Method for preparing aluminum chloride by leaching coal ash through ammonium bisulfate-sulfuric acid mixed solution

Abstract

The invention discloses a method for preparing aluminum chloride by leaching coal ash through an ammonium bisulfate-sulfuric acid mixed solution, and particularly relates to the field of chemical industry and solid industry waste treatment, and the method comprises the following steps: carrying out pre-desilicication treatment on coal ash by using a sodium hydroxide solution; and S2, adding a mixed solution of ammonium bisulfate and sulfuric acid into the desiliconized fly ash obtained in the step S1, and carrying out solid-liquid separation after high-pressure leaching. The fly ash is subjected to pre-desiliconization treatment by adopting alkali liquor, so that favorable conditions are created for reaction of a mixed solution of ammonium bisulfate and sulfuric acid and an aluminum compound. According to the technology, the aluminum element in the fly ash can be efficiently extracted within 90 minutes, resource utilization of solid waste is promoted, aluminum resources in the ash residues are recycled to the maximum extent, and the problems proposed in the background technology are solved.

Description

Technical Field

[0001] This invention relates to the fields of chemical industry and solid industrial waste treatment, and more specifically, to a method for preparing aluminum chloride by leaching coal ash with a mixture of ammonium bisulfate and sulfuric acid. Background Technology

[0002] Fly ash is a solid waste generated during the combustion of coal in coal-fired power plants. It mainly consists of silica, bauxite, iron oxides, and small amounts of carbon. The composition and properties of fly ash vary depending on its source and combustion conditions, but it typically contains 25%-40% alumina, giving it potential economic and environmental value in certain industrial applications. In particular, the alumina in fly ash can serve as a substitute for aluminum hydroxide in the production of chemical products such as aluminum chloride coagulants.

[0003] Aluminum chloride coagulant is widely used in water treatment, especially in drinking water purification and industrial wastewater treatment. Aluminum chloride is a highly effective water treatment chemical, primarily removing suspended solids, fine particles, and harmful substances from water through its coagulation properties. Traditional aluminum chloride production processes typically require expensive aluminum hydroxide or metallic aluminum as raw materials, significantly increasing production costs.

[0004] This leads to the core issue: In traditional processes, aluminum hydroxide is typically obtained by reacting bauxite (which contains a large amount of bauxite ore) with a strong alkali. However, the production process of aluminum hydroxide is not only complex but also requires a large amount of energy, resulting in high production costs. Summary of the Invention

[0005] To overcome the aforementioned deficiencies of the prior art, embodiments of the present invention provide a method for preparing aluminum chloride by leaching coal ash with a mixture of ammonium bisulfate and sulfuric acid. By pre-desilicationally treating the fly ash with an alkaline solution, favorable conditions are created for the reaction between the ammonium bisulfate and sulfuric acid mixture and aluminum compounds. This technology can achieve efficient extraction of aluminum from fly ash within 90 minutes, not only promoting the resource utilization of solid waste but also maximizing the recovery of aluminum resources from the ash residue. The ion exchange adsorption process can significantly reduce the iron content in the solution, while the alumina obtained from calcined ammonium alum has a well-developed porous structure, allowing it to easily dissolve in hydrochloric acid and prepare an aluminum chloride solution of the desired concentration.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing aluminum chloride by leaching coal ash with a mixture of ammonium bisulfate and sulfuric acid, comprising:

[0007] S1. Take a certain amount of raw fly ash, prepare a NaOH solution with a concentration of 400-450g / L, mix the fly ash and NaOH solution at a mass-volume ratio of 1:5 to 1:15, and use sodium hydroxide solution to pre-desiliconize the fly ash.

[0008] S2. Add a mixed solution of ammonium bisulfate and sulfuric acid to the desiliconized fly ash obtained in step S1, and then perform solid-liquid separation after high-pressure leaching.

[0009] S3. Adjust the aluminum ammonium sulfate leaching solution obtained in step S2 to 25-50℃, carefully adjust the pH value of the solution to 2.0-3.0 with acid or alkali, pack a certain amount of Purolite S957 resin into the ion exchange column, rinse the resin column with deionized water until the effluent is clear, collect the solution flowing out from the bottom of the resin column, and obtain the purified aluminum ammonium sulfate solution.

[0010] S4. Aluminum is precipitated in the purified aluminum ammonium sulfate solution obtained in step S3 in the form of ammonium alum, and then reacted by heating in a furnace to generate aluminum oxide powder.

[0011] S5. Add hydrochloric acid solution to the alumina powder obtained in step S4, and obtain aluminum chloride solution through leaching reaction.

[0012] In a preferred embodiment, in S1, fly ash is a solid waste from a coal-fired power plant, and its components are Al2O3, SiO2, Fe2O3, CaO, Na2O, MgO and TiO2.

[0013] In a preferred embodiment, during S1, the slurry is heated to a reaction temperature of 90-110°C for 10-40 minutes during mixing.

[0014] During the reaction, continuous stirring ensures that the fly ash particles and the alkaline solution are in full contact, guaranteeing a uniform reaction.

[0015] In a preferred embodiment, in S2, the concentration of ammonium bisulfate solution is 20-50%, the concentration of sulfuric acid solution is 365-1150 g / L, and the ratio in the mixture ranges from 3:1 to 1:3.

[0016] During the reaction, the volume is heated to 130-220°C and maintained at the target temperature for 30-240 minutes.

[0017] In a preferred embodiment, in S3, the temperature of the aluminum ammonium sulfate solution is 25-50°C, the pH value is 2-3, and the volume ratio of Purolite S957 resin to aluminum ammonium sulfate solution is 1:50-1:1000.

[0018] In a preferred embodiment, S4 includes:

[0019] S4-1. Transfer the pure ammonium aluminum sulfate solution obtained in step S3, which has had iron impurities removed by ion exchange, into a reaction crystallization vessel equipped with a stirring and cooling jacket.

[0020] S4-2. Through the cooling jacket of the crystallizer, introduce cooling medium to rapidly cool the solution to 2-25°C. At the target low temperature, maintain stirring and keep it at that temperature for 15-90 minutes.

[0021] S4-3. After crystallization, the slurry is sent to a filtration device. The separated solid is wet ammonium alum crystals. The crystals are washed with ice water or cold alcohol.

[0022] In a preferred embodiment, S4 further includes:

[0023] S4-4. Place the ammonium alum crystals obtained in the above steps into a high-temperature resistant container, spread them out evenly and thinly, and place the container into a muffle furnace preheated to the target temperature.

[0024] S4-5. Calcine in a muffle furnace at a high temperature of 800-1000℃, hold at the target temperature for 30-120 minutes, and allow the material to cool naturally to room temperature in the furnace. After cooling, remove it from the muffle furnace; the container contains alumina powder.

[0025] In a preferred embodiment, S5 includes:

[0026] S5-1. Take a certain amount of the pure alumina powder obtained by calcination in step S4, prepare a hydrochloric acid solution with a concentration of 220-425 g / L, and add the alumina powder and hydrochloric acid solution to the reactor at a mass-volume ratio of 1:2.5 to 1:10.

[0027] S5-2. Start stirring to fully mix the alumina powder and acid solution to form a slurry. Heat the reaction system to 60-110℃ and maintain the reaction at the target temperature for 15-240 minutes.

[0028] S5-3. After the predetermined reaction time is reached, stop heating and stirring, allow the reaction solution to cool naturally to room temperature, and filter the cooled solution.

[0029] S5-4. The filtrate obtained after filtration is an aluminum chloride solution.

[0030] The technical effects and advantages of this invention are as follows:

[0031] 1. In existing technologies, aluminum hydroxide is typically obtained by reacting bauxite (which contains a large amount of bauxite ore) with a strong alkali. However, the production process of aluminum hydroxide is not only complex but also requires a large amount of energy, resulting in high production costs. This solution uses alkaline solution to pre-desilicate fly ash, thereby creating favorable conditions for the reaction of ammonium bisulfate and sulfuric acid solutions with aluminum compounds. This technology can achieve efficient extraction of aluminum from fly ash within 90 minutes, not only promoting the resource utilization of solid waste but also maximizing the recovery of aluminum resources from the ash residue.

[0032] 2. The ion exchange adsorption process in this scheme can significantly reduce the iron content in the solution, and the alumina obtained by calcining ammonium alum has a well-developed porous structure, which makes it easy to dissolve in hydrochloric acid and prepare an aluminum chloride solution of the required concentration.

[0033] 3. This solution greatly reduces production costs and enhances the market competitiveness of the product by replacing expensive raw materials (such as aluminum hydroxide or metallic aluminum) required for the traditional production of aluminum chloride with free fly ash.

[0034] 4. This solution reduces the need for bauxite mining and decreases dependence on natural resources by recovering aluminum from fly ash. Attached Figure Description

[0035] Figure 1 This is a flowchart of the method steps of the present invention;

[0036] Figure 2 Here is a SEM image of the original fly ash from this invention;

[0037] Figure 3 Here is a SEM image of the desiliconized fly ash of this invention;

[0038] Figure 4 This is a SEM image of fly ash leached under high pressure using a mixed solution of ammonium bisulfate and sulfuric acid according to the present invention.

[0039] Figure 5 Here is a SEM image of the ammonium alum of the present invention;

[0040] Figure 6 This is a SEM image of the alumina of the present invention. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Refer to the instruction manual appendix Figures 1-6 The present invention discloses a method for preparing aluminum chloride by leaching coal ash with a mixture of ammonium bisulfate and sulfuric acid, comprising:

[0043] S1. Take a certain amount of raw fly ash, prepare a NaOH solution with a concentration of 400-450 g / L, preferably 420 g / L, mix the fly ash and NaOH solution at a mass-volume ratio of 1:5 to 1:15, preferably 1:10, and use sodium hydroxide solution to pre-desiliconize the fly ash.

[0044] In S1, fly ash is a solid waste from coal-fired power plants, and its components are Al2O3, SiO2, Fe2O3, CaO, Na2O, MgO and TiO2.

[0045] In S1, during mixing, the mixed slurry is heated to a reaction temperature of 90-110°C, preferably 105°C, preferably 1:10, and the reaction time is 10-40 minutes, preferably 20 minutes.

[0046] During the reaction, continuous stirring ensures that the fly ash particles are in full contact with the alkaline solution, guaranteeing a uniform reaction.

[0047] Pre-desilicon treatment of fly ash using sodium hydroxide solution removes a large amount of silica from the fly ash, increases the relative content of alumina in subsequent raw materials, reduces the interference of silica on subsequent processes, and avoids the formation of silica gel and other substances that may affect filtration or contaminate products. Silica is an amphoteric oxide that can react with strong alkalis to form soluble sodium silicate, thereby separating it from solid residues. The reaction equation is: SiO2 + 2NaOH → Na2SiO3 + H2O.

[0048] The core control parameters and their preferred ranges for this step are shown in the table below:

[0049]

[0050] S2. Add a mixed solution of ammonium bisulfate and sulfuric acid to the desiliconized fly ash obtained in step S1, and then perform solid-liquid separation after high-pressure leaching.

[0051] Take a certain amount of the desiliconized fly ash obtained in step S1;

[0052] Preparation of leaching agent: Prepare ammonium bisulfate solution with a concentration of 20-50%, preferably 40%; prepare sulfuric acid solution with a concentration of 365-1150 g / L, preferably 735 g / L; mix the two solutions in a volume ratio of 3:1 to 1:3, preferably 1:1.

[0053] The desiliconized fly ash and the mixed leaching agent are mixed in a mass-volume ratio of 1:3 to 1:10, preferably 1:6. Sufficient liquid volume ensures that the reaction system has good fluidity and mass transfer effect.

[0054] Heat the system to 130-220°C, preferably 170°C, and maintain it at the target temperature for 30-240 minutes, preferably 90 minutes. Stir continuously throughout the reaction process. Cool the reaction system temperature to a safe range using the cooling system (jacket) of the reactor or by natural cooling. After the predetermined reaction time is reached, stop the reaction and slowly release the pressure generated by heating inside the reactor until it is equal to atmospheric pressure.

[0055] Open the reaction vessel, remove the slurry after the reaction, filter the slurry to achieve solid-liquid separation, and the filtrate is rich in ammonium aluminum sulfate and iron ions (Fe). 3+ The leachate contains impurities. This is the raw material for the next step of ion exchange to remove iron.

[0056] Wash the filter residue with clean water to remove the valuable entrained solution and add it to the filtrate, thereby improving the aluminum recovery rate.

[0057] The alumina in pre-desiliconized fly ash is converted into soluble ammonium aluminum sulfate, thus separating aluminum from insoluble residues. Under high temperature and pressure conditions, the mixed acid solution of ammonium bisulfate and sulfuric acid exhibits strong reactivity. The role of ammonium bisulfate is to decompose at high temperatures to produce ammonium sulfate and sulfuric acid, providing a high-acidity environment and introducing ammonium ions (NH4+). + The latter forms complex ammonium aluminum sulfate double salts with aluminum and sulfate ions;

[0058] The role of sulfuric acid: to provide a high concentration of H+. + Ions disrupt the stable structure of aluminum oxides or aluminosilicates, causing them to dissolve.

[0059] The role of high pressure: It allows the reaction temperature to be much higher than the boiling point of the solution under normal pressure. The high temperature greatly accelerates the reaction kinetics, so that substances that are difficult to react under normal pressure can be rapidly decomposed.

[0060] The parameters and their preferred ranges are shown in the table below:

[0061]

[0062] S3. Adjust the aluminum ammonium sulfate leaching solution obtained in step S2 to 25-50℃, carefully adjust the pH value of the solution to 2.0-3.0 with acid or alkali, pack a certain amount of Purolite S957 resin into the ion exchange column, rinse the resin column with deionized water until the effluent is clear, collect the solution flowing out from the bottom of the resin column, and obtain the purified aluminum ammonium sulfate solution.

[0063] In S3, the temperature of the aluminum ammonium sulfate solution is 25-50℃, the pH value is 2-3, and the volume ratio of Purolite S957 resin to aluminum ammonium sulfate solution is 1:50-1:1000.

[0064] Temperature adjustment: Adjust the aluminum ammonium sulfate leachate obtained in step S2 to 25-50℃, preferably 40℃. A suitable temperature can maintain a suitable solution viscosity, optimize ion exchange kinetics, and ensure good adsorption efficiency.

[0065] Adjust the pH value: Carefully adjust the pH value of the solution to 2.0-3.0, preferably 2.5, using a small amount of acid (such as sulfuric acid) or base.

[0066] Under acidic conditions (pH 2-3), it still exists in cationic form and is easily chelated by resin. Purolite S957 resin, however, exhibits good adhesion to Fe within this pH range. 3+ The selectivity is much higher than that for Al 3+ Selectivity. If the pH is too high, Al... 3+ Hydrolysis may occur, forming precipitates that can clog the resin bed; if the pH is too low...

[0067] H + Excessive concentration will react with Fe 3+ Competition for active sites on the resin reduces iron removal efficiency.

[0068] Column packing: A certain amount of Purolite S957 resin is packed into the ion exchange column. The resin bed should be uniformly packed and free of air bubbles.

[0069] Pretreatment: Rinse the resin column with deionized water until the effluent is clear.

[0070] Sample loading and adsorption: The pretreated aluminum ammonium sulfate solution is pumped from the top of the exchange column at a **controlled flow rate**, allowing it to flow through the resin bed.

[0071] Adsorption process: Fe in solution 3+ Ions are selectively captured by chelating groups on the resin and adsorbed onto the resin. Meanwhile, Al in the aluminum ammonium sulfate solution... 3+ NH4 + SO4 2- The main components are rarely adsorbed and flow out with the solution.

[0072] Volume ratio control: The ratio of the amount of solution to the volume of resin, resin:solution = 1:50-1:1000, preferably 1:400. 1L of resin can treat 50 to 1000 liters of solution, showing the resin's extremely high adsorption capacity and efficiency.

[0073] Collect the effluent: The solution flowing out from the bottom of the resin column is the purified aluminum ammonium sulfate solution, in which the iron content has been greatly reduced, with an iron removal rate of 92%.

[0074] Resin Regeneration

[0075] Once the resin becomes saturated with iron, it needs to be regenerated for reuse.

[0076] The regeneration steps are typically as follows:

[0077] Backwash: Rinse the resin bed with water in the backwash to remove solid impurities and air bubbles.

[0078] Acid elution: A 4-6% hydrochloric acid or sulfuric acid solution is passed through the resin bed to remove the adsorbed Fe. 3+ The solution is washed off, producing a waste acid solution rich in iron.

[0079] Wash with water: Rinse with deionized water until neutral to remove residual acid.

[0080] The parameters and their preferred ranges are shown in the table below:

[0081]

[0082] S4. Aluminum is precipitated in the purified aluminum ammonium sulfate solution obtained in step S3 in the form of ammonium alum, and then reacted by heating in a furnace to generate aluminum oxide powder.

[0083] S4 includes:

[0084] S4-1. Transfer the pure ammonium aluminum sulfate solution obtained in step S3, which has had iron impurities removed by ion exchange, into a reaction crystallization vessel equipped with a stirring and cooling jacket.

[0085] S4-2. Through the cooling jacket of the crystallizer, a cooling medium is introduced to rapidly cool the solution to 2-25°C, preferably 5°C; at the target low temperature, stirring is maintained for 15-90 minutes, preferably 60 minutes.

[0086] S4-3. After crystallization, the slurry is sent to a filtration device. The separated solid is wet ammonium alum crystals. The crystals are washed with ice water or cold alcohol.

[0087] The above describes the crystallization steps.

[0088] S4-4. Place the ammonium alum crystals obtained in the above steps into a high-temperature resistant container, spread them out evenly and thinly, and place the container into a muffle furnace preheated to the target temperature.

[0089] S4-5. Calcination is carried out in a muffle furnace at a high temperature of 800-1000℃, preferably 900℃, and the material is held at the target temperature for 30-120 minutes, preferably 60 minutes. The material is then allowed to cool naturally to room temperature in the furnace. After cooling, the material is removed from the muffle furnace, and the container contains alumina powder.

[0090] The above describes the calcination steps.

[0091] The solubility of ammonium alum decreases significantly with decreasing temperature. Operating at low temperatures (even close to freezing point) can minimize its solubility, thereby improving the precipitation recovery rate of aluminum and promoting the precipitation of more ammonium alum crystals from the solution.

[0092] Allow sufficient time for the crystals to grow slowly, resulting in larger, purer crystals. Larger crystals are easier to separate from the mother liquor during subsequent filtration and washing steps, and contain fewer impurities.

[0093] The decomposition of ammonium alum requires very high temperatures. Within this temperature range (800-1000℃), the following reaction occurs:

[0094] 2NH4Al(SO4)2·12H2O→Al2O3+2NH3↑+4SO3↑+25H2O↑.

[0095] The key parameters are shown in the table below:

[0096]

[0097]

[0098] S5. Add hydrochloric acid solution to the alumina powder obtained in step S4, and obtain aluminum chloride solution through leaching reaction.

[0099] S5-1. Take a certain amount of the pure alumina powder obtained by calcination in step S4, prepare a hydrochloric acid solution with a concentration of 220-425 g / L, preferably 350 g / L, and add the alumina powder and hydrochloric acid solution to the reactor at a mass-volume ratio of 1:2.5 to 1:10, preferably 1:2.7.

[0100] S5-2. Start stirring to fully mix the alumina powder and acid solution to form a slurry. Heat the reaction system to 60-110°C, preferably 80°C, and maintain the reaction at the target temperature for 15-240 minutes, preferably 30 minutes.

[0101] S5-3. After the predetermined reaction time is reached, stop heating and stirring, allow the reaction solution to cool naturally to room temperature, and filter the cooled solution.

[0102] S5-4. The filtrate obtained after filtration is an aluminum chloride solution.

[0103] The control parameters and their preferred ranges are shown in the table below:

[0104]

[0105]

[0106] Example

[0107] The fly ash used as raw material has the following main components: Al2O3 content 26.76wt%, SiO2 content 65.10wt%, Fe2O3 content 2.48wt%, CaO content 1.40wt%, Na2O content 0.53wt%, MgO content 0.77wt%, and TiO2 content 1.20wt%.

[0108] S1. Add 1000 mL of 420 g / L NaOH solution to 100 g of fly ash, heat to 105 °C and stir for 20 minutes. Then filter, wash and dry the solid ash residue of the slurry to finally obtain 65 g of desiliconized fly ash (yield 65%).

[0109] S2. Add 600 mL of a mixed solution of 40% ammonium bisulfate and 735 g / L sulfuric acid to 100 g of desilication fly ash. The ratio of the mixture is 1:1. Heat to 170 °C and stir continuously for 90 minutes. Then filter, wash and dry the solid residue. The aluminum extraction rate reaches 93%.

[0110] S3. Ion exchange adsorption: The aluminum ammonium sulfate solution obtained after high-pressure leaching of fly ash is purified by iron removal through a Purolite S957 resin column. The solution temperature is maintained at 40℃, the pH value is 2.5, and the volume ratio of solution to resin is 1:400. The iron ion adsorption removal rate reaches 92%.

[0111] S4. Ammonium alum precipitation and calcination: The purified aluminum ammonium sulfate solution was reacted at 5°C for 60 minutes to precipitate ammonium alum. The obtained ammonium alum was then calcined at 900°C in an oxidizing atmosphere for 60 minutes to finally obtain the alumina product.

[0112] S5. Alumina-hydrochloric acid leaching at atmospheric pressure: 100g of alumina is leached by reacting with 350g / L hydrochloric acid at 80℃ for 30 minutes, with the solid-liquid ratio controlled at 1:2.7, finally obtaining an aluminum chloride solution. The concentration of Al3+ in the solution reaches 70g / L.

[0113] Working principle:

[0114] S1. Take a certain amount of raw fly ash and prepare a NaOH solution with a concentration of 400-450 g / L. Mix the fly ash and NaOH solution at a mass-volume ratio of 1:5 to 1:15. Use sodium hydroxide solution to pre-desiliconize the fly ash. In S1, the fly ash is a solid waste from a coal-fired power plant, and its components are Al2O3, SiO2, Fe2O3, CaO, Na2O, MgO, and TiO2. When mixing, heat the mixed slurry to a reaction temperature of 90-110℃, with a solid-liquid ratio of 1:5-1:15 and a reaction time of 10-40 minutes. Stir continuously during the reaction to ensure that the fly ash particles are in full contact with the alkaline solution and that the reaction is uniform. Breaking the structure and activating the aluminum source: This step effectively breaks the stable mullite structure in the fly ash, exposing the encapsulated alumina and transforming it from an "inert state" to an "active state," creating decisive conditions for subsequent efficient acid leaching.

[0115] Aluminum enrichment: The removal of a large amount of silicon significantly increases the relative content of alumina in the remaining solid residue (desiliconized fly ash), making subsequent treatment more focused and efficient.

[0116] Reduced interference from impurities: Most of the silicon is removed in advance, avoiding the formation of silica gel during the subsequent acid leaching process, thereby preventing filtration difficulties and damage to the equipment, and ensuring a smooth process.

[0117] S2. Add a mixed solution of ammonium bisulfate and sulfuric acid to the desilicationized fly ash obtained in step S1. After high-pressure leaching, separate the solid and liquid phases. The concentration of the ammonium bisulfate solution is 20-50%, and the concentration of the sulfuric acid solution is 365-1150 g / L. The ratio of the mixture is between 3:1 and 1:3. During the reaction, the volume is heated to 130-220℃ and maintained at the target temperature for 30-240 minutes. The high-pressure and high-temperature conditions overcome the limitations of atmospheric pressure reactions, completely decomposing the activated aluminum minerals and achieving a dissolution rate of over 93% for aluminum. This is the core manifestation of the advanced nature of this process technology. The reaction is highly efficient and rapid: Under optimized conditions, the reaction can be completed in a relatively short time, balancing efficiency and energy consumption, which is beneficial for industrial scale-up.

[0118] S3. Adjust the aluminum ammonium sulfate leaching solution obtained in step S2 to 25-50℃, and carefully adjust the pH of the solution to 2.0-3.0 with acid or alkali. Load a certain amount of Purolite S957 resin into an ion exchange column, and rinse the resin column with deionized water until the effluent is clear. The temperature of the aluminum ammonium sulfate solution should be 25-50℃, and the pH should be 2-3. The volume ratio of Purolite S957 resin to aluminum ammonium sulfate solution should be 1:50-1:1000. Collect the solution flowing from the bottom of the resin column to obtain a purified aluminum ammonium sulfate solution. This step is highly specific and efficient, capable of removing more than 92% of iron ions, solving the key problem of high iron content in fly ash raw materials, and ensuring the high purity and excellent quality of the final aluminum chloride product (such as a lighter color and better water treatment effect). The operation is simple and economical: the ion exchange method operates at room temperature, has low energy consumption, and the resin can be regenerated and reused, reducing the raw material consumption cost for long-term operation.

[0119] S4. Precipitate aluminum in the form of ammonium alum in the purified aluminum sulfate solution obtained in step S3.

[0120] S4-1. Transfer the pure ammonium aluminum sulfate solution obtained in step S3, which has had iron impurities removed by ion exchange, into a reaction crystallization vessel equipped with a stirring and cooling jacket.

[0121] S4-2. Through the cooling jacket of the crystallizer, introduce cooling medium to rapidly cool the solution to 2-25°C. At the target low temperature, maintain stirring and keep it at that temperature for 15-90 minutes.

[0122] S4-3. After crystallization, the slurry is sent to a filtration device. The separated solid is wet ammonium alum crystals. The crystals are washed with ice water or cold alcohol.

[0123] In a preferred embodiment, S4 further includes:

[0124] S4-4. Place the ammonium alum crystals obtained in the above steps into a high-temperature resistant container, spread them out evenly and thinly, and place the container into a muffle furnace preheated to the target temperature.

[0125] S4-5. Calcination is carried out in a muffle furnace at a high temperature of 800-1000℃, and the target temperature is held for 30-120 minutes. The material is then allowed to cool naturally to room temperature inside the furnace. After cooling, it is removed from the muffle furnace. The container contains alumina powder, which is produced by the reaction in the furnace. The crystallization process itself is a highly efficient refining method, which can remove residual trace soluble impurities from the crystals, further improving the purity of aluminum. A highly active intermediate is obtained: The alumina obtained by calcination is in a porous, loose, and highly active form, rather than dense corundum. This makes its reaction with hydrochloric acid in the final step very rapid, complete, and easy to control. It facilitates storage and transportation: Converting aluminum from solution to a stable solid oxide makes it easier to store for a long time and transport over long distances.

[0126] S5. Add hydrochloric acid solution to the alumina powder obtained in step S4, and obtain aluminum chloride solution by leaching reaction.

[0127] S5-1. Take a certain amount of the pure alumina powder obtained by calcination in step S4, prepare a hydrochloric acid solution with a concentration of 220-425 g / L, and add the alumina powder and hydrochloric acid solution to the reactor at a mass-volume ratio of 1:2.5 to 1:10.

[0128] S5-2. Start stirring to fully mix the alumina powder and acid solution to form a slurry. Heat the reaction system to 60-110℃ and maintain the reaction at the target temperature for 15-240 minutes.

[0129] S5-3. After the predetermined reaction time is reached, stop heating and stirring, allow the reaction solution to cool naturally to room temperature, and filter the cooled solution.

[0130] S5-4. The filtrate obtained after filtration is an aluminum chloride solution.

[0131] Mild reaction conditions: Thanks to the highly active alumina obtained in the previous step, this step can be carried out at normal pressure and relatively low temperature. The equipment requirements are low, the safety is high, the operation is simple, and the product is directly usable: The product is an aluminum chloride solution that can be directly used for water treatment. The concentration is controllable, realizing a perfect transformation from waste to high value-added commodity and completing a green closed loop: The final product is used to purify water quality, while its production process also consumes solid waste, forming a complete environmental protection technology closed loop with significant environmental and social benefits.

[0132] The above description is merely 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 preparing aluminum chloride by leaching coal ash with a mixture of ammonium bisulfate and sulfuric acid, characterized in that, include: S1. Take a certain amount of raw fly ash, prepare a NaOH solution with a concentration of 400-450g / L, mix the fly ash and NaOH solution at a mass-volume ratio of 1:5 to 1:15, and use sodium hydroxide solution to pre-desiliconize the fly ash. S2. Add a mixed solution of ammonium bisulfate and sulfuric acid to the desiliconized fly ash obtained in step S1, and then perform solid-liquid separation after high-pressure leaching. S3. Adjust the aluminum ammonium sulfate leaching solution obtained in step S2 to 25-50℃, carefully adjust the pH value of the solution to 2.0-3.0 with acid or alkali, pack a certain amount of Purolite S957 resin into the ion exchange column, rinse the resin column with deionized water until the effluent is clear, collect the solution flowing out from the bottom of the resin column, and obtain the purified aluminum ammonium sulfate solution. S4. Aluminum is precipitated in the purified aluminum ammonium sulfate solution obtained in step S3 in the form of ammonium alum, and aluminum oxide powder is generated by heating the reaction in a furnace. S5. Add hydrochloric acid solution to the alumina powder obtained in step S4, and obtain aluminum chloride solution through leaching reaction.

2. The method for preparing aluminum chloride by leaching coal ash with an ammonium bisulfate-sulfuric acid mixture according to claim 1, characterized in that: In S1, fly ash is a solid waste from coal-fired power plants, and its components are Al2O3, SiO2, Fe2O3, CaO, Na2O, MgO and TiO2.

3. The method for preparing aluminum chloride by leaching coal ash with an ammonium bisulfate-sulfuric acid mixture according to claim 1, characterized in that: In S1, during mixing, the mixed slurry is heated to a reaction temperature of 90-110℃, and the reaction time is 10-40 minutes; During the reaction, continuous stirring ensures that the fly ash particles and the alkaline solution are in full contact, guaranteeing a uniform reaction.

4. The method for preparing aluminum chloride by leaching coal ash with an ammonium bisulfate-sulfuric acid mixture according to claim 3, characterized in that: In S2, the concentration of ammonium bisulfate solution is 20-50%, the concentration of sulfuric acid solution is 365-1150 g / L, and the ratio in the mixture ranges from 3:1 to 1:

3. During the reaction, the volume is heated to 130-220°C and maintained at the target temperature for 30-240 minutes.

5. The method for preparing aluminum chloride by leaching coal ash with an ammonium bisulfate-sulfuric acid mixture according to claim 4, characterized in that: In S3, the temperature of the aluminum ammonium sulfate solution is 25-50℃, the pH value is 2-3, and the volume ratio of Purolite S957 resin to aluminum ammonium sulfate solution is 1:50-1:1000.

6. The method for preparing aluminum chloride by leaching coal ash with an ammonium bisulfate-sulfuric acid mixture according to claim 5, characterized in that: S4 includes: S4-1. Transfer the pure ammonium aluminum sulfate solution obtained in step S3, which has had iron impurities removed by ion exchange, into a reaction crystallization vessel equipped with a stirring and cooling jacket. S4-2. Through the cooling jacket of the crystallizer, introduce cooling medium to rapidly cool the solution to 2-25°C. At the target low temperature, maintain stirring and keep it at that temperature for 15-90 minutes. S4-3. After crystallization, the slurry is sent to a filtration device. The separated solid is wet ammonium alum crystals. The crystals are washed with ice water or cold alcohol.

7. The method for preparing aluminum chloride by leaching coal ash with an ammonium bisulfate-sulfuric acid mixture according to claim 6, characterized in that: S4 also includes: S4-4. Place the ammonium alum crystals obtained in the above steps into a high-temperature resistant container, spread them out evenly and thinly, and place the container into a muffle furnace preheated to the target temperature. S4-5. Calcine in a muffle furnace at a high temperature of 800-1000℃, hold at the target temperature for 30-120 minutes, and allow the material to cool naturally to room temperature in the furnace. After cooling, remove it from the muffle furnace; the container contains alumina powder.

8. The method for preparing aluminum chloride by leaching coal ash with ammonium bisulfate-sulfuric acid mixture according to claim 1, characterized in that: S5 includes: S5-1. Take a certain amount of the pure alumina powder obtained by calcination in step S4, prepare a hydrochloric acid solution with a concentration of 220-425 g / L, and add the alumina powder and hydrochloric acid solution to the reactor at a mass-volume ratio of 1:2.5 to 1:

10. S5-2. Start stirring to fully mix the alumina powder and acid solution to form a slurry. Heat the reaction system to 60-110℃ and maintain the reaction at the target temperature for 15-240 minutes. S5-3. After the predetermined reaction time is reached, stop heating and stirring, allow the reaction solution to cool naturally to room temperature, and filter the cooled solution. S5-4. The filtrate obtained after filtration is an aluminum chloride solution.

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