Composite aerogel for adsorbing Cs < + > and Sr < 2 + > in radioactive wastewater under acidic condition and preparation method thereof

Abstract

The invention belongs to the technical field of radioactive wastewater treatment, and particularly relates to composite aerogel for adsorbing Cs < + > and Sr < 2 + > in radioactive wastewater under an acidic condition and a preparation method of the composite aerogel. The preparation method of the composite aerogel comprises the following steps: (1) synthesizing ammonium phosphomolybdate / sodium alginate aerogel; (2) growing ZIF-8 on the surface of the ammonium phosphomolybdate / sodium alginate aerogel; and (3) modifying the surface of the material obtained in the step (2) by using potassium permanganate to generate MnO2, thereby obtaining the composite aerogel. The composite aerogel can efficiently adsorb Cs < + > and Sr < 2 + > in wastewater to realize efficient co-adsorption of double ions, and has the advantages of low energy consumption, high selective separation efficiency, capability of carrying out one-step curing separation, no secondary pollution and capability of effectively avoiding the defects of redundant separation operation and large waste liquid amount in a traditional method, and a high-capacity and easily-recycled adsorbent scheme is provided for radioactive wastewater treatment.

Description

Technical Field

[0001] The present invention belongs to the technical field of radioactive wastewater treatment, and particularly relates to a composite aerogel for adsorbing Cs + and Sr 2+ in radioactive wastewater under acidic conditions and a preparation method thereof. Background Art

[0002] With the rapid increase in population and the high-speed development of industry, the global energy demand has shown an explosive growth. Nuclear power has become one of the most important resources to cope with energy shortages. Among radioactive nuclides, 137 Cs and 90 Sr are one of the most harmful radioactive elements. First, 137 Cs and 90 Sr have very long half-lives, 30.12 years and 28.79 years respectively, and they will damage the environment for a long time. Second, 137 Cs and 90 Sr usually exist in ionic form. Due to their high water solubility and high environmental mobility, they can quickly migrate into the food chain. In addition, because Cs + has similar chemical properties to K + and Na + , while Sr 2+ has similar chemical properties to Ca 2+ , so they can be easily assimilated by terrestrial and aquatic organisms and then enter the human food chain and are easily absorbed by the body. Therefore, it is crucial to develop effective methods to remove 137 Cs and 90 Sr from aqueous nuclear waste. Summary of the Invention

[0003] The present invention provides a composite aerogel for adsorbing Cs + and Sr 2+ in radioactive wastewater under acidic conditions. The aerogel is prepared by sequentially compounding ammonium phosphomolybdate / sodium alginate aerogel (AMP@SA) with ZIF-8 and MnO2. Specifically, ammonium phosphomolybdate / sodium alginate aerogel (AMP@SA) is synthesized first, and then ZIF-8 is grown on the surface by cyclic growth and modified with potassium permanganate to obtain the composite aerogel (MnO2@ZIF-8 / AMP@SA). Applying the composite aerogel to adsorb Cs + and Sr 2+ in radioactive wastewater can not only stably, efficiently and rapidly remove Cs + and Sr 2+ in radioactive wastewater under acidic conditions, but also be separated, recovered and reused, solving the problems that the adsorbent is easily dispersed in wastewater and difficult to recover, and has broad application potential.

[0004] The present invention provides a method for preparing a composite aerogel for adsorbing Cs + and Sr 2+ in radioactive wastewater under acidic conditions, comprising the following steps:

[0005] (1) Preparation of ammonium phosphomolybdate (AMP): Weigh ammonium molybdate tetrahydrate and dissolve it in deionized water. After complete dissolution, add phosphoric acid solution while stirring. Add nitric acid under constant temperature conditions until a yellow precipitate appears, and continue stirring for 0.5 h. Let it stand, filter to obtain the precipitate, wash it, and after filtering to obtain the precipitate, dry it in a constant temperature oven to obtain yellow powder ammonium phosphomolybdate (AMP).

[0006] (2) Preparation of AMP@SA aerogel: Take a specific mass of ammonium phosphomolybdate (AMP) and add it to a sodium alginate (SA) solution, stir and ultrasonicate, and obtain a sodium alginate aerogel carrier containing AMP through freeze-drying. Add the sodium alginate aerogel carrier containing AMP to a calcium nitrate solution with a specific concentration for cross-linking, wash it with deionized water, and then freeze-dry to obtain ammonium phosphomolybdate / sodium alginate gas (AMP@SA aerogel).

[0007] (3) Preparation of ZIF-8 / AMP@SA aerogel: Immerse the AMP@SA aerogel in an aqueous solution of zinc acetate dihydrate, and then immerse it in an aqueous solution of 2-methylimidazole for one growth cycle to obtain a hydrogel with ZIF-8 grown once. Repeat the above growth steps. After three growth cycles, freeze-dry to obtain ZIF-8 / AMP@SA aerogel; the AMP@SA aerogel is fully immersed and reacted in the zinc acetate dihydrate and 2-methylimidazole solutions, and small spherical particles with smooth surfaces and distinct boundaries are formed.

[0008] The aqueous solution of zinc acetate dihydrate is prepared by mixing zinc acetate dihydrate and valine and dissolving them in water;

[0009] (4) Modifying and growing MnO2 on ZIF-8 / AMP@SA aerogel to prepare a composite aerogel: Immerse the ZIF-8 / AMP@SA aerogel in a potassium permanganate solution, stir and soak it, and then freeze-dry. Wash it with pure water and take it out to obtain the composite aerogel (MnO2@ZIF-8 / AMP@SA).

[0010] Preferably, the mass ratio of ammonium phosphomolybdate (AMP), sodium alginate (SA), zinc acetate dihydrate, 2-methylimidazole, valine, and potassium permanganate is 0.5-2:0.5-2:0.216-1.296:0.662-3.972:2.033-4.066:0.050-0.2:0.050-0.2.

[0011] Preferably, the mass ratio of ammonium phosphomolybdate (AMP) to sodium alginate (SA) is 2:1.

[0012] Preferably, the dosage ratio of ammonium molybdate tetrahydrate, phosphoric acid solution, and nitric acid in step (1) is 0.93 g: 0.5 mL: 0.5 mL.

[0013] Preferably, the concentration of the phosphoric acid solution in step (1) is 0.25 mol·L -1 .

[0014] Preferably, the constant temperature condition in step (1) is 70 °C.

[0015] Preferably, the concentration of the nitric acid in step (1) is 6 mol·L -1 .

[0016] Preferably, the washing in step (1) uses nitric acid and deionized water, and the concentration of the nitric acid is 1 mol·L -1 .

[0017] Preferably, the stirring rate in step (1) is 300 - 500 r / min.

[0018] Preferably, the drying time in step (1) is 24 - 48 h.

[0019] Preferably, in step (2), the reaction temperature of stirring and ultrasonic treatment is 30 - 50 °C, and the time is 0 - 2 h (excluding 0); the stirring speed is 300 - 500 r / min; the concentration of the calcium nitrate solution is 0.1 - 1 mol / L, and after freeze-drying for 24 - 72 h, the AMP@SA aerogel is obtained.

[0020] Preferably, the soaking time in step (2) is 3 - 6 h; the freeze-drying time is 24 - 72 h.

[0021] Preferably, the soaking time in step (3) is 24 - 48 h; the stirring speed is 300 - 500 r / min; the freeze-drying time is 24 - 72 h.

[0022] Preferably, the stirring and soaking time in step (4) is 24 h.

[0023] The present invention also provides an application of the composite aerogel prepared by the above method for adsorbing Cs + and Sr 2+ in water.

[0024] The specific application method of the present invention is: adding the composite aerogel (MnO2@ZIF-8 / AMP@SA) to the water containing Cs + and Sr 2 +In the solution, it is placed in a constant temperature shaker for shaking adsorption. After the composite aerogel is adsorbed, it is separated by simple drying.

[0025] Preferably, the solution containing Cs + and Sr 2+ has a pH of 1 to 7.

[0026] Using an aqueous solution containing Cs + and Sr 2+ (the concentrations of Cs + and Sr 2+ are both 50 mg / L) as the detection solution, under the condition of adding 20 mg of the composite adsorbent, the removal rates of Cs + , Sr 2+ can reach 95.3% and 97.8% respectively at most, achieving the purpose of purifying Cs + , Sr 2+ in radioactive wastewater.

[0027] The beneficial effects of the present invention are:

[0028] (1) The MnO2@ZIF-8 / AMP@SA aerogel has a large specific surface area, a high porosity, strong flexibility, stable chemical properties and is easy to modify on the surface. The experimental process is controllable. The composite MnO2@ZIF-8 / AMP@SA aerogel can efficiently adsorb Cs + and Sr 2+ in wastewater, realizing the efficient co-adsorption of dual ions and breaking through the limitation of single materials only targeting single ions; through the synergistic enhancement of multiple mechanisms, the adsorption efficiency is as high as 95.3% and 97.8% respectively;

[0029] (2) After using the composite aerogel to adsorb Cs + and Sr 2+ in water, it can be effectively separated from the action system through simple drying separation technology without secondary pollution, providing a high-capacity and easy-to-recycle adsorbent solution for radioactive wastewater treatment;

[0030] (3) The overall treatment structure of the present invention is relatively simple, light in weight, small in floor area, and efficient, convenient and low in energy consumption during operation. Description of the Drawings

[0031] Figure 1 It is the SEM pattern of the MnO2@ZIF-8 / AMP@SA aerogel of Example 1;

[0032] Figure 2 It is the XRD pattern of the MnO2@ZIF-8 / AMP@SA aerogel of Example 1 and the comparative materials;

[0033] Figure 3TGA spectra of the MnO2@ZIF-8 / AMP@SA aerogel and comparative materials in Example 1;

[0034] Figure 4 Cyclic regeneration spectrum of the MnO2@ZIF-8 / AMP@SA aerogel in Example 1;

[0035] Figure 5 Adsorption behaviors of the AMP@SA aerogel, ZIF-8 / AMP@SA aerogel, and MnO2@ZIF-8 / AMP@SA aerogel in Example 1 in different pH environments, where (a) is the cesium ion adsorption curve spectrum, (b) is the strontium ion adsorption curve spectrum, and (c) is the Zeta potential analysis spectrum. Detailed implementation manners

[0036] The present invention will be further described below with reference to the accompanying drawings. The following examples are only used to more clearly illustrate the technical solutions of the present invention and cannot be used to limit the protection scope of the present invention.

[0037] Example 1:

[0038] (1) Weigh 0.93 g of (NH4)6Mo7O 24 ·4H2O and dissolve it in 10 mL of deionized water. After complete dissolution, slowly add 2 mL of 0.25 mol·L -1 H3PO4 to the solution while stirring; gradually add 0.5 mL of 6 mol·L -1 HNO3 to adjust the pH of the mixed solution at a constant temperature of 70 °C until a yellow precipitate appears, and continue to stir for 0.5 h and then let it stand; filter to obtain the precipitate, wash it three times with 1 mol·L -1 HNO3 solution and once with deionized water, and then filter to obtain the precipitate. Dry it in an oven at (40 ± 1) °C to obtain yellow powdery AMP (ammonium phosphomolybdate).

[0039] Slowly add 0.5 g of sodium alginate to 100 mL of deionized water, then stir at 40 °C for 20 min, and then perform ultrasonic treatment for 10 min to obtain a sodium alginate solution. Subsequently, add 1 g of AMP to the sodium alginate solution, stir for 10 min, and then perform ultrasonic treatment for 10 min. Pour the solution into a petri dish and perform freeze-drying to form a sodium alginate aerogel carrier doped with AMP.

[0040] Immerse the sodium alginate aerogel carrier doped with AMP in 0.1 mol / L calcium nitrate solution for cross-linking reaction for 30 min, and then wash it three times with deionized water. After freeze-drying, a calcium alginate sponge-like aerogel doped with AMP is obtained, denoted as AMP@SA aerogel.

[0041] (2) The AMP@SA aerogel was taken out and immersed in a zinc acetate dihydrate solution (0.432 g of zinc acetate dihydrate + 20 mL of water + 60 mg of valine) for 3 h, and then immersed in a 2-methylimidazole aqueous solution (1.324 g of 2-methylimidazole + 20 mL of water) for 3 h. After three cycles of growth, it was placed in a freeze dryer (-55 °C, 72 h) for drying to obtain ZIF-8 / AMP@SA aerogel.

[0042] (3) The ZIF-8 / AMP@SA aerogel was taken and immersed in a potassium permanganate solution (63 mg of potassium permanganate + 20 mL of water) and stirred and immersed for 24 h for the modified growth of MnO2. After the stirring was completed, it was freeze-dried (-55 °C, 72 h) to obtain MnO2@ZIF-8 / AMP@SA aerogel.

[0043] Figure 1 It is the SEM image of MnO2@ZIF-8 / AMP@SA aerogel. It can be observed that well-dispersed surface-rough small spheres grow tightly on the surface of the AMP@SA aerogel. The spherical structure of ZIF-8 not only brings porosity and a large specific surface area to the aerogel, but also increases the number of adsorption sites and improves the adsorption capacity of the adsorbent. The core-shell structure characteristics of the MnO2@ZIF-8 nanocomposite are considered to contribute to maximizing the adsorption capacity of the hybrid material.

[0044] Figure 2 It is the XRD pattern of AMP, AMP@SA aerogel, ZIF-8 / AMP@SA aerogel, and MnO2@ZIF-8 / AMP@SA aerogel. In the XRD test pattern, the strong diffraction peaks of AMP at 2θ = 10.7°, 15.1°, 21.5°, 26.4°, 30.6°, 36.3° and 55.6° correspond to the 110, 200, 220, 222, 440, 550 and 732 crystal planes respectively. These crystal diffraction peaks indicate the successful preparation of the AMP powder. Compared with the ZIF-8 / AMP@SA aerogel, sharp diffraction peaks are found at 2θ = 12.8°, 18.2°, 28.6°, 37.3° and 41.7° in the XRD pattern of the MnO2@ZIF-8 / AMP@SA aerogel, corresponding to the 110, 200, 310, 211 and 301 crystal planes of the MnO2@ZIF-8 nanocomposite respectively, indicating the successful growth of MnO2 on the surface of the ZIF-8 / AMP@SA aerogel by potassium permanganate.

[0045] Figure 3TGA diagrams of AMP@SA aerogel, ZIF-8 / AMP@SA aerogel, and MnO2@ZIF-8 / AMP@SA aerogel. As can be seen from the figure, all materials show three mass losses. In the first stage of the thermogravimetric curve, all materials show a slight mass loss, which is mainly due to the evaporation of adsorbed water in the cavities or on the surfaces of the adsorbents. Specifically, the mass loss ratios of AMP@SA aerogel, ZIF-8 / AMP@SA aerogel, and MnO2@ZIF-8 / AMP@SA aerogel are 8.46%, 3.03%, and 22.93% respectively. The reason for the relatively large mass loss of MnO2@ZIF-8 / AMP@SA aerogel is that the material has too high water content after repeated soaking during the preparation of MnO2@ZIF-8 / AMP@SA aerogel. The mass loss in the second stage is caused by the partial collapse of the structure of the adsorbent and the decomposition of organic substances in the material. Among them, ZIF-8 / AMP@SA aerogel shows a faster mass loss at high temperatures, which is due to the dehydration of the polymer and the hydrolysis of ZIF-8 during the modification process. In the third stage after the mass loss in the second stage, the mass loss of the material tends to be stable, and the reasons for the loss are the hydrolysis of functional groups and the collapse of the structure. It should be noted that after three stages of mass loss, the three materials in the thermogravimetric curve tend to be stable, indicating that the adsorbent has good thermal stability and can therefore be reused multiple times in wastewater.

[0046] Example 2:

[0047] (1) Weigh 1.86 g of (NH4)6Mo7O 24 ·4H2O and dissolve it in 20 mL of deionized water. After complete dissolution, slowly add 4 mL of 0.25 mol·L -1 H3PO4 to the solution while stirring. Add 1 mL of 6 mol·L -1 HNO3 dropwise at a constant temperature of 70 °C to adjust the pH of the mixed solution until a yellow precipitate appears, and continue stirring for 0.5 h and then let it stand. Filter to obtain the precipitate, wash it 3 times with 1 mol·L -1 HNO3 solution and 1 time with deionized water, then filter to obtain the precipitate, and dry it in an oven at (40 ± 1) °C to obtain yellow powdery AMP.

[0048] Slowly add 0.5 g of sodium alginate to 100 mL of deionized water, then stir at 40 °C for 20 min, and then perform ultrasonic treatment for 10 min to obtain a sodium alginate solution. Subsequently, add 1 g of AMP to the sodium alginate solution, stir for 10 min and then perform ultrasonic treatment for 10 min. Pour the solution into a petri dish and perform freeze-drying to form a sodium alginate aerogel carrier doped with AMP.

[0049] The sodium alginate aerogel carrier doped with AMP was immersed in a 0.5 mol / L calcium nitrate solution for a cross-linking reaction for 30 min, and then washed three times with deionized water. After freeze-drying, a calcium alginate sponge-like aerogel doped with AMP was obtained, denoted as AMP@SA aerogel.

[0050] (2) The AMP@SA aerogel was taken out and immersed in a zinc acetate dihydrate solution (0.432 g zinc acetate dihydrate + 20 mL water + 120 mg valine) for 3 h, and then immersed in a 2-methylimidazole aqueous solution (1.324 g 2-methylimidazole + 20 mL water) for 3 h. After three cycles of growth, it was placed in a freeze-dryer (-55 °C, 72 h) for drying to obtain ZIF-8 / AMP@SA aerogel.

[0051] (3) The ZIF-8 / AMP@SA aerogel was taken and immersed in a potassium permanganate solution (126 mg potassium permanganate + 20 mL) and stirred and immersed for 24 h to grow MnO2 by modification. After the stirring ended, it was freeze-dried (-55 °C, 72 h) to obtain MnO2@ZIF-8 / AMP@SA aerogel.

[0052] Example 3:

[0053] (1) Weigh 1.86 g of (NH4)6Mo7O 24 ·4H2O and dissolve it in 20 mL of deionized water. After complete dissolution, slowly add 4 mL of 0.25 mol·L -1 H3PO4 dropwise to the solution while stirring; add 1 mL of 6 mol·L -1 HNO3 dropwise at a constant temperature of 70 °C to adjust the pH of the mixed solution until a yellow precipitate appears, and continue to stir for 0.5 h and then let it stand; filter to obtain the precipitate, wash it 3 times with a 1 mol·L -1 HNO3 solution, wash it once with deionized water and then filter to obtain the precipitate, and dry it in an oven at (40 ± 1) °C to obtain yellow powdery AMP.

[0054] Slowly add 0.5 g of sodium alginate to 100 mL of deionized water, then stir at 40 °C for 20 min, and then perform ultrasonic treatment for 10 min to obtain a sodium alginate solution. Subsequently, add 1 g of AMP to the sodium alginate solution, stir for 10 min and then perform ultrasonic treatment for 10 min. Pour the solution into a petri dish and perform freeze-drying to form a sodium alginate aerogel carrier doped with AMP.

[0055] The sodium alginate aerogel carrier doped with AMP was immersed in a 0.5 mol / L calcium nitrate solution for a cross-linking reaction for 30 min, and then washed three times with deionized water. After freeze-drying, a calcium alginate sponge-like aerogel doped with AMP was obtained, denoted as AMP@SA aerogel.

[0056] (2) The AMP@SA aerogel was taken out and immersed in a zinc acetate dihydrate solution (0.684 g zinc acetate dihydrate + 40 mL water + 60 mg valine) for 3 h, and then immersed in a 2-methylimidazole aqueous solution (2.648 g 2-methylimidazole + 40 mL water) for 3 h. After three cycles of growth, it was placed in a freeze-dryer (-55 °C, 72 h) for drying to obtain ZIF-8 / AMP@SA aerogel.

[0057] (3) The ZIF-8 / AMP@SA aerogel was taken out and immersed in a potassium permanganate solution (63 mg potassium permanganate + 20 mL water) and stirred and immersed for 24 h for the modified growth of MnO2. After the stirring was completed, it was freeze-dried (-55 °C, 72 h) to obtain MnO2@ZIF-8 / AMP@SA aerogel.

[0058] Comparative Example 1:

[0059] The AMP@SA aerogel was prepared in the same manner as in Example 1. The removal rates of Cs + and Sr 2+ can reach 86.1% and 49.2% respectively.

[0060] Comparative Example 2:

[0061] The ZIF-8 / AMP@SA aerogel was prepared in the same manner as in Example 1. The removal rates of Cs + and Sr 2+ can reach 81.4% and 53.1% respectively.

[0062] Comparative Example 3

[0063] (1) Weigh 0.93 g of (NH4)6Mo7O 24 ·4H2O and dissolve it in 10 mL of deionized water. After complete dissolution, slowly add 2 mL of 0.25 mol·L -1 H3PO4 to the solution, stirring while adding; add 0.5 mL of 6 mol·L -1 HNO3 dropwise at a constant temperature of 70 °C to adjust the pH of the mixed solution until a yellow precipitate appears, and continue stirring for 0.5 h and then let it stand; filter to obtain the precipitate, wash it 3 times with a 1 mol·L -1 HNO3 solution, wash it once with deionized water and then filter to obtain the precipitate, and dry it in an oven at (40 ± 1) °C to obtain yellow powdery AMP (ammonium phosphomolybdate).

[0064] Slowly add 0.5 g of sodium alginate into 100 mL of deionized water, then stir at 40 °C for 20 min, followed by ultrasonic treatment for 10 min to obtain a sodium alginate solution. Subsequently, add 1 g of AMP into the sodium alginate solution, stir for 10 min and then perform ultrasonic treatment for 10 min. Pour the solution into a petri dish and perform freeze-drying to form a sodium alginate aerogel carrier doped with AMP.

[0065] Immerse the sodium alginate aerogel carrier doped with AMP in 0.1 mol / L calcium nitrate solution for cross-linking reaction for 30 min, and then wash it three times with deionized water. After freeze-drying, a calcium alginate sponge-like aerogel doped with AMP is obtained, denoted as AMP@SA aerogel.

[0066] (2) Take the AMP@SA aerogel and immerse it in a potassium permanganate solution (63 mg potassium permanganate + 20 mL water), stir and soak for 24 h for the modified growth of MnO2. After stirring, perform freeze-drying (-55 °C, 72 h) to obtain MnO2@ZIF-8 / AMP@SA aerogel.

[0067] Comparative Example 4

[0068] (1) Prepare a zinc acetate dihydrate solution (0.432 g zinc acetate dihydrate + 20 mL water + 60 mg of valine), then add 1.324 g of 2-methylimidazole, stir and react for 3 h. After the reaction, centrifuge, wash three times with deionized water and three times with ethanol. Place the obtained white viscous solid product in a vacuum and dry at 80 °C for 24 h to obtain white powder ZIF-8.

[0069] (2) Take the ZIF-8 powder and immerse it in a potassium permanganate solution (63 mg potassium permanganate + 20 mL water), stir and soak for 24 h for the modified growth of MnO2. After stirring, perform freeze-drying (-55 °C, 72 h) to obtain MnO2@ZIF-8.

[0070] Effect Example

[0071] Take 20 mg of the aerogel prepared in the examples and comparative examples and add it to an aqueous solution with a system of 20 mL, pH of 6, and the concentrations of Cs + and Sr 2+ being 50 mg / L (or 100 mg / L) respectively. Place it in a constant temperature shaker and shake and adsorb at 220 r / min for 24 h. Then, use the flame atomic absorption spectrometer of Jinan Jiedao Analytical Instrument Co., Ltd. to detect the contents of Cs + and Sr 2+ in the wastewater, and calculate the removal rate according to the following formula Ⅰ and the adsorption capacity according to formula Ⅱ. The specific data are shown in Table 1 and Table 2.

[0072] Formula Ⅰ:

[0073] Formula Ⅱ:

[0074] Table 1

[0075] Adsorbent <![CDATA[Cs + 、Sr 2+ concentration]]> <![CDATA[Cs + Removal rate (%)]]> <![CDATA[Sr 2+ Removal rate (%)]]> Example 1 <![CDATA[MnO2@ZIF-8 / AMP@SA]]> 50 95.3 97.8 Example 2 <![CDATA[MnO2@ZIF-8 / AMP@SA]]> 50 82.1 85.6 Example 3 <![CDATA[MnO2@ZIF-8 / AMP@SA]]> 50 90.8 92.7 Comparative Example 1 AMP@SA 50 86.1 49.2 Comparative Example 2 ZIF-8 / AMP@SA 50 81.4 53.1

[0076] Table 2

[0077]

[0078] Figure 4 It is the cyclic regeneration diagram of the MnO2@ZIF-8 / AMP@SA aerogel in Example 1. The adsorbent after adsorption was eluted with 20 mL of 1 mol / L hydrochloric acid for the aerogel, dried in an oven for 24 h, and then used again for the adsorption experiment with Cs + , Sr 2+ solution. This process was repeated five times to study their cyclic performance. As can be seen from Figure 4 , after five cycles, the adsorption capacity for Cs + dropped to 25.24 ± 1 mg / g, and the adsorption efficiency only decreased by 10%. For Sr 2+ , the adsorption capacity dropped to 50.24 ± 1 mg / g, and the adsorption efficiency also only decreased by 10%. The results show that the MnO2@ZIF-8 / AMP@SA aerogel still has an adsorption efficiency as high as 90% for Cs + and Sr 2+ after five cycles, indicating that it is an adsorbent with good cyclic regeneration ability and can be used for repeated treatment of wastewater contaminated with Cs + and Sr 2+ .

[0079] Table 4

[0080] Adsorbent <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Pore volume (cm 3 / g)]]> Pore diameter (nm) Example 1 <![CDATA[MnO2@ZIF-8 / AMP@SA]]> 142.6182 0.3241 24.2445 Example 1 AMP@SA 89.1279 0.0124 17.2962 Example 1 ZIF-8 / AMP@SA 259.5692 0.4862 76.1443

[0081] Table 4 shows the BET test results of the adsorbent.

[0082] The specific surface areas of the AMP@SA aerogel, ZIF-8 / AMP@SA aerogel, and MnO2@ZIF-8 / AMP@SA aerogel obtained by multi-point BET calculation are 89.1279, 259.5692, and 142.6182 m 2 / g respectively. The specific surface area, pore volume, and pore diameter of the MnO2@ZIF-8 / AMP@SA aerogel decreased slightly compared with those of the ZIF-8 / AMP@SA aerogel. Considering that the loading of MnO2 increased the weight of the material, resulting in a decrease in the specific surface area, this is reasonable. The adsorption experiment also shows that as the materials are gradually compounded, the specific surface area increases, and the adsorption of Cs+ and Sr 2+ The ability is also enhanced.

[0083] Figure 5 Figure for the adsorption effect of the MnO2@ZIF-8 / AMP@SA aerogel in Example 1 at different pH values. It can be seen from the figure that at pH 3-7, the MnO2@ZIF-8 / AMP@SA aerogel adsorbs Cs + The capacity value remains above 30 mg / g, a decrease of about 25%, showing a relatively high adsorption capacity; for Sr 2+ The adsorption curve shows that at pH 3-6, the MnO2@ZIF-8 / AMP@SA aerogel has an adsorption capacity for Sr 2+ The capacity value remains above 40 mg / g, a decrease of about 12.5%.

[0084] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for adsorbing Cs from radioactive wastewater under acidic conditions + and Sr 2+ A method for preparing a composite aerogel, characterized in that: The steps include: (1) Synthesis of ammonium phosphomolybdate / sodium alginate aerogel; (2) Growth of ZIF-8 on the surface of ammonium phosphomolybdate / sodium alginate aerogel; (3) The material obtained in step (2) is modified to generate MnO2 to obtain a composite aerogel.

2. The method for preparing the composite aerogel according to claim 1, characterized in that: The specific steps of synthesizing the ammonium phosphomolybdate / sodium alginate aerogel in step (1) are: Ammonium phosphomolybdate is added to a sodium alginate solution, stirred, ultrasonicated, and freeze-dried to obtain a sodium alginate aerogel carrier containing ammonium phosphomolybdate, which is then immersed in a calcium nitrate solution for cross-linking, washed, and freeze-dried to obtain an ammonium phosphomolybdate / sodium alginate aerogel.

3. The method for preparing the composite aerogel according to claim 2, characterized in that: The mass ratio of ammonium phosphomolybdate to sodium alginate is 0.5-2:0.5-2; The concentration of the calcium nitrate solution is 0.1-1 mol / L; The stirring and ultrasonic reaction temperature is 30-50° C. and the time is 0-2 h.

4. The method for preparing the composite aerogel according to claim 1, characterized in that: The specific steps of growing ZIF-8 on the surface of ammonium phosphomolybdate / sodium alginate aerogel in step (2) are as follows: immersing the ammonium phosphomolybdate / sodium alginate aerogel in a zinc acetate dihydrate aqueous solution and a 2-methylimidazole aqueous solution in turn for a growth cycle, repeating the above growth steps three times, and freeze-drying; the zinc acetate dihydrate aqueous solution is prepared by dissolving zinc acetate dihydrate and valine in water.

5. The method for preparing the composite aerogel according to claim 4, characterized in that: The mass ratio of the ammonium phosphomolybdate, zinc acetate dihydrate, 2-methylimidazole and valine is: 0.5-2: 0.216-1.296: 0.662-3.972: 2.033-4.

066.

6. The method for preparing the composite aerogel according to claim 1, characterized in that: The specific steps of compounding MnO2 with the material obtained in step (2) in step (3) are: immersing the material obtained in step (2) in a potassium permanganate solution, stirring, freeze-drying, and washing.

7. The method for preparing the composite aerogel according to claim 6, characterized in that: The mass ratio of the ammonium phosphomolybdate and potassium permanganate is 0.5-2:0.05-0.

2.

8. A composite aerogel prepared according to the method according to any one of claims 1 to 7.

9. A composite aerogel according to claim 8 in adsorption of Cs + and Sr 2+ application.

10. The use according to claim 9, characterized in that: The steps include: adding the composite aerogel to a Cs-containing + and Sr 2+ The composite aerogel is washed, dried and separated after adsorption and can be reused. + and Sr 2+ The pH of the solution is 1-7.

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