Method for preparing hierarchical porous aluminum oxide from secondary aluminum ash

Abstract

The invention discloses a method for preparing hierarchical porous alumina from secondary aluminum ash, which comprises the following steps: reducing the secondary aluminum ash by using a reducing agent to obtain reduced aluminum ash; mixing the reduced aluminum ash with water, filtering and drying to obtain desalted aluminum ash; mixing the desalted aluminum ash with mixed acid, filtering and concentrating to obtain an aluminum salt solution; and mixing the aluminum salt solution, an alkali source and a pore-enlarging agent, and roasting to obtain the hierarchical porous aluminum oxide. Harmless, high-valued and resource utilization of the secondary aluminum ash is achieved, the obtained hierarchical pore aluminum oxide is excellent in comprehensive performance, the maximum value of the specific surface area is 420 cm < 3 > / g, the maximum value of the pore volume is 3.8 cm < 3 > / g, and meanwhile the hierarchical pore aluminum oxide has the advantages of being simple in process and easy to industrialize.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary aluminum ash recycling, and specifically relates to a method for preparing hierarchical porous alumina from secondary aluminum ash. Background Art

[0002] Secondary aluminum ash is a hazardous waste generated during aluminum processing and secondary aluminum smelting, mainly composed of metallic aluminum, aluminum nitride, oxides, and salts. Its harmfulness stems from the reaction of aluminum nitride with water to generate ammonia gas and the potential leaching risk of heavy metals.

[0003] At present, the harmless and resourceful treatment technologies for secondary aluminum ash include pyrometallurgical treatment and hydrometallurgical treatment. The main disadvantages of pyrometallurgical treatment are high energy consumption, easy generation of secondary pollution, and low aluminum recovery rate; the disadvantages of hydrometallurgical treatment are complex process flow, high wastewater treatment cost, and difficulty in completely removing aluminum nitride.

[0004] Although the current secondary aluminum ash treatment technologies can achieve partial harmlessness and resource utilization, they generally have problems such as high cost, low added value of products, and risk of secondary pollution. In the future, technological innovation is needed to promote the large-scale application of green and low-carbon processes. Summary of the Invention

[0005] In one aspect, the present invention provides a method for preparing hierarchical porous alumina from secondary aluminum ash, comprising the following steps:

[0006] (1) Reducing secondary aluminum ash with a reducing agent to obtain reduced aluminum ash;

[0007] (2) Mixing the reduced aluminum ash with water, filtering, and drying to obtain desalted aluminum ash;

[0008] (3) Mixing the desalted aluminum ash with a mixed acid, filtering, and concentrating to obtain an aluminum salt solution;

[0009] (4) Mixing the aluminum salt solution, an alkali source, and a pore-expanding agent, and calcining to obtain hierarchical porous alumina.

[0010] In some embodiments, in step (1), the reducing agent is at least one of coke, charcoal, graphite, and activated carbon, wherein the particle size of the reducing agent is less than 1 mm.

[0011] In some embodiments, in step (1), the mass ratio of the secondary aluminum ash to the reducing agent is 10:5 - 2.

[0012] In some embodiments, in step (1), the mixture of the secondary aluminum ash and the reducing agent is calcined in a high-temperature furnace, the calcination temperature is 900 - 1300 °C, and the calcination time is 6 - 12 h.

[0013] In some embodiments, in step (2), the mass ratio of the reduced aluminum ash to water is 1:3 - 10.

[0014] In some embodiments, in step (2), the reduced aluminum ash and water are mixed in a first microwave reactor with a microwave power of 500 - 2000 W, a microwave frequency of 1500 - 3000 MHz, a reaction temperature of 80 - 150 °C, and a reaction time of 6 - 24 h. After washing with water until neutral, gravity sedimentation, and drying, desalted aluminum ash is obtained, and the drying temperature is 110 - 120 °C.

[0015] In some embodiments, in step (3), the mixed acid conforms to the A - B - C configuration, where A is sulfuric acid; B includes one of hydrochloric acid, hydrogen fluoride, hydrogen bromide, and hydrogen iodide; C includes one of perchloric acid, nitric acid, and phosphoric acid; the mass ratio of A:B:C = 1:1 - 2:1 - 3.

[0016] In some embodiments, in step (3), the mass ratio of the desalted aluminum ash to the mixed acid is 1:2 - 5, where the mass fraction of the mixed acid is 15% - 40%.

[0017] In some embodiments, in step (3), the mixing is completed in a second microwave reactor with a microwave power of 500 - 2000 W, a microwave frequency of 1500 - 3000 MHz, a reaction temperature of 80 - 150 °C, and a reaction time of 6 - 24 h. After washing with water until neutral and gravity sedimentation, a filtrate is obtained, and the evaporation and concentration temperature is 110 - 120 °C, where the alumina content in the filtrate is 40 - 75% (XRF).

[0018] In some embodiments, in step (4), the alkali source includes one of sodium hydroxide, potassium hydroxide, sodium oxide, and sodium peroxide; the pore - expanding agent is ammonium bicarbonate. Further, the ammonium bicarbonate can be ammonium bicarbonate synthesized from ammonia and carbon dioxide generated during the treatment of secondary aluminum ash.

[0019] In some embodiments, in step (4), the mass ratio of the aluminum salt solution, alkali source, and pore - expanding agent is 100:5 - 35:1 - 25. The mixing is completed in a third microwave reactor with a microwave power of 500 - 2000 W, a microwave frequency of 1500 - 3000 MHz, a reaction temperature of 120 - 180 °C, and a reaction time of 12 - 24 h. After washing with water until neutral and gravity sedimentation, a multi - pore alumina precursor is obtained. Further, in step (4), the calcination temperature is 500 - 800 °C, and the calcination time is 1 - 3 h.

[0020] In a second aspect, the present invention provides the multi - pore alumina prepared by the above method.

[0021] In some embodiments, the specific surface area and pore volume of the hierarchical porous alumina are 420 cm 3 / g and 3.8 cm 3 / g, respectively.

[0022] Technical Effects

[0023] The present invention provides a method for preparing hierarchical porous alumina from secondary aluminum ash, realizing the harmless, high-value and resource utilization of secondary aluminum ash at the same time. The comprehensive performance of the hierarchical porous alumina product obtained by the present invention is excellent, and the maximum values of the specific surface area and pore volume are 420 cm 3 / g and 3.8 cm 3 / g, respectively, and it also has the advantages of simple process and easy industrialization. Brief Description of the Drawings

[0024] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

[0025] Figure 1 is a schematic diagram of the production process flow for preparing hierarchical porous alumina from secondary aluminum ash in some embodiments of the present invention;

[0026] Figure 2 shows the internal structure of the microwave reactor in some embodiments of the present invention.

[0027] Specific Embodiment Modes

[0028] In order to make the purpose, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with specific embodiments.

[0029] In some embodiments, the present invention provides a method for preparing hierarchical porous alumina from secondary aluminum ash, and its production process flow is as Figure 1 shown. First, the secondary aluminum ash is mixed with a reducing agent and sent to a mixing stirrer, and then enters a reduction furnace for reduction to obtain reduced aluminum ash; the reduced aluminum ash obtained in the reduction furnace is mixed with water and sent to a first microwave reactor, and then washed with water through a sedimentation tank to obtain desalted aluminum ash; subsequently, the desalted aluminum ash and mixed acid are sent to a second microwave reactor, and then washed with water through a sedimentation tank to obtain an aluminum salt solution; then, the aluminum salt solution, a pore-expanding agent and an alkali source are mixed and sent to a third microwave reactor to react to obtain a hierarchical porous alumina precursor; finally, the hierarchical porous alumina precursor is calcined in a calcination furnace to obtain hierarchical porous alumina.

[0030] The internal structures of the first microwave reactor, the second microwave reactor and the third microwave reactor can be the same or different, as Figure 2 shown.

[0031] Example 1

[0032] The secondary aluminum ash is sourced from aluminum processing enterprise A in Henan Province

[0033] (1) Mix the secondary aluminum ash and coke (particle size 0.5 mm) evenly at a mass ratio of 5:1, roast and reduce in a high-temperature furnace at a roasting temperature of 900 °C for 6 h to obtain reduced aluminum ash;

[0034] (2) Mix the reduced aluminum ash and water at a mass ratio of 1:3 in the first microwave reactor, with a microwave power of 1000 W, a microwave frequency of 1500 MHz, a reaction temperature of 80 °C, and a reaction time of 6 h; wash with water until neutral and filter by gravity sedimentation to obtain filter residue, dry at 110 °C to obtain desalted aluminum ash;

[0035] (3) Mix the desalted aluminum ash and mixed acid at a mass ratio of 1:2 in the second microwave reactor, where the mass ratio of sulfuric acid:hydrochloric acid:phosphoric acid is 1:1:1 and the mass fraction of the mixed acid is 15%; the parameters of the microwave reactor are a microwave power of 1500 W, 3000 MHz, and a reaction temperature of 100 °C, wash with water until neutral and filter by gravity to obtain filtrate, concentrate at 110 °C to obtain aluminum salt solution, where the alumina content in the filtrate is 40% (XRF).

[0036] (4) Mix and react the aluminum salt solution, sodium hydroxide, and ammonium bicarbonate at a mass ratio of 100:5:1 in the third microwave reactor, with a microwave power of 1000 W, a microwave frequency of 1500 MHz, a reaction temperature of 120 °C, and a reaction time of 12 h; wash with water until neutral and filter by gravity sedimentation to obtain a hierarchical pore alumina precursor, roast at 500 °C for 1 h to obtain hierarchical pore alumina.

[0037] Example 2

[0038] The secondary aluminum ash is sourced from metallurgical aluminum enterprise B in Guizhou Province

[0039] (1) Mix the secondary aluminum ash and charcoal (particle size 0.8 mm) evenly at a mass ratio of 2:1, roast and reduce in a high-temperature furnace at a roasting temperature of 1300 °C for 8 h to obtain reduced aluminum ash;

[0040] (2) Mix the reduced aluminum ash and water at a mass ratio of 1:10 in the first microwave reactor, with a microwave power of 1800 W, a microwave frequency of 2800 MHz, a reaction temperature of 100 °C, and a reaction time of 24 h; wash with water until neutral and filter by gravity sedimentation to obtain filter residue, dry at 120 °C to obtain desalted aluminum ash;

[0041] (3) Mix the desalted aluminum ash and the mixed acid at a mass ratio of 1:3 in the second microwave reactor, where the mass ratio of sulfuric acid: hydrogen fluoride: nitric acid is 1:2:3, and the mass fraction of the mixed acid is 30%; the parameters of the microwave reactor are 1500 W microwave power, 3000 MHz, 120 °C reaction temperature, and 6 h reaction time. Wash with water until neutral and perform gravity filtration to obtain the filtrate. Concentrate at 120 °C to obtain the aluminum salt solution, where the alumina content in the filtrate is 52% (XRF).

[0042] (4) Mix and react the aluminum salt solution, potassium hydroxide, and ammonium bicarbonate at a mass ratio of 100:11:25 in the third microwave reactor. The microwave power is 1800 W, the microwave frequency is 3000 MHz, the reaction temperature is 180 °C, and the reaction time is 18 h; wash with water until neutral and perform gravity sedimentation filtration to obtain the hierarchical pore alumina precursor. The calcination temperature is 800 °C and the calcination time is 2 h to obtain the hierarchical pore alumina.

[0043] Example 3

[0044] The secondary aluminum ash is from C Metallurgical Aluminum Enterprise in Shandong Province

[0045] (1) Mix the secondary aluminum ash and graphite (particle size of 1 mm) evenly at a mass ratio of 5:2, and calcine and reduce in a high-temperature furnace. The calcination temperature is 1000 °C and the calcination time is 12 h to obtain the reduced aluminum ash;

[0046] (2) Mix the reduced aluminum ash and water at a mass ratio of 1:8 in the first microwave reactor. The microwave power is 2000 W, the microwave frequency is 3000 MHz, the reaction temperature is 150 °C, and the reaction time is 18 h; wash with water until neutral and perform gravity sedimentation filtration to obtain the filter residue. Dry at 115 °C to obtain the desalted aluminum ash;

[0047] (3) Mix the desalted aluminum ash and the mixed acid at a mass ratio of 1:3 in the second microwave reactor, where the mass ratio of sulfuric acid: hydrogen bromide: perchloric acid is 1:2:2, and the mass fraction of the mixed acid is 40%; the parameters of the microwave reactor are 2000 W microwave power, 3000 MHz, 150 °C reaction temperature, and 24 h reaction time. Wash with water until neutral and perform gravity filtration to obtain the filtrate. Concentrate at 120 °C to obtain the aluminum salt solution, where the alumina content in the filtrate is 75% (XRF).

[0048] (4) Mix and react the aluminum salt solution, sodium oxide, and ammonium bicarbonate at a mass ratio of 100:35:23 in the third microwave reactor. The microwave power is 1800 W, the microwave frequency is 3000 MHz, the reaction temperature is 150 °C, and the reaction time is 24 h; wash with water until neutral and perform gravity sedimentation filtration to obtain the hierarchical pore alumina precursor. The calcination temperature is 750 °C and the calcination time is 1.5 h to obtain the hierarchical pore alumina.

[0049] Example 4

[0050] The secondary aluminum ash is sourced from Aluminum Processing Enterprise D in Shanxi Province

[0051] (1) Mix the secondary aluminum ash and activated carbon (particle size 0.4 mm) evenly at a mass ratio of 5:3, roast and reduce in a high-temperature furnace at a roasting temperature of 1100 °C for a roasting time of 10 h to obtain reduced aluminum ash;

[0052] (2) Mix the reduced aluminum ash and water at a mass ratio of 1:7 in a first microwave reactor with a microwave power of 1200 W, a microwave frequency of 2400 MHz, a reaction temperature of 140 °C, and a reaction time of 24 h; wash with water until neutral and filter by gravity sedimentation to obtain the filter residue, dry at 110 °C to obtain desalted aluminum ash;

[0053] (3) Mix the desalted aluminum ash and mixed acid at a mass ratio of 1:3 in a second microwave reactor, where the mass ratio of sulfuric acid: hydrogen iodide: phosphoric acid is 1:2:3 and the mass fraction of the mixed acid is 38%; the parameters of the microwave reactor are a microwave power of 2000 W, 3000 MHz, a reaction temperature of 150 °C, and a reaction time of 24 h, wash with water until neutral and filter by gravity to obtain the filtrate, concentrate at 110 °C to obtain an aluminum salt solution, where the alumina content in the filtrate is 55% (XRF).

[0054] (4) Mix and react the aluminum salt solution, sodium peroxide, and ammonium bicarbonate at a mass ratio of 100:23:23 in a third microwave reactor with a microwave power of 1800 W, a microwave frequency of 1700 MHz, a reaction temperature of 180 °C, and a reaction time of 24 h; wash with water until neutral and filter by gravity sedimentation to obtain a multi-porous alumina precursor, roast at a roasting temperature of 650 °C for a roasting time of 3 h to obtain multi-porous alumina.

[0055] Comparative Example 1

[0056] The secondary aluminum ash is sourced from Aluminum Processing Enterprise D in Shanxi Province

[0057] (1) Roast the secondary aluminum ash in a high-temperature furnace at a roasting temperature of 1100 °C for a roasting time of 10 h to obtain cooked aluminum ash;

[0058] (2) Mix the cooked aluminum ash and water at a mass ratio of 1:7 in a first microwave reactor with a microwave power of 1200 W, a microwave frequency of 2400 MHz, a reaction temperature of 140 °C, and a reaction time of 24 h; wash with water until neutral and filter by gravity sedimentation to obtain the filter residue, dry at 110 °C to obtain desalted aluminum ash;

[0059] (3) Mix the desalted aluminum ash and the mixed acid at a mass ratio of 1:3 in the second microwave reactor. Among them, the mass ratio of sulfuric acid: hydrogen iodide: phosphoric acid is 1:2:3, and the mass fraction of the mixed acid is 38%; the parameters of the microwave reactor are a microwave power of 2000 W, a frequency of 3000 MHz, a reaction temperature of 150 °C, and a reaction time of 24 h. Wash with water until neutral and filter by gravity to obtain the filtrate, and concentrate it at 110 °C to obtain the aluminum salt solution, where the alumina content in the filtrate is 55% (XRF).

[0060] (4) Mix and react the aluminum salt solution, the same mass of sodium peroxide and ammonium bicarbonate added in Example 4 in the third microwave reactor. The microwave power is 1800 W, the microwave frequency is 1700 MHz, the reaction temperature is 180 °C, and the reaction time is 24 h; wash with water until neutral and filter by gravity sedimentation to obtain the hierarchical pore alumina precursor, and the calcination temperature is 650 °C and the calcination time is 3 h to obtain the hierarchical pore alumina.

[0061] Comparative Example 2

[0062] The secondary aluminum ash is from D Aluminum Processing Enterprise in Shanxi Province

[0063] (1) Mix the secondary aluminum ash and activated carbon (particle size of 0.4 mm) evenly at a mass ratio of 5:3, and calcine and reduce in a high-temperature furnace. The calcination temperature is 1100 °C and the calcination time is 10 h to obtain the reduced aluminum ash;

[0064] (2) Mix the cooked aluminum ash and water at a mass ratio of 1:7 in a container. The reaction temperature is 140 °C and the reaction time is 24 h; wash with water until neutral and filter by gravity sedimentation to obtain the filter residue, and dry it at 110 °C to obtain the desalted aluminum ash;

[0065] (3) Mix the desalted aluminum ash and the mixed acid at a mass ratio of 1:3 in the second microwave reactor. Among them, the mass ratio of sulfuric acid: hydrogen iodide: phosphoric acid is 1:2:3, and the mass fraction of the mixed acid is 38%; the parameters of the microwave reactor are a microwave power of 2000 W, a frequency of 3000 MHz, a reaction temperature of 150 °C, and a reaction time of 24 h. Wash with water until neutral and filter by gravity to obtain the filtrate, and concentrate it at 110 °C to obtain the aluminum salt solution, where the alumina content in the filtrate is 55% (XRF).

[0066] (4) Mix and react the aluminum salt solution, sodium peroxide and ammonium bicarbonate at a mass ratio of 100:23:23 in the third microwave reactor. The microwave power is 1800 W, the microwave frequency is 1700 MHz, the reaction temperature is 180 °C, and the reaction time is 24 h; wash with water until neutral and filter by gravity sedimentation to obtain the hierarchical pore alumina precursor, and the calcination temperature is 650 °C and the calcination time is 3 h to obtain the hierarchical pore alumina.

[0067] Comparative Example 3

[0068] The secondary aluminum ash is sourced from Aluminum Processing Enterprise D in Shanxi Province

[0069] (1) Mix the secondary aluminum ash and activated carbon (particle size 0.4 mm) evenly at a mass ratio of 5:3, roast and reduce in a high-temperature furnace, with a roasting temperature of 1100 °C and a roasting time of 10 h to obtain reduced aluminum ash;

[0070] (2) Mix the reduced aluminum ash and water at a mass ratio of 1:7 in the first microwave reactor, with a microwave power of 1200 W, a microwave frequency of 2400 MHz, a reaction temperature of 140 °C, and a reaction time of 24 h; wash with water until neutral and filter by gravity sedimentation to obtain filter residue, dry at 110 °C to obtain desalted aluminum ash;

[0071] (3) Place the desalted aluminum ash in the second microwave reactor, with microwave reactor parameters of a microwave power of 2000 W, 3000 MHz, a reaction temperature of 150 °C, and a reaction time of 24 h; wash with water until neutral and filter by gravity to obtain filtrate, concentrate at 110 °C to obtain an aluminum salt solution, where the alumina content in the filtrate is 55% (XRF).

[0072] (4) Mix and react the aluminum salt solution, sodium peroxide, and ammonium bicarbonate at a mass ratio of 100:23:23 in the third microwave reactor, with a microwave power of 1800 W, a microwave frequency of 1700 MHz, a reaction temperature of 180 °C, and a reaction time of 24 h; wash with water until neutral and filter by gravity sedimentation to obtain a hierarchical pore alumina precursor, roast at 650 °C for 3 h to obtain hierarchical pore alumina.

[0073] Comparative Example 4

[0074] The secondary aluminum ash is sourced from Aluminum Processing Enterprise D in Shanxi Province

[0075] (1) Mix the secondary aluminum ash and activated carbon (particle size 0.4 mm) evenly at a mass ratio of 5:3, roast and reduce in a high-temperature furnace, with a roasting temperature of 1100 °C and a roasting time of 10 h to obtain reduced aluminum ash;

[0076] (2) Mix the reduced aluminum ash and water at a mass ratio of 1:7 in the first microwave reactor, with a microwave power of 1200 W, a microwave frequency of 2400 MHz, a reaction temperature of 140 °C, and a reaction time of 24 h; wash with water until neutral and filter by gravity sedimentation to obtain filter residue, dry at 110 °C to obtain desalted aluminum ash;

[0077] (3) Mix the desalted aluminum ash and the mixed acid at a mass ratio of 1:3 in the second microwave reactor. Among them, the mass ratio of sulfuric acid: hydrogen iodide: phosphoric acid is 1:2:3, and the mass fraction of the mixed acid is 38%; the parameters of the microwave reactor are 2000W microwave power, 3000MHz, 150°C reaction temperature, and 24h reaction time. Wash with water until neutral and filter by gravity to obtain the filtrate. Concentrate at 110°C to obtain the aluminum salt solution. Among them, the alumina content in the filtrate is 55% (XRF).

[0078] (4) Mix and react the aluminum salt solution and ammonium bicarbonate at a mass ratio of 100:23 in the third microwave reactor. The microwave power is 1800W, the microwave frequency is 1700MHz, the reaction temperature is 180°C, and the reaction time is 24h; wash with water until neutral and filter by gravity sedimentation to obtain the hierarchical pore alumina precursor. The calcination temperature is 650°C and the calcination time is 3h to obtain the hierarchical pore alumina.

[0079] Comparative Example 5

[0080] The secondary aluminum ash is from D Aluminum Processing Enterprise in Shanxi Province

[0081] (1) Mix the secondary aluminum ash and activated carbon (particle size of 0.4mm) evenly at a mass ratio of 5:3, and calcine and reduce in a high-temperature furnace. The calcination temperature is 1100°C and the calcination time is 10h to obtain the reduced aluminum ash;

[0082] (2) Mix the reduced aluminum ash and water at a mass ratio of 1:7 in the first microwave reactor. The microwave power is 1200W, the microwave frequency is 2400MHz, the reaction temperature is 140°C, and the reaction time is 24h; wash with water until neutral and filter by gravity sedimentation to obtain the filter residue. Dry at 110°C to obtain the desalted aluminum ash;

[0083] (3) Mix the desalted aluminum ash and the mixed acid at a mass ratio of 1:3 in the second microwave reactor. Among them, the mass ratio of sulfuric acid: hydrogen iodide: phosphoric acid is 1:2:3, and the mass fraction of the mixed acid is 38%; the parameters of the microwave reactor are 2000W microwave power, 3000MHz, 150°C reaction temperature, and 24h reaction time. Wash with water until neutral and filter by gravity to obtain the filtrate. Concentrate at 110°C to obtain the aluminum salt solution. Among them, the alumina content in the filtrate is 55% (XRF).

[0084] (4) Mix and react the aluminum salt solution and sodium peroxide at a mass ratio of 100:23 in the third microwave reactor. The microwave power is 1800W, the microwave frequency is 1700MHz, the reaction temperature is 180°C, and the reaction time is 24h; wash with water until neutral and filter by gravity sedimentation to obtain the hierarchical pore alumina precursor. The calcination temperature is 650°C and the calcination time is 3h to obtain the hierarchical pore alumina.

[0085] Comparative Example 6

[0086] The secondary aluminum ash is sourced from Aluminum Processing Enterprise D in Shanxi Province

[0087] (1) Mix the secondary aluminum ash and activated carbon (particle size 0.4 mm) evenly at a mass ratio of 5:3, roast and reduce in a high-temperature furnace at a roasting temperature of 1100 °C and a roasting time of 10 h to obtain reduced aluminum ash;

[0088] (2) Mix the reduced aluminum ash and water at a mass ratio of 1:7 in the first microwave reactor, with a microwave power of 1200 W, a microwave frequency of 2400 MHz, a reaction temperature of 140 °C, and a reaction time of 24 h; wash with water until neutral and filter by gravity sedimentation to obtain filter residue, dry at 110 °C to obtain desalted aluminum ash;

[0089] (3) Mix the desalted aluminum ash and mixed acid at a mass ratio of 1:3, where the mass ratio of sulfuric acid:hydrogen iodide:phosphoric acid is 1:2:3, and the mass fraction of the mixed acid is 38%; use a kettle reactor, with a reaction temperature of 150 °C and a reaction time of 24 h, wash with water until neutral and filter by gravity to obtain filtrate, concentrate at 110 °C to obtain an aluminum salt solution, where the alumina content in the filtrate is 55% (XRF).

[0090] (4) Mix and react the aluminum salt solution, sodium peroxide, and ammonium bicarbonate at a mass ratio of 100:23:23 in the third microwave reactor, with a microwave power of 1800 W, a microwave frequency of 1700 MHz, a reaction temperature of 180 °C, and a reaction time of 24 h; wash with water until neutral and filter by gravity sedimentation to obtain a multi-porous alumina precursor, roast at a temperature of 650 °C and a roasting time of 3 h to obtain multi-porous alumina.

[0091] Table 1 Performance parameters of multi-porous alumina in examples and comparative examples

[0092] Example <![CDATA[Specific surface area (cm 2 / g)]]> <![CDATA[Mesoporous pore volume (cm 3 / g)]]> Average pore diameter (nm) Example 1 369.5 2.8 2.6 Example 2 398.7 3.0 2.8 Example 3 420.2 3.2 2.9 Example 4 416.9 3.1 2.9 Comparative Example 1 128.5 1.7 1.6 Comparative Example 2 277.3 2.2 2.0 Comparative Example 3 74.1 1.3 1.5 Comparative Example 4 196.8 1.9 1.7 Comparative Example 5 140.6 1.8 1.6 Comparative Example 6 201.2 1.9 1.7

[0093] Based on the comparison between Example 4 and Comparative Example 1, it shows that mixing and roasting the secondary aluminum ash with a reducing agent can effectively reduce metal oxides to carbides, and this method utilizes the increase in the total mass of aluminum atoms precipitated from the aluminum salts in the secondary aluminum ash. Although the mass percentage of alumina in the aluminum salt solution is 55% in both cases, the total mass of alumina in the aluminum salt solution in Example 4 is much higher than that in Comparative Example 1. Compared with the optimal mass ratio of the aluminum salt solution, sodium peroxide, and ammonium bicarbonate in Example 4, the mass ratio of sodium peroxide and ammonium bicarbonate to alumina in the aluminum salt in Comparative Example 1 is excessive. Compared with Example 4, the relative content of the pore-expanding agent and alkali amount in Comparative Example 1 increases, resulting in a decrease in the pore structure parameters of the multi-porous alumina synthesis material.

[0094] Based on the comparison between Example 4 and Comparative Example 2, it shows that simple impregnation and water washing cannot remove the miscellaneous salts in secondary aluminum ash, and at the same time, the presence of miscellaneous salts affects the formation of pore structure during the preparation of hierarchical porous alumina.

[0095] Based on the comparison between Example 4 and Comparative Example 3, it shows that the mixed acid directly affects the total amount of aluminum atoms precipitated in secondary aluminum ash, and further affects the formation of pore structure during the preparation of hierarchical porous alumina.

[0096] Based on the comparison between Example 4 and Comparative Example 4, the alkali source converts the aluminum salt into aluminum hydroxide and sodium aluminate, which is the optimal precursor for the synthesis of hierarchical porous alumina materials. Compared with Example 4, the pore structure parameters of the hierarchical porous alumina synthesized from aluminum-containing miscellaneous salts are relatively low.

[0097] Based on the comparison between Example 4 and Comparative Example 5, it shows that ammonium bicarbonate is used as a pore-expanding agent during the synthesis of hierarchical porous alumina.

[0098] Based on the comparison between Example 4 and Comparative Example 6, it shows that the effect of using a microwave heating reactor in the dealumination process of secondary aluminum ash is better than that of a kettle heating reactor.

Claims

1. A method for preparing multi-level porous alumina from secondary aluminum ash, comprising the following steps: (1) reducing the secondary aluminum ash with a reducing agent to obtain reduced aluminum ash; (2) mixing the reduced aluminum ash with water, filtering and drying to obtain desalted aluminum ash; (3) mixing the desalted aluminum ash and mixed acid, filtering and concentrating to obtain an aluminum salt solution; (4) The aluminum salt solution, alkali source and pore expanding agent are mixed and calcined to obtain hierarchical pore alumina.

2. The method according to claim 1, wherein: In step (1), the reducing agent is at least one of coke, charcoal, graphite and activated carbon, and the particle size of the reducing agent is less than 1 mm.

3. The method according to claim 1, wherein: In step (1), the mixture of secondary aluminum ash and reducing agent is roasted in a high temperature furnace at a roasting temperature of 900-1300° C. for a roasting time of 6-12 h.

4. The method according to claim 1, wherein: In step (2), at least one of the following conditions must be met: a. The mass ratio of the reduced aluminum ash to water is 1: 3-10; b. The reduced aluminum ash is mixed with water in a first microwave reactor, the microwave power is 500-2000W, the microwave frequency is 1500-3000MHz, the reaction temperature is 80-150 ℃, the reaction time is 6-24h; c. Wash with water until neutral, settle by gravity, and dry to obtain desalted aluminum ash at a drying temperature of 110-120°C.

5. The method according to claim 1, wherein: In step (3), at least one of the following conditions must be met: a. The mixed acid conforms to the ABC configuration, wherein A is sulfuric acid; B includes one of hydrochloric acid, hydrogen fluoride, hydrogen bromide, and hydrogen iodide; C includes one of perchloric acid, nitric acid, and phosphoric acid; A:B:C=1:1-2:1-3; b. The mass ratio of the desalted aluminum ash and the mixed acid is 1:2-5, wherein the mass fraction of the mixed acid is 15%-40%; c. The mixing is completed in a second microwave reactor, the microwave power is 500-2000W, the microwave frequency is 1500-3000MHz, the reaction temperature is 80-150 ℃, the reaction time is 6-24h; d. The evaporation concentration temperature is 110-120°C, and the alumina content in the filtrate is 40-75%.

6. The method according to claim 1, wherein: In step (4), the alkali source includes one of sodium hydroxide, potassium hydroxide, sodium oxide, and sodium peroxide; and the pore expanding agent is ammonium bicarbonate.

7. The method according to claim 1, wherein: In step (4), the mass ratio of the aluminum salt solution, the alkali source and the pore expanding agent is 100:5-35:1-25, and the mixing is completed in a third microwave reactor with a microwave power of 500-2000 W, a microwave frequency of 1500-3000 MHz, a reaction temperature of 120-180° C., a reaction time of 12-24 h, and the mixture is washed with water until neutral and a multi-level porous alumina precursor is obtained by gravity sedimentation.

8. The method according to claim 1, wherein: In step (4), the calcination temperature is 500-800°C and the calcination time is 1-3h.

9. The multi-level porous alumina prepared by the method according to any one of claims 1 to 8.

10. The multi-level porous alumina according to claim 9, wherein: The specific surface area and pore volume of the multi-level porous alumina are 420 cm 3 / g and 3.8 cm 3 / g.

Images