A method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen

Abstract

The present invention provides a method for the comprehensive recycling and utilization of secondary aluminum ash and the co-production of high-purity hydrogen. In the method, the secondary aluminum ash is first pretreated with an ammonium chloride solution to hydrolyze aluminum nitride, aluminum carbide, and other substances in the aluminum ash, dissolving and recovering salts to increase process safety. The waste liquid is then recycled and reused multiple times through evaporation and crystallization to reduce carbon and recover salts, thereby increasing the utilization efficiency of the sodium element during the alkaline treatment process. The gas recovery and utilization during the aluminum ash hydrolysis process is then optimized, using the low-concentration ammonia water obtained through absorption to absorb carbon dioxide, and ammonium chloride is recycled and accumulated, avoiding the use of strong acid absorption and reducing equipment costs. Pressure swing adsorption is used to purify the gaseous components to the purity required for fuel cells. The method provided by the present invention reduces the high-temperature and corrosion resistance requirements of the equipment during the alkaline wet treatment of secondary aluminum ash, fully recovers the sodium element input during the alkaline treatment process and the soluble salts in the secondary aluminum ash, and achieves harmless treatment of the aluminum ash, with outstanding economic and environmental benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste treatment, and in particular relates to a method for comprehensive recycling and utilization of secondary aluminum ash and co-production of high-purity hydrogen. Background Art

[0002] China is the world's largest aluminum producer and consumer, and has long accounted for over half of global aluminum production. Aluminum ash, a solid waste produced during the electrolysis, recycling, and processing of aluminum, is generated when molten aluminum oxidizes in contact with air. Statistics show that 110 kg of aluminum ash is generated for every ton of aluminum produced. During high-temperature smelting of aluminum, aluminum reacts with oxygen, nitrogen, and carbon dioxide to produce oxides, nitrides, and carbides. Generally, aluminum ash contains aluminum, Al2O3, AlN, magnesium-aluminum spinel, and metal salts. The hazards of aluminum ash primarily lie in its nitrides (such as AlN and FeN). For example, AlN reacts with water to produce the irritating and toxic gas ammonia. Ammonia is an irritant that can cause severe air pollution, exacerbating irritation and leading to various illnesses, including lung infections. Aluminum ash has long been listed on the National Hazardous Substances List as Class HW48 non-ferrous metal smelting waste.

[0003] The treatment methods of aluminum ash are divided into pyrolysis, wet treatment and a combination of wet and pyrolysis. The core of pyrolysis treatment is to make the reactive active components in the secondary aluminum ash fully react with O2 by heating to eliminate the reactivity of the aluminum ash. Aluminum ash is mixed with limestone and added to a rotary kiln, sintered at 1200~1350℃ to prepare calcium aluminate refining slag for steelmaking: 7Al2O3+12CaCO3=12CaO∙7Al2O3+12CO2. This method requires coal or natural gas as fuel and has high energy consumption. Wet treatment is the most effective method for removing active components from secondary aluminum ash, and it is also the most commonly used harmless treatment method. Wet treatment includes acid leaching and alkaline leaching. The acid leaching method uses a strong acid solution to dissolve all the soluble components in the secondary aluminum ash, and then filters and adds excess sodium hydroxide to the filtrate to make Al 3+The aluminum ash is converted into aluminate, which then undergoes a series of steps, including pH adjustment, precipitation, filtration, and calcination, to yield the final Al2O3 product. The acid method removes nitrogen and forms ammonium salts, preventing the harmful effects of ammonia on personnel, equipment, and the environment, while fully recovering the aluminum element. However, the acid method requires a large amount of solvent, resulting in high raw material costs. Furthermore, alkaline oxides such as Fe and Ca dissolve into the solution, leading to a complex solution composition, cumbersome subsequent purification processes, and the generation of a large amount of acidic wastewater requiring treatment. The alkaline leaching method uses an alkali catalyst to catalytically deaminate the secondary aluminum ash during water leaching. During the alkaline treatment, trivalent nitrogen evaporates as ammonia gas, which is recovered by an absorption device. The alkaline leaching method reduces impurities (primarily Si) when recovering the aluminum product, resulting in a higher purity. However, the aluminum recovery rate is low, with only approximately 30% of the aluminum entering the solution. Improving the recovery rate requires conducting the reaction under high temperature, high pressure, and high alkaline conditions. Overall, pyrometallurgical treatment of aluminum ash is energy-intensive, and both acid and alkaline methods have their own advantages and disadvantages. Summary of the Invention

[0004] To address the issues of wet processing, such as high wastewater levels from acid leaching, high sodium hydroxide consumption from alkaline leaching, low aluminum extraction rates, low ammonia concentrations, and low combustible gas recovery efficiency, a method for comprehensive recovery and utilization of secondary aluminum ash with co-production of high-purity hydrogen has been proposed. Compared to traditional alkaline wet processes, this process offers advantages such as increased safety, reduced waste, multiple products, and high element recovery rates.

[0005] To solve the above problems, the technical solutions of the present invention are as follows:

[0006] A method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen, comprising the following steps:

[0007] Step S1, a raw material preparation process, uses a grinder to grind the secondary aluminum ash to break up the large agglomerated particles in the aluminum ash. The particle size of the ground secondary aluminum ash is 60-100 mesh to increase the reaction contact area. A magnetic attraction device is used to recover the magnetic iron element in the aluminum ash;

[0008] Step S2, a first-stage hydrolysis process, wherein the aluminum ash treated in step S1 is transported through a pipe chain into a reactor, and then an ammonium chloride solution at 50-80°C is added. The mixture is hydrolyzed for 1-3 hours under stirring, and an acid pretreatment is performed to remove some active substances and improve the purity of hydrogen during the second-stage hydrolysis. At the same time, soluble salts in the aluminum ash are recovered, and the reaction solution is simply filtered and recovered into a salt solution storage tank;

[0009] Step S3, a second-stage hydrolysis process, when the temperature in the reactor drops to 25-30°C, sodium hydroxide solution is pumped into the reactor and the hydrolysis reaction is carried out for 2-6 hours under stirring. Circulating water is used for heat removal to control the reaction temperature to be no higher than 90°C. The entire process is carried out under a slightly positive pressure to prevent air from entering the system and causing an explosion.

[0010] Step S4, filtration process: when the hydrolyzed slurry is cooled to below 45°C, it is sent to a vacuum rotary filter to recover the solids, and the filtrate is sent to the next stage for further recovery;

[0011] Step S5, a dealkalization process, introducing CO2 gas into the filtrate obtained in step S4 to adjust the solution pH to <11, and filtering and recovering the aluminum hydroxide product using a plate and frame filter;

[0012] Step S6, a concentration and carbonization process, wherein CO2 gas and ammonia gas are introduced into the filtrate obtained in step S5, and the sodium bicarbonate product and the concentrated ammonium chloride solution are recovered by evaporation and crystallization;

[0013] Step S7, tail gas recovery process, for the gas phase components after the reaction, use the low concentration of ammonium chloride solution in the brine storage tank to absorb ammonia and cool down; the mixed gas mainly composed of hydrogen, methane and nitrogen is purified by pressure swing adsorption to obtain high-purity hydrogen, with high-quality hydrogen as the product, and low-quality waste gas is burned for heat.

[0014] Furthermore, in step S2, the ammonium chloride solution includes ammonium chloride, ammonia water, and sodium chloride, and is obtained from a brine storage tank. The mass fraction of ammonium chloride in the ammonium chloride solution is not less than 1%; the mass ratio of the ammonium chloride solution to the aluminum ash fed into the reactor is 2-4:1.

[0015] Furthermore, in step S3, the sodium hydroxide solution is recycled for 3 to 5 times, and the solutes contained are NaOH, NaAlO2, and NH3; the NaOH concentration in the sodium hydroxide solution used should be greater than 2.5 mol / L, and the mass ratio of the added sodium hydroxide solution to the aluminum ash is 2 to 5:1.

[0016] Furthermore, in step S3, the slightly positive pressure condition refers to being 1-10 kPa higher than the standard atmospheric pressure.

[0017] Furthermore, in step S6, the heat required for the evaporation and crystallization is provided by the by-product H2 and CH4 mixed gas; the ammonia gas is preferably the low-concentration ammonia water produced by the absorption tower.

[0018] Furthermore, in step S7, the solution in the brine storage tank is used to absorb ammonia to cool down, the mass fraction of ammonium chloride in the solution is less than 1%, the solution temperature is preferably 20-30°C, and the volume liquid-gas ratio of the solution in the brine storage tank to ammonia is 3-7:1.

[0019] The mechanism of the present invention includes:

[0020] The method provided by the present invention first uses an acidic ammonium chloride solution to consume a portion of the active components of the aluminum ash, dissolve and extract the soluble salts in the aluminum ash, and then uses a high-concentration sodium hydroxide solution to efficiently denitrify and extract aluminum, completely converting AlN into aluminate and ammonia, and converting the aluminum element in the aluminum ash into the form of aluminic acid. After the recovered high pH filtrate is used multiple times, it is passed through carbon dioxide for treatment to completely convert the aluminate into aluminum hydroxide. Finally, carbon dioxide and low-concentration ammonia water are added to produce sodium bicarbonate to recover the sodium element and a low-solubility ammonium chloride solution to recover chlorine and nitrogen. The hydrogen-rich gas produced by hydrolysis is further purified by pressure swing adsorption.

[0021] The above method involves the following reactions:

[0022] Al2O3+NaOH→NaAlO2+ H2O

[0023] Al + NaOH → H2↑ + NaAlO2

[0024] AlN+NaOH→NH3↑+NaAlO2

[0025] NaAlO2+CO2→Na2CO3+ Al(OH)3↓

[0026] Na2CO3+CO2+ H2O→2NaHCO3

[0027] NaCl+NH3+CO2→NaHCO3↓+ NH4Cl

[0028] The addition of the primary hydrolysis process reduces reactive components in the aluminum ash, while the secondary hydrolysis process produces less heat, making temperature control easier and more convenient for large-scale production. The sodium and chlorine added to the reaction system are recovered, improving production efficiency and being more environmentally friendly. The ammonia absorption tower utilizes solution recovered from the brine storage tank rather than traditional sulfuric acid, reducing equipment corrosion and production costs. The entire process produces high-quality aluminum hydroxide, hydrogen, and sodium bicarbonate, offering excellent economic benefits and promising industrial applications.

[0029] The recovered high-pH filtrate contains NaOH, NaAlO2, and NH3. During the aluminum ash hydrolysis process, the reaction between sodium hydroxide solution and the ash is relatively intense. NaAlO2 and NH3 can buffer the pH of the system, maintaining it within a relatively stable range. This facilitates the continued hydrolysis of the aluminum ash and reduces localized overheating, thereby mitigating potential safety risks such as splashing caused by excessively intense reactions. Furthermore, the presence of sodium metaaluminate promotes the dissolution and reaction of aluminum in the ash. Under appropriate conditions, it can react with some insoluble aluminum compounds in the ash, converting more aluminum into soluble aluminates, thereby increasing aluminum recovery. NH3 can also react with impurities in the ash (such as metal ions, forming complexes), improving the separation of aluminum from impurities and improving aluminum purity and recovery.

[0030] Compared with the existing technology, the present invention has the following advantages and beneficial effects:

[0031] (1) The present invention reduces the reaction temperature of the secondary aluminum ash alkali treatment reaction by a two-stage reaction method, thereby increasing the reaction ignition point and reducing the heat transfer burden.

[0032] (2) The present invention uses a new process idea to utilize the waste liquid generated in the original alkali leaching process, thereby achieving efficient recovery of sodium, chlorine, aluminum and ammonia nitrogen.

[0033] (3) The present invention optimizes the ammonia absorption process and uses ammonium chloride solution to absorb ammonia. Unlike the existing method of utilizing nitrogen resources from aluminum ash, it achieves high-quality recovery of nitrogen resources without increasing operating costs and equipment costs.

[0034] (4) The present invention adds a high-quality hydrogen recovery process, greatly improving the purity of the recovered hydrogen and increasing the product value.

[0035] (5) The present invention recycles and utilizes the generated carbon dioxide, which meets the needs of the national dual carbon strategy. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the method provided by the present invention

[0037] Figure 2 This is a schematic diagram of the main process flow of the present invention

[0038] Figure 3 This is a schematic diagram of the triple-effect evaporation crystallization process of the present invention.

[0039] Figure 4 Schematic diagram of a dual-bed pressure swing adsorption model DETAILED DESCRIPTION

[0040] In order to make researchers more clearly understand the technical solutions and technical advantages of the present invention, the present invention will be described in detail below with reference to the embodiments. It is particularly noted that the embodiments are only used to clearly and completely describe the present invention and should not be regarded as limiting the scope of the present invention.

[0041] Example 1

[0042] This embodiment provides a method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen, comprising the following steps:

[0043] S1: Raw material preparation process, using a grinder to grind the secondary aluminum ash, after grinding, taking the secondary aluminum ash between 60 and 100 meshes, and using a magnetic suction device to recover the magnetic iron elements in the secondary aluminum ash.

[0044] S2: A hydrolysis process, in which the secondary aluminum ash treated in S1 is transported through a pipe chain into the reactor, and then a 70°C, 1wt% ammonium chloride solution is added. The mass ratio of the added ammonium chloride solution to the aluminum ash is 2:1. No external heating treatment is performed, and the hydrolysis reaction is carried out under stirring for 1 hour. At this time, part of the aluminum, aluminum carbide, and aluminum nitride react with water, and the generated ammonia gas dissolves in the reaction solution. The soluble salts in the aluminum ash dissolve in the reaction solution, and the mass loss rate of the aluminum ash is 7~15% (the results of 6 experiments are statistically analyzed due to the differences in the component content in the aluminum ash).

[0045] S3: Secondary hydrolysis process: After the temperature in the reactor drops to 28°C, simple filtration and separation are performed. After oxygen displacement with nitrogen, a 5 mol / L sodium hydroxide solution at room temperature is pumped into the reactor. The mass ratio of sodium hydroxide solution to aluminum ash is 5:1. The hydrolysis reaction is carried out under stirring for 2 hours. Circulating water is used for heat removal, and the reactor temperature is controlled below 90°C to obtain a completely hydrolyzed slurry. The reaction is carried out under a slight positive pressure (106.4 kPa) to prevent air from entering the system and causing explosion. The collected gas composition after the reaction and ammonia removal is H2:CH4:N2 = 90.89%:0.75%:8.36%.

[0046] S4: Filtration process: the hydrolyzed slurry is cooled to 40°C and sent to a vacuum rotary filter to recover the solids. The filtrate is sent to the next stage for further recovery.

[0047] S5: dealkalization process, slowly introducing CO2 gas into the filtrate obtained in step S4 to make the solution pH <11, after standing and settling, using a plate and frame filter to filter and recover the aluminum hydroxide product.

[0048] S6: Concentration step, CO2 gas and ammonia water are introduced into the filtrate obtained in step S5, and the sodium bicarbonate product and concentrated NH4Cl solution are recovered by evaporation and crystallization.

[0049] S7: Tail gas recovery process, the following method is used to separate the gases NH3, H2, CH4, water vapor and venting nitrogen produced by the second-stage hydrolysis: For NH3, use 20℃, 0.5wt% ammonium chloride solution for absorption, with a volume liquid-to-gas ratio of 6:1, to obtain a mixed liquid of ammonium chloride and ammonia water, thereby increasing the mass fraction of ammonia nitrogen in the absorption liquid; for H2, after drying and removing water, use pressure swing adsorption technology to continuously produce high-quality hydrogen. The waste gas is used for combustion and heat supply, and the carbon dioxide is used in the S5 and S6 processes.

[0050] Example 2

[0051] This embodiment provides a method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen, comprising the following steps:

[0052] S1: Raw material preparation process, using a grinder to grind the secondary aluminum ash, after grinding, taking the secondary aluminum ash between 60 and 100 meshes, and using a magnetic suction device to recover the magnetic iron elements in the secondary aluminum ash.

[0053] S2: A hydrolysis process, wherein the aluminum ash treated in step S1 is transported through a pipe chain into a reactor, and then a 1.5 wt% ammonium chloride solution is added at 60°C, with a mass ratio of the added ammonium chloride solution to the aluminum ash of 2.5:1. No external heating treatment is performed, and the hydrolysis reaction is carried out under stirring for 2 hours. At this time, part of the aluminum, aluminum carbide, and aluminum nitride react with water, and the generated ammonia gas dissolves in the reaction solution. The soluble salts in the aluminum ash dissolve in the reaction solution, and the mass loss rate of the aluminum ash is 6-14%.

[0054] S3: Secondary hydrolysis process: After the temperature in the reactor drops to 28°C, simple filtration and separation are performed. NaOH is added to the sodium hydroxide solution recovered in step S3 (containing NaOH, NaAlO₂, and NH₃) to produce a 4 mol / L sodium hydroxide solution. This is pumped into the reactor, with a mass ratio of sodium hydroxide solution to aluminum ash of 4:1. The hydrolysis reaction is carried out under stirring for 3 hours. Circulating water is used for heat removal, and the reactor temperature is controlled below 90°C to obtain a completely hydrolyzed slurry. The entire reaction is carried out under a slight positive pressure (106.3 kPa) to prevent air from entering the system and causing an explosion. The collected gas composition after the reaction and ammonia removal is 92.46% H₂:CH₄:N₂:0.67%:6.87%.

[0055] S4: Filtration process: the hydrolyzed slurry is cooled to 38°C and sent to a vacuum rotary filter to recover the solids. The filtrate is sent to the next stage for further recovery.

[0056] S5: dealkalization process, CO2 gas is introduced into the filtrate obtained in S4 to make the solution pH <11, and the aluminum hydroxide product is recovered by filtering using a plate and frame filter.

[0057] S6: Concentration step, CO2 gas and ammonia water are introduced into the filtrate obtained in step S5, and the sodium bicarbonate product and concentrated NH4Cl solution are recovered by evaporation and crystallization.

[0058] S7: Tail gas recovery process, the following method is used to separate the gases NH3, H2, CH4, water vapor and venting nitrogen produced by the second-stage hydrolysis: For NH3, use 25℃, 0.2wt% ammonium chloride solution for absorption, with a liquid-to-gas ratio of 7:1, to obtain a mixed liquid of ammonium chloride and ammonia water, thereby increasing the mass fraction of ammonia nitrogen in the absorption liquid; for H2, after drying and removing water, use pressure swing adsorption technology to continuously produce high-quality hydrogen. The waste gas is used for combustion and heat supply, and the carbon dioxide is used in the S5 and S6 processes.

[0059] Example 3

[0060] This embodiment provides a method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen, comprising the following steps:

[0061] S1: Raw material preparation process, using a grinder to grind the secondary aluminum ash, after grinding, taking the secondary aluminum ash between 60 and 100 meshes, and using a magnetic suction device to recover the magnetic iron elements in the secondary aluminum ash.

[0062] S2: A hydrolysis process, wherein the aluminum ash treated in step S1 is transported through a pipe chain into a reactor, and then the ammonium chloride solution (ammonium chloride, ammonia water mixture) recovered from step S7 is added, at 60°C, 1 wt%, with a mass ratio of the added ammonium chloride solution to the aluminum ash of 3:1. No external heating treatment is performed, and the hydrolysis reaction is carried out under stirring for 3 hours. At this time, part of the aluminum, aluminum carbide, and aluminum nitride react with water, and the generated ammonia gas dissolves in the reaction solution. The soluble salts in the aluminum ash dissolve in the reaction solution, and the mass loss rate of the aluminum ash is 5-15%.

[0063] S3: Secondary hydrolysis process: After the temperature in the reactor drops to 25°C, simple filtration and separation are performed. A 3 mol / L sodium hydroxide solution at room temperature is pumped into the reactor, with a mass ratio of sodium hydroxide solution to aluminum ash of 2:1. The hydrolysis reaction is carried out under stirring for 6 hours. Circulating water is used for heat transfer, and the reactor temperature is controlled below 90°C to obtain a completely hydrolyzed slurry. The entire reaction is carried out under a slight positive pressure (106.1 kPa) to prevent air from entering the system and causing explosions. The collected gas composition after the reaction and ammonia removal is H2:CH4:N2 = 90.97%:0.83%:9.2%.

[0064] S4: Filtration process: the hydrolyzed slurry is cooled to 38°C and sent to a vacuum rotary filter to recover the solids. The filtrate is sent to the next stage for further recovery.

[0065] S5: dealkalization process, CO2 gas is introduced into the filtrate obtained in S4 to make the solution pH <11, and the aluminum hydroxide product is recovered by filtering using a plate and frame filter.

[0066] S6: Concentration step, CO2 gas and ammonia water are introduced into the filtrate obtained in step S5, and the sodium bicarbonate product and concentrated NH4Cl solution are recovered by evaporation and crystallization.

[0067] S7: Tail gas recovery process, the following method is used to separate the gases NH3, H2, CH4, water vapor and venting nitrogen produced by the second-stage hydrolysis: For NH3, use 20℃, 0.1wt% ammonium chloride solution for absorption, with a liquid-to-gas ratio of 5:1, to obtain a mixed liquid of ammonium chloride and ammonia water, thereby increasing the mass fraction of ammonia nitrogen in the absorption liquid; for H2, after drying and dehydration, use pressure swing adsorption technology to continuously produce high-quality hydrogen. The waste gas is used for combustion and heat supply, and the carbon dioxide is used in the S5 and S6 processes.

[0068] Example 4

[0069] This embodiment provides a method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen, comprising the following steps:

[0070] S1: Raw material preparation process, using a grinder to grind the secondary aluminum ash, after grinding, taking the secondary aluminum ash between 60 and 100 meshes, and using a magnetic suction device to recover the magnetic iron elements in the secondary aluminum ash.

[0071] S2: A hydrolysis process, in which the aluminum ash treated in S1 is transported to the reactor through a pipe chain, and then the ammonium chloride solution recovered from the S7 process is added, at 55°C, 2wt%, and the mass ratio of the added ammonium chloride solution to the aluminum ash is 4:1. No external heating treatment is performed, and the hydrolysis reaction is carried out under stirring for 2 hours. At this time, part of the aluminum, aluminum carbide, and aluminum nitride react with water, and the generated ammonia gas dissolves in the reaction solution. The soluble salts in the aluminum ash dissolve in the reaction solution. The mass loss rate of the aluminum ash is 5~11%.

[0072] S3: Secondary hydrolysis process: After the temperature in the reactor drops to 30°C, simple filtration and separation are performed. NaOH is added to the sodium hydroxide solution recovered in step S3 (containing NaOH, NaAlO₂, and NH₃), resulting in a 3 mol / L sodium hydroxide solution. This solution is pumped into the reactor, with a mass ratio of sodium hydroxide solution to aluminum ash of 3:1. Hydrolysis is carried out under stirring for 4 hours. Circulating water is used for heat removal, and the reaction temperature is controlled below 90°C to obtain a completely hydrolyzed slurry. The entire reaction is carried out under a slight positive pressure (104.67 kPa) to prevent air from entering the system and causing an explosion. The collected gas composition after the reaction and ammonia removal is 91.67% H₂:CH₄:N₂:0.53%:7.8%.

[0073] S4: Filtration process: the hydrolyzed slurry is cooled to 43°C and sent to a vacuum rotary filter to recover the solids. The filtrate is sent to the next stage for further recovery.

[0074] S5: dealkalization process, CO2 gas is introduced into the filtrate obtained in S4 to make the solution pH <11, and the aluminum hydroxide product is recovered by filtering using a plate and frame filter.

[0075] S6: Concentration step, CO2 gas and ammonia water are introduced into the filtrate obtained in step S5, and the sodium bicarbonate product and concentrated NH4Cl solution are recovered by evaporation and crystallization.

[0076] S7: Tail gas recovery process, the following method is used to separate the gases NH3, H2, CH4, water vapor and venting nitrogen produced by the second-stage hydrolysis: For NH3, use 20℃, 0.3wt% ammonium chloride solution for absorption, with a liquid-to-gas ratio of 3:1, to obtain a mixed liquid of ammonium chloride and ammonia water, thereby increasing the mass fraction of ammonia nitrogen in the absorption liquid; for H2, after drying and removing water, use pressure swing adsorption technology to continuously produce high-quality hydrogen. The waste gas is used for combustion and heat supply, and the carbon dioxide is used in the S5 and S6 processes.

[0077] Comparative Example 1

[0078] S1: Raw material preparation process, using a grinder to grind the secondary aluminum ash, after grinding, taking the secondary aluminum ash between 60 and 100 meshes, and using a magnetic suction device to recover the magnetic iron elements in the secondary aluminum ash.

[0079] S2: A hydrolysis process, the aluminum ash treated in S1 is transported to the reactor through a pipe chain, and then 70°C water is added. The mass ratio of the added water to the aluminum ash is 2:1. No external heating treatment is performed, and the hydrolysis reaction is carried out under stirring for 1 hour.

[0080] Phenomenon: After adding the 70℃ aqueous solution, the temperature continued to rise within 20 minutes, and at 22 minutes, the temperature rose to 175℃.

[0081] Table 1 Hydrogen content and aluminum ash mass loss rate in Examples 1-4

[0082] Hydrogen content (%) Aluminum ash mass loss rate (%) Example 1 90.89 7~ 15 Example 2 92.46 6~ 14 Example 3 90.97 5~ 15 Example 4 91.67 5~ 11

[0083] The above results demonstrate that Examples 1-4 reflect the varying effects of secondary aluminum ash hydrolysis under different conditions. The results indicate that a two-stage wet treatment of aluminum ash facilitates controlling the reaction temperature of the secondary aluminum ash alkaline treatment reaction, raising the ignition point and reducing the heat transfer burden. The primary hydrolysis process facilitates the hydrolysis of active substances such as aluminum nitride and aluminum carbide, thereby increasing the hydrogen purity in the secondary hydrolysis. The purity of the hydrogen produced after the addition of sodium hydroxide solution can reach over 90%.

[0084] Pressure swing adsorption tail gas treatment and purification

[0085] For the gas components in Examples 1 to 4, numerical simulation analysis was performed using Aspen Adsorption. A dual-bed pressure swing adsorption process was used to simulate two parallel adsorption beds to simulate the purification of hydrogen to the standard for fuel cell proton membrane hydrogen.

[0086] I. Bed 1 Feed Pressurization, Bed 2 Depressurization (Pressurization Bed 1, Depressurization Bed 2): Feed gas is introduced into adsorption bed 1 through inlet valve F1. The pressure in the adsorption bed gradually increases from the pressure after the equalization phase to the adsorption pressure. Exhaust gas from adsorption bed 2 exits through exhaust outlet W2. The pressure rapidly decreases to atmospheric pressure, and impurities in the adsorption bed are desorbed from the adsorbent due to the pressure drop and flow out through the exhaust outlet.

[0087] II. Adsorption Bed 1 and Bed 2 Purge: During this process, the pressure in the adsorption bed is the higher pressure established after the feed gas is introduced, and this pressure is maintained throughout the adsorption process. As the adsorption process progresses, a large amount of impurities are absorbed into the pores of the adsorbent, completing the purification of the hydrogen. The less adsorbable hydrogen flows out of the adsorption bed, with some being concentrated at the product outlet and the rest flowing to Bed 2 for purging.

[0088] Ⅲ. Pressure equalization (PPE): Close all valves except the purge valve. The gas in the adsorption beds will automatically flow due to the pressure difference between the two towers. The pressure in the higher-pressure adsorption bed Bed1 will drop, and the pressure in the adsorption bed Bed2 will increase, eventually completing the pressure equalization.

[0089] IV. Bed 2 Feed Pressurization and Bed 1 Depressurization (Pressurization Bed 2, Depressurization Bed 1): Feed gas is introduced into adsorption bed Bed 2 through inlet valve F2. The pressure in the adsorption bed gradually increases from the pressure at the end of the equalization phase to the adsorption pressure. Exhaust gas from adsorption bed Bed 2 exits through exhaust outlet W2. The pressure rapidly decreases to atmospheric pressure, and impurities in the adsorption bed are desorbed from the adsorbent due to the pressure drop and flow out through the exhaust outlet.

[0090] V. Adsorption Bed 2 (Purge Bed 1): During this process, the pressure in the adsorption bed is the higher pressure established after the feed gas is introduced, and this pressure is maintained throughout the adsorption process. As the adsorption process progresses, a large amount of impurities are absorbed into the pores of the adsorbent, completing the purification of the hydrogen. The less adsorbable hydrogen flows out of the adsorption bed, with a portion passing through P2 and being enriched in the product tank, while the remaining portion (determined by the purge ratio) flows to Bed 1 for flushing.

[0091] VI. Pressure equalization (PPE): Close all valves except the purge valve. The gas in the adsorption bed will automatically flow due to the pressure difference between the two towers. The pressure in the adsorption bed Bed1 will rise, and eventually the pressure equalization will be completed.

[0092] The initial stage of the cycle is the adsorption step, where the adsorbent adsorbs the mixed gas. Therefore, the pressure in the adsorption beds is maintained at a uniform adsorption pressure of 10 bar. The second stage, the pressure reduction and equalization step, then begins. The pressure difference between the two adsorption beds is equalized via a valve, reducing the pressure in bed 1. The third stage is the purge step, where the waste gas valve connected to the outside world is opened, rapidly reducing the pressure to atmospheric pressure. Remaining impurities in the adsorption bed are desorbed and flow through the waste gas valve into the waste gas tank. The fourth stage is the flushing step, where the other adsorption bed is in the adsorption stage. A portion of the generated hydrogen flows through the valve into the adsorption bed, flushing out the remaining impurities and filling the bed with hydrogen for reuse. During this stage, the pressure is maintained at a uniform atmospheric pressure, and the waste gas valve remains open. The fifth stage is the boosting and equalization step. In contrast to the pressure reduction and equalization step, the pressure in the adsorption bed increases due to equalization. Finally, the feed pressurization step occurs, where a large amount of feed gas enters the adsorption bed through a valve, bringing the gas in the bed back to the adsorption pressure of 10 bar, completing the cycle.

[0093] Example 5

[0094] A three-component mixed gas (H2:CH4:N2=84.67:0.53:14.8) was used as the feed gas and passed into the double-tower single-layer adsorption bed. Activated carbon was selected as the adsorbent. The adsorption pressure was set to 10 bar, the ratio of the amount of hydrogen used in the flushing step during the cycle to the total amount of hydrogen in the feed gas (P / F ratio) was 0.15, the adsorption time was 3 s, and the temperature was 298.15 K.

[0095] Example 6

[0096] A three-component mixed gas (H2:CH4:N2=90.89%:0.75%:8.36%) was used as the feed gas and passed into a double-tower single-layer adsorption bed. Activated carbon was selected as the adsorbent. The adsorption pressure was set to 10 bar, the ratio of the amount of hydrogen used in the flushing step during the cycle to the total amount of hydrogen in the feed gas (P / F ratio) was 0.2, the adsorption time was 3 s, and the temperature was 298.15 K.

[0097] Example 7

[0098] A three-component mixed gas (H2:CH4:N2=90.89%:0.75%:8.36%) was used as the feed gas and passed into a double-tower single-layer adsorption bed. Activated carbon was selected as the adsorbent. The adsorption pressure was set to 10 bar, the ratio of the amount of hydrogen used in the flushing step during the cycle to the total amount of hydrogen in the feed gas (P / F ratio) was 0.25, the adsorption time was 3 s, and the temperature was 298.15 K.

[0099] Example 8

[0100] A three-component mixed gas (H2:CH4:N2=90.89%:0.75%:8.36%) was used as the feed gas and passed into a double-tower single-layer adsorption bed. Activated carbon was selected as the adsorbent. The adsorption pressure was set to 10 bar, the ratio of the amount of hydrogen used in the flushing step during the cycle to the total amount of hydrogen in the feed gas (P / F ratio) was 0.2, the adsorption time was 5 s, and the temperature was 298.15 K.

[0101] Example 9

[0102] A three-component mixed gas (H2:CH4:N2=90.89%:0.75%:8.36%) was used as the feed gas and passed into a double-tower single-layer adsorption bed. Activated carbon was selected as the adsorbent. The adsorption pressure was set to 10 bar, the ratio of the amount of hydrogen used in the flushing step during the cycle to the total amount of hydrogen in the feed gas (P / F ratio) was 0.2, the adsorption time was 7 s, and the temperature was 298.15 K.

[0103] Example 10

[0104] A three-component mixed gas (H2:CH4:N2=90.89%:0.75%:8.36%) was used as the feed gas and passed into a double-tower single-layer adsorption bed. Activated carbon was selected as the adsorbent. The adsorption pressure was set to 15 bar, the ratio of the amount of hydrogen used in the flushing step during the cycle to the total amount of hydrogen in the feed gas (P / F ratio) was 0.2, the adsorption time was 3 s, and the temperature was 298.15 K.

[0105] Table 2 Activated carbon adsorption bed purification performance parameters in Examples 5 to 10

[0106] Hydrogen purity% Hydrogen yield% Example 5 96.734 71.31 Example 6 99.995 64.35 Example 7 98.853 64.08 Example 8 98.943 61.52 Example 9 98.858 64.08 Example 10 99.996 52.51

[0107] The above results demonstrate that Examples 5-10 reflect the results of pressure swing adsorption of secondary aluminum ash hydrolysis gas under different conditions. The results show that under the conditions of an adsorption pressure of 10 bar, a P / F ratio of 0.2, and an adsorption time of 3 seconds, a gas separation effect with a hydrogen purity greater than 99.99% and a yield of 64.35% was achieved. This meets the requirements of GB / T 34872-2017, "Technical Requirements for Hydrogen Supply Systems of Proton Exchange Membrane Fuel Cells," and achieves high-value recovery of wet-process gas produced from aluminum ash.

[0108] The above description of the embodiments is intended to facilitate understanding and use of the present invention by those skilled in the art. Those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring creative effort. Therefore, the present invention is not limited to the above-described embodiments. Any improvements or modifications made by those skilled in the art based on the principles of the present invention that do not depart from the scope of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen, characterized in that: The following steps are involved: Step S1, raw material preparation process, using a grinder to grind the secondary aluminum ash, grind the large particles in the aluminum ash to increase the reaction contact area, and use a magnetic suction device to recover the magnetic iron elements in the aluminum ash; Step S2, a hydrolysis process, wherein the secondary aluminum ash treated in step S1 is transported through a pipe chain into a reactor, and then an ammonium chloride solution at 50-80°C is added to carry out a primary hydrolysis reaction under stirring. At this time, part of the aluminum, aluminum carbide, and aluminum nitride react with water, and the generated ammonia dissolves in the reaction solution. The soluble salt in the aluminum ash dissolves in the reaction solution. The reaction solution is filtered and recovered into a salt solution storage tank; Step S3, a secondary hydrolysis process, when the temperature in the reactor drops to 25-30°C, sodium hydroxide solution is pumped into the reactor and a secondary hydrolysis reaction is carried out under stirring. Circulating water is used for heat removal, and the reaction temperature is controlled to be no higher than 90°C. The process must be carried out under a slightly positive pressure to prevent air from entering the system and causing an explosion. Step S4, filtration process, the slurry after hydrolysis in step S3 is cooled and sent to a vacuum rotary disk filter to recover the solids, and the filtrate is sent to the next stage for further recovery; Step S5, a dealkalization process, introducing carbon dioxide gas into the filtrate obtained in step S4 to adjust the solution pH to <11, and filtering and recovering the aluminum hydroxide product using a plate and frame filter; Step S6, a concentration process, wherein carbon dioxide gas and ammonia gas are introduced into the filtrate obtained in step S5, and the sodium bicarbonate product and the concentrated ammonium chloride solution are recovered by evaporation and crystallization; Step S7, the tail gas recovery process, for ammonia, uses the solution in the brine storage tank to absorb it to increase the mass fraction of ammonia nitrogen in the absorption liquid; for hydrogen, after drying and removing water, pressure swing adsorption technology is used to continuously produce new energy green hydrogen products.

2. The method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen according to claim 1, characterized in that: In step S1, the particle size of the ground secondary aluminum ash is 60-100 mesh.

3. The method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen according to claim 1, characterized in that: In step S2, the ammonium chloride solution is obtained from a brine storage tank, the mass fraction of ammonium chloride in the ammonium chloride solution is required to be no less than 1%, and the mass ratio of the added ammonium chloride solution to the secondary aluminum ash is 2-4:

1.

4. The method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen according to claim 1, characterized in that: In step S2, the primary hydrolysis reaction takes 1 to 3 hours.

5. The method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen according to claim 1, characterized in that: In step S3, the NaOH concentration in the sodium hydroxide solution should be no less than 2.5 mol / L, the sodium hydroxide solution is recycled, the number of recycling times is 3 to 5 times, and the mass ratio of the added sodium hydroxide solution to the secondary aluminum ash is 2 to 5:

1.

6. The method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen according to claim 1, characterized in that: In step S3, the secondary hydrolysis reaction time is 2 to 6 hours; the slightly positive pressure refers to 1 to 10 kPa higher than the standard atmospheric pressure.

7. The method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen according to claim 1, characterized in that: In step S4, the temperature of the slurry fed into the vacuum rotary disc filter should be lower than 45°C.

8. The method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen according to claim 1, characterized in that: In step S7, the volume liquid-to-gas ratio of the solution in the brine storage tank to the ammonia gas is 3-7:

1.

9. The method for comprehensive recovery and utilization of secondary aluminum ash and co-production of high-purity hydrogen according to claim 1, characterized in that: In step S7, the high-quality hydrogen generated by the pressure swing adsorption technology can be used in fuel cells, and the low-quality hydrogen is used for combustion to provide heat.

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