Method for preparing aluminum sulfate from secondary aluminum ash

Abstract

The invention discloses a method for preparing aluminum sulfate by using secondary aluminum ash, which comprises the following steps: mixing dried secondary aluminum ash particles with a pretreating agent, and transferring into a ball mill for mechanical activation treatment to obtain activated aluminum ash composite powder; mixing the activated aluminum ash composite powder with water, hydrolyzing, and carrying out filter pressing on the slurry to obtain a denitrified and desalted aluminum ash filter cake and a filtrate containing soluble salt; mixing the denitrified and desalted aluminum ash filter cake with sulfuric acid, and reacting under corresponding pressure; cooling and releasing pressure, discharging the slurry, and filtering or carrying out filter pressing treatment to obtain an aluminum sulfate coarse solution and waste residues; heating the aluminum sulfate crude solution, slowly adding an oxidizing agent under intense stirring, and separating to obtain a refined aluminum sulfate solution and iron-containing waste residues; according to the technical scheme, metastable state aluminum oxide and other indissolvable substances activated through pretreatment can be efficiently dissociated, so that the leaching rate of aluminum is greatly increased, and a reliable solution is provided for achieving high value-added resource utilization.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial solid waste resource utilization and sewage treatment agent preparation, and particularly relates to a method for preparing aluminum sulfate by using secondary aluminum dross. BACKGROUND

[0002] Secondary aluminum dross is a hazardous waste (HW48) generated in the process of aluminum electrolysis, smelting and regeneration, generally in the form of loose small particles or dust particles, containing aluminum nitride, fluoride, chloride and a small amount of harmful components such as heavy metal elements, and its environmental risk mainly lies in: ① aluminum nitride will hydrolyze when it comes into contact with water, releasing ammonia gas and hydrogen gas which are irritating and explosive; ② soluble fluoride and chloride are easily leached out under the action of rainwater, which may lead to soil salinization, groundwater pollution and vegetation destruction, posing a long-term threat to the ecological environment and public health.

[0003] According to statistics, the primary aluminum output in China reached 4021 tons in 2022, and about 0.03-0.25 tons of aluminum dross is generated per ton of aluminum produced, with an annual aluminum dross production of more than 400 tons. The aluminum content in secondary aluminum dross accounts for about 5%-20% of the total mass, which has certain economic value. At present, the main method for the resource utilization of secondary aluminum dross is wet acid leaching process, which can prepare sewage purifying agents (such as aluminum sulfate and polyaluminum chloride) from the secondary aluminum dross. However, the wet acid leaching process has the following problems: 1. Low aluminum leaching rate and difficulty in utilizing inert components After recovery or heat treatment, the aluminum oxide in secondary aluminum dross has been completely converted into α-type aluminum oxide (α-Al2O3) which has stable crystal structure and is chemically inert. At the same time, under the action of high temperature, the Si-Al-O bond reorganizes to form a large amount of stable mullite crystal phase. The above products have very low reactivity under conventional acid leaching conditions, resulting in low aluminum leaching efficiency; 2. Safety risk is prominent in the reaction process When aluminum nitride and aluminum are in contact with acid, they will react violently, releasing a large amount of gas and strong heat at once, which may lead to the risk of material spraying, expansion of the reactor and even explosion; 3. It is difficult to separate impurities in the product The fluoride, chloride and heavy metal ions contained in the leaching solution form stable coordination compounds, which are difficult to remove.

[0004] Therefore, there is an urgent need for a secondary aluminum dross treatment method that can realize efficient, safe and high-value utilization at the same time, improve the aluminum recovery rate, reduce energy consumption and cost, and realize the unity of environmental and economic benefits. SUMMARY

[0005] The main purpose of the present application is to provide a method for preparing aluminum sulfate from secondary aluminum dross, aiming to safely and efficiently remove aluminum nitride and soluble salt through pretreatment, eliminate the risk of concentrated release of harmful gas from the source, strengthen the reaction kinetics through pressurized acid leaching on the basis of mechanical activation of aluminum dross, realize efficient leaching of aluminum, finally establish a short-process and low-cost secondary aluminum dross resource utilization process, realize the recovery of valuable components, and minimize the amount of final waste residue.

[0006] To achieve the above-mentioned purpose, the method for preparing aluminum sulfate from secondary aluminum dross provided by the present application comprises the following steps: Step S1: dry secondary aluminum dross particles are mixed with a pretreatment agent in a preset ratio, then transferred into a ball mill jar of a ball mill, grinding balls are loaded into the ball mill jar according to a preset ball-to-material ratio, mechanical activation treatment is carried out, and after screening, activated aluminum dross composite powder is obtained; Step S2: the activated aluminum dross composite powder obtained in step S1 is mixed with water at a solid-to-liquid ratio of 1:3-5, stirring and hydrolysis reaction are carried out at a temperature of 80-95℃ for 2-3 hours, after the completion of the hydrolysis reaction, the slurry is pressure-filtered to obtain denitrified and desalted aluminum dross filter cake and a filtrate containing soluble salt; Step S3: the denitrified and desalted aluminum dross filter cake obtained in step S2 is put into a corrosion-resistant high-pressure reaction kettle together with sulfuric acid, after being sealed, the temperature is raised to 130-160℃ under stirring, and reaction is carried out under corresponding pressure for 1-6 hours; Step S4: after the reaction is completed, cooling and pressure relief are carried out, the slurry is discharged for filtration or pressure filtration treatment, and aluminum sulfate crude solution and waste residue mainly composed of calcium sulfate, calcium fluoride and silicate are obtained; Step S5: the aluminum sulfate crude solution obtained in step S4 is heated to 80-95℃, an oxidizing agent is slowly added under strong stirring, then the pH value of the solution is controlled to 1.5-2.5, and the solution is kept at temperature and stirred for 0.5-1.5 hours, after the reaction is completed, refined aluminum sulfate solution and iron-containing waste residue are separated by hot filtration.

[0007] Optionally, step S6 is further included, the refined aluminum sulfate solution obtained in step S5 is evaporated and concentrated, then cooled and crystallized, and solid aluminum sulfate is separated by filtration.

[0008] Optionally, in step S1, the pretreatment agent is calcium carbonate powder, which is used to promote the refinement of aluminum dross particles during mechanical activation and provide a calcium source for fixing fluoride ions in the subsequent steps.

[0009] Optionally, in step S1, the mass ratio of the pretreatment agent to secondary aluminum dross particles is 0.1-0.3:1.

[0010] Optionally, in the step S1, the diameter of the grinding ball is 3mm-12mm, the rotating speed of the ball mill is 400rpm-600rpm, and the mechanical activation treatment time is 2-4 hours.

[0011] Optionally, in the step S1, the mechanical activation treatment is carried out under a protective gas, which can prevent some components in the aluminum ash from being oxidized.

[0012] Optionally, the protective gas is one or more of carbon dioxide, nitrogen and argon.

[0013] Optionally, in the step S2, the method further comprises: The ammonia gas generated in the hydrolysis reaction is discharged through a closed pipeline and absorbed by an acid to prepare an ammonium salt, and the filtrate containing soluble salt is evaporated and crystallized to recover sodium salt and potassium salt.

[0014] Optionally, in the step S3, the concentration of the sulfuric acid is 40%-60%, and the mass ratio of the denitrification and desalination aluminum ash to the sulfuric acid is 1:0.8-2.

[0015] Optionally, in the step S5, the oxidizing agent is a hydrogen peroxide solution with a mass concentration of 5%-10%. Optionally, in the step S4, the waste residue is generated by the reaction of the pretreatment agent calcium carbonate added in the step S1 and the fluoride in the raw material, and has stable properties, and can be used as a building material raw material (such as a cement admixture) for resource utilization.

[0016] The technical scheme of the present application has the following advantages: 1. The technical scheme of the present application can make the pretreatment agent calcium carbonate and the aluminum ash fully mixed and refined through mechanical activation, which not only destroys the stable crystal structure of the inert alpha-Al2O3, so that a large number of lattice defects, lattice distortion and even surface amorphization are generated, but also activates the silicon aluminum compounds in the form of mullite or glass phase, so that they are converted into metastable substances with high reactivity, which improves the reactivity of subsequent acid leaching and the leaching efficiency of aluminum. At the same time, the uniformly dispersed calcium carbonate provides a reaction basis for in-situ fixation of impurities such as fluoride (to generate insoluble calcium fluoride) in subsequent steps.

[0017] 2. After the mechanical activation treatment, the particle size of the aluminum ash composite powder is reduced, and part of the aluminum nitride is oxidized or hydroxylated to form aluminum oxide or aluminum hydroxide. In addition, the specific surface area of the aluminum nitride powder is increased, so that the hydrolysis reaction is faster and more complete, and deep denitrification can be achieved under milder conditions, which reduces the safety hazards of subsequent acid leaching process (avoiding the generation of a large amount of ammonia gas and hydrogen gas).

[0018] 3. The technical solution of this invention uses a pressurized acid leaching process to replace the traditional atmospheric pressure reaction. By increasing the reaction temperature and pressure, the mass transfer efficiency and reaction kinetics are significantly enhanced, effectively breaking the Al2O3-SiO2 chemical bonds in mullite. This allows for the efficient dissociation of pretreated and activated metastable alumina and other sparingly soluble substances, thereby significantly increasing the aluminum leaching rate and providing a reliable solution for achieving high-value-added resource utilization. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0020] Figure 1 This is a flowchart illustrating the steps of a method for preparing aluminum sulfate using secondary aluminum ash according to an embodiment of the present invention.

[0021] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0022] 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 a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] Furthermore, the technical solutions of the various embodiments can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0024] This invention proposes a method for preparing aluminum sulfate using secondary aluminum ash.

[0025] like Figure 1 As shown, the method for preparing aluminum sulfate using secondary aluminum ash includes the following steps: Step S1: Mix the dried secondary aluminum ash particles with the pretreatment agent according to the preset ratio, and then transfer them into the ball mill jar of the ball mill. Load the grinding balls into the ball mill jar according to the preset ball-material ratio, carry out mechanical activation treatment, and obtain activated aluminum ash composite powder after sieving. Step S2: The activated aluminum ash composite powder obtained in step S1 is mixed with water at a solid-liquid ratio of 1:3-5, and a hydrolysis reaction is carried out at 80-95°C for 2-3 hours. After the hydrolysis reaction is completed, the slurry is filtered to obtain a denitrified and desalted aluminum ash filter cake and a filtrate containing soluble salts; Step S3: The denitrified and desalted aluminum ash filter cake obtained in step S2 is put into a corrosion-resistant high-pressure reaction kettle together with sulfuric acid. After being sealed, the temperature is raised to 130-160°C under stirring, and a reaction is carried out under corresponding pressure for 1-6 hours; Step S4: After the reaction is completed, the reaction kettle is cooled and depressurized, and the slurry is discharged and filtered or pressure-filtered to obtain a crude aluminum sulfate solution and a waste residue mainly containing calcium sulfate, calcium fluoride and silicates; Step S5: The crude aluminum sulfate solution obtained in step S4 is heated to 80-95°C, and an oxidizing agent is slowly added under strong stirring. Then, the pH value of the solution is controlled to 1.5-2.5, and a reaction is carried out under stirring for 0.5-1.5 hours. After the reaction is completed, a refined aluminum sulfate solution and a waste residue containing iron are separated by hot filtration.

[0026] Example 1 Step S1: 20g of dry secondary aluminum ash is mixed with 6g of calcium carbonate powder (mass ratio 1:0.3), transferred into a ball mill jar, loaded with 200g of grinding balls (ball-to-material ratio 7.7:1), and ball-milled at a speed of 500 rpm for 3 hours. After screening, an activated aluminum ash composite powder is obtained.

[0027] Step S2: The activated powder is mixed with 100mL of water, and a hydrolysis reaction is carried out at 90°C for 2 hours. After the reaction is completed, the reaction mixture is filtered to obtain a denitrified and desalted aluminum ash filter cake; Step S3: The filter cake is mixed with 40g of 50% sulfuric acid to form a slurry, which is put into a high-pressure reaction kettle. After being sealed, the temperature is raised to 150°C, and a reaction is carried out for 3 hours; Step S4: After the reaction is completed, the reaction kettle is naturally cooled and depressurized, and a crude aluminum sulfate solution and a waste residue mainly containing calcium sulfate and calcium fluoride are obtained after filtration; Step S5: The crude solution is heated to 90°C, and 10% hydrogen peroxide solution is slowly added under strong stirring. The pH value of the solution is controlled to 2.0 by using a pH adjuster. After a reaction is carried out for 1 hour, the reaction mixture is hot-filtered to obtain a refined aluminum sulfate solution.

[0028] Example 2 Step S1: 20g of dry secondary aluminum ash is mixed with 2g of calcium carbonate powder (mass ratio 1:0.1), transferred into a ball mill jar, loaded with 120g of grinding balls (ball-to-material ratio 5.5:1), and ball-milled at a speed of 400 rpm for 2 hours. After screening, an activated aluminum ash composite powder is obtained; Step S2: The activated powder is mixed with 60 mL of water, hydrolyzed at 90°C for 2 hours, filtered after the reaction is completed, and a denitrified and desalted aluminum ash filter cake is obtained; Step S3: The filter cake is mixed with 40 g of 50% sulfuric acid to form a slurry, which is put into a high-pressure reaction kettle, heated to 150°C after being sealed, and reacted for 3 hours; Step S4: After the reaction is completed, the reaction kettle is naturally cooled and depressurized, and after filtration, an aluminum sulfate crude solution and a waste residue mainly containing calcium sulfate and calcium fluoride are obtained; Step S5: The crude solution is heated to 90°C, 10% hydrogen peroxide solution is slowly added under strong stirring, the pH of the solution is controlled to 2.5 by a pH adjuster, and after 1 hour of reaction, it is filtered while hot to obtain a refined aluminum sulfate solution.

[0029] Example 3 Step S1: 20 g of dry secondary aluminum ash is mixed with 4 g of calcium carbonate powder (mass ratio 1:0.2), transferred into a ball mill jar, loaded with 300 g of grinding balls (ball-to-material ratio 12.5:1), the diameters of the grinding balls are 3 mm and 10 mm, the proportions are 70% and 30%, and the ball milling is carried out at a speed of 500 rpm for 3 hours. After screening, an activated aluminum ash composite powder is obtained; Step S2: The activated powder is mixed with 100 mL of water, hydrolyzed at 90°C for 2 hours, filtered after the reaction is completed, and a denitrified and desalted aluminum ash filter cake is obtained; Step S3: The filter cake is mixed with 30 g of 40% sulfuric acid to form a slurry, which is put into a high-pressure reaction kettle, heated to 120°C after being sealed, and reacted for 2 hours; Step S4: After the reaction is completed, the reaction kettle is naturally cooled and depressurized, and after filtration, an aluminum sulfate crude solution and a waste residue mainly containing calcium sulfate and calcium fluoride are obtained; Step S5: The crude solution is heated to 90°C, 10% hydrogen peroxide solution is slowly added under strong stirring, the pH of the solution is controlled to 2.0 by a pH adjuster, and after 1 hour of reaction, it is filtered while hot to obtain a refined aluminum sulfate solution. Example 4 Step S1: 20 g of dry secondary aluminum ash is mixed with 4 g of calcium carbonate powder (mass ratio 1:0.2), transferred into a ball mill jar, loaded with 300 g of grinding balls (ball-to-material ratio 12.5:1), the diameters of the grinding balls are 3 mm and 10 mm, the proportions are 70% and 30%, and the ball milling is carried out at a speed of 500 rpm for 3 hours. After screening, an activated aluminum ash composite powder is obtained; Step S2: The activated powder is mixed with 100 mL of water, hydrolyzed at 90°C for 2 hours, filtered after the reaction is completed, and a denitrified and desalted aluminum ash filter cake is obtained; Step S3: The filter cake is mixed with 40 g of 60% sulfuric acid to form a slurry, which is put into a high-pressure reaction kettle, heated to 160°C after being sealed, and reacted for 1 hour; Step S4: After the reaction, the reactor was naturally cooled and depressurized, and the aluminum sulfate crude solution and waste residue mainly containing calcium sulfate and calcium fluoride were obtained after filtration; Step S5: The crude solution was heated to 90°C, and 10% hydrogen peroxide solution was slowly added dropwise under strong stirring. The pH of the solution was controlled to 2.0 by a pH adjuster. After 1 hour of reaction, hot filtration was performed to obtain a refined aluminum sulfate solution.

[0030] Comparative Example 1 Step S1: 20 g of dry secondary aluminum ash was mixed with 100 mL of water, and hydrolysis was performed at 90°C for 2 hours. After the reaction, the aluminum ash filter cake was obtained by filtration.

[0031] Step S2: The filter cake was mixed with 40 g of 60% sulfuric acid to form a slurry, and the slurry was heated to 100°C for reflux reaction for 4 hours.

[0032] Step S3: After the reaction, hot filtration was performed to obtain an aluminum sulfate crude solution.

[0033] Step S4: The crude solution was heated to 90°C, and 10% hydrogen peroxide solution was slowly added dropwise under strong stirring. The pH of the solution was controlled to 2.5 by a pH adjuster. After 1 hour of reaction, hot filtration was performed to obtain an iron-removed aluminum sulfate solution.

[0034] Comparative Example 2 Step S1: 20 g of dry secondary aluminum ash was mixed with 4 g of calcium carbonate powder (mass ratio 1:0.2), and was transferred into a ball mill pot. 240 g of grinding balls (ball-to-material ratio 10:1) were loaded, with ball diameters of 3 mm and 10 mm, accounting for 70% and 30%, respectively. Ball milling was performed at a speed of 500 rpm for 3 hours. After screening, an activated aluminum ash composite powder was obtained; Step S2: The activated powder was mixed with 100 mL of water, and hydrolysis was performed at 90°C for 2 hours. After the reaction, the denitrified and desalted aluminum ash filter cake was obtained by filtration. Step S3: The filter cake was mixed with 40 g of 50% sulfuric acid to form a slurry, and the slurry was heated to 100°C for reflux reaction for 6 hours. Step S4: After the reaction, hot filtration was performed to obtain an aluminum sulfate crude solution. Step S5: The crude solution was heated to 90°C, and 10% hydrogen peroxide solution was slowly added dropwise under strong stirring. The pH of the solution was controlled to 2.0 by a pH adjuster. After 1 hour of reaction, hot filtration was performed to obtain a refined aluminum sulfate solution.

[0035] Comparative Example 3 Step S1: 20 g of dry secondary aluminum dross was mixed with 4 g of calcium carbonate powder (mass ratio 1:0.2), transferred into a ball mill tank, loaded with 250 g of grinding balls (ball-to-material ratio 12.5:1), the grinding balls had diameters of 3 mm and 10 mm, and the proportion was 70% and 30%, and the ball milling was performed at a speed of 500 rpm for 3 hours. After screening, the activated aluminum dross composite powder was obtained; Step S2: The activated powder was mixed with 100 mL of water, and hydrolysis was performed at 90°C for 2 hours. After the reaction was completed, filtration was performed, and the denitrified and desalted aluminum dross filter cake was obtained; Step S3: The filter cake was mixed with 40 g of 50% sulfuric acid to form a slurry, which was then put into a high-pressure reaction kettle. After being sealed, the temperature was increased to 150°C, and the reaction was performed for 4 hours; Step S4: After the reaction was completed, the reaction kettle was naturally cooled and depressurized. After filtration, the crude aluminum sulfate solution and the waste residue mainly containing calcium sulfate and calcium fluoride were obtained; Step S5: The crude solution was heated and evaporated to concentrate, and then cooled and crystallized to separate the solid aluminum sulfate.

[0036] Aluminum sulfate index detection According to the standard method of “Water Treatment Agent Aluminum Sulfate (GB / T 31060-2014)”, the aluminum oxide content and pH of the aluminum sulfate solution were determined. The contents of metal elements such as Al and Fe in the solution were detected by inductively coupled plasma optical emission spectrometry (ICP-OES), and the detection results of each example are shown in Table 1.

[0037] Table 1

[0038] Referring to Table 1, the key indicators of the obtained aluminum sulfate in each example all meet the standard requirements of the water treatment agent. In Example 1, the aluminum oxide content reached 8.34% under the optimal process conditions. When the mechanical activation intensity was reduced in Example 2, although there were no abnormalities in the acid leaching process, the aluminum oxide content decreased, indicating that insufficient activation intensity directly limited the conversion efficiency of aluminum, confirming the key role of sufficient mechanical activation in releasing the reaction activity. In Example 3 and Example 4, mild pressure acid leaching and high-temperature short-time process were used respectively, and the aluminum oxide contents reached 7.79% and 8.21% respectively. The reaction process was stable, proving that the process parameters have good operation flexibility and optimization potential, and can balance efficiency and stability.

[0039] The results of Comparative Example 1 show that the lack of activation and harmless treatment of the front-end process will directly lead to incomplete reaction of aluminum ash with acid and out-of-control impurities. Comparative Example 2, under the premise of mechanical activation, has a higher alumina content than Comparative Example 1, but is still significantly lower than any of the pressurized examples, which clearly confirms that the pressurized environment plays an important role in completely destroying the structure of inert alumina and achieving efficient conversion. The iron content of the product of Comparative Example 3 is as high as 1.96%, and the product is unqualified, which shows that the iron removal process used in the technical solution of the present application is crucial to ensuring the purity of the final product and is a key link in the process that is efficient and reliable.

[0040] In summary, the innovation of the present application not only lies in the breakthrough of a single technology, but also in the precise coupling and synergistic effect of multiple steps. Examples 3 and 4 further demonstrate that the process parameter window is wide and has the potential for industrialization through optimization to achieve energy saving and cost reduction (such as high-temperature short-time process). Therefore, the present application solves the three core problems of low activity, high safety risk and poor product purity in the secondary aluminum ash resource utilization process, and provides a reliable and economic technical route for the high-value utilization of hazardous waste.

[0041] Specifically, the technical solution of the present application has the following advantages: (1) The existing aluminum ash harmless disposal technology first needs to treat the aluminum ash with water to make the aluminum nitride in it hydrolyze to form aluminum hydroxide and ammonia gas, and the aluminum carbide and metallic aluminum hydroxide, methane and hydrogen gas. At the same time, the water-soluble fluorides and heavy metals are stabilized by adding a solidifying agent.

[0042] However, the aluminum hydroxide produced by the hydrolysis of aluminum nitride, aluminum carbide and metallic aluminum in the aluminum ash will form a colloid, which will wrap the surface of the unreacted aluminum nitride particles, thereby blocking their further contact with water, making it difficult for the hydrolysis reaction to proceed fully. Therefore, the denitrification rate of the conventional water immersion process is generally low, usually only about 60%.

[0043] The technical solution of the present application mixes the pre-treatment agent calcium carbonate with aluminum ash through mechanical activation, which not only destroys the stable crystal structure of inert a-Al2O3, making it produce a large number of lattice defects, lattice distortion and even surface amorphization, but also activates the silicon-aluminum compounds in the form of mullite or glass phase, making them transform into high-reactivity metastable substances, improving the reaction activity of subsequent acid leaching and increasing the leaching efficiency of aluminum. At the same time, the uniformly dispersed calcium carbonate provides a reaction basis for the in-situ fixation of impurities such as fluorides (forming insoluble calcium fluoride) in the subsequent steps.

[0044] On the other hand, after mechanical activation treatment, the particle size of aluminum ash composite powder is reduced, part of aluminum nitride is oxidized or hydroxylated to form aluminum oxide or aluminum hydroxide. In addition, the specific surface area of aluminum nitride powder increases, so that the hydrolysis reaction is faster and more complete, and deep denitrification can be achieved under milder conditions, reducing the safety hazards of subsequent acid leaching process (avoiding the generation of a large amount of ammonia and hydrogen).

[0045] (2) The existing aluminum ash wet resource disposal technology usually first leaches the aluminum component in the aluminum ash to form an aluminum salt solution, and then prepares aluminum sulfate, polyaluminum chloride and the like through different subsequent processes. But this technical route has obvious bottlenecks. The chemically inert α-Al2O3 in the aluminum ash has very low reactivity under conventional acid leaching conditions, and is difficult to be effectively dissolved, resulting in low effective component of the obtained aluminum sulfate solution, small product added value, and poor overall economy, and it is almost difficult to achieve profit.

[0046] The technical scheme of the present application adopts pressurized acid leaching process instead of traditional atmospheric reaction. By increasing the reaction temperature and pressure, the mass transfer efficiency and reaction kinetics process are significantly strengthened, the mullite Al2O3-SiO2 chemical bond is effectively destroyed, and the metastable aluminum oxide and other insoluble substances activated by pretreatment can be efficiently dissociated, thereby greatly improving the leaching rate of aluminum, and providing a reliable solution for high value-added resource utilization.

[0047] The above only describes the preferred embodiments of the present application, and does not limit the patent scope of the present application, and any equivalent structural transformation made under the inventive concept of the present application, or direct / indirect application in other related technical fields is included in the patent protection scope of the present application.

Claims

1. A method for preparing aluminum sulfate using secondary aluminum dross, characterized by, The method comprises the following steps: Step S1: dry secondary aluminum ash particles are mixed with a pretreatment agent in a preset ratio, and then are transferred into a ball mill tank of a ball mill, grinding balls are loaded into the ball mill tank according to a preset ball-to-material ratio, mechanical activation treatment is performed, and after screening, activated aluminum ash composite powder is obtained; Step S2: the activated aluminum ash composite powder obtained in step S1 is mixed with water in a solid-to-liquid ratio of 1:3-5, a hydrolysis reaction is performed under stirring at a temperature of 80-95 ℃ for 2-3 hours, after the hydrolysis reaction is completed, the slurry is pressure-filtered to obtain denitrified and desalted aluminum ash filter cake and a filtrate containing soluble salts; Step S3: the denitrified and desalted aluminum ash filter cake obtained in step S2 is put into a corrosion-resistant high-pressure reaction kettle together with sulfuric acid, after being sealed, the temperature is increased to 130-160 ℃ under stirring, and a reaction is performed under a corresponding pressure for 1-6 hours; Step S4: after the reaction is completed, the temperature is cooled and the pressure is released, the slurry is discharged and filtered or pressure-filtered to obtain a crude aluminum sulfate solution and waste residue mainly composed of calcium sulfate, calcium fluoride and silicates; Step S5: the crude aluminum sulfate solution obtained in step S4 is heated to 80-95 ℃, an oxidizing agent is slowly added under strong stirring, then the pH value of the solution is controlled to 1.5-2.5, and a reaction is performed under stirring and heat for 0.5-1.5 hours, after the reaction is completed, refined aluminum sulfate solution and iron-containing waste residue are separated by hot filtration.

2. The method for preparing aluminum sulfate using secondary aluminum dross according to claim 1, characterized by, Step S6: the refined aluminum sulfate solution obtained in step S5 is evaporated and concentrated, and then is cooled and crystallized to obtain solid aluminum sulfate by filtration and separation. 3.The method of preparing aluminum sulfate using secondary aluminum dross according to claim 1, characterized by, In step S1, the pretreatment agent is calcium carbonate powder, which is used to promote the refinement of aluminum ash particles during mechanical activation and to provide a calcium source for fixing fluoride ions in subsequent steps. 4.The method of preparing aluminum sulfate using secondary aluminum dross according to claim 1, characterized by, In step S1, the mass ratio of the pretreatment agent to secondary aluminum ash particles is 0.1-0.3:

1. 5.The method of preparing aluminum sulfate using secondary aluminum dross according to claim 1, characterized by, In step S1, the diameter of the grinding balls is 3-12 mm, the rotation speed of the ball mill is 400-600 rpm, and the mechanical activation treatment time is 2-4 hours. 6.The method of preparing aluminum sulfate using secondary aluminum dross according to claim 1, wherein the secondary aluminum dross is prepared by the method according to any one of claims 1 to 5. In step S1, the mechanical activation treatment is performed under a protective gas. 7.The method of preparing aluminum sulfate using secondary aluminum dross according to claim 6, characterized by, The protective gas is one or more of carbon dioxide, nitrogen and argon. 8.The method of preparing aluminum sulfate using secondary aluminum dross according to claim 1, characterized by, In step S2, the following steps are further included: Ammonia gas generated in the hydrolysis reaction is discharged through a sealed pipeline and is absorbed with an acid to prepare an ammonium salt, and sodium salt and potassium salt are recovered from the filtrate containing soluble salts by evaporation and crystallization. 9.The method of preparing aluminum sulfate using secondary aluminum dross according to claim 1, characterized by, In step S3, the concentration of the sulfuric acid is 40-60%, and the mass ratio of the denitrified and desalted aluminum ash to sulfuric acid is 1:0.8-2. 10.The method of preparing aluminum sulfate using secondary aluminum dross according to claim 1, wherein the secondary aluminum dross is prepared by the method according to any one of claims 1 to 9. In step S5, the oxidizing agent is a hydrogen peroxide solution with a mass concentration of 5-10%.

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