A method for calcining and water quenching to purify quartz sand

Abstract

The present invention discloses a method for calcining and water quenching to purify quartz sand, belonging to the technical field of deep purification and processing of quartz sand, and comprising the following steps: calcining and water quenching the quartz sand. When calcining and water quenching, the quartz sand is heated to 1200-1300 °C for calcination, and then water quenched with pure water at 0-70 °C; when calcining and water quenching, the particle size of the quartz sand is 0.05-0.15 mm. This method increases the calcination temperature of the quartz sand, enlarges the temperature difference during water quenching, and combines quartz sand with a suitable particle size for calcination and water quenching, which can promote the bursting of the quartz sand to form more cracks and stress concentration, and improve the removal rate of gas-liquid inclusions in the quartz sand.

Description

Technical Field

[0001] The present invention relates to the technical field of deep purification processing of quartz sand, and specifically, to a method for purifying quartz sand by calcination and water quenching. Background Art

[0002] In addition to well-known metal elements, harmful impurities in quartz sand, such as micron- and even nano-scale gas-liquid inclusions, not only exist widely but are also more difficult to remove, becoming the primary problem in the production of high-purity quartz sand worldwide today, and also the main difficulty hindering the true realization of domestic substitution of raw materials and products of high-purity quartz sand in China.

[0003] In order to remove gas-liquid inclusion impurities in high-purity quartz sand, in recent years, researchers and production enterprises in China have proposed and practiced various process methods, including calcination and water quenching, flotation, microwave high-temperature explosion, etc., but all have little effect in actual production applications.

[0004] For example, in the invention patent application "A high-temperature cyclic treatment and preparation process of high-purity quartz sand" with the publication number CN115367763 A, the quartz sand is repeatedly heated and cyclically treated within the temperature ranges of 1000 - 1500 °C and 600 - 950 °C for multiple times, which can cause volume changes in the quartz sand and promote the enrichment of lattice impurities on the surface of the quartz sand under the action similar to recrystallization; however, multiple high-temperature treatments will cause adhesion between the particles of the quartz sand, resulting in a reduction in the removal effect of gas-liquid inclusions, and the process method of multiple high-temperature cycles is complex and has a high operation difficulty. Another example is the invention patent application "A process method for removing gas-liquid inclusions in high-purity quartz sand" with the publication number CN 105036545A, where the high-purity quartz sand is subjected to microwave radiation treatment, and the power of the microwave is 1000 - 4000 w, the radiation treatment time is 1 - 10 h, and the one-time treatment amount of the high-purity quartz sand is 100 - 600 g; this method uses the process of microwave radiation for treatment, which has a high operation difficulty, high requirements for equipment, and a limited one-time treatment amount, and it is difficult to meet the large-scale industrial practical needs.

[0005] Currently, the entire industry still relies on finding ore raw materials with very few gas-liquid inclusions themselves and is basically completely dependent on imports. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for purifying quartz sand by calcination and water quenching to solve the problems raised in the above background art.

[0007] To achieve the above purpose, the present invention provides the following technical solution: A method for purifying quartz sand by calcination and water quenching, comprising the following steps:

[0008] Calcine and water-quench quartz sand. When calcining and water-quenching, heat the quartz sand to 1200 - 1300 °C for calcination, and then water-quench it with pure water at 0 - 70 °C;

[0009] When calcining and water-quenching, the particle size of the quartz sand is 0.05 - 0.15 mm.

[0010] Furthermore, before calcining and water-quenching the quartz sand, it is first pretreated, and the pretreatment includes one or several of hand selection, crushing and classification, weak magnetic separation, flotation, pickling, ultrasonic cleaning, dehydration and drying.

[0011] Furthermore, prepare a 7 - 15 wt% aqueous solution of polyvinyl alcohol with pure water above 95 °C, add the quartz sand after calcination and water-quenching to the aqueous solution of polyvinyl alcohol to form a sol, and form a quartz sand-hydrogel system through multiple freeze-thaw cycles; obtain a quartz sand-aerogel system after drying; perform vacuum adsorption treatment on the quartz sand-aerogel system; finally remove the aerogel on the surface of the quartz sand.

[0012] Furthermore, the drying method is vacuum drying or supercritical drying.

[0013] Furthermore, the drying conditions for supercritical carbon dioxide drying are: pressure 7.5 - 11 MPa, temperature 35 - 40 °C, and drying time 9 - 12 h.

[0014] Furthermore, when performing vacuum adsorption treatment, first mechanically crush the quartz sand-aerogel system to form particles with a size of 0.1 - 0.3 mm, and then place it in a vacuum environment of 0.1 - 0.2 Pa and let it stand for adsorption for 10 - 20 h.

[0015] Furthermore, after vacuum adsorption treatment, take out the quartz sand-aerogel system, add a large amount of pure water above 95 °C, and perform ultrasonic treatment to dissolve and discharge the polyvinyl alcohol.

[0016] Furthermore, after pure water treatment, the quartz sand is further washed with a mixed acid, and the mixed acid includes one or several of sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, and oxalic acid.

[0017] Furthermore, the polyvinyl alcohol is low molecular weight polyvinyl alcohol with a molecular weight of 20,000 - 35,000.

[0018] Compared with the prior art, the method for calcining and water-quenching and purifying quartz sand of the present invention has the following beneficial effects:

[0019] The present invention first increases the calcination temperature of the quartz sand, increases the temperature difference during water quenching, and combines with quartz sand of appropriate particle size for calcination and water quenching, which can promote the bursting of the quartz sand to form more cracks and stress concentration, and improve the removal rate of gas-liquid inclusions in the quartz sand.

[0020] In the present invention, a polyvinyl alcohol hydrogel is further in-situ coated on the surface of quartz sand, dried to form an aerogel, and subjected to vacuum adsorption treatment. By utilizing the high adsorption property of the aerogel, impurities in the quartz sand are fully adsorbed, greatly improving the purification precision of the quartz sand; moreover, polyvinyl alcohol is easy to remove and will not introduce other impurities. Detailed implementation mode

[0021] The present invention provides a method for purifying quartz sand, which includes the following steps:

[0022] (I) Pretreatment

[0023] The pretreatment method may optionally include various means such as handpicking, crushing and grading, weak magnetic separation, flotation, pickling, ultrasonic cleaning, dehydration, drying, etc.

[0024] The specific operation steps of the pretreatment can refer to the prior art, such as the relevant technical means in the invention patent applications with publication numbers CN115849393A, CN101337767A, etc., which will not be elaborated here.

[0025] (II) Calcination and water quenching

[0026] Select quartz sand with a particle size of 0.05 - 0.15 mm, heat it to 1200 - 1300 °C for calcination, and then quench it with pure water at 0 - 70 °C to promote the bursting of the quartz sand, form cracks, and release gas-liquid inclusions.

[0027] In the present invention, the calcination and water quenching process can be carried out continuously. First, turn on the electric furnace, and after preheating to the set temperature, continuous feeding, calcination through a carrier quartz tube (or silicon carbide ceramic tube), and discharging and water quenching can be carried out.

[0028] When calcining the quartz sand, it is found that when the calcination temperature is higher than 1300 °C, the quartz sands adhere to each other and form a certain agglomeration. After water quenching, not only the original gas-liquid inclusions cannot be removed, but new gas-liquid inclusions and other impurities are introduced; when the calcination temperature is lower than 1200 °C, the temperature difference during water quenching is lower, and the maximum bursting cannot be formed to remove the most gas-liquid inclusions. Therefore, the present invention limits the optimal calcination temperature to 1200 - 1300 °C.

[0029] (III) Post-treatment

[0030] The quartz sand after calcination and water quenching is conveyed by a belt elevator, subjected to pickling and water washing, and then dehydrated by a belt vacuum dehydrator (or centrifuge) and other processing.

[0031] Specifically, the quartz sand is washed with a mixed acid. During the washing, the pulp mass concentration is 8-12%, and the mixed acid includes sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, oxalic acid, etc.; then it is washed, dehydrated, and dried with pure water above 95°C to obtain high-purity quartz sand.

[0032] In a specific preferred embodiment, before the post-treatment, it further includes an in-situ formation of aerogel on the surface of the quartz sand and a vacuum adsorption step:

[0033] (1) Prepare a quartz sand-hydrogel system:

[0034] Prepare a 7-15% aqueous solution of polyvinyl alcohol with pure water above 95°C, and add the calcined and water-quenched quartz sand to make the aqueous solution of polyvinyl alcohol completely submerge the quartz sand, and form a uniform sol system through ultrasonic dispersion, and then fill it into a closed container;

[0035] Perform 3-5 freeze-thaw cycles on the above sol system to form a quartz sand-hydrogel system: First, quickly cool the sol system to -20°C to -25°C and freeze it for 20-30h, then take it out and thaw it at room temperature of 20-25°C, and repeat 3-5 times to form a quartz sand-hydrogel system in-situ coated with polyvinyl alcohol.

[0036] In the process of forming the quartz sand-hydrogel system, first, in the sol state, the polyvinyl alcohol solution will penetrate into the cracks or stress concentration areas formed due to calcination and water quenching in the quartz sand. After slow cooling, the polyvinyl alcohol molecular chains form a network cross-linking in the cracks of the quartz sand, and this force will further promote the opening of the cracks or stress concentration areas, which is beneficial to the release of gas-liquid inclusions.

[0037] (2) Prepare a quartz sand-aerogel system:

[0038] Dry the above quartz sand-hydrogel system to form a quartz sand-aerogel system in-situ coated with polyvinyl alcohol.

[0039] The drying method can be selected from vacuum drying or supercritical drying, and supercritical carbon dioxide drying is preferred: First, place the quartz sand-hydrogel system in absolute ethanol for solvent replacement, and replace the absolute ethanol multiple times, once every 6-12h, and replace it 3-5 times to form an alcogel; then perform supercritical carbon dioxide drying on the alcogel, and the drying conditions are: pressure 7.5-11MPa, temperature 35-40°C, and drying time 9-12h. Obtain a quartz sand-aerogel system.

[0040] During supercritical carbon dioxide drying, carbon dioxide in the supercritical state will penetrate into all pores in the quartz sand-hydrogel system, and bring out the residual gas, liquid or gas-liquid inclusions in the quartz sand, improving the purification effect.

[0041] (3) Vacuum adsorption treatment:

[0042] After mechanically crushing the quartz sand - aerogel system, particles with a size of 0.1 - 0.3 mm are formed and placed in a vacuum environment of 0.1 - 0.2 Pa. After standing for 10 - 20 h, polyvinyl alcohol aerogel has a huge specific surface area and surface energy, with strong adsorption ability. Vacuum treatment can avoid the interference of other substances and further promote the polyvinyl alcohol aerogel to adsorb the residual gas, liquid, gas - liquid inclusions and other micro - impurities in the quartz sand. Other micro - impurities include molecules, ions, etc., such as Al 3+ , K + , Na + , Ca 2+ , Mg 2+ , Ti 4 + and other metal ion impurities.

[0043] (4) Impurity removal:

[0044] Add the quartz sand - aerogel system after vacuum adsorption treatment to a large amount of pure water above 95 °C and perform ultrasonic treatment to dissolve and discharge the polyvinyl alcohol.

[0045] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0046] Example 1

[0047] In this example, a "box - type double - pipe bottom - discharging high - temperature calcination and water - quenching furnace" is used as the test equipment. The loading pipes of this electric furnace are two parallel high - purity silicon carbide ceramic pipes with an outer diameter of 300 mm, an inner diameter of 280 mm, and a total length of 5700 mm. The silicon carbide ceramic pipe is sealed from the inside at a distance of 500 mm from the tail, and 4 discharging holes with a size of 30×50 mm are opened in the front part close to the sealing position. Quartz sand discharges from these 4 small holes. The equipment uses silicon carbide rods for heating with a power of 180 KW. The height difference between the feeding port and the discharging port is about 150 mm. The motor drives the rollers, and the rollers drive the silicon carbide ceramic pipe to slowly rotate at a speed of 5 - 6 rpm, driving the quartz sand to slowly roll forward towards the discharging port. After reaching the discharging holes, it falls into the quartz glass water tank closely below and is immediately submerged in pure water at 0 - 70 °C for water quenching.

[0048] This example uses high - quality quartz ore imported from India as the raw material and is purified through the following steps:

[0049] Manually select, crush and classify, weakly magnetic separate, float, wash with mixed acid in a reaction kettle, wash with pure water in an ultrasonic cleaner, dehydrate, and dry to make a quartz sand sample with a particle size range of 0.05 - 0.15 mm.

[0050] Add the quartz sand sample after pretreatment and particle size screening into the electric furnace, turn on the electric furnace, preheat to the target working temperature of 1250 °C, and calcine for 2 h after the electric furnace reaches the set working temperature. Turn on the pure water switch before the quartz sand flows out of the carrier pipe, so that the quartz sand flowing out of the carrier pipe after calcination is immediately saturated and soaked with pure water at 0 - 70 °C and water quenched.

[0051] Then dehydrate the quartz sand product after calcination and water quenching with a centrifuge, dry it in an electric furnace at 600 °C in a box-type quartz tube, and cool it with a quartz tube cooler.

[0052] Then, wash the quartz sand with mixed acid. During the washing, the pulp concentration is 10%, and the mixed acid includes 10% sulfuric acid, 10% hydrochloric acid, and 10% oxalic acid; then ultrasonically clean, dehydrate, and dry it with pure water above 95 °C to obtain high-purity quartz sand.

[0053] Example 2

[0054] In this example, a "box-type double-tube bottom-discharging high-temperature calcination and water quenching furnace" is used as the test equipment. The carrier pipe of this electric furnace is two high-purity silicon carbide ceramic pipes with an outer diameter of 300 mm, an inner diameter of 280 mm, and a total length of 5700 mm installed in parallel. The silicon carbide ceramic pipe is closed from the inside at a distance of 500 mm from the tail, and 4 discharge holes of 30×50 mm are opened in the front close to the closed position. The quartz sand is discharged from these 4 small holes. The equipment uses silicon carbide rods for heating with a power of 180 KW. The height difference between the feed port end and the discharge port is about 150 mm. The motor drives the rollers, and the rollers drive the silicon carbide ceramic pipe to slowly rotate at a speed of 5 - 6 rpm, driving the quartz sand to slowly roll forward towards the discharge port. After reaching the discharge holes, it falls into the closely attached quartz glass water tank below and is immediately submerged in pure water at 0 - 70 °C for water quenching.

[0055] This example uses high-quality quartz ore imported from India as the raw material and purifies it through the following steps:

[0056] Manually select, crush and classify, weakly magnetic separate, float, wash with mixed acid in a reaction kettle, wash with pure water in an ultrasonic cleaner, dehydrate, and dry to make a quartz sand sample with a particle size range of 0.05 - 0.15 mm.

[0057] Add the quartz sand sample after pretreatment and particle size screening into the electric furnace, turn on the electric furnace, preheat to the target working temperature of 1200 °C, and calcine for 2 h after the electric furnace reaches the set working temperature. Turn on the pure water switch before the quartz sand flows out of the carrier pipe, so that the quartz sand flowing out of the carrier pipe after calcination is immediately saturated and soaked with pure water at 0 - 70 °C and water quenched.

[0058] Then dehydrate the calcined and water-quenched quartz sand product with a centrifuge, dry it in an electric furnace at 600 °C in a box-type quartz tube, and cool it with a quartz tube cooler.

[0059] Then, prepare a quartz sand-hydrogel system: prepare a 10% aqueous solution of polyvinyl alcohol (molecular weight 20,000) with pure water above 95 °C, and add the calcined and water-quenched quartz sand to make the aqueous polyvinyl alcohol solution completely submerge the quartz sand, and form a uniform sol system through ultrasonic dispersion, and fill it into a closed container;

[0060] Perform 3 freeze-thaw cycles on the above sol system to form a quartz sand-hydrogel system: first quickly cool the sol system to -20 °C and freeze it for 20 h, then take it out and thaw it at room temperature of 20-25 °C, and repeat 3 times to form a quartz sand-hydrogel system with in-situ coating of polyvinyl alcohol.

[0061] Perform supercritical drying on the above quartz sand-hydrogel system: first place the quartz sand-hydrogel system in absolute ethanol for solvent replacement, change it every 6-12 h, and form an alcogel after changing 3-5 times; then perform supercritical carbon dioxide drying on the alcogel, and the drying conditions are: pressure 10 MPa, temperature 38 °C, and drying time 10 h, to form a quartz sand-aerogel system with in-situ coating of polyvinyl alcohol.

[0062] Mechanically crush the quartz sand-aerogel system to form particles of 0.1-0.3 mm, place it in a vacuum environment of 0.1-0.2 Pa, and let it stand for 15 h for vacuum adsorption and impurity removal.

[0063] Add a large amount of pure water above 95 °C to the quartz sand-aerogel system after vacuum adsorption treatment, and perform ultrasonic treatment to dissolve and discharge the polyvinyl alcohol.

[0064] Then, leach the quartz sand with a mixed acid. During leaching, the pulp concentration is 10%, and the mixed acid includes 10% sulfuric acid, 10% hydrochloric acid, and 10% oxalic acid; then ultrasonically clean, dehydrate, and dry it with pure water above 95 °C to obtain high-purity quartz sand.

[0065] Example 3

[0066] In this embodiment, a "box-type double-tube bottom-discharge high-temperature calcination and water quenching furnace" is used as the test equipment. The loading tubes of this electric furnace are two high-aluminum quartz glass tubes with an outer diameter of 220 mm, an inner diameter of 200 mm, and a total length of 6500 mm, which are installed in parallel. The quartz glass tube is sealed from the inside at a distance of 550 mm from the tail, and 4 discharge holes with a size of 30×40 mm are opened in the front part close to the sealed position. Quartz sand is discharged from these 4 small holes. The equipment uses silicon carbide rods for heating with a power of 160 KW. The height difference between the feeding port and the discharging port is about 150 mm. The motor drives the rollers, and the rollers drive the quartz glass tube to slowly rotate at a speed of 5-6 rpm, driving the quartz sand to slowly roll forward in the direction of the discharging port. After reaching the discharge holes, it falls into the quartz glass water tank closely attached below and is immediately submerged in pure water at 0-70 °C for water quenching.

[0067] In this embodiment, high-quality quartz ore imported from India is used as the raw material, and the purification is carried out through the following steps:

[0068] Manual selection, crushing and classification, weak magnetic separation, flotation, mixed acid leaching and washing in a reaction kettle, cleaning with pure water in an ultrasonic cleaner, dehydration, and drying are carried out to produce a quartz sand sample with a particle size range of 0.05-0.15 mm.

[0069] The quartz sand sample after pretreatment and particle size screening is added into the electric furnace. The electric furnace is started and preheated to the target working temperature of 1300 °C. After the electric furnace reaches the set working temperature, it is calcined for 1.5 h. Before the quartz sand flows out of the loading tube, the pure water switch is turned on, so that the quartz sand flowing out of the loading tube after calcination is immediately saturatedly soaked and water quenched by pure water at 0-70 °C.

[0070] Then, the quartz sand product after calcination and water quenching is dehydrated by a centrifuge, dried in a box-type quartz tube electric furnace at 600 °C, and cooled by a quartz tube cooler.

[0071] Then, a quartz sand-hydrogel system is prepared: an aqueous solution of 10% polyvinyl alcohol (with a molecular weight of 22,000) is prepared with pure water above 95 °C, and the quartz sand after calcination and water quenching is added to make the polyvinyl alcohol aqueous solution completely submerge the quartz sand. After ultrasonic dispersion, a uniform sol system is formed and filled into a sealed container;

[0072] The above sol system is subjected to 4 freeze-thaw cycles to form a quartz sand-hydrogel system: first, the sol system is rapidly cooled to -25 °C and frozen for 18 h, then taken out and thawed at room temperature of 20-25 °C. After repeating 4 times, a quartz sand-hydrogel system with polyvinyl alcohol in-situ coating is formed.

[0073] The above quartz sand-hydrogel system is subjected to supercritical drying: First, the quartz sand-hydrogel system is placed in absolute ethanol for solvent replacement, which is replaced every 6 - 12 h, and after 3 - 5 replacements, an alcogel is formed; then the alcogel is subjected to supercritical carbon dioxide drying, and the drying conditions are: pressure 9.5 MPa, temperature 40 °C, and drying time 9 h, to form a quartz sand-aerogel system coated with polyvinyl alcohol in-situ.

[0074] The quartz sand-aerogel system is mechanically crushed to form particles with a size of 0.1 - 0.3 mm, placed in a vacuum environment of 0.1 - 0.2 Pa, and left standing for 12 h for vacuum adsorption and impurity removal.

[0075] The quartz sand-aerogel system after vacuum adsorption treatment is added to a large amount of pure water above 95 °C and subjected to ultrasonic treatment to dissolve and discharge the polyvinyl alcohol.

[0076] Then, the quartz sand is washed with a mixed acid. During the washing, the pulp concentration is 15%, and the mixed acid includes 18% sulfuric acid, 18% hydrochloric acid, and 12% hydrofluoric acid; then it is ultrasonically cleaned, dehydrated, and dried with pure water above 95 °C to obtain high-purity quartz sand.

[0077] Example 4

[0078] In this example, a "box-type double-tube bottom-discharge high-temperature calcination and water quenching furnace" is used as the test equipment. The charge-carrying tubes of this electric furnace are two parallelly installed high-aluminum quartz glass tubes with an outer diameter of 220 mm, an inner diameter of 200 mm, and a total length of 6500 mm. The quartz glass tube is sealed from the inside at a distance of 550 mm from the tail, and 4 discharge holes with a size of 30×40 mm are opened in the front part close to the sealed position, and the quartz sand is discharged from these 4 small holes. The equipment is heated by silicon carbide rods with a power of 160 KW. The height difference between the feed port end and the discharge port is about 150 mm. The motor drives the rollers, and the rollers drive the quartz glass tube to slowly rotate at a speed of 5 - 6 rpm, driving the quartz sand to slowly roll forward towards the discharge port. After reaching the discharge holes, it falls into the quartz glass water tank closely below and is immediately submerged in pure water at 0 - 70 °C for water quenching.

[0079] In this example, high-quality quartz ore purchased from Xinjiang, China, is used as the raw material, and the purification is carried out through the following steps:

[0080] Manual selection, crushing and grading, weak magnetic separation, flotation, mixed acid leaching in a reaction kettle, pure water cleaning with an ultrasonic cleaner, dehydration, and drying to make a quartz sand sample with a particle size range of 0.05 - 0.15 mm.

[0081] Add the quartz sand sample after pretreatment and size screening into an electric furnace, and perform calcination and water quenching operations using the same electric furnace as in Example 1. Turn on the electric furnace and preheat it to the target working temperature of 1250 °C. After the electric furnace reaches the set working temperature, calcine for 2.5 h. Before the quartz sand flows out of the loading pipe, turn on the pure water switch so that the quartz sand flowing out of the loading pipe after calcination is immediately saturated and soaked and water quenched by pure water at 0 - 70 °C.

[0082] Then dehydrate the quartz sand product after calcination and water quenching using a centrifuge, dry it in an electric furnace at 600 °C in a box-type quartz tube, and cool it with a quartz tube cooler.

[0083] Then, prepare a quartz sand-hydrogel system: Prepare a 15% aqueous solution of polyvinyl alcohol (molecular weight of 30,000) with pure water above 95 °C, and add the quartz sand after calcination and water quenching so that the polyvinyl alcohol aqueous solution completely submerges the quartz sand, and form a uniform sol system through ultrasonic dispersion, and fill it into a closed container;

[0084] Perform 5 freeze-thaw cycles on the above sol system to form a quartz sand-hydrogel system: First, quickly cool the sol system to -20 °C and freeze it for 20 h, then take it out and thaw it at room temperature of 20 - 25 °C. Repeat 5 times to form a quartz sand-hydrogel system with in-situ coating of polyvinyl alcohol.

[0085] Perform supercritical drying on the above quartz sand-hydrogel system: First, place the quartz sand-hydrogel system in absolute ethanol for solvent replacement, replace it every 6 - 12 h, and replace it 3 - 5 times to form an alcogel; then perform supercritical carbon dioxide drying on the alcogel, and the drying conditions are: pressure 11 MPa, temperature 38 °C, drying time 10 h, to form a quartz sand-aerogel system with in-situ coating of polyvinyl alcohol.

[0086] Mechanically crush the quartz sand-aerogel system to form particles with a size of 0.1 - 0.3 mm, place it in a vacuum environment of 0.1 - 0.2 Pa, and let it stand for 18 h for vacuum adsorption and impurity removal.

[0087] Add the quartz sand-aerogel system after vacuum adsorption treatment into a large amount of pure water above 95 °C, and perform ultrasonic treatment to dissolve and discharge the polyvinyl alcohol.

[0088] Then, perform mixed acid leaching on the quartz sand. During leaching, the pulp concentration is 10%, and the mixed acid includes 15% sulfuric acid, 10% hydrochloric acid, 10% oxalic acid, and 12% hydrofluoric acid; then ultrasonically clean, dehydrate, and dry it with pure water above 95 °C to obtain high-purity quartz sand.

[0089] Example 5

[0090] In this embodiment, a "box-type double-tube bottom-discharge high-temperature calcination and water quenching furnace" is used as the test equipment. The charge-carrying tubes of this electric furnace are two high-purity silicon carbide ceramic tubes with an outer diameter of 300 mm, an inner diameter of 280 mm, and a total length of 5700 mm, which are installed in parallel. The silicon carbide ceramic tubes are sealed from the inside at a distance of 500 mm from the tail, and 4 discharge holes with a size of 30×50 mm are opened in the front part close to the sealed position. Quartz sand is discharged from these 4 small holes. The equipment uses silicon carbide rods for heating with a power of 180 KW. The height difference between the feed port end and the discharge port is about 150 mm. The motor drives the rollers, and the rollers drive the silicon carbide ceramic tubes to slowly rotate at a speed of 5-6 rpm, driving the quartz sand to slowly roll forward in the direction of the discharge port. After reaching the discharge holes, it falls into the quartz glass water tank closely attached below and is immediately submerged by pure water at 0-70°C for water quenching.

[0091] In this embodiment, high-quality quartz ore imported from India is used as the raw material, and it is purified through the following steps:

[0092] Manual selection, crushing and classification, weak magnetic separation, flotation, mixed acid leaching and washing in a reaction kettle, pure water washing in an ultrasonic cleaning machine, dehydration, and drying are carried out to produce a quartz sand sample with a particle size range of 0.05-0.15 mm.

[0093] The quartz sand sample after pretreatment and particle size screening is added into the electric furnace, the electric furnace is turned on, and it is preheated to the target working temperature of 1200°C. After the electric furnace reaches the set working temperature, it is calcined for 2 h. Before the quartz sand flows out of the charge-carrying tube, the pure water switch is turned on so that the quartz sand flowing out of the charge-carrying tube after calcination is promptly saturatedly soaked and water quenched by pure water at 0-70°C.

[0094] Then, the quartz sand product after calcination and water quenching is dehydrated by a centrifuge, dried in a box-type quartz tube electric furnace at 600°C, and cooled by a quartz tube cooler.

[0095] Then, a quartz sand-hydrogel system is prepared: An aqueous solution of 10% polyvinyl alcohol (with a molecular weight of 20,000) is prepared with pure water above 95°C, and the quartz sand after calcination and water quenching is added to make the polyvinyl alcohol aqueous solution completely submerge the quartz sand, and it is ultrasonically dispersed to form a uniform sol system, which is filled into a sealed container;

[0096] The above sol system is subjected to 3 freeze-thaw cycles to form a quartz sand-hydrogel system: First, the sol system is rapidly cooled to -20°C and frozen for 20 h, then taken out and thawed at room temperature of 20-25°C. After repeating 3 times, a quartz sand-hydrogel system with polyvinyl alcohol in-situ coating is formed.

[0097] The above quartz sand-hydrogel system is subjected to vacuum drying, and the conditions for vacuum drying are: the drying temperature is 40°C, and the drying time is 20 h, to form a quartz sand-aerogel system with polyvinyl alcohol in-situ coating.

[0098] The quartz sand-aerogel system is mechanically crushed to form particles with a size of 0.1 - 0.3 mm, placed in a vacuum environment of 0.1 - 0.2 Pa, left standing for 15 h, and impurities are removed by vacuum adsorption.

[0099] The quartz sand-aerogel system after vacuum adsorption treatment is added to a large amount of pure water at a temperature above 95 °C, and ultrasonic treatment is carried out to dissolve polyvinyl alcohol and then discharge it.

[0100] Then, the quartz sand is washed with a mixed acid. During the washing, the pulp concentration is 10%, and the mixed acid includes 10% sulfuric acid, 10% hydrochloric acid, and 10% oxalic acid; then it is ultrasonically cleaned, dehydrated, and dried with pure water at a temperature above 95 °C to obtain high-purity quartz sand.

[0101] Comparative Example 1

[0102] Compared with Example 1, the difference is that during calcination and water quenching, the calcination temperature is 900 °C.

[0103] Comparative Example 2

[0104] Compared with Example 1, the difference is that during calcination and water quenching, the particle size of the quartz sand is 0.25 - 0.5 mm.

[0105] Comparative Example 3

[0106] Compared with Example 2, the difference is that during calcination and water quenching, the calcination temperature is 900 °C, and the particle size of the quartz sand during calcination and water quenching is 0.25 - 0.5 mm.

[0107] Finally, performance tests are carried out:

[0108] The content of gas-liquid inclusions in the quartz sand products obtained in Examples 1 - 5 and Comparative Examples 1 - 3 is detected respectively, and the obtained data are shown in Table 1.

[0109] Table 1 Proportion of permeable and non-permeable particles, characteristic categories of gas-liquid inclusions

[0110]

[0111] The quartz sand products obtained in each group are melted into 18-inch arc quartz crucibles, and then the quartz crucibles are sliced. The detection values of the bubble content and distribution characteristics in the inner layer of the quartz crucibles are shown in Table 2.

[0112] Table 2 Transparency performance detection of quartz crucibles

[0113]

[0114]

[0115] Meanwhile, the percentage content of main metal impurity elements (%) in the processed quartz sand of each group was detected, and the detection results are shown in Table 3.

[0116] Table 3 Percentage content of main metal impurity elements in the processed quartz sand

[0117]

[0118] All of the above detections of the characteristics of gas-liquid inclusions in quartz sand, the comparison of the thickness and bubble content of the transparent layer of the quartz crucible melted with quartz sand, and the comparison of the detection results of the main metal impurity content of the quartz sand product indicate that the technical solution of the present invention can very effectively open and remove the gas-liquid inclusions in the quartz sand, greatly improve the thickness and clarity of the transparent layer of the quartz crucible, and at the same time correspondingly reduce the content of main metal impurities in the quartz sand product, thereby improving the purity of the quartz sand product.

[0119] Meanwhile, polyvinyl alcohol hydrogel is in-situ coated on the surface of the quartz sand, dried by supercritical drying to form an aerogel, and vacuum adsorption treatment is carried out. By using the high adsorption characteristics of the aerogel, the impurities in the quartz sand can be fully adsorbed, and the gas-liquid inclusions can be further removed to improve the purification accuracy of the quartz sand.

[0120] The above embodiments are merely descriptions made to clearly illustrate the present invention and are not limitations on the implementation manners. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here, and the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A method for calcining and water quenching to purify quartz sand, characterized in that: It includes the following steps: Calcine and water-quench quartz sand. When calcining and water-quenching, heat the quartz sand to 1200 - 1300 °C for calcination, and then water-quench it with pure water at 0 - 70 °C; When calcining and water-quenching, the particle size of the quartz sand is 0.05 - 0.15 mm; Prepare a 7 - 15 wt% polyvinyl alcohol aqueous solution with pure water above 95 °C. Add the quartz sand after calcination and water-quenching into the polyvinyl alcohol aqueous solution to form a sol, and form a quartz sand-hydrogel system through multiple freeze-thaw cycles; obtain a quartz sand-aerogel system after drying; perform vacuum adsorption treatment on the quartz sand-aerogel system; finally remove the aerogel on the surface of the quartz sand.

2. The method for calcining, water quenching and purifying quartz sand according to claim 1, characterized in that: Before calcining and water-quenching the quartz sand, first perform pretreatment, and the pretreatment includes one or several of hand selection, crushing and classification, weak magnetic separation, flotation, pickling, ultrasonic cleaning, dehydration and drying.

3. The method for calcining and water-quenching and purifying quartz sand according to claim 1, wherein: The drying method is vacuum drying or supercritical drying.

4. The method for calcining, water quenching and purifying quartz sand according to claim 3, wherein: The drying conditions for supercritical carbon dioxide drying are: pressure 7.5 - 11 MPa, temperature 35 - 40 °C, and drying time 9 - 12 h.

5. The method for calcining, water quenching and purifying quartz sand according to claim 1, wherein: When performing vacuum adsorption treatment, first mechanically crush the quartz sand-aerogel system to form particles with a size of 0.1 - 0.3 mm, and then place it in a vacuum environment of 0.1 - 0.2 Pa and let it stand for adsorption for 10 - 20 h.

6. The method for calcining, water quenching and purifying quartz sand according to claim 1, characterized in that: After vacuum adsorption treatment, take out the quartz sand-aerogel system, add a large amount of pure water above 95 °C, and perform ultrasonic treatment to dissolve and discharge the polyvinyl alcohol.

7. The method for calcining, water quenching and purifying quartz sand according to claim 6, characterized in that: After pure water treatment, perform mixed acid leaching on the quartz sand, and the mixed acid includes several of sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, and oxalic acid.

8. The method for calcining and water quenching to purify quartz sand according to claim 1, characterized in that: The polyvinyl alcohol is low molecular weight polyvinyl alcohol with a molecular weight of 20,000 - 35,000.

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