A method for preparing Na-A type molecular sieves and controlling impurity cations using a one-step alkaline fusion hydrothermal method based on high-alumina and high-silicon coal gangue.

Abstract

The application provides a method for preparing NaA type molecular sieve and impurity cation quality control based on one-step alkali fusion hydrothermal method of high-aluminum and high-silicon coal gangue, relates to the field of chemical engineering and material cross discipline, and comprises the following steps: 1) mixing and grinding coal gangue and NaOH; 2) calcining the mixed raw materials; 3) adding NaOH, Na2SiO3 and distilled water to prepare a mixed solution according to the content of Al2O3 and SiO2 in the coal gangue; 4) adding appropriate Ca 2+ and K + ; 5) transferring the mixed solution to a magnetic stirrer for aging reaction; 6) performing crystallization reaction on the mixed solution; 7) performing washing, filtering and drying on the slurry to obtain the product. The application realizes the selection and control of cations in the coal gangue, the molecular sieve yield reaches more than 80%, the solid waste is basically completely converted, the whole process is free of secondary emission, the process is simple, there is no special requirement for the equipment, the cost is low, the product has wide application fields, and the high-value utilization of the coal gangue is realized.

Description

Technical Field

[0001] This invention relates to the interdisciplinary field of chemical engineering and materials science, and in particular to a method for preparing Na-A type molecular sieves and controlling impurity cations using a one-step alkaline fusion hydrothermal method based on high-alumina and high-silicon coal gangue. Background Technology

[0002] Coal gangue is mainly composed of rock and coal, with coal content typically ranging from 20% to 30%. It exhibits a multi-phase structure including kaolinite, illite, and muscovite, and its chemical composition is diverse, primarily consisting of SiO2 and Al2O3, while also containing some impurity cations. Furthermore, the chemical composition of coal gangue varies significantly depending on the location of its extraction. Currently, its main utilization methods include landfilling, road construction, and the production of building materials. Coal gangue is primarily used for backfilling mining areas, lacking in-depth utilization. Therefore, activating the silicon and aluminum elements in coal gangue as raw materials for synthesizing molecular sieves represents a high-value utilization method for coal gangue.

[0003] Research on the high-value utilization of coal gangue involves activating the silicon and aluminum elements in the coal gangue and then synthesizing NaA-type molecular sieves via hydrothermal reaction. In their paper, "A Method for Preparing 4A Molecular Sieves from Coal Gangue," Jia Min et al. first calcined the coal gangue, then mixed and ground it with sodium hydroxide to obtain a molten product at 500℃-650℃. This molten product was then subjected to two calcinations before hydrothermal synthesis to finally obtain the molecular sieve product.

[0004] In their paper, "A Technical Method for Preparing 4A Molecular Sieves via Alkali Leaching of Coal Gangue in One Step," Bai Jie et al. first activated coal gangue from Inner Mongolia, then mixed it with sodium hydroxide. Without the need for additional silicon or aluminum sources, they directly synthesized 4A molecular sieves. This method is simple to operate and has a high yield. However, this invention did not further investigate the cations involved. Treating impurity cations in the early stages could improve the performance of the molecular sieve.

[0005] Kang Le et al., in their paper "A Coal Gangue-Based Molecular Sieves and Their Alkali-Fusing-Hydrothermal Preparation Method," directly calcined a mixture of coal gangue and sodium hydroxide to obtain a molten product. Water and a silicon source were then added, followed by hydrothermal synthesis to obtain the molecular sieve product. Liang Zhishui et al., in their paper "Preparation and Application Method of Coal Gangue-Based Sodium Ion Molecular Sieves Based on Alkali Fusing," utilized coal gangue from the Ordos region without adding silicon or aluminum sources to prepare sodium ion molecular sieves via alkali fusing, achieving adsorption rates of over 90% for Cd and Cu.

[0006] Because the impurity cations contained in coal gangue can affect the synthesis of molecular sieves, but they are difficult to remove during the synthesis stage and the removal cost is too high, making it difficult to achieve industrial application. Summary of the Invention

[0007] The purpose of this invention is to achieve high-value utilization of coal gangue. Using the silicon and aluminum elements contained in coal gangue as the main raw material, Na-A type molecular sieves are prepared first through alkali fusion calcination activation, and then through hydrothermal crystallization synthesis. Furthermore, the quality control requirements for coal gangue are established by analyzing the content of impurity cations.

[0008] To achieve the above objectives, this invention provides a method for preparing Na-A type molecular sieves and controlling impurity cations using a one-step alkaline fusion hydrothermal method based on high-alumina, high-silicon coal gangue, comprising the following steps:

[0009] 1) Add NaOH particles according to the content of SiO2 and Al2O3 in the chemical composition of coal gangue, so that the Na / Si molar ratio is (2.1~2.6):1, and mix and grind the coal gangue and NaOH particles.

[0010] The main chemical components of the coal gangue described in this invention include SiO2, Al2O3, Fe2O3, CaO, MgO, and loss on ignition (LOI), with kaolinite being the main mineral component. LOI represents the carbon present in the coal gangue. Furthermore, the selected coal gangue has a high silicon and aluminum content, requiring only the addition of a small amount of silicon source later, eliminating the need for additional aluminum source. Specifically, the mass percentage of SiO2 in the coal gangue is ≥40%, and the mass percentage of Al2O3 is ≥40%.

[0011] Furthermore, it is necessary to ensure that the added NaOH can fully react with the silicon and aluminum elements contained in the coal gangue to obtain the silicon and aluminum sources required for the subsequent synthesis of molecular sieves. However, if the amount of NaOH added is too high, the alkalinity of the resulting molten product will be too strong, which may lead to the subsequent formation of X-type zeolite. Therefore, the Na / Si molar ratio is controlled at (2.1~2.6):1.

[0012] 2) Calcine the raw materials mixed and ground in step 1), and obtain a molten product after cooling;

[0013] The present invention involves calcining the mixed product to activate the stable silica and aluminum in coal gangue at high temperature, and then reacting it with NaOH at high temperature to obtain aluminosilicates and sodium aluminate. Therefore, the calcination temperature is set at 760℃~800℃ and the calcination time is set at 2~2.5h. The molten product is Al. 1.95 Na 1.95 Si 0.05 O4 and NaAlO2. Sufficient temperature is required to ensure that the mixed raw materials can react. If the calcination temperature is below 760℃, the reaction will not be complete. If the calcination temperature is too high, the kaolinite will react to form mullite, which is not conducive to the formation of molten products. If the calcination time is too long, the degree of reaction will not be significantly improved, and the energy consumption will be high. Therefore, the calcination time is controlled at 2~2.5h.

[0014] 3) Grind the molten product obtained in step 2) to obtain a powdered material;

[0015] The molten product must be ground; otherwise, the reaction will be incomplete in the subsequent hydrothermal synthesis, increasing the overall synthesis time. If there is a large amount of lumpy product, it cannot be fully dissolved in the alkali solution during subsequent stirring, resulting in a low molecular sieve yield. If the grinding degree is too fine, it will place higher demands on the equipment and increase the energy consumption of the entire process. Preferably, the fineness of the powdered material is ≤74μm.

[0016] 4) Mix the powdered material obtained in step 3) with NaOH, Na2SiO3 and distilled water to obtain a reaction solution;

[0017] Since coal gangue contains low levels of silicon, some silicon source is added during the hydrothermal synthesis process, and NaOH is added to prepare an alkaline environment. Distilled water is added to adjust the water-to-sodium ratio. In this step, all the raw materials required for the synthesis of molecular sieves are prepared. The preferred mass ratio of NaOH to Na2SiO3 is (1.2~1.3):1, and the mass ratio of distilled water to Na2SiO3 is (20~22):1.

[0018] 5) Add impurity cations to the reaction solution obtained in step 4) to obtain a mixed solution;

[0019] Different impurity cations have different effects on the synthesis of the final product, K + Mg 2+ These metal cations can react with Na in Na A-type molecular sieves + Ion exchange occurs, thus affecting the synthesis of Na₂A type molecular sieves. The presence of cations affects the structural stability of the molecular sieve crystals, leading to changes in the crystal structure. The properties of the cations affect the adsorption performance of the molecular sieve. The concentration of calcium ions in the reaction solution is ≤1.21 μg / ml, the concentration of potassium ions is ≤51.5 μg / ml, and the concentration of Ca is ≤1.21 μg / ml. 2+ K + The content is insufficient, therefore CaCl2 and / or KCl need to be added separately, and the contents of MgO and Fe2O3 in the coal gangue need to be controlled. In this application, CaCl2 and KCl are added to provide impurity cations, so that the Na / Ca molar ratio in the mixed solution is (10000~11000):1, and the Na / K molar ratio is (100~120):1. This results in a molecular sieve with better adsorption performance. In the mixed solution, the iron ion concentration is ≤160ug / ml, and the magnesium ion concentration is ≤300ug / ml; otherwise, it will affect the synthesis of the molecular sieve and reduce its adsorption performance. Therefore, it can be deduced that the MgO content in the coal gangue should not exceed 2.1%, and the Fe2O3 content should not exceed 1.1%.

[0020] 6) Place the mixed solution obtained in step 5) into a magnetic stirrer for aging reaction to obtain the aging product;

[0021] During the synthesis process, aging the synthesized mixture at a relatively high temperature for a short period of time can promote crystal nucleation and growth. High-temperature aging provides sufficient thermal energy to accelerate the reaction rate, promoting rapid crystal growth and resulting in larger and more uniform molecular sieve crystals. Appropriate aging temperatures can further promote crystal nucleation and growth, enhance crystal stability and adsorption properties, and also influence crystal morphology, crystal form, and pore structure. The aging reaction conditions were set as follows: rotation speed 500 r / min, aging temperature 45–55 °C, and aging time 2–2.5 h.

[0022] 7) The aged product obtained in step 6) is subjected to a hydrothermal crystallization reaction to obtain a crystallized product;

[0023] Crystallization conditions affect the nucleation and growth rate of crystals. Shorter crystallization times may lead to incomplete nucleation and growth, resulting in smaller crystal sizes; while longer crystallization times promote more complete nucleation and growth, which is beneficial for the perfection and stability of the crystal structure, forming a regular and ordered crystal structure, generating larger NaA-type molecular sieve crystals, and improving the crystallization quality of NaA-type molecular sieves. Appropriate crystallization time can improve the crystallinity and structural stability of molecular sieves. Therefore, the crystallization conditions are set as follows: crystallization temperature 80~90℃, crystallization time 5~6h.

[0024] 8) The crystallized product obtained in step 7) is washed and filtered in a vacuum filter, then the product is dried in a drying oven and ground into powder to obtain the final molecular sieve product. The drying temperature is 60℃.

[0025] This invention, based on alkali-fusion hydrothermal synthesis, requires only a small amount of silicon source supplementation and investigates the enhancing or inhibiting effects of different cations on molecular sieve performance. It achieves the addition of appropriate cations, such as Ca, during the synthesis stage. 2+ K + To promote molecular sieve synthesis; for cations with inhibitory effects, such as Fe... 3+ Mg 2+ Limiting its content upper limit and imposing relevant requirements on the composition of coal gangue during the raw material selection stage ensures that subsequent synthesis is not affected by impurity cations.

[0026] The present invention also provides a molecular sieve prepared by the method, and the application of the molecular sieve in ion adsorption.

[0027] This technology has the following advantages:

[0028] (1) High-value utilization of silicon and aluminum components in high-alumina and high-silicon coal gangue has been realized;

[0029] (2) NaOH is added during the calcination stage to activate the silicon and aluminum in the coal gangue;

[0030] (3) The overall preparation process is highly efficient and environmentally friendly, with no waste gas or solid waste generated throughout the process;

[0031] (4) It is easy to operate, has low raw material costs, and the coal gangue conversion efficiency reaches 90%, which is conducive to realizing industrial production;

[0032] (5) Quality control selection of coal gangue; the selection of raw materials helps to improve the synthesis yield.

[0033] (6) The molecular sieve products prepared have a wide range of applications, high added value, and significant economic benefits. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a process flow diagram of the preparation of NaA-type molecular sieves using high-alumina coal gangue according to the present invention;

[0036] Figure 2 The image shows the XRD pattern of the high-alumina, high-silicon coal gangue used in Example 1.

[0037] Figure 3 Here is a SEM image of the high-alumina, high-silicon coal gangue from Example 1;

[0038] Figure 4 XRD pattern of the melt product in Example 1;

[0039] Figure 5 SEM image of the molten product in Example 1;

[0040] Figure 6 The image shows the XRD pattern of the final product in Example 1.

[0041] Figure 7 This is a SEM image of the final product in Example 1;

[0042] Figure 8 The image shows the XRD pattern of the final product in Example 2.

[0043] Figure 9 This is a SEM image of the final product in Example 2;

[0044] Figure 10 The image shows the XRD pattern of the final product in Example 3.

[0045] Figure 11 This is a SEM image of the final product in Example 3;

[0046] Figure 12 The XRD pattern of the final product in Comparative Example 1;

[0047] Figure 13 The XRD pattern of the final product in Comparative Example 2;

[0048] Figure 14 The image shows the XRD pattern of the final product in Comparative Example 3. Detailed Implementation

[0049] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0050] The chemical composition of the high-alumina coal gangue used in Examples 1 and 3 and Comparative Examples 2 and 3 is shown in Table 1, where the values ​​are mass percentages. Coal gangue powder was obtained by crushing, grinding, sieving, and drying. 3g of the coal gangue powder was weighed, mixed with 3g of NaOH, and ground to obtain a mixed raw material. This mixture was then placed in a crucible and calcined in a muffle furnace. Comparative experiments were conducted by adding cations to the raw material, and the adsorption capacity of the synthesized Na₂A molecular sieve was tested.

[0051] Table 1 Chemical composition (%) of coal gangue raw material

[0052]

[0053] Example 1:

[0054] The process flow diagram for preparing NaA-type molecular sieves using high-alumina coal gangue in this invention is shown below. Figure 1 As shown. The calcination temperature was set at 800℃, and the calcination time was 2 hours. The product of the calcination reaction of coal gangue and sodium hydroxide at a mass ratio of 1:1 was ground into powder. Sodium silicate powder, sodium hydroxide, and distilled water were added to make the mass ratio of NaOH to Na2SiO3 1.2:1 and the mass ratio of distilled water to Na2SiO3 20:1. The mixed solution was transferred to a magnetic stirrer and heated to 50℃ at a heating rate of 5℃ / min, with a stirring speed of 500 r / min, and aged for 2 hours. The aged product was then kept at 90℃ for 6 hours to carry out the crystallization stage reaction. After the aging period, the slurry was allowed to cool to room temperature, discharged, and filtered. The filter cake was washed with distilled water to obtain Na A-type molecular sieves. The molecular sieves were then dried in an oven at 60℃ for 12 hours to obtain the final molecular sieve product. The calcium ion adsorption capacity was tested and found to be 276 mg / g.

[0055] Example 2:

[0056] The chemical composition of the high-alumina coal gangue used in Example 2 below is shown in Table 2. The values ​​in the table are mass percentages, of which SiO2 content is ≥45% and Al2O3 content is ≥45%.

[0057] Table 2 Chemical composition (%) of coal gangue raw materials

[0058]

[0059] Coal gangue and sodium hydroxide were calcined at 790℃ for 2.5 h at a mass ratio of 1:1. The coal gangue and sodium hydroxide were then melted together, and the resulting molten product was mixed with sodium silicate powder, sodium hydroxide, and distilled water to achieve a NaOH to Na2SiO3 mass ratio of 1.2:1 and a distilled water to Na2SiO3 mass ratio of 20:1. The mixture was heated to 45℃ at a rate of 5℃ / min, stirred at 500 r / min, and aged for 2.5 h. The mixture was then held at 80℃ for 5.5 h to induce crystallization. After the slurry cooled to room temperature, it was discharged and filtered. The filter cake was washed with distilled water to obtain Na A-type molecular sieves. These molecular sieves were then dried in an oven at 60℃ for 12 h to obtain the final molecular sieve product. The calcium ion adsorption capacity was tested to reach 280 mg / g, and the performance of the synthesized molecular sieve was improved in coal gangue with high silicon and aluminum content.

[0060] Example 3:

[0061] like Figure 1 As shown in the process flow diagram, coal gangue and sodium hydroxide are mixed and calcined at a mass ratio of 1:1 at 800℃ for 2 hours. Sodium silicate powder, sodium hydroxide, and distilled water are then added to achieve a NaOH to Na2SiO3 mass ratio of 1.2:1 and a distilled water to Na2SiO3 mass ratio of 20:1. CaCl2 and KCl powders are then added to the solution to achieve a Na / Ca ratio of 10000~11000 and a Na / K ratio of 100~120, and the mixture is stirred thoroughly. The aging temperature is then set at 50℃, the stirring speed at 500 r / min, and the aging time is 2 hours. The temperature is then raised to 90℃ and held for 6 hours to induce crystallization. After the holding period, the slurry is allowed to cool to room temperature, discharged, and filtered. The filter cake is washed with distilled water to obtain NaA-type molecular sieves. These molecular sieves are then dried in a 60℃ oven for 12 hours to obtain the final molecular sieve product. The calcium ion adsorption capacity of the molecular sieve synthesized after adding potassium ions was tested and found to be 289 mg / g, which is an improvement over the calcium ion adsorption capacity of the molecular sieve product in Example 1.

[0062] Comparative Example 1:

[0063] The chemical composition of the high-alumina coal gangue used in Comparative Example 1 below is shown in Table 3. The values ​​in the table are mass percentages, with SiO2 content ≤40% and Al2O3 content ≤40%.

[0064] Table 3 Chemical composition (%) of coal gangue raw material

[0065]

[0066] Coal gangue and sodium hydroxide were mixed and calcined at a mass ratio of 1:1 at 790℃ for 2 hours. The molten product was then mixed with sodium silicate powder, sodium hydroxide, and distilled water to achieve a NaOH to Na₂SiO₃ mass ratio of 1.2:1 and a distilled water to Na₂SiO₃ mass ratio of 20:1. The mixture was aged at 50℃ with a stirring speed of 500 r / min for 2 hours, followed by a crystallization reaction at 90℃ for 5 hours. After the crystallization, the slurry was allowed to cool to room temperature, discharged, and filtered. The filter cake was washed with distilled water to obtain Na₂A type molecular sieves. These molecular sieves were then dried in an oven at 60℃ for 12 hours to obtain the final molecular sieve product. The calcium ion adsorption capacity was tested to be 270 mg / g. This indicates that the low silicon and aluminum content cannot provide sufficient silicon and aluminum sources for subsequent molecular sieve synthesis, leading to a decrease in the quality of the final synthesized molecular sieve.

[0067] Comparative Example 2:

[0068] Coal gangue and sodium hydroxide were melted together at a mass ratio of 1:1 at 800℃. Sodium silicate powder, sodium hydroxide, and distilled water were added to achieve a NaOH to Na₂SiO₃ mass ratio of 1.2:1 and a distilled water to Na₂SiO₃ mass ratio of 20:1. KCl and CaCl₂ were added to the solution to achieve a Na / Ca ratio of 12000 and a Na / K ratio of 150, and the mixture was stirred thoroughly. The solution was aged at 50℃ with a stirring speed of 500 r / min for 2 hours, followed by crystallization at 90℃ for 6 hours. After crystallization, the liquid was drained, washed, filtered, and dried. The molecular sieve was then dried in a 60℃ oven for 12 hours to obtain the final molecular sieve product. The results showed that when the calcium and potassium ion content in the solution exceeded a certain limit, the calcium ion adsorption capacity decreased to 242 mg / g, inhibiting the performance of the molecular sieve.

[0069] Comparative Example 3:

[0070] Coal gangue and sodium hydroxide were calcined at 800℃ for 2 hours at a mass ratio of 1:1 to induce a melting reaction. The molten product was then mixed with sodium silicate powder, sodium hydroxide, and distilled water to achieve a NaOH to Na2SiO3 mass ratio of 1.2:1 and a distilled water to Na2SiO3 mass ratio of 20:1. FeCl3 and MgCl2 were then added to the solution to achieve an iron ion concentration of 170 μg / ml and a magnesium ion concentration of 310 μg / ml, and the mixture was stirred thoroughly. The temperature was increased to 50℃ at a rate of 5℃ / min, with a stirring speed of 500 r / min, and the reaction was allowed to proceed for 2 hours. The temperature was then increased to 90℃ and held for 6 hours to induce a crystallization reaction. After the holding period, the slurry was allowed to cool to room temperature and then washed, filtered, and dried in a filter medium to obtain Na A-type molecular sieves. These molecular sieves were then dried in an oven at 60℃ for 12 hours to obtain the final molecular sieve product. The synthesized molecular sieve exhibited a calcium ion adsorption capacity of 242 mg / g. This indicates that the addition of iron and magnesium ions significantly inhibited the synthesis of the molecular sieve.

[0071] Table 4. Performance test results of the Na A-type molecular sieves synthesized in the examples and comparative examples.

[0072]

[0073] The formula for calculating calcium ion adsorption capacity in Table 4 is as follows:

[0074] E= (1)

[0075] Where: Ca in E-Na type A molecular sieve 2+ Exchange capacity, mg / g; CO-CaC l2 Concentration of standard solution, mol / L; concentration of c1-EDTA standard titration solution, mol / L; V0-after Ca 2+ Volume of filtrate taken after exchange, mL; V E - Volume of EDTA standard titration solution consumed, mL; mass of m-Na A molecular sieve, g; hygroscopic water content of W-Na A molecular sieve, %; millimolecular mass of 100.08-CaCO3, mg / mmol.

[0076] Figure 2 The XRD pattern of the high-alumina, high-silicon coal gangue used in Example 1 shows that the main phase of the coal gangue is kaolinite, and the characteristic mountain-shaped diffraction peak of kaolinite appears between 2θ and 35° and 40°. Figure 4The XRD pattern of the molten product in Example 1 shows that after the coal gangue and NaOH were mixed and calcined, the characteristic mountain-shaped diffraction peak of kaolinite at 2θ=35°~40° disappeared, and a new diffraction peak with greater intensity and sharper shape was generated between 2θ=30°~35°, indicating the presence of sodium aluminate NaAlO2 and Al with a porous structure. 1.95 Na 1.95 O4Si 0.05 The diffraction peaks indicate that the silica-alumina components in the coal gangue reacted with NaOH at high temperature to form aluminosilicates.

[0077] Figure 6 , Figure 8 , Figure 10 The XRD patterns of the final products from Examples 1-3 are shown below. All exhibit a zeolite phase with sharp peaks, indicating that NaA-type molecular sieves were synthesized under different conditions. In Example 3, the diffraction peaks are even sharper, indicating good crystallinity. Adsorption capacity tests show that the calcium ion adsorption capacity of the molecular sieves synthesized in Examples 2 and 3 is improved compared to that in Example 1. In Example 3, the adsorption performance is significantly improved after the addition of calcium and potassium ions.

[0078] Figure 12 , Figure 13 , Figure 14 The images show the XRD patterns of the final products from Comparative Examples 1 to 3. Figure 12 and 13 Zeolite crystal phase appeared in it. Figure 14 After the addition of iron and magnesium ions, zeolite and Na were formed. 96 Al 96 Si 96 H 432 O 600 In Comparative Example 1, the low silica-alumina content of the coal gangue resulted in no significant change in the XRD pattern of the synthesized molecular sieve, but combined with the above tests, its calcium ion adsorption capacity decreased. In Comparative Example 2, when the added calcium and potassium ion content exceeded a certain limit, the XRD pattern of the molecular sieve exhibited a certain degree of dispersion, indicating a decrease in crystalline state. In Comparative Example 3, the addition of iron and magnesium ions resulted in the appearance of other phases, indicating the production of other substances in the system, which is detrimental to the synthesis of the molecular sieve.

[0079] Figure 3 The image shows an SEM image of the high-alumina, high-silicon coal gangue from Example 1. It can be seen that the microstructure of the coal gangue exhibits a disordered state, such as stacked flakes and book pages. Figure 5 The image shown is an SEM image of the molten product in Example 1. It can be seen that the layered structure of the molten product obtained after mixing and calcination disappears, and it presents as a clump. Figure 7 , Figure 9 , Figure 11The XRD patterns of the final products of Examples 1-3 are shown respectively. It can be seen that the synthesized molecular sieves exhibit a complete cubic state and are evenly distributed.

[0080] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing NaA-type molecular sieves using a one-step alkaline fusion hydrothermal method based on high-alumina, high-silicon coal gangue, characterized in that, Includes the following steps: 1) Add NaOH particles according to the content of SiO2 and Al2O3 in the chemical composition of coal gangue, so that the Na / Si molar ratio is (2.1~2.6):1, and mix and grind the coal gangue and NaOH particles. 2) Calcine the raw materials mixed and ground in step 1), and obtain a molten product after cooling; 3) Grind the molten product obtained in step 2) to obtain a powdered material; 4) Mix the powdered material obtained in step 3) with NaOH, Na2SiO3 and distilled water to obtain a reaction solution; 5) Add impurity cations to the reaction solution obtained in step 4) to obtain a mixed solution; 6) The mixed solution obtained in step 5) is subjected to an aging reaction to obtain the aged product; 7) The aged product obtained in step 6) is subjected to a hydrothermal crystallization reaction to obtain a crystallized product; 8) The crystallized product obtained in step 7) is sequentially washed, filtered, dried, and ground to obtain the molecular sieve; In step 1), the coal gangue contains SiO2 with a mass percentage ≥ 40%, Al2O3 with a mass percentage ≥ 40%, MgO with a mass percentage ≤ 2.1%, and Fe2O3 with a mass percentage ≤ 1.1%. In step 4), the mass ratio of NaOH to Na2SiO3 is (1.2~1.3):1, and the mass ratio of distilled water to Na2SiO3 is (20~22):

1. In step 5), the concentration of calcium ions in the reaction solution is ≤1.21 μg / ml, the concentration of potassium ions is ≤51.5 μg / ml, and after adding CaCl2 and / or KCl, the Na / Ca molar ratio in the mixed solution is (10000~11000):1, and the Na / K molar ratio is (100~120):1; the concentration of iron ions in the mixed solution is ≤160 μg / ml, and the concentration of magnesium ions is ≤300 μg / ml.

2. The method according to claim 1, characterized in that, In step 2), the calcination temperature is 760℃~800℃ and the calcination time is 2~2.5h.

3. The method according to claim 1, characterized in that, In step 3), the fineness of the powdered material is ≤74μm.

4. The method according to claim 1, characterized in that, In step 5), the impurity cation is Ca. 2+ and / or K + .

5. The method according to claim 1, characterized in that, In step 6), the aging reaction speed is 500 r / min, the aging temperature is 45~55℃, and the aging time is 2~2.5h.

6. The method according to claim 1, characterized in that, In step 7), the hydrothermal crystallization temperature is 80~90℃ and the crystallization time is 5~6h.

7. The application of the molecular sieve prepared by the method according to any one of claims 1 to 6 in ion adsorption.

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