A method and product for purifying low-impurity quartz sand

Abstract

This invention discloses a method and product for purifying low-impurity quartz sand, relating to the field of quartz sand purification technology. The method includes: Step 1: Crushing and screening to obtain pretreated pure quartz sand; Step 2: Calcination-water quenching to obtain lattice-activated quartz sand; Step 3: Magnetic separation to obtain deeply purified quartz sand; Step 4: Ultrasonic-flotation synergistic treatment to obtain purified quartz sand; Step 5: Pressure acid leaching to obtain deeply purified quartz sand; Step 6: High-temperature chlorination and inert atmosphere cooling to obtain chlorinated purified quartz sand; Step 7: Dehydroxylation treatment to obtain dehydroxylated quartz sand; Step 8: Plasma purification to obtain a low-impurity quartz sand product with a purity ≥99.9999%. In this invention, pressure acid leaching directly acts on the surface and inside microcracks, allowing for faster acid penetration and more thorough dissolution. This synergistic effect of flotation and acid leaching increases the product purity from 99.78% to over 99.9999% with the same acid consumption.

Description

Technical Field

[0001] This invention relates to the field of quartz sand purification technology, specifically to a method and product for purifying low-impurity quartz sand. Background Technology

[0002] Quartz sand purification is a crucial step in the preparation of high-purity quartz materials, widely used in photovoltaics, semiconductors, fiber optic communications, and high-end optical devices. Currently, the commonly used industrial quartz sand purification processes mainly include crushing and classification, magnetic separation, roasting-water quenching, acid leaching, flotation, and drying. Magnetic separation removes magnetic mineral impurities, roasting-water quenching exposes inclusions within the quartz, acid leaching dissolves surface and shallow lattice impurities, and flotation separates silicate minerals such as feldspar and mica. These processes are effective in reducing the content of metallic impurities such as Fe, Al, and Ti in quartz sand, and conventional processes can yield quartz sand products with a SiO2 content of 99.5%–99.8%.

[0003] However, existing technologies still have significant shortcomings in treating adsorbed impurities on the surface of quartz sand and residual metallic impurities in the crystal lattice. Specifically, conventional flotation processes rely solely on the surface interaction between reagents and impurities for separation, which is insufficient for effectively removing submicron-sized encapsulated impurities and reagent films remaining on the surface of mineral particles. This results in trace amounts of impurities and reagent residues still adhering to the surface of the quartz sand after flotation. Conventional roasting and acid leaching are also insufficient to reach the trace metallic elements remaining inside the quartz lattice. These residual metallic impurities are prone to migration and precipitation at high temperatures, affecting the purity and stability of the product.

[0004] In response to this problem, this application proposes a method and product for purifying low-impurity quartz sand. Summary of the Invention

[0005] The purpose of this invention is to provide a method and product for purifying low-impurity quartz sand, in order to solve the problem that conventional flotation processes in the prior art rely solely on the surface interaction between reagents and impurities for separation. This makes it difficult to effectively remove the reagent film remaining on the surface of submicron-sized encapsulated impurities and mineral particles, resulting in trace amounts of impurities and reagent residues still adhering to the surface of the quartz sand after flotation. Conventional roasting and acid leaching are also unable to reach the trace metal elements remaining inside the quartz lattice. These residual metal impurities are prone to migration and precipitation in high-temperature applications, affecting the purity and stability of the product.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] In a first aspect, this application provides a method for purifying low-impurity quartz sand, comprising:

[0008] Step 1: Crush and screen the impure quartz sand to obtain pretreated pure quartz sand;

[0009] Step 2: The pretreated pure quartz sand is subjected to calcination-water quenching treatment to expose the inclusions and impurities inside the quartz sand to the surface, thereby obtaining lattice-activated quartz sand.

[0010] Step 3: Perform magnetic separation on the lattice-activated quartz sand to remove magnetic impurities and obtain deeply purified quartz sand;

[0011] Step 4: The deeply purified quartz sand is subjected to ultrasonic-flotation synergistic treatment. The ultrasonic cavitation effect is used to remove the combination of flotation reagent and impurity particles to obtain purified quartz sand.

[0012] Step 5: Place the purified quartz sand in a composite acid solution for pressurized acid leaching treatment to dissolve surface and shallow lattice impurities, thereby obtaining deeply purified quartz sand;

[0013] Step 6: The deeply purified quartz sand is subjected to high-temperature chlorination and inert atmosphere cooling treatment to convert the residual metal impurities into volatile chlorides, which are then discharged with the airflow to obtain chlorinated purified quartz sand.

[0014] Step 7: The chlorinated purified quartz sand is subjected to dehydroxylation treatment to remove hydroxyl groups inside and on the surface of the quartz sand lattice, thereby obtaining dehydroxylated quartz sand.

[0015] Step 8: The dehydroxylated quartz sand is subjected to plasma purification treatment, and nanoscale impurities on the surface are removed by plasma bombardment to obtain a low-impurity quartz sand product with a purity ≥99.9999%.

[0016] Furthermore, the roasting-water quenching treatment in step two employs a process combining gradient temperature rise roasting and multi-stage water quenching, including:

[0017] The pre-purified quartz sand is heated from room temperature to 600℃ at a rate of 3-5℃ / min and held for 1-2 hours. Then, it is heated to 900-1100℃ at a rate of 2-3℃ / min and held for 2-4 hours. Subsequently, the calcined quartz sand is sequentially immersed in a 60-80℃ warm water bath and a 0-5℃ cold water bath for two-stage water quenching, so that the inclusions and impurities inside the quartz sand are fully exposed on the particle surface, thus obtaining lattice-activated quartz sand.

[0018] Furthermore, in step five, the pressurized acid leaching treatment is carried out in a closed pressurized reactor, with the pressure inside the reactor controlled at 0.3-0.8 MPa and the leaching temperature at 120-180℃. The composite acid solution is prepared by mixing hydrochloric acid, oxalic acid and hydrofluoric acid in a volume ratio of 5-8:2-3:0.5-1, and the leaching time is 2-6 hours to obtain deeply impurity-free quartz sand.

[0019] In step five, the waste acid solution after leaching with the composite acid solution is recycled and regenerated via membrane separation.

[0020] The waste acid solution is separated and recovered by nanofiltration membrane module to recover hydrofluoric acid and oxalic acid. The metal ions in the retentate are neutralized and precipitated before being discharged. The recovered regenerated acid solution is returned to step five for recycling. The volume concentration of acid in the regenerated acid solution is not less than 85% of the initial concentration.

[0021] Furthermore, the ultrasonic-flotation synergistic treatment method in step four is as follows:

[0022] Deeply purified quartz sand is prepared into a slurry with a mass concentration of 25%–35%. After adding collectors and frothers, it is introduced into a flotation cell. During the flotation process, ultrasonic waves with a frequency of 25–40 kHz and an ultrasonic power density of 0.3–0.8 W / mL are applied for 15–30 min. The ultrasonic cavitation effect generates micro-jets at the interface between the flotation reagent and the impurity particles, which peels off the reagent film on the surface of the mineral particles and promotes the desorption of impurity particles from the surface of the quartz sand, thus obtaining purified quartz sand.

[0023] Furthermore, the high-temperature chlorination and inert atmosphere cooling treatment in step six is ​​performed as follows:

[0024] The purified quartz sand is placed in a chlorination roasting furnace and roasted at 900–1200℃ for 1–3 hours in a mixed atmosphere of chlorine and nitrogen, with a chlorine flow rate of 0.5–2 L / min. After roasting, it is rapidly cooled to below 150℃ at a rate of 20–50℃ / min in a nitrogen protective atmosphere, and then naturally cooled to room temperature to obtain a low-impurity quartz sand product.

[0025] Furthermore, the crushing and screening in step one includes:

[0026] Quartz sand raw material is crushed to particles with a particle size of 0.1-0.8 mm and then screened and classified to remove coarse particles larger than 0.8 mm and fine powder smaller than 0.1 mm, so as to obtain quartz sand raw material with uniform particle size.

[0027] The magnetic separation process in step three employs a two-stage magnetic separation method combining wet high-gradient magnetic separation and dry permanent magnet magnetic separation, including:

[0028] First, a wet high-gradient magnetic separation with a magnetic field strength of 1.2 to 1.8 T is used to remove strongly magnetic impurities, resulting in first-grade magnetically separated quartz sand.

[0029] After the primary magnetically separated quartz sand is dehydrated and dried, it is then subjected to dry permanent magnet separation with a magnetic field strength of 0.6 to 1.0 T to remove weakly magnetic impurities, thus obtaining pre-purified quartz sand.

[0030] Furthermore, after step four and before step five, a deionized water ultrasonic cleaning step is also included: the purified quartz sand is ultrasonically cleaned in deionized water 3 to 5 times, each cleaning time is 15 to 30 minutes, the ultrasonic frequency is 35 to 45 kHz, to remove the residual flotation reagents and impurity ions on the surface of the quartz sand, and the cleaned quartz sand is obtained.

[0031] Further, in step seven, the chlorinated purified quartz sand undergoes a dehydroxylation treatment, including:

[0032] Chlorinated purified quartz sand is placed in an esterification reactor, and esterification agents such as acetyl chloride or acetic anhydride are added. The amount of esterification agent is 0.5% to 2% of the mass of quartz sand. The reaction is carried out at 80 to 120°C for 1 to 3 hours to convert the silanol groups on the surface of the quartz sand into hydrophobic ester groups, thereby obtaining an esterification intermediate. The esterification intermediate is then placed in a vacuum heating furnace with a vacuum degree ≤10. -2 Pa is heated to 800-1000℃ at a rate of 5-10℃ / min under an inert atmosphere and held for 2-5 hours to remove residual hydroxyl groups in the crystal lattice in the form of water molecules, thus obtaining dehydroxylated quartz sand.

[0033] Furthermore, the method for plasma purification of the dehydroxylated quartz sand in step eight is as follows:

[0034] Hydroxylated quartz sand is placed in a plasma reaction chamber, and argon or an argon-oxygen mixture is introduced at a flow rate of 50–200 mL / min. The pressure in the reaction chamber is controlled at 10–100 Pa. A radio frequency plasma source is used with a power of 200–500 W, and the processing time is 10–60 min. High-energy plasma bombards the surface of the quartz sand particles, causing the residual nanoscale metal oxides, carbides, and other impurities on the surface to be vaporized and removed, resulting in a low-impurity quartz sand product with a purity ≥99.9999%.

[0035] Secondly, this application provides a low-impurity quartz sand product, which is obtained by the purification method of low-impurity quartz sand as described in the first aspect;

[0036] The low-impurity quartz sand product contains SiO2 content ≥ 99.99%, Fe content ≤ 0.0005%, Al content ≤ 0.001%, Ti content ≤ 0.0003%, and gas-liquid inclusion content ≤ 20 inclusions / cm³. 3 Furthermore, there are no residual acid radicals or flotation reagents on the surface of the quartz sand particles.

[0037] Compared with existing technologies, this invention provides a method and product for purifying low-impurity quartz sand. This invention places magnetic separation after calcination and water quenching. Calcination and water quenching cause microcracks to form along the grain boundaries within the quartz sand inclusions, fully exposing the previously encapsulated magnetic impurities. Subsequent secondary magnetic separation can directly capture these newly exposed impurities, improving the removal rate of iron impurities by more than 30% compared to traditional pre-magnetic separation processes. This invention also arranges ultrasonic-flotation synergistic treatment before pressurized acid leaching. Ultrasonic cavitation first strips away the reagent film and floatable impurities from the quartz sand surface, obtaining a fresh, active surface. Subsequently, pressurized acid leaching directly acts on this surface and the interior of the microcracks, resulting in faster acid penetration and more thorough dissolution. This sequence superimposes the effects of flotation and acid leaching, increasing product purity from 99.78% to over 99.9999% with the same acid consumption, and shortening the acid leaching time from 24 hours to 2–6 hours. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0039] Figure 1 This is a flowchart of a method for purifying low-impurity quartz sand, provided as an embodiment of the present invention. Detailed Implementation

[0040] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0041] As attached Figure 1 As shown:

[0042] Example 1:

[0043] This embodiment is specifically applied to the purification treatment of pegmatite-type quartz sand (Qinghai) in a certain region.

[0044] The quartz sand raw material has a SiO2 content of 98.56%, an Fe content of 0.052%, an Al content of 0.035%, a Ti content of 0.012%, and a gas-liquid inclusion content of approximately 450 inclusions / cm³. 3 The raw material particle size distribution is in the range of 0.1 to 0.8 mm, of which particles with a diameter of 0.1 to 0.5 mm account for more than 75%.

[0045] Particle size analysis was performed using the standard sieving method, with a Φ200mm standard test sieve, a sieving time of 15 minutes, and a vibrating sieve frequency of 50Hz.

[0046] The content of impurity elements was determined by inductively coupled plasma mass spectrometry (ICP-MS) using an Agilent 7800 ICP-MS instrument. The sample digestion was carried out using a hydrofluoric acid-nitric acid high-pressure closed digestion system.

[0047] The content of gas-liquid inclusions was determined by microscopic statistical method. The quartz sand sample was made into a thin section, and the representative particles were counted under a polarizing microscope. The number of particles counted for each sample was not less than 200.

[0048] Step 1: Sand making (crushing and grading):

[0049] Quartz sand raw material is crushed to a particle size of 0.1-0.8 mm and then screened and graded using a Φ200 mm standard test sieve (screening for 15 min, vibrating screen at 50 Hz) to remove coarse particles larger than 0.8 mm and fine powder smaller than 0.1 mm, thus obtaining quartz sand raw material with uniform particle size.

[0050] Step 2: Calcination-water quenching treatment:

[0051] The pre-purified quartz sand was loaded into a calcining furnace and heated from room temperature to 600℃ at a heating rate of 4℃ / min, and held at that temperature for 1.5h; then it was heated to 1000℃ at a heating rate of 2.5℃ / min and held at that temperature for 3h.

[0052] During the roasting process, the furnace is filled with air, and the furnace temperature is monitored and recorded in real time by thermocouples. After roasting, the quartz sand is quickly poured into a 60°C warm water bath for primary water quenching, which takes about 5 seconds. Then, the quartz sand is removed and quickly transferred to a 0°C cold water bath for secondary water quenching, which takes about 10 seconds.

[0053] Two-stage water quenching fully exposes the impurities within the quartz sand to the particle surface, resulting in lattice-activated quartz sand.

[0054] After water quenching, the particle size of the quartz sand did not change significantly, but microcracks appeared on the particle surface, and the exposure rate of gas-liquid inclusions was about 85% as determined by microscopy.

[0055] Step 3: Magnetic separation treatment:

[0056] Quartz sand raw material was fed into a wet high-gradient magnetic separator at a feed rate of 15 kg / h. The magnetic field strength was set to 1.6T, the slurry concentration was controlled at 30%, and the washing water pressure was 0.3 MPa. The wet high-gradient magnetic separation removed strongly magnetic impurities (including magnetite, hematite, etc.) to obtain primary magnetically separated quartz sand. The magnetic field strength was measured at multiple points within the working interval of the magnetic separator using a gaussmeter, and the average value was taken.

[0057] The primary magnetically separated quartz sand is dewatered to a moisture content of ≤8% by a plate and frame filter press, and then fed into a dry permanent magnet separator. The magnetic field strength is set to 0.8T and the vibrating feed speed is 10kg / h. The dry permanent magnet separator removes weakly magnetic impurities (including limonite, biotite, etc.) to obtain pre-purified quartz sand.

[0058] After magnetic separation, the Fe content in the pre-purified quartz sand decreased to 0.008%, the Al content decreased to 0.012%, and the SiO2 content increased to 99.12%.

[0059] Step 4: Ultrasonic-flotation synergistic treatment:

[0060] Deeply impurity-removed quartz sand was prepared into a slurry with a mass concentration of 30%, and a collector (dodecylamine, dosage 0.8 kg / t) and a foaming agent (No. 2 oil, dosage 0.1 kg / t) were added. The natural pH value of the slurry was approximately 7.2.

[0061] After the slurry is introduced into the flotation cell, ultrasonic waves with a frequency of 30 kHz are applied simultaneously during the flotation process. The ultrasonic power density is 0.5 W / mL, and the action time is 20 min. The ultrasonic probe is immersed to a depth of approximately 5 cm below the surface of the slurry, and the volume of the flotation cell is 5 L.

[0062] The ultrasonic cavitation effect generates micro-jet impacts at the interface between flotation reagents and impurity particles, which peels off the reagent film on the surface of mineral particles and promotes the desorption of impurity particles from the surface of quartz sand.

[0063] During the flotation process, the frothing speed is 5 times / min. After the flotation is completed, the solid and liquid are separated, and the quartz sand is washed three times with deionized water for 10 minutes each time to obtain purified quartz sand.

[0064] ICP-MS analysis showed that the Fe content in the purified quartz sand decreased to 0.0008%, the Al content decreased to 0.0015%, the Ti content decreased to 0.0004%, and the SiO2 content increased to 99.92%.

[0065] Step 5: Pressure acid leaching treatment:

[0066] The lattice-activated quartz sand was placed in a sealed pressurized reactor, and the pressure inside the reactor was controlled at 0.6 MPa. The leaching temperature was 150℃. The composite acid solution was prepared by mixing industrial-grade hydrochloric acid (concentration 36%), oxalic acid (purity 99.5%) and hydrofluoric acid (concentration 40%) in a volume ratio of 7:2.5:0.8. The acid leaching solution solid ratio was 3:1 (mL / g), and the leaching time was 4h.

[0067] The reaction was continuously stirred at a speed of 200 rpm. The pressure was monitored in real time by a pressure sensor integrated into the reactor, and the temperature was monitored by an insertion thermocouple inside the reactor.

[0068] After the reaction is complete, solid and liquid are separated. The solid product is washed with deionized water until the pH of the washing solution reaches 5-6, thus obtaining deeply purified quartz sand.

[0069] ICP-MS analysis showed that the Fe content in the deeply purified quartz sand decreased to 0.0015%, the Al content decreased to 0.003%, the Ti content decreased to 0.0008%, and the SiO2 content increased to 99.78%.

[0070] Step Six: High-temperature chlorination and inert atmosphere cooling treatment:

[0071] The purified quartz sand was placed in a chlorination roasting furnace, and a mixed atmosphere of chlorine and nitrogen was introduced (chlorine gas fraction of 20%, nitrogen gas fraction of 80%), with a chlorine flow rate of 1.0 L / min and a nitrogen flow rate of 4.0 L / min.

[0072] The calcination temperature was 1050℃, and the holding time was 2 hours. During the calcination process, residual metallic impurities (Fe, Al, Ti, etc.) in the quartz sand reacted with chlorine gas to generate gaseous chlorides (such as FeCl3, AlCl3, TiCl4, etc.), which were discharged from the system with the gas flow.

[0073] After roasting, the furnace was switched to a nitrogen protective atmosphere at a flow rate of 5.0 L / min, and rapidly cooled to below 150°C at a rate of 40°C / min, followed by natural cooling to room temperature to obtain a low-impurity quartz sand product. The temperature of the material inside the furnace was monitored in real time using an infrared thermometer, and the cooling rate was adjusted by controlling the nitrogen flow rate.

[0074] Step 7: Dehydroxylation treatment:

[0075] The chlorinated purified quartz sand obtained in step six was placed in an esterification reactor, and acetyl chloride was added as an esterifying agent at a concentration of 1.2% of the quartz sand mass. The reaction was carried out at 100°C for 2 hours to convert the silanol groups on the surface of the quartz sand into hydrophobic ester groups, yielding an esterification intermediate. The esterification intermediate was then placed in a vacuum furnace, and the vacuum level inside the furnace was evacuated to 5 × 10⁻⁶. -3 Argon gas was introduced as a protective atmosphere (flow rate 50 mL / min), and the mixture was heated to 900 °C at a rate of 8 °C / min and held at that temperature for 3 hours to remove residual hydroxyl groups from the crystal lattice as water molecules. The treated quartz sand was then analyzed by Fourier transform infrared spectroscopy (FTIR), and the results showed a wavelength of 3740 cm⁻¹. -1 The near-disappearance of the characteristic Si-OH absorption peak indicates that the hydroxyl removal rate is ≥98%, resulting in dehydroxylated quartz sand.

[0076] Step 8: Plasma purification treatment:

[0077] The dehydroxylated quartz sand obtained in step seven was placed in a plasma reaction chamber, and high-purity argon gas (99.999% purity) was introduced at a flow rate of 100 mL / min, with the chamber pressure controlled at 30 Pa. A radio frequency plasma source was used with a power of 350 W, and the treatment time was 30 min. The radio frequency power supply frequency was 13.56 MHz, and the plasma self-bias voltage was approximately -200 V. During the treatment, high-energy argon ions bombarded the surface of the quartz sand particles, causing residual nanoscale metal oxides, carbides, and other impurities to vaporize and be removed, which were then discharged through a vacuum system. After treatment, the sand was naturally cooled to room temperature to obtain the final low-impurity quartz sand product.

[0078] The final product, analyzed by ICP-MS, showed a SiO2 content of 99.9999%, an Fe content of 0.000045%, an Al content of 0.000009%, a Ti content of 0.000025%, and a gas-liquid inclusion content of 2 inclusions / cm³. 3 The particle size distribution of the product is 0.1–0.5 mm.

[0079] Example 2:

[0080] This embodiment specifically applies to the purification of quartz sand from a geological vein (Henan). The quartz sand raw material has a SiO2 content of 99.01%, an Fe content of 0.038%, an Al content of 0.028%, a Ti content of 0.009%, and a gas-liquid inclusion content of approximately 380 inclusions / cm³. 3 .

[0081] Step 1: Sand making (crushing and grading):

[0082] Quartz sand raw material is crushed to a particle size of 0.1-0.8 mm and then screened and graded using a Φ200 mm standard test sieve (screening for 15 min, vibrating screen at 50 Hz) to remove coarse particles larger than 0.8 mm and fine powder smaller than 0.1 mm, thus obtaining quartz sand raw material with uniform particle size, of which particles with a particle size of 0.1-0.5 mm account for more than 80%.

[0083] Step 2: Calcination-water quenching treatment:

[0084] The pre-purified quartz sand was loaded into a calcining furnace and heated from room temperature to 600℃ at a heating rate of 3.5℃ / min, and held at that temperature for 2 hours.

[0085] The temperature was then increased to 950℃ at a rate of 2℃ / min and held for 3.5 hours. After calcination, the quartz sand was quickly poured into a 70℃ warm water bath for primary water quenching, and then transferred to a 2℃ cold water bath for secondary water quenching to obtain lattice-activated quartz sand. The gas-liquid inclusion exposure rate was approximately 82% as determined by microscopy.

[0086] Step 3: Magnetic separation treatment:

[0087] Quartz sand raw material is fed into a wet high-gradient magnetic separator at a feed rate of 20 kg / h. The magnetic field strength is set to 1.4T, the slurry mass concentration is controlled at 28%, and the washing water pressure is 0.35 MPa to obtain first-grade magnetically separated quartz sand.

[0088] First-stage magnetically separated quartz sand was dehydrated and dried before being fed into a dry permanent magnet separator. The magnetic field strength was set to 0.7T, and the vibrating feed speed was 12kg / h to obtain pre-purified quartz sand. After magnetic separation, the Fe content in the pre-purified quartz sand decreased to 0.006%, the Al content decreased to 0.009%, and the SiO2 content increased to 99.28%.

[0089] Step 4: Ultrasonic-flotation synergistic treatment:

[0090] Deeply purified quartz sand was prepared into a slurry with a mass concentration of 28%, and a collector (dodecylamine, dosage 0.7 kg / t) and a frother (No. 2 oil, dosage 0.08 kg / t) were added. Ultrasonic waves with a frequency of 28 kHz, an ultrasonic power density of 0.45 W / mL, and a reaction time of 25 min were applied simultaneously to obtain purified quartz sand.

[0091] ICP-MS analysis showed that the Fe content in the purified quartz sand decreased to 0.0006%, the Al content decreased to 0.0012%, the Ti content decreased to 0.00035%, and the SiO2 content increased to 99.95%.

[0092] Step 5: Pressure acid leaching treatment:

[0093] Lattice-activated quartz sand was placed in a sealed pressurized reactor, with the pressure inside the reactor controlled at 0.5 MPa and the leaching temperature at 140℃. The composite acid solution was prepared by mixing hydrochloric acid, oxalic acid and hydrofluoric acid in a volume ratio of 6:2:0.6, with an acid-solid ratio of 2.5:1 (mL / g). The leaching time was 5 h, and the stirring speed was 180 r / min, resulting in deeply purified quartz sand.

[0094] ICP-MS analysis showed that the Fe content in the deeply purified quartz sand decreased to 0.0012%, the Al content decreased to 0.0025%, the Ti content decreased to 0.0006%, and the SiO2 content increased to 99.85%.

[0095] Step Six: High-temperature chlorination and inert atmosphere cooling treatment:

[0096] The purified quartz sand was placed in a chlorination roasting furnace, and a mixed atmosphere of chlorine and nitrogen (chlorine content 18%) was introduced. The chlorine flow rate was 0.8 L / min, and the nitrogen flow rate was 3.6 L / min. The roasting temperature was 1000℃, and the holding time was 2.5 h.

[0097] After calcination, the atmosphere is switched to nitrogen protection and the temperature is rapidly cooled to below 150°C at a rate of 35°C / min, and then naturally cooled to room temperature to obtain a low-impurity quartz sand product.

[0098] Step 7: Dehydroxylation treatment:

[0099] The chlorinated purified quartz sand obtained in step five was placed in an esterification reactor, and acetyl chloride was added as an esterifying agent at a concentration of 1.5% of the quartz sand mass. The reaction was carried out at 105°C for 2 hours to convert the silanol groups on the surface of the quartz sand into hydrophobic ester groups, yielding an esterification intermediate. The esterification intermediate was then placed in a vacuum furnace, and the vacuum level inside the furnace was evacuated to 5 × 10⁻⁶. -3 Argon gas was introduced as a protective atmosphere (flow rate 50 mL / min), and the mixture was heated to 900 °C at a rate of 8 °C / min and held at that temperature for 3 hours to remove residual hydroxyl groups from the crystal lattice as water molecules. The treated quartz sand was then analyzed by Fourier transform infrared spectroscopy (FTIR), and the results showed a wavelength of 3740 cm⁻¹. -1 The near-disappearance of the characteristic Si-OH absorption peak indicates that the hydroxyl removal rate is ≥98%, resulting in dehydroxylated quartz sand.

[0100] Step 8: Plasma purification treatment:

[0101] The dehydroxylated quartz sand obtained in step seven was placed in a plasma reaction chamber, and high-purity argon gas (99.999% purity) was introduced at a flow rate of 100 mL / min, with the chamber pressure controlled at 32 Pa. A radio frequency plasma source was used with a power of 350 W, and the treatment time was 30 min. The radio frequency power supply frequency was 13.56 MHz, and the plasma self-bias voltage was approximately -200 V. During the treatment, high-energy argon ions bombarded the surface of the quartz sand particles, causing residual nanoscale metal oxides, carbides, and other impurities to vaporize and be removed, which were then discharged through a vacuum system. After treatment, the sand was naturally cooled to room temperature to obtain the final low-impurity quartz sand product.

[0102] The final product, analyzed by ICP-MS, showed a SiO2 content of 99.99993%, an Fe content of 0.000045%, an Al content of 0.000009%, a Ti content of 0.000025%, and a gas-liquid inclusion content of 2 inclusions / cm³. 3 The particle size distribution of the product is 0.1–0.5 mm.

[0103] Comparative example:

[0104] A comparative treatment was conducted on the same batch of raw materials using conventional quartz sand purification processes. The raw material was pegmatite-type quartz sand from Qinghai Province, with the same specifications as in Example 1. The comparative process specifically consisted of a combined flow of "crushing and grading—single magnetic separation—single roasting and water quenching—atmospheric pressure acid leaching—conventional flotation," with the specific steps as follows:

[0105] Crushing and grading: The quartz sand raw material is crushed and screened to a particle size of 0.1-0.5 mm. The screening is carried out using a standard test sieve, with a screening time of 15 minutes and a vibrating screen frequency of 50 Hz.

[0106] Single magnetic separation: The crushed and graded quartz sand is fed into a wet high gradient magnetic separator (magnetic field strength 1.2T, slurry mass concentration 30%) at a feed rate of 15kg / h for one magnetic separation treatment without secondary dry magnetic separation, to obtain magnetically separated quartz sand.

[0107] Single-stage roasting and water quenching: The magnetically separated quartz sand is directly heated to 900℃ and kept at that temperature for 4 hours. After roasting, the quartz sand is quickly immersed in room temperature water (about 25℃) for a single water quenching to obtain roasted and water-quenched quartz sand.

[0108] Atmospheric pressure acid leaching: The calcined water-quenched quartz sand is placed in an atmospheric pressure acid leaching tank, and a mixed acid solution of hydrochloric acid and hydrofluoric acid is used (the volume ratio of hydrochloric acid to hydrofluoric acid is 10:1, and the total acid concentration is 15%). The leaching temperature is 80℃, the liquid-solid ratio is 4:1, and the leaching time is 24h.

[0109] After leaching, solid and liquid are separated, and the sand is washed with deionized water until the pH of the washing solution reaches 5-6 to obtain acid-leached quartz sand.

[0110] Conventional flotation: Acid-leached quartz sand is prepared into a slurry with a mass concentration of 30%, and a collector (dodecylamine, dosage 1.0 kg / t) and a frother (No. 2 oil, dosage 0.12 kg / t) are added. The slurry is then floated for 30 minutes without ultrasonic assistance to obtain flotated quartz sand.

[0111] Drying: The flotation quartz sand is dried at 110℃ for 6 hours to obtain the final product.

[0112] The comparative product, analyzed by ICP-MS, showed a SiO2 content of 99.78%, an Fe content of 0.0025%, an Al content of 0.008%, a Ti content of 0.0015%, and a gas-liquid inclusion content of 95 inclusions / cm³. 3 The testing instruments and methods are the same as in Example 1.

[0113] Product performance comparison:

[0114] The product performance indicators of Example 1, Example 2 and the comparative example are summarized in Table 1 below.

[0115] Table 1

[0116] Performance indicators Example 1 (Qinghai pegmatite type) Example 2 (Henan vein quartz type) Comparative example (conventional process) <![CDATA[SiO2 content (%)]]> 99.99992 99.99993 99.78 Fe content (%) ≤0.00002 ≤0.00002 0.0025 Al content (%) ≤0.00005 ≤0.00003 0.008 Ti content (%) ≤0.00001 ≤0.00001 0.0015 <![CDATA[Gas-liquid inclusion content (number / cm 3 ).]]> ≤5 ≤4 95 Hydroxyl content (ppm) ≤5 ≤4 Unable to detect effectively (>100) Purity grade 6N 6N 3N~4N

[0117] As shown in the table above, the low-impurity quartz sand product prepared using the technical solution of this invention has an SiO2 content that is increased from 99.78% in conventional processes to over 99.9999% (99.99992% in Example 1 and 99.99993% in Example 2), reaching the 6N level. The above data indicate that the multi-unit synergistic purification process of this invention, which involves "secondary magnetic separation, gradient roasting and water quenching, pressurized acid leaching, ultrasonic flotation synergy, and high-temperature chlorination and inert atmosphere cooling," has achieved significantly better technical effects than conventional processes in terms of deep impurity removal and efficient removal of gas-liquid inclusions. The low-impurity quartz sand prepared can meet the application requirements of high-purity quartz sand in high-end fields such as photovoltaics and semiconductors.

[0118] As can be seen from the above, the present invention places magnetic separation after calcination and water quenching. Calcination and water quenching cause microcracks to form along the grain boundaries of the inclusions inside the quartz sand, fully exposing the magnetic impurities that were originally encapsulated. The subsequent secondary magnetic separation can directly capture these newly exposed impurities, improving the removal rate of iron impurities by more than 30% compared with the traditional pre-magnetic separation process.

[0119] This invention arranges the ultrasonic-flotation synergistic treatment before pressurized acid leaching. Ultrasonic cavitation first removes the reagent film and floatable impurities from the surface of the quartz sand, obtaining a fresh, active surface. Subsequently, pressurized acid leaching directly acts on this surface and the interior of microcracks, resulting in faster acid penetration and more thorough dissolution. This sequence superimposes the effects of flotation and acid leaching, increasing product purity from 99.78% to over 99.9999% with the same acid consumption, and shortening the acid leaching time from 24 hours to 2–6 hours.

[0120] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for purifying low-impurity quartz sand, characterized in that, include: Step 1: Crush and screen the impure quartz sand to obtain pretreated pure quartz sand; Step 2: The pretreated pure quartz sand is subjected to calcination-water quenching treatment to expose the inclusions and impurities inside the quartz sand to the surface, thereby obtaining lattice-activated quartz sand. Step 3: Perform magnetic separation on the lattice-activated quartz sand to remove magnetic impurities and obtain deeply purified quartz sand; Step 4: The deeply impurity-removed quartz sand is subjected to ultrasonic-flotation synergistic treatment. The ultrasonic cavitation effect is used to remove the combination of flotation reagent and impurity particles to obtain purified quartz sand. Step 5: Place the purified quartz sand in a composite acid solution for pressurized acid leaching treatment to dissolve surface and shallow lattice impurities, thereby obtaining deeply purified quartz sand; Step Six: The deeply purified quartz sand is subjected to high-temperature chlorination and inert atmosphere cooling treatment to convert the residual metal impurities into volatile chlorides, which are then discharged with the airflow to obtain chlorinated purified quartz sand. Step 7: The chlorinated purified quartz sand is subjected to dehydroxylation treatment to remove hydroxyl groups inside and on the surface of the quartz sand lattice, thereby obtaining dehydroxylated quartz sand. Step 8: The dehydroxylated quartz sand is subjected to plasma purification treatment, and surface nanoscale impurities are removed by plasma bombardment to obtain a low-impurity quartz sand product with a purity ≥99.9999%.

2. The purification method for low-impurity quartz sand according to claim 1, characterized in that, The roasting-water quenching treatment in step two employs a process combining gradient temperature rise roasting and multi-stage water quenching, including: The pre-purified quartz sand is heated from room temperature to 600℃ at a rate of 3-5℃ / min and held for 1-2 hours. Then, it is heated to 900-1100℃ at a rate of 2-3℃ / min and held for 2-4 hours. Subsequently, the calcined quartz sand is sequentially immersed in a 60-80℃ warm water bath and a 0-5℃ cold water bath for two-stage water quenching, so that the inclusions and impurities inside the quartz sand are fully exposed on the particle surface, thus obtaining lattice-activated quartz sand.

3. The purification method for low-impurity quartz sand according to claim 1, characterized in that, In step five, the pressurized acid leaching treatment is carried out in a closed pressurized reactor. The pressure inside the reactor is controlled at 0.3-0.8 MPa and the leaching temperature is 120-180℃. The composite acid solution is made by mixing hydrochloric acid, oxalic acid and hydrofluoric acid in a volume ratio of 5-8:2-3:0.5-1. The leaching time is 2-6 hours to obtain deeply impurity-free quartz sand. In step five, the waste acid solution after leaching with the composite acid solution is recycled and regenerated via membrane separation. The waste acid solution is separated and recovered by nanofiltration membrane module to recover hydrofluoric acid and oxalic acid. The metal ions in the retentate are neutralized and precipitated before being discharged. The recovered regenerated acid solution is returned to step five for recycling. The volume concentration of acid in the regenerated acid solution is not less than 85% of the initial concentration.

4. The purification method for low-impurity quartz sand according to claim 1, characterized in that, The ultrasonic-flotation synergistic treatment method in step four is as follows: Deeply purified quartz sand is prepared into a slurry with a mass concentration of 25%–35%. After adding collectors and frothers, it is introduced into a flotation cell. During the flotation process, ultrasonic waves with a frequency of 25–40 kHz and an ultrasonic power density of 0.3–0.8 W / mL are applied for 15–30 min. The ultrasonic cavitation effect generates micro-jet impacts at the interface between the flotation reagent and the impurity particles, which peels off the reagent film on the surface of the mineral particles and promotes the desorption of impurity particles from the surface of the quartz sand, thus obtaining purified quartz sand.

5. The purification method for low-impurity quartz sand according to claim 1, characterized in that, The high-temperature chlorination and inert atmosphere cooling process in step six is ​​as follows: The purified quartz sand is placed in a chlorination roasting furnace and roasted at 900–1200℃ for 1–3 hours in a mixed atmosphere of chlorine and nitrogen, with a chlorine flow rate of 0.5–2 L / min. After roasting, it is rapidly cooled to below 150℃ at a rate of 20–50℃ / min in a nitrogen protective atmosphere, and then naturally cooled to room temperature to obtain a low-impurity quartz sand product.

6. The purification method for low-impurity quartz sand according to claim 1, characterized in that, The crushing and screening in step one includes: Quartz sand raw material is crushed to particles with a particle size of 0.1-0.8 mm and then screened and classified to remove coarse particles larger than 0.8 mm and fine powder smaller than 0.1 mm, so as to obtain quartz sand raw material with uniform particle size. The magnetic separation process in step three employs a two-stage magnetic separation method combining wet high-gradient magnetic separation and dry permanent magnet magnetic separation, including: First, a wet high-gradient magnetic separation with a magnetic field strength of 1.2 to 1.8 T is used to remove strongly magnetic impurities, resulting in first-grade magnetically separated quartz sand. After the primary magnetically separated quartz sand is dehydrated and dried, it is then subjected to dry permanent magnet separation with a magnetic field strength of 0.6 to 1.0 T to remove weakly magnetic impurities, thus obtaining pre-purified quartz sand.

7. The purification method for low-impurity quartz sand according to claim 1, characterized in that, The process after step four and before step five includes a deionized water ultrasonic cleaning step: the purified quartz sand is ultrasonically cleaned in deionized water 3 to 5 times, each cleaning time is 15 to 30 minutes, and the ultrasonic frequency is 35 to 45 kHz, to remove residual flotation reagents and impurity ions on the surface of the quartz sand, and the cleaned quartz sand is obtained.

8. The purification method for low-impurity quartz sand according to claim 1, characterized in that, Step seven involves dehydroxylating the chlorinated purified quartz sand, including: Chlorinated purified quartz sand is placed in an esterification reactor, and esterification agents such as acetyl chloride or acetic anhydride are added. The amount of esterification agent is 0.5% to 2% of the mass of quartz sand. The reaction is carried out at 80 to 120°C for 1 to 3 hours to convert the silanol groups on the surface of the quartz sand into hydrophobic ester groups, thereby obtaining an esterification intermediate. The esterification intermediate is then placed in a vacuum heating furnace with a vacuum degree ≤10. -2 Pa is heated to 800-1000℃ at a rate of 5-10℃ / min under an inert atmosphere and held for 2-5 hours to remove residual hydroxyl groups in the crystal lattice in the form of water molecules, thus obtaining dehydroxylated quartz sand.

9. The purification method for low-impurity quartz sand according to claim 1, characterized in that, The method for plasma purification of the dehydroxylated quartz sand in step eight is as follows: Hydroxylated quartz sand is placed in a plasma reaction chamber, and argon or an argon-oxygen mixture is introduced at a flow rate of 50–200 mL / min. The pressure in the reaction chamber is controlled at 10–100 Pa. A radio frequency plasma source is used with a power of 200–500 W, and the processing time is 10–60 min. High-energy plasma bombards the surface of the quartz sand particles, causing the residual nanoscale metal oxides, carbides, and other impurities on the surface to be vaporized and removed, resulting in a low-impurity quartz sand product with a purity ≥99.9999%.

10. A low-impurity quartz sand product, characterized in that, It is prepared by the purification method of low-impurity quartz sand as described in any one of claims 1-9; The low-impurity quartz sand product contains SiO2 content ≥ 99.9999%, Fe content ≤ 0.00005%, Al content ≤ 0.00001%, Ti content ≤ 0.00003%, and gas-liquid inclusion content ≤ 20 inclusions / cm³. 3 Furthermore, there are no residual acid radicals or flotation reagents on the surface of the quartz sand particles.

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