A method for preparing silver-based molecular sieves and its application

Abstract

This invention relates to a method for preparing silver-based molecular sieves and their applications. The method involves uniformly mixing a template agent and a liquid alkali solution in a container, followed by mechanical stirring for a first preset time; adding an aluminum source and mechanically stirring for a second preset time; adding a silicon source and deionized water and mechanically stirring for a third preset time; adding a silver-based precursor and mechanically stirring for a fourth preset time; and finally, after uniform stirring, transferring the mixture to a stainless steel reactor for crystallization to prepare the silver-based molecular sieve. Compared to traditional ion exchange methods, the preparation method disclosed in this invention shortens the process flow, improves silver utilization, and reduces production costs. The prepared silver-based molecular sieve exhibits strong adsorption performance in the purification process of gaseous radioactive elemental iodine and organic iodine.

Description

Technical Field

[0001] This invention belongs to the field of radioactive waste treatment and environmental protection, specifically relating to a method for preparing silver-based molecular sieves and their applications. Background Technology

[0002] With the booming development of nuclear energy and nuclear power, the installed capacity of nuclear power equipment put into commercial operation has been increasing continuously, with a compound annual growth rate of 11.1%, resulting in a large amount of nuclear fuel waste generated every year. Consequently, the spent fuel reprocessing industry has been vigorously developed in recent years.

[0003] In the wet reprocessing of spent fuel, most processes, including cutting, dissolving, separation, collection, and solidification, release iodine to varying degrees. This released iodine becomes part of the process waste gas, which mainly exists as elemental iodine and organic iodine (such as CH3I). Because the dissolved waste gas contains approximately 1% NOx and nitric acid vapor, it may ignite activated carbon. Furthermore, due to the volatility of the activated carbon impregnating agent under high temperature and humidity conditions, traditional activated carbon cannot be used for iodine removal under these circumstances.

[0004] Another type of radioactive gaseous iodine adsorbent is the silver-modified solid adsorbent, mainly silver-coated silica gel and silver-coated molecular sieve materials. Silver-coated silica gel exhibits good adsorption performance for radioactive gaseous iodine, but its performance in practical applications is greatly affected by humidity and other gaseous impurities. Furthermore, silica gel is prone to breakage, and the adsorbed iodine easily migrates, making the secondary waste generated from the adsorption of radioactive iodine by silver-coated silica gel difficult to treat. In contrast, silver-coated molecular sieves possess excellent chemical and thermal stability, a certain degree of mechanical strength, and their pore structure increases the contact area between the gas and the adsorbent, resulting in excellent adsorption effects for both elemental and organic iodine. They are currently commonly used adsorbents in spent fuel reprocessing plants abroad. Existing research reports mainly focus on silver-coated mordenite zeolite and silver-coated octahedral zeolite. Due to the high price of silver, improving its utilization rate and regeneration frequency to reduce costs is a key research focus for this type of adsorbent material. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a method for preparing silver-based molecular sieves and their applications. Compared with the traditional ion exchange method, it can shorten the synthesis process, improve the utilization rate of silver, and reduce production costs.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, a method for preparing a silver-based molecular sieve, the method comprising the following steps:

[0008] S1. Mix the template agent and liquid alkali solution evenly in a container and mechanically stir for the first preset time;

[0009] S2. Add aluminum source and mechanically stir for the second preset time;

[0010] S3. Add silicon source and deionized water, and mechanically stir for the third preset time;

[0011] S4. Add the silver-based precursor and mechanically stir for the fourth preset time.

[0012] S5. After stirring evenly, the mixture is placed into a stainless steel reactor for crystallization.

[0013] Furthermore, the concentration of the liquid alkali solution in step S1 is 45 wt%.

[0014] Furthermore, the aluminum source mentioned in step S2 is either boehmite or aluminum sulfate.

[0015] Furthermore, the silicon source mentioned in step S3 is one of a 25 wt% silica sol solution and sodium silicate.

[0016] Furthermore, the silver-based precursor mentioned in step S4 is one of silver nitrate and silver acetate.

[0017] Furthermore, the template agent mentioned in step S1 is tetraethylammonium hydroxide.

[0018] Furthermore, the template agent in step S1 comprises a mixture of hexadecyltrimethylammonium bromide and triethanolamine.

[0019] Furthermore, the template agent mentioned in step S1 includes N,N,N,-trimethyl-1-adamantyl ammonium hydroxide and polyvinyl alcohol.

[0020] Furthermore, the first, third, and fourth preset times are all in the range of 30 to 90 minutes, and the second preset time is in the range of 0.5 to 3 hours.

[0021] In a second aspect, a silver-based molecular sieve is prepared using the preparation method of a silver-based molecular sieve described in the first aspect of the present invention and any optional embodiment thereof, wherein the silver-based molecular sieve is used to adsorb gaseous radioactive elemental iodine and organic iodine.

[0022] The beneficial technical effects of this invention are as follows: by mixing a template agent with liquid alkali, adding a certain amount of aluminum and silicon sources, and adding a specific silver-based precursor, silver-based molecular sieves are obtained by crystallization in a hydrothermal reactor at a certain temperature for several days. The prepared silver-based molecular sieves have a three-dimensional channel structure, uniform pore size distribution, and orderly structural arrangement, with highly dispersed silver. They exhibit superior iodine adsorption performance compared to traditional silver-coated silica gel and most silver-coated mordenite and silver-coated octahedral zeolite materials. Attached Figure Description

[0023] Figure 1Transmission electron microscope image of a silver-based molecular sieve prepared using the method for preparing a silver-based molecular sieve as shown in Embodiment 1 of the present invention;

[0024] Figure 2 The XRD pattern of a silver-based molecular sieve prepared using the method for preparing a silver-based molecular sieve as shown in Example 1 of this invention;

[0025] Figure 3 Transmission electron microscope image of a silver-based molecular sieve prepared using a method for preparing a silver-based molecular sieve as shown in Example 2 of this invention;

[0026] Figure 4 The XRD pattern of a silver-based molecular sieve prepared using the method for preparing a silver-based molecular sieve as shown in Example 2 of this invention;

[0027] Figure 5 Transmission electron microscope image of a silver-based molecular sieve prepared using a method for preparing a silver-based molecular sieve as shown in Example 3 of this invention;

[0028] Figure 6 The XRD pattern of a silver-based molecular sieve prepared using the method for preparing a silver-based molecular sieve as shown in Example 3 of this invention;

[0029] Figure 7 The graph shows a comparison of the adsorption and breakthrough curves of silver-based molecular sieves prepared using the method described in Examples 1 to 3 of this invention, and the methyl iodine adsorption curves of the comparative examples. Detailed Implementation

[0030] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0031] Example 1

[0032] This invention provides a method for preparing a silver-based molecular sieve, the method comprising the following steps:

[0033] S1. Weigh 50-75g of tetraethylammonium hydroxide and 1-5g of liquid alkali solution (45wt%) and mix them evenly in a flask. Stir mechanically for 30-90 minutes.

[0034] S2. Add 1.0–5.0 g of pseudoboehmite and mechanically stir for 0.5–3 hours;

[0035] S3. Add 50-75g of silica sol solution (25wt%) and 20-50g of deionized water, and stir mechanically for 30-90 minutes.

[0036] S4. Add 0.2–0.6 g of silver nitrate and mechanically stir for 30–90 min.

[0037] S5. After stirring evenly, the mixture is placed in a 200mL stainless steel reactor and crystallized in an oven at 100-160℃ for 48-96 hours. After the crystallization process, the mixture is cooled to room temperature, centrifuged and washed with water to obtain the product, and dried at 100℃ for 12 hours. The template agent is removed by calcination: the powder sample is heated to 650℃ in a muffle furnace at a rate of 2℃ / min and maintained for 4 hours.

[0038] The silver-based molecular sieve prepared using the silver-based molecular sieve preparation method described in Embodiment 1 and its optional embodiments of the present invention was subjected to electron microscopy transmission and X-ray diffraction, respectively, to obtain the following results: Figure 1 The electron microscope images shown and such Figure 2 The XRD pattern shown.

[0039] Example 2

[0040] This invention provides a method for preparing a silver-based molecular sieve, the method comprising the following steps:

[0041] S1. Weigh 30-55g of cetyltrimethylammonium bromide, 5-10g of triethanolamine and 1-5g of liquid alkali solution (45wt%) and mix them evenly in a flask. Stir mechanically for 30-90 minutes.

[0042] S2. Add 1.0–5.0 g of aluminum sulfate and mechanically stir for 0.5–3 hours;

[0043] S3. Add 50-75g of silica sol solution (25wt%) and 20-50g of deionized water, and stir mechanically for 30-90 minutes.

[0044] S4. Add 0.2–0.6 g of silver acetate and stir mechanically for 30–90 min.

[0045] S5. After stirring evenly, the mixture is placed in a 200mL stainless steel reactor and crystallized in an oven at 100-160℃ for 48-96 hours. After the crystallization process, the mixture is cooled to room temperature, centrifuged and washed with water to obtain the product, and dried at 100℃ for 12 hours. The template agent is removed by calcination: the powder sample is heated to 650℃ in a muffle furnace at a rate of 2℃ / min and maintained for 4 hours.

[0046] The silver-based molecular sieve prepared using the silver-based molecular sieve preparation method described in Embodiment 2 and its optional embodiments of the present invention was subjected to electron microscopy transmission and X-ray diffraction, respectively, to obtain the following results: Figure 3 The electron microscope images shown and such Figure 4 The XRD pattern shown.

[0047] Example 3

[0048] This invention provides a method for preparing a silver-based molecular sieve, the method comprising the following steps:

[0049] S1. Weigh 30-55g of N,N,N,-trimethyl-1-adamantyl ammonium hydroxide, 15-25g of polyvinyl alcohol and 1-5g of liquid alkali solution (45wt%) and mix them evenly in a flask. Stir mechanically for 30-90 minutes.

[0050] S2. Add 1.0–5.0 g of aluminum sulfate and mechanically stir for 0.5–3 hours;

[0051] S3. Add 30-60g sodium silicate (25wt%) and 20-50g deionized water, and stir mechanically for 30-90 minutes.

[0052] S4. Add 0.2–0.6 g of silver acetate and stir mechanically for 30–90 min.

[0053] S5. After stirring evenly, the mixture is placed in a 200mL stainless steel reactor and crystallized in an oven at 100-160℃ for 48-96 hours. After the crystallization process, the mixture is cooled to room temperature, centrifuged and washed with water to obtain the product, and dried at 100℃ for 12 hours. The template agent is removed by calcination: the powder sample is heated to 650℃ in a muffle furnace at a rate of 2℃ / min and maintained for 4 hours.

[0054] The silver-based molecular sieve prepared using the silver-based molecular sieve preparation method described in Embodiment 3 and its optional embodiments of the present invention was subjected to electron microscopy transmission and X-ray diffraction, respectively, to obtain the following results: Figure 5 The electron microscope images shown and such Figure 6 The XRD pattern shown.

[0055] Comparative Example

[0056] A comparative example illustrates the preparation method of silver-coated silica gel. The method involves sieving colorless silica gel with a specific particle size and pore size, pre-treating it with heat, immersing it in silver nitrate solution, decanting the residual liquid, and drying it at a constant temperature. The silver loading is determined by back-titration of NaCl with standard silver nitrate. The silver loading was found to be 6.2%.

[0057] Example 4

[0058] This invention provides a silver-based molecular sieve, which is prepared by a silver-based molecular sieve preparation method described in any one of the embodiments of this invention (1 to 3) and its optional embodiments. The silver-based molecular sieve is used to adsorb gaseous radioactive elemental iodine and organic iodine.

[0059] The silver-based molecular sieves prepared using the methods described in Examples 1 to 3 of this invention and the silver-coated silica gel prepared in the comparative example were subjected to methyl iodine adsorption capacity experiments:

[0060] The silver-based molecular sieves prepared using the methods described in Examples 1 to 3 of this invention and the silver-coated silica gel prepared in the comparative example were respectively loaded into a fixed-bed reactor with an inner diameter of 9 mm and a height of 120 mm, and placed in a constant temperature chamber to control the adsorption temperature. The experimental temperature range was 30–150 °C. The inlet gas velocity was 0.2 m / s, the relative humidity of the gas flow was 3–95%, and the operating pressure was 101 kPa. The test process consisted of three stages: equilibration, feeding, and purging. After all operating parameters stabilized, feeding began for 60 minutes, and the mass concentration of radiolabeled methyl iodine was 1.75 mg / m³. 3 The sample was then purged with high-purity nitrogen for 60 minutes. Following the test bed, two backup beds containing highly efficient adsorbents for removing methyl iodine were used to completely capture the radioactive methyl iodine that had passed through the test bed. After purging, the gamma radioactivity counts of the materials in the test and backup beds were measured using a gamma counter or multichannel gamma spectrometer, resulting in Table 1, a comparison of the adsorption performance of different materials for radioactive methyl iodine.

[0061] Table 1 compares the adsorption performance of radioactive methyl iodine in the comparative examples and the embodiments.

[0062] Adsorbent materials <![CDATA[CH3 131 I Adsorption efficiency]]> Comparative Example 99.2 Example 1 99.9 Example 2 99.5 Example 3 99.0

[0063] As shown in Table 1, the purification efficiency of radioactive methyl iodine by the silver-based molecular sieves prepared using the methods described in Examples 1 to 3 of this invention is better than or no less than the adsorption performance of the silver-coated silica gel prepared using the comparative example. A comparison of the methyl iodine adsorption breakthrough curves of the silver-based molecular sieves prepared using the methods described in Examples 1 to 3 of this invention and the silver-coated silica gel prepared using the comparative example is shown in the figure. Figure 7 As shown.

[0064] Depend on Figure 7 It can be seen that the methyl iodine adsorption capacity of the silver-based molecular sieve prepared by the methods described in Examples 1 and 2 of this invention is greater than that of the silver-coated silica gel prepared in the comparative example, while the methyl iodine adsorption capacity of the silver-based molecular sieve prepared by the method described in Example 3 of this invention is less than that of the silver-coated silica gel prepared in the comparative example. This also demonstrates that the preparation process can affect the adsorption capacity of the silver-based molecular sieve for methyl iodine.

[0065] As can be seen from the above embodiments, the silver-based molecular sieve preparation method and its application disclosed in this invention, compared with the traditional ion exchange method, can shorten the process flow, improve the utilization rate of silver, and reduce the production cost. The prepared silver-based molecular sieve has strong adsorption performance in the purification process of gaseous radioactive elemental iodine and organic iodine.

[0066] The method described in this invention is not limited to the embodiments described in the specific implementation. Other implementation methods derived by those skilled in the art based on the technical solution of this invention also fall within the scope of technical innovation of this invention.

Claims

1. A method for preparing a silver-based molecular sieve, the method comprising the following steps: S1. Mix the template agent and liquid alkali solution evenly in a container and mechanically stir for the first preset time; S2. Add aluminum source and mechanically stir for the second preset time; S3. Add silicon source and deionized water, and mechanically stir for the third preset time; S4. Add the silver-based precursor and mechanically stir for the fourth preset time. S5. After stirring evenly, the mixture is placed into a stainless steel reactor for crystallization. The first, third, and fourth preset times all range from 30 to 90 minutes, while the second preset time ranges from 0.5 to 3 hours.

2. The method for preparing a silver-based molecular sieve as described in claim 1, characterized in that: The concentration of the liquid alkali solution in step S1 is 45 wt%.

3. The method for preparing a silver-based molecular sieve as described in claim 1, characterized in that: The aluminum source mentioned in step S2 is either boehmite or aluminum sulfate.

4. The method for preparing a silver-based molecular sieve as described in claim 1, characterized in that: The silicon source mentioned in step S3 is one of a 25 wt% silica sol solution and sodium silicate.

5. The method for preparing a silver-based molecular sieve as described in claim 1, characterized in that: The silver-based precursor mentioned in step S4 is one of silver nitrate and silver acetate.

6. The method for preparing a silver-based molecular sieve as described in claim 1, characterized in that: The template agent mentioned in step S1 is tetraethylammonium hydroxide.

7. The method for preparing a silver-based molecular sieve as described in claim 1, characterized in that: The template agent mentioned in step S1 comprises a mixture of hexadecyltrimethylammonium bromide and triethanolamine.

8. The method for preparing a silver-based molecular sieve as described in claim 1, characterized in that: The template agent mentioned in step S1 includes N,N,N,-trimethyl-1-adamantyl ammonium hydroxide and polyvinyl alcohol.

9. A silver-based molecular sieve, prepared by the method for preparing a silver-based molecular sieve as described in any one of claims 1-8, characterized in that: The silver-based molecular sieve is used to adsorb gaseous radioactive elemental iodine and organic iodine.

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