Preparation method of high-purity silicon dioxide

Abstract

The invention belongs to the technical field of chemical production, and particularly discloses a preparation method of high-purity silicon dioxide, which comprises the following steps: S1, grinding: crushing and grinding minerals or waste residues containing silicon dioxide or silicate; s2, leaching: mixing with a leaching agent according to a ratio, carrying out a leaching reaction, and carrying out solid-liquid separation to obtain a fluorine ion complex solution containing fluosilicic acid; s3, extraction: separating fluosilicic acid from fluorine ion complex impurities by adopting an extraction method to obtain a high-purity fluosilicic acid or fluosilicate solution; s4, pH adjustment: carrying out a double decomposition reaction by adjusting the pH, and carrying out solid-liquid separation to obtain a silicic acid solid and soluble fluoride; and S5, obtaining high-purity silicon dioxide. The preparation method of the high-purity silicon dioxide is suitable for most silicon-containing raw materials, the content of impurities in the silicon slag is effectively reduced, and the purity of the prepared high-purity silicon dioxide can reach 99.99%.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical production, and in particular to a method for preparing high-purity silica. Background Art

[0002] Silica has superior properties such as high dielectric constant, high heat resistance, high filling amount, low expansion, low stress, and low friction coefficient, and can be used in fields such as solar energy, optical fibers, electric light sources, semiconductors, electronics, communications, optical instruments, integrated circuits, electronic packaging, and precision ceramics. There are various raw materials for preparing silica, such as silane, water glass, quartz sand, granite pegmatite-type lithium feldspar (refer to patent CN112047350A), iron tailings (refer to patent CN208308443U), fluorosilicic acid (refer to patent CN118929679A), silicon powder or silicon slag (refer to patent CN111498854B), black talc (refer to patent CN117566748B), etc. According to different raw materials, different process routes or methods are adopted to prepare silica with different purities.

[0003] In the prior art, when producing silica using silane as a raw material, the hydrolysis method is usually used to prepare high-purity and specific-shaped silica. For example, patents CN112551534B, CN114195158B, CN118929677A, CN117361872A, CN116969476B, CN115974087A, CN112194142B, and CN107298446B all disclose using silane as a raw material, and through different media and acid-base adjustment to promote the hydrolysis of silane, high-purity silica is obtained, and the final product is obtained through washing, filtration, and calcination. The characteristics of this type of method are high raw material purity, many process condition changes, the product morphology and particle size can meet different requirements, and high-purity products can be obtained without further purification basically.

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

[0005] Patent CN107298446A discloses a method for preparing high-purity micron-sized spherical silica powder. Silane undergoes microemulsion preparation and hydrolysis to obtain high-purity silica with a specific morphology. Water glass is an inexpensive and easily obtainable silicon-containing raw material, and high-purity silica can also be produced using it as a raw material. It should be emphasized that when using water glass as a raw material to produce high-purity silica, the hydrolysis product needs to be further purified. For example, patent CN118183758A uses water glass as a raw material, adds a promoter, and adopts an online sequential supplementary hydrothermal crystallization synthesis process to produce silica. Patent CN112573525A provides a method for preparing high-purity silica. The sodium silicate solution containing impurities undergoes an ozone reaction and is washed with an acidic solution to obtain a silica suspension. Patent CN110255570B dilutes water glass with pure water to prepare water glass solutions with different concentrations, and after dealkalization treatment, a silicic acid aqueous solution is obtained. Iron ions and alkaline earth metal ions are removed to obtain silica. Patent CN114853025A discloses the precipitation of metal impurities in liquid sodium silicate with 8-hydroxyquinoline, and high-purity sodium silicate is obtained after filtration. High-purity sodium silicate is salted out with an acid, and the precipitate silicic acid is calcined to obtain high-purity silica. Patent CN103848429A uses sodium silicate as a raw material, undergoes acidification and dispersion in an ethanol and ammonia medium to obtain a white precipitate, and after washing to remove impurities such as iron ions, chloride ions, and sodium ions contained therein, silica powder is obtained after calcination. The methods for producing silica using quartz sand as a raw material are mainly divided into two categories. One category is that the raw materials undergo physical purification or repeated calcination or melting under different high-temperature conditions to separate silica and impurities, obtaining silica products with a certain purity. Patent CN117023595A calcines under three different high-temperature conditions to reduce the hydroxyl group, carbon content, and chlorine content in silica and improve 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 active ultrafine fused quartz silica powder through processes such as crushing, flotation, color sorting, magnetic separation, grinding, classification, activation, and microwave treatment.Another type is the method that combines physical beneficiation, calcination, and acid-base washing. For example, patents CN110963498B, CN114804130A, CN118529736A, CN110615687B, CN111892059B, CN110510620A, CN107626437A, and CN111646691A disclose a method for preparing high-purity quartz sand with ultra-low metal content. It includes processes such as material selection, calcination, alkaline water quenching, crushing, magnetic separation, electrostatic separation, acid washing, flotation, cleaning, etc., and a special detergent is added to further remove impurities. Based on the above processes, patents CN110950346B, CN108298547A, and CN119080011A use reducing agents and organic acids to reduce and wash the high-valence elements in quartz sand to improve product purity. Patent CN112919478A uses an alkali washing method to replace hydrofluoric acid washing to avoid 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 acid washing solution and achieve the recycling of the acid washing solution. Patent CN115806296A discloses a method for purifying silica using a washing solution containing thiourea or sodium dimethyldithiocarbamate. Patent CN117566748B details the composition of the washing solution and the washing method for obtaining quartz sand through an acid washing process containing hydrogen fluoride using black talc as the raw material. Patent CN113307275B discloses a method for preparing large-particle high-purity and ultra-high-purity crystalline silica. Using amorphous silica powder with a particle size of more than 50 μm as the raw material, and then obtaining crystalline silica through hydrothermal method or high-temperature treatment. The obtained crystalline silica has a particle size distribution range of 45 - 400 μm, and the total content of impurity elements is less than 20 ppm or 30 ppb. A simple and controllable preparation process is used to artificially synthesize large-particle high-purity and ultra-high-purity crystalline silica.

[0006] Patent CN118929679A discloses a method for preparing silica through the hydrolysis of fluorosilicic acid. Hydrofluoric acid reacts with quartz sand to form fluorosilicic acid, and fluorosilicic acid reacts with sulfuric acid by heating to generate silicon tetrafluoride gas. The hydrolysis reaction of silicon tetrafluoride produces silicic acid, and hydrogen fluoride gas is cryogenically absorbed in the subsequent production process to generate hydrofluoric acid. Hydrofluoric acid reacts with quartz to form fluorosilicic acid and returns to the system to achieve the recycling of hydrofluoric acid. Patent CN107902673 discloses a new production process for co-producing sodium fluoride and white carbon black using fluorosilicic acid, sodium silicate, and soda ash as the main raw materials. Patent CN114604879B uses a micro-liquid membrane reaction device to prepare high-purity potassium fluoride and co-produce nano-silica. Using the functions of the micro-liquid membrane reaction device for crushing, depolymerization, dispersion, and strengthening of mixing and reaction as a means of process intensification, the crushing of potassium fluorosilicate particles is realized, and the dispersion and reaction of potassium fluorosilicate particles in the alkali solution are carried out synchronously to obtain nano-silica with a narrow particle size distribution and uniform particle size.

[0007] In summary, regardless of the raw materials used and the methods employed, there has been no effective control over the purity of silicon raw materials in the preparation of high-purity silica. When using silane as the raw material, the raw material purity determines the product purity. Silane is relatively expensive, and hydrolysis and washing also generate a large amount of wastewater. The cheap and easily available water glass has limited purity. When producing high-purity silica, heavy metals need to be specifically removed, and impurities such as iron ions, chloride ions, and sodium ions need to be removed through washing, generating a large amount of salt and waste acid water. When producing silica using quartz sand as the raw material, regardless of the method used, complicated processes such as high-temperature treatment and acid-base washing are required to remove impurities. This not only results in high energy consumption but also large amounts of acid and alkali usage, making wastewater treatment difficult. When producing silica through fluosilicic acid and its salts, the recycling of hydrofluoric acid can be achieved, but no method for purifying fluosilicic acid and its salts has been disclosed. Summary of the Invention

[0008] The object of the present 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 the silicon slag, and prepares high-purity silica with a purity of up to 99.99%.

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

[0010] S1. Grinding: Crushing and grinding minerals or waste residues containing silica or silicate.

[0011] S2. Leaching: Mixing the ground minerals or waste residues with a leaching agent in proportion for a leaching reaction, followed by solid-liquid separation to obtain a fluoride complex solution of fluosilicic acid.

[0012] S3. Extraction: Using the fluoride complex solution of fluosilicic acid as the raw material, separating fluosilicic acid from fluoride complex impurities by extraction to obtain a high-purity fluosilicic acid or fluosilicate solution.

[0013] S4. pH adjustment: Conducting a metathesis reaction by adjusting the pH of the high-purity fluosilicic acid or fluosilicate solution, followed by solid-liquid separation to obtain solid silica and soluble fluorides.

[0014] S5. The solid silica is washed, dried, and calcined to obtain high-purity 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 anions are one or more of fluoride ions, sulfate ions, chloride ions, and nitrate ions, and its fluoride ion concentration is 0.5 - 8 mol / L.

[0016] Preferably, in S2, the solid-liquid ratio (mass to volume ratio) of the ground mineral 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 °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-current manner.

[0018] Preferably, one of fluosilicic acid or fluorosilicate is obtained by the solvent extraction, and one of ammonium fluosilicate solution, sodium fluosilicate solution or potassium fluosilicate solution is obtained by the solvent back-extraction.

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

[0020] Preferably, in S4, the metathesis reaction is specifically as follows:

[0021] Adjust the pH of the ammonium fluosilicate solution with hydrofluoric acid or ammonia water to hydrolyze it into silicic acid and ammonium fluoride;

[0022] Adjust the pH of the sodium fluosilicate solution with hydrofluoric acid or sodium hydroxide to hydrolyze it into silicic acid and sodium fluoride;

[0023] Adjust the pH of the potassium fluosilicate solution with hydrofluoric acid or potassium hydroxide to hydrolyze it into silicic acid and potassium fluoride.

[0024] Preferably, in S4, one or more of silicic acid solid, ammonium fluoride solution, sodium fluoride solution or potassium fluoride solution are obtained after the solid-liquid separation.

[0025] Preferably, S5 is specifically as follows:

[0026] The silicic acid solid is washed, dried, calcined, and then ball-milled to obtain high-purity silica.

[0027] Preferably, after S5, it further includes:

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

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

[0030] (1) The present 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 form stable soluble fluorine complexes.

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

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

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

[0034] The technical solution of the present invention will be further described in detail through the following examples. Detailed implementation manners

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

[0036] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention belongs.

[0037] Example 1

[0038] A method for preparing high-purity silica:

[0039] S1. Using third-grade quartz sand with a silica content of 90.28% as raw material, in which the iron oxide content is 2.24%, aluminum oxide 3.86%, calcium oxide 0.53%, potassium oxide 0.2%, sodium oxide 0.05%, magnesium oxide 0.34%, titanium dioxide 0.21% and other impurities. Grind it to more than 200 meshes.

[0040] S2. The ground third-grade quartz sand and a leaching agent (hydrofluoric acid solution) with a liquid-solid ratio of 5:1 and a hydrogen ion concentration of 3.5 mol / L are stirred and leached at 40 °C for 5 h, and then filtered to obtain a fluoride ion complex solution (filtrate) containing fluosilicic acid.

[0041] By analyzing the composition of the filter residue, the dissolution rate of quartz sand was calculated to be 96.83% and the leaching rate of silicon dioxide was 97.85% according to the law of conservation of mass; the leaching rates of iron oxide, aluminum oxide and titanium dioxide were 98.33%, 98.35% and 98.42% respectively; the leaching rates of sodium oxide and magnesium oxide were both greater than 99%, and the 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 the raw material, with a phase ratio of 4:1, a mixing time of 6 min, a temperature of 30 °C, and through 6-stage countercurrent extraction, fluorosilicic acid was transferred from the leaching solution to the organic phase to complete the extraction process. The extraction rate of fluorosilicic acid reached 98.76%, and the extraction rates of other impurities were all less than 2% for the purification of fluorosilicic acid. Using a high-purity fluorosilicic acid (purity greater than 99.99%) solution 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%. After washing, the organic solvent was subjected to back-extraction. If the back-extraction agent was one of ammonia water, sodium hydroxide or potassium hydroxide, the back-extraction product obtained was a high-purity ammonium fluorosilicate solution, sodium fluorosilicate solution or potassium fluorosilicate solution. In this example, the back-extraction agent was ammonia water, the back-extraction stage was 5, the ammonia water concentration was 4.5 mol / L, the pH of the ammonium fluorosilicate back-extraction solution was controlled at 7-8, and the back-extraction rate of fluorosilicic acid was 99.5%. The purity of ammonium fluorosilicate was 99.99%, and the total yield of ammonium fluorosilicate was 95% to obtain a high-purity ammonium fluorosilicate solution.

[0043] S4. Using the above back-extraction solution (ammonium fluorosilicate solution) as the raw material, adjusting the pH of ammonium fluorosilicate to 9.5-10.5 with ammonia water, ammonium fluorosilicate was converted into silicic acid and ammonium fluoride. Maintaining the system temperature at 60 °C, aging for 6 h according to the conventional method and then filtering, the filtrate was ammonium fluoride solution and the silicic acid was solid.

[0044] In the same way, when using sodium fluorosilicate or potassium fluorosilicate as the raw material, sodium hydroxide or potassium hydroxide was added to the sodium fluorosilicate or potassium fluorosilicate solution to about pH 10 to form silicic acid and sodium fluoride or potassium fluoride, and then similar processes such as aging, washing, drying and calcination were carried out.

[0045] S5. The solid was washed until there were no ammonium ions and fluoride ions and then dried and calcined to obtain high-purity silicon dioxide with a purity greater than 99.99%.

[0046] Example 2

[0047] A kind of high-purity silicon dioxide and its preparation method:

[0048] S1. Use the third-grade quartz sand with a silica content of 90.28% as the raw material, where the iron oxide content is 2.24%, aluminum oxide is 3.86%, calcium oxide is 0.53%, potassium oxide is 0.2%, sodium oxide is 0.05%, magnesium oxide is 0.34%, titanium dioxide is 0.21%, and other impurities. Grind it to more than 200 mesh.

[0049] S2. The ground third-grade quartz sand and a leaching agent with a liquid-solid ratio of 8:1 and a hydrogen ion concentration of 3.5 mol / L (hydrofluoric acid solution, where the concentration of hydrofluoric acid is 2.0 mol / L and the sulfuric acid concentration is 0.75 mol / L.) are stirred and leached at 60 °C for 3 h, filtered to obtain a fluoride ion complex solution (filtrate) containing fluosilicic acid.

[0050] By analyzing the composition of the filter residue and calculating according to the law of conservation of mass, the dissolution rate of quartz sand is 95.75%, and the leaching rate of silica is 98.62%; the leaching rates of iron oxide, aluminum oxide, and titanium dioxide are 99.10%, 98.54%, and 98.37% respectively; the leaching rates of sodium oxide and magnesium oxide are both greater than 99%, and the leaching rates of potassium oxide and calcium oxide are 3.43% and 1.08% respectively.

[0051] S3. Using the filtrate obtained from the above leaching process as the raw material, with a phase ratio of 4:1, a mixing time of 6 min, a temperature of 30 °C, and through 6-stage countercurrent extraction, transfer the fluosilicic acid from the leaching solution to the organic phase to complete the extraction process. The extraction rate of fluosilicic acid reaches 97.88%, and the extraction rates of other impurities are all less than 1.02% for purifying fluosilicic acid. Use a high-purity fluosilicic acid (purity greater than 99.99%) solution for countercurrent washing at a ratio of 15:1, with 15 washing stages. The washing rate of fluosilicic acid is 2.08%, and the washing rate of impurities is 99.95%. After washing, the organic solvent is subjected to back-extraction. In this example, the back-extraction agent is sodium hydroxide with a concentration of 4.0 mol / L, controlling the pH of the sodium fluorosilicate back-extraction solution to 8, and the back-extraction rate of fluosilicic acid is 99.5%. The purity of sodium fluorosilicate is 99.99%, and the total yield of sodium fluorosilicate is greater than 94% to obtain a high-purity sodium fluorosilicate solution.

[0052] S4. Using the above back-extraction solution (sodium fluorosilicate solution) as the raw material, adjust the pH of ammonium fluosilicate to 9.5 - 10.5 with ammonia water, and sodium fluorosilicate is converted into silicic acid, ammonium fluoride, and sodium fluoride. Maintain the system temperature at 60 °C, age for 6 h according to the conventional method, and then filter. The filtrate is a solution of ammonium fluoride and sodium fluoride, and silicic acid is a solid.

[0053] S5. Wash the solid until there are no ammonium ions and fluoride ions, then dry and calcine to obtain high-purity silica with a purity greater than 99.99%.

[0054] Example 3

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

[0056] S1. Use granite with a silica content of 71.63% as the raw material, where the iron oxide content is 3.61%, aluminum oxide is 18.48%, calcium oxide is 2.16%, potassium oxide is 5.66%, sodium oxide is 3.89%, magnesium oxide is 0.62%, titanium dioxide is 0.16%, and other impurities. Grind it to more than 200 meshes.

[0057] S2. The ground granite is stirred and leached with a leaching agent (hydrofluoric acid solution, where the hydrofluoric acid concentration is 3.0 mol / L and the hydrogen chloride concentration is 3.0 mol / L.) with a liquid-solid ratio of 6:1 and a hydrogen ion concentration of 5.5 mol / L at 40 °C for 6 h, and then filtered to obtain a fluoride ion complex solution (filtrate) containing fluosilicic acid.

[0058] By analyzing the composition of the filter residue and calculating according to the law of conservation of mass, the dissolution rate of quartz sand is 90.42%, and the leaching rate of silica is 97.66%; the leaching rates of iron oxide, aluminum oxide, and titanium dioxide are 97.73%, 97.92%, and 99.34% respectively. The leaching rates of sodium oxide and magnesium oxide are both greater than 99%, and the leaching rates of potassium oxide and calcium oxide are 7.39% and 3.74% respectively.

[0059] S3. Using the filtrate obtained from the above leaching process as the raw material, with a phase ratio of 2.5 to 1, a mixing time of 6 min, a temperature of 30 °C, and through 8-stage countercurrent extraction, transfer the fluosilicic acid from the leaching solution to the organic phase to complete the extraction process. The extraction rate of fluosilicic acid reaches 99.26%, and the extraction rates of other impurities are all less than 4.89% to purify the fluosilicic acid. Use a high-purity fluosilicic acid (purity greater than 99.99%) solution for countercurrent washing at a ratio of 10:1, with 23 washing stages. The washing rate of fluosilicic acid is 3.18%, and the washing rate of impurities is 99.76%. After washing, the organic solvent is subjected to back-extraction. In this example, the back-extraction agent is a potassium hydroxide solution with a concentration of 3.2 mol / L, the back-extraction stage is 5, control the pH of the potassium fluorosilicate back-extraction solution to 7 - 8, and the back-extraction rate of fluosilicic acid is 99.6%. The purity of potassium fluorosilicate is greater than 99.99%, and the total yield of potassium fluorosilicate is greater than 93% to obtain a high-purity potassium fluorosilicate solution.

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

[0061] S5. Wash with solid until there are no potassium ions and fluoride ions, then dry and calcine to obtain high-purity silica with a purity greater than 99.99%.

[0062] Example 4

[0063] A method for preparing high-purity silica:

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

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

[0066] By analyzing the composition of the filter residue and calculating according to the law of conservation of mass, the dissolution rate of fly ash is 96.33%, and the leaching rate of silica is 98.12%; the leaching rates of iron oxide, alumina, and titanium dioxide are 98.46%, 98.21%, and 98.47% respectively; the leaching rates of sodium oxide and magnesium oxide are both greater than 99%, and the leaching rates of potassium oxide and calcium oxide are 10.29% and 3.91% respectively.

[0067] S3. Using the filtrate obtained from the above leaching process as the raw material, with a phase ratio of 2.0:1, a mixing time of 6 min, a temperature of 30 °C, and through 6-stage countercurrent extraction, transfer fluosilicic acid from the leaching solution to the organic phase to complete the extraction process. The extraction rate of fluosilicic acid reaches 98.49%, and the extraction rates of other impurities are all less than 6.43% for purifying fluosilicic acid. Use a high-purity fluosilicic acid (purity greater than 99.99%) solution for countercurrent washing at a ratio of 8:1, with 20 washing stages. The washing rate of fluosilicic acid is 4.61%, and the washing rate of impurities is 99.33%. After washing, the organic solvent is subjected to back-extraction. The back-extraction agent is an ammonia water solution with a concentration of 2.5 mol / L, and the back-extraction stage is 5. Control the pH of the ammonium fluosilicate back-extraction solution to 7-8. The back-extraction rate of fluosilicic acid is 99.6%. The purity of ammonium fluosilicate is greater than 99.99%, and the total yield of ammonium fluosilicate is greater than 91% to obtain a high-purity ammonium fluosilicate solution.

[0068] S4. Using the above stripping solution (ammonium fluorosilicate solution) as the raw material, adjust the pH of ammonium fluorosilicate to 9.5 - 10.5 with ammonia water, and ammonium fluorosilicate is converted into silicic acid and ammonium fluoride. Maintain the system temperature at 60 °C, age for 6 h according to the conventional method and then filter. The filtrate is ammonium fluoride solution, and the silicic acid is solid.

[0069] S5. Wash the solid until there are no ammonium ions and fluoride ions, then dry and calcine to obtain high-purity silica with a purity greater than 99.99%.

[0070] Example 5

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

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

[0073] S2. The sorted blast furnace slag and the leaching agent with a liquid-solid ratio of 10:1 and a hydrogen ion concentration of 4.0 mol / L (hydrofluoric acid solution, in which the hydrofluoric acid concentration is 2.0 mol / L and the sulfuric acid concentration is 1.0 mol / L.) are stirred and leached at 40 °C for 8 h, and then filtered to obtain a fluoride ion complex solution (filtrate) containing fluorosilicic acid.

[0074] By analyzing the composition of the filter residue and calculating according to the law of conservation of mass, the dissolution rate of blast furnace slag is 57.92%, and the leaching rate of silica is 96.28%; the leaching rates of iron oxide, aluminum oxide and titanium dioxide are 97.95%, 97.83% and 97.18% respectively; the leaching rates of sodium oxide and magnesium oxide are both greater than 99%, and the leaching rates of potassium oxide and calcium oxide are 3.38% and 2.51% respectively.

[0075] S3. Using the filtrate obtained from the above leaching process as the raw material, with a phase ratio of 1.8:1, a mixing time of 6 min, a temperature of 30 °C, and through 6-stage countercurrent extraction, transfer fluosilicic acid from the leaching solution to the organic phase to complete the extraction process. The extraction rate of fluosilicic acid reaches 98.75%, and the extraction rates of other impurities are all less than 8.90% for the purification of fluosilicic acid. Use a high-purity fluosilicic acid (purity greater than 99.99%) solution for countercurrent washing at a ratio of 10:1, with 30 washing stages. The washing rate of fluosilicic acid is 6.80%, and the washing rate of impurities is 99.53%. After washing, the organic solvent is subjected to back-extraction. The back-extraction agent is an ammonia water solution with a concentration of 2.0 mol / L, and the number of back-extraction stages is 5. Control the pH of the ammonium fluosilicate back-extraction solution to 7 - 8, and the back-extraction rate of fluosilicic acid is 99.3%. The purity of ammonium fluosilicate is greater than 99.99%, and the total yield of ammonium fluosilicate is greater than 87%.

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

[0077] S5. Wash the solid until there are no ammonium ions and fluoride ions, then dry and calcine to obtain high-purity silica with a purity greater than 99.99%.

[0078] Experimental test

[0079] Use the high-purity silica prepared in Example 1 for detection by inductively coupled plasma mass spectrometry to test the content of each element in the silica. The test results are shown in Table 1.

[0080] Table 1 Content of each element in silica

[0081]

[0082] As can be seen from Table 1, it is confirmed that high-purity silica is prepared, and the purity can reach 99.99%.

[0083] Therefore, the present invention adopts the above method for preparing high-purity silica, which is applicable to most silicon-containing raw materials, effectively reduces the content of impurities 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 are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions of the present invention or make equivalent replacements, and these modifications or equivalent replacements do not enable 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 silicon dioxide, characterized in that: The following steps are involved: S1. Grinding: crushing and grinding the minerals or waste residues containing silicon dioxide or silicates; S2, leaching: mixing the ground mineral or waste residue with a leaching agent in proportion to carry out a leaching reaction, and obtaining a fluoride ion complex solution containing fluorosilicic acid through solid-liquid separation; S3, extraction: using the fluoride ion complex solution containing fluorosilicic acid as raw material, using extraction method to separate fluorosilicic acid and fluoride ion complex impurities to obtain high-purity fluorosilicic acid or fluorosilicate solution; S4, pH adjustment: by adjusting the pH of high-purity fluorosilicic acid or fluorosilicate solution to perform double decomposition reaction, solid-liquid separation is performed to obtain silicic acid solid and soluble fluoride; S5. The silicic acid solid is washed, dried and calcined to obtain high-purity silicon dioxide.

2. The method for preparing high-purity silicon dioxide according to claim 1, characterized in that: In S2, the leaching agent is an acidic solution containing fluoride ions, the hydrogen ion concentration of which is 0.5-18 mol / L, and the anion is one or more of fluoride ions, sulfate ions, chloride ions, and nitrate ions, and the fluoride ion concentration of which is 0.5-8 mol / L.

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

4. The method for preparing high-purity silicon dioxide according to claim 1, characterized in that: In S3, the extraction method includes solvent extraction and solvent stripping, which are performed in a single-stage, two-stage or multi-stage cross-current or counter-current manner.

5. The method for preparing high-purity silicon dioxide according to claim 4, characterized in that: The solvent extraction obtains one of fluorosilicic acid or fluorosilicate, and the solvent back extraction obtains one of ammonium fluorosilicate solution, sodium fluorosilicate solution or potassium fluorosilicate solution.

6. The method for preparing high-purity silicon dioxide according to claim 5, characterized in that: During the solvent extraction or the solvent stripping process, the ratio of the organic phase to the aqueous phase is 1-20:1-20, the temperature is 10-90° C., the reaction time is 1-30 min, and the delamination time is 1-60 min.

7. The method for preparing high-purity silicon dioxide according to claim 1, characterized in that: In S4, the metathesis reaction is specifically: Adjust the pH of the ammonium fluorosilicate solution with hydrofluoric acid or ammonia water to hydrolyze it into silicic acid and ammonium fluoride; Adjust the pH of the sodium fluorosilicate solution with hydrofluoric acid or sodium hydroxide to hydrolyze it into silicic acid and sodium fluoride; The pH of potassium fluorosilicate solution is adjusted with hydrofluoric acid or potassium hydroxide to hydrolyze it into silicic acid and potassium fluoride.

8. The method for preparing high-purity silicon dioxide according to claim 1, characterized in that: In S4, after the solid-liquid separation, one or more of silicic acid solid, ammonium fluoride solution, sodium fluoride solution or potassium fluoride solution is obtained.

9. The method for preparing high-purity silicon dioxide according to claim 8, characterized in that: S5 is as follows: The silicic acid solid is washed, dried, calcined, and then ball-milled to obtain high-purity silicon dioxide.

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

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