Method for utilizing a fau molecular sieve crystallization mother liquor

Abstract

A utilization method of FAU molecular sieve crystallization mother liquor, characterized in that, comprising: uniformly mixing FAU molecular sieve mother liquor, silicon source, inorganic alkali, water and aluminum source to obtain a type molecular sieve synthesis system mixture with a molar ratio of SiO2 / Al2O3=1.85-1.99, Na2O / SiO2=1.0-1.6, H2O / SiO2=45-65; aging and hydrothermal crystallization are performed on the mixture, and the product is recovered to obtain a type molecular sieve and a type molecular sieve filtration mother liquor; or further uniformly mixing the type molecular sieve filtration mother liquor and an aluminum-containing compound, stirring at 160-200 DEG C for 2-8 hours to obtain a recycled aluminum source with a SiO2 content of 50-300 ppm; uniformly mixing silicon source, inorganic alkali, recycled aluminum source and water to obtain a FAU molecular sieve synthesis system mixture, aging and hydrothermal crystallization are performed on the mixture, and the product is recovered to obtain a FAU molecular sieve and a FAU molecular sieve crystallization mother liquor. The method can not only completely recycle the FAU molecular sieve mother liquor, avoid waste water discharge, reduce the consumption of inorganic alkali and deionized water, and significantly reduce the production cost, but also can be flexibly used for preparing FAU molecular sieve and / or a type molecular sieve.

Description

Technical Field

[0001] This invention relates to a method for utilizing mother liquor from molecular sieve crystallization, specifically a method for recycling mother liquor from FAU molecular sieve crystallization. Background Technology

[0002] FAU molecular sieves exhibit high adsorption capacity due to their large micropore size, and their low framework silica-alumina ratio endows them with excellent adsorption and ion exchange properties. Therefore, FAU molecular sieves are widely used in separation, catalysis, and ion exchange. Currently, FAU molecular sieves are mainly produced industrially using liquid-phase hydrothermal synthesis. However, this production method generates a large amount of mother liquor from molecular sieve crystallization, which contains high levels of inorganic alkali and silicon, making environmental treatment very difficult.

[0003] CN106430228A discloses a method for treating molecular sieve crystallization mother liquor. The method involves drawing the molecular sieve crystallization mother liquor into a vacuum distillation kettle, heating the kettle by introducing steam into its jacket, causing the organic amines and water in the mother liquor to evaporate. The evaporated material then enters a condenser, and the condensate enters a solvent storage tank. A stirring device is installed in the kettle to continuously agitate the evaporated material and prevent coking on the chamber walls. Once the moisture content of the residue in the kettle reaches the standard, the residue is automatically discharged. This method can completely reuse the organic amines and water in the crystallization mother liquor, achieving zero wastewater discharge.

[0004] CN105000642B discloses a method for treating silicon-containing wastewater generated during the preparation of molecular sieves. The method involves collecting and adjusting the filtrate, mother liquor, and washing liquid generated during the preparation of molecular sieves to form gel wastewater. A lime slurry with a concentration of 8-10% is added, stirred for a period of time, and then allowed to stand. The soluble silicon content in each liter of gel wastewater is 500-1000 mg. The supernatant is reused, and the bottom sludge is discharged.

[0005] CN104556460B discloses a method for removing fluoride and phosphorus from PSRY molecular sieve production wastewater. The method involves first mixing the PSRY molecular sieve production wastewater with solid waste residue generated during the treatment of other molecular sieve production wastewater, causing the aluminum in the solid waste residue to be converted into Al... 3+ The form of Al dissolves into the wastewater, and then the pH of the mixed system is adjusted to above 6, so that Al 3+ With F - PO4 3- The reaction forms a precipitate, and then a coagulant aid (PAM) is added to continue the reaction. Solid-liquid separation is then performed. This method can effectively remove fluoride and phosphorus from wastewater. Summary of the Invention

[0006] The purpose of this invention is to provide a method for utilizing FAU molecular sieve crystallization mother liquor that differs from existing technologies. This method can not only completely reuse FAU molecular sieve mother liquor, avoid the discharge of mother liquor wastewater, reduce the consumption of inorganic alkali and deionized water, and significantly reduce production costs, but can also be flexibly used to prepare FAU molecular sieves and / or type A molecular sieves.

[0007] Therefore, the method for utilizing the FAU molecular sieve crystallization mother liquor provided by the present invention is characterized by comprising: uniformly mixing the FAU molecular sieve mother liquor, silicon source, inorganic alkali, water and aluminum source to obtain a mixture of A-type molecular sieve synthesis system with a material molar ratio of SiO2 / Al2O3 = 1.85-1.99, Na2O / SiO2 = 1.0-1.6, and H2O / SiO2 = 45-65; aging and hydrothermal crystallizing the mixture to recover the product and obtain A-type molecular sieve and A-type molecular sieve filtration mother liquor; or further mixing the A-type molecular sieve filtration mother liquor and aluminum-containing compound uniformly, stirring at 160-200℃ for 2-8 hours to obtain a recycled aluminum source with a SiO2 content of 50-300ppm; uniformly mixing the silicon source, inorganic alkali, recycled aluminum source and water to obtain a FAU molecular sieve synthesis system mixture; aging and hydrothermal crystallizing the mixture to recover the product and obtain FAU molecular sieve and FAU molecular sieve mother liquor.

[0008] The method for utilizing FAU molecular sieve crystallization mother liquor provided by this invention first uses FAU molecular sieve crystallization mother liquor with a high silica content to synthesize type A molecular sieves. Since the silica content in the resulting type A molecular sieve crystallization mother liquor is significantly reduced, the type A molecular sieve crystallization mother liquor is then used to prepare recycled aluminum source. This allows the obtained recycled aluminum source to be used for the synthesis of FAU molecular sieves and type A molecular sieves without any post-processing, thereby achieving complete recycling of FAU molecular sieve crystallization mother liquor, avoiding the discharge of crystallization mother liquor wastewater, making production more environmentally friendly, reducing the use of inorganic alkali and deionized water, which helps to reduce production costs, and can also produce type A molecular sieves as a byproduct. Attached Figure Description

[0009] Figure 1 The XRD pattern of the type A molecular sieve prepared in Example 1 of this invention.

[0010] Figure 2 The XRD pattern of the FAU molecular sieve prepared in Example 1 of this invention.

[0011] Figure 3 The XRD pattern of the type A molecular sieve prepared in Example 2 of this invention.

[0012] Figure 4 The XRD pattern of the FAU molecular sieve prepared in Example 3 of this invention.

[0013] Figure 5The image shows the XRD pattern of the product obtained in Comparative Example 1.

[0014] Figure 6 The image shows the XRD pattern of the product obtained in Comparative Example 2. Detailed Implementation

[0015] The mother liquor for FAU molecular sieve crystallization mainly contains components such as Na, Si and Al. It is difficult to separate the different components using conventional methods. Directly reusing the mother liquor for FAU molecular sieve crystallization in the synthesis system, or preparing the mother liquor for FAU molecular sieve crystallization into an aluminum source and then using the obtained aluminum source to synthesize FAU molecular sieve, both easily lead to the formation of impurity crystals.

[0016] The inventors discovered that by first using the crystallization mother liquor of FAU molecular sieve with a high silicon content to synthesize type A molecular sieve, a crystallization mother liquor of type A molecular sieve with a low silicon content is obtained. Then, the obtained crystallization mother liquor of type A molecular sieve is used to prepare a recycled aluminum source. The obtained recycled aluminum source can be directly used to synthesize FAU molecular sieve without any treatment.

[0017] The method for utilizing FAU molecular sieve crystallization mother liquor provided by the present invention is characterized by comprising: uniformly mixing FAU molecular sieve crystallization mother liquor, silicon source, inorganic alkali, water and aluminum source to obtain a mixture of A-type molecular sieve synthesis system with material molar ratios of SiO2 / Al2O3 = 1.85-1.99, Na2O / SiO2 = 1.0-1.6, and H2O / SiO2 = 45-65; aging and hydrothermal crystallizing the mixture to recover the product and obtain A-type molecular sieve and A-type molecular sieve filtration mother liquor; or further mixing the A-type molecular sieve filtration mother liquor and aluminum-containing compound uniformly, stirring at 160-200℃ for 2-8 hours to obtain a recycled aluminum source with SiO2 content of 50-300ppm; uniformly mixing silicon source, inorganic alkali, recycled aluminum source and water to obtain FAU molecular sieve synthesis system mixture; aging and hydrothermal crystallizing the mixture to recover the product and obtain FAU molecular sieve and FAU molecular sieve crystallization mother liquor.

[0018] In this invention, the mixture of the type A molecular sieve synthesis system is subjected to aging and hydrothermal crystallization. The aging temperature is 20-35℃, and the aging time is 3-12 hours. The hydrothermal crystallization temperature is 90-130℃, and the hydrothermal crystallization time is 6-16 hours. The mother liquor of the type A molecular sieve filtration contains 100-900 ppm SiO2 and 500-2000 ppm Al2O3.

[0019] In this invention, the molar ratio of materials in the FAU molecular sieve synthesis system mixture is SiO2 / Al2O3 = 2.6-10.0, Na2O / SiO2 = 0.25-1.5, and H2O / SiO2 = 20-70. The FAU molecular sieve synthesis system mixture is subjected to aging and hydrothermal crystallization. The aging temperature is 25-40℃, and the aging time is 12-24 hours. The hydrothermal crystallization temperature is 95-120℃, and the hydrothermal crystallization time is 2-48 hours.

[0020] In this invention, the aluminum source can also be replaced by the recycled aluminum source. In the preparation of the recycled aluminum source, NaOH and deionized water are preferably added to the mixture of the mother liquor from the A-type molecular sieve filtration and the aluminum-containing compound. The Na₂O / Al₂O₃ molar ratio of the recycled aluminum source is 1.6-2.8, the Al₂O₃ content is 16.0-22.0% by mass, and the SiO₂ content is 50-300 ppm.

[0021] In this invention, the Al2O3 content in the recycled aluminum source is calculated from the amount of aluminum-containing compounds added during its preparation process, the SiO2 content is calculated from the amount of A-type molecular sieve filtration mother liquor added during its preparation process and its SiO2 content, and the Na2O content is measured by acid-base titration.

[0022] In this invention, the aluminum-containing compound is selected from at least one of metallic aluminum, aluminum oxide, aluminum hydroxide, boehmite, aluminum sulfate, aluminum chloride, aluminum nitrate, and sodium aluminate.

[0023] In this invention, the silicon source is selected from at least one of tetraethyl orthosilicate, silica sol, water glass, sodium silicate, silica gel, and precipitated silica. When the silicon source is water glass, the mass fraction of Na₂O is 6.0%-12.0%, and the mass fraction of SiO₂ is 25%-35%. The inorganic alkali is sodium hydroxide or potassium hydroxide. The SiO₂ content in the FAU molecular sieve crystallization mother liquor is 3000-80000 mg / L.

[0024] As is known to those skilled in the art, the strong diffraction peaks appearing near 2θ = 6.1°, 10.0°, 11.7°, and 15.4° in the XRD pattern of molecular sieves are characteristic diffraction peaks of FAU molecular sieves. The absence of other diffraction peaks in the range of 2θ = 6.1° to 15.4° indicates that the sample contains no impurities and is a pure-phase FAU molecular sieve.

[0025] The present invention will be described in detail below with examples, but the present invention is not limited thereto.

[0026] Example 1

[0027] This example illustrates the use of FAU molecular sieve crystallization mother liquor to prepare type A molecular sieves and FAU molecular sieves.

[0028] (1) Preparation of aluminum source

[0029] 100 kg of aluminum hydroxide, 90.91 kg of sodium hydroxide and 210 kg of deionized water were added to a reaction vessel, heated to 100°C and stirred for 1 hour to obtain an aluminum source, wherein the content of Al2O3 was 18.52% by mass, the content of Na2O was 20.26% by mass, and the molar ratio of Na2O / Al2O3 was 1.80.

[0030] (2) Synthesis of type A molecular sieves

[0031] 61.36 kg of FAU molecular sieve mother liquor (SiO2 content of 9755 mg / L), 46.35 kg of deionized water, 43.92 kg of aluminum source obtained in step (1) and 29.12 kg of water glass (SiO2 content of 29.17% by mass and Na2O content of 8.12% by mass in water glass, the same below) were added to the reactor and mixed evenly to obtain a mixture of type A molecular sieve synthesis system. The molar ratio of each material in the mixture was SiO2 / Al2O3 = 1.90, Na2O / SiO2 = 1.44, and H2O / SiO2 = 55. The mixture was aged at 30°C for 8 hours, hydrothermally crystallized at 100°C for 12 hours, and filtered to obtain molecular sieve filter cake and its mother liquor.

[0032] The filter cake was then washed and dried at 120°C to obtain the product, the XRD pattern of which is shown in the figure. Figure 1 The results showed strong diffraction peaks near 2θ = 7.2°, 10.1°, 12.4°, and 16.1°, indicating that the obtained product was a type A molecular sieve. The mother liquor composition of the type A molecular sieve was 4.03% by mass of Na2O, 587 ppm of SiO2, and 1366 ppm of Al2O3.

[0033] (3) Preparation of recycled aluminum source

[0034] Add 100 kg of aluminum hydroxide, 90.91 kg of sodium hydroxide, 60 kg of deionized water and 120 kg of the mother liquor of the A-type molecular sieve obtained in step (2) into the reactor and seal the reactor. Heat to 170°C and stir for 5 hours to obtain a recycled aluminum source. In the recycled aluminum source, the content of Al2O3 is 17.41% by mass, the content of Na2O is 20.30% by mass, the content of SiO2 is 189.91 ppm, and the molar ratio of Na2O / Al2O3 is 1.92.

[0035] (4) Synthesis of FAU molecular sieve

[0036] 59.13 kg of deionized water, 13.92 kg of recycled aluminum source obtained in step (3) and 14.66 kg of water glass were added to the reactor and mixed evenly to obtain a mixture of FAU molecular sieve synthesis system. The molar ratio of each material in the mixture was SiO2 / Al2O3 = 3.00, Na2O / SiO2 = 0.91 and H2O / SiO2 = 60. The mixture was aged at 30°C for 24 hours, hydrothermally crystallized at 100°C for 8 hours, and filtered to obtain molecular sieve filter cake and molecular sieve crystallization mother liquor.

[0037] The molecular sieve filter cake was washed and dried at 80℃ to obtain the product, and its XRD pattern is shown in the figure. Figure 2 The results showed strong diffraction peaks near 2θ = 6.1°, 10.0°, 11.7°, and 15.4°, while no diffraction peaks were observed near 2θ = 7.2°, 10.1°, 12.4°, and 16.1°. This indicates that the obtained product contains no type A molecular sieve impurities and is a pure-phase FAU molecular sieve. The SiO2 content in the FAU molecular sieve crystallization mother liquor was 8908 mg / L.

[0038] Example 2

[0039] This example illustrates the use of recycled aluminum source prepared in Example 1(3) to replace aluminum source in the synthesis of type A molecular sieves:

[0040] 53.68 kg of FAU molecular sieve crystallization mother liquor (SiO2 content of 8908 mg / L), 43.38 kg of deionized water, 54.98 kg of recycled aluminum source prepared in Example 1 (3) (Al2O3 content of 17.41% by mass, Na2O content of 20.30% by mass, SiO2 content of 189.91 ppm, Na2O / Al2O3 molar ratio of 1.92), and 34.07 kg of water glass were added to a reactor and mixed evenly to obtain a mixture of type A molecular sieve synthesis system. The molar ratio of each material in the mixture was SiO2 / Al2O3 = 1.85, Na2O / SiO2 = 1.50, and H2O / SiO2 = 48. After static aging at 33℃ for 10 hours, hydrothermal crystallization at 105℃ for 8 hours, and filtration, molecular sieve filter cake and its filtration mother liquor were obtained.

[0041] The filter cake was then washed and dried at 120°C to obtain the product, the XRD pattern of which is shown in the figure. Figure 3 The results show strong diffraction peaks near 2θ = 7.2°, 10.1°, 12.4°, and 16.1°, indicating that it is a type A molecular sieve.

[0042] The mother liquor of type A molecular sieve filtration has a Na2O content of 5.39% by mass, a SiO2 content of 629 ppm, and an Al2O3 content of 1506 ppm.

[0043] Example 3

[0044] This example illustrates the use of FAU molecular sieve crystallization mother liquor for the preparation of FAU molecular sieves.

[0045] (1) Preparation of recycled aluminum source

[0046] 100 kg of aluminum hydroxide, 101.01 kg of sodium hydroxide, 40 kg of deionized water, and 160 kg of the mother liquor from the type A molecular sieve filtration obtained in Example 2 were added to a reaction vessel and the reaction vessel was sealed. The mixture was heated to 180°C and stirred for 4 hours to obtain a recycled aluminum source, in which the Al2O3 content was 16.11% by mass, the Na2O content was 21.67% by mass, the SiO2 content was 250.97 ppm, and the Na2O / Al2O3 molar ratio was 2.21.

[0047] (2) Synthesis of FAU molecular sieves

[0048] 54.26 kg of deionized water, 18.84 kg of recycled aluminum source prepared in step (1) and 17.60 kg of water glass were added to the reactor and mixed evenly to obtain a mixture of FAU molecular sieve synthesis system. The molar ratio of each material in the mixture was SiO2 / Al2O3 = 2.88, Na2O / SiO2 = 1.04, and H2O / SiO2 = 50. The mixture was aged at 30°C for 20 hours, hydrothermally crystallized at 95°C for 24 hours, and filtered to obtain molecular sieve filter cake and molecular sieve crystallization mother liquor.

[0049] The molecular sieve filter cake was washed and dried at 80℃ to obtain the product, and its XRD pattern is shown in the figure. Figure 4 The results showed strong diffraction peaks near 2θ = 6.1°, 10.0°, 11.7°, and 15.4°, while no diffraction peaks were observed near 2θ = 7.2°, 10.1°, 12.4°, and 16.1°. This indicates that the product contains no type A molecular sieve impurities and is a pure phase FAU molecular sieve.

[0050] The SiO2 content in the mother liquor of FAU molecular sieve crystallization is 8467 mg / L.

[0051] Example 4

[0052] This example illustrates the synthesis of type A molecular sieves using the recycled aluminum source prepared in step (1) of Example 3 and the FAU molecular sieve crystallization mother liquor obtained in step (2).

[0053] 53.26 kg of FAU molecular sieve mother liquor (SiO2 content of 8467 mg / L), 54.00 kg of deionized water, 45.10 kg of recycled aluminum source prepared in step 1(3) and 27.02 kg of water glass were added to the reactor and mixed evenly to obtain a mixture of type A molecular sieve synthesis system. The molar ratio of each material in the mixture was SiO2 / Al2O3 = 1.95, Na2O / SiO2 = 1.60 and H2O / SiO2 = 60. After being aged at 33°C for 8 hours and hydrothermally crystallized at 95°C for 15 hours, the mixture was filtered to obtain molecular sieve filter cake and molecular sieve filter mother liquor.

[0054] The molecular sieve filter cake was washed and dried at 120℃ to obtain the product, whose XRD pattern showed... Figure 3 The same characteristics indicate that the obtained product is a type A molecular sieve; the composition of the mother liquor of the type A molecular sieve filtration is 5.72% by mass of Na2O, 705 ppm of SiO2, and 1583 ppm of Al2O3.

[0055] Example 5

[0056] This example illustrates the synthesis of type A molecular sieves using the recycled aluminum source prepared in step 1(3).

[0057] 120.31 kg of FAU molecular sieve mother liquor (SiO2 content of 32700 mg / L), 0.84 kg of sodium hydroxide, 42.98 kg of recycled aluminum source prepared in step 1(3) and 14.16 kg of water glass were added to the reactor and mixed evenly. The molar ratio of each material was SiO2 / Al2O3 = 1.98, Na2O / SiO2 = 1.60 and H2O / SiO2 = 62. After aging at 35°C for 6 hours and hydrothermal crystallization at 98°C for 12 hours, molecular sieve filter cake and molecular sieve filter mother liquor were obtained by filtration.

[0058] The molecular sieve filter cake was washed and dried at 120℃ to obtain the product, whose XRD pattern showed... Figure 3 The same characteristics indicate that the obtained product is a type A molecular sieve; the composition of the mother liquor of the type A molecular sieve filtration is 5.43% by mass of Na2O, 722 ppm of SiO2, and 1429 ppm of Al2O3.

[0059] Example 6

[0060] This example illustrates the synthesis of FAU molecular sieves using the recycled aluminum source prepared in step 3(1).

[0061] 43.12 kg of deionized water, 7.97 kg of recycled aluminum source prepared in step (1), 8.84 kg of aluminum sulfate solution (Al2O3 content), and 35.20 kg of water glass were added to a reactor and mixed evenly to obtain a mixture of FAU molecular sieve synthesis system materials. The molar ratio of each material in the mixture was SiO2 / Al2O3 = 8.80, Na2O / SiO2 = 0.32, and H2O / SiO2 = 25. The mixture was transferred to a sealed reactor, aged at 30°C for 24 hours, hydrothermally crystallized at 95°C for 48 hours, and filtered to obtain molecular sieve filter cake and molecular sieve crystallization mother liquor.

[0062] The molecular sieve filter cake was washed and dried at 80℃ to obtain the product, whose XRD pattern showed... Figure 2 The similar characteristics indicate that the obtained product is a pure-phase FAU molecular sieve. The SiO2 content in the FAU molecular sieve crystallization mother liquor is 40300 mg / L.

[0063] Comparative Example 1

[0064] This comparative example illustrates the use of the FAU molecular sieve crystallization mother liquor obtained in step 4 of Example 1 and the aluminum source obtained in step 1 of Example 1 for the direct synthesis of FAU molecular sieve.

[0065] 37.91 kg of FAU molecular sieve crystallization mother liquor from step 4 of Example 1, 73.71 kg of deionized water, 31.87 kg of aluminum source obtained from step 1 of Example 1, and 33.13 kg of water glass were added to a reactor and mixed evenly to obtain a molecular sieve synthesis system mixture. The molar ratio of each material in the mixture was SiO2 / Al2O3 = 2.88, Na2O / SiO2 = 1.04, and H2O / SiO2 = 50. The mixture was transferred to a sealed reactor and aged at 30°C for 20 hours, followed by hydrothermal crystallization at 95°C for 24 hours. The resulting crystallized product was filtered, washed, and dried at 80°C. Its XRD pattern is shown in the figure. Figure 5 ,Depend on Figure 5 It can be seen that strong diffraction peaks appear near 2θ = 6.1°, 10.0°, 11.7°, and 15.4°, indicating that the product is mainly composed of FAU molecular sieve. However, weaker diffraction peaks also appear near 2θ = 7.2°, 10.1°, 12.4°, and 16.1°, indicating that a small amount of type A molecular sieve impurities are present in the product.

[0066] Comparative Example 2

[0067] This comparative example illustrates the use of the FAU molecular sieve crystallization mother liquor obtained in step 1(4) to prepare a recycled aluminum source for direct synthesis of FAU molecular sieve.

[0068] (1) Preparation of recycled aluminum source

[0069] 100 kg of aluminum hydroxide, 90.91 kg of sodium hydroxide, 60 kg of deionized water and 120 kg of the FAU molecular sieve crystallization mother liquor obtained in step 1(4) were added to the reactor and the reactor was sealed. The reactor was heated to 120°C and stirred for 5 hours to obtain a recycled aluminum source, in which the Al2O3 content was 17.36% by mass, the Na2O content was 20.34% by mass, the SiO2 content was 2881.99 ppm, and the Na2O / Al2O3 molar ratio was 1.93.

[0070] (2) Synthesis of FAU molecular sieves

[0071] 107.01 kg of deionized water, 1.35 kg of NaOH, 34.00 kg of recycled aluminum source obtained in step (1), and 34.28 kg of water glass were added to a reactor and mixed evenly to obtain a molecular sieve synthesis system mixture. The molar ratio of each material in the mixture was SiO2 / Al2O3 = 2.88, Na2O / SiO2 = 1.04, and H2O / SiO2 = 50. The mixture was transferred to a sealed reactor and aged at 30°C for 24 hours, followed by hydrothermal crystallization at 95°C for 24 hours. The resulting crystallized product was filtered, washed, and dried at 80°C. Its XRD pattern is shown in the figure. Figure 6 ,Depend on Figure 6 It can be seen that strong diffraction peaks appear near 2θ = 6.1°, 10.0°, 11.7°, and 15.4°, indicating that the product is mainly composed of FAU molecular sieve. However, weaker diffraction peaks also appear near 2θ = 7.2°, 10.1°, 12.4°, and 16.1°, indicating that a small amount of type A molecular sieve impurities are present in the product.

Claims

1. A method for utilizing FAU molecular sieve crystallization mother liquor, characterized in that, include: FAU molecular sieve mother liquor, silicon source, inorganic alkali, water, and aluminum source were mixed evenly to obtain a mixture of A-type molecular sieve synthesis system with material molar ratios of SiO2 / Al2O3=1.85-1.99, Na2O / SiO2=1.0-1.6, and H2O / SiO2=45-65. This mixture was then aged and hydrothermally crystallized to recover the product, yielding A-type molecular sieve and its filtration mother liquor. The filtration mother liquor of the A-type molecular sieve was further mixed evenly with an aluminum-containing compound. Stirring at 160-200℃ for 2-8 hours yields a recycled aluminum source with a SiO2 content of 50-300ppm. The silicon source, inorganic alkali, recycled aluminum source, and water are mixed uniformly to obtain a FAU molecular sieve synthesis system mixture. This mixture is then aged and hydrothermally crystallized. The recovered product yields FAU molecular sieve and FAU molecular sieve mother liquor. The mother liquor from the A-type molecular sieve contains 100-900ppm SiO2 and 500-2000ppm Al2O3.

2. The method according to claim 1, characterized in that, The aluminum source has a Na2O / Al2O3 molar ratio of 1.6-2.8 and an Al2O3 content of 16.5-22.0% by mass.

3. The method according to claim 1, characterized in that, The mixture of type A molecular sieve synthesis system was aged at a temperature of 20-35℃ for 3-12 hours.

4. The method according to claim 1, characterized in that, The mixture of the A-type molecular sieve synthesis system was subjected to hydrothermal crystallization at a temperature of 90-130℃ for 6-16 hours.

5. The method according to claim 1, characterized in that, The aluminum source is replaced by the recycled aluminum source.

6. The method according to claim 1 or 5, characterized in that, The Na2O / Al2O3 molar ratio of the recycled aluminum source is 1.6-2.8, and the Al2O3 content is 16.0-22.0% by mass.

7. The method according to claim 1, characterized in that, The aluminum-containing compound is selected from at least one of aluminum oxide, aluminum hydroxide, boehmite, aluminum sulfate, aluminum chloride, aluminum nitrate, and sodium aluminate.

8. The method according to claim 1, characterized in that, In the FAU molecular sieve synthesis system mixture, the material molar ratio is SiO2 / Al2O3=2.6-10.0, Na2O / SiO2=0.25-1.5, and H2O / SiO2=20-70.

9. The method according to claim 1, characterized in that, The FAU molecular sieve synthesis system mixture was aged at a temperature of 25-40℃ for 12-24 hours.

10. The method according to claim 1, characterized in that, The FAU molecular sieve synthesis system mixture was subjected to hydrothermal crystallization at a temperature of 95-120℃ for 2-48 hours.

11. The method according to claim 1, characterized in that, The silicon source is selected from at least one of tetraethyl orthosilicate, silica sol, water glass, sodium silicate, silica gel, and silica fume.

12. The method according to claim 11, characterized in that, The water glass has a Na2O mass fraction of 6.0%-10.0% and a SiO2 mass fraction of 20%-30%.

13. The method according to claim 1, characterized in that, The inorganic base mentioned is sodium hydroxide or potassium hydroxide.

14. The method according to claim 1, characterized in that, The SiO2 content in the FAU molecular sieve mother liquor is 3000-80000 mg / L.

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