Preparation and Application of a Biomass-Based Composite Thermosensitive Material for Enrichment and Separation of Radioactive Elements

Abstract

The present invention discloses the preparation and application of a biomass-based composite thermosensitive material for radioactive element enrichment and separation, including: dissolving KGM and FeSO4·7H2O in deionized water, then adding an EDTA-2Na solution, and then dropping an NH3·H2O solution into the above solution and stirring. After the reaction, it is left to age; adding Na2CO3 to the aged solution, stirring, then adding absolute ethanol and slowly stirring, and then filtering. The obtained flocculent material is washed with ethanol solutions of different concentrations until neutral, the ethanol is volatilized and then dried, and ground to the microgel level with a ball mill; the ground material is dispersed in water, NIPAM and (NH4)2S2O8 are added, and after heating and reacting under a nitrogen atmosphere, it is washed and dried to obtain a biomass-based composite thermosensitive material. The biomass-based composite thermosensitive material prepared by the present invention can realize an arbitrary transformation from a dispersed state with a high specific surface area at low temperature to a stable aggregated state at high temperature, and can also capture dissociated uranyl ions through rich oxygen-containing functional groups, and then realize the reduction and fixation of uranium through active substances.

Description

Technical Field

[0001] The present invention belongs to the field of radioactive element treatment. More specifically, the present invention relates to the preparation and application of a biomass-based composite thermosensitive material for radioactive element enrichment and separation. Background Art

[0002] Nuclear energy has become an increasingly important clean energy globally due to its safety and reliability. However, the production of nuclear fuel, the operation of nuclear power plants, and the decommissioning of nuclear facilities generate a large amount of radioactive wastewater. Among them, uranium (U(VI)) is one of the harmful radioactive nuclides in such wastewater. Due to the strong coordination ability of uranyl ions (UO2 2+ ) with carbonate ligands (k = 2×10 18 ), carbonate complexes such as UO2(CO3)3 4- , UO2(OH)3 - and UO2(CO3)2 2- are easily formed in radioactive wastewater, making the enrichment and removal of uranium complex. Therefore, developing new uranium extraction technologies to replace traditional adsorption and membrane separation technologies to remove and recover uranium from carbonate-containing uranium wastewater is one of the urgent challenges in the field of nuclear waste treatment.

[0003] Photo-assisted uranium extraction, as an emerging technology, provides new ideas for extracting uranium from carbonate-containing uranium wastewater due to the electron-driven accelerated extraction kinetics and selectivity for non-reducing coexisting ions. However, traditional photocatalysts mainly rely on powdered nano-photocatalysts, and their difficult separation from the reaction medium limits their practical applications. To solve this problem, hydrogels are being explored as three-dimensional network photocatalytic carriers. Hydrogels provide a porous framework structure that can prevent catalyst leakage and allow a large amount of catalyst loading. However, the contact area between the loaded photocatalyst and the target reactant metal ions in the aqueous solution is limited, which results in limited removal ability of the hydrogel photocatalyst. One of the key challenges that must be solved is how to effectively combine the advantages of high-contact area powdered photocatalysts with the favorable simple recovery characteristics of bulk hydrogels. Fortunately, the emergence of intelligent thermosensitive materials indicates a breakthrough in solving the above challenges. Among them, the research on intelligent thermosensitive materials represented by poly(N-isopropylacrylamide) (PNIPAM) has been mature. The originality of intelligent thermosensitive materials lies in their ability to dynamically change their physical state. At high temperatures, these materials seamlessly aggregate to form a cohesive structure with enhanced stability and functionality. When exposed to a colder temperature, they disperse, thus achieving a high reaction rate. Therefore, introducing intelligent thermosensitive materials into photocatalytic hydrogels is a promising strategy for efficiently extracting uranium from carbonate-containing uranium wastewater. Summary of the Invention

[0004] An object of the present invention is to solve at least the above problems and / or deficiencies and provide at least the advantages described hereinafter.

[0005] To achieve these objects and other advantages of the present invention, a preparation method of a biomass-based composite thermosensitive material for radioactive element enrichment and separation is provided, including the following steps:

[0006] Step 1: Dissolve KGM and FeSO4·7H2O in deionized water, and then add an EDTA-2Na aqueous solution; dropwise add an NH3·H2O aqueous solution to the above solution and stir until the pH value of the solution is 7-9, the color of the solution is dark green, then stir for 0.5-1.5 hours, the color of the solution changes from dark green to yellowish brown, the pH value of the solution is 4.5-5.5, and let it stand for aging for 1-3 hours;

[0007] Step 2: Add Na2CO3 to the aged solution, stir for 1-3 hours, then add absolute ethanol to the obtained mixed solution and stir slowly and then filter. The flocculent material obtained after filtration is washed with ethanol solutions with decreasing concentrations until neutral, the ethanol is volatilized and then dried, and the obtained material is ground by a ball mill to the microgel level;

[0008] Step 3: Disperse the ground microgel-level material in water, add N-isopropylacrylamide (NIPAM) and (NH4)2S2O8, heat in a nitrogen atmosphere at 70-80 °C for 30-50 minutes, then wash with water 2-4 times, and then dry the material to obtain a biomass-based composite thermosensitive material for radioactive element enrichment and separation, that is, a γ-FeOOH / KGM / PNIPAM composite thermosensitive material.

[0009] Preferably, in the step 1, the mass-volume ratio of KGM, FeSO4·7H2O and deionized water is 10 g: 1-5 g: 200-300 mL.

[0010] Preferably, in the step 1, the concentration of the EDTA-2Na aqueous solution is 0.05-0.15 mol / L, and the molar ratio of Fe 2+ and EDTA-2Na is 1:0.03.

[0011] Preferably, in the step 1, the volume ratio of NH3·H2O to water in the NH3·H2O aqueous solution is 1:0.8-1.2.

[0012] Preferably, in the step 2, the mass percentage of Na2CO3 to the deionized water in the step 1 is 1.5-2.5%; the volume ratio of absolute ethanol to the mixed solution is 1:0.8-1.2.

[0013] Preferably, in the second step, the concentrations of the ethanol solutions are 100%, 95%, 75%, and 50% from high to low, respectively.

[0014] Preferably, in the third step, the mass-to-volume ratio of the ground microgel-level material to water is 1 g: 80 - 120 mL; the mass ratio of the ground microgel-level material, NIPAM, and (NH4)2S2O8 is 20: 40 - 50: 2.5 - 3.5.

[0015] Preferably, in the first and third steps, drying is carried out by vacuum drying at 50 - 70 °C.

[0016] The present invention also provides an application of a biomass-based composite thermosensitive material prepared by the above preparation method in the enrichment and separation of radioactive elements. It is characterized in that the biomass-based composite thermosensitive material is added to carbonate uranium-containing wastewater, and the reaction is carried out in a light and ventilated environment. The reacted biomass-based composite thermosensitive material is put into an eluent, stirred and washed, and reused by circulation.

[0017] Preferably, the eluent is a 0.1 mol / L HCl solution.

[0018] The present invention has at least the following beneficial effects: The present invention provides a preparation method of a biomass-based composite thermosensitive material for the enrichment and separation of radioactive elements. A temperature-sensitive material PNIPAM is introduced into the γ-FeOOH / KGM hydrogel to achieve an arbitrary transition from a dispersed state with a high specific surface area at low temperature to a stable aggregated state at high temperature. The uranyl ions are captured by the abundant oxygen-containing functional groups on konjac glucomannan (KGM) and γ-FeOOH, and then the reduction and fixation of free uranyl ions are achieved through active substances such as e - and ·O2 - etc. The biomass-based composite thermosensitive material prepared by the present invention shows a higher uranium removal rate and cycle stability in carbonate uranium-containing wastewater, providing a promising solution for treating radioactive wastewater and having great potential in water purification applications.

[0019] Other advantages, objectives, and features of the present invention will be partially reflected by the following description and partially understood by those skilled in the art through the research and practice of the present invention. Description of the Drawings

[0020] Figure 1 SEM image of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4;

[0021] Figure 2FT-IR spectra of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4, the 0.6% γ-FeOOH / KGM hydrogel prepared in Comparative Example 1, and PNIPAM prepared in Comparative Example 2 from 4000 cm -1 to 400 cm -1 ;

[0022] Figure 3 XRD patterns of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4, the 0.6% γ-FeOOH / KGM hydrogel prepared in Comparative Example 1, and γ-FeOOH;

[0023] Figure 4 Water contact angle images of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4;

[0024] Figure 5 DSC images of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4 and PNIPAM prepared in Comparative Example 2;

[0025] Figure 6 Comparison chart of uranium removal rates of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4 with different addition amounts (10 - 110 mg);

[0026] Figure 7 Comparison chart of uranium removal rates of γ-FeOOH / KGM / PNIPAM composite thermosensitive materials with different γ-FeOOH contents (10% - 50%) prepared in Examples 1 - 5;

[0027] Figure 8 Uranium removal rates of γ-FeOOH / KGM / PNIPAM composite thermosensitive materials with different γ-FeOOH contents (10% - 50%) prepared in Examples 1 - 5 at different pH values (7 - 11);

[0028] Figure 9 Comparison chart of uranium removal rates of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4, the 0.6% γ-FeOOH / KGM hydrogel prepared in Comparative Example 1, and γ-FeOOH;

[0029] Figure 10 Comparison of uranium removal rates of the first and fifth continuous cycle uranium removal of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4, the 0.6% γ-FeOOH / KGM hydrogel prepared in Comparative Example 1, and γ-FeOOH;

[0030] Figure 11 Uranium removal rates of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4 under different inhibitors (methanol, KBrO3, tert-butanol, and p-benzoquinone);

[0031] Figure 12 ·O2 - and ·OH EPR images of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4;

[0032] Figure 13 Transient photocurrent response images of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4;

[0033] Figure 14 FT-IR spectra of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4 before and after the uranium removal reaction. Detailed implementation mode

[0034] The following further describes the present invention in detail with reference to the accompanying drawings, so that those skilled in the art can implement it according to the text of the specification.

[0035] It should be understood that terms such as "having", "comprising", and "including" used herein do not exclude the presence or addition of one or more other elements or their combinations.

[0036] Example 1

[0037] A preparation method of a biomass-based composite thermosensitive material for radioactive element enrichment and separation, comprising the following steps:

[0038] Step 1: Dissolve KGM and FeSO4·7H2O in deionized water, and the mass-volume ratio of KGM, FeSO4·7H2O, and deionized water is 10 g:1 g:250 mL. Then add an EDTA-2Na aqueous solution (0.1 mol / L) to keep the molar ratio of Fe 2+ and EDTA-2Na at 1:0.03. Prepare an NH3·H2O aqueous solution (volume ratio of 1:1), and then drop it into the above solution and stir vigorously until the pH value is 8. The color of the solution turns dark green, and then stir vigorously for 1 hour. After that, the color of the solution changes from dark green to brownish yellow, and the final pH value of the solution is 5. Let it age for 2 hours;

[0039] Step 2: Add Na2CO3 to the aged solution. The mass percentage of Na2CO3 to the deionized water in Step 1 is 2%. Stir for 2 hours. After stirring, add the same volume of absolute ethanol and stir slowly, then filter. Wash the obtained flocculent material with ethanol solutions of decreasing concentration until neutral, evaporate the ethanol, and dry it in vacuum at 60°C. Then grind the obtained material with a ball mill to the microgel level. The concentrations of the ethanol solutions from high to low are 100%, 95%, 75%, and 50% in sequence.

[0040] Step 3: Disperse the ground microgel-level material in water. The mass-volume ratio of the ground material to water is 1 g:100 mL. Add NIPAM and (NH4)2S2O8. The mass ratio of the ground material, NIPAM, and (NH4)2S2O8 is 20:45:3. Heat in a nitrogen atmosphere at 75°C for 40 minutes, then wash three times with water. Finally, dry the material in vacuum at 60°C to obtain a biomass-based composite thermosensitive material for radioactive element enrichment and separation, namely 10% γ-FeOOH / KGM / PNIPAM composite thermosensitive material.

[0041] Example 2

[0042] A preparation method of a biomass-based composite thermosensitive material for radioactive element enrichment and separation, comprising the following steps:

[0043] Step 1: Dissolve KGM and FeSO4·7H2O in deionized water. The mass-volume ratio of KGM, FeSO4·7H2O, and deionized water is 5 g:1 g:125 mL. Then add an EDTA-2Na aqueous solution (0.1 mol / L), and keep the molar ratio of Fe 2+ and EDTA-2Na as 1:0.03. Prepare an NH3·H2O aqueous solution (volume ratio of 1:1), then drop it into the above solution and stir vigorously until the pH value is 8 and the color of the solution turns dark green. Stir vigorously for 1 hour, then the color of the solution changes from dark green to yellowish brown, and the final pH value of the solution is 5. Let it stand and age for 2 hours;

[0044] Step 2: Add Na2CO3 to the aged solution. The mass percentage of Na2CO3 to the deionized water in Step 1 is 2%. Stir for 2 hours. After stirring, add the same volume of absolute ethanol and stir slowly, then filter. Wash the obtained flocculent material with ethanol solutions of decreasing concentration until neutral, evaporate the ethanol, and dry it in vacuum at 60°C. Then grind the obtained material with a ball mill to the microgel level. The ethanol concentrations from high to low are 100%, 95%, 75%, and 50% in sequence.

[0045] Step 3: Disperse the ground microgel-level material in water. The mass-volume ratio of the ground material to water is 1 g: 100 mL. Add NIPAM and (NH4)2S2O8. The mass ratio of the ground material, NIPAM, and (NH4)2S2O8 is 20:45:3. Heat in a nitrogen atmosphere at 75 °C for 40 minutes, then wash three times with water. Finally, dry the material in vacuum at 60 °C to obtain a biomass-based composite thermosensitive material for radioactive element enrichment and separation, namely 20% γ-FeOOH / KGM / PNIPAM composite thermosensitive material.

[0046] Example 3

[0047] A preparation method of a biomass-based composite thermosensitive material for radioactive element enrichment and separation, comprising the following steps:

[0048] Step 1: Dissolve KGM and FeSO4·7H2O in deionized water. The mass-volume ratio of KGM, FeSO4·7H2O, and deionized water is 10 g: 3 g: 250 mL. Then add an EDTA-2Na aqueous solution (0.1 mol / L), and keep the molar ratio of Fe 2+ and EDTA-2Na as 1:0.03. Prepare an NH3·H2O aqueous solution (volume ratio of 1:1), then drop it into the above solution and stir vigorously until the pH value reaches 8 and the color of the solution turns dark green. Then stir vigorously for 1 hour, and the color of the solution changes from dark green to yellowish brown, and the final pH value of the solution is 5. Let it stand and age for 2 hours;

[0049] Step 2: Add Na2CO3 to the aged solution. The mass percentage of Na2CO3 to the deionized water in Step 1 is 2%. Stir for 2 hours. After stirring, add the same volume of absolute ethanol and stir slowly, then filter. Wash the obtained flocculent material with ethanol solutions of decreasing concentration until it is neutral. After volatilizing the ethanol, dry it in vacuum at 60 °C. Then grind the obtained material with a ball mill to the microgel level; the ethanol concentration decreases in turn as 100%, 95%, 75%, 50%.

[0050] Step 3: Disperse the ground microgel-level material in water. The mass-volume ratio of the ground material to water is 1 g: 100 mL. Add NIPAM and (NH4)2S2O8. The mass ratio of the ground material, NIPAM, and (NH4)2S2O8 is 20:45:3. Heat in a nitrogen atmosphere at 75 °C for 40 minutes, then wash three times with water. Finally, dry the material in vacuum at 60 °C to obtain a biomass-based composite thermosensitive material for radioactive element enrichment and separation, namely 30% γ-FeOOH / KGM / PNIPAM composite thermosensitive material.

[0051] Example 4

[0052] A preparation method of a biomass-based composite thermosensitive material for radioactive element enrichment and separation, comprising the following steps:

[0053] Step 1: Dissolve KGM and FeSO4·7H2O in deionized water. The mass-volume ratio of KGM, FeSO4·7H2O, and deionized water is 5 g: 2 g: 125 mL. Then add an EDTA-2Na aqueous solution (0.1 mol / L), and maintain the molar ratio of Fe 2+ and EDTA-2Na at 1:0.03. Prepare an NH3·H2O aqueous solution (volume ratio of 1:1), and then drop it into the above solution and stir vigorously until the pH value reaches 8 and the color of the solution turns dark green. After stirring vigorously for 1 hour, the color of the solution changes from dark green to brownish yellow, and the final pH value of the solution is 5. Let it stand and age for 2 hours;

[0054] Step 2: Add Na2CO3 to the aged solution. The mass percentage of Na2CO3 in the deionized water in Step 1 is 2%. Stir for 2 hours. After the stirring ends, add the same volume of absolute ethanol and stir slowly, then filter. Wash the obtained flocculent material with ethanol solutions with decreasing concentrations until it is neutral. After volatilizing the ethanol, dry it in vacuum at 60°C. Then grind the obtained material with a ball mill to the microgel level; the ethanol concentrations decrease from high to low in turn as 100%, 95%, 75%, 50%.

[0055] Step 3: Disperse the ground microgel-level material in water. The mass-volume ratio of the ground material to water is 1 g: 100 mL. Add NIPAM and (NH4)2S2O8. The mass ratio of the ground material, NIPAM, and (NH4)2S2O8 is 20:45:3. Heat it in a nitrogen atmosphere at 75°C for 40 minutes, then wash it three times with water. Finally, dry the material in vacuum at 60°C to obtain a biomass-based composite thermosensitive material for radioactive element enrichment and separation, namely a 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material.

[0056] Example 5

[0057] A preparation method of a biomass-based composite thermosensitive material for radioactive element enrichment and separation, comprising the following steps:

[0058] Step 1: Dissolve KGM and FeSO4·7H2O in deionized water. The mass-volume ratio of KGM, FeSO4·7H2O, and deionized water is 2 g: 1 g: 50 mL. Then add an EDTA-2Na aqueous solution (0.1 mol / L), and maintain the molar ratio of Fe 2+The molar ratio of [substance] to EDTA-2Na is 1:0.03. Prepare an aqueous solution of NH₃·H₂O (volume ratio 1:1), then add it dropwise to the above solution and stir vigorously until the pH value reaches 8 and the color of the solution turns dark green. After stirring vigorously for 1 hour, the color of the solution changes from dark green to brownish-yellow, and the final pH value of the solution after the reaction is 5. Let it stand and age for 2 hours;

[0059] Step 2: Add Na₂CO₃ to the aged solution. The mass percentage of Na₂CO₃ to the deionized water in Step 1 is 2%. Stir for 2 hours. After the stirring ends, add an equal volume of absolute ethanol and stir slowly, then filter. Wash the obtained flocculent material with ethanol solutions of decreasing concentration until it is neutral. Evaporate the ethanol and dry it in a vacuum at 60 °C. Then grind the obtained material with a ball mill to the microgel level; the ethanol concentrations from high to low are 100%, 95%, 75%, and 50% in turn.

[0060] Step 3: Disperse the ground microgel-level material in water. The mass-volume ratio of the ground material to water is 1 g:100 mL. Add NIPAM and (NH₄)₂S₂O₈. The mass ratio of the ground material, NIPAM, and (NH₄)₂S₂O₈ is 20:45:3. Heat it in a nitrogen atmosphere at 75 °C for 40 minutes, then wash it three times with water. Finally, dry the material in a vacuum at 60 °C to obtain a biomass-based composite thermosensitive material for radioactive element enrichment and separation, namely a 50% γ-FeOOH / KGM / PNIPAM composite thermosensitive material.

[0061] Comparative Example 1

[0062] A preparation method of a biomass-based hydrogel, comprising the following steps:

[0063] Step 1: Dissolve KGM and FeSO₄·7H₂O in deionized water. The mass-volume ratio of KGM, FeSO₄·7H₂O, and deionized water is 20 g:3 g:500 mL. Then add an aqueous solution of EDTA-2Na (0.1 mol / L), keeping the molar ratio of Fe 2+ / EDTA-2Na as 1:0.03. Prepare an aqueous solution of NH₃·H₂O (volume ratio 1:1), then add it dropwise to the above solution and stir vigorously until the pH value reaches 8 and the color of the solution turns dark green. After stirring vigorously for 1 hour, the color of the solution changes from dark green to brownish-yellow, and the final pH value of the solution is 5. Let it stand and age for 2 hours;

[0064] Step 2: Add Na2CO3 to the aged solution to make the concentration of Na2CO3 0.3 mol / L (the solvent is the deionized water in Step 1), stir for 2 hours, let it stand at room temperature for 30 min, then heat at 80 °C for 40 min, and let it stand at 4 °C for 12 h. Prepare a 0.1 M hydrochloric acid solution, soak the obtained hydrogel material in the hydrochloric acid solution for 2 d, and then soak it in ultrapure water for 1 - 2 d to obtain a biomass-based hydrogel, that is, 0.6%

[0065] γ-FeOOH / KGM hydrogel.

[0066] Comparative Example 2

[0067] The preparation method of PNIPAM includes the following steps:

[0068] Add NIPAM and (NH4)2S2O8 to water, and the mass-volume ratio of NIPAM, (NH4)2S2O8 and water is 45 g: 3 g: 2 L. Heat it in a nitrogen atmosphere at 75 °C for 40 minutes, then wash it three times with water, and finally dry the material in vacuum at 60 °C to obtain PNIPAM.

[0069] Figure 1 The SEM image of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4 is shown. It can be seen that it has a three-dimensional porous network structure with interconnected pores. These interconnected cavities increase the contact area between the composite thermosensitive material and uranyl ions in the solution, making up for the defect that the photocatalytic hydrogel has a lower reaction rate compared with the powder photocatalyst. There is a PNIPAM film-like structure on the surface of γ-FeOOH / KGM, which tightly wraps it. When the solution temperature is lower than the lower critical solution temperature (LCST) of the material, the hydrophilic groups are exposed, and the material can be well dispersed in water. When the solution temperature is higher than the LCST of the material, the hydrophobic groups are exposed, resulting in the spontaneous aggregation of the microgels. This is also the reason why the γ-FeOOH / KGM / PNIPAM composite thermosensitive material changes from the dispersed state to the gel state.

[0070] Figure 2 The FT-IR spectra of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4, the 0.6% γ-FeOOH / KGM hydrogel prepared in Comparative Example 1, and the PNIPAM prepared in Comparative Example 2 from 4000 cm -1 to 400 cm -1 For the 0.6% γ-FeOOH / KGM hydrogel, the absorption band at 3416.7 cm -1 is attributed to the stretching vibration of hydroxyl groups, and the absorption bands at 2921.1, 1631.6, 1055.4 cm -1The absorption peaks are respectively attributed to C-H, C-O and C6-OH groups, 804.1 cm -1 The absorption band is the characteristic vibration of mannose units in KGM. PNIPAM mainly produces conjugated carbonyl (C=O, 1648 cm -1 ), amide (-NH, 1533 cm -1 ), isopropyl (1375 cm -1 and 1385 cm -1 ), methyl (-CH3, 2973 cm -1 ), methylene (-CH2, 2924 cm -1 ), and ether bond (C-O-C, 1128 cm -1 ). The results show that PNIPAM is covalently bonded to γ-FeOOH / KGM hydrogel through ether bonds.

[0071] Figure 3 XRD patterns of 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4, 0.6% γ-FeOOH / KGM hydrogel prepared in Comparative Example 1, and γ-FeOOH. It can be seen that the diffraction peaks of γ-FeOOH are observed in the XRD pattern of γ-FeOOH / KGM / PNIPAM. The peaks of γ-FeOOH / KGM / PNIPAM at 2θ = 14.19°, 27.09°, 36.39° and 47.07° are related to γ-FeOOH, indicating the successful preparation of γ-FeOOH / KGM / PNIPAM composite thermosensitive material.

[0072] Figure 4 Water contact angle images of 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4. It can be seen that above and below the critical solution temperature, the hydrophilicity and hydrophobicity of the γ-FeOOH / KGM / PNIPAM composite thermosensitive material change greatly, proving that the γ-FeOOH / KGM / PNIPAM composite thermosensitive material has temperature response ability. Figure 5 Differential scanning calorimetry (DSC) images of 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4 and PNIPAM prepared in Comparative Example 2. It can be seen that the LCST of the γ-FeOOH / KGM / PNIPAM composite thermosensitive material is 41.6 °C, slightly higher than that of PNIPAM, which is attributed to the grafting of PNIPAM on the surface of γ-FeOOH / KGM, hindering the conformational change of polymer chains and resulting in a slight delay in the phase transition temperature.

[0073] Uranium removal experiment: Use 100 mL of pre-prepared carbonate uranium (VI) solution with C(U) = 100 mg / L and C(NaHCO3) = 2 mM, and adjust the pH value of the system to 8 - 8.2 using 0.1 M HNO3 and / or NaOH solution. After adding 70 mg of sample material to the uranium (VI) solution, stir it and place it in a dark environment for 120 min to ensure adsorption - desorption equilibrium. Then, add a simulated light source and ventilation, and maintain the irradiation reaction for 3 hours. After the reaction, incubate the blended solution in an oil bath at 50 °C for 3 hours, filter the solid matter, transfer about 1.0 mL of the suspension through a pipeline, and filter it with a 0.22 μm filter for analysis. Measure the refractive value of the clarified liquid. The simulated light source for this experiment is a xenon lamp (PLS - SXE 300+), and U(VI) is determined by the arsenazo III colorimetric method (wavelength 651.8 nm) on a UV - 2365 spectrophotometer. Calculate the uranium removal efficiency (η, %) of the sample material, and the calculation formula is as follows:

[0074]

[0075] In the formula, C e is the concentration (mg / L) of the remaining uranium solution after the reaction, and C0 is the initial concentration (mg / L) of the uranium solution.

[0076] The addition amount of γ - FeOOH / KGM / PNIPAM composite thermosensitive material affects the uranium removal ability. Under the same uranium solution volume, concentration, and adsorption time, the uranium removal ability of the 40% γ - FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4 with an addition amount ranging from 10 to 110 mg was experimentally studied, and the results are as Figure 6 shown. It can be seen that when the addition amount is 70 mg, the 40% γ - FeOOH / KGM / PNIPAM composite thermosensitive material has the highest uranium removal rate. The uranium removal rate of the 40% γ - FeOOH / KGM / PNIPAM composite thermosensitive material increases with the increase of the addition amount, but the removal rate slightly decreases after reaching 70 mg. This is because when the γ - FeOOH / KGM / PNIPAM composite thermosensitive material is in excess in the solution, the active sites aggregated on the hydrogel overlap with the unbound active sites, resulting in a decrease in its effective specific surface area.

[0077] Figure 7 It is a comparison chart of the uranium removal rates of γ - FeOOH / KGM / PNIPAM composite thermosensitive materials with different γ - FeOOH contents prepared in Examples 1 - 5. It can be seen that when the γ - FeOOH content is 40%, the γ - FeOOH / KGM / PNIPAM composite thermosensitive material has the highest uranium removal rate, and the maximum removal rate is 92.3%.

[0078] Figure 8 The uranium removal rates of γ-FeOOH / KGM / PNIPAM composite thermosensitive materials with different γ-FeOOH contents prepared in Examples 1-5 at pH = 7-11 are shown. It can be seen that the uranium removal ability of the γ-FeOOH / KGM / PNIPAM composite thermosensitive material increases as the pH increases from 7 to 8 and slightly decreases at pH = 9-11. In addition, it can be seen that at different pH values, the uranium removal rate of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material is the highest, reaching 92.3% at pH = 8.

[0079] Figure 9 The comparison chart of the uranium removal rates of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4, the 0.6% γ-FeOOH / KGM hydrogel prepared in Comparative Example 1, and γ-FeOOH is shown. It can be seen that the uranium removal rates of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material and γ-FeOOH are comparable, both higher than that of the 0.6% γ-FeOOH / KGM hydrogel.

[0080] The reusability of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4 was tested through five consecutive cyclic uranium removal experiments, with 0.1M HCL as the eluent, and the 0.6% γ-FeOOH / KGM hydrogel and γ-FeOOH prepared in Comparative Example 1 were used as comparisons. The results are as Figure 10 shown. It can be seen that after five consecutive cycles, the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material has excellent cyclic stability, and the uranium removal rate hardly decreases.

[0081] Figure 11 The effects of different inhibitors on the uranium removal rate of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4 are shown. The influence of free radicals on photocatalytic reduction was further verified through free radical triggering experiments, where added methanol, KBrO3, tert-butanol, and p-benzoquinone were used as hole scavengers, electron scavengers, ·OH radical scavengers, and ·O2 - radical scavengers respectively. Through the change in the uranium removal rate, it was found that the uranium removal rates with added p-benzoquinone and KBrO3 decreased significantly, and the influence caused by KBrO3 was greater, indicating that ·O2 - radicals and photogenerated electrons are key substances for U(VI) reduction. In addition, electron paramagnetic resonance (EPR) and free radical trapping studies were conducted on the U(VI) reduction active substances ·OH and ·O2 - for research. As Figure 12As shown, no EPR signal was observed in the dark, but under visible light irradiation, the typical peaks of DMPO-·O2 - and DMPO-·OH adducts of the γ-FeOOH / KGM / PNIPAM composite thermosensitive material were observed, indicating the generation of ·O2 - and ·OH free radicals. The transient photocurrent response performance of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material prepared in Example 4 is as Figure 13 shown, indicating that when the environment changes from dark to light, the γ-FeOOH / KGM / PNIPAM composite thermosensitive material generates a photocurrent, which confirms that the γ-FeOOH / KGM / PNIPAM composite thermosensitive material can photocatalytically reduce U(VI).

[0082] Figure 14 Figure 10 is the FT-IR spectra of the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material before and after the uranium removal reaction prepared in Example 4, denoted as γ-FeOOH / KGM / PNIPAM-U after the reaction. It can be seen that the peak at 3100 cm -1 is related to the stretching vibration of ·OH. Due to the interaction between ·OH and the uranium complex, the intensity of the unique peak of the hydroxyl group is greatly reduced. The absorption peaks of ·OH at 3379 cm -1 , 1625 cm -1 , 1398 cm -1 , 1045 cm -1 and 879 cm -1 all shift after reacting with uranium, indicating that the 40% γ-FeOOH / KGM / PNIPAM composite thermosensitive material has successfully removed uranium.

[0083] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those skilled in the art, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to the specific details and the examples shown and described herein.

Claims

1. A preparation method of a biomass-based composite thermosensitive material for radioactive element enrichment and separation, characterized in that, It includes the following steps: Step 1: Dissolve KGM and FeSO4·7H2O in deionized water, and then add an aqueous solution of EDTA-2Na. Dropwise add the aqueous solution of NH3·H2O to the above solution and stir until the pH value of the solution is 7-9 and the color of the solution is dark green. Stir for another 0.5-1.5 hours until the color of the solution changes from dark green to brownish yellow and the pH value of the solution is 4.5-5.

5. Let it stand for aging for 1-3 hours; Step 2: Add Na2CO3 to the aged solution and stir for 1-3 hours. Then add anhydrous ethanol to the obtained mixed solution and stir slowly and then filter. Wash the flocculent material obtained after filtration with ethanol solutions with decreasing concentrations until it is neutral. Evaporate the ethanol and then dry it. Grind the obtained material with a ball mill to the microgel level; Step 3: Disperse the ground microgel-level material in water, add N-isopropylacrylamide (NIPAM) and (NH4)2S2O8, heat it in a nitrogen atmosphere at 70-80 °C for 30-50 minutes, then wash it 2-4 times with water, and then dry the material to obtain a biomass-based composite thermosensitive material for radioactive element enrichment and separation, that is, a γ-FeOOH / KGM / PNIPAM composite thermosensitive material.

2. The preparation method of the biomass-based composite thermosensitive material for radioactive element enrichment and separation according to claim 1, characterized in that In the said Step 1, the mass-volume ratio of KGM, FeSO4·7H2O and deionized water is 10 g: 1-5 g: 200-300 mL.

3. The preparation method of a biomass-based composite thermosensitive material for radioactive element enrichment and separation according to claim 1, characterized in that, In the first step, the concentration of the EDTA-2Na aqueous solution is 0.05 to 0.15 mol / L, and the molar ratio of Fe 2+ to EDTA-2Na is 1:0.

03.

4. The preparation method of a biomass-based composite thermosensitive material for radioactive element enrichment and separation according to claim 1, characterized in that In the said Step 1, the volume ratio of NH3·H2O to water in the aqueous solution of NH3·H2O is 1: 0.8-1.

2.

5. The preparation method of a biomass-based composite thermosensitive material for radioactive element enrichment and separation according to claim 1, characterized in that, In the said Step 2, the mass percentage of Na2CO3 to the deionized water in Step 1 is 1.5-2.5%; the volume ratio of anhydrous ethanol to the mixed solution is 1: 0.8-1.

2.

6. The preparation method of a biomass-based composite thermosensitive material for radioactive element enrichment and separation according to claim 1, characterized in that, In the said Step 2, the concentrations of the ethanol solutions from high to low are 100%, 95%, 75%, 50% respectively.

7. The preparation method of a biomass-based composite thermosensitive material for radioactive element enrichment and separation according to claim 1, characterized in that, In the said Step 3, the mass-volume ratio of the ground microgel-level material and water is 1 g: 80-120 mL; the mass ratio of the ground microgel-level material, NIPAM and (NH4)2S2O8 is 20: 40-50: 2.5-3.

5.

8. The preparation method of a biomass-based composite thermosensitive material for radioactive element enrichment and separation according to claim 1, characterized in that, In the said Step 1 and Step 3, drying is carried out by vacuum drying at 50-70 °C.

9. Use of the biomass-based composite thermosensitive material prepared by the preparation method according to any one of claims 1 to 8 in radioactive element enrichment and separation, characterized in that, Add the biomass-based composite thermosensitive material to the carbonate uranium-containing wastewater, place it in a light and ventilated environment for reaction, put the biomass-based composite thermosensitive material after reaction into the eluent, stir and wash, and use it again in a cycle.

10. Use of a biomass-based composite thermosensitive material in the enrichment and separation of radioactive elements as described in claim 9, characterized in that, The said eluent is a 0.1 mol / L HCl solution.

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