Phytic acid functionalized porous biochar material and preparation method and application thereof

Abstract

This invention belongs to the field of environmental functional materials and water pollution control technology, and discloses a phytic acid-functionalized porous biochar material, its preparation method, and its application. The method involves first activating biomass with potassium hydroxide, followed by pyrolysis, acid washing, and then activation with nitric acid. Finally, phytic acid is cross-linked and anchored using glutaraldehyde. This preparation method is simple, and the resulting material exhibits a distinct porous structure and excellent adsorption performance, with an adsorption capacity for uranyl ions exceeding 500 mg / g, making it suitable for large-scale industrial production. When this phytic acid-functionalized porous biochar material is used as a flowing electrode slurry in electro-adsorption deionization technology, it can reduce the initial concentration of uranyl ions from 100 µg / L to below 30 µg / L within 3 hours, meeting the "Standards for Drinking Water Quality" (GB 5749-2022). It shows promising application prospects in the deep purification treatment of uranium-containing wastewater.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional materials and water pollution control technology, specifically relating to an acid-functionalized porous biochar material and its preparation method, as well as the application of this material in the treatment of uranium-containing wastewater. Background Technology

[0002] Against the backdrop of the global low-carbon energy transition, nuclear energy, with its extremely low carbon footprint, has become one of the key clean energy sources supporting my country. Uranium resources, as the core "granary" of the nuclear energy system, generate large amounts of high-concentration uranium-containing wastewater during their mining and processing. However, according to the "Regulations on Radiation Protection and Radiation Environmental Safety Management of Uranium Mining and Metallurgy" (GB 23727—2020), the uranium concentration limit for uranium mining and metallurgical wastewater discharge outlets is 0.05 mg / L, and current processes often struggle to consistently meet this stringent standard.

[0003] Currently, the main methods for treating uranium-containing wastewater include adsorption and ion exchange, but these methods generally suffer from low treatment efficiency, poor selectivity, or secondary pollution. Flow-electrode capacitive deionization (FCDI) technology, with its advantages of simple operation, high ion separation efficiency, and low energy consumption, shows promising application prospects in the advanced treatment of uranium-containing wastewater and uranium resource recovery. The key to FCDI performance lies in the electrode material, among which biochar, due to its wide availability, low cost, and simple preparation process, has become a highly promising uranium adsorption electrode material.

[0004] In recent years, researchers have conducted extensive work on biochar modification. For example, CN109569525A discloses a method for preparing amino-magnetic rice husk biochar, which involves high-temperature pyrolysis, acidification with concentrated sulfuric acid and concentrated nitric acid, and then amino-modification to load Fe3O4 particles to improve the adsorption capacity for uranyl ions. However, the adsorption capacity of this material is only 93.5 mg·g⁻¹, which is insufficient to meet the requirements for high-efficiency treatment. Another example is CN117085654B, which discloses a biochar adsorbent loaded with poly(amine oxime), whose biochar carrier is derived from Penicillium chrysogenum mycelial spheres obtained through high-temperature carbonization. The adsorption capacity for uranium reaches 211.35 mg·g⁻¹, but the mycelial culture cycle is long and the yield is low, making it difficult to achieve large-scale production and engineering applications. Summary of the Invention

[0005] This invention aims to overcome the aforementioned shortcomings of existing technologies and provide a phytic acid-functionalized porous biochar material, its preparation method, and its applications. The material uses biochar as a matrix. First, a porous structure is constructed through activation with potassium hydroxide and acid washing with hydrochloric acid. Then, rich oxygen-containing functional groups are introduced through nitric acid activation. Finally, phytic acid is stably anchored to the biochar surface via a cross-linking reaction using glutaraldehyde, significantly improving the robustness and uniformity of the phytic acid loading. The prepared phytic acid-functionalized porous biochar material exhibits excellent adsorption performance and long-term stability for uranyl ions, making it suitable for the practical engineering needs of large-scale uranium-containing wastewater treatment.

[0006] The technical solution adopted in this invention is as follows: In a first aspect, the present invention provides a method for preparing phytic acid-functionalized porous biochar materials.

[0007] The method for preparing phytic acid-functionalized porous biochar material provided by this invention includes the following steps: (1) The biomass raw material is cleaned, dried and crushed to obtain pretreated biomass; the pretreated biomass is activated with potassium hydroxide, dried and pyrolyzed and then acid washed and dried to obtain potassium hydroxide activated biochar. (2) The potassium hydroxide activated biochar was placed in a nitric acid solution and heated in a water bath, then filtered, washed and dried to obtain nitric acid activated biochar; (3) The nitric acid activated biochar was placed in a glutaraldehyde solution and heated in a water bath, then filtered, washed and dried to obtain glutaraldehyde-loaded biochar; (4) The glutaraldehyde-loaded biochar and phytic acid solution are mixed in a predetermined ratio and hydrothermally reacted in a reactor for 24 h. Then the mixture is filtered, washed and dried to obtain phytic acid-functionalized porous biochar material.

[0008] Preferably, in step (1) of the above method, the biomass raw material is selected from plant biomass or agricultural waste, and the agricultural waste includes, but is not limited to, cottonseed hulls and mushroom husks; The cleaning and drying process involves washing with water to remove impurities from the surface of the biomass and then drying it in an oven for 24 hours. The crushing process involves crushing the biomass to a size that can pass through a 10-mesh sieve. The potassium hydroxide activation can be achieved by immersing the pretreated biomass in a potassium hydroxide solution at a solid-liquid ratio of 1:8 to 12 (w / v) and soaking it at room temperature for 24 hours. The concentration of potassium hydroxide solution can be 3–7 mol / L; The pyrolysis treatment can be carried out under a nitrogen protective atmosphere, heating from room temperature to 600-900 ℃ at a heating rate of 5 ℃·min⁻¹, holding at that temperature for 1-3 h, and then naturally cooling to room temperature.

[0009] The pickling treatment can be performed by immersing the pyrolyzed biochar in an excess of 1-3 mol / L hydrochloric acid solution for 24 hours.

[0010] Preferably, in step (2) of the above method, the solid-liquid ratio of potassium hydroxide activated biochar to nitric acid solution is 1:10-15 (w / v). The nitric acid solution can be prepared by mixing concentrated nitric acid and deionized water in a volume ratio of 1:(4-6); The water bath heating temperature can be 50–80 °C, and the heat preservation time can be 4–10 h.

[0011] Preferably, in step (3) of the above method, the solid-liquid ratio of nitric acid-activated biochar to glutaraldehyde solution is 1:10-15 (w / v). The concentration of the glutaraldehyde solution can be 1–3 mol / L; The water bath heating temperature can be 50–80 °C, and the heat preservation time can be 4–10 h.

[0012] Preferably, in step (4) of the above method, the solid-liquid ratio of the glutaraldehyde-supported biochar to the phytic acid solution can be 1:10-15 (w / v). The concentration of the phytic acid solution can be 30% to 70%.

[0013] The hydrothermal reaction temperature is 120–180 °C.

[0014] In a second aspect, the present invention provides a phytic acid-functionalized porous biochar material, wherein the phytic acid-functionalized porous biochar material is prepared by the above-described method for preparing phytic acid-functionalized porous biochar material.

[0015] A third aspect of the present invention provides the application of the phytic acid-functionalized porous biochar material in the electroadsorption treatment of uranium-containing wastewater using a flowing electrode.

[0016] A fourth aspect of the present invention provides a flowing electrode slurry. The flowing electrode slurry includes an electroadsorption material, wherein the electroadsorption material is the aforementioned phytic acid-functionalized porous biochar material.

[0017] In some embodiments, the mass concentration of phytic acid-functionalized porous biochar material in the flowing electrode slurry is 5–20 g / L.

[0018] A fifth aspect of the present invention provides a flow electrode capacitive deionization device. The flow electrode capacitive deionization device includes the aforementioned flow electrode slurry, uranium-containing waste liquid to be treated, and anion-selective permeation membranes and cation-selective permeation membranes.

[0019] In some embodiments, the flow rates of the flowing electrode slurry and the uranium-containing waste liquid to be treated in the flowing electrode capacitive deionization device are both 10 to 50 mL / min.

[0020] In some embodiments, the flowing electrode capacitor deionization device employs a constant voltage power-on mode. Preferably, the constant voltage ranges from 0.8 to 1.8 V.

[0021] A sixth aspect of the present invention provides a method for uranium removal from wastewater using the electro-adsorption uranyl ion removal device described above, comprising the following steps: A slurry of a flowing electrode made of phytic acid-functionalized porous biochar material is circulated into the electro-adsorption device for removing uranium ions, and the uranium-containing waste liquid to be treated is subjected to electro-adsorption uranium removal treatment under an applied electric field.

[0022] The beneficial effects of this invention are as follows: This invention provides a method for preparing phytic acid-functionalized porous biochar materials. The method involves activating the biochar material with potassium hydroxide followed by acid washing with hydrochloric acid, and further introducing abundant oxygen-containing functional groups through nitric acid treatment to enhance the surface reactivity of the material. Simultaneously, glutaraldehyde is used as a crosslinking agent to stably anchor phytic acid to the biochar surface via an acetal reaction, thereby significantly improving the loading stability of phytic acid on the material surface.

[0023] Phytic acid molecules contain abundant phosphate groups, which can form stable complexes with uranyl ions, thus endowing the material with excellent uranyl ion adsorption capacity. This allows the material to maintain stable uranium removal performance during long-term operation, making it suitable for large-scale uranium-containing wastewater treatment. When the phytic acid-functionalized porous biochar material is applied to a flowing electrode slurry and used in a flowing electrode capacitive deionization (FCDI) system, it can significantly improve the adsorption rate and capacity of uranyl ions, thereby enhancing the overall efficiency of the flowing electrode system. Compared with traditional porous carbon materials, the phytic acid-functionalized porous biochar material of this invention has higher capacitive adsorption performance and superior uranium removal effect, and can be widely used in the deep purification treatment of uranium-containing wastewater, solving the problems of low adsorption capacity and insufficient uranium removal efficiency of existing flowing electrode materials. Attached Figure Description

[0024] Figure 1 This is a SEM image of the potassium hydroxide activated biochar prepared in Example 1 of the present invention.

[0025] Figure 2 This is a SEM image of the phytic acid-functionalized porous biochar prepared in Example 1 of the present invention.

[0026] Figure 3 This is a schematic diagram of the flow electrode capacitor deionization device in Embodiment 2 of the present invention.

[0027] Figure 4 The results show the adsorption capacity test results of uranyl ion adsorption capacity of the phytic acid-functionalized porous biochar material in Example 1 of this invention.

[0028] Figure 5 This is a comparison chart of the adsorption of uranyl ions in static adsorption of Example 1, Comparative Example 1, and Comparative Example 2 of the present invention.

[0029] Figure 6 This is a diagram showing the effect of electro-adsorption of uranyl ions on the phytic acid-functionalized porous biochar flow electrode slurry in Example 2 of the present invention under different initial concentrations of uranyl ions.

[0030] Figure 7 This is a comparison graph showing the adsorption of uranyl ions by the flow electrode electroadsorption in Example 2 and Comparative Example 3 of the present invention. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Those skilled in the art can make various equivalent substitutions or improvements based on the content of this specification without departing from the spirit and substance of the present invention, and such substitutions or improvements should all fall within the scope of protection of the present invention.

[0032] In the following examples, the experimental materials and reagents used were as follows: cottonseed hulls were purchased from Hebei Tengying Technology Co., Ltd.; potassium hydroxide (KOH), hydrochloric acid (HCl, 36%), and glutaraldehyde were purchased from Aladdin Biotechnology Co., Ltd.; nitric acid (HNO3, 68%) was purchased from Sinopharm Chemical Reagent Co., Ltd.; phytic acid (PA, 50 wt%) was used as a loading material and purchased from Ron Chemical Reagent Co., Ltd.; uranyl nitrate hexahydrate (UO2(NO3)2·6H2O) was used to prepare uranium-containing solutions; arsine III was used as a colorimetric reagent for the spectrophotometric determination of uranium content and was purchased from Maclean's Reagent Co., Ltd. Unless otherwise specified, all reagents were of analytical grade, and the experimental water was deionized water.

[0033] Example 1

[0034] This invention provides a phytic acid-functionalized porous biochar material, prepared according to the following steps: Cottonseed hulls are used as biomass raw material, repeatedly washed with deionized water to remove surface mud and impurities, and then dried in a forced-air drying oven at 105 °C for 24 h. The dried cottonseed hulls are crushed by a pulverizer and passed through a 10-mesh sieve to obtain pretreated biomass. The pretreated biomass is mixed with a potassium hydroxide solution, wherein the concentration of the potassium hydroxide solution is 5 mol / L, and the solid-liquid ratio of potassium hydroxide to biomass is 1:10 (w / v), and impregnated at room temperature for 24 h. After impregnation, the sample is dried for later use. The dried sample is placed in a tube furnace and heated from room temperature to 800 °C at a heating rate of 5 °C·min⁻¹ under a nitrogen protective atmosphere, held at this temperature for 2 h, and then naturally cooled to room temperature to obtain pyrolysis products. The obtained pyrolysis products are immersed in a 2 mol / L hydrochloric acid solution for 24 h to remove residual inorganic salts and impurities. The filtrate was then repeatedly washed with deionized water until the pH of the filtrate was close to neutral, and then dried to obtain potassium hydroxide activated biochar.

[0035] Take 2 g of the above potassium hydroxide activated biochar and add it to 25 mL of nitric acid solution prepared by mixing concentrated nitric acid and deionized water at a volume ratio of 1:5.25. Heat the solution in a water bath at 60 °C for 6 h. After the reaction is complete, filter the solution and wash it with deionized water until neutral. Then dry the solution at 80 °C for 12 h to obtain nitric acid activated biochar.

[0036] Take 5 g of nitric acid-activated biochar and add it to 50 mL of 2 mol / L glutaraldehyde solution. React at 60 ℃ in a water bath for 6 h. After the reaction is complete, filter the solution and wash with deionized water to remove unreacted glutaraldehyde. Dry the biochar to obtain glutaraldehyde-supported biochar.

[0037] The obtained glutaraldehyde-supported biochar was mixed with a phytic acid solution at a solid-liquid ratio of 1:12 (w / v), wherein the phytic acid solution concentration was 50%. The mixture was transferred to a reactor and reacted at 140 °C for 24 h. After the reaction, the mixture was allowed to cool naturally to room temperature, filtered, and washed with deionized water until the pH of the filtrate stabilized. Subsequently, it was dried at 80 °C for 24 h to obtain phytic acid-functionalized porous biochar material.

[0038] Example 2

[0039] This embodiment provides a method for uranium removal from uranium-containing wastewater using a flowing electrode slurry. The steps are as follows: the phytic acid-functionalized porous biochar material prepared in Example 1 is added to deionized water and ultrasonically dispersed to prepare a flowing electrode slurry, wherein the concentration of the phytic acid-functionalized porous biochar material in the slurry is 5 g / L.

[0040] See Figure 3The aforementioned flowing electrode slurry and uranium-containing wastewater are separately circulated into an electro-adsorption uranium removal device (i.e., a flowing electrode capacitive deionization device), and the solutions on both sides are separated by an ion exchange membrane. During system operation, the solution flow rate is 40 mL / min, and under a constant voltage of 1.2 V, uranium-containing wastewater with an initial concentration of 50 mg / L is subjected to electro-adsorption uranium removal. In this embodiment, the flowing electrode slurry is used as both the cathode and anode flowing electrodes, and after adsorbing uranyl ions, it circulates within the same storage container, forming a short-circuit closed-loop (SCC) operating mode. Figure 6 and Figure 7 All were carried out under these conditions. Figure 6 The initial uranyl ion concentrations were 0.1, 0.5, 5, and 50 mg / L. Figure 7 (The concentration of the flow electrode slurry was 5 g / L at different concentrations).

[0041] Comparative Example 1 Comparative Example 1 is basically the same as Example 1, except that the biochar was not activated with nitric acid. The specific preparation steps are as follows: Cottonseed hulls were used as biomass feedstock. They were repeatedly washed with deionized water to remove surface mud and impurities, and then dried in a forced-air drying oven at 105 °C for 24 h. The dried cottonseed hulls were then crushed using a pulverizer and passed through a 10-mesh sieve to obtain pretreated biomass.

[0042] Pretreated biomass was mixed with a potassium hydroxide solution (5 mol / L) at a solid-liquid ratio of 1:10 (w / v) and impregnated at room temperature for 24 h. After impregnation, the sample was dried. The dried sample was placed in a tube furnace and heated from room temperature to 800 °C at a rate of 5 °C·min⁻¹ under a nitrogen atmosphere. After holding at this temperature for 2 h, the sample was allowed to cool naturally to room temperature to obtain the pyrolysis product.

[0043] The obtained pyrolysis product was immersed in 2 mol / L hydrochloric acid solution for 24 h to remove residual inorganic salts and impurities. It was then repeatedly washed with deionized water until the pH of the filtrate was close to neutral, and dried to obtain potassium hydroxide-activated biochar.

[0044] The obtained potassium hydroxide-activated biochar was directly used for subsequent modification treatment. Specifically, 5 g of potassium hydroxide-activated biochar was added to 50 mL of 2 mol / L glutaraldehyde solution, and the reaction was carried out in a 60 ℃ water bath for 6 h. After the reaction was completed, the mixture was filtered, and unreacted glutaraldehyde was removed by washing with deionized water. The biochar was then dried to obtain glutaraldehyde-supported biochar.

[0045] The obtained glutaraldehyde-supported biochar was mixed with phytic acid solution at a solid-liquid ratio of 1:12 (w / v), wherein the phytic acid solution concentration was 50%. The mixture was transferred to a reactor and reacted at 140 °C for 24 h. After the reaction, the mixture was allowed to cool naturally to room temperature, filtered, and washed with deionized water until the pH of the filtrate stabilized. Subsequently, it was dried at 80 °C for 24 h to obtain the material of Comparative Example 1.

[0046] Comparative Example 2 Comparative Example 2 is basically the same as Example 1, except that it did not undergo phytic acid loading treatment. The specific preparation steps are as follows: Cottonseed hulls were used as biomass feedstock. They were repeatedly washed with deionized water to remove surface mud and impurities, and then dried in a forced-air drying oven at 105 °C for 24 h. The dried cottonseed hulls were then crushed using a pulverizer and passed through a 10-mesh sieve to obtain pretreated biomass.

[0047] Pretreated biomass was mixed with a potassium hydroxide solution (5 mol / L) at a solid-liquid ratio of 1:10 (w / v) and impregnated at room temperature for 24 h. After impregnation, the sample was dried. The dried sample was placed in a tube furnace and heated from room temperature to 800 °C at a rate of 5 °C·min⁻¹ under a nitrogen atmosphere. After holding at this temperature for 2 h, the sample was allowed to cool naturally to room temperature to obtain the pyrolysis product.

[0048] The obtained pyrolysis product was immersed in 2 mol / L hydrochloric acid solution for 24 h to remove residual inorganic salts and impurities. It was then repeatedly washed with deionized water until the pH of the filtrate was close to neutral, and dried to obtain potassium hydroxide-activated biochar.

[0049] Take 2 g of the above potassium hydroxide activated biochar and add it to 25 mL of nitric acid solution prepared by mixing concentrated nitric acid and deionized water at a volume ratio of 1:5.25. Heat the solution in a water bath at 60 °C for 6 h. After the reaction is complete, filter the solution and wash it with deionized water until neutral. Then dry the solution at 80 °C for 12 h to obtain nitric acid activated biochar.

[0050] Take 5 g of nitric acid-activated biochar and add it to 50 mL of 2 mol / L glutaraldehyde solution. React at 60 ℃ in a water bath for 6 h. After the reaction is complete, filter the solution and wash with deionized water to remove unreacted glutaraldehyde. Dry the biochar to obtain glutaraldehyde-supported biochar.

[0051] Comparative Example 3 Comparative Example 3 is the same as Example 2, except that only commercial activated carbon (purchased from McLean Ltd.) is used as the electroadsorption material to form a simple porous carbon flow electrode slurry for uranium removal.

[0052] To verify the structural and performance advantages of the material of this invention, the following characterization and testing were performed: 1. Morphological characteristics (corresponding to) Figure 1 , Figure 2 The microstructure of the potassium hydroxide-activated biochar and the final phytic acid-functionalized porous biochar material obtained in Example 1 were observed using scanning electron microscopy (SEM). The results are as follows: Figure 1 , Figure 2 As shown, Figure 1 The KOH activation confirmed the successful construction of a porous network structure in the material. Figure 2 The change in surface morphology of the modified material indicates that phytic acid has been successfully loaded, and the material synthesis process is reliable.

[0053] 2. Static adsorption performance test (1) Adsorption isotherm test (corresponding to) Figure 4 5.0 mg of the phytic acid-functionalized porous biochar material prepared in Example 1 was accurately weighed and placed into several 50 mL centrifuge tubes. 20 mL of uranyl ion solution (prepared from UO2(NO3)2·6H2O) with initial concentrations (C0) of 0, 10, 20, 50, 100, 150, and 200 mg / L were added respectively, and the initial pH of each solution was adjusted to 5.0 ± 0.1 to eliminate the influence of pH fluctuations on the uranyl ion speciation and adsorption performance. The centrifuge tubes were placed in a constant temperature shaking incubator and shaken at 25°C and 180 rpm for 24 h to ensure adsorption equilibrium was reached. Subsequently, the supernatant was used to determine the equilibrium concentration (C0) of uranyl ions using the azoarsine III spectrophotometric method. e ).

[0054] According to formula Q e =(C0-C e The equilibrium adsorption capacity was calculated as V × V / m, where V is the solution volume (L) and m is the adsorbent mass (g). The obtained data were fitted and analyzed using Langmuir and Freundlich isothermal adsorption models, respectively.

[0055] Figure 4 The results of static adsorption experiments on uranyl ions (UO2²⁺) of the phytic acid-functionalized porous biochar material prepared in Example 1 are shown (adsorbent dosage 5 mg, solution volume 20 mL, initial uranyl ion concentration 0-200 mg / L, temperature 25℃). Figure 4 It can be seen that the phytic acid-functionalized porous biochar material prepared in the embodiments of the present invention exhibits a high adsorption capacity for uranyl ions, with a theoretical maximum adsorption capacity of 504.9 mg / g.

[0056] The adsorption isotherm data were fitted using both the Langmuir and Freundlich models. The results showed that the correlation coefficients (R²) between the Langmuir and Freundlich models were 0.9987 and 0.913, respectively. The Langmuir model showed a higher correlation coefficient, indicating that the adsorption process of uranyl ions by this material better conforms to the Langmuir monolayer adsorption model. This suggests that adsorption mainly occurs on relatively uniform active sites on the material surface. Uranyl ions form a monolayer by coordinating with functional groups such as phosphate groups (–PO4³⁻) on the material surface or through electrostatic interactions, thereby achieving efficient adsorption of uranyl ions. Meanwhile, the Freundlich model also showed a high degree of fit, indicating that there are still some differences in energy distribution and multilayer adsorption characteristics on the material surface. This suggests that the phytic acid-functionalized porous biochar material has a rich pore structure and diverse adsorption sites, which is beneficial for improving its adsorption capacity for uranyl ions.

[0057] (2) Adsorption kinetics comparison test (corresponding to) Figure 5 ): Accurately weigh 50.0 mg of the materials from Example 1, Comparative Example 1, and Comparative Example 2, and place them separately into three beakers containing 50 mL of uranyl ion solution with an initial concentration of 50 mg / L. Adjust the initial pH of the solution to 5.0 ± 0.1. Stir magnetically at 500 rpm at 25°C. Samples were taken at 5, 10, 20, 30, 45, and 60 minutes after the start of the reaction. After rapid filtration through a 0.22 μm filter membrane, the instantaneous concentration of uranyl ions in the solution was determined using arsene III spectrophotometry. The adsorption amount at each time point was calculated, and adsorption kinetic curves were plotted for comparison.

[0058] Figure 5 The changes in uranyl ion concentration in the solution of Examples 1, Comparative Example 1, and Comparative Example 2 under static adsorption conditions (adsorbent dosage 50 mg, solution volume 50 mL, initial uranyl ion concentration 50 mg / L, adsorption time 1 h) are shown. The results indicate that the adsorbent prepared in Example 1 has a significantly improved adsorption capacity for uranyl ions compared to Comparative Example 1 and Comparative Example 2. This result fully demonstrates that nitric acid acidification and phytic acid loading have a significant impact on the adsorbent performance.

[0059] Specifically, nitric acid acidification introduces more oxygen-containing functional groups onto the surface of carbon materials, thereby increasing the surface reactivity and providing more binding sites for the stable loading of phytic acid molecules. Furthermore, the abundant phosphate groups in phytic acid molecules can coordinate or interact electrostatically with uranyl ions, significantly enhancing the material's adsorption capacity for uranyl ions. This allows the adsorbent to capture uranyl ions more efficiently per unit time, effectively reducing the uranium concentration in wastewater.

[0060] 3. Electroadsorption performance test of the flowing electrode (1) Treatment efficacy at different initial concentrations (corresponding to) Figure 6 The flow electrode capacitive deionization (FCDI) device and operating parameters (slurry concentration 5 g / L, flow rate 40 mL / min, voltage 1.2 V, SCC mode) described in Example 2 were used. Uranium-containing simulated wastewater with initial concentrations of 0.1 mg / L, 0.5 mg / L, 5 mg / L, and 50 mg / L were used as the treatment solutions, with the initial pH value of each solution controlled at 6.0 ± 0.1. Electroadsorption treatment was performed continuously for 3 hours. During operation, samples were taken from the wastewater at regular intervals to measure the uranyl ion concentration, calculate the removal rate, and evaluate the system's treatment efficiency and deep purification potential for uranium-containing wastewater of different concentrations.

[0061] Figure 6 The electroadsorption performance of Example 2 under different initial uranyl ion concentrations is shown. The results indicate that as the initial uranyl ion concentration gradually decreases from 50 mg / L to 0.1 mg / L, the removal rate of uranyl ions decreases from 95.08% to 72.45% during the 3-hour electroadsorption process. This is because at lower initial concentrations, the number of uranyl ions in the solution decreases, weakening the mass transfer driving force and leading to a corresponding decrease in adsorption rate and removal rate. However, it is noteworthy that even at a lower concentration (0.1 mg / L), the system can still reduce the uranyl ion concentration in the solution to below 30 µg / L, meeting the limits set by the "Standards for Drinking Water Quality" (GB 5749-2022), indicating that this material system has good application potential in the deep purification treatment of low-concentration uranium-containing wastewater.

[0062] (2) Comparison of electrode material properties (corresponding) Figure 7Using the phytic acid-functionalized porous biochar material prepared in Example 1 (i.e., the flowing electrode slurry prepared in Example 2) and the commercial activated carbon used in Comparative Example 3 as electrode active materials, flowing electrode slurries were prepared according to the same method (concentration 5 g / L, ultrasonic dispersion). Under identical FCDI apparatus and operating conditions (initial concentration of the solution to be treated 50 mg / L, pH 6.0 ± 0.1, flow rate 40 mL / min, voltage 1.2 V, SCC mode), an electro-adsorption uranium removal experiment was conducted for 3 hours. Changes in uranium ion concentration on the wastewater side were monitored periodically, and the uranium removal rates of the two materials as flowing electrodes were calculated and compared to verify the performance advantages of the material of the present invention.

[0063] Figure 7 The comparison of the uranyl ion removal performance of Example 2 and Comparative Example 3 under electroadsorption conditions is shown. The results indicate that, compared with traditional commercial activated carbon materials, the phytic acid-functionalized porous biochar prepared in this invention, when formulated as a flowing electrode slurry under the same conditions, significantly improves the uranyl ion removal performance. During the 3-hour electroadsorption process, the material of this invention achieved a uranyl ion removal rate of 95.08%, while the flowing electrode slurry prepared using commercial activated carbon only achieved a removal efficiency of 73.17%. This result further demonstrates that the phytic acid-functionalized porous biochar prepared in this invention has good practical value and technological advancement in the field of uranium-containing wastewater electroadsorption treatment.

[0064] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Without departing from the spirit and essence of the present invention, any modifications, equivalent substitutions, or improvements made by those skilled in the art to relevant parameters, concentrations, and process conditions through conventional experiments or equivalent substitutions based on the technical solutions disclosed in the present invention should fall within the scope of protection of the present invention. Reasonable optimizations or extensions made by those skilled in the art to the present invention based on the disclosure of this specification and in conjunction with conventional technical means in the field should also be considered to fall within the scope of protection of the present invention.

Claims

1. A method for preparing an acid-functionalized porous biochar material, characterized in that, Includes the following steps: (1) The biomass raw materials are cleaned, dried and crushed to obtain pretreated biomass; The pretreated biomass was activated with potassium hydroxide, dried and pyrolyzed, then acid-washed and dried to obtain potassium hydroxide activated biochar. (2) The potassium hydroxide activated biochar was placed in a nitric acid solution and heated in a water bath, then filtered, washed and dried to obtain nitric acid activated biochar; (3) The nitric acid activated biochar was placed in a glutaraldehyde solution and heated in a water bath, then filtered, washed and dried to obtain glutaraldehyde-loaded biochar; (4) The glutaraldehyde-loaded biochar and phytic acid solution are mixed in a predetermined ratio and hydrothermally reacted in a reactor for 24 h. Then the mixture is filtered, washed and dried to obtain phytic acid-functionalized porous biochar material.

2. The preparation method according to claim 1, characterized in that, In step (1): The biomass raw materials are selected from plant biomass or agricultural waste, and the agricultural waste includes, but is not limited to, cottonseed hulls and mushroom residue; The crushing process involves crushing the biomass to pass through a 10-mesh sieve. The potassium hydroxide activation involves immersing the pretreated biomass in a potassium hydroxide solution with a concentration of 3-7 mol / L at a solid-liquid ratio of 1:8-12 (w / v). The pyrolysis process involves heating from room temperature to 600–900 °C at a heating rate of 5 °C·min⁻¹ under a nitrogen protective atmosphere, holding at that temperature for 1–3 h, and then naturally cooling to room temperature. The acid washing process involves immersing the pyrolyzed biochar in a 1–3 mol / L hydrochloric acid solution.

3. The preparation method according to claim 1, characterized in that, In step (2): The solid-liquid ratio of potassium hydroxide-activated biochar to nitric acid solution is 1:10-15; The nitric acid solution is prepared by mixing concentrated nitric acid and deionized water at a volume ratio of 1:(4-6); The water bath heating temperature is 50–80 °C, and the heat preservation time is 4–10 h.

4. The preparation method according to claim 1, characterized in that, In step (3): The solid-liquid ratio of nitric acid-activated biochar to glutaraldehyde solution is 1:10-15; The concentration of the glutaraldehyde solution is 1–3 mol / L; The water bath heating temperature is 50–80 °C, and the heat preservation time is 4–10 h.

5. The preparation method according to claim 1, characterized in that, In step (4): The solid-liquid ratio of the glutaraldehyde-loaded biochar to the phytic acid solution is 1:10-15. The concentration of the phytic acid solution is 30% to 70%. The hydrothermal reaction temperature is 120–180 °C.

6. An acid-functionalized porous biochar material, characterized in that, The phytic acid-functionalized porous biochar material is prepared by any one of claims 1 to 5.

7. The application of the phytic acid-functionalized porous biochar material according to claim 6 in the electroadsorption treatment of uranium-containing wastewater using a flowing electrode.

8. A flowable electrode slurry, characterized in that, The flowing electrode slurry includes an electroadsorption material, which is the phytic acid-functionalized porous biochar material as described in claim 6.

9. An apparatus for electroadsorption removal of uranyl ions, characterized in that, It includes the flowing electrode slurry as described in claim 8, the uranium-containing waste liquid to be treated, the anion-selective permeation membrane, and the cation-selective permeation membrane.

10. A method for removing uranium from wastewater using the electro-adsorption uranyl ion removal device according to claim 9, characterized in that, Includes the following steps: A slurry of a flowing electrode made of phytic acid-functionalized porous biochar material is circulated into the electro-adsorption device for removing uranium ions, and the uranium-containing waste liquid to be treated is subjected to electro-adsorption uranium removal treatment under an applied electric field.

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