A multi-level pore cement-based seawater uranium extraction material and a preparation method thereof

Abstract

This application provides a hierarchical porous cement-based seawater uranium extraction material and its preparation method. The material is in the form of a multi-layered roll with directional channels inside and macroscopic gaps between the layers. Calcium carbonate whiskers are grown in situ on the inner walls of the directional channels. The final raw materials for the hierarchical porous cement-based seawater uranium extraction material include 100-150 parts of sulfoaluminate cement, 50-120 parts of finely ground steel slag powder, 15-40 parts of acrylamide monomer, 0.4-1.5 parts of N,N'-methylenebisacrylamide, 0.05-0.4 parts of ammonium persulfate, and 70-150 parts of deionized water. The preparation method involves first preparing a KH-550 modified solution and a PAN / DMSO solution, followed by amination of the material, vacuum impregnation to form a PAN coating layer, and then a metamine oxime reaction. The material of this application significantly improves the efficiency of marine uranium extraction and the overall performance of the material. The method itself is flexible and controllable, possessing good potential for industrial scale-up.

Description

Technical Field

[0001] This application relates to the field of seawater uranium extraction materials technology, and in particular to a multi-level porous cement-based seawater uranium extraction material and its preparation method. Background Technology

[0002] Uranium is a core feedstock in the nuclear fuel cycle of nuclear power plants. Currently, the world's proven uranium reserves are only about 7 million tons, enough to meet demand for only about 100 years. In contrast, the total reserves of dissolved uranium in the ocean are as high as 4.5 billion tons, nearly a thousand times the reserves on land, and with continuous replenishment through continental weathering, it constitutes a nearly unlimited resource pool. Therefore, developing economical and efficient seawater uranium extraction technology is the only way to overcome the bottleneck of uranium resource scarcity and ensure the long-term development of nuclear energy.

[0003] However, the concentration of uranium in seawater is extremely low (approximately 3.3 μg / L), and it mainly exists in the form of extremely stable uranyl carbonate complexes. Furthermore, the concentrations of competing ions such as sodium, magnesium, and calcium are several orders of magnitude higher than those of uranium, making highly selective uranium capture extremely difficult. Moreover, the complex marine environment, with its high salt corrosion, biofouling, and ocean current erosion characteristics, places high demands on the chemical stability and mechanical strength of uranium capture and adsorption materials. This necessitates that uranium capture and adsorption materials possess both high adsorption capacity and rapid adsorption kinetics to offset the preparation and maintenance costs within a reasonable timeframe.

[0004] Current research largely focuses on seawater uranium extraction materials such as amylopectin-functionalized polymer fibers, metal-organic frameworks (MOFs), and gels. Among these, amylopectin fibers prepared by radiation grafting have become a research hotspot due to their excellent adsorption selectivity. However, these materials generally suffer from low mass transfer efficiency in practical applications: traditional fiber bundles or particle stacks form beds with large pressure drops in ocean currents, allowing seawater to flow only over the outer surface of the material, while a large number of active sites inside are shielded. The adsorption equilibrium time can be as long as several weeks to months, significantly limiting uranium extraction yield and increasing the time cost and engineering risks of offshore operations. Amylopectin-functionalized metal-organic frameworks (MOFs) themselves have poor water stability and are prone to structural collapse in complex seawater environments. Furthermore, MOF raw materials are expensive and the preparation process is complex. Gel-based substrates possess excellent hydrophilicity and mass transfer efficiency due to their three-dimensional network high porosity structure, but they generally suffer from insufficient mechanical properties, poor resistance to seawater erosion, and are prone to swelling, breakage, or structural deformation in dynamic ocean current environments. Furthermore, some gel substrates have poor chemical stability, and long-term immersion in seawater can lead to the loss of functional groups, resulting in a rapid decline in uranium adsorption performance, making it difficult to meet the requirements for long-term continuous uranium extraction at sea.

[0005] In summary, developing a novel organic-inorganic material that can significantly increase the effective specific surface area, construct an open and efficient mass transfer channel, and achieve continuous preparation is key to breaking through the bottleneck of uranium extraction efficiency from seawater.

[0006] This application innovatively proposes a curling molding method based on ice templates. This method utilizes the synergistic effect of natural curling and directional crystallization during the scraping of frozen films to induce the formation of a unique multi-level curled layered structure in the material, which greatly increases the specific surface area of ​​the material and allows the internal adsorption sites to be fully exposed. This effectively solves the problems of limited mass transfer and low preparation efficiency caused by dense structure in the prior art. Summary of the Invention

[0007] The purpose of this application is to provide a multi-level porous cement-based seawater uranium extraction material and its preparation method, which can help solve or improve the problems of existing seawater uranium extraction materials, such as large mass transfer resistance, insufficient exposure of adsorption sites, difficulty in continuous preparation process, and difficulty in balancing mechanical properties and adsorption properties, so as to achieve efficient, rapid and low-cost extraction of marine uranium resources.

[0008] To achieve the above objectives, this application provides the following technical solution: A multi-level porous cement-based seawater uranium extraction material, The multi-level porous cement-based seawater uranium extraction material is made by the directional ice template method. The multi-level porous cement-based seawater uranium extraction material has directional channels inside, and calcium carbonate whiskers are grown in situ on the inner wall of the directional channels. The final form of the multi-level porous cement-based seawater uranium extraction material is a multi-layer roll with macroscopic gaps between the layers. The raw materials for the multi-level porous cement-based seawater uranium extraction material include the following components in parts by weight: 100-150 parts of sulfoaluminate cement, 50-120 parts of finely ground steel slag powder, 15-40 parts of acrylamide monomer, 0.4-1.5 parts of N,N'-methylenebisacrylamide, 0.05-0.4 parts of ammonium persulfate, and 70-150 parts of deionized water.

[0009] Furthermore, the total porosity of the seawater uranium extraction material is 60-85%, and the BET specific surface area is 80-300 m². 2 / g.

[0010] Furthermore, the pore size of the directional channel is 5-100 μm, and the pore size of the micro-nano pores formed between the calcium carbonate whiskers is 2-500 nm.

[0011] Furthermore, the sulfoaluminate cement is 52.5 rapid-hardening sulfoaluminate cement or ferrophase sulfoaluminate cement; the finely ground steel slag powder is obtained by ultrafine grinding of converter steel slag or electric furnace steel slag, with a median particle size d. 50 Less than 10 μm, specific surface area greater than 400 m² 2 / kg, with a calcium oxide content of 30-50wt% and a free calcium oxide content of less than 5wt%.

[0012] Furthermore, the maximum outer circle diameter of the multi-level porous cement-based seawater uranium extraction material is 20-200 mm, the interlayer spacing is 0.5-5 mm, and the number of rolled layers in the multi-layer rolled structure is 3-20.

[0013] This application also proposes a method for preparing the above-mentioned multi-level porous cement-based seawater uranium extraction material, including the following steps: S1. Mix all the raw materials of the multi-level porous cement-based seawater uranium extraction material to prepare a uniform composite slurry; S2. Spread the composite slurry obtained in S1 onto a low-temperature shell with an internal cold source, with a spreading thickness of 0.3-5 mm. After spreading, the composite slurry is rapidly frozen. Then, the frozen film is peeled off by a scraper attached to the surface of the low-temperature shell, causing the frozen film to continuously curl under the synergistic effect of shear force and internal stress gradient, resulting in a rolled frozen body. The angle between the scraper and the surface of the low-temperature shell is 10°-60°. S3. Vacuum freeze-dry the roll-shaped frozen body to remove the ice crystal template and obtain a freeze-dried material with a directional pore structure. S4. The freeze-dried material is subjected to high-temperature heat treatment for 2-5 hours in an inert atmosphere and an atmosphere containing 0.5-5% carbon dioxide by volume to obtain the carbonized and mineralized material; in the carbonized and mineralized material, calcium carbonate whiskers are grown in situ on the inner wall of the directional channels. S5. After carbonization and mineralization, a genoamine oxime functional group is introduced through impregnation to obtain seawater uranium extraction material.

[0014] Further, in step S1, sulfoaluminate cement is mixed with finely ground steel slag powder to obtain an inorganic solid phase, and acrylamide monomer, N,N'-methylenebisacrylamide, and ammonium persulfate are dissolved in deionized water to obtain an organic phase; then, the inorganic solid phase is added to the organic phase in batches, stirred and mixed, and an in-situ polymerization reaction is triggered to form a uniform composite slurry; the water-cement ratio of the composite slurry is 0.4-0.6; in step S2, the temperature of the surface of the low-temperature shell is -40℃ to -196℃.

[0015] Furthermore, the low-temperature shell is flat, and the relative speed between the scraper and the low-temperature shell is 1-10 cm / s; Alternatively, the cryogenic housing may be a rotating cryogenic drum with a diameter of 20-80 cm and a rotation speed of 3-10 r / min.

[0016] Furthermore, in step S4, the calcium carbonate whiskers are subjected to high-temperature heat treatment at 650-800℃ for 2-5 hours; the calcium carbonate whiskers are spindle-shaped or needle-shaped, with a diameter of 50-500nm, a length of 0.5-10μm, and an aspect ratio of 5-30.

[0017] Furthermore, step S5 includes the following steps: S5.1 Preparation of reaction solution: Mix anhydrous ethanol and deionized water at a volume ratio of 9:1, add 2%-5% by mass of silane coupling agent KH-550, adjust the pH to 4-5 and hydrolyze for later use; Separately, use dimethyl sulfoxide (DMSO) as solvent to prepare a 5%-8% by mass polyacrylonitrile (PAN) solution, stir until completely dissolved to obtain a PAN / DMSO solution; S5.2 Surface amination modification: Immerse the material obtained in S4 in the above-mentioned KH-550 modification solution, ultrasonically impregnate for 30-60 min, take it out and place it in a 105℃ oven for heat treatment for 1-2 h. S5.3 Vacuum impregnation and phase inversion film formation: The modified material is immersed in PAN / DMSO solution and impregnated under vacuum for 15 minutes; after removal, it is immediately immersed in sufficient deionized water, and PAN is precipitated and formed on the inner wall of the directional channel by phase inversion method to obtain the material coated with PAN layer. S5.4, Amine oxime reaction: Prepare a 6%-10% (w / w) aqueous solution of hydroxylamine hydrochloride and adjust the pH to 7-8; immerse the above-mentioned PAN-coated material in the solution with a liquid-to-solid ratio of (30-50):1, and react for 8-12 hours in a constant temperature water bath at 65-75℃. The cyano group is converted into amine oxime group through the oxime reaction. After thorough washing and drying, a seawater uranium extraction material with a surface rich in amine oxime functional groups is obtained.

[0018] Furthermore, in step S1, the raw materials are mixed and stirred using a planetary mixer at a speed of 1200-1800 r / min for a time of 5-8 min.

[0019] Furthermore, in step S3, the conditions for vacuum freeze drying are: temperature -40℃ to -60℃, vacuum degree 10-50Pa, and drying time 24-72h.

[0020] The technical solution of this application has the following beneficial effects: The seawater uranium extraction material prepared in this application significantly improves the efficiency of marine uranium extraction and the overall performance of the material, solving the technical challenges of traditional adsorption materials in terms of mass transfer resistance, structural stability, preparation continuity, and functionalization efficiency. This application utilizes a continuous ice-template rolling molding process to construct a gradient pore structure with macroscopic rolled gaps, intralayer directional channels, and micro / nano whisker networks, achieving high-flux flow of seawater within the material and rapid mass transfer of uranyl ions.

[0021] In the seawater uranium extraction material of this application, the inorganic framework composed of sulfoaluminate cement and finely ground steel slag provides excellent mechanical strength and seawater corrosion resistance. Acrylamide monomers are polymerized in situ to form a three-dimensional network, which not only stabilizes the slurry but also transforms into a porous carbon framework after high-temperature carbonization, endowing the material with conductivity and toughness. The in-situ growth of calcium carbonate whiskers significantly increases the specific surface area and surface roughness of the material, providing abundant anchoring points for the loading of amine oxime functional groups. The amine oxime groups are firmly fixed to the material surface through chemical grafting, achieving highly selective capture of uranyl ions. This application, through the systematic integration of organic-inorganic composites, dynamic molding, in-situ mineralization, and surface functionalization, successfully constructs a seawater uranium extraction material with high mass transfer efficiency, high adsorption capacity, excellent mechanical properties, and good cycle stability, providing a new material solution for the efficient development of marine uranium resources.

[0022] This application innovatively introduces a roll-up molding method based on ice templates, achieving highly efficient production from slurry to rolled frozen bodies and overcoming the problem of the single structure of traditional uranium extraction materials. By adjusting the temperature of the cryogenic shell, the relative speed between the scraper and the surface of the cryogenic shell, the coating thickness of the composite slurry, and the distance and angle between the scraper and the surface of the cryogenic shell, the roll-up structure, interlayer spacing, and porosity characteristics of the material can be precisely controlled. The process is flexible and controllable, and has good potential for industrial scale-up. Attached Figure Description

[0023] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. Wherein: Figure 1 This is a SEM image of the inner wall of the directional pores inside the multi-level porous cement-based seawater uranium extraction material in Example 5.

[0024] Figure 2 The physical object of the rolled frozen body prepared in Example 5 of this application. Figure 1 .

[0025] Figure 3 The physical object of the rolled frozen body prepared in Example 5 of this application. Figure 2 .

[0026] Figure 4 This is a process diagram of preparing the rolled frozen body in Example 5 of this application.

[0027] Figure 5 This is a schematic diagram of the structure of a cryogenic rotary drum that can be used in this application.

[0028] Explanation of reference numerals in the attached drawings: Hollow steel roller-1; Hollow shaft-2; Baffle plate-3; Slurry supply trough-4; Scraper-5. Detailed Implementation

[0029] The present application will now be described in detail with reference to the accompanying drawings and embodiments. The various examples are provided by way of explanation and not for limitation of the present application.

[0030] A multi-level porous cement-based seawater uranium extraction material, wherein the multi-level porous cement-based seawater uranium extraction material is made by directional ice template method, wherein the multi-level porous cement-based seawater uranium extraction material has directional channels inside, and calcium carbonate whiskers are grown in situ on the inner wall of the directional channels. The raw materials for the multi-level porous cement-based seawater uranium extraction material include the following components in parts by weight: 100-150 parts of sulfoaluminate cement (e.g., 100, 110, 120, 130, 140, or 150 parts), 50-120 parts of finely ground steel slag powder (e.g., 50, 70, 90, 100, or 120 parts), 15-40 parts of acrylamide monomer (e.g., 15, 20, 25, 30, 35, or 40 parts), N,N' - 0.4-1.5 parts of methylenebisacrylamide (e.g., 0.4, 0.6, 0.8, 1.0, 1.2, or 1.5 parts), 0.05-0.4 parts of ammonium persulfate (e.g., 0.05, 0.1, 0.2, 0.3, or 0.4 parts), and 70-150 parts of deionized water (e.g., 70, 90, 110, 130, or 150 parts).

[0031] In this application, the sulfoaluminate cement and finely ground steel slag powder together form an inorganic framework in the seawater uranium extraction material, which helps to improve the material's mechanical strength and durability. Preferably, the sulfoaluminate cement is 52.5 rapid-hardening sulfoaluminate cement or ferrophase sulfoaluminate cement (fineness ≤350 μm). 2 / kg, initial setting time 12-25min, final setting time 20-35min;); the finely ground steel slag powder is obtained by ultrafine grinding of converter steel slag or electric furnace steel slag, with a median particle size d 50 Less than 10 μm, specific surface area greater than 400 m² 2 The calcium oxide content is 30-50 wt%, and the free calcium oxide content is less than 5 wt%. Sulfoaluminate cement can rapidly form ettringite and hydrated calcium silicate gel during hydration, imparting early strength to the material. Finely ground steel slag powder, as an industrial byproduct, provides a sufficient calcium source for subsequent carbonization and mineralization processes due to its high calcium oxide content. Simultaneously, its fine particles can fill the micropores of the cement matrix, improving the material's density. The specific surface area of ​​finely ground steel slag powder is greater than 400 m² / kg. 2 / kg ensures good dispersibility and reactivity in composite slurries.

[0032] The acrylamide monomer, N,N'-methylenebisacrylamide, and ammonium persulfate in the seawater uranium extraction material of this application constitute an in-situ polymerization system, which helps to improve the structural stability of the material. The acrylamide monomer undergoes free radical polymerization under the initiation of ammonium persulfate, forming a long-chain polyacrylamide network, which stabilizes the dispersion of inorganic particles and prevents sedimentation and stratification. N,N'-methylenebisacrylamide, as a crosslinking agent, copolymerizes with the acrylamide monomer through its vinyl groups at both ends, forming a three-dimensional crosslinked network structure, which improves the mechanical strength and thermal stability of the organic phase. This crosslinked network transforms into a porous carbon skeleton during subsequent high-temperature carbonization, not only endowing the material with conductivity and toughness but also providing a stable support for the loading of amine oxime functional groups.

[0033] The seawater uranium extraction material of this application possesses a unique hierarchical porous structure. The spacing (interlayer spacing) of the macroscopic slits is 0.5-5 mm (e.g., 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, or 5 mm), the pore size of the oriented channels is 5-100 μm (e.g., 5 μm, 20 μm, 40 μm, 60 μm, 80 μm, or 100 μm), and the pore size of the micro-nano pores composed of calcium carbonate whiskers is 2-500 nm (e.g., 2 nm, 10 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, or 500 nm). The micro-nano pores refer to the whisker gaps formed on the inner wall of the oriented channels due to the in-situ growth, accumulation, and staggered arrangement of numerous spindle-shaped or needle-shaped calcium carbonate whiskers. The gradient pore structure, ranging from millimeter to nanometer scale among the macroscopic slits, oriented channels, and micro-nano pores, enables high-flux flow of seawater within the material and rapid mass transfer of uranyl ions. Macroscopic gaps (multi-layered structure) serve as rapid flow channels for seawater, significantly reducing flow resistance and allowing seawater to quickly penetrate the material. Directional channels, acting as the primary transport pathways for uranyl ions, ensure rapid ion access to the channel walls through their continuous, interconnected nature. Micro- and nano-pores formed by calcium carbonate whiskers provide a large specific surface area and abundant adsorption sites, with amine oxime groups anchored on these micro- and nano-surfaces, ensuring full contact with uranyl ions. The material has a total porosity of 60-85% (e.g., 60%, 65%, 70%, 75%, 80%, or 85%) and a BET specific surface area of ​​80-300 m². 2 / g (e.g., 80m) 2 / g、120m 2 / g、160m 2 / g、200m 2 / g、240m 2 / g、280m 2 / g or 300m 2 The high porosity ensures that the material has sufficient open space for seawater flow and ion diffusion, while the high specific surface area provides a large number of adsorption sites.

[0034] This invention also proposes a method for preparing the above-mentioned multi-level porous cement-based seawater uranium extraction material, comprising the following steps: S1. Mix all the raw materials of the multi-level porous cement-based seawater uranium extraction material to prepare a uniform composite slurry; S2. The composite slurry obtained in S1 is spread onto a cryogenic shell with an internal cold source, with a spreading thickness of 0.3-5 mm. The composite slurry is rapidly frozen after spreading. Then, the frozen film is peeled off by a scraper attached to the surface of the cryogenic shell, causing the frozen film to continuously curl under the synergistic effect of shear force and internal stress gradient, resulting in a rolled frozen body. The rolled frozen body is formed by the natural continuous curling of the film at the moment of peeling by the scraper, due to the synergistic effect of shear force and internal stress gradient, as well as the anisotropy caused by the directional growth of ice crystals. The cryogenic shell can be a flat plate or a rotating cryogenic roller. The resulting multi-layered rolled uranium trapping material is not much different and does not require manual shaping or special guiding molds. The angle between the scraper and the surface of the cryogenic shell is 10°-60°, and the gap between the scraper and the surface of the cryogenic shell is adjusted within 0.1-1 mm according to the spreading thickness. S3. Vacuum freeze-dry the roll-shaped frozen body to remove the ice crystal template and obtain a freeze-dried material with a directional pore structure. S4. The freeze-dried material is subjected to high-temperature heat treatment for 2-5 hours (e.g., 2 hours, 3 hours, 4 hours, or 5 hours) in an inert atmosphere and an atmosphere containing 0.5%-5% (e.g., 0.5%, 1%, 2%, 3%, 4%, or 5% by volume) carbon dioxide to obtain a carbonized and mineralized material; in the carbonized and mineralized material, calcium carbonate whiskers are grown in situ on the inner wall of the directional channels; S5. After carbonization and mineralization, a genoamine oxime functional group is introduced through impregnation to obtain seawater uranium extraction material.

[0035] In step S1, sulfoaluminate cement and finely ground steel slag powder are mixed to obtain an inorganic solid phase. Acrylamide monomer, N,N'-methylenebisacrylamide, and ammonium persulfate are dissolved in deionized water to obtain an organic phase. Then, the inorganic solid phase is added to the organic phase in batches, stirred and mixed, and an in-situ polymerization reaction is triggered to form a uniform composite slurry. The water-cement ratio of the composite slurry is 0.4-0.6 (e.g., 0.4, 0.45, 0.5, 0.55, or 0.6), where "cement" in the water-cement ratio refers to sulfoaluminate cement and finely ground steel slag powder. Preferably, a planetary mixer is used for stirring at a speed of 1200-1800 r / min (e.g., 1200 r / min, 1400 r / min, 1600 r / min or 1800 r / min) for a time of 5-8 min (e.g., 5 min, 6 min, 7 min or 8 min). The strong shear force of high-speed stirring can effectively break up inorganic particle agglomerates, so that sulfoaluminate cement and finely ground steel slag powder are uniformly dispersed in the organic phase. At the same time, it promotes the in-situ polymerization reaction of acrylamide monomers, so that polymer chains grow on the surface of inorganic particles, forming an organic-inorganic interface bonding layer, which enhances the compatibility between the two phases.

[0036] Step S2 is the core innovation of this application. The slurry obtained in S1 is coated onto a cryogenic shell with a surface temperature of -40℃ to -196℃ (e.g., -40℃, -80℃, -120℃, -160℃, or -196℃). The composite slurry is spread by a spreading mechanism, and there is a uniform linear relative motion between the spreading mechanism and the cryogenic shell. The composite slurry spreads into a thin film at the moment of spreading, and the water molecules in the composite slurry undergo directional crystallization along the direction perpendicular to the surface of the cryogenic shell to form columnar ice crystal templates. In this process, the extremely low temperature gradient drives the water molecules to crystallize rapidly, and the formed ice crystals grow directionally along the direction of the maximum temperature gradient (i.e., perpendicular to the surface of the cryogenic shell), displacing the surrounding organic-inorganic composite phase, and finally leaving through directional channels after the ice crystals disappear. Then, a scraper peels off the frozen film, causing it to continuously curl under the action of shear force and internal stress, forming a rolled frozen body with multiple layers of gaps. The thickness of the composite slurry coating layer is controlled within 0.3-5 mm (e.g., 0.3 mm, 1 mm, 2 mm, 3 mm, or 5 mm). This thickness range ensures that ice crystals can completely penetrate the film thickness to form continuous channels, while avoiding uneven internal and external temperature gradients caused by excessively thick coatings, resulting in non-directional channels. The angle between the scraper and the surface of the cryogenic shell is 10-60° (e.g., 10°, 20°, 30°, 40°, 50°, or 60°), and the minimum gap between the scraper and the surface of the cryogenic shell is adjustable from 0.1-1 mm (e.g., 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, or 1 mm). Precise control of the scraper angle and gap is key to achieving continuous curling molding. An appropriate angle allows the shear force generated during the peeling process to be distributed along the film plane, inducing plastic deformation rather than brittle fracture of the film. Combined with the internal stress of the frozen film itself, this causes it to naturally curl into a spiral shape.

[0037] The low-temperature shell can be a flat plate or a rotating low-temperature drum; the flat plate low-temperature shell can be an existing ice cream maker (yogurt maker) or a self-made one (e.g., placing a copper plate on an open container filled with liquid nitrogen); the rotating low-temperature drum can be an existing rotary drum freeze dryer or a self-made one, e.g., passing liquid nitrogen through a rotating hollow steel roller. Figure 5This is a schematic diagram of the cross-sectional structure of a rotating cryogenic drum. A hollow steel roller 1 is mounted on a rotating frame via a hollow shaft 2 and is driven to rotate by a motor. The hollow shaft 2 is connected to the inlet and outlet of a liquid nitrogen refrigeration system, which provides a constant low temperature. A baffle plate 3 and a slurry supply trough 4 are suspended and fixed above the hollow steel roller 1. The lower surface of the baffle plate 3 slides in contact with the surface 1 of the hollow steel roller. A scraper 5 is fixed diagonally below the hollow steel roller 1. Preferably, the cryogenic shell is a rotating cryogenic drum; its diameter is 20-80 cm (e.g., 20 cm, 40 cm, 60 cm, or 80 cm), and its rotational speed is 3-10 r / min (e.g., 3 r / min, 5 r / min, 7 r / min, or 10 r / min). The combination of the drum diameter and rotational speed determines the residence time and freezing rate of the slurry on the drum surface, thus affecting the growth morphology of ice crystals and the uniformity of the pore structure.

[0038] The vacuum freeze-drying process in step S3 is used to remove the ice crystal template while preserving the oriented pore structure and curled morphology. The vacuum freeze-drying conditions are: temperature -40℃ to -60℃ (e.g., -40℃, -45℃, -50℃, -55℃, or -60℃), vacuum degree 10-50 Pa (e.g., 10 Pa, 20 Pa, 30 Pa, 40 Pa, or 50 Pa), and drying time 24-72 h (e.g., 24 h, 36 h, 48 h, 60 h, or 72 h). Under vacuum, the ice crystals directly transform into a gaseous phase through sublimation and are removed, avoiding damage to the pore structure from liquid water during ice melting. The low temperature ensures the material matrix remains frozen, preventing pore collapse. Sufficient drying time allows for complete sublimation of the ice crystals, keeping residual moisture at an extremely low level, preparing for subsequent high-temperature processing.

[0039] In step S4, the high-temperature heat treatment heating rate is 2-10℃ / min (e.g., 2℃ / min, 4℃ / min, 6℃ / min, 8℃ / min or 10℃ / min), the target temperature is 650-800℃, and the high-temperature heat treatment lasts for 2-5 hours after the temperature is reached. The high-temperature carbonization and mineralization treatment in step S4 is a key step in forming a porous carbon skeleton and growing calcium carbonate whiskers in situ. In this process, the polyacrylamide in the organic phase undergoes pyrolysis and carbonization under an inert atmosphere, transforming into a carbon skeleton with abundant micropores. This carbon skeleton not only provides electrical conductivity and toughness, but also increases the specific surface area of ​​the material. Simultaneously, the active calcium components (mainly calcium oxide and calcium hydroxide) in steel slag and cement react with CO2 generated by pyrolysis or exogenous CO2, resulting in the in-situ growth of micro / nano-scale spindle-shaped or needle-shaped calcium carbonate whiskers on the inner wall of the pores. These whiskers are spindle-shaped or needle-shaped, with a diameter of 50-500 nm (e.g., 5, 10, 15, 20, 25, or 30 nm), a length of 0.5-10 μm (e.g., 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, or 500 nm), and an aspect ratio of 5-30 (e.g., 0.5 μm, 2 μm, 4 μm, 6 μm, 8 μm, or 10 μm). These calcium carbonate whiskers form a micro-rough surface on the inner wall of the pores, significantly increasing the specific surface area of ​​the material and providing abundant anchoring points for the subsequent loading of amine oxime functional groups. The growth of calcium carbonate whiskers follows the following reaction mechanism: the active calcium component first reacts with CO2 in the atmosphere to generate calcium carbonate crystal nuclei, and then preferentially grows along specific crystal planes under the drive of concentration gradient and surface energy to form spindle-shaped or needle-shaped crystals with high aspect ratio.

[0040] The surface activation treatment and amylopectin functionalization in step S5 are key to endowing the material with highly selective uranium adsorption capacity. Step S5 includes the following steps: S5.1 Preparation of reaction solution: Mix anhydrous ethanol and deionized water at a volume ratio of 9:1, add 2%-5% (e.g., 2%, 3%, 4% or 5%) of silane coupling agent KH-550, adjust the pH to 4-5 for hydrolysis; under weakly acidic conditions, the methoxy groups in KH-550 undergo hydrolysis to form silanol groups, preparing for subsequent condensation reaction with hydroxyl groups on the material surface; separately, using dimethyl sulfoxide (DMSO) as solvent, prepare a 5%-8% (e.g., 5%, 6%, 7% or 8%) polyacrylonitrile (PAN) solution, stirring until completely dissolved to obtain a PAN / DMSO solution; DMSO, as a strongly polar aprotic solvent, can effectively dissolve high molecular weight PAN, and its high boiling point ensures the stability of the solution; S5.2 Surface Aminoation Modification: Immerse the material obtained in S4 into the above-mentioned KH-550 modification solution and ultrasonically impregnate for 30-60 min (e.g., 30 min, 40 min, 50 min or 60 min). After removal, place it in a 105℃ oven for heat treatment for 1-2 h. The cavitation effect of ultrasound promotes the penetration of the modification solution into the internal pores of the material, so that KH-550 is uniformly attached to the inner wall of the pores. The 105℃ treatment promotes the condensation reaction between KH-550 and the hydroxyl groups on the material surface to form stable Si-O-Si chemical bonds, while introducing amino functional groups on the material surface. S5.3 Vacuum Impregnation and Phase Inversion Film Formation: The modified material is immersed in a PAN / DMSO solution under vacuum for 15 minutes. The negative pressure removes the gas inside the pores, and the PAN solution quickly fills the pores after the pressure is restored. After impregnation, the material is immediately immersed in sufficient deionized water. The phase inversion method is used to precipitate PAN on the inner wall of the oriented pores and form a coating layer. The PAN-coated material is obtained by precipitating PAN on the inner wall of the material pores. In this process, DMSO diffuses from the PAN solution into the aqueous phase as a good solvent, while water enters the PAN solution as a non-solvent, causing the PAN solubility to decrease sharply and precipitate out, forming a porous coating film. S5.4, Amine Oxime Reaction: Prepare a 6%-10% (e.g., 6%, 7%, 8%, 9%, or 10%) aqueous solution of hydroxylamine hydrochloride, adjusting the pH to 7-8; immerse the PAN-coated material in this solution and react it in a constant temperature water bath at 65-75°C (e.g., 65°C, 70°C, or 75°C) for 8-12 hours (e.g., 8 hours, 9 hours, 10 hours, or 12 hours). The hydroxylamine groups in the hydrochloride undergo a nucleophilic addition reaction with the cyano groups in the PAN, converting the cyano groups into amine oxime groups. After thorough washing to remove residual hydroxylamine hydrochloride and reaction byproducts, and drying, a seawater uranium extraction material with a surface rich in amine oxime functional groups is obtained. The amine oxime group shell interacts with uranyl ions (UO2) through the lone pair electrons on its nitrogen and oxygen atoms. 2+ This forms stable five- or six-membered chelate rings, enabling highly selective capture of uranium.

[0041] The following description is based on different embodiments and comparative examples. The raw materials used in the embodiments and comparative examples include: Sulfoaluminate cement: Tangshan Arctic Bear Building Materials Co., Ltd., fineness ≤350 μm 2 / kg, initial setting time 12-25min, final setting time 20-35min; Finely ground steel slag powder: Henan Borun New Materials Co., Ltd., with a median particle size (d50) of 7.5 μm and a specific surface area of ​​520 m². 2 / kg, calcium oxide content is 45wt%, free calcium oxide content is 2.8wt%; Acrylamide monomer: Sinopharm Chemical Reagent Co., Ltd. (purity ≥ 99.5%) Ammonium persulfate (analytical grade): Sinopharm Chemical Reagent Co., Ltd.; N,N-Methylenebisacrylamide (analytical grade): Aladdin Reagent Company.

[0042] The test methods used in this embodiment and the comparative example are as follows: 1. Compressive strength and flexural strength are tested according to GB / T 17671-2021 "Test Method for Strength of Cement Mortar"; specific surface area is tested according to GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Substance by Gas Adsorption BET Method"; 2. Uranium adsorption performance test, including the following: 2.1 Preparation of uranium-containing simulated seawater: A simulated seawater solution was prepared based on the main ionic composition of natural seawater, specifically: sodium chloride 24.53 g / L, magnesium chloride 11.11 g / L, sodium sulfate 4.09 g / L, calcium chloride 1.16 g / L, potassium chloride 0.695 g / L, sodium bicarbonate 0.201 g / L, potassium bromide 0.101 g / L, boric acid 0.027 g / L, strontium chloride 0.025 g / L, and sodium fluoride 0.003 g / L. The simulated seawater was prepared using deionized water, and the pH was adjusted to 8.0 ± 0.1 using 0.1 mol / L sodium hydroxide or hydrochloric acid solution to simulate the real seawater environment. After preparation, uranyl nitrate (UO2(NO3)2·6H2O) was added to the simulated seawater to achieve a uranium concentration of 8 mg / L. This concentration is significantly higher than that in natural seawater, allowing for the adsorption experiment to be completed within a reasonable timeframe and for obtaining reliable test data.

[0043] 2.2 Static adsorption capacity test: Accurately weigh 1g of thoroughly dried hierarchical porous cement-based seawater uranium extraction material sample and place it in a 1500mL Erlenmeyer flask. Add 1000mL of uranium-containing simulated seawater. Place the Erlenmeyer flask in a constant-temperature shaker and shake for adsorption at 25±1℃ and 120rpm. During the adsorption process, samples were taken at 1h, 3h, 6h, 12h, 24h, 48h, and 72h, with 5mL of solution taken each time. After filtration through a 0.45μm microporous membrane, the residual uranium concentration in the filtrate was determined using the azoarsine III spectrophotometric method. The specific determination method is as follows: Take 1mL of the test solution into a 25mL colorimetric tube, add 5mL of acetate-sodium acetate buffer solution (pH=7.0), add 2mL of 0.05% azoarsine III solution, dilute to the mark with deionized water, shake well, and let stand for 10min. Measure the absorbance at 650nm using a 1cm cuvette, and calculate the uranium concentration using a standard curve. Equilibrium adsorption capacity q e (mg / g) is calculated using the following formula: q e =(C0-C e )×V / m Where C0 is the initial uranium concentration (mg / L), C e The uranium concentration at equilibrium is (mg / L), V is the solution volume (L), and m is the adsorbent mass (g).

[0044] 2.3 Adsorption kinetics test: Using the same experimental conditions as the static adsorption capacity test, uranium concentration was measured at different time points (e.g., 0.5h, 1h, 2h, 4h, 8h, 16h, 24h, 36h, 48h, 60h, 72h), and the adsorption capacity was plotted as a function of time. The experimental data were fitted and analyzed using a pseudo-first-order kinetic model and a pseudo-second-order kinetic model to determine the adsorption equilibrium time.

[0045] 2.4 Dynamic Adsorption Performance Test: 5g of seawater uranium extraction material was packed into a glass column with an inner diameter of 2.5cm and a height of 30cm to form a packed bed. Uranium-containing simulated seawater was pumped through the bed at a flow rate of 2BV / h (BV being the bed volume) using a peristaltic pump. The effluent was continuously collected, with samples taken every 2 hours to determine the uranium concentration. Breakthrough was considered achieved when the uranium concentration in the effluent reached more than 90% of the influent uranium concentration. The total volume of the solution and the total amount of uranium adsorbed before breakthrough were calculated to evaluate the dynamic adsorption capacity and uranium removal rate of the material. The uranium removal rate was calculated using the following formula: Uranium removal rate = [(C0 × Vtotal - ΣC)] i ×V i [(C0×Vtotal)]×100% Where C0 is the uranium concentration in the liquid, Vtotal is the total liquid volume in the liquid before penetration, and Ctotal is the total liquid volume in the liquid before penetration. i Let V be the uranium concentration in the effluent from the i-th sample. i This represents the corresponding outflow volume.

[0046] 2.5 Selective Adsorption Test: In simulated seawater containing uranium, uranium exists as uranyl ions, while the seawater contains high concentrations of competing ions such as sodium, magnesium, and calcium ions. Adsorption experiments were conducted according to the static adsorption capacity test method. After adsorption equilibrium was reached, the concentrations of uranium, sodium, magnesium, and calcium in the solution were simultaneously measured using inductively coupled plasma optical emission spectrometry (ICP-OES), and the adsorption capacity of each ion was calculated. The selectivity coefficient K was calculated using the following formula: K(U / M) = (q u / C u ) / (q m / C m ); Where q u and qm The adsorption capacities (mg / g) of uranium and competing metal ion M are respectively, and C u and C m These represent the solution concentrations (mg / L) of uranium and the competing metal ion M at equilibrium, respectively. A higher selectivity coefficient indicates better selectivity of the material for uranium.

[0047] 2.6 Cyclic Regeneration Performance Test: After completing one adsorption experiment, the saturated material was removed, rinsed with deionized water until neutral, and then immersed in a 0.5 mol / L sodium carbonate-sodium bicarbonate mixed solution (pH=10.5). Desorption was performed by shaking at 40℃ and 150 rpm for 4 hours. After desorption, the material was thoroughly washed with deionized water until neutral, dried at 60℃, and then used for the next adsorption experiment. The adsorption-desorption cycle was repeated 5 times, and the adsorption capacity was measured after each cycle. The adsorption capacity retention rate was calculated. The adsorption capacity retention rate (%) was calculated using the following formula: Adsorption capacity retention rate = (adsorption capacity in the nth cycle / adsorption capacity in the first cycle) × 100%.

[0048] 3. Seawater corrosion resistance test, including the following tests: 3.1 Long-term immersion test: Uranium-extracting materials from seawater were prepared into cubic samples with dimensions of 40mm × 40mm × 40mm. The initial mass m0 and dimensions were accurately measured. The samples were completely immersed in simulated uranium-containing seawater. Every 7 days, the samples were removed, the surface moisture was blotted with filter paper, and the weight and dimensions were measured. The mass m was recorded. t And dimensional changes. The soaking period is 90 days. The quality retention rate (%) is calculated according to the following formula: Quality retention rate = (m t / m0)×100%; At the same time, observe and record changes in the surface morphology of the sample, including whether corrosion phenomena such as cracks, peeling, and discoloration occur.

[0049] 3.2 Mechanical property degradation test: Uranium-extracting materials from seawater were prepared into 40mm×40mm×160mm specimens and immersed in uranium-containing simulated seawater for 30, 60, and 90 days, respectively. The compressive and flexural strengths were then determined according to GB / T 17671-2021 "Test Method for Strength of Cement Mortar," and compared with the mechanical properties of unimmersed specimens to calculate the retention rate of mechanical properties. The retention rate of mechanical properties (%) was calculated using the following formula: Mechanical property retention rate = (mechanical strength after immersion / initial mechanical strength) × 100%.

[0050] Example 1 A multi-level porous cement-based seawater uranium extraction material, wherein the raw material of the multi-level porous cement-based seawater uranium extraction material comprises the following components in parts by weight: 125 parts of sulfoaluminate cement, 85 parts of finely ground steel slag powder, 27.5 parts of acrylamide monomer, 0.95 parts of N,N'-methylenebisacrylamide, 0.225 parts of ammonium persulfate, and 110 parts of deionized water.

[0051] In this embodiment, the cryogenic shell is a self-made rotating cryogenic roller with a diameter of 50cm and a length of 80cm. The roller is kept at a constant low temperature by a liquid nitrogen refrigeration system, and the surface temperature of the roller is -80℃. The angle between the scraper and the tangent direction of the roller is set to 35°, and the gap between the scraper and the surface of the roller is 0.3mm.

[0052] The preparation method of seawater uranium extraction material in this embodiment includes the following steps: S1. Sulfoaluminate cement and finely ground steel slag powder are mixed for 5 min to obtain an inorganic solid phase. Acrylamide monomer, N,N'-methylenebisacrylamide and ammonium persulfate are dissolved in deionized water and stirred at room temperature for 10 min to obtain an organic phase. Then, the inorganic solid phase is added to the organic phase in 3 batches. After each batch is added, the mixture is stirred at 1500 r / min for 2 min using a planetary stirrer to ensure that the inorganic particles are fully dispersed. After all the particles have been added, the mixture is stirred for another 2 min. The in-situ polymerization reaction occurs automatically, forming a uniform and stable organic-inorganic composite slurry. S2. Spread the composite slurry obtained in S1 onto a low-temperature shell (rotating low-temperature drum) with an internal cold source. The drum speed is set to 6 r / min and the spreading thickness is 1.5 mm. The composite slurry is rapidly frozen instantly after spreading to form a frozen film. Water molecules in the composite slurry crystallize in a direction perpendicular to the drum surface to form columnar ice crystal templates that penetrate the thickness of the film. After the frozen film rotates about 1 / 4 turn with the drum, it is continuously peeled off by a stainless steel scraper device attached to the drum surface to form a roll-shaped frozen body with a diameter of about 7.5 cm and multiple spiral gaps. The number of curled layers is 5, and the gap between the layers is about 1 mm. The roll-shaped frozen body is continuously collected and immediately transferred to a -20℃ environment for storage. S3. The rolled frozen body is placed in a vacuum freeze dryer for vacuum freeze drying to remove the ice crystal template and obtain a freeze-dried material with a directional pore structure. The freeze drying conditions are: temperature -50℃, vacuum degree 30Pa, and drying time 48h. During this process, the ice crystals are directly converted into water vapor through sublimation and are removed by the vacuum pump. The material matrix remains frozen, and the directional pore structure and rolled morphology are completely preserved. After freeze drying, a lightweight porous material with a rolled layered structure is obtained. S4. The freeze-dried material is subjected to high-temperature carbonization and mineralization treatment in a tubular furnace. First, nitrogen gas at a flow rate of 200 mL / min is introduced to purge the air from the furnace. Then, a mixture of nitrogen and carbon dioxide is introduced, with a carbon dioxide volume fraction of 2.5% and a total flow rate of 200 mL / min. The mixture is heated to 700°C at a heating rate of 5°C / min and held at this temperature for 3.5 hours. During this process, the polyacrylamide in the organic phase undergoes pyrolysis and carbonization, transforming into a black porous carbon skeleton. Simultaneously, the active calcium components such as calcium oxide and calcium hydroxide in the steel slag and cement react with CO2 in the atmosphere: CaO + CO2 → CaCO3, resulting in the in-situ growth of spindle-shaped and needle-shaped calcium carbonate whiskers on the inner wall of the pores. After the holding period, the material is naturally cooled to room temperature under nitrogen protection to obtain the black carbonized and mineralized material. S5. Surface activation treatment and amine oxime functionalization are performed on the carbonized and mineralized material, including the following steps: S5.1 Preparation of reaction solution: Mix 90 mL of anhydrous ethanol with 10 mL of deionized water, add 3.5 g of silane coupling agent KH-550, adjust the pH to 4.5 with dilute hydrochloric acid, and stir for 30 min at room temperature for later use; Separately prepare polyacrylonitrile solution: Weigh 6.5 g of polyacrylonitrile (PAN) and dissolve it in 100 mL of dimethyl sulfoxide (DMSO), stir in a 50 °C water bath for 4 h until completely dissolved, and obtain a clear pale yellow solution for later use; the molecular weight of polyacrylonitrile is 100 kDa; Mix anhydrous ethanol and deionized water at a volume ratio of 9:1, add 2%-5% by mass of silane coupling agent KH-550, adjust the pH to 4-5 and hydrolyze for later use; separately, use dimethyl sulfoxide (DMSO) as solvent to prepare a 5%-8% by mass polyacrylonitrile (PAN) solution, stir until completely dissolved, to obtain a PAN / DMSO solution. S5.2 Surface Aminoation Modification: The material obtained in S4 is immersed in the above-mentioned KH-550 modification solution with a liquid-to-solid ratio of 50m:1g. It is placed in an ultrasonic cleaner for ultrasonic impregnation with an ultrasonic power of 300W and an ultrasonic time of 45min, so that the modification solution can fully penetrate into the directional channels inside the material. After that, the material is taken out, and the excess modification solution on the surface is quickly rinsed with deionized water. It is then placed in a 105℃ oven for heat treatment for 1.5h to promote the condensation reaction between KH-550 and the hydroxyl groups on the surface of the material, and introduce amino functional groups into the inner wall of the directional channels.

[0053] S5.3 Vacuum Impregnation and Phase Inversion Film Formation: The aminated modified material is placed in a vacuum dryer, and a PAN / DMSO solution is poured in. The vacuum is drawn to -0.09 MPa and maintained for 15 min, so that the solution fully fills the interior of the oriented channels under negative pressure. After restoring normal pressure, the material is immediately taken out and quickly immersed in a large amount of deionized water (in this embodiment, the liquid-to-solid ratio is 100:1). The material is kept in deionized water for 12 h to ensure complete phase inversion. During this period, the deionized water is replaced every 4 h to obtain a material coated with a PAN layer. In the deionized water, dimethyl sulfoxide, as a good solvent, rapidly diffuses into the aqueous phase, while water, as a non-solvent, enters the polyacrylonitrile solution, causing the solubility of polyacrylonitrile to decrease sharply and precipitate on the inner wall of the channels, forming a uniform coating layer. S5.4, Amine oxime reaction: Prepare an 8wt% aqueous solution of hydroxylamine hydrochloride, and adjust the pH to 7.5 with sodium hydroxide solution; immerse the material coated with polyacrylonitrile layer into the solution at a liquid-to-solid ratio of 40:1, and place it in a 70℃ constant temperature water bath for 10 hours under magnetic stirring; during the reaction, the hydroxylamine group (-NH2OH) in hydroxylamine hydrochloride undergoes a nucleophilic addition reaction with the cyano group (-CN) in polyacrylonitrile to generate amine oxime group; after the reaction, remove the material and wash it thoroughly with deionized water, 0.1mol / L dilute hydrochloric acid, and deionized water in sequence to remove residual hydroxylamine hydrochloride and reaction byproducts until the pH of the washing water is close to neutral; finally, dry it in a vacuum oven at 60℃ for 24 hours to obtain a seawater uranium extraction material with a surface rich in amine oxime functional groups (i.e., a hierarchical porous cement-based seawater uranium extraction material).

[0054] The test results of the multi-level porous cement-based seawater uranium extraction material in this embodiment are as follows: BET specific surface area 180m² 2 / g, static adsorption capacity 5.8mg / g, adsorption equilibrium time 56h, uranium removal rate 88% under dynamic adsorption conditions, uranium selectivity coefficients K(U / Na) 850, K(U / Mg) 920, K(U / Ca) 780, adsorption capacity retention rate 84% after 5 cycles, compressive strength 15.2MPa, flexural strength 3.8MPa, mass retention rate 96.5% and compressive strength retention rate 82% after 90 days of seawater immersion.

[0055] Example 2 The raw material components in Example 2 are different from those in Example 1.

[0056] A multi-level porous cement-based seawater uranium extraction material, wherein the raw material of the multi-level porous cement-based seawater uranium extraction material comprises the following components in parts by weight: 100 parts of sulfoaluminate cement, 50 parts of finely ground steel slag powder, 15 parts of acrylamide monomer, 0.4 parts of N,N'-methylenebisacrylamide, 0.05 parts of ammonium persulfate, and 70 parts of deionized water.

[0057] The preparation method in this embodiment is basically the same as that in Example 1, except that: In step S1, a planetary mixer is used to stir at a speed of 1200 r / min for a total stirring time of 8 min. In step S2, the surface temperature of the rotating low-temperature roller is -40℃, the roller diameter is 20cm, the rotation speed is 3r / min, the coating thickness is 0.3mm, the angle between the scraper and the tangent direction of the roller is 10°, and the gap between the scraper and the roller surface is 0.1mm; in this step, a roll-shaped frozen body with the same shape and size as in Example 1 is prepared. In step S3, the freeze-drying conditions are -40℃, vacuum degree 10Pa, and drying time 72h; In step S4, the heating rate is 2℃ / min, the carbon dioxide volume fraction is 0.5%, the holding temperature is 650℃, and the holding time is 2h. In step S5, KH-550 has a mass fraction of 2%, is ultrasonically impregnated for 30 min, and is heat-treated at 105℃ for 1 h; polyacrylonitrile solution has a mass fraction of 5%; hydroxylamine hydrochloride solution has a mass fraction of 6%, pH value of 7.0, reaction temperature of 65℃, and reaction time of 8 h.

[0058] Test results: BET specific surface area 95m² 2 / g, static adsorption capacity 3.5mg / g, adsorption equilibrium time 68h, uranium removal rate 85% under dynamic adsorption conditions, uranium selectivity coefficients K(U / Na) 680, K(U / Mg) 720, K(U / Ca) 650, adsorption capacity retention rate 80% after 5 cycles, compressive strength 22.5MPa, flexural strength 5.2MPa, mass retention rate 97.8% and compressive strength retention rate 88% after 90 days of seawater immersion.

[0059] Example 3 The raw material components in Example 3 are different from those in Example 1.

[0060] A multi-level porous cement-based seawater uranium extraction material, wherein the raw material of the multi-level porous cement-based seawater uranium extraction material comprises the following components in parts by weight: 150 parts of sulfoaluminate cement, 120 parts of finely ground steel slag powder, 40 parts of acrylamide monomer, 1.5 parts of N,N'-methylenebisacrylamide, 0.4 parts of ammonium persulfate, and 150 parts of deionized water.

[0061] The preparation method in this embodiment is basically the same as that in Example 1, except that: In step S1, a high-shear disperser is used to stir at a speed of 1800 r / min for a total stirring time of 5 min; In step S2, the surface temperature of the rotating low-temperature roller is -196℃, the roller diameter is 80cm, the rotation speed is 10r / min, the coating thickness is 5mm, the angle between the scraper and the tangent direction of the roller is 60°, and the gap between the scraper and the roller surface is 0.5mm; in this step, a roll-shaped frozen body with the same shape and size as in Example 1 is prepared. In step S3, the freeze-drying conditions are -60℃, vacuum degree 50Pa, and drying time 24h; In step S4, the heating rate is 10℃ / min, the carbon dioxide volume fraction is 5%, the holding temperature is 800℃, and the holding time is 5h. In step S5, KH-550 is 5% by mass, ultrasonically impregnated for 60 min, and heat-treated at 105℃ for 2 h; polyacrylonitrile solution is 8% by mass; hydroxylamine hydrochloride solution is 10% by mass, pH 8.0, reaction temperature is 75℃, and reaction time is 12 h.

[0062] Test results: BET specific surface area 265m² 2 / g, static adsorption capacity 7.5mg / g, adsorption equilibrium time 48h, uranium removal rate 91% under dynamic adsorption conditions, uranium selectivity coefficients K(U / Na) 980, K(U / Mg) 1050, K(U / Ca) 920, adsorption capacity retention rate 87% after 5 cycles, compressive strength 9.8MPa, flexural strength 2.5MPa, mass retention rate 94.2% and compressive strength retention rate 76% after 90 days of seawater immersion.

[0063] Example 4 The raw material components in Example 4 are different from those in Example 1.

[0064] A multi-level porous cement-based seawater uranium extraction material, wherein the raw material of the multi-level porous cement-based seawater uranium extraction material comprises the following components in parts by weight: 135 parts of sulfoaluminate cement, 100 parts of finely ground steel slag powder, 30 parts of acrylamide monomer, 1.0 part of N,N'-methylenebisacrylamide, 0.3 parts of ammonium persulfate, and 130 parts of deionized water.

[0065] The preparation method in this embodiment is basically the same as that in Example 1, except that: In step S2, the surface temperature of the rotating low-temperature roller is -120℃, the roller diameter is 60cm, the rotation speed is 8r / min, the coating thickness is 3mm, the angle between the scraper and the tangent direction of the roller is 45°, and the gap between the scraper and the roller surface is 0.35mm; in this step, a roll-shaped frozen body with the same shape and size as in Example 1 is prepared. In step S4, the heating rate is 7℃ / min, the carbon dioxide volume fraction is 3.5%, the holding temperature is 750℃, and the holding time is 4h. In step S5, KH-550 has a mass fraction of 3.5%, is ultrasonically impregnated for 45 min, and is heat-treated at 105℃ for 1.5 h; the polyacrylonitrile solution has a mass fraction of 6.5%; the hydroxylamine hydrochloride solution has a mass fraction of 8%, a pH value of 7.5, a reaction temperature of 70℃, and a reaction time of 10 h. Test results: BET specific surface area 220m² 2 / g, static adsorption capacity 6.8mg / g, adsorption equilibrium time 52h, uranium removal rate 90% under dynamic adsorption conditions, uranium selectivity coefficients K(U / Na) 920, K(U / Mg) 990, K(U / Ca) 860, adsorption capacity retention rate 86% after 5 cycles, compressive strength 11.5MPa, flexural strength 3.0MPa, mass retention rate 95.5% and compressive strength retention rate 79% after 90 days of seawater immersion.

[0066] Example 5 The raw material components in Example 5 are the same as those in Example 1.

[0067] The difference in the preparation method is that a flat low-temperature shell is used; the flat low-temperature shell (copper cold plate) is fixed in position, and the scraper moves linearly to peel off the film; the rotation speed of the roller in Example 1 is converted into the moving speed of the scraper, and the linear moving speed of the scraper is set to 6 cm / s. Figure 1 The SEM image of the inner wall of the internal oriented pores of the rolled frozen body prepared in this embodiment shows the micro-nano pore network formed between the spindle-shaped calcium carbonate whiskers grown in situ; since the raw materials in this embodiment are the same as those in Example 1, therefore... Figure 1 It can also be regarded as the SEM image of Example 1; Figure 2 , Figure 3 The image shows the actual rolled frozen body prepared in this embodiment. The prepared rolled frozen body has 3 layers and the gap between the layers is about 1 mm. Figure 4 The image shows the preparation process of this rolled-up frozen body; the small shovel in the picture is a scraper.

[0068] Test results: BET specific surface area 182m² 2 / g, static adsorption capacity 5.9mg / g, adsorption equilibrium time 55h, uranium removal rate 89% under dynamic adsorption conditions, uranium selectivity coefficients K(U / Na) 860, K(U / Mg) 930, K(U / Ca) 790, adsorption capacity retention rate 85% after 5 cycles, compressive strength 15.5MPa, flexural strength 3.9MPa, mass retention rate 96.8% and compressive strength retention rate 83% after 90 days of seawater immersion.

[0069] Comparative Example 1 The difference between this comparative example and Example 1 is that a rotating low-temperature roller and scraper are not used, and a block-shaped frozen body is finally produced.

[0070] Specific preparation method: The composite slurry of the formulation in Example 1 was directly poured into a polytetrafluoroethylene mold pre-cooled to -20°C. The bottom of the mold was in contact with a copper cold plate, and the temperature of the copper cold plate was maintained at -80°C. The slurry was induced to freeze unidirectionally from the bottom up for 24 hours to form a blocky frozen body with a directional channel structure. The subsequent freeze-drying, carbonization and mineralization, and surface functionalization steps were the same as in Example 1.

[0071] Test results: BET specific surface area 85m² 2 / g, static adsorption capacity 2.8mg / g, adsorption equilibrium time 120h, uranium removal rate under dynamic adsorption conditions 62%, adsorption capacity retention rate after 5 cycles 75%, compressive strength 16.8MPa, flexural strength 4.1MPa, mass retention rate 96.8% and compressive strength retention rate 83% after 90 days of seawater immersion.

[0072] Comparative Example 2 The difference between the seawater uranium extraction material in this comparative example and that in Example 1 is that finely ground steel slag powder is not added, and in-situ growth of calcium carbonate whiskers is not performed in step S4.

[0073] The raw material formulation for this seawater uranium extraction material is as follows: 125 parts sulfoaluminate cement, 27.5 parts acrylamide monomer, 0.95 parts N,N'-methylenebisacrylamide, 0.225 parts ammonium persulfate, and 110 parts deionized water. Step S4 involves carbonization in a pure nitrogen atmosphere without the introduction of carbon dioxide. The remaining steps are the same as in Example 1.

[0074] Test results: BET specific surface area 68m² 2 / g, static adsorption capacity 2.2mg / g, adsorption equilibrium time 72h, uranium removal rate under dynamic adsorption conditions 58%, adsorption capacity retention rate after 5 cycles 72%, compressive strength 10.5MPa, flexural strength 2.6MPa, mass retention rate 93.5% and compressive strength retention rate 68% after 90 days of seawater immersion.

[0075] Comparative Example 3 The seawater uranium extraction material in this comparative example differs from that in Example 1 in that it does not contain acrylamide monomer, N,N'-methylenebisacrylamide, and ammonium persulfate, but only uses cement-based materials.

[0076] The raw material formula for this seawater uranium extraction material is: 125 parts sulfoaluminate cement, 85 parts finely ground steel slag powder, and 110 parts deionized water. The carbonation temperature in step S4 is reduced to 500℃ to avoid excessive decomposition of the cement matrix. The remaining steps are the same as in Example 1.

[0077] Test results: BET specific surface area 52m² 2 / g, static adsorption capacity 1.8mg / g, adsorption equilibrium time 96h, uranium removal rate under dynamic adsorption conditions 48%, adsorption capacity retention rate after 5 cycles 68%, compressive strength 28.5MPa, flexural strength 6.5MPa, mass retention rate 98.5% and compressive strength retention rate 92% after 90 days of seawater immersion.

[0078] Comparative Example 4 The difference between the seawater uranium extraction material in this comparative example and that in Example 1 is that it does not undergo amylopectin functionalization; the process is stopped after step S4, carbonization and mineralization.

[0079] Test results: BET specific surface area 175m² 2 / g, static adsorption capacity 0.5mg / g, adsorption equilibrium time 150h, uranium removal rate under dynamic adsorption conditions 15%, poor selectivity for uranium, adsorption capacity retention rate 45% after 5 cycles, compressive strength 14.8MPa, flexural strength 3.7MPa, mass retention rate 95.8% and compressive strength retention rate 80% after 90 days of seawater immersion.

[0080] Comparative Example 5 The difference between the seawater uranium extraction material in this comparative example and that in Example 1 is that step S2 does not involve continuous curling; instead, the slurry is directly frozen into a flat film on a low-temperature roller and then peeled off, without forming a curled structure.

[0081] Specific adjustments: The angle between the scraper and the tangent direction of the roller is adjusted to 90° (vertical peeling), allowing the film to peel off directly without curling. Subsequent steps are the same as in Example 1.

[0082] Test results: BET specific surface area 120m² 2 / g, static adsorption capacity 3.2mg / g, adsorption equilibrium time 88h, uranium removal rate under dynamic adsorption conditions 68%, adsorption capacity retention rate after 5 cycles 78%, compressive strength 13.2MPa, flexural strength 3.3MPa, mass retention rate 96.0% and compressive strength retention rate 81% after 90 days of seawater immersion.

[0083] Comparative Example 6 This comparative example uses the traditional polyacrylamide hydrogel freezing method to prepare seawater uranium extraction materials, without using cement-based materials.

[0084] Specific formula: 30 parts acrylamide monomer, 1.2 parts N,N'-methylenebisacrylamide, 0.3 parts ammonium persulfate, and 150 parts deionized water.

[0085] Preparation method: Prepare an acrylamide solution, pour it into a mold and freeze it unidirectionally at -20°C. After freeze-drying, a pure organic hydrogel is obtained, and then the same oxime functionalization treatment as in Example 1 is performed.

[0086] Test results: BET specific surface area 45m² 2 / g, static adsorption capacity 4.2mg / g, adsorption equilibrium time 80h, uranium removal rate under dynamic adsorption conditions 72%, adsorption capacity retention rate after 5 cycles 82%, compressive strength 0.8MPa (severely insufficient), flexural strength 0.2MPa, after 90 days of seawater immersion, significant swelling and deformation occurred, mass increased by 15%, and structural integrity was lost.

[0087] This application utilizes a low-temperature dynamic curling forming technology to construct a three-level gradient pore structure consisting of "macroscopic curled gaps - directional channels - calcium carbonate whisker micro / nano pores," achieving a good balance between adsorption performance and mechanical strength. Examples 1-5 exhibit compressive strengths of 9.8-22.5 MPa, adsorption capacities of 3.5-7.5 mg / g, and dynamic uranium removal rates of 85%-91%. Example 3, in particular, possesses the optimal pore structure and specific surface area (265 m²). 2 ( / g), with an adsorption capacity of 7.5 mg / g, and adsorption equilibrium is achieved in just 48 hours.

[0088] The hierarchical porous cement-based seawater uranium extraction materials in Examples 1-5 exhibited an adsorption capacity retention rate of 80%-87% after 5 cycles and a strength retention rate of 76%-96.8% after 90 days of seawater immersion, demonstrating excellent stability and recycling capacity. This verifies the synergistic effect of the organic-inorganic composite system and the functionalization of amine oxime.

[0089] Comparing Examples 1 and 5 with Comparative Example 1, it can be seen that regardless of whether the method is a rotating low-temperature drum or a flat low-temperature shell combined with a dynamic scraper, water molecules can be oriented to crystallize and form a continuous multi-level channel. The multi-layered spiral gaps formed by continuous curling further improve the channel connectivity. However, the channels of static unidirectional freezing are prone to blockage and poor connectivity. Moreover, the lack of a curled structure leads to a significant reduction in specific surface area, which directly weakens the number of adsorption sites and the mass transfer efficiency of uranium ions.

[0090] Comparing Example 2 and Comparative Example 2, it can be seen that when steel slag is lacking in the raw material, the static adsorption capacity decreases by 62.1%, the uranium removal rate decreases by 34.1% under dynamic adsorption conditions, and the seawater immersion pressure resistance retention rate decreases by 17.1%. This indicates that the spindle-shaped / needle-shaped calcium carbonate whiskers generated by the reaction of the active components in the steel slag with CO2 can form a "skeleton support" on the inner wall of the pores, which not only expands the specific surface area to provide additional adsorption sites, but also enhances the resistance of the pore structure to seawater erosion. If there are no calcium carbonate whiskers, the pores are prone to collapse, resulting in a double decrease in adsorption performance and stability.

[0091] Comparing Example 1 and Comparative Example 3, it can be seen that if no acrylamide monomer, N,N'-methylenebisacrylamide, and ammonium persulfate are used, and only cement-based materials are employed, the BET is only 52m. 2 / g (down 71.1%), static adsorption 1.8mg / g (down 68.9%), dynamic removal rate 48% (down 45.5%). Although it has the highest compressive strength, it sacrifices pore structure and adsorption performance, indicating that the organic phase is the core component that balances the mechanical strength and porous adsorption structure of cement-based materials.

[0092] Comparing Example 1 and Comparative Example 4, without the oxime functionalization treatment, the static adsorption was only 0.5 mg / g (a decrease of 91.4%), the dynamic removal rate was 15% (a decrease of 83%), the selectivity for uranium was extremely poor, and the retention rate after 5 cycles was only 45% (a decrease of 46.5%). This indicates that simple physical adsorption is not specific and is easily affected by high concentrations of Na in seawater. + Mg 2+ Interference from competing ions significantly reduces adsorption efficiency and selectivity.

[0093] Comparative Example 1 and Comparative Example 5, if the film is not curled, BET120m 2 / g (decreased by 33.3%), static adsorption 3.2mg / g (decreased by 44.8%), adsorption equilibrium time extended to 88h, dynamic removal rate 68% (decreased by 22.7%). This indicates that the multi-layered coiled structure formed by the coiling increases the contact area with uranium-containing seawater and shortens the diffusion path of uranium ions through the pores; while the planar film has a two-dimensional structure with limited contact area and low pore utilization, resulting in decreased adsorption efficiency and prolonged equilibrium time.

[0094] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A multi-level porous cement-based seawater uranium extraction material, characterized in that: The multi-level porous cement-based seawater uranium extraction material is prepared by the directional ice template method. The multi-level porous cement-based seawater uranium extraction material has directional channels inside, and calcium carbonate whiskers are grown in situ on the inner wall of the directional channels. The final form of the multi-level porous cement-based seawater uranium extraction material is a multi-layer roll with macroscopic gaps between the layers. The oxime group is fixed on the surface of the multi-level porous cement-based seawater uranium extraction material by chemical grafting. The raw materials for the multi-level porous cement-based seawater uranium extraction material include the following components in parts by weight: 100-150 parts of sulfoaluminate cement, 50-120 parts of finely ground steel slag powder, 15-40 parts of acrylamide monomer, 0.4-1.5 parts of N,N'-methylenebisacrylamide, 0.05-0.4 parts of ammonium persulfate, and 70-150 parts of deionized water.

2. The hierarchical porous cement-based seawater uranium extraction material according to claim 1, characterized in that: The total porosity of the seawater uranium extraction material is 60-85%, and the BET specific surface area is 80-300 m 2 / g.

3. The hierarchical porous cement-based seawater uranium extraction material of claim 1, wherein: The pore size of the directional channels is 5-100 μm, and the pore size of the micro-nano pores formed between the calcium carbonate whiskers is 2-500 nm.

4. The multi-level porous cement-based seawater uranium extraction material according to claim 1, characterized in that: The sulphoaluminate cement is a 52.5 fast-hardening sulphoaluminate cement or an iron phase sulphoaluminate cement; the fine ground steel slag powder is a converter steel slag or an electric furnace steel slag which is obtained by superfine grinding, and has a particle size median diameter d 50 less than 10 μm, a specific surface area greater than 400 m 2 / kg, a calcium oxide content of 30-50 wt%, and a free calcium oxide content less than 5 wt%.

5. The multi-stage porous cement-based seawater uranium extraction material according to claim 1, characterized in that: The maximum outer circle diameter of the multi-level porous cement-based seawater uranium extraction material is 20-200 mm, the interlayer spacing is 0.5-5 mm, and the number of rolled layers of the multi-layer rolled structure is 3-20.

6. A method for preparing a multi-level porous cement-based seawater uranium extraction material as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Mix all the raw materials of the multi-level porous cement-based seawater uranium extraction material to prepare a uniform composite slurry; S2. Spread the composite slurry obtained in S1 onto a low-temperature shell with an internal cold source, with a spreading thickness of 0.3-5 mm. After spreading, the composite slurry is rapidly frozen. Then, the frozen film is peeled off by a scraper attached to the surface of the low-temperature shell, causing the frozen film to continuously curl under the synergistic effect of shear force and internal stress gradient, resulting in a rolled frozen body. The angle between the scraper and the surface of the low-temperature shell is 10°-60°. S3. The rolled frozen body is subjected to vacuum freeze-drying to remove the ice crystal template and obtain a freeze-dried material with a directional pore structure. S4. The freeze-dried material is subjected to high-temperature heat treatment for 2-5 hours in an inert atmosphere containing 0.5-5% carbon dioxide by volume to obtain the carbonized and mineralized material; in the carbonized and mineralized material, calcium carbonate whiskers are grown in situ on the inner wall of the directional channels. S5. The carbonized and mineralized material is infused with a metallo-oxime functional group to obtain seawater uranium extraction material.

7. The method for preparing multi-level porous cement-based seawater uranium extraction material according to claim 6, characterized in that: In step S1, sulfoaluminate cement is mixed with finely ground steel slag powder to obtain an inorganic solid phase. Acrylamide monomer, N,N'-methylenebisacrylamide, and ammonium persulfate are dissolved in deionized water to obtain an organic phase. Then, the inorganic solid phase is added to the organic phase in batches, stirred and mixed, and an in-situ polymerization reaction is triggered to form a uniform composite slurry. The water-cement ratio of the composite slurry is 0.4-0.

6. In step S2, the temperature of the surface of the low-temperature shell is -40℃ to -196℃.

8. The method for preparing multi-level porous cement-based seawater uranium extraction material according to claim 6, characterized in that: The low-temperature shell is flat, and the relative speed between the scraper and the low-temperature shell is 1-10 cm / s; Alternatively, the cryogenic housing may be a rotating cryogenic drum with a diameter of 20-80 cm and a rotation speed of 3-10 r / min.

9. The method for preparing multi-level porous cement-based seawater uranium extraction material according to claim 6, characterized in that: In step S4, the calcium carbonate whiskers are subjected to high-temperature heat treatment at 650-800℃ for 2-5 hours; the calcium carbonate whiskers are spindle-shaped or needle-shaped, with a diameter of 50-500nm, a length of 0.5-10μm, and an aspect ratio of 5-30.

10. The method for preparing multi-level porous cement-based seawater uranium extraction material according to claim 6, characterized in that: Step S5 includes the following steps: S5.1 Preparation of reaction solution: Mix anhydrous ethanol and deionized water at a volume ratio of 9:1, add 2%-5% by mass of silane coupling agent KH-550, adjust the pH to 4-5 and hydrolyze for later use; Separately, use dimethyl sulfoxide (DMSO) as solvent to prepare a 5%-8% by mass polyacrylonitrile (PAN) solution, stir until completely dissolved to obtain a PAN / DMSO solution; S5.2 Surface amination modification: Immerse the material obtained in S4 in the above-mentioned KH-550 modification solution, ultrasonically impregnate for 30-60 min, take it out and place it in a 105℃ oven for heat treatment for 1-2 h. S5.3 Vacuum impregnation and phase inversion film formation: The modified material is immersed in PAN / DMSO solution and impregnated under vacuum for 15 minutes; after removal, it is immediately immersed in sufficient deionized water, and PAN is precipitated and formed on the inner wall of the directional channel by phase inversion method to obtain the material coated with PAN layer. S5.4, Amine oxime reaction: Prepare a 6%-10% (w / w) aqueous solution of hydroxylamine hydrochloride and adjust the pH to 7-8; immerse the above-mentioned PAN-coated material in the solution with a liquid-to-solid ratio of (30-50):1, and react for 8-12 hours in a constant temperature water bath at 65-75℃. The cyano group is converted into amine oxime group through the amine oxime reaction. After thorough washing and drying, a seawater uranium extraction material with a surface rich in amine oxime functional groups is obtained.

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