Mg-Fe-CLDH composite material and preparation method and application thereof

Abstract

The invention relates to the technical field of adsorption composite material preparation, in particular to an Mg-Fe-CLDH composite material and a preparation method and application thereof. The preparation method comprises the following steps: dissolving a soluble magnesium salt and a soluble iron salt in water together to obtain a mixed cation solution; mixing the mixed cation solution with alkali liquor, carrying out coprecipitation reaction, crystallizing, separating and drying to obtain Mg-Fe-LDH; the Mg-Fe-CLDH composite material with high adsorption activity is obtained by calcining the Mg-Fe-LDH, so that the problem of potential toxicity of an aluminum element in traditional Mg-Al-LDH is successfully solved, and the adsorption activity and anti-interference performance on radioactive selenium oxygen-containing anions are remarkably improved through structural optimization; the method has important significance in improving the treatment efficiency of radioactive selenium oxygen-containing anions and realizing the stability of material application.

Description

Technical Field

[0001] This invention relates to the field of adsorption composite material preparation technology, specifically to a Mg-Fe-CLDH composite material, its preparation method, and its application. Background Technology

[0002] Nuclear energy, as a clean energy source with high energy density and low carbon emissions, boasts advantages such as stable power generation and minimal land occupation. It is currently the only non-fossil energy source capable of replacing fossil fuels on a large scale and providing baseload power. During nuclear fission reactions and the disposal of depleted fuel, a large amount of highly radioactive fission products are generated, among which selenium is… 235 One of the representative products of U fission, it is characterized by a long half-life, strong geochemical mobility, and high biotoxicity, such as... 79 Se has 3.7710 5 With a half-life of 1000 years, selenium poses a potential threat to the environment and human health if not properly disposed of. Especially in oxidizing environments, selenium often exists in highly soluble anionic forms, such as SeO3. 2- and SeO4 2- It is extremely easy for it to penetrate the soil and enter the water system.

[0003] In recent years, layered bimetallic hydroxides (LDHs) have shown broad application prospects in the field of environmental remediation due to their structural characteristics, including interlayer exchangeability, strong anion adsorption selectivity, and "memory effect." LDHs consist of a layered framework of divalent and trivalent metal cations connected by hydroxyl bridges, with exchangeable anions intercalated between the layers, enabling them to adsorb radioactive anions such as SeO3. 2- and SeO4 2- It has good adsorption and fixation capabilities.

[0004] However, although existing LDH materials show some potential, they still suffer from insufficient adsorption activity and weak anti-interference ability in the adsorption of radioactive selenium oxyanions, especially in complex nuclear waste systems, where it is difficult to balance high-efficiency adsorption with long-term stability. Among them, Mg-Al-LDH, prepared from magnesium nitrate and aluminum nitrate via a co-precipitation-hydrothermal method, has shown some potential in treating nuclear waste containing radioactive selenium oxyanions, but its widespread application in drinking water treatment is limited by the potential toxicity of aluminum. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a Mg-Fe-CLDH composite material, its preparation method, and its applications. The invention involves dissolving soluble magnesium and iron salts together in water to obtain a mixed cation solution. This mixed cation solution is then mixed with an alkaline solution and subjected to a co-precipitation reaction to obtain Mg-Fe-LDH. The Mg-Fe-LDH is then calcined to obtain a Mg-Fe-CLDH composite material with high adsorption activity. This invention uses iron ions as the layer metal ion, overcoming the potential toxicity problem of aluminum in traditional Mg-Al-LDH. Furthermore, the Mg-Fe-CLDH composite material of this invention significantly improves the adsorption activity and anti-interference performance for radioactive selenium-containing oxygen anions through structural optimization, which is of great significance for improving the treatment efficiency of radioactive selenium-containing oxygen anions and achieving stability in material applications.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first objective of this invention is to provide a method for preparing a Mg-Fe-CLDH composite material, comprising the following steps: S1. Dissolve soluble magnesium salt and soluble iron salt together in water to obtain a mixed cation solution.

[0007] S2. Mix the mixed cation solution with the alkaline solution and carry out a coprecipitation reaction. During the coprecipitation reaction, Mg... 2+ Under alkaline conditions, Mg(OH)₂ with a layered structure of brucite is first formed, followed by Fe. 3+ Replace some of the Mg in Mg(OH)2 2+ After crystallization, separation and drying, Mg-Fe-LDH was obtained.

[0008] S3. Calcine Mg-Fe-LDH. During the calcination process, the layered structure of Mg-Fe-LDH is destroyed, and MgFe2O4, MgO and Fe2O3 are formed to obtain Mg-Fe-CLDH composite material. The calcination conditions are: calcination at 400℃ for 4h~6h.

[0009] Preferably, in the mixed cation solution, Mg 2+ with Fe 3+ The molar ratio is 2~3:1; at this molar ratio, the Mg-Fe-CLDH composite material exhibits excellent adsorption performance; at the same time, this ratio can ensure a sufficient content of Fe ions in the system, so that they can play a more important role in the adsorption process.

[0010] Preferably, the alkaline solution is selected from sodium hydroxide solution or potassium hydroxide solution, and the concentration of the alkaline solution is 1.8 mol / L to 2.2 mol / L; more preferably, the alkaline solution is sodium hydroxide solution, and the concentration is 2 mol / L. Wherein, when the mixed cation solution and the sodium hydroxide solution are mixed, a 2 mol / L sodium hydroxide solution ensures that the two are mixed at similar titration rates, maintaining the pH value of the system relatively stable during the titration process.

[0011] Preferably, the crystallization conditions are: stirring at room temperature for at least 24 hours, the prototype structure of LDH recrystallizes under long-term stirring to form an ordered Mg-Fe-LDH layered structure.

[0012] A second objective of this invention is to provide a Mg-Fe-CLDH composite material prepared by the above-described preparation method.

[0013] Preferably, the Mg-Fe-CLDH composite material is composed of MgFe2O4, MgO and Fe2O3, where MgO and MgFe2O4 have a cubic structure and Fe2O3 has a strip structure.

[0014] A third objective of this invention is to provide the application of the above-mentioned Mg-Fe-CLDH composite material in the preparation of radioactive selenium oxygen-containing anion adsorbents.

[0015] Preferably, the radioactive selenium oxyanion is selected from SeO3. 2- SeO4 2- At least one of them.

[0016] The preferred application method is as follows: The Mg-Fe-CLDH composite material was mixed with a solution containing radioactive selenium-containing oxygen anions and stirred at 25°C and 200 rpm for 24 h. The Mg-Fe-CLDH composite material was then used to adsorb the radioactive selenium-containing oxygen anions. During adsorption, Fe₂O₃ and MgO in the Mg-Fe-CLDH composite material underwent a rehydration reaction, reforming the Mg-Fe-LDH phase. Simultaneously, the exposed metal-oxygen octahedral / tetrahedral structure on the surface of the MgFe₂O₄ spinel provided new active sites. These two factors synergistically enabled the Mg-Fe-CLDH composite material to efficiently immobilize radioactive selenium-containing oxygen anions while maintaining both interlayer anion exchange and metal coordination. Furthermore, the Mg-Fe-CLDH composite material calcined at 300°C only experienced edge collapse, while the main LDH layer remained intact, limiting the specific surface area and the number of active sites. The Mg-Fe-CLDH composite material calcined at 500°C, due to excessive granulation and agglomeration, lost the unique exchange function and porous advantages of the LDH layer, performing worse than the 400°C calcined composite material.

[0017] Preferably, the mass-to-volume ratio of the Mg-Fe-CLDH composite material to the solution containing radioactive selenium oxyanions is 100 mg: 50 mL, and the concentration of radioactive selenium oxyanions in the solution is 20 ppm to 100 ppm.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention provides a method for preparing a Mg-Fe-CLDH composite material, comprising dissolving soluble magnesium salt and soluble iron salt together in water to obtain a mixed cation solution; mixing the mixed cation solution with an alkaline solution and carrying out a co-precipitation reaction, wherein during the co-precipitation reaction, Mg... 2+ Under alkaline conditions, Mg(OH)₂ with a layered structure of brucite is first formed, followed by Fe. 3+ Replace some of the Mg in Mg(OH)2 2+ After crystallization, separation, and drying, Mg-Fe-LDH is obtained. Mg-Fe-LDH is then calcined, during which its layered structure is destroyed, forming MgFe₂O₄, MgO, and Fe₂O₃, resulting in a Mg-Fe-CLDH composite material. This invention uses iron ions as the layer metal ions, successfully solving the problem of potential aluminum toxicity in traditional Mg-Al-LDH and expanding its application range in drinking water treatment. By calcining Mg-Fe-LDH at 400℃, this invention achieves the coexistence of metal oxides and magnesium-iron oxides, giving the resulting Mg-Fe-CLDH composite material high adsorption activity and strong structural reconfigurability, effectively overcoming the shortcomings of existing LDH materials in complex nuclear waste systems where it is difficult to achieve both high-efficiency adsorption and long-term stability.

[0019] 2. The Mg-Fe-CLDH composite material provided by this invention exhibits excellent resistance to interference from coexisting ions and the significant advantage of non-toxic layer metals. This characteristic is mainly attributed to the fact that iron ions are used as layer metal ions, and that metal oxides and magnesium iron oxides coexist at a high temperature of 400℃. During adsorption, Fe2O3 and MgO in the Mg-Fe-CLDH composite material undergo a rehydration reaction and reform the Mg-Fe-LDH phase. Simultaneously, the exposed metal-oxygen octahedral / tetrahedral structure on the surface of MgFe2O4 spinel provides new active sites. These two factors synergistically enable the Mg-Fe-CLDH composite material to efficiently immobilize radioactive selenium oxygen-containing anions while maintaining the dual functions of interlayer anion exchange and metal coordination. These two factors work together to give the Mg-Fe-CLDH composite material a stronger adsorption efficiency and superior anti-interference ability during adsorption.

[0020] 3. The Mg-Fe-CLDH composite material of the present invention exhibits excellent adsorption capacity for radioactive selenium oxygen-containing anions of different valence states, namely SeO3. 2- and SeO4 2- Especially for SeO3 2- Its adsorption capacity is as high as 52.18 mg / g, demonstrating its great application potential in nuclear waste treatment. Attached Figure Description

[0021] Figure 1 The XRD patterns are of the Mg-Fe-CLDH composite materials of Example 1, Comparative Examples 1 to 2.

[0022] Figure 2 This is the TG-DTA curve of Mg-Fe-LDH.

[0023] Figure 3 The images are SEM images of Example 1 and Comparative Examples 1 to 2; where (a) is Mg-Fe-LDH, (b) is Comparative Example 1, (c) is Example 1, and (d) is Comparative Example 2.

[0024] Figure 4 The Mg-Fe-CLDH composite materials of Examples 1 and 2, as well as the effects of SeO3 on the reaction of these materials, are used in Examples 1 and 2. 2- SeO4 2- The fitting diagram of the dynamic adsorption model; where (a) is SeO3 2- (b) is SeO4 2- .

[0025] Figure 5 The adsorption of SeO3 by Mg-Fe-CLDH composite materials at different time points in Example 1 and Comparative Examples 1-2. 2- The XRD patterns are shown; where (a) is Comparative Example 1, (b) is Example 1, and (c) is Comparative Example 2.

[0026] Figure 6 The adsorption of SeO4 by the Mg-Fe-CLDH composite materials of Example 1 and Comparative Examples 1-2 at different time points. 2- The XRD patterns are shown; where (a) is Comparative Example 1, (b) is Example 1, and (c) is Comparative Example 2.

[0027] Figure 7 The Mg-Fe-CLDH composite materials of Examples 1 and 2, as well as the effects of SeO3 on the reaction of these materials, are used in Examples 1 and 2. 2- SeO4 2- The isothermal adsorption model fitting diagram; where (a) is SeO3 2- (b) is SeO4 2- .

[0028] Figure 8 The Mg-Fe-CLDH composite materials of Examples 1 and Comparative Examples 1-2, under the presence of different coexisting ions, showed the effect of Mg-Fe-CLDH on SeO3. 2- The adsorption effect diagram.

[0029] Figure 9 To illustrate the adsorption of SeO3 by Mg-Fe-CLDH composite materials in Examples 1 and 2 (Comparative Examples 1-2) under the presence of different coexisting ions. 2- The XRD patterns are shown below; (a) is Comparative Example 1, (b) is Example 1, and (c) is Comparative Example 2.

[0030] Figure 10 The Mg-Fe-CLDH composite materials of Examples 1 and Comparative Examples 1-2, under the presence of different coexisting ions, showed the effect of Mg-Fe-CLDH on SeO4. 2- The adsorption effect diagram.

[0031] Figure 11 To illustrate the adsorption of SeO4 by Mg-Fe-CLDH composite materials in Examples 1 and 2 (Comparative Examples 1 and 2) under the presence of different coexisting ions. 2- The XRD patterns are shown below; (a) is Comparative Example 1, (b) is Example 1, and (c) is Comparative Example 2. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below with reference to the data in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased on the market or prepared by existing methods.

[0034] In existing technologies, the potential toxicity of aluminum limits the widespread application of traditional Mg-Al-LDH materials in drinking water treatment. Furthermore, existing LDH materials exhibit low adsorption activity, weak anti-interference ability, and poor structural stability when adsorbing radioactive selenium oxygen anions, making it difficult to achieve a balance between efficient adsorption and long-term stability in complex nuclear waste systems.

[0035] To address the problems existing in the prior art, the present invention dissolves soluble magnesium salt and soluble iron salt together in water to obtain a mixed cation solution; mixes the mixed cation solution with an alkaline solution and performs a co-precipitation reaction to obtain Mg-Fe-LDH; calcines the Mg-Fe-LDH at 400°C to obtain a Mg-Fe-CLDH composite material that achieves the coexistence of metal oxides and magnesium iron oxides. This invention uses iron ions as the metal ions in the layers, overcoming the potential toxicity problem of aluminum in traditional Mg-Al-LDH. The Mg-Fe-CLDH composite material of this invention has the characteristics of high adsorption activity and strong structural reconfigurability. When used to adsorb radioactive selenium oxygen-containing anions, Fe2O3 and MgO in the Mg-Fe-CLDH composite material undergo a rehydration reaction during the adsorption process, and reform the Mg-Fe-LDH phase. At the same time, the metal-oxygen octahedral / tetrahedral structure exposed on the surface of MgFe2O4 spinel brings new active sites. The synergy of these two factors enables the Mg-Fe-CLDH composite material to efficiently fix radioactive selenium oxygen-containing anions while maintaining the dual functions of interlayer anion exchange and metal coordination. This significantly improves the adsorption activity and anti-interference performance of Mg-Fe-LDH, solves the problem of difficulty in balancing high-efficiency adsorption and long-term stability in the prior art, and achieves efficient and selective fixation of radioactive selenium oxygen-containing anions, providing a safer and more efficient solution for nuclear waste treatment.

[0036] To enable those skilled in the art to more clearly understand the technical solution of the present invention, the following will provide a detailed description in conjunction with specific embodiments: The Mg-Fe-LDH in this embodiment of the invention is prepared by the following method: Method 1: S1, based on Mg 2+ with Fe 3+ Weigh MgCl2 and FeCl3·6H2O in a molar ratio of 2:1, place them in a beaker and stir to obtain a mixed cation solution.

[0037] S2. Transfer 50 mL of the mixed cation solution into a PTFE burette. Simultaneously, inject 50 mL of 2 mol / L sodium hydroxide solution into another burette. Start the co-current titration program, keeping the pH constant at 13 during titration to obtain a precipitate. After titration, continue stirring at room temperature for 24 h to allow the precipitate to crystallize. Then, centrifuge at 6000 rpm for 5 min until the supernatant is neutral. Finally, collect the centrifuged precipitate and freeze-dry it for 24 h to obtain Mg-Fe-LDH for later use.

[0038] Method 2: S1, based on Mg 2+ with Fe 3+Weigh MgCl2 and FeCl3·6H2O in a molar ratio of 3:1, place them in a beaker and stir to obtain a mixed cation solution.

[0039] S2. Transfer 50 mL of the mixed cation solution into a PTFE burette. Simultaneously, inject 50 mL of 2 mol / L sodium hydroxide solution into another burette. Start the co-current titration program, keeping the pH constant at 13 during titration to obtain a precipitate. After titration, continue stirring at room temperature for 24 h to allow the precipitate to crystallize. Then, centrifuge at 6000 rpm for 5 min until the supernatant is neutral. Finally, collect the centrifuged precipitate and freeze-dry it for 24 h to obtain Mg-Fe-LDH for later use.

[0040] In Example 1 and Comparative Examples 1 to 2 of this invention, the Mg-Fe-LDH was prepared by Method 1.

[0041] Example 1 A method for preparing a Mg-Fe-CLDH composite material includes the following steps: Mg-Fe-LDH was placed in a box furnace and heated to 400℃ at a heating rate of 5℃ / min, and calcined for 5h to obtain Mg-Fe-CLDH composite material, denoted as 400℃.

[0042] Example 2 A method for preparing a Mg-Fe-CLDH composite material includes the following steps: Mg-Fe-LDH was placed in a box furnace and heated to 400℃ at a heating rate of 5℃ / min, and calcined for 4h to obtain Mg-Fe-CLDH composite material.

[0043] Example 3 A method for preparing a Mg-Fe-CLDH composite material includes the following steps: Mg-Fe-LDH was placed in a box furnace and heated to 400℃ at a heating rate of 5℃ / min, and calcined for 6 hours to obtain Mg-Fe-CLDH composite material.

[0044] Comparative Example 1 A method for preparing a Mg-Fe-CLDH composite material is the same as that in Example 1, except that the calcination temperature is changed from 400℃ to 300℃, and includes the following steps: Mg-Fe-LDH was placed in a box furnace and heated to 300℃ at a heating rate of 5℃ / min, and calcined for 5h to obtain Mg-Fe-CLDH composite material, denoted as 300℃.

[0045] Comparative Example 2 A method for preparing a Mg-Fe-CLDH composite material is the same as that in Example 1, except that the calcination temperature is changed from 400℃ to 500℃, and includes the following steps: Mg-Fe-LDH was placed in a box furnace and heated to 500℃ at a heating rate of 5℃ / min, and calcined for 5h to obtain Mg-Fe-CLDH composite material, namely MgFe2O4 spinel, denoted as 500℃.

[0046] a. Characterization: from Figure 1 The appearance of the (003) and (006) crystal plane diffraction peaks confirms the successful preparation of Mg-Fe-LDH. Compared with Mg-Fe-LDH, the (003) and (006) crystal plane diffraction peaks of the Mg-Fe-CLDH composite material disappeared after calcination, indicating that the layered structure collapsed. Among them, the Mg-Fe-CLDH composite material of Comparative Example 1 showed weak broad peaks at 35° and 43°, further indicating that calcination at 300°C destroyed the layered structure of Mg-Fe-LDH, and water molecules and some hydroxyl groups in the layer were removed. The sharpness and intensity of the characteristic peaks of MgO, Fe2O3 and MgFe2O4 in the Mg-Fe-CLDH composite material of Example 1 were significantly improved, indicating the formation of well-crystallized metal oxides and spinel phases, proving that the Mg-Fe-CLDH composite material of Example 1 is mainly composed of MgO, Fe2O3 and MgFe2O4. With the increase of calcination temperature, that is, the intensity of each oxide diffraction peak in the Mg-Fe-CLDH composite material of Comparative Example 2 increased synchronously, indicating that the content of crystalline phases continued to increase.

[0047] observe Figure 2 It was found that the Mg-Fe-LDH composite material undergoes two stages of weight loss: first, the removal of adsorbed and interlayer water in the 31℃~182℃ range, resulting in a 13% mass loss; and second, the breakage and escape of lamellar hydroxyl groups in the 182℃~600℃ range, leading to a 21% weight loss, which is the dominant stage of total weight loss. A slight fluctuation at 51℃ indicates simultaneous desorption of weakly bound water. The extreme value at 296℃ indicates that the decomposition rate of lamellar hydroxyl groups reaches its maximum, and the decomposition rate approaches 0 at 600℃, indicating that the LDH layered structure completely collapses at this temperature.

[0048] Depend on Figure 3 As shown in (a), Mg-Fe-LDH exhibits a typical lamellar structure with a relatively uniform distribution. Figure 3 As shown in (b) of Comparative Example 1, the lamellar edges of the Mg-Fe-LDH composite material exhibit bending and collapse, and the boundaries between the lamellars become blurred, indicating that the layered structure is disrupted. Figure 3As shown in (c), the lamellar structure on the surface of the Mg-Fe-LDH composite material in Example 1 completely disappeared, revealing a large amount of cubic MgO and MgFe2O4, and a small amount of strip-shaped Fe2O3. Figure 3 As shown in (d), the surface of the Mg-Fe-LDH composite material in Comparative Example 2 exhibits a uniformly distributed cubic structure or agglomerated morphology, without obvious independent strip-shaped Fe2O3 structural features, indicating that the Fe species mainly enter the spinel phase.

[0049] Taking the Mg-Fe-CLDH composite materials of Example 1 and Comparative Examples 1 to 2 as examples, their adsorption performance was studied, specifically as follows: (1) Adsorption kinetics of Mg-Fe-CLDH composite material: Prepare a 20 ppm Na₂SeO₃ / Na₂SeO₄ solution for later use. Mix 100 mg of the Mg-Fe-CLDH composite material from Example 1 and Comparative Examples 1-2 with 50 mL of the 20 ppm Na₂SeO₃ / Na₂SeO₄ solution, respectively, and place them in a constant temperature shaking incubator at 25 °C and 200 rpm for 5 min, 30 min, 1 h, 5 h, 7 h, 12 h, and 24 h, respectively. After shaking, take 10 mL of the supernatant and collect the filtrate through a 0.45 μm filter. Collect the solid by vacuum filtration and store it in a vacuum desiccator to dry at room temperature, and weigh it.

[0050] To investigate the effect of Mg-Fe-CLDH composites prepared at different calcination temperatures on SeO3 2- The adsorption process and rate control mechanism were analyzed by fitting a pseudo-first-order kinetic model and a pseudo-second-order kinetic model. The fitting results are shown in Table 1.

[0051] The pseudo-first-order dynamics formula is as follows: .

[0052] In the formula, q t mg / g represents the amount of adsorption at a specific moment. q e mg / g represents the equilibrium adsorption capacity. t min represents the reaction time. k 1 , 1 / min, is the pseudo-first-order rate constant.

[0053] The pseudo-second-order dynamics formula is: .

[0054] In the formula, q t mg / g represents the amount of adsorption at a specific moment. q emg / g represents the equilibrium adsorption capacity. t min represents the reaction time. k 2 , g / mg·min, is the pseudo-second-order rate constant.

[0055] Table 1 shows the effect of Mg-Fe-CLDH composite materials on SeO3 in Example 1 and Comparative Examples 1-2. 2- Table of fitting parameters for the dynamic adsorption model Among them, Q e cal R represents the theoretical equilibrium adsorption amount, K represents the adsorption rate constant, and R represents the adsorption rate constant. 2 Indicates the goodness of fit.

[0056] from Figure 4 The fitting results show that the Mg-Fe-CLDH composite materials of Example 1 and Comparative Examples 1-2 exhibit some differences in kinetic behavior. Their adsorption behavior all conforms to the pseudo-second-order adsorption kinetic model, indicating that the Mg-Fe-CLDH composite materials of Example 1 and Comparative Examples 1-2 show some differences in kinetic behavior. 2- Chemical bonding occurs during adsorption.

[0057] Depend on Figure 5 Figures (a) and (b) show that, during the adsorption process, the Mg-Fe-CLDH composite materials of Comparative Example 1 and Example 1 both exhibit a memory effect that induces structural reconstruction, thereby forming a structure more conducive to SeO3. 2- Adsorption interlayer structure. With increasing adsorption time, the Mg-Fe-CLDH composite material of Comparative Example 1 exhibited weak characteristic peaks on the (003) and (006) crystal planes, and no significant new crystalline phase was formed throughout the process. This result indicates that the Mg-Fe-CLDH composite material underwent layered structure reconstruction, i.e., magnesium oxide and iron oxide reconstituted into layered Mg-Fe-CLDH, but the reconstruction trend was relatively slow and weaker than that of the Mg-Fe-CLDH composite material of Example 1. Observation Figure 5 Figure (b) shows that during the adsorption process, the Mg-Fe-CLDH composite material of Example 1 exhibits significant structural dynamics: its layered structure is not only significantly restored, but its diffraction peak intensity gradually increases over time, demonstrating the progressive reconstruction of the Mg-Fe-CLDH phase; while the diffraction peak of MgFe2O4 remains stable throughout and does not disappear.

[0058] Furthermore, based on the parameters in Table 1, the adsorption rate constants K2 of the Mg-Fe-CLDH composites in Comparative Example 1 and Comparative Example 2 are relatively low, at 0.00502 g / mg·min and 0.00039 g / mg·min, respectively. This result indicates that the Mg-Fe-CLDH composites in Comparative Example 1 and Comparative Example 2 exhibit a more moderate adsorption process, and the time required to reach adsorption equilibrium is longer than that of the Mg-Fe-CLDH composite in Example 1. Figure 5 Figure (c) shows that no layered structure reconstruction was observed at the calcination temperature of 500℃, indicating that high-temperature calcination completely transformed the Mg-Fe-LDH in Comparative Example 2 into MgFe2O4 spinel. Therefore, the Mg-Fe-CLDH composite material in Comparative Example 2 exhibits good adhesion to SeO3. 2- The adsorption is actually achieved by using MgFe2O4 as the main adsorbent.

[0059] Table 2 shows the effect of Mg-Fe-CLDH composite materials on SeO4 in Example 1 and Comparative Examples 1 to 2. 2- Table of fitting parameters for the dynamic adsorption model Among them, Q e cal R represents the theoretical equilibrium adsorption amount, K represents the adsorption rate constant, and R represents the adsorption rate constant. 2 Indicates the goodness of fit.

[0060] Combine Table 2 and Figure 6 It was found that the Mg-Fe-CLDH composite materials of Example 1 and Comparative Examples 1 to 2 showed good efficacy against SeO4. 2- The adsorption of all of them follows pseudo-second-order kinetic adsorption, and with SeO3 2- Its adsorption behavior is consistent with that of SeO4; and its adsorption behavior for SeO4 is consistent with that of SeO4. 2- However, the adsorption capacity of the Mg-Fe-CLDH composite material decreased to varying degrees, which means that the adsorption capacity of the Mg-Fe-CLDH composite material for SeO3... 2- It has higher adsorption efficiency and selectivity.

[0061] (2) Isothermal adsorption of Mg-Fe-CLDH composite material: Prepare Na₂SeO₃ / Na₂SeO₄ solutions with concentrations of 20 ppm, 30 ppm, 40 ppm, 50 ppm, 60 ppm, 80 ppm, and 100 ppm for later use. Mix 50 mL of each of the Na₂SeO₃ / Na₂SeO₄ solutions with concentrations of 20 ppm, 30 ppm, 40 ppm, 50 ppm, 60 ppm, 80 ppm, and 100 ppm with 100 mg of the Mg-Fe-CLDH composite material from Example 1 and Comparative Examples 1 to 2, and shake continuously in a constant temperature shaking oven at 25 °C and 200 rpm for 24 h. After shaking, take 10 mL of the supernatant and collect the filtrate through a 0.45 μm filter. Collect the solid by vacuum filtration and store it in a vacuum desiccator to dry at room temperature, and weigh it.

[0062] The isothermal adsorption experimental data of Mg-Fe-CLDH composite material were fitted using Langmuir and Freundlich models, and the results are shown in Table 3.

[0063] The nonlinear form of the Langmuir model is: .

[0064] In the formula, q e mg / g represents the equilibrium adsorption capacity. C e mg / L represents the equilibrium concentration. q max mg / g indicates the maximum adsorption capacity. K L L / mg represents the Langmuir constant.

[0065] The nonlinear form of the Freundlich model is: .

[0066] In the formula ，q e mg / g represents the equilibrium adsorption capacity. C e mg / L represents the equilibrium concentration. q max mg / g indicates the maximum adsorption capacity. K F (mg / g)·(L / mg) 1 / n This represents the Langmuir constant.

[0067] Table 3 shows the effect of Mg-Fe-CLDH composite materials on SeO3 in Example 1 and Comparative Examples 1 to 2. 2- Table of fitting parameters for the isothermal adsorption model in,q m cal This represents the theoretical maximum adsorption capacity. K L This represents the equilibrium constant for adsorption. R 2 Indicates the goodness of fit; n It reflects the heterogeneity of surface sites and the degree to which adsorption strength changes with concentration. K F This represents the "overall capacity / affinity index" of the adsorbent for the adsorbate at a given temperature. R 2 Indicates the goodness of fit.

[0068] Depend on Figure 7 Figure (a) shows that the Mg-Fe-CLDH composite materials of Example 1 and Comparative Examples 1-2 are more consistent with the Freundlich adsorption model, indicating that SeO3 2- They occupy surface sites with uneven energy distribution through multi-molecule stacking or gradient methods. Among them, the Mg-Fe-CLDH composite material in Example 1 has a higher adsorption capacity, which is attributed to its "semi-dehydrated" state. Figure 2 TG-DTA analysis showed that at 400℃, only interlayer water and some hydroxyl groups were removed, while Mg-OH and Fe-OH were partially retained. The metal centers were not completely oxidized and fixed, achieving an optimal balance between memory effect and surface activity. Simultaneously, the specific surface area did not shrink due to excessive sintering, and interlayer chloride ions did not completely escape, leaving potential sites for further exposure and synergistically enhancing SeO3 content. 2- The adsorption capacity, therefore, the Mg-Fe-CLDH composite material of Example 1 for SeO3 2- The adsorption mechanism involves ion exchange during the reconstruction of the layered structure, i.e., electrostatic adsorption and the adsorption of SeO3 by metal oxides. 2- The outer sphere coordination effect, while the Mg in the Mg-Fe-CLDH composite material of Comparative Example 1... 2+ Fe 3+ It remains tightly bound to the hydroxyl group and is fixed by the hydroxyl group, unable to form an active oxide. The theoretical adsorption capacity of the Mg-Fe-CLDH composite material in Example 1 for Se(Ⅳ) is the highest at 52.182 mg / g, indicating that the active sites of the Mg-Fe-CLDH composite material in Example 1 reach their maximum value, exhibiting the best adsorption capacity. The theoretical adsorption capacity of the Mg-Fe-CLDH composite material in Comparative Example 2 is similar to that of the Mg-Fe-CLDH composite material in Comparative Example 1, but the Mg-Fe-CLDH composite material in Comparative Example 2 has lost its memory effect reconstruction ability. Therefore, its adsorption mechanism has changed to MgFe2O4 adsorbing SeO3. 2- The external sphere combination effect.

[0069] Table 4 shows the effect of Mg-Fe-CLDH composite materials on SeO4 in Example 1 and Comparative Examples 1 to 2. 2- Table of fitting parameters for the isothermal adsorption model Combine Table 4 and Figure 7 (b) It is concluded that the Mg-Fe-CLDH composite materials of Example 1 and Comparative Examples 1 to 2 are effective for SeO4 2- The adsorption also better conforms to the Freundlich model of adsorption. The Mg-Fe-CLDH composite material in Example 1 shows significantly higher adsorption capacity, a phenomenon consistent with the previous analysis of SeO3. 2- The results of the adsorption capacity difference analysis were consistent. However, the Mg-Fe-CLDH composite material in Example 1 showed consistent adsorption capacity differences for SeO4. 2- The adsorption capacity is significantly lower than that for SeO3. 2- The adsorption capacity of the Mg-Fe-CLDH composite material in Example 1 shows that the adsorption mechanisms of the two Se valence states are not entirely the same. This is mainly because the adsorption capacity of the Mg-Fe-CLDH composite material in Example 1 for SeO3 is different. 2- In addition to ion exchange and the outer sphere coordination effect, there is also an inner sphere coordination effect that makes SeO3... 2- Compared to SeO4 2- More is adsorbed, and the binding becomes tighter.

[0070] (3) Competitive adsorption experiment of coexisting anions: According to Mg 2+ Fe 3+ A 0.6 mmol / L Na₂SeO₃ / Na₂SeO₄ solution was prepared as a solvent with an anion in a molar ratio of 2-3:1:1. 250 mL of the required solute mass for the 0.6 mmol / L competing ion solution was weighed and mixed with 100 mg of the Mg-Fe-CLDH composite material from Example 1 and Comparative Examples 1-2. The mixture was then continuously shaken in a constant temperature shaking oven at 25°C and 200 rpm for 24 h. After shaking, 10 mL of the supernatant was collected through a 0.45 μm filter. The solid was collected by vacuum filtration and dried at room temperature in a vacuum desiccator, then weighed. The competing ions were selenite, silicate, hydrogen phosphate, carbonate, sulfate, aspartic acid, and cysteine.

[0071] Different coexisting anions affect the adsorption of SeO3 on Mg-Fe-CLDH composite materials. 2- The impact such as Figure 8 As shown. In the presence of coexisting anions, the Mg-Fe-CLDH composite material of Example 1 shows its effect on SeO3. 2-The adsorption effect of HPO4 was superior to that of the Mg-Fe-CLDH composite materials in Comparative Examples 1 and 2, which is consistent with the aforementioned conclusions. Regarding the influence of different coexisting ions, HPO4... 2- CO3 2- and SO4 2- The presence of SeO3 significantly reduced 2- Retention of HPO4 in Mg-Fe-CLDH composites, especially 2- The impact is most pronounced on CO3. 2- SO4 2- For Mg-Fe-CLDH composites on SeO3 2- The adsorption mechanism of SiO3 is interlayer ion exchange, while the Mg-Fe-CLDH composite material in Comparative Example 2, having lost its layered structure, is mainly affected by the external spherical coordination effect. 2- The formation of hydrated magnesium silicate by coating the surface of the Mg-Fe-CLDH composite material with MgO affected the Mg-Fe-CLDH composite material's ability to resist SeO3. 2- The adsorption of [something] also inhibited the recovery of the layered structure of the Mg-Fe-CLDH composite material, which is related to [something]. Figure 9 The XRD results in Figure (b) are consistent.

[0072] The Mg-Fe-CLDH composite material in Comparative Example 2 formed stable MgFe2O4 due to high-temperature calcination, and could no longer react with SiO3. 2- A reaction occurs, therefore SiO3 2- At this calcination temperature, it mainly reacts with CO3. 2- SO4 2- Similarly, through the external sphere coordination effect with SeO3 2- Competing for adsorption sites. The amino acid molecules aspartic acid and cysteine ​​inhibit the adsorption of SeO3 by the Mg-Fe-CLDH composite materials of Comparative Example 1 and Example 1. 2- The impact is relatively small. Aspartic acid and cysteine ​​have larger molecular radii compared to other coexisting ions, making it difficult for them to enter the interlayer for ion exchange. Therefore, the Mg-Fe-CLDH composite materials in Comparative Example 1 and Example 1 mainly affect SeO3 through ion exchange. 2- The adsorption of Asp is affected. Furthermore, Asp affects the adsorption of SeO3 by the Mg-Fe-CLDH composite material in Comparative Example 2. 2- The effect of the Mg-Fe-CLDH composite material in Comparative Example 2 on SeO3 is significantly greater than that on the Mg-Fe-CLDH composite material in Comparative Example 2. 2- The adsorption no longer involves interlayer ion exchange; it can only adsorb SeO3 through the outer sphere coordination effect. 2- This gives Asp more opportunities to interact with SeO3.2- Competitive adsorption occurs.

[0073] Different coexisting anions affect the adsorption of SeO4 on Mg-Fe-CLDH composite materials. 2- The impact such as Figure 10 and Figure 11 As shown, the Mg-Fe-CLDH composite material in Example 1 exhibits the highest adsorption capacity, and different coexisting ions show varying adsorption rates for SeO4. 2- The adsorption mechanism of SeO3 2- Basically the same.

[0074] By comparing the effects of Mg-Fe-CLDH composites on SeO3 at different calcination temperatures... 2- SeO4 2- The adsorption characteristics revealed that the Mg-Fe-CLDH composite material exhibits good adsorption properties for SeO3. 2- It exhibits higher adsorption capacity, especially the Mg-Fe-CLDH composite material of Example 1. Coexisting ion pair SeO4 2- The leaching effect is much greater than that of SeO3. 2- This indicates that, compared to the Mg-Fe-CLDH composites of Comparative Examples 1 and 2, the Mg-Fe-CLDH composite of Example 1 exhibits better performance in terms of SeO3 content. 2- The adsorption of Mg-Fe-CLDH composite material is more stable, further demonstrating its effectiveness in adsorbing SeO3. 2- In addition to interlayer ion exchange and the outer sphere coordination effect of metal oxides, there is also an inner sphere coordination reaction that enables SeO3 to... 2- Compared to SeO4 2- More is adsorbed, and the binding becomes tighter and more stable.

[0075] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

Claims

1. A method for preparing a Mg-Fe-CLDH composite material, characterized in that, Includes the following steps: Soluble magnesium salt and soluble iron salt are dissolved together in water to obtain a mixed cation solution; The mixed cation solution is mixed with a lye and a coprecipitation reaction is carried out, during which Mg 2+ Under alkaline conditions, Mg(OH)2of brucite layer structure is first formed, and then Fe 3+ substitutes part of Mg in Mg(OH)2 2+ , and after crystallization, separation and drying, Mg-Fe-LDH is obtained; Mg-Fe-LDH was calcined. During the calcination process, the layered structure of Mg-Fe-LDH was destroyed, and MgFe2O4, MgO and Fe2O3 were formed to obtain Mg-Fe-CLDH composite material. The calcination conditions are as follows: calcination at 400℃ for 4 to 6 hours.

2. The preparation method of the Mg-Fe-CLDH composite material according to claim 1, characterized in that, Mg 2+ 3+ The molar ratio of Mg to Fe is 2-3:1.​ 3. The method for preparing the Mg-Fe-CLDH composite material according to claim 1, characterized in that, The alkaline solution is selected from sodium hydroxide solution or potassium hydroxide solution, and the concentration of the alkaline solution is 1.8 mol / L to 2.2 mol / L.

4. The method for preparing the Mg-Fe-CLDH composite material according to claim 1, characterized in that, The crystallization conditions are: stirring at room temperature for at least 24 hours.

5. A Mg-Fe-CLDH composite material, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 4.

6. The Mg-Fe-CLDH composite material according to claim 5, characterized in that, The Mg-Fe-CLDH composite material is composed of MgFe2O4, MgO and Fe2O3. MgO and MgFe2O4 have a cubic structure, while Fe2O3 has a strip structure.

7. The application of the Mg-Fe-CLDH composite material of claim 6 in the preparation of a radioactive selenium oxygen-containing anion adsorbent.

8. The application of the Mg-Fe-CLDH composite material according to claim 7 in the preparation of a radioactive selenium oxygen-containing anion adsorbent, characterized in that, The radioactive selenium oxoanion is selected from at least one of SeO3 2- , SeO4 2- .

9. The application of the Mg-Fe-CLDH composite material according to claim 7 in the preparation of a radioactive selenium oxygen-containing anion adsorbent, characterized in that, The application method is as follows: The Mg-Fe-CLDH composite material was mixed with a solution containing radioactive selenium oxygen-containing anions and stirred at 25℃ and 200 rpm for 24 h to adsorb radioactive selenium oxygen-containing anions. During the adsorption process, Fe2O3 and MgO in the Mg-Fe-CLDH composite material undergo a rehydration reaction and reform the Mg-Fe-LDH phase. At the same time, the metal-oxygen octahedral / tetrahedral structure exposed on the surface of MgFe2O4 spinel brings new active sites. The two work together to enable the Mg-Fe-CLDH composite material to efficiently immobilize radioactive selenium oxygen-containing anions while maintaining the dual functions of interlayer anion exchange and metal coordination.

10. The application of the Mg-Fe-CLDH composite material according to claim 9 in the preparation of a radioactive selenium oxygen-containing anion adsorbent, characterized in that, The mass-to-volume ratio of the Mg-Fe-CLDH composite material to the solution containing radioactive selenium oxyanions is 100 mg: 50 mL. The concentration of radioactive selenium oxyanions in the solution is 20 ppm to 100 ppm.

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