Preparation of UiO-66-NH2 (at) CdZnS2 (at) Cd, Zn-ZIF-8 composite structure photocatalytic material and application of extraction and removal of uranium in solution

Abstract

The invention discloses preparation of a UiO-66-NH2 (at) CdZnS2 (at) Cd and Zn-ZIF-8 composite structure photocatalytic material and application of extraction and removal of uranium in a solution. The method comprises the steps that zirconium chloride and 2-aminoterephthalic acid are dissolved in DMF, acetic acid is dropwise added under continuous stirring to regulate the morphology, then a UiO-66-NH2 solution is obtained through a traditional hydrothermal method, DMF and methyl alcohol are used for alternate washing, precipitates are collected, and the UiO-66-NH2 (at) CdZnS2 (at) Cd and Zn-ZIF-8 composite structure photocatalytic material is obtained. Performing vacuum drying to obtain a UiO-66-NH2 precursor; then, dissolving a proper amount of cadmium chloride and zinc acetate in ethanol, magnetically stirring until the cadmium chloride and the zinc acetate are completely dissolved, adding the UiO-66-NH2 precursor, performing ultrasonic treatment and fully stirring to form a coprecipitate, dropwise adding a mixed solution of 2-methylimidazole and CTAB, fully stirring, dropwise adding thioacetamide dissolved in the ethanol, heating in a water bath to obtain a solution, washing with the ethanol, and drying to obtain the cadmium-zinc composite material. The invention discloses a preparation method of a UiO-66-NH2 (at) CdZnS2 (at) Cd and Zn-ZIF-8 photocatalytic material, the UiO-66-NH2 (at) CdZnS2 (at) Cd and Zn-ZIF-8 photocatalytic material containing a ZIF structure is prepared by taking UiO-66-NH2 as a precursor, and the UiO-66-NH2 (at) CdZnS2 (at) Cd and Zn-ZIF-8 photocatalytic material has excellent uranium extraction and removal capability.

Description

Technical Field

[0001] The present invention relates to a photocatalytic material, and particularly to a UiO-66-NH2@CdZnS2@Cd, Zn-ZIF-8 composite structure photocatalytic material and its preparation and application in the extraction and removal of uranium in solution. Background Art

[0002] Uranium (U) resources are the foundation for the booming development of the nuclear industry. Nuclear energy has received extensive attention and high regard from all sectors of society due to its significant advantages of being clean and pollution-free and having excellent efficiency. Currently, the main way to obtain uranium resources is to mine terrestrial uranium ore, which is difficult to mine and has a low effective uranium content. Therefore, attention has been turned to seawater with a large amount of uranium resources. Uranium in seawater exists in the form of uranyl ions. At the same time, in the spent fuel cycle, uranyl ions enter various water bodies in the form of a heavy metal pollutant and cannot be directly discharged. Therefore, the extraction and removal of uranium in liquid solutions are very important for the stable development and efficient utilization of nuclear energy. Adsorption is an effective solid-liquid separation method, but traditional materials have defects such as low adsorption capacity and slow adsorption kinetics for uranyl ions. By using materials with photocatalytic reduction performance to reduce uranyl ions to insoluble uranium compounds during the adsorption process, the extraction and removal efficiency of uranium in the solution by the materials can be enhanced.

[0003] MOF: Metal-organic Frameworks are a class of typical porous crystalline materials, also known as Porous Coordination Polymers (PCPs). It is a crystalline framework material with open pores constructed by connecting metal nodes (i.e., secondary building units, SBUs) and organic ligands in a regular and orderly geometric form. Due to its diverse SBUs, organic ligands, and unique framework structure, MOFs have a large specific surface area, significant porous characteristics, and good structural adjustability. Therefore, the properties of MOFs have received extensive attention in the field of photocatalysis.

[0004] UiO-66 is one of the MOFs. UiO-66 is a coordination compound formed with metal ion Zr as the coordination center (Zr6O4(OH)4) and terephthalic acid (H2BDC) as the organic ligand framework. However, due to the π-π electron transition of the ligand aromatic ring, the optical absorption edge of UiO-66 is only 310 nm, indicating that it only responds to the ultraviolet region. Moreover, the Zr oxygen cluster of UiO-66 has a high redox potential energy, and the efficiency of electrons transferring from the organic ligand to the Zr oxygen cluster is low, resulting in rapid recombination of photogenerated carriers on the organic ligand, which severely limits the practical application of UiO-66 in the field of photocatalysis.

[0005] CdZnS2 (hereinafter referred to as SCZ) is a typical ternary sulfide composed of cadmium, zinc, and sulfur elements. CdZnS2 is a solid solution of ZnS (wide bandgap of 3.6 eV) and CdS (narrow bandgap of 2.4 eV). By adjusting the Zn / Cd ratio, the bandgap can be adjusted in the range of 2.4–3.6 eV, which can effectively absorb ultraviolet-visible light and is suitable for driving various photocatalytic reactions. Moreover, its energy band structure is easy to form Type-II or Z-scheme heterojunctions with other semiconductors, promoting the separation of photo-generated electron-hole pairs and thus enhancing the catalytic efficiency. In addition, CdZnS2 has the advantages of simple preparation process, strong response to visible light, and strong anti-photocorrosion ability. However, Cd 2+ has poor chemical stability and is easily oxidized by photo-generated holes or affected by strong oxidants in the solution during the photocatalytic process, resulting in ion dissolution, catalyst deactivation, and environmental pollution. In addition, the material itself may undergo structural decomposition under long-term light irradiation, affecting the cycle service life, and its efficiency far from meets the requirements of practical applications. To address the above problems, some methods have been adopted to improve its photocatalytic performance, such as constructing heterojunctions and composite systems, defect engineering and doping modification, morphology and size regulation, etc. For example, it is compounded with wide bandgap semiconductors (such as TiO2, ZnO) or narrow bandgap materials (such as CuInS2, BiVO4) to promote the separation of photo-generated electron-hole pairs by using energy band misalignment. In addition, graphene (GO / rGO), carbon nanofibers (CNF), or biomass carbon can be introduced to utilize the high conductivity and high specific surface area of carbon materials to accelerate charge transfer and inhibit carrier recombination, while enhancing the adsorption capacity of the material for organic pollutants; for metal doping, transition metals or rare earth elements are doped as charge capture centers or active sites to inhibit carrier recombination and thus promote photocatalytic performance.

[0006] MOF and heterojunction composite: In photocatalysis, the high porosity of MOF can provide abundant active sites, and heterojunctions (such as TiO2 / g-C3N4) can promote the separation of photo-generated carriers, which can improve photocatalytic efficiency and is commonly used for water splitting for hydrogen production, CO2 reduction, pollutant degradation, etc.; in electrocatalysis, in reactions such as oxygen reduction (ORR) and oxygen evolution (OER), the combination of MOF-derived materials and heterojunctions (such as Co-MOF / graphene) can optimize the electronic structure of the material and improve catalytic activity and stability; in pollutant degradation, the adjustable pore size of MOF can be combined with heterojunctions for modification to enhance the selective adsorption of specific gases (such as CO2, CH4); in energy storage and conversion, the high specific surface area of MOF provides more energy storage sites, and the heterojunction structure (such as MOF / conductive polymer) enhances electron conduction, improving capacity and cycle performance. Summary of the Invention

[0007] The object of the present invention is to provide a preparation method of a UiO-66-NH2@CdZnS2@Cd, Zn-ZIF-8 photocatalytic material and its application in the extraction and removal of uranium in solution, and to improve the performance of extracting and removing uranium in the photocatalytic solution of CdZnS2 by controlling the amount of UiO-66-NH2 loaded in CdZnS2.

[0008] To achieve the above object, the present invention provides a preparation method of a UiO-66-NH2@CdZnS2@Cd, Zn-ZIF-8 photocatalytic material, and the method comprises:

[0009] Dissolve 1 mmol of zirconium chloride and 1 mmol of 2-aminoterephthalic acid in 50 ml of DMF respectively, and stir ultrasonically until completely dissolved. Then, drop the zirconium chloride solution into the 2-aminoterephthalic acid solution, and drop acetic acid (5 mol in excess relative to the concentration of 2-aminoterephthalic acid) for 30 min during continuous stirring. Transfer the obtained homogeneous solution to a 100 ml autoclave lined with Teflon, and perform hydrothermal treatment at 120 °C for a certain time. After the solvothermal treatment is completed, centrifuge at 3000 rpm to obtain a solid product, then wash it 3 times with DMF and methanol, and then dry the product in vacuo at 80 °C to obtain a UiO-66-NH2 crystalline solid. Then, weigh 50 mg of UiO-66-NH2, 1 mmol of zinc acetate, and 1 mmol of cadmium chloride, disperse them in 20 ml of water, stir to form a coprecipitate, then dropwise add a mixed solution of 5 ml of CTAB and dimethylimidazole, stir evenly, heat in a water bath at 60 °C for 2 h, centrifuge to obtain a precursor, then dissolve 0.2 g of thioacetamide in 20 ml of ethanol, stir until completely dissolved, add the precursor, heat in a water bath at 70 °C for 6 h to obtain a UiO-66-NH2@SCZ solution, centrifuge, wash with ethanol and water, and dry in vacuo to obtain a UiO-66-NH2@CdZnS2@Cd, Zn-ZIF-8 photocatalytic material.

[0010] Preferably, the molar ratio of the cadmium salt or zinc salt to 2-methylimidazole is 1:1 to 1:20.

[0011] Preferably, the heating rate is 1 to 20 °C / min.

[0012] Preferably, in the organic solvent solution containing a sulfur source, the amount of the sulfur source is 0.1 g - 0.4 g; the amount of the organic solvent is 5 - 40 ml.

[0013] Preferably, stir at room temperature for 1 to 24 h and stand for 1 to 24 h.

[0014] Preferably, heat in a water bath to 40 - 80 °C and then maintain for 1 to 12 h.

[0015] Preferably, the cadmium salt is selected from any one or more of CdI2, CdCl2, CdBr2, CdAc2, Cd(SO4)2, and Cd(NO3)2; the zinc salt is selected from any one or more of ZnI2, ZnCl2, ZnBr2, ZnAc2, Zn(SO4)2, and Zn(NO3)2.

[0016] Preferably, after the solid-liquid separation, alcohols are used to disperse the solid, and then solid-liquid separation is carried out to remove unreacted substances.

[0017] Another object of the present invention is to provide the UiO-66-NH2@CdZnS2@Cd and Zn-ZIF-8 photocatalytic materials prepared by the above method.

[0018] Another object of the present invention is to provide the application of the UiO-66-NH2@CdZnS2@Cd and Zn-ZIF-8 photocatalytic materials in photocatalytic uranyl reduction, i.e., the extraction and removal of uranium in solution.

[0019] The UiO-66-NH2@CdZnS2@Cd and Zn-ZIF-8 photocatalytic materials of the present invention, their preparation and application have the following advantages:

[0020] (1) In the present invention, a UiO-66-NH2@CdZnS2@Cd and Zn-ZIF-8 composite structure is prepared by using UiO-66-NH2@CdZnS2 with a high specific surface area, which has excellent uranyl reduction ability;

[0021] (2) By controlling the molar ratio of cadmium salt to solvent, zinc salt to solvent, and the molar ratio of UiO-66-NH2 to cadmium salt and zinc salt solvent during the reaction process, the size of CdZnS2 and the mass ratio of UiO-66-NH2 to CdZnS2 can be controlled. The preparation process parameters are easy to control, the preparation method is simple, highly controllable, and the yield is high.

[0022] (3) The obtained UiO-66-NH2@CdZnS2@Cd and Zn-ZIF-8 photocatalytic materials of the present invention have a high specific surface area and a wide visible light absorption range, and can be used in fields such as photocatalytic uranyl reduction, i.e., uranium extraction from seawater, photocatalytic degradation, photocatalytic hydrogen production, or solar cells. Description of the Drawings

[0023] Figure 1 It is the XRD pattern of the photocatalytic materials prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention.

[0024] Figure 2 It is the scanning electron microscope image of the photocatalytic material prepared in Example 1 of the present invention.

[0025] Figure 3 The UV-visible absorption spectra of the photocatalytic materials prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention.

[0026] Figure 4 The photocatalytic reduction uraniumyl effect diagrams of the photocatalytic materials prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention. Detailed implementation manners

[0027] Next, the technical solutions in the embodiments of the present invention will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] Example 1

[0029] A preparation method of a UiO-66-NH2@CdZnS2@Cd, Zn-ZIF-8 photocatalytic material is as follows:

[0030] (1) Preparation of UiO-66-NH2 precursor

[0031] Dissolve 1 mmol of zirconium chloride and 1 mmol of 2-aminoterephthalic acid in 50 ml of DMF respectively, ultrasonically stir until completely dissolved, then drop the zirconium chloride solution into the 2-aminoterephthalic acid solution, and drop acetic acid (5 mol in excess relative to the concentration of 2-aminoterephthalic acid) for 30 min during continuous stirring. Transfer the obtained uniform solution to a 100 ml autoclave lined with Teflon, and perform hydrothermal treatment at 120 °C for a certain time. After the solvent heat treatment is completed, centrifuge at 3000 rpm to obtain a solid product, then wash it 3 times with DMF and methanol, and then vacuum dry the product at 80 °C overnight to obtain the UiO-66-NH2 precursor.

[0032] (2) Preparation of Zn 2+ , Cd 2+ and the precursor solution of 2-MIM

[0033] Dissolve 0.01 mol of C4H6O4Zn·2H2O, 0.01 mol of CdCl2·2.5H2O, and 0.2 mol of 2-methylimidazole (2-MIM) in 250 ml of DI H2O, 250 ml of DI H2O, and 200 ml of an aqueous solution containing 14 mg of CTAB and 62.4 g of 2-methylimidazole respectively to form clear solutions, and obtain the Zn 2+ precursor solution, Cd 2+ precursor solution, and 2-MIM precursor solution respectively.

[0034] (3) Preparation of UiO-66-NH2@CdZnS2@Cd, Zn-ZIF-8 photocatalytic material

[0035] Weigh 50 mg of UiO-66-NH2, 1 mmol of zinc acetate, and 1 mmol of cadmium chloride, disperse them in 20 ml of water, stir to form a coprecipitate, then add dropwise a mixed solution of 5 ml of CTAB and dimethylimidazole, stir evenly, heat in a water bath at 60 °C for 2 h, centrifuge to obtain the CdZnS2 precursor. Then dissolve 0.2 g of thioacetamide in 20 ml of ethanol, stir until completely dissolved, add the precursor, heat in a water bath at 70 °C for 6 h to obtain the UiO-66-NH2@SCZ@Cd, Zn-ZIF-8 solution, centrifuge, wash with ethanol and water, and vacuum dry to obtain the UiO-66-NH2@SCZ@Cd, Zn-ZIF-8 photocatalytic material.

[0036] Comparative Example 1

[0037] A preparation method of UiO-66-NH2 precursor is as follows:

[0038] Dissolve 1 mmol of zirconium chloride and 1 mmol of 2-aminoterephthalic acid in 50 ml of DMF respectively, stir ultrasonically until completely dissolved, then add the zirconium chloride solution dropwise to the 2-aminoterephthalic acid solution, add acetic acid (5 mol in excess relative to the concentration of 2-aminoterephthalic acid) dropwise for 30 min during continuous stirring, transfer the obtained homogeneous solution to a 100 ml autoclave lined with Teflon, and perform hydrothermal treatment at 120 °C for a certain time. After the solvothermal treatment is completed, centrifuge at 3000 rpm to obtain the solid product, then wash it 3 times with DMF and methanol, and then vacuum dry the product at 80 °C overnight to obtain the UiO-66-NH2 precursor.

[0039] Comparative Example 2

[0040] A preparation method of CdZnS2 photocatalytic material is as follows:

[0041] (1) Preparation of Zn 2+ , Cd 2+ and the precursor solution of 2-MIM

[0042] Dissolve 0.01 mol of C4H6O4Zn·2H2O, 0.01 mol of CdCl2·2.5H2O, and 0.2 mol of 2-methylimidazole (2-MIM) in 250 ml of DI H2O, 250 ml of DI H2O, and 200 ml of an aqueous solution containing 14 mg of CTAB and 62.4 g of 2-methylimidazole respectively to form clear solutions, and obtain the Zn 2+ precursor solution, Cd 2+Precursor solution and 2-MIM precursor solution,

[0043] (2) Synthesis of CdZnS2 photocatalytic material

[0044] Take an appropriate amount of precursor solution, stir evenly, heat in a water bath at 60 °C for 2 h, and obtain the CdZnS2 precursor after centrifugation. Dissolve 0.2 g of thioacetamide in 20 ml of ethanol, stir until completely dissolved, add the CdZnS2 precursor, and heat in a water bath at 70 °C for 6 h to obtain the CdZnS2 photocatalytic material

[0045] Comparative Example 3

[0046] The synthesis scheme is generally the same as that of UiO-66-NH2@CdZnS2@Cd, Zn-ZIF-8, except that the amount of UiO-66-NH2 is changed to 25 mg

[0047] As Figure 1 shown, the XRD patterns of the photocatalysts prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention are shown. The abscissa in the figure is the diffraction angle, and the ordinate is the relative intensity. It can be seen from the figure that the prepared UiO-66-NH2@CdZnS2@Cd, Zn-ZIF-8 is a solid solution (cubic structure), rather than a mixture. The diffraction peaks of Comparative Example 1 are those of UiO-66-NH2, and the corresponding crystal planes of UiO-66-NH2 can be clearly seen. The diffraction peaks of Comparative Example 2 are those of SCZ, and the diffraction peaks of Example 1 and Comparative Example 3 are those of UiO-66-NH2@CdZnS2@Cd, Zn-ZIF-8 with different ratios, indicating that the samples contain doping of UiO-66-NH2

[0048] Experimental Example 1 Photocatalytic reduction of uranyl

[0049] The photocatalytic reduction experiment of uranyl was carried out under the irradiation of a 300 W xenon lamp (CEL-PF300-T8E) using a 420 nm cut-off filter. The specific process is as follows:

[0050] Disperse 20 mg of the photocatalyst (the photocatalytic material prepared in each example or comparative example) in 50 ml of a 200 mg / L aqueous solution of UO2(NO3)2·6H2O, and pass 25 °C condensed water to simulate the seawater temperature and avoid the volatilization of the liquid due to the heat generated by light. After stirring in the dark for 1 h under light shielding, irradiate for a period of time to allow sufficient reaction. Record the initial uranyl concentration as C0, take an appropriate amount of the sample at intervals, and record the uranyl concentration at this time as C. Filter the photocatalyst using a 0.22 μm filter head, color the sample using the arsenazo colorimetric method, and finally use a UV-vis absorption spectrum to detect the residual uranyl concentration in the sample to evaluate the reduction ability of the catalyst. As Figure 3, with the absorbance (Abs) at 651 nm as the final uranyl concentration, after stirring for 1 h in the dark in Comparative Example 1 (UiO-66-NH2) and then irradiating for 90 min, the removal rate (C / C0) of uranyl was measured to be 21.4%; in Comparative Example 2 (CdZnS2), after stirring for 1 h in the dark and then irradiating to 90 min, the removal rate (C / C0) of uranyl was measured to reach 69.6%; in Comparative Example 3 (UiO-66-NH2@SCZ - loaded with 50 mg UiO-66-NH2), after stirring for 1 h in the dark and then irradiating to 90 min, the removal rate (C / C0) of uranyl was measured to reach 83%; in Example 1 (UiO-66-NH2@SCZ - loaded with 25 mg UiO-66-NH2), after stirring for 1 h in the dark and then irradiating to 90 min, the removal rate (C / C0) of uranyl was measured to reach 87.1%. As Figure 4 , the negative coordinate represents the reaction time under dark conditions, and the positive coordinate represents the reaction time under light conditions. In Comparative Example 1, the reaction rate for uranyl is low and the reduction ability is weak; in Comparative Example 2, the reaction rate is fast under dark conditions, but the uranyl reduction ability is weak; after compounding the samples, the reaction rates and the uranyl reduction abilities of Comparative Example 3 and Example 1 have been greatly improved. After adjusting the proportion of loaded UiO-66-NH2, the photocatalytic performance of Example 1 is the best.

[0051] Although the content of the present invention has been introduced in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as a limitation of the present invention. After those skilled in the art have read the above content, various modifications and substitutions to the present invention will be obvious. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims

1. UiO-66-NH2@CdZnS2@Cd, Zn-ZIF-8 composite structure photocatalytic material, the method comprising: Dissolve 1 mmol of zirconium chloride and 1 mmol of 2-aminoterephthalic acid in 50 ml of DMF respectively, ultrasonically stir until completely dissolved, then add the zirconium chloride solution dropwise to the 2-aminoterephthalic acid solution, and dropwise add acetic acid (5 mol in excess relative to the concentration of 2-aminoterephthalic acid) for 30 min during continuous stirring. Transfer the obtained homogeneous solution to a 100 ml autoclave lined with Teflon and hydrothermally treat at 120 °C for a certain time. After the solvent heat treatment is completed, centrifuge at 3000 rpm to obtain a solid product, then wash it 3 times with DMF and methanol, and subsequently dry the product under vacuum at 80 °C overnight to obtain a crystalline solid of UiO-66-NH2. Then weigh 50 mg of UiO-66-NH2, 1 mmol of zinc acetate, and 1 mmol of cadmium chloride, disperse them in 20 ml of water, stir to form a coprecipitate, then add dropwise a mixed solution of 5 ml of CTAB and dimethylimidazole, stir evenly, and heat in a water bath at 60 °C for 2 h. After centrifugation, obtain a precursor. Then dissolve 0.2 g of thioacetamide in 20 ml of ethanol, stir until completely dissolved, add the precursor, and heat in a water bath at 70 °C for 6 h to obtain a UiO-66-NH2@SCZ solution. After centrifugation, wash it with ethanol and water, and dry it under vacuum to obtain the UiO-66-NH2@CdZnS2@Cd, Zn-ZIF-8 photocatalytic material.

2. The preparation method of the UiO-66-NH2@CdZnS2@Cd, Zn-ZIF-8 photocatalytic material according to claim 1, wherein The molar ratio of the cadmium salt to the zinc salt and 2-methylimidazole is 1:1 to 1:

20.

3. The preparation method of the UiO-66-NH2@CdZnS2@Cd, Zn-ZIF-8 photocatalytic material according to claim 1, characterized in that, The heating rate is 1 to 20 °C / min.

4. The preparation method of the UiO-66-NH2@CdZnS2@Cd, Zn-ZIF-8 photocatalytic material according to claim 1, characterized in that, In the organic solvent solution containing a sulfur source, the amount of the sulfur source is 0.1 g - 0.4 g; the amount of the organic solvent is 5 - 40 ml.

5. The preparation method of the UiO-66-NH2@CdZnS2@Cd, Zn-ZIF-8 photocatalytic material according to claim 1, characterized in that, Stir at room temperature for 1 to 24 h and stand for 1 to 24 h.

6. The preparation method of the UiO-66-NH2@CdZnS2@Cd, Zn-ZIF-8 photocatalytic material according to claim 1, characterized in that, Heat in a water bath to 40 - 80 °C and maintain for 1 to 12 h.

7. The preparation method of the UiO-66-NH2@CdZnS2@Cd, Zn-ZIF-8 photocatalytic material according to claim 1, characterized in that, The cadmium salt is selected from any one or more of CdI2, CdCl2, CdBr2, CdAc2, Cd(SO4)2, and Cd(NO3)2; the zinc salt is selected from any one or more of ZnI2, ZnCl2, ZnBr2, ZnAc2, Zn(SO4)2, and Zn(NO3)2.

8. The preparation method of the UiO-66-NH2@CdZnS2@Cd, Zn-ZIF-8 photocatalytic material according to any one of claims 1-7, characterized in that, After the solid-liquid separation, disperse the solid with methanol and then perform solid-liquid separation again to remove unreacted substances.

9. The UiO-66-NH2@CdZnS2@Cd, Zn-ZIF-8 photocatalytic material prepared by the method according to any one of claims 1 - 8.

10. Application of the UiO-66-NH2@CdZnS2@Cd, Zn-ZIF-8 photocatalytic material according to claim 9 in the extraction and removal of uranium in solution.

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