Mechanical energy driven integrated uranium extraction system and method based on piezoelectric porous medium

Abstract

The invention discloses a mechanical energy driven uranium extraction system and method based on a piezoelectric porous medium, and belongs to the technical field of functional materials and water treatment. According to the invention, a porous medium (such as a polyvinylidene fluoride porous membrane) with intrinsic piezoelectric activity is used as a core functional unit, and any adsorption functional group or catalytic active component does not need to be added. When a water body containing uranyl ions (U (VI)) passes through the medium in a dynamic flowing mode such as a pulse mode, the kinetic energy of fluid can excite the medium to generate a strong built-in electric field, and the flowing U (VI) can be directly reduced into insoluble uranium dioxide in situ. The invention also provides a preparation method of the piezoelectric porous medium, which is characterized in that self-polarization is induced by combining a phase inversion process with a crystal phase regulating agent, or post-polarization treatment is carried out, so that the material has a porous structure and high piezoelectric property at the same time. The technology has the advantages of high efficiency, simplicity, large-scale preparation and application and the like, and is particularly suitable for efficiently recovering uranium from seawater or uranium-containing wastewater.

Description

Technical Field

[0001] This invention belongs to the field of functional materials and water treatment technology, specifically relating to a piezoelectric material for extracting and fixing uranium from water, its preparation method, and application system. In particular, this invention relates to a porous polymer medium with piezoelectric activity, which can drive the efficient reduction and deposition of uranyl ions using only fluid mechanical energy. Background Technology

[0002] Uranium is an important strategic resource with significant applications in clean energy, nuclear weapons, and many other fields. Due to the limited uranium reserves on land, extracting uranium from various bodies of water has become a current research hotspot. Adsorption and photo / electrocatalytic reduction are the main methods for extracting uranium from aqueous solutions, but these methods face a dilemma in achieving both scalability and high uranium extraction performance. While fiber and membrane-based adsorption materials can be prepared and applied on a large scale, they suffer from low adsorption efficiency and poor selectivity. Photo / electrocatalytic methods, although highly efficient, face challenges such as the difficulty in scaling and applying core materials and poor selectivity.

[0003] Separation membranes have advantages such as high specific surface area and adjustable pore structure. If membranes can be made from materials with catalytic reduction properties, and separation mass transfer and uranium reduction can be coupled together, it will help promote the large-scale application of separation membranes in the field of uranium extraction.

[0004] A search revealed that Chinese patent document CN119455910A discloses a method for preparing a fouling-resistant, high-voltage electrocatalytically active polyvinylidene fluoride (PVDF) uranium adsorbent material. This method uses PVDF as the substrate material and co-mixes polyacrylonitrile with a amine oxime (PAO) functionalized polyacrylonitrile and Bi₄Ti₃O₃ in a casting solution. 12 A PVDF membrane was fabricated using a SnO2 piezoelectric heterostructure via cryogenic phase transformation and applied to the removal of uranium from water. The PAO group enhances the removal rate of uranyl ions in the prepared PVDF membrane material; Bi4Ti3O... 12When the SnO2 piezoelectric heterojunction is subjected to external vibration, it generates piezoelectric electrons, which can reduce adsorbed U(VI) to insoluble U(IV), thereby separating uranyl ions from the solution and exhibiting excellent antibacterial properties. The significant limitations of this technology are: first, its design concept remains a "functional grafting" paradigm, with PVDF serving only as a mechanical support and lacking active uranium extraction capabilities; second, it relies on external chemisorption sites such as PAO to pre-capture uranium, and the process is still limited by adsorption kinetics; third, its piezoelectric catalytic activity depends entirely on the added heterojunction particles, and the piezoelectric properties of the PVDF itself are not effectively utilized, resulting in a complex structure and high cost. The comparative examples in this patent also confirm that pure PVDF films without added PAO and piezoelectric heterojunctions do not exhibit significant uranium extraction performance, reflecting the limitations of existing technology in understanding PVDF—treating it merely as an inert substrate.

[0005] In summary, existing uranium extraction technologies are generally facing a dilemma: either they rely on chemical adsorption but cannot be solidified in situ (such as the chemical adsorption method), or the raw materials for catalytic reduction are expensive to prepare and difficult to scale up for application. Summary of the Invention

[0006] This invention aims to overcome the shortcomings of the prior art and provide a revolutionary, simple, low-cost, and truly integrated uranium extraction solution. It abandons the traditional approach of "inert substrate + functional grafting" and, for the first time, discovers and utilizes the previously unrecognized intrinsic properties of pure polymer materials with specific structural morphologies to achieve "pass-through reduction" uranium extraction driven solely by mechanical energy.

[0007] The core concept of this invention is to prepare a piezoelectric membrane with self-polarizing properties, high β-phase content, and hierarchical interconnected porous structure by precisely controlling the microstructure and crystalline phase of the polymer membrane. When uranium-containing fluid flows through the membrane in a dynamic manner (such as pulsed flow), the microscopic deformation induced by the fluid kinetic energy can generate a strong piezoelectric field in the entire three-dimensional space inside the membrane. This electric field directly drives the transfer of electrons from the polymer matrix to the uranyl ions flowing through the pores, reducing them in situ to insoluble uranium dioxide (UO2) and depositing them in the membrane channels without any pre-adsorption steps or external chemical functionalization.

[0008] Based on the above concept, the present invention provides the following technical solution:

[0009] In a first aspect, the present invention provides a piezoelectric porous membrane for the integrated extraction and fixation of uranium from uranium-containing water bodies, characterized in that:

[0010] The membrane is prepared from a piezoelectric polymer and has self-polarizing properties or can be polarized by external polarization.

[0011] The membrane has a hierarchical porous structure, including micron-sized macropores and nano-sized micropores;

[0012] The main crystalline phase of the piezoelectric polymer in the membrane is the β phase, and the relative content of the β phase is not less than 60%, preferably not less than 80%, and more preferably not less than 95%.

[0013] When subjected to dynamic mechanical stimulation, the membrane can generate an internal electric field within its bulk phase for the direct reduction of target metal ions.

[0014] Preferably, the piezoelectric polymer is at least one selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-tetrafluoroethylene, polylactic acid, polyacrylonitrile, and polyhydroxybutyrate.

[0015] In a second aspect, the present invention provides a method for preparing the piezoelectric porous membrane described in the first aspect, characterized by comprising the following steps:

[0016] S1: Provides a casting solution containing a piezoelectric polymer, a solvent, and a structure modifier;

[0017] S2: The casting solution undergoes a phase transformation process to form a gel membrane with a porous structure;

[0018] S3: Post-process the gel membrane to obtain the piezoelectric porous membrane; wherein, the post-processing may optionally include a step of polarizing the membrane.

[0019] Thirdly, the present invention provides a uranium extraction system based on the membrane described in the first aspect, characterized in that it comprises:

[0020] The membrane processing unit is equipped with the piezoelectric porous membrane.

[0021] A fluid transport unit is used to transport uranium-containing water through the membrane in a dynamic flow manner. The dynamic flow manner is a manner that can generate periodic pressure or shear stress on the membrane pore wall, including but not limited to pulsed flow, oscillating flow, or controlled turbulence.

[0022] Fourthly, the present invention provides a method for extracting uranium using the membrane described in the first aspect or the system described in the third aspect, characterized in that it comprises:

[0023] The water containing uranyl ions (U(VI)) is allowed to flow dynamically through the piezoelectric porous membrane;

[0024] During the flow process, the kinetic energy of the water is converted into mechanical energy acting on the membrane structure, which excites the membrane to generate a strong internal piezoelectric field.

[0025] When uranyl ions flow through the membrane channels, they are directly reduced to insoluble U(IV) compounds by electrons driven by the piezoelectric field and deposited in the membrane channels, thereby achieving one-step extraction and fixation of uranium.

[0026] The essential differences between this invention and the closest prior art (CN119455910A) are shown in the table below:

[0027] Table 1

[0028] The beneficial effects of this invention include:

[0029] A true material innovation and mechanism breakthrough: For the first time, it was revealed that pure polymer PVDF films can efficiently extract uranium through their own piezoelectric effect, breaking the traditional understanding that "PVDF must be functionalized or composited to extract uranium" and discovering a brand-new uranium extraction mechanism based on intrinsic piezoelectric reduction.

[0030] Extremely simplified and efficient process: The traditional multi-step process of "adsorption-desorption-reduction" is simplified into a single-step process of "passing through and fixing", with mass transfer and reaction synchronized, resulting in higher efficiency.

[0031] Excellent energy efficiency and economy: Driven solely by the mechanical energy of the water flow itself, requiring no external electrical, light, or high-frequency ultrasonic power, resulting in extremely low energy consumption. Material costs are comparable to those of commercial membranes, and it is easily processed into industrial membrane modules (such as spiral wound membranes), demonstrating clear prospects for large-scale application. Attached Figure Description

[0032] Figure 1 This is a SEM image of the hierarchical pore structure of the self-polarized piezoelectric porous membrane (PSPM) of this invention.

[0033] Figure 2 The figures show the crystal structure (XRD / FTIR) and piezoelectric response (KPFM / voltage output) characterization of the film.

[0034] Figure 3 The image shows the uranium extraction performance (kinetic curve) of the membrane under dynamic flow conditions and a comparison of the morphology before and after extraction.

[0035] Figure 4 The valence state and structure characterization diagrams (XPS, XANES) of the extracted products are shown.

[0036] Figure 5 The graph shows the effect of key operating parameters (β phase content, film thickness, flow rate, pH) on uranium extraction performance.

[0037] Figure 6 This is a diagram showing the long-term stability test of the membrane and a schematic diagram of the application of large-scale spiral wound membrane elements. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are only for explaining the invention and are not intended to limit the scope of protection of the invention. Where there is no conflict, the following embodiments can be combined with each other.

[0039] The choice of piezoelectric polymer described in this invention is not limited to PVDF. Based on the principles of this invention, any polymer that can form a porous structure through phase separation and possesses, or can obtain, a piezoelectric response through polarization, such as polyvinylidene fluoride-trifluoroethylene copolymer and polylactic acid, can be used as a candidate material. Those skilled in the art can determine the optimal polymer type and corresponding film-forming and polarization process parameters through conventional experiments based on the properties of the target water body.

[0040] Example 1: Preparation of self-polarized piezoelectric PVDF porous membrane (PSPM)

[0041] The core of the membrane described in this invention is to achieve the construction of a porous structure and the in-situ formation of a high-voltage β phase in one step through a phase transformation method under the induction of a crystallization phase regulator.

[0042] Method Overview: A piezoelectric polymer (such as PVDF) and a regulator that induces the formation of its β-phase are co-dissolved in a suitable solvent to form a homogeneous casting solution. The polymer is then solidified through any applicable phase inversion process (such as immersion in a non-solvent bath, cooling-induced phase separation, or solvent evaporation) to form a gel membrane with interconnected pores. After washing and drying, a self-polarized piezoelectric porous membrane is obtained. Throughout the process, the regulator guides the polymer chains to align in an all-trans conformation and crystallize through intermolecular interactions, simultaneously forming a template-like porous structure. Furthermore, the dipoles spontaneously align along a specific direction during film formation, achieving self-polarization.

[0043] As non-limiting examples, the following are some specific implementation methods:

[0044] Non-solvent-induced phase separation method: 10-15 wt% PVDF and 5-20 wt% cationic regulator dodecyltrimethylammonium chloride (DTAC) are dissolved in N-methylpyrrolidone. After scraping the membrane, it is immersed in a water coagulation bath. DTAC efficiently induces the β phase through ion-dipole interaction.

[0045] Similarly, by replacing the regulator: replacing DTAC with the anionic regulator sodium dodecyl sulfate, or adding a small amount of hydrogen bonding regulator such as water, β-phase induction can be achieved through different intermolecular forces.

[0046] Thermally induced phase separation method: PVDF is mixed uniformly with dibutyl phthalate (DTB) as both a regulator and diluent at high temperature. After cooling and phase separation, the diluent is extracted with a low-boiling-point solvent to form a porous membrane. The regulator also plays a crystallization guiding role during the thermal process.

[0047] The PSPM membrane prepared by the non-solvent phase separation method exhibits a microstructure with finger-like pores of micrometer-sized cross-sections, as revealed by SEM. Figure 1 a), further magnified, reveals a nanoscale network-like porous structure. Figure 1 b). Figure 2 a is the XRD pattern of PSPM. Figure 2 b is the FTIR spectrum. Figure 2 c represents the β phase content, and it can be found that the β phase content in PSPM is as high as 95% or more. Figure 2 d represents the piezoelectric output of the PSPM under different pressures. Figure 2 e and Figure 2 f represents the test results of PSPM using KPFM and the corresponding surface potential distribution, respectively. The above data demonstrates that PSPM possesses a high β-crystal content and excellent piezoelectric response.

[0048] Example 2: Verification of Uranium Extraction Performance

[0049] The membrane prepared in Example 1 was placed in a flow apparatus, and a 5 ppm UO2(NO3)2 solution (pH = 8) was passed through it in a pulsed mode. As direct evidence, the uranium concentration dropped below the detection limit within 20 minutes. Figure 3 a). The surface color of PSPM changed from white before uranium extraction ( Figure 3 b(1)) turned into the yellow color after uranium extraction ( Figure 3 c(1)), SEM images show that compared to the relatively "clean" PVDF film surface before uranium extraction ( Figure 3 b(2)), after uranium extraction, a large number of stacked nanoscale spheroids were generated on the surface of the PSPM. Figure 3 c(2)).

[0050] Characterization of the membrane after use: XPS analysis showed that the U 4f spectrum of the uranium products on the PSPM surface indicated a valence state of U(IV). Figure 4 a) Synchrotron radiation test data showed that the uranium products on the PSPM surface almost overlapped with standard UO2. Figure 4 (b~d) Further analysis confirms that the product is uranium dioxide (UO2).

[0051] Example 3: Verification of the essential differences from existing technical solutions

[0052] To highlight the fundamental difference between this invention and CN119455910A, the following comparative tests were conducted:

[0053] Comparative Example A (simulating "inert PVDF" in CN119455910A): A conventional PVDF porous membrane (predominantly α-phase) was prepared without the addition of any modifiers. In the same dynamic tests, its uranium removal rate was extremely low (<10%), demonstrating that the non-piezoelectric PVDF membrane indeed lacks effective uranium extraction capabilities.

[0054] Conclusion: The above comparative tests fully demonstrate that the integrated piezoelectric porous membrane provided by this invention has far superior uranium extraction efficiency and simplicity compared to traditional 'functional grafting' materials. This is not a simple improvement on existing technology, but rather a breakthrough at the principle level achieved by endowing the material with a completely new intrinsic piezoelectric structure and activity, opening up a new path for efficient and low-energy uranium extraction technology.

[0055] Example 4: Performance Optimization and Scalability

[0056] System tests show that the uranium extraction capacity of the membrane increases with increasing β-phase content. Figure 5 a) As the membrane thickness increases (from 0.1 to 0.6 mm), the uranium extraction performance of PSPM shows a trend of first increasing and then stabilizing. Figure 5 b); As the peristaltic pump speed (i.e., mechanical stimulation frequency) increases, the uranium extraction performance of PSPM shows a trend of first increasing and then stabilizing. Figure 5 c); Uranium extraction performance is optimal near the pH range of seawater, specifically around pH 8 in the uranium solution. Figure 5 d) Furthermore, the uranium extraction performance of PSPM is almost unaffected within the uranium solution temperature range of 25–40°C. Figure 6 a represents PSPM prepared on a large scale. Figure 6 b is to assemble the membrane into an industrial-grade spiral wound membrane element. Figure 6 c is a diagram of an apparatus built to process 15L of uranium-containing solution using PSPM membrane elements. Figure 6 The d-display indicates that the PSPM membrane element still maintains highly efficient uranium extraction performance. Figure 6 d) proved its engineering feasibility.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. For example, the piezoelectric polymer is not limited to PVDF, but may also be other polymers that can form a β phase; the dynamic mechanical stimulation is not limited to pulsed flow, but also includes other methods that can cause periodic deformation of the membrane, such as ultrasound. These modifications should all fall within the protection scope of the present invention.

Claims

1. A method for extracting and fixing uranium from uranium-containing water bodies, characterized in that, Includes the following steps: Water containing uranyl ions (U(VI)) is allowed to flow dynamically through a piezoelectric porous body; The dynamic flow provides dynamic mechanical stimulation to the piezoelectric porous body, causing it to generate an internal bulk electric field. When the uranyl ions (U(VI)) in the water flow through the piezoelectric porous body, they are directly reduced to insoluble U(IV) compounds by the built-in electric field of the bulk phase and deposited in the piezoelectric porous body.

2. The method according to claim 1, characterized in that, The piezoelectric porous body is a piezoelectric porous membrane.

3. A piezoelectric porous membrane for extracting target metal ions from a fluid, characterized in that, The membrane is made of a piezoelectric polymer and has a through-porous structure. The membrane is configured to generate an internal electric field when subjected to dynamic mechanical stimulation, which is used to directly reduce the target metal ions flowing through it.

4. The piezoelectric porous membrane according to claim 3, characterized in that, The piezoelectric polymer includes at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-tetrafluoroethylene, and polylactic acid.

5. The piezoelectric porous membrane according to claim 4, characterized in that, The piezoelectric polymer is PVDF.

6. The piezoelectric porous membrane according to claim 5, characterized in that, The PVDF has a β-phase as the main crystal phase.

7. The piezoelectric porous membrane according to claim 6, characterized in that, The relative content of the β-phase in the membrane is not less than 60%.

8. The piezoelectric porous membrane according to any one of claims 3 to 7, characterized in that, The membrane has self-polarizing properties.

9. A method for preparing the piezoelectric porous membrane as described in claim 3, characterized in that, Including the following steps: S1: A casting solution is provided, the casting solution comprising a piezoelectric polymer and a solvent; S2: The casting solution undergoes a phase transformation process to form a gel membrane with a porous structure; S3: Post-process the gel membrane to obtain the piezoelectric porous membrane.

10. The method according to claim 9, characterized in that, The casting solution also contains a crystallization phase regulator, which can induce the piezoelectric polymer to form a crystalline structure dominated by the β-phase.

11. The method according to claim 10, characterized in that, The crystallization phase regulator is selected from at least one of ionic surfactants and hydrogen bond regulators.

12. The method according to claim 9, characterized in that, In step S3, the post-processing includes drying the gel membrane; optionally, before or after drying, it also includes a step of polarizing the membrane.

13. A uranium extraction system, characterized in that, include: The piezoelectric porous membrane as described in any one of claims 3 to 8; A fluid drive device configured to cause uranium-containing water to flow dynamically through the piezoelectric porous membrane and to provide dynamic mechanical stimulation to the membrane.

14. The uranium extraction system according to claim 13, characterized in that, The dynamic flow mode is to allow the uranium-containing water to pass through the membrane in the form of pulsed flow, oscillating flow, or controlled turbulence.

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