Method for preparing high-purity synthetic quartz sand from white carbon black

Abstract

The application discloses a method for preparing high-purity synthetic quartz sand from white carbon black. The method comprises the following steps: S1, soaking the white carbon black in a mixed acid solution of hydrofluoric acid and hydrochloric acid, taking out the solid and cleaning and drying the solid to obtain high-purity SiO2 powder; S2, high-temperature treatment of the high-purity SiO2 powder to remove residual water and hydroxyl groups; S3, crushing the product of step S2 into powder and then pressing the powder into a block; S4, densification heat treatment of the block obtained in step S3 by a two-step calcination method, i.e., first heating to a lower temperature t1 for a shorter time, then heating to a higher temperature t2 for a longer time, and obtaining high-density quartz block after cooling; t1 is selected from 1100-1200 DEG C, and the t1 holding time is 1-2 h; t2 is selected from 1300-1500 DEG C, and the t2 holding time is 2-10 h; and S5, crushing the high-density quartz block to obtain high-purity quartz sand with high density.

Description

Technical Field

[0001] This invention relates to the field of high-purity quartz sand preparation technology, specifically to a method for preparing high-purity synthetic quartz sand from silica. Background Technology

[0002] With the rapid development of the global semiconductor industry and the rapid iteration of chip technology, the miniaturization of process technology has placed higher demands on chip manufacturing processes, especially in the manufacturing of high-end integrated circuits such as logic and memory. These processes have reduced the tolerance for defects in silicon wafers to extremely low levels, and the requirements for the cleanliness and consistency of semiconductor crucibles have also increased accordingly. In particular, the inner layer purity requirement for high-purity semiconductor synthetic quartz crucibles has reached a high standard of 6N or higher. At the same time, as quartz crucibles are disposable consumables, the demand for high-purity quartz sand is increasing year by year.

[0003] Currently, the synthesis of high-purity quartz sand mainly focuses on two directions: purification of natural quartz sand and chemical synthesis of quartz sand. The purity of natural quartz sand in my country is relatively low, and purification is quite difficult. Therefore, synthesizing high-purity quartz sand is more suitable for my country's development trend. Synthetic quartz sand can achieve extremely high purity through methods such as chemical liquid phase deposition, reaching the 6N-7N level, or over 99.99999%, far exceeding that of natural quartz sand. The synthesis process can be strictly controlled to produce quartz sand with high consistency, reducing impurities and variability present in natural ores. Using silica, a byproduct of silane production, to prepare high-purity synthetic quartz sand can reduce dependence on traditional natural quartz sand resources and decrease environmental pollution. It not only solves the waste disposal problem but also provides a low-cost silicon source, making silica an ideal raw material for the preparation of synthetic quartz. Utilizing silane byproducts to prepare quartz sand aligns with the circular economy and green development model, helping to reduce the environmental impact of waste while providing a sustainable resource utilization method. By converting industrial by-products into high-purity synthetic quartz sand, the economic added value of industrial by-product silica is effectively increased, resulting in high market demand and prices in the semiconductor, photovoltaic, and optical fiber fields.

[0004] Currently, the main method for densifying silica is to perform a one-step calcination process under normal pressure. However, this method results in relatively loose nanoparticles with large distances between them, which is not conducive to the formation of sintering necks between particles. Furthermore, the one-step densification process involves high temperatures, leading to rapid grain growth and the quick sealing of internal bubbles and pores. Consequently, the degree of densification of silica is relatively low, affecting the application of silica sand in quartz crucibles.

[0005] The advantage of this invention's two-step pressurized heat treatment method for improving the density of silica lies in the fact that under pressure, the silica nanoparticles have smaller inter-particle spacing during densification. Simultaneously, the increased pressure facilitates the formation of sintering necks between particles. As these necks grow, particle fusion occurs, promoting particle regrowth. Furthermore, the two-step heat treatment method of this invention keeps the grains small at lower temperatures, facilitating the migration and removal of internal air bubbles. At higher temperatures, particle growth fills the internal pores and inter-particle voids, achieving high densification. Therefore, developing this two-step heat treatment method is beneficial for improving the densification degree of silica, meeting the product standards of high-quality silica sand. Summary of the Invention

[0006] This invention provides a method for preparing high-purity synthetic quartz sand from silica. The method involves sequentially performing acid washing purification, dehydroxylation, and densification operations on silica, a byproduct of silane production, to successfully prepare high-density, high-purity quartz sand.

[0007] [1] A method for preparing high-purity synthetic quartz sand from silica includes the following steps:

[0008] S1, after soaking the silica in a mixed acid solution of hydrofluoric acid and hydrochloric acid, the solid was removed, washed, and dried to obtain high-purity SiO2 powder.

[0009] S2, High-temperature treatment of the high-purity SiO2 powder to remove residual moisture and hydroxyl groups;

[0010] S3, crush the product processed in step S2 into powder and then press it into blocks;

[0011] S4. The block obtained in step S3 is subjected to densification heat treatment by a two-step calcination method. First, it is heated to a lower temperature t1 (bubble migration temperature) and held for a short time. Then, it is heated to a higher temperature t2 (densification temperature) and held for a longer time. After cooling, a high-density quartz block is obtained. t1 is selected from 1100 to 1200℃, and the holding time of t1 is 1 to 2 hours, which is conducive to the full expulsion of bubbles. t2 is selected from 1300 to 1500℃, and the holding time of t2 is 2 to 10 hours (e.g., 4 hours, 6 hours, 8 hours, etc.).

[0012] S5, the high-density quartz block is crushed to obtain high-density, high-purity quartz sand.

[0013] In step S1, the molar ratio of hydrofluoric acid to hydrochloric acid in the mixed acid solution can be 1:1 to 5, for example, 1:1, 1:2, 1:3, 1:4, 1:5, etc.

[0014] In step S1, the mass ratio of the silica to the mixed acid solution can be 1:1 to 3, for example, 1:1, 1:2, 1:3, etc.

[0015] In step S1, the soaking time can be 10 to 20 hours.

[0016] In step S1, the cleaning process may specifically include: repeatedly washing with deionized water and ethanol several times in sequence, followed by centrifugation. The resulting solid is then used for subsequent drying to obtain high-purity SiO2 powder. Furthermore, the centrifugation speed is preferably not less than 6000 rpm.

[0017] In step S1, the drying can be vacuum drying. Further, the vacuum drying temperature can be 100–105°C, and the vacuum drying time can be 1–24 hours.

[0018] In step S2, the heating rate of the high-temperature treatment can be 5-10℃ / min. -1 .

[0019] In step S2, the temperature of the high-temperature treatment can be 800-1000℃.

[0020] In step S2, the high-temperature treatment time can be 6 to 10 hours.

[0021] In some preferred embodiments, in step S2, the atmosphere for the high-temperature treatment is a negative pressure inert environment of -0.1 MPa or lower. The inert environment refers to an atmosphere that does not participate in the reaction, such as nitrogen and / or rare gases (e.g., argon). The negative pressure can be achieved by methods such as inert gas purging followed by vacuuming. The inert gas refers to a gas that does not participate in the reaction, such as nitrogen and / or rare gases (e.g., argon).

[0022] In step S2, the high-purity SiO2 powder can be placed in an alumina crucible for high-temperature treatment.

[0023] In some embodiments, in step S3, the area where pressure is applied is 0.785 cm². 2 .

[0024] In step S3, the pressing pressure can be 100-400 MPa, preferably 300-400 MPa, which is beneficial to improving the density of high-purity quartz sand.

[0025] In some preferred embodiments, in step S4, the block obtained in step S3 undergoes a two-step densification heat treatment by calcination in a negative pressure inert environment of -0.1 MPa or lower. The inert environment refers to an atmosphere that does not participate in the reaction, such as nitrogen and / or a rare gas (e.g., argon). The negative pressure can be achieved by methods such as inert gas purging followed by vacuuming. The inert gas refers to a gas that does not participate in the reaction, such as nitrogen and / or a rare gas (e.g., argon).

[0026] Compared to the traditional one-step sintering process, the two-step vacuum sintering process of this invention, which involves "low temperature followed by high temperature," is more conducive to the densification of nano-sized SiO2 particles. Under applied pressure (e.g., 400 MPa), the relatively low temperature holding at t1 effectively converts residual hydroxyl and chloride ions into bubbles. These bubbles migrate along the particle interface and internal pores to the pressureless environment and are expelled from the bulk. At the higher temperature and internal pressure at t2, grains begin to grow. Sintering necks are formed between particles under high interfacial energy and diffusion. As the sintering necks grow, they promote particle fusion and regrowth, gradually filling the pores inside the particles and the voids at the interfaces between particles, thereby achieving the synthesis of highly dense quartz sand particles from nano-sized SiO2 particles.

[0027] In step S4, the heating rate to the lower temperature t1 can be 2–5 °C / min. -1 For example, 3℃min -1 wait.

[0028] In step S4, the heating rate to the higher temperature t2 can be 2–5 °C / min. -1 Preferably 2-3℃ min -1 This is beneficial for improving the density of high-purity quartz sand.

[0029] In step S4, t2 is preferably between 1400 and 1500°C, which is beneficial for improving the density of high-purity quartz sand.

[0030] In step S4, the heat preservation time t2 can be 6 to 10 hours.

[0031] In step S4, the cooling can be staged. Further, the cooling rate in the first stage can be 1–10 °C / min. -1 For example, 5℃min -1 The first stage of cooling can end at 300℃.

[0032] Figure 1 The diagram shows an example of the densification heat treatment temperature rise and fall curves in a method for preparing high-purity synthetic quartz sand from silica according to the present invention.

[0033] In step S5, the particle size of the high-purity quartz sand can be 50-310 μm, and can be further classified into 50-60 μm, 100-110 μm, 150-160 μm, 200-210 μm, 250-260 μm, and 300-310 μm.

[0034] In step S5, the tapped density of the high-purity quartz sand is greater than 0.8 g / cm³. -3 Further greater than 1.2g cm -3 Furthermore, it is greater than 1.4g cm -3 .

[0035] In step S5, the purity of SiO2 in the high-purity quartz sand is greater than 4N8.

[0036] [2] Application of the method described in [1] in the synthesis of high-purity quartz sand.

[0037] This invention uses a mixture of hydrofluoric acid and hydrochloric acid to acid wash and purify silica to remove metallic impurities; the obtained precipitate is separated, washed, and dried to obtain high-purity SiO2 powder; high-temperature heating under vacuum conditions is used for dehydroxylation treatment; the dehydroxylated product is crushed and pressurized to form blocks; a two-step calcination method is used to densify the blocks to obtain high-density quartz blocks; and crushing and sieving are performed to prepare high-density, high-purity quartz sand.

[0038] The method of this invention can effectively utilize the by-products in the silane production process, reducing environmental pollution and resource waste; through high-temperature calcination and acid washing purification, the purity of quartz sand is significantly improved, making it reach semiconductor-grade standards; the method is simple to operate, low in cost, and easy to industrialize.

[0039] This invention solves the problem of reusing silica, a byproduct of existing silane production, and improves the utilization efficiency of silicon resources. At the same time, it produces high-density, high-purity quartz sand with high economic benefits, which is suitable for related semiconductor, optoelectronic, and photovoltaic industries.

[0040] Compared with the prior art, the beneficial effects of this invention are as follows:

[0041] This invention employs a two-step sintering method to produce high-density quartz sand from silica. Silica mainly consists of amorphous SiO2 particles with a particle size of 80-100 nm, which is insufficient for practical applications of quartz sand. Therefore, it is necessary to improve the particle size and density of the SiO2 particles. This invention utilizes a two-step sintering technique, which optimizes the microstructure of the material by controlling the sintering process, thereby improving the material's density. The two-step sintering method effectively controls grain growth. By pre-sintering at a lower temperature (t1) for a short time and then holding at a higher temperature (t2) for a longer time to complete the sintering, the grains can be refined, resulting in a more uniform and finer grain structure. This method helps increase the material's density without significantly increasing the grain size, which is crucial for improving the material's mechanical strength and hardness. Due to grain refinement, the two-step sintering method typically improves the material's fracture toughness, hardness, and wear resistance. By controlling the sintering temperature and time, abnormal grain growth can be reduced, which is essential for maintaining the material's uniformity and reliability. Compared with the traditional one-step high-temperature sintering method, the two-step sintering method can achieve high density at a lower temperature, thus saving energy and costs. Attached Figure Description

[0042] Figure 1This is an example of a densification heat treatment temperature rise and fall curve in a method for preparing high-purity synthetic quartz sand from silica according to the present invention.

[0043] Figure 2 The image shows the X-ray diffraction (XRD) pattern of the SiO2 powder particles in step 3 of Example 1.

[0044] Figure 3 The image shows the thermogravimetric analysis (TG-DTG) results of SiO2 powder particles in step 3 of Example 1.

[0045] Figure 4 The graph shows the results of the thermal expansion test of SiO2 powder particles in step 3 of Example 1.

[0046] Figure 5 Metallographic photographs of high-density quartz blocks after heat treatment in step 4 of Examples 1(a), 4(b), 6(c), 9(d), and 10(e). Figure 6 This is a scanning electron microscope image of high-purity quartz sand from Example 4.

[0047] Figure 7 This is a scanning electron microscope image of the high-purity quartz sand in Example 9.

[0048] Figure 8 The diagram shows a comparison of the nitrogen adsorption BET specific surface area of ​​the powdered SiO2 particles (Sample 1) in step 3 of Example 4, the high-purity quartz sand (Sample 2) in step 5, and the powdered SiO2 particles (Sample 3) in step 3 and the high-purity quartz sand (Sample 4) in step 5 of Example 6.

[0049] Figure 9 The nitrogen adsorption curves are for the powdered SiO2 particles (a) in step 3 of Example 4, the high-purity quartz sand (b) in step 5, and the powdered SiO2 particles (c) in step 3 and the high-purity quartz sand (d) in step 5 of Example 6.

[0050] Figure 10 The pore size distribution diagrams are shown for the powdered SiO2 particles (a) in step 3 of Example 4, the high-purity quartz sand (b) in step 5, and the powdered SiO2 particles (c) in step 3 and the high-purity quartz sand (d) in step 5 of Example 6.

[0051] Figure 11 The above are comparison charts showing the tap density of high-purity quartz sand obtained under different pressures in Examples 1-4.

[0052] Figure 12 The above are comparison charts showing the tap density of high-purity quartz sand obtained at different heating rates in Examples 4-6.

[0053] Figure 13 The above are comparison charts showing the tap density of high-purity quartz sand obtained at different reaction times in Examples 6-9.

[0054] Figure 14 This is a photograph of the high-purity quartz sand from Example 9.

[0055] Figure 15 The images and metallographic photographs are for comparative example 1, showing the one-step sintering process: (a) one-step sintering at 800℃ for 10h, 900℃ for 10h, and 1000℃ for 10h; (b) samples subjected to a pressure of 100MPa for 2℃ min. -1 (c) The heating rate was increased to 1400℃; (d) The sample was subjected to a pressure of 400MPa for 2℃ min. -1 (d) The heating rate was increased to 1400℃; the sample was subjected to a pressure of 100MPa for 2℃ min. -1 (e) The heating rate is increased to 1500℃; (f) The sample is subjected to a pressure of 400MPa for 2℃ min. -1 The heating rate was increased to 1500℃. Detailed Implementation

[0056] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0057] Example 1

[0058] Step 1: Prepare 10 mL of a 1:1 mixture of hydrofluoric acid and hydrochloric acid; weigh 10 g of silica powder using an electronic balance and add it to the mixed acid solution, soaking for 20 h. Remove the supernatant, and take out the lower white precipitate, washing it repeatedly several times with deionized water and ethanol, at 6000 rpm. -1 After centrifugation, a white powder was obtained, which was then dried under vacuum at 100°C for 24 hours to obtain high-purity SiO2 powder.

[0059] Step 2: Transfer high-purity SiO2 powder into an alumina crucible and place it in a tube furnace. Purge with nitrogen gas of ≥99.999% purity, then evacuate to a negative pressure of -0.1 MPa. Repeat the purging and vacuuming process three times, setting the temperature to 10℃ for 1 minute. -1 The temperature was increased to 800℃ and held for 10 hours, then cooled to room temperature to remove residual moisture and hydroxyl groups from the powder.

[0060] Step 3: Crush the block obtained after removing the hydroxyl group in Step 2 into powdered SiO2 particles, transfer the powdered SiO2 particles into a room temperature pressing mold with a diameter of 10 mm, and apply a pressure of 100 MPa to press it into a cylindrical block.

[0061] Step 4: The compacted cylindrical block undergoes a two-step calcination heat treatment for densification. The heat treatment atmosphere is achieved through the following steps: purging with nitrogen gas of ≥99.999% purity, followed by evacuation to a negative pressure of -0.1 MPa, repeated three times. The heat treatment program is set as follows: first, at 5℃ for 1 minute... -1 Heat to t1 temperature (1200℃) at a heating rate of [temperature value], hold for 2 hours, and then heat at 5℃ / min [temperature value]. -1 The temperature was increased to 1400℃ at the specified heating rate and held for 2 hours. After the reaction was completed, the temperature was increased to 5℃ per minute. -1 After the cooling rate was reduced to 300°C, the sample was cooled to room temperature to obtain a high-density quartz block.

[0062] Step 5: The high-density quartz blocks are crushed, ground, sieved and classified to obtain high-density high-purity quartz sand with the required particle size and SiO2 purity greater than 4N8.

[0063] Figure 2 The XRD pattern of the SiO2 powder particles in step 3 of Example 1 shows that the diffraction peak of the synthesized SiO2 powder is located at 22°, which is consistent with the standard amorphous SiO2 (JCPDS29-0085) card, proving that the obtained product is amorphous SiO2 powder and there are no other impurity phases present.

[0064] To investigate the physical and chemical changes of nanoscale SiO2 powder during heating, including weight loss, endothermic and exothermic reactions, TG-DTG analysis was performed on the SiO2 particles from step 3 of Example 1. The test temperature range was 0–1500 °C. The test results are as follows: Figure 3 As shown, at approximately 160℃, the mass loss was 4.5%. The DTG curve results showed the highest mass loss rate at 97.15℃, indicating that the mass loss in this temperature range was mainly due to free water and coordinated water in the SiO2 structure. At approximately 800℃, the tested sample also experienced a 4.5% mass loss. The DTG curve results showed the highest mass loss rate at 428.33℃, indicating that the mass loss in this temperature range was mainly due to hydroxyl groups formed during SiO2 synthesis. Within the temperature range of 800–1500℃, the TG curve remained relatively stable, demonstrating that all hydroxyl groups were completely removed at 800℃.

[0065] To select the optimal test temperature for the two-step method, thermal expansion tests were conducted on the SiO2 powder particles in step 3 to study their volume change process during heating. Figure 4As shown, when the temperature rises to 150℃, the sample volume begins to shrink until 400℃. This shrinkage is mainly due to the loss of free and coordinated water in the SiO2 structure, causing the internal structure of SiO2 to shrink, with a volume reduction of 0.9%. When the temperature rises from 400℃ to 1000℃, this volume shrinkage is mainly due to the gradual loss of hydroxyl groups in the sample, resulting in a further volume shrinkage of 4.0%. When the temperature rises from 1000℃ to 1200℃, this volume shrinkage is mainly attributed to the sliding of bubbles formed inside the sample at the grain interface. Small bubbles mainly merge into large bubbles, and under vacuum negative pressure, the large bubbles gradually migrate to the sample surface and are gradually expelled from the body, resulting in a volume shrinkage of 5.3%. As the temperature further rises to 1500℃, the sample volume shrinks further, forming a dense structure. The thermal expansion curves indicate that the bubble migration temperature t1 in the sample is mainly concentrated between 1000 and 1200℃, and the densification temperature t2 is above 1400℃.

[0066] Examples 2-4

[0067] The only difference from Example 1 is that the pressing pressure in step 3 is changed to 200MPa (Example 2), 300MPa (Example 3), and 400MPa (Example 4) in sequence. All other aspects are the same, and high-density high-purity quartz sand with SiO2 purity greater than 4N8 is obtained.

[0068] Examples 5-6

[0069] The only difference from Example 4 is that in step 4, the heating rate to t2 temperature 1400℃ is changed to 3℃ / min. -1 (Example 5) and 2℃ min -1 (Example 6) The rest are the same, and high-density high-purity quartz sand with SiO2 purity greater than 4N8 is obtained.

[0070] Examples 7-9

[0071] The only difference from Example 6 is that the holding time at t2 temperature of 1400℃ in step 5 is changed to 4h (Example 7), 6h (Example 8), and 10h (Example 9) respectively. All other steps are the same, and high-density high-purity quartz sand with SiO2 purity greater than 4N8 is obtained.

[0072] Example 10

[0073] The only difference from Example 9 is that the temperature t2 in step 5 is changed to 1500℃, and the rest are the same, resulting in high-density high-purity quartz sand with SiO2 purity greater than 4N8.

[0074] like Figure 5As shown in (a), when the pressure applied to the sample in Example 1 was 100 MPa, the sample exhibited a large number of bubbles after heat treatment, and the interparticle structure was relatively loose. In Example 4 ( Figure 5 (b) When the sample pressure was applied to 400 MPa, under the same heat treatment conditions, the bubble content in the resulting sample was significantly reduced, and the microstructure between particles was relatively dense. As the heating rate increased from 5 °C / min... -1 Reduce to 2℃ min -1 (Example 6, Figure 5 (c) The reaction time was extended from 2 hours to 10 hours (Example 9). Figure 5 (d) As the bubble content inside the sample gradually disappeared, the particles became more tightly packed, and the particle size was 100–200 μm. With the reaction temperature increasing to 1500 °C (Example 10), the reaction continued. Figure 5 (e)) No obvious bubbles were present inside the sample, and the particles were stacked very tightly.

[0075] Example 4 ( Figure 6 ) and Example 9 ( Figure 7 The scanning electron microscope (SEM) images show that as the heating rate decreases and the reaction time increases, the pores on the sample surface gradually close, forming a dense SiO2 bulk structure.

[0076] BET test results ( Figures 8 to 10 The results show that as pressure and reaction time increase, the specific surface area of ​​the sample gradually decreases, proving that the pores inside the particles gradually close. This indicates that increasing pressure and reaction time can promote the growth and densification of SiO2 particles.

[0077] Further analysis of the tap density distribution of calcined quartz sand particles... Figures 11 to 13 The results show that the tap density of the quartz sand particles increases significantly with increasing pressure. Simultaneously, the tap density of the quartz sand gradually increases with decreasing heating rate and increasing reaction time. The tap density of Example 9 reaches 1.41 g / cm³. -3 It has already met the density requirements for commercial quartz sand. Figure 14 The above results indicate that increasing external pressure and decreasing the heating rate can effectively increase the activation energy of the SiO2 particle interface, enhance the driving force for atomic diffusion at the interface, and promote the formation of sintering necks. Simultaneously, as the particles grow, the internal pores gradually fill and close, and the bubbles at the particle interface gradually migrate and are removed, thereby increasing the density of the SiO2 particles.

[0078] Comparative Example 1

[0079] Referring to Example 1, the SiO2 powder obtained in step 3 was subjected to a one-step densification heat treatment. First, the SiO2 powder was subjected to a heat treatment at 10°C for 1 minute without pressure. -1 The heating rates were adjusted to 800℃, 900℃, and 1000℃, respectively. For example... Figure 15 As shown in (a), the heat-treated sample remained in a powder state, making it impossible to densify the SiO2 powder particles. The samples were pressurized to 100 MPa and 400 MPa, respectively, and heated at 2 °C for 2 min. -1 Heating rate to 1400℃ and 1500℃ ( Figure 15 (be)), metallographic images reveal a large number of air bubbles and pores on the sample surface and inside. This is mainly due to the one-step calcination method, where the temperature cannot reach the densification temperature for nanoscale particles at low temperatures; at high temperatures, as the temperature increases, the grains grow, and the air bubbles inside the sample cannot migrate out of the sample. A large number of air bubbles are fixed inside the particles, thus reducing the density of the quartz sand.

[0080] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for preparing high-purity synthetic quartz sand from silica, characterized in that, Including the following steps: S1, after soaking the silica in a mixed acid solution of hydrofluoric acid and hydrochloric acid, the solid was removed, washed, and dried to obtain high-purity SiO2 powder. S2, High-temperature treatment of the high-purity SiO2 powder to remove residual moisture and hydroxyl groups; S3, the product processed in step S2 is crushed into powder and then pressed into blocks; the pressing pressure is 400MPa; S4. The block obtained in step S3 is subjected to a two-step calcination heat treatment for densification. First, it is heated to a lower temperature t1 and held for a short time. Then, it is heated to a higher temperature t2 and held for a longer time. After cooling, a high-density quartz block is obtained. t1 is selected from 1000 to 1200℃, and the holding time for t1 is 1 to 2 hours. t2 is selected from 1400 to 1500℃, and the holding time for t2 is 10 hours. The heating rate to the higher temperature t2 is 2℃ / min. -1 ; S5, the high-density quartz block is crushed to obtain high-density, high-purity quartz sand; the tap density of the high-purity quartz sand is greater than 1.4 g / cm³. -3 .

2. The method according to claim 1, characterized in that, In step S1: In the mixed acid solution, the molar ratio of hydrofluoric acid to hydrochloric acid is 1:1 to 5; The mass ratio of the silica to the mixed acid solution is 1:1 to 3; The soaking time is 10–20 hours; The cleaning process specifically includes: repeatedly washing with deionized water and ethanol several times in sequence, followed by centrifugation, and the resulting solid is used for subsequent drying to obtain high-purity SiO2 powder; the centrifugation speed is not less than 6000 rpm; The drying process is vacuum drying, with a vacuum drying temperature of 100–105°C and a vacuum drying time of 1–24 hours.

3. The method according to claim 1, characterized in that, In step S2: The heating rate of the high-temperature treatment is 5–10 °C / min. -1 ; The high-temperature treatment temperature is 800–1000℃; The high-temperature treatment time is 6–10 hours; The atmosphere for the high-temperature treatment is a negative pressure inert environment of -0.1MPa or lower. The high-purity SiO2 powder is placed in an alumina crucible for high-temperature treatment.

4. The method according to claim 1, characterized in that, In step S4, the block obtained in step S3 is subjected to densification heat treatment by a two-step calcination method in a negative pressure inert environment of -0.1MPa or lower.

5. The method according to claim 1 or 4, characterized in that, In step S4: The heating rate to a lower temperature t1 is 2–5 °C / min. -1 ; The cooling is staged, with the first stage having a cooling rate of 1–10 °C / min. -1 The first stage of cooling ends at 300℃.

6. The method according to claim 1, characterized in that, In step S5: The particle size of the high-purity quartz sand is 50–310 μm; The purity of SiO2 in the high-purity quartz sand is greater than 4N8.

7. The method according to claim 6, characterized in that, In step S5, the particle size classification of the high-purity quartz sand is 50-60μm, 100-110μm, 150-160μm, 200-210μm, 250-260μm, and 300-310μm.

8. The application of the method according to any one of claims 1 to 7 in the synthesis of high-purity quartz sand.

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