Preparation method of structured adsorbent and application of structured adsorbent in extraction of uranium from seawater

Abstract

The invention discloses a preparation method of a structured adsorbent and application of the structured adsorbent in extraction of uranium from seawater. The preparation method comprises the following steps: (1) heating iron salt at 85-120 DEG C until the iron salt is completely molten; (2) carrying out ultrasonic cleaning on the foamed nickel in diluted hydrochloric acid, absolute ethyl alcohol and deionized water for 10-20 minutes in sequence, and then blow-drying the foamed nickel with nitrogen; and (3) completely immersing the cleaned foamed nickel into molten ferric salt to react for 2-10 minutes, then taking out the foamed nickel, washing the foamed nickel with deionized water, and placing the foamed nickel in air to be naturally aired after unreacted ferric salt on the surface is completely washed away, so that the structured adsorbent is obtained. The material shows excellent performance when being applied to the process of adsorbing uranium in seawater. The invention provides a new material for efficiently extracting uranium from seawater, does not need complex operation steps, effectively avoids the generation of wastes in the material preparation process, is simpler and more environment-friendly in synthesis method, and provides possibility for large-scale preparation.

Description

Technical Field

[0001] The present invention belongs to the technical field of uranium extraction from seawater, and specifically relates to a preparation method of a structured nickel-iron hydrotalcite adsorbent and its application in uranium extraction from seawater. Background Art

[0002] As an important nuclear energy fuel, the full development and efficient utilization of uranium resources are of great significance for the sustainable development of energy. Although the reserves of uranium in the earth's crust are limited, seawater contains huge potential resources (the total amount of uranium is about 4.5 billion tons). This provides broad prospects for the development and utilization of uranium resources in the future. However, the uranium concentration in seawater is extremely low (about 3 μg / L), the salt content is high, and there are various coexisting ions. Therefore, achieving efficient selective extraction of uranium has always been a huge technical challenge. Summary of the Invention

[0003] The purpose of the present invention is to provide a preparation method of a structured adsorbent and its application in uranium extraction from seawater. In the synthesis process of the present invention, only iron salts containing crystal water are used as raw materials. For example, the mass fraction of water in ferric nitrate nonahydrate is as high as 40%. Therefore, during the heating process, the iron salt is relatively easy to form a molten liquid, and the molten iron salt has strong acidity, which can corrode the surface of nickel foam in micro-regions. This corrosion process not only provides the active sites required for the growth of nickel-iron hydrotalcite, but also can provide Ni for the synthesis of nickel-iron hydrotalcite. 2+ The prepared structured nickel-iron hydrotalcite shows excellent performance in the process of adsorbing uranium from seawater. The present invention provides a new material for efficient uranium extraction from seawater, effectively avoiding the generation of waste during the material preparation process, and without complex operation steps. The synthesis method is simpler and more environmentally friendly, providing the possibility for large-scale preparation.

[0004] The preparation method of the structured adsorbent is as follows: (1) Heat the iron salt to complete melting at 85 - 120 °C; (2) Ultrasonically clean the nickel foam in dilute hydrochloric acid, absolute ethanol, and deionized water for 10 - 20 min in sequence, and then dry it with nitrogen; (3) Immerse the cleaned nickel foam completely into the molten iron salt, react for 2 - 10 minutes, then take it out, rinse with deionized water, and place it in the air to dry naturally after the unreacted iron salt on the surface is completely washed off, thus obtaining the structured adsorbent.

[0005] The iron salt is selected from one or more of ferric nitrate, ferric chloride, ferric sulfate, and ferric acetate containing crystal water.

[0006] The mass fraction of the dilute hydrochloric acid is 2 - 5%.

[0007] The application of the above-prepared structured adsorbent in extracting uranium from seawater. Beneficial effects

[0008] 1. The process of the present invention is simple, and the raw materials used are only iron salts without adding external water, so there will be no wastewater generated. In addition, this method can easily scale up the preparation of large-area structural materials (see the subsequent examples for details), which is difficult to achieve by the existing hydrothermal method and electrodeposition.

[0009] 2. The structured nickel-iron layered double hydroxide provided by the present invention shows very good selectivity and extraction ability in the actual application of uranium extraction from seawater. Most of the existing uranium adsorbents have only been tested in simulated seawater, and the application effects in actual seawater are not provided or are poor. Description of the drawings

[0010] Figure 1 Photographs of iron nitrate before and after melting in Example 1.

[0011] Figure 2 XRD pattern of NiFe-LDH@NF prepared in Example 1.

[0012] Figure 3 Low-magnification SEM image of NiFe-LDH@NF prepared in Example 1.

[0013] Figure 4 High-magnification SEM image of NiFe-LDH@NF prepared in Example 1.

[0014] Figure 5 TEM image of NiFe-LDH@NF nanosheets prepared in Example 1.

[0015] Figure 6 HRTEM image of NiFe-LDH@NF nanosheets in Example 1.

[0016] Figure 7 Digital photograph of NiFe-LDH@NF in Example 2.

[0017] Figure 8 XRD pattern of NiFe-LDH@NF in Example 2.

[0018] Figure 9 XPS spectrum of uranium after adsorption by NiFe-LDH@NF in Application Example 3. Detailed implementation manners Example 1

[0019] (1) Weigh 15 g of ferric nitrate nonahydrate and place it in a petri dish (Φ = 5 cm), and heat it at 110 °C for 20 min to make it completely melt. Figure 1 Photographs during the melting process of ferric nitrate.

[0020] (2) The nickel foam (NF) substrate with a size of 1.0×1.5 cm² was ultrasonically cleaned with dilute hydrochloric acid (3%), absolute ethanol, and deionized water for 10 min each, and then dried with nitrogen.

[0021] (3) The pretreated NF substrate was quickly immersed in molten iron(III) nitrate nonahydrate for 3 minutes. After the reaction was completed, the NF substrate was quickly taken out, rinsed with deionized water to remove the residual molten salt on the surface, and the attached liquid was wiped off with filter paper. Finally, it was air-dried at room temperature to obtain NiFe-LDH@NF. Figure 2 The X-ray diffraction (XRD) pattern of the NiFe-LDH@NF material prepared by the molten salt method is shown. It can be observed from the figure that the diffraction peak at 11.5° corresponds to the (003) crystal plane of LDHs, which is a characteristic peak of the LDH structure, indicating that the material has a highly ordered layered structure. The diffraction peaks at 44.5° and 51.8° are attributed to the characteristic peaks of the nickel foam substrate. Figure 3 The low-magnification scanning electron microscope (SEM) image of the NiFe-LDH@NF material is shown. It can be clearly observed from the figure that the NiFe-LDH material is uniformly loaded on the surface of the nickel foam (NF) substrate, and no obvious agglomeration or local enrichment phenomenon appears. The three-dimensional network structure of the nickel foam provides sufficient support space for the growth of the LDH material, enabling NiFe-LDH to form a continuous covering layer on its surface. This uniformly distributed property not only helps to increase the specific surface area of the material but also provides more active sites for subsequent adsorption reactions. Figure 4 is the SEM image of the NiFe-LDH@NF material at a high magnification. It can be seen from the figure that the NiFe-LDH material is composed of a large number of nanosheet units. These nanosheets exhibit a typical corrugated structure and are arranged in an interlaced manner to form a porous three-dimensional network. Figure 5 is the TEM image of NiFe-LDH. It can be seen that the NiFe-LDH material exhibits a typical two-dimensional transparent nanosheet structure. Figure 6 is the characterization diagram of the lattice fringes of NiFe-LDH@NF by high-resolution transmission electron microscopy (HR-TEM). By measuring the lattice fringe spacing, the lattice spacings of 0.23 nm and 0.19 nm are measured, corresponding to the (015) and (018) crystal planes of hydrotalcite, further confirming that the material is NiFe-LDH@NF. Example 2

[0022] (1) Weigh 150 g of iron(III) nitrate nonahydrate and place it in a petri dish (Φ = 10 cm), and heat it at 120 °C for 15 min to make it completely molten.

[0023] (2) The nickel foam (NF) substrate with a diameter of 6.0 cm was ultrasonically cleaned with dilute hydrochloric acid (3%), absolute ethanol, and deionized water for 10 min each, and then dried with nitrogen.

[0024] (3) The pretreated NF substrate was quickly immersed in molten iron(III) nitrate nonahydrate for 3 minutes. After the reaction was completed, the NF substrate was quickly taken out, rinsed with deionized water to remove the residual molten salt on the surface, and the attached liquid was wiped off with filter paper. Finally, it was air-dried at room temperature to obtain NiFe-LDH@NF. Figure 7 Figure 1 is the physical digital photo of the obtained NiFe-LDH@NF. Figure 8 Figure 2 is the XRD pattern of the prepared NiFe-LDH@NF. It can be seen that the characteristic peaks at 11.5° and 34.4° can be attributed to the (003) and (101) diffraction peaks of the typical LDH phase, and the diffraction peaks at 44.5° and 51.8 ° are attributed to the characteristic peaks of the nickel foam substrate, indicating the successful preparation of the material.

[0025] Application Example 1: The NiFe-LDH@NF adsorbent obtained in Example 1 was placed in a 200 mL beaker, and 100 mL of uranium-containing solution prepared with deionized water was added, where the concentration of uranium was 5 mg / L. After magnetic stirring at room temperature for 60 minutes, the upper layer solution was taken and filtered through a 0.22 μm filter membrane, and then the concentration of uranium ions in it was measured by ICP-MS. The results showed that the removal rate of uranium in the solution by the prepared NiFe-LDH@NF reached 99.5%, showing extremely high removal efficiency. To prove that NiFe-LDH in NiFe-LDH@NF plays a major role, we conducted a comparative experiment, that is, using NF obtained in the second step of Example 1 as the adsorbent and placing it under the conditions of Application Example 1 to investigate the adsorption effect of NF itself on uranium. The results showed that the removal rate of uranium in the solution by NF was only 8%, proving that NiFe-LDH in NiFe-LDH@NF plays a major role in the adsorption process.

[0026] Application Example 2: The NiFe-LDH@NF adsorbent obtained in Example 1 was placed in a 200 mL beaker, and 100 mL of uranium-containing solution was added, where the concentration of uranium was 5 mg / L. To explore its good selectivity and anti-interference ability, the solution also contained Na + (400 mg / L), K + (400 mg / L), Mg 2+ (400 mg / L), Ca 2+ (400 mg / L), Cl − (400 mg / L), SO4 2−(400 mg / L). After magnetic stirring at room temperature for 60 minutes, the upper layer solution was taken and filtered through a 0.22 μm filter membrane, and then the uranium ion concentration in it was measured by ICP-MS. The results showed that the removal rate of uranium in the solution by the prepared NiFe-LDH@NF reached 99.2%. Combining with Application Example 1, it can be seen that the prepared NiFe-LDH@NF showed extremely high removal efficiency and anti-interference ability under the conditions of calcium and magnesium ion contents in simulated seawater.

[0027] Application Example 3: The NiFe-LDH@NF adsorbent obtained in Example 1 was placed in a 200 mL beaker, and 100 ml of natural seawater (the natural seawater was collected from the sea area of Huangdao District near Lingshan Island, Qingdao, and the specific geographical location was 35.82°N, 120.18°E) was added, in which the uranium concentration was 3.2 μg / L. After magnetic stirring at room temperature for 12 hours, the upper layer solution was taken and filtered through a 0.22 μm filter membrane, and then the uranium ion concentration in it was measured by ICP-MS. The results showed that the removal rate of uranium in the solution by the prepared NiFe-LDH@NF reached 98.5%. Combining with Application Example 1 and Application Example 2, it can be seen that the prepared NiFe-LDH@NF still showed excellent removal efficiency and anti-interference ability in real seawater. Figure 9 It is the XPS diagram of NiFe-LDH@NF after adsorption. It can be clearly seen that characteristic peaks of hexavalent uranium appeared at 381.6 and 392.7 eV, indicating that uranium in seawater was significantly adsorbed on NiFe-LDH@NF.

Claims

1. A method for preparing a structured adsorbent, characterized in that: The specific steps of the preparation method are: (1) Heat the iron salt at 85-120°C until it is completely melted; (2) ultrasonically clean the nickel foam in dilute hydrochloric acid, anhydrous ethanol, and deionized water for 10-20 min, and then blow dry with nitrogen; (3) The cleaned nickel foam is completely immersed in molten iron salt and reacted for 2-10 minutes, then taken out and rinsed with deionized water. After the unreacted iron salt on the surface is completely washed away, it is placed in the air to dry naturally, thereby obtaining a structured adsorbent.

2. The preparation method according to claim 1, characterized in that: The iron salt is selected from one or more of ferric nitrate, ferric chloride, ferric sulfate and ferric acetate containing crystal water.

3. The preparation method according to claim 1, characterized in that: The mass fraction of the dilute hydrochloric acid is 2-5%.

4. Use of the structured adsorbent prepared according to the method according to any one of claims 1 to 3 in extracting uranium from seawater.

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