Preparation and application of hydroxyl group-rich cobalt oxide nanosheet for uranium separation

Abstract

The application discloses preparation and application of a uranium separation hydroxyl-rich cobalt oxide nanosheet, and comprises the following steps: Co(NO3)2.6H2O and C 19 H 42 BrN are added into deionized water, stirred uniformly until completely dissolved, then NaBH4 is added, and stirring is conducted at room temperature by using a magnetic stirrer until air bubbles disappear; the obtained mixed solution is centrifuged, the precipitate is collected, washed by anhydrous ethanol and deionized water in sequence, and vacuum dried to obtain the hydroxyl-rich cobalt oxide nanosheet. The hydroxyl-rich cobalt oxide nanosheet prepared by the application is used as an electrocatalyst for extracting uranium from fluorine-containing uranium wastewater; due to the existence of a large number of hydroxyl groups, the affinity to uranium can be enhanced, the capture capacity to dissociated uranyl ions can be improved, uranium species is grown from an initial uranium monatomic atom to a uranium oxide nanosheet on the surface of the cobalt oxide nanosheet through electric driving fluorine uranium separation, a firm 2O ax -1U-3O eq configuration is formed, and the problem that uranium fluoride complexes are difficult to separate in the prior art is solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of radioactive element treatment, and more particularly, relates to a preparation and application of a hydroxyl group-rich cobalt oxide nanosheet separated from uranium. BACKGROUND

[0002] In the production process of uranium enrichment plants and nuclear fuel plants, a large amount of fluorine-containing uranium wastewater is generated. The competition between fluorine and uranium will form UO2F + , UO2F2(aq), UO2F3 - and other complexes, making it difficult to extract uranium. The traditional treatment method adopts a combined process of ammonium salt precipitation and anion resin column multi-stage adsorption, which is limited by the adsorption capacity of the adsorption column, and the process is complicated and easy to produce solid waste. Therefore, developing a new uranium extraction technology to remove and recover uranium from fluorine-containing uranium wastewater is one of the engineering problems to be solved in uranium enrichment plants and nuclear fuel plants.

[0003] As a new technology, electrically assisted uranium extraction provides new insights for uranium extraction from wastewater or seawater due to the accelerated extraction kinetics driven by the electric field and the selectivity to non-reducing coexisting ions. For example, Liu et al. used an electrochemical method based on an amine oxime functionalized carbon electrode to extract uranium from seawater. However, there are still challenges and knowledge gaps in removing and extracting uranium from fluorine-containing uranium wastewater by electrochemical reduction. Electrode materials with high electrical conductivity and abundant active centers are the key to achieving efficient electrochemical uranium extraction. Transition metal oxides are considered ideal electrode materials for electrically assisted uranium extraction due to their low cost, high electrical activity and good stability. In fact, transition metal oxide electrode materials not only need coordination sites to bind with uranyl ions, but also need active centers for electrochemical reduction, which can effectively coordinate and reduce uranyl ions in aqueous solution. However, the uranium coordination sites on traditional electrode materials are physically separated from the electrochemical reduction active centers, and the efficiency of electrically assisted uranium extraction is greatly limited by the loss of electrons transferred from the active center to the coordination site. Based on the hard-soft acid-base (HSAB) theory, defects of metal oxide active centers are introduced to construct metal-oxygen-hydrogen (M-O-H, hard base) metal bonds with specific recognition of uranyl ions (hard acid), which is expected to unify the surface coordination sites and reduction active sites. Therefore, it is of great significance to study the in-situ construction of M-O-H-rich groups on the surface of transition metal oxides to separate fluorine and uranium by electric drive, which is important for effectively recovering uranium from fluorine-containing uranium wastewater. SUMMARY

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

[0005] To achieve these objects and other advantages and in accordance with the purpose of the application, as embodied and broadly described herein, there is provided a method for preparing cobalt oxide nanosheets rich in hydroxyl groups for uranium separation, comprising the following steps:

[0006] Step one, adding Co(NO3)2·6H2O and C 19 H 42 BrN into deionized water, stirring until completely dissolved, then adding NaBH4, stirring at room temperature using a magnetic stirrer until the bubbles disappear.

[0007] Step two, centrifuging the mixed solution obtained in step one, collecting the precipitate, washing with anhydrous ethanol and deionized water in turn, and vacuum drying to obtain cobalt oxide nanosheets rich in hydroxyl groups.

[0008] Preferably, in step one, the mass-volume ratio of Co(NO3)2·6H2O, C 19 H 42 BrN and deionized water is 0.291g:1.5-2g:40-60mL; the mass ratio of NaBH4 and Co(NO3)2·6H2O is 0.05-0.15:0.291.

[0009] Preferably, in step one, the speed of the magnetic stirrer is 100-300r / min.

[0010] Preferably, in step two, the centrifugal speed is 7000-9000r / min, and the centrifugal time is 4-6min.

[0011] Preferably, in step two, the washing times of anhydrous ethanol and deionized water are 3-5 times.

[0012] Preferably, in step two, the vacuum drying temperature is 50-70℃, and the drying time is 20-28h.

[0013] Preferably, in step two, it further comprises: treating the obtained cobalt oxide nanosheets rich in hydroxyl groups using a low-temperature plasma treatment instrument for 2-4min.

[0014] Preferably, the atmosphere of the low-temperature plasma treatment instrument is oxygen or hydrogen, the frequency is 30-50KHz, the power is 400-600W, and the pressure of the atmosphere is 70-90Pa.

[0015] The application of cobalt oxide nanosheets rich in hydroxyl groups prepared by the above-mentioned preparation method in uranium separation, characterized in that the cobalt oxide nanosheets rich in hydroxyl groups are added as a working electrode into fluorine-containing uranium wastewater to perform electrocatalytic reaction, the reacted cobalt oxide nanosheets rich in hydroxyl groups are placed into an eluent, stirred and washed, and recycled again.

[0016] Preferably, the eluent is a 0.1 mol / L HCl solution or a 0.1 mol / L NaHCO3 solution.

[0017] The present application at least includes the following beneficial effects: the present application provides a preparation method of a hydroxyl-rich cobalt oxide nanosheet for uranium separation, the prepared hydroxyl-rich cobalt oxide nanosheet is used as an electrocatalyst for extracting uranium from fluorine-containing uranium wastewater, and the problem that uranium fluoride complexes are difficult to separate in traditional technologies is solved. The hydroxyl-rich cobalt oxide nanosheet of the present application has a large number of hydroxyl groups, can enhance the affinity for uranium, and improve the capture capacity for dissociated uranyl ions, and through electro-driven uranium separation, uranium species grow from the initial uranium monomer to uranium oxide nanosheets on the surface of the cobalt oxide nanosheet, and a solid 2O ax -1U-3O eq configuration. The hydroxyl-rich cobalt oxide nanosheet of the present application exhibits excellent uranium(VI) removal capacity in the presence of a certain amount of fluoride ions, and the uranium(VI) removal rate reaches 96%. The present application not only provides a new way for developing a cheap electrocatalyst for efficiently extracting uranium from fluorine-containing uranium wastewater, but also provides a new way for studying the evolution mechanism of uranium species.

[0018] Other advantages, objects, and features of the present application will be apparent from the following description, and will be understood by those skilled in the art. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 CoO prepared for Example 1 x (a) and A-CoO prepared for Comparative Example 1 x (b) TEM image;

[0020] Figure 2 CoO prepared for Example 1 x A-CoO prepared for Comparative Example 1 x XRD pattern of;

[0021] Figure 3 CoO prepared for Example 1 x A-CoO prepared for Comparative Example 1 x water contact angle comparison chart;

[0022] Figure 4 CoO prepared for Example 1 x A-CoO prepared for Comparative Example 1 x FTIR spectrum of;

[0023] Figure 5 CoO prepared for Example 1 x (a), A-CoO prepared for Comparative Example 1 x(b) and CoO prepared in Example 2 x The relationship between uranium extraction amount and reaction time in -1(c) is shown in the figure.

[0024] Figure 6 CoO prepared in Example 1 x Uranium removal rates at different pH values ​​(4–9);

[0025] Figure 7 CoO prepared in Example 1 x In interfering ions (Cl - C2O4 2- SO4 2- NO3 - CO3 2- uranium removal rate under ( )

[0026] Figure 8 CoO prepared in Example 1 x Uranium removal rate in fluorine-free uranium (VI) solutions with different uranium (VI) concentrations (10–100 mg / L);

[0027] Figure 9 CoO prepared in Example 1 x Uranium removal rates at different fluorine-uranium ratios (molar ratios of 10:1 to 1000:1). Detailed Implementation

[0028] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0029] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0030] Example 1

[0031] A method for preparing uranium-separated hydroxycobalt oxide nanosheets includes the following steps:

[0032] Step 1: Mix 0.291g Co(NO3)2·6H2O and 1.82g C 19 H 42 Add BrN to 50 mL of deionized water and stir until completely dissolved. Then add 0.0946 g of NaBH4 and stir with a magnetic stirrer at room temperature until the bubbles disappear. The magnetic stirrer speed is 200 r / min.

[0033] Step two, the mixed solution obtained in step one is centrifuged at 8000 r / min for 5 min, the precipitate is collected, washed with ethanol solution and deionized water for 4 times, and vacuum dried at 60℃ for 24 h to obtain the hydroxyl-rich cobalt oxide nanosheet, namely CoO x .

[0034] Example 2

[0035] A method for preparing a hydroxyl-rich cobalt oxide nanosheet for uranium separation, comprising the following steps:

[0036] Step one, 0.291g Co(NO3)2·6H2O and 1.82g C 19 H 42 BrN are added into 50mL deionized water, stirred until completely dissolved, then 0.0946g NaBH4 is added, and stirred at room temperature using a magnetic stirrer at a speed of 200r / min until the bubbles disappear;

[0037] Step two, the mixed solution obtained in step one is centrifuged at 8000 r / min for 5 min, the precipitate is collected, washed with ethanol solution and deionized water for 4 times, and vacuum dried at 60℃ for 24 h to obtain the hydroxyl-rich cobalt oxide nanosheet, namely CoO x .

[0038] Step three, the hydroxyl-rich cobalt oxide nanosheet obtained in step two is treated for 3 min using a low-temperature plasma treatment instrument to obtain the hydroxyl-rich cobalt oxide nanosheet, namely CoO x -1; wherein the atmosphere of the low-temperature plasma treatment instrument is oxygen, the frequency is 40KHz, the power is 500W, and the pressure of the atmosphere is 80Pa.

[0039] Comparative Example 1

[0040] A method for preparing a cobalt oxide nanosheet without hydroxyl, comprising the following steps:

[0041] The hydroxyl-rich cobalt oxide nanosheet prepared in Example 1 is placed in a muffle furnace and annealed at 300℃ for 2h to obtain a cobalt oxide nanosheet without hydroxyl, namely A-CoO x .

[0042] Figure 1 TEM images of CoO x (a) prepared in Example 1 and A-CoO x (b) prepared in Comparative Example 1, it can be seen that CoO x is a wrinkled nanosheet morphology with an ultra-thin thickness, while A-CoOx shows a fragmented nanosheet morphology. Figure 2 TEM images of CoO xA-CoO prepared in Comparative Example 1 x The XRD pattern shows that CoO x The XRD pattern did not show specific diffraction peaks, indicating that CoO x It is an amorphous oxide, while A-CoO x Diffraction peaks appeared at 19.00°, 31.27°, 36.84°, 44.81°, 59.35°, and 65.23°, corresponding to the (111), (220), (311), (400), and (511) and (440) crystal planes of Co3O4 (JCPDS No. 43-1003), respectively, indicating that high-temperature annealing effectively removed CoO. x hydroxyl groups on the surface.

[0043] CoO prepared in Example 1 x A-CoO prepared in Comparative Example 1 x A water contact angle experiment was conducted, and the results are as follows: Figure 3 As shown, it can be seen that, compared with A-CoO x In comparison, CoO x The complete penetration indicates that the presence of a large number of hydroxyl groups improves the wettability of the material, which can effectively increase its probability of capturing uranyl ions. For the CoO prepared in Example 1... x A-CoO prepared in Comparative Example 1 x Fourier transform infrared spectroscopy (FTIR) experiments were performed, and the results are as follows: Figure 4 As shown, it can be seen that CoO x Between 1400 and 1260 cm -1 and 3000~3700cm -1 Two distinct characteristic peaks are observed at this point, corresponding to the bending vibrations of hydroxyl groups. After annealing, A-CoO... x The area of ​​the hydroxyl characteristic peak decreased significantly, further indicating that CoO x The surface is rich in hydroxyl groups.

[0044] Uranium removal experiment: A fluorinated uranium (VI) solution was prepared using Na₂SO₄, NaF, uranyl nitrate, and deionized water, with a uranium (VI) concentration of 50 mg / L, a Na₂SO₄ concentration of 0.5 mol / L, and a NaF concentration of 100 mg / L. The pH of the system was adjusted to 6–6.2 using 0.1 M HCl and / or NaOH solution. Tests were conducted using an electrochemical workstation (CHI660e) under a standard three-electrode system. CoO x CoO x -1 or A-CoO x The electrode was used as the working electrode, and the platinum wire and saturated Ag / AgCl electrode were used as the counter electrode and reference electrode, respectively. A fluorinated uranium (VI) solution was prepared as the electrolyte. The uranium removal rate was calculated using the following formula:

[0045]

[0046]

[0047] In the formula, C0 (mg / L) is the initial concentration of uranium (VI), and C t (mg / L) is the uranium(VI) concentration after adsorption time t, V(L) is the volume of the solution, and q t (mg / g) represents the uranium extraction amount at time t, and m(g) represents the CoO content. x CoO x -1 or A-CoO x The quality.

[0048] Figure 5 CoO prepared in Example 1 x (a) A-CoO prepared in Comparative Example 1 x (b) and CoO prepared in Example 2 x The graph showing the relationship between uranium extraction amount and reaction time for -1(c) indicates that CoO x Uranium extraction reached a basic equilibrium after about 6 hours, with the extracted uranium content exceeding 230 mg / g, which is higher than that of A-CoO. x CoO x -1 yields higher uranium extraction rates than CoO. x and A-CoO x The uranium extraction yield reached over 240 mg / g, indicating that treating the hydroxyl-rich cobalt oxide nanosheets with a low-temperature plasma treatment instrument further increased the surface hydroxyl content and improved its uranium removal capacity. The CoO prepared in Example 1... x Experiments were conducted on uranium removal rates at different pH values ​​(4–9). The pH of the fluorinated uranium (VI) solution was adjusted using 0.1 M HCl and / or NaOH solutions. The results are as follows: Figure 6 As shown in the figure, it can be seen that as the pH increases from 4 to 5, CoO x The uranium removal rate increased, reaching its peak within the pH range of 5–6 with no significant change. As the pH increased further from 6 to 9, the uranium removal rate decreased slightly. Under high pH conditions, uranium and fluorine in the wastewater mainly exist as negatively charged complexes with high reduction overpotentials. In the electrochemically assisted uranium extraction process, Coulomb force drives the separation of fluorine-uranium complexes, leading to the separation of CoO₂. x It exhibits excellent uranium removal capabilities over a wide pH range.

[0049] Because the actual composition of fluorinated uranium wastewater is very complex, with many coexisting anions, it may interfere with the uranium extraction process, further affecting the CoO prepared in Example 1. xThe selectivity and anti-interference properties were tested, with interfering ions (Cl) being used. - C2O4 2- SO4 2- NO3 - CO3 2- The concentration of ) is 200 mg / L, such as Figure 7 As shown, in Cl - C2O4 2- NO3 - and SO4 2- In the presence of CO3, the uranium removal rates reached as high as 94.6%, 87.0%, 76.35%, and 92.9%, respectively. 2- In the uranium solution, the uranium removal rate was still as high as 80%, indicating that CoO x It has excellent anti-interference capabilities.

[0050] CoO prepared in Example 1 x Experiments were conducted to determine the uranium removal rate in fluorine-free uranium (VI) solutions with different uranium (VI) concentrations (10–100 mg / L). Figure 8 As shown, in the absence of fluoride ions, CoO x It maintained a high uranium removal capacity over a wide range of uranium (VI) concentrations, with an average uranium removal rate exceeding 95%. The CoO prepared in Example 1... x Experiments were conducted to determine the uranium removal rate in uranium (VI)-containing solutions with different fluorine-to-uranium ratios (molar ratios ranging from 10:1 to 1000:1). Figure 9 As shown, CoO x Although the uranium removal rate gradually decreases with increasing fluorine-uranium ratio, it remains above 60%, indicating that CoO2 has good uranium removal efficiency. x It can still maintain a high uranium removal capacity under high fluoride ion conditions.

[0051] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. An application of hydroxyl-rich cobalt oxide nanosheets in uranium separation, characterized in that, include: Hydroxycobalt oxide nanosheets were added to fluorine-containing uranium wastewater as working electrodes to carry out an electrocatalytic reaction. The reacted hydroxycobalt oxide nanosheets were then placed in 0.1 mol / L HCl solution or 0.1 mol / L NaHCO3 solution, stirred, washed, and recycled. The method for preparing the hydroxyl-rich cobalt oxide nanosheets includes the following steps: Step 1: Combine Co(NO3)2•6H2O and C 19 H 42 BrN was added to deionized water and stirred until completely dissolved. Then NaBH4 was added, and the mixture was stirred with a magnetic stirrer at room temperature until the bubbles disappeared. Co(NO3)2•6H2O and C... 19 H 42 The mass-to-volume ratio of BrN to deionized water is 0.291 g: 1.5~2 g: 40~60 mL; the mass ratio of NaBH4 to Co(NO3)2•6H2O is 0.05~0.15:0.

291. Step 2: Centrifuge the mixed solution obtained in Step 1, collect the precipitate, wash it with anhydrous ethanol and deionized water in sequence, and vacuum dry it to obtain hydroxyl-rich cobalt oxide nanosheets. Step two further includes: treating the obtained hydroxyl-rich cobalt oxide nanosheets with a low-temperature plasma treatment instrument for 2-4 minutes; the atmosphere of the low-temperature plasma treatment instrument is oxygen, the frequency is 30-50 kHz, the power is 500 W, and the pressure of the atmosphere is 70-90 Pa.

2. The application of hydroxyl-rich cobalt oxide nanosheets in uranium separation as described in claim 1, characterized in that, In step one, the rotation speed of the magnetic stirrer is 100~300 r / min.

3. The application of the hydroxyl-rich cobalt oxide nanosheets as described in claim 1 in uranium separation, characterized in that, In step two, the centrifugation speed is 7000~9000 r / min and the centrifugation time is 4~6 min.

4. The application of the hydroxyl-rich cobalt oxide nanosheets as described in claim 1 in uranium separation, characterized in that, In step two, the washing with anhydrous ethanol and deionized water is performed 3 to 5 times.

5. The application of hydroxyl-rich cobalt oxide nanosheets as described in claim 1 in uranium separation, characterized in that, In step two, the vacuum drying temperature is 50~70 ℃ and the drying time is 20~28 h.

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