Method for extracting silicon dioxide from red mud

Abstract

The invention relates to the technical field of resource utilization, in particular to a method for extracting silicon dioxide from red mud, which comprises the following steps: 1) calcining original red mud to obtain calcined red mud; 2) carrying out waste sulfuric acid leaching on the calcined red mud to obtain primary acid leaching liquid and primary acid leaching residues; (3) the primary acid leaching residues are subjected to waste hydrochloric acid leaching, and secondary acid leaching liquid and secondary acid leaching residues are obtained; (4) carrying out neutralization and precipitation treatment on the primary acid leaching solution and the secondary acid leaching solution by adopting a sodium carbonate solution to obtain a precipitate and CO2; and (5) fully dissolving the secondary acid leaching residues by using a sodium hydroxide solution, separating out a dissolving solution, filling CO2 into the dissolving solution, filtering, and washing and drying the precipitate, thereby obtaining the secondary acid leaching residues. According to the method for extracting the silicon dioxide from the red mud, through calcination pretreatment, crystal water removal and aluminum-silicon symbiotic structure weakening, the bubbling problem of the red mud in the acid leaching process is effectively inhibited, meanwhile, separation of iron, aluminum and silicon is promoted, and the purity of a subsequent silicon extraction product is improved.

Description

Technical Field

[0001] This invention relates to the field of resource utilization technology, and in particular to a method for extracting silica from red mud. Background Technology

[0002] Red mud is a large quantity of industrial solid waste discharged during alumina production. It is characterized by its strong alkalinity, complex composition, and large stockpile size. Red mud typically contains multiple components such as Fe2O3, Al2O3, SiO2, CaO, and TiO2, with a silica content generally ranging from 15% to 25%, and thus possesses potential resource value.

[0003] Existing red mud treatment technologies mostly focus on the recovery of metal components such as iron and aluminum. Silica usually exists as inert residue, making further utilization difficult. Conventional acid leaching methods have the following shortcomings: 1. Residual alkaline substances in red mud easily react violently with acid during acid leaching, generating a large amount of gas and foam, leading to severe foaming of the system and affecting reaction safety and operational stability; 2. Aluminum and silicon components in red mud often exist in a symbiotic or encapsulated state, making it difficult to effectively separate aluminum and silicon under conventional acid leaching conditions. This results in insufficient aluminum leaching and aluminum impurities in the silica in the tailings, affecting the purity of subsequent silicon extraction; the silica in the tailings after acid leaching has a stable structure and low activity, making direct utilization of it low; 3. Some processes require the introduction of additional high-purity chemicals or external carbon dioxide, increasing treatment costs.

[0004] Therefore, developing a process that can suppress acid leaching foaming, synergistically utilize industrial waste acid and react to generate carbon dioxide, and achieve efficient recovery of silica from red mud is of great significance for the reduction and resource utilization of red mud. Summary of the Invention

[0005] To address the above problems, this invention provides a method for extracting silica from red mud, comprising the following steps: 1) Red mud pretreatment The original red mud was calcined to obtain calcined red mud. 2) One-time acid leaching The calcined red mud obtained in step 1) is leached with waste sulfuric acid to obtain a primary acid leaching solution and a primary acid leaching residue. 3) Secondary acid leaching The primary acid leaching residue obtained in step 2) is leached with waste hydrochloric acid to obtain secondary acid leaching solution and secondary acid leaching residue; 4) Neutralize and precipitate the acid leaching solution The primary acid leaching solution obtained in step 2) and the secondary acid leaching solution obtained in step 3) are neutralized and precipitated using sodium carbonate solution to obtain precipitate and CO2. 5) Silicon extraction The secondary acid leaching residue obtained in step 3) is fully dissolved in sodium hydroxide solution, the solution is separated, and then CO2 obtained in step 4) is introduced into the solution. After filtration, the precipitate is washed and dried to obtain the silicon dioxide product.

[0006] The main components and contents of the red mud raw material used in this invention are as follows: Al2O3 22.9%, Fe2O3 21.83%, Na2O 10.77%, SiO2 17.02%, CaO 1.32%, TiO2 4.81%. Before calcination, it is ball-milled to select particles with a D90 of less than 100 μm. The specific chemical agents used in each step are as follows: waste sulfuric acid with a mass concentration of 22.9%; waste hydrochloric acid with a mass concentration of 34.6%; sodium carbonate solution with a concentration of 2.5 mol / L; and sodium hydroxide solution with a mass fraction of 33.25%.

[0007] Specifically, in step 1), the ball-milled raw red mud is placed in a muffle furnace and calcined at 500℃~600℃ for 40~80 minutes, then cooled for later use. The purpose of calcination in the muffle furnace is to decompose the insoluble carbonates (such as calcium carbonate, sodium carbonate, etc.) and some hydroxides in the red mud at high temperature, while destroying the original dense structure of the red mud, changing the bonding state of metal oxides such as aluminum and iron with silicon dioxide, destroying the aluminum-silicon symbiotic structure, separating the aluminum and silicon phases, improving the leaching efficiency of metal ions in the subsequent acid leaching process, and reducing the phenomenon of a large amount of foam generated by the reaction of carbonates and acids during acid leaching. Calcination can also remove volatile impurities such as organic matter in the red mud, further optimizing the physicochemical properties of the red mud, and creating favorable conditions for the subsequent acid leaching and silicon extraction processes.

[0008] Specifically, in step 2), the weight ratio of calcined red mud to waste sulfuric acid is 1:(3~7), the leaching temperature is 85℃~95℃, and the leaching time is 3~4h. The single acid leaching process can fully dissolve iron and some free aluminum from the red mud. After the reaction, pressure filtration is performed, and the resulting primary acid leaching solution is used for subsequent iron and aluminum recovery. The primary acid leaching residue is washed with hot water until the pH of the effluent is 6, and the washing solution is recycled.

[0009] Specifically, in step 3), the amount of waste hydrochloric acid used is 2 to 4 times the weight of the calcined red mud obtained in step 1), the leaching temperature is 85℃ to 95℃, and the leaching time is 2 to 4 hours. The secondary acid leaching process fully dissolves the aluminum element, and the resulting secondary acid leaching solution is used for subsequent aluminum element recovery. The secondary acid leaching residue is rich in silicon element. The secondary acid leaching residue is washed until the pH of the effluent is 6, and the washing solution is recycled.

[0010] The purpose of the two acid leaching processes is to achieve efficient separation of metal and silicon elements in red mud through stepwise leaching with waste sulfuric acid and waste hydrochloric acid. First, waste sulfuric acid preferentially leaches iron and some free aluminum, creating conditions for subsequent deep leaching of aluminum. Then, waste hydrochloric acid is used for a second leaching of the primary acid leaching residue, fully dissolving the remaining aluminum. This allows most metal impurities to enter the solution phase and be removed, while silicon mainly remains in the secondary acid leaching residue, laying a solid foundation for the subsequent extraction of high-purity silica. Furthermore, using industrial waste acid as the leaching agent not only reduces processing costs but also facilitates waste recycling, aligning with the concept of green and environmentally friendly development.

[0011] Specifically, in step 4), the neutralization and precipitation treatment of the primary or secondary acid leaching solution is as follows: the acid leaching solution is diluted with water washing solution at a mass ratio of (1.5~2):1, sodium carbonate solution is slowly added dropwise at 65°C, the pH is adjusted to 7.0, the temperature is maintained at 60°C~70°C, and the solution is slowly stirred and aged for 0.5~1h before filtration. The resulting filter cake is an iron-aluminum composite hydroxide precipitate, and the filtrate enters the subsequent sodium carbonate extraction or recycling process.

[0012] Specifically, in step 5), the solid-liquid ratio of sodium hydroxide solution and secondary leaching residue is 1:(4~6), the dissolution temperature is 85℃~95℃, and the dissolution time is 2~4h; when CO2 is introduced, the temperature of the solution is 50℃~70℃, and the introduction of CO2 is stopped when the pH of the solution is 7.8~8.5.

[0013] Steps 4) and 5) are crucial, closely linked steps, with the core being the efficient enrichment and conversion of silicon. In step 5), the silicon in the secondary acid leaching residue mainly exists in the form of silicon dioxide and silicates. By adding a 33.25% sodium hydroxide solution and stirring at 85℃~95℃ for 2~4 hours, the silicon reacts with the sodium hydroxide to form water-soluble sodium silicate (Na₂SiO₃), which then enters the solution, achieving the initial separation of silicon from other insoluble residues. The separated solution mainly consists of sodium silicate. At this point, CO₂ generated during the precipitation process in step 4) is introduced, and at 50℃~70℃, CO₂ reacts with the sodium silicate solution. With the continuous introduction of CO₂, the silicate ions (SiO₃) in the solution... 2-The silica reacts with CO2 and water to form silicic acid (H2SiO3) precipitate. When the pH of the solution drops to 7.8-8.5, CO2 addition is stopped, at which point the silicic acid precipitation reaction is nearing completion. The resulting silicic acid precipitate is filtered and separated, then thoroughly washed with deionized water to remove impurities such as sodium ions adhering to the precipitate surface. Finally, the washed precipitate is dried to obtain a high-purity silica product. This process cleverly utilizes the CO2 generated from the neutralization precipitation as a precipitant, not only achieving internal resource recycling and reducing the consumption of additional reagents, but also effectively avoiding the introduction of new impurities, further ensuring the purity of the silica product.

[0014] The technical effects of this invention are as follows: 1. This invention provides a method for extracting silicon dioxide from red mud. Through calcination pretreatment, the water of crystallization is removed and the aluminum-silicon symbiotic structure is weakened, effectively suppressing the foaming problem of red mud during acid leaching, while promoting the separation of iron, aluminum and silicon, and improving the purity of the subsequent silicon-extracted product; 2. This invention provides a method for extracting silicon dioxide from red mud, using waste sulfuric acid as a leaching agent to realize the resource utilization of industrial waste acid and reduce treatment costs; 3. This invention provides a method for extracting silicon dioxide from red mud, using the carbon dioxide generated in situ during the neutralization and precipitation of iron and aluminum by sodium carbonate to precipitate silicon, without the need for external carbon dioxide, realizing the internal circulation of gas resources; 4. This invention provides a method for extracting silicon dioxide from red mud, further extracting silicon dioxide after removing iron and aluminum, significantly reducing the amount of final tailings and improving the overall resource utilization level of red mud; 5. This invention provides a method for extracting silicon dioxide from red mud with a simple process flow and high coupling degree, suitable for laboratory scale-up and industrial application. Attached Figure Description

[0015] Figure 1 This is a SEM image of the silica-rich tailings obtained in Example 1 of the present invention; Figure 2 for Figure 1 Elemental distribution map at EDS Spot 1; Figure 3 for Figure 1 Elemental distribution map at EDS Spot 2; Figure 4 for Figure 1 Elemental distribution map at EDS Spot 3; Figure 5 for Figure 1 Elemental distribution map at EDS Spot 4; Figure 6 for Figure 1 Elemental distribution map at EDS Spot 5; Figure 7 for Figure 1Elemental distribution at EDS Spot 6; Figure 8 This is a SEM image of the silica-rich tailings obtained in Example 2 of the present invention; Figure 9 This is a SEM image of the silica-rich tailings obtained in Example 3 of the present invention; Figure 10 for Figure 9 Elemental distribution map at EDS Spot 1; Figure 11 for Figure 9 Elemental distribution map at EDS Spot 2; Figure 12 for Figure 9 Elemental distribution map at EDS Spot 3; Figure 13 for Figure 9 Elemental distribution map at EDS Spot 4; Figure 14 for Figure 9 Elemental distribution map at EDS Spot 5; Figure 15 for Figure 9 Elemental distribution map at EDS Spot 6. Detailed Implementation

[0016] The present invention will be described below with reference to examples. These examples are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0017] I. Raw Materials and Equipment 1. Calcination treatment of raw red mud. The raw red mud was ball-milled until D90 was less than 100μm, then placed in a muffle furnace and calcined at 500~600℃ for 40~80min. After cooling, it was ready for use to obtain calcined red mud.

[0018] 2. Chemical agents used ① Industrial-grade waste sulfuric acid, mass concentration 22.9%, corresponding to a molar concentration of 3.07 mol / L; ② Industrial-grade waste hydrochloric acid, with a mass concentration of 34.6% and a corresponding molar concentration of 10.74 mol / L; ③ Industrial grade sodium hydroxide solution, mass fraction 33.25%, diluted to 6 mol / L with alkali solution to water at a mass ratio of 721.8:497.8; ④ Industrial grade sodium carbonate: purity ≥ 98%, prepared into a 2.5 mol / L solution.

[0019] 3. Equipment Commercially available ball mills, muffle furnaces, constant temperature water bath reactors, filter presses, pH meters, and vacuum filtration devices.

[0020] II. Examples of Silica Extraction A method for extracting silica from red mud includes the following steps: Step 1: Based on 6 kg of calcined red mud corresponding to 30 kg of waste sulfuric acid, add the waste sulfuric acid to the reactor, start stirring and heat to 60°C, then add the red mud powder, continue heating and adjust the stirring speed, so that the system reacts at 85°C~95°C for 3.5 h to fully dissolve the iron and free aluminum components in the red mud; after the reaction, perform pressure filtration to separate the primary acid leaching solution and the primary acid leaching residue. The primary acid leaching solution is used for subsequent iron and aluminum recovery processes, and the primary acid leaching residue is washed with hot water until the pH of the effluent is 6, and the washing liquid is recycled.

[0021] Step 2: Based on the 6 kg of calcined red mud used in Step 1 corresponding to 18 kg of waste hydrochloric acid, the waste hydrochloric acid is added to the reactor, heated to 60°C, and then the primary acid leaching residue is added. The temperature is raised and stirred to 80°C~90°C for 3 hours to allow the aluminum components to fully dissolve. After the reaction is completed, the mixture is separated by pressure filtration to obtain secondary acid leaching solution and secondary acid leaching residue. The secondary acid leaching solution is used for subsequent aluminum recovery. The secondary acid leaching residue is washed until the pH is 6, which is a silica-rich tailings.

[0022] Step 3: Dilute the primary acid leaching solution with water washing solution at a mass ratio of 2:1. Slowly add sodium carbonate solution at 65℃ to directly adjust the pH of the system to 7, causing the iron and aluminum components to precipitate simultaneously as hydroxides. CO2 gas is generated and released during the addition process. Control the liquid level to avoid splashing. Maintain the temperature at 60℃~70℃ and slowly stir and age for 0.5~1 hours before filtration. The resulting filter cake is an iron-aluminum composite hydroxide precipitate. The filtrate enters the subsequent sodium carbonate extraction or recycling process. The CO2 generated during the reaction is collected for later use. Dilute the secondary acid leaching solution with water washing solution at a mass ratio of 1.5:1. Slowly add sodium carbonate solution at 65℃ to directly adjust the pH of the system to 7, causing the iron and aluminum components to precipitate simultaneously as hydroxides. CO2 is released during the reaction. Maintain the temperature at 60℃~70℃ and stir and age for 0.5~1 hours before filtration. The resulting filter cake is an iron-aluminum composite hydroxide precipitate. The filtrate can enter the subsequent sodium carbonate extraction or recycling process.

[0023] Step 4: Mix the silica-rich tailings obtained in Step 2 with sodium hydroxide solution at a solid-liquid ratio of 1:(4~6), and stir the mixture at 85~95℃ for 2~4 hours to convert silica into soluble sodium silicate. After the reaction is complete, filter the mixture to obtain a sodium silicate solution. Then, pass the CO2 generated and collected in Step 3 into the sodium silicate solution and carry out a precipitation reaction at 50℃~70℃. Control the final pH to 7.8~8.5 to generate silica precipitate. Aging, filtering, washing and drying the resulting slurry will yield the silica product.

[0024] In this method, the filtrate obtained after silica precipitation is evaporated and concentrated at a temperature of 50℃~80℃ and then filtered. The filtrate mainly contains sodium carbonate, sodium bicarbonate and a small amount of soluble salts, which can be reused in the iron and aluminum neutralization precipitation process in step 3; or the filtrate containing sodium bicarbonate can be heated and decomposed to convert it into sodium carbonate and release CO2, which can be used in the silica extraction process in step 4 to achieve the recycling of sodium carbonate and CO2.

[0025] Example 1: Silica was extracted from red mud using the above method. The specific process parameters for each step were controlled as follows: Step 1: Mix calcined red mud and waste sulfuric acid at a mass ratio of 1:5, react at 85℃ for 3.5 hours, and remove a total of 1287.5g of iron and aluminum. Step 2: Mix the primary acid leaching residue and hydrochloric acid at a mass ratio of 1:3, react at 80℃ for 3 hours, and remove a total mass of 1091.2g of iron and aluminum. Step 3: The primary acid leaching solution and water are diluted at a mass ratio of 2:1, the reaction temperature is 60℃, and the reaction time is 0.5h to obtain an iron-aluminum composite hydroxide precipitate with a mass of 1365.8g; the secondary acid leaching solution and water are diluted at a mass ratio of 1.5:1, the reaction temperature is 60℃, and the reaction time is 0.5h to obtain an iron-aluminum composite hydroxide precipitate with a mass of 1121.5g. Step 4: Mix the silica-rich tailings with sodium hydroxide at a solid-liquid ratio of 1:4, react at 85℃ for 2 hours to obtain tailings with a mass of 932.2g; after passing CO2 into the sodium silicate solution at 50℃, silica precipitate with a mass of 930.5g is obtained.

[0026] Example 2: Silica was extracted from red mud using the above method. The specific process parameters for each step were controlled as follows: Step 1: Mix calcined red mud and waste sulfuric acid at a mass ratio of 1:5, react at 90℃ for 3.5 hours, and remove a total of 1370.5g of iron and aluminum. Step 2: Mix the primary acid leaching residue and hydrochloric acid at a mass ratio of 1:3, react at 85℃ for 3 hours, and remove a total mass of 1148.7g of iron and aluminum. Step 3: The first acid leaching solution and water are diluted at a mass ratio of 2:1, the reaction temperature is 65℃, and the reaction time is 1h to obtain an iron-aluminum composite hydroxide precipitate with a mass of 1416.3g; the second acid leaching solution and water are diluted at a mass ratio of 1.5:1, the reaction temperature is 65℃, and the reaction time is 1h to obtain an iron-aluminum composite hydroxide precipitate with a mass of 1170.2g. Step 4: Mix the silica-rich tailings with sodium hydroxide at a solid-liquid ratio of 1:4, react at 95℃ for 4 hours to obtain tailings with a mass of 1010.8g; after passing CO2 into the sodium silicate solution at 60℃, silica precipitate with a mass of 964.0g is obtained.

[0027] Example 3: Silica was extracted from red mud using the above method. The specific process parameters for each step were controlled as follows: Step 1: Calcinated red mud and waste sulfuric acid are mixed in a mass ratio of 1:5, the reaction temperature is 95℃, the reaction time is 3.5h, and the total mass of iron and aluminum removed is 1465.9g. Step 2: Mix the primary acid leaching residue and hydrochloric acid at a mass ratio of 1:3, react at 90℃ for 3 hours, and remove a total mass of 1204.9g of iron and aluminum. Step 3: The first acid leaching solution and water are diluted at a mass ratio of 2:1, the reaction temperature is 70℃, and the reaction time is 1h to obtain an iron-aluminum composite hydroxide precipitate with a mass of 1452.4g; the second acid leaching solution and water are diluted at a mass ratio of 1.5:1, the reaction temperature is 70℃, and the reaction time is 1h to obtain an iron-aluminum composite hydroxide precipitate with a mass of 1205.1g. Step 4: Mix the silica-rich tailings with sodium hydroxide at a solid-liquid ratio of 1:6, react at 95℃ for 4 hours to obtain tailings with a mass of 1016.9g; after passing CO2 into the sodium silicate solution at 70℃, silica precipitate with a mass of 999.4g is obtained.

[0028] The differences in process parameters between Examples 1 and 3 show that processing temperature and processing time are crucial indicators determining yield. As temperature increases and reaction time extends, the removal efficiency of impurities such as iron and aluminum gradually improves, and the precipitated silica mass also increases accordingly. For example, in Example 3, the reaction temperature in step 1 was increased to 95°C. Compared to 85°C in Example 1, the total removed iron and aluminum mass increased from 1287.5g to 1465.9g. In step 2, the reaction temperature was increased from 80°C to 90°C, and the total removed iron and aluminum mass increased from 1091.2g to 1204.9g. This indicates that higher temperatures are beneficial for the dissolution of metal oxides from red mud by acid. Furthermore, in step 4, Example 3 extended the reaction time to 4 hours and increased the reaction temperature to 95°C. Compared to the 2-hour reaction time and 85°C reaction temperature in Example 1, with a solid-liquid ratio increased to 1:6, the silica precipitated mass increased from 930.5g to 999.4g, further verifying the significant impact of process parameters on silica extraction efficiency. Furthermore, the control of the dilution ratio and aging time of the primary and secondary acid leaching solutions in different embodiments ensured the sufficient formation and separation of the iron-aluminum composite hydroxide precipitate, creating favorable conditions for the subsequent extraction of high-purity silica. In practice, a balance between output and energy consumption should be comprehensively considered, and an appropriate combination of process parameters should be selected according to actual production needs to maximize economic benefits and resource utilization.

[0029] III. Characterization and Detection Figure 1 , Figure 8 and Figure 9 The images show SEM images of the silica-rich tailings obtained in Examples 1 to 3. As can be seen from the images, the silica-rich tailings exhibit a relatively loose porous structure, which is closely related to the dissolution of soluble components such as iron and aluminum in the red mud during the acid leaching process. This provides a large contact area for the subsequent reaction with sodium hydroxide solution, which is conducive to the efficient dissolution of silica.

[0030] Figures 2-7 , Figures 10-15 They are respectively Figure 1 and Figure 9Compositional analysis of six randomly selected points in the samples showed significant differences in elemental distribution between the six random points of the silicon-rich tailings obtained in Examples 1 and 3, indicating elemental enrichment. However, the silicon content at most random points was at a high level, sufficient to support the efficient execution of subsequent silicon extraction processes. Specifically, as shown in Tables 1-12, the atomic percentages of silicon at EDS Spots 1 to 6 in Example 1 were 9.17%, 12.45%, 2.98%, 16.83%, 21.57%, and 29.43%, respectively, while the corresponding atomic percentages at the points in Example 3 were 16.13%, 1.16%, 5.24%, 17.72%, 13.68%, and 17.78%. Besides silicon, the main metal elements detected were Al, Fe, and Ti, with significant fluctuations in their content distribution at different points. This may be related to the heterogeneity of the red mud's composition and the local differences in the acid leaching reaction.

[0031] Table 1: Elemental composition at EDS Spot 1 in silica-rich tailings of Example 1

[0032] Table 2: Elemental percentages at two EDS spots in the silica-rich tailings of Example 1

[0033] Table 3: Elemental percentages at three EDS spots in silica-rich tailings from Example 1

[0034] Table 4: Elemental percentages at four EDS spots in silica-rich tailings from Example 1

[0035] Table 5: Elemental percentages at 5 EDS spots in silica-rich tailings from Example 1

[0036] Table 6: Elemental percentages at 6 EDS spots in silica-rich tailings from Example 1

[0037] Table 7: Elemental composition at EDS Spot 1 in silica-rich tailings of Example 3

[0038] Table 8: Elemental percentages at two EDS spots in the silica-rich tailings of Example 3

[0039] Table 9: Elemental percentages at three EDS spots in the silica-rich tailings of Example 3

[0040] Table 10: Elemental percentages at four EDS spots in the silica-rich tailings of Example 3

[0041] Table 11: Elemental percentages at 5 EDS spots in silica-rich tailings from Example 3

[0042] Table 12: Elemental percentages at 6 EDS spots in silica-rich tailings from Example 3

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for extracting silica from red mud, characterized in that, Includes the following steps: 1) Red mud pretreatment The original red mud was calcined to obtain calcined red mud. 2) One-time acid leaching The calcined red mud obtained in step 1) is leached with waste sulfuric acid to obtain a primary acid leaching solution and a primary acid leaching residue. 3) Secondary acid leaching The primary acid leaching residue obtained in step 2) is leached with waste hydrochloric acid to obtain secondary acid leaching solution and secondary acid leaching residue; 4) Neutralize and precipitate the acid leaching solution The primary acid leaching solution obtained in step 2) and the secondary acid leaching solution obtained in step 3) are neutralized and precipitated using sodium carbonate solution to obtain precipitate and CO2. 5) Silicon extraction The secondary acid leaching residue obtained in step 3) is fully dissolved in sodium hydroxide solution, the solution is separated, and then CO2 obtained in step 4) is introduced into the solution. After filtration, the precipitate is washed and dried to obtain the silicon dioxide product.

2. The method for extracting silica from red mud according to claim 1, characterized in that, In step 1), the raw red mud is ball-milled until D90 is less than 100 μm; in step 2), the mass concentration of waste sulfuric acid is 22.9%; in step 3), the mass concentration of waste hydrochloric acid is 34.6%; in step 4), the concentration of sodium carbonate solution is 2.5 mol / L; in step 5), the mass fraction of sodium hydroxide solution is 33.25%.

3. The method for extracting silica from red mud according to claim 2, characterized in that, Step 1) Calcination treatment: Place the ball-milled raw red mud in a muffle furnace and calcine at 500℃~600℃ for 40~80 minutes, then cool for later use.

4. The method for extracting silica from red mud according to claim 2, characterized in that, In step 2), the weight ratio of calcined red mud to waste sulfuric acid is 1:(3~7); the leaching temperature is 85℃~95℃, and the leaching time is 3~4h.

5. The method for extracting silica from red mud according to claim 2, characterized in that, In step 3), the amount of waste hydrochloric acid used is 2 to 4 times the weight of the calcined red mud obtained in step 1); the leaching temperature is 85℃ to 95℃, and the leaching time is 2 to 4 hours.

6. The method for extracting silica from red mud according to claim 2, characterized in that, In step 4), the neutralization and precipitation treatment of the primary or secondary acid leaching solution is as follows: the acid leaching solution is diluted with water washing solution at a mass ratio of (1.5~2):1, sodium carbonate solution is slowly added dropwise at 65°C to adjust the pH to 7.0, the temperature is maintained at 60°C~70°C, and the solution is slowly stirred and aged for 0.5~1h before filtration. The resulting filter cake is an iron-aluminum composite hydroxide precipitate, and the filtrate enters the subsequent sodium carbonate extraction or recycling process.

7. The method for extracting silica from red mud according to claim 2, characterized in that, In step 5), the solid-liquid ratio of sodium hydroxide solution and secondary leaching residue is 1:(4~6), the dissolution temperature is 85℃~95℃, and the dissolution time is 2~4h; when CO2 is introduced, the temperature of the solution is 50℃~70℃, and the CO2 introduction is stopped when the pH of the solution is 7.8~8.5.

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