Method for preparing composite aerogel for treating radioactive contamination and application thereof

Abstract

The application discloses a preparation method and application of a composite aerogel for treating radioactive contamination, and comprises the following steps: soaking Physocarpus amurensis seeds in ultrapure water, then oscillating and stirring, rotating evaporation of a polysaccharide solution obtained to 1 / 4 of the original volume, and storing in an ethanol solution overnight; collecting precipitates and redissolving in ultrapure water, freeze-drying to obtain Physocarpus amurensis seed glue; mixing ultrapure water with the Physocarpus amurensis seed glue and calcium nitrate, and simultaneously performing mechanical stirring; adding (NH4)2HPO4 while stirring, and maintaining the pH level at about 10; aging the mixture, and then freeze-drying; and obtaining a natural polymer Physocarpus amurensis seed glue / hydroxyapatite aerogel. The composite gel freeze-drying technology is used to combine the large contact area of three-dimensional materials with the effective adsorption characteristics of nanometer adsorption materials, and the prepared Physocarpus amurensis seed glue / hydroxyapatite composite aerogel has a remarkable adsorption effect on uranium in radioactive wastewater.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of aerogel preparation and application, and particularly relates to a preparation method and application of a composite aerogel for treating radioactive pollution. BACKGROUND

[0002] With the continuous development of industrialization, nuclear energy, as a safe and reliable clean energy, plays an increasingly important role in the global energy system. Uranium can be released into the environment through uranium leaching, natural uranium deposits and nuclear facility decommissioning. Therefore, people can easily consume uranium through all food supplies, and uranium can accumulate in the body, causing various diseases and eventually death. Uranium has been removed and recovered through coagulation and sedimentation, ion exchange, electrochemistry and photocatalytic reduction technology. Among the currently used technologies, adsorption has become one of the most promising technologies. In recent years, it has been found that nano-adsorbents have strong enrichment capacity for uranium in wastewater, especially nano-hydroxyapatite for uranium adsorption. Hydroxyapatite (HAP) is a mineral type calcium phosphate compound. Due to the ion exchange capacity of Ca 2+ and OH - and the affinity of PO4 3- for certain ions, it contacts with metal cations in wastewater to form insoluble and stable minerals. HAP also has many unique properties, including good biocompatibility and bioactivity, non-toxicity, availability, low cost, ion exchange properties and low solubility due to its special crystal structure. Due to these excellent properties, HAP has been used to remove heavy metals in aqueous solutions, and the immobilization of uranium on HAP is one of the current research hotspots. However, the small size and obvious agglomeration tendency of nano-adsorbent particles hinder the adsorption capacity, making it difficult for HAP to expose the surface active sites. Therefore, manufacturing bulk nano-adsorbent materials is a direction to solve the problem of overlapping adsorption sites.

[0003] Due to its ultra-low density, high specific surface area and high porosity, three-dimensional aerogels are often used in the field of uranium removal and recovery. According to the different raw materials, aerogels can be divided into inorganic aerogels, organic aerogels and carbon aerogels. Silica and zinc oxide are the most commonly used inorganic aerogels, but they are scarce, pollute the environment and are not renewable. Organic aerogels are mainly natural polysaccharide aerogels and protein aerogels, and polysaccharide aerogels have attracted great attention in the field of environmental wastewater treatment due to their low density and good biodegradability. These polysaccharides and their derivatives contain functional groups such as hydroxyl, carboxyl and amino in their structures, have high chemical activity, and provide natural adsorption sites for uranium in water, but the adsorption capacity is limited, the efficiency is low, and there is no selectivity. Therefore, the combination of polysaccharides and their derivatives with nano-adsorbents to form three-dimensional biomimetic assemblies with high active site exposure is an effective way to achieve high adsorption capacity of materials. SUMMARY

[0004] An object of the present application is to solve at least the above problems and / or drawbacks, and to provide at least the advantages later described.

[0005] To achieve these objects and other advantages in accordance with the purpose of the application, as embodied and broadly described herein, there is provided a method for preparing a composite aerogel for treating radioactive contamination, comprising the steps of:

[0006] Step one, soaking the physic nut seed in ultrapure water, then oscillating and stirring, the obtained polysaccharide solution is rotary evaporated to 1 / 4 of its original volume, and stored in an ethanol solution overnight; collecting the precipitate and redissolving in ultrapure water, freeze-drying to obtain physic nut seed gum;

[0007] Step two, mixing ultrapure water with physic nut seed gum and calcium nitrate, while mechanical stirring; while stirring, adding (NH4)2HPO4, and maintaining the pH level at about 10; aging the mixture, then freeze-drying; obtaining a natural polymer physic nut seed gum / hydroxyapatite aerogel.

[0008] Preferably, in the step one, the mass-volume ratio of the physic nut seed to ultrapure water is 1g:8-12mL.

[0009] Preferably, in the step one, the soaking time is 5-15min; the oscillation time is 5-15min, and the stirring time is 20-40min.

[0010] Preferably, in the step one, the temperature of the ethanol solution is 2-6℃.

[0011] Preferably, in the step one, the physic nut seed gum is pretreated, and the pretreatment process is: adding 3-5g of physic nut seed gum in a supercritical CO2 reaction device, then filling 10MPa CO2, heating to 40-45℃, again filling CO2 to a pressure of 15-25MPa, soaking in the formed supercritical CO2 for 30-60min, then depressurizing at a speed of 0.5MPa / min; obtaining pretreated physic nut seed gum.

[0012] Preferably, in the step two, the mass-volume ratio of the physic nut seed gum to ultrapure water is 1g:150-250mL; the mass ratio of the physic nut seed gum to calcium nitrate is 1:0.4-0.8.

[0013] Preferably, in the step two, the mass ratio of the physic nut seed gum to (NH4)2HPO4 is 1:0.1-0.3.

[0014] Preferably, in the step two, the aging time is 18-36 hours.

[0015] Preferably, the freezing drying time in the step two is 60-80 hours; and the freezing drying condition is -50℃ to -60℃ and 4-8 Pa.

[0016] The application further provides a composite aerogel prepared by the preparation method, the composite aerogel having a three-dimensional structure and a specific surface area of 30-35 m 2 / g

[0017] The application further provides application of the composite aerogel prepared by the preparation method in radioactive pollution treatment, wherein the composite aerogel is added into uranium-containing radioactive wastewater and stirred to realize adsorption of uranium in the radioactive wastewater.

[0018] The application has at least the following beneficial effects: the composite gel freezing drying technology is used to combine the large contact area of the three-dimensional material with the effective adsorption characteristics of the nanometer adsorption material, and the prepared physalis seed gum / hydroxyapatite composite aerogel has a remarkable adsorption effect on uranium in radioactive wastewater.

[0019] Other advantages, objects and features of the application will be apparent from the following description, and will be understood by those skilled in the art. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 (a) is an SEM image of NPG, Figure 1 (b) is an SEM image of NPG-HAP, Figure 1 (c) is an FT-IR image of NPG and NPG-HAP, Figure 1 (d) is an XRD image of NPG and NPG-HAP;

[0021] Figure 2 (a) is an adsorption effect image of NPG, HAP and NPG-HAP under different pH conditions, Figure 2 (b) is a Zeta potential of NPG and NPG-HAP under different pH conditions, Figure 2 (c) is an existing form of uranium in aqueous solution at various pH values, Figure 2 (d) is an effect of the adsorbent dosage on the uranium removal efficiency;

[0022] Figure 3 is an effect image of NPG, HAP and NPG-HAP on removal of uranium under different initial uranium concentrations;

[0023] Figure 4 is an effect image of NPG-HAP and NPG-HAP-1 on removal of uranium under different initial uranium concentrations;

[0024] Figure 5Figure showing the variation of uranium removal with time for NPG, HAP, NPG-HAP;

[0025] Figure 6 Figure showing the variation of uranium removal with time for NPG-HAP, NPG-HAP-1;

[0026] Figure 7 (a) FT-IR spectra of NPG-HAP before and after adsorption of uranium, Figure 7 (b) XRD patterns of NPG-HAP before and after adsorption of uranium; Figure 7 (c) N2 adsorption-desorption isotherms of NPG-HAP before and after adsorption of uranium, Figure 7 (d) Pore size distribution of NPG-HAP. DETAILED DESCRIPTION

[0027] The application will be further described in conjunction with the drawings, so that those skilled in the art can implement the application according to the description and drawings.

[0028] It should be understood that the terms such as "have", "contain" and "include" used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0029] Example 1:

[0030] A preparation method of a composite aerogel for treating radioactive contamination, comprising the following steps:

[0031] Step one, 10g of fructus physaliis seeds are soaked in 100mL of ultrapure water for 10 minutes, then oscillated for 10 minutes and stirred for 30 minutes. The obtained polysaccharide solution is rotary evaporated to 1 / 4 of its original volume and stored in an ethanol solution at 4℃ overnight. The precipitate is collected and redissolved in ultrapure water, and freeze-dried to obtain fructus physaliis seed gum (NPG);

[0032] Step two, 100mL of ultrapure water is mixed with 0.5g of fructus physaliis seed gum and 0.295g of calcium nitrate (Ca(NO3)2·4H2O) while mechanical stirring is carried out; at the same time, 0.1g of (NH4)2HPO4 is added, and the pH level is maintained at about 10; the mixture is aged for 24 hours, and then freeze-dried for 72 hours (freeze-drying conditions are -56℃ and 6Pa); a natural polymer fructus physaliis seed gum / hydroxyapatite aerogel (NPG-HAP) is obtained.

[0033] Example 2:

[0034] A preparation method of a composite aerogel for treating radioactive contamination, comprising the following steps:

[0035] Step one, 10 g of Fructus Physalis seed was soaked in 100 mL of ultrapure water for 10 minutes, then shaken for 10 minutes and stirred for 30 minutes, the obtained polysaccharide solution was rotary evaporated to 1 / 4 of its original volume, and stored in an ethanol solution at 4℃ overnight; the precipitate was collected and redissolved in ultrapure water, freeze-dried to obtain Fructus Physalis seed gum (NPG); the Fructus Physalis seed gum (NPG) was pretreated, and the pretreatment process was as follows: 4 g of Fructus Physalis seed gum was added to a supercritical CO2 reaction device, then 10 MPa of CO2 was filled, heated to 45℃, 20 MPa of CO2 was filled again, and soaked in the formed supercritical CO2 for 45 min, then depressurized at a speed of 0.5 MPa / min; the pretreated Fructus Physalis seed gum was obtained;

[0036] Step two, 100 mL of ultrapure water was mixed with 0.5 g of pretreated Fructus Physalis seed gum and 0.295 g of calcium nitrate (Ca(NO3)2·4H2O) while mechanical stirring was carried out; while stirring, 0.1 g of (NH4)2HPO4 was added, and the pH level was maintained at about 10; the mixture was aged for 24 hours, then freeze-dried for 72 hours (freeze-drying conditions were -56℃ and 6 Pa); a natural polymer Fructus Physalis seed gum / hydroxyapatite aerogel (NPG-HAP-1) was obtained.

[0037] The NPG-HAP prepared in Example 1 was tested for relevant performance, and the scanning electron microscope images of NPG and NPG-HAP are shown in Figure 1 (a)、 Figure 1 (b). The results show that the surface of the original NPG is smooth, but the surface of the NPG-HAP is rough, which indicates that the two molecules are successfully combined together, and the morphology of the NPG-HAP is inclined to the original NPG.

[0038] The chemical structure of NPG and NPG-HAP was analyzed by infrared spectrum and X-ray diffraction pattern. Figure 1 (c) shows the FT-IR spectra of NPG and NPG-HAP in the range of 4000 cm -1 to 500 cm -1 . The peak at 2882 cm -1 belongs to the vibration of C-H bond. Although the peaks at 1409 cm -1 and 820 cm -1 belong to CO3 2- groups, the peak at 1600 cm -1 in NPG and NPG-HAP belongs to the stretching vibration of COO-. The peaks at 604 cm -1 and 564 cm -1 belong to the anti-symmetry and symmetry bending modes of phosphate respectively, while the peaks at 900-1100 cm-1 The peaks of NPG-HAP are related to the stretching vibration band of P-O bond in hydroxyapatite. Figure 1 (d) shows the X-ray diffraction patterns of NPG and NPG-HAP. Compared with pure NPG, the diffraction peaks of HAP are observed on the X-ray diffraction image of NPG-HAP aerogel, which indicates that NPG is successfully combined with HAP. For example, the peaks of NPG-HAP aerogel at 2q = 25.5°, 31.7°, 39.6°, 46.3° and 49.3° are related to HAP, further proving the successful preparation of NPG-HAP.

[0039] The adsorption properties of the prepared aerogels on uranium were tested by creating a series of adsorption tests controlling various variables (pH, time, adsorbent mass, anions and cations, initial concentration of uranium solution, etc.). Specifically, in the adsorption tests, 5 mg of the prepared sample was added to a solution containing 20 mL of a determined concentration of configured uranium solution and magnetic stirring was used to stir at 250 rpm until the adsorption was complete. The measurements of U(VI) were determined on a UV-2365 spectrophotometer using the arsenazo III colorimetric method to calculate the adsorption efficiency (η, %) and the adsorption capacity (qe, mg / g) of the synthetic material on uranium, calculated as follows:

[0040]

[0041]

[0042] where C e (mg / L) represents the amount of uranium solution remaining after adsorption, C0(g / L) represents the concentration of the uranium solution before adsorption. m (g) represents the weight of the sample and V (mL) represents the volume of the uranium solution used in the adsorption test.

[0043] The pH value changes the chemical state of the active sites of the adsorbent and the form of uranium in the solution, thus affecting the adsorption capacity of the adsorbent on uranium. In different pH ranges, the uranyl ion can present as UO2 2+ , (UO2)2(OH)2 2+ , [UO2)3(OH) 2+ , [UO2]4(OH) 7+ , and so on Figure 2 (c)). The effect of the pH of the solution in the range of 2 to 7 on the uranium extraction performance was studied by adding 5 mg of adsorbent to 20 mL of solution (uranium concentration: 100 mg / L) Figure 2(a)). The uranium adsorption capacity of NPG-HAP increased when the pH increased from 2 to 3, remained stable at pH = 3-4, and sharply decreased between pH 4 and 7. Moreover, NPG-HAP had a higher uranium adsorption capacity than pure NPG and HAP, with a removal rate of 93.2% at pH 3-4. The Zeta potential of NPG and NPG-HAP is shown in Figure 2 (b). The zeta potential of NPG-HAP was relatively stable between pH = 5 and pH = 7, while the zeta potential of NPG only slightly decreased as the pH increased from 2 to 7. At pH = 5, the surface charge of NPG-HAP was -41.23 mV, while that of NPG was -19.56 mV. NPG-HAP had a higher uranium extraction capacity than NPG over a certain pH range. In solutions with a pH lower than 7.0, the uranyl ion mainly exists in the form of a cation, and the lower surface charge of NPG-HAP enhances the adsorption of UO2 2+ by electrostatic interaction.

[0044] The solid-liquid ratio of the adsorbent also affects the performance of the adsorption material. The present invention studied the adsorption capacity of adsorbents with a range of 5 to 30 g of adsorption material added under the same volume, concentration, and adsorption time, and the results are shown in Figure 2 (d). According to the results of this experiment, the uranium adsorption capacity was the largest at a mass of 5 mg of NPG-HAP, which was used for other tests. The adsorption capacity of NPG, HAP, and NPG-HAP for uranium showed similar trends. The removal rate of uranium by the adsorption material increased with the increase in the amount of adsorbent, but the change in the adsorption capacity was exactly the opposite of the removal rate. This is because when the adsorbent is in excess in the solution, the active sites of the adsorbent aggregation overlap with the unbound active sites, resulting in a decrease in the effective specific surface area of the adsorbent. Importantly, the uranium adsorption efficiency of NPG-HAP exceeded that of NPG and HAP regardless of the mass of the adsorbent, which indicates that NPG-HAP provides more active sites for binding with uranium.

[0045] Adsorption tests were conducted at five initial uranium concentrations and under the same conditions (20 mL of uranium solution, 5 mg of adsorbent (aerogel), pH = 4, 250 rpm stirring) to further study the relationship between the concentration of the starting solution and the adsorption performance of the produced material, and the results are shown in Figure 3 and Figure 4 As the concentration of UO2 2+ increased, the adsorption capacity of UO2 2+ on NPG-HAP increased faster than the adsorption capacity of NPG and HAP, and the adsorption capacity of UO2 2+The adsorption capacity on NPG-HAP-1 is higher than that of NPG-HAP, which shows that the pretreatment of the seed glue of F. limonia L. achieves better experimental results.

[0046] The prepared aerogel material was tested for its adsorption performance for uranium within 6 hours (20 mL of 100 mg / L uranium solution, 5 mg of adsorbent (aerogel), pH = 4, 250 rpm stirring). The results are shown in Figure 5 and 6 , wherein the adsorption capacity of uranium increases rapidly in a short time as the contact time increases, and when the adsorption capacity reaches the highest point, it reaches equilibrium near 1 hour.

[0047] FT-IR spectroscopy, X-ray diffraction and specific surface area measurement were used to evaluate the changes of the manufactured material after adsorption to study the adsorption strategy of NPG-HAP for uranium. The results of FT-IR spectroscopy are shown in Figure 7 (a). The peaks at 1090, 1035, 614 and 560 cm -1 are related to the stretching of phosphate, and it is found that the intensity of the unique peak of the phosphate group is greatly reduced due to the interaction of the phosphate and uranium complex. The material after adsorbing uranium shows a new peak at 914 cm -1 , which is caused by the unpaired stretching of uranyl ion, indicating that the NPG-HAP aerogel material successfully adsorbs uranium.

[0048] Additional changes in the elemental content and chemical valence of the material surface before and after adsorption were obtained using X-ray photoelectron spectroscopy Figure 7 (b)). In contrast, diffraction peaks with new species were observed, especially at 10.36°, 19.18° and 23.3°, which are well matched with the (001), (110) and (102) crystal planes of Ca(UO2)2(PO4)2, respectively, proving that the subsequent precipitation formation fixes uranium on the NPG-HAP aerogel.

[0049] The pore size of the N2 adsorption / desorption isotherm of NPG-HAP before and after adsorbing uranium was analyzed. The BET surface area of NPG-HAP before adsorption is 31.91 m 2 / g, and the BET specific surface area of NPG-HAP after adsorbing uranium decreases to 4.03 m 2 / g Figure 7 (c), and the average pore size decreases from 12.1759 nm to 15.8739 nm (see Figure 7 (d)). It can be seen that the precipitation of Ca(UO2)2(PO4)2 formed by the contact of the aerogel with uranium, which fixes the uranium on the surface of NPG-HAP, leads to a decrease in specific surface area and an increase in average pore size.

[0050] While embodiments of the application have been disclosed in connection with the above specification and drawings this description is not intended to limit the scope of the application and many modifications, enhancements, alternatives, and variations will become apparent to those skilled in the art from this disclosure. Accordingly, it is intended that the application not be limited to the described embodiments, but that it include all variations falling within the scope of the claims, and their equivalents.

Claims

1. A method for preparing a composite aerogel for treating radioactive contamination, characterized in that: The following steps are involved: Step 1: soaking Physalis alkekengi seeds in ultrapure water, then shaking and stirring, rotary evaporating the obtained polysaccharide solution to 1 / 4 of its original volume, and storing it in an ethanol solution overnight; collecting the precipitate and redissolving it in ultrapure water, freeze-drying it, and obtaining Physalis alkekengi seed gum; The Physalis alkekengi seed glue is pretreated, and the pretreatment process is as follows: adding 3-5 g of Physalis alkekengi seed glue to a supercritical CO2 reaction device, then charging 10 MPa CO2, heating to 40-45° C., charging CO2 again to a pressure of 15-25 MPa, soaking in the formed supercritical CO2 for 30-60 minutes, and then releasing the pressure at a rate of 0.5 MPa / min; obtaining pretreated Physalis alkekengi seed gum; Step 2: Mixing ultrapure water with pretreated Physalis alkekengi seed gum and calcium nitrate while mechanically stirring; adding (NH4)2HPO4 while stirring, and maintaining the pH level at 10; aging the mixture, and then freeze-drying it to obtain a natural polymer Physalis alkekengi seed gum / hydroxyapatite aerogel; In the step 2, the mass volume ratio of the pseudophragmites seed gum to ultrapure water is 1g:150-250mL; the mass volume ratio of the pseudophragmites seed gum to calcium nitrate is 1:0.4-0.8; In the step 2, the mass ratio of Physalis alkekengi seed gum to (NH4)2HPO4 is 1:0.1-0.

3.

2. The method for preparing a composite aerogel for treating radioactive contamination according to claim 1, wherein: In the step 1, the mass volume ratio of Physalis alkekengi seeds to ultrapure water is 1 g:8-12 mL.

3. The method for preparing a composite aerogel for treating radioactive contamination according to claim 1, wherein: In the step 1, the soaking time is 5 to 15 minutes; the shaking time is 5 to 15 minutes, and the stirring time is 20 to 40 minutes.

4. The method for preparing a composite aerogel for treating radioactive contamination according to claim 1, wherein: In the step 1, the temperature of the ethanol solution is 2-6°C.

5. The method for preparing a composite aerogel for treating radioactive pollution according to claim 1, wherein: In the step 2, the aging time is 18 to 36 hours.

6. The method for preparing a composite aerogel for treating radioactive pollution according to claim 1, wherein: In the step 2, the freeze-drying time is 60 to 80 hours; and the freeze-drying conditions are -50°C to -60°C and 4 to 8 Pa.

7. A composite aerogel for treating radioactive contamination prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The pseudophysalis seed gum / hydroxyapatite aerogel has a three-dimensional structure and a specific surface area of ​​30-35 m 2 / g.

8. Use of a composite aerogel for treating radioactive contamination prepared by the preparation method according to any one of claims 1 to 6 in treating radioactive wastewater, characterized in that: The composite aerogel is added into uranium-containing radioactive wastewater and stirred to achieve adsorption of uranium in the radioactive wastewater.

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