Uranium extraction system and uranium extraction method

Abstract

The present invention relates to a uranium extraction method and system, which comprises: pre-reducing an adsorbent to make the adsorbent reducible; placing the adsorbent in a uranium-containing solution, causing the adsorbent to undergo an oxidation-reduction reaction with a uranium-containing compound or uranium-containing ion in the uranium-containing solution and adsorbing uranium in the solution; separating the adsorbent from the uranium-containing solution to obtain an adsorbent adsorbed with uranium; placing the adsorbent adsorbed with uranium in a deuranization solution to desorb uranium from the adsorbent to obtain uranium enrichment. The method or system decouples the application of reducing charge to the adsorbent and the reaction of the adsorbent with the uranium-containing solution in time and space, thereby avoiding the generation of ion polarization during the reaction and greatly reducing the competition of other ions in the uranium-containing solution.

Description

Technical Field

[0001] The invention relates to a uranium extraction system and a uranium extraction method, belonging to the field of metal resource development and utilization. Background Art

[0002] Nuclear energy is widely regarded as an efficient and clean energy source because of its advantages such as high energy density and low carbon emissions. As a representative nuclear fuel, uranium has an increasing demand. At present, the main uranium resource supply comes from uranium mining. However, a large amount of polluting uranium-containing wastewater will be produced during the uranium mining process. If not properly treated, these uranium-containing wastewater may pollute nearby rivers, lakes and other water sources, threatening the local ecological environment. In addition, due to long-term and large-scale mining, the shortage of uranium reserves on land has caused widespread concern. With the current growth rate of people's demand for uranium, the uranium mines on land are likely to be exhausted within a century. Therefore, people are in urgent need of developing new uranium resources. According to scholars' research, the ocean is rich in uranium resources, with reserves of up to 4.5 billion tons, which is thousands of times the uranium reserves on land, enough to supply human use for nearly 10,000 years. It can be seen that it is extremely necessary to extract uranium from water bodies. On the one hand, it can reduce the environmental pollution caused by the supply of front-end raw materials for the nuclear industry, and on the other hand, it can also alleviate the problem of future uranium resource supply.

[0003] In order to extract uranium resources from water, people have developed a series of methods including direct adsorption, electrochemical method, reduction adsorption method, etc. Among them, the direct adsorption method uses the selective adsorption capacity of functional groups. Uranium is present in water as uranyl ions (UO2 2+ ) exists in the form of uranium. Studies have shown that materials rich in nitrogen-oxygen functional groups, represented by amidoxime groups, or materials containing metal-oxygen bonds can specifically bind to uranyl ions through coordination, thereby capturing and separating uranium from water. However, the concentration of uranium in water is generally very low, for example, it is only about 3 ppb in seawater. In contrast, sodium, magnesium, potassium, calcium and other ions that are widely present in seawater have a concentration of 10 of uranium. 5 ~10 6 The competition of impurity ions and the limitation of adsorption kinetics make the direct adsorption method slow and low in capacity. For example, in the literature (Adv. Funct. Mater., 2023, 33, 2212819), when the uranium concentration is magnified by 10 3 Even in simulated seawater with a concentration more than times that of water, it still takes more than 36 hours to achieve adsorption equilibrium.

[0004] The electrochemical method introduces an external electric field to force the uranyl ions in the solution to move toward the cathode of the electrode. The uranyl ions can be captured by the adsorption sites on the electrode and undergo a reduction reaction, reducing the dissolved uranyl ions (+6 valence) to insoluble uranium precipitates (+4 / +5 valence) and separating them from the solution. The reduction transformation of uranium species promotes the movement of the adsorption equilibrium and effectively improves the adsorption rate at low concentrations. For example, the literature (Nat. Energy 2017, 2, 17007) uses this method to achieve a uranium extraction efficiency four times that of the adsorption method in actual seawater. However, in the electrochemical process, the application of the reduction potential and the movement of ions are carried out simultaneously, which brings about severe ion polarization, thereby hindering the migration of uranyl ions to the electrode surface, and the higher reaction potential (~-5V) also has application limitations. Summary of the invention

[0005] The present invention provides a uranium extraction method and a uranium extraction system to solve the problem of slow adsorption rate caused by adsorption equilibrium in the existing direct adsorption method and the problem of limited mass transfer of uranium-containing ions caused by ion polarization in the electrochemical method. The method or system decouples two steps of applying reduction charge to an adsorbent and chemically reacting the adsorbent with a uranium-containing compound or uranium-containing ion in a uranium-containing solution in time and space, thereby avoiding the generation of ion polarization during the reaction, greatly reducing the competition of other ions in the uranium-containing solution, and facilitating the conversion of soluble uranium-containing compounds or uranium-containing ions into insoluble uranium-containing products. In addition, by dispersing the adsorbent in the uranium-containing solution, the contact area can be increased, the reaction rate can be accelerated, and the problems of reaction equilibrium, ion polarization, limited mass transfer, etc. in the direct adsorption method and the electrochemical method are solved.

[0006] The technical scheme adopted by the present invention is: a uranium extraction method, comprising pre-reduction of adsorbent, uranium extraction, separation and deuranization processes. In the pre-reduction of adsorbent, the oxidized adsorbent is converted into the reduced adsorbent, and the adsorbent has reducing property; in the uranium extraction process, the adsorbent with reducing property is placed in a uranium-containing solution, and the adsorbent undergoes an oxidation-reduction reaction with the soluble uranium (uranium-containing compound or uranium-containing ion) in the uranium-containing solution, the adsorbent is converted from the reduced state to the oxidized state, and the uranium in the uranium-containing compound or the uranium-containing ion is reduced and converted into insoluble uranium, and then precipitates from the solution and is deposited on the adsorbent. In this process, the soluble uranium in the solution is gradually reduced, and uranium extraction is realized; in the separation process, the adsorbent adsorbed with uranium is separated from the uranium-containing solution; in the deuranization process, the adsorbent adsorbed with uranium is placed in the deuranization solution, and uranium is desorbed from the adsorbent, and uranium enrichment is obtained. The above-mentioned adsorbent is a substance insoluble in the uranium-containing solution, which can be solid or liquid. If it is solid, it can be particles or powders, which is conducive to increasing the contact area. The particles and powders can be directly dispersed in the uranium-containing solution or loaded on a carrier, such as a metal mesh or a hydrophilic mesh cloth, carbon paper, etc. The dispersion of the powder or particles on the hydrophilic substrate is conducive to separation and recovery, and the specific surface area can also be adjusted by controlling the load density; the particles or powders are moved in the uranium-containing solution by stirring or water circulation, so that the adsorbent and the uranium-containing solution react fully. If it is a powder, the particle size is preferably 0.1 to 10 μm, which is conducive to obtaining the maximum contact efficiency. If it is a particle, the particle size is preferably within 1 mm. The separation form of the adsorbent and the solution can be physical separation, chemical separation or electrochemical separation; deuranization can be uranium desorbed from the adsorbent by physical methods or chemical methods. The present invention adopts a chemical reaction method to make the uranium in the uranium-containing solution react with the adsorbent, and enrich the uranium in the solution to the adsorbent based on the reaction kinetics and ion concentration differences.

[0007] As a preferred embodiment, the soluble uranium in the present invention is uranyl ions, and the adsorbent in the present invention reduces the uranyl ions in the solution to insoluble uranium compounds, and is oxidized itself. The reduced uranium compounds are insoluble in water, and form a precipitate attached to the adsorbent. As a preferred embodiment, the adsorbent in the present invention needs to have an active site for adsorbing uranyl ions. This feature is conducive to the adsorption of uranyl ions in the solution, increases the reaction rate of the two, and still has high reaction activity at low ion concentrations; more preferably, the adsorbent has redox reversibility, increases the recycling of materials, and reduces costs; the adsorbent has catalytic reduction ability for uranyl ions, converts uranyl ions into insoluble uranium compounds, promotes the positive shift of uranyl ion adsorption equilibrium, and adapts to the extraction of uranium at low concentrations; as a more specific implementation form, the adsorbent is an electrode material for a sodium battery or a lithium battery, and more preferably, it is a positive electrode material for a sodium battery or a lithium battery, such as lithium vanadium phosphate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, sodium iron phosphate, one or a combination of two or three thereof. When it is lithium iron phosphate, it can be Li x FePO4 or / and Li x FePO4 / C (carbon-coated lithium iron phosphate), where 0<x≤1; when it is lithium manganese iron phosphate, it can be Li x Mn y Fe 1-y PO4 or / and Li x Mn y Fe 1-y PO4 / C (carbon-coated lithium manganese iron phosphate), where 0<x≤1, 0<y<1; when it is lithium vanadium phosphate, it can be Li x V2(PO4)3 or / and Li x V2(PO4)3 / C(Carbon-coated Li x V2(PO4)3), where 1<x≤3; when it is sodium iron phosphate, it can be Na x FePO4、Na x FePO4 / C (carbon-coated Na x FePO4), Na y FeP2O7、Na y FeP2O7 / C (Carbon-coated Na y FeP2O7), Na z Fe3(PO4)2(P2O7), Na z Fe3(PO4)2(P2O7) / C(Carbon-coated Na z One or more of Fe3(PO4)2(P2O7)). The above substances are easy to obtain, have redox reversibility, and have adsorption active sites.

[0008] If the redox method is adopted, the uranyl ions are converted into insoluble uranium compounds and deposited on the adsorbent. As a preferred method, the insoluble uranium compounds react with the deuranization solution during the deuranization process and dissolve again. After deuranization, the adsorbent can recover its structure so that it has the performance of extracting uranium again. As a preferred method, carbonate or bicarbonate solution is selected as the deuranization solution, and the deuranization is carried out by using the effect of carbonate ions being coordinated with uranyl ions and then being dissolved again. An oxidizing substance is also required to be added to the deuranization solution to re-oxidize the uranium precipitate reduced to an insoluble state on the surface of the adsorbent into uranyl ions. The oxidizing substance is preferably hydrogen peroxide or persulfate. The sum of the concentrations of carbonate and bicarbonate in the deuranization solution is preferably 0.01 to 2 mol / L. If the concentration is lower than 0.01 mol / L, it will affect the dissolution rate and effect. If the concentration is higher than 2 mol / L, it will have an adverse effect on the adsorbent. The concentration of the oxidizing substance is preferably 0.01 to 0.5 mol / L. If the concentration is too high, the adsorbent will be damaged due to excessive oxidizing properties.

[0009] As a preferred method, lithium iron phosphate is used as an adsorbent, and sodium bicarbonate and hydrogen peroxide are used as deuranium solutions, specifically the following steps:

[0010] S01 places lithium iron phosphate in a uranium-containing solution to reduce the uranyl ions in the solution, and the uranyl ions are converted into insoluble uranium compounds (represented by uranium dioxide), and the reaction (1) occurs.

[0011] 2LiFePO4+UO2 2+ →2FePO4+UO2+2Li + Response (1)

[0012] S02 filtering the uranium-containing solution to obtain solid particles, i.e., adsorbent having insoluble uranium compounds deposited thereon;

[0013] S03 placing the filtered precipitate in a mixed solution of sodium bicarbonate and hydrogen peroxide to cause reactions (2) and (3) to desorb uranium from the adsorbent;

[0014] UO2+H2O2+3HCO3 - →UO2(CO3)3 4- +H + +2H2O reaction (2)

[0015]

[0016] The adsorbent that has completed uranium desorption in S04 is separated from the solution and placed in a reducing solution. The oxidized iron in the iron phosphate is reduced, and at the same time, the lithium ions in the solution are embedded in the crystal lattice to maintain electrical balance and structural stability. The adsorbent returns to the form of lithium iron phosphate and has the ability to adsorb uranium again.

[0017] As a preferred method, lithium iron phosphate is obtained by pre-reduction of iron phosphate, and lithium iron phosphate is pre-reduced again after uranium extraction and deuranization of lithium iron phosphate to regain the ability to adsorb uranium. Figure 1 , the adsorbent after pre-reduction is converted into a reduced state, which has good reaction activity. It is put into the uranium-containing solution for the uranium adsorption step. The adsorbent freely contacts and adsorbs uranyl ions in the solution, reduces the uranyl ions to insoluble uranium precipitates, and is continuously oxidized. When the uranyl ion concentration in the uranium-containing solution drops to a certain level, or the adsorbent is oxidized to a certain level, the adsorbent can be collected for the uranium desorption step. The deuranium solution can dissolve the uranium precipitate captured and converted by the adsorbent, and the deuranium solution can be recycled to achieve uranium enrichment. The adsorbent after the reaction is in an oxidized state. It is put into a reducing solution. The reduced state molecules can react with the adsorbent and regenerate it to a reduced state. The adsorbent after reduction regains the ability of reduction adsorption and can be put into the uranium-containing solution again for reaction. Through multiple cycles, a batch of adsorbents can process a large amount of uranium-containing solution and enrich the extracted uranium in a small amount of desorption solution for subsequent use. Due to the different solution systems in the three steps of the reaction process, the adsorbent needs to be washed and dried before entering the next step.

[0018] The pre-reduction process can reduce the oxidized adsorbent after uranium extraction and elution to its initial state. Since the transition metal element undergoes oxidation reaction during the oxidation process of uranium extraction, alkali metal ions are removed from the material to maintain charge balance. Therefore, the reduction solution needs to contain corresponding ions and adaptable reducing substances to restore the adsorbent structure. According to the type of alkali metal ions used to balance the charge in the adsorbent, the corresponding ions used to restore the adsorbent structure include lithium sulfate, lithium chloride, sodium sulfate, sodium chloride, etc. The concentration of the adsorbent in the reduction solution is selected as needed. The preferred molar ratio of the corresponding ion to the adsorbent is ≥4. If it is lower than this molar ratio, there will be insufficient ion supply in the later stage of the reaction due to the consumption of ions during the reduction process, resulting in a slow reaction rate or inadequate reaction; when the concentration of the adsorbent is low, the proportion of the corresponding ions should be increased. After the corresponding ions are consumed, they can be supplemented by directly adding relevant reagents to the solution. As a preferred method, the pre-reduction step of the adsorbent can be carried out by chemical method or electrochemical method. The chemical method is to place the adsorbent in a reducing solution to reduce it, and the electrochemical method is to reduce the adsorbent using the electrochemical redox performance. The reducing agent used in the chemical method can be sulfite, thiosulfate, etc. According to the content of the adsorbent to be reduced in the reducing solution, the preferred molar ratio of the reducing agent to the adsorbent is>4. If it is lower than this molar ratio, the consumption of the reducing agent during the reduction process will lead to insufficient ion supply in the later stage of the reaction, resulting in a slow reaction rate or inadequate reaction; when the adsorbent content is low, the proportion of the reducing agent should be increased to ensure sufficient reduction barrier, and after consumption, it can be supplemented by directly adding relevant chemical reducing agents to the solution. If an electrochemical method is selected, the reducing agent used is a reducing molecule with redox reversibility, and its oxidation potential should be lower than the reduction potential of the adsorbent, so that the redox reaction can occur thermodynamically. The reducing agents that can be used include but are not limited to methyl amethyst and its derivatives, benzoquinone molecules and their derivatives, naphthoquinone molecules and their derivatives, anthraquinone molecules and their derivatives, etc. Due to the existence of the reduction barrier, the reducing molecules in the solution can conduct electrons to the oxidized adsorbent to achieve the reduction of the adsorbent, and the reducing molecules that lose electrons in the oxidized state can contact the cathode in the electrochemical reaction, obtain electrons in the external circuit, and return to the reduced state. Since the reducing molecules can be continuously regenerated by electrochemical means, a small amount of reducing molecules can achieve the reduction of the adsorbent. The preferred molar ratio of reducing molecules to adsorbent is ≥0.5. If it is lower than this molar ratio, the current density in the electrochemical process will be low due to the low concentration of reducing molecules, resulting in slow reaction rate or incomplete reaction. When the concentration of the adsorbent is low, the proportion of reducing molecules should be appropriately increased to ensure sufficient reduction barrier and reduction current density in the solution.

[0019] The present invention also provides a uranium extraction system, which includes a uranium extraction device: used to carry out the uranium extraction process of the above method, that is, to mix the uranium-containing solution with an adsorbent, the adsorbent reacts with the uranium-containing compound or uranium-containing ion in the uranium-containing solution, and adsorbs the uranium in the solution; a separation device: used to carry out the separation process of the above method, separate the adsorbent from the uranium-containing solution, and obtain an adsorbent adsorbed with uranium; a deuranization device: used to carry out the deuranization process of the above method, place the adsorbent adsorbed with uranium in the deuranization solution, desorb uranium from the adsorbent, and obtain uranium enrichment. The system is adapted to the same as the above method, realizes the operation of the above method, and its preferred scheme is consistent with the above method, and no repetitive description is given here.

[0020] The beneficial effects of the present invention include: 1. The method proposed by the present invention first gives the adsorbent reducing properties in the pre-reduction solution, and then places the adsorbent in the uranium-containing solution for uranium extraction, decoupling the two steps of applying reducing charge to the adsorbent and chemically reacting the adsorbent with the uranium-containing solution in time and space, overcoming the limitations of the traditional adsorption method due to adsorption equilibrium, avoiding the shortcomings of ion polarization and high energy consumption in electrochemical uranium extraction, improving the extraction efficiency, and also optimizing the reaction activity and stability of the material in the ordinary reduction adsorption method, thereby achieving rapid, efficient and high-capacity uranium extraction. 2. In the preferred embodiment, the present invention screens the adsorbent in multiple dimensions, and the selected materials have the advantages of rich catalytic active sites, high redox activity, high conductivity, high reaction capacity, structural stability, etc., and can stably extract uranium in a highly dispersed state in the uranium-containing solution, greatly increasing the contact area with the solution, effectively improving the mass transfer limitation problem in the traditional method, and having the advantages of fast adsorption rate and large adsorption capacity in uranium-containing solutions of different concentrations. 3. In the preferred embodiment, the present invention selects carbonate and bicarbonate as the deuranization system, and uses sulfite and thiosulfate as the reduction system, which has excellent effects and short processing time, and is conducive to reducing time costs and improving work efficiency. 4. The method proposed in the present invention can efficiently extract and separate uranium from the solution, solve the key problems in the low-concentration uranium extraction process, and at the same time, the proposed circulation process is consistent with the characteristics of the material, showing good circulation capacity, achieving cost reduction and efficiency improvement, and is easy to operate and easy to apply on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A cycle diagram of the uranium extraction method of the present invention;

[0022] Figure 2 UO2 in the uranium-containing solution in Example 1 2+ Concentration versus reaction time curve;

[0023] Figure 3 UO2 in the deuranization solution in Example 1 2+Concentration versus reaction time curve;

[0024] Figure 4 The degree of pre-reduction of lithium iron phosphate in Example 1;

[0025] Figure 5 Adsorption capacity utilization curve of lithium iron phosphate in Example 2;

[0026] Figure 6 XRD patterns of lithium iron phosphate at various stages;

[0027] Figure 7 Uranium adsorption rate during multiple cycles;

[0028] Figure 8 During multiple cycles, the desorption efficiency;

[0029] Fig. 9 UO2 in uranium-containing solution during uranium adsorption 2+ Concentration changes DETAILED DESCRIPTION

[0030] The present invention is further explained in detail below in conjunction with the accompanying drawings and specific embodiments, but it should be understood that the protection scope of the present invention is not limited to the specific embodiments.

[0031] The system or method of the present invention is explained in detail below using lithium iron phosphate as an adsorbent. Figure 1 , pre-reduction, uranium adsorption (uranium extraction), and uranium desorption (uranium removal) form a cyclic process. There is a separation step between uranium adsorption and uranium desorption, which is not shown in the figure.

[0032] Uranium adsorption - Lithium iron phosphate is used as a pre-reduced adsorbent and is placed in simulated seawater containing a certain concentration of uranyl ions, and the lithium iron phosphate is fully and evenly dispersed in the solution. Lithium iron phosphate particles adsorb uranyl ions in the solution through surface functional groups, and use catalytic reduction to convert uranyl ions into insoluble uranium compounds (represented by uranium dioxide), while the particles themselves are oxidized to iron phosphate. Reaction (1)

[0033] 2LiFePO4+UO2 2+ →2FePO4+UO2+2Li + Reaction (1).

[0034] Uranium desorption - the iron phosphate that has been used to extract uranium is separated from the solution and placed in a sodium bicarbonate and hydrogen peroxide solution of a certain concentration. The uranium precipitate on the surface of the iron phosphate is dissolved into the solution under the synergistic effect of sodium bicarbonate and hydrogen peroxide. The iron phosphate itself does not participate in the reaction in this process. The deuranium solution can be maintained at a certain concentration by appropriately supplementing the corresponding reagents to achieve repeated use and further uranium enrichment. Reactions (2) and (3) occur.

[0035] UO2+H2O2+3HCO3 - →UO2(CO3)3 4- +H + +2H2O reaction (2)

[0036]

[0037] Pre-reduction - chemical method

[0038] The iron phosphate that has completed uranium desorption is separated from the solution and placed in a certain concentration of sodium thiosulfate and lithium sulfate solution. Under the action of the reducing agent, the oxidized iron in the iron phosphate is reduced, and the lithium ions in the solution are embedded in the lattice to maintain electrical balance and structural stability. The adsorbent returns to the form of lithium iron phosphate and has the ability to adsorb uranium again, and a reaction occurs (4). The reduction solution can be maintained at a certain concentration by appropriately supplementing the corresponding reagents to achieve repeated use.

[0039] 2Li + +2FePO4+2S2O3 2- →2LiFePO4+S4O6 2- Reaction (4);

[0040] Pre-reduction - electrochemical method

[0041] The electrochemical reaction can be carried out in an electrolytic cell, which is divided into a cathode chamber and an anode chamber, which are separated by an anion exchange membrane. The cathode chamber stores a solution containing reducing molecules, oxidized adsorbents and corresponding ions, and the anode chamber stores a solution of corresponding ions. The electrodes used in the electrolytic cell include but are not limited to carbon cloth, carbon paper, carbon felt, graphite rods, stainless steel mesh, titanium sheets, titanium mesh, platinum sheets, etc. The iron phosphate that has completed uranium desorption is separated from the solution and put into a certain concentration of methyl viologen and lithium chloride solution. A certain voltage is applied to the electrolytic cell. Under the action of the reducing molecules, the oxidized iron in the iron phosphate is reduced. At the same time, the lithium ions in the solution are embedded in the lattice to maintain electrical balance and structural stability. The adsorbent returns to the form of lithium iron phosphate and has the ability to adsorb uranium again, and a reaction occurs (5). The methyl viologen that has lost electrons is reduced at the cathode of the electrolytic cell and has the ability to pre-react with the iron phosphate again, and a reaction occurs (6). The reducing solution can be maintained at a certain Li by appropriately supplementing lithium chloride. + concentration for reuse.

[0042]

[0043] The uranium extraction system is used to implement the above-mentioned uranium extraction method, including a uranium extraction device, a separation device, a deuranium device and a pre-reduction device. Each device can exist separately or be combined into one device. The uranium extraction device is used to perform a uranium adsorption step, mix the adsorbent with the uranium-containing solution and realize uranium extraction. The separation device is used to separate the adsorbent from the uranium-containing solution. The deuranium device is used to perform a uranium desorption step to desorb uranium on the adsorbent. The pre-reduction device is used to reduce the desorbed adsorbent to its initial state so that it can be used for uranium adsorption again.

[0044] The method of the present invention converts uranium-containing ions in the solution into insoluble uranium-containing components through the action of the adsorbent on the uranium-containing solution, and then adsorbs the uranium ions on the adsorbent, thereby reducing the concentration of uranium ions in the uranium-containing solution, allowing the uranium ions to diffuse toward the adsorbent, thereby promoting the reaction and being unaffected by ion polarization; the method of the present invention realizes ion conversion through oxidation-reduction, promotes the movement of adsorption equilibrium, and improves the uranium extraction efficiency of the adsorbent at low concentrations.

[0045] The adsorbent in the present invention reacts only in the first stage, has stable performance, and has redox reversibility, which is conducive to structural recovery and realizes the recycling of materials.

[0046] The present invention disperses the pre-reduced powdered adsorbent in the uranium-containing solution, thereby greatly increasing the contact between the material and the uranyl ions, and can eliminate the ion polarization and overpotential problems caused by the external battery in the electrochemical method.

[0047] The method or system of the present invention is applicable to seawater, simulated seawater, uranium mine wastewater, brine, groundwater, uranium contaminated water, etc. with any concentration of uranyl ions, and a high uranium recovery rate is achieved in the concentration range of 10 μg / L to 1000 mg / L. The higher the uranyl ion concentration in the solution, the higher the utilization rate of the adsorbent and the uranyl ion removal rate will be.

[0048] The present invention is further described in detail below in the form of specific embodiments.

[0049] Example 1

[0050] The uranium extraction method includes the following steps:

[0051] (1) Uranium adsorption: 50 mL of uranium-containing solution is placed in a container. The composition and concentration of the main ions in the uranium-containing solution are: UO2 2+ 500mg / L, Na + 11g / L, the pH of the solution is 6.5, 50mg of lithium iron phosphate powder is added to the uranium-containing solution, and the reaction is carried out under magnetic stirring for 24h to make the adsorbent react with the UO2 in the solution. 2+ The reaction was fully contacted and the reaction temperature was 25°C.

[0052] (2) Separation: Separating the reacted lithium iron phosphate powder from the uranium-containing solution and drying it.

[0053] (3) Uranium desorption: Add dry lithium iron phosphate powder into 20 mL of deuranium solution. The composition and concentration of the main ions in the deuranium solution are: HCO3 - 0.1mol / L, HO2 - 0.05mol / L; react for 24h under magnetic stirring to completely dissolve the uranium on the surface of lithium iron phosphate in the solution; the reaction temperature is 25℃.

[0054] (4) Pre-reduction: The lithium iron phosphate powder after the reaction was separated from the deuranium solution and dried, and added to 50 mL of the reducing solution. The composition and concentration of the main ions of the reducing solution were S2O3 2- 0.3mol / L, Li + 0.1mol / L, react for 24h under magnetic stirring to completely reduce the lithium iron phosphate to its initial state, the reaction temperature is 25℃.

[0055] Testing UO2 in uranium-containing solutions during uranium adsorption 2+ The concentration changes with reaction time, such as Figure 2 As shown, it can be seen that as time goes by, the UO2 in the solution 2+ It gradually decreases and reaches 50 mg / L in 6 hours. Uranium adsorption is basically completed within 24 hours. The adsorption rate is fast, the capacity is large, and the adsorption is thorough.

[0056] Testing UO2 in solution during deuranization 2+ The concentration changes with reaction time, such as Figure 3 As shown, it can be seen that as time goes by, the UO2 in the solution 2+ The content increased and approached 25 mg at 24 h, which was comparable to the uranium content in the uranium-containing solution, indicating that the extraction rate of this method was very high.

[0057] The degree of reduction of the lithium iron phosphate structure and components in the pre-reduction step was tested, such as Figure 4 As shown, it can be seen that the selected uranium desorption system and reduction system can well achieve the goal of rapidly recovering enriched uranium and efficiently restoring material performance.

[0058] Example 2

[0059] The uranium extraction method in this embodiment comprises the following steps:

[0060] (1) Uranium adsorption: 100 mL of uranium-containing solution is placed in a container. The composition and concentration of the main ions in the uranium-containing solution are: UO2 2+ 100mg / L, Na + 10g / L,Mg 2+2g / L, the pH of the solution was 7, 20mg of lithium iron phosphate powder was added, and the mixture was reacted for 24h under magnetic stirring to allow the adsorbent to react with the UO2 in the solution. 2+ The reaction was fully contacted and the reaction temperature was 25°C.

[0061] (2) separation: separating the reacted lithium iron phosphate powder from the uranium-containing solution and drying it;

[0062] (3) Uranium desorption: The dried lithium iron phosphate powder was added to 20 mL of deuranium solution, in which the composition and concentration of the main ions CO3 2 - is 0.1 mol / L, HO2- is 0.05 mol / L, and the reaction is carried out for 24 hours under magnetic stirring to completely dissolve the uranium on the surface of lithium iron phosphate in the solution. The reaction temperature is 25°C.

[0063] (4) Pre-reduction: The reacted lithium iron phosphate powder is separated from the deuranium solution and dried, and added to the cathode chamber of the electrolytic cell, which contains 20 mL of a reducing solution, wherein the composition and concentration of the main ions are 0.1 mol / L of methyl viologen, Li + is 0.15 mol / L, and the anode chamber contains 20 mL of electrolyte solution, in which the composition and concentration of the main ions are Li + The cathode and anode electrodes of the electrolytic cell are carbon cloth, and the current density of the electrolytic cell is 50mA / cm 2 , react for 1h under magnetic stirring, so that the lithium iron phosphate is completely reduced to the initial state, and the reaction temperature is 25°C. During the electrochemical reduction process, the reactions occurring at the electrodes are:

[0064] cathode:

[0065]

[0066] anode:

[0067] H2O→1 / 2O2+2H + +2e -

[0068] The changes in the adsorption capacity utilization rate of lithium iron phosphate and the reaction time during the test of uranium adsorption, such as Figure 5 It can be seen that the utilization rate is close to 100% after 24 hours. XRD analysis was performed on lithium iron phosphate before uranium adsorption, lithium iron phosphate after uranium adsorption, and lithium iron phosphate after pre-reduction. Figure 6 As shown, it can be seen that lithium iron phosphate is completely oxidized after uranium adsorption and loses the lattice structure of the raw material. After the reduction step, the material returns to its initial state and has the ability to cycle again.

[0069] Example 3

[0070] The method for extracting uranium in this embodiment comprises the following steps:

[0071] (1) Uranium adsorption: 100 mL of uranium-containing solution is placed in a container. The composition and concentration of the main ions in the uranium-containing solution are UO2 2 + 32mg / L, Na + 11g / L, the pH of the solution was 6, 30mg of lithium iron phosphate powder was added, and the mixture was reacted for 12h under magnetic stirring to allow the adsorbent to react with the UO2 in the solution. 2+ The reaction was fully contacted and the reaction temperature was 25°C.

[0072] (2) Separation: Separating the reacted lithium iron phosphate powder from the uranium-containing solution and drying it.

[0073] (3) Uranium desorption: Lithium iron phosphate powder was added to 20 mL of deuranium solution. The composition and concentration of the main ions in the deuranium solution were 2- 0.1mol / L, HO2 - The concentration of uranium on the surface of lithium iron phosphate was 0.05 mol / L, and the reaction was carried out for 0.5 h under magnetic stirring to completely dissolve the uranium on the surface of lithium iron phosphate in the solution. The reaction temperature was 25 °C.

[0074] (4) Pre-reduction: The lithium iron phosphate powder after the reaction was separated from the deuranium solution and dried, and then added to 20 mL of the reducing solution. The composition and concentration of the main ions in the reducing solution were determined by the following equation: SO3 2- 0.3 mol / L, Li + The concentration of lithium iron phosphate was 0.2 mol / L and the reaction was carried out for 4 hours under magnetic stirring to completely reduce the lithium iron phosphate to its initial state. The reaction temperature was 25°C.

[0075] (5) The pre-reduced lithium iron phosphate is subjected to step (1) again. The cycle is repeated multiple times, and the uranium removal rate in each cycle is tested. Figure 7 As shown in the figure, it can be seen that during multiple cycles, lithium iron phosphate can maintain a high uranium adsorption rate in the uranium adsorption step. Figure 8 It can be seen that during multiple cycles, lithium iron phosphate can be efficiently desorbed in the uranium desorption step, and the uranium enrichment effect is obvious.

[0076] Example 4

[0077] The method for uranium extraction in this embodiment includes the following steps: (1) Uranium adsorption: 1000 mL of uranium-containing solution is placed in a container, wherein the composition and concentration of the main ions are UO2 2+ 0.1mg / L, Na + 11g / L, the pH of the solution was 7, 50mg of lithium iron manganese phosphate powder was added, and the mixture was reacted for 48h under magnetic stirring to allow the adsorbent to react with the UO2 in the solution. 2+Fully contact and react, the reaction temperature is 25°C. (2) Separation: The reacted lithium manganese iron phosphate powder is separated from the uranium-containing solution and dried.

[0078] (3) Uranium desorption: Lithium manganese iron phosphate powder was added to 20 mL of deuranium solution. The composition and concentration of the main ions in the deuranium solution were 2- 0.1mol / L, HO2 - The concentration of uranium was 0.05 mol / L and the reaction was carried out for 1 hour under magnetic stirring to completely dissolve the uranium on the surface of lithium manganese iron phosphate in the solution. The reaction temperature was 25°C.

[0079] (4) Pre-reduction: The reacted lithium iron manganese phosphate powder was separated from the deuranium solution and dried, and added to 20 mL of reducing solution, in which the composition and concentration of the main ions S2O3 2- 0.3 mol / L, Li + The concentration of lithium manganese iron phosphate was 0.2 mol / L and the reaction was carried out for 6 hours under magnetic stirring to completely reduce the lithium manganese iron phosphate to its initial state. The reaction temperature was 25°C.

[0080] Testing UO2 in uranium-containing solutions 2+ Changes in ion concentration, such as Fig. 9 It can be seen that uranium adsorption in low concentration uranium-containing solution also has a faster adsorption rate and better adsorption effect.

[0081] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for extracting uranium, characterized in that: include Pre-reduced adsorbent: the adsorbent is reduced from an oxidized state to a reduced state to obtain a reduced state adsorbent, and the reduced state adsorbent has reducing properties; Extracting uranium: placing a reduced adsorbent in a uranium-containing solution, the reduced adsorbent undergoes an oxidation-reduction reaction with the uranium-containing compound or uranium-containing ion in the uranium-containing solution, so that the uranium in the uranium-containing compound or uranium-containing ion is precipitated from the solution and adsorbed on the adsorbent; Separation: Separating the adsorbent with uranium from the uranium-containing solution; Deuranization: The separated adsorbent is placed in a deuranization solution to desorb uranium from the adsorbent to obtain uranium enrichment; The adsorbent is a solid electrode material, and the reduced state adsorbent is a reduced state of the solid electrode material; The uranium element in the uranium-containing solution exists in the form of uranyl ions, and there are active sites for adsorbing uranyl ions on the adsorbent; The adsorbent has catalytic reduction capability for uranyl ions, and the adsorbent is a combination of one or more of lithium iron phosphate, lithium iron manganese phosphate, lithium vanadium phosphate, and sodium iron phosphate.

2. The uranium extraction method according to claim 1, characterized in that: The adsorbent is lithium iron phosphate, and the lithium iron phosphate is Li x FePO4、Li x A mixture of one or more of FePO4 / C, wherein 0<x≤1.

3. The uranium extraction method according to claim 1, characterized in that: The adsorbent is lithium iron manganese phosphate, and the lithium iron manganese phosphate is Li x Mn y Fe 1-y PO4、Li x Mn y Fe 1-y A mixture of one or more of PO4 / C, wherein 0<x≤1, 0<y<1.

4. The uranium extraction method according to claim 1, characterized in that: The adsorbent is lithium vanadium phosphate, and the lithium vanadium phosphate is Li x V2(PO4)3、Li x A mixture of one or more of V2(PO4)3 / C, wherein 1<x≤3.

5. The uranium extraction method according to claim 1, characterized in that: The adsorbent is sodium iron phosphate, and the sodium iron phosphate is Na x FePO4、Na x FePO4 / C、Na y FeP2O7、Na y FeP2O7 / C、Na z Fe3(PO4)2(P2O7), Na z A mixture of one or more of Fe3(PO4)2(P2O7) / C, wherein 0<x≤1, 1<y≤2, 1<z≤4.

6. The uranium extraction method according to claim 1, characterized in that: In the deuranization process, the deuranization solution reacts with the uranium on the adsorbent, so that the uranium is converted into soluble uranium, which is dissolved in the deuranization solution.

7. The uranium extraction method according to claim 1, characterized in that: The uranium in the uranium-containing solution exists in the form of uranyl ions, and the uranium extraction method is as follows: Extracting uranium: The adsorbent acts as a reducing agent to reduce the uranium in the uranyl ions, so that the uranium exists in the form of an insoluble uranium compound and is deposited on the adsorbent, and the adsorbent is converted into an oxidized state; Separation: separating the adsorbent from the uranium-containing solution to obtain an adsorbent adsorbed with insoluble uranium compounds; Deuranization: The adsorbent is placed in a deuranization solution containing carbonate or bicarbonate ions. During the deuranization process, the carbonate or bicarbonate ions react with insoluble uranium compounds to dissolve the uranium in the solution again in the form of ions, and the uranium is desorbed from the adsorbent.

8. The uranium extraction method according to claim 7, characterized in that: The concentration of carbonate or bicarbonate ions or the sum of the concentrations of the carbonate or bicarbonate ions in the deuranium solution is 0.01-2 mol / L.

9. The uranium extraction method according to claim 7, characterized in that: The deuranization solution also contains oxidizing substances, which act together with carbonate and / or bicarbonate to convert the insoluble uranium compound into soluble uranium.

10. The uranium extraction method according to claim 9, characterized in that: The oxidizing substance is hydrogen peroxide, persulfate or a combination of the two.

11. The uranium extraction method according to claim 10, characterized in that: The sum of the concentrations of the hydrogen peroxide or persulfate or both is 0.01-0.5 mol / L.

12. The uranium extraction method according to claim 7, characterized in that: The reduced adsorbent is obtained through chemical reaction or electrochemical reaction.

13. The uranium extraction method according to claim 7, characterized in that: Using lithium iron phosphate as an adsorbent, the uranium extraction method includes the following steps: S01 places lithium iron phosphate in a uranium-containing solution to reduce the uranyl ions in the solution, converting the uranyl ions into insoluble uranium compounds, and a reaction occurs (1) Reactions (1) S02 filtering the uranium-containing solution to obtain solid particles, i.e. adsorbent with insoluble uranium compounds deposited thereon; S03 The solid particles obtained by filtration are placed in a mixed solution of sodium bicarbonate and hydrogen peroxide, and reactions (2) and (3) occur, and uranium is desorbed from the adsorbent; Reactions (2) React (3); S04 The adsorbent that has completed uranium desorption is separated from the solution and placed in a reducing solution. The oxidized iron in the iron phosphate is reduced, and at the same time, the lithium ions in the solution are embedded in the crystal lattice to maintain electrical balance and structural stability. The adsorbent returns to the form of lithium iron phosphate and has the ability to adsorb uranium again.

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