Preparation method of low-cost high-purity synthetic quartz sand

Abstract

The present application relates to the technical field of semiconductor-grade quartz crucible, quartz sand or quartz glass, and particularly relates to a preparation method of low-cost high-purity synthetic quartz sand. The present application aims at the main challenge of high price of raw materials such as tetraethyl orthosilicate and other compounds of high-purity synthetic quartz sand, and uses cheap alkali metal silicate as a substitute raw material to greatly reduce the cost of high-purity synthetic quartz. In addition, the normal temperature and pressure process with simple and controllable equipment can be applied to large-scale industrial production. The present application mainly comprises the following steps: firstly, the alkali metal silicate is diluted with high-purity water, and then a decontaminating agent is added to remove impurity elements and sodium ions are removed through ion exchange; secondly, the sol is left to stand and age to obtain a wet gel; finally, high-purity synthetic quartz sand is obtained through normal temperature and pressure drying, crushing and high-temperature calcination.

Description

Technical Field

[0001] This invention relates to the field of semiconductor-grade quartz crucibles, quartz sand, or quartz glass technology, and specifically to a method for preparing low-cost, high-purity synthetic quartz sand. Background Technology

[0002] High-purity synthetic quartz (SiO2 ≥ 99.9%) typically possesses extremely high chemical purity and excellent physicochemical properties, such as high hardness, wear resistance, high temperature resistance (melting point approximately 1713℃), and corrosion resistance, making it a high-end industrial product. Furthermore, quartz exhibits high mechanical strength and toughness, is easily processed into various shapes, and demonstrates excellent electrical properties and chemical stability under high temperature and pressure conditions. Therefore, high-purity synthetic quartz is an ideal choice for manufacturing high-performance electronic components and is widely used in high-tech fields such as optics, photovoltaics, and semiconductors. High-purity synthetic quartz sand is a key raw material for the inner layer of quartz crucibles, requiring extremely high purity to ensure product performance and quality during silicon rod crystal pulling.

[0003] Currently, the main methods for producing high-purity synthetic quartz sand include the oxyhydrogen flame method and the sol-gel method. The oxyhydrogen flame method decomposes silicon tetrachloride (SiCl4) at high temperatures in a hydrogen atmosphere to generate silicon dioxide, which then forms quartz sand. However, the product has a high content of hydroxyl groups and impurities such as chlorine. The sol-gel method uses silicon sources such as orthosilicates, such as methyl orthosilicate (TMOS) and tetraethyl orthosilicate (TEOS), dissolved in a solvent (such as ethanol) to form a transparent and uniform sol. The quartz product is then obtained through subsequent drying, pulverization, and high-temperature sintering. In the sol-gel method, the sol composition and preparation conditions can be precisely controlled, resulting in synthetic quartz with extremely high purity and relatively dispersed particle size. However, the high cost of raw materials such as high-purity orthosilicates is a major factor restricting the large-scale industrial production of high-purity synthetic quartz sand.

[0004] Furthermore, the complexity of the process is also one of the bottlenecks in the development of high-purity synthetic quartz sand. In the sol-gel method, commonly used drying methods include atmospheric pressure drying, supercritical drying, and freeze-drying. Supercritical drying and freeze-drying can avoid the surface tension effect during the process, reducing crack formation, while preserving the unique porous structure formed in the sol-gel method, which is beneficial for subsequent sintering and the formation of a dense structure in synthetic quartz. However, they have stringent equipment requirements, long preparation cycles, high energy consumption, and high costs, making them unsuitable for large-scale industrial production. Atmospheric pressure drying is a simple method suitable for small-scale production and situations where high drying speed is not required. It evaporates the solvent through methods such as heated air; the drying time is long and surface cracks may occur, but it is safer and less expensive.

[0005] Sodium silicate, also known as water glass, is an inorganic compound. It is a glassy substance obtained by reacting silicates with hydroxides of alkali metals (such as sodium) under certain conditions, exhibiting gelling and adhesive properties. When sodium metasilicate dissolves in water, it forms an alkaline aqueous solution. Sodium silicate is stable in neutral and alkaline solutions, but in acidic solutions, silicate ions tend to react with hydrogen ions to form silicic acid, easily decomposing into hydrated silica gel. Inorganic silicon sources such as water glass are only one-tenth or even less expensive than orthosilicate compounds, making them relatively inexpensive and readily available, thus a cost-effective silicon source option. However, sodium silicate as a silicon source generally only yields low-purity silica, and there are still technical challenges in obtaining high-purity quartz materials suitable for semiconductor applications.

[0006] Chinese patent CN94117058 discloses a method for precipitating silica, mainly including the following steps: first, an alkali metal silicate is reacted with an inorganic acid for precipitation; then, after filtration, precipitation, washing, and drying, silica particles with a particle size range of 150-250 nm are obtained. This method uses precipitation to prepare silica, but the purity of the silica obtained by this method is difficult to meet requirements, and the impurity content is relatively high. Furthermore, the waste liquid generated by the precipitation method contains a certain amount of harmful substances, increasing the cost of waste disposal.

[0007] Chinese patent CN97125800 discloses a method for preparing nano-sized silica particles, mainly including the following steps: First, a surfactant is dissolved in a non-polar organic solvent to prepare a solution. Based on the desired size of the silica nanoparticles, an aqueous solution of alkali metal silicate is prepared. These two solutions are mixed, and the aqueous solution of alkali metal silicate is gradually added to the non-polar organic solvent solution of the surfactant under stirring to prepare a reverse micelle solution of alkali metal silicate. Finally, this reverse micelle solution is slowly added to an acidified polar organic solvent dispersion phase for aging, separation, and preparation of nano-sized silica particles. This method utilizes surfactants to encapsulate silicate particles, forming a microemulsion, thereby controlling particle growth and achieving the preparation of nano-sized silica particles. However, the use of large amounts of surfactants increases the complexity of post-processing and may affect product purity. Furthermore, the cost of surfactant microemulsion treatment is high, making it unsuitable for large-scale industrial production.

[0008] Chinese patent CN1626440A discloses a method for preparing highly dispersible, amorphous nano-silica, mainly including the following steps: adding an organic hydroxy acid to a silicate solution to form a silica gel solution; washing and filtering the obtained silica sol with deionized water; then washing several times with anhydrous ethanol until the water contained in the sol is displaced; filtering to obtain a silica / ethanol gel; and finally supercritical drying to obtain nano-silica dry gel powder. This method uses CO2 as a supercritical drying medium to replace the original solvent in the pores of the wet gel, requires high temperature and high pressure conditions, places stringent requirements on equipment, and has a long preparation cycle, which is not conducive to industrial production.

[0009] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the present invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0010] The main objective of this invention is to provide a low-cost, high-purity synthetic silica sand preparation method. It aims to utilize inexpensive silicon sources to replace traditional orthosilicate compounds, thereby achieving the preparation of synthetic silica sand at a lower cost under ambient temperature and pressure conditions. This invention is of great significance for reducing the production cost of synthetic silica sand and provides a feasible technical approach for its industrial production.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0012] A method for preparing low-cost, high-purity synthetic quartz sand includes the following steps:

[0013] Step 1: Dilute the alkali metal silicates with high-purity water at 35-55°C until they are completely dissolved; wherein, the alkali metal silicates include anhydrous sodium silicate, sodium silicate pentahydrate, and sodium silicate nonahydrate.

[0014] Step 2: Add the impurity remover to the diluted alkali metal silicate solution obtained in Step 1, stir thoroughly and mix evenly. The impurity remover includes CaO and Ca(OH)2. The Ca(OH)2 added in this invention removes heavy metal ions first by controlling the amount added, so that it is only enough to precipitate heavy metal ions without reacting too much with silicate. The precipitated heavy metal hydroxide can be separated by filtration, and it has no effect on subsequent ion exchange impurity removal.

[0015] The reaction equation for removing metal ions is as follows:

[0016] CaO + H₂O → Ca(OH)₂

[0017] Mg 2+ +2OH - →Mg(OH)2↓

[0018] Fe 2+ +2OH - →Fe(OH)2↓

[0019] Fe 3+ +3OH - →Fe(OH)3↓

[0020] Al 3+ +3OH - →Al(OH)3↓

[0021] Ca(OH)2+M n+ →M(OH) n ↓+Ca 2+

[0022] Ca(OH)2+Na2SiO3→CaSiO3↓+2NaOH

[0023] 3CaO + 2Al(OH)4 - +SiO2(OH)2 2- →2Al(OH)3↓+CaSiO3↓+4OH - +H2O

[0024] Na2SiO3+CaO+NaAlO2+2H2O→CaSiO3↓+Al(OH)3↓+2NaOH;

[0025] Step 3: Filter the sol after impurity removal in Step 2 to remove precipitated impurities. The filter screen accuracy is 0.1-1 μm.

[0026] Specifically, the filtration process is divided into three stages: coarse filtration with a filter screen precision of 0.6–1 μm, medium filtration with a precision of 0.3–0.6 μm, and fine filtration with a precision of 0.1–0.3 μm. This invention employs a multi-stage filtration system, filtering particles step by step according to their size, which can significantly improve filtration efficiency and final purity.

[0027] Step 4: The sol obtained in Step 3 is passed through a strong acid cation exchange column to remove calcium and sodium ions, with a solution flow rate of 83–168 L / min. This step ensures that all sodium silicate is converted to silicic acid. Specifically, the cation exchange resin exists in the hydrogen form, and calcium and sodium ions can be removed through ion exchange. Calcium ion reaction and regeneration process:

[0028] 2R-Na+Ca 2 +→R2Ca+2Na + ;

[0029] R-H+Na + →R-Ca+2Na+ .

[0030] Step 5: Transfer the sol from Step 4 into a reaction vessel and keep stirring under an inert atmosphere; wherein the stirring rate is 100-300 r / min, the stirring temperature is 50-100℃, and the stirring time is 3-12 h.

[0031] Step 6: After stirring, let stand for 0.5 to 2 hours to allow the sol to turn into a gel, and continue aging under an inert atmosphere for 2 to 24 hours; the aging temperature is 55 to 120℃.

[0032] Step 7: Soak the aged wet gel in high-purity water for 2-12 hours and wash it 1-3 times; wherein, the high-purity water is the same as in step 1.

[0033] Step 8: Dry the cleaned wet gel under an inert atmosphere;

[0034] Step 9: Remove the dried gel and crush it using a roller crusher. Adjust the roller gap to 0.1-1 mm and control the target particle size within the range of 200-500 μm through a sieve to suit the preparation of the quartz crucible.

[0035] Step 10: The crushed dry gel is placed in a high-temperature rotary furnace for sintering to obtain high-purity synthetic quartz sand. The sintering temperature is 800–1250℃, and the sintering time is 6–48 hours. Sintering temperature and time are key factors affecting the quality of high-purity synthetic quartz sand products. Correct sintering temperature and time can help eliminate impurities and improve the purity and crystallinity of the material, thereby meeting the stringent requirements of semiconductor applications. 800℃ to 900℃: preliminary sintering, which can remove some volatile impurities and organic matter; 900℃ to 1250℃: improves the crystallinity of the quartz sand, further removes impurities, and improves the purity of the material.

[0036] Preferably, in step 1, the alkali metal silicate is in the form of granules or powder with a purity of ≥99%, and the mass fraction of the alkali metal silicate in the diluted solution is 2wt.% to 10wt.%.

[0037] Preferably, in step 1, the high-purity water has a pH of 6.5–7.0, a total organic carbon (TOC) content ≤20 μg / L, and a resistivity of 15–18.2 MΩ·cm. High-purity water is a crucial component in the preparation of high-purity synthetic quartz sand. The high resistivity and low TOC content of high-purity water indicate very low levels of ionic impurities and organic matter. This minimizes impurities introduced during the sol-gel preparation process, ensuring the high purity of the synthetic quartz sand. The pH of the high-purity water, between 6.5 and 7.0, is close to neutral, which is beneficial for the stability of the sol and gel. During the sol-gel process, pH changes affect gel formation and structure; a stable pH ensures consistency and controllability in the preparation process. High resistivity indicates extremely low ion content in the water; ionic impurities can affect the electrical properties of the quartz sand.

[0038] Preferably, in step 2, the amount of the impurity remover is 1–30 g / L, the stirring time is 0.5–3 h, and the stirring temperature is 40–80 °C. Adding impurity removers such as CaO and Ca(OH)₂ can cause impurity elements to form silicon slag, and metal elements such as Fe and Al to form complex compound precipitates with very low solubility.

[0039] Preferably, in step 4, the strong acid cation exchange resin is type 732, the pH value of the sol after the ion exchange column is in the range of 2-3, and the temperature is maintained at 5-10℃ during the process to prevent the sol from forming a gel prematurely. Specifically, lowering the temperature can slow down the chemical reaction rate in the sol-gel process, thereby prolonging the gel formation time. A slower gel formation process helps to form a more uniform and dense gel structure, reducing defects and porosity; at the same time, lower temperature makes the gel formation process more controllable, reduces fluctuations in process parameters, and ensures the consistency and repeatability of each batch of products; furthermore, lower temperature provides a longer reaction time, allowing for more adjustments and optimizations in the process to achieve the best results. In addition, the sol should avoid contact with metal containers or inner walls to prevent metal ion contamination, and the lining material is a corrosion-resistant and high-temperature-resistant polytetrafluoroethylene coating with a thickness ≥10μm.

[0040] Preferably, in step 5, the lining of the reactor is made of polytetrafluoroethylene coating or high-temperature and corrosion-resistant coating material, and the inert gas includes nitrogen or argon with a purity ≥99.995%.

[0041] Preferably, in step 6, the inert gas includes nitrogen or argon with a purity ≥99.995% and a flow rate of 40–85 L / min.

[0042] Preferably, in step 8, the drying temperature is 160–240°C and the drying time is 12–24 hours.

[0043] Preferably, in step 9, the rollers of the double-roll crusher are made of high-purity quartz with a purity ≥99.995% and a rotational speed range of 20–100 r / min. Compared to the nanoscale particle size of silica prepared by traditional methods, which cannot be used in semiconductor manufacturing processes, the synthetic quartz of this patent has a particle size range in the micrometer range and can be used in the preparation of quartz products.

[0044] Preferably, during the high-temperature calcination process in step 10, the furnace tubes of the high-temperature rotary kiln are kept rotating at a speed of 2 to 10 r / min, and the synthetic quartz sand is kept at a height difference of 40 to 75 mm inside the furnace tubes to prevent the synthetic quartz sand from agglomerating during the high-temperature calcination process.

[0045] The beneficial effects of this invention are:

[0046] This invention addresses the major challenge of high-purity synthetic silica sand made from expensive orthosilicate compounds by using inexpensive alkali metal silicates as substitutes, significantly reducing the cost of high-purity synthetic silica. Furthermore, the simple and controllable ambient temperature and pressure process allows for large-scale industrial production. The main steps include: first, diluting the alkali metal silicate with high-purity water, then adding an impurity remover to remove impurity elements and removing sodium ions through ion exchange; second, allowing the sol to stand and age to obtain a wet gel; and finally, obtaining high-purity synthetic silica sand through ambient temperature and pressure drying, crushing, and high-temperature calcination.

[0047] This invention uses a low-cost silicon source to replace traditional orthosilicate compounds, significantly reducing the production cost of high-purity synthetic quartz sand. This helps improve product competitiveness and market share. High purity (≥99.995%) can be achieved through preliminary impurity removal and purification processes, ensuring good chemical stability and inertness of the synthetic quartz under high temperature and high pressure environments. The preparation process under ambient temperature and pressure conditions is simpler and more stable than traditional methods, reducing energy consumption and production cycle time, and improving production efficiency.

[0048] Unlike existing technologies that use sodium silicate as a raw material, which typically contains numerous impurities such as metal ions (sodium, calcium, aluminum, etc.) and organic impurities, this invention removes metal ion impurities through precipitation and ion exchange. These impurities are difficult to completely remove during precipitation, resulting in low purity of the final silica. Furthermore, unlike precipitation methods that produce nano-sized silica particles, this invention removes metal ion impurities through precipitation and ion exchange, resulting in synthetic quartz particles with a particle size range of 200-500 μm, achieving semiconductor-grade purity, and suitable for manufacturing quartz crucibles. Attached Figure Description

[0049] 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 recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 This is a flowchart illustrating the preparation process of high-purity synthetic quartz sand in this embodiment of the invention;

[0051] Figure 2 This is an optical microscope image of high-purity synthetic quartz sand in an embodiment of the present invention; Detailed Implementation

[0052] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific implementation methods, features and effects of the technical solutions proposed according to the present invention are described in detail below.

[0053] In this embodiment of the invention, the commercially available materials are sourced as follows:

[0054] Anhydrous sodium silicate Shangdong Kunsheng Chemical Co., Ltd. Sodium silicate pentahydrate Shandong Zhekun Chemical Co., Ltd. Sodium silicate nonahydrate Hubei Watson Chemical Technology Co., Ltd. High purity water self made CaO Shenyang Senio Chemical Co., Ltd. <![CDATA[Ca(OH)2]]> Shenyang Senio Chemical Co., Ltd. Strong acid cation exchange column Anhui Samsung Resin Technology Co., Ltd. Nitrogen Huazhong Gas Co., Ltd.

[0055] Example 1

[0056] A method for preparing low-cost, high-purity synthetic quartz sand includes the following steps:

[0057] Step 1: Dilute the alkali metal silicate (anhydrous sodium silicate) with high-purity water at 50°C until completely dissolved; the mass fraction of the alkali metal silicate in the diluted solution is 4.8 wt.%. The high-purity water has a pH of 6.5–7.0, a total organic carbon (TOC) content ≤20 μg / L, and a resistivity of 15 MΩ·cm.

[0058] Step 2: Add CaO impurity remover to the diluted alkali metal silicate solution obtained in Step 1, stir thoroughly and mix evenly; the amount of CaO impurity remover is 8 g / L, the stirring time is 2 hours, and the stirring temperature is 50℃. This causes the impurity elements to form silicon slag.

[0059] Step 3: Filter the sol after impurity removal in Step 2 to remove precipitated impurities. This includes coarse filtration with a filter screen precision of 0.6–1 μm, medium filtration with a precision of 0.3–0.6 μm, and fine filtration with a precision of 0.1–0.3 μm. The filter screen precision is 0.2 μm.

[0060] Step 4: The sol obtained in Step 3 is passed through a strong acid cation exchange column to remove sodium ions, wherein the solution flow rate is 110 L / min; the strong acid cation exchange resin is type 732; the pH value of the sol after the ion exchange column is in the range of 2 to 3; the temperature is maintained at 5°C during the process to prevent the sol from forming a gel prematurely.

[0061] Step 5: Transfer the sol from Step 4 into a reaction vessel and keep stirring under a high-purity nitrogen atmosphere (purity ≥99.995%). The stirring rate is 150 r / min, the stirring temperature is 58℃, and the stirring time is 3 h. The lining of the reaction vessel is a polytetrafluoroethylene coating.

[0062] Step 6: After stirring, let stand for 0.5 hours to allow the sol to turn into a gel, and continue aging for 8 hours under a high-purity nitrogen atmosphere (purity ≥99.995%); the aging temperature is 90℃.

[0063] Step 7: Soak the aged wet gel in high-purity water for 8 hours, then drain the wastewater after cleaning, and rinse twice with high-purity water; the high-purity water is the same as in Step 1.

[0064] Step 8: Dry the cleaned wet gel in a high-purity nitrogen atmosphere (purity ≥99.995%); the drying temperature is 186℃ and the drying time is 14h.

[0065] Step 9: Remove the dried gel and crush it using a roller crusher. Adjust the roller gap to 0.25 mm and control the target particle size within the range of 200-500 μm through a sieve. The rollers of the roller crusher are made of high-purity quartz with a purity ≥99.995% and a rotation speed range of 50 r / min.

[0066] Step 10: The crushed dry gel is placed in a high-temperature rotary furnace for sintering to obtain high-purity synthetic quartz sand. The calcination temperature is 1200℃, and the calcination time is 24 hours. During the high-temperature calcination process, the furnace tubes of the high-temperature rotary furnace are kept rotating at a speed of 5 r / min. The synthetic quartz sand is kept at a height difference of 40-75 mm inside the furnace tubes to prevent agglomeration of the synthetic quartz sand during the high-temperature calcination process.

[0067] The composition of high-purity synthetic quartz is shown in Table 1:

[0068] Table 1. Synthetic Quartz in Example 1 (Unit: ppm)

[0069] SQ1 0.04 0.03 0.02 0.02 0.02 0.01 0.01 0.01 0.1 0.01 0.02 0.01 0.01 0.31

[0070] Example 2

[0071] A method for preparing low-cost, high-purity synthetic quartz sand includes the following steps:

[0072] Step 1: Dilute the alkali metal silicate (sodium silicate pentahydrate) with high-purity water at 55°C until completely dissolved; the mass fraction of the alkali metal silicate in the diluted solution is 8.5 wt.%. The high-purity water has a pH of 6.5–7.0, a total organic carbon (TOC) content ≤20 μg / L, and a resistivity of 18.2 MΩ·cm.

[0073] Step 2: Add Ca(OH)₂ impurity remover to the diluted alkali metal silicate solution obtained in Step 1, stir thoroughly and mix evenly; the amount of Ca(OH)₂ impurity remover is 18 g / L, the stirring time is 2 h, and the stirring temperature is 50℃. This causes the impurity elements to form silicon slag.

[0074] Step 3: Filter the sol after impurity removal in Step 2 to remove precipitated impurities. The filter screen accuracy is 0.2μm.

[0075] Step 4: The sol obtained in Step 3 is passed through a strong acid cation exchange column to remove sodium ions, wherein the solution flow rate is 105 L / min; the strong acid cation exchange resin is type 732; the pH value of the sol after the ion exchange column is in the range of 2 to 3; the temperature is maintained at 5°C during the process to prevent the sol from forming a gel prematurely.

[0076] Step 5: Transfer the sol from Step 4 into a reaction vessel and keep stirring under a high-purity nitrogen atmosphere (purity ≥99.995%). The stirring rate is 180 r / min, the stirring temperature is 75℃, and the stirring time is 2 h. The lining of the reaction vessel is a polytetrafluoroethylene coating.

[0077] Step 6: After stirring, let stand for 1 hour to allow the sol to turn into a gel, and continue aging for 15 hours under a high-purity nitrogen atmosphere (purity ≥99.995%); the aging temperature is 90℃.

[0078] Step 7: Soak the aged wet gel in high-purity water for 12 hours, then drain the wastewater after cleaning, and rinse it three times with high-purity water; the high-purity water is the same as in Step 1.

[0079] Step 8: Dry the cleaned wet gel in a high-purity nitrogen atmosphere (purity ≥99.995%); the drying temperature is 210℃ and the drying time is 18h.

[0080] Step 9: Remove the dried gel and crush it using a roller crusher. Adjust the roller gap to 0.25 mm and control the target particle size within the range of 200-300 μm through a sieve. The rollers of the roller crusher are made of high-purity quartz with a purity ≥99.995% and a rotation speed range of 50 r / min.

[0081] Step 10: The crushed dry gel is placed in a high-temperature rotary furnace for sintering to obtain high-purity synthetic quartz sand. The calcination temperature is 1250℃, and the calcination time is 36 hours. During the high-temperature calcination process, the furnace tubes of the high-temperature rotary furnace are kept rotating at a speed of 5 r / min. The synthetic quartz sand is kept at a height difference of 40-75 mm inside the furnace tubes to prevent agglomeration of the synthetic quartz sand during the high-temperature calcination process.

[0082] The composition of high-purity synthetic quartz is shown in Table 2:

[0083] Table 2. Synthetic Quartz in Example 2 (Unit: ppm)

[0084] SQ2 0.06 0.01 0.06 0.07 0.06 0.03 0.02 0.01 0.1 0.02 0.01 0.02 0.03 0.40

[0085] Example 3

[0086] A method for preparing low-cost, high-purity synthetic quartz sand includes the following steps:

[0087] Step 1: Dilute the alkali metal silicate (sodium silicate nonahydrate) with high-purity water at 55°C until completely dissolved; the mass fraction of the alkali metal silicate in the diluted solution is 7 wt.%. The high-purity water has a pH of 6.5–7.0, a total organic carbon (TOC) content ≤20 μg / L, and a resistivity of 18.2 MΩ·cm.

[0088] Step 2: Add CaO impurity remover to the diluted alkali metal silicate solution obtained in Step 1, stir thoroughly and mix evenly; the amount of CaO impurity remover is 18 g / L, the stirring time is 2 hours, and the stirring temperature is 50℃. This causes the impurity elements to form silicon slag.

[0089] Step 3: Filter the sol after impurity removal in Step 2 to remove precipitated impurities. The filter screen accuracy is 0.15μm.

[0090] Step 4: The sol obtained in Step 3 is passed through a strong acid cation exchange column to remove calcium and sodium ions, wherein the solution flow rate is 132 L / min; the strong acid cation exchange resin is type 732; the pH value of the sol after the ion exchange column is in the range of 2 to 3; the temperature is maintained at 10℃ during the process to prevent the sol from forming a gel prematurely.

[0091] Step 5: Transfer the sol from Step 4 into a reaction vessel and keep stirring under a high-purity nitrogen atmosphere (purity ≥99.995%). The stirring rate is 160 r / min, the stirring temperature is 65℃, and the stirring time is 4 h. The lining of the reaction vessel is a polytetrafluoroethylene coating.

[0092] Step 6: After stirring, let stand for 0.5 hours to allow the sol to turn into a gel, and continue aging for 15 hours under a high-purity nitrogen atmosphere (purity ≥99.995%); the aging temperature is 90℃.

[0093] Step 7: Soak the aged wet gel in high-purity water for 12 hours, then drain the wastewater after cleaning, and rinse it three times with high-purity water; the high-purity water is the same as in Step 1.

[0094] Step 8: Dry the cleaned wet gel in a high-purity nitrogen atmosphere (purity ≥99.995%); the drying temperature is 210℃ and the drying time is 18h.

[0095] Step 9: Remove the dried gel and crush it using a roller crusher. Adjust the roller gap to 0.25 mm and control the target particle size within the range of 200-300 μm through a sieve. The rollers of the roller crusher are made of high-purity quartz with a purity ≥99.995% and a rotation speed range of 50 r / min.

[0096] Step 10: The crushed dry gel is placed in a high-temperature rotary furnace for sintering to obtain high-purity synthetic quartz sand. The calcination temperature is 1250℃, and the calcination time is 36 hours. During the high-temperature calcination process, the furnace tubes of the high-temperature rotary furnace are kept rotating at a speed of 5 r / min. The synthetic quartz sand is kept at a height difference of 40-75 mm inside the furnace tubes to prevent agglomeration of the synthetic quartz sand during the high-temperature calcination process.

[0097] The composition of high-purity synthetic quartz is shown in Table 3:

[0098] Table 3. Synthetic Quartz in Example 3 (Unit: ppm)

[0099] SQ3 0.03 / 0.08 0.04 0.03 0.05 / 0.06 0.11 0.01 0.01 0.02 / 0.44

[0100] Comparative Example 1

[0101] The material ratios and preparation methods of this comparative example are the same as those of Example 1, except that the removal of impurities from CaO or Ca(OH)2 is omitted in step 2.

[0102] Comparative Example 2

[0103] The material ratios and preparation methods of this comparative example are the same as those of Example 2, except that the ion exchange step in step 4 is omitted.

[0104] Comparative Example 3

[0105] The material ratios and preparation methods of this comparative example are the same as those of Example 2, except that the sol temperature is maintained at 30°C in step 4.

[0106] The compositions of the high-purity synthetic quartz in Comparative Examples 1–3 are shown in Table 4:

[0107] Table 4. Synthetic Quartz of Comparative Examples 1–3 (unit, ppm)

[0108] Comparative Example 1 3.4 4.9 3.1 0.5 0.6 0.8 0.5 0.5 5.6 0.4 3.7 0.3 8.2 32.5 Comparative Example 2 1.7 0.3 1.4 0.3 0.2 0.9 0.7 0.3 4.2 0.4 2.9 0.7 3.7 17.7 Comparative Example 3 2.1 0.3 1.8 0.6 0.3 1.5 0.5 0.7 6.1 0.3 3.2 0.6 4.8 22.8

[0109] A comparison of the purity data of the quartz sand obtained in Example 1 and Comparative Example 1 shows that omitting the purification steps of CaO and Ca(OH)2 significantly increases the amount of impurities, highlighting the importance and effectiveness of CaO and Ca(OH)2 in the purification process. Calcium oxide is typically used to react with metal ions in solution to form insoluble precipitates, thereby effectively removing these impurities. Omitting this step results in the ineffective removal of impurities in solution, especially metal ions, ultimately affecting the purity and quality of the product.

[0110] A comparison of the purity data of the quartz sand obtained in Example 2 and Comparative Example 2 shows that omitting the ion exchange step significantly increases the impurity content. Ion exchange resins are commonly used to adsorb metal ions in solution, especially calcium and sodium ions, which can affect the purity of the final product.

[0111] A comparison of the purity data of the quartz sand obtained in Example 2 and Comparative Example 3 shows that a sol temperature 5-10°C higher leads to a significant increase in impurity elements. This indicates that temperature control during gel formation is crucial to the quality of the final product. Higher temperatures accelerate gel formation, but may also cause impurities in the solution to react more readily with the sol or become encapsulated within the formed gel, making them difficult to remove. Consequently, the impurity content of the final product is significantly increased, directly affecting its purity and performance.

[0112] Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing low-cost, high-purity synthetic quartz sand, characterized in that, Includes the following steps: Step 1: Dilute the alkali metal silicates with high-purity water at 35-55°C until they are completely dissolved; wherein, the alkali metal silicates include anhydrous sodium silicate, sodium silicate pentahydrate, and sodium silicate nonahydrate. Step 2: Add the impurity remover to the diluted alkali metal silicate solution obtained in Step 1, stir thoroughly and mix evenly. The impurity remover includes CaO and Ca(OH)2. Step 3: Filter the sol after impurity removal in Step 2 to remove precipitated impurities. The filter screen accuracy is 0.1-1 μm. Step 4: Remove sodium ions from the sol obtained in step 3 by passing it through a strong acid cation exchange column, wherein the solution flow rate is 83-168 L / min. Step 5: Transfer the sol from Step 4 into a reaction vessel and keep stirring under an inert atmosphere; wherein the stirring rate is 100-300 r / min, the stirring temperature is 50-100℃, and the stirring time is 3-12 h. Step 6: After stirring, let stand for 0.5 to 2 hours to allow the sol to turn into a gel, and continue aging under an inert atmosphere for 2 to 24 hours; the aging temperature is 55 to 120℃. Step 7: Soak the aged wet gel in high-purity water for 2-12 hours and wash it 1-3 times; Step 8: Dry the cleaned wet gel under an inert atmosphere; Step 9: Remove the dried gel and crush it using a roller crusher. Adjust the roller gap to 0.1-1 mm and control the target particle size within the range of 200-500 μm through a sieve. Step 10: The crushed dry gel is placed in a high-temperature rotary furnace for sintering to obtain high-purity synthetic quartz sand. The calcination temperature is 800-1250℃ and the calcination time is 6-48h. In step 2, the amount of the impurity removal agent is 1-30 g / L, the stirring time is 0.5-3 h, and the stirring temperature is 40-80 °C. In step 4, the strong acid cation exchange resin is type 732, the pH value of the sol after the ion exchange column is in the range of 2 to 3, and the temperature is maintained at 5 to 10℃ during the process.

2. The preparation method according to claim 1, characterized in that, In step 1, the alkali metal silicate is in the form of granules or powder with a purity of ≥99%, and the mass fraction of the alkali metal silicate in the diluted solution is 2wt.% to 10wt.%.

3. The preparation method according to claim 1 or 2, characterized in that, In step 1, the high-purity water has a pH of 6.5 to 7.0, a total organic carbon content of ≤20 μg / L, and a resistivity of 15 to 18.2 MΩ·cm.

4. The preparation method according to claim 1, characterized in that, In step 5, the lining of the reactor is coated with polytetrafluoroethylene, and the inert gas includes nitrogen or argon with a purity ≥99.995%.

5. The preparation method according to claim 1, characterized in that, In step 6, the inert gas includes nitrogen or argon with a purity ≥99.995% and a flow rate of 40–85 L / min.

6. The preparation method according to claim 1, characterized in that, In step 8, the drying temperature is 160–240℃ and the drying time is 12–24 hours.

7. The preparation method according to claim 1, characterized in that, In step 9, the rollers of the roller crusher are made of high-purity quartz with a purity ≥99.995% and a rotational speed range of 20~100r / min.

8. The preparation method according to claim 1, characterized in that, During the high-temperature roasting process in step 10, the furnace tubes of the high-temperature rotary furnace continue to rotate at a speed of 2 to 10 r / min, and the synthetic quartz sand maintains a height difference of 40 to 75 mm inside the furnace tubes.

Images