A method for producing high purity quartz for quartz glass raw material

Abstract

The application discloses a preparation method of high-purity quartz for quartz glass raw materials, and relates to the field of high-purity quartz sand purification, and comprises the following steps: S1, high-temperature calcination is carried out on quartz fine sand, and after heat preservation, water quenching is rapidly carried out, and after drying, pretreated quartz sand is obtained; S2, the quartz fine sand is uniformly mixed with anhydrous potassium carbonate powder at a mass ratio of 100:1 to 100:5; S3, under the protection of an inert gas atmosphere, the mixture is heated to 1050 DEG C-1150 DEG C, and heat preservation is carried out for 60-180 minutes; S4, after heat preservation, slow cooling is carried out at a cooling rate of 0.5-3 DEG C / minute to 800 DEG C-900 DEG C; according to the method, the potassium metasilicate liquid film generated by the reaction of anhydrous potassium carbonate and quartz is combined with heat preservation dissolution and controlled-rate cooling recrystallization, so that the aluminum impurities in the quartz lattice in the form of isomorphism can be effectively transferred to the soluble glass phase, and deep removal of the lattice aluminum is realized.

Description

Technical Field

[0001] This invention relates to high-purity quartz sand purification technology, specifically to a method for preparing high-purity quartz for use as a raw material for quartz glass. Background Technology

[0002] High-purity quartz sand is a fundamental raw material for industries such as semiconductors, photovoltaics, fiber optic communications, and the manufacturing of high-end optical devices. Its purity directly affects the performance of downstream products. Impurities in natural quartz minerals mainly exist in three forms: independent gangue minerals, gas-liquid inclusions, and impurity ions that substitute for silicon ions in the crystal lattice in isomorphous forms. Among these, independent gangue minerals and most gas-liquid inclusions can be effectively separated using physical beneficiation methods such as magnetic separation, flotation, and high-temperature detonation.

[0003] However, aluminum ions, existing in the quartz lattice in an isomorphous form, are the most prevalent and difficult-to-remove impurity after physical beneficiation. Because aluminum ions have a similar ionic radius to silicon ions and often undergo charge compensation with alkali metal ions such as sodium and lithium ions, they are stably bonded within the lattice. Traditional physical methods and chemical acid leaching that only acts on the particle surface are extremely difficult to destroy and remove them.

[0004] In existing technologies, the most effective method for removing such lattice-state aluminum impurities is high-temperature chlorination roasting. This method requires introducing chlorine or hydrogen chloride gas into the quartz powder at a high temperature of 1200℃ to 1600℃, causing the impurity elements to be converted into volatile chlorides and separated from the quartz.

[0005] The main technical problems of the chlorination roasting method are: firstly, the operating temperature is extremely high, resulting in huge energy consumption; secondly, it is necessary to use highly corrosive and toxic gases such as chlorine and hydrogen chloride as working media, which places extremely high demands on the corrosion resistance, sealing and safe production management of the reaction equipment, resulting in high construction and operation costs, and significant environmental and safety risks. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing high-purity quartz for quartz glass raw materials, so as to solve the problem that the high-temperature chlorination roasting method in the prior art requires the use of highly corrosive and toxic gases such as chlorine or hydrogen chloride.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing high-purity quartz for quartz glass raw materials, comprising the following steps:

[0008] S1. Provide quartz sand purified by physical mineral processing as raw material, calcine the quartz sand at 700℃-900℃, keep it at the temperature for 10-30 minutes, and then quickly put it into cold water for water quenching. After drying, pretreated quartz sand is obtained.

[0009] S2. The quartz sand and anhydrous potassium carbonate powder are mixed uniformly at a mass ratio of 100:1 to 100:5 to obtain a mixture.

[0010] S3. Under an inert gas protective atmosphere, the mixture is heated to 1050℃-1150℃ and kept at that temperature for 60-180 minutes to allow anhydrous potassium carbonate to react with the surface of quartz particles to form a potassium metasilicate liquid film.

[0011] S4. After the heat preservation is completed, slowly cool down to 800℃-900℃ at a cooling rate of 0.5-3℃ / min, so that the silica dissolved in the liquid film recrystallizes and precipitates on the surface of the quartz particles.

[0012] S5. Continue cooling to room temperature at a cooling rate higher than the stated cooling rate, so that the residual liquid phase solidifies into an amorphous glass phase, and the processed material is obtained.

[0013] S6. The material to be processed is washed with water or acid to remove the surface glass phase, and then filtered and dried to obtain high-purity quartz sand.

[0014] The silica content of the quartz concentrate should preferably be no less than 99.9%. Physical beneficiation includes processes such as magnetic separation and flotation, which aim to pre-separate independent solid impurities and reduce the processing load of subsequent steps.

[0015] Furthermore, the anhydrous potassium carbonate powder mentioned in step S2 is of analytical grade, and the particle size range of the pretreated quartz sand is 80-200 mesh.

[0016] To provide a suitable specific surface area, the mass ratio of anhydrous potassium carbonate to pretreated quartz sand is controlled within the range of 1:100 to 5:100, ensuring that the reaction generates a micron-thick liquid film that only coats the surface of the particles, thus avoiding the formation of excessive liquid phase that leads to excessive adhesion between particles.

[0017] Furthermore, the inert gas in step S3 is nitrogen or argon, and the heating rate is 5-10°C / minute.

[0018] Keep it at a high temperature for 60-180 minutes to allow the dissolution of the quartz surface lattice and the release of impurities to proceed fully.

[0019] Furthermore, the potassium metasilicate liquid film mentioned in step S3 is a liquid film with a thickness of micrometers that coats the surface of quartz particles.

[0020] Furthermore, the cooling rate described in step S4 is 0.8-1.5℃ / min, which helps to achieve the segregation effect.

[0021] Furthermore, the cooling rate described in step S5 is 5-10°C / minute.

[0022] Rapid cooling at this stage prevents the residual liquid phase from crystallizing and causes it to solidify into an amorphous glass phase. This glass phase loosely coats the surface of the quartz particles, making it easy to remove later.

[0023] Furthermore, the water washing in step S6 is ultrasonic stirring and immersion in deionized water at 70℃-90℃ for 30-60 minutes.

[0024] This stage is used to dissolve the potassium silicate glass phase.

[0025] Furthermore, the pickling in step S6 involves immersing the sample in dilute hydrochloric acid with a concentration of no more than 3% at 60°C-80°C for 15-30 minutes.

[0026] This stage is used for insoluble impurities. After washing, the sand is rinsed with deionized water until neutral, filtered, and dried at 100-120℃ to obtain high-purity quartz sand.

[0027] Furthermore, the silica content of the quartz sand in step S1 is not less than 99.9%.

[0028] Furthermore, the high-temperature calcination temperature in step S1 is 750℃-850℃, and the temperature of the cold water is 5℃-25℃.

[0029] This invention utilizes the reaction of anhydrous potassium carbonate with the surface of quartz particles at a target temperature to generate a potassium metasilicate liquid film in situ. During the heat treatment stage, this liquid film dissolves the surface lattice of the quartz, releasing aluminum impurities trapped within the lattice into the liquid phase. In the subsequent slow cooling stage, the impurity segregation effect at the solid-liquid interface is utilized, causing the dissolved silica to preferentially recrystallize on the surface of pure crystal nuclei, while the aluminum impurities are repelled and enriched in the residual liquid phase. Finally, rapid cooling solidifies the impurity-rich residual liquid phase into a water-soluble or acid-soluble glassy phase, which is then removed by gentle chemical cleaning.

[0030] Compared with the prior art, the present invention provides a method for preparing high-purity quartz for quartz glass raw materials, which uses solid anhydrous potassium carbonate as a flux precursor. The entire process does not introduce any chlorine- or fluorine-containing chemicals, thus avoiding the risks of equipment corrosion, environmental emissions and personnel safety caused by hazardous gases from the source.

[0031] The maximum operating temperature of the method of the present invention is 1050℃-1150℃, which is significantly lower than the 1200℃-1600℃ usually required by the traditional chlorination roasting method. This helps to reduce process energy consumption, reduce the performance requirements of furnace body refractory materials and heating elements, thereby improving equipment service life and reducing operating costs.

[0032] High-temperature bursting breaks up gas-liquid inclusions and creates microcrack channels. Potassium metasilicate liquid film penetrates into the particle interior along the microcracks, dissolving the quartz surface lattice while incorporating the burst-released inclusion impurities and isomorphic aluminum impurities into the liquid phase. Then, through temperature-controlled partial solidification and recrystallization, the impurities are expelled and enriched in the soluble glass phase for removal, resulting in high-purity quartz sand with an aluminum content of less than 5 ppm and a silica content of more than 99.999%. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0034] Figure 1 A flowchart illustrating the method steps provided in an embodiment of the present invention. Detailed Implementation

[0035] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0036] As attached Figure 1 As shown:

[0037] Example 1:

[0038] This invention provides a method for preparing high-purity quartz for use as a raw material for quartz glass.

[0039] Raw material analysis:

[0040] 1000g of quartz concentrate was obtained from a granite pegmatite-type quartz ore after crushing, grinding, classification, high-gradient magnetic separation, and reverse flotation to remove gangue minerals such as feldspar and mica. Analysis showed that the main chemical composition of the quartz concentrate was: SiO2 content 99.91%, and the main impurity elements were Al 310ppm, Fe 35ppm, Na 48ppm, K 42ppm, Ca 18ppm, and Li 8ppm. The particle size distribution of the concentrate was 80-200 mesh, and the volumetric cumulative distribution (D50) was approximately 140 mesh. Microscopic observation revealed a certain number of gas-liquid inclusions within the quartz particles, with particle sizes mostly ranging from 2-10μm.

[0041] High-temperature bursting pretreatment:

[0042] The above-mentioned quartz sand was spread evenly in a corundum crucible to a thickness of approximately 20 mm and then pushed into a box furnace. The temperature was increased to 800°C at a rate of 10°C / min and held for 20 minutes. After the holding period, the furnace door was quickly opened, and the material was poured into a stainless steel bucket containing 10L of cold water (approximately 15°C) for water quenching. During the water quenching process, obvious bubbles were observed escaping and bursting sounds were heard, indicating that the gas-liquid inclusions ruptured under thermal stress. The water-quenched quartz sand was then removed and dried in a 110°C oven for 4 hours to obtain pretreated quartz sand.

[0043] Flux mixing:

[0044] Weigh 1000g of the pretreated quartz sand and 25g of anhydrous potassium carbonate powder, with a mass ratio of 100:2.5. Place both into a V-type mixer, set the speed to 25 r / min, and the mixing time to 30 minutes to obtain a mixture in which anhydrous potassium carbonate powder is uniformly dispersed among the quartz particles. After mixing, take a sample for observation; a trace amount of white potassium carbonate powder can be seen uniformly adhering to the surface of the quartz particles, without obvious agglomeration.

[0045] High-temperature heat treatment:

[0046] The above mixture was spread evenly in a 2000mL high-purity corundum crucible, with a thickness of approximately 25mm. The crucible was then pushed into a box-type atmosphere furnace. After sealing the furnace door, the furnace chamber was evacuated and purged three times with 99.99% pure nitrogen to ensure an inert atmosphere inside the furnace. Thereafter, nitrogen was continuously purged at a flow rate of 2L / min.

[0047] The heating program was initiated, raising the temperature from room temperature to 1100°C at a rate of 5°C / min, and holding for 150 minutes. During the heating process, at approximately 900-950°C, anhydrous potassium carbonate began to undergo a solid-phase reaction with SiO2 on the surface of the quartz particles and the walls of the burst microcracks, forming potassium metasilicate. The liquid film then penetrated along the microcracks into the particle interior, dissolving the surface lattice and capturing released inclusion impurities and lattice aluminum impurities.

[0048] After reaching 1100℃, the process enters a heat preservation stage, which lasts for 120 minutes. During this heat preservation period, the SiO2 on the surface and within a few micrometers of the near-surface layer of the quartz particles dissolves in the potassium metasilicate liquid film. As the surface SiO2 dissolves, the Al atoms previously confined within the quartz lattice... 3+ And Na, which compensates for its charge + Li + As impurity ions are released into the liquid film, they form freely moving ionic states within the highly ionic potassium metasilicate melt. Simultaneously, some gas-liquid inclusions distributed on the shallow surface of the quartz particles are dissolved and absorbed by the liquid film during this process, and the H2O and impurities contained within them also enter the liquid phase.

[0049] Controlled-rate cooling recrystallization:

[0050] After holding at this temperature for 120 minutes, the cooling program was initiated. The temperature was slowly reduced from 1100℃ to 800℃ at a rate of 0.8℃ / min, a range of 250℃, taking approximately 375 minutes. During this slow cooling process, the solubility of SiO2 in the potassium metasilicate liquid film gradually decreased with decreasing temperature. The SiO2 in the liquid film gradually reached a supersaturated state and began to recrystallize epitaxially onto the surface of undissolved high-purity quartz crystal nuclei as an α-quartz structure. Due to the impurity segregation effect, Al... 3+ Na + Li + Impurity ions are rejected during recrystallization, remain and accumulate in the residual potassium metasilicate liquid phase, and the newly formed quartz layer has a purity much higher than that of the original quartz.

[0051] Rapid cooling:

[0052] After cooling to 800℃, the cooling rate was switched to 6℃ / min for further cooling. During this cooling stage, as the temperature further decreased, the residual potassium metasilicate liquid phase lost its crystallization ability due to a sharp increase in viscosity. When the temperature dropped to below approximately 200℃, the residual liquid phase completely solidified into an amorphous potassium silicate glass phase, loosely coating the surface of the recrystallized quartz particles. Upon removal of the material, the product was observed to be a slightly adherent light gray mass that could be easily dispersed into powder with a light press of a finger, with no obvious sintering observed, indicating that the total liquid film volume was properly controlled.

[0053] Post-processing:

[0054] The obtained powder was transferred entirely to a 5L glass beaker, and 3000mL of preheated deionized water to 80℃ was added. The beaker was placed in an ultrasonic cleaning tank, with the ultrasonic frequency set to 40kHz, and mechanically stirred for 60 minutes. During this process, the potassium silicate glass phase gradually dissolved in the water, and the pH of the aqueous solution rose to approximately 11-12, indicating that the KOH generated from the hydrolysis of potassium silicate had entered the solution. After 60 minutes, the mixture was filtered, and the filter cake was rinsed three times with 80℃ deionized water, with approximately 1000mL of water each time. The conductivity of the final rinse water was analyzed, confirming that it had decreased to below 5μS / cm.

[0055] The washed filter cake was placed in an electric heating drying oven and dried at 110°C for 4 hours. After cooling to room temperature, it was sealed and packaged to obtain the high-purity quartz sand product of this embodiment.

[0056] Results analysis:

[0057] Chemical analysis of the finished product revealed a SiO2 content of 99.999%, with impurities present at concentrations of Al 3.2 ppm, Fe 1.2 ppm, Na 1.5 ppm, K 0.8 ppm, Ca 0.5 ppm, and Li 0.2 ppm. Compared to the raw material, the Al removal rate was approximately 99%, while the removal rates of other impurities were all above 95%. The results indicate that the method of this invention effectively removes the predominantly dominant lattice aluminum impurities from the quartz sand, while other alkali metal impurities are also significantly reduced simultaneously, achieving a product quality level of 5N.

[0058] The wastewater collected during the above treatment process was analyzed by ICP-OES. The concentrations of aluminum ions were 115.3 mg / L, potassium ions were 8920 mg / L, sodium ions were 15.6 mg / L, and calcium ions were 6.8 mg / L. This confirmed that various impurities dissolved into the washing solution through the glass phase and were separated from the quartz matrix.

[0059] Example 2:

[0060] This invention provides a method for preparing high-purity quartz for use as a raw material for quartz glass.

[0061] 1000g of hydrothermal vein quartz sand from another source was collected. The SiO2 content was 99.92%, and the aluminum impurity content reached 650ppm, classifying it as a highly difficult-to-process raw material. Other impurities included Fe 30ppm, Na 45ppm, K 38ppm, Ca 14ppm, and Li 7ppm. Microscopic observation revealed well-developed gas-liquid inclusions.

[0062] High-temperature bursting pretreatment:

[0063] The temperature is increased to 850℃ at a rate of 8℃ / min, held for 15 minutes, and then quenched in cold water at 10℃. After drying, pretreated quartz sand is obtained.

[0064] Flux mixing:

[0065] Given the high aluminum content and well-developed inclusions in the raw material, the flux ratio was appropriately increased. 40g of anhydrous potassium carbonate powder was weighed and mixed with 1000g of pretreated quartz sand at a mass ratio of 100:4.

[0066] High-temperature heat treatment:

[0067] Under an argon protective atmosphere (purity 99.99%, flow rate 3L / min), the temperature was increased to 1130℃ at a rate of 5℃ / min and held for 180 minutes to provide more reaction time for the liquid film to penetrate along the burst microcracks and dissolve the quartz with high impurity content.

[0068] Controlled-rate cooling recrystallization:

[0069] After the heat preservation period, the temperature is slowly reduced to 820°C at a rate of 0.5°C / minute. This cooling rate is a relatively slow value within the preferred range of this invention, which is beneficial for fully utilizing the impurity segregation effect under near-equilibrium conditions. This cooling stage takes approximately 620 minutes.

[0070] Rapid cooling and post-processing:

[0071] The product was rapidly cooled to room temperature at a rate of 10°C / min. It was then added to 3000 mL of a 2% dilute hydrochloric acid solution (prepared from analytical grade hydrochloric acid and deionized water), and the temperature was maintained at 70°C. The mixture was mechanically stirred and washed for 20 minutes. After acid washing, the mixture was filtered and repeatedly rinsed with deionized water until the pH of the filtrate was neutral. The filter cake was then dried in an oven at 120°C for 3 hours.

[0072] Results analysis:

[0073] Testing revealed that the finished product contained 99.999% SiO2, with the Al content reduced to 4.5 ppm, representing an Al removal rate of approximately 99.3%. Other impurities included Fe 1.5 ppm, Na 1.8 ppm, K 1.0 ppm, Ca 0.6 ppm, and Li 0.4 ppm. These results demonstrate that even for difficult-to-process raw materials with high aluminum and high inclusion content, achieving a 5N purity level is still possible by increasing the flux ratio, extending the holding time, and employing a slower cooling rate.

[0074] Comparative Example 1: Traditional High-Temperature Chlorination Roasting Method

[0075] Take 500g of the same batch of quartz sand as in the example and process it using the traditional high-temperature chlorination roasting process.

[0076] Quartz sand was placed in a high-purity quartz boat within a tubular atmosphere furnace, and a nitrogen mixture containing 0.5% vol% chlorine was introduced at a total flow rate of 1.5 L / min. The temperature was increased to 1200℃ at a rate of 5℃ / min and held for 4 hours. The chlorine mixture was continuously introduced during the holding period. After the holding period, the chlorine supply was stopped, and pure nitrogen was used for purging. The mixture was then allowed to cool naturally to room temperature. The product was removed, washed three times with deionized water, and dried at 110℃.

[0077] Testing revealed that the SiO2 content of the product obtained in the comparative example was 99.997%, and the contents of various impurities were: Al 15ppm, Fe 4ppm, Na 3ppm, K 2ppm, and Ca 1ppm. Compared with Example 1, this method operates at a temperature more than 100°C higher and uses toxic chlorine gas as the reaction medium. Furthermore, the residual aluminum impurities in the product are also lower than in Example 1.

[0078] Comparative Example 2: Molten salt treatment only, without high-temperature bursting

[0079] Take 200g of quartz sand from the same batch as in the example, without high-temperature cracking pretreatment, mix it directly with anhydrous potassium carbonate at a ratio of 100:2.5, keep it at 1100℃ for 150 minutes, cool it down to 800℃ at a rate of 0.8℃ / minute, cool it rapidly, and wash it with water.

[0080] Testing revealed that the product contained 99.998% SiO2 (4N8 grade) and 8 ppm Al. Compared to Example 1, without the high-temperature bursting step, although lattice aluminum impurities could be effectively removed through the liquid film dissolution-separation recrystallization mechanism, the removal effect on impurities in the gas-liquid inclusions was limited, resulting in the product purity failing to reach the 5N grade. This comparative example demonstrates the necessity of high-temperature bursting pretreatment for opening up the pathway for impurity removal from inclusions.

[0081] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for preparing high-purity quartz for use as a raw material in quartz glass, characterized in that, Includes the following steps: S1. Provide quartz sand purified by physical mineral processing as raw material, calcine the quartz sand at 700℃-900℃, keep it at the temperature for 10-30 minutes, and then quickly put it into cold water for water quenching. After drying, pretreated quartz sand is obtained. S2. The pretreated quartz sand and anhydrous potassium carbonate powder are uniformly mixed at a mass ratio of 100:1 to 100:5 to obtain a mixture. S3. Under an inert gas protective atmosphere, the mixture is heated to 1050℃-1150℃ and kept at that temperature for 60-180 minutes to allow anhydrous potassium carbonate to react with the surface of quartz particles to form a potassium metasilicate liquid film. S4. After the heat preservation is completed, slowly cool down to 800℃-900℃ at a cooling rate of 0.5-3℃ / min, so that the silica dissolved in the liquid film recrystallizes and precipitates on the surface of the quartz particles. S5. Continue cooling to room temperature at a cooling rate higher than the stated cooling rate, so that the residual liquid phase solidifies into an amorphous glass phase, and the processed material is obtained. S6. The material to be processed is washed with water or acid to remove the surface glass phase, and then filtered and dried to obtain high-purity quartz sand.

2. The method for preparing high-purity quartz for quartz glass raw materials according to claim 1, characterized in that, The anhydrous potassium carbonate powder mentioned in step S2 is of analytical grade, and the particle size range of the pretreated quartz sand is 80-200 mesh.

3. The method for preparing high-purity quartz for quartz glass raw materials according to claim 1, characterized in that, The inert gas mentioned in step S3 is nitrogen or argon, and the heating rate is 5-10℃ / minute.

4. The method for preparing high-purity quartz for quartz glass raw materials according to claim 1, characterized in that, The potassium metasilicate liquid film mentioned in step S3 is a micron-thick liquid film that coats the surface of quartz particles.

5. The method for preparing high-purity quartz for quartz glass raw materials according to claim 1, characterized in that, The cooling rate described in step S4 is 0.8-1.5℃ / minute.

6. The method for preparing high-purity quartz for quartz glass raw materials according to claim 1, characterized in that, The cooling rate described in step S5 is 5-10°C / minute.

7. The method for preparing high-purity quartz for quartz glass raw materials according to claim 1, characterized in that, The water washing in step S6 involves ultrasonically stirring and immersing the water in deionized water at 70℃-90℃ for 30-60 minutes.

8. The method for preparing high-purity quartz for quartz glass raw materials according to claim 1, characterized in that, The pickling described in step S6 involves immersing the food in dilute hydrochloric acid with a concentration of no more than 3% at 60℃-80℃ for 15-30 minutes.

9. A method for preparing high-purity quartz for quartz glass raw materials according to claim 1, characterized in that, The silica content of the quartz sand in step S1 is not less than 99.9%.

10. A method for preparing high-purity quartz for quartz glass raw materials according to claim 1, characterized in that, The high-temperature calcination temperature in step S1 is 750℃-850℃, and the temperature of the cold water is 5℃-25℃.

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