Closed-loop recycling method for SO2 and CO2 in aluminum electrolysis flue gas

Abstract

The present invention discloses a closed-loop recycling method for SO2 and CO2 in aluminum electrolysis flue gas, comprising: (1) defluorinating and dust-removing the aluminum electrolysis flue gas; (2) passing high-concentration SO2 and CO2 flue gas into water; (3) diluting concentrated sulfuric acid into dilute sulfuric acid, mixing the dilute sulfuric acid with aluminum ash, and then performing solid-liquid separation; (4) leaching a mixed aluminum sulfate solution, carbon slag, and acid solution; (5) leaching a mixed first alkaline solution containing sodium ions and aluminum electrolysis overhaul slag; (6) neutralizing and precipitating the first leachate, and then performing solid-liquid separation; (7) calcining the precipitate to obtain a mixture of AlF3 and Al2O3; and (8) passing the high-concentration CO2 gas obtained in step (2) into a second leachate for carbon neutralization, and then evaporating and crystallizing to obtain sodium carbonate. The method realizes the closed-loop recycling of SO2 and CO2 gases in aluminum electrolysis flue gas in the field of aluminum electrolysis production, while reducing the treatment cost of aluminum electrolysis waste and the cost of aluminum electrolysis production.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial waste gas treatment, and in particular to a method for closed-loop recycling of SO2 and CO2 in aluminum electrolysis flue gas. Background Art

[0002] Modern aluminum electrolysis primarily utilizes cryolite-alumina molten salt electrolysis, using molten cryolite as the solvent, alumina as the solute, carbonite as the anode, and molten aluminum as the cathode. Direct current is applied to the electrolytic cell, where an electrochemical reaction occurs at 950-970°C to produce molten aluminum. This reaction continuously emits large amounts of harmful gases such as CO2, SO2, and fluoride, as well as dust particles.

[0003] Currently, the dry flue gas purification process used in aluminum electrolysis production has effectively addressed the issue of fluorine pollution from electrolytic cells during aluminum production. However, while existing technologies for SO2 treatment in aluminum electrolysis flue gas capture and recycle SO2, they have yet to achieve closed-loop resource utilization within the aluminum electrolysis production sector. Furthermore, existing solutions for CO2 treatment in aluminum electrolysis flue gas are relatively complex, requiring companies to purchase all new equipment and resulting in high investment costs. This makes implementation difficult for existing aluminum electrolysis companies, and engineering implementation is challenging.

[0004] Therefore, it is necessary to provide a method for resource utilization of CO2 and SO2 in aluminum electrolysis flue gas to achieve closed-loop resource utilization of CO2 and SO2 in the aluminum electrolysis production process. Summary of the Invention

[0005] The present invention aims to solve, at least to a certain extent, one of the technical problems in the related art. To this end, one object of the present invention is to provide a closed-loop recycling method for SO2 and CO2 in aluminum electrolysis flue gas, which realizes the closed-loop recycling of SO2 and CO2 gases in aluminum electrolysis flue gas in the field of aluminum electrolysis production, reduces the cost of aluminum electrolysis waste treatment and the cost of aluminum electrolysis production, is beneficial to environmental protection, and generates significant economic benefits. At the same time, the method is simple to operate and the operation process is easy to control.

[0006] In one aspect of the present invention, a closed-loop method for recycling SO2 and CO2 in aluminum electrolysis flue gas is provided. According to an embodiment of the present invention, the method comprises:

[0007] (1) Defluorination and dust removal of aluminum electrolysis flue gas to obtain high-concentration SO2 and CO2 flue gas;

[0008] (2) passing the high-concentration SO2 and CO2 flue gases into water to obtain concentrated sulfuric acid and high-concentration CO2 gas;

[0009] (3) diluting the concentrated sulfuric acid into dilute sulfuric acid, mixing the dilute sulfuric acid with aluminum ash, and then performing solid-liquid separation to obtain an aluminum sulfate solution;

[0010] (4) mixing the aluminum sulfate solution, the carbon residue, and the acid solution for leaching to obtain a first leachate;

[0011] (5) mixing and leaching the first alkaline solution containing sodium ions and the aluminum electrolysis overhaul slag to obtain a second leachate;

[0012] (6) neutralizing and precipitating the first leachate, and then performing solid-liquid separation to obtain a filtrate and a precipitate;

[0013] (7) calcining the precipitate to obtain a mixture of AlF3 and Al2O3;

[0014] (8) The high-concentration CO2 gas obtained in step (2) is introduced into the second leachate to neutralize the carbon component, and then evaporated and crystallized to obtain sodium carbonate.

[0015] According to an embodiment of the present invention, a closed-loop method for recycling SO2 and CO2 from aluminum electrolysis flue gas involves defluorination and dust removal of the aluminum electrolysis flue gas to remove fluorine-containing gases and dust from the flue gas, producing flue gas with high concentrations of SO2 and CO2. The high-concentration SO2 and CO2 flue gas is then passed through water, where the high-concentration SO2 is absorbed by the water and oxidized to form concentrated sulfuric acid, thereby producing concentrated sulfuric acid and high-concentration CO2 gas. The concentrated sulfuric acid is then diluted to dilute sulfuric acid and mixed with aluminum ash, the main components of which are aluminum oxide and metallic aluminum. The dilute sulfuric acid reacts fully with the aluminum oxide and metallic aluminum to form aluminum sulfate, which is then separated into solid and liquid to produce an aluminum sulfate solution. The aluminum sulfate solution, carbon slag, and an acid solution are then mixed and leached to produce a first leachate. The carbon slag mainly consists of carbon and aluminum electrolyte. The mixing of the aluminum sulfate solution and acid solution with the carbon slag adjusts the pH of the first leachate and provides the necessary aluminum ions for subsequent neutralization and precipitation. Simultaneously, a first alkaline solution containing sodium ions is mixed with aluminum electrolysis overhaul slag to produce a second leachate. The first leachate is then neutralized and precipitated in order to allow aluminum ions and fluoride ions to form a fluoroaluminum precursor, and a filtrate and a precipitate are obtained after solid-liquid separation. The precipitate is then calcined, and the fluoroaluminum precursor is decomposed after calcination to obtain a mixture of AlF3 and Al2O3. At the same time, high-concentration CO2 gas is introduced into the second leachate for carbon neutralization, and then evaporated and crystallized to obtain sodium carbonate. The high-concentration CO2 gas reacts with the sodium hydroxide in the second leachate to generate sodium carbonate. Thus, this method realizes the closed-loop recycling of SO2 and CO2 gases in aluminum electrolysis flue gas in the field of aluminum electrolysis production, and reduces the cost of treating aluminum electrolysis waste and the cost of aluminum electrolysis production, which is beneficial to environmental protection and produces significant economic benefits. At the same time, the method is simple to operate and the operation process is easy to control.

[0016] In addition, the closed-loop recycling method for SO2 and CO2 in aluminum electrolysis flue gas according to the above embodiment of the present invention may also have the following additional technical features:

[0017] In some embodiments of the present invention, in step (3), the mass concentration of the dilute sulfuric acid is 20-30%, thereby ensuring that the dilute sulfuric acid fully reacts with the aluminum oxide and metallic aluminum in the aluminum ash to form aluminum sulfate.

[0018] In some embodiments of the present invention, in step (3), the solid-liquid ratio of the aluminum ash to the dilute sulfuric acid is 1:(5-8), thereby ensuring that the dilute sulfuric acid fully reacts with the aluminum oxide and metallic aluminum in the aluminum ash to form aluminum sulfate.

[0019] In some embodiments of the present invention, in step (4), the concentration of the aluminum sulfate solution is 230-280 g / L, and the pH of the first leaching solution is 0.8-1.2. Thus, the leaching rate of elements such as aluminum and fluorine in the carbon residue is high, and other impurities are less likely to be generated.

[0020] In some embodiments of the present invention, in step (4), the leaching temperature is 50-60° C., and the leaching time is 20-24 h.

[0021] In some embodiments of the present invention, in step (5), the concentration of the first alkaline solution containing sodium ions is 30 g / L to 60 g / L, and the pH of the second leachate is 13 to 14. This facilitates the recovery and utilization of high-concentration CO2 gas.

[0022] In some embodiments of the present invention, in step (6), the neutralization precipitation includes: mixing the first leachate and the second alkaline solution, and adjusting the pH of the first leachate to 5-6 to obtain a fluoroaluminum precursor.

[0023] In some embodiments of the present invention, in step (6), the calcination temperature is 520-550° C. and the time is 2-3 hours, thereby allowing the fluorinated aluminum precursor to be fully calcined and converted into a mixture of AlF 3 and Al 2 O 3 .

[0024] In some embodiments of the present invention, in step (6), before calcination, the precipitate is dried at 100-120°C for 4-5 hours, and then dehydrated at 270-300°C for 2-3 hours. This ensures the yield of AlF3 and increases the product value.

[0025] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0027] Figure 1 This is a closed-loop method for recycling SO2 and CO2 in aluminum electrolysis flue gas according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0029] In one aspect of the present invention, the present invention provides a closed-loop method for recycling SO2 and CO2 in aluminum electrolysis flue gas. Figure 1 , the method comprising:

[0030] S100: Defluorination and dust removal of aluminum electrolysis flue gas

[0031] In this step, the aluminum electrolysis flue gas is defluorinated and dusted to produce flue gas with high concentrations of SO2 and CO2. The aluminum electrolysis flue gas is generated during the aluminum electrolysis process. The inventors have discovered that the aluminum electrolysis flue gas contains fluorine-containing gases and dust as well as SO2 and CO2 flue gas. After defluorination and dust removal, the fluorine-containing gases and dust in the aluminum electrolysis flue gas can be effectively removed, resulting in flue gas with high concentrations of SO2 and CO2.

[0032] S200: Passing high concentration SO2 and CO2 flue gas into water

[0033] In this step, high-concentration SO2 and CO2 flue gases are passed into water to produce concentrated sulfuric acid and high-concentration CO2 gas. The inventors discovered that when high-concentration SO2 and CO2 flue gases are passed into water, the SO2 is absorbed by the water and oxidized to form concentrated sulfuric acid. The chemical equation for the reaction is: SO2 + H2O = H2SO3, 2H2SO3 + O2 = 2H2SO4, and the remainder is high-concentration CO2 gas.

[0034] S300: After diluting concentrated sulfuric acid into dilute sulfuric acid, the dilute sulfuric acid is mixed with aluminum ash, and then the solid-liquid separation is carried out.

[0035] In this step, concentrated sulfuric acid is diluted into dilute sulfuric acid, and then the dilute sulfuric acid is mixed with aluminum ash, and then solid-liquid separation is performed to obtain aluminum sulfate solution. The inventors found that the main components of aluminum ash are aluminum oxide and metallic aluminum. Dilute sulfuric acid can fully react with aluminum oxide and metallic aluminum to form aluminum sulfate. The chemical reaction equation is: Al2O3+3H2SO4=3H2O+Al2(SO4)3, 2Al+3H2SO4=Al2(SO4)3+3H2↑. After solid-liquid separation, aluminum sulfate solution is obtained. Among them, the solid is mainly impurities such as SiO2 that are insoluble in sulfuric acid. It should be noted that the specific method of solid-liquid separation is not particularly limited, and those skilled in the art can choose according to needs. For example, it can be filtration.

[0036] Furthermore, the mass concentration of the dilute sulfuric acid is 20-30%. The inventors have found that if the mass concentration of the dilute sulfuric acid is too high, it will passivate the aluminum and prevent it from fully reacting with the aluminum; if the mass concentration of the dilute sulfuric acid is too low, the reaction with aluminum oxide and aluminum will be slow, affecting production efficiency.

[0037] Furthermore, the solid-liquid ratio of the aluminum ash to the dilute sulfuric acid is 1:(5-8). The inventors have found that if the solid-liquid ratio is too high, the aluminum ash cannot fully react to produce aluminum sulfate, while if the solid-liquid ratio is too low, the residual sulfuric acid is large, increasing the difficulty of waste liquid treatment.

[0038] S400: Mix aluminum sulfate solution, carbon residue and acid solution for leaching

[0039] In this step, the aluminum sulfate solution, carbon slag, and acid solution are mixed and leached to obtain a first leachate. The inventors discovered that the main components of carbon slag are carbon and aluminum electrolyte. Mixing aluminum sulfate solution and acid solution with them can adjust the pH of the resulting leachate and provide the necessary aluminum ions for subsequent neutralization and precipitation. Specifically, concentrated sulfuric acid with a mass concentration of 98% can be added to the leachate to adjust the pH of the leachate. The inventors discovered that by adding concentrated sulfuric acid, on the one hand, the leaching efficiency can be increased, and on the other hand, sulfate ions can be enriched through a nanofiltration system to produce sodium sulfate for export, thereby increasing the added value of the product.

[0040] Furthermore, the concentration of the aluminum sulfate solution is 230-280 g / L, and the pH of the leachate is 0.8-1.2. The inventors have found that if the concentration of the aluminum sulfate solution is too high, the pH value of the solution is difficult to control during the addition process, resulting in uneven pH values ​​and affecting leaching efficiency; if the concentration of the aluminum sulfate solution is too low, a large amount of aluminum sulfate solution needs to be added, which increases production costs and affects production efficiency; if the pH of the leachate is too high, other impurities will be formed, affecting the purity of the AlF3 and Al2O3 products; if the pH of the leachate is too low, the amount of sulfuric acid added increases, which will increase production costs.

[0041] Furthermore, the leaching temperature is 50-60°C and the time is 20-24 hours. The inventors have found that if the leaching temperature is too high, energy consumption will increase and production costs will increase. If the leaching temperature is too low, the leaching efficiency will be reduced, thereby reducing production efficiency.

[0042] S500: Mixing the first alkaline solution containing sodium ions and the aluminum electrolysis overhaul slag for leaching

[0043] In this step, a first alkaline solution containing sodium ions is mixed with aluminum electrolytic overhaul slag for leaching to produce a second leachate. The inventors have discovered that mixing aluminum electrolytic overhaul slag with the first alkaline solution increases the leaching rate of fluorine in the overhaul slag, effectively rendering the overhaul slag harmless.

[0044] Furthermore, the concentration of the first alkaline solution containing sodium ions is 30 g / L to 60 g / L, and the pH of the second leachate is 13 to 14. The inventors have found that if the concentration of the first alkaline solution is too low, the leaching efficiency of the fluorine element in the overhaul slag is low, and harmless treatment cannot be achieved. If the concentration of the first alkaline solution is too high, the treatment cost will increase, the service life of the equipment will be reduced, and the operational safety will be reduced.

[0045] S600: Neutralize and precipitate the first leachate, and then separate the solid and liquid

[0046] In this step, the first leachate is neutralized and precipitated, and then the solid and liquid are separated to obtain a filtrate and a precipitate. The inventors found that after the first leachate is neutralized and precipitated, aluminum ions and fluoride ions form a fluorinated aluminum precursor. The ionic equation of the neutralization and precipitation process is: 0.76Al 3+ +3.24AlF 2+ →2Al2F 3.24 (OH) 2.76 ·H2O↓. It should be noted that the specific method of the above solid-liquid separation is the same as described above and will not be repeated here.

[0047] S700: Calcination of the precipitate

[0048] In this step, the precipitate is calcined to obtain a mixture of AlF3 and Al2O3. The inventors found that the chemical reaction equation for calcining the precipitate is: 3Al2F 3.24 (OH) 2.76 H2O→3.24AlF3+1.38Al2O3+7.14H2O. The AlF3 and Al2O3 mixture obtained by calcination can be returned to aluminum electrolysis production for use.

[0049] Furthermore, the calcination temperature is 520-550°C and the time is 2-3 hours. The inventors have found that if the calcination temperature is too high, energy consumption is high and the cost is high; if the calcination temperature is too low, the conversion efficiency of AlF3 and Al2O3 is low and the impurity content is high.

[0050] Furthermore, before calcination, the precipitate is dried at 100-120°C for 4-5 hours, and then dehydrated at 270-300°C for 2-3 hours. This allows the fluoroaluminum precursor to be fully dehydrated, preventing the presence of water vapor during the calcination process, which would cause aluminum fluoride to decompose at high temperatures and generate hydrogen fluoride gas that would overflow.

[0051] S800: The high concentration CO2 gas obtained in S200 is passed into the second leachate to neutralize the carbon content, and then evaporated and crystallized

[0052] In this step, the high-concentration CO2 gas obtained in S200 is passed into the second leachate for carbon neutralization, followed by evaporation and crystallization to produce sodium carbonate. The inventors discovered that the CO2 gas reacts with the sodium hydroxide formed in the second leachate to produce sodium carbonate. The chemical reaction equation is: CO2 + 2NaOH = Na2CO3 + 2H2O. This allows the CO2 gas in the aluminum electrolysis flue gas to be utilized in a closed-loop manner. The generated sodium carbonate, meanwhile, serves as an auxiliary material in the aluminum electrolysis production process and can be further returned to aluminum electrolysis production for use. Specifically, after the high-concentration CO2 gas is passed into the second leachate, carbon neutralization can be achieved under the synergistic effect of ultrasound.

[0053] The inventors discovered that the present invention collects SO₂ and CO₂ gases from aluminum electrolysis flue gas and then prepares them into sulfuric acid and carbon fractions, which are then neutralized into Na₂CO₃. The sulfuric acid is then recycled as a raw material for treating waste materials such as aluminum electrolysis overhaul slag, carbon slag, and aluminum ash. These waste materials are generated during the aluminum electrolysis production process. Specifically, overhaul slag is produced during the maintenance of aluminum electrolytic cells; carbon slag is produced during the aluminum electrolysis process when anode carbon blocks oxidize and fall off the electrolytic cell; and aluminum ash is the product of cooling slag produced in the electrolytic or cast aluminum production process. The Na₂CO₃ is then recycled as an auxiliary material in the aluminum electrolysis production process for use in the aluminum electrolysis process. This achieves a closed-loop utilization of SO₂ and CO₂ gases in the aluminum electrolysis production process and effectively reduces the waste treatment costs of aluminum electrolysis overhaul slag, carbon slag, and aluminum ash, as well as the production costs of aluminum electrolysis. This method reduces the environmental burden on aluminum electrolysis companies while generating significant economic benefits. Furthermore, the implementation process is simple and easy to manage.

[0054] The present invention is described below with reference to specific examples. It should be noted that these examples are merely illustrative and do not limit the present invention in any way.

[0055] Example 1

[0056] (1) Defluorination and dust removal of aluminum electrolysis flue gas to obtain high-concentration SO2 and CO2 flue gas;

[0057] (2) passing the obtained high-concentration SO2 and CO2 flue gas into water to obtain concentrated sulfuric acid and high-concentration CO2 gas;

[0058] (3) After diluting concentrated sulfuric acid to a mass concentration of 20%, the aluminum ash and the dilute sulfuric acid were mixed at a solid-liquid ratio of 1:5, and then filtered to obtain an aluminum sulfate solution with a concentration of 230 g / L;

[0059] (4) mixing the aluminum sulfate solution and the carbon residue and leaching them, while adding concentrated sulfuric acid with a mass concentration of 98%, the leaching temperature is 50° C., the time is 24 hours, and a first leachate with a pH value of 0.8 is obtained;

[0060] (5) mixing sodium hydroxide having a concentration of 30 g / L and aluminum electrolysis overhaul slag for leaching to obtain a second leachate having a pH value of 13;

[0061] (6) adding sodium hydroxide solution to the first leachate to adjust the pH of the first leachate to 5, and then filtering to obtain a filtrate and a precipitate;

[0062] (7) The precipitate was dried at 100°C for 4 h, then dehydrated at 270°C for 2 h, and then calcined at 520°C for 2 h to obtain a mixture of AlF3 and Al2O3;

[0063] (8) The high-concentration CO2 gas obtained in step (2) is introduced into the second leachate to neutralize the carbon component, and then evaporated and crystallized to obtain sodium carbonate.

[0064] Example 2

[0065] (1) Defluorination and dust removal of aluminum electrolysis flue gas to obtain high-concentration SO2 and CO2 flue gas;

[0066] (2) passing the obtained high-concentration SO2 and CO2 flue gas into water to obtain concentrated sulfuric acid and high-concentration CO2 gas;

[0067] (3) After diluting concentrated sulfuric acid to a mass concentration of 25% dilute sulfuric acid, the aluminum ash and the dilute sulfuric acid were mixed at a solid-liquid ratio of 1:6, and then filtered to obtain an aluminum sulfate solution with a concentration of 250 g / L;

[0068] (4) mixing the aluminum sulfate solution and the carbon residue and leaching them, while adding concentrated sulfuric acid with a mass concentration of 98%, the leaching temperature is 55° C., the time is 24 hours, and a first leachate with a pH value of 1.0 is obtained;

[0069] (5) mixing sodium hydroxide having a concentration of 40 g / L and aluminum electrolysis overhaul slag for leaching to obtain a second leachate having a pH value of 13.5;

[0070] (6) adding sodium hydroxide solution to the first leachate to adjust the pH of the first leachate to 5.5, and then filtering to obtain a filtrate and a precipitate;

[0071] (7) The precipitate was dried at 100°C for 4.5 h, then dehydrated at 280°C for 2.5 h, and then calcined at 530°C for 2.5 h to obtain a mixture of AlF3 and Al2O3;

[0072] (8) The high-concentration CO2 gas obtained in step (2) is introduced into the second leachate to neutralize the carbon component, and then evaporated and crystallized to obtain sodium carbonate.

[0073] Example 3

[0074] (1) Defluorination and dust removal of aluminum electrolysis flue gas to obtain high-concentration SO2 and CO2 flue gas;

[0075] (2) passing the obtained high-concentration SO2 and CO2 flue gas into water to obtain concentrated sulfuric acid and high-concentration CO2 gas;

[0076] (3) After diluting concentrated sulfuric acid to a mass concentration of 30% dilute sulfuric acid, the aluminum ash and the dilute sulfuric acid were mixed at a solid-liquid ratio of 1:8, and then filtered to obtain an aluminum sulfate solution with a concentration of 280 g / L;

[0077] (4) mixing the aluminum sulfate solution and the carbon residue and leaching them, while adding concentrated sulfuric acid with a mass concentration of 98%, the leaching temperature is 60° C., the time is 24 hours, and a first leachate with a pH value of 1.2 is obtained;

[0078] (5) mixing sodium hydroxide having a concentration of 60 g / L and aluminum electrolysis overhaul slag for leaching to obtain a second leachate having a pH value of 14;

[0079] (6) adding sodium hydroxide solution to the first leachate to adjust the pH of the first leachate to 6, and then filtering to obtain a filtrate and a precipitate;

[0080] (7) The precipitate was dried at 100°C for 4 h, then dehydrated at 300°C for 3 h, and then calcined at 550°C for 3 h to obtain a mixture of AlF3 and Al2O3;

[0081] (8) The high-concentration CO2 gas obtained in step (2) is introduced into the second leachate to neutralize the carbon component and obtain sodium carbonate.

[0082] It can be seen from Examples 1-3 that by collecting SO2 and CO2 gases in the aluminum electrolysis flue gas and preparing them into sulfuric acid and carbon respectively, and neutralizing them into Na2CO3 substances, the sulfuric acid is recycled as a raw material for treating wastes such as aluminum electrolysis overhaul slag, carbon slag and aluminum ash, and the Na2CO3 substance is returned to the aluminum electrolysis production as an auxiliary material in the aluminum electrolysis production process for use, thereby realizing the closed-loop utilization of SO2 and CO2 gases in the aluminum electrolysis production field, and effectively reducing the treatment costs of wastes such as aluminum electrolysis overhaul slag, carbon slag and aluminum ash and the aluminum electrolysis production costs.

[0083] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0084] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A closed-loop method for recycling SO2 and CO2 in aluminum electrolysis flue gas, characterized in that: include: (1) Defluorination and dust removal of aluminum electrolysis flue gas to obtain high-concentration SO2 and CO2 flue gas; (2) passing the high-concentration SO2 and CO2 flue gases into water to obtain concentrated sulfuric acid and high-concentration CO2 gas; (3) diluting the concentrated sulfuric acid into dilute sulfuric acid, mixing the dilute sulfuric acid with aluminum ash, and then performing solid-liquid separation to obtain an aluminum sulfate solution; (4) mixing the aluminum sulfate solution, the carbon residue, and the acid solution for leaching to obtain a first leachate; (5) mixing and leaching the first alkaline solution containing sodium ions and the aluminum electrolysis overhaul slag to obtain a second leachate; (6) neutralizing and precipitating the first leachate, and then performing solid-liquid separation to obtain a filtrate and a precipitate; (7) calcining the precipitate to obtain a mixture of AlF3 and Al2O3; (8) passing the high-concentration CO2 gas obtained in step (2) into the second leachate to neutralize the carbon component, and then evaporating and crystallizing to obtain sodium carbonate; In step (3), the mass concentration of the dilute sulfuric acid is 20-30%; In step (3), the solid-liquid ratio of the aluminum ash to the dilute sulfuric acid is 1:(5-8).

2. The method according to claim 1, characterized in that In step (4), the concentration of the aluminum sulfate solution is 230-280 g / L, and the pH of the first leachate is 0.8-1.

2.

3. The method according to claim 1, characterized in that In step (4), the leaching temperature is 50-60° C. and the leaching time is 20-24 hours.

4. The method according to claim 1, wherein In step (5), the concentration of the first alkaline solution containing sodium ions is 30 g / L to 60 g / L, and the pH of the second leachate is 13 to 14.

5. The method according to claim 1, wherein In step (6), the neutralization precipitation includes: mixing the first leachate and the second alkaline solution, and adjusting the pH of the first leachate to 5-6 to obtain a fluoroaluminum precursor.

6. The method according to claim 1, wherein In step (7), the calcination temperature is 520-550° C. and the calcination time is 2-3 hours.

7. The method according to claim 1, characterized in that In step (7), before calcination, the precipitate is dried at 100-120° C. for 4-5 hours, and then dehydrated at 270-300° C. for 2-3 hours.

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