A method for preparing high-purity quartz sand based on low-temperature solvent freezing

Abstract

This invention belongs to the field of quartz sand preparation technology and discloses a method for preparing high-purity quartz sand based on low-temperature solvent freezing. The preparation method provided by this invention uses silicic acid as a raw material, adding silicic acid sol to accelerate gelation. The 10-20 nm silicic acid particles formed in the silicic acid sol act as "seeds" and are mixed with the silicic acid, shortening the gelation time from the traditional 12-24 hours to 1-3 hours, and improving the uniformity of gel particle size by 50%. This invention, with low-temperature solvent freezing control as its core, integrates a rotating quartz tube furnace for integrated processing and a high-temperature calcination method using a vacuum alumina ceramic inner furnace for high-purity quartz sand preparation. This yields quartz sand with a purity ≥99.9999%, sphericity ≥0.88, particle size distribution CV ≤5%, hydroxyl content ≤20 ppm, and total metallic impurity content ≤1 ppm. It is suitable for fields with stringent requirements regarding quartz sand purity, morphology, particle size uniformity, hydroxyl content, and impurity content.

Description

Technical Field

[0001] This invention belongs to the field of quartz sand preparation technology, and relates to a method for preparing high-purity quartz sand based on low-temperature solvent freezing. Background Technology

[0002] High-purity quartz sand is quartz sand with SiO2 purity ≥ 99.995% (4N5 grade) and Fe2O3 ≤ 0.001%. It has the characteristics of low thermal expansion coefficient, high temperature resistance (melting point about 1750℃), and high insulation (resistivity > 10). 16 With its high strength (Ω·cm), high hardness (Mohs 7), and resistance to strong acid and alkali corrosion, as well as light transmittance >92% and refractive index of 1.54~1.55, it is a key material for manufacturing optical devices and is widely used in high-tech fields such as semiconductors, photovoltaics, optical fiber communication, and aerospace.

[0003] Currently, high-purity quartz sand on the market is mainly obtained through natural mineral purification methods. However, high-purity natural quartz deposits rely on imports, and domestic resources lack 4N5 grade or higher mineral sources, resulting in high costs. Furthermore, gas-liquid inclusions in natural ores are difficult to completely remove in conventional processes, affecting the purity of the quartz sand. Chemical synthesis of quartz sand is also a major technical approach. For example, based on liquid-phase synthesis, sodium silicate reacts with acid to generate a precipitate, which is then washed, dried, and calcined to obtain quartz sand. However, this preparation process suffers from problems such as easy agglomeration and limited purity of the finished product (usually <4N).

[0004] Meanwhile, existing processes for preparing quartz sand also suffer from large coefficients of variation (CV) in particle size distribution and low sphericity, making it difficult to meet the extremely high requirements for particle morphology and distribution consistency in high-end packaging, precision casting, and other applications. The CV of quartz sand prepared by existing processes is generally between 10% and 30%. Since inclusions in natural quartz ore and the uniformity of the quartz ore's crystal structure directly affect the particle size distribution of quartz sand, airflow classification technology can significantly reduce the CV to around 15%, but this requires significant equipment investment. Quartz sand prepared by this process is mostly irregularly angular, with a sphericity generally between 0.6 and 0.7. Even with ball milling, this can only be improved to approximately 0.8.

[0005] Therefore, it is of great significance to explore a method for preparing high-purity quartz sand and solve the problems of easy agglomeration, difficulty in removing inclusions and impurities, uneven particle size distribution, and low sphericity in existing processes. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for preparing high-purity quartz sand based on a low-temperature solvent freezing method. The method uses ultra-high-purity silica as a raw material, adding silica sol to accelerate gelation. The 10-20 nm silica particles formed in the silica sol act as "seed crystals" and are mixed with the ultra-high-purity silica, shortening the gelation time from the traditional 12-24 hours to 1-3 hours, and improving the uniformity of gel particle size by 50%. This invention, with low-temperature solvent freezing control as its core, integrates a rotating quartz tube furnace for processing with a high-temperature static calcination process in a vacuum alumina ceramic-lined furnace, resulting in high-purity quartz sand with a purity ≥99.9999%, sphericity ≥0.88, particle size distribution CV ≤5%, hydroxyl content ≤20 ppm, and total metallic impurity content ≤1 ppm. This method is suitable for fields with stringent requirements regarding purity, morphology, particle size uniformity, hydroxyl content, and impurity content.

[0007] On the one hand, the present invention provides a method for preparing high-purity quartz sand based on low-temperature solvent freezing, specifically including the following steps:

[0008] S1: Preparation of silica sol: Dissolve silica with a purity ≥ 99.9999% in ultrapure water to prepare a 0.3~0.8wt% silica solution; transfer the silica solution into a 99.99% quartz stirring vessel, stir at 1000~1500 rpm, add 0.5~2mol / L electronic grade hydrochloric acid dropwise at a rate of 1~3mL / min, adjust the pH to 1.5~2.5, and continue stirring for 30~60min to obtain a uniformly dispersed silica sol.

[0009] S2: Gel preparation: Take silicic acid with a water content of 90~95wt%, mix it with the silicic acid sol of S1 at a volume ratio of 10:1~3, place it in a 99.99% quartz reactor, and stir it at 25~40℃ and 500~800rpm for 1~3h to form a uniform block gel with a water content of 85~90wt%.

[0010] S3: Gel crushing and centrifugal dehydration: The blocky gel is crushed into particles of 0.5~2mm using a 99.99% quartz crusher. The particles are then transferred into a polytetrafluoroethylene centrifuge bag and centrifuged at 8000~10000rpm for 10~15min to remove free water and obtain gel particles with a water content of 70~75wt%.

[0011] S4: Low-temperature solvent freezing treatment: Add the gel particles to a low-temperature solvent pre-cooled to -5 to -30°C at a solid-liquid ratio of 1:8~12 (g:mL). Stir at 400~600 rpm for 20~120 min at a constant temperature of -5~-30°C, maintaining temperature fluctuations ≤±2°C. The low-temperature solvent is one of methanol, n-hexane, or cyclohexane, and the viscosity of the solvent at -5~-30°C is 0.8~1.8 mPa·s.

[0012] S5: Filtration, washing and thawing: Frozen particles are separated by filtration using a 0.1μm quartz fiber filter membrane, washed 3-5 times with ultrapure water at 0-10℃, and centrifuged at 8000rpm for 5-8min after each wash; after washing, the particles are slowly thawed at 25℃ for 3-4h to obtain wet silica particles.

[0013] S6: Integrated Drying-Calcination in Rotary Quartz Tube Furnace: Wet particles are transferred into a rotating quartz tube furnace (inner wall roughness Ra≤0.1μm). The furnace temperature is controlled at 120~180℃, and the rotation speed at 15~20rpm. Drying is performed for 30min to remove surface adsorbed water and residual solvent, yielding dry particles with a moisture content ≤1%. While maintaining rotation, oxygen with a purity ≥99.999% is introduced at a flow rate of 30~50mL / min. The temperature is increased to 400℃ at 5℃ / min and held for 2h, then increased to 600℃ and held for 3h, and finally increased to 800℃ and held for 2h to complete gradient calcination. This removes carbon impurities and some low-boiling-point inclusions. After removal, the carbon impurity content of the particles is ≤0.001wt%, and the low-boiling-point inclusion content is ≤0.5vol.

[0014] S7: Static calcination in a vacuum alumina ceramic-lined high-temperature furnace: The calcined particles are transferred into a vacuum alumina ceramic-lined high-temperature furnace (the inner furnace material is 99.9% high-purity alumina ceramic). After closing the furnace door, a vacuum is drawn to ≤10. -4 Pa (preferably ≤5×10) -5 (Pa), heat to 1000~1300℃ at 2℃ / min, hold statically for 4~6h, during which argon gas with a purity ≥99.999% is introduced at a flow rate of 20~30mL / min (20mL / min at 1000℃ and 30mL / min at 1300℃) to remove hydroxyl groups and remaining inclusions, thus obtaining dense silica particles.

[0015] S8: Grading process: The dense silica particles of S7 are lightly crushed using a 99.99% quartz double roller mill with a roller gap of 300μm, a roller speed of 100~200r / min, and a roller pressure of 50~200MPa; then classified by an air classifier with an air velocity of 20~25m / s and a classifier wheel speed of 4000~5000rpm. Particles with a particle size distribution CV≤5% are collected to obtain high-purity quartz sand.

[0016] The high-purity quartz sand prepared by the method of this invention has a purity ≥99.9999%, sphericity ≥0.88, particle size distribution CV ≤5%, hydroxyl content ≤20ppm, inclusion content ≤0.1vol%, and tap density ≥1.70g / cm³. 3 Bulk density ≥ 1.45 g / cm³ 3The total content of metallic impurities is ≤1ppm (Fe, Al, and Na are each ≤0.3ppm).

[0017] On the other hand, this invention claims protection for a high-purity quartz sand prepared by the above-described method. The high-purity quartz sand has a purity ≥99.9999%, sphericity ≥0.88, particle size distribution (CV) ≤5%, hydroxyl content ≤20ppm, and total metallic impurity content ≤1ppm.

[0018] The high-purity quartz sand prepared by the method of this invention has good application prospects in high-end fields with strict requirements for purity, morphology and hydroxyl content, such as quartz crucibles for semiconductor chip manufacturing, high-end optical lens substrates or quartz components for radio frequency plasma etching equipment.

[0019] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages:

[0020] (1) This invention provides a method for preparing high-purity quartz sand based on low-temperature solvent freezing. Using ultra-high purity silicic acid with a purity ≥99.9999% and a water content of 90-95% as raw material, silicic acid sol is added to accelerate gelation. In this invention, a 0.3-0.8 wt% silicic acid solution is adjusted to pH 1.5-2.5 with hydrochloric acid, forming 10-20 nm nano-sized silicic acid particles in the silicic acid sol. These particles are then mixed with the ultra-high purity silicic acid as "seed crystals," shortening the gelation time from the traditional 12-24 h to 1-3 h, and improving the uniformity of gel particle size by 50%. This invention controls the drop rate of the hydrochloric acid solution to 1-3 mL / min to avoid rapid polymerization of silicic acid molecules caused by a sudden drop in local pH, preventing gel agglomeration, thereby reducing the content of impurities and inclusions in the quartz sand and improving the purity and bulk density of the quartz sand.

[0021] (2) The present invention uses a low-temperature solvent freezing method to prepare quartz sand and control the particle morphology. Methanol, n-hexane, and cyclohexane are used as low-temperature solvents. The viscosity of the low-temperature solvent is 0.8~1.8 mPa·s at a temperature of -5~-30℃. The viscosity of the traditional solvent ethanol is 1.5~2.0 mPa·s in the temperature range of -5~-30℃. The low-temperature solvent selected in the present invention has a lower viscosity, which can fully penetrate the gaps between gel particles, destroy the hydrogen bonds between particles, and inhibit agglomeration. The surface tension of cyclohexane is 21~23 mN / m, which can guide the particles to spontaneously form a spherical structure during stirring, improve the sphericity of quartz sand. The sphericity of the quartz sand prepared by the present invention is ≥0.88, which can reduce mechanical wear during use, reduce material porosity, improve material density, and extend service life. This invention controls the freezing temperature to -5 to -30°C and the freezing time to 20 to 120 minutes, providing a slow freezing environment to avoid rapid freezing forming large ice crystals that damage the particle morphology. The particle size can be controlled by adjusting the stirring time. A freezing time of 20 minutes can prepare quartz sand with a particle size of 5 to 8 μm, while a freezing time of 120 minutes can prepare quartz sand with a particle size of 10 to 15 μm, meeting the needs of different application scenarios.

[0022] (3) The present invention adopts a rotating quartz tube furnace to integrate drying and calcination to ensure the purity of quartz sand. Drying is carried out at 120~180℃ and 15-20rpm to ensure uniform heating of particles. The moisture content can be reduced to ≤1% within 30min. A gradient calcination scheme is provided, which removes residual solvent at 400℃, oxidizes carbon impurities at 600℃, and decomposes low-boiling-point inclusions at 800℃. Oxygen is introduced while maintaining rotation, and the oxygen flow rate is 30~50mL / min to ensure sufficient oxidation. The carbon impurity content is reduced from 0.005wt% to below 0.001wt%. The integrated process provided by the present invention does not transfer materials during drying and calcination. Compared with the traditional process that requires material transfer between the drying box and the tube furnace, the risk of impurity contamination is reduced by 60%. The present invention also polishes the inner wall of the quartz tube to Ra≤0.1μm, which can reduce particle adhesion and avoid morphological damage.

[0023] (4) The present invention uses a vacuum alumina ceramic inner high-temperature furnace for static calcination to achieve deep removal of impurities and morphology protection. The inner chamber of the high-temperature furnace is made of 99.9% high-purity alumina ceramic, which is resistant to high temperature (≥1600℃) and has no metal ion leaching, thus solving the pollution problem of traditional metal inner furnaces. During the static calcination process, the particles do not collide or shift, ensuring that the spherical morphology formed in the early stage is not destroyed and the sphericity is maintained at ≥0.88.

[0024] (5) The quartz sand prepared by this invention has a purity ≥99.9999%, sphericity ≥0.88, particle size distribution CV ≤5%, hydroxyl content ≤20ppm, inclusion content ≤0.1vol%, and tap density ≥2.20g / cm³. 3Bulk density ≥ 1.45 g / cm³ 3 The total content of metallic impurities is ≤1ppm (Fe, Al, and Na are each ≤0.3ppm), which solves the problems of particle agglomeration, impurity contamination, equipment compatibility, and low sphericity in traditional processes. It is suitable for fields with strict requirements for purity, morphology, and hydroxyl content, such as semiconductor chip manufacturing and high-end optical lenses. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 These are scanning electron microscope (SEM) and optical microscope (OEM) images of high-purity quartz sand. Figure 1 In the image, A represents a scanning electron microscope (SEM) image of high-purity quartz sand. Figure 1 B in the image is an optical microscope image of high-purity quartz sand. Detailed Implementation

[0027] The technical solution of the present invention will be described below with reference to embodiments. However, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental methods and detection methods described in each embodiment are conventional methods; unless otherwise specified, the reagents and materials can be purchased commercially. Unless otherwise specified, the percentages in the following embodiments refer to mass percentages.

[0028] Ultrapure water resistivity ≥18.2 MΩ·cm; silicic acid purchased from Xi'an Lanqiao New Energy Technology Co., Ltd., purity ≥99.9999%; methanol purchased from Sinopharm Chemical Reagent Co., Ltd., purity ≥99.999%; n-hexane purchased from Sinopharm Chemical Reagent Co., Ltd., purity ≥99.99%; cyclohexane purchased from Sinopharm Chemical Reagent Co., Ltd., purity ≥99.99%.

[0029] The mixing tank, reactor, and crusher are all made of 99.99% quartz or polytetrafluoroethylene, with quartz being the preferred material. The quartz mixing tank, reactor, crusher, and roller mill were all purchased from Wuxi Noah Machinery Co., Ltd.

[0030] The quartz fiber filter membrane was purchased from Tianjin Kuaci New Materials Technology Co., Ltd.

[0031] The rotating quartz tube furnace and the vacuum alumina ceramic-lined high-temperature furnace were both purchased from Luoyang Juxing Kiln Co., Ltd.

[0032] This invention relates to a method for preparing high-purity quartz sand based on a low-temperature solvent freezing method. The entire process is carried out in a Class 100 cleanroom and includes the following steps:

[0033] S1: Preparation of silica sol: Dissolve silica with a purity ≥ 99.9999% in ultrapure water to prepare a 0.3~0.8wt% silica solution; transfer the silica solution into a 99.99% quartz stirring vessel, stir at 1000~1500 rpm, add 0.5~2mol / L electronic grade hydrochloric acid dropwise at a rate of 1~3mL / min, adjust the pH to 1.5~2.5, and continue stirring for 30~60min to obtain a uniformly dispersed silica sol.

[0034] S2: Gel preparation: Take silicic acid with a water content of 90~95wt%, mix it with the silicic acid sol of S1 at a volume ratio of 10:1~3, place it in a 99.99% quartz reactor, and stir it at 25~40℃ and 500~800rpm for 1~3h to form a uniform block gel with a water content of 85~90wt%.

[0035] S3: Gel crushing and centrifugal dehydration: The blocky gel is crushed into particles of 0.5~2mm using a 99.99% quartz crusher. The particles are then transferred into a polytetrafluoroethylene centrifuge bag and centrifuged at 8000~10000rpm for 10~15min to remove free water and obtain gel particles with a water content of 70~75wt%.

[0036] S4: Low-temperature solvent freezing treatment: Add the gel particles to a low-temperature solvent pre-cooled to -5 to -30°C at a solid-liquid ratio of 1:8~12 (g:mL). Stir at 400~600 rpm for 20~120 min at a constant temperature of -5~-30°C, maintaining temperature fluctuations ≤±2°C. The low-temperature solvent is one of methanol, n-hexane, or cyclohexane, and the viscosity of the solvent at -5~-30°C is 0.8~1.8 mPa·s.

[0037] S5: Filtration, washing and thawing: Frozen particles are separated by filtration using a 0.1μm quartz fiber filter membrane, washed 3-5 times with ultrapure water at 0-10℃, and centrifuged at 8000rpm for 5-8min after each wash; after washing, the particles are slowly thawed at 25℃ for 3-4h to obtain wet silica particles.

[0038] S6: Integrated Drying-Calcination in Rotary Quartz Tube Furnace: Wet particles are transferred into a rotating quartz tube furnace (inner wall roughness Ra≤0.1μm). The furnace temperature is controlled at 120~180℃, and the rotation speed at 15~20rpm. Drying is performed for 30min to remove surface adsorbed water and residual solvent, yielding dry particles with a moisture content ≤1%. While maintaining rotation, oxygen with a purity ≥99.999% is introduced at a flow rate of 30~50mL / min. The temperature is increased to 400℃ at 5℃ / min and held for 2h, then increased to 600℃ at 5℃ / min and held for 3h, and finally increased to 800℃ at 5℃ / min and held for 2h, completing gradient calcination to remove carbon impurities and some low-boiling-point inclusions. After removal, the carbon impurity content of the particles is ≤10ppm, and the low-boiling-point inclusion content is ≤0.1vol.

[0039] S7: Static calcination in a vacuum alumina ceramic-lined high-temperature furnace: The calcined particles are transferred into a vacuum alumina ceramic-lined high-temperature furnace (the inner furnace material is 99.9% high-purity alumina ceramic). After closing the furnace door, a vacuum is drawn to ≤10. -4 Pa (preferably ≤5×10) -5 (Pa), heat to 1000~1300℃ at 2℃ / min, hold statically for 4~6h, during which argon gas with a purity ≥99.999% is introduced at a flow rate of 20~30mL / min (20mL / min at 1000℃ and 30mL / min at 1300℃) to remove hydroxyl groups and remaining inclusions, thus obtaining dense silica particles.

[0040] S8: Grading Process: The dense silica particles of S7 are lightly pulverized using a 99.99% quartz double-roll mill with a roller gap of 300 μm, a roller speed of 100~200 r / min, and a roller pressure of 50~200 MPa. The particles are then classified using an air classifier with an air velocity of 20~25 m / s and a classifying wheel speed of 4000~5000 rpm. Particles with a particle size distribution (CV) ≤ 5% are collected to obtain high-purity quartz sand (recovery rate ≥ 80%). The high-purity quartz sand prepared by the method of this invention has a purity ≥ 99.9999%, sphericity ≥ 0.88, particle size distribution (CV) ≤ 5%, hydroxyl content ≤ 20 ppm, inclusion content ≤ 0.1 vol%, and tap density ≥ 2.20 g / cm³. 3 Bulk density ≥ 1.45 g / cm³ 3 The total content of metallic impurities is ≤1ppm (Fe, Al, and Na are each ≤0.3ppm).

[0041] Example 1

[0042] This embodiment provides a method for preparing high-purity quartz sand based on low-temperature solvent freezing, specifically including the following steps:

[0043] S1: Dissolve silicic acid in ultrapure water to prepare a 0.3wt% silicic acid solution. Transfer the silicic acid solution into a 99.99% quartz stirring tank and stir at 1200 rpm. Add 2 mol / L electronic grade hydrochloric acid dropwise at a rate of 1 mL / min to adjust the pH to 1.5~2.5. Continue stirring for 60 min to obtain a uniformly dispersed silicic acid sol.

[0044] S2: Take silicic acid with a water content of 90wt%, mix it with the silicic acid sol of S1 at a volume ratio of 10:3, place it in a 99.99% quartz reactor, and stir for 2 hours at 25℃ and 800rpm to form a uniform block gel with a water content of 90wt%.

[0045] S3: Gel crushing and centrifugal dehydration: The blocky gel was crushed into particles of 0.5~2mm using a 99.99% quartz crusher. The particles were then transferred into a polytetrafluoroethylene centrifuge bag and centrifuged at 8000rpm for 15min to remove free water, resulting in gel particles with a water content of 75wt%.

[0046] S4: Low-temperature solvent freezing treatment: Add the gel particles to methanol, a low-temperature solvent pre-cooled to -20℃, at a solid-liquid ratio of 1:8 (g:mL). The viscosity of methanol at -20℃ is 1.2 mPa·s. Stir at 500 rpm for 80 min at a constant temperature of -20℃, maintaining a temperature fluctuation of ≤±2℃.

[0047] S5: Frozen particles are separated by filtration using a 0.1μm quartz fiber filter membrane, washed 3-5 times with ultrapure water at 0-10℃, and centrifuged at 8000rpm for 5-8min after each wash; the particles are then slowly thawed at 25℃ for 3-4h to obtain wet silica particles.

[0048] S6: Transfer the wet granules into a rotating quartz tube furnace, control the furnace temperature at 120℃ and the rotation speed at 20 rpm, and dry for 30 min to remove surface adsorbed water and residual solvent, obtaining dry granules with a moisture content ≤1%. Maintain the rotation state, introduce oxygen with a purity ≥99.999% at a flow rate of 50 mL / min, raise the temperature to 400℃ at 5℃ / min and hold for 2 h, raise the temperature to 600℃ and hold for 3 h, raise the temperature to 800℃ and hold for 2 h to complete the gradient calcination, removing carbon impurities and some low-boiling-point inclusions.

[0049] S7: Transfer the calcined particles into a high-temperature vacuum alumina ceramic inner furnace, close the furnace door, and evacuate to ≤5×10⁻⁶. -5 Pa was heated to 1000℃ at a rate of 2℃ / min and held statically for 6 hours. During this period, argon gas with a purity of ≥99.999% was introduced at a flow rate of 20 mL / min to remove hydroxyl groups and remaining inclusions, resulting in dense silica particles.

[0050] S8: Grading process: The dense silica particles of S7 are lightly pulverized using a 99.99% quartz double-roll mill with a roller gap of 300 μm, a roller speed of 100 r / min, and a roller pressure of 200 MPa; then classified by an air classifier with an air velocity of 20 m / s and a classifier wheel speed of 4000 rpm. Particles with a particle size distribution CV ≤ 5% are collected to obtain high-purity quartz sand. Figure 1 The performance parameters are shown in Table 1.

[0051] Example 2

[0052] S1: Dissolve silicic acid in ultrapure water to prepare a 0.5wt% silicic acid solution. Transfer the silicic acid solution into a 99.99% quartz stirring tank and stir at 1000 rpm. Add 1 mol / L electronic grade hydrochloric acid dropwise at a rate of 2 mL / min to adjust the pH to 1.5~2.5. Continue stirring for 50 min to obtain a uniformly dispersed silicic acid sol.

[0053] S2: Take silicic acid with a water content of 93wt%, mix it with the silicic acid sol of S1 at a volume ratio of 10:2, place it in a 99.99% quartz reactor, and stir for 3 hours at 30℃ and 500rpm to form a uniform block gel with a water content of 86wt%.

[0054] S3: Gel crushing and centrifugal dehydration: The blocky gel was crushed into particles of 0.5~2mm using a 99.99% quartz crusher. The particles were then transferred into a polytetrafluoroethylene centrifuge bag and centrifuged at 9000rpm for 12min to remove free water, resulting in gel particles with a water content of 73wt%.

[0055] S4: Low-temperature solvent freezing treatment: Add the gel particles to hexane, a low-temperature solvent pre-cooled to -5℃, at a solid-liquid ratio of 1:10 (g:mL). The viscosity of hexane at -5℃ is 0.421mPa·s. Stir at 400rpm for 120min at a constant temperature of -5℃, maintaining a temperature fluctuation of ≤±2℃.

[0056] S5: Frozen particles are separated by filtration using a 0.1μm quartz fiber filter membrane, washed 3-5 times with ultrapure water at 0-10℃, and centrifuged at 8000rpm for 5-8min after each wash; the particles are then slowly thawed at 25℃ for 3-4h to obtain wet silica particles.

[0057] S6: Transfer the wet granules into a rotating quartz tube furnace, control the furnace temperature at 150℃ and the rotation speed at 15 rpm, and dry for 30 min to remove surface adsorbed water and residual solvent, obtaining dry granules with a moisture content ≤1%. Keep the furnace rotating, introduce oxygen with a purity ≥99.999% at a flow rate of 30 mL / min, raise the temperature to 400℃ at 5℃ / min and hold for 2 h, raise the temperature to 600℃ and hold for 3 h, raise the temperature to 800℃ and hold for 2 h to complete the gradient calcination, removing carbon impurities and some low-boiling-point inclusions.

[0058] S7: Transfer the calcined particles into a high-temperature vacuum alumina ceramic inner furnace, close the furnace door, and evacuate to ≤10. - 4 Pa was heated to 1200℃ at a rate of 2℃ / min and held at that temperature for 5 hours. During this time, argon gas with a purity of ≥99.999% was introduced at a flow rate of 25 mL / min to remove hydroxyl groups and remaining inclusions, resulting in dense silica particles.

[0059] S8: Grading process: The dense silica particles of S7 are lightly crushed using a 99.99% quartz double roller mill with a roller gap of 300 μm, a roller speed of 150 r / min, and a roller pressure of 100 MPa. The particles are then classified by an air classifier with an air velocity of 20 m / s and a classifier wheel speed of 4500 rpm. Particles with a particle size distribution CV ≤ 5% are collected to obtain high-purity quartz sand. The performance parameters are shown in Table 1.

[0060] Example 3

[0061] S1: Dissolve silicic acid in ultrapure water to prepare a 0.8 wt% silicic acid solution. Transfer the silicic acid solution into a 99.99% quartz stirring tank and stir at 1500 rpm. Add 0.5 mol / L electronic grade hydrochloric acid dropwise at a rate of 3 mL / min to adjust the pH to 1.5~2.5. Continue stirring for 30 min to obtain a uniformly dispersed silicic acid sol.

[0062] S2: Take silicic acid with a water content of 95wt%, mix it with the silicic acid sol of S1 at a volume ratio of 10:1, place it in a 99.99% quartz reactor, and stir for 1 hour at 40℃ and 800rpm to form a uniform block gel with a water content of 86wt%.

[0063] S3: Gel crushing and centrifugal dehydration: The blocky gel was crushed into particles of 0.5~2mm using a 99.99% quartz crusher. The particles were then transferred into a polytetrafluoroethylene centrifuge bag and centrifuged at 10,000 rpm for 10 minutes to remove free water, resulting in gel particles with a water content of 70wt%.

[0064] S4: Low-temperature solvent freezing treatment: Add the gel particles to a low-temperature solvent pre-cooled to -25℃ at a solid-liquid ratio of 1:12 (g:mL). The viscosity of n-hexane at -25℃ is 0.467mPa·s. Stir at 600rpm for 20min at a constant temperature of -25℃, maintaining temperature fluctuation ≤±2℃.

[0065] S5: Frozen particles are separated by filtration using a 0.1μm quartz fiber filter membrane, washed 3-5 times with ultrapure water at 0-10℃, and centrifuged at 8000rpm for 5-8min after each wash; the particles are then slowly thawed at 25℃ for 3-4h to obtain wet silica particles.

[0066] S6: Transfer the wet granules into a rotating quartz tube furnace, control the furnace temperature at 180℃ and the rotation speed at 15 rpm, and dry for 30 min to remove surface adsorbed water and residual solvent, obtaining dry granules with a moisture content ≤1%. Maintain the rotation state, introduce oxygen with a purity ≥99.999% at a flow rate of 40 mL / min, raise the temperature to 400℃ at 5℃ / min and hold for 2 h, raise the temperature to 600℃ and hold for 3 h, raise the temperature to 800℃ and hold for 2 h to complete the gradient calcination, removing carbon impurities and some low-boiling-point inclusions.

[0067] S7: Transfer the calcined particles into a high-temperature vacuum alumina ceramic inner furnace, close the furnace door, and evacuate to ≤5×10⁻⁶. -5 Pa was heated to 1300℃ at a rate of 2℃ / min and held at that temperature for 4 hours. During this time, argon gas with a purity of ≥99.999% was introduced at a flow rate of 30 mL / min to remove hydroxyl groups and remaining inclusions, resulting in dense silica particles.

[0068] S8: Grading process: The dense silica particles of S7 are lightly crushed using a 99.99% quartz double roller mill with a roller gap of 300μm, a roller speed of 200r / min, and a roller pressure of 50MPa. The particles are then classified by an air classifier with an air velocity of 25m / s and a classifier wheel speed of 5000rpm. Particles with a particle size distribution CV≤5% are collected to obtain high-purity quartz sand. The performance parameters are shown in Table 1.

[0069] Comparative Example 1

[0070] The preparation method of the comparative example quartz sand is the same as that in Example 1, except that the dropping rate in S1 is 5 mL / min. If the dropping rate is too fast, the local pH of the solution system will drop sharply, causing the silica molecules to polymerize and gel aggregate too quickly. The performance parameters of the prepared quartz sand are shown in Table 1.

[0071] Comparative Example 2

[0072] The preparation method of the comparative example quartz sand is the same as that of Example 1, except that: ethanol is used as a low-temperature solvent in S4, and the viscosity of ethanol is 2.0 mPa·s at -20℃. The performance parameters of the prepared quartz sand are shown in Table 1.

[0073] Comparative Example 3

[0074] The preparation method of the comparative example quartz sand is the same as that of Example 1, except that: in S4, the low-temperature solvent is pre-cooled to -40°C and stirred at 400 rpm for 10 min in a constant temperature environment of -40°C. The performance parameters of the prepared quartz sand are shown in Table 1.

[0075] Comparative Example 4

[0076] The preparation method of the comparative example quartz sand is the same as that of Example 1, except that: in S6, a drying oven is used for drying and a tube furnace is used for calcination, and in S7, a vacuum high-temperature sintering furnace (purchased from Luoyang Juxing Kiln Co., Ltd., with a metal inner chamber) is used. The performance parameters of the prepared quartz sand are shown in Table 1.

[0077] Table 1 Performance parameters of quartz sand

[0078]

[0079] Note: Values ​​exceeding the performance range of the quartz sand of this invention are indicated in bold.

[0080] As shown in Table 1, the quartz sand prepared by the method of the present invention has a purity ≥99.9999%, sphericity ≥0.88, particle size distribution CV ≤5%, hydroxyl content ≤20ppm, inclusion content ≤0.1vol%, and tap density ≥1.70g / cm³. 3 Bulk density ≥ 1.45 g / cm³ 3 The total content of metallic impurities is ≤1ppm (Fe, Al, and Na are each ≤0.3ppm). Excessive acceleration of the electronic-grade hydrochloric acid droplet rate can lead to gel agglomeration, significantly increasing the content of impurities and inclusions after sintering, and reducing the bulk density of the prepared quartz sand particles. Ethanol has a viscosity of 1.5~2.0 mPa·s in the temperature range of -5 to -30℃, which is higher than the low-temperature solvent used in this invention. The high viscosity of ethanol cannot fully penetrate the gaps between gel particles, disrupt interparticle hydrogen bonds, or inhibit agglomeration, resulting in larger particle size and lower sphericity of the prepared quartz sand. This invention provides a slow freezing process of -5 to -30℃ with stirring for 20~120 min, which can avoid large ice crystals generated by rapid freezing and improve sphericity. However, beyond the slow freezing range provided by this invention, the sphericity is poor. Traditional drying-calcination methods, involving the transfer of materials between the drying oven and the tubular furnace, easily introduce impurities. Vacuum high-temperature sintering furnace calcination can cause metal ion dissolution, contaminating the quartz sand.

[0081] As described above, the basic principles, main features, and advantages of the present invention have been well described. The above embodiments and specifications are merely descriptions of preferred embodiments of the present invention, and the present invention is not limited to the above embodiments. Various changes and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit and scope of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A method for preparing high-purity quartz sand based on low-temperature solvent freezing, characterized in that, include: A gel was obtained by adding silica sol and stirring with silica sol. The gel was broken into particles of 0.5-2 mm and centrifuged to obtain gel particles; The gel particles were added to a low-temperature solvent pre-cooled to -5 to -30°C and stirred at -5 to -30°C and 400 to 600 rpm for 20 to 120 minutes to obtain frozen particles. The frozen particles were filtered, washed, and thawed to obtain wet silica particles. The wet silica particles are transferred into a rotating quartz tube furnace, dried, and then subjected to gradient calcination. The high-purity quartz sand is obtained by sintering in a vacuum high-temperature furnace. The low-temperature solvent is one of methanol, n-hexane, or cyclohexane; The method for preparing the silica sol includes: preparing a 0.3-0.8 wt% silica solution, stirring at 1000-1500 rpm, adding 0.5-2 mol / L hydrochloric acid dropwise at a rate of 1-3 mL / min, adjusting the pH to 1.5-2.5, and stirring continuously for 30-60 min to obtain the silica sol; The inner chamber of the vacuum high-temperature furnace is made of alumina ceramic, and the purity of the alumina ceramic is 99.9%. The calcination is a gradient calcination, with oxygen introduced simultaneously at a flow rate of 30-50 mL / min.

2. The preparation method according to claim 1, characterized in that, The water content of the silicic acid is 90-95 wt%, and the volume ratio of silicic acid to silicic acid sol is 10:1-3. The addition of silica sol and stirring are carried out at 25~40℃, with a stirring speed of 500~800rpm, for 1~3 hours.

3. The preparation method according to claim 1, characterized in that, The centrifugation speed is 8000~10000 rpm, and the centrifugation time is 10~15 min. The water content of the gel particles is 70~75 wt%. The mass-to-volume ratio of the gel particles to the low-temperature solvent is 1:8~12.

4. The preparation method according to claim 1, characterized in that, The filtration uses a 0.1μm quartz fiber filter membrane; The cleaning process uses ultrapure water at 0~10℃, followed by centrifugation at 8000rpm for 5~8min. The thawing temperature is room temperature, and the thawing time is 3-4 hours.

5. The preparation method according to claim 1, characterized in that, The drying temperature is 120~180℃, the rotation speed is 15~20rpm, and the drying time is 30min; Drying yields dry granules with a moisture content of ≤1%.

6. The preparation method according to claim 1, characterized in that, The gradient calcination includes: heating at 5℃ / min to 400℃ and holding for 2 hours, heating to 600℃ and holding for 3 hours, and heating to 800℃ and holding for 2 hours.

7. The preparation method according to claim 1, characterized in that, The vacuum during sintering is below 10. -4 Pa; The sintering process includes: heating to 1000~1300℃ at a rate of 2℃ / min, holding at a static temperature for 4~6 hours, and introducing argon gas during the process at a flow rate of 20~30mL / min.

8. The preparation method according to claim 1, characterized in that, After sintering, the material is further pulverized and subjected to airflow classification. The crushing is achieved by a roller mill with a roller gap of 300μm, a roller speed of 100~200r / min, and a roller pressure of 50~200MPa. The airflow velocity for the airflow classification is 20~25m / s, and the classification wheel speed is 4000~5000rpm.

9. A high-purity quartz sand, characterized in that, The high-purity quartz sand is prepared by any one of the preparation methods described in claims 1 to 8, and the purity of the high-purity quartz sand is ≥99.9999%, the sphericity is ≥0.88, the particle size distribution CV is ≤5%, the hydroxyl content is ≤20ppm, and the total content of metal impurities is ≤1ppm.

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