A method for synthesizing zeolite by regulating silicon-aluminum ratio of coal gangue based on desert sand

Abstract

The application provides a zeolite synthesis method based on desert sand for regulating a coal gangue silicon aluminum ratio, the coal gangue raw material is subjected to drying, crushing and grinding treatment, is mixed with the pretreated desert sand according to a set proportion, the raw material system is regulated to be a reaction system with a SiO2 / Al2O3 mass ratio of 2-7, a sodium hydroxide solution is added to form a reaction slurry, and the reaction is carried out under hydrothermal conditions, after the reaction is completed, solid-liquid separation, washing and drying are carried out, and a coal gangue-based zeolite material is obtained. The application regulates the silicon aluminum ratio of the coal gangue system by taking the desert sand as a natural additional silicon source, high-temperature calcination pretreatment is omitted, the reaction condition is mild, the process is simplified, the energy consumption is low, the adjustable control preparation of the crystal phase composition and the micro morphology of the zeolite product can be realized, and the collaborative high-value utilization of the coal-based solid waste and the natural mineral resources is promoted.

Description

Technical Field

[0001] This invention belongs to the field of inorganic material preparation technology and relates to a method for synthesizing zeolite. Background Technology

[0002] Coal gangue is a typical solid waste generated during coal mining and washing, with large emissions and stockpiles. Long-term stockpiling occupies land resources and causes environmental problems such as dust and leaching pollution. Coal gangue is rich in silicon and aluminum components, mainly existing in the form of minerals such as kaolinite and quartz, and has the potential to be used as a silicon-aluminum source for zeolite synthesis. Zeolites are a class of hydrous aluminosilicate materials with regular framework structures, possessing ion exchange, adsorption, and sieving properties, and have broad application prospects in environmental remediation and industrial separation. Desert sand is widely available, with SiO2 as its main component, and can be used as a natural external silicon source. In some areas with concentrated coal mines, coal gangue and desert sand coexist, and their synergistic utilization is expected to achieve high-value resource utilization of coal-based solid waste and natural mineral resources.

[0003] Currently, the technology for synthesizing zeolite using coal gangue as a silicon-aluminum source mainly faces the following problems: 1. High energy consumption and complex process in pretreatment: Coal gangue has a complex mineral composition and relatively stable crystal structure. Direct hydrothermal reaction results in insufficient reactivity and difficulty in controlling the crystal phase of the product. Existing processes usually require high-temperature calcination to convert kaolinite into metakaolinite before alkali dissolution and hydrothermal synthesis, which has disadvantages such as high energy consumption, long process, and complex process. 2. Difficulty in effectively controlling the silicon-aluminum ratio of the system: The ratio of silicon and aluminum sources in coal gangue is limited by the original mineral composition, and the SiO2 / Al2O3 ratio of the system is not easy to adjust. This ratio is closely related to the crystal phase composition, crystallinity, and microstructure of the zeolite product. The lack of effective control will make it difficult to directionally construct the target zeolite phase. 3. High cost of external silicon source: Existing technologies mostly use chemical reagents such as sodium silicate as external silicon sources to adjust the silicon-aluminum ratio of the system, resulting in high raw material costs. Moreover, the preparation process often requires high reaction temperature or high alkali concentration, which is not conducive to process simplification, low-cost application, and the synergistic resource utilization of solid waste. Summary of the Invention

[0004] To address the problems of high energy consumption, complex processes, difficulty in effectively controlling the silicon-to-aluminum ratio, and high cost of external silicon sources in the pretreatment of zeolite synthesis using coal gangue as a silicon-aluminum source, as described in the background technology, this invention provides a zeolite synthesis method based on controlling the silicon-to-aluminum ratio of coal gangue using desert sand. Coal gangue is used as the main aluminum-silicon resource, and desert sand is used as an external silicon source. By adjusting the ratio of the two, the SiO2 / Al2O3 ratio of the system is changed. Under alkaline hydrothermal conditions, the crystal phase composition and microstructure of the zeolite product can be controlled, achieving the synergistic resource utilization of coal gangue and desert sand. This method has advantages such as readily available raw materials, simple process, mild reaction conditions, and low energy consumption. The resulting coal gangue-based zeolite material can be applied in water treatment, gas adsorption, or ion exchange.

[0005] The method of the present invention includes the following steps: S1. Coal gangue is directly crushed, ground, and screened without calcination or alkali fusion activation pretreatment to obtain coal gangue powder; desert sand is washed and dried to obtain pretreated desert sand. S2. Mix coal gangue powder and pretreated desert sand in a set ratio, and adjust the raw material system to a reaction system with a SiO2 / Al2O3 mass ratio of 2-7 to obtain mixed solid raw materials; S3. Add sodium hydroxide solution to the mixed solid raw materials and stir evenly to form a reaction slurry; S4. Place the reaction slurry in a sealed reaction vessel and perform a hydrothermal reaction at 80-120℃ for 3-12 hours. S5. After the reaction is complete, cool the mixture, perform solid-liquid separation, wash the solid product until it is neutral, and then dry it to obtain coal gangue-based zeolite material.

[0006] The basic principle of this invention is as follows: by adjusting the ratio of coal gangue to desert sand, the relative content of available silicon and aluminum sources in the system is changed, and under alkaline hydrothermal conditions, the silica-alumina minerals in the coal gangue undergo a dissolution-reconstruction reaction, thereby forming zeolite-like crystal products.

[0007] Furthermore, the coal gangue is clay-type coal gangue, whose main mineral phases are quartz and kaolinite, and the SiO2 / Al2O3 mass ratio of the coal gangue raw material itself is 1.08.

[0008] Furthermore, in step S1, the coal gangue powder has a particle size of less than 1 mm after sieving. Crushing the coal gangue to a smaller particle size helps increase the specific surface area and reactivity of the solid particles, thereby promoting the dissolution and transformation of the silicon-aluminum components under alkaline conditions.

[0009] Furthermore, in S1, the desert sand is mainly composed of SiO2, and the mass content of SiO2 is not less than 85%.

[0010] Furthermore, in step S3, the concentration of the sodium hydroxide solution is 0.25-0.5 mol / L; the liquid-to-solid ratio of the sodium hydroxide solution to the mixed solid raw material is (5-10):1, where the unit of the liquid-to-solid ratio is mL:g. Within this concentration range of 0.25-0.5 mol / L, the sodium hydroxide solution can effectively dissolve the silica-alumina minerals in the coal gangue and promote the formation of zeolite structures. If the liquid-to-solid ratio of the sodium hydroxide solution to the mixed solid raw material is too low, the solution cannot fully wet the solid particles, which is detrimental to the dissolution and diffusion of the silica-alumina components; if the liquid-to-solid ratio is too high, it will reduce the utilization rate of the alkali solution and increase operating costs.

[0011] Furthermore, in step S3, the concentration of the sodium hydroxide solution is 0.5 mol / L, and the liquid-to-solid ratio of the sodium hydroxide solution to the mixed solid raw material is (8-10):1, with the unit of the liquid-to-solid ratio being mL:g.

[0012] Furthermore, in S4, the sealed reaction vessel is a stainless steel reactor lined with polytetrafluoroethylene; the hydrothermal reaction temperature is 100°C, and the reaction time is 12 hours.

[0013] Furthermore, in step S5, the drying is vacuum drying, the drying temperature is 50-80℃, and the drying time is 8-24h.

[0014] Furthermore, when the mass ratio of SiO2 / Al2O3 in the reaction system described in S2 is 2-4, the coal gangue-based zeolite material obtained in S5 is mainly composed of a low-crystallinity zeolite phase.

[0015] Furthermore, when the mass ratio of SiO2 / Al2O3 in the reaction system described in S2 is 5-7, the coal gangue-based zeolite material obtained in S5 is mainly composed of the analcime phase.

[0016] The preferred hydrothermal reaction conditions of this invention are: sodium hydroxide concentration of 0.5 mol / L, liquid-to-solid ratio of 10:1 mL:g, reaction temperature of 100℃, and reaction time of 12 h. Studies have shown that under conditions of 100℃ and 0.5 mol / L sodium hydroxide, the dissolution and reconstruction of silica-alumina components in coal gangue to form zeolite products can be achieved. Compared to zeolite synthesis methods that typically employ higher temperatures and higher alkali concentrations, this invention has advantages in reducing reaction temperature and alkali consumption. Furthermore, under these conditions, the obtained product exhibits distinct zeolite characteristics, and the process conditions are mild, demonstrating good feasibility.

[0017] This invention achieves control over the crystal phase composition and morphology of zeolite by introducing desert sand to adjust the SiO2 / Al2O3 ratio. Studies have shown that when the SiO2 / Al2O3 ratio changes, the hydrothermal products exhibit a clear mineral phase evolution pattern: the hydrothermal products from the original coal gangue, and the products obtained when the SiO2 / Al2O3 ratio is 2-4, are mainly low-crystallinity zeolites; when the SiO2 / Al2O3 ratio increases to 5-7, the products mainly transform into analcime. With further increases in the SiO2 / Al2O3 ratio, the product morphology gradually evolves from a less irregular aggregate structure to a more dense aggregate structure. These results demonstrate that by adjusting the SiO2 / Al2O3 ratio, the crystal phase structure and microstructure of coal gangue-based zeolite materials can be controlled.

[0018] Compared with the prior art, the present invention has the following advantages: (1) Realize the synergistic resource utilization of coal-based solid waste and natural minerals: This invention uses coal gangue as the main source of silicon and aluminum and desert sand as an additional source of silicon. Both are widely available and inexpensive solid waste or natural mineral resources, especially in coal mining areas where coal gangue and desert sand coexist. By using both as raw materials for zeolite synthesis, this invention avoids dependence on chemical reagents such as sodium silicate, which reduces raw material costs and expands the high-value utilization pathways of coal-based solid waste and natural mineral resources. This is conducive to reducing the land occupation and environmental pollution problems caused by long-term stockpiling of coal gangue. (2) Eliminating the need for high-temperature calcination pretreatment, reducing energy consumption and simplifying the process: Existing coal gangue zeolite preparation technology usually requires high-temperature calcination to convert kaolinite into more active metakaolinite, followed by alkali dissolution and hydrothermal synthesis, which has problems such as high energy consumption and long process; This invention adjusts the silica-alumina ratio of the system by introducing desert sand, so that the silica-alumina minerals in coal gangue can directly undergo dissolution-reconstruction reaction under alkaline hydrothermal conditions, without the need for calcination or alkali fusion activation pretreatment, and can be used directly after crushing, grinding and screening, which significantly shortens the process and reduces energy consumption; (3) Mild reaction conditions: The hydrothermal reaction temperature of the present invention is only 80-120℃ and the reaction time is 3-12h. Compared with the higher reaction temperature and higher alkali concentration required by the existing process, the present invention can realize the dissolution of silica-alumina minerals in coal gangue and the reorganization of zeolite skeleton structure under milder temperature and alkaline conditions, further reducing reaction energy consumption and equipment requirements, which is conducive to the low-cost promotion and application of the process. (4) Effective control of the SiO2 / Al2O3 ratio in the system: Coal gangue is limited by its original mineral composition, and the silicon-aluminum ratio is difficult to adjust independently. This invention adjusts the ratio of coal gangue to desert sand, so that the mass ratio of SiO2 / Al2O3 in the reaction system can be flexibly controlled within the range of 2-7. This overcomes the limitation that the silicon-aluminum ratio of a single raw material system of coal gangue is difficult to adjust, and provides a new technical means for the precise control of the silicon-aluminum ratio in the zeolite synthesis system. (5) Adjustable crystal phase composition and microstructure of zeolite products: Since the crystal phase composition, degree of crystallization and microstructure of zeolite products are closely related to the SiO2 / Al2O3 ratio of the system, this invention can achieve the directional construction of zeolite products with different crystal phase compositions by adjusting the amount of desert sand to control the Si-Al ratio of the system, and can control the microstructure of the products, providing a new technical path for the structural design and functional application of coal gangue-based zeolite materials.

[0019] In summary, this invention involves drying, crushing, and grinding coal gangue raw materials, mixing them with pretreated desert sand in a predetermined ratio, adding sodium hydroxide solution to form a reaction slurry, and reacting under hydrothermal conditions. After the reaction, solid-liquid separation, washing, and drying are performed to obtain coal gangue-based zeolite materials. This invention uses desert sand as a natural external silicon source to regulate the silicon-aluminum ratio of the coal gangue system, eliminating the need for high-temperature calcination pretreatment. The reaction conditions are mild, the process is simplified, and energy consumption is low. It enables the controllable preparation of the crystal phase composition and microstructure of zeolite products and promotes the synergistic high-value utilization of coal-based solid waste and natural mineral resources. Attached Figure Description

[0020] Figure 1 The X-ray diffraction patterns of the products obtained under different SiO2 / Al2O3 ratios in this invention are shown.

[0021] Figure 2 Here are scanning electron microscope images of representative samples of the present invention, wherein, Figure 2 (a) is the hydrothermal product of raw coal gangue. Figure 2 (b) is the sample obtained when the SiO2 / Al2O3 ratio of the system is 3. Figure 2 (c) is the sample obtained when the SiO2 / Al2O3 ratio of the system is 6.

[0022] Figure 3 The energy dispersive spectroscopy (EDS) spectrum and elemental distribution map of the original hydrothermal products of coal gangue in this invention are shown.

[0023] Figure 4 The energy dispersive spectroscopy (EDS) spectrum and elemental distribution diagram of the sample obtained when the SiO2 / Al2O3 ratio is 3 in the system of this invention.

[0024] Figure 5The energy dispersive spectroscopy (EDS) spectrum and elemental distribution diagram of the sample obtained when the SiO2 / Al2O3 ratio is 6 in the system of this invention.

[0025] Figure 6 The nitrogen adsorption-desorption isotherms and pore size distribution curves of the original hydrothermal products of coal gangue in this invention are shown.

[0026] Figure 7 The nitrogen adsorption-desorption isotherm and pore size distribution curve of the sample obtained when the SiO2 / Al2O3 ratio is 3 in the system of this invention are shown.

[0027] Figure 8 The nitrogen adsorption-desorption isotherm and pore size distribution curve of the sample obtained when the SiO2 / Al2O3 ratio of the system of this invention is 6. Detailed Implementation

[0028] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0029] A method for synthesizing zeolite based on the control of the silica-alumina ratio of coal gangue using desert sand is described in detail below.

[0030] S1. Coal gangue is directly crushed, ground, and screened without calcination or alkali fusion activation pretreatment to obtain coal gangue powder; desert sand is washed and dried to obtain pretreated desert sand.

[0031] Specifically, the coal gangue is clay-type coal gangue, and its main mineral phases are quartz and kaolinite. More specifically, the SiO2 / Al2O3 mass ratio of the coal gangue raw material itself is 1.08.

[0032] Specifically, the coal gangue powder has a particle size of less than 1 mm after sieving. Crushing the coal gangue into smaller particle sizes helps to increase the specific surface area and reactivity of the solid particles, thereby promoting the dissolution and transformation of the silicon-aluminum components under alkaline conditions.

[0033] Specifically, the desert sand is mainly composed of SiO2, and the mass content of SiO2 is not less than 85%.

[0034] S2. Mix coal gangue powder and pretreated desert sand in a set ratio, and adjust the raw material system to a reaction system with a SiO2 / Al2O3 mass ratio of 2-7 to obtain mixed solid raw materials.

[0035] Specifically, by supplementing the silicon source with desert sand, the SiO2 / Al2O3 mass ratio of the coal gangue raw material itself, which is 1.08, is adjusted to a reaction system with a SiO2 / Al2O3 mass ratio of 2-7.

[0036] Specifically, when the mass ratio of SiO2 / Al2O3 in the reaction system described in S2 is 2-4, the coal gangue-based zeolite material obtained in S5 is mainly composed of a low-crystallinity zeolite phase. When the mass ratio of SiO2 / Al2O3 in the reaction system described in S2 is 5-7, the coal gangue-based zeolite material obtained in S5 is mainly composed of analcime phase.

[0037] By introducing desert sand to adjust the SiO2 / Al2O3 ratio, the crystal phase composition and morphology of zeolite can be controlled. The study found that when the SiO2 / Al2O3 ratio changes, the hydrothermal products exhibit a clear mineral phase evolution pattern: the hydrothermal products from the original coal gangue, and the products obtained when the SiO2 / Al2O3 ratio is 2-4, are mainly low-crystallinity zeolites; when the SiO2 / Al2O3 ratio increases to 5-7, the products mainly transform into analcime. With further increases in the SiO2 / Al2O3 ratio, the product morphology gradually evolves from a relatively irregular aggregate structure to a more compact aggregate structure. These results indicate that by adjusting the SiO2 / Al2O3 ratio, the crystal phase structure and microstructure of coal gangue-based zeolite materials can be controlled.

[0038] S3. Add sodium hydroxide solution to the mixed solid raw materials and stir evenly to form a reaction slurry.

[0039] Specifically, the concentration of the sodium hydroxide solution is 0.25-0.5 mol / L; the liquid-to-solid ratio of the sodium hydroxide solution to the mixed solid raw material is (5-10):1, where the unit of the liquid-to-solid ratio is mL:g. Within this concentration range of 0.25-0.5 mol / L, the sodium hydroxide solution can effectively dissolve the silica-alumina minerals in the coal gangue and promote the formation of zeolite structures. If the liquid-to-solid ratio of the sodium hydroxide solution to the mixed solid raw material is too low, the solution cannot fully wet the solid particles, which is detrimental to the dissolution and diffusion of the silica-alumina components; if the liquid-to-solid ratio is too high, it will reduce the utilization rate of the alkali solution and increase operating costs.

[0040] Preferably, the concentration of the sodium hydroxide solution is 0.5 mol / L, and the liquid-to-solid ratio of the sodium hydroxide solution to the mixed solid raw material is (8-10):1, wherein the unit of the liquid-to-solid ratio is mL:g.

[0041] S4. Place the reaction slurry in a sealed reaction vessel and perform a hydrothermal reaction at 80-120℃ for 3-12 hours.

[0042] The hydrothermal reaction temperature is 80-120℃, and the reaction time is 3-12h. Within this range, the silica-alumina minerals in coal gangue can gradually dissolve in an alkaline environment to form silica-alumina species, and further recombine under hydrothermal conditions to form a zeolite framework structure.

[0043] Specifically, the sealed reaction vessel is a stainless steel reactor lined with polytetrafluoroethylene.

[0044] Preferably, the hydrothermal reaction temperature is 100°C and the reaction time is 12 hours.

[0045] Under the above conditions, the preferred hydrothermal reaction conditions are: sodium hydroxide concentration 0.5 mol / L, liquid-to-solid ratio 10:1 mL:g, reaction temperature 100℃, and reaction time 12 h. Under these conditions, the obtained product exhibits distinct zeolite characteristics, and the process is mild, demonstrating good feasibility.

[0046] S5. After the reaction is complete, cool the mixture, perform solid-liquid separation, wash the solid product until it is neutral, and then dry it to obtain coal gangue-based zeolite material.

[0047] Specifically, the drying process is vacuum drying, with a drying temperature of 50-80℃ and a drying time of 8-24 hours.

[0048] The present invention and its technical effects will be further illustrated below through examples and comparative examples.

[0049] The coal gangue used in the following examples was obtained from a coal mine in Northwest China and is a typical clay-type coal gangue. The coal gangue raw material was dried, crushed, and ground, and then screened to obtain coal gangue powder with a particle size of less than 1 mm for later use. The desert sand was also obtained from a sandy area in Northwest China, washed with deionized water, and then dried at 105°C for later use.

[0050] X-ray fluorescence spectroscopy (XRF) analysis was performed on the raw coal gangue samples, and the main elemental composition and loss on ignition are shown in Table 1.

[0051] Table 1. Main components and loss on ignition of coal gangue As can be seen from Table 1, the coal gangue has a high content of SiO2 and Al2O3, belonging to a typical high-silicon-alumina mineral system, which provides the necessary silicon and aluminum source for the formation of the zeolite framework structure.

[0052] Based on the SiO2 and Al2O3 contents in Table 1, the SiO2 / Al2O3 mass ratio of the original coal gangue is calculated to be 1.08.

[0053] It must be noted that the silicon-to-aluminum ratio mentioned in this invention refers to the SiO2 / Al2O3 mass ratio. Specifically, the SiO2 / Al2O3 mass ratio of the coal gangue raw material itself is 1.08; the SiO2 / Al2O3 ratio of the system described in the examples refers to the SiO2 / Al2O3 mass ratio of the reaction system obtained after mixing coal gangue powder and desert sand.

[0054] Example 1 Hydrothermal synthesis of coal gangue-based zeolite materials (SiO2 / Al2O3 ratio of 2).

[0055] Dryed and ground coal gangue powder was mixed with desert sand in a certain proportion, and the SiO2 / Al2O3 ratio of the system was controlled to be 2 by adjusting the ratio of the two. 3 g of the mixed solid raw material was placed in a beaker, and 30 mL of 0.5 mol / L sodium hydroxide solution (liquid-solid ratio 10:1 mL:g) was added. The mixture was stirred thoroughly to form a homogeneous reaction slurry.

[0056] The obtained slurry was transferred to a 50 mL polytetrafluoroethylene-lined stainless steel high-pressure reactor and subjected to hydrothermal reaction at 100 °C for 12 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and the slurry was centrifuged to collect the solid product. The solid product was repeatedly washed with deionized water until neutral and then vacuum dried at 60 °C for 12 h to obtain coal gangue-based zeolite material.

[0057] The SiO2 / Al2O3 ratio of the product obtained in this embodiment is 2, which is in the range of 2-4. The obtained coal gangue-based zeolite material is mainly composed of a low-crystallinity zeolite phase.

[0058] Example 2 Hydrothermal synthesis of coal gangue-based zeolite materials (SiO2 / Al2O3 ratio of 3).

[0059] Dryed and ground coal gangue powder was mixed with desert sand in a certain proportion, and the SiO2 / Al2O3 ratio of the system was controlled to be 3 by adjusting the ratio of the two. 3 g of the mixed solid raw material was placed in a beaker, and 30 mL of 0.5 mol / L sodium hydroxide solution (liquid-solid ratio 10:1 mL:g) was added. The mixture was stirred thoroughly to form a homogeneous reaction slurry.

[0060] The obtained slurry was transferred to a 50 mL polytetrafluoroethylene-lined stainless steel high-pressure reactor and subjected to hydrothermal reaction at 100 °C for 12 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and the slurry was centrifuged to collect the solid product. The solid product was repeatedly washed with deionized water until neutral and then vacuum dried at 60 °C for 12 h to obtain coal gangue-based zeolite material.

[0061] The SiO2 / Al2O3 ratio of the product obtained in this embodiment is 3, falling within the 2-4 range. The resulting coal gangue-based zeolite material is mainly composed of a low-crystallinity zeolite phase. SEM observation reveals that the product exhibits a distinct flower-like or radial aggregate structure, consisting of numerous plate-like or short-plate-like crystals, indicating that zeolite crystals have begun to form and undergo directional stacking under this Si / Al ratio condition. The sample obtained in this embodiment is used as a representative sample for further SEM, EDS / Mapping, and BET analyses.

[0062] Example 3 Hydrothermal synthesis of coal gangue-based zeolite materials (SiO2 / Al2O3 ratio of 4).

[0063] Dryed and ground coal gangue powder was mixed with desert sand in a certain proportion, and the SiO2 / Al2O3 ratio of the system was controlled to be 4 by adjusting the ratio of the two. 3 g of the mixed solid raw material was placed in a beaker, and 30 mL of 0.5 mol / L sodium hydroxide solution (liquid-solid ratio 10:1 mL:g) was added. The mixture was stirred thoroughly to form a homogeneous reaction slurry.

[0064] The obtained slurry was transferred to a 50 mL polytetrafluoroethylene-lined stainless steel high-pressure reactor and subjected to hydrothermal reaction at 100 °C for 12 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and the slurry was centrifuged to collect the solid product. The solid product was repeatedly washed with deionized water until neutral and then vacuum dried at 60 °C for 12 h to obtain coal gangue-based zeolite material.

[0065] The SiO2 / Al2O3 ratio of the product obtained in this embodiment is 4, which is at the upper limit of the 2-4 range. The obtained coal gangue-based zeolite material is mainly composed of low-crystallinity zeolite phase, which is in the transition range from low-crystallinity zeolite to analcime.

[0066] Example 4 Hydrothermal synthesis of coal gangue-based zeolite materials (SiO2 / Al2O3 ratio of 5).

[0067] Dryed and ground coal gangue powder was mixed with desert sand in a certain proportion, and the SiO2 / Al2O3 ratio of the system was controlled to be 5 by adjusting the ratio of the two. 3 g of the mixed solid raw material was placed in a beaker, and 30 mL of 0.5 mol / L sodium hydroxide solution (liquid-solid ratio 10:1 mL:g) was added. The mixture was stirred thoroughly to form a homogeneous reaction slurry.

[0068] The obtained slurry was transferred to a 50 mL polytetrafluoroethylene-lined stainless steel high-pressure reactor and subjected to hydrothermal reaction at 100 °C for 12 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and the slurry was centrifuged to collect the solid product. The solid product was repeatedly washed with deionized water until neutral and then vacuum dried at 60 °C for 12 h to obtain coal gangue-based zeolite material.

[0069] The SiO2 / Al2O3 ratio of the product obtained in this embodiment is 5, which is in the range of 5-7. The obtained coal gangue-based zeolite material is mainly composed of analcime phase, indicating that as the available silicon source in the system increases, the crystal phase of the product gradually changes from low crystallinity zeolite to higher crystallinity analcime.

[0070] Example 5 Hydrothermal synthesis of coal gangue-based zeolite materials (SiO2 / Al2O3 ratio of 6).

[0071] Dryed and ground coal gangue powder was mixed with desert sand in a certain proportion, and the SiO2 / Al2O3 ratio of the system was controlled to be 6 by adjusting the ratio of the two. 3 g of the mixed solid raw material was placed in a beaker, and 30 mL of 0.5 mol / L sodium hydroxide solution (liquid-solid ratio 10:1 mL:g) was added. The mixture was stirred thoroughly to form a homogeneous reaction slurry.

[0072] The obtained slurry was transferred to a 50 mL polytetrafluoroethylene-lined stainless steel high-pressure reactor and subjected to hydrothermal reaction at 100 °C for 12 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and the slurry was centrifuged to collect the solid product. The solid product was repeatedly washed with deionized water until neutral and then vacuum dried at 60 °C for 12 h to obtain coal gangue-based zeolite material.

[0073] The SiO2 / Al2O3 ratio of the product obtained in this embodiment is 6, falling within the 5-7 range. The resulting coal gangue-based zeolite material is mainly composed of analcime phase. SEM observation reveals that the sample contains relatively regular blocky or polyhedral crystals with relatively clear crystal faces and a high degree of crystal development. The sample obtained in this embodiment is used as a representative sample for further SEM, EDS / Mapping, and BET analyses.

[0074] Example 6 Hydrothermal synthesis of coal gangue-based zeolite materials (SiO2 / Al2O3 ratio of 7).

[0075] Dryed and ground coal gangue powder was mixed with desert sand in a certain proportion, and the SiO2 / Al2O3 ratio of the system was controlled to be 7 by adjusting the ratio of the two. 3 g of the mixed solid raw material was placed in a beaker, and 30 mL of 0.5 mol / L sodium hydroxide solution (liquid-solid ratio 10:1 mL:g) was added. The mixture was stirred thoroughly to form a homogeneous reaction slurry.

[0076] The obtained slurry was transferred to a 50 mL polytetrafluoroethylene-lined stainless steel high-pressure reactor and subjected to hydrothermal reaction at 100 °C for 12 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and the slurry was centrifuged to collect the solid product. The solid product was repeatedly washed with deionized water until neutral and then vacuum dried at 60 °C for 12 h to obtain coal gangue-based zeolite material.

[0077] The SiO2 / Al2O3 ratio of the product obtained in this embodiment is 7, which is in the range of 5-7. The obtained coal gangue-based zeolite material is mainly composed of analcime phase. As the SiO2 / Al2O3 ratio of the system further increases, the morphology of the product gradually evolves from a relatively irregular aggregate structure to a more compact aggregate structure.

[0078] Comparative Example 1 Control experiment on hydrothermal reaction of raw coal gangue.

[0079] Take 3 g of dried and ground coal gangue powder, without adding desert sand, and add 30 mL of 0.5 mol / L sodium hydroxide solution (liquid-to-solid ratio 10:1 mL:g). Stir thoroughly to form a homogeneous reaction slurry. Transfer the resulting slurry to a 50 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene (PTFE), and carry out a hydrothermal reaction at 100 °C for 12 h. After the reaction is complete, allow it to cool naturally to room temperature, centrifuge the reaction slurry, and collect the solid product. Wash the solid product repeatedly with deionized water until neutral, and then vacuum dry at 60 °C for 12 h to obtain the final product.

[0080] The product obtained in this comparative example was prepared without introducing desert sand to adjust the SiO2 / Al2O3 ratio in the system. The resulting product had low crystallinity and indistinct zeolite characteristics. It was used as a control sample for comparative analysis with the products obtained in each example.

[0081] X-ray diffraction (XRD) analysis was performed on the samples obtained in Examples 1 to 6 and Comparative Example 1. The sample with SiO2 / Al2O3=3 prepared in Example 2, the sample with SiO2 / Al2O3=6 prepared in Example 5, and the original coal gangue control sample of Comparative Example 1 were selected as representative samples for further SEM, EDS / Mapping and BET analysis, as detailed below.

[0082] I. Analysis of the crystal phase structure of the product X-ray diffraction (XRD) analysis was performed on the samples obtained in Examples 1 to 6 and Comparative Example 1. The results are as follows: Figure 1 As shown.

[0083] Depend on Figure 1 It can be seen that the main mineral phases of the original coal gangue sample are quartz and kaolinite. After alkaline hydrothermal reaction, the diffraction peaks of the sample changed significantly. The intensity of the original mineral peaks decreased significantly, and new zeolite characteristic diffraction peaks appeared. This indicates that the silica-alumina components in the coal gangue dissolved and reorganized under alkaline hydrothermal conditions, gradually forming a new zeolite-like crystal structure.

[0084] Comparative Example 1: XRD results show that, under the condition of not introducing desert sand to adjust the SiO2 / Al2O3 ratio, although the product shows zeolite characteristic diffraction peaks, the peak intensity is weak and the peak shape is wide. It also retains many original mineral diffraction peaks, has low crystallinity, and the zeolite characteristics are not obvious. This indicates that it is difficult to form zeolite crystals with regular structures when using only original coal gangue for hydrothermal reaction.

[0085] Examples 1 to 3: Samples with a SiO2 / Al2O3 ratio of 2-4 all showed characteristic diffraction peaks of zeolite, but their peak intensity was relatively weak and the peak shape was relatively broad. They also retained some original mineral diffraction peaks, indicating that the products formed under these conditions were mainly low-crystallinity zeolite with a relatively low degree of crystallinity and insufficient crystal development.

[0086] Examples 4 to 6: When the SiO2 / Al2O3 ratio of the system is increased to 5-7, the diffraction peaks of the sample are further enhanced, the peak shapes are sharper and clearer, and the characteristic diffraction peaks of analcime appear, indicating that as the available silicon source in the system increases, the crystal phase of the product gradually changes from low crystallinity zeolite to higher crystallinity analcime.

[0087] The above results indicate that by adjusting the ratio of coal gangue to desert sand to change the SiO2 / Al2O3 ratio of the system, the crystal phase composition of the product can be effectively controlled, thereby achieving the directional transformation from low-crystallinity zeolite to analcime.

[0088] II. Morphological and Structural Analysis of Products The representative samples obtained from Examples 2, 5, and Comparative Example 1 were analyzed by scanning electron microscopy (SEM), and the results are as follows: Figure 2 As shown.

[0089] Figure 2 (a) is a SEM image of the hydrothermal products of the original coal gangue in Comparative Example 1. The sample is an irregular aggregate with uneven particle size distribution and a rough surface. Figure 2 (b) is a SEM image of the SiO2 / Al2O3=3 sample obtained in Example 2. It can be observed that the product has a relatively obvious flower-like or radial aggregate structure, which is composed of a large number of plate-like or short plate-like crystals, indicating that zeolite crystals have begun to form and undergo directional stacking under this silicon-aluminum ratio. Figure 2 (c) is a SEM image of the SiO2 / Al2O3=6 sample obtained in Example 5. The sample shows relatively regular blocky or polyhedral crystals with relatively clear crystal faces and a high degree of crystal development.

[0090] Depend on Figure 2It can be seen that as the SiO2 / Al2O3 ratio of the system increases from the original level of 1.08 to 3 and 6, the morphology of the product gradually evolves from irregular aggregates to a more regular crystal structure, indicating that the introduction of desert sand not only changes the chemical composition of the system, but also has a significant impact on the crystal nucleation and growth process.

[0091] III. Elemental Composition and Distribution Analysis Energy dispersive spectroscopy (EDS) and elemental mapping analyses were performed on representative samples obtained from Examples 2, 5, and Comparative Example 1. The results are as follows: Figure 3 , Figure 4 and Figure 5 As shown.

[0092] EDS analysis results showed that the main elements in the sample were Si, Al, O and Na, indicating that a typical sodium aluminosilicate structure was formed in the system.

[0093] Elemental mapping results show that Si and Al elements are evenly distributed in the sample, indicating that the silicon source provided by desert sand can effectively participate in the construction of zeolite framework structure.

[0094] As the SiO2 / Al2O3 ratio of the system increases, the relative content of Si in the sample gradually increases, while the proportion of Al decreases relatively, further demonstrating that the composition of the zeolite framework structure can be controlled by adjusting the Si / Al ratio of the system through desert sand.

[0095] IV. Analysis of Pore Structure Properties Nitrogen adsorption-desorption tests were performed on representative samples obtained from Examples 2, 5, and Comparative Example 1. The results are as follows: Figures 6 to 8 As shown.

[0096] Depend on Figures 6 to 8 As can be seen, each sample exhibits certain pore structure characteristics. The specific surface area, pore volume, and average pore diameter of different samples are shown in Table 2.

[0097] Table 2 Pore structure parameters of different representative samples Table 2 shows that the SiO2 / Al2O3=3 sample obtained in Example 2 has a larger specific surface area and pore volume, indicating that the crystal structure formed under these conditions has abundant channels and a well-developed surface structure. The SiO2 / Al2O3=6 sample obtained in Example 5 has a relatively large average pore size, indicating that the pore structure characteristics of the material are adjusted accordingly with further changes in crystal phase and morphology. The above results demonstrate that by adjusting the blending ratio of coal gangue and desert sand, not only can the crystal phase composition and morphological characteristics of the product be controlled, but its pore structure properties can also be affected.

[0098] comprehensive Figure 1The crystal phase evolution law shown and Figures 2 to 8 As shown by the morphology, elemental composition and pore structure characteristics, it can be seen that by introducing desert sand to adjust the SiO2 / Al2O3 ratio of the coal gangue system, different types of zeolites can be controllably prepared under relatively mild alkaline hydrothermal conditions.

[0099] Preferably, the synthesis conditions include: using coal gangue and desert sand as a composite silicon-aluminum source, employing 0.5 mol / L sodium hydroxide solution as the alkaline activation medium, a liquid-to-solid ratio of 10:1 mL / g, and hydrothermal reaction at 100℃ for 12 h. The preferred SiO2 / Al2O3 ratio is 3-6. Within this range, the product exhibits well-defined zeolite characteristic peaks, a relatively complete crystal morphology, uniform elemental distribution, and good pore structure characteristics.

[0100] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings and specific examples. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A method for synthesizing zeolite based on the controlled silica-alumina ratio of coal gangue using desert sand, characterized in that, Includes the following steps: S1. Coal gangue is directly crushed, ground, and screened without calcination or alkali fusion activation pretreatment to obtain coal gangue powder; desert sand is washed and dried to obtain pretreated desert sand. S2. Mix coal gangue powder and pretreated desert sand in a set ratio, and adjust the raw material system to a reaction system with a SiO2 / Al2O3 mass ratio of 2-7 to obtain mixed solid raw materials; S3. Add sodium hydroxide solution to the mixed solid raw materials and stir evenly to form a reaction slurry; S4. Place the reaction slurry in a sealed reaction vessel and perform a hydrothermal reaction at 80-120℃ for 3-12 hours. S5. After the reaction is complete, cool the mixture, perform solid-liquid separation, wash the solid product until it is neutral, and then dry it to obtain coal gangue-based zeolite material.

2. The method for synthesizing zeolite based on the controlled silica-alumina ratio of coal gangue using desert sand according to claim 1, characterized in that: The coal gangue is clay-type coal gangue, and its main mineral phases are quartz and kaolinite. The SiO2 / Al2O3 mass ratio of the coal gangue raw material itself is 1.

08.

3. The method for synthesizing zeolite based on the control of the silica-alumina ratio of coal gangue using desert sand according to claim 1, characterized in that: In S1, the coal gangue powder has a particle size of less than 1 mm after sieving.

4. The method for synthesizing zeolite based on the control of the silica-alumina ratio of coal gangue using desert sand according to claim 1, characterized in that: In S1, the desert sand is mainly composed of SiO2, and the mass content of SiO2 is not less than 85%.

5. A method for synthesizing zeolite based on the controlled silica-alumina ratio of coal gangue using desert sand, as described in any one of claims 1-4, characterized in that: In step S3, the concentration of the sodium hydroxide solution is 0.25-0.5 mol / L; the liquid-to-solid ratio of the sodium hydroxide solution to the mixed solid raw material is (5-10):1, and the unit of the liquid-to-solid ratio is mL:g.

6. A method for synthesizing zeolite based on the control of the silica-alumina ratio of coal gangue using desert sand, as described in any one of claims 1-4, characterized in that: In step S3, the concentration of the sodium hydroxide solution is 0.5 mol / L, and the liquid-to-solid ratio of the sodium hydroxide solution to the mixed solid raw material is (8-10):1, with the unit of the liquid-to-solid ratio being mL:g.

7. The method for synthesizing zeolite based on the control of the silica-alumina ratio of coal gangue using desert sand according to claim 1, characterized in that: In S4, the sealed reaction vessel is a stainless steel reactor lined with polytetrafluoroethylene; the hydrothermal reaction temperature is 100℃ and the reaction time is 12h.

8. The method for synthesizing zeolite based on the control of the silica-alumina ratio of coal gangue using desert sand according to claim 1, characterized in that: In step S5, the drying is performed under vacuum, with a drying temperature of 50-80℃ and a drying time of 8-24 hours.

9. The method for synthesizing zeolite based on the control of the silica-alumina ratio of coal gangue using desert sand according to claim 1, characterized in that: When the mass ratio of SiO2 / Al2O3 in the reaction system described in S2 is 2-4, the coal gangue-based zeolite material obtained in S5 is mainly composed of a low-crystallinity zeolite phase.

10. The method for synthesizing zeolite based on the control of the silica-alumina ratio of coal gangue using desert sand according to claim 1, characterized in that: When the mass ratio of SiO2 / Al2O3 in the reaction system described in S2 is 5-7, the coal gangue-based zeolite material obtained in S5 is mainly composed of analcime phase.

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