A method for preparing high-purity silica

Abstract

This invention belongs to the field of chemical production technology, specifically disclosing a method for preparing high-purity silica, comprising the following steps: S1, grinding: crushing and grinding minerals or waste containing silica or silicates; S2, leaching: mixing with a leaching agent in a certain proportion to carry out a leaching reaction, followed by solid-liquid separation to obtain a fluoride ion complex solution containing fluorosilicic acid; S3, extraction: separating fluorosilicic acid from fluoride ion complex impurities using an extraction method to obtain a high-purity fluorosilicic acid or fluorosilicate solution; S4, pH adjustment: performing a metathesis reaction by adjusting the pH, followed by solid-liquid separation to obtain solid silica and soluble fluorides; S5, obtaining high-purity silica. This invention, employing the above-mentioned method for preparing high-purity silica, is applicable to most silicon-containing raw materials, effectively reducing the impurity content in silicon slag, and preparing high-purity silica with a purity of up to 99.99%.

Description

Technical Field

[0001] This invention relates to the field of chemical production technology, and in particular to a method for preparing high-purity silicon dioxide. Background Technology

[0002] Silica possesses superior properties such as high dielectric constant, high heat resistance, high filling capacity, low expansion, low stress, and low coefficient of friction, making it suitable for applications in solar energy, optical fibers, electric light sources, semiconductors, electronics, communications, optical instruments, integrated circuits, electronic packaging, and precision ceramics. A variety of raw materials can be used to prepare silica, including silanes, water glass, quartz sand, granite pegmatite-type lithium feldspar (reference patent CN112047350A), iron tailings (reference patent CN208308443U), fluorosilicic acid (reference patent CN118929679A), silica powder or silica slag (reference patent CN111498854B), and black talc (reference patent CN117566748B). Depending on the raw materials, different process routes or methods are used to prepare silica of varying purities.

[0003] In existing technologies, when producing silica from silanes, a hydrolysis method is typically used to prepare high-purity silica with specific morphologies. Patents CN112551534B, CN114195158B, CN118929677A, CN117361872A, CN116969476B, CN115974087A, CN112194142B, and CN107298446B all disclose methods that use silanes as raw materials, and through different media and acid-base adjustments to induce silane hydrolysis, high-purity silica is obtained. The final product is then obtained through washing, filtration, and calcination. The characteristics of this type of method are high raw material purity, versatility in process conditions, and the ability to meet different requirements for product morphology and particle size. High-purity products are generally obtained without further purification.

[0004] Patent CN115744919B discloses a method for preparing ultra-high purity silica particles using silane as a raw material via chemical vapor deposition. The silica particles are acid-leached to remove soluble iron, and then calcined under a chlorine atmosphere to further remove impurities, yielding ultra-high purity silica particles. Patent CN116789141A uses TEOS as a raw material, adjusts the pH with ammonia, and continues hydrolysis in anhydrous ethanol. The precipitate is washed with acetone and ultrapure water, and then the solid particles are dispersed in anhydrous ethanol. The pH of the reaction solution is then adjusted with ammonia, and organic and alkaline substances are washed away to obtain high-purity silica particles. Patent CN114315106A uses silane as a raw material and produces glassy silica by heating with a plasma torch.

[0005] Patent CN107298446A discloses a method for preparing high-purity micron-sized spherical silica powder. Silane is prepared through microemulsion and hydrolysis to obtain high-purity silica with a specific morphology. Water glass is an inexpensive and readily available silicon-containing raw material, and it can also be used to produce high-purity silica. It is important to emphasize that when using water glass as a raw material to produce high-purity silica, further purification of the hydrolysis products is required. For example, patent CN118183758A uses water glass as a raw material, adds an accelerator, and employs an online sequential replenishment hydrothermal crystallization synthesis process to produce silica. Patent CN112573525A provides a method for preparing high-purity silica, in which a sodium silicate solution containing impurities is reacted with ozone and washed with an acidic solution to obtain a silica suspension. Patent CN110255570B dilutes water glass with pure water to prepare water glass solutions of different concentrations, and after dealkalization treatment, obtains a silicic acid aqueous solution. Iron ions and alkaline earth metal ions are then removed to obtain silica. Patent CN114853025A discloses the precipitation of metallic impurities in liquid sodium silicate by 8-hydroxyquinoline, followed by filtration to obtain high-purity sodium silicate. The high-purity sodium silicate is then salted out with acid, and the precipitate of silicic acid is calcined to obtain high-purity silica. Patent CN103848429A uses sodium silicate as a raw material, and after acidification and dispersion in a medium of ethanol and ammonia, a white precipitate is obtained. After washing to remove impurities such as iron ions, chloride ions, and sodium ions, the precipitate is calcined to obtain silica powder. Patent CN104176739B involves adding sulfuric acid solution dropwise to a sodium silicate solution until the pH reaches 11-13, filtering out the impurity-rich solid precipitate, and then continuing to add sulfuric acid solution dropwise to the filtrate until complete precipitation. After filtration, a certain amount of acid and water is added to the precipitate, and the mixture is stirred, filtered, washed, dried, and calcined to obtain high-purity silica powder. Methods for producing silica from quartz sand mainly fall into two categories. One involves physically purifying the raw materials or repeatedly calcining or melting them under different high-temperature conditions to separate silica from impurities, obtaining a silica product of a certain purity. Patent CN117023595A calcines the silica under three different high-temperature conditions to reduce the hydroxyl, carbon, and chlorine content, thereby increasing the purity of silica. Patents CN110143596A, CN118270795A, CN112047350A, CN118594754A, CN108928824A, CN110665631A, CN109384240A, and CN109384241A use high-quality, high-purity quartz blocks and active liquids as raw materials, and produce activated ultrafine fused silica powder through processes such as crushing, flotation, color sorting, magnetic separation, grinding, grading, activation, and microwave treatment.Another type of method combines physical beneficiation, calcination, and acid-base washing. Patents CN110963498B, CN114804130A, CN118529736A, CN110615687B, CN111892059B, CN110510620A, CN107626437A, and CN111646691A disclose a method for preparing high-purity quartz sand with ultra-low metal content. This method includes processes such as material selection, calcination, alkaline water quenching, crushing, magnetic separation, electrostatic separation, acid washing, flotation, and cleaning, with the addition of special detergents to further remove impurities. Patents CN110950346B, CN108298547A, and CN119080011A, based on the above processes, use reducing agents and organic acids to reduce and wash high-valence elements in the quartz sand, thereby improving product purity. Patent CN112919478A uses alkaline washing to replace hydrofluoric acid washing, avoiding the use of fluorides. Patent CN108190894B discloses using a solution containing sodium alginate, chitosan, and cellulose to reduce the concentration of heavy metal ions in the pickling solution, enabling the recycling of the pickling solution. Patent CN115806296A discloses a method for purifying silica using a washing solution containing thiourea or sodium dimethyl dithiocarbamate. Patent CN117566748B details the composition of the washing solution and the washing method for obtaining quartz sand from black talc through an acid washing process containing hydrogen fluoride. Patent CN113307275B discloses a method for preparing large-particle high-purity and ultra-high-purity crystalline silica. The method uses amorphous silica powder with a particle size of more than 50 μm as raw material, and then obtains crystalline silica through hydrothermal method or high-temperature treatment. The particle size distribution range of the obtained crystalline silica is 45-400 μm, and the total content of impurity elements is less than 20 ppm or 30 ppb. The method uses a simple and controllable preparation process to artificially synthesize large-particle high-purity and ultra-high-purity crystalline silica.

[0006] Patent CN118929679A discloses a method for preparing silica via the hydrolysis of fluorosilicic acid. Hydrofluoric acid reacts with quartz sand to generate fluorosilicic acid, which then reacts with sulfuric acid upon heating to generate silicon tetrafluoride gas. Silicon tetrafluoride hydrolyzes to produce silicic acid, and in subsequent production processes, hydrogen fluoride gas is absorbed by freezing to generate hydrofluoric acid. Hydrofluoric acid reacts with quartz to generate fluorosilicic acid, which is then returned to the system, achieving the recycling of hydrofluoric acid. Patent CN107902673 discloses a novel production process for the co-production of sodium fluoride and silica using fluorosilicic acid, sodium silicate water glass, and soda ash as main raw materials. Patent CN114604879B discloses a method for preparing high-purity potassium fluoride and co-producing nano-silica using a micro-liquid membrane reactor. The micro-liquid membrane reactor utilizes its functions of crushing, deagglomerating, dispersing, and enhanced mixing and reaction as a means of process intensification, achieving the crushing of potassium fluorosilicate particles and simultaneous dispersion and reaction in the alkaline solution, resulting in nano-silica with a narrow particle size distribution and uniform particle size.

[0007] In summary, regardless of the raw materials or methods used, there is no effective way to control the purity of silicon raw materials when preparing high-purity silica. When using silanes as raw materials, the purity of the raw materials determines the purity of the product. Silanes are expensive, and hydrolysis and washing generate large amounts of wastewater. Inexpensive and readily available water glass has limited purity; producing high-purity silica requires special removal of heavy metals and washing to remove impurities such as iron, chloride, and sodium ions, resulting in wastewater containing large amounts of salt and acid. When using quartz sand as raw material to produce silica, regardless of the method used, complex processes such as high-temperature and acid-alkali washing are involved to remove impurities. This not only consumes a lot of energy but also requires large amounts of acids and alkalis, making wastewater treatment difficult. While the production of silica using fluorosilicic acid and its salts allows for the recovery and recycling of hydrofluoric acid, no method for purifying fluorosilicic acid and its salts has been publicly disclosed. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing high-purity silica, which is applicable to most silicon-containing raw materials, effectively reduces the impurity content in silicon slag, and prepares high-purity silica with a purity of up to 99.99%.

[0009] To achieve the above objectives, the present invention provides a method for preparing high-purity silica, comprising the following steps:

[0010] S1. Grinding: Crushing and grinding minerals or waste containing silicon dioxide or silicates;

[0011] S2. Leaching: The ground minerals or waste residues are mixed with the leaching agent in proportion to carry out the leaching reaction. After solid-liquid separation, a fluoride complex solution containing fluorosilicic acid is obtained.

[0012] S3. Extraction: Using a fluoride ion complex solution containing fluorosilicic acid as raw material, the fluorosilicic acid and fluoride ion complex impurities are separated by extraction to obtain a high-purity fluorosilicic acid or fluorosilicate solution.

[0013] S4. pH adjustment: The double decomposition reaction is carried out by adjusting the pH of high-purity fluorosilicic acid or fluorosilicate solution. After solid-liquid separation, silicic acid solid and soluble fluoride are obtained.

[0014] S5. High-purity silicon dioxide is obtained by washing, drying and calcining solid silica.

[0015] Preferably, in S2, the leaching agent is an acidic solution containing fluoride ions, with a hydrogen ion concentration of 0.5-18 mol / L, and its anion is one or more of fluoride ions, sulfate ions, chloride ions, and nitrate ions, with a fluoride ion concentration of 0.5-8 mol / L.

[0016] Preferably, in S2, the solid-liquid ratio (mass to volume ratio) of the ground minerals or waste residue to the leaching agent is 1 kg: 0.5 to 10 L, the leaching time is 0.5 to 10 h, and the leaching temperature is 10 to 90 °C.

[0017] Preferably, in S3, the extraction method includes solvent extraction and solvent back-extraction, and is carried out in a single-stage, two-stage or multi-stage cross-flow or counter-flow manner.

[0018] Preferably, the solvent extraction yields one of fluorosilicic acid or fluorosilicate, and the solvent back-extraction yields one of ammonium fluorosilicate solution, sodium fluorosilicate solution, or potassium fluorosilicate solution.

[0019] Preferably, during the solvent extraction or solvent back-extraction process, the ratio of the organic phase to the aqueous phase is 1-20:1-20, the temperature is 10-90℃, the reaction time is 1-30 min, and the separation time is 1-60 min.

[0020] Preferably, in S4, the metathesis reaction specifically comprises:

[0021] The pH of the ammonium fluorosilicate solution is adjusted with hydrofluoric acid or ammonia to hydrolyze it into silicic acid and ammonium fluoride.

[0022] The pH of the sodium fluorosilicate solution is adjusted with hydrofluoric acid or sodium hydroxide to hydrolyze it into silicic acid and sodium fluoride.

[0023] The pH of potassium fluorosilicate solution is adjusted with hydrofluoric acid or potassium hydroxide to hydrolyze it into silicic acid and potassium fluoride.

[0024] Preferably, in S4, the solid-liquid separation yields one or more of the following: solid silica, ammonium fluoride solution, sodium fluoride solution, or potassium fluoride solution.

[0025] Preferably, S5 is as follows:

[0026] After washing, drying, and calcining, solid silica is ball-milled to obtain high-purity silicon dioxide.

[0027] Preferably, S5 also includes:

[0028] The ammonium fluoride solution, the sodium fluoride solution, or the potassium fluoride solution are concentrated to obtain a solid product.

[0029] Therefore, the present invention employs the above-mentioned method for preparing high-purity silica, and the beneficial effects are as follows:

[0030] (1) This invention is applicable to most silicon-containing raw materials. During the leaching process, high-valence elements such as silicon, aluminum, iron, titanium, vanadium, zirconium, and hafnium are completely dissolved and stable soluble fluorine complexes are formed.

[0031] (2) In the extraction process, the present invention separates fluorosilicic acid from other impurities such as titanium, aluminum, iron, zirconium, etc. In the back-extraction process, fluorosilicic acid is converted into fluorosilicates (such as ammonium fluorosilicate, sodium fluorosilicate and potassium fluorosilicate, etc.). By controlling the distribution ratio and separation coefficient of fluorosilicic acid with other compounds, the extraction system achieves high selectivity for fluorosilicic acid.

[0032] (3) In this invention, the pH of ammonium fluorosilicate solution is adjusted by hydrofluoric acid or ammonia water to hydrolyze it into silicic acid and ammonium fluoride; the pH of sodium fluorosilicate solution is adjusted by hydrofluoric acid or sodium hydroxide to hydrolyze it into silicic acid and sodium fluoride; the pH of potassium fluorosilicate solution is adjusted by hydrofluoric acid or potassium hydroxide to hydrolyze it into silicic acid and potassium fluoride; after solid-liquid separation, solid silicic acid and corresponding solutions of ammonium fluoride, sodium fluoride and potassium fluoride are obtained; the ammonium fluoride, sodium fluoride and potassium fluoride are concentrated to obtain the corresponding solid products, and after drying and calcination, high-purity silicon dioxide is obtained with a purity of up to 99.99%.

[0033] (4) On the one hand, the present invention provides a new approach for synthesizing high-purity silicon dioxide. On the other hand, the synthesis process is simple and suitable for large-scale preparation, effectively solving the limitation of silicon-containing raw materials in actual production process.

[0034] The technical solution of the present invention will be further described in detail below through embodiments. Detailed Implementation

[0035] The technical solution of the present invention will be further described below through embodiments.

[0036] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0037] Example 1

[0038] A high-purity silica, and its preparation method:

[0039] S1. Using grade III quartz sand with a silica content of 90.28% as raw material, containing 2.24% iron oxide, 3.86% aluminum oxide, 0.53% calcium oxide, 0.2% potassium oxide, 0.05% sodium oxide, 0.34% magnesium oxide, 0.21% titanium dioxide, and other impurities. Grind to a mesh size of 200 or higher.

[0040] S2. The ground grade III quartz sand is leached with a leaching agent (hydrofluoric acid solution) with a liquid-to-solid ratio of 5:1 and a hydrogen ion concentration of 3.5 mol / L at 40°C for 5 hours by stirring. After filtration, a fluoride complex solution containing fluorosilicic acid is obtained (filtrate).

[0041] Analysis of the filter residue composition, based on the law of conservation of mass, yielded a dissolution rate of 96.83% for quartz sand and a leaching rate of 97.85% for silica; leaching rates of 98.33%, 98.35%, and 98.42% for iron oxide, aluminum oxide, and titanium dioxide, respectively; leaching rates of sodium oxide and magnesium oxide were both greater than 99%; and leaching rates of potassium oxide and calcium oxide were 6.78% and 2.86%, respectively.

[0042] S3. Using the filtrate obtained from the above leaching process as raw material, a 4:1 ratio, 6-minute mixing time, and 30°C countercurrent extraction process is performed to transfer fluorosilicic acid from the leachate to the organic phase, completing the extraction process. The extraction rate of fluorosilicic acid reaches 98.76%, and the extraction rates of other impurities are all less than 2%, thus purifying the fluorosilicic acid. A high-purity fluorosilicic acid solution (purity greater than 99.99%) is used for countercurrent washing at a ratio of 15:1, with 15 washing stages. The washing rate of fluorosilicic acid is 2.08%, and the washing rate of impurities is 99.95%. The washed organic solvent is then used for back-extraction. If the back-extraction agent is one of ammonia, sodium hydroxide, or potassium hydroxide, the resulting back-extraction product is a high-purity ammonium fluorosilicate solution, sodium fluorosilicate solution, or potassium fluorosilicate solution. In this embodiment, the stripping agent is ammonia, the stripping stage is 5 stages, the ammonia concentration is 4.5 mol / L, the pH of the ammonium fluorosilicate stripping solution is controlled at 7-8, and the stripping rate of fluorosilicic acid is 99.5%. The purity of ammonium fluorosilicate is 99.99%, the total yield of ammonium fluorosilicate is 95%, and a high-purity ammonium fluorosilicate solution is obtained.

[0043] S4. Using the above-mentioned back-extraction solution (ammonium fluorosilicate solution) as raw material, adjust the pH of the ammonium fluorosilicate to 9.5-10.5 with ammonia water, converting the ammonium fluorosilicate into silicic acid and ammonium fluoride. Maintain the system temperature at 60℃, age for 6 hours according to conventional methods, and then filter. The filtrate is an ammonium fluoride solution, and the silicic acid is a solid.

[0044] Using the same method, when sodium fluorosilicate or potassium fluorosilicate is used as raw material, sodium hydroxide or potassium hydroxide is added to the sodium fluorosilicate or potassium fluorosilicate solution to a pH of about 10 to form silicic acid and sodium fluoride or potassium fluoride. Then, similar aging, washing, drying and calcination processes are carried out.

[0045] S5. After washing the solid until no ammonium or fluoride ions remain, dry it and calcine it to obtain high-purity silicon dioxide with a purity greater than 99.99%.

[0046] Example 2

[0047] A high-purity silica, and its preparation method:

[0048] S1. Using grade III quartz sand with a silica content of 90.28% as raw material, containing 2.24% iron oxide, 3.86% aluminum oxide, 0.53% calcium oxide, 0.2% potassium oxide, 0.05% sodium oxide, 0.34% magnesium oxide, 0.21% titanium dioxide, and other impurities. Grind to a mesh size of 200 or higher.

[0049] S2. Grinded grade III quartz sand and a leaching agent (hydrofluoric acid solution, with a liquid-to-solid ratio of 8:1 and a hydrogen ion concentration of 3.5 mol / L, wherein the concentration of hydrofluoric acid is 2.0 mol / L and the concentration of sulfuric acid is 0.75 mol / L) are stirred and leached at 60℃ for 3 hours, and then filtered to obtain a fluoride complex solution containing fluorosilicic acid (filtrate).

[0050] Analysis of the filter residue composition, based on the law of conservation of mass, yielded a dissolution rate of 95.75% for quartz sand and a leaching rate of 98.62% for silica; leaching rates of 99.10%, 98.54%, and 98.37% for iron oxide, aluminum oxide, and titanium dioxide, respectively; leaching rates of sodium oxide and magnesium oxide were both greater than 99%; and leaching rates of potassium oxide and calcium oxide were 3.43% and 1.08%, respectively.

[0051] S3. Using the filtrate obtained from the above leaching process as raw material, a 4:1 ratio, a mixing time of 6 minutes, and a temperature of 30°C were used for 6-stage countercurrent extraction to transfer fluorosilicic acid from the leachate to the organic phase, completing the extraction process. The extraction rate of fluorosilicic acid reached 97.88%, and the extraction rates of other impurities were all less than 1.02%, thus purifying the fluorosilicic acid. A high-purity fluorosilicic acid solution (purity greater than 99.99%) was used for countercurrent washing at a ratio of 15:1, with 15 washing stages. The washing rate of fluorosilicic acid was 2.08%, and the washing rate of impurities was 99.95%. The washed organic solvent was then used for back-extraction. In this embodiment, the back-extraction agent was sodium hydroxide with a concentration of 4.0 mol / L. The pH of the sodium fluorosilicate back-extraction solution was controlled at 8, and the back-extraction rate of fluorosilicic acid was 99.5%. The purity of sodium fluorosilicate was 99.99%, and the total yield of sodium fluorosilicate was greater than 94%, resulting in a high-purity sodium fluorosilicate solution.

[0052] S4. Using the above-mentioned back-extraction solution (sodium fluorosilicate solution) as raw material, the pH of the ammonium fluorosilicate is adjusted to 9.5-10.5 with ammonia water, and the sodium fluorosilicate is converted into silicic acid, ammonium fluoride, and sodium fluoride. The system temperature is maintained at 60℃, and after aging for 6 hours according to conventional methods, it is filtered. The filtrate is an ammonium fluoride and sodium fluoride solution, and the silicic acid is solid.

[0053] S5. After washing the solid until no ammonium or fluoride ions remain, dry it and calcine it to obtain high-purity silicon dioxide with a purity greater than 99.99%.

[0054] Example 3

[0055] A high-purity silica, and its preparation method:

[0056] S1. Using granite with a silica content of 71.63% as raw material, containing 3.61% iron oxide, 18.48% aluminum oxide, 2.16% calcium oxide, 5.66% potassium oxide, 3.89% sodium oxide, 0.62% magnesium oxide, 0.16% titanium dioxide, and other impurities. Grind to a fineness of 200 mesh or higher.

[0057] S2. The ground granite was leached with a leaching agent (hydrofluoric acid solution, of which hydrofluoric acid concentration is 3.0 mol / L and hydrogen chloride concentration is 3.0 mol / L) with a liquid-to-solid ratio of 6:1 and a hydrogen ion concentration of 5.5 mol / L at 40℃ for 6 hours. After filtration, a fluoride complex solution containing fluorosilicic acid (filtrate) was obtained.

[0058] Analysis of the filter residue composition, based on the law of conservation of mass, yielded a dissolution rate of 90.42% for quartz sand and a leaching rate of 97.66% for silica; the leaching rates for iron oxide, aluminum oxide, and titanium dioxide were 97.73%, 97.92%, and 99.34%, respectively. The leaching rates for sodium oxide and magnesium oxide were both greater than 99%, while the leaching rates for potassium oxide and calcium oxide were 7.39% and 3.74%, respectively.

[0059] S3. Using the filtrate obtained from the above leaching process as raw material, a countercurrent extraction process with a ratio of 2.5:1, a mixing time of 6 minutes, and a temperature of 30°C was performed, transferring fluorosilicic acid from the leachate to the organic phase through 8 stages, thus completing the extraction process. The extraction rate of fluorosilicic acid reached 99.26%, and the extraction rates of other impurities were all less than 4.89%, thus purifying the fluorosilicic acid. A high-purity fluorosilicic acid solution (purity greater than 99.99%) was used for countercurrent washing at a ratio of 10:1, with 23 washing stages. The washing rate of fluorosilicic acid was 3.18%, and the washing rate of impurities was 99.76%. The washed organic solvent was then used for back-extraction. In this embodiment, the back-extraction agent was potassium hydroxide solution with a concentration of 3.2 mol / L, and the back-extraction stage was 5 stages. The pH of the potassium fluorosilicate back-extraction solution was controlled at 7-8, and the back-extraction rate of fluorosilicic acid was 99.6%. The purity of potassium fluorosilicate is greater than 99.99%, and the total yield of potassium fluorosilicate is greater than 93%, thus obtaining a high-purity potassium fluorosilicate solution.

[0060] S4. Using the above-mentioned back-extraction solution (potassium fluorosilicate solution) as raw material, adjust the pH of potassium fluorosilicate to 9.5-10.5 with potassium hydroxide solution, converting potassium fluorosilicate into silicic acid and potassium fluoride. Maintain the system temperature at 80℃, age for 4 hours according to conventional methods, and then filter. The filtrate is a potassium fluoride solution, and the silicic acid is solid.

[0061] S5. After washing the solid until no potassium and fluoride ions remain, dry it and calcine it to obtain high-purity silicon dioxide with a purity greater than 99.99%.

[0062] Example 4

[0063] A high-purity silica, and its preparation method:

[0064] S1. Using fly ash with a silica content of 36.64% as raw material, containing 2.18% iron oxide, 51.82% aluminum oxide, 4.24% calcium oxide, 0.53% potassium oxide, 0.26% sodium oxide, 0.19% magnesium oxide, 0.23% titanium dioxide, and other impurities, the material is sorted.

[0065] S2. The sorted fly ash and a leaching agent (hydrofluoric acid solution with a liquid-to-solid ratio of 7:1 and a hydrogen ion concentration of 3.0 mol / L, wherein the concentration of hydrofluoric acid is 2.0 mol / L and the concentration of sulfuric acid is 0.5 mol / L) are stirred and leached at 60℃ for 4 hours, and then filtered to obtain a fluoride complex solution containing fluorosilicic acid (filtrate).

[0066] Analysis of the filter residue composition, based on the law of conservation of mass, yielded a fly ash dissolution rate of 96.33% and a silica leaching rate of 98.12%; ferric oxide, alumina, and titanium dioxide leaching rates of 98.46%, 98.21%, and 98.47%, respectively; sodium oxide and magnesium oxide leaching rates of over 99%; and potassium oxide and calcium oxide leaching rates of 10.29% and 3.91%, respectively.

[0067] S3. Using the filtrate obtained from the above leaching process as raw material, a 6-stage countercurrent extraction was performed at a ratio of 2.0:1, a mixing time of 6 minutes, and a temperature of 30°C to transfer fluorosilicic acid from the leachate to the organic phase, completing the extraction process. The extraction rate of fluorosilicic acid reached 98.49%, and the extraction rates of other impurities were all less than 6.43%, thus purifying the fluorosilicic acid. A high-purity fluorosilicic acid solution (purity greater than 99.99%) was used for countercurrent washing at a ratio of 8:1, with 20 washing stages. The washing rate of fluorosilicic acid was 4.61%, and the washing rate of impurities was 99.33%. The washed organic solvent was then used for back-extraction. The back-extraction agent was an ammonia solution with a concentration of 2.5 mol / L, with 5 back-extraction stages. The pH of the ammonium fluorosilicate back-extraction solution was controlled at 7-8, and the back-extraction rate of fluorosilicic acid was 99.6%. The purity of ammonium fluorosilicate was greater than 99.99%, and the total yield of ammonium fluorosilicate was greater than 91%, yielding a high-purity ammonium fluorosilicate solution.

[0068] S4. Using the above-mentioned back-extraction solution (ammonium fluorosilicate solution) as raw material, adjust the pH of the ammonium fluorosilicate to 9.5-10.5 with ammonia water, converting the ammonium fluorosilicate into silicic acid and ammonium fluoride. Maintain the system temperature at 60℃, age for 6 hours according to conventional methods, and then filter. The filtrate is an ammonium fluoride solution, and the silicic acid is a solid.

[0069] S5. After washing the solid until no ammonium or fluoride ions remain, dry it and calcine it to obtain high-purity silicon dioxide with a purity greater than 99.99%.

[0070] Example 5

[0071] A high-purity silica, and its preparation method:

[0072] S1. Using blast furnace slag with a silica content of 32.47% as raw material, containing 3.72% iron oxide, 51.82% aluminum oxide, 36.16% calcium oxide, 11.06% magnesium oxide, 7.56% titanium dioxide, 0.65% potassium oxide, 0.39% sodium oxide, and other impurities, the material is sorted.

[0073] S2. The separated blast furnace slag and a leaching agent (hydrofluoric acid solution, of which hydrofluoric acid concentration is 2.0 mol / L and sulfuric acid concentration is 1.0 mol / L) with a liquid-to-solid ratio of 10:1 were stirred and leached at 40℃ for 8 hours. After filtration, a fluoride complex solution containing fluorosilicic acid (filtrate) was obtained.

[0074] Analysis of the filter residue composition, based on the law of conservation of mass, yielded a blast furnace slag dissolution rate of 57.92% and a silica leaching rate of 96.28%. The leaching rates of iron oxide, aluminum oxide, and titanium dioxide were 97.95%, 97.83%, and 97.18%, respectively. The leaching rates of sodium oxide and magnesium oxide were both greater than 99%, while the leaching rates of potassium oxide and calcium oxide were 3.38% and 2.51%, respectively.

[0075] S3. Using the filtrate obtained from the above leaching process as raw material, a 6-stage countercurrent extraction was performed at a ratio of 1.8:1, a mixing time of 6 minutes, and a temperature of 30°C to transfer fluorosilicic acid from the leachate to the organic phase, completing the extraction process. The extraction rate of fluorosilicic acid reached 98.75%, and the extraction rates of other impurities were all less than 8.90%, thus purifying the fluorosilicic acid. A high-purity fluorosilicic acid solution (purity greater than 99.99%) was used for countercurrent washing at a ratio of 10:1, with 30 washing stages. The washing rate of fluorosilicic acid was 6.80%, and the washing rate of impurities was 99.53%. The washed organic solvent was then used for back-extraction. The back-extraction agent was an ammonia solution with a concentration of 2.0 mol / L, with 5 back-extraction stages. The pH of the ammonium fluorosilicate back-extraction solution was controlled at 7-8, and the back-extraction rate of fluorosilicic acid was 99.3%. The purity of the ammonium fluorosilicate was greater than 99.99%, and the total yield of ammonium fluorosilicate was greater than 87%.

[0076] S4. Using the above-mentioned back-extraction solution (ammonium fluorosilicate solution) as raw material, adjust the pH of the ammonium fluorosilicate to 9.5-10.5 with ammonia water, converting the ammonium fluorosilicate into silicic acid and ammonium fluoride. Maintain the system temperature at 60℃, age for 6 hours according to conventional methods, and then filter. The filtrate is an ammonium fluoride solution, and the silicic acid is a solid.

[0077] S5. After washing the solid until no ammonium or fluoride ions remain, dry it and calcine it to obtain high-purity silicon dioxide with a purity greater than 99.99%.

[0078] Test

[0079] The high-purity silica prepared in Example 1 was analyzed by inductively coupled plasma mass spectrometry (ICP-MS) to determine the content of each element in silica. The test results are shown in Table 1.

[0080] Table 1. Element content of silicon dioxide

[0081]

[0082] As shown in Table 1, high-purity silica was successfully prepared, with a purity of up to 99.99%.

[0083] Therefore, the above-mentioned method for preparing high-purity silica is applicable to most silicon-containing raw materials, effectively reduces the impurity content in silicon slag, and prepares high-purity silica with a purity of up to 99.99%.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing high-purity silica, characterized in that, Includes the following steps: S1. Grinding: Crushing and grinding minerals or waste containing silicon dioxide or silicates; S2. Leaching: The ground minerals or waste residues are mixed with the leaching agent in proportion to carry out the leaching reaction. After solid-liquid separation, a metal fluorine complex solution containing fluorosilicic acid is obtained. S3. Extraction: Using a metal fluorine complex solution containing fluorosilicic acid as raw material, the fluorosilicic acid and metal fluorine complex impurities are separated by extraction to obtain a high-purity fluorosilicate solution. S4. pH adjustment: The hydrolysis reaction is carried out by adjusting the pH of the high-purity fluorosilicate solution. After solid-liquid separation, solid silicic acid and soluble fluoride are obtained. S5. High-purity silicon dioxide is obtained by washing, drying and calcining solid silica. In S3, the extraction method includes sequential solvent extraction and solvent back-extraction, wherein the solvent extraction yields fluorosilicic acid, and the solvent back-extraction yields a high-purity fluorosilicate solution.

2. The method for preparing high-purity silica according to claim 1, characterized in that, In S2, the leaching agent is an acidic solution with a hydrogen ion concentration of 0.5~18 mol / L and anions including fluoride ions and one or more selected from sulfate, chloride, and nitrate ions, with a fluoride ion concentration of 0.5~8 mol / L.

3. The method for preparing high-purity silica according to claim 1, characterized in that, In S2, the solid-liquid ratio of the ground minerals or waste residue to the leaching agent is 1 kg: 0.5~10 L, the leaching time is 0.5~10 h, and the leaching temperature is 10~90℃.

4. The method for preparing high-purity silica according to claim 1, characterized in that, In S3, the solvent extraction is carried out in a single-stage or multi-stage cross-flow or counter-flow manner.

5. The method for preparing high-purity silica according to claim 1, characterized in that, The high-purity fluorosilicate solution is one of ammonium fluorosilicate solution, sodium fluorosilicate solution, or potassium fluorosilicate solution.

6. The method for preparing high-purity silica according to claim 1, characterized in that, In the solvent extraction, the ratio of organic phase to aqueous phase is 1~20:1~20, the temperature is 10~90℃, the reaction time is 1~30min, and the separation time is 1~60min.

7. The method for preparing high-purity silica according to claim 5, characterized in that, In S4, the hydrolysis reaction is one of the following: The pH of the ammonium fluorosilicate solution was adjusted with ammonia water, causing it to hydrolyze into silicic acid and ammonium fluoride; The pH of the sodium fluorosilicate solution was adjusted with sodium hydroxide to hydrolyze it into silicic acid and sodium fluoride. The pH of the potassium fluorosilicate solution was adjusted with potassium hydroxide, causing it to hydrolyze into silicic acid and potassium fluoride.

8. The method for preparing high-purity silica according to claim 1, characterized in that, In S4, the solid-liquid separation yields a silica solid and one of the following: an ammonium fluoride solution, a sodium fluoride solution, or a potassium fluoride solution.

9. The method for preparing high-purity silica according to claim 8, characterized in that, S5 specifically refers to: After washing, drying and calcining, solid silica is ball-milled to obtain high-purity silicon dioxide.

10. The method for preparing high-purity silica according to claim 8, characterized in that, S5 also includes: The ammonium fluoride solution, the sodium fluoride solution, or the potassium fluoride solution are concentrated to obtain a solid product.

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