Method for producing high-purity quartz

Abstract

The application discloses a preparation method of high-purity quartz, and relates to the technical field of quartz sand purification. The preparation method realizes high-selectivity targeted capture of aluminum ions, efficient mass transfer and dissolution of deep impurities in micro-cracks of quartz sand, and step-by-step and accurate removal of surface iron and lattice aluminum, so that the quartz sand product has the advantages of low aluminum residue, a short leaching period and low acid consumption, and the targeted aluminum removal composite ligand can be recycled after being recovered through magnetic separation, thereby meeting the strict requirements of high-purity quartz on impurity content.

Description

Technical Field

[0001] This application relates to the field of quartz sand purification technology, and in particular to a method for preparing high-purity quartz. Background Technology

[0002] High-purity quartz sand is a key raw material for strategic emerging industries such as semiconductors, photovoltaics, fiber optic communications, and precision optics. The presence of impurities such as aluminum, iron, calcium, and magnesium in quartz sand severely reduces the high-temperature performance, light transmittance, and electrical insulation of quartz products. Therefore, thorough impurity removal is a crucial step in the preparation of high-purity quartz. Acid leaching, due to its high impurity removal efficiency and strong process adaptability, has become the mainstream technology for quartz sand purification. Among these methods, acid leaching using fluorinated mixed acids (oxalic acid + hydrofluoric acid) as the leaching agent is the most widely used.

[0003] However, existing acid leaching and purification technologies for quartz sand face the following technical bottlenecks: First, the lattice aluminum contained in associated silicate minerals (such as feldspar and mica) is difficult to effectively dissolve with conventional mixed acids. After dissolution, aluminum ions lack highly selective collection methods and easily redeposit on the quartz surface during the alkaline water washing stage, resulting in persistently high aluminum residue levels. While existing complexing agents (such as oxalic acid) have some complexing ability for iron ions, their selective complexing constant for aluminum ions is low, making targeted aluminum removal difficult. Second, quartz sand particles contain micron-sized cracks and inclusions, which cannot be effectively removed by conventional constant-pressure leaching. Due to concentration gradient-driven diffusion mass transfer, acid solution has difficulty penetrating deep into the cracks, resulting in a slow dissolution rate of inclusion impurities. This leads to long leaching times and high acid consumption. Simply increasing the temperature or acid concentration will exacerbate hydrofluoric acid volatilization losses and excessive corrosion of the quartz matrix, reducing product yield. In addition, conventional pickling processes are single-stage isothermal operations that do not distinguish the dissolution kinetics differences between surface-adsorbed impurities and lattice-borne impurities. Simultaneous dissolution of impurities such as iron and aluminum causes competitive side reactions, and there is a lack of means to target impurities in stages at different temperature windows, resulting in limited overall impurity removal efficiency.

[0004] To address the aforementioned technical shortcomings, there is an urgent need to improve existing technologies. Summary of the Invention

[0005] In view of this, this application provides a method for preparing high-purity quartz. This method achieves highly selective targeted capture of aluminum ions, efficient mass transfer dissolution of impurities deep within the microcracks of quartz sand, and stepwise precise removal of surface iron and lattice aluminum. This results in quartz sand products with the advantages of low aluminum residue, short leaching cycle, and low acid consumption. Furthermore, the targeted aluminum removal composite ligand can be recycled after magnetic separation, meeting the stringent requirements for impurity content in high-purity quartz.

[0006] This application discloses a method for preparing high-purity quartz, the technical solution of which is as follows:

[0007] A method for preparing high-purity quartz includes the following steps:

[0008] After mixing the quartz sand to be purified, the mixed acid solution, and the aluminum removal composite ligand, the first leaching treatment was carried out at 45~55℃ to obtain the first leachate and the first leached sand.

[0009] The first leaching sand and hydrofluoric acid are mixed and then subjected to a second leaching treatment at 60-75°C to obtain a second leachate and a second leaching sand.

[0010] The second leaching sand was subjected to magnetic separation treatment to obtain high-purity quartz.

[0011] Optionally, the method for preparing the aluminum-free composite ligand includes the following steps:

[0012] Ferric chloride, ferrous chloride and water are mixed and heated to 80-90°C under nitrogen protection. Then ammonia water is added to carry out a co-precipitation reaction to obtain magnetic particles.

[0013] The magnetic particles, anhydrous ethanol, water, ammonia, and tetraethyl orthosilicate are mixed and stirred to obtain primary particles.

[0014] The primary particles, anhydrous ethanol, surfactant and tetrabutyl titanate were mixed and subjected to hydrolysis. The hydrolysis product was then calcined under nitrogen protection to obtain coated particles.

[0015] The coated particles, anhydrous ethanol, and silane coupling agent were mixed and subjected to a reflux reaction to obtain modified coated particles.

[0016] After mixing polyacrylic acid, aluminum salt and water, the pH was adjusted to 4-6 and pre-complexed to obtain a primary complex.

[0017] The modified coated particles, primary complex and condensing agent are mixed and then subjected to a grafting reaction to obtain the grafted product.

[0018] The grafted product and the crosslinking agent are mixed and then subjected to a crosslinking reaction to obtain a crosslinked product;

[0019] The crosslinked product was subjected to acid washing and activation treatment in sequence to obtain the aluminum-free composite ligand.

[0020] Optionally, the mass-volume ratio of ferric chloride, ferrous chloride, water and ammonia is 1g:(0.3~0.7)g:(10~30)mL:(2~5)mL, and the volume concentration of the ammonia is 25%~28%.

[0021] Optionally, the coprecipitation reaction is carried out at a temperature of 80-90°C for a time of 0.5-1.5 h.

[0022] Optionally, the mass-to-volume ratio of the magnetic particles, anhydrous ethanol, water, ammonia, and tetraethyl orthosilicate is 1g:(30~60)mL:(5~15)mL:(0.5~1.5)mL:(0.1~0.5)g.

[0023] Optionally, the temperature of the stirring reaction is 20~35℃ and the time is 10~14h.

[0024] Optionally, the mass-to-volume ratio of the primary particles, anhydrous ethanol, surfactant, and tetrabutyl titanate is 1 g : (30~60) mL : (0.01~0.05) g : (0.5~2) g.

[0025] Optionally, the hydrolysis reaction is carried out at a temperature of 50-70°C for 5-7 hours.

[0026] Optionally, the calcination treatment is carried out at a temperature of 500~700℃ for a time of 1.5~2.5h.

[0027] Optionally, the mass-to-volume ratio of the coated particles, anhydrous ethanol, and silane coupling agent is 1 g : (20~50) mL : (0.02~0.1) g.

[0028] Optionally, the silane coupling agent is selected from one or both of γ-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane.

[0029] Optionally, the reflux reaction is carried out at a temperature of 60-80°C for 7-9 hours.

[0030] Optionally, the mass-volume ratio of the polyacrylic acid, aluminum salt, and water is 1 g : (0.02~0.1) g : (20~50) mL, the aluminum salt is selected from one or more of aluminum chloride, aluminum nitrate, or aluminum sulfate, and the molecular weight of the polyacrylic acid is 2000~10000.

[0031] Optionally, the reagent used to adjust the pH to 4-6 is acetic acid or sodium acetate solution.

[0032] Optionally, the pre-complexation treatment is performed at a temperature of 20~35℃ for 1.5~2.5h.

[0033] Optionally, the mass-to-volume ratio of the modified coated particles, the primary complex, and the condensing agent is 1 g: (10~30) mL: (0.02~0.1) g, and the condensing agent is selected from one or both of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide or N-hydroxysuccinimide.

[0034] Optionally, the grafting reaction is carried out at a temperature of 20-35°C for 22-26 hours.

[0035] Optionally, the mass-to-volume ratio of the grafted product to the crosslinking agent is 1 g: (0.05~0.3) g, and the crosslinking agent is selected from one or more of ethylene glycol diglycidyl ether, epichlorohydrin, or N,N'-methylenebisacrylamide.

[0036] Optionally, the crosslinking reaction is carried out at a temperature of 50-70°C for 5-7 hours.

[0037] Optionally, the pickling treatment specifically includes the following steps: washing the crosslinking product 1 to 3 times with hydrochloric acid solution with pH 0.5 to 2.0 at 20 to 30°C, each time for 20 to 40 minutes.

[0038] Optionally, the activation treatment specifically includes the following steps: soaking the acid-washed crosslinking product in an acetate buffer solution with a pH of 3-5 for 20-40 minutes at 20-30°C.

[0039] Optionally, the first leaching treatment and the second leaching treatment are carried out under alternating pressure conditions. The alternating pressure is to increase the pressure inside the reaction vessel from atmospheric pressure to 0.2~0.6MPa, maintain it for 5~30min, and then depressurize it to atmospheric pressure and maintain it for 5~15min. This is one cycle. The first leaching treatment is repeated 2~6 times, and the second leaching treatment is repeated 2~6 times.

[0040] Optionally, the pressurization is achieved by filling the reactor with compressed air or inert gas through a compressed gas source, wherein the pressure of the compressed gas source is 0.3~1.0MPa and the pressurization rate is 0.02~0.2MPa / s.

[0041] Optionally, the depressurization is achieved by opening the pressure relief valve to discharge the gas in the reaction vessel, with a depressurization rate of 0.05-0.5 MPa / s.

[0042] Optionally, the mass-to-volume ratio of the quartz sand to be purified, the mixed acid solution, and the aluminum-removing composite ligand is 1g:(0.5~5)mL:(0.1~10)mg.

[0043] Optionally, the mass-to-volume ratio of the first leachate sand to hydrofluoric acid is 1 g: (0.05~0.5) mL.

[0044] Optionally, the magnetic separation process specifically includes the following steps:

[0045] The second leaching sand is passed through an external magnetic field region to obtain high-purity quartz.

[0046] Optionally, the magnetic field strength of the external magnetic field region is 0.3~1.5T, and the magnetic field gradient is 10~100T / m.

[0047] Optionally, the mixed acid solution includes oxalic acid, ammonium bifluoride and hydrofluoric acid, wherein the mass-to-volume ratio of oxalic acid, ammonium bifluoride and hydrofluoric acid is (0.3~1.0) g : (0.1~0.6) g : (0.2~0.8) mL.

[0048] Optionally, the first leaching treatment and the second leaching treatment are performed under ultrasonic conditions, wherein the ultrasonic power is 0.5~5W / L and the frequency is 20~80kHz.

[0049] The high-purity quartz preparation method provided in this application has the core advantages of high selective aluminum removal, high leaching mass transfer efficiency, low acid consumption, and recyclable ligands, avoiding the problems of poor aluminum removal selectivity, slow mass transfer in deep fissures, interference between simultaneous iron and aluminum leaching, and low acid utilization rate in existing acid washing processes. Therefore, compared with the prior art, the high-purity quartz preparation method provided in this application has the characteristics of low aluminum residue, short leaching cycle, high acid utilization rate, and recyclable ligands. At the same time, the process is controllable, the ratio is adjustable, and the raw material adaptability is wide, making it both practically applicable in engineering and promising for market promotion. Detailed Implementation

[0050] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. In addition, it should be understood that the specific implementation methods described herein are only for illustration and explanation of this application and are not intended to limit this application.

[0051] In this application, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in its actual use or operating state; while "inner" and "outer" refer to the outline of the device. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". The terms first, second, third, etc., are used merely as illustrative purposes and do not impose numerical requirements or establish an order.

[0052] In this application, "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural.

[0053] In this application, "at least one" means one or more, and "more than one" means two or more. "One or more", "at least one of the following", or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0054] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0055] The present application will be specifically described below through specific embodiments. The following embodiments are only some embodiments of the present application and are not intended to limit the present application.

[0056] This application discloses a method for preparing high-purity quartz, comprising the following steps:

[0057] After mixing the quartz sand to be purified, the mixed acid solution, and the aluminum removal composite ligand, the first leaching treatment was carried out at 45~55℃ to obtain the first leachate and the first leached sand.

[0058] The first leaching sand and hydrofluoric acid are mixed and then subjected to a second leaching treatment at 60-75°C to obtain a second leachate and a second leaching sand.

[0059] The second leaching sand was subjected to magnetic separation treatment to obtain high-purity quartz.

[0060] In this application, the quartz sand to be purified is a natural quartz sand raw material containing impurities such as aluminum, iron, calcium, and magnesium; the mixed acid solution provides an acidic leaching environment; the aluminum-removing composite ligand targets and captures aluminum ions during the leaching process; the first leaching treatment preferentially complexes and removes surface-adsorbed iron impurities under mild conditions of 45~55℃, while the aluminum-removing composite ligand begins to capture dissolved aluminum ions, avoiding competitive side reactions caused by the simultaneous dissolution of iron and aluminum; the second leaching treatment adds hydrofluoric acid and raises the temperature to 60~75℃ to dissolve silicate inclusions such as feldspar and mica, and the released lattice aluminum is immediately captured by the aluminum-removing composite ligand, preventing aluminum ions from redepositing on the quartz surface; the magnetic separation treatment utilizes the magnetic core-shell structure of the aluminum-removing composite ligand to efficiently separate the ligands that capture aluminum ions from the quartz sand through an external magnetic field, obtaining high-purity quartz.

[0061] In some embodiments, the mass-to-volume ratio of the quartz sand to be purified, the mixed acid solution, and the aluminum removal composite ligand is 1 g : (0.5~5) mL : (0.1~10) mg. This ratio ensures that the acid solution fully wets the quartz sand particles, the aluminum removal composite ligand is uniformly dispersed in the system, and aluminum ions are effectively captured, avoiding the magnetic separation burden caused by excessive ligand or the incomplete aluminum removal caused by insufficient ligand.

[0062] In some embodiments, the mixed acid solution comprises oxalic acid, ammonium bifluoride, and hydrofluoric acid, wherein the mass-to-volume ratio of oxalic acid, ammonium bifluoride, and hydrofluoric acid is (0.3~1.0) g : (0.1~0.6) g : (0.2~0.8) mL. Oxalic acid provides iron ion complexing ability, ammonium bifluoride slowly decomposes at 65~70°C to release hydrogen fluoride for slow-release dissolution, and hydrofluoric acid provides an immediate fluorine source to rapidly dissolve silicate minerals, achieving stepwise removal of iron and aluminum and maximizing acid utilization.

[0063] In some embodiments, the mass-to-volume ratio of the first leaching sand to hydrofluoric acid is 1 g: (0.05~0.5) mL. The addition of hydrofluoric acid in the second leaching stage can compensate for the consumption of fluorine source in the first leaching stage, increase the fluoride ion concentration to deeply dissolve silicate inclusions, and simultaneously avoid volatilization loss and excessive corrosion of the quartz matrix caused by adding excessive hydrofluoric acid at once.

[0064] In some embodiments, the first and second leaching treatments are performed under alternating pressure conditions. The alternating pressure is achieved by increasing the pressure inside the reaction vessel from atmospheric pressure to 0.2-0.6 MPa, maintaining it for 5-30 minutes, then depressurizing it back to atmospheric pressure and maintaining it for 5-15 minutes. This constitutes one cycle. The first leaching treatment is repeated 2-6 times, and the second leaching treatment is repeated 2-6 times. The alternating pressure pulsation forces the acid and aluminum-removing composite ligands deep into the micron-sized fissures of the quartz sand through periodic pressure increases. During the pressure holding phase, the acid reacts fully with the inclusion impurities. During the pressure release phase, the fluid inside the fissures is discharged outwards, carrying away the chelated aluminum ions. In the next pressure increase cycle, the acid and ligands re-enter the fissures, forming a dynamic mass transfer cycle.

[0065] In some embodiments, the pressurization is achieved by introducing compressed air or inert gas into the reactor through a compressed gas source. The pressure of the compressed gas source is 0.3~1.0 MPa, and the pressurization rate is 0.02~0.2 MPa / s. Controlling the pressurization rate can avoid mechanical damage and microcrack propagation to the quartz sand particles caused by a sudden pressure increase, while ensuring that the acid solution enters the cracks smoothly without creating gas resistance.

[0066] In some embodiments, the pressure relief is achieved by opening a pressure relief valve to discharge the gas inside the reaction vessel, with a pressure relief rate of 0.05~0.5 MPa / s. Rapid pressure relief can create an instantaneous pressure difference inside and outside the fissure, driving the fluid rich in impurity ions inside the fissure to be discharged outward, thereby improving mass transfer efficiency. If the pressure relief rate is too fast, it may cause the liquid to be entrained and flushed out, while if the pressure relief rate is too slow, it will weaken the pulsation effect.

[0067] In some embodiments, the first and second leaching treatments are performed under ultrasonic conditions, wherein the ultrasonic power is 0.5~5W / L and the frequency is 20~80kHz. The cavitation effect of ultrasound can instantly peel off the adhered mineral film on the surface of quartz sand, open the inclusion fissures, and promote the contact between the acid and the impurity phase. At the same time, ultrasound helps to uniformly disperse the aluminum-removing composite ligands in the slurry, increasing the probability of collision and capture of the ligands with aluminum ions.

[0068] In some embodiments, the magnetic separation process specifically includes the following steps: passing the second leaching sand through an external magnetic field region to obtain high-purity quartz.

[0069] In some embodiments, the magnetic field strength of the applied magnetic field region is 0.3~1.5T, and the magnetic field gradient is 10~100T / m. This range of magnetic field strength and gradient can effectively capture aluminum-removing composite ligands while ensuring that quartz sand and waste acid can pass smoothly through the magnetic field region, achieving rapid and efficient separation of ligands and products.

[0070] In some embodiments, the method for preparing the aluminum-free composite ligand includes the following steps:

[0071] Ferric chloride, ferrous chloride and water are mixed and heated to 80-90°C under nitrogen protection. Then ammonia water is added to carry out a co-precipitation reaction to obtain magnetic particles.

[0072] The magnetic particles, anhydrous ethanol, water, ammonia, and tetraethyl orthosilicate are mixed and stirred to obtain primary particles.

[0073] The primary particles, anhydrous ethanol, surfactant and tetrabutyl titanate were mixed and subjected to hydrolysis. The hydrolysis product was then calcined under nitrogen protection to obtain coated particles.

[0074] The coated particles, anhydrous ethanol, and silane coupling agent were mixed and subjected to a reflux reaction to obtain modified coated particles.

[0075] After mixing polyacrylic acid, aluminum salt and water, the pH was adjusted to 4-6 and pre-complexed to obtain a primary complex.

[0076] The modified coated particles, primary complex and condensing agent are mixed and then subjected to a grafting reaction to obtain the grafted product.

[0077] The grafted product and the crosslinking agent are mixed and then subjected to a crosslinking reaction to obtain a crosslinked product;

[0078] The crosslinked product was subjected to acid washing and activation treatment in sequence to obtain the aluminum-free composite ligand.

[0079] In this application, ferric chloride and ferrous chloride are used as iron sources to generate magnetite nanoparticles through a co-precipitation reaction, providing magnetic separation driving force for the ligands. Tetraethyl orthosilicate hydrolyzes and condenses on the surface of the magnetic particles to form a silica intermediate layer, improving the lattice matching of subsequent titanium dioxide coating and preventing magnetic attenuation caused by the phase transition from magnetite to ferric oxide during calcination. Tetrabutyl titanate forms a dense rutile titanium dioxide shell through hydrolysis and calcination, blocking the corrosion of the magnetic core by hydrofluoric acid and ensuring the structural integrity of the ligands in a strong acid environment. A silane coupling agent introduces amino groups onto the surface of titanium dioxide, providing chemical anchors for subsequent covalent grafting of polyacrylic acid. Polyacrylic acid is rich in carboxyl groups. It exhibits multidentate chelating ability for aluminum ions; aluminum salt provides an aluminum ion template, guiding carboxyl groups to spatially pre-organize around aluminum ions during the pre-complexation process of polyacrylic acid chains; condensing agent activates carboxyl groups to form amide bonds, covalently grafting the polyacrylic acid-aluminum ion complex onto the surface of aminated titanium dioxide, avoiding the shedding of the coating layer caused by physical adsorption; crosslinking agent fixes the spatial conformation of polyacrylic acid chains, locking the spatial arrangement of carboxyl groups around aluminum ions; acid washing removes the aluminum ion template, leaving an ion-imprinted cavity in the crosslinked polyacrylic acid layer that precisely matches the size and coordination geometry of aluminum ions, achieving highly selective targeted capture of aluminum ions; activation treatment restores the carboxyl groups in the imprinted cavity to protonated carboxyl groups, restoring chelating activity.

[0080] In some embodiments, the mass-to-volume ratio of ferric chloride, ferrous chloride, water, and ammonia is 1 g : (0.3~0.7) g : (10~30) mL : (2~5) mL, and the volume concentration of the ammonia is 25%~28%. The use of ferric chloride and ferrous chloride ensures that the co-precipitated product is pure-phase iron(III) oxide, avoiding the formation of impurities such as ferric oxide or ferrous oxide.

[0081] In some embodiments, the co-precipitation reaction is carried out at a temperature of 80-90°C for a time of 0.5-1.5 hours. High-temperature, rapid precipitation is beneficial for forming magnetic nanoparticles with uniform particle size and high crystallinity, while nitrogen protection prevents oxidation by ferrous ions.

[0082] In some embodiments, the mass-to-volume ratio of the magnetic particles, anhydrous ethanol, water, ammonia, and tetraethyl orthosilicate is 1 g : (30~60) mL : (5~15) mL : (0.5~1.5) mL : (0.1~0.5) g. This application, by limiting the mass-to-volume ratio of the magnetic particles, anhydrous ethanol, water, ammonia, and tetraethyl orthosilicate, ensures the acquisition of a silicon dioxide interlayer with a thickness of 2~5 nm, which serves as a lattice buffer without significantly reducing the saturation magnetization of the ligands.

[0083] In some embodiments, the stirring reaction is carried out at a temperature of 20-35°C for 10-14 hours. Long-term hydrolysis at room temperature ensures the slow and uniform hydrolysis of tetraethyl orthosilicate, forming a dense, defect-free silica coating layer.

[0084] In some embodiments, the mass-to-volume ratio of the primary particles, anhydrous ethanol, surfactant, and tetrabutyl titanate is 1 g : (30~60) mL : (0.01~0.05) g : (0.5~2) g. The surfactant can improve the dispersibility of the primary particles in ethanol, avoid the self-nucleation and agglomeration of titanium dioxide caused by the localized excessively rapid hydrolysis of tetrabutyl titanate, and ensure that titanium dioxide is uniformly coated on the particle surface.

[0085] In some embodiments, the hydrolysis reaction is carried out at a temperature of 50–70°C for 5–7 hours. The temperature specified in this application promotes complete hydrolysis and condensation of tetrabutyl titanate while avoiding a loose and porous coating layer caused by excessively rapid hydrolysis.

[0086] In some embodiments, the calcination treatment is carried out at a temperature of 500-700°C for 1.5-2.5 hours. This temperature range allows titanium dioxide to be transformed from anatase to rutile. Rutile titanium dioxide is chemically more inert and has better resistance to hydrofluoric acid corrosion than anatase. Nitrogen protection prevents the oxidation of iron(III) oxide.

[0087] In some embodiments, the mass-to-volume ratio of the coated particles, anhydrous ethanol, and silane coupling agent is 1 g : (20~50) mL : (0.02~0.1) g. The amount of silane coupling agent is 2%~10% of the mass of the coated particles, which can ensure sufficient amination of the titanium dioxide surface and avoid the self-condensation of the silane coupling agent to form a free polymer.

[0088] In some embodiments, the reflux reaction is carried out at a temperature of 60–80°C for 7–9 hours. Reflux conditions promote the de-alcoholization condensation reaction between the ethoxy / methoxy groups of the silane coupling agent and the hydroxyl groups on the surface of titanium dioxide, forming stable covalent bonds.

[0089] In some embodiments, the silane coupling agent is selected from one or both of γ-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane. The silane coupling agent provides a chemical anchor for subsequent polyacrylic acid grafting.

[0090] In some embodiments, the mass-to-volume ratio of polyacrylic acid, aluminum salt, and water is 1 g : (0.02~0.1) g : (20~50) mL, wherein the aluminum salt is selected from one or more of aluminum chloride, aluminum nitrate, or aluminum sulfate, and the molecular weight of the polyacrylic acid is 2000~10000. Controlling the mass-to-volume ratio of aluminum salt and polyacrylic acid allows aluminum ions to be fully coordinated by 4~6 carboxyl groups to form an octahedral complex, while retaining enough free carboxyl groups for subsequent covalent grafting and the formation of imprinted cavities.

[0091] In some embodiments, the reagent used to adjust the pH to 4-6 is acetic acid or sodium acetate solution. A weak acid-weak acid salt buffer system controls the pH, preventing strong acids and bases from damaging the conformation of the polyacrylic acid chains. Within this pH range, the carboxyl groups of polyacrylic acid ionize, and aluminum ions exist in a free state, which is beneficial for the coordination complexation reaction.

[0092] In some embodiments, the pre-complexation treatment is performed at a temperature of 20–35°C for 1.5–2.5 hours. The room temperature and mild conditions ensure that aluminum ions and polyacrylic acid fully complex to form a stable conformation, while avoiding the increased thermal motion of the polyacrylic acid chains caused by high temperatures, which is detrimental to subsequent cross-linking and fixation of the imprinted cavity.

[0093] In some embodiments, the mass-to-volume ratio of the modified coated particles, the primary complex, and the condensing agent is 1 g: (10~30) mL: (0.02~0.1) g, and the condensing agent is selected from one or both of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide or N-hydroxysuccinimide.

[0094] In some embodiments, the grafting reaction is carried out at a temperature of 20–35°C for 22–26 hours. The temperature specified in this application ensures complete amidation grafting and avoids conformational changes in the polyacrylic acid-aluminum ion complex caused by heating, which could affect the subsequent imprinting effect.

[0095] In some embodiments, the mass-to-volume ratio of the grafted product to the crosslinking agent is 1 g: (0.05~0.3) g, and the crosslinking agent is selected from one or more of ethylene glycol diglycidyl ether, epichlorohydrin, or N,N'-methylenebisacrylamide. The crosslinking agent connects the carboxyl groups between polyacrylic acid chains through ester or amide bonds to form a three-dimensional crosslinked network, locking the spatial conformation of the polyacrylic acid chains around the aluminum ions, providing a structural basis for the formation of stable ion-imprinted cavities during subsequent template elution.

[0096] In some embodiments, the crosslinking reaction is carried out at a temperature of 50–70°C for 5–7 hours. Moderate heating promotes complete crosslinking, while excessively high temperatures may cause conformational changes in the polyacrylic acid chains, damaging the pre-organized structure of the imprinted cavity.

[0097] In some embodiments, the acid washing treatment specifically includes the following steps: washing the crosslinked product 1-3 times with a hydrochloric acid solution with a pH of 0.5-2.0 at 20-30°C, each time for 20-40 minutes. The strong acid conditions cause aluminum ions to dissociate and dissolve from the carboxyl coordination sites of the polyacrylic acid, leaving three-dimensional nanocavities in the crosslinked polyacrylic acid layer that match the size and coordination geometry of the aluminum ions. Simultaneously, the chloride ions in the hydrochloric acid do not form stable complexes with the aluminum ions, ensuring complete elution of the aluminum ions.

[0098] In some embodiments, the activation treatment specifically includes the following steps: soaking the acid-washed crosslinked product in an acetate buffer solution with a pH of 3-5 at 20-30°C for 20-40 minutes. The weak acid buffer solution re-protonates the carboxylate ions in the imprint cavity to carboxyl groups, restoring their chelating activity for aluminum ions. The mild pH conditions of the acetate buffer solution avoid damaging the structure of the imprint cavity.

[0099] In this application, the aluminum-free composite ligands recovered through magnetic separation are recycled after regeneration. The regeneration process involves eluting the captured aluminum ions with an acidic solution at pH 0.5–2.0, washing with water until neutral, and then activating with a buffer solution at pH 3–5. This regeneration process achieves aluminum ion desorption and ligand activity recovery under mild conditions that do not damage the ion-imprinted cavity structure. After 10 cycles of reuse, the ligand retains at least 90% of its aluminum ion adsorption capacity.

[0100] The present application will be specifically described below through specific embodiments. The following embodiments are only some embodiments of the present application and are not intended to limit the present application.

[0101] Example 1

[0102] This embodiment provides a method for preparing high-purity quartz, including the following technical solution:

[0103] A method for preparing high-purity quartz includes the following steps:

[0104] 1000g of quartz sand to be purified, 2500mL of mixed acid solution, and 5g of aluminum-removing composite ligand were mixed and subjected to a first leaching treatment at 50℃ under alternating pressure to obtain a first leachate and a first leached sand. The mixed acid solution included 6g of oxalic acid, 3g of ammonium bifluoride, and 4mL of hydrofluoric acid. The alternating pressure condition was to increase the pressure in the reaction vessel from atmospheric pressure to 0.4MPa, maintain it for 15min, then depressurize it to atmospheric pressure and maintain it for 10min, which constituted one cycle. The first leaching treatment was repeated for 4 cycles. The first leaching treatment was accompanied by ultrasonic-assisted treatment with an ultrasonic power of 2W / L and a frequency of 40kHz.

[0105] The first leaching sand and 150 mL of hydrofluoric acid were mixed and subjected to a second leaching treatment at 65°C under alternating pressure to obtain a second leachate and a second leaching sand. The alternating pressure condition was to increase the pressure in the reaction vessel from atmospheric pressure to 0.4 MPa, maintain it for 15 min, then depressurize it to atmospheric pressure and maintain it for 10 min. This was one cycle, and the second leaching treatment was repeated for 4 cycles. The second leaching treatment was accompanied by ultrasonic-assisted treatment with an ultrasonic power of 2 W / L and a frequency of 40 kHz.

[0106] The second leaching sand is subjected to magnetic separation treatment in an external magnetic field region. The magnetic field strength of the external magnetic field region is 0.8T and the magnetic field gradient is 50T / m. Except for the aluminum composite ligands being captured and retained by the magnetic field, the quartz sand flows out through the magnetic field region to obtain high-purity quartz.

[0107] The quartz sand to be purified is grade III quartz sand, with a silicon dioxide content of 90.28%, an iron oxide content of 2.24%, an aluminum oxide content of 3.86%, a calcium oxide content of 0.53%, a potassium oxide content of 0.20%, a sodium oxide content of 0.05%, a magnesium oxide content of 0.34%, a titanium dioxide content of 0.21%, and a particle size of 200 mesh or larger.

[0108] The preparation method of the aluminum-free composite ligand includes the following steps:

[0109] 10g of ferric chloride, 5g of ferrous chloride, and 200mL of water were added to a 500mL three-necked flask. The mixture was heated to 85°C under nitrogen protection with stirring. 30mL of ammonia (26% by volume) was rapidly injected while stirring vigorously. The system quickly turned black. The mixture was kept at this temperature and stirred for another hour. After the reaction was completed, the magnetic particles were precipitated using an external magnet. The supernatant was discarded, and the mixture was repeatedly washed with deionized water until the pH of the washing solution reached 7. The mixture was then washed twice with ethanol and dried under vacuum at 60°C to obtain 8.5g of magnetite magnetic nanoparticles with a particle size of 50-80nm and a saturation magnetization of 65emu / g.

[0110] 5g of the magnetic particles were dispersed in a mixed solution of 200mL anhydrous ethanol and 50mL water, and ultrasonically dispersed for 30min. 5mL of ammonia was added, and 1.5g of tetraethyl orthosilicate dissolved in 20mL anhydrous ethanol was slowly added dropwise under mechanical stirring over 1h. After the addition was complete, the mixture was stirred at room temperature for 12h. After the reaction was completed, the product was separated with a magnet, washed with ethanol and water in sequence, and dried under vacuum at 60℃ to obtain 5.8g of primary particles. The thickness of the silica intermediate layer was observed to be 3-5nm under transmission electron microscopy.

[0111] 4g of the primary particles were dispersed in 180mL of anhydrous ethanol, and 0.12g of the surfactant hexadecyltrimethylammonium bromide was added. The mixture was ultrasonically dispersed for 30min. Under mechanical stirring, a solution of 4g of tetrabutyl titanate dissolved in 40mL of anhydrous ethanol was slowly added dropwise over 1h. The mixture was then heated to 60℃ for hydrolysis for 6h. After the reaction, the product was separated by a magnet, washed with ethanol, and vacuum dried at 80℃. The dried product was placed in a tube furnace and calcined at 600℃ for 2h under a nitrogen atmosphere at a rate of 5℃ / min. After cooling, the calcined product was dispersed again in 180mL of anhydrous ethanol. The above process of adding tetrabutyl titanate, hydrolysis, and calcination was repeated once to obtain 5.2g of coated particles. Transmission electron microscopy showed that the total thickness of the titanium dioxide shell was 18nm. X-ray diffraction analysis indicated that the titanium dioxide was rutile.

[0112] 3g of the coated particles were dispersed in 100mL of anhydrous ethanol and ultrasonically dispersed for 30min. 0.15g of the silane coupling agent γ-aminopropyltriethoxysilane was added, and the mixture was refluxed and stirred at 70℃ under nitrogen protection for 8h. After the reaction, the product was separated using a magnet, washed three times repeatedly with anhydrous ethanol, and vacuum dried at 80℃ to obtain 3.1g of modified coated particles. The infrared spectrum was at 2920cm⁻¹. -1 and 2850cm -1 A characteristic absorption peak of methylene appears at 1050 cm⁻¹. -1 The presence of Si-O-Ti characteristic peaks indicates that the silane coupling agent was successfully grafted.

[0113] Dissolve 2g of polyacrylic acid (molecular weight 5000) in 80mL of deionized water and stir until completely dissolved. Add 0.15g of aluminum chloride dissolved in 10mL of deionized water. Adjust the pH to 5 with acetic acid solution and stir at room temperature for 2h to perform pre-complexation treatment to obtain a primary complex solution.

[0114] 2g of the modified coated particles were dispersed in 30mL of deionized water and ultrasonically dispersed for 20min. The above primary complex solution was added under mechanical stirring and ultrasonically dispersed for 30min to make the system homogeneous. 0.1g of condensing agent 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 0.06g of N-hydroxysuccinimide were added and the amidation grafting reaction was carried out at room temperature for 24h. After the reaction was completed, the product was separated by a magnet and washed three times with deionized water to obtain 2.3g of grafted product.

[0115] 1.5 g of the grafted product was dispersed in 30 mL of deionized water. 0.2 g of crosslinking agent ethylene glycol diglycidyl ether was added under mechanical stirring. The temperature was raised to 60 °C and the crosslinking reaction was carried out for 6 h. After the reaction was completed, the product was separated by a magnet and washed twice each with ethanol and deionized water to obtain 1.6 g of crosslinked product.

[0116] The crosslinked product was washed with hydrochloric acid solution at pH 1.0 at room temperature with stirring for 30 minutes each time, repeated 3 times. After each washing, the product was separated with a magnet and the eluent was discarded. Then, it was washed with deionized water until the pH of the washing solution was 7. Then, acetate buffer solution at pH 4.0 was added, and the product was soaked at room temperature for 30 minutes for activation treatment. The product was separated with a magnet, washed with deionized water, and vacuum dried at 60°C to obtain 1.4 g of aluminum-free complex ligand.

[0117] The saturation magnetization of the aluminum-removing composite ligand is 52 emu / g, the adsorption capacity for aluminum ions is 85 mg / g, and the selectivity coefficients for aluminum ions under the coexistence of calcium and magnesium ions are k(Al / Ca)=62 and k(Al / Mg)=38.

[0118] The aluminum-free composite ligand recovered by the magnetic separation process is recycled after regeneration. The regeneration process is as follows: the captured aluminum ions are eluted with hydrochloric acid solution at pH 1.0 for 30 minutes each time, repeated twice, washed with water until neutral, and then activated by soaking in acetate buffer solution at pH 4.0 for 30 minutes.

[0119] Example 2

[0120] This embodiment provides a method for preparing high-purity quartz, the raw material composition of which is exactly the same as that in Example 1, except that the amount of aluminum-free composite ligand is adjusted to 1g;

[0121] Preparation method:

[0122] The preparation steps are the same as in Example 1, and will not be repeated here.

[0123] Example 3

[0124] This embodiment provides a method for preparing high-purity quartz, the raw material composition of which is exactly the same as that in Example 1, except that the amount of aluminum-free composite ligand is adjusted to 10g.

[0125] Preparation method:

[0126] The preparation steps are the same as in Example 1, and will not be repeated here.

[0127] Example 4

[0128] This embodiment provides a method for preparing high-purity quartz. The raw material composition is exactly the same as that in Example 1. The difference is that the alternating pressure condition is adjusted to be increased to 0.2 MPa, maintained for 30 min, then depressurized to atmospheric pressure, maintained for 15 min, and the first leaching treatment cycle is repeated for 2 cycles, and the second leaching treatment cycle is repeated for 2 cycles.

[0129] Preparation method:

[0130] The preparation steps are the same as in Example 1, and will not be repeated here.

[0131] Example 5

[0132] This embodiment provides a method for preparing high-purity quartz. The raw material composition is exactly the same as that in Example 1. The difference is that the alternating pressure condition is adjusted to be increased to 0.6 MPa, held for 5 min, then depressurized to atmospheric pressure, held for 5 min, and the first leaching treatment cycle is 6 cycles, and the second leaching treatment cycle is 6 cycles.

[0133] Preparation method:

[0134] The preparation steps are the same as in Example 1, and will not be repeated here.

[0135] Example 6

[0136] This embodiment provides a method for preparing high-purity quartz, the raw material composition of which is exactly the same as that in Example 1, except that the amount of oxalic acid, ammonium bifluoride, and hydrofluoric acid in the mixed acid solution is adjusted to 3g, 1g, and 2mL.

[0137] Preparation method:

[0138] The preparation steps are the same as in Example 1, and will not be repeated here.

[0139] Example 7

[0140] This embodiment provides a method for preparing high-purity quartz, the raw material composition of which is exactly the same as that in Example 1, except that the amount of oxalic acid, ammonium bifluoride and hydrofluoric acid in the mixed acid solution is adjusted to 10g, 6g and 8mL respectively.

[0141] Preparation method:

[0142] The preparation steps are the same as in Example 1, and will not be repeated here.

[0143] Example 8

[0144] This embodiment provides a method for preparing high-purity quartz, the raw material composition of which is exactly the same as that in Example 1, except that the first leaching treatment temperature is 45°C and the second leaching treatment temperature is 60°C.

[0145] Preparation method:

[0146] The preparation steps are the same as in Example 1, and will not be repeated here.

[0147] Example 9

[0148] This embodiment provides a method for preparing high-purity quartz, the raw material composition of which is exactly the same as that in Example 1, except that the first leaching treatment temperature is 55°C and the second leaching treatment temperature is 75°C.

[0149] Preparation method:

[0150] The preparation steps are the same as in Example 1, and will not be repeated here.

[0151] Comparative Example 1

[0152] This comparative example provides a method for preparing high-purity quartz, including the following technical solution:

[0153] A method for preparing high-purity quartz includes the following steps:

[0154] 1000g of quartz sand to be purified and 2500mL of mixed acid solution were mixed and leached at 50℃ and normal pressure for 6 hours. The mixed acid solution included 6g of oxalic acid, 3g of ammonium bifluoride and 4mL of hydrofluoric acid. Stirring was carried out during the leaching process.

[0155] After leaching, the quartz sand is washed with water until neutral and dried to obtain the quartz sand product.

[0156] The specifications of the quartz sand to be purified are the same as those in Example 1.

[0157] Comparative Example 2

[0158] This comparative example provides a method for preparing high-purity quartz, the raw material composition of which differs from that of Example 1 in that no aluminum-removing composite ligand is added;

[0159] Preparation method:

[0160] 1000g of quartz sand to be purified and 2500mL of mixed acid solution were mixed and subjected to a first leaching treatment at 50℃ under alternating pressure to obtain a first leachate and a first leached sand. The mixed acid solution included 6g of oxalic acid, 3g of ammonium bifluoride and 4mL of hydrofluoric acid. The alternating pressure condition was to increase the pressure in the reaction vessel from atmospheric pressure to 0.4MPa, maintain it for 15min, then depressurize it to atmospheric pressure and maintain it for 10min. This was one cycle, and the first leaching treatment was repeated for 4 cycles.

[0161] The first leaching sand and 150 mL of hydrofluoric acid were mixed and subjected to a second leaching treatment at 65°C and under alternating pressure to obtain a second leachate and a second leaching sand; the alternating pressure conditions were the same as those for the first leaching treatment.

[0162] The second leached sand is washed with water and dried to obtain quartz sand product.

[0163] The remaining preparation steps are the same as in Example 1, and will not be repeated here.

[0164] Comparative Example 3

[0165] This comparative example provides a method for preparing high-purity quartz. The raw material composition differs from that of Example 1 in that the first leaching treatment and the second leaching treatment are both carried out under normal pressure conditions without applying alternating pressure pulsation.

[0166] Preparation method:

[0167] 1000g of quartz sand to be purified, 2500mL of mixed acid solution and 5g of aluminum-removing composite ligand were mixed and stirred at 50℃ and normal pressure for the first leaching treatment for 2 hours to obtain the first leachate and the first leachate sand; the mixed acid solution included 6g of oxalic acid, 3g of ammonium bifluoride and 4mL of hydrofluoric acid.

[0168] The first leaching sand and 150 mL of hydrofluoric acid were mixed and stirred at 65°C and normal pressure for a second leaching treatment. The leaching time was 2 hours, resulting in a second leaching solution and a second leaching sand.

[0169] The second leached sand is subjected to magnetic separation treatment in an external magnetic field region. The magnetic field strength of the external magnetic field region is 0.8T and the magnetic field gradient is 50T / m, resulting in quartz sand product.

[0170] The remaining preparation steps are the same as in Example 1, and will not be repeated here.

[0171] Comparative Example 4

[0172] This comparative example provides a method for preparing high-purity quartz. The raw material composition differs from that of Example 1 in that the first leaching treatment and the second leaching treatment are both carried out at 65°C, without gradient heating and segmented leaching.

[0173] Preparation method:

[0174] 1000g of quartz sand to be purified, 2500mL of mixed acid solution, and 5g of aluminum-removing composite ligand were mixed and subjected to a first leaching treatment at 65℃ under alternating pressure to obtain a first leachate and a first leached sand. The mixed acid solution included 6g of oxalic acid, 3g of ammonium bifluoride, and 4mL of hydrofluoric acid. The alternating pressure condition was to increase the pressure in the reaction vessel from atmospheric pressure to 0.4MPa, maintain it for 15min, then depressurize it to atmospheric pressure and maintain it for 10min. This was one cycle, and the first leaching treatment was repeated for 4 cycles.

[0175] The first leaching sand and 150 mL of hydrofluoric acid were mixed and subjected to a second leaching treatment at 65°C and under alternating pressure to obtain a second leachate and a second leaching sand; the alternating pressure conditions were the same as those for the first leaching treatment.

[0176] The second leached sand is subjected to magnetic separation treatment in an external magnetic field area to obtain quartz sand product.

[0177] The remaining preparation steps are the same as in Example 1, and will not be repeated here.

[0178] Comparative Example 5

[0179] This comparative example provides a method for preparing high-purity quartz, the raw material composition of which differs from that of Example 1 in that an equal mass of oxalic acid is used to replace the aluminum-removing composite ligand;

[0180] Preparation method:

[0181] The preparation steps are the same as in Example 1, and will not be repeated here.

[0182] Comparative Example 6

[0183] This comparative example provides a method for preparing high-purity quartz. The raw material composition differs from that of Example 1 in that the aluminum composite ligand is not subjected to aluminum ion template imprinting treatment. That is, the pre-complexation treatment, cross-linking reaction, acid washing treatment and activation treatment steps are omitted in the preparation process. Polyacrylic acid is only physically adsorbed onto the surface of the modified coated particles.

[0184] The preparation steps of the aluminum-free composite ligand in the preparation method are as follows:

[0185] Dissolve 2g of polyacrylic acid (molecular weight 5000) in 80mL of deionized water and stir until completely dissolved to obtain a polyacrylic acid solution.

[0186] 2g of modified coated particles were dispersed in 30mL of deionized water and ultrasonically dispersed for 20min. The above polyacrylic acid solution was added under mechanical stirring, and the mixture was stirred and adsorbed at room temperature for 24h. The product was separated by a magnet, washed with deionized water, and vacuum dried at 60℃ to obtain a non-imprinted aluminum-removing composite ligand.

[0187] The remaining preparation steps are the same as in Example 1, and will not be repeated here.

[0188] The performance of the high-purity quartz in Examples 1-9 and the quartz sand products in Comparative Examples 1-6 was tested, and the test results are shown in Table 1. Among them:

[0189] Aluminum residue test: The aluminum content in quartz sand was determined by inductively coupled plasma mass spectrometry. The sample amount was 0.5g, which was digested with a mixed acid of hydrofluoric acid and nitric acid by microwave digestion. After being brought to a certain volume, the sample was tested. Three samples were tested in each group, and the average value was taken.

[0190] Iron residue test: The iron content in quartz sand was determined by inductively coupled plasma mass spectrometry, and the pretreatment method was the same as that for aluminum residue test.

[0191] Calcium residue test: The calcium content in quartz sand was determined by inductively coupled plasma mass spectrometry, and the pretreatment method was the same as that for aluminum residue test.

[0192] Magnesium Residue Test: The magnesium content in quartz sand was determined by inductively coupled plasma mass spectrometry, and the pretreatment method was the same as that for aluminum residue test.

[0193] Silica purity test: The difference method is used to calculate the silica purity = 100% - Σ impurity oxide content. The impurity oxide content is obtained by converting the content of each element by inductively coupled plasma mass spectrometry.

[0194] Total leaching time test: Record the total time from the start of the first leaching treatment to the end of the second leaching treatment, in hours;

[0195] Acid consumption test: The total volume of mixed acid solution consumed per ton of quartz sand is measured in L / t. The volume of mixed acid solution includes the sum of the volume of mixed acid solution used in the first leaching treatment and the volume of hydrofluoric acid added in the second leaching treatment.

[0196] Ligand recovery rate test: After magnetic separation treatment, aluminum-free composite ligands are collected using an external magnet, washed with water, dried and weighed, and the recovery rate is calculated by comparing with the initial addition amount. Ligand recovery rate = (mass of recovered ligands / mass of initial added ligands) × 100%. Each group is tested 3 times and the average value is taken.

[0197] Ligand cycling performance test: The recovered aluminum-free composite ligands were regenerated and reused. The change in aluminum residue after each cycle was tested. The cycle was performed 10 times, and the rate of change of aluminum residue after the 10th cycle relative to the aluminum residue after the 1st cycle was recorded.

[0198] Table 1 Performance Test Results

[0199] Example 1 18 22 15 8 99.992 3.3 2650 98.2 +8.5 Example 2 35 24 18 10 99.988 3.3 2650 97.5 +10.2 Example 3 15 21 14 7 99.993 3.3 2650 98.5 +7.8 Example 4 28 26 20 12 99.988 3.5 2650 97.8 +9.5 Example 5 22 23 16 9 99.991 3.2 2650 98.0 +8.8 Example 6 42 45 22 13 99.985 3.3 2850 98.2 +8.5 Example 7 20 25 17 11 99.990 3.3 2580 98.2 +8.5 Example 8 30 20 25 15 99.987 3.3 2650 98.2 +8.5 Example 9 16 28 13 7 99.993 3.3 2650 98.2 +8.5 Comparative Example 1 386 1120 265 170 99.81 6.0 2900 - - Comparative Example 2 186 32 58 42 99.95 3.3 2650 - - Comparative Example 3 120 38 45 35 99.96 4.0 2650 98.0 +9.0 Comparative Example 4 95 85 42 30 99.97 3.3 2650 98.2 +8.5 Comparative Example 5 290 26 210 145 99.88 3.3 2650 - - Comparative Example 6 78 25 38 28 99.97 3.3 2650 97.8 +25.6

[0200] As shown in Table 1, the aluminum residue in Example 1 was only 18 ppm, which is 4.7% of the aluminum residue (386 ppm) in Comparative Example 1 using the traditional single-stage atmospheric pressure pickling process. The iron residue was only 22 ppm, which is 2.0% of the iron residue (1120 ppm) in Comparative Example 1. The silica purity increased from 99.81% to 99.992%. Compared with Comparative Example 2 without the addition of the aluminum removal composite ligand, the aluminum residue in Example 1 was reduced by 90.3%, confirming that the targeted capture of aluminum ions by the aluminum removal composite ligand is the key to achieving deep aluminum removal. Compared with Comparative Example 6 using a non-imprinted ligand, the aluminum residue in Example 1 was reduced by 76.9%. Moreover, the change rate of aluminum residue after 10 cycles of the ligand in Example 1 was only 8.5%, while that in Comparative Example 6 was as high as 25.6%, indicating that aluminum ion imprinting improved the selectivity and cycling stability of the ligand. Examples 2 and 3 adjusted the amount of aluminum removal composite ligand. In Example 3, when the amount of ligand was increased to 10g, the aluminum residue was further reduced to 15ppm. However, in Example 2, when the amount of ligand was 1g, the aluminum residue increased to 35ppm. This shows that increasing the amount of ligand within a certain range is beneficial to improving the aluminum removal efficiency, but there is an optimization range.

[0201] As shown in Table 1, the total leaching time of Example 1 was only 3.3 hours, which is 45% shorter than the 6 hours of the conventional process in Comparative Example 1, and the acid consumption was reduced by 8.6%. Compared with Comparative Example 3 without alternating pressure pulsation, the total leaching time of Example 1 was shortened by 17.5%, and the aluminum residue was reduced by 85%. This indicates that the alternating pressure pulsation forces the acid and ligands into the depth of the microfractures in the quartz sand through periodic pressure increase, pressure holding, and pressure release operations. During pressure release, the fluid in the fractures is discharged outward and carries away the chelated aluminum ions, forming a dynamic mass transfer cycle and enhancing the mass transfer efficiency. Examples 4 and 5 adjusted the alternating pressure parameters. In Example 4, the aluminum residue was 28 ppm when the pressure was increased to 0.2 MPa and the cycle was repeated 2 times, and the total leaching time was extended to 3.5 h. In Example 5, the aluminum residue was 22 ppm when the pressure was increased to 0.6 MPa and the cycle was repeated 6 times, and the total leaching time was shortened to 3.2 h. This shows that the pressure amplitude and the number of cycles have a significant impact on the aluminum removal efficiency and leaching time, and need to be optimized within the mechanical tolerance range of the quartz sand particles.

[0202] As shown in Table 1, the residual iron content in Example 1 was 22 ppm, the residual calcium content was 15 ppm, and the residual magnesium content was 8 ppm, all of which were at relatively low levels. Compared with Comparative Example 4, which did not undergo gradient heating and staged leaching, the residual iron content in Example 1 was reduced by 74.1%, and the residual aluminum content was reduced by 81.1%. This indicates that the surface-adsorbed iron impurities were preferentially complexed and removed under mild conditions of 45-55℃, and then hydrofluoric acid was added to raise the temperature to 60-75℃ to deeply dissolve the silicate inclusions and target and capture the released lattice aluminum. This avoided the competitive side reactions caused by the simultaneous dissolution of iron and aluminum and the reprecipitation of aluminum ions in the subsequent water washing stage. Examples 8 and 9 adjusted the leaching temperature. In Example 8, the aluminum residue was 30 ppm when the first leaching treatment temperature was 45°C and the second leaching treatment temperature was 60°C. In Example 9, the aluminum residue was 16 ppm when the first leaching treatment temperature was 55°C and the second leaching treatment temperature was 75°C. This shows that higher temperatures are beneficial to improving aluminum removal efficiency, but a balance must be made between hydrofluoric acid volatilization loss and excessive corrosion of the quartz matrix.

[0203] As shown in Table 1, the ligand recovery rate of Example 1 was 98.2%, and the change rate of aluminum residue after 10 cycles was only 8.5%, indicating that the core-shell structure of the aluminum-free composite ligand has good structural stability in the hydrofluoric acid environment and high magnetic separation recovery efficiency. In Comparative Example 6, the aluminum residue of the non-imprinted ligand increased with the number of cycles, reaching a change rate of 25.6% after 10 cycles, confirming the crucial role of ion imprinting technology in ligand selectivity and cycling stability.

[0204] Comparative Example 7

[0205] This comparative example provides an aluminum-removing composite ligand, whose raw material composition is exactly the same as that of the aluminum-removing composite ligand in Example 1, except that the amount of aluminum chloride used in the pre-complexation treatment step is 0.05g.

[0206] Preparation method:

[0207] The preparation steps are the same as in Example 1, and will not be repeated here. The resulting aluminum-free composite ligand has an adsorption capacity of 42 mg / g for aluminum ions, and the selectivity coefficients for aluminum ions under the coexistence of calcium and magnesium ions are k(Al / Ca)=18 and k(Al / Mg)=12.

[0208] Comparative Example 8

[0209] This comparative example provides an aluminum-removing composite ligand, whose raw material composition is exactly the same as that of the aluminum-removing composite ligand in Example 1. The difference is that the amount of aluminum chloride used in the pre-complexation treatment step is 0.5g, and the amount of crosslinking agent ethylene glycol diglycidyl ether used is 0.5g.

[0210] Preparation method:

[0211] The preparation steps are the same as in Example 1, and will not be repeated here. The resulting aluminum-free composite ligand has an adsorption capacity of 65 mg / g for aluminum ions, and the selectivity coefficients for aluminum ions under the coexistence of calcium and magnesium ions are k(Al / Ca)=28 and k(Al / Mg)=18.

[0212] The performance of the aluminum-free composite ligands in Examples 1, 6, 7, and 8 was tested, and the results are shown in Table 2. Wherein:

[0213] Adsorption capacity: 0.1 g of aluminum-free composite ligand was added to a simulated leaching solution with pH 1.5 and an initial aluminum ion concentration of 100 mg / L. The solution was stirred at 50 °C for 2 h for adsorption. After magnetic separation, the aluminum ion concentration in the supernatant was determined by ICP-MS. The adsorption capacity was calculated as follows: Adsorption capacity = (initial concentration - equilibrium concentration) × solution volume / ligand mass.

[0214] Selectivity coefficient: Prepare a mixed solution containing 50 mg / L each of aluminum ions, calcium ions, and magnesium ions, adjust the pH to 1.5, add 0.1 g of aluminum-removing complex ligand, stir and adsorb at 50 °C for 2 h, and after magnetic separation, determine the concentration of each ion in the supernatant by ICP-MS, calculate the partition coefficient and selectivity coefficient, and selectivity coefficient k(Al / M) = partition coefficient of ligand to aluminum / partition coefficient of ligand to M;

[0215] Imprinting factor: Imprinting factor = adsorption capacity of ion-imprinted ligands / adsorption capacity of non-imprinted ligands, reflecting the factor by which ion imprinting technology improves adsorption capacity;

[0216] Cyclic adsorption capacity retention rate: The aluminum-free composite ligand was subjected to 10 adsorption-desorption-activation cycles. The adsorption capacity of the 10th cycle was measured and compared with that of the 1st cycle to calculate the retention rate.

[0217] Table 2 Performance test results of aluminum-free composite ligands

[0218] project Example 1 Comparative Example 6 Comparative Example 7 Comparative Example 8 Adsorption capacity (mg / g) 85 45 42 65 Selectivity coefficient k(Al / Ca) 62 8 18 28 Selectivity coefficient k(Al / Mg) 38 5 12 18 Imprinting factor 1.89 - - - Adsorption capacity retention rate after 10 cycles (%) 91.5 58.2 63.5 72.8

[0219] As shown in Table 2, the adsorption capacity of the aluminum-free composite ligand in Example 1 was 85 mg / g, which was 1.89 times that of the non-imprinted Comparative Example 6. This indicates that the imprinted cavity constructed in the polyacrylic acid layer by ion imprinting technology, which precisely matches the spatial size and coordination geometry of aluminum ions, increased the density of effective chelation sites. The selectivity coefficient k(Al / Ca) of Example 1 was as high as 62, which was 7.75 times that of Comparative Example 6; k(Al / Mg) reached 38, which was 7.6 times that of Comparative Example 6. This confirms the high selective recognition ability of aluminum ions by the size sieving effect of the imprinted cavity and the coordination geometry pre-organization. Calcium ions and magnesium ions, due to their larger ionic radii, had difficulty entering the imprinted cavity. In Comparative Example 7, the amount of template ions was too low, resulting in an insufficient number of imprinted cavities, and both the adsorption capacity and selectivity coefficient decreased significantly. In Comparative Example 8, the amount of template ions and crosslinking agent was too high, and the excessive crosslinking density led to increased rigidity but insufficient elasticity of the imprinted cavity, hindering the entry and exit of aluminum ions. The adsorption capacity and cycle retention rate were both lower than those of Example 1.

[0220] The technical solutions provided by the embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for preparing high-purity quartz, characterized in that, Includes the following steps: After mixing the quartz sand to be purified, the mixed acid solution, and the aluminum removal composite ligand, the first leaching treatment was carried out at 45~55℃ to obtain the first leachate and the first leached sand. The first leaching sand and hydrofluoric acid are mixed and then subjected to a second leaching treatment at 60-75°C to obtain a second leaching solution and a second leaching sand. The second leaching sand was subjected to magnetic separation treatment to obtain high-purity quartz.

2. The method for preparing high-purity quartz according to claim 1, characterized in that, The method for preparing the aluminum-free composite ligand includes the following steps: Ferric chloride, ferrous chloride and water are mixed and heated to 80-90°C under nitrogen protection. Then ammonia water is added to carry out a co-precipitation reaction to obtain magnetic particles. The magnetic particles, anhydrous ethanol, water, ammonia, and tetraethyl orthosilicate are mixed and stirred to obtain primary particles. The primary particles, anhydrous ethanol, surfactant and tetrabutyl titanate were mixed and subjected to hydrolysis. The hydrolysis product was then calcined under nitrogen protection to obtain coated particles. The coated particles, anhydrous ethanol, and silane coupling agent were mixed and subjected to a reflux reaction to obtain modified coated particles. After mixing polyacrylic acid, aluminum salt and water, the pH was adjusted to 4-6 and pre-complexed to obtain a primary complex. The modified coated particles, primary complex and condensing agent are mixed and then subjected to a grafting reaction to obtain the grafted product. The grafted product and the crosslinking agent are mixed and then subjected to a crosslinking reaction to obtain a crosslinked product; The crosslinked product was subjected to acid washing and activation treatment in sequence to obtain the aluminum-free composite ligand.

3. The method for preparing high-purity quartz according to claim 2, characterized in that, The mass-to-volume ratio of ferric chloride, ferrous chloride, water, and ammonia is 1 g : (0.3~0.7) g : (10~30) mL : (2~5) mL, and the volume concentration of the ammonia is 25%~28%; and / or The coprecipitation reaction is carried out at a temperature of 80-90°C for a time of 0.5-1.5 h; and / or The mass-to-volume ratio of the magnetic particles, anhydrous ethanol, water, ammonia, and tetraethyl orthosilicate is 1 g : (30~60) mL : (5~15) mL : (0.5~1.5) mL : (0.1~0.5) g; and / or The stirring reaction is carried out at a temperature of 20-35°C for a time of 10-14 hours; and / or The mass-to-volume ratio of the primary particles, anhydrous ethanol, surfactant, and tetrabutyl titanate is 1 g : (30~60) mL : (0.01~0.05) g : (0.5~2) g; and / or The hydrolysis reaction is carried out at a temperature of 50-70°C for a time of 5-7 hours; and / or The calcination treatment is performed at a temperature of 500~700℃ for a time of 1.5~2.5h; and / or The mass-to-volume ratio of the coated particles, anhydrous ethanol, and silane coupling agent is 1 g : (20~50) mL : (0.02~0.1) g; and / or The silane coupling agent is selected from one or both of γ-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane; and / or The reflux reaction is carried out at a temperature of 60-80°C for 7-9 hours; and / or The mass-to-volume ratio of the polyacrylic acid, aluminum salt, and water is 1 g : (0.02~0.1) g : (20~50) mL, wherein the aluminum salt is selected from one or more of aluminum chloride, aluminum nitrate, or aluminum sulfate, and the molecular weight of the polyacrylic acid is 2000~10000; and / or The reagent used to adjust the pH to 4-6 is acetic acid or sodium acetate solution; and / or The pre-complexation treatment is performed at a temperature of 20-35°C for 1.5-2.5 hours; and / or The mass-to-volume ratio of the modified coated particles, the primary complex, and the condensing agent is 1 g : (10~30) mL : (0.02~0.1) g, wherein the condensing agent is selected from one or both of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide or N-hydroxysuccinimide; and / or The grafting reaction is carried out at a temperature of 20-35°C for a time of 22-26 hours; and / or The mass-to-volume ratio of the grafted product to the crosslinking agent is 1 g : (0.05~0.3) g, and the crosslinking agent is selected from one or more of ethylene glycol diglycidyl ether, epichlorohydrin, or N,N'-methylenebisacrylamide; and / or The crosslinking reaction is carried out at a temperature of 50-70°C for a time of 5-7 hours; and / or The pickling treatment specifically includes the following steps: washing the crosslinked product 1-3 times with a hydrochloric acid solution with a pH of 0.5-2.0 at 20-30°C, each time for 20-40 minutes; and / or The activation treatment specifically includes the following steps: soaking the acid-washed crosslinked product in an acetate buffer solution with a pH of 3-5 for 20-40 minutes at 20-30°C.

4. The method for preparing high-purity quartz according to claim 1, characterized in that, The first leaching treatment and the second leaching treatment are carried out under alternating pressure conditions. The alternating pressure is to increase the pressure in the reaction vessel from atmospheric pressure to 0.2~0.6MPa, maintain it for 5~30min, and then depressurize it to atmospheric pressure and maintain it for 5~15min. This is one cycle. The first leaching treatment is repeated 2~6 times and the second leaching treatment is repeated 2~6 times.

5. The method for preparing high-purity quartz according to claim 4, characterized in that, The pressurization is achieved by introducing compressed air or inert gas into the reactor through a compressed gas source. The pressure of the compressed gas source is 0.3~1.0 MPa, and the pressurization rate is 0.02~0.2 MPa / s; and / or The depressurization is achieved by opening the pressure relief valve to discharge the gas in the reaction vessel, with a depressurization rate of 0.05~0.5MPa / s.

6. The method for preparing high-purity quartz according to claim 1, characterized in that, The mass-to-volume ratio of the quartz sand to be purified, the mixed acid solution, and the aluminum-removing composite ligand is 1 g : (0.5~5) mL : (0.1~10) mg; and / or The mass-to-volume ratio of the first leachable sand to hydrofluoric acid is 1 g: (0.05~0.5) mL.

7. The method for preparing high-purity quartz according to claim 1, characterized in that, The magnetic separation process specifically includes the following steps: The second leaching sand is passed through an external magnetic field region to obtain high-purity quartz.

8. The method for preparing high-purity quartz according to claim 7, characterized in that, The magnetic field strength of the external magnetic field region is 0.3~1.5T, and the magnetic field gradient is 10~100T / m.

9. The method for preparing high-purity quartz according to claim 1, characterized in that, The mixed acid solution includes oxalic acid, ammonium bifluoride and hydrofluoric acid, and the mass-volume ratio of oxalic acid, ammonium bifluoride and hydrofluoric acid is (0.3~1.0) g : (0.1~0.6) g : (0.2~0.8) mL.

10. The method for preparing high-purity quartz according to claim 1, characterized in that, The first leaching treatment and the second leaching treatment are carried out under ultrasonic conditions, wherein the ultrasonic power is 0.5~5W / L and the frequency is 20~80kHz.