Preparation method of ultra-pure synthetic quartz sand

Abstract

The invention relates to the technical field of quartz sand preparation, in particular to a preparation method of ultra-pure synthetic quartz sand. Pretreating the silicon dioxide wet gel which is determined to be qualified based on the viscosity growth rate to obtain flat silicon dioxide dry gel; determining whether the pretreatment reaches the standard based on a purification potential index; a roasting index is determined based on the impurity content reaching the standard after pretreatment; determining to start high-temperature roasting on the flat silicon dioxide xerogel based on the roasting admission index; determining roasting parameters based on the reference roasting intensity; determining whether the impurity removal rate reaches the standard based on the reaction intensity index; and based on the purity value of the quartz sand finished product, determining whether the quality of the single batch of quartz sand finished product is qualified or not so as to adjust the flat thickness value or preset roasting temperature of the next batch of preparation process. The purity of the quartz sand is improved.

Description

Technical Field

[0001] This invention relates to the field of quartz sand preparation technology, and in particular to a method for preparing ultrapure synthetic quartz sand. Background Technology

[0002] With the rapid development of the semiconductor, optical communication, and photovoltaic industries, the demand for high-purity synthetic quartz sand is increasing daily, and its purity directly affects the performance and reliability of downstream products. Traditional quartz sand preparation processes face technical bottlenecks when dealing with ultra-high purity requirements, including unstable control of metallic impurities, reliance on experience for process parameter adjustments, and poor batch-to-batch consistency. Existing synthetic quartz sand preparation methods often focus on optimizing single processes, lacking systematic control over the correlation between precursor quality and final purity, resulting in significant fluctuations in product quality.

[0003] Existing preparation processes generally suffer from a disconnect in quality control between processes, lacking effective quality transfer and feedback mechanisms between production stages. Particularly in critical processes such as gelation, aging, and drying, there is a lack of monitoring and quantitative assessment methods for key parameters affecting final purity (such as gel network structure, pore characteristics, and organic residues), causing process parameter adjustments to lag behind quality fluctuations. Furthermore, traditional methods rely heavily on subsequent purification processes to control metal impurities, failing to establish a systematic purity control strategy from the precursor formation stage. This makes it difficult for the final metal content of the product to consistently reach the ultrapure standard of below 100 ppb, resulting in both energy and raw material waste and hindering the supply of materials for high-end applications.

[0004] Chinese Patent Publication No. CN115490240A discloses a method and system for preparing high-purity quartz sand. The method includes: step S1, mixing a silicon-containing compound and water, and performing a hydrolysis reaction to obtain a paste-like product; step S2, purifying the paste-like product to obtain a quartz sand precursor; and step S3, sintering the quartz sand precursor to obtain high-purity quartz sand. The silicon-containing compound includes at least one of tetrachlorosilane or tetraethyl orthosilicate. The method for preparing high-purity quartz sand provided in this application uses a silicon-containing compound and water as raw materials to synthesize a paste-like product, purifies the paste-like product, and then sintersulates it to obtain high-purity quartz sand. The raw materials are inexpensive and readily available, the process is simple, and the obtained high-purity quartz sand has a purity of 99.998%, which can effectively meet the domestic production needs of photovoltaic monocrystalline silicon wafers and semiconductor silicon wafers.

[0005] Therefore, the aforementioned method and system for preparing high-purity quartz sand have the following problems: 1. The process is crude, lacking refined precursor quality assessment and access control; 2. The quality control process is lagging and simplistic, lacking adaptive and cross-batch optimization capabilities. Summary of the Invention

[0006] Therefore, the present invention provides a method for preparing ultrapure synthetic quartz sand to overcome the problems of lagging purity control and poor consistency of quartz sand in the prior art.

[0007] To achieve the above objectives, the present invention provides a method for preparing ultrapure synthetic quartz sand, comprising: The pretreatment of qualified silica wet gel based on viscosity growth rate was used to obtain flat silica dry gel; Based on the average pore size and loss on ignition of the flat silica dry gel, the purification potential index of the flat silica dry gel is determined, and the pretreatment is determined to meet the standard based on the comparison result between the purification potential index and the preset purification potential index. The impurity content was determined after the pretreatment of the flat silica dry gel met the standards, so as to determine the calcination index of the flat silica dry gel. The calcination admission index is determined based on the purification potential index and the calcination index to initiate high-temperature calcination of the flat silica dry gel. The benchmark calcination intensity is determined based on the calcination access index in order to determine the calcination parameters of the flat silica dry gel. The reaction intensity index of the flat silica dry gel was determined based on the infrared thermographic characteristics during the calcination process, in order to determine whether the impurity removal rate of the flat silica dry gel met the standard. After the quartz sand product is obtained after calcination, the purity value of the quartz sand product is measured to determine whether the quality of a single batch of the quartz sand product is qualified, so as to adjust the flatness thickness value or preset calcination temperature of the next batch preparation process.

[0008] Furthermore, the process of determining the preparation of qualified silica wet gel based on viscosity growth rate includes: The viscosity growth rate is compared with the preset maximum viscosity growth rate and the preset minimum viscosity growth rate, respectively; Based on the viscosity growth rate being greater than or equal to the preset minimum viscosity growth rate and the viscosity growth rate being less than or equal to the preset maximum viscosity growth rate, the silica wet gel is determined to be of qualified quality. Based on the fact that the viscosity growth rate is less than the preset minimum viscosity growth rate, the silica wet gel is determined to be of substandard quality. Based on the viscosity growth rate being greater than the preset maximum viscosity growth rate, the silica wet gel is determined to be of substandard quality.

[0009] Furthermore, the process of determining whether the pretreatment meets the standard based on the purification potential index includes: The purification potential index is compared with the preset purification potential index; Based on the purification potential index being greater than or equal to the preset purification potential index, the pretreatment is determined to be up to standard; Based on the fact that the purification potential index is less than the preset purification potential index, it is determined that the pretreatment is substandard.

[0010] Furthermore, the process of determining the calcination index based on the pretreatment meeting the standards includes: The impurity content is compared with the preset impurity content; Based on the impurity content being greater than or equal to a preset impurity content, the calcination index is determined to be the first calcination index; Based on the fact that the impurity content is less than the preset impurity content, the roasting index is determined to be the second roasting index.

[0011] Furthermore, the process of determining the calcination threshold index to initiate high-temperature calcination of the flat silica dry gel includes: The roasting access index is compared with the preset roasting access index range; Based on the fact that the calcination access index is within the preset calcination access index range, it is determined that calcination will be initiated on the flat silica dry gel.

[0012] Furthermore, the process of determining the baseline calcination intensity to determine the calcination parameters of the flat silica dry gel includes: Compare the benchmark roasting intensity with the preset roasting intensity; Based on the benchmark calcination intensity being greater than or equal to the preset calcination intensity, the calcination parameters of the flat silica dry gel are determined as the first calcination parameters. If the reference calcination intensity is less than the preset calcination intensity, the calcination parameters of the flat silica dry gel are determined as the second calcination parameters.

[0013] Furthermore, the process of determining whether the impurity removal rate of the flat silica dry gel meets the standard includes: The reaction intensity index is compared with the preset reaction intensity index; Based on the reaction intensity index being greater than or equal to the preset reaction intensity index, it is determined that the impurity removal rate of the flat silica dry gel meets the standard. Based on the fact that the reaction intensity index is less than the preset reaction intensity index, it is determined that the impurity removal rate of the flat silica dry gel does not meet the standard.

[0014] Furthermore, the process of determining whether the quality of a single batch of the finished quartz sand product is qualified includes: The purity value of the finished quartz sand product is compared with the preset purity value; Based on the purity value being greater than or equal to a preset purity value, the quality of a single batch of the finished quartz sand is determined to be qualified. Based on the purity value being less than the preset purity value, it is determined that the quality of a single batch of the finished quartz sand is unqualified.

[0015] Furthermore, the process of determining the flatness thickness value for the next batch of preparation process based on the substandard quality of the quartz sand product in a single batch includes: Obtain the purity deviation value between the purity value and the preset purity value; The purity deviation value is compared with a preset purity deviation threshold. Based on the purity deviation value being less than or equal to a preset purity deviation threshold, the flatness thickness value for the next batch preparation process is determined to be increased by a first adjustment coefficient.

[0016] Furthermore, based on the fact that the purity deviation value is greater than the preset purity deviation threshold, a preset calcination temperature for the next batch preparation process is determined by increasing the second adjustment coefficient.

[0017] Compared with existing technologies, the beneficial effects of this invention are as follows: Specifically, this invention achieves control over the preparation process of ultrapure silica sand through multi-parameter synergy. It assesses gel quality compliance based on viscosity growth rate, determines the purification potential index by combining average pore size and loss on ignition, and determines whether pretreatment meets standards. It determines the calcination index of flat silica dry gel based on impurity content, determines the calcination access index based on the purification potential index and calcination index to initiate high-temperature calcination, optimizes calcination process parameters by combining benchmark calcination intensity, and achieves batch quality closed-loop feedback through purity deviation values. This improves the precision of ultrapure silica sand preparation. The quality assessment of flat silica dry gel and the matching of calcination intensity provide data support for dynamic control of process parameters, avoiding energy waste and optimizing production resource allocation. The multi-dimensional index system constructs quantitative process standards, improving the quality control efficiency of the ultrapure silica sand preparation process, thereby enhancing the consistency and reliability of purity control in synthetic silica sand products.

[0018] Furthermore, this invention achieves monitoring and control of the hydrolysis-condensation reaction kinetics by comparing the viscosity growth rate with the preset viscosity growth rate. A viscosity growth rate less than the preset minimum viscosity growth rate indicates insufficient reaction activity or uneven mixing, requiring enhanced mixing to promote mass transfer and reaction integrity. A viscosity growth rate greater than the preset maximum viscosity growth rate indicates a violent reaction that may cause local overheating and stress concentration in the network structure, requiring reduced mixing to slow down the reaction process. This adjustment mechanism ensures the uniformity and mechanical stability of the silica gel network structure, providing high-quality flat silica dry gel for subsequent aging, drying, and calcination processes. This ensures the ultra-high purity of the final synthesized quartz sand from the source, thereby improving the robustness of the entire preparation process and the consistency of the finished product.

[0019] Furthermore, this invention determines the purification potential index of the flat silica dry gel by the average pore size and the loss on ignition. The purification potential index establishes a clear standard for pretreatment, indicating that the flat silica dry gel has good impurity diffusion channels and contaminant loading levels. The purification potential index provides a preliminary assessment for subsequent calcination treatment, significantly improving the predictability and controllability of the ultrapure quartz sand preparation process. While ensuring the purity of quartz sand, it optimizes energy consumption, reduces production costs, and thus improves the effectiveness and consistency of purity control of synthetic quartz sand products.

[0020] Furthermore, this invention obtains the calcination access index of flat silica dry gel through the purification potential index and the calcination index, establishing a quantitative standard for starting the high-temperature calcination process. When the calcination access index is within the qualified range, it indicates that the flat silica dry gel has ideal heat treatment characteristics and can directly enter the calcination stage. When the calcination access index deviates from the qualified range, the corresponding optimization treatment of the flat silica dry gel is initiated according to the direction of deviation. Through structural improvement or contaminant removal, the controllability and intelligence level of the ultrapure quartz sand preparation process are significantly improved. While ensuring the purity of quartz sand, energy waste and production interruption are effectively avoided, thereby improving the consistency of synthetic quartz sand product quality and the economy of the production process.

[0021] Furthermore, this invention determines the baseline roasting intensity based on the roasting access index, establishing a quantitative correlation between precursor quality characteristics and heat treatment intensity. A high baseline roasting intensity indicates good uniformity of the flat silica degel network and a large potential for impurity removal, allowing for the full utilization of the material's purification limit using an enhanced roasting scheme. Conversely, a low baseline roasting intensity suggests structural defects or contamination risks in the flat silica degel, necessitating a mild roasting scheme to avoid lattice defects caused by over-treatment. This graded roasting parameter control achieves precise matching between the roasting process and the flat silica degel, overcoming the limitations of traditional fixed roasting curves, ensuring the purity of the quartz sand product, and improving the adaptability of the ultrapure quartz sand preparation process.

[0022] Furthermore, by determining the purity value of the finished quartz sand, and comparing the purity values ​​of the finished quartz sand products, this invention determines the qualification of the batch of finished quartz sand products, thereby improving the consistency and stability of quartz sand quality, reducing energy consumption and material loss during the production process, avoiding resource waste caused by unqualified quartz sand flowing into subsequent stages, adapting to the impact of raw material characteristic fluctuations on the production process, shortening the response time for identifying and adjusting abnormal quartz sand quality, and improving the adaptability of production. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the steps of the method for preparing ultrapure synthetic quartz sand according to an embodiment of the present invention; Figure 2 This is a logic diagram for determining whether the pretreatment of flat silica dry gel meets the standards in an embodiment of the present invention. Figure 3 A logic diagram for determining the calcination index of flat silica dry gel in an embodiment of the present invention; Figure 4 The logic diagram for determining the calcination parameters of flat silica dry gel in an embodiment of the present invention is shown. Detailed Implementation

[0024] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0025] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0026] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0027] Please see Figure 1 As shown, it is a flowchart of the steps of the method for preparing ultrapure synthetic quartz sand according to the present invention.

[0028] The present invention provides a method for preparing ultrapure synthetic quartz sand, comprising: S1, based on the viscosity growth rate, pretreatment of qualified silica wet gel is used to obtain flat silica dry gel; S2, based on the average pore size and loss on ignition of the flat silica dry gel, determine the purification potential index of the flat silica dry gel, and determine whether the pretreatment meets the standard based on the comparison result of the purification potential index and the preset purification potential index. S3, based on the pretreatment of flat silica dry gel to meet the standard, the impurity content is determined to determine the calcination index of the flat silica dry gel; S4, Based on the purification potential index and the calcination index, determine the calcination access index to initiate high-temperature calcination of the flat silica dry gel; S5, determine the benchmark calcination intensity based on the calcination access index, so as to determine the calcination parameters of the flat silica dry gel; S6. The reaction intensity index of the flat silica dry gel is determined based on the infrared thermographic characteristics during the calcination process, so as to determine whether the impurity removal rate of the flat silica dry gel meets the standard. S7. Based on the quartz sand finished product obtained after calcination, measure the purity value of the quartz sand finished product to determine whether the quality of a single batch of the quartz sand finished product is qualified, so as to adjust the flatness thickness value or preset calcination temperature of the next batch preparation process.

[0029] In this embodiment of the invention, the preparation process of the silica wet gel is as follows: 40 mL of electronic grade tetraethyl orthosilicate (TEOS) and 80 mL of anhydrous ethanol are mixed in a quartz beaker to prepare solution A; simultaneously, 20 mL of ultrapure water, 80 mL of anhydrous ethanol, and 0.5 mL of high-purity hydrochloric acid are mixed in another beaker to prepare solution B; then, solution A is transferred to a 500 mL three-necked quartz flask, placed in a 60°C constant temperature water bath, and a magnetic stirrer is started to perform non-contact uniform mixing at 300 rpm; next, solution B is slowly added to the reaction system at a rate of 2 mL / min through a constant pressure dropping funnel. After the addition is completed, the temperature and stirring are maintained, and the viscosity change of the system is continuously monitored using a rotational viscometer. When the silica wet gel reaches the gel point, the gelation time is recorded.

[0030] In this embodiment of the invention, the viscosity growth rate is a process kinetic indicator for monitoring the sol-to-gel process. It reflects the hydrolysis and condensation reaction of electronic grade tetraethyl orthosilicate under acidic conditions to form a silica network. The viscosity growth rate directly reflects the formation rate of the three-dimensional network structure. If the viscosity growth rate is too slow, it indicates that the reaction is insufficient, the network structure is loose, and the strength is insufficient. If the viscosity growth rate is too fast, it may lead to excessive local cross-linking, causing network stress concentration and uneven pore size distribution, which may create hidden dangers for subsequent impurity residues.

[0031] In this embodiment of the invention, the gel point is determined using the pouring method: when the container holding the wet silica gel is tilted at 45°, the liquid surface of the wet silica gel remains stable and no longer flows, indicating that the gel point has been reached. The rotational viscometer has a measurement accuracy of ±1%, and the measurement frequency is once every 5 minutes.

[0032] In this embodiment of the invention, the non-contact mixing method includes, but is not limited to, bubbling, magnetic stirring, and ultrasonic mixing. The non-contact mixing ensures that the reaction system is not contaminated by metals, and the constant temperature control ensures the consistency of reaction kinetics.

[0033] Specifically, this invention achieves control over the preparation process of ultrapure silica sand through multi-parameter synergy. It assesses gel quality compliance based on viscosity growth rate, determines the purification potential index by combining average pore size and loss on ignition, and confirms whether pretreatment meets standards. It determines the calcination index of the flat silica dry gel based on impurity content, and uses the purification potential index and calcination index to determine the calcination threshold and initiate high-temperature calcination. It optimizes calcination process parameters by combining a benchmark calcination intensity, and achieves batch quality closed-loop feedback through purity deviation values, thereby improving the precision of ultrapure silica sand preparation. The quality assessment of the flat silica dry gel and the matching of calcination intensity provide data support for dynamic control of process parameters, avoiding energy waste and optimizing production resource allocation. A multi-dimensional index system is used to construct quantitative process standards, improving the quality control efficiency of the ultrapure silica sand preparation process, thus enhancing the consistency and reliability of purity control in synthetic silica sand products.

[0034] Specifically, the process of obtaining the viscosity growth rate based on the viscosity and determining the preparation of a qualified silica wet gel based on the comparison result of the viscosity growth rate and the preset viscosity growth rate includes: If the viscosity growth rate is greater than or equal to the preset minimum viscosity growth rate and the viscosity growth rate is less than or equal to the preset maximum viscosity growth rate, the silica wet gel is determined to be of qualified quality. If the viscosity growth rate is less than the preset minimum viscosity growth rate, the silica wet gel is determined to be of substandard quality. If the viscosity growth rate is greater than the preset maximum viscosity growth rate, then the silica wet gel is determined to be of substandard quality.

[0035] In this embodiment of the invention, the preset viscosity growth rate ranges from [6.0, 10.0] (mPa·s) / min. The minimum preset viscosity growth rate is preferably set to 6.0 (mPa·s) / min, and the maximum preset viscosity growth rate is preferably set to 10.0 (mPa·s) / min. However, the above values ​​are not limited to these, and those skilled in the art can adjust the values ​​according to actual needs.

[0036] In this embodiment of the invention, the viscosity growth rate is obtained by the ratio of the gel point viscosity to the gel time. The gel point viscosity is the instantaneous viscosity of the reaction system when it reaches the gel point, which is obtained by measuring with a rotational viscometer. The gel time is the time recorded from the start of adding liquid B until the gel point is reached.

[0037] Specifically, if the quality of the silica wet gel is determined to be substandard, a benchmark value for adjusting the non-contact mixing strength of the next batch of silica wet gel is determined based on the comparison between the viscosity growth rate and the preset maximum or minimum viscosity growth rate. If the viscosity growth rate is less than the preset minimum viscosity growth rate, then the benchmark value of the non-contact mixing intensity for the next batch is increased to the corresponding value by a first adjustment factor of 1.1. If the viscosity growth rate is greater than the preset maximum viscosity growth rate, then the benchmark value of the non-contact mixing intensity for the next batch is determined to be reduced to the corresponding value by a second adjustment factor of 0.9.

[0038] In this embodiment of the invention, the non-contact mixing intensity is defined as the gas flow rate for the bubbling method, with a reference value of 2.0 L / min; the rotation speed for the magnetic stirring method, with a reference value of 400 rpm; and the power for the ultrasonic method, with a reference value of 500 W.

[0039] In this embodiment of the invention, the pretreatment process of the silica wet gel is as follows: the wet gel that has reached the gelation point is sealed together with the container with plastic wrap (with ventilation holes reserved), and placed in a constant temperature and humidity chamber for aging at 40°C and 80% relative humidity for 48 hours. After aging, the silica wet gel block is rolled into a continuous gel flat sheet with a thickness of 1.5 mm using a polytetrafluoroethylene double roller device and then transferred to a programmable temperature controlled drying oven for drying using a stepped temperature rise mode: first, drying at 60°C for 12 hours, then drying at 80°C for 8 hours, and finally drying at 100°C for 4 hours to obtain a flat silica dry gel.

[0040] In this embodiment of the invention, the temperature-controlled drying oven has a heating rate of 2℃ / min and a temperature uniformity of ±1℃. During the drying process, the mass change of the silica wet gel is recorded every 2 hours until the difference between two consecutive weighings is less than 0.1%, at which point the drying is considered complete. The crushing process is performed using polytetrafluoroethylene (PTFE) cutters to avoid metal contamination.

[0041] In this embodiment of the invention, the aging process further condenses the silica wet gel network, enhancing its mechanical stability. Rolling it into a flat shape greatly increases the specific surface area and optimizes the mass and heat transfer efficiency during heat treatment.

[0042] Specifically, this invention monitors and controls the kinetics of hydrolysis-condensation reaction by comparing the viscosity growth rate with the preset viscosity growth rate. A viscosity growth rate less than the preset minimum viscosity growth rate indicates insufficient reaction activity or uneven mixing, requiring enhanced mixing to promote mass transfer and reaction integrity. A viscosity growth rate greater than the preset maximum viscosity growth rate indicates a violent reaction that may cause local overheating and stress concentration in the network structure, requiring reduced mixing to slow down the reaction process. This adjustment mechanism ensures the uniformity and mechanical stability of the silica gel network structure, providing high-quality flat silica dry gel for subsequent aging, drying, and calcination processes. It guarantees the ultra-high purity of the final synthesized quartz sand from the source, thereby improving the robustness of the entire preparation process and the consistency of the finished product.

[0043] Please see Figure 2 As shown, it is a logic judgment diagram for determining whether the pretreatment of flat silica dry gel meets the standards in an embodiment of the present invention.

[0044] Specifically, the purification potential index of the flat silica dry gel is determined based on the average pore size and loss on ignition, and the pretreatment is determined to be satisfactory based on the comparison between the purification potential index and the preset purification potential index. If the purification potential index is greater than or equal to the preset purification potential index, the pretreatment of the silica wet gel is deemed to have met the standard. If the purification potential index is less than the preset purification potential index, the pretreatment of silica dry gel is determined to be substandard.

[0045] In this embodiment of the invention, the average pore size is measured as follows: about 0.3 g of the dried and aged flat silica dry gel sample is degassed at 150°C for 6 h in a vacuum environment, and adsorption-desorption isotherm test is performed using a nitrogen adsorption instrument at 77 K. The test process conforms to GB / T 19587-2017 standard.

[0046] In this embodiment of the invention, the measurement process of the loss on ignition is as follows: Take about 2.0 g of the same batch of flat silica dry gel sample and place it in a pre-weighed quartz crucible. Use an analytical balance to accurately weigh and record the initial mass M1 (accuracy ±0.0001 g). Place the sample in a muffle furnace, heat it to 800℃ at 5℃ / min and keep it at that temperature for 2 h. After taking it out, cool it to room temperature in a desiccator and weigh it again to obtain the mass M2 after ignition. Calculate the loss on ignition value by using the loss on ignition (%) = [(M1-M2) / M1] × 100%. Take the arithmetic mean of three parallel measurements as the loss on ignition.

[0047] In this embodiment of the invention, the preset purification potential index ranges from [0.7, 1.3], preferably 1.0; the preset average pore size ranges from [24, 26] nm, preferably 25 nm; and the preset loss on ignition ranges from [2%, 4%], preferably 3%. However, the above values ​​are not limited to these values, and those skilled in the art can adjust the values ​​according to actual needs.

[0048] In this embodiment of the invention, the purification potential index is obtained by multiplying the ratio of the average pore size to the preset average pore size and the ratio of the loss on ignition to the preset loss on ignition.

[0049] In this embodiment of the invention, a suitable pore size (24-26 nm) provides a smooth channel for the diffusion of impurity elements (such as Fe and Al) and the escape of gaseous products (such as chlorides) during the subsequent calcination process. The loss on ignition mainly comes from residual ethanol, water and incompletely condensed silanol groups. The loss on ignition (2%-4%) indicates that the organic solvent has been fully volatilized and an appropriate amount of silanol groups has been retained. The latter can participate in the reaction to generate Si-Cl during calcination in a chlorine atmosphere, which helps to remove metal impurities bonded to the silicon-oxygen network.

[0050] Specifically, this invention determines the purification potential index of the flat silica dry gel by the average pore size and the loss on ignition. The purification potential index establishes a clear standard for pretreatment, indicating that the flat silica dry gel has good impurity diffusion channels and contaminant loading levels. The purification potential index provides a preliminary assessment for subsequent calcination treatment, significantly improving the predictability and controllability of the ultrapure quartz sand preparation process. While ensuring the purity of quartz sand, it optimizes energy consumption, reduces production costs, and thus improves the effectiveness and consistency of purity control of synthetic quartz sand products.

[0051] Please see Figure 3 As shown, it is a logic judgment diagram for determining the calcination index of flat silica dry gel in an embodiment of the present invention.

[0052] Specifically, the impurity content is determined based on the pretreatment of the flat silica dry gel to determine the calcination index of the flat silica dry gel. If the impurity content is greater than or equal to the preset impurity content, the roasting index is determined to be the first roasting index. If the impurity content is less than the preset impurity content, the roasting index is determined to be the second roasting index.

[0053] In this embodiment of the invention, the impurity content is obtained by non-destructive measurement of the flat silica dry gel using X-ray fluorescence spectroscopy. The specific measurement process is as follows: three samples are randomly selected from the same batch of flat silica dry gel, and a wavelength dispersive X-ray fluorescence spectrometer is used to test the samples under the conditions of Rh target X-ray tube, voltage 50kV, and current 50mA. The measurement time is 300 seconds. The total metal impurity content is calculated using a standard curve established from historical data. The arithmetic mean of the three samples is taken as the impurity content of this batch of flat silica dry gel. The preset impurity content range is [10ppm, 15ppm], preferably set to 12ppm. Based on the statistical analysis of historical production data, when the impurity content of the dry gel is controlled within this range, there is a greater than 95% probability that the total metal impurity content of the final quartz sand product can be stably controlled below 100ppb after subsequent calcination.

[0054] In this embodiment of the invention, the first calcination index is obtained by the ratio of the impurity content to the preset impurity content, and the second calcination index is obtained by the product of the ratio of the impurity content to the preset impurity content and the compensation coefficient. The compensation coefficient has a value range of [0.1, 0.3], and is preferably set to 0.2.

[0055] In this embodiment of the invention, the level of impurity content directly determines the difficulty of calcination. Impurities may exist in silica gel in various forms such as surface adsorption, network encapsulation, or lattice substitution. High impurity content (≥12 ppm) usually means more stubborn impurities existing in the encapsulated or lattice state, requiring higher energy (temperature / time) to diffuse to the surface and react for removal.

[0056] Specifically, a calcination access index is determined based on the purification potential index and the calcination index to initiate high-temperature calcination of the flat silica dry gel. If the calcination access index is within the preset calcination access index range, then calcination is initiated for the flat silica dry gel.

[0057] In this embodiment of the invention, the preset roasting access index range is [0.5, 2.0], but the above value is not limited to this, and those skilled in the art can adjust the value according to actual needs.

[0058] In this embodiment of the invention, the calcination access index is the ratio of the purification potential index to the preset purification potential index multiplied by the ratio of the preset calcination index to the calcination index.

[0059] Specifically, if the calcination access index is not within the preset calcination access index range, it is determined that high-temperature calcination will be initiated after the current flat silica dry gel is treated. If the calcination access index is less than the minimum value of the preset calcination access index range, then it is determined to re-age and dry the current flat silica dry gel. If the calcination access index is greater than the maximum value of the preset calcination access index range, then the current flat silica dry gel is determined to be crushed, extracted, and dried.

[0060] In this embodiment of the invention, the process of re-aging and drying the current flat silica dry gel is as follows: the current flat silica dry gel is returned to the aging process and re-aged at 40°C for 72 hours. A three-step drying procedure is adopted: first, drying at 60°C for 12 hours, then drying at 80°C for 8 hours, and finally drying at 100°C for 4 hours.

[0061] In this embodiment of the invention, the process of crushing, extracting and drying the current flat silica dry gel is as follows: the current flat silica dry gel is crushed to a particle size of 0.5-1.0 mm, and a mixed solvent of anhydrous ethanol and deionized water at a volume ratio of 1:1 is used for extraction at 60°C for 4 h. The amount of solvent used is 5 times the mass of the dry gel. After extraction, it is gently dried at 80°C for 24 h.

[0062] Specifically, this invention obtains the calcination access index of flat silica dry gel through the purification potential index and the calcination index, establishing a quantitative standard for starting the high-temperature calcination process. When the calcination access index is within the qualified range, it indicates that the flat silica dry gel has ideal heat treatment characteristics and can directly enter the calcination stage. When the calcination access index deviates from the qualified range, the corresponding optimization treatment of the flat silica dry gel is initiated according to the direction of deviation. Through structural improvement or contaminant removal, the controllability and intelligence level of the ultrapure quartz sand preparation process are significantly improved. While ensuring the purity of quartz sand, energy waste and production interruption are effectively avoided, thereby improving the consistency of synthetic quartz sand product quality and the economy of the production process.

[0063] Please see Figure 4 As shown, it is a logic diagram for determining the calcination parameters of flat silica dry gel in an embodiment of the present invention.

[0064] Specifically, the benchmark calcination intensity of the flat silica dry gel is obtained based on the calcination access index, and the calcination parameters of the flat silica dry gel are determined according to the comparison between the benchmark calcination intensity and the preset calcination intensity. If the reference calcination intensity is greater than or equal to the preset calcination intensity, then the calcination parameters of the flat silica dry gel are determined as the first calcination parameters. If the reference calcination intensity is less than the preset calcination intensity, then the calcination parameters of the flat silica dry gel are determined as the second calcination parameters.

[0065] In this embodiment of the invention, the preset calcination intensity ranges from [0.4, 2.5], preferably set to 1.0, but the above value is not limited to this, and those skilled in the art can adjust the value according to actual needs.

[0066] In this embodiment of the invention, the reference calcination intensity is the product of the calcination admission index and the weighting coefficient. The value of the weighting coefficient is determined based on the calcination index. If the calcination index is the first calcination index, the weighting coefficient is 1.2. If the calcination index is the second calcination index, the weighting coefficient is 0.8. The first calcination parameter is to heat to [1200, 1250]℃ at 5℃ / min and hold for [170, 190]min. The second calcination parameter is to heat to [1100, 1200]℃ at 3℃ / min and hold for [110, 130]min.

[0067] In this embodiment of the invention, the first calcination parameters are used under high calcination intensity conditions. By increasing the final temperature and extending the holding time, structural densification and sufficient volatilization of impurities are ensured. Historical experiments have verified that these parameters effectively remove encapsulated metallic impurities, achieving deep densification of the silica network. Sufficient activation energy is provided for encapsulated metallic impurities deep in the lattice or with high diffusion resistance, allowing them to diffuse and vaporize fully. This has been verified to be particularly effective in removing impurities such as Fe and Al encapsulated in the SiO2 network in an ionic state. The second calcination parameters are suitable for low calcination intensity conditions. While ensuring effective removal of surface and free impurities, they significantly reduce the risk of lattice defects caused by over-sintering.

[0068] In this embodiment of the invention, the infrared irradiation calcination process of the flat silica dry gel is executed according to the following procedure based on the determined calcination parameter instructions: Under the condition of using the first calcination parameters, the following enhanced calcination procedure is performed: (1) Preheating stage: Start the medium-wave infrared tube (wavelength 2.0-3.5 μm), heat up to 600℃ at 8℃ / min, and keep warm for 30 min; (2) High temperature stage: switch to short-wave infrared tube (wavelength 1.0-1.8 μm), continue to heat up to 1250℃ at 5℃ / min, and keep warm for 180 min; (3) Atmosphere control: A nitrogen mixture containing 1% chlorine is introduced throughout the process at a flow rate of 1.0 L / min.

[0069] Under the condition of using the second calcination parameters, the following mild calcination procedure was performed: (1) Preheating stage: Start the medium-wave infrared tube (wavelength 2.0-3.5 μm), heat up to 600℃ at 5℃ / min, and keep warm for 30 min; (2) High temperature stage: switch to short-wave infrared tube (wavelength 1.0-1.8 μm), continue to heat up to 1150℃ at 3℃ / min, and keep warm for 120 min; (3) Atmosphere control: A nitrogen mixture containing 0.5% chlorine is introduced throughout the process at a flow rate of 0.8 L / min.

[0070] In this embodiment of the invention, temperature monitoring is performed in real time using a non-contact infrared thermometer with a control accuracy of ±3℃.

[0071] Specifically, this invention determines the baseline roasting intensity based on the roasting access index, establishing a quantitative correlation between precursor quality characteristics and heat treatment intensity. A high baseline roasting intensity indicates good uniformity of the flat silica degel network and a large potential for impurity removal, allowing for the full utilization of the material's purification limit using an enhanced roasting scheme. Conversely, a low baseline roasting intensity suggests structural defects or contamination risks in the flat silica degel, necessitating a mild roasting scheme to avoid lattice defects caused by over-treatment. This graded roasting parameter control achieves precise matching between the roasting process and the flat silica degel, overcoming the limitations of traditional fixed roasting curves, ensuring the purity of the quartz sand product, and improving the adaptability of the ultrapure quartz sand preparation process.

[0072] Specifically, the reaction intensity index of the flat silica dry gel is determined based on the infrared thermographic characteristics during the calcination process, in order to determine whether the impurity removal rate of the flat silica dry gel meets the standard. If the reaction intensity index is greater than or equal to the preset reaction intensity index, the impurity removal rate of the flat silica dry gel is determined to meet the standard. If the reaction intensity index is less than the preset reaction intensity index, it is determined that the impurity removal rate of the flat silica dry gel does not meet the standard.

[0073] In this embodiment of the invention, the process of acquiring and processing the infrared thermal image features includes: acquiring the temperature field distribution on the surface of the flat silica dry gel using a high-temperature resistant infrared thermal imager installed in the observation window of the calcining furnace; processing the acquired thermal image data; and extracting at least one feature parameter related to the intensity of the impurity gasification reaction. The reaction intensity index is a quantized value calculated based on the at least one feature parameter.

[0074] In this embodiment of the invention, the reaction intensity index is obtained by multiplying the hot spot area ratio, the hot spot temperature coefficient, and the distribution uniformity index. The preset reaction intensity index ranges from [0.15, 0.35], preferably set to 0.25. However, the above value is not limited to this, and those skilled in the art can adjust the value according to actual needs.

[0075] In this embodiment of the invention, under a chlorine atmosphere, the reaction between impurities and chlorine is an exothermic or endothermic process, which will form a temperature anomaly zone ("hot spot") on the sample surface. The reaction intensity index integrates the area, temperature, and distribution uniformity of the hot spot, and is a quantification of the intensity and extent of the in-situ chemical reaction. A qualified index indicates that the chlorination reaction is active and uniform, and the impurities are being effectively removed.

[0076] Specifically, based on the quartz sand finished product obtained after calcination, the purity value of the quartz sand finished product is measured to determine whether the quality of a single batch of the quartz sand finished product is qualified, so as to adjust the flatness thickness value or preset calcination temperature of the next batch preparation process. If the purity value is greater than or equal to the preset purity value, the quality of the finished quartz sand product in a single batch is determined to be qualified. If the purity value is less than the preset purity value, the quality of the finished quartz sand in a single batch is determined to be unqualified.

[0077] Specifically, based on the fact that the quality of the finished quartz sand in a single batch is unqualified, it is determined to adjust the flatness or preset calcination temperature of the next batch preparation process; If the purity deviation value is less than or equal to the preset purity deviation threshold, the flatness thickness value of the next batch preparation process is increased to the corresponding value by a first adjustment coefficient of 1.05. If the purity deviation value is greater than the preset purity deviation threshold, the preset calcination temperature of the next batch preparation process is increased to the corresponding value by a second adjustment coefficient of 1.1.

[0078] In this embodiment of the invention, the preset purity value ranges from [0, 0.2], preferably set to 0. The preset purity value is based on a total metal impurity content of no more than 100 ppb. The range of [0, 0.2] corresponds to the control target of 100-80 ppb of actual impurity content. However, the above value is not limited to this. Those skilled in the art can adjust it according to actual requirements.

[0079] In this embodiment of the invention, the purity value of the finished quartz sand is obtained as follows: Purity value = 100% - (Measured total metal impurity content (ppb) / 10 7 ).

[0080] In this embodiment of the invention, the purity deviation value is obtained by calculating the difference between the purity value of the finished quartz sand and the preset purity value.

[0081] In this embodiment of the invention, the preset purity deviation threshold ranges from [0.05, 0.15], but the above value is not limited to this, and those skilled in the art can adjust it according to actual requirements.

[0082] In this embodiment of the invention, moderately increasing the thickness can slightly extend the impurity diffusion path and provide more sufficient reaction time under the same calcination conditions, which helps to remove deeper encapsulated impurities. Larger purity deviations usually mean that existing thermodynamic conditions are insufficient to remove stubborn impurities. Increasing the temperature can directly provide higher activation energy and enhance diffusion and reaction kinetics.

[0083] Specifically, this invention determines the purity value of the finished quartz sand and, based on the comparison results of the purity values ​​of the finished quartz sand, determines the qualification of the quality of the batch of finished quartz sand, thereby improving the consistency and stability of quartz sand quality, reducing energy consumption and material loss in the production process, avoiding resource waste caused by unqualified quartz sand flowing into subsequent stages, adapting to the impact of raw material characteristic fluctuations on the production process, shortening the response time for identifying and adjusting abnormal quartz sand quality, and improving the adaptability of production.

[0084] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for preparing ultrapure synthetic quartz sand, characterized in that, include: The pretreatment of qualified silica wet gel based on viscosity growth rate was used to obtain flat silica dry gel; Based on the average pore size and loss on ignition of the flat silica dry gel, the purification potential index of the flat silica dry gel is determined, and the pretreatment is determined to meet the standard based on the comparison result between the purification potential index and the preset purification potential index. The impurity content was determined after the pretreatment of the flat silica dry gel met the standards, so as to determine the calcination index of the flat silica dry gel. The calcination admission index is determined based on the purification potential index and the calcination index to initiate calcination of the flat silica dry gel. The benchmark calcination intensity is determined based on the calcination access index in order to determine the calcination parameters of the flat silica dry gel. The reaction intensity index of the flat silica dry gel was determined based on the infrared thermographic characteristics during the calcination process, in order to determine whether the impurity removal rate of the flat silica dry gel met the standard. After the quartz sand product is obtained after calcination, the purity value of the quartz sand product is measured to determine whether the quality of a single batch of the quartz sand product is qualified, so as to adjust the flatness thickness value or preset calcination temperature of the next batch preparation process.

2. The method for preparing ultrapure synthetic quartz sand according to claim 1, characterized in that, The process of determining the preparation of qualified silica wet gel based on viscosity growth rate includes: The viscosity growth rate is compared with the preset maximum viscosity growth rate and the preset minimum viscosity growth rate, respectively; Based on the viscosity growth rate being greater than or equal to the preset minimum viscosity growth rate and the viscosity growth rate being less than or equal to the preset maximum viscosity growth rate, the silica wet gel is determined to be of qualified quality. Based on the fact that the viscosity growth rate is less than the preset minimum viscosity growth rate, the silica wet gel is determined to be of substandard quality. Based on the viscosity growth rate being greater than the preset maximum viscosity growth rate, the silica wet gel is determined to be of substandard quality.

3. The method for preparing ultrapure synthetic quartz sand according to claim 1, characterized in that, The process of determining whether the pretreatment meets the standard based on the purification potential index includes: The purification potential index is compared with the preset purification potential index; Based on the purification potential index being greater than or equal to the preset purification potential index, the pretreatment is determined to be up to standard; Based on the fact that the purification potential index is less than the preset purification potential index, it is determined that the pretreatment is substandard.

4. The method for preparing ultrapure synthetic quartz sand according to claim 1, characterized in that, The process of determining the calcination index based on the pretreatment standards includes: The impurity content is compared with the preset impurity content; Based on the impurity content being greater than or equal to a preset impurity content, the roasting index is determined to be the first roasting index. Based on the fact that the impurity content is less than the preset impurity content, the roasting index is determined to be the second roasting index.

5. The method for preparing ultrapure synthetic quartz sand according to claim 1, characterized in that, The process of determining the calcination admission index to initiate calcination of the flat silica dry gel includes: The roasting access index is compared with the preset roasting access index range; Based on the fact that the calcination access index is within the preset calcination access index range, it is determined that calcination will be initiated on the flat silica dry gel.

6. The method for preparing ultrapure synthetic quartz sand according to claim 1, characterized in that, The process of determining the baseline calcination intensity to determine the calcination parameters of the flat silica dry gel includes: Compare the benchmark roasting intensity with the preset roasting intensity; Based on the benchmark calcination intensity being greater than or equal to the preset calcination intensity, the calcination parameters of the flat silica dry gel are determined as the first calcination parameters. If the reference calcination intensity is less than the preset calcination intensity, the calcination parameters of the flat silica dry gel are determined as the second calcination parameters.

7. The method for preparing ultrapure synthetic quartz sand according to claim 1, characterized in that, The process for determining whether the impurity removal rate of the flat silica dry gel meets the standard includes: The reaction intensity index is compared with the preset reaction intensity index; Based on the reaction intensity index being greater than or equal to the preset reaction intensity index, it is determined that the impurity removal rate of the flat silica dry gel meets the standard. Based on the fact that the reaction intensity index is less than the preset reaction intensity index, it is determined that the impurity removal rate of the flat silica dry gel does not meet the standard.

8. The method for preparing ultrapure synthetic quartz sand according to claim 1, characterized in that, The process of determining whether the quality of a single batch of finished quartz sand is up to standard includes: The purity value of the finished quartz sand product is compared with the preset purity value; Based on the purity value being greater than or equal to a preset purity value, the quality of a single batch of the finished quartz sand is determined to be qualified. Based on the purity value being less than the preset purity value, it is determined that the quality of a single batch of the finished quartz sand is unqualified.

9. The method for preparing ultrapure synthetic quartz sand according to claim 8, characterized in that, The process of determining the flatness thickness value for the next batch of quartz sand preparation process based on the substandard quality of the single batch includes: Obtain the purity deviation value between the purity value and the preset purity value; The purity deviation value is compared with a preset purity deviation threshold. Based on the purity deviation value being less than or equal to a preset purity deviation threshold, the flatness thickness value for the next batch preparation process is determined to be increased by a first adjustment coefficient.

10. The method for preparing ultrapure synthetic quartz sand according to claim 9, characterized in that, Based on the fact that the purity deviation value is greater than the preset purity deviation threshold, the preset calcination temperature for the next batch preparation process is determined to be increased by a second adjustment coefficient.

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