ZSM-5 molecular sieve prepared from secondary aluminum ash and fly ash, and preparation method and application thereof

Abstract

This invention belongs to the field of solid waste resource utilization technology. It discloses a ZSM-5 molecular sieve prepared using secondary aluminum ash and fly ash, its preparation method, and its applications. The preparation method involves mixing fly ash with sodium carbonate, calcining to activate it, and then acid leaching to extract the silicon-aluminum source. Simultaneously, secondary aluminum ash reacts with calcium oxide in an aqueous phase to obtain a supplementary aluminum source. The two extracts are mixed in a specific ratio, and a template agent, alkali additive, and seed crystals are added. After grinding, a homogeneous mixture is formed, and the mixture is crystallized at a suitable temperature for a certain time. Finally, through cooling, separation, washing, drying, and calcination steps, nano-ZSM-5 molecular sieves are obtained. This method achieves synergistic high-value utilization of two solid wastes. The prepared ZSM-5 molecular sieve has the characteristics of fine grains, adjustable silicon-aluminum ratio, and hierarchical porous structure, and can be used as a denitrification catalyst or adsorbent in the fields of waste gas treatment and gas separation.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization technology, and in particular to a ZSM-5 molecular sieve prepared using secondary aluminum ash and fly ash, its preparation method, and its application. Background Technology

[0002] Secondary aluminum ash generated during aluminum smelting and fly ash from coal-fired power plants are two types of industrial solid waste produced in large quantities. Secondary aluminum ash contains harmful components such as fluorides, chlorides, and trace heavy metals, making its harmless disposal a persistent challenge in the industry. Large-scale stockpiling not only occupies land but also poses environmental risks. While fly ash has found some applications in building materials and other fields, these are mostly low-value-added uses, and its rich silicon and aluminum content has not been fully extracted and utilized.

[0003] Molecular sieves, especially ZSM-5 molecular sieves, play an irreplaceable role in petrochemical and environmental protection fields such as catalysis and adsorption separation due to their unique pore structure and tunable surface acidity. Currently, the industrial synthesis of ZSM-5 molecular sieves mainly relies on chemical raw materials, such as sodium silicate, water glass, silica sol, sodium aluminate, and aluminum sulfate, resulting in high production costs and the consumption of a large amount of non-renewable mineral resources.

[0004] To reduce costs and achieve waste resource utilization, researchers have attempted to use silicon-aluminum-containing solid waste as alternative raw materials. While existing technologies have reported the use of fly ash to obtain silicon-aluminum sources for molecular sieve synthesis via an alkali-melting-acid leaching process, this method often suffers from problems such as long process flows, low silicon-aluminum extraction rates, and a fixed, difficult-to-adjust ratio. The resulting molecular sieve products often exhibit a narrow silicon-aluminum ratio range, and their crystallinity and catalytic performance are frequently inferior to those of chemical raw materials. Furthermore, some studies have explored using secondary aluminum ash as an aluminum source, but its complex composition and the presence of harmful impurities can poison the crystallization process of molecular sieves, leading to crystallization failure or poor product purity; therefore, successful cases are few and far between.

[0005] More importantly, existing technologies are mostly limited to the utilization of single solid wastes, failing to fundamentally solve the problem of co-processing and high-value utilization of two types of waste. A technical solution for effectively co-processing fly ash and secondary alumina ash, and precisely controlling their ratio as silicon and aluminum sources to prepare high-performance ZSM-5 molecular sieves, remains undeveloped. Therefore, developing a new method that can economically and efficiently co-utilize secondary alumina ash and fly ash to prepare ZSM-5 molecular sieves with ideal structure and properties not only has significant environmental benefits but also possesses important economic value and industrial prospects. Summary of the Invention

[0006] The purpose of this invention is to solve the technical problem that existing technologies cannot efficiently prepare high-performance ZSM-5 molecular sieves by synergistically utilizing two solid wastes, secondary aluminum ash and fly ash.

[0007] To achieve the above objectives, the present invention provides the following technical solutions.

[0008] This invention provides a method for preparing ZSM-5 molecular sieves using secondary aluminum ash and fly ash, comprising the following steps:

[0009] S1. Activated fly ash is obtained by mixing fly ash with sodium carbonate and then calcining it.

[0010] S2. Aluminum-containing silica gel was obtained by leaching activated fly ash in hydrochloric acid.

[0011] S3. Mix the secondary aluminum ash, water and calcium oxide and centrifuge to obtain the supernatant;

[0012] S4. After mixing aluminum-containing silica gel, supernatant, template agent, R crystallization regulator, alkali aid and structure regulator, crystallization reaction, cooling, separation, washing, drying and calcination are carried out in sequence to obtain ZSM-5 molecular sieve.

[0013] Furthermore, in step S1, the mass ratio of fly ash to sodium carbonate is 1:0.4~1.5.

[0014] Furthermore, in step S1, the calcination temperature is 600~1000℃, and the calcination time is 1~5h.

[0015] Furthermore, in step S2, the hydrochloric acid concentration is 1~5 mol / L; the leaching temperature is 60~100℃; and the leaching time is 10~90 min.

[0016] Furthermore, in step S3, the ratio of secondary aluminum ash, water, and calcium oxide is 1g: 5~20mL: 0.1~0.5g.

[0017] Furthermore, in step S3, the mixing temperature is 25~80℃, and the mixing time is 30~120min.

[0018] Furthermore, in step S4, the mass ratio of aluminum-containing silica gel, supernatant, template agent, R crystallization regulator, alkali aid and structure regulator is 100:10~50:5~25:0.5~30:3~15:1~20;

[0019] The template agent is tetrapropylammonium hydroxide and / or polyethyleneimine;

[0020] The R crystallization regulator is an organic amine compound;

[0021] The alkaline additive is sodium hydroxide or potassium hydroxide;

[0022] The structure modifier is a seed crystal, which is a nano ZSM-5 molecular sieve with a particle size of 50~500nm.

[0023] Furthermore, in step S4, the temperature of the crystallization reaction is 150~250℃, and the crystallization time is 24~72h;

[0024] The roasting temperature is 500~800℃, and the roasting time is 4~12h.

[0025] This invention provides ZSM-5 molecular sieve prepared by the above preparation method.

[0026] This invention also provides the application of the above-mentioned ZSM-5 molecular sieve in denitrification catalysts or adsorbents.

[0027] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] This invention achieves complementary advantages and synergistic transformation of two waste materials at the elemental and phase levels. After roasting and activation, the glassy structure of fly ash is destroyed, and the resulting aluminates and silicates are separated during subsequent acid leaching, yielding an active aluminosilicate colloid dominated by silicon and containing a suitable amount of aluminum. This process solves the problem of low aluminosilicate reactivity in fly ash. Simultaneously, the active aluminum component in the secondary aluminosilicate ash is selectively extracted to the liquid phase through a calcification reaction with calcium oxide, forming a supplementary solution rich in calcium aluminate. This crucial step not only effectively avoids the poisoning effect of impurities such as fluorine and chlorine in the secondary aluminosilicate ash on molecular sieve crystallization, but more importantly, it creatively mixes and assembles the aluminosilicate colloid extracted from fly ash and the aluminum source solution extracted from the secondary aluminosilicate ash at the molecular level. Guided by template agents and seed crystals, the two silicon and aluminum species from different sources jointly constitute a richer and more diverse nucleation precursor, thus providing a wider nucleation window in crystallization kinetics and promoting uniform crystal growth.

[0029] At the material construction level, the combination of this unique composite precursor and seed-induction technology allows the crystallization process of the molecular sieve to follow a more controllable path. The seed crystal, as the core of structure guidance, not only lowers the nucleation energy barrier but also guides the epitaxial growth of new crystals on its surface, effectively suppressing the formation of impurity crystals. The ZSM-5 molecular sieve prepared in this way achieves intrinsic optimization of its microstructure, exhibiting characteristics of fine grains, high crystallinity, and hierarchical pores. Fine grains imply a large external surface area and shortened pore diffusion paths, while the formation of hierarchical pores achieves a perfect synergy between the inherent shape selectivity of microporous crystals and the mass transport efficiency provided by mesopores / macropores.

[0030] When applied in catalysis, this molecular sieve not only provides abundant and tunable acidic active sites, but its unique diffusion properties also ensure that reactant molecules can reach and leave the active centers more quickly, thus significantly improving catalytic efficiency and resistance to carbon buildup. In adsorption separation applications, the hierarchical porous structure provides adsorbate molecules with more unobstructed diffusion channels and more accessible sites, resulting in faster adsorption kinetics and higher adsorption capacity. Detailed Implementation

[0031] This invention provides a method for preparing ZSM-5 molecular sieves using secondary aluminum ash and fly ash, comprising the following steps:

[0032] S1. Activated fly ash is obtained by mixing fly ash with sodium carbonate and then calcining it.

[0033] S2. Aluminum-containing silica gel was obtained by leaching activated fly ash in hydrochloric acid.

[0034] S3. Mix the secondary aluminum ash, water and calcium oxide and centrifuge to obtain the supernatant;

[0035] S4. After mixing aluminum-containing silica gel, supernatant, template agent, R crystallization regulator, alkali aid and structure regulator, crystallization reaction, cooling, separation, washing, drying and calcination are carried out in sequence to obtain ZSM-5 molecular sieve.

[0036] In this invention, in step S1, the mass ratio of fly ash to sodium carbonate is 1:0.4~1.5, preferably 1:0.5~1.2, and more preferably 1:0.8~1.0.

[0037] In this invention, in step S1, the calcination temperature is 600~1000℃, preferably 700~900℃, and more preferably 900℃; the calcination time is 1~5h, preferably 2~4h, and more preferably 3h.

[0038] In this invention, in step S2, the concentration of hydrochloric acid is 1~5 mol / L, preferably 2~4 mol / L, and more preferably 3 mol / L; the leaching temperature is 60~100℃, preferably 70~90℃, and more preferably 80℃; the leaching time is 10~90 min, preferably 20~80 min, and more preferably 40~60 min.

[0039] In this invention, in step S3, the ratio of secondary aluminum ash, water and calcium oxide is 1g:5~20mL:0.1~0.5g, preferably 1g:8~16mL:0.2~0.4g, and more preferably 1g:10~12mL:0.3g.

[0040] In this invention, in step S3, the mixing temperature is 25~80℃, preferably 40~60℃, and more preferably 50℃; the mixing time is 30~120min, preferably 50~100min, and more preferably 60~70min.

[0041] In this invention, in step S4, the mass ratio of aluminum-containing silica gel, supernatant, template agent, R crystallization regulator, alkali aid, and structure regulator is 100:10~50:5~25:0.5~30:3~15:1~20, preferably 100:20~40:8~22:1~25:5~12:5~16, and more preferably 100:30:10~15:5~15:8~10:8~12;

[0042] The template agent is tetrapropylammonium hydroxide and / or polyethyleneimine;

[0043] The R crystallization regulator is an organic amine compound, preferably tetrapropylammonium hydroxide, ethylenediamine, or triethanolamine;

[0044] The alkaline additive is sodium hydroxide or potassium hydroxide;

[0045] The structure modifier is a seed crystal, which is a nano ZSM-5 molecular sieve with a particle size of 50~500nm.

[0046] In this invention, in step S4, the temperature of the crystallization reaction is 150~250℃, preferably 160~220℃, and more preferably 180~200℃; the crystallization time is 24~72h, preferably 30~60h, and more preferably 40~50h; the crystallization process is accompanied by microwave assistance, and the microwave power is 300~800W, preferably 400~700W, and more preferably 500~600W;

[0047] The roasting temperature is 500~800℃, preferably 600~700℃; the roasting time is 4~12h.

[0048] The present invention provides a ZSM-5 molecular sieve prepared by the above preparation method, wherein the ZSM-5 molecular sieve has a crystal size of <50nm, a silicon-to-aluminum ratio of 20~200, and a hierarchical porous structure.

[0049] In this invention, aluminum-containing silica gel is used as the main silicon-aluminum source, and the supernatant is used as a supplementary aluminum source.

[0050] This invention also provides the application of the above-mentioned ZSM-5 molecular sieve in denitrification catalysts or adsorbents.

[0051] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0052] Example 1

[0053] Weigh 100g of fly ash and 80g of sodium carbonate (mass ratio 1:0.8) and mix them thoroughly in a mixer. Transfer the mixture to a muffle furnace and calcine at 900℃ for 3 hours. After natural cooling, activated fly ash is obtained. Transfer the activated fly ash to a beaker and add 1500mL of 3mol / L hydrochloric acid solution. Stir and leach in an 80℃ constant temperature water bath for 50 minutes. After the reaction is complete, centrifuge to collect the solid gel-like substance, which is aluminum-containing silica gel and the main source of silicon and aluminum.

[0054] Weigh 50g of secondary aluminum ash and place it in 500mL of deionized water (solid-liquid ratio 1:10), stirring to form a suspension. Add 15g of calcium oxide (mass ratio 1:0.3) to the secondary aluminum ash suspension and stir continuously at 50℃ for 60min. After the reaction is complete, centrifuge and collect the supernatant as a supplementary aluminum source.

[0055] Take 100g of aluminum-containing silica gel and mix it with 30g of supernatant. Add 10g of tetrapropylammonium hydroxide (template agent), 5g of tetrapropylammonium hydroxide (also used as an R crystallization regulator), 8g of sodium hydroxide (alkali aid), and 8g of nano-ZSM-5 seed crystals with a particle size of approximately 100nm (structure regulator) sequentially. Grind these components thoroughly in a mortar for 30 minutes until a homogeneous paste mixture is formed. Transfer the homogeneous paste to a hydrothermal reactor with a polytetrafluoroethylene liner, filling it to 70%. Place the reactor in a microwave synthesizer, set the microwave power to 500W, and crystallize at 180℃ for 48 hours. After crystallization, allow it to cool naturally to room temperature. Remove the product and wash it repeatedly with deionized water until the filtrate is neutral (pH≈7). Then dry it in an oven at 110℃ for 12 hours. Place the dried powder in a muffle furnace and calcine at 600℃ for 6 hours to remove the template agent. The final product was a white powder, named ZSM-5-A.

[0056] Example 2

[0057] Weigh 100g of fly ash and 100g of sodium carbonate (mass ratio 1:1) and mix them evenly in a mixer. Transfer the mixture to a muffle furnace and calcine at 800℃ for 4 hours. After natural cooling, activated fly ash is obtained. Transfer the activated fly ash to a beaker and add 1500mL of 2mol / L hydrochloric acid solution. Stir and leach in a 90℃ constant temperature water bath for 40 minutes. After the reaction is complete, centrifuge to collect the solid gel-like substance, which is aluminum-containing silica gel and the main source of silicon and aluminum.

[0058] Weigh 50g of secondary aluminum ash and place it in 600mL of deionized water (solid-liquid ratio 1:12), stirring to form a suspension. Add 20g of calcium oxide (mass ratio 1:0.4) to the secondary aluminum ash suspension and stir continuously at 60℃ for 50min. After the reaction is complete, centrifuge and collect the supernatant as a supplementary aluminum source.

[0059] Take 100g of aluminum-containing silica gel and mix it with 20g of supernatant. Then, add 15g of polyethyleneimine (template agent), 1g of ethylenediamine (R crystallization regulator), 10g of sodium hydroxide (alkali aid), and 10g of ZSM-5 nano-crystals with a particle size of approximately 100nm (structure regulator) sequentially. Grind these components thoroughly in a mortar for 30 minutes until a homogeneous paste is formed. Transfer the homogeneous paste to a hydrothermal reactor with a polytetrafluoroethylene liner, filling it to 70%. Place the reactor in a microwave synthesizer, set the microwave power to 600W, and crystallize at 200℃ for 36 hours. After crystallization, allow it to cool naturally to room temperature. Remove the product and wash it repeatedly with deionized water until the filtrate is neutral (pH≈7). Then, dry it in an oven at 110℃ for 12 hours. Place the dried powder in a muffle furnace and calcine at 650℃ for 8 hours to remove the template agent. The final product is a white powder, named ZSM-5-B.

[0060] Example 3

[0061] Weigh 100g of fly ash and 120g of sodium carbonate (mass ratio 1:1.2) and mix them thoroughly in a mixer. Transfer the mixture to a muffle furnace and calcine at 700℃ for 5 hours. After natural cooling, activated fly ash is obtained. Transfer the activated fly ash to a beaker and add 1500mL of 4mol / L hydrochloric acid solution. Stir and leach in a 70℃ constant temperature water bath for 60 minutes. After the reaction is complete, centrifuge to collect the solid gel-like substance, which is aluminum-containing silica gel and the main source of silicon and aluminum.

[0062] Weigh 50g of secondary aluminum ash and place it in 800mL of deionized water (solid-liquid ratio 1:16), stirring to form a suspension. Add 12.5g of calcium oxide (mass ratio 1:0.25) to the secondary aluminum ash suspension and stir continuously at 40℃ for 100min. After the reaction is complete, centrifuge and collect the supernatant as a supplementary aluminum source.

[0063] Take 100g of aluminum-containing silica gel and mix it with 40g of supernatant. Add 12g of tetrapropylammonium hydroxide (template agent), 15g of triethanolamine (R crystallization regulator), 5g of potassium hydroxide (alkali aid), and 8g of nano-ZSM-5 seed crystals with a particle size of approximately 100nm (structure regulator). Grind these components thoroughly in a mortar for 30 minutes until a homogeneous paste mixture is formed. Transfer the homogeneous paste to a hydrothermal reactor with a polytetrafluoroethylene liner, with a filling degree of 70%. Place the reactor in a microwave synthesizer, set the microwave power to 400W, and crystallize at 160℃ for 60h. After crystallization, allow it to cool naturally to room temperature. Remove the product and wash it repeatedly with deionized water until the filtrate is neutral (pH≈7). Then dry it in an oven at 110℃ for 12h. Place the dried powder in a muffle furnace and calcine at 700℃ for 5h to remove the template agent. The final product is a white powder, named ZSM-5-C.

[0064] Comparative Example 1

[0065] Weigh 100g of fly ash and 80g of sodium carbonate (mass ratio 1:0.8) and mix them thoroughly in a mixer. Transfer the mixture to a muffle furnace and calcine at 900℃ for 3 hours. After natural cooling, activated fly ash is obtained. Transfer the activated fly ash to a beaker and add 1500mL of 3mol / L hydrochloric acid solution. Stir and leach in an 80℃ constant temperature water bath for 50 minutes. After the reaction is complete, centrifuge to collect the solid gel-like substance, which is aluminum-containing silica gel and the main source of silicon and aluminum.

[0066] Take 100g of aluminum-containing silica gel and mix it with 30g of secondary aluminum ash. Then, add 10g of tetrapropylammonium hydroxide (template agent), 8g of sodium hydroxide (alkali additive), and 8g of nano-ZSM-5 seed crystals with a particle size of approximately 100nm (structure modifier). Grind these components thoroughly in a mortar for 30 minutes until a homogeneous paste-like mixture is formed. Transfer the homogeneous paste to a hydrothermal reactor with a polytetrafluoroethylene liner, with a filling density of 70%. Crystallize at 180℃ for 48 hours. After crystallization, allow it to cool naturally to room temperature. Remove the product and wash it repeatedly with deionized water until the filtrate is neutral (pH≈7). Then, dry it in an oven at 110℃ for 12 hours. Place the dried powder in a muffle furnace and calcine at 600℃ for 6 hours to remove the template agent. The final product is a white powder, named ZSM-5-D.

[0067] Performance testing

[0068] 1. Static n-hexane adsorption capacity test

[0069] Prepare a desiccator containing an appropriate amount of anhydrous calcium chloride to create a dry environment. Weigh four clean, dry, and constant-weight weighing bottles (denoted as W0), accurate to 0.0001 g. Add approximately 0.5000 g (denoted as W1) of the sample to be tested (ZSM-5-A, ZSM-5-B, ZSM-5-C, ZSM-5-D) to each weighing bottle and record the total weight. Open the caps of the weighing bottles containing the samples and place them together in the desiccator. Pour sufficient analytical-grade n-hexane into the bottom of the desiccator, ensuring that the liquid surface does not contact the weighing bottles. Seal the desiccator and let it stand at room temperature (25°C) for 24 hours to allow the molecular sieve to fully adsorb n-hexane vapor. After 24 hours, quickly remove the weighing bottles and tighten the caps, then weigh them immediately (denoted as W2). The static n-hexane adsorption capacity is calculated using the following formula:

[0070] Adsorption capacity (%) = [(W2-W1-W0) / W1] × 100%. The calculation results are shown in Table 1.

[0071] Table 1. Results of Static n-hexane Adsorption Capacity Test

[0072]

[0073] 2. Catalytic cracking model reaction performance testing

[0074] A fixed-bed microreactor was constructed using a quartz reaction tube with an inner diameter of 6 mm. For each test, 0.1000 g (20-40 mesh) of molecular sieve sample was weighed and placed in the isothermal zone of the reaction tube. The reaction system was heated to 350 °C and activated for 1 h under nitrogen carrier gas (flow rate 30 mL / min). After activation, cumene was injected into the vaporization chamber at a rate of 0.1 mL / h using a micro-injection pump, and carried into the reactor by nitrogen gas. After the reaction stabilized for 30 min, the reaction product was collected in a receiving flask cooled with ice water, and collection continued for 30 min. The composition of the collected liquid product was analyzed by gas chromatography. The conversion rate of cumene was calculated using the following formula:

[0075] The conversion rate of cumene (%) is calculated as follows: [(moles of cumene in the feed - moles of cumene in the product) / moles of cumene in the feed] × 100%. The calculation results are shown in Table 2.

[0076] Table 2. Performance test results of the catalytic cracking model reaction

[0077]

[0078] 3. Thermal stability test (loss on ignition method)

[0079] Four crucibles were ignited at 900°C to constant weight, and the weight was recorded (M0). Approximately 1.0000 g (M1) of the sample to be tested was added to each crucible. The crucibles were placed in a muffle furnace preheated to 900°C and ignited for 2 hours. After 2 hours, the crucibles were removed and cooled to room temperature in a desiccator. The total weight of the crucibles and the ignited sample was quickly measured (M2). The loss on ignition was calculated using the following formula:

[0080] Loss on ignition (%) = [(M1-(M2-M0)) / M1] × 100%. The calculation results are shown in Table 3.

[0081] Table 3 Thermal stability test results

[0082]

[0083] 4. Ion exchange capacity test

[0084] 0.5000 g of each of the four molecular sieve samples were weighed into four conical flasks. 100 mL of a 1.0 mol / L ammonium chloride solution (adjusted to pH 7 with ammonia) was added to each flask. The flasks were sealed and placed in a constant-temperature shaker at 80°C and 150 rpm for 6 hours for ion exchange. After exchange, the samples were cooled, filtered, and the molecular sieve solids were thoroughly washed with deionized water. All filtrates and washings were collected in 250 mL volumetric flasks and diluted to volume. The concentration of unexchanged ammonium ions in the filtrate was determined by acid-base titration: 50.00 mL of the diluted filtrate was taken, excess sodium hydroxide solution was added, ammonia gas was distilled off, absorbed with boric acid solution, and finally titrated with standard hydrochloric acid solution. The ammonium ion exchange capacity was obtained by calculating the amount of ammonium ions adsorbed by the molecular sieve. The calculation results are shown in Table 4.

[0085] Table 4. Ion exchange capacity test results

[0086]

[0087] As shown in Tables 1-4, the ZSM-5 molecular sieves prepared in Examples 1, 2, and 3 are superior to the product of Comparative Example 1 in terms of adsorption performance, catalytic activity, and thermal stability. They possess well-developed pore structures, abundant acidic sites, and stable frameworks. By adjusting the ratio of the secondary aluminum ash supernatant, the silica-alumina ratio of the product was successfully controlled, which was directly reflected in the ion exchange capacity and catalytic activity. The product of Comparative Example 1, due to the lack of secondary aluminum ash pretreatment and extraction steps, and the absence of R crystallization regulator, exhibits low crystallinity, underdeveloped pores, few active centers, and poor thermal stability, fully demonstrating the necessity of the synergistic effect of the components in the technical solution of this invention.

[0088] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing ZSM-5 molecular sieve using secondary aluminum ash and fly ash, characterized in that, Includes the following steps: S1. Activated fly ash is obtained by mixing fly ash with sodium carbonate and then calcining it. S2. Aluminum-containing silica gel was obtained by leaching activated fly ash in hydrochloric acid. S3. Mix the secondary aluminum ash, water and calcium oxide and centrifuge to obtain the supernatant; S4. After mixing aluminum-containing silica gel, supernatant, template agent, R crystallization regulator, alkali aid and structure regulator, crystallization reaction, cooling, separation, washing, drying and calcination are carried out in sequence to obtain ZSM-5 molecular sieve. In step S1, the calcination temperature is 700~900℃ and the calcination time is 3~5h; In step S3, the mixing temperature is 40~60℃ and the mixing time is 50~100min; In step S4, the mass ratio of aluminum-containing silica gel, supernatant, template agent, R crystallization regulator, alkali aid and structure regulator is 100:20~40:10~15:1~15:5~10:8~10; The template agent is tetrapropylammonium hydroxide and / or polyethyleneimine; The R crystallization regulator is an organic amine compound; The alkaline additive is sodium hydroxide or potassium hydroxide; The structure modifier is a seed crystal, which is a nano ZSM-5 molecular sieve with a particle size of 50~500 nm. In step S4, the temperature of the crystallization reaction is 160~200℃, and the crystallization time is 36~60h; In step S4, the crystallization reaction is carried out under microwave assistance, with a microwave power of 400~600W. In step S4, the calcination temperature is 600~700℃ and the calcination time is 5~8h.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of fly ash to sodium carbonate is 1:0.8~1.

2.

3. The preparation method according to claim 1, characterized in that, In step S2, the hydrochloric acid concentration is 2-4 mol / L; the leaching temperature is 70-90℃; and the leaching time is 40-60 min.

4. The preparation method according to claim 1, characterized in that, In step S3, the ratio of secondary aluminum ash, water, and calcium oxide is 1g: 10~16mL: 0.25~0.4g.

5. The ZSM-5 molecular sieve prepared by the preparation method according to any one of claims 1 to 4.

6. The application of the ZSM-5 molecular sieve according to claim 5 in denitrification catalysts or adsorbents.

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