinding classification process, fast feeding, high spheroidization rate and other advantages in spheroidization process.

Description

Technical Field

[0001] This invention relates to a method for the efficient and high-value utilization of waste quartz crucibles, belonging to the technical field of efficient utilization of secondary resources and preparation of high-value spherical silicon micropowder. Background Technology

[0002] Quartz crucibles are a core consumable in the crystalline silicon pulling process. Due to their high purity, high temperature resistance, and low coefficient of thermal expansion, they are widely used in photovoltaic silicon wafer and semiconductor wafer manufacturing, with global annual consumption exceeding 500,000 tons. However, during the growth of single-crystal silicon, the inner wall of the quartz crucible becomes unusable due to high-temperature erosion, metal impurity penetration, and lattice distortion, thus becoming waste crucibles. Currently, these waste crucibles are mostly simply crushed and used to prepare refractory materials and low-end glass products, resulting in a waste of high-value silica resources.

[0003] High-purity spherical silicon micropowders at the micron and submicron levels are widely used in integrated circuit packaging, 5G substrate filling, and other fields due to their unique physicochemical properties, and are regarded as key materials for the next generation. However, their industrialization process is constrained by the multi-step precision control requirements of the synthesis process and the marginal cost dilemma: taking the gas-phase oxidation method using precursors such as silane / silicon tetrachloride as an example, nucleation-growth kinetics need to be controlled in a high-temperature flame or specific temperature field environment. This process not only requires the purity of raw materials to be ≥99.999% and the pressure fluctuation of the reactor to be controlled within ±5Pa, but also requires particle size classification through multi-stage cyclone separation and other processes, resulting in problems such as large equipment investment and high unit energy consumption.

[0004] In recent years, the technology of preparing high-purity spherical silica powder by high-temperature spheroidization of natural high-purity quartz sand has gradually attracted attention. However, this process has a high proportion of raw material costs, complex purification processes, and the over-exploitation of natural quartz has led to resource depletion and ecological controversies. Summary of the Invention

[0005] To address the problems of large quantities of waste quartz crucibles, low utilization levels, and high dependence on natural quartz resources in the preparation of high-purity spherical silicon micropowder, the present invention aims to provide a method for the efficient and high-value utilization of waste quartz crucibles. Based on the special physicochemical properties of waste quartz crucibles, this method achieves efficient and high-value utilization of waste quartz crucibles through coordinated control of the entire process. It also has the advantages of simple production process, uniform particle size, high purity, and high sphericity of the product.

[0006] To achieve the above-mentioned technical objectives, this invention provides a method for the efficient and high-value utilization of waste quartz crucibles. The method uses waste quartz crucibles as raw materials and employs a closed-circuit crushing and grinding process to coarsely crush to 20-50 mm, medium crush to 5-15 mm, and finely grind to <3 mm. After acid washing to remove impurities, ultrafine grinding and classification, and high-temperature spheroidization, submicron-sized spherical silicon micropowder with a purity of 4N or higher is obtained. The waste quartz crucible has a composite structure of a brittle crystallization layer and a tough body.

[0007] This invention achieves its technical solution through the synergistic effect of low-energy crushing, targeted impurity removal, efficient ultrafine grinding, and spheroidization of waste crucibles. The efficient design of the closed-circuit crushing and grinding process is key to achieving energy saving and consumption reduction. Based on the physicochemical properties of quartz crucibles and combined with the technological foundation of mainstream crushing and grinding equipment, this invention achieves low-energy crushing through a two-crushing-one-grinding process. Furthermore, the crushing and fine grinding process exposes the impurity components inside the waste quartz crucibles, creating favorable conditions for subsequent acid leaching for impurity removal. According to the basic physicochemical properties of quartz crucibles, the internal impurities are mainly Al, Na, K, and Fe, along with metallic impurities introduced during the crushing and fine grinding process. Based on previous research, this invention rationally configures parameters such as acid type, concentration, temperature, and time to achieve efficient impurity removal. To avoid introducing impurity components during the ultrafine grinding process, silicon-based wear-resistant components are used as the grinding media, or a silicon-based wear-resistant layer is coated on the inner wall of the equipment. Finally, the spheroidization process, based on the micro-particle size and chemical characteristics, rationally configures the spheroidization process parameters to achieve a highly efficient synergy in output, spheroidization rate, and spheroidization degree.

[0008] In this invention, the brittle crystallization layer refers to the silicon dioxide crystallization layer.

[0009] In this invention, waste quartz crucibles, after high-temperature use, form a composite structure with a brittle crystalline layer and a tough bulk. Direct fine grinding can easily lead to asynchronous crushing of the two phases: the crystalline layer prematurely pulverizes while the bulk still contains coarse particles, requiring repeated material recycling, resulting in a surge in circulating load and energy consumption, and increasing metal contamination during the crushing and fine grinding process. The technical solution of this invention, however, employs a closed-circuit crushing process with staged crushing of waste quartz crucibles, effectively resolving the contradiction between the mechanical properties of quartz materials, balanced particle size control, and energy efficiency. Specifically, this invention uses staged closed-circuit crushing to progressively reduce the crushing ratio, ensuring that the crushing force at each stage precisely targets the target particle size range: coarse crushing uses jaw crushers and other high-efficiency methods to handle large pieces, avoiding over-crushing; medium crushing uses cone crushers and other methods to prioritize the crushing of the crystalline layer through layered crushing, reducing angular particles generated by excessive crushing of the bulk; the fine grinding stage uses rod mills and other methods with line contact grinding instead of the point contact impact of ball mills, achieving uniform refinement of materials <3mm at low speeds while keeping Fe contamination at a low level. Vibrating screens at each stage allow substandard coarse particles to be returned to the next stage for further crushing, ultimately improving product qualification rate, reducing overall power consumption per ton, and ensuring concentrated particle size distribution, providing ideal raw materials for subsequent pickling and spheroidization. This process chain essentially achieves dynamic adaptation between energy input and material crushing state through fractal crushing, avoiding the shortcomings of the crude grinding model and laying a foundation for high-value utilization with low-impurity, narrow-distribution powders.

[0010] As a preferred embodiment, the waste quartz crucibles include defective products from the quartz crucible production process and / or quartz crucibles that have reached the end of their service life, wherein the SiO2 content is ≥99.5wt%.

[0011] As a preferred embodiment, the impurities removed by the acid rinsing include impurities on the surface of the crucible fine powder and internal lattice impurities.

[0012] As a preferred embodiment, the acid washing and impurity removal conditions are as follows: a mixed acid of hydrofluoric acid and at least one of hydrochloric acid, nitric acid, and sulfuric acid is used, the total volume concentration of the mixed acid is 10-40%, the acid washing temperature is 20-65℃, the time is 0.5-2h, and the mass ratio of crucible fine powder to mixed acid is (0.5-2.5):1. The impurity components of the waste quartz crucible micropowder mainly consist of metal components introduced during the crushing and grinding process and residual Al, Ca, and other components from the raw materials used in the preparation of the quartz crucible. The former mainly adheres to the surface of the micropowder or in the pores of the particles; its particles are small and easily dissolved by acid, and can be removed by acid washing with hydrochloric acid, nitric acid, sulfuric acid, etc. However, lattice impurities have a stable chemical interaction with the quartz crystal; hydrochloric acid, nitric acid, and sulfuric acid are difficult to break these chemical bonds, while hydrofluoric acid can break the silicon-oxygen bonds, thereby achieving the removal of lattice impurities. When the volume concentration of the mixed acid is below 10%, the complexation and dissolution rate of Al decreases significantly; while a volume concentration exceeding 40% leads to an exponential increase in the risk of acid mist emission and a sharp increase in the requirements for equipment corrosion resistance. Hydrofluoric acid has strong dissolving power, and its large dosage helps to dissolve and remove impurities, but it also leads to the dissolution of a large amount of silicon, causing material loss on the one hand, and the gel-like products generated by dissolution on the other hand, affecting subsequent acid removal. In the acid washing process of this invention, the surface adsorbed impurities are mainly removed below 40°C, while impurities dissolved in the lattice can be effectively decomposed above 40°C; when the solid-liquid ratio is too high, particle accumulation leads to obstruction of acid penetration, resulting in a high amount of impurities remaining in the central area of ​​the material; while too low a ratio results in acid waste. Under the acid washing and impurity removal parameters set in this invention, the purity of silicon micropowder can reach 99.99% (4N grade) within 2 hours, laying the foundation for the subsequent high-temperature spherical preparation of submicron-sized spherical silicon micropowder.

[0013] Furthermore, if the volume concentration of hydrofluoric acid in the mixed acid is greater than or equal to 5%, and its concentration is too low, its ability to remove lattice impurities is limited, resulting in the product's impurity content exceeding the standard.

[0014] As a preferred embodiment, the ultrafine grinding and classification employs at least one of high-energy ball milling, nano-grinding, and air jet milling to grind the acid-washed and impurity-removed crucible powder to a particle size ≤5μm. Ultrafine grinding is crucial for obtaining submicron-sized silicon micropowder. To achieve high efficiency and low consumption in this process, and to obtain easily spheroidized micropowder, the waste quartz crucible powder contains lattice distortion zones and microcracks caused by high-temperature use. Conventional grinding processes easily lead to irregular fractures along these defects, forming sharp-edged, flaky particles. This morphology can easily cause incomplete melting or local sintering and agglomeration during the subsequent high-temperature spheroidization stage. Therefore, effective methods must be used to control the particle size and morphology of the crucible powder. This invention uses high-energy ball milling, which can uniformly refine particles and reduce surface roughness through the synergistic effect of shear force and impact force. Its advantages include large throughput and simultaneous particle surface activation, making it particularly suitable for subsequent applications requiring high tap density. Nano-grinding, on the other hand, mainly uses gentle frictional cleavage, using the microfluidic field generated by the high-speed movement of the medium to peel away particles and homogenize their internal stress distribution. Air jet milling, utilizing the self-sharpening pulverization mechanism generated by high-speed airflow collisions, can produce near-spherical particles without media contact. Its eddy current classification system can precisely remove coarse particles. Furthermore, the micropowders obtained by the above three processes not only have uniform particle size but also an aspect ratio of less than 2, creating favorable conditions for subsequent spheroidization. High-energy ball milling is further optimized for ultrafine grinding and classification.

[0015] As a preferred approach, the high-temperature spheroidization includes flame and / or plasma methods. While ultrafine milled and graded silicon micropowder possesses a particle size of ≤5μm, its irregular surface edges directly affect the filling performance of the encapsulation material. The flame method utilizes the instantaneous high temperature generated by a high-speed turbulent flow field to selectively melt the particle surface. The surface tension-dominated morphology reconstruction results in a sphericity >0.98, while the short contact time effectively suppresses the transformation of silica to the cristobalite phase. The plasma method, with its high jet velocity and ultra-high temperature, achieves full-domain melting of the particles. Its containerless contact characteristic eliminates metal contamination, making it particularly suitable for the preparation of semiconductor-grade silicon micropowder.

[0016] As a preferred embodiment, the high-temperature spheroidization temperature is ≥1500℃, and the spheroidization time is 0.1~2 min. Since the effective surface melting required for spheroidization necessitates overcoming the lattice energy barrier, when the temperature is ≥1500℃, the atomic mobility on the particle surface increases. At this point, surface tension can dominate morphological reconstruction, causing a rapid decrease in the sharpness index of the edges. The 0.1~2 min time window closely matches the critical equilibrium of quartz micropowder melting-solidification: when the time is <0.1 min, only a nanometer-thick molten layer forms on the surface of the particles, failing to completely eliminate grain boundary stress; while when the time is >2 min, excessive melt diffusion occurs, not only reducing production efficiency but also causing deformation during the droplet solidification process.

[0017] As a preferred embodiment, the submicron-sized spherical silicon powder has a particle size ≤5μm and a sphericity ≥98%. Through the staged crushing and fine grinding process of this invention, combined with other processes, the prepared silicon powder exhibits high sphericity, high purity, and small, uniform particle size, demonstrating excellent application prospects.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) Based on the special physical and chemical properties and high-temperature softening characteristics of waste quartz crucibles, this invention combines the advantages of staged crushing and fine grinding, ultrafine grinding, chemical impurity removal and high-temperature spheroidizing technology and the synergistic effect between processes, and achieves the advantages of low energy consumption and less impurity introduction in the crushing and fine grinding process, mild conditions and less pollution in the acid washing and impurity removal process, fine particle size and narrow range in the ultrafine grinding and classification process, and fast feeding and high spheroidization rate in the spheroidizing process.

[0020] (2) The product prepared by the method of the present invention can reach a purity of 4N or above, a particle size of submicron, and a sphericity of more than 98%. The product is suitable for high-end fields such as electronic packaging. Moreover, the efficient synergy between the processes of the present invention means that the ultrafine powder does not need to be modified before spheroidization, which reduces the consumption of coupling agent.

[0021] (3) The raw materials of this invention are widely available, which not only realizes the secondary use of waste quartz crucibles, but also expands the range of high-quality spherical silicon micro powder raw materials, which helps to realize the sustainable development of high-quality silicon resources.

[0022] (4) The process equipment used in this invention is highly mature, with diverse equipment options, which can meet the production needs of different regions and different target products. It is highly operable and has the potential for large-scale industrial application. Attached Figure Description

[0023] Figure 1 The morphology of the high-purity spherical silicon micropowder product prepared by the preparation method of the present invention is shown. Detailed Implementation

[0024] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0025] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0026] Unless otherwise specified, all reagents and raw materials used in this invention are commercially available products or products that can be prepared by known methods.

[0027] In the embodiments and comparative examples of this invention, a jaw crusher is used for coarse crushing, a cone crusher for medium crushing, and a rod mill for fine grinding. Each stage is equipped with a vibrating screen to return substandard coarse particles to the next stage for further crushing. All waste quartz crucibles used are quartz crucibles that have reached the end of their service life, containing 99.5 wt% SiO2 and exhibiting a composite structure of a brittle crystalline layer and a tough body. The brittle crystalline layer refers to a silicon dioxide crystalline layer.

[0028] Example 1

[0029] Waste quartz crucibles were coarsely crushed, medium crushed, and finely ground using a closed-circuit crushing and grinding process to obtain crucible powder with particle sizes of 20-50 mm, 5-15 mm, and <3 mm, respectively, while controlling the Fe content to <120 ppm and the Al content to <100 ppm, resulting in fine crucible powder. The obtained fine crucible powder was mixed with acid, specifically a mixture of hydrofluoric acid and hydrochloric acid, with volume concentrations of 5% and 25%, respectively. The acid washing temperature was 40℃ for 1 hour, and the mass ratio of the fine crucible powder to the acid solution was 0.5:1. After deacidification and drying, the powder was ultra-finely ground to ≤5 μm using a high-energy ball mill. Subsequently, it was plasma spheroidized at 9000 K for 0.1 min. Product testing results showed that the product had a SiO2 content of 99.993 wt%, a sphericity of 99%, an Fe content of 11 ppm, and an Al content of 23 ppm.

[0030] Example 2

[0031] Waste quartz crucibles were coarsely crushed, medium crushed, and finely ground using a closed-circuit crushing and grinding process to achieve crucible powder particle sizes of 20-50 mm, 5-15 mm, and <3 mm, respectively, while controlling the Fe content to <100 ppm and the Al content to <100 ppm. The resulting crucible powder was mixed with an acid mixture of hydrofluoric acid and sulfuric acid, with volume concentrations of 5% and 5%, respectively. The acid washing temperature was 65℃ for 2 hours, and the mass ratio of crucible powder to acid solution was 1:1. After deacidification and drying, the powder was ultra-finely ground to ≤5 μm using a high-energy ball mill. Subsequently, it was flame-spheroidized at 1700℃ for 1 minute. Product testing results showed that the product had a SiO2 content of 99.992 wt%, a sphericity of 99%, an Fe content of 17 ppm, and an Al content of 30 ppm.

[0032] Example 3

[0033] Waste quartz crucibles were coarsely crushed, medium crushed, and finely ground using a closed-circuit crushing and grinding process to obtain crucible powder with particle sizes of 20-50 mm, 5-15 mm, and <3 mm, respectively, while controlling the Fe content to <100 ppm and the Al content to <100 ppm, thus obtaining fine crucible powder. The obtained fine crucible powder was mixed with acid, specifically a mixture of hydrofluoric acid, hydrochloric acid, and sulfuric acid, with volume concentrations of 5%, 8%, and 3%, respectively. The acid washing temperature was 30℃ for 1.5 h, and the mass ratio of fine crucible powder to acid solution was 1.5:1. After deacidification and drying, the powder was ultra-finely ground to ≤5 μm using a high-energy ball mill, followed by flame spheroidization at 1500℃ for 1.5 min. Product testing results showed that the product had a SiO2 content of 99.991 wt%, a sphericity of 98%, an Fe content of 9 ppm, and an Al content of 28 ppm.

[0034] Example 4

[0035] Waste quartz crucibles were coarsely crushed, medium crushed, and finely ground using a closed-circuit crushing and grinding process to obtain crucible powder with particle sizes of 20-50 mm, 5-15 mm, and <3 mm, respectively, while controlling the Fe content to <110 ppm and the Al content to <100 ppm, resulting in fine crucible powder. The obtained fine crucible powder was mixed with acid, specifically a mixture of hydrofluoric acid, hydrochloric acid, and sulfuric acid, with volume concentrations of 5%, 8%, and 3%, respectively. The acid washing temperature was 20℃ for 1.5 h, and the mass ratio of fine crucible powder to acid solution was 2.5:1. After deacidification and drying, the powder was ultra-finely ground to ≤5 μm using a high-energy ball mill, followed by flame spheroidization at 1500℃ for 2 min. Product testing results showed that the product had a SiO2 content of 99.991 wt%, a sphericity of 98%, an Fe content of 15 ppm, and an Al content of 31 ppm.

[0036] Example 5

[0037] Waste quartz crucibles were coarsely crushed, medium crushed, and finely ground using a closed-circuit crushing and grinding process to obtain crucible powder with particle sizes of 20-50 mm, 5-15 mm, and <3 mm, respectively, while controlling the Fe content to <110 ppm and the Al content to <110 ppm, thus obtaining fine crucible powder. The obtained fine crucible powder was mixed with acid, specifically a mixture of hydrofluoric acid and hydrochloric acid, with volume concentrations of 10% and 8%, respectively. The acid washing temperature was 50℃ for 0.5 h, and the mass ratio of the fine crucible powder to the acid solution was 1:1. After deacidification and drying, the powder was ultra-finely ground to ≤5 μm using a high-energy ball mill. Subsequently, it was plasma spheroidized at a temperature of 10000 K for a high-temperature residence time of 0.5 min. Product testing results showed that the product had a SiO2 content of 99.994 wt%, a sphericity of 99.5%, an Fe content of 11 ppm, and an Al content of 18 ppm.

[0038] Example 6

[0039] The only difference compared to Example 1 is that the high-temperature dwell time is 3 seconds.

[0040] The final product has a SiO2 content of 99.992% and a sphericity of 87%.

[0041] Example 7

[0042] The only difference compared to Example 4 is that the temperature is 1350°C.

[0043] The final product has a SiO2 content of 99.99% and a sphericity of 76%.

[0044] Comparative Example 1

[0045] The only difference compared to Example 2 is that hydrofluoric acid was not used.

[0046] The final product has a SiO2 content of 99.92% and a sphericity of 98%.

[0047] Comparative Example 2

[0048] The only difference between this comparative example and Example 1 is that a closed-circuit crushing and grinding process was used to coarsely crush, medium crush, and finely grind the powder to crucible particles of 50-80 mm, 15-25 mm, and < 5 mm, respectively. All other steps and conditions were the same.

[0049] The final product has a SiO2 content of 99.95% and a sphericity of 94%.

[0050] Comparative Example 3

[0051] The only difference between this comparative example and Example 3 is that the closed-circuit crushing process only performs coarse crushing to a particle size of 20~50mm, without medium crushing and fine grinding; the other steps and conditions are the same.

[0052] The final product has a SiO2 content of 99.97 wt% and a sphericity of 73%.

[0053] Comparative Example 4

[0054] The only difference between this comparative example and Example 1 is that ultrafine grinding and classification are not performed; all other steps and conditions are the same.

[0055] The final product has a SiO2 content of 99.982 wt% and a sphericity of 68%.

Claims

1. A method for efficient and high-value utilization of waste quartz crucible, characterized by comprising the following steps: The waste quartz crucible is used as raw material to adopt closed-circuit crushing process to be coarsely crushed to 20-50 mm, to be medium crushed to 5-15 mm and to be finely ground to be less than 3 mm, then to be cleaned by acid, to be finely ground by superfine grinding and to be spheroidized at high temperature, so as to obtain sub-micron spherical silicon powder with purity of 4N or above; ​ The waste quartz crucible has a composite structure of brittle crystallization layer and ductile body; The superfine grinding adopts at least one of high-energy ball milling, nano grinding and jet mill to finely grind the crucible fine powder after cleaning by acid to a particle size of less than or equal to 5 microns; The spheroidization at high temperature is at a temperature of more than or equal to 1500 degrees Celsius for a time of 0.1-2 minutes.

2. The method according to claim 1, wherein the method is characterized by: The waste quartz crucible includes defective products in the production process of quartz crucible and / or quartz crucible reaching the service life and being scrapped, wherein the purity of SiO2 is more than or equal to 99.5wt%.

3. The method according to claim 1 or 2, characterized in that: The impurities removed by cleaning by acid include impurities on the surface of the crucible fine powder and lattice impurities in the interior.

4. The method according to claim 3, wherein the method is characterized by: The cleaning by acid adopts a mixed acid of hydrofluoric acid and at least one of hydrochloric acid, nitric acid and sulfuric acid, the total volume concentration of the mixed acid is 10-40%, the acid cleaning temperature is 20-65 degrees Celsius, the time is 0.5-2 hours, and the mass ratio of the crucible fine powder to the mixed acid is (0.5-2.5):

1.

5. The method according to claim 1 or 4, characterized in that: The superfine grinding adopts a silicon-based wear-resistant component as a grinding medium or coats a silicon-based wear-resistant material on the inner wall of the equipment.

6. The method according to claim 5, wherein the method is characterized by: The spheroidization at high temperature includes flame method and / or plasma method.

7. The method according to claim 2, 4 or 6, characterized in that: The sub-micron spherical silicon powder has a particle size of less than or equal to 5 microns and a sphericity of more than or equal to 98%.

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