A tetrachloroaluminate modified type a molecular sieve, a preparation method and application thereof

Abstract

This invention discloses a tetrachloroaluminate-modified type A molecular sieve, its preparation method, and its application. The invention uses fly ash cenospheres as the main raw material to prepare a type A molecular sieve. Through modification with a mixture of fly ash and tetrachloroaluminate, it exhibits excellent adsorption performance for cobalt, cesium, and strontium ions. The type A molecular sieve prepared in this application has a good synergistic effect with tetrachloroaluminate, effectively solving the problems of complex processes, high costs, and poor adhesion of existing molecular sieve adsorbent preparation methods in the market. 137 Cs, 60 Co, 90 This method addresses the problem of low adsorption rates of major hazardous nuclides in radioactive wastewater such as Sr, and can be used to adsorb radionuclides in nuclear wastewater.

Description

Technical Field

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

[0002] With the rapid development of the global nuclear energy industry, the safe disposal of radioactive waste has become an increasingly prominent issue. 60 Co, 135 Sr, 90 Radioactive nuclides such as Cs are among the most hazardous components of radioactive waste, posing an irreversible threat to human health and the ecological environment.

[0003] While current adsorption technologies on the market, such as those using gel balls, resins, and molecular sieves, have achieved some success, they generally suffer from problems such as complex operating procedures, high costs, long processing times, and large amounts of waste, which limit their widespread application.

[0004] For example, a Chinese invention patent CN115672286A from Sichuan University proposes a method for loading potassium zirconium pyrophosphomolybdate onto collagen fibers as a carrier for efficient adsorption and separation. 135 Cs and 90 Sr was applied to chromatographic column packing material and showed good adsorption effect. However, the raw materials used in this method are expensive and the process is complicated.

[0005] Furthermore, chemical modification of zeolite molecular sieves has been widely studied as a potential solution, especially the use of specific solutions to perform ion exchange on zeolite molecular sieves to enhance their ability to remove metal ions from radioactive solutions. For example, using acids or alkalis to dissolve the molecular sieve framework and change the silica-alumina ratio can improve the adsorption rate of the molecular sieve to some extent, but it causes significant damage to the molecular sieve crystals, and the waste liquid after the reaction is difficult to treat. Another approach is to use amino acids to modify the molecular sieve surface through graft adsorption, but this requires complex modification conditions and is unstable in high-concentration or strong acid / alkali solutions, resulting in poor adsorption effects. Finally, when using amination-modified molecular sieves, the modification process inevitably generates a large amount of waste liquid and waste gas, causing significant environmental pollution and failing to meet green environmental protection requirements. Summary of the Invention

[0006] The technical problem this invention aims to solve is to provide a tetrachloroaluminate-modified type A molecular sieve. This sieve reduces the original aluminum-to-silicon ratio and alters the original pore size and shape through ion exchange between metal cations and Al in the molecular sieve framework. Simultaneously, during the ion exchange process, tetrachloroaluminate ions adsorb onto the pores and surface of the molecular sieve, providing more active sites and thus improving the adsorption rate. This preparation method is simple, easy to operate and implement at room temperature, and exhibits excellent adsorption performance for a variety of ions.

[0007] To address the aforementioned technical problems, the first aspect of this invention provides a method for preparing tetrachloroaluminate-modified type A molecular sieves, specifically comprising the following steps:

[0008] S1. Add fly ash cenospheres and alkaline compounds to water and mix thoroughly to obtain a mixed solution;

[0009] S2. The mixed solution is reacted using a hydrothermal method to obtain type A molecular sieve;

[0010] S3. The type A molecular sieve is added to the mixture to react and obtain the modified type A molecular sieve; the mixture is a mixture of saturated tetrachloroaluminate aqueous solution and chloride salt solution.

[0011] Furthermore, 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.

[0012] Furthermore, the mass ratio of the fly ash cenospheres, alkaline compound, and water is 1:(0.5-4):(20-40); preferably 1:2.32:20.

[0013] Furthermore, the tetrachloroaluminate is selected from lithium tetrachloroaluminate and / or sodium tetrachloroaluminate.

[0014] 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.

[0015] Furthermore, in step S3, the purpose of adding chloride is to improve the stability of tetrachloroaluminate and facilitate ion exchange with molecular sieves.

[0016] Furthermore, in step S3, the concentration of chloride in the mixture can range from 0.1 mol / L to a saturated solution; the chloride is selected from one or more of sodium chloride, potassium chloride, and lithium chloride, preferably sodium chloride.

[0017] Further, in step S3, the solid-liquid ratio of the type A molecular sieve to the tetrachloroaluminate solution is 1g:(10-35)mL; preferably 1g:(15-35)mL.

[0018] Further, in step S3, the reaction time is 10-24 hours; for example, 10 hours, 15 hours, 20 hours or 24 hours, etc., including but not limited to the times listed above; preferably 15-24 hours.

[0019] A second aspect of the present invention is to provide a modified type A molecular sieve prepared by the method described in the first aspect.

[0020] 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.

[0021] Furthermore, the ions in the radioactive solution are cobalt ions, strontium ions, or cesium ions.

[0022] Furthermore, the concentration of the radioactive solution is 100-1000 mg / L.

[0023] The beneficial effects of this invention are:

[0024] 1. This invention utilizes sodium tetrachloroaluminate-modified type A molecular sieves to prepare high-performance modified molecular sieve adsorbents by leveraging the synergistic effect of tetrachloroaluminate ions and the pore size of type A molecular sieves. The adsorption and removal rate can reach 99%, and it can adsorb various radioactive elements. On one hand, the metal cations in tetrachloroaluminate can undergo ion exchange with Al in the molecular sieve framework; on the other hand, tetrachloroaluminate ions can adsorb inside or on the surface of the molecular sieve pores, providing more exchange active sites.

[0025] 2. The fly ash cenospheres used in this invention are inexpensive, obtained from industrial waste fly ash, and have advantages such as uniform particle size, low impurity content, and easy activation. The molecular sieve preparation process does not require the addition of silicon or aluminum sources, nor does it require the use of complex modifiers. Compared with existing molecular sieve synthesis technologies, this not only simplifies the production process but also reduces energy consumption and costs.

[0026] 3. The molecular sieve prepared by this invention is more conducive to the adsorption of radioactive element ions in solutions with higher concentrations. Attached Figure Description

[0027] Figure 1 These are X-ray diffraction (XRD) patterns of the modified molecular sieves prepared in Examples 1 and 2 and Comparative Examples 2, 3 and 6 of this invention.

[0028] Figure 2This is a scanning electron microscope (SEM) image of the sodium tetrachloroaluminate modified type A molecular sieve prepared in Example 1 of the present invention. Detailed Implementation

[0029] 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.

[0030] Example 1

[0031] This embodiment relates to a method for preparing tetrachloroaluminate-modified type A molecular sieves, including the following steps:

[0032] (1) Add 10g of fly ash cenospheres and 23.2g of NaOH additive to 200mL of deionized water, reflux at 80℃ for 2h, and stir continuously to allow the fly ash cenospheres and NaOH additive to react fully to form a mixed solution.

[0033] (2) The mixed solution in step (1) is crystallized in a hydrothermal reactor at 100°C for 3 hours. The resulting molecular sieve turbid liquid is ultrasonically treated for 1 minute, centrifuged to separate the solid and liquid phases, and the aqueous phase is removed. The liquid is then dried in an oven at 95°C for 24 hours to obtain type A molecular sieve.

[0034] (3) Dissolve excess sodium tetrachloroaluminate in 100 mL of deionized water at 30 °C, add NaCl to the solution until saturated, and filter to obtain a mixture.

[0035] (4) The type A molecular sieve obtained in step (2) is placed into the mixture obtained in step (3) and mixed at a solid-liquid ratio (S / L) of 1g:15mL. The mixture is stirred and heated at 35℃ for 15h to allow the molecular sieve to react with the mixture. After ultrasonic treatment for 1 minute, the mixture is centrifuged and then dried in a 95℃ oven for 24h to obtain the modified type A molecular sieve.

[0036] Example 2

[0037] This embodiment relates to a method for preparing tetrachloroaluminate modified type A molecular sieve. The only difference between this embodiment and Example 1 is that sodium tetrachloroaluminate in step (3) is replaced with lithium tetrachloroaluminate.

[0038] Example 3

[0039] This embodiment relates to a method for preparing sodium tetrachloroaluminate modified type A molecular sieve. The only difference between this embodiment and Example 1 is that the solid-liquid ratio (S / L) in step (4) of Example 1 is changed to 1g:35mL.

[0040] Example 4: 0.1 g / mL sodium chloride + saturated sodium tetrachloroaluminate

[0041] This embodiment relates to a method for preparing sodium tetrachloroaluminate modified type A molecular sieve. The difference between this embodiment and embodiment 1 is only in step (3).

[0042] The operating steps are as follows: Dissolve sodium chloride in 100 mL of deionized water at 30 °C, wherein the concentration of sodium chloride is 0.1 g / mL, add sodium tetrachloroaluminate until saturated, and filter to obtain a mixed solution.

[0043] Example 5: Temperature is room temperature

[0044] This embodiment relates to a method for preparing sodium tetrachloroaluminate modified type A molecular sieve. The only difference between this embodiment and Example 1 is that there is no heating step in step (4).

[0045] The operation steps are as follows: The type A molecular sieve obtained in step (2) is placed into the mixture in step (3), the solid-liquid ratio (S / L) is 1g:15mL, and the mixture is stirred at room temperature for 15h to allow the molecular sieve to react with the mixture. After ultrasonic treatment for 1 minute, the mixture is centrifuged and then placed in a 95℃ oven to dry for 24h to obtain the modified type A molecular sieve.

[0046] Example 6: Increase reaction time by 24 hours

[0047] This embodiment relates to a method for preparing sodium tetrachloroaluminate modified type A molecular sieve. The only difference between this embodiment and embodiment 1 is that the heating time in step (4) is 24 hours.

[0048] Comparative Example 1

[0049] This comparative example relates to a method for preparing a molecular sieve. The only difference between this comparative example and Example 1 is that this comparative example only has steps (1) and (2).

[0050] Comparative Example 2

[0051] This comparative example uses standard 4A type zeolite molecular sieve produced by the Catalyst Factory of Nankai University, Tianjin.

[0052] Comparative Example 3

[0053] This comparative example relates to a method for preparing NaCl-modified type A molecular sieves. The specific preparation method is as follows:

[0054] (1) Add 10g of fly ash cenospheres and 23.2g of NaOH additive to 200mL of deionized water, reflux at 80℃ for 2h, and stir constantly to allow the fly ash cenospheres and NaOH additive to react fully to form a mixed solution.

[0055] (2) Crystallize the mixed solution in step (1) in a 100℃ reactor for 3 hours, sonicate the obtained molecular sieve turbid liquid for 1 minute, centrifuge to separate the solid and liquid and remove it, and dry it in a 95℃ oven for 24 hours to obtain type A molecular sieve.

[0056] (3) Dissolve excess sodium chloride in 100 mL of deionized water at 30 °C, and filter to obtain a mixed solution;

[0057] (4) The type A molecular sieve obtained in step (2) is placed into the sodium chloride saturated solution in step (3) and mixed at a solid-liquid ratio of 1g:15mL (S / L). The mixture is stirred and heated at 35°C for 15h to allow the molecular sieve to react with the sodium chloride saturated solution. After ultrasonic treatment for 1 minute, the mixture is centrifuged and then dried in an 80°C oven for 24h to obtain the Na-A type molecular sieve.

[0058] Comparative Example 4

[0059] This comparative example relates to a method for preparing inorganic acid-modified type A molecular sieves. The specific preparation method is as follows:

[0060] (1) Add 10g of fly ash cenospheres and 23.2g of NaOH additive to 200mL of deionized water, reflux at 80℃ for 2h, and stir constantly to allow the fly ash cenospheres and NaOH additive to react fully to form a mixed solution.

[0061] (2) Crystallize the mixed solution in step (1) in a 100℃ reactor for 3 hours, sonicate the obtained molecular sieve turbid liquid for 1 minute, centrifuge to separate the solid and liquid and remove it, and dry it in a 95℃ oven for 24 hours to obtain type A molecular sieve.

[0062] (3) The type A molecular sieve prepared in step (2) is mixed with 1 mol / L sulfuric acid solution at a solid-liquid ratio (S / L) of 1 g: 50 mL to form a mixed solution.

[0063] (4) The mixed solution in step (3) is refluxed at 90°C for 6 hours to allow the molecular sieve and sulfuric acid to undergo an ion exchange reaction. Then, it is ultrasonically treated for 1 minute, centrifuged to separate the solid and liquid, and placed in a 95°C oven to dry for 24 hours to obtain HA type molecular sieve.

[0064] Comparative Example 5

[0065] The only difference between this comparative example and Example 1 is that the 10g fly ash cenospheres in step (1) are replaced with an equal mass of fly ash; the fly ash was purchased directly from Shanghai Thermal Power Plant.

[0066] Comparative Example 6

[0067] This comparative example relates to a method for preparing sodium tetrachloroaluminate modified ZSM-5 molecular sieve. The specific operation steps are as follows:

[0068] (1) Dissolve excess sodium tetrachloroaluminate in 100 mL of deionized water at 30 °C, add NaCl to it until saturated, and filter to obtain a mixture;

[0069] (2) The ZSM-5 molecular sieve is placed into the mixture in step (1), the solid-liquid ratio (S / L) is 1g:15mL, and the mixture is stirred and heated at 35℃ for 15h to allow the molecular sieve to react with the mixture. After ultrasonic treatment for 1 minute, the mixture is centrifuged and then dried in a 95℃ oven for 24h to obtain sodium tetrachloroaluminate modified ZSM-5 molecular sieve.

[0070] Comparative Example 7: 0.1 g / mL sodium tetrachloroaluminate + saturated sodium chloride

[0071] This comparative example relates to a method for preparing sodium tetrachloroaluminate modified type A molecular sieve. The only difference between this comparative example and Example 1 is step (3).

[0072] The operating steps are as follows: Dissolve sodium tetrachloroaluminate in 100 mL of deionized water at 30 °C. The concentration of sodium tetrachloroaluminate is 0.1 g / mL. Add sodium chloride to the solution until saturation. After filtration, a mixed solution is obtained.

[0073] Comparative Example 8

[0074] This comparative example relates to a method for preparing sodium tetrachloroaluminate modified type A molecular sieve. The only difference between this comparative example and Example 1 is that the solid-liquid ratio in step (4) of Example 1 is 1g:5mL.

[0075] The results showed that the molecular sieve was not completely dissolved, and the solid-liquid ratio was not suitable for adsorption experiments.

[0076] Comparative Example 9: Temperature 60℃

[0077] This comparative example relates to a method for preparing sodium tetrachloroaluminate modified type A molecular sieve. The only difference between this comparative example and Example 1 is that there is no heating step in step (4) of the reaction.

[0078] The operation steps are as follows: The type A molecular sieve obtained in step (2) is placed into the saturated sodium tetrachloroaluminate solution in step (3), and mixed at a solid-liquid ratio of 1g:15mL (S / L). The mixture is refluxed and stirred at 60℃ for 15h to allow the molecular sieve to react with the sodium tetrachloroaluminate solution. After ultrasonic treatment for 1 minute, the mixture is centrifuged and then dried in a 95℃ oven for 24h to obtain the modified type A molecular sieve.

[0079] Comparative Example 10: Time reduced by 3 hours

[0080] This comparative example relates to a method for preparing sodium tetrachloroaluminate modified type A molecular sieve. The only difference between this comparative example and Example 1 is that the heating time in step (4) is 3 hours.

[0081] Test case

[0082] 1. Characterization

[0083] like Figure 1 The X-ray diffraction (XRD) spectra of the modified molecular sieves prepared in the examples and comparative examples are shown. The results show that the tetrachloroaluminate modified type A molecular sieve prepared in the examples has fewer impurity phases. Compared with the standard type 4A molecular sieve in comparative example 2, the peak widths of the characteristic diffraction peaks are similar, the peak intensities are stronger, and the crystallinity is good. Figure 2 The image shows a scanning electron microscope (SEM) image of the sodium tetrachloroaluminate modified type A molecular sieve prepared in Example 1. The results show that Example 1 has the typical characteristics of type A molecular sieve.

[0084] 2. Adsorption performance test

[0085] Calculate Cs using the following formula + Removal efficiency (R), adsorption capacity Q e (mg / g) and partition coefficient K d (mL / g).

[0086] The formula for calculating removal efficiency is:

[0087]

[0088] The formula for calculating adsorption capacity is:

[0089]

[0090] The formula for calculating the allocation coefficient is:

[0091]

[0092] Where C i and C e These are the initial and equilibrium concentrations (mg / L) of Cs₂CO₃, respectively, and Q. m is the maximum equilibrium adsorption capacity (mg / g), b is the adsorption energy constant, which can be obtained by fitting the Langmuir model, V is the solution volume (L), and m is the adsorbent mass (g).

[0093] When testing the prepared modified type A molecular sieve, the sample needs to be activated at 200℃ under vacuum for 2 hours. After the sample cools, it is added to the container at a solid-liquid ratio of 1g:100mL to the solution to be adsorbed. The solution to be adsorbed is a solution of 100mg / L Cs2CO3, 500mg / L Cs2CO3, 1000mg / L Cs2CO3, 1000mg / L Co(NO3)2, or 1000mg / L Sr(NO3)3. The container is fixed on a long-axis mixer and mixed for 9 hours to ensure sufficient adsorption. Then, it is immediately filtered through a PES membrane. The filtrate is then diluted 10,000 times with a 2% dilute nitric acid solution to obtain the sample solution. The ion concentration in the sample solution is measured by ICP-OES (or ICP-MS).

[0094] Table 1 shows the removal rates of Cs2CO3 at concentrations of 100 mg / L to 1000 mg / L by the sodium tetrachloroaluminate modified type A molecular sieve prepared in Example 1. The results show that the prepared modified molecular sieve has good adsorption performance for both low and high concentration solutions, and has good application prospects in the adsorption of ions from high concentration radioactive solutions.

[0095] Table 1

[0096] Example 1: Adsorption performance at different concentrations - Cs Removal efficiency R (%) <![CDATA[Adsorption capacity Q e (mg / g)]]> <![CDATA[Partition coefficient K d (mL / g)]]> When 100 mg / L is completely adsorbed 97.4 454.5 <![CDATA[2.18×10 4 ]]> When 500 mg / L is fully adsorbed 97.9 454.5 <![CDATA[3.32×10 4 ]]> When 1000 mg / L is completely adsorbed 99.5 454.5 <![CDATA[4.94×10 4 ]]>

[0097] The modified molecular sieves prepared in the examples and comparative examples showed adsorption of 1000 mg / L Cs₂CO₃, 1000 mg / L Co(NO₃)₂, and 1000 mg / L Sr(NO₃)₃, respectively. Specific results are shown in Tables 2, 3, and 4. As shown in Table 2, the molecular sieves prepared in Examples 1-6 all showed adsorption of Cs₂CO₃. + The adsorption effect was very good. The lithium tetrachloroaluminate modified molecular sieve in Example 2 performed worse than the sodium tetrachloroaluminate modified molecular sieve in Example 1. This may be because Na... + Radius greater than Li + It is easier for it to exchange with Al, resulting in more Lewis acid exchange sites and enhancing the adsorption performance of the molecular sieve. Increasing the reflux temperature during the preparation of modified molecular sieves (Comparative Example 9) will cause tetrachloroaluminate decomposition, leading to less than ideal modification effect. Too short a reaction time (Comparative Example 10) will result in insufficient modification of the molecular sieve, leading to poor ion removal efficiency. Compared with NaCl modified molecular sieves (Comparative Examples 3 and 7), Examples 1 and 4 have better adsorption effects because tetrachloroaluminate ions enter the molecular sieve channels or adsorb on the surface of the molecular sieve during the dealumination process, making it more effective than pure NaCl. + Modification provides more coordination sites, resulting in a larger theoretical adsorption capacity and higher adsorption rate for the molecular sieve. When sodium tetrachloroaluminate modifies ZSM-5 molecular sieve, the adsorption capacity for Cs... + Co 2+and Sr 3+ The adsorption rate of elements is generally not high, which may be due to the difference in pore size and other properties between ZSM-5 molecular sieve and type A molecular sieve, resulting in differences in performance.

[0098] As shown in Table 2-4, the prepared molecular sieves have different effects on Cs. + Co 2+ and Sr 3+ They all exhibited excellent adsorption performance.

[0099] Table 2

[0100]

[0101]

[0102] Table 3

[0103] <![CDATA[Sample-Co 2+ > Removal efficiency R (%) <![CDATA[Adsorption capacity Q e (mg / g)]]> <![CDATA[Partition coefficient K d (mL / g)]]> Example 1 94.3 242.3 <![CDATA[1.02×10 5 <!-- 6 -->]]> Example 2 84.3 201.4 5.17×104 Comparative Example 1 40.3 40.4 <![CDATA[4.10×10 2 ]]> Comparative Example 2 84.2 205.9 <![CDATA[6.78×10 4 ]]> Comparative Example 3 93.4 220.8 <![CDATA[1.73×10 5 ]]> Comparative Example 4 45.2 59.6 <![CDATA[4.93×10 2 ]]> Comparative Example 5 70.7 150.4 <![CDATA[1.17×10 3 ]]> Comparative Example 6 71.7 184.0 <![CDATA[1.11×10 5 ]]>

[0104] Table 4

[0105] <![CDATA[Sample - Sr 3+ > Removal efficiency R (%) Adsorption capacity Qe (mg / g) Partition coefficient Kd (mL / g) Example 1 99.4 323.1 1.47×105 Example 2 92.9 299.9 3.88×104 Comparative Example 1 80.7 254.4 1.21×104 Comparative Example 2 99.3 303.0 4.37×104 Comparative Example 3 92.1 298.9 1.28×105 Comparative Example 4 50.1 123.3 5.23×103 Comparative Example 5 83.4 265.8 5.33×104 Comparative Example 6 74.4 274.5 9.24×103

[0106] 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 tetrachloroaluminate-modified type A molecular sieve, characterized in that, Includes the following steps: S1. Add fly ash cenospheres and alkaline compounds to water and mix thoroughly to obtain a mixed solution; S2. The mixed solution is reacted using a hydrothermal method to obtain type A molecular sieve; S3. The type A molecular sieve is added to the mixture to react and obtain the modified type A molecular sieve; the mixture is a mixture of saturated tetrachloroaluminate aqueous solution and chloride salt solution; the tetrachloroaluminate is selected from lithium tetrachloroaluminate and / or sodium tetrachloroaluminate; the chloride salt is selected from one or more of sodium chloride, potassium chloride and lithium chloride.

2. The preparation method according to claim 1, characterized in that, In step S3, the solid-liquid ratio of the type A molecular sieve to the mixed liquid is 1 g:(10-35) mL.

3. The preparation method according to claim 1, characterized in that, In step S3, the reaction time is 10-24 h.

4. The preparation method according to claim 1, characterized in that, In step S3, the reaction temperature is 25-35 ℃.

5. A modified type A molecular sieve prepared by the method according to any one of claims 1-4.

6. The application of the modified type A molecular sieve as described in claim 5 in the adsorption of ions in a radioactive solution.

7. The application as described in claim 6, characterized in that, The ions in the radioactive solution are cobalt ions, strontium ions, or cesium ions.

8. The application as described in claim 6 or 7, characterized in that, The concentration of the radioactive solution is 100-1000 mg / L.

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