Method for preparing molecular sieve from kaolin through ice crystal crystallization and application of molecular sieve

Abstract

The invention provides a method for preparing a molecular sieve from kaolin through ice crystal crystallization and application, the method for preparing the molecular sieve from kaolin through ice crystal crystallization comprises the following steps: calcining purified kaolin in a muffle furnace; dissolving the calcined kaolin and sodium silicate nonahydrate in deionized water, adding a surfactant tetrapropylammonium hydroxide and a gemini ionic surfactant butane-1, 4-bis (dodecyl dimethyl ammonium bromide), and stirring and heating; adjusting the pH value, forming a colloidal body, stirring to fully disperse and uniformly mix the precipitate, immersing the precursor in an ice-water bath, placing the precursor in an ultrasonic oscillator after the ice-water bath for ultrasonic oscillation treatment, standing, placing the precursor in a 25 DEG C water bath for gradient temperature recovery to avoid cracks formed by thermal shock, then heating the precursor in a water bath for aging, placing the precursor in the ultrasonic oscillator for ultrasonic oscillation treatment again, and drying to obtain the composite material. And carrying out hydrothermal crystallization reaction, washing, drying, grinding and calcining to remove the template agent. The molecular sieve prepared by the method is used for adsorbing and recycling phosphorus and fluorine in phosphogypsum leachate.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of molecular sieve synthesis, and particularly relates to a method for preparing molecular sieve from ice crystal crystallized kaolin and application thereof. BACKGROUND

[0003] As a natural, inexpensive and abundant layered silicate mineral (main component is kaolinite, chemical formula is Al2Si2O5(OH)4), kaolin exhibits significant advantages in hydrothermal crystallization synthesis of ZSM-5 molecular sieve, which is mainly due to its unique physical and chemical properties, and the close aluminum-silicon ratio: the theoretical silicon-aluminum molar ratio (SiO2 / Al2O3) of kaolinite is about 2.0, which is not directly matched with the typical high silicon-aluminum ratio (usually >10) of ZSM-5 molecular sieve, but provides a natural and closely combined silicon source and aluminum source. The uncalcined kaolin has low reactivity. However, after calcination at an appropriate temperature (usually 550-900°C), the kaolinite structure is destroyed, and the hydroxyl water is removed, and the amorphous metakaolin with significantly improved chemical activity is converted. The Si and Al atoms in metakaolin are in a highly disordered state, and the bond energy is reduced, so that it is easier to dissolve and rearrange under alkaline hydrothermal conditions, becoming an effective precursor for synthesizing molecular sieve. This "in situ" provided aluminum-silicon source avoids the addition of expensive and possibly impurity-introducing chemical raw materials, in addition, kaolin benefits from its unique mineral structure, and the kaolin sheet structure or the local ordered region formed after calcination may play a certain induction role in the formation of the MFI topology structure of ZSM-5.

[0004] Hydrothermal synthesis method for preparing molecular sieve is considered as one of the most economical methods, among the existing zeolite preparation methods, the hydrothermal synthesis method has the unique advantages of easy to control solution or interface reaction, simple operation and the like, and is more reliable. In the process, water is used as a solvent, and an aluminum source, a silicon source and a template agent are reacted in an autoclave reactor, but in the traditional hydrothermal crystallization synthesis of ZSM molecular sieve, the high-temperature stage (usually > 150°C) of hydrothermal crystallization, the dissolution and rearrangement speed of silicon-aluminum species is very fast, which is easy to cause explosive nucleation (a large number of crystal nuclei are formed instantaneously in a short time). This can cause problems such as uneven crystal size, excessive small crystals, crystal agglomeration, and increased structural defects caused by rapid nucleation. Ice crystal crystallization is carried out under low temperature and slow conditions, which promotes the formation of high-quality crystal nucleus precursor / pre-assembled body with controllable quantity, uniform size and regular structure, and can avoid the problems of uneven crystal size and agglomeration caused by a large number of instant nucleation at high temperature, so that the template agent has sufficient time to organize silicon-aluminum species to form a stable complex, optimize the efficiency of the template agent, promote the dissolution of the raw materials, and improve the quality of the product: ultimately, a ZSM-5 molecular sieve with higher crystallinity, more uniform crystal size, more regular morphology, fewer defects and better phase purity is obtained. Introducing the ice crystal crystallization method into the synthesis of ZSM-5 type molecular sieve to improve the overall quality of the molecular sieve and thus improve the overall performance of the molecular sieve has extremely high practical significance for removing phosphorus and fluorine pollution in phosphogypsum leaching solution. SUMMARY

[0005] In view of the above technical problems, the present application provides a method for preparing molecular sieve by ice crystal crystallization of kaolin and application thereof. The method uses kaolin as raw material, utilizes aluminum in kaolin as the only aluminum source, controls the amount of added silicon source, and adopts the hydrothermal crystallization method to prepare ZSM-5 type molecular sieve which is economical and efficient, has highly uniform particle size, and has regular crystal grain external shape. The present application optimizes the traditional hydrothermal crystallization synthesis steps, innovatively adds an ice crystal crystallization process before water bath aging after adjusting pH, improves the stability of crystal nucleus formation and the order of local target MFI topology, forms a product with uniform crystal grain size and regular morphology, and uses multiple small amounts of surfactants to jointly optimize the synthesis effect of molecular sieve, guide the formation of inorganic framework, control the size of mesopores, and make the morphology of molecular sieve more regular. At the same time, the aluminum source of kaolin itself is fully utilized in the synthesis process, and only the amount of added silicon source needs to be controlled to control the silicon-aluminum ratio in the overall system, so that the preparation process is more economical and efficient. The technical scheme of the present application is as follows: A method for preparing molecular sieve by ice crystal crystallization of kaolin, the method comprising the following steps: S1: calcine the purified kaolin in a muffle furnace to destroy the internal structure, make the structure more loose, increase the specific surface area, and prepare for use; S2: The calcined kaolin and sodium silicate with nine water were dissolved in deionized water, and the surfactants tetrapropyl ammonium hydroxide (TPAOH) and gemini surfactant butane-1, 4-bis (dodecyl dimethyl ammonium bromide) (gBDDA) were added and stirred and heated uniformly; S3: H2SO4 was used to adjust the pH, and the gel was stirred after the formation of the precipitate to fully disperse and mix; S4: The precursor was immersed in an ice water bath at 0°C, and after the ice water bath, it was taken out and ultrasonically treated; S5: After ultrasonic treatment, the water bath was warmed and maintained, and then the water bath was warmed and aged; S6: After aging, the system was ultrasonically treated at room temperature again; S7: The gel after ultrasonic treatment was transferred to a hydrothermal reactor for hydrothermal crystallization reaction; S8: The product was taken out and centrifuged and washed, the substrate was placed in an evaporating dish and dried, and after grinding, it was placed in a muffle furnace to remove the template agent by calcination; The preparation of kaolin molecular sieve was completed. Preferably, in step S1, calcination is performed at 500-800°C for 1-2h. Preferably, in step S2, the molar ratio of elements Si and Al in the system is (8-10):1; the molar ratio of tetrapropyl ammonium hydroxide (TPAOH) to Si and H2O is 1:(8-12):(800-1200); the molar ratio of TPAOH to gBDDA is (8-10):1, and the uniform stirring time is 1-2h.

[0006] Preferably, in step S3, the concentration of H2SO4 solution is 1-3mol / L, and H2SO4 is used to adjust the pH to 9-11.

[0007] Preferably, in step S4, the ice crystal is crystallized in an ice water bath at 0°C±0.5°C for 12-18h, with stirring at 200-300rpm during the ice water bath, and the ultrasonic treatment conditions are 100-300w, 20-40kHz, and 90-150s.

[0008] Preferably, in step S5, after ultrasonic treatment, the water bath is warmed at a rate of 0.5-1.5°C / min from 0°C to 25°C and maintained for 25-35min, and then the water bath is warmed to 70-85°C for aging for 5-8h.

[0009] Preferably, in step S6, after aging, the ultrasonic treatment conditions are 100-300W, 20-40kHz, and 30-60s.

[0010] Preferably, in step S7, the temperature of the hydrothermal crystallization reaction is 140~160℃, and the hydrothermal crystallization time is 48~72h. Preferably, in step S8, the drying conditions are 115~125℃ for 2~4 hours; the calcination temperature is 500~600℃ for 3~5 hours to remove the template agent.

[0011] The molecular sieve prepared by the method of preparing molecular sieve by ice crystal crystallization of kaolin is used in the adsorption and recovery of phosphorus and fluorine in phosphogypsum leachate. The beneficial effects of this invention are as follows: 1. This invention uses kaolin as the main raw material and makes full use of the silicon and aluminum elements in kaolin. It adopts the hydrothermal crystallization method optimized by ice crystal crystallization to efficiently and economically prepare ZSM-5 molecular sieves with highly uniform particle size and more regular crystal surface. It provides a more efficient and economical preparation process for the traditional hydrothermal crystallization synthesis of molecular sieves and obtains more regular and uniform ZSM-5 molecular sieves more efficiently. 2. This invention innovatively proposes the use of a mixture of multiple surfactants working together, and innovatively proposes the synergistic effect of multiple combined surfactants TPAOH and gBDDA. TPAOH guides the formation of the main framework of ZSM-5 molecular sieve, while the twin surfactant gBDDA acts as an auxiliary modifier to modify the internal pore size and structure of the molecular sieve. The combination of the two results in ZSM-5 molecular sieve with highly uniform particle size and more regular crystal surface. 3. In this invention, after adjusting the pH to form a gel, the precipitate is stirred to fully disperse and mix it. The precursor is then immersed in an ice-water bath, followed by ultrasonic treatment in an ultrasonic oscillator. This process breaks down the "ice crystal-gel" network into uniform gel particles, preventing Ostwald ripening when the temperature rises. The local hot spots generated by the ultrasonic treatment can instantly promote the formation of a more stable precursor core and shell. The gradient temperature recovery in the water bath prevents thermal shock from causing cracks. Subsequently, the precursor system is aged in a heated water bath and then placed in an ultrasonic oscillator again for ultrasonic treatment, making the distribution of the precursor system more uniform and facilitating the subsequent crystallization reaction.

[0012] 4. This invention optimizes the traditional hydrothermal crystallization synthesis steps and significantly reduces the reaction rate by combining the low-temperature environment of the ice crystallization step, allowing the silicon-aluminum species and the template agent to fully and orderly self-assemble and form a well-structured crystal nucleus precursor. The low-temperature crystallization prolongs the interaction time between the template agent and the aluminosilicate, promoting more complete encapsulation and directional alignment of the template agent molecules, enhancing the silicon-aluminum-oxygen tetrahedron. The synergistic effect of the two template agents forms a stable complex that highly matches the MFI structure of ZSM-5, reducing the risk of impurity phase formation when multiple template agents are mixed and reducing the amount of template agent used. Attached Figure Description

[0013] Figure 1 XRD pattern of kaolin-based ZSM-5 molecular sieve; Figure 2 This is a SEM image of a kaolin-based ZSM-5 molecular sieve. Detailed Implementation

[0014] The technical solution of the present invention will be further explained and described below with reference to specific embodiments. It is worth noting that the following embodiments are only preferred embodiments of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention should be determined by the contents of the claims. Modifications and substitutions made by those skilled in the art to the technical solution of the present invention without creative effort all fall within the scope of protection of the present invention. Example 1: Basic Scheme of the Invention The preparation method of kaolin-based ZSM-5 molecular sieve includes the following steps: 1) Place the purified kaolin in a muffle furnace and calcine it to 650℃ for 1 hour; 2) Weigh 5g of kaolin calcined at 650℃ and 80g of sodium silicate nonahydrate and dissolve them in 558mL of deionized water. Then add 6.293g of TPAOH template agent and 0.614g of BDDA surfactant and stir well on a magnetic stirrer.

[0015] 3) Adjust the pH of the solution to 10±0.1 by adding 2M sulfuric acid solution dropwise. The solution will gradually form a gel. Then, use a stirrer to thoroughly mix the gel for 2 hours to ensure that the precipitate and solution are fully and evenly mixed.

[0016] 4) The precursor was then immediately immersed in a 0°C ice water bath and stirred at 250 rpm for 16 hours. After that, it was taken out and placed in an ultrasonic oscillator and ultrasonically oscillated at 300W and 40kHz for 120 seconds. 5) After ultrasound, let stand for 5 minutes, then raise the water bath temperature from 0℃ to 25℃ at a rate of 1℃ / min and maintain it for 30 minutes to avoid thermal shock. Then slowly heat to 80℃ and age in water bath for 6 hours. 6) After aging, the precursor is subjected to ultrasonic treatment again at 200W, 30kHz for 60s. Then the precursor is transferred to a hydrothermal reactor. 7) After sealing the reactor, place it in an oven and carry out a hydrothermal crystallization reaction at 150℃ for 72 hours. After the reaction is complete, remove the product from the reactor, wash it repeatedly with ultrapure water, centrifuge it three times, and then transfer it to an evaporating dish; 8) Dry the product in a drying oven at 120℃ for 2 hours to remove residual moisture. Remove the product and grind it using a mortar and pestle. Place the ground powder in a muffle furnace and calcine it at 550℃ for 4 hours to remove the template and obtain the final product.

[0017] Example 2 The preparation method of kaolin-based ZSM-5 molecular sieve includes the following steps: 1) After purification, the kaolin was placed in a muffle furnace and calcined to 650°C for 1 hour; 2) Weigh 2g of kaolin calcined at 650℃ and 38.4g of sodium silicate nonahydrate and dissolve them in 223.2mL of deionized water. Add 2.014g of TPAOH template agent and 0.197g of BDDA surfactant. Then stir on a constant temperature magnetic stirrer and heat the mixed solution to 70℃ to promote dissolution and mixing reaction.

[0018] 3) Adjust the pH of the solution to 10 ± 0.1 by adding 2M sulfuric acid solution dropwise. The solution will gradually form a gel. Then, use a stirrer to thoroughly mix the gel for 1 hour to ensure that the precipitate and solution are fully and evenly mixed.

[0019] 4) The precursor was then immediately immersed in a 0°C ice water bath and stirred at 200 rpm for 12 hours. After that, it was taken out and placed in an ultrasonic oscillator and ultrasonically oscillated at 200W and 30kHz for 90 seconds. 5) After ultrasound, let stand for 5 minutes, then raise the water bath temperature from 0℃ to 25℃ at a rate of 1℃ / min and maintain it for 30 minutes to avoid thermal shock. Then slowly heat to 70℃ and age in water bath for 8 hours. 6) After aging, the precursor is subjected to ultrasonic treatment again at 100W, 20kHz for 60s. Then the precursor is transferred to a hydrothermal reactor. 7) After sealing the reactor, place it in an oven and carry out a hydrothermal crystallization reaction at 150℃ for 48 hours. After the reaction is complete, remove the product from the reactor, wash it repeatedly with ultrapure water, centrifuge it 3 times, and then transfer it to an evaporating dish; 8) Dry the product in a drying oven at 110℃ for 2 hours to remove residual moisture. Remove the product and grind it using a mortar and pestle. Place the ground powder in a muffle furnace and calcine it at 550℃ for 4 hours to remove the template and obtain the final product. Comparative Example 1: Traditional hydrothermal method (no ice bath, no ultrasound, no gBDDA, only TPAOH).

[0020] 1) Place the purified kaolin in a muffle furnace and calcine it to 650℃ for 1 hour; 2) Weigh 5g of kaolin calcined at 650℃ and 80g of sodium silicate nonahydrate and dissolve them in 558mL of deionized water. Then add 6.293g of TPAOH template agent and stir and mix them on a magnetic stirrer.

[0021] 3) Adjust the pH of the solution to 10±0.1 by adding 2M sulfuric acid solution dropwise. The solution will gradually form a gel. Then, use a stirrer to thoroughly mix the gel for 2 hours to ensure that the precipitate and solution are fully and evenly mixed.

[0022] 4) After mixing evenly, place the mixture in a water bath and heat to 80°C for 6 hours. 5) After aging, the precursor was transferred to a hydrothermal reactor. The reactor was sealed and placed in an oven for hydrothermal crystallization at 150°C for 72 hours. After the reaction, the product was removed from the reactor, washed repeatedly with ultrapure water, centrifuged three times, and then transferred to an evaporating dish. 6) Dry the product in a drying oven at 120℃ for 2 hours to remove residual moisture. Remove the product and grind it using a mortar and pestle. Place the ground powder in a muffle furnace and calcine it at 550℃ for 4 hours to remove the template and obtain the final product.

[0023] Comparative Example 2: Ice bath + TPAOH (without gBDDA), without two ultrasound sessions.

[0024] 1) Place the purified kaolin in a muffle furnace and calcine it to 650℃ for 1 hour; 2) Weigh 5g of kaolin calcined at 650℃ and 80g of sodium silicate nonahydrate and dissolve them in 558mL of deionized water. Then add 6.293g of TPAOH template agent and stir and mix them on a magnetic stirrer.

[0025] 3) Adjust the pH of the solution to 10±0.1 by adding 2M sulfuric acid solution dropwise. The solution will gradually form a gel. Then, use a stirrer to thoroughly mix the gel for 2 hours to ensure that the precipitate and solution are fully and evenly mixed.

[0026] 4) The precursor was then immediately immersed in a 0°C ice-water bath with stirring at 250 rpm for 16 hours. Afterward, it was heated to 80°C and aged in a water bath for 6 hours. The precursor was then transferred to a hydrothermal reactor, sealed, and placed in an oven for hydrothermal crystallization at 150°C for 72 hours. After the reaction, the product was removed from the reactor, repeatedly washed with ultrapure water, centrifuged three times, and then transferred to an evaporating dish. 5) Dry the product in a drying oven at 120℃ for 2 hours to remove residual moisture. Remove the product and grind it using a mortar and pestle. Place the ground powder in a muffle furnace and calcine it at 550℃ for 4 hours to remove the template and obtain the final product.

[0027] Comparative Example 3: gBDDA+TPAOH was present, but no ice bath or two ultrasonic steps were performed (traditional hydrothermal).

[0028] 1) Place the purified kaolin in a muffle furnace and calcine it to 650℃ for 1 hour; 2) Weigh 5g of kaolin calcined at 650℃ and 80g of sodium silicate nonahydrate and dissolve them in 558mL of deionized water. Then add 6.293g of TPAOH template agent and 0.614g of BDDA surfactant and stir well on a magnetic stirrer.

[0029] 3) Adjust the pH of the solution to 10±0.1 by adding 2M sulfuric acid solution dropwise. The solution will gradually form a gel. Then, use a stirrer to thoroughly mix the gel for 2 hours to ensure that the precipitate and solution are fully and evenly mixed.

[0030] 4) After mixing evenly, place the mixture in a water bath and slowly heat it to 80°C for 6 hours. 5) Transfer the precursor to a hydrothermal reactor, seal the reactor, and place it in an oven for hydrothermal crystallization at 150°C for 72 hours. After the reaction, remove the product from the reactor, wash it repeatedly with ultrapure water, centrifuge it three times, and then transfer it to an evaporating dish. 6) Dry the product in a drying oven at 120℃ for 2 hours to remove residual moisture. Remove the product and grind it using a mortar and pestle. Place the ground powder in a muffle furnace and calcine it at 550℃ for 4 hours to remove the template and obtain the final product.

[0031] Comparative Example 4: Only the first ultrasound was performed; no second ultrasound was performed. The preparation method of kaolin-based ZSM-5 molecular sieve includes the following steps: 1) Place the purified kaolin in a muffle furnace and calcine it to 650℃ for 1 hour; 2) Weigh 5g of kaolin calcined at 650℃ and 80g of sodium silicate nonahydrate and dissolve them in 558mL of deionized water. Then add 6.293g of TPAOH template agent and 0.614g of BDDA surfactant and stir well on a magnetic stirrer.

[0032] 3) Adjust the pH of the solution to 10±0.1 by adding 2M sulfuric acid solution dropwise. The solution will gradually form a gel. Then, use a stirrer to thoroughly mix the gel for 2 hours to ensure that the precipitate and solution are fully and evenly mixed.

[0033] 4) The precursor was then immediately immersed in a 0°C ice water bath and stirred at 250 rpm for 16 hours. After that, it was taken out and placed in an ultrasonic oscillator and ultrasonically oscillated at 300W and 40kHz for 120 seconds. 5) After ultrasound, let stand for 5 minutes, then raise the water bath temperature from 0℃ to 25℃ at a rate of 1℃ / min and maintain it for 30 minutes to avoid thermal shock. Then slowly heat to 80℃ and age in water bath for 6 hours. 6) After aging, transfer the precursor to a hydrothermal reactor; 7) After sealing the reactor, place it in an oven and carry out a hydrothermal crystallization reaction at 150℃ for 72 hours. After the reaction is complete, remove the product from the reactor, wash it repeatedly with ultrapure water, centrifuge it three times, and then transfer it to an evaporating dish; 8) Dry the product in a drying oven at 120℃ for 2 hours to remove residual moisture. Remove the product and grind it using a mortar and pestle. Place the ground powder in a muffle furnace and calcine it at 550℃ for 4 hours to remove the template and obtain the final product.

[0034] Comparative Example 5: Only the second ultrasound was performed; the first ultrasound was not performed. The preparation method of kaolin-based ZSM-5 molecular sieve includes the following steps: 1) Place the purified kaolin in a muffle furnace and calcine it to 650℃ for 1 hour; 2) Weigh 5g of kaolin calcined at 650℃ and 80g of sodium silicate nonahydrate and dissolve them in 558mL of deionized water. Then add 6.293g of TPAOH template agent and 0.614g of BDDA surfactant and stir well on a magnetic stirrer.

[0035] 3) Adjust the pH of the solution to 10±0.1 by adding 2M sulfuric acid solution dropwise. The solution will gradually form a gel. Then, use a stirrer to thoroughly mix the gel for 2 hours to ensure that the precipitate and solution are fully and evenly mixed.

[0036] 4) The precursor was then immediately immersed in a 0°C ice water bath and stirred at 250 rpm for 16 hours before being removed. 5) Then raise the water bath temperature from 0°C to 25°C at a rate of 1°C / min and maintain it for 30 minutes to avoid thermal shock, and then slowly heat it to 80°C and age it in the water bath for 6 hours. 6) After aging, ultrasonic treatment is performed at 200W, 30kHz for 60s. The precursor is then transferred to a hydrothermal reactor. 7) After sealing the reactor, place it in an oven and carry out a hydrothermal crystallization reaction at 150℃ for 72 hours. After the reaction is complete, remove the product from the reactor, wash it repeatedly with ultrapure water, centrifuge it three times, and then transfer it to an evaporating dish; 8) Dry the product in a drying oven at 120℃ for 2 hours to remove residual moisture. Remove the product and grind it using a mortar and pestle. Place the ground powder in a muffle furnace and calcine it at 550℃ for 4 hours to remove the template and obtain the final product.

[0037] Table 1

[0038] The samples obtained in Example 1 and each comparative example were added at a rate of 0.05 g to 10 mL of a simulated fluoride and phosphorus pollution solution prepared with K₂HPO₄ and NaF. The fluoride concentration in the pollution solution was 10 mg / L, and the phosphorus concentration was 30 mg / L. After 2 hours of water remediation, the fluoride and phosphorus removal rates were compared. The adsorption experiment results showed that the kaolin-based ZSM molecular sieve obtained by adding the gemini surfactant gBDDA and adding an ice-water bath treatment significantly improved the adsorption efficiency for fluoride and phosphorus. Comparing with Comparative Example 1, the addition of the gemini surfactant gBDDA, with its dual quaternary ammonium groups, can simultaneously guide the formation of micropores and mesopores, resulting in a better pore structure in the molecular sieve and thus a better adsorption capacity for fluoride and phosphorus. Comparing with Comparative Example 2 (ice bath only, no gBDDA, no ultrasound), the adsorption capacity was lower than that of the examples. This shows that the ice bath reduces the reaction and diffusion rates during the formation process, allowing for a more uniform distribution of silicon and aluminum species, which is beneficial for subsequent nucleation. Although it may reduce the aging rate, the negative effects of the ice bath can be effectively avoided by ultrasound treatment. The comparison with Comparative Examples 4 and 5 shows that the first ultrasonic treatment after the ice bath is aimed at the precursor after the ice bath to avoid Ostwald ripening when the temperature rises. At the same time, the local hot spots generated by ultrasonic cavitation can also promote the formation of the core and shell of the precursor, thus obtaining a molecular sieve with stronger adsorption capacity. In contrast, the ultrasonic treatment after the water bath is more to make the precursor system more uniformly distributed and promote the subsequent crystallization reaction. Figure 1The image shows the XRD pattern of a kaolin-based ZSM molecular sieve synthesized using ice crystal crystallization optimization (Example 1 product). It clearly exhibits the unique five-finger peak pattern characteristic of ZSM-5 molecular sieves, with its characteristic waveform mainly existing between 2θ values ​​of "7°~9°" and "22°~25°", typical of crystalline materials. Analysis using Jade software shows that the molecular sieve prepared by the method of this invention has a relative crystallinity exceeding 110% compared to commercially available molecular sieves. This indicates that the molecular sieve synthesized using the optimized method has stronger crystallinity. Compared to commercially available ZSM-5 molecular sieves, its pore structure is more regular and uniform, with better consistency in pore size. This means it can more accurately selectively adsorb molecules based on their size, shape, and other characteristics. This indicates that the improved molecular sieve has a more developed pore structure and a larger specific surface area, providing more adsorption sites for molecules, enabling the molecular sieve to adsorb more target molecules and resulting in better catalytic and adsorption performance.

[0039] SEM characterization of kaolin-based ZSM molecular sieve (Example 1) Figure 2 (Example 1 Product) shows that the ZSM-5 method with optimized ice crystal crystallization used in this invention gives the material a regular and smooth particle morphology. The morphology and size of each grain are highly uniform, with a particle size of about 25um×25um×15um. The dispersion and uniformity are good, the crystallization is good, the crystal morphology is complete, and the grain surface is smoother and has fewer impurities than the traditional method. This shows that the optimized ice crystal crystallization in the synthesis route plays a key role in suppressing poor crystallization and reducing the formation of impurities.

[0040] The adsorption and solidification of fluoride and phosphorus pollution in water was studied using the kaolin-based ZSM-5 molecular sieve prepared in Example 1. A certain amount of K₂HPO₄ and NaF were weighed to prepare a fluoride and phosphorus pollution simulation solution. Adding a certain amount of this kaolin-based ZSM-5 molecular sieve to the solution showed that 0.05g of this kaolin-based ZSM-5 molecular sieve achieved a fluoride removal efficiency of over 80% and a phosphorus removal rate of over 85% for 2 hours in 10mL of water with a fluoride concentration of 10mg / L and a phosphorus concentration of 30mg / L. This demonstrates that the optimized method using ice crystal crystallization... Compared to traditional commercial ZSM-5 molecular sieves, ZSM-5 molecular sieves are more effective at treating phosphorus and fluoride pollution in water. The kaolin-based ZSM-5 molecular sieve exhibits excellent remediation efficiency. When the dosage of ZSM-5 molecular sieve increases from 0.02g to 0.05g, the fluoride removal efficiency increases from 45% to 80% within 2 hours, and the phosphorus removal rate increases from 50% to over 85%. These results demonstrate that the ice-crystallized kaolin-based ZSM-5 molecular sieve is characterized by rapid onset and high efficiency in treating fluoride and phosphorus pollution in water. Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of preparing a molecular sieve from ice crystal crystallized kaolin, characterized by: The method comprises the following steps: S1: Put the purified kaolin in a muffle furnace to calcine and destroy the internal structure, ready for use; S2: Take the calcined kaolin and dissolve it in deionized water with sodium silicate nonahydrate, add the surfactants tetrapropylammonium hydroxide and gemini surfactant butane-1, 4-bis (dodecyl dimethyl ammonium bromide), stir and heat to uniformity; S3: Use H2SO4 to adjust the pH, form a colloidal body, and stir to fully disperse and mix the precipitate; S4: Immerse the precursor in a 0℃ ice water bath, take it out after the ice water bath, and perform ultrasonic oscillation treatment; S5: After ultrasonic treatment, stand still, then warm up the water bath and keep it, then warm up the water bath and age; S6: After aging, ultrasonically treat the system at room temperature again; S7: Transfer the gel after ultrasonic treatment to a hydrothermal reaction kettle and perform hydrothermal crystallization reaction; S8: Take out the product, centrifuge and wash it, put the substrate in an evaporating dish, dry it, grind it, and then put it in a muffle furnace to calcine and remove the template agent; Complete the preparation of the kaolin molecular sieve.

2. The method for preparing molecular sieves from kaolin crystallized ice crystals according to claim 1, characterized in that: In the step S1, calcine to 500~800℃, and calcine for 1~2h.

3. The method of claim 1, wherein the ice crystal grown kaolin is prepared by the steps of: In the step S2, the molar ratio of the elements Si and Al in the system is (8~10):1; the molar ratio of tetrapropylammonium hydroxide, Si, and H2O is 1:(8~12):(800~1200); the molar ratio of tetrapropylammonium hydroxide to butane-1, 4-bis (dodecyl dimethyl ammonium bromide) is (8~10):1, and the uniform stirring time is 1~2h. ​ 4. The method of claim 1, wherein the ice crystal grown kaolin is prepared by the steps of: In the step S3, the concentration of the H2SO4 solution is 1~3mol / L, and the pH is adjusted to 9~11 using H2SO4. ​ 5. The method for preparing molecular sieves from kaolin crystallized ice crystals according to claim 1, characterized in that: In the step S4, the ice crystal crystallization is in an ice water bath at 0℃±0.5℃ for 12~18h, with stirring at 200~300 rpm, and the ultrasonic oscillation treatment conditions are 100~300w, 20~40kHz, and 90~150s.

6. The method for preparing molecular sieves from kaolin crystallized ice crystals according to claim 1, characterized in that: In the step S5, after ultrasonic treatment, stand still for 4~6min, then warm up the water bath temperature from 0℃ to 25℃ at a rate of 0.5~1.5℃ / min and keep it for 25~35min, then warm up the water bath to 70~85℃, and age for 5~8h.

7. The method for preparing molecular sieves from kaolin crystallized ice crystals according to claim 1, characterized in that: In the step S6, after aging, the ultrasonic treatment conditions are 100~300W, 20~40kHz, and 30~60s.

8. The method of claim 1, wherein the ice crystal grown kaolin is prepared by the steps of: In the step S7, ​ The temperature of the hydrothermal crystallization reaction is 140~160℃, and the time of the hydrothermal crystallization is 48~72h.

9. The method for preparing molecular sieves from kaolin crystallized ice crystals according to claim 1, characterized in that: In the step S8, the drying conditions are 115~125℃ for 2~4h, and the calcination temperature is 500~600℃ for 3~5h to remove the template agent.

10. The application of the molecular sieve prepared by the method of claim 1-9 for the adsorption and recovery of phosphorus and fluorine in phosphogypsum leaching solution.

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