Green and environment-friendly high-alumina fly ash multi-component synergistic extraction method

Abstract

The invention provides a green and environment-friendly high-alumina fly ash multi-component synergistic extraction method, and belongs to the technical field of fly ash extraction. The preparation method comprises the following steps: adding sodium carbonate into fly ash serving as a raw material, mixing and calcining to obtain a nepheline phase which is easily soluble in an acidic medium; then adding sulfuric acid to decompose the sintered product to dissolve the sintered product, heating and aging to separate silicon from aluminum to obtain silica gel and a metal salt solution, using the silica gel to prepare white carbon black, and separating and purifying the metal salt solution to prepare aluminum oxide, iron oxide, calcium hydroxide and magnesium hydroxide. According to the method, the problems of low utilization rate and impure product in the traditional extraction process are better solved, the utilization rate of useful substances in the fly ash can reach 95% or above, and the method is more environment-friendly, so that green, refined and efficient utilization of the fly ash is realized.

Description

Technical Field

[0001] This invention relates to the field of fly ash extraction technology, and in particular to a green and environmentally friendly multi-component synergistic extraction technology for high-alumina fly ash. Background Technology

[0002] Fly ash is an industrial waste residue discharged from coal-fired power plants. It is the dust produced when pulverized coal is burned at 1000℃~1500℃, carried out by the flue gas and collected by a dust collector. Burning 1 ton of coal produces 250~300 kg of fly ash. With the rapid development of my country's power industry, fly ash emissions are increasing daily. Statistics show that in 2024, the national fly ash emissions exceeded approximately 850 million tons, while the utilization rate was less than 80%. The increasing emissions and low utilization rate of fly ash lead to waste of land and water resources, and increasingly serious environmental pollution. Traditional methods of fly ash disposal include landfilling and manufacturing building materials, but these methods cannot prevent fly ash from polluting the environment. Because fly ash contains a large and varied amount of elements, and its composition is unstable, extraction processes are challenging and costly. The main components of fly ash are silica, alumina, and iron oxide. Due to its high aluminum content and high added value, numerous processes for extracting alumina from fly ash have emerged in recent years. However, these processes often produce single-component extracts, hindering efficient utilization of fly ash and potentially causing adverse environmental impacts. For example, some literature describes methods such as:

[0003] CN201010172140 A method for the ecological comprehensive utilization of fly ash: (1) Fly ash with a mass content of 20-45% alumina, 10-40% iron oxide and 30-50% silicon oxide as raw material is selected, ground and leached; (2) Filtered to separate leachate and leach residue; Tributyl phosphate and diluent are added to the leachate for extraction, aluminum enters the raffinate phase to form aluminum chloride solution, and iron enters the extraction phase; (3) The aluminum chloride solution is atomized and pyrolyzed to obtain alumina; (4) Water is used as a back-extraction agent in the extraction phase for back-extraction, and iron enters the back-extraction water to form ferric chloride solution; The ferric chloride solution is atomized and pyrolyzed to obtain iron oxide. The method of the present invention comprehensively utilizes valuable elements such as aluminum, iron and silicon in fly ash, with a short process flow and simple operation, realizing the comprehensive utilization of all valuable elements such as aluminum, iron and silicon in fly ash.

[0004] CN201710833934 A Method for Extracting Alumina from High-Alumina Fly Ash: This invention relates to a method for extracting alumina from high-alumina fly ash. The method includes the following steps: heating ammonium sulfate to decompose it into ammonium bisulfate and ammonia; preparing the ammonium bisulfate into a solution; mixing the ammonia with air to achieve a suitable concentration; grinding the fly ash raw material and mixing it with the ammonium bisulfate solution in a certain proportion; heating under stirring conditions to react and generate ammonium aluminum sulfate; after recrystallization and purification, the purified ammonium aluminum sulfate powder particles react with ammonia to generate aluminum hydroxide; the reacted material is dissolved, filtered, and washed, the filter residue is aluminum hydroxide, which is dried and then calcined to generate alumina; the filtrate, ammonium sulfate solution, is evaporated and crystallized before being recycled; the tail gas after the gas-solid reaction is absorbed by an absorption device to become ammonia water, which is then heated to become ammonia gas and returned to the system for gas distribution. The alumina extracted by this invention has advantages such as uniform particle size, low water content of aluminum hydroxide, and high strength; moreover, the method of this invention has a short process flow, simple equipment, and is easy to realize large-scale industrial production.

[0005] CN202110844582 A Method for Comprehensive Utilization of Fly Ash: This invention discloses a method for comprehensive utilization of fly ash, belonging to the field of fly ash resource utilization technology. The method first involves grinding fly ash with water to obtain a slurry, then separating carbon by flotation to obtain fly ash tailings slurry. The tailings slurry is then magnetically separated to obtain iron concentrate, a magnetic material containing a large amount of iron. The non-magnetic material is then treated with a nitric acid leaching process. The leachate is oxidized with hydrogen peroxide under acidic conditions to generate Fe(OH)3 precipitate. After filtration, the filtrate is extracted using an extraction process to obtain scandium, gallium, germanium, and gallium rare metals. The purified aluminum nitrate solution is evaporated and concentrated to obtain aluminum nitrate crystals, which are then calcined to obtain alumina. The nitrogen oxide gas generated during calcination is regenerated by a nitric acid absorption device and returned to the leaching process for reuse. This method eliminates the need for acid to leach large amounts of iron, offering advantages such as low acid consumption, low impurity content in the leachate, low impurity removal cost, recyclable nitric acid as the leaching agent, low equipment requirements, and a simple process.

[0006] CN201811287832 Comprehensive Utilization Method of Fly Ash and Chlorinated Waste Acid: This invention discloses a comprehensive utilization method of fly ash and chlorinated waste acid, belonging to the field of metallurgical technology. The method includes: mixing fly ash with water, adding flocculant and activated carbon to obtain filtrate A and filter cake A; adjusting the pH of the filtrate with chlorinated waste acid, concentrating and crystallizing, and repeatedly recrystallizing to obtain potassium chloride; mixing filter cake A with chlorinated waste acid to obtain filtrate B and filter cake B; washing and drying filter cake B to obtain silicon dioxide; adjusting the pH of filtrate B to 9-12 to obtain filtrate C; adding chlorinated waste acid to filtrate C, adjusting the pH to 5-8, filtering, washing, and drying to obtain aluminum hydroxide. This invention utilizes industrial waste acid to process valuable elements such as potassium, silicon, and aluminum in fly ash, achieving high-yield, high-quality silicon dioxide, aluminum oxide, and potassium chloride, turning waste into treasure and reducing environmental pollution.

[0007] Some of the above methods involve direct acid leaching, extraction of a single product, crystallization purification, etc., which have problems such as low extraction rate, secondary pollution caused by waste generation, single extracted elements, and low purity, making it difficult to realize the true value of fly ash. Summary of the Invention

[0008] In view of this, the present invention provides a green and environmentally friendly method for the synergistic extraction of multiple components from high-alumina fly ash, comprising the following steps:

[0009] (1) Grinding: The fly ash is crushed by a crusher and then passed through a 200-mesh sieve;

[0010] (2) Calcination: The sieved fly ash is placed in a muffle furnace and calcined to obtain calcined fly ash;

[0011] (3) Activation: Calcinated fly ash and sodium carbonate are mixed at a mass ratio of 1:0.7-1, ground and passed through a 200-mesh sieve, and then heated in a muffle furnace to activate the fly ash.

[0012] (4) Acid dissolution: Deionized water and concentrated sulfuric acid are added to activated fly ash in sequence, and stirred at 70-80℃ for 1-2 hours. Filter to obtain calcium sulfate precipitate and filtrate.

[0013] (5) Preparation of silica: The filtrate is heated and aged to coagulate silicic acid to form silica gel. The silica gel and separation liquid are obtained by centrifugation. The silica gel is washed repeatedly with deionized water 3-5 times to obtain washing liquid. The washed silica gel is placed in an oven to dry to obtain silica. The washing liquid and separation liquid are combined to obtain a mixture.

[0014] (6) Extraction of aluminum and iron: Add sodium carbonate solution with a concentration of 2-3 mol / L to the mixture to adjust the pH value to 6-7. CO2 gas is generated in the solution and a mixed precipitate of aluminum hydroxide and iron hydroxide is formed. Collect the CO2 gas, filter the precipitate, and the filtrate can be recycled.

[0015] (7) Extraction of iron oxide: The mixed precipitate is placed in an 8-10 mol / L sodium hydroxide solution, heated and stirred until dissolved to obtain sodium aluminate solution and iron hydroxide precipitate. The iron hydroxide precipitate is calcined to obtain iron oxide.

[0016] (8) Preparation of aluminum oxide: The CO2 gas described in step (6) is introduced into the sodium aluminate solution until no more white precipitate is produced. The solution is filtered to obtain sodium bicarbonate solution and aluminum hydroxide precipitate. The aluminum hydroxide precipitate is washed, dried and calcined to obtain aluminum oxide. The sodium bicarbonate solution is evaporated, crystallized and calcined to obtain sodium carbonate solid product.

[0017] (9) Extracting magnesium: Add sodium hydroxide solution to the filtrate from step (6) to adjust the pH to 11.5-12 to form magnesium hydroxide precipitate. After filtration, washing and drying, magnesium hydroxide is obtained. The remaining filtrate is used in the next step.

[0018] (10) Extraction of sodium sulfate: Add sulfuric acid and sodium hydroxide to the filtrate from step (9) to completely neutralize it, and then evaporate and crystallize to obtain sodium sulfate product.

[0019] Preferably, the calcination temperature in step (2) is 600-800℃ and the time is 2-3h.

[0020] Preferably, the temperature for heating and activating in step (3) is 700-800℃ and the activation time is 1-2h.

[0021] Preferably, in step (4), the mass ratio of activated fly ash to water is 1:8-11, the mass ratio of activated fly ash to concentrated sulfuric acid is 1:0.8-1, and the concentration of concentrated sulfuric acid is 10%-15%.

[0022] Preferably, the aging temperature in step (5) is 40-50℃ and the time is 5-8h; the drying temperature is 120-150℃ and the time is 10-12h.

[0023] Preferably, the ratio of the mixed precipitate and sodium hydroxide solution in step (7) is 1g:2-3ml; the calcination temperature is 600-650℃ and the time is 2-3h.

[0024] Preferably, the drying temperature in step (8) is 50-60℃ and the drying time is 4-5h.

[0025] Preferably, the calcination temperature of the alumina in step (8) is 550-600℃ and the time is 2-3h; the calcination temperature of the sodium carbonate is 550-600℃ and the time is 2-3h.

[0026] Preferably, the drying temperature in step (9) is 50-60℃ and the drying time is 4-5h.

[0027] Preferably, the volume ratio of the filtrate to sulfuric acid in step (10) is 60-70:1.

[0028] Grinding fly ash can increase the specific surface area and also has a certain activation effect, making the subsequent calcination activation effect better. The purpose of calcining fly ash first is to remove the unburned carbon during the coal combustion process and avoid generating more impurities in the subsequent activation and purification. The alkali as an activator and the above-mentioned calcined fly ash mixed and sintered can destroy the mullite phase in the fly ash to the greatest extent and decompose the fly ash to obtain the nepheline phase that is easily soluble in acid. Sodium carbonate as an activator has a better activation effect than other activators and the product state is more stable. The activation temperature, time and alkali-ash ratio are examined to improve the activation efficiency. The main chemical reaction formulas are as follows (1)-(3):

[0029] 2SiO2+Al2O3+Na2CO3=2NaAlSiO4+CO2↑ (1)

[0030] Al2O3+Na2CO3=2NaAlO2+CO2↑ (2)

[0031] Fe3O4+1.5Na2CO3+0.25O2=1.5Na2Fe2O4+1.5CO2↑ (3)

[0032] Sintered products can be acid-leached to extract 95%-99% of the effective elements from fly ash, maximizing their utilization. By controlling factors such as the type of acid, the amount added, the amount of water added, and the reaction time during the acid dissolution process, the optimal dissolution conditions can be obtained, ensuring the extraction rate while minimizing resource consumption. The main chemical reaction formulas are shown in formulas (4)-(8):

[0033] 2NaAlSiO4+4H2SO4→ Na2SO4+Al2(SO4)3+2H2SiO3(colloid)+2H2O (4)

[0034] 2NaAlO2+4H2SO4→Al2(SO4)3+Na2SO4+4H2O (5)

[0035] 2Na2Fe2O4+4H2SO4→Fe2(SO4)3+Na2SO4+4H2O (6)

[0036] MgO + H2SO4 → MgSO4 + H2O (7)

[0037] CaO+H2SO4→CaSO4↓+H2O (8)

[0038] The aging time and temperature of the filtrate after acid dissolution also need to be examined. Only after the silicic acid is completely coagulated into silica gel can silicon be separated from other elements. The separated silica gel is decomposed at 150-200℃ to produce fumed silica.

[0039] The separation and purification of various elements in metal salt solutions mainly rely on adjusting the pH to produce precipitation, thereby extracting various substances through solid-liquid separation. By adjusting the pH through an alkali gradient, aluminum hydroxide and iron hydroxide precipitates are first separated, and then the pH of the remaining solution is further increased to separate magnesium hydroxide and sodium sulfate solutions. The reaction formulas are shown in equations (9)-(11):

[0040] Al2(SO4)3+3Na2CO3+3H2O=2Al(OH)3↓+3Na2SO4+3CO2↑ (9)

[0041] 3Na2CO3+Fe2(SO4)3+3H2O=2Fe(OH)3↓+3Na2SO4+3CO2↑ (10)

[0042] 2NaOH+MgSO4=Mg(OH)2↓+Na2SO4 (11)

[0043] Because the concentration of ferric hydroxide is too low, it exists in the solution in the form of a sol, which is difficult to completely separate during filtration. It is necessary to obtain an aluminum-iron coprecipitate and then separate it according to the amphoteric nature of aluminum hydroxide. The coprecipitate is placed in a strong alkaline solution and heated to dissolve the aluminum hydroxide in the alkaline solution, while the ferric hydroxide cannot be dissolved. After filtration, sodium aluminate solution and insoluble ferric hydroxide precipitate are obtained. Finally, the pH of the sodium aluminate solution needs to be adjusted to precipitate the aluminum hydroxide again. In this way, pure aluminum hydroxide can be extracted, and then aluminum oxide can be obtained by drying and calcination. The reaction formulas are as shown in formulas (12)-(13):

[0044] Al(OH)3+NaOH = NaA2+H2O (12)‌

[0045] NaAlO2+CO2+2H2O=Al(OH)3↓+NaHCO3 (13)‌

[0046] Ultimately, only sodium sulfate solution and sodium bicarbonate solution remain. Sodium sulfate is stable and does not easily volatilize, so it is evaporated and crystallized to obtain solid sodium sulfate. Sodium bicarbonate solution is heated, evaporated, crystallized, and decomposed to obtain solid sodium carbonate product.

[0047] The main components of fly ash—silicon dioxide, aluminum oxide, iron oxide, and other trace elements—can be separated into single products with high purity.

[0048] Sodium carbonate, sodium hydroxide, sulfuric acid, etc. are added during the process to form sodium sulfate and sodium carbonate as byproducts. Sodium sulfate is widely used as a filler in detergents and can also be used in analytical reagents, chemicals, papermaking and glass, dyes, printing and dyeing and pharmaceuticals. Sodium carbonate is one of the important chemical raw materials, widely used in light industry, daily chemicals, building materials, chemical industry, food industry, metallurgy, textiles, petroleum, national defense and pharmaceuticals. It is used as a raw material for manufacturing other chemicals, cleaning agents and detergents, and also in photography and analysis.

[0049] The combined acid-base method for treating fly ash has the following significant advantages: most fly ash types are suitable for the combined acid-base process; the components of fly ash can be effectively extracted, maximizing its value; the operation method is simple and convenient, requiring no stringent processes, making it suitable for large-scale fly ash treatment; the raw materials can be recycled, for example, the carbon dioxide generated during the process can be used in subsequent experiments; there is no waste residue, no waste liquid, and no waste gas emission, making it a green and pollution-free treatment of fly ash.

[0050] The method of this invention involves first breaking down the mullite phase in fly ash using a two-step acid-base process, then extracting elements such as silicon, aluminum, iron, calcium, magnesium, and sodium through acid dissolution. The components are then initially separated by forming a precipitation method. The hydroxides and sulfates obtained after separation are then extracted by calcination or evaporation crystallization to obtain the corresponding products, which meet the corresponding index requirements.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] (1) Compared with the traditional acid method, the present invention can extract various elements to a greater extent, making fly ash more efficient. The acid method requires repeated acid leaching to effectively extract the elements, while the acid-base combined method can achieve an extraction efficiency of over 95% in one extraction.

[0053] (2) Compared with the alkaline solution impregnation method, the alkaline addition and high temperature calcination can more effectively decompose fly ash. After comparing the two methods, it was found that the most important factors affecting the decomposition rate of fly ash are temperature and alkali concentration. In this invention, the temperature is higher than the melting point of the alkaline solution during sintering, so that the alkali melts and reacts with the fly ash to maximize the completeness of the reaction.

[0054] (3) Sulfuric acid is used in the acid dissolution process because its chemical properties do not require heating during use and require less addition than other acids. It is not easily volatilized and will not produce toxic or harmful gases, and its use cost is lower.

[0055] (4) The process of this invention is simple, the raw materials can be recycled and no waste residue, waste gas or wastewater is generated. The overall process is energy-saving and environmentally friendly, which can reduce pollutant emissions and reduce production costs. Attached Figure Description

[0056] Figure 1 This is a process flow diagram of the extraction of alumina, silica, and other products from fly ash according to this application.

[0057] Figure 2 This is an X-ray powder diffraction pattern of the fly ash raw material used in Example 1 of this application.

[0058] Figure 3 This is an X-ray powder diffraction pattern of the silica produced in Example 1 of this application. Detailed Implementation

[0059] The present invention will be further described below with reference to the embodiments.

[0060] Example 1

[0061] A green and environmentally friendly method for the synergistic extraction of multiple components from high-alumina fly ash includes the following steps:

[0062] (1) Grinding: The fly ash is crushed by a crusher and then passed through a 200-mesh sieve;

[0063] The chemical elemental composition of the fly ash is shown in Table 1:

[0064] Table 1. Chemical composition analysis results of fly ash samples

[0065]

[0066] (2) Calcination: The sieved fly ash is placed in a muffle furnace and calcined at 600℃ for 2 hours to obtain calcined fly ash;

[0067] (3) Activation: Calcinated fly ash and sodium carbonate are mixed at a mass ratio of 1:0.85, ground and passed through a 200-mesh sieve, placed in a muffle furnace and heated at 700℃ for 2 hours to obtain activated fly ash;

[0068] (4) Acid dissolution: Deionized water and concentrated sulfuric acid are added sequentially to the activated fly ash, stirred at 70°C for 1 hour, and filtered to obtain calcium sulfate precipitate and filtrate; the mass ratio of activated fly ash to water is 1:10, and the mass ratio of activated fly ash to concentrated sulfuric acid is 1:0.8; the concentration of concentrated sulfuric acid is 10%;

[0069] (5) Preparation of silica: The filtrate is heated at 50°C and aged for 5 hours to coagulate silicic acid into silica gel. The silica gel and separation liquid are obtained by centrifugation. The silica gel is washed three times with deionized water (the solid-liquid ratio of silica gel to deionized water is 1g:5ml) to obtain washing liquid. The washed silica gel is placed in an oven and dried at 150°C for 12 hours to obtain silica. It is then ground to the required particle size. The washing liquid and separation liquid are combined to obtain a mixture.

[0070] The chemical elemental composition of silica is shown in Table 2:

[0071] Table 2. Chemical composition analysis results of silica

[0072]

[0073] (6) Extraction of aluminum and iron: Add sodium carbonate solution with a concentration of 2 mol / L to the mixture to adjust the pH value to 6.0. CO2 gas is generated in the solution and a mixed precipitate of aluminum hydroxide and iron hydroxide is formed. Collect the CO2 gas, filter the precipitate, and the filtrate can be recycled.

[0074] (7) Extraction of iron oxide: The mixed precipitate was placed in an 8 mol / L sodium hydroxide solution at a ratio of 1 g to 2 ml, and heated and stirred at 70 °C until dissolved to obtain sodium aluminate solution and iron hydroxide precipitate. The iron hydroxide precipitate was calcined at 600 °C for 3 h to obtain iron oxide.

[0075] The chemical elemental composition of iron oxide is shown in Table 3:

[0076] Table 3. Chemical composition analysis results of iron oxide

[0077]

[0078] (8) Preparation of alumina: The CO2 gas described in step (6) is introduced into the sodium aluminate solution until no more white precipitate is produced. The solution is filtered to obtain sodium bicarbonate solution and aluminum hydroxide precipitate. The aluminum hydroxide precipitate is washed, dried at 60°C for 4 hours, and calcined at 600°C for 2 hours to obtain alumina. The sodium bicarbonate solution is evaporated and crystallized, and then calcined at 600°C for 2 hours in a muffle furnace to obtain sodium carbonate solid product.

[0079] The chemical elemental composition of alumina is shown in Table 4:

[0080] Table 4. Chemical composition analysis results of alumina

[0081]

[0082] (9) Extracting magnesium: Add sodium hydroxide solution to the filtrate from step (6) to bring the pH to 11.5, forming magnesium hydroxide precipitate. After filtration, washing, and drying at 60°C for 4 hours, magnesium hydroxide is obtained. The remaining filtrate is used in the next step.

[0083] (10) Extraction of sodium sulfate: Add 2 mol / L sulfuric acid to the filtrate of step (9) and react it with sodium hydroxide to completely neutralize it. Evaporate and crystallize to obtain sodium sulfate product; the ratio of filtrate to sulfuric acid is 60:1.

[0084] Example 2

[0085] A green and environmentally friendly method for the synergistic extraction of multiple components from high-alumina fly ash includes the following steps:

[0086] (1) Grinding: The fly ash is crushed by a crusher and then passed through a 200-mesh sieve;

[0087] The chemical elemental composition of the fly ash is shown in Table 5:

[0088] Table 5. Chemical composition analysis results of fly ash samples

[0089]

[0090] (2) Calcination: The sieved fly ash is placed in a muffle furnace and calcined at 600℃ for 2 hours to obtain calcined fly ash;

[0091] (3) Activation: Calcinated fly ash and sodium carbonate are mixed at a mass ratio of 1:1, ground and passed through a 200-mesh sieve, placed in a muffle furnace and heated at 750℃ for 2 hours to obtain activated fly ash;

[0092] (4) Acid dissolution: Deionized water and concentrated sulfuric acid are added sequentially to the activated fly ash. The mixture is stirred at 70°C for 1 hour, and then filtered to obtain calcium sulfate precipitate and filtrate. The mass ratio of activated fly ash to water is 1:11, and the mass ratio of activated fly ash to concentrated sulfuric acid is 1:0.9. The concentration of the concentrated sulfuric acid is 12.5%.

[0093] (5) Preparation of silica: The filtrate is heated at 50°C and aged for 5 hours to coagulate silicic acid into silica gel. The silica gel and separation liquid are obtained by centrifugation. The silica gel is washed three times with deionized water (the solid-liquid ratio of silica gel to deionized water is 1g:5ml) to obtain washing liquid. The washed silica gel is placed in an oven and dried at 150°C for 12 hours to obtain silica. It is then ground to the required particle size. The washing liquid and separation liquid are combined to obtain a mixture.

[0094] The chemical elemental composition of silica is shown in Table 6:

[0095] Table 6. Chemical composition analysis results of silica

[0096]

[0097] (6) Extraction of aluminum and iron: Add sodium carbonate solution with a concentration of 2 mol / L to the mixture to adjust the pH value to 6.0. CO2 gas is generated in the solution and a mixed precipitate of aluminum hydroxide and iron hydroxide is formed. Collect the CO2 gas, filter the precipitate, and the filtrate can be recycled.

[0098] (7) Extraction of iron oxide: The mixed precipitate and sodium hydroxide solution are mixed in a ratio of 1g:2.5ml. The mixed precipitate is placed in an 8mol / L sodium hydroxide solution and heated and stirred at 70°C until dissolved to obtain sodium aluminate solution and iron hydroxide precipitate. The iron hydroxide precipitate is calcined at 600°C for 2h to obtain iron oxide.

[0099] The chemical elemental composition of iron oxide is shown in Table 7:

[0100] Table 7. Chemical composition analysis results of iron oxide

[0101]

[0102] (8) Preparation of aluminum oxide: CO2 gas from step (6) is introduced into the sodium aluminate solution until no more white precipitate is produced. The solution is filtered to obtain sodium bicarbonate solution and aluminum hydroxide precipitate. The aluminum hydroxide precipitate is washed, dried at 60°C for 4 hours, and calcined at 600°C for 2 hours to obtain aluminum oxide. The sodium bicarbonate solution is evaporated and crystallized to obtain sodium carbonate solid product.

[0103] The chemical elemental composition of alumina is shown in Table 8:

[0104] Table 8. Chemical composition analysis results of alumina

[0105]

[0106] (9) Extracting magnesium: Add sodium hydroxide solution to the filtrate from step (6) to bring the pH to 11.5, forming magnesium hydroxide precipitate. After filtration, washing, and drying at 60°C for 4 hours, magnesium hydroxide is obtained. The remaining filtrate is used in the next step.

[0107] (10) Extraction of sodium sulfate: Add 2 mol / L sulfuric acid to the filtrate of step (9) and react it with sodium hydroxide to completely neutralize it. Evaporate and crystallize to obtain sodium sulfate product; the ratio of the filtrate to sulfuric acid is 65:1.

[0108] Example 3

[0109] A green and environmentally friendly method for the synergistic extraction of multiple components from high-alumina fly ash includes the following steps:

[0110] (1) Grinding: The fly ash is crushed by a crusher and then passed through a 200-mesh sieve;

[0111] The chemical elemental composition of the fly ash is shown in Table 9:

[0112] Table 9. Chemical composition analysis results of fly ash samples

[0113]

[0114] (2) Calcination: The sieved fly ash is placed in a muffle furnace and calcined at 600℃ for 2 hours to obtain calcined fly ash;

[0115] (3) Activation: Calcinated fly ash and sodium carbonate are mixed at a mass ratio of 1:1, ground and passed through a 200-mesh sieve, placed in a muffle furnace and heated at 800℃ for 2 hours to obtain activated fly ash;

[0116] (4) Acid dissolution: Deionized water and concentrated sulfuric acid are added sequentially to the activated fly ash, stirred at 70°C for 1 hour, and filtered to obtain calcium sulfate precipitate and filtrate; the mass ratio of activated fly ash to water is 1:11, and the mass ratio of activated fly ash to concentrated sulfuric acid is 1:1; the concentration of the concentrated sulfuric acid is 15%;

[0117] (5) Preparation of silica: The filtrate is heated at 50°C and aged for 5 hours to coagulate silicic acid into silica gel. The silica gel and separation liquid are obtained by centrifugation. The silica gel is washed three times with deionized water (the solid-liquid ratio of silica gel to deionized water is 1g:5ml) to obtain washing liquid. The washed silica gel is placed in an oven and dried at 150°C for 12 hours to obtain silica. It is then ground to the required particle size. The washing liquid and separation liquid are combined to obtain a mixture.

[0118] The chemical elemental composition of silica is shown in Table 10:

[0119] Table 10 Chemical composition analysis results of silica

[0120]

[0121] (6) Extraction of aluminum and iron: Add sodium carbonate solution with a concentration of 2 mol / L to the mixture to adjust the pH value to 6.0. CO2 gas is generated in the solution and a mixed precipitate of aluminum hydroxide and iron hydroxide is formed. Collect the CO2 gas, filter the precipitate, and the filtrate can be recycled.

[0122] (7) Extraction of iron oxide: The mixed precipitate was placed in an 8 mol / L sodium hydroxide solution at a ratio of 1 g: 3 ml, heated and stirred until dissolved to obtain sodium aluminate solution and iron hydroxide precipitate. The iron hydroxide precipitate was calcined at 600℃ for 2 h to obtain iron oxide. The chemical elemental composition of iron oxide is shown in Table 11.

[0123] Table 11 Chemical composition analysis results of iron oxide

[0124]

[0125] (8) Preparation of aluminum oxide: CO2 gas from step (6) is introduced into the sodium aluminate solution until no more white precipitate is produced. The solution is filtered to obtain sodium bicarbonate solution and aluminum hydroxide precipitate. The aluminum hydroxide precipitate is washed, dried at 60°C for 4 hours, and calcined at 600°C for 2 hours to obtain aluminum oxide. The sodium bicarbonate solution is evaporated and crystallized to obtain sodium carbonate solid product.

[0126] The chemical elemental composition of aluminum oxide is shown in Table 12:

[0127] Table 12 Chemical composition analysis results of alumina

[0128]

[0129] (9) Extracting magnesium: Add sodium hydroxide solution to the filtrate from step (6) to adjust the pH to 11.5-12 to form magnesium hydroxide precipitate. After filtration, washing, and drying at 60°C for 4 hours, magnesium hydroxide is obtained. The remaining filtrate is used in the next step.

[0130] (10) Extraction of sodium sulfate: Add 2 mol / L sulfuric acid to the filtrate of step (9) and react it with sodium hydroxide to completely neutralize it. Evaporate and crystallize to obtain sodium sulfate product; the ratio of filtrate to sulfuric acid is 70:1.

[0131] To compare the differences in product extraction from fly ash using existing methods, the main parameters of the sample extracted in Example 1 of this invention were compared with those of other patented synthesis methods, as shown in the table below. Comparative Example 1 was extracted using the method described in the specific implementation of patent (CN101284668A), Comparative Example 2 was extracted using the method described in Example 1 of patent (CN1792802A), and Comparative Example 3 was extracted using the optimal process parameters described in the paper (Xu Sujuan. "One Acid Two Immersions / Two Alkali Combined" Method to Achieve Full Utilization of Fly Ash [D]. Henan Polytechnic University, 2009). The results are shown in Table 13.

[0132] Table 13

[0133]

[0134] The above comparison reveals that existing patented technologies for the extraction of high-alumina fly ash generally suffer from core defects such as "single extraction method, low efficiency, heavy pollution, and high cost," failing to simultaneously meet the comprehensive needs of resource utilization, environmental protection, efficiency, and economy. This application, through innovative designs such as multi-component synergistic extraction, reagent recycling, and simplified process flow, comprehensively overcomes the shortcomings of existing technologies, demonstrating significant advantages in resource utilization, environmental friendliness, efficiency, and economy, and possessing strong technological advancement and industrial application value.

[0135] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A green and environmentally friendly method for the synergistic extraction of multiple components from high-alumina fly ash, characterized in that, Includes the following steps: (1) Grinding: The fly ash is crushed by a crusher and then passed through a 200-mesh sieve; (2) Calcination: The sieved fly ash is placed in a muffle furnace and calcined to obtain calcined fly ash; (3) Activation: Calcinated fly ash and sodium carbonate are mixed at a mass ratio of 1:0.7-1, ground and passed through a 200-mesh sieve, and then heated in a muffle furnace to activate the fly ash. (4) Acid dissolution: Deionized water and concentrated sulfuric acid are added to activated fly ash in sequence, and stirred at 70-80℃ for 1-2 hours. Filter to obtain calcium sulfate precipitate and filtrate. (5) Preparation of silica: The filtrate is heated and aged to coagulate silicic acid to form silica gel. The silica gel and separation liquid are obtained by centrifugation. The silica gel is washed repeatedly with deionized water 3-5 times to obtain washing liquid. The washed silica gel is placed in an oven to dry to obtain silica. The washing liquid and separation liquid are combined to obtain a mixture. (6) Extraction of aluminum and iron: Add sodium carbonate solution with a concentration of 2-3 mol / L to the mixture to adjust the pH value to 6-7. CO2 gas is generated in the solution and a mixed precipitate of aluminum hydroxide and iron hydroxide is formed. Collect the CO2 gas, filter the precipitate, and the filtrate can be recycled. (7) Extraction of iron oxide: The mixed precipitate is placed in an 8-10 mol / L sodium hydroxide solution, heated and stirred until dissolved to obtain sodium aluminate solution and iron hydroxide precipitate. The iron hydroxide precipitate is calcined to obtain iron oxide. (8) Preparation of aluminum oxide: The CO2 gas described in step (6) is introduced into the sodium aluminate solution until no more white precipitate is produced. The solution is filtered to obtain sodium bicarbonate solution and aluminum hydroxide precipitate. The aluminum hydroxide precipitate is washed, dried and calcined to obtain aluminum oxide. The sodium bicarbonate solution was evaporated, crystallized, and calcined to obtain a solid sodium carbonate product. (9) Extracting magnesium: Add sodium hydroxide solution to the filtrate from step (6) to adjust the pH to 11.5-12 to form magnesium hydroxide precipitate. After filtration, washing and drying, magnesium hydroxide is obtained. The remaining filtrate is used in the next step. (10) Extraction of sodium sulfate: Add sulfuric acid to the filtrate from step (9) to completely neutralize it, and then evaporate and crystallize to obtain sodium sulfate product.

2. The green and environmentally friendly multi-component synergistic extraction method for high-alumina fly ash according to claim 1, characterized in that, The calcination temperature in step (2) is 600-800℃ and the time is 2-3h.

3. The green and environmentally friendly multi-component synergistic extraction method for high-alumina fly ash according to claim 1, characterized in that, The heating activation temperature in step (3) is 700-800℃, and the activation time is 1-2h.

4. The green and environmentally friendly multi-component synergistic extraction method for high-alumina fly ash according to claim 1, characterized in that, In step (4), the mass ratio of activated fly ash to water is 1:8-11, and the mass ratio of activated fly ash to concentrated sulfuric acid is 1:0.8-1; the concentration of the concentrated sulfuric acid is 10%-15%.

5. The green and environmentally friendly multi-component synergistic extraction method for high-alumina fly ash according to claim 1, characterized in that, The aging temperature in step (5) is 40-50℃ and the time is 5-8h; the drying temperature is 120-150℃ and the time is 10-12h.

6. The green and environmentally friendly multi-component synergistic extraction method for high-alumina fly ash according to claim 1, characterized in that, In step (7), the ratio of the mixed precipitate and sodium hydroxide solution is 1g:2-3ml; the calcination temperature is 600-650℃ and the time is 2-3h.

7. The green and environmentally friendly multi-component synergistic extraction method for high-alumina fly ash according to claim 1, characterized in that, The drying temperature in step (8) is 50-60℃ and the drying time is 4-5h.

8. The green and environmentally friendly multi-component synergistic extraction method for high-alumina fly ash according to claim 1, characterized in that, In step (8), the alumina is calcined at a temperature of 550-600℃ for 2-3 hours; the sodium carbonate is calcined at a temperature of 550-600℃ for 2-3 hours.

9. The green and environmentally friendly multi-component synergistic extraction method for high-alumina fly ash according to claim 1, characterized in that, The drying temperature in step (9) is 50-60℃ and the drying time is 4-5h.

10. The green and environmentally friendly multi-component synergistic extraction method for high-alumina fly ash according to claim 1, characterized in that, The volume ratio of the filtrate to sulfuric acid in step (10) is 60-70:1.

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