A method for preparing amorphous silicon dioxide using tungsten tailings

Abstract

The present application belongs to the technical field of solid waste resource utilization and inorganic non-metallic material preparation, and relates to a method for preparing amorphous silicon dioxide by using tungsten tailings. The preparation process of the present application uses tungsten tailings as raw material, and the stable lattice structure of the tungsten tailings is destroyed by mechanical activation + roasting activation to improve the reactivity of the minerals. Then, the deep removal of impurities wrapped in the lattice is realized by inorganic-organic mixed acid-ultrasonic field strengthening to obtain high-purity acid leaching material. The acid leaching material is subjected to alkali addition and salt roasting with NaOH to realize the conversion of silicon dioxide into water-soluble sodium silicate. Subsequently, the pure sodium silicate solution is obtained by water leaching and filtration to remove insoluble residues. Finally, the morphology control and purification of amorphous silicon dioxide are realized through two-stage pH adjustment, aging, washing, filtration, drying and roasting steps, and finally the amorphous silicon dioxide product is obtained. The whole process is controllable, no fluorine-containing reagent is used throughout the process, and the reaction conditions are mild, which is easy to industrialize and scale up.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization and inorganic non-metallic material preparation technology, and relates to a method for preparing amorphous silicon dioxide using tungsten tailings. Background Technology

[0002] Global tungsten production was approximately 80,000 tons in 2024, with production steadily increasing. my country is the world's richest and largest producer of tungsten resources, accounting for over 85% of global tungsten concentrate production. Tungsten tailings are solid waste generated during tungsten mining and beneficiation. Their formation is closely related to the type of tungsten ore, primarily originating from the beneficiation stages of wolframite (Fe,Mn)WO4 and scheelite (CaWO4). They consist of unused gangue minerals and a small amount of unrecovered tungsten after beneficiation. Wolframite is often associated with gangue minerals such as quartz and feldspar, and is treated using a combined gravity separation-flotation process. After crushing and grinding, the raw ore is enriched with tungsten minerals using gravity separation equipment such as shaking tables and jigs. Impurities are then separated by flotation, and the remaining gangue minerals after separation form wolframite tailings. my country's tungsten tailings have a low comprehensive utilization rate, with over 10 million tons of tailings already generated and stored in tailings ponds or tungsten tailings ponds. This occupies a large amount of land and damages the surface ecology. Tailings ponds also face the risks of collapse and leakage, and contain various heavy metal elements, posing environmental risks. Furthermore, components such as silicon and aluminum in the tailings are not utilized, especially the SiO2 content, which is as high as 40%-80%. Idle storage leads to resource waste.

[0003] The core components of tungsten tailings are silicate minerals (70%-90%), mainly including quartz (SiO2) and feldspar (KAlSi3O8, NaAlSi3O8, CaAl2Si2O8). They also contain small amounts of tungsten (WO3 residue 0.01%-0.1%), iron oxides (Fe2O3), aluminum oxides (Al2O3), calcium and magnesium compounds (CaO, MgO), and other impurities. Some tailings contain trace amounts of heavy metals (such as Mn, Pb, and As). Silicon is a core raw material in modern industry. Its high melting point, semiconductor properties, good chemical stability, and physicochemical properties make it a cornerstone of modern industrial systems. It is widely used in semiconductor chips, solar photovoltaics, building materials (such as sodium silicate), electronic devices, and other fields. High-purity silicon (such as 4N grade) is an indispensable basic material for high-end manufacturing. Therefore, extracting silicon from tungsten tailings can, on the one hand, realize the resource utilization of solid waste, transform "waste" into high-value silicon products, and improve the overall economic benefits of tungsten mining; on the other hand, it can reduce the environmental pressure caused by tailings storage and reduce land occupation and pollution control costs.

[0004] However, existing technologies for extracting silicon from tungsten tailings, a specific and complex mineral system, suffer from technical challenges such as difficulty in impurity removal, high reaction temperatures, low product purity, and difficulty in controlling morphology. Therefore, a method for preparing amorphous silica from tungsten tailings is needed. Summary of the Invention

[0005] In view of the above-mentioned technical problems, the present invention provides a method for preparing amorphous silica using tungsten tailings. The present invention solves the technical problems of difficult impurity removal, high reaction temperature, low product purity, and difficulty in controlling the morphology when preparing amorphous silica from tungsten tailings.

[0006] To achieve the above objectives, the present invention adopts the following technical solution.

[0007] A method for preparing amorphous silica using tungsten tailings includes the following steps: Step S1: Crush and grind the tungsten tailings, mechanically activate them, and then roast them to obtain activated mineral powder; Step S2: Prepare an inorganic-organic mixed acid solution, add activated mineral powder to the mixed acid solution, carry out an external field enhanced ultrasonic heating leaching reaction, and then heat in a water bath under stirring. After the reaction is completed, filter and separate to obtain acid leaching material and filtrate containing impurities. Step S3: Mix the acid-leaching material with NaOH and carry out a molten salt roasting reaction to obtain the roasted product; Step S4: Dissolve the calcined product in water, stir, leach in a water bath, filter to remove insoluble residue, and obtain sodium silicate solution; Step S5: Add sodium chloride as a dispersant to the sodium silicate solution, then add hydrochloric acid, adjust the pH value in two stages, and after aging, filtering, washing and drying the precipitate, obtain the amorphous silica precursor. Step S6: Calcine the amorphous silica precursor to obtain amorphous silica.

[0008] Furthermore, in step S1, the tungsten tailings are tungsten tailings after gravity separation, with a SiO2 mass fraction of 60%-80%, containing lattice-encapsulated Fe2O3 and Al2O3 impurities, a WO3 residue of 0.01%-0.1%, and containing feldspar minerals such as KAlSi3O8, NaAlSi3O8, and CaAl2Si2O8.

[0009] Furthermore, in step S1, the mechanical activation is performed using a planetary ball mill with a ball milling speed of 300 r / min-500 r / min, a ball-to-material ratio of 6:1-8:1, and a mechanical activation time of 2 h-4 h, until the particle size is less than 74 μm.

[0010] Furthermore, in step S1, the calcination activation temperature is 600℃-800℃, and the calcination activation time is 1h-3h.

[0011] Further, in step S2, the inorganic-organic mixed acid solution contains at least one of hydrochloric acid, sulfuric acid, and nitric acid, and at least one of oxalic acid, citric acid, and EDTA; the inorganic acid concentration is 3 mol / L-5 mol / L, and the organic acid concentration is 0.05 mol / L-0.15 mol / L; the ratio of inorganic-organic mixed acid solution to activated mineral powder (liquid-solid ratio) is 5 mL-15 mL:1 g.

[0012] Furthermore, in step S2, the parameters for the external field enhanced ultrasonic heating leaching reaction are: ultrasonic power 200W-400W, ultrasonic time 15min-60min, and heating temperature 50℃-90℃; the reaction parameters for water bath heating are: heating temperature 60℃-90℃, rotation speed 100r / min-150r / min, and heating time 2h-3h.

[0013] Furthermore, in step S3, the molar ratio of acid leaching material to NaOH is 1:2-1:3; the molten salt roasting temperature is 400℃-500℃, and the roasting time is 2h-3h.

[0014] Furthermore, in step S4, the water bath temperature is 80°C and the leaching time is 3 hours.

[0015] Furthermore, in step S5, the mass ratio of tungsten tailings to sodium chloride is 10:1 to 10:3.

[0016] Furthermore, in step S5, the pH value is adjusted in two stages: first, acid solution is added dropwise at a rate of 5 mL / min until pH=9.5-10.5 and kept warm for 20 min-45 min; then, acid solution is added dropwise at a rate of 1 mL / min until pH=8-9.

[0017] Furthermore, in step S6, the calcination temperature is 300℃-500℃, and the calcination time is 1h-3h.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: The preparation method of this invention destroys the original stable lattice energy of tungsten tailings through "mechanical activation + roasting activation", and provides an excellent liquid phase reaction environment through low-temperature alkaline fusion with NaOH. This greatly reduces the activation energy and reaction temperature, allowing the silicon conversion reaction to proceed efficiently at 400℃-500℃. It also significantly reduces energy consumption and equipment corrosion. In other words, the ternary synergy of "activation-complexation-molten salt" achieves deep impurity removal, enabling the extraction of amorphous silica products from complex waste tungsten tailings with a purity of over 99.5%.

[0019] (1) Unlike other silicon-containing solid wastes such as silica sand (only a thin film of iron on the surface) and oil shale waste (no impurities encased in the lattice), the tungsten tailings targeted in this invention have a unique "quartz-feldspar symbiosis" structure, which causes impurities to be encased in the lattice. The silicate minerals (such as quartz, feldspar, mica, etc.) in the tungsten tailings have extremely stable lattice structures and high lattice energies, which makes the interfacial reaction kinetics between the acid and the minerals slow, resulting in a very low silicon leaching rate. Moreover, the impurities encased in the silicate lattice are difficult to release, resulting in incomplete impurity removal. Existing fluorine-free acid leaching methods directly enrich silicon dioxide by dissolving impurities with inorganic acids; for example, hydrofluoric acid reacts with the target product silicon dioxide to generate silicon tetrafluoride gas (SiF4) or fluorosilicic acid (H2SiF6), which leads to a significant decrease in silicon recovery rate and makes it difficult to accurately control the reaction endpoint. Unlike traditional single inorganic acid leaching, this invention adopts a composite impurity removal process of "inorganic acid-organic acid-external field strengthening", which uses inorganic acid to provide H + This invention dissolves metal oxides, utilizes the strong complexing ability of organic acids for iron and aluminum ions, and combines this with ultrasonic waves to disrupt the mineral surface layer through cavitation. These three methods work synergistically to achieve deep removal of lattice-encapsulated impurities and effectively prevent hydrolysis and re-precipitation of impurity ions when local acidity decreases. Compared to leaching rates with a single acid, iron leaching rate is increased by more than 15%, and aluminum leaching rate by more than 20%. Compared to conditions without ultrasonic field enhancement, iron leaching rate is increased by more than 8.9%, further improving the purity of the amorphous silica prepared by this invention.

[0020] (2) The hydrofluoric acid used in the existing process is highly corrosive and toxic, and has strict requirements on equipment materials. The cost of treating the volatilized acid mist and the generated fluorine-containing wastewater is extremely high and difficult, which is not in line with the current trend of green chemical development. In contrast, the present invention does not use highly toxic fluorine-containing reagents throughout the process, thus avoiding the loss of silicon resources (SiF4 volatilization) and the risk of fluorine pollution. At the same time, the acid leaching waste liquid is cooled and crystallized to recover ferric oxalate and aluminum chloride byproducts. The crystallization mother liquor can be recycled for the preparation of mixed acid solution.

[0021] (3) Traditional alkali fusion sintering processes, which use high-temperature (>1000℃) alkali fusion or soda ash sintering methods, consume huge amounts of energy. Moreover, in a high-temperature, strongly alkaline environment, impurities such as iron and aluminum are prone to form eutectic with silicon, causing impurities to dissolve along with silicon during subsequent water immersion. Ultimately, this results in a decrease in the whiteness of the amorphous silica product and an excess of iron and aluminum content. The low-temperature alkali fusion of this invention is also different from the low-temperature alkali reaction (75℃-85℃, non-molten state, slow reaction kinetics). Through the strong mass transfer capability of molten alkali, the silicon conversion efficiency reaches over 95%, and there is no eutectic phenomenon of impurities.

[0022] (4) In the precipitation stage, i.e. step S4, the present invention introduces a stepwise pH control mechanism, firstly rapidly adding acid solution to achieve heat preservation and nucleation, and then slowly adding acid solution to promote grain growth, so as to precisely control the final pH value in the range of 8-9, effectively balancing the polymerization rate and nucleation rate of silicic acid, thereby facilitating the obtaining of amorphous silica precursor and effectively avoiding excessive aggregation of colloids. Attached Figure Description

[0023] The present invention is described with reference to the following figures: Figure 1 The XRD pattern of amorphous silica prepared in Example 1 of this invention; Figure 2 This is a SEM image of amorphous silica prepared in Example 1 of the present invention; Figure 3 The image shows the XRD pattern of amorphous silica prepared in Comparative Example 1 of this invention. Figure 4 The image shows the XRD pattern of amorphous silica prepared in Comparative Example 2 of this invention. Figure 5 This is a macroscopic comparison diagram of the acid leaching materials in step S2 of Embodiment 1, Comparative Examples 1 to 3 of the present invention (wherein, Figure 5 A is Example 1. Figure 5 B is Comparative Example 1. Figure 5 C is comparative example 2. Figure 5 D is comparative example 3); Figure 6 This is a macroscopic image of the precipitate after adjusting the pH in step S5 of Example 1 of the present invention. Detailed Implementation

[0024] The technical solutions of this invention will now be clearly and completely described. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0025] This invention provides a method for preparing amorphous silica using tungsten tailings, the method comprising the following steps: Step S1: The tungsten tailings are crushed, ground, and mechanically activated using a planetary ball mill at a speed of 300-500 r / min, a ball-to-material ratio of 6:1-8:1, and a activation time of 2-4 hours. The tungsten tailings are then ball-milled until the particle size is less than 74 μm (200 mesh), thus disrupting the mineral surface structure. Subsequently, the tungsten tailings are roasted at 600-800℃ for 1-3 hours to further disrupt the crystal structure of the silicate minerals and enhance their reactivity, resulting in activated mineral powder. In step S1, the tungsten tailings are tungsten tailings after gravity separation, with a SiO2 mass fraction of 60%-80%. The tungsten tailings contain lattice-encapsulated Fe2O3 and Al2O3 impurities, with a WO3 residue of 0.01%-0.1%, and contain difficult-to-process silicate feldspar minerals such as KAlSi3O8, NaAlSi3O8, and CaAl2Si2O8.

[0026] Step S2: Prepare an inorganic-organic mixed acid solution. Add activated mineral powder to the mixed acid solution and perform an external field-enhanced ultrasonic heating leaching reaction. The ultrasonic power is 200W-400W, the ultrasonic time is 15min-60min, and the heating temperature is 50℃-90℃. Then, under stirring conditions, heat in a water bath at 60℃-90℃ for 2h-3h at a rotation speed of 100r / min-150r / min. After the reaction is complete, filter to separate the acid leaching material and the filtrate containing impurities. In the inorganic-organic mixed acid solution, the inorganic acid is at least one of hydrochloric acid, sulfuric acid, and nitric acid, and the organic acid is at least one of oxalic acid, citric acid, and EDTA. The concentration of the inorganic acid is 3mol / L-5mol / L, and the concentration of the organic acid is 0.05mol / L-0.15mol / L. The liquid-solid ratio of the inorganic-organic mixed acid solution to the activated mineral powder is 5mL-15mL:1g. The inorganic acid serves as the main leaching agent to provide H2O. + Organic acids, acting as complexing agents, react with dissolved Fe through the carboxyl groups to dissolve metal oxides. 3 + / Al 3+ Impurity ions form stable water-soluble chelates, and ultrasound breaks down the mineral surface layer through cavitation. The three work together to achieve deep removal of impurities encapsulated in the crystal lattice. After solid-liquid separation, a silicon-based precursor (acid-leached material) is obtained. Step S3: Mix the acid leaching material with NaOH in a molar ratio of 1:2-1:3 and carry out a molten salt roasting reaction. The molten salt roasting temperature is 400℃-500℃ and the roasting time is 2h-3h to obtain the roasting product. By utilizing the liquid phase mass transfer characteristics of molten salt, the reaction kinetics are enhanced, and the inert mineral phases such as quartz and feldspar are rapidly transformed into water-soluble silicates. Step S4: Dissolve the calcined product in water and stir. Immerse in a water bath at 80°C for 3 hours. Filter to remove insoluble residues to obtain a sodium silicate solution. Step S5: Add sodium chloride as a dispersant to the sodium silicate solution. The mass ratio of tungsten tailings to sodium chloride is 10:1-10:3. The addition of the dispersant prevents excessive aggregation of the colloid. Add hydrochloric acid in two stages to adjust the pH value. First, add hydrochloric acid dropwise at a rate of 5 mL / min until the pH reaches 9.5-10.5 and keep it at this temperature for 20-45 minutes to allow nucleation. Then, add hydrochloric acid dropwise at a rate of 1 mL / min until the pH reaches 8-9 to allow grain growth. The precipitate is aged, filtered, washed, and dried to obtain an amorphous silica precursor. Step S6: Calcine the amorphous silica precursor at 300℃-500℃ for 1h-3h to obtain amorphous silica. The purity of the prepared amorphous silica product is above 99.5%.

[0027] The preparation process of this invention uses tungsten tailings as raw material. Pretreatment (mechanical activation + roasting activation) disrupts the stable crystal structure of the tungsten tailings, enhancing the mineral's reactivity. Then, a deep removal of impurities encapsulated in the crystal lattice is achieved through inorganic-organic mixed acid and ultrasonic external field enhancement, yielding a high-purity acid-leached material. This acid-leached material is then roasted with NaOH using alkali-added molten salt to convert silica into water-soluble sodium silicate. Subsequent water leaching and filtration remove insoluble residues to obtain a pure sodium silicate solution. Finally, through two stages of pH adjustment, aging, washing, filtration, drying, and roasting, the morphology of amorphous silica is controlled and purified, ultimately yielding the amorphous silica product. The entire process is seamless, with controllable steps, uses no fluorine-containing reagents, is environmentally friendly, and operates under mild reaction conditions, making it suitable for large-scale industrial production.

[0028] The whiteness of the products prepared in the following examples and comparative examples was determined using the method of GB / T5950-2008; the leaching rate of iron / aluminum impurities was detected using the ICP-OES method; the purity of amorphous silica was determined using the gravimetric method of GB / T14506.3-2010; the silicon conversion efficiency was determined using the national standard method (GB / T14506.3-2010 gravimetric method) consistent with the SiO2 purity detection method of this patent. It was calculated by measuring the total SiO2 mass in the acid-leached material and the actual SiO2 mass dissolved in the sodium silicate solution after water leaching. This is a conventional industry method for determining the conversion efficiency of silicon-containing minerals. Silicon conversion efficiency (%) = (total mass of SiO2 in the sodium silicate solution after water leaching ÷ total mass of SiO2 in the acid-leached material participating in the reaction) × 100%.

[0029] Example 1 includes the following steps: S1: Take tungsten tailings from a certain area in Jiangxi Province, and ball mill them to a particle size of less than 74μm (200 mesh). The ball mill speed is 400r / min, the ball milling time is 2h, and the material-to-ball ratio is 6:1. Then, roast and activate them at 650℃ for 1.5h to obtain activated mineral powder. S2: Prepare an inorganic-organic mixed acid solution, wherein the inorganic acid is 4 mol / L hydrochloric acid and the organic acid is 0.1 mol / L oxalic acid. Add 10 g of activated tailings powder at a liquid-to-solid ratio of 10 mL: 1 g. Perform ultrasonic oxidation leaching for 15 min with an ultrasonic power of 300 W, and then stir and react in an 80℃ water bath for 3 h. Filter the solution, and wash the acid-leached material (filter cake) with deionized water until neutral. The leaching rate of iron was 91.8% and the leaching rate of aluminum was 82.5% at this point. S3: Mix the acid leaching material with NaOH solid at a molar ratio of 1:2.5, place it in a corundum crucible, and calcine it in a muffle furnace at 400℃ for 2 hours to obtain the calcined product; S4: After cooling the calcined product, add water and stir. Immerse in an 80°C water bath for 3 hours. Filter to remove insoluble residues to obtain sodium silicate solution. S5: Add 1g of dispersant (NaCl) to the sodium silicate solution and adjust the pH in stages while stirring: first, add hydrochloric acid dropwise at a rate of 5mL / min until pH=10.0, and keep warm for 30min to induce nucleation; then add hydrochloric acid dropwise at a rate of 1mL / min until pH=8.5 to control the uniform growth of silicate crystals. S6: After aging for 2 hours, the precipitate is filtered and repeatedly washed to remove Na. + and Cl - The silica was dried at 105°C and then calcined at 300°C for 2 hours to obtain amorphous silica.

[0030] Example 1 prepared amorphous silica with a purity of 99.7%, a whiteness of 96.2%, and no obvious agglomeration.

[0031] like Figure 1 As shown, the product prepared in Example 1 exhibits a typical broadened diffraction peak at approximately 2Theta of 23° (see [reference]). Figure 1 (Dashed box) No obvious sharp crystal diffraction peaks are present, which is consistent with the XRD characteristics of amorphous silica. This indicates that the product prepared by the process of this invention is a pure amorphous silica structure, without residual crystal impurities such as quartz and feldspar, and without metal oxide impurity peaks such as Fe2O3 and Al2O3. This proves that the process of this invention removes impurities thoroughly and has excellent silicon conversion effect, and can prepare high-purity amorphous silica.

[0032] like Figure 2 As shown, the amorphous silica particles prepared in Example 1 have a uniform particle size distribution and no obvious hard agglomeration. The uniform particle size distribution and non-agglomeration characteristics fully demonstrate that the step of segmented pH control + sodium chloride dispersant in this invention achieves precise control of the product morphology.

[0033] like Figure 5 As shown in Figure A, the acid leaching material obtained by filtering after inorganic-organic mixed acid leaching with ultrasonic treatment in Example 1 is a loose, grayish-white powder with no obvious clumping. The acid leaching material has a uniform color and is free of yellowish-brown (iron oxide), grayish-black (unremoved impurities), and other discolorations, which clearly reflects that lattice-encapsulated impurities such as iron and aluminum have been deeply removed. This is consistent with the high leaching rate results detected by ICP-OES, proving the effectiveness of the "inorganic acid-organic acid-ultrasonic" ternary composite impurity removal process.

[0034] like Figure 6As shown, the precipitate formed in step S5 after two-stage pH adjustment in Example 1 is a milky white flocculent precipitate with no obvious sedimentation or agglomeration. The precipitate has a uniform color and good fluidity, which reflects the synergistic effect of staged pH control (nucleation before growth) and sodium chloride dispersant, effectively avoiding excessive aggregation of colloids. This corresponds to the microscopic characteristics of "uniform particle size and no hard agglomeration" in the SEM image and the high purity test results.

[0035] The final product of Example 1, after calcination at 300℃, is a snow-white, loose powder with good flowability, free from lumps and discoloration. Its macroscopic appearance perfectly matches the tested results of "purity 99.7% and whiteness 96.2%", meeting the appearance and performance requirements for rubber reinforcing agents and coating fillers.

[0036] Example 2 includes the following steps: S1: Take tungsten tailings from a certain place in Jiangxi Province, and ball mill it to a particle size of less than 74μm (200 mesh). The ball mill speed is 450r / min, the ball milling time is 2h, and the material-to-ball ratio is 6:1. Then, roast and activate it at 700℃ for 1h to obtain activated mineral powder. S2: Prepare an inorganic-organic mixed acid solution, wherein the inorganic acid is 3.5 mol / L hydrochloric acid and the organic acid is 0.1 mol / L citric acid. Add 10 g of activated tailings powder at a liquid-to-solid ratio of 8 mL: 1 g. Perform ultrasonic oxidation leaching for 30 min with an ultrasonic power of 350 W, and then stir and react in a 75℃ water bath for 3 h. Filter the solution, and wash the acid-leached material (filter cake) with deionized water until neutral. The leaching rate of iron was 93.4% and the leaching rate of aluminum was 84.7% at this point. S3: Mix the acid leaching material with NaOH solid at a molar ratio of 1:2.5, place it in a corundum crucible, and calcine it in a muffle furnace at 450℃ for 2 hours to obtain the calcined product; S4: After cooling the calcined product, add water and stir. Soak in an 80°C water bath for 3 hours to dissolve. Filter to remove insoluble residues to obtain sodium silicate solution. S5: Add 1g of dispersant (NaCl) to the sodium silicate solution and adjust the pH in stages while stirring: first, add hydrochloric acid dropwise at a rate of 5mL / min until pH=10.0, and keep warm for 25min to induce nucleation; then add hydrochloric acid dropwise at a rate of 1mL / min until pH=8.3 to control the uniform growth of silicate crystals. S6: After aging for 3 hours, the precipitate is filtered and repeatedly washed to remove Na. + and Cl - The silica was dried at 105°C and then calcined at 400°C for 2 hours to obtain amorphous silica.

[0037] Example 2 prepared amorphous silica with a purity of 99.8%, a whiteness of 96.8%, and no obvious agglomeration.

[0038] Example 2 (hydrochloric acid + citric acid system): The precipitate after step S5 was a milky white, fluffy colloidal substance with a uniform texture. Citric acid has a better complexing ability for iron and aluminum ions than oxalic acid, resulting in superior impurity removal. The precipitate was white and well-dispersed, consistent with the test results (purity 99.8%, whiteness 96.8%), demonstrating the influence of different organic acid systems on precipitation characteristics.

[0039] Example 3 includes the following steps: S1: Take tungsten tailings from a certain place in Jiangxi Province, and ball mill them to a particle size of less than 74μm (200 mesh). The ball mill speed is 350r / min, the ball milling time is 2h, and the material-to-ball ratio is 8:1. Then, roast and activate them at 750℃ for 1h to obtain activated mineral powder. S2: Prepare an inorganic-organic mixed acid solution, wherein the inorganic acid is 3 mol / L hydrochloric acid + 2 mol / L sulfuric acid, and the organic acid is 0.12 mol / L EDTA. Add 10 g of activated tailings powder at a liquid-to-solid ratio of 10 mL: 1 g, and perform ultrasonic oxidation leaching for 30 min at an ultrasonic power of 280 W. Then, stir and react in an 85℃ water bath for 3 h. Filter the solution, and wash the acid-leached material (filter cake) with deionized water until neutral. The leaching rate of iron was 94.8% and the leaching rate of aluminum was 87.3% at this point. S3: Mix the acid leaching material with NaOH solid at a molar ratio of 1:3, place it in a corundum crucible, and calcine it in a muffle furnace at 450℃ for 2 hours to obtain the calcined product; S4: After cooling the calcined product, add water and stir. Soak in an 80°C water bath for 3 hours to dissolve. Filter to remove insoluble residues to obtain sodium silicate solution. S5: Add 1.5g of dispersant (NaCl) to the sodium silicate solution and adjust the pH in stages while stirring: first, add hydrochloric acid dropwise at a rate of 5mL / min until pH=10.0, and keep warm for 25min to induce nucleation; then add hydrochloric acid dropwise at a rate of 1mL / min until pH=8.8 to control the uniform growth of silicate crystals. S6: The sediment is aged for 2 hours, then filtered and repeatedly washed to remove Na. + and Cl - The silica was dried at 105°C and then calcined at 300°C for 2 hours to obtain amorphous silica.

[0040] Example 3 prepared amorphous silica with a purity of 99.9% and a whiteness of 97.2%, with no obvious agglomeration, reaching the purity standard of high-end amorphous silica.

[0041] In Example 3 (mixed inorganic acid + EDTA system), the precipitate after step S5 was a snow-white, fluffy colloidal substance. Because the mixed inorganic acid increased the H⁺ concentration, the strong complexing property of EDTA further improved the impurity removal effect, resulting in a higher purity and whiter color of the precipitate, consistent with the highest purity (99.9%) detected in Example 3.

[0042] Example 4 includes the following steps: S1: Take tungsten tailings from a certain place in Jiangxi Province, and ball mill them to a particle size of less than 74μm (200 mesh). The ball mill speed is 350r / min, the ball milling time is 2h, and the material-to-ball ratio is 7:1. Then, roast and activate them at 700℃ for 1h to obtain activated mineral powder. S2: Prepare an inorganic-organic mixed acid solution, wherein the inorganic acid is 5 mol / L hydrochloric acid and the organic acid is 0.08 mol / L EDTA. Add 10 g of activated tailings powder at a liquid-to-solid ratio of 10 mL: 1 g. Perform ultrasonic oxidation leaching for 30 min at an ultrasonic power of 320 W, and then stir the reaction in a 75℃ water bath for 2 h. Filter the solution, and wash the acid-leached material (filter cake) with deionized water until neutral. The leaching rate of iron was found to be 92.3% and the leaching rate of aluminum was 84.1% at this point. S3: Mix the acid-leaching material with NaOH solid at a molar ratio of 1:2.5, place it in a corundum crucible, and calcine it in a muffle furnace at 450℃ for 2.5h to obtain the calcined product; S4: After cooling the calcined product, add water and stir. Soak in an 80°C water bath for 3 hours to dissolve. Filter to remove insoluble residues to obtain sodium silicate solution. S5: Add 1.5g of dispersant (NaCl) to the sodium silicate solution and adjust the pH in stages while stirring: first, add hydrochloric acid dropwise at a rate of 5mL / min until pH=10.0, and keep warm for 30min to induce nucleation; then add hydrochloric acid dropwise at a rate of 1mL / min until pH=8.2 to control the uniform growth of silicate crystals. S6: After aging for 2 hours, the precipitate is filtered and repeatedly washed to remove Na. + and Cl - The silica was dried at 105°C and then calcined at 300°C for 2 hours to obtain amorphous silica.

[0043] Example 4 prepared amorphous silica with a purity of 99.7%, a whiteness of 96.3%, and no obvious agglomeration.

[0044] The final product of Example 4, after calcination at 300℃, is a snow-white, loose powder with excellent flowability, free of lumps and discolored particles. The macroscopic appearance of the product is completely consistent with the test data of "purity 99.7% and whiteness 96.3%". Due to the thorough acid leaching for impurity removal and precise segmented pH control, the product maintains both high purity and good dispersibility, further demonstrating the adaptability of the preparation method of this invention to different acid systems and the stability of the prepared product quality.

[0045] Example 5 includes the following steps: S1: Take tungsten tailings from a certain area in Jiangxi Province, and ball mill them to a particle size of less than 74μm (200 mesh). The ball mill speed is 420r / min, the ball milling time is 2.5h, and the material-to-ball ratio is 7:1. Then, roast and activate them at 750℃ for 1h to obtain activated mineral powder. S2: Prepare an inorganic-organic mixed acid solution, wherein the inorganic acid is 3 mol / L hydrochloric acid + 2 mol / L nitric acid, and the organic acid is 0.1 mol / L citric acid. Add 10 g of activated tailings powder at a liquid-to-solid ratio of 10 mL: 1 g, and perform ultrasonic oxidation leaching for 30 min at an ultrasonic power of 250 W. Then, stir and react in an 80℃ water bath for 3 h. Filter the solution, and wash the acid-leached material (filter cake) with deionized water until neutral. The leaching rate of iron was found to be 94.5% and the leaching rate of aluminum was 86.8% at this point. S3: Mix the acid leaching material with NaOH solid at a molar ratio of 1:3, place it in a corundum crucible, and calcine it in a muffle furnace at 480℃ for 2 hours to obtain the calcined product; S4: After cooling the calcined product, add water and stir. Soak in an 80°C water bath for 3 hours to dissolve. Filter to remove insoluble residues to obtain sodium silicate solution. S5: Add 2.5g of dispersant (NaCl) to the sodium silicate solution and adjust the pH in stages while stirring: first, add hydrochloric acid dropwise at a rate of 5mL / min until pH=10.0, and keep warm for 20min to induce nucleation; then add hydrochloric acid dropwise at a rate of 1mL / min until pH=8.8 to control the uniform growth of silicate crystals. S6: After aging for 2 hours, the precipitate is filtered and repeatedly washed to remove Na. + and Cl - The silica was dried at 105°C and then calcined at 450°C for 2 hours to obtain amorphous silica.

[0046] Example 5 prepared amorphous silica with a purity of 99.8%, a whiteness of 96.7%, and no obvious agglomeration.

[0047] Example 5 (Hydrochloric acid + nitric acid mixed acid + citric acid system): The precipitate after step S5 was a milky white, fine colloidal substance without any clumping. Thanks to the synergistic dissolution of the mixed inorganic acids and the strong complexing effect of citric acid, the precipitate had extremely low impurity content and excellent colloidal dispersibility, laying the foundation for the subsequent preparation of high-purity, high-whiteness products, consistent with the test results (purity 99.8%, whiteness 96.7%).

[0048] Example 6 includes the following steps: S1: Take tungsten tailings from a certain area in Jiangxi Province, and ball mill them to a particle size of less than 74μm (200 mesh). The ball mill speed is 480r / min, the ball milling time is 2.5h, and the material-to-ball ratio is 8:1. Then, roast and activate them at 600℃ for 2h to obtain activated mineral powder. S2: Prepare an inorganic-organic mixed acid solution, wherein the inorganic acid is 4 mol / L nitric acid and the organic acid is 0.15 mol / L oxalic acid. Add 10g of activated tailings powder at a liquid-to-solid ratio of 15:1. Perform ultrasonic oxidation leaching for 60 minutes with an ultrasonic power of 400W, and then stir the reaction in an 80℃ water bath for 2 hours. Filter the solution, and wash the acid-leached material (filter cake) with deionized water until neutral. The leaching rate of iron is 93.1% and the leaching rate of aluminum is 85.2% at this point. S3: Mix the acid leaching material with NaOH solid at a molar ratio of 1:2.2, place it in a corundum crucible, and calcine it in a muffle furnace at 420℃ for 3 hours to obtain the calcined product; S4: After cooling the calcined product, add water and stir. Soak in an 80°C water bath for 3 hours to dissolve. Filter to remove insoluble residues to obtain sodium silicate solution. S5: Add 3g of dispersant (NaCl) to the sodium silicate solution and adjust the pH in stages while stirring: first add hydrochloric acid dropwise at a rate of 5mL / min until pH=10.0, and keep warm for 40min to induce nucleation; then add hydrochloric acid dropwise at a rate of 1mL / min until pH=8.3 to control the uniform growth of silicate crystals; S6: After aging for 4 hours, the precipitate is filtered and repeatedly washed to remove Na. + and Cl - The silica was dried at 105°C and then calcined at 300°C for 1 hour to obtain amorphous silica.

[0049] Example 6 prepared amorphous silica with a purity of 99.7%, a whiteness of 96.3%, and no obvious agglomeration.

[0050] Example 7 includes the following steps: S1: Take tungsten tailings from a certain area in Jiangxi Province, and ball mill them to a particle size of less than 74μm (200 mesh). The ball mill speed is 300r / min, the ball milling time is 2h, and the material-to-ball ratio is 6:1. Then, roast and activate them at 800℃ for 1h to obtain activated mineral powder. S2: Prepare an inorganic-organic mixed acid solution, wherein the inorganic acid is 3 mol / L sulfuric acid and the organic acid is 0.05 mol / L citric acid. Add 10 g of activated tailings powder at a liquid-to-solid ratio of 5 mL: 1 g. Perform ultrasonic oxidation leaching for 15 min with an ultrasonic power of 225 W, and then stir and react in a 70℃ water bath for 3 h. Filter the solution, and wash the acid-leached material (filter cake) with deionized water until neutral. The leaching rate of iron was found to be 89.7% and the leaching rate of aluminum was 80.6% at this point. S3: Mix the acid leaching material with NaOH solid at a molar ratio of 1:3, place it in a corundum crucible, and calcine it in a muffle furnace at 500℃ for 2 hours to obtain the calcined product; S4: After cooling the calcined product, add water and stir. Soak in an 80°C water bath for 3 hours to dissolve. Filter to remove insoluble residues to obtain sodium silicate solution. S5: Add 1g of dispersant (NaCl) to the sodium silicate solution and adjust the pH in stages while stirring: first, add hydrochloric acid dropwise at a rate of 5mL / min until pH=10.0, and keep warm for 25min to induce nucleation; then add hydrochloric acid dropwise at a rate of 1mL / min until pH=8.9 to control the uniform growth of silicate crystals. S6: After aging for 2 hours, the precipitate is filtered and repeatedly washed to remove Na. + and Cl - The silica was dried at 105°C and then calcined at 350°C for 3 hours to obtain amorphous silica.

[0051] Example 7 prepared amorphous silica with a purity of 99.6%, a whiteness of 95.5%, and no obvious agglomeration.

[0052] Comparative Example 1 differs from Example 1 in that oxalic acid is not added in step 2; only 4 mol / L hydrochloric acid is used for leaching. The specific steps of Comparative Example 1 are as follows: S1: Take tungsten tailings from a certain area in Jiangxi Province, and ball mill them to a particle size of less than 74μm (200 mesh). The ball mill speed is 400r / min, the ball milling time is 2h, and the material-to-ball ratio is 6:1. Then, roast and activate them at 650℃ for 1.5h to obtain activated mineral powder. S2: Prepare an inorganic-organic mixed acid solution, wherein the inorganic acid is 4 mol / L hydrochloric acid. Add 10 g of activated tailings powder at a liquid-to-solid ratio of 10 mL: 1 g. Perform ultrasonic oxidation leaching for 15 min with an ultrasonic power of 300 W, and then stir and react in an 80℃ water bath for 3 h. Filter the solution, and wash the acid-leached material (filter cake) with deionized water until neutral. The leaching rate of iron was found to be 81.2% and the leaching rate of aluminum was 70.7% at this point. S3: Mix the acid leaching material with NaOH solid at a molar ratio of 1:2.5, place it in a corundum crucible, and calcine it in a muffle furnace at 400℃ for 2 hours to obtain the calcined product; S4: After cooling the calcined product, add water and stir. Soak in an 80°C water bath for 3 hours to dissolve. Filter to remove insoluble residues to obtain sodium silicate solution. S5: Add 1g of dispersant (NaCl) to the sodium silicate solution and adjust the pH in stages while stirring: first, add hydrochloric acid dropwise at a rate of 5mL / min until pH=10.0, and keep warm for 30min to induce nucleation; then add hydrochloric acid dropwise at a rate of 1mL / min until pH=8.5 to control the uniform growth of silicate crystals. S6: After aging for 2 hours, the precipitate is filtered and repeatedly washed to remove Na. + and Cl - The silica was dried at 105°C and then calcined at 300°C for 2 hours to obtain amorphous silica.

[0053] Comparative Example 1 prepared amorphous silica with a purity of 98.5% and a whiteness of 90.2%. It contained a small amount of Fe2O3 and Al2O3 impurity crystal peaks. The amorphous structure had low purity, and the product showed slight hard agglomeration, indistinct flocculent structure, uneven particle size distribution, and poor morphology controllability.

[0054] like Figure 3 As shown, the product prepared in Comparative Example 1 (without organic acid, leaching only with hydrochloric acid) exhibits multiple sharp small impurity crystal peaks interspersed within a broad diffraction peak at approximately 2Theta of 23° (see [reference]). Figure 3 The dashed box indicates that the diffraction peaks (marked as characteristic diffraction peaks of Fe2O3 and Al2O3) are less broadened than those in Example 1. This suggests that due to the lack of complexation and impurity removal by organic acids, impurities such as iron and aluminum were not completely removed, and the residual metal oxides exist in the product in crystalline form, resulting in a significant reduction in the purity of the amorphous structure. Therefore, this demonstrates that the complexation effect of organic acids in the steps of this invention achieves deep impurity removal, further improving the purity of amorphous silica.

[0055] like Figure 5 As shown in Figure B, the acid leaching material of Comparative Example 1 (leaching with only hydrochloric acid, no organic acid) is a yellowish-brown powder with localized fine lumps. Due to the lack of complexation by organic acid, iron and aluminum impurities were not completely removed. The residual iron oxides give the acid leaching material a yellowish-brown color, which is consistent with the Fe2O3 and Al2O3 impurity crystal peaks detected in the XRD pattern, indicating that the leaching effect of single inorganic acid is limited.

[0056] In Comparative Example 1 (pH adjusted after leaching without organic acid), the precipitate after step S5 was a milky yellow colloid with a small amount of yellowish-brown particles. The residual Fe2O3 and Al2O3 in the acid-leached material entered the precipitate along with the sodium silicate solution, causing the colloid to appear milky yellow. This corresponds perfectly with the measured "precipitate purity 98.5%, whiteness 89.2%" and the Fe2O3 and Al2O3 impurity peaks in the XRD pattern, demonstrating the impact of front-end impurity removal on the purity of the precipitate.

[0057] The product prepared in Comparative Example 1 is a light grayish-white powder with localized agglomeration and a darker color. Due to incomplete impurity removal at the front end, residual Al2O3 caused the product to appear grayish, which is consistent with the tested "purity 98.5% and whiteness 90.2%", highlighting the decisive role of the core process of this invention in product quality.

[0058] Comparative Example 2 differs from Example 1 in that ultrasound is not used in step 2; only water bath heating leaching is performed. The specific steps of Comparative Example 2 are as follows: S1: Take tungsten tailings from a certain area in Jiangxi Province, and ball mill them to a particle size of less than 74μm (200 mesh). The ball mill speed is 400r / min, the ball milling time is 2h, and the material-to-ball ratio is 6:1. Then, roast and activate them at 650℃ for 1.5h to obtain activated mineral powder. S2: Prepare an inorganic-organic mixed acid solution, wherein the inorganic acid is 4 mol / L hydrochloric acid and the organic acid is 0.1 mol / L oxalic acid. Add 10 g of activated tailings powder at a liquid-to-solid ratio of 10 mL: 1 g, and then stir and react in an 80℃ water bath for 3 h. Filter, and wash the acid-leached material (filter cake) with deionized water until neutral. After testing, the leaching rate of iron is 82.9% and the leaching rate of aluminum is 73.2%. S3: Mix the acid leaching material with NaOH solid at a molar ratio of 1:2.5, place it in a corundum crucible, and calcine it in a muffle furnace at 400℃ for 2 hours to obtain the calcined product; S4: After cooling the calcined product, add water and stir. Soak in an 80°C water bath for 3 hours to dissolve. Filter to remove insoluble residues to obtain sodium silicate solution. S5: Add 1g of dispersant (NaCl) to the sodium silicate solution and adjust the pH in stages while stirring: first, add hydrochloric acid dropwise at a rate of 5mL / min until pH=10.0, and keep warm for 30min to induce nucleation; then add hydrochloric acid dropwise at a rate of 1mL / min until pH=8.5 to control the uniform growth of silicate crystals. S6: After aging for 2 hours, the precipitate is filtered and repeatedly washed to remove Na. + and Cl - The silica was dried at 105°C and then calcined at 300°C for 2 hours to obtain amorphous silica.

[0059] The amorphous silica prepared in Comparative Example 2 had a purity of 98.6% and a whiteness of 91.4%, and the integrity of the amorphous structure was generally poor. The product showed moderate agglomeration, with local hard agglomerated particles, uneven particle size distribution, and poor morphology controllability.

[0060] like Figure 4As shown, the product prepared in Comparative Example 2 (without ultrasonic external field enhancement, only water bath leaching) still exhibits a broad diffraction peak at around 2Theta 23°, characteristic of amorphous silica. However, the broad diffraction peak contains trace amounts of feldspar, quartz crystal-type impurity peaks, and a small amount of Fe2O3 impurity crystal peaks (see...). Figure 4 The dashed box indicates that due to the lack of ultrasonic cavitation effect, the surface layer and crystal structure of tungsten tailings cannot be effectively destroyed. Impurities encased in the crystal lattice, as well as small amounts of unreacted feldspar and quartz residue, cannot be completely removed, leading to a decrease in the integrity of the amorphous structure of the product and an increase in impurity residue. Therefore, this fully demonstrates that ultrasonic field enhancement effectively promotes mineral lattice destruction and impurity release, achieving deep impurity removal.

[0061] like Figure 5 As shown in Figure C, the acid leaching material of Comparative Example 2 (without ultrasound, only water bath leaching) is a grayish-white powder with a small amount of light gray particles. Due to the lack of ultrasonic cavitation effect, the mineral surface layer was not effectively destroyed, and some impurities encased in the crystal lattice were not released, resulting in a small amount of feldspar and quartz particles remaining in the acid leaching material. This is consistent with the trace feldspar impurity peaks detected in the XRD pattern, further proving the important role of ultrasonic field enhancement in impurity removal.

[0062] In Comparative Example 2 (pH adjusted after ultrasonic leaching), the precipitate after step S5 was a grayish-white colloid with localized fine gray particles. Due to residual feldspar in the acid-leached material, these particles mixed into the precipitate, forming discolored particles. This is consistent with the measured "precipitate purity 98.6%, whiteness 90.5%" and the feldspar impurity peaks in the XRD pattern, further demonstrating the indirect influence of ultrasound on the subsequent precipitation quality.

[0063] Comparative Example 3 differs from Example 1 in that hydrochloric acid is not used in step 2; only oxalic acid is used for leaching. The specific steps of Comparative Example 3 are as follows: S1: Take tungsten tailings from a certain area in Jiangxi Province, and ball mill them to a particle size of less than 74μm (200 mesh). The ball mill speed is 400r / min, the ball milling time is 2h, and the material-to-ball ratio is 6:1. Then, roast and activate them at 650℃ for 1.5h to obtain activated mineral powder. S2: Prepare a 0.1 mol / L oxalic acid solution, add 10 g of activated tailings powder at a liquid-to-solid ratio of 10 mL: 1 g, and then stir and react in an 80℃ water bath for 3 h; filter, wash the acid-leached material (filter cake) with deionized water until neutral, and test it. At this time, the leaching rate of iron is 35.6% and the leaching rate of aluminum is 28.9%; S3: Mix the acid leaching material with NaOH solid at a molar ratio of 1:2.5, place it in a corundum crucible, and calcine it in a muffle furnace at 400℃ for 2 hours to obtain the calcined product; S4: After cooling the calcined product, add water and stir. Soak in an 80°C water bath for 3 hours to dissolve. Filter to remove insoluble residues to obtain sodium silicate solution. S5: Add 1g of dispersant (NaCl) to the sodium silicate solution and adjust the pH in stages while stirring: first, add hydrochloric acid dropwise at a rate of 5mL / min until pH=10.0, and keep warm for 30min to induce nucleation; then add hydrochloric acid dropwise at a rate of 1mL / min until pH=8.5 to control the uniform growth of silicate crystals. S6: After aging for 2 hours, the precipitate is filtered and repeatedly washed to remove Na. + and Cl - The silica was dried at 105°C and then calcined at 300°C for 2 hours to obtain amorphous silica.

[0064] The amorphous silica prepared in Comparative Example 3 had a purity of 94.1% and a whiteness of 82.4%. It contained a large number of Fe2O3, Al2O3, and feldspar impurity crystal peaks, and the amorphous structure was destroyed. The product showed severe hard agglomeration, forming large blocky particles without flocculent structure. The particle size distribution was extremely uneven, and the morphology was completely uncontrollable.

[0065] like Figure 5 As shown in Figure D, the acid leaching material of Comparative Example 3 (leaching with only oxalic acid and no inorganic acid) appears as a yellowish-brown, blocky agglomerate with a hard texture. Due to the lack of H⁺ from inorganic acids to dissolve metal oxides, only a small amount of impurities such as iron and aluminum dissolve. The large amount of impurities remaining keeps the acid leaching material yellowish-brown, and the unreacted mineral particles agglomerate together, consistent with the detected low leaching rate (35.6% iron, 28.9% aluminum) and severe agglomeration.

[0066] In Comparative Example 3 (no inorganic acid, only oxalic acid leaching followed by pH adjustment), the precipitate after step S5 was a yellowish-brown turbid colloid with lumpy precipitate at the bottom. Due to the large amount of Fe2O3, Al2O3, and feldspar remaining in the acid-leached material, these substances entered the precipitate with the solution, causing the colloid to become turbid and agglomerate. This corresponds to the test results of "precipitate purity 95.2%" and "severe hard agglomeration," demonstrating the destructive impact of incomplete front-end impurity removal on the final precipitate.

[0067] The difference between Comparative Example 4 and Example 1 is that the pH value in step 5 is directly adjusted to 8.5 without segmented adjustment. The specific steps of Comparative Example 4 are as follows: S1: Take tungsten tailings from a certain area in Jiangxi Province, and ball mill them to a particle size of less than 74μm (200 mesh). The ball mill speed is 400r / min, the ball milling time is 2h, and the material-to-ball ratio is 6:1. Then, roast and activate them at 650℃ for 1.5h to obtain activated mineral powder. S2: Prepare an inorganic-organic mixed acid solution, wherein the inorganic acid is 4 mol / L hydrochloric acid and the organic acid is 0.1 mol / L oxalic acid. Add 10 g of activated tailings powder at a liquid-to-solid ratio of 10 mL: 1 g. Perform ultrasonic oxidation leaching for 15 min with an ultrasonic power of 300 W, and then stir and react in an 80℃ water bath for 3 h. Filter the solution, and wash the acid-leached material (filter cake) with deionized water until neutral. The leaching rate of iron was 91.8% and the leaching rate of aluminum was 82.5% at this point. S3: Mix the acid leaching material with NaOH solid at a molar ratio of 1:2.5, place it in a corundum crucible, and calcine it in a muffle furnace at 400℃ for 2 hours to obtain the calcined product; S4: After cooling the calcined product, add water and stir. Immerse in an 80°C water bath for 3 hours. Filter to remove insoluble residues to obtain sodium silicate solution. S5: Add 1g of dispersant (NaCl) to the sodium silicate solution, and adjust the pH to 8.5 by adding hydrochloric acid dropwise at a rate of 5mL / min while stirring. S6: After aging for 2 hours, the precipitate is filtered and repeatedly washed to remove Na. + and Cl - The silica was dried at 105°C and then calcined at 300°C for 2 hours to obtain amorphous silica.

[0068] Comparative Example 4 prepared amorphous silica with a purity of 99.1% and a whiteness of 93.6%. The product showed severe hard agglomeration, and the original loose flocculent structure completely disappeared, forming a dense block agglomerate.

[0069] The final product of Comparative Example 4 was a white, blocky agglomerate that required grinding to disperse, with some localized fine clumps. Because the pH adjustment stage was not segmented, the hard agglomerates formed during the precipitation stage could not be eliminated after calcination, resulting in severe product agglomeration, consistent with the test data indicating "severe hard agglomeration." Although the purity reached 99.1%, the morphology did not meet application requirements, highlighting the crucial impact of segmented pH control on the practicality of the final product.

[0070] Comparative Example 5 differs from Example 1 in that step 3 uses an 85°C water bath for heating and is not an alkali fusion reaction. The specific steps of Comparative Example 5 are as follows: S1: Take tungsten tailings from a certain area in Jiangxi Province, and ball mill them to a particle size of less than 74μm (200 mesh). The ball mill speed is 400r / min, the ball milling time is 2h, and the material-to-ball ratio is 6:1. Then, roast and activate them at 650℃ for 1.5h to obtain activated mineral powder. S2: Prepare an inorganic-organic mixed acid solution, wherein the inorganic acid is 4 mol / L hydrochloric acid and the organic acid is 0.1 mol / L oxalic acid. Add 10 g of activated tailings powder at a liquid-to-solid ratio of 10 mL: 1 g. Perform ultrasonic oxidation leaching for 15 min with an ultrasonic power of 300 W, and then stir and react in an 80℃ water bath for 3 h. Filter the solution, and wash the acid-leached material (filter cake) with deionized water until neutral. The leaching rate of iron was 91.8% and the leaching rate of aluminum was 82.5% at this point. S3: Mix the acid pickling material with NaOH solid at a molar ratio of 1:2.5, put it into a beaker, add 100mL of deionized water, react in a water bath at 85℃ for 2h, and filter to obtain sodium silicate solution; S4: Add 1g of dispersant (NaCl) to the sodium silicate solution and adjust the pH in stages while stirring: first, add hydrochloric acid dropwise at a rate of 5mL / min until pH=10.0, and keep warm for 30min to induce nucleation; then add hydrochloric acid dropwise at a rate of 1mL / min until pH=8.5 to control the uniform growth of silicate crystals. S5: After aging for 2 hours, the precipitate is filtered and repeatedly washed to remove Na. + and Cl - The silica was dried at 105°C and then calcined at 300°C for 2 hours to obtain amorphous silica.

[0071] Comparative Example 5 prepared amorphous silica with a purity of 96.8% and a whiteness of 88.7%. The product showed moderate hard agglomeration, incomplete flocculent structure, uneven particle size distribution, and poor morphological controllability. The silicon conversion efficiency was only 31.3%, with a large amount of quartz and feldspar not being converted, resulting in an extremely low product yield. The amorphous structure also had low purity.

[0072] In Comparative Example 5 (non-molten reaction, no molten salt roasting), the precipitate after step S5 was a light gray, sparse precipitate, small in quantity and unevenly settled. Because NaOH cannot form a molten salt phase in the non-molten state at 75℃, the silicon conversion efficiency was only 31.3%, the sodium silicate solution concentration was low, and the amount of precipitate formed was small. Furthermore, unconverted feldspar and quartz residues were mixed into the precipitate, resulting in a grayish color, corresponding to the detected low purity (96.8%) and low yield.

[0073] Comparative Example 6 differs from Example 1 in that step 3 employs a high-temperature alkali fusion method. The specific steps of Comparative Example 6 are as follows: S1: Take tungsten tailings from a certain area in Jiangxi Province, and ball mill them to a particle size of less than 74μm (200 mesh). The ball mill speed is 400r / min, the ball milling time is 2h, and the material-to-ball ratio is 6:1. Then, roast and activate them at 650℃ for 1.5h to obtain activated mineral powder. S2: Prepare an inorganic-organic mixed acid solution, wherein the inorganic acid is 4 mol / L hydrochloric acid and the organic acid is 0.1 mol / L oxalic acid. Add 10g of activated tailings powder at a liquid-to-solid ratio of 10:1. Perform ultrasonic oxidation leaching for 15 minutes with an ultrasonic power of 300W, and then stir the reaction in an 80℃ water bath for 3 hours. Filter the solution, and wash the acid-leached material (filter cake) with deionized water until neutral. The leaching rate of iron is 91.8% and the leaching rate of aluminum is 82.5% at this point. S3: Mix the acid-etched material with Na2CO3 solid at a molar ratio of 1:2.5, place it in a corundum crucible, and calcine it in a muffle furnace at 1000℃ for 2 hours to obtain the calcined product; S4: After cooling the calcined product, add water and stir. Immerse in an 80°C water bath for 3 hours. Filter to remove insoluble residues to obtain sodium silicate solution. S5: Add 1g of dispersant (NaCl) to the sodium silicate solution and adjust the pH in stages while stirring: first, add hydrochloric acid dropwise at a rate of 5mL / min until pH=10.0, and keep warm for 30min to induce nucleation; then add hydrochloric acid dropwise at a rate of 1mL / min until pH=8.5 to control the uniform growth of silicate crystals. S6: After aging for 2 hours, the precipitate is filtered and repeatedly washed to remove Na. + and Cl - The silica was dried at 105°C and then calcined at 300°C for 2 hours to obtain amorphous silica.

[0074] Comparative Example 6 prepared amorphous silica with a purity of 98.3% and a whiteness of 87.5%. It contained Fe2O3, Al2O3, and impurity crystal peaks, and the amorphous structure had low purity. The energy consumption of this process increased compared to Example 1, the equipment corrosion rate increased, and iron, aluminum and silicon formed a eutectic at high temperature, which caused impurities to dissolve with silicon, resulting in a decrease in product purity.

[0075] Comparative Example 6 (conventional high-temperature alkali fusion, calcination at 1100℃): The precipitate after step S5 was a milky yellow colloidal substance with uneven color and fine impurity particles. Because iron, aluminum, and silicon form a eutectic at high temperature, impurities dissolve with the silicon and enter the sodium silicate solution, resulting in residual Fe2O3 and Al2O3 impurities in the precipitate, giving it a yellowish color, consistent with the results for low purity (98.3%).

Claims

1. A method for preparing amorphous silica using tungsten tailings, characterized in that, Includes the following steps: Step S1: Crush and grind the tungsten tailings, mechanically activate them, and then roast them to obtain activated mineral powder; Step S2: Prepare an inorganic-organic mixed acid solution, add activated mineral powder to the mixed acid solution, carry out an external field enhanced ultrasonic heating leaching reaction, and then heat in a water bath under stirring. After the reaction is completed, filter and separate to obtain acid leaching material and filtrate containing impurities. Step S3: Mix the acid-leaching material with NaOH and carry out a molten salt roasting reaction to obtain the roasted product; Step S4: Dissolve the calcined product in water, stir, leach in a water bath, filter to remove insoluble residue, and obtain sodium silicate solution; Step S5: Add sodium chloride as a dispersant to the sodium silicate solution, then add hydrochloric acid, adjust the pH value in two stages, and after aging, filtering, washing and drying the precipitate, obtain the amorphous silica precursor. Step S6: Calcine the amorphous silica precursor to obtain amorphous silica.

2. The method for preparing amorphous silica from tungsten tailings according to claim 1, characterized in that, In step S1, the tungsten tailings are tungsten tailings after gravity separation, with a SiO2 mass fraction of 60%-80%, containing lattice-encapsulated Fe2O3 and Al2O3 impurities, a WO3 residue of 0.01%-0.1%, and containing insoluble silicate feldspar minerals such as KAlSi3O8, NaAlSi3O8, and CaAl2Si2O8.

3. The method for preparing amorphous silica from tungsten tailings according to claim 1, characterized in that, In step S1, the mechanical activation is performed using a planetary ball mill with a ball milling speed of 300 r / min-500 r / min, a ball-to-material ratio of 6:1-8:1, and a mechanical activation time of 2 h-4 h, until the particle size is less than 74 μm.

4. The method for preparing amorphous silica from tungsten tailings according to claim 1, characterized in that, In step S1, the calcination activation temperature is 600℃-800℃, and the calcination activation time is 1h-3h.

5. The method for preparing amorphous silica from tungsten tailings according to claim 1, characterized in that, In step S2, the inorganic-organic mixed acid solution contains at least one inorganic acid selected from hydrochloric acid, sulfuric acid, and nitric acid, and at least one organic acid selected from oxalic acid, citric acid, and EDTA. The inorganic acid concentration is 3 mol / L-5 mol / L, and the organic acid concentration is 0.05 mol / L-0.15 mol / L. The liquid-to-solid ratio of the inorganic-organic mixed acid solution to the activated mineral powder is 5 mL-15 mL:1 g.

6. The method for preparing amorphous silica from tungsten tailings according to claim 1, characterized in that, In step S2, the parameters for the external field enhanced ultrasonic heating leaching reaction are: ultrasonic power 200W-400W, ultrasonic time 15min-60min, and heating temperature 50℃-90℃; the parameters for water bath heating are: heating temperature 60℃-90℃, rotation speed 100r / min-150r / min, and heating time 2h-3h.

7. The method for preparing amorphous silica from tungsten tailings according to claim 1, characterized in that, In step S3, the molar ratio of acid leaching material to NaOH is 1:2-1:3; the molten salt roasting temperature is 400℃-500℃, and the roasting time is 2h-3h.

8. The method for preparing amorphous silica from tungsten tailings according to claim 1, characterized in that, In step S5, the mass ratio of tungsten tailings to sodium chloride is 10:1 to 10:

3.

9. The method for preparing amorphous silica from tungsten tailings according to claim 1, characterized in that, In step S5, the pH value is adjusted in two stages: first, acid solution is added dropwise at a rate of 5 mL / min until pH=9.5-10.5 and kept warm for 20 min-45 min; then, acid solution is added dropwise at a rate of 1 mL / min until pH=8-9.

10. The method for preparing amorphous silica from tungsten tailings according to claim 1, characterized in that, In step S6, the calcination temperature is 300℃-500℃ and the calcination time is 1h-3h.

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