Method for recycling aluminum ash

Abstract

The application belongs to the technical field of metal recycling and utilization, and provides an aluminum ash resource utilization method, in which metallic aluminum in aluminum ash is separated out first, and the remaining pretreated aluminum ash with low metallic aluminum content is washed with water, and then gamma type aluminum oxide and aluminum nitride in the aluminum ash are dissolved with sulfuric acid to obtain aluminum ammonium sulfate, aluminum sulfate solution and sulfuric acid insoluble alpha type aluminum oxide, the sulfuric acid insoluble alpha type aluminum oxide is mixed with calcium carbonate, and then high-temperature calcination and melting reaction are carried out to produce calcium aluminate, the calcium aluminate can be used as an aluminum source for subsequent production of polyaluminum chloride, the method of the application does not produce nitrogen gas, reduces the generation of hydrogen, has small danger and small pollution, eliminates the influence of fluoride, improves the resource utilization value of aluminum ash, and the recovery rate of metallic aluminum can reach 89.2%.

Description

Technical Field

[0001] The present invention relates to the technical field of metal recycling, and more specifically, to a method for resource utilization of aluminum ash. Background Art

[0002] During the production and casting of aluminum profiles, a large amount of aluminum ash is generated. The main components of aluminum ash include: metallic aluminum (greater than 15wt%), aluminum oxide, aluminum nitride, silicon, salts, incompletely burned carbon powder, and fluoride (fluoride is also generated due to the addition of sodium fluoroaluminate during the aluminum smelting process). Metallic aluminum dissolves in acid to produce hydrogen gas, which is prone to explosion, and aluminum nitride produces ammonia gas when it comes into contact with water, which pollutes the environment. To eliminate the harmfulness of aluminum ash and realize the resource utilization of aluminum, the following treatment methods are currently available: (1) cement kiln co-solidification method; (2) use as a building brick material; (3) direct landfill after calcination with oxygen without recycling; (4) use in the production of polyaluminum chloride water purifier. However, method (1) is limited in use because aluminum ash contains some chloride salts that have adverse effects on cement, and it is unable to process a large amount of aluminum ash, resulting in low-value utilization of aluminum resources; methods (2) and (3) use aluminum ash as building brick making material or directly landfill it, which has low utilization value, wastes aluminum resources, and also produces ammonia and pollutes the environment; method (4) uses aluminum ash to produce polyaluminum chloride water purifier, generally directly using aluminum ash and calcium carbonate through high-temperature melting reaction and phase change reaction to produce calcium aluminate, which is further used to produce polyaluminum chloride water purifier, but because the fluorine in the aluminum ash is not recovered, the above process will also produce calcium fluoride (generally, the mass proportion of fluorine in aluminum ash is between 1.5-3wt%, and the fluorine content in the obtained polyaluminum chloride is about 2.3wt%), which is not conducive to the production of polyaluminum chloride and increases the slag ratio. In addition, the calcination process produces a large amount of nitrogen oxides that pollute the environment, so it is necessary to install a denitrification device at the tail of the calcination kiln, resulting in cumbersome and high cost. The generation of hydrogen also has the risk of explosion. In summary, the current recycling methods have low aluminum ash utilization rates (aluminum ash utilization rate <30%), imperfect processes, and various defects.

[0003] Therefore, there is an urgent need to develop a method for resource utilization of aluminum ash that can improve the utilization rate of aluminum ash, reduce the generation of ammonia and hydrogen, avoid environmental pollution, and improve the utilization value of aluminum ash. Summary of the Invention

[0004] The present invention aims to address at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention provides a method for resource utilization of aluminum ash. The method utilizes a staged treatment process to recycle the substances in the aluminum ash separately, achieving a metallic aluminum recovery rate of 70.3-89.2% and an aluminum ash utilization rate of 17-84%. No ammonia is generated, hydrogen production is reduced, nitrogen is fully utilized to produce ammonium aluminum sulfate, and fluorine is recovered.

[0005] A first aspect of the present invention provides a method for resource utilization of aluminum ash.

[0006] Specifically, a method for resource utilization of aluminum ash comprises the following steps:

[0007] (1) Grinding and separating the aluminum ash to obtain metallic aluminum and pretreated aluminum ash, and transporting the metallic aluminum to the melting and casting process;

[0008] (2) washing the aluminum ash pretreated in step (1) with water, and then dissolving it with sulfuric acid to obtain ammonium aluminum sulfate, aluminum sulfate solution, and sulfuric acid-insoluble α-alumina;

[0009] (3) The sulfuric acid-insoluble α-alumina in step (2) is washed with water, and then calcium carbonate is added to carry out a high-temperature calcination and melting reaction to obtain calcium aluminate.

[0010] The present invention first uses a physical separation method to separate metallic aluminum from aluminum ash through grinding and separation, thus avoiding the generation of hydrogen and ammonia in subsequent processes. The remaining pre-treated aluminum ash has a low metallic aluminum content. After water washing, fluoride in the aluminum ash is dissolved and fluorine is recovered. The pre-treated aluminum ash is cyclically defluorinated and then dissolved in sulfuric acid to produce ammonium aluminum sulfate, aluminum sulfate solution, and sulfuric acid-insoluble α-alumina. This not only produces ammonium aluminum sulfate solution and aluminum sulfate solution, fully utilizing nitrogen and eliminating the harmful effects of ammonia, but also allows the sulfuric acid-insoluble α-alumina to be further washed with water, then added with calcium carbonate, and subjected to a high-temperature calcination and melting reaction to produce calcium aluminate, one of the raw materials for preparing polyaluminum chloride water purifiers. The present invention eliminates the hazards of traditional aluminum ash treatment processes through a staged treatment method, utilizing both aluminum and nitrogen resources as production raw materials.

[0011] The pretreated aluminum ash contains aluminum oxide, aluminum nitride, and silicon oxide. The aluminum oxide includes soluble gamma aluminum oxide and sulfuric acid-insoluble alpha aluminum oxide. The particle size of the soluble gamma aluminum oxide is less than 80 mesh.

[0012] Preferably, in step (1), the aluminum ash is aluminum-containing waste ash produced by smelting and casting in the production of aluminum profiles.

[0013] Preferably, in step (1), the equipment used for grinding and separation is a Raymond mill and an air separation separator.

[0014] Preferably, in step (1), the melting and casting process is carried out in a melting and casting furnace.

[0015] Preferably, in step (1), the metal aluminum is a metal aluminum sheet, the diameter of the metal aluminum sheet is 1-25 mm, and the thickness of the metal aluminum sheet is 0.05-10 mm.

[0016] Preferably, in step (2), the washing liquid after the water washing comprises a fluorine-containing substance. The fluorine-containing substance can be used to produce calcium fluoride.

[0017] Preferably, in step (2), the concentration of sulfuric acid is 21-25%.

[0018] Preferably, in step (2), the mass of the sulfuric acid is 0.5-3 times the mass of the pretreated aluminum ash.

[0019] Further preferably, in step (2), the mass of the sulfuric acid is 1.1-1.2 times the mass of the pretreated aluminum ash.

[0020] Preferably, in step (2), the dissolving with sulfuric acid is carried out in a glass fiber reinforced plastic reaction tank.

[0021] Preferably, in step (3), the mass of the sulfuric acid-insoluble α-alumina accounts for 55-75% of the total mass of the sulfuric acid-insoluble α-alumina and the alkaline substance.

[0022] Preferably, in step (3), the alkaline substance is at least one of calcium carbonate, sodium hydroxide and sodium carbonate.

[0023] Further preferably, in step (3), the alkaline substance is calcium carbonate. Using calcium carbonate can reduce costs, produce polyaluminium chloride products with high basicity and good water treatment effect.

[0024] Preferably, in step (3), the water washing is performed using a plate-and-frame filter press, which is an acid- and alkali-resistant reinforced polypropylene filter press used for solid-liquid separation.

[0025] Preferably, in step (3), the temperature of the high-temperature calcination melting reaction is 1300-1450° C., and the time is 40-60 minutes.

[0026] Preferably, in step (3), the high-temperature calcination and melting reaction is carried out in a rotary kiln.

[0027] Preferably, step (3) further comprises reacting calcium aluminate with acid and aluminum hydroxide to produce polyaluminum chloride. Calcium aluminate is a traditional raw material for producing polyaluminum chloride, which is commonly used as a water purifier.

[0028] Preferably, the preparation of polyaluminium chloride comprises the following steps:

[0029] Add 10-20% hydrochloric acid by mass into a glass fiber reinforced plastic reaction tank, then add aluminum hydroxide to dissolve, heat to 90-110°C and react for 1-3 hours; add calcium aluminate, react at 90-110°C for 1.5-2 hours, filter and obtain polyaluminum chloride.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention first separates the metallic aluminum from the aluminum ash by grinding and separation, thereby eliminating the explosion hazard of hydrogen generated in the subsequent acid dissolution process; the remaining pre-treated aluminum ash has a low metallic aluminum content, and is washed with water to dissolve the fluoride in the aluminum ash, and then sulfuric acid is used to dissolve the γ-type aluminum oxide and aluminum nitride therein to obtain ammonium aluminum sulfate, aluminum sulfate solution and sulfuric acid-insoluble α-type aluminum oxide, thereby eliminating the problem of aluminum nitride generating ammonia when it comes into contact with water; the sulfuric acid-insoluble α-type aluminum oxide is further washed with water and then reacted with calcium carbonate, and calcium aluminate is produced through high-temperature calcination and melting reaction. The calcium aluminate can be used as an aluminum source for producing polyaluminum chloride, which can play a role in adjusting the base. The aluminum ash is processed in sections and the material properties obtained in different stages are used for recycling and separation, thus avoiding the production of dangerous and toxic products. The aluminum ash with chemical reaction hazards and toxicity produced by the aluminum profile industry is fully utilized as a resource, and the metal aluminum recovery rate can reach 89.2%. In addition, the metal aluminum is removed by grinding and separation, sulfuric acid is dissolved to remove nitrogen with ammonia, and sulfuric acid-insoluble α-alumina is recovered to produce calcium aluminate, which is used to produce polyaluminum chloride. Any three consecutive processes can be used in the same industrial park to reduce production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of the process flow of the aluminum ash resource utilization method of Example 1 of the present invention. DETAILED DESCRIPTION

[0033] In order to make the technical solution of the present invention more clearly understood by those skilled in the art, the following examples are given for illustration. It should be noted that the following examples do not limit the scope of protection claimed by the present invention.

[0034] Unless otherwise specified, the raw materials, reagents, or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0035] Example 1

[0036] A method for resource utilization of aluminum ash, comprising the following steps:

[0037] (1) Aluminum separation: Aluminum ash (the metallic aluminum content in the initial aluminum ash is greater than 15%) is taken and ground and separated using a Raymond mill air separation separator (YGM95B model, manufactured by Zhengzhou General Mining Machinery Co., Ltd., which includes a Raymond suspension mill analyzer, a cyclone separator, and other devices). The particle size of aluminum oxide is controlled by adjusting the Raymond suspension mill analyzer, and the particle size of aluminum flakes is controlled by adjusting the circulating fan current to 55A. Finally, the metallic aluminum is ground into small aluminum flakes and the aluminum oxide is broken into fine powder. The aluminum ash is then separated using a cyclone separator to obtain metallic aluminum and pretreated aluminum ash. The metallic aluminum is returned to the melting and casting process for use, while the pretreated aluminum ash (containing aluminum oxide, aluminum nitride, and silicon oxide) is transported to the fiberglass reinforced plastic reaction tank;

[0038] (2) The pretreated aluminum ash is washed with water to obtain a component containing soluble aluminum oxide and aluminum nitride, which is placed in a glass fiber reinforced plastic reaction tank and dissolved with sulfuric acid (sulfuric acid concentration is 25%). The amount of sulfuric acid used is 1.15 times the weight of the pretreated aluminum ash. After sufficient reaction, it is transported to a filter press through a filter press pump for solid-liquid separation. The liquid is ammonium aluminum sulfate and aluminum sulfate solution, which are introduced into an ammonium aluminum sulfate semi-finished product tank. The filter residue is sulfuric acid-insoluble α-alumina, which enters the next step;

[0039] (3) After the filter residue obtained in step (2) is washed with water, the water is returned to be used for the next sulfuric acid preparation. The filter residue after washing (sulfuric acid-insoluble α-alumina) is added with calcium carbonate (the mass of calcium carbonate is 60% of the mass of alumina, which varies according to the alumina content) and transported to a mixer. The mixed material is transported to a rotary kiln and calcined and melted in the rotary kiln at a high temperature of 1380° C. for 60 minutes to produce calcium aluminate.

[0040] (4) Calcium aluminate: Add 15%±0.5% hydrochloric acid by mass to a glass fiber reinforced plastic reaction tank, then dissolve aluminum hydroxide, add 13% calcium aluminate, heat to 104°C and react for 2 hours, filter, and obtain polyaluminum chloride (which can be used as a water purifier).

[0041] The above process flow is as follows Figure 1 As shown, 1 is a suspension powder mill, 2 is a glass fiber reinforced plastic reaction tank, 3 is a filter press pump, 4 is a filter press, 5 is a mixer, 6 is a rotary kiln, and 7 is a polyaluminum chloride glass fiber reinforced plastic reaction tank. Equipment 1-7 are connected in sequence, and the aluminum ash resource processing and utilization method of the present invention is carried out in the above-mentioned equipment 1-7 in sequence.

[0042] Example 2

[0043] This embodiment provides a method for resource utilization of aluminum ash. The difference from Example 1 is that the aluminum separation method in step (1) is replaced by directly using a ball mill to make flakes, and using two layers of drums to screen out aluminum flakes and alumina powder.

[0044] Comparative Example 1

[0045] This comparative example provides a method for utilizing aluminum ash, wherein the aluminum ash is directly calcined with oxygen and then landfilled.

[0046] Product effect testing

[0047] 1. Residual amount of metallic aluminum powder: Residual amount of metallic aluminum in aluminum ash after pretreatment / total mass of aluminum ash × 100%.

[0048] 2. Aluminum metal recovery rate: B = A2 / A1 × 100%

[0049] Among them, B is the metal aluminum recovery rate; A1 is the total content of metal aluminum in aluminum ash; A2 is the mass of metal aluminum recovered from aluminum ash.

[0050] 3. Aluminum ash utilization rate: B1 = (A1 + A3 + A4) / C × 100%. (i.e., total aluminum ash utilization / total aluminum ash mass × 100%). Where B1 is the aluminum ash utilization rate; A1 is the total metallic aluminum content in the aluminum ash (18%-50%, normal range is approximately 22.5%); A3 is the aluminum nitride content (16%); A4 is the aluminum oxide content (45%); and C is the total amount of aluminum ash.

[0051] Table 1 Comparison of results of each embodiment and comparative example

[0052] Example 1 Example 2 Comparative Example 1 Residual aluminum ＜2％ 5.5％ 100％ Aluminum metal recycling rate 89.2％ 70.3％ 62.2％ Aluminum ash utilization rate 84％ 17％ 0％

[0053] As shown in Table 1 above, the method of Example 1 of the present invention can effectively separate metallic aluminum from aluminum ash. After aluminum separation in step (1), the residual amount of metallic aluminum is less than 2%, and the vast majority of the metallic aluminum is separated and utilized. Aluminum nitride is used to produce ammonium aluminum sulfate, acid-soluble alumina is used to produce aluminum sulfate, and acid-insoluble α-alumina is used to produce calcium aluminate. Calcium aluminate can be used as a refining agent for steelmaking or for producing polyaluminum chloride water purifiers. The utilization rate of the aluminum ash is high. In Comparative Example 1, the aluminum ash is directly calcined with oxygen and then landfilled. In this case, all the metallic aluminum is also landfilled, and 100% of the metallic aluminum remains. The aluminum ash cannot be recycled, resulting in waste.

[0054] Furthermore, the residual aluminum content after pretreatment in Example 1 was less than 2%. However, in Example 2, which used a ball mill for flaking and two rollers for separation, the separation efficiency was somewhat reduced, with the residual aluminum content in the pretreated aluminum ash being approximately 5.5%. This demonstrates that the use of a Raymond mill and air separation separator for separation can reduce residual aluminum. Furthermore, aluminum costs over 18,000 yuan per ton, and refining one ton of aluminum from ore consumes over 8,000 degrees of electricity. This demonstrates that the method of the present invention effectively recycles aluminum, reducing production costs and energy consumption.

[0055] The calcium aluminate prepared by the present invention can be further used to prepare polyaluminum chloride, which is often used as a water purifier. It can not only improve the utilization rate of aluminum oxide, but also directly reduce the fluorine content in polyaluminum chloride by 3.3% after defluorination treatment, which can reduce the waste residue output rate of polyaluminum chloride production by 50%. The waste residue output rate of polyaluminum chloride produced by directly using aluminum ash is greater than 50% (the polyaluminum chloride semi-finished product is filtered and separated by a plate and frame filter press, and the waste residue output rate = the weight of the separated and settled solid matter / the total weight ratio of the semi-finished product sample × 100%). No nitrogen oxides are generated, thus avoiding the risk of ammonia generation in the traditional polyaluminum chloride water purifier production process, reducing hydrogen generation, eliminating the need to install a denitrification device, simplifying the recovery method, reducing costs, solving the problem of low-value disposal of acid-insoluble α-type aluminum oxide, and improving the utilization rate of aluminum ash resources by at least 40% (sulfuric acid-insoluble α-type aluminum oxide accounts for ≥40% of the total weight of the aluminum ash).

Claims

1. A method for resource utilization of aluminum ash, characterized in that: The steps include: (1) Grinding and separating the aluminum ash to obtain metallic aluminum and pre-treated aluminum ash, and transporting the metallic aluminum to the melting and casting process; (2) washing the aluminum ash pretreated in step (1) with water to obtain a component containing soluble aluminum oxide and aluminum nitride, and then dissolving the component containing soluble aluminum oxide and aluminum nitride with sulfuric acid to obtain ammonium aluminum sulfate, aluminum sulfate solution and sulfuric acid-insoluble α-alumina; the washing liquid after the washing includes a fluorine-containing substance; (3) washing the sulfuric acid-insoluble α-alumina in step (2) with water, then adding calcium carbonate and performing a high-temperature calcination and melting reaction to obtain calcium aluminate; In step (1), the aluminum ash is aluminum-containing waste ash produced by the casting of aluminum profiles; In step (2), the concentration of the sulfuric acid is 21-25%.

2. The method for resource utilization of aluminum ash according to claim 1, characterized in that: In step (1), the equipment used for grinding and separation is a Raymond mill and an air separation separator.

3. The aluminum ash resource utilization method according to claim 2, characterized in that: In step (1), the metal aluminum is a metal aluminum sheet, the diameter of the metal aluminum sheet is 1-25 mm, and the thickness of the metal aluminum sheet is 0.05-10 mm.

4. The method for resource utilization of aluminum ash according to claim 1, characterized in that: In step (2), the mass of the sulfuric acid is 0.5-3 times the mass of the pretreated aluminum ash.

5. The aluminum ash resource utilization method according to claim 1, characterized in that: In step (3), the temperature of the high-temperature calcination melting reaction is 1300-1450°C, and the time is 40-60 minutes.

6. The aluminum ash resource utilization method according to claim 1, characterized in that: Step (3) also includes reacting calcium aluminate with acid and aluminum hydroxide to produce polyaluminum chloride.

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