Modified zeolite a, method for preparing the same, and use thereof

Abstract

The application discloses modified A-type molecular sieves, a preparation method and application thereof. The A-type molecular sieves are prepared by taking fly ash floating beads as a main raw material, alkali active sites are generated by ion exchange between the A-type molecular sieves and ammonium fluoride, the alkali active sites on the surface of the molecular sieves are reacted with ammonia water, a coordination reaction between lone pair electrons and heavy metal ions is generated, and the purpose of adsorption is achieved.

Description

A modified type A molecular sieve, its preparation method and application Technical Field

[0001] This invention relates to the field of molecular sieve adsorption, specifically to a modified type A molecular sieve, its preparation method, and its application. Background Technology

[0002] Traditional methods for treating nuclear wastewater include chemical precipitation, ion exchange, and membrane separation. While these methods can remove radioactive substances from wastewater to some extent, they suffer from low efficiency, high cost, and the potential for secondary pollution. In recent years, molecular sieve technology, due to its unique pore structure and highly selective adsorption performance, has been introduced into the field of nuclear wastewater treatment, demonstrating promising application prospects.

[0003] The synthesis of type A molecular sieves is typically affected by the purity of the raw materials. Impurities in the raw materials can lead to irregular molecular sieve structures, low product purity, and pore blockage. To meet the different adsorption requirements of molecular sieves, modification is usually necessary, which necessitates considering the impact of the modification process on ion adsorption. Currently, several problems remain in the modification process of molecular sieves, such as insufficient adsorption capacity for ions, inadequate adsorption removal rates, and secondary pollution caused during modification. Existing molecular sieves used in nuclear wastewater treatment are either too expensive to be widely applied, or have complex synthesis steps and poor adsorption performance. These factors significantly limit the efficient treatment of nuclear wastewater. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a modified type A molecular sieve, its preparation method, and its application. This invention prepares type A molecular sieves using fly ash cenospheres as the main raw material. The sieves undergo ion exchange with ammonium fluoride to generate basic active sites. These basic sites on the surface of the molecular sieve then react with ammonia water, where the lone pairs of electrons on the ammonia water surface coordinate with heavy metal ions, thereby achieving adsorption.

[0005] To address the aforementioned technical problems, the first aspect of this invention is to provide a method for preparing modified type A molecular sieves, specifically comprising the following steps:

[0006] S1. Add fly ash cenospheres and alkaline compounds to water and mix thoroughly to obtain a mixed solution;

[0007] S2. The mixed solution is reacted using a hydrothermal method to obtain type A molecular sieve;

[0008] S3. Add type A molecular sieve to ammonium fluoride solution, sonicate and then calcine to obtain activated type A molecular sieve;

[0009] S4. The activated type A molecular sieve from S3 is added to an ammonia solution to react and obtain the modified type A molecular sieve.

[0010] Further, in step S1, the alkaline compound is selected from one or more of sodium hydroxide, lithium hydroxide, and potassium hydroxide; the purpose is to provide an alkaline environment to dissolve fly ash cenospheres.

[0011] Further, in step S1, the mass ratio of the fly ash cenospheres, alkaline compound and water is 1:(0.5-4):(20-40); preferably 1:2.32:20.

[0012] Further, in step S2, the hydrothermal temperature is 90-110℃, and the purpose of hydrothermal treatment is to promote the crystallization of type A molecular sieves; preferably 100℃; the hydrothermal reaction time is 3-12h; preferably 3h; the synthesis of type A molecular sieves is affected by the hydrothermal temperature or hydrothermal time. When the hydrothermal temperature is below 90℃ or when the hydrothermal time is less than 3h, the crystallization of type A molecular sieves is insufficient and molecular sieves with good crystallinity cannot be formed.

[0013] Further, in step S3, the calcination temperature is 350-600℃, for example, 350℃, 400℃, 500℃ and 600℃, including but not limited to the temperatures listed above, preferably 350-500℃, more preferably 450℃.

[0014] Furthermore, in step S3, the calcination time is 1-8 hours, for example, 1 hour, 3 hours, 5 hours, 8 hours, etc., including but not limited to the temperatures listed above; preferably 3 hours.

[0015] Further, in step S3, the ultrasonication time is 1-12 hours; preferably 2-4 hours. Ultrasonication helps ammonium fluoride enter the pores of the molecular sieve. During high-temperature calcination, ammonium ions lose protons and transform into ammonia gas, which then leaves. The protons react with the Al sites in the molecular sieve framework to generate aluminate ions; fluoride ions react with the aluminum in the framework to generate hexafluoroaluminate ions, thereby achieving dealuminization of the type A molecular sieve and activating the basic sites.

[0016] Further, in step S4, the mass fraction of ammonia in the ammonia solution is 8-12%; for example, 8%, 9%, 10%, 11%, 12%, etc., including but not limited to the mass fractions listed above.

[0017] Furthermore, in step S4, the reaction time is 21-24 hours; for example, 21 hours, 22 hours, 23 hours, and 24 hours, including but not limited to the times listed above.

[0018] The second aspect of the present invention is to provide a modified type A molecular sieve prepared by the preparation method described in the first aspect.

[0019] A third aspect of the present invention is to provide the application of the modified type A molecular sieve described in the second aspect in the adsorption of ions in a radioactive solution.

[0020] Furthermore, the radioactive solution ions are cobalt ions, cesium ions, samarium ions, or praseodymium ions.

[0021] Furthermore, the concentration of the radioactive solution is 500-1250 mg / L.

[0022] Furthermore, the solid-liquid ratio of the modified type A molecular sieve to the radioactive solution is 1g:(100-1000)mL; for example, 1g:100mL, 1g:200mL, 1g:300mL, 1g:400mL, 1g:500mL, 1g:600mL, 1g:700mL, 1g:800mL, 1g:900mL, 1g:1000mL, etc., including but not limited to the liquid-solid ratios listed above; preferably 1g:(100-600)mL.

[0023] The beneficial effects of this invention are:

[0024] 1. This invention first activates type A molecular sieves with ammonium fluoride solution to expose more alkaline sites, and then modifies them with ammonia water. The modified molecular sieve contains lone pairs of electrons in NH3, which can undergo coordination reactions with metal ions, thereby achieving the purpose of adsorption.

[0025] 2. The modified type A molecular sieve prepared by this invention is simple to prepare, and the modification process is carried out at room temperature without the need for a heating step. Its high adsorption performance and good selectivity make it a promising candidate for application in environmental pollution problems. Attached Figure Description

[0026] Figure 1 shows the XRD patterns of the A-24 modified molecular sieve prepared in Example 1 of this invention and the commercial 4A type molecular sieve;

[0027] Figure 2 is a graph showing the adsorption rate of 1000 mg / L Co(NO3)2 by the A-24 modified molecular sieve prepared in Example 1 of this invention. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0029] In an embodiment of the present invention, the preparation method of type A molecular sieve is as follows: 10g of fly ash cenospheres and 23.2g of sodium hydroxide are dissolved in 200mL of deionized water, mixed, and then microwave-heated at 80°C for 2h to obtain mixture I. Mixture I is transferred to a hydrothermal synthesis reactor and crystallized at 100°C for 3h to obtain primary product I. Primary product I is ultrasonically washed, centrifuged, and subjected to solid-liquid separation. After drying at 105°C for 3 hours, the final product, type A molecular sieve, is obtained.

[0030] Example 1

[0031] This embodiment relates to a series of methods for preparing modified type A molecular sieves, and the specific operation steps are as follows:

[0032] 3g of type A molecular sieve was added to 60mL of 0.5mol / L ammonium fluoride aqueous solution and ultrasonically vibrated at room temperature for 4h. After washing and filtering the product, it was calcined at 450℃ for 3h and cooled to obtain activated type A molecular sieve. The activated type A molecular sieve was added to 60mL of 10% ammonia aqueous solution and magnetically stirred at 60℃ for 18h, 21h, 24h, 27h, and 30h, respectively. After washing, solid-liquid separation, and drying, modified type A molecular sieve was obtained. The modified type A molecular sieve with magnetic stirring time of 24h was named A-24.

[0033] The modified molecular sieves prepared at different reaction times were tested for adsorption on a 1000 mg / L Co(NO3)2 sample solution at a solid-liquid ratio of 1:100 g / mL. The test results are shown in Table 1.

[0034] Table 1

[0035] Magnetic stirring time (h) Co 2+ Adsorption rate (%) 1887.22 190.32 493.22 787.93 084.6 surface

[0036] The results showed that within 24 hours, extending the stirring time was beneficial for Co 2+ The adsorption of Co occurs; however, as the reaction time increases further, the molecular sieve framework is corroded, leading to the adsorption of Co. 2+ The adsorption rate decreases.

[0037] The prepared A-24 molecular sieve was used to perform adsorption tests on Pr(NO3)3 samples of 500, 750, 1000, and 1250 mg / L at a solid-liquid ratio of 1:200 g / mL. The test results are shown in Table 2.

[0038] Table 2

[0039] Pr 3+ Ion concentration (mg / L) Pr 3+Adsorption capacity (mg / g): 500 144.67, 50 177.4, 1000 192.3, 1250 202.5 surface

[0040] As the ion concentration increases, the adsorption capacity gradually increases, and the molecular sieve's adsorption capacity for Pr... 3+ The maximum ion adsorption capacity is 202.5 mg / g.

[0041] Example 2

[0042] This embodiment relates to a series of methods for preparing modified type A molecular sieves. To investigate the effect of ammonia concentration on the performance of the modified molecular sieves at a preferred reaction time of 24 hours, the following experiment was designed, and the specific operating steps are as follows:

[0043] 3g of the obtained type A molecular sieve was added to 60mL of 0.5mol / L ammonium fluoride aqueous solution and ultrasonically vibrated at room temperature for 4h. After washing and filtering the product, it was calcined at 450℃ for 3h and cooled to obtain activated type A molecular sieve. The activated type A molecular sieve was then added to 60mL of 8%, 9%, 10%, 11%, or 12% ammonia aqueous solution, respectively, and magnetically stirred at 60℃ for 24h. After washing, solid-liquid separation, and drying, the modified type A molecular sieve was obtained.

[0044] The modified molecular sieves prepared with different ammonia concentrations were tested for adsorption on a 1000 mg / L Co(NO3)2 sample solution at a solid-liquid ratio of 1:100 g / mL. The test results are shown in Table 3.

[0045] Table 3

[0046] Ammonia concentration (%) Co 2+ Adsorption rate (%) 889.1 991.4 1093.2 1188.7 1287.5 surface

[0047] The results showed that the adsorption effect of cobalt ions was best when the mass fraction of ammonia was 8-10%.

[0048] Example 3

[0049] This embodiment relates to a method for preparing modified type A molecular sieves. To investigate the effect of different inorganic ammonia on molecular sieve modification, the specific operation steps are as follows:

[0050] 3g of the obtained type A molecular sieve was added to 60mL of 0.5 mol / L aqueous solutions of ammonium fluoride, ammonium chloride, ammonium nitrate, and ammonium oxalate, respectively. The solutions were ultrasonically vibrated at room temperature for 4 hours. After washing and filtering, the products were calcined at 450℃ for 3 hours and cooled to obtain activated type A molecular sieves. The activated type A molecular sieves were then added to 60mL of 10% ammonia aqueous solution and magnetically stirred at 60℃ for 24 hours. After washing, solid-liquid separation, and drying, modified type A molecular sieves were obtained.

[0051] The modified molecular sieves prepared with different inorganic ammonia concentrations were tested for adsorption on a 750 mg / L Cs(NO3)2 sample solution at a solid-liquid ratio of 1:300 g / mL. The test results are shown in Table 4.

[0052] Table 4

[0053] Types of inorganic ammonium aqueous solutions Cs 2+ Adsorption rates (%): Ammonium fluoride 89.3%, Ammonium chloride 80.1%, Ammonium sulfate 73.9%, Ammonium nitrate 74.5%, Ammonium oxalate 73.1%. surface

[0054] The results showed that fluoride and ammonium ions in ammonium fluoride aqueous solution had a synergistic effect on the dealumination of type A molecular sieves, with the best activation effect. In aqueous solutions of ammonium sulfate, ammonium nitrate, and ammonium oxalate, the anions were too large to enter the pores of type A molecular sieves and interact with the framework aluminum, resulting in a weakened activation effect.

[0055] Example 4

[0056] This embodiment relates to a method for preparing a modified type A molecular sieve, and the specific operation steps are as follows:

[0057] 3g of type A molecular sieve was added to 60mL of 0.5mol / L ammonium fluoride aqueous solution, and ultrasonically vibrated at room temperature for 2h, 4h, 8h, and 12h respectively. After washing and filtering the product, it was calcined at 450℃ for 3h, and after cooling, activated type A molecular sieve was obtained. The activated type A molecular sieve was added to 60mL of 10% ammonia aqueous solution, and magnetically stirred at 60℃ for 24h. After washing, solid-liquid separation, and drying, modified type A molecular sieve was obtained.

[0058] The adsorption of modified type A molecular sieve prepared with different ultrasonic oscillation times on 750 mg / L Sm(NO3)3 sample solution was tested at a solid-liquid ratio of 1:600 ​​g / mL. The test results are shown in Table 5.

[0059] Table 5

[0060]

[0061]

[0062] The results showed that, within 2-4 hours, extending the ultrasonic oscillation time facilitated the entry of fluoride and ammonium ions into the pores of the type A molecular sieve. With prolonged ultrasonic time, excess fluoride and ammonium ions entered the pores of the type A molecular sieve. During calcination, excessive aluminum framework was removed, leading to the collapse of the molecular sieve framework and a significant decrease in adsorption efficiency.

[0063] Comparative Example 1

[0064] This comparative example relates to a method for preparing a modified molecular sieve, and the specific operation steps are as follows:

[0065] 3g of type A molecular sieve was added to 60mL of 10% ammonia solution and magnetically stirred at 60℃ for 24h. After washing, solid-liquid separation and drying, the modified type A molecular sieve was obtained.

[0066] Comparative Example 2

[0067] This comparative example relates to a method for preparing a modified molecular sieve, and the specific operation steps are as follows:

[0068] 3g of type A molecular sieve was added to 60mL of 0.5mol / L ammonium fluoride aqueous solution, and ultrasonically vibrated at room temperature for 4h. After washing and filtering the product, it was calcined at 450℃ for 3h, and after cooling, activated type A molecular sieve was obtained. The activated type A molecular sieve was added to 60mL of 10% cysteine ​​aqueous solution, and magnetically stirred at 60℃ for 24h. After washing, solid-liquid separation, and drying, modified type A molecular sieve was obtained.

[0069] Performance testing and characterization

[0070] 1. Characterization

[0071] Figure 1 shows a comparison of the XRD patterns of the A-24 molecular sieve prepared in Example 1 and the commercially available 4A molecular sieve. The XRD peak positions are consistent, indicating that the present invention has successfully prepared the A-type molecular sieve.

[0072] 2. Adsorption performance test

[0073] Figure 2 shows the time adsorption curve of 1000 mg / L Co(NO3)2 on the A-24 modified type A molecular sieve prepared in Example 1. The results show that the adsorption was completed in 240 min.

[0074] To test the adsorption of different elements by the prepared molecular sieves, the specific testing procedure is as follows: Mother liquors of Co(NO3)2, Cs2CO3, Sm(NO3)3, and Pr(NO3)3 were prepared, each with a concentration of 10 g / L. The mother liquors were diluted with deionized water to 1 g / L, and the modified molecular sieves were added according to different solid-liquid ratios. The mixtures were then fixed on a long-axis mixer and mixed for 3 hours to ensure sufficient adsorption, followed by immediate filtration. The filtrate was diluted with a 2% dilute nitric acid solution to obtain a sample solution. The ion concentration in the sample solution was measured by ICP-OES (or ICP-MS).

[0075] Table 6 shows the adsorption performance of the 4A type molecular sieve (purchased directly from Nankai University Catalyst Factory) on 1000 mg / L of Co(NO3)2, Cs2CO3, Sm(NO3)3, and Pr(NO3)3, in the examples, comparative examples, and adsorption tests. The solid-liquid ratio of the molecular sieve to the Co(NO3)2 and Cs2CO3 solutions was 1:250 g / mL, and the solid-liquid ratio to the Sm(NO3)3 and Pr(NO3)3 solutions was 1:500 g / mL.

[0076] Table 6

[0077]

[0078] The results showed that the unmodified commercial 4A molecular sieve exhibited the worst adsorption performance for radioactive ions. The ammonium fluoride-activated molecular sieve exposed more basic sites, which facilitated the complete modification of ammonia water and thus improved the adsorption effect on elements (Comparative Example 1). The activated molecular sieve modified with organic amines (Comparative Example 2) showed a worse adsorption effect for radioactive ions compared to A-24. This may be because the molecular weight of the organic amine is too large, and the chain-like alkanes of the organic amine hinder ion exchange between organic ammonia and the molecular sieve.

[0079] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing modified type A molecular sieves, characterized in that, Includes the following steps: S1. Fly ash cenospheres and an alkaline compound are added to water and mixed evenly to obtain a mixed solution; the mass ratio of fly ash cenospheres, alkaline compound, and water is 1:(0.5-4):(20-40); S2. The mixed solution is reacted using a hydrothermal method to obtain type A molecular sieve; the hydrothermal temperature is 90-110 ℃, and the hydrothermal reaction time is 3-12 h; S3. The type A molecular sieve from S2 is added to an ammonium fluoride solution, sonicated for 2-4 h, and then calcined to obtain an activated type A molecular sieve; the calcination temperature is 350-600 ℃; S4. The activated type A molecular sieve from S3 is added to an ammonia solution and reacted to obtain the modified type A molecular sieve; the mass fraction of ammonia in the ammonia solution is 8-12%.

2. The preparation method according to claim 1, characterized in that, In step S4, the reaction time is 21-24 h.

3. A modified type A molecular sieve prepared by the method according to any one of claims 1-2.

4. The application of the modified type A molecular sieve as described in claim 3 in the adsorption of ions in radioactive solutions.

5. The application as described in claim 4, characterized in that, The ions are cobalt ions, cesium ions, samarium ions, or praseodymium ions.

6. The application as described in claim 4, characterized in that, The concentration of the radioactive solution is 500-1250 mg / L.

7. The application as described in claim 4, characterized in that, The solid-liquid ratio of the modified type A molecular sieve to the radioactive solution is 1g:(100-1000)mL.

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