A method for preparing high-purity ultrafine alumina from industrial waste aluminum

Abstract

This invention relates to the field of alumina preparation technology, and particularly to a method for preparing high-purity ultrafine alumina from industrial waste aluminum, comprising the following steps: (1) dissolving industrial profile waste aluminum with acid, adding excess aluminum powder, stirring and reacting, filtering, heating and concentrating the filtrate, cooling and crystallizing, and performing two sublimation purifications to obtain chemically pure aluminum chloride; (2) washing the chemically pure aluminum chloride multiple times with high-purity hydrochloric acid, and drying at low temperature to obtain spectroscopically pure aluminum chloride; (3) purifying industrial ammonium bicarbonate and synthesizing an aluminum ammonium carbonate precursor with a spectroscopically pure aluminum chloride solution at a molar ratio of 1.5-2.5:1, and pyrolyzing the aluminum ammonium carbonate precursor at high temperature to obtain high-purity ultrafine alumina. This invention obtains spectroscopically pure aluminum chloride (≥99.99%) raw material from industrial waste aluminum, which can be used to prepare alumina with higher purity, and can be industrialized and commercialized.

Description

Technical Field

[0001] This invention relates to the field of alumina preparation technology, and in particular to a method for preparing high-purity ultrafine alumina using industrial waste aluminum. Background Technology

[0002] High-purity ultrafine alumina powder is widely used in high-tech fields such as integrated circuit substrates, electrical insulation materials, electronic packaging, aerospace, and national defense due to its excellent physicochemical properties. However, naturally occurring alumina contains trace impurities such as K, Na, Ca, Mg, Fe, and Si, which severely affect its physicochemical properties, such as decreased luminescence performance, reduced dielectric loss in sintered ceramics, decreased sintering performance, and reduced alumina content. Furthermore, the presence of the impurity element Mn within the alumina crystals further contributes to its problems. 4+ Cr 3+ Ti 4 + This can cause color centers to absorb light of specific wavelengths, thus affecting the use of the crystal.

[0003] Currently, there are three main technical routes for producing high-purity alumina: direct hydrolysis, alkoxide hydrolysis, and pyrolysis of ammonium aluminum sulfate or ammonium aluminum carbonate. Direct hydrolysis uses 99.95% pure aluminum as raw material. Its main drawback is the inability to further purify the alumina, and it easily introduces impurities such as Fe, Ti, Ni, and Zr. Aluminum alkoxide hydrolysis produces high-purity ultrafine alumina powder through processes such as synthesis, purification, hydrolysis, and calcination of aluminum and isopropanol with a catalyst. This method effectively removes metallic impurities such as iron, titanium, nickel, zirconium, lead, and magnesium. The condensed high-purity aluminum isopropoxide can be further purified to remove free metallic impurities such as potassium, sodium, and zinc. The resulting product has high purity and small particle size, but the process is complex and costly. The aluminum ammonium sulfate pyrolysis method requires first dissolving aluminum hydroxide in sulfuric acid to obtain an aluminum sulfate solution, then adding ammonium sulfate to react with it to produce ammonium vanadium. This solution is then recrystallized multiple times according to purity requirements to obtain refined ammonium vanadium. Finally, the refined ammonium vanadium is decomposed at 1250℃ to produce alumina powder. However, the aluminum ammonium sulfate pyrolysis method has difficulty removing ions such as iron, nickel, titanium, and zirconium, as well as halogen elements. The improved aluminum ammonium carbonate method also suffers from the difficulty in removing free metallic impurities such as potassium, sodium, and zinc ions. The purity of products from both the aluminum ammonium sulfate and aluminum ammonium carbonate methods is difficult to exceed 4N.

[0004] There are also processes in this field that directly use high-purity aluminum chloride or sulfuric acid as raw materials to produce high-purity alumina. However, the current production process does not have a purification process to deeply remove trace impurities, and the purity of the produced product is limited to the purity range of the aluminum raw material. It has high requirements for the purity of the raw material, is expensive, and the high-purity alumina produced is difficult to meet the application requirements. Summary of the Invention

[0005] This invention provides a method for preparing high-purity ultrafine alumina from industrial waste aluminum. The purpose is to use industrial profile waste aluminum as raw material, first prepare spectrally pure aluminum chloride, and then produce high-purity alumina, thereby realizing the high-value utilization of industrial profile waste aluminum and solving the problem of impurities in high-purity alumina.

[0006] To achieve the above objectives, the present invention provides a method for preparing high-purity ultrafine alumina from industrial waste aluminum, comprising the following steps: (1) After dissolving industrial profile waste aluminum with acid, add excess aluminum powder, stir and react, filter, heat the filtrate to concentrate and cool to crystallize to obtain aluminum chloride crystals without iron ions, and then sublimate the crystals twice to obtain chemically pure aluminum chloride. (2) Wash the chemically pure aluminum chloride obtained in step (1) multiple times with high-purity hydrochloric acid, and dry at low temperature to obtain spectrally pure aluminum chloride; (3) After purifying industrial ammonium bicarbonate, it is synthesized into an aluminum ammonium carbonate precursor by combining it with the spectrally pure aluminum chloride solution obtained in step (2) at a molar ratio of 1.5-2.5:1. The aluminum ammonium carbonate precursor is then pyrolyzed at high temperature to obtain high-purity ultrafine alumina.

[0007] Preferably, the industrial profile waste aluminum includes waste aluminum recovered from one or more industrial profiles such as building doors and windows, curtain walls, profile processing scraps, or mechanical frames, containing iron, silicon, and magnesium element impurities, wherein, by mass percentage, the iron element impurity content in the total industrial profile waste aluminum is ≤1.2%, the silicon element impurity content accounts for 0.2-0.6% of the total industrial profile waste aluminum, and the magnesium element impurity content accounts for 0.45-0.9% of the total industrial profile waste aluminum.

[0008] The main impurities in industrial profile scrap aluminum are iron, silicon, and magnesium, with iron ≤1.2%, silicon 0.2-0.6%, and magnesium 0.45-0.9%. Other trace impurities include sodium, potassium, calcium, titanium, vanadium, chromium, manganese, cobalt, nickel, copper, and zinc. Because the sublimation temperatures of different metal chlorides differ, the chlorides of impurities such as silicon, titanium, and vanadium sublimate at temperatures lower than aluminum chloride. Sublimation below the sublimation temperature of aluminum chloride can remove these impurities. Sodium, potassium, magnesium, calcium, chromium, manganese, barium, and iron (Fe) are also impurities. 2+ The sublimation temperatures of chlorides such as sodium, potassium, magnesium, calcium, chromium, manganese, barium, and iron (Fe) are much higher than those of aluminum chloride. Sodium, potassium, magnesium, calcium, chromium, manganese, barium, and iron (Fe) sublime at the sublimation temperature of aluminum chloride. 2+ Impurities such as ferric chloride (Fe) remain inside the sublimation furnace; 3+ The sublimation temperature of ferric iron (Fe) is close to that of aluminum chloride, so it cannot be removed by sublimation. However, it can remove ferric iron (Fe) from aluminum chloride. 3+ ) converts to divalent iron (Fe) 2+After being purified by two sublimations, the impurities in anhydrous aluminum chloride are removed by high-temperature sublimation. The aluminum chloride purified by two sublimations still contains trace impurities and has a purity of chemically pure or analytically pure (99.5% or 99.7%). When washed multiple times with high-purity hydrochloric acid, the impurity chloride salts will dissolve in the high-purity hydrochloric acid and be washed away. The dried aluminum chloride can reach spectrally pure (≥99.99%) and can be used as a raw material for the production of high-purity alumina.

[0009] This application employs a deep impurity removal process involving precipitation, recrystallization, sublimation, and high-purity acid washing. It targets industrial waste aluminum containing complex trace impurities, offering broad adaptability to various raw material waste aluminum. The process is not only simple and low-cost, but also yields aluminum chloride with a purity exceeding 4N, ultimately enabling the production of ultra-high-purity alumina up to 5N. Furthermore, based on the preceding sublimation purification steps, the purity of the obtained aluminum chloride can be freely adjusted, allowing for the generation of corresponding high-purity alumina from aluminum chloride of varying purities. This broad application range demonstrates significant practical value.

[0010] Preferably, the acid dissolution in step (1) uses one or more of hydrochloric acid, nitric acid, or sulfuric acid. More preferably, the acid is hydrochloric acid.

[0011] The aluminum chloride solution prepared by dissolving waste aluminum profiles in hydrochloric acid contains ferrous ions (Fe). 2+ ) and iron ions (Fe 3+ It is difficult to remove impurities such as iron (Fe) using chemical methods. 3+ and Fe 2+ Iron (Fe) is removed by resin adsorption. 3+ and Fe 2+ The cost is very high, and the purity of aluminum chloride after chemical precipitation and resin adsorption is usually only chemically pure or analytically pure (99.5% or 99.7%).

[0012] The purpose of the acid dissolution, heating concentration, and cooling crystallization processes in this application is to remove free ferric ions from aluminum chloride; when the aluminum chloride solution contains Fe... 3+ When aluminum powder is added, the following reaction occurs: 2Al + 6Fe 3+ → 2Al 3+ +6Fe 2+ Because its oxidizing properties are further weakened, aluminum powder no longer has the ability to convert Fe... 2+ The thermodynamic driving force for further reduction to elemental iron is that this reaction can only reduce Fe to elemental iron. 3+ Reduced to Fe 2+ Therefore, when aluminum powder is in excess, Fe 2+ It will exist stably in solution. After stirring and reacting an aluminum chloride solution containing aluminum powder, the mixture is filtered, the filtrate is heated and concentrated, then cooled and crystallized to obtain a solution free of iron ions (Fe). 3+ Aluminum chloride.

[0013] Anhydrous aluminum chloride is highly hygroscopic and hydrolyzable. It reacts rapidly with water to form hydrochloric acid and aluminum hydroxide, releasing a large amount of heat and potentially causing the solution to boil or splash while producing a corrosive white fumes. Therefore, dilute hydrochloric acid is used as the initial solvent when preparing its aqueous solution to inhibit hydrolysis and ensure a clear solution. The dried aluminum chloride is first dissolved in 1-2 mol / L dilute hydrochloric acid, and then diluted with pure water to prepare a 0-2 mol / L aluminum chloride solution. Preferably, the two sublimation purification steps in step (1) specifically include: Aluminum chloride crystals were placed in a sublimation machine and sublimated twice to remove impurities. The sublimation temperatures were 180~185℃ and 150~160℃, respectively.

[0014] Preferably, the purity of the chemically pure aluminum chloride in step (1) is ≥99.5%, and the purity of the spectrally pure aluminum chloride in step (2) is ≥99.99%.

[0015] Preferably, the industrial ammonium bicarbonate in step (3) is produced by absorbing carbon dioxide with ammonia water, and the impurity components contained therein, by mass percentage, are: iron element impurities ≤0.006% in the total industrial ammonium bicarbonate, heavy metal ions (Pb) ≤0.0012% in the total industrial ammonium bicarbonate, and insoluble matter ≤0.55% in the total industrial ammonium bicarbonate.

[0016] Preferably, the purification in step (3) includes adsorption treatment using an anion exchange resin, specifically: the industrial ammonium bicarbonate solution is adsorbed onto a pre-activated resin and then cooled and crystallized to obtain ammonium bicarbonate with a purity of 99.9% or higher. More preferably, the pre-activated resin is a pre-activated D201 anion exchange resin.

[0017] Industrial ammonium bicarbonate solution is adsorbed using D201 or similar anion exchange resin to remove impurity ions such as sulfate, calcium, and magnesium, resulting in a product with a purity of over 99.9%.

[0018] Preferably, in step (3), when synthesizing the aluminum ammonium carbonate precursor, polyethylene glycol, a morphology modifier, is added to the ammonium bicarbonate solution, and the amount added is 5% to 30% of the mass fraction of the reactant aluminum chloride; the thermal decomposition temperature of the spray pyrolysis is 1100 to 1200°C.

[0019] This step involves adding PEG, a morphology-co-controlling component, to the ammonium bicarbonate solution. This synergistic control of alumina morphology helps to obtain high-purity alumina with ultrafine particle size.

[0020] Preferably, the spray pyrolysis in step (3) is carried out in a pyrolysis furnace, the lining of which is high-purity alumina bricks to prevent impurities from being introduced during the high-temperature pyrolysis process.

[0021] The above-described solution of the present invention has the following beneficial effects: (1) The raw materials used in this application are industrial profile waste aluminum and industrial ammonium bicarbonate. First, spectrally pure aluminum chloride is prepared, and then high-purity alumina is prepared. Compared with the method of simply using high-purity aluminum chloride or aluminum sulfate with a purity of more than 99% to produce high-purity alumina, this technology can obtain spectrally pure aluminum chloride (≥99.99%) raw materials from industrial waste aluminum, and can prepare alumina with higher purity. It can be industrialized and commercialized. Attached Figure Description

[0022] 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 SEM image of the high-purity ultrafine alumina powder prepared in the embodiments of the present invention. Figure 2-4 The XRD patterns are of the high-purity ultrafine alumina powder prepared in Examples 1-3 of this invention after being calcined at 1100℃ for 2 hours. Detailed Implementation

[0024] To make the technical problems, solutions, and advantages of this invention clearer, a detailed description will be provided below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0025] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0026] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a locking connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0027] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] The technical solution adopted in this invention is as follows: A method for preparing ultrafine, high-purity, ultrafine alumina powder includes the following steps: (1) Preparation of aluminum chloride: Industrial profile waste aluminum is dissolved in hydrochloric acid. The main impurity ion in the solution is ferrous ion (Fe). 2+ ) and iron ions (Fe 3 Since the sublimation temperature of ferric chloride is close to that of aluminum chloride, while the sublimation temperature of ferrous chloride is much higher, the conversion of iron ions to ferrous ions allows for the removal of iron impurities from aluminum chloride through sublimation. When an aluminum chloride solution contains Fe... 3+ When impurities are present, the addition of aluminum powder results in the following reaction: 2Al + 6Fe 3+ → 2Al 3+ +6Fe 2+ As its oxidizing power further weakens, aluminum powder no longer possesses the thermodynamic driving force to further reduce it to elemental iron; the reaction can only reduce Fe... 3+ Reduced to Fe 2+ Therefore, Fe 2+ It will exist stably in solution. After heating and concentrating the aluminum chloride solution, cooling it, adding excess aluminum powder, stirring, and then filtering, the filtrate is cooled and crystallized to obtain a solution free of iron ions (Fe). 3+ Aluminum chloride crystals.

[0029] (2) Purification of aluminum chloride: Aluminum chloride crystals are placed in a continuous vacuum sublimation and deposition machine, and the sublimation temperature is set at 180~185℃. The sublimation product is aluminum chloride containing impurities such as silicon, titanium, and vanadium. The residue is sodium, potassium, magnesium, calcium, chromium, manganese, barium, and iron (Fe). 2+The aluminum chloride obtained by condensation is then sublimated at 150-160℃ to remove impurities such as silicon, titanium, and vanadium, leaving chemically pure aluminum chloride in the sublimation machine. Alternatively: A constant temperature sublimation treatment at 150-160℃ is used to remove impurities such as silicon, titanium, and vanadium. The residue in the sublimation machine is then sublimated at a constant temperature of 180-185℃ to collect the condensed aluminum chloride product. The residue consists of sodium, potassium, magnesium, calcium, chromium, manganese, barium, and iron (Fe). 2+ The aluminum chloride obtained by two sublimation processes was chemically pure (≥99.5%). Trace impurities such as Mg, Ca, Fe, Cu, Na, K, Ni, Cr, Pb, and Mn were repeatedly eluted with high-purity hydrochloric acid. After washing, the aluminum chloride was dried at 70~80℃ to obtain spectrally pure aluminum chloride (≥99.99%).

[0030] (3) Compared with the method of directly using high-purity aluminum chloride or aluminum sulfate with a purity of over 99% to produce high-purity alumina, this technology can obtain spectrally pure aluminum chloride (≥99.99%) raw materials from industrial waste aluminum, and can prepare alumina with higher purity.

[0031] (4) Anhydrous aluminum chloride has extremely strong hygroscopicity and hydrolytic properties. It reacts rapidly with water to produce hydrochloric acid and aluminum hydroxide, releasing a large amount of heat, which can cause the solution to boil or splash and produce a corrosive white mist. Therefore, dilute hydrochloric acid is used as the initial solvent when preparing its aqueous solution to inhibit hydrolysis and ensure a clear solution. The dried aluminum chloride is first dissolved in 1~2 mol / L dilute hydrochloric acid and then diluted with pure water to prepare a 0~2 mol / L aluminum chloride solution.

[0032] (5) Purification of industrial ammonium bicarbonate: Dissolve industrial ammonium bicarbonate in pure water, adsorb it with pre-activated D201 resin, concentrate and crystallize it at low temperature to obtain a product with a purity of more than 99.9%, then prepare ammonium bicarbonate into a 2~4 mol / L solution with pure water (prepare immediately before use) and add morphology synergistic control component PEG, the amount added is 5%~30% of the mass fraction of reactant aluminum chloride.

[0033] (6) Synthesis reaction: The aluminum chloride solution and ammonium bicarbonate solution are combined according to the designed stoichiometric ratio to synthesize a suspension of aluminum ammonium carbonate precursor; (7) Thermal decomposition: The aluminum ammonium carbonate precursor suspension is thermally decomposed at high temperature using a spray thermal decomposition furnace. The furnace temperature is 1100~1200℃. To prevent the introduction of impurities during the high-temperature pyrolysis process, the lining of the thermal decomposition furnace is made of high-purity alumina bricks.

[0034] (8) Compared with existing industrial production technologies, the preparation method of the present invention has the following advantages: the raw materials are industrial profile waste aluminum and industrial ammonium bicarbonate. First, spectrally pure aluminum chloride is prepared, and then high-purity aluminum oxide is prepared, which can be industrialized and commercialized.

[0035] Example 1: This embodiment provides a method for preparing high-purity ultrafine alumina from industrial waste aluminum. The specific steps are as follows: (1) Take 20 kg of mixed industrial waste aluminum (impurity elements: Si 0.25%, Fe 1.15%, Cu 0.15%, Mn 0.05%, Mg 0.85%, Ca 0.15%, Ti 0.03%) containing building doors and windows, curtain walls, profile processing scraps and mechanical frames in any proportion, soak it in 10% sodium hydroxide solution for 10 minutes to remove surface oil stains, then dissolve it with 20% hydrochloric acid, filter to obtain aluminum chloride solution, add aluminum powder to the solution, stir to react and filter, heat the filtrate to evaporate part of the water and then cool to crystallize, to obtain a solution free of iron ions (Fe 3+ Aluminum chloride hexahydrate crystals (impurity elements: Si 0.07%, Fe 0.05%, Cu 0.01%, Mn 0.08%, Mg 0.21%, Ca 0.09%, Ti 0.03%) are available for use. (2) Take 1 kg of the above-mentioned aluminum chloride hexahydrate and place it into a continuous vacuum sublimation and deposition machine for constant temperature sublimation at 185℃. Then, sublimate the deposited aluminum chloride again at constant temperature at 160℃. Chemically pure anhydrous aluminum chloride (impurity elements: Si 0.0045%, Fe 0.002%, Cu 0.003%, Mn 0.004%, Mg 0.001%, Ca 0.001%, Ti 0.001%) is left in the sublimation machine. (3) The above anhydrous aluminum chloride was washed three times with high-purity hydrochloric acid and then dried at a constant temperature of 80℃ to obtain spectrally pure anhydrous aluminum chloride (each impurity element ≤ 0.5%). %), then slowly add to a 2 mol / L dilute hydrochloric acid solution while stirring to dissolve, and then add pure water to make a 0.4 mol / L aluminum chloride solution; (4) Industrial ammonium bicarbonate was dissolved in pure water, adsorbed with pre-activated D201 resin and then cooled to crystallize. At room temperature, a 2 mol / L ammonium bicarbonate solution was prepared with cold pure water and 5% PGE of aluminum chloride was added and stirred evenly (prepared on demand). The aluminum chloride solution and ammonium bicarbonate solution were combined at a volume ratio of 8:3 to synthesize aluminum ammonium carbonate precursor. The powder obtained by thermal decomposition of the precursor at high temperature was calcined at 1100℃ for 2 hours to obtain alumina with a purity of 99.995%. Figure 1 This is a SEM image of alumina, a product of thermal decomposition. Figure 2 The image shows the XRD pattern of the thermally decomposed powder after calcination at 1100℃ for 2 hours.

[0036] Example 2 This embodiment provides a method for preparing high-purity ultrafine alumina from industrial waste aluminum. The specific steps are as follows: (1) Take 1 kg of aluminum chloride hexahydrate crystals obtained in step (1) of Example 1 and sublimate them at 160°C in a continuous vacuum sublimation and deposition machine, and then sublimate them at 182°C. The deposition product is chemically pure anhydrous aluminum chloride (impurity elements: Si 0.0045%, Fe 0.003%, Cu 0.003%, Mn 0.0041%, Mg 0.0011%, Ca 0.001%, Ti 0.001%).

[0037] (2) The above anhydrous aluminum chloride was washed four times with high-purity hydrochloric acid and then dried at a constant temperature of 78°C to obtain spectrally pure aluminum chloride (each impurity element ≤ 0.5%). %), then slowly add to a 2 mol / L dilute hydrochloric acid solution while stirring to dissolve, and then add pure water to make a 0.3 mol / L aluminum chloride solution; (3) Purify industrial ammonium bicarbonate according to the method of Example 1. Prepare a 4 mol / L ammonium bicarbonate solution with cold pure water at room temperature and add 7% of aluminum chloride PGE and stir evenly (prepare immediately before use). Combine aluminum chloride solution and ammonium bicarbonate solution at a volume ratio of 8:3 to synthesize aluminum ammonium carbonate precursor. The aluminum ammonium carbonate precursor is thermally decomposed at high temperature to obtain powder. Calcine at 1100℃ for 2 hours to obtain alumina with a purity of 99.991%. Figure 1 This is a SEM image of alumina, a product of thermal decomposition. Figure 3 The image shows the XRD pattern of the thermally decomposed powder after constant temperature calcination at 1100℃ for 2 hours.

[0038] Example 3 This embodiment provides a method for preparing high-purity ultrafine alumina from industrial waste aluminum. The specific steps are as follows: (1) Take 2 kg of aluminum chloride hexahydrate crystals obtained in step (1) of Example 1 and sublimate them at a constant temperature of 182°C in a continuous vacuum sublimation sublimation machine. Then, sublimate the sublimated aluminum chloride again at a constant temperature of 160°C. What remains in the sublimation machine is purified chemically pure anhydrous aluminum chloride (impurity elements: Si 0.0047%, Fe 0.0018%, Cu 0.0026%, Mn 0.0032%, Mg 0.0008%, Ca 0.0012%, Ti 0.0009%).

[0039] (2) Take 1 kg of the above-mentioned anhydrous aluminum chloride (the remaining anhydrous aluminum chloride is reserved), wash it 5 times with high-purity hydrochloric acid, and then dry it at a constant temperature of 75℃ to obtain spectrally pure anhydrous aluminum chloride (each impurity element ≤ 0.5%). %), then slowly add to a 2 mol / L dilute hydrochloric acid solution while stirring to dissolve, and then add pure water to make a 0.4 mol / L aluminum chloride solution; (3) Purify industrial ammonium bicarbonate according to the method of Example 1. Prepare a 3 mol / L ammonium bicarbonate solution with cold pure water at room temperature and add 10% of aluminum chloride PGE and stir evenly (prepare immediately before use). Combine aluminum chloride solution and ammonium bicarbonate solution at a volume ratio of 8:3 to synthesize aluminum ammonium carbonate precursor. The aluminum ammonium carbonate precursor is thermally decomposed at high temperature to obtain powder, which is calcined at 1100℃ for 2 hours to obtain alumina with a purity of 99.996%. Figure 1 This is a SEM image of alumina, a product of thermal decomposition. Figure 4 The image shows the XRD pattern of the thermally decomposed powder from Example 3 after constant temperature calcination at 1100℃ for 2 hours.

[0040] Comparative Example 1 This comparative example provides a method for preparing high-purity ultrafine alumina from industrial waste aluminum. The specific steps are as follows: (1) Take the anhydrous aluminum chloride obtained in step (1) of Example 3 and slowly add it to a 2 mol / L dilute hydrochloric acid solution while stirring to dissolve it. Then add pure water to make a 0.4 mol / L aluminum chloride solution. (2) Purify industrial ammonium bicarbonate according to the method of Example 1. Prepare a 3 mol / L ammonium bicarbonate solution with cold pure water at room temperature and add 10% of aluminum chloride PGE and stir evenly (prepare immediately before use). Combine aluminum chloride solution and ammonium bicarbonate solution at a volume ratio of 8:3 to synthesize aluminum ammonium carbonate precursor. The aluminum ammonium carbonate precursor is thermally decomposed at high temperature to obtain powder, which is calcined at 1100℃ for 2 hours to obtain alumina with a purity of 99.93%.

[0041] (3) This comparative example shows that the alumina prepared by using anhydrous aluminum chloride that has not been washed with high-purity hydrochloric acid has low purity. As the number of times the anhydrous aluminum chloride is washed with high-purity hydrochloric acid increases, the purity of the produced alumina also increases accordingly.

Claims

1. A method for preparing high-purity ultrafine alumina from industrial waste aluminum, characterized in that, Includes the following steps: (1) After dissolving industrial profile waste aluminum with acid, add excess aluminum powder, stir and react, filter, heat the filtrate to concentrate and cool to crystallize to obtain aluminum chloride crystals without iron ions, and then sublimate the crystals twice to obtain chemically pure aluminum chloride. (2) Wash the chemically pure aluminum chloride obtained in step (1) multiple times with high-purity hydrochloric acid, and dry at low temperature to obtain spectrally pure aluminum chloride; (3) After purifying industrial ammonium bicarbonate, it is synthesized into an aluminum ammonium carbonate precursor by combining it with the spectrally pure aluminum chloride solution obtained in step (2) at a molar ratio of 1.5-2.5:

1. The aluminum ammonium carbonate precursor is then pyrolyzed at high temperature to obtain high-purity ultrafine alumina.

2. The method as described in claim 1, characterized in that, The industrial profile waste aluminum includes waste aluminum recovered from one or more industrial profiles such as building doors and windows, curtain walls, profile processing scraps, or mechanical frames. It contains iron, silicon, and magnesium element impurities. By mass percentage, the iron element impurity content in the total industrial profile waste aluminum is ≤1.2%, the silicon element impurity content accounts for 0.2-0.6% of the total industrial profile waste aluminum, and the magnesium element impurity content accounts for 0.45-0.9% of the total industrial profile waste aluminum.

3. The method as described in claim 1, characterized in that, The acid dissolution in step (1) uses one or more of hydrochloric acid, nitric acid or sulfuric acid.

4. The method as described in claim 1, characterized in that, The two sublimation and purification processes mentioned in step (1) specifically include: Aluminum chloride crystals were placed in a sublimation machine and sublimated twice to remove impurities. The sublimation temperatures were 180~185℃ and 150~160℃, respectively.

5. The method as described in claim 1, characterized in that, The purity of the chemically pure aluminum chloride in step (1) is ≥99.5%, and the purity of the spectrally pure aluminum chloride in step (2) is ≥99.99%.

6. The method as described in claim 1, characterized in that, The industrial ammonium bicarbonate mentioned in step (3) is produced by absorbing carbon dioxide with ammonia water. The impurity components contained therein, by mass percentage, are: iron element impurities ≤0.006% in the total industrial ammonium bicarbonate, heavy metal ions (Pb) ≤0.0012% in the total industrial ammonium bicarbonate, and insoluble matter ≤0.55% in the total industrial ammonium bicarbonate.

7. The method as described in claim 1, characterized in that, The purification described in step (3) includes adsorption treatment using anion exchange resin, specifically: after the industrial ammonium bicarbonate solution is adsorbed by a pre-activated resin, it is cooled and crystallized to obtain ammonium bicarbonate with a purity of over 99.9%.

8. The method as described in claim 1, characterized in that, In step (3), when synthesizing the aluminum ammonium carbonate precursor, polyethylene glycol, a morphology modifier, is added to the ammonium bicarbonate solution. The amount added is 5% to 30% of the mass fraction of the reactant aluminum chloride. The thermal decomposition temperature of the spray pyrolysis is 1100 to 1200°C.

9. The method as described in claim 1, characterized in that, The spray pyrolysis described in step (3) is carried out in a pyrolysis furnace, the lining of which is high-purity alumina brick.

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