Bamboo powder-based plant acidified porous biochar material as well as preparation method and application thereof

Abstract

The invention discloses a phytic acid porous biochar material based on bamboo powder and a preparation method and application thereof, and relates to the technical field of nuclear wastewater treatment.The preparation method comprises the steps that the bamboo powder and a phytic acid solution are mixed, then the phytic acid and the bamboo powder are subjected to a chemical reaction through heating and drying, then high-temperature carbonization treatment is conducted, and the phytic acid porous biochar material is obtained. The plant acidified porous biochar material based on the bamboo powder is obtained. The raw materials are rich, the cost is low, and large-scale production and application are easy. The biochar material activated and modified by phytic acid has excellent adsorption performance and regeneration performance, and is high in U (VI) removal efficiency and good in selectivity. And the material has a good practical application effect on a fixed bed column, and can effectively reduce the concentration of uranium in practical nuclear wastewater. In addition, the preparation method is simple, easy to operate and suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear wastewater, and in particular to a phytate-based porous biochar material made from bamboo powder, a preparation method thereof, and an application thereof. Background Art

[0002] With the development of the global nuclear energy industry, the treatment of nuclear wastewater has become a crucial environmental issue. Nuclear wastewater contains various radioactive substances, and U(VI) has attracted much attention due to its long-term environmental persistence and potential biological toxicity. After uranium enters the water body, it will accumulate in organisms and pose a serious threat to the ecosystem and human health through the food chain, such as causing cancer, kidney diseases, etc. Therefore, developing efficient, economical, and sustainable uranium removal technologies is an urgent task in the field of nuclear wastewater treatment.

[0003] Currently, existing adsorption materials have problems such as high cost, low efficiency, or poor regeneration performance in removing U(VI). For example, activated carbon has a developed pore structure and a large specific surface area, but its selective adsorption ability for uranium is limited, and some adsorption performance may be lost during the regeneration process. Zeolite has a certain adsorption affinity for uranium, but its adsorption capacity is relatively low, and the raw material source and preparation process may be restricted. Although MOF materials have a highly ordered pore structure and adjustable chemical functionalization sites, they face problems such as poor stability and difficulty in large-scale preparation in practical applications.

[0004] As a new type of adsorption material, biochar has attracted attention due to its wide source, environmental friendliness, low price, and certain adsorption performance. Biochar is mainly prepared by pyrolysis of biomass under anoxic or oxygen-limited conditions. Its surface is rich in oxygen-containing functional groups, such as carboxyl groups, hydroxyl groups, etc., which can coordinate with metal ions to achieve the adsorption of uranium. However, traditional biochar still has some deficiencies in adsorbing uranium, such as the adsorption capacity needs to be improved, the pore structure is not optimized enough, the selective adsorption ability for uranium is not strong enough, and the regeneration performance is poor, which limits its efficient application in nuclear wastewater treatment. Therefore, it is particularly important to develop an economical and efficient adsorption material that is easy to regenerate. Summary of the Invention

[0005] One of the purposes of the present invention is to overcome the defects of the above-mentioned existing technologies and provide a phytate-based porous biochar material made from bamboo powder that is economical, efficient, and easy to regenerate.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions: A phytic acid-modified porous biochar material based on bamboo powder is prepared by the following preparation method: Mix bamboo powder with a phytic acid solution, and then heat and dry to cause a chemical reaction between phytic acid and bamboo powder, and then perform high-temperature carbonization treatment on it to obtain the phytic acid-modified porous biochar material based on bamboo powder.

[0007] Preferably, it specifically includes the following steps:

[0008] (1) Raw material selection and pretreatment: Select bamboo powder as the basic raw material, and perform crushing and screening pretreatment on it to obtain bamboo powder with uniform particle size;

[0009] (2) Activation modification: Mix the pretreated bamboo powder with a phytic acid solution, and perform impregnation and stirring treatment to allow phytic acid to fully penetrate and adsorb on the surface of bamboo powder, and then heat and dry to cause a chemical reaction between phytic acid and bamboo powder to form a phytic acid-modified porous biochar material;

[0010] (3) High-temperature synthesis: Perform carbonization treatment on the obtained phytic acid-modified porous biochar material under high-temperature conditions to obtain the phytic acid-modified porous biochar material based on bamboo powder.

[0011] Among them, in step (1), select high-quality Moso bamboo as the basic raw material, cut and crush the Moso bamboo to obtain delicate bamboo powder, then dry the bamboo powder at 80 °C until constant weight to ensure complete removal of moisture, and then use an 80-mesh sieve to screen the dried bamboo powder to obtain bamboo powder with uniform particle size.

[0012] Preferably, in step (2), weigh bamboo powder and a phytic acid solution with a concentration of 85%, mix them in a mass ratio of 1:2, stir the bamboo powder and the phytic acid solution evenly to ensure complete fusion of the two, and then stir the mixture at 25 °C at a speed of 180 rpm for 24 hours to ensure uniform mixing.

[0013] More preferably, in step (2), dry the stirred mixture at 80 °C for 10 hours to further remove moisture, then transfer the dried mixture to a muffle furnace and perform pyrolysis under the condition of passing air. Starting from room temperature, heat it to the target temperature of 400 °C at a heating rate of 5 °C / min, and keep it at 400 °C for 1 hour to ensure full progress of the pyrolysis process.

[0014] More preferably, in step (2), after the pyrolysis is completed, let the mixture cool naturally to room temperature, collect the carbonized material, and wash it with ultrapure water to remove excess free acid and other inorganic substances. The washing process is continued until the pH value of the filtrate reaches 6-7.

[0015] More preferably, in step (3), the washed carbonized material is dried at 80 °C, and the dried carbonized material is sieved again using an 80-mesh sieve to obtain the final phytic acid-activated porous biochar material based on bamboo powder.

[0016] The phytic acid-activated porous biochar material based on bamboo powder prepared by the present invention can be applied to the removal of radioactive U(VI) in wastewater.

[0017] Compared with the prior art, the phytic acid-activated porous biochar material based on bamboo powder provided by the present invention has rich raw materials, low cost, and is easy to be mass-produced and applied. The biochar material after phytic acid activation modification has excellent adsorption performance and regeneration performance, high removal efficiency and good selectivity for U(VI). And the actual application effect of this material on the fixed-bed column is good, which can effectively reduce the concentration of uranium in actual nuclear wastewater. In addition, the preparation method of the present invention is simple and easy to operate, and is suitable for industrial production. Description of the Drawings

[0018] Figure 1 It is a schematic flow chart of the preparation method of the present invention;

[0019] Figure 2 (a) is the SEM image of the product of Comparative Example 1 (BC-400-0); Figure 2 (b) is the SEM image (2 μm) of the product of Example 2 (BC-400-PO 4 ); Figure 2 (c) is the SEM image (10 μm) of the product of Example 2 (BC-400-PO 4 ); Figure 2 (d) is the SEM mapping image of the product of Example 2 (BC-400-PO 4 );

[0020] Figure 3 (a) is the FTIR spectrogram of the products of each example and comparative example; Figure 3 (b) is the XPS full spectrum of the products of each example and comparative example; Figure 3 (c) is the P 2p XPS spectrum of the products of each example; Figure 3 (d) is the O 1s XPS spectrum of the products of each example;

[0021] Figure 4 (a) is the N 2 adsorption and desorption isotherm of the products of each example and comparative example; Figure 4 (b) is the pore size distribution curve of the products of each example and comparative example;

[0022] Figure 5(a) Adsorption efficiency of the products of the comparative example and each example (m / V = 0.06 g / L, C0 = 10 mg / L, pH = 6, T = 298.15 K); Figure 5 (b) Influence of the adsorption dose on the product of Example 2 (V = 50 mL, C0 = 10 mg / L, pH = 6, T = 298.15 K); Figure 5 (c) Influence of the solution pH value on the product of Example 2 (m / V = 0.06 g / L, C0 = 10 mg / L, T = 298.15 K); Figure 5 (d) Distribution of U(VI) species at different pH values; Figure 5 (e) Zeta potential of the product of Example 2 at different pH values; Figure 5 (f) Influence of the ionic strength on the product of Example 2 (m / V = 0.06 g / L, C0 = 10 mg / L, pH = 6, T = 298.15 K);

[0023] Figure 6 (a) Time optimization of the product of Example 2 (m / V = 0.06 g / L, C0 = 10 mg / L, pH = 6, T = 298.15 K); Figure 6 (b) Pseudo-first-order and pseudo-second-order kinetic models for the adsorption of U(VI) by the product of Example 2 (BC-400-PO 4 ); Figure 6 (c) Isothermal adsorption model for the adsorption of U(VI) by the product of Example 2 (BC-400-PO 4 );

[0024] Figure 7 (a) Influence of different temperatures on the adsorption of uranium(VI) by the products of Example 2 and Comparative Example 1 (m / V = 0.06 g / L, C0 = 10 mg / L, pH = 6); Figure 7 (b) Schematic diagram of the adsorption thermodynamics of the products of Example 2 and Comparative Example 1; Figure 7 (c) Schematic diagram of the experimental results of competitive adsorption of metal ions (m / V = 0.06 g / L, pH = 6); Figure 7 (d) Schematic diagram of the regeneration test results of the product of Example 2 (m / V = 0.06 g / L, C0 = 10 mg / L, pH = 6, T = 298.15 K);

[0025] Figure 8 (a) Schematic diagram of the dynamic adsorption of uranium from real nuclear wastewater by the product of Example 2 in a fixed-bed column (m = 120 mg, C0 = 0.456 mg / L, pH = 5.8, T = 298.15 K); Figure 8 (b) Schematic diagram of the fixed-bed post-treatment equipment;

[0026] Figure 9(a) BC-400-PO 4 -SEM mapping of U; Figure 9 (b) is the FT-IR spectrum of the product of Example 2 before and after uranium adsorption; Figure 9 (c) BC-400-PO 4 -U 4f XPS spectrum of U; Figure 9 (d) is the high-resolution U 4f XPS spectrum of adsorbed uranium; Figure 9 (e) is the P 2p XPS spectrum of the product of Example 2 before and after uranium adsorption; Figure 9 (f) is the O 1s spectrum of the product of Example 2 before and after uranium adsorption. DETAILED DESCRIPTION

[0027] In order to facilitate the understanding of those skilled in the art, the present invention is further described below in conjunction with the examples and drawings. The contents mentioned in the embodiments are not intended to limit the present invention. It should be noted in advance that the phytic acid involved in the present invention is inositol hexaphosphate, with a molecular formula of C 6 H 18 O 24 P 6 , the PA solution in the subsequent embodiments refers to the phytic acid solution.

[0028] Example 1

[0029] like Figure 1 As shown, a phytic acidified porous biochar material based on bamboo powder is prepared as follows: first, the bamboo is placed in a blast drying oven and dried at a constant temperature of 80°C for 24 hours. After cooling to room temperature, the bamboo is further ground into fine powder. Then, the powder is sieved through an 80-mesh sieve to obtain uniform bamboo powder. Next, the bamboo powder is dispersed in an 85wt% PA solution, and the mass ratio of bamboo powder to phytic acid solution is maintained at 1:2. After thorough mixing, the mixture is dried again at 80°C for 10 hours. After that, it is transferred to a muffle furnace. The temperature is raised to a target temperature of 350°C at a heating rate of 5°C per minute, and then the constant temperature is maintained for 1 hour to complete the pyrolysis process. After pyrolysis, the obtained solid product is washed with ultrapure water until the pH value reaches neutral. Finally, these washed products are dried at 80°C to obtain the desired biochar material, and the product prepared in this embodiment is named BC-350-PO 4 .

[0030] Example 2

[0031] The only difference between this embodiment and embodiment 1 is the carbonization target temperature. Specifically, the carbonization target temperature of this embodiment is 400°C, and the final product prepared is named BC-400-PO 4 .

[0032] Example 3

[0033] The difference between this example and Example 1 lies only in the different carbonization target temperatures. Specifically, the carbonization target temperature of this example is 450 °C, and the finally prepared product is named BC-450-PO 4 .

[0034] Comparative Example 1

[0035] The difference between this example and Example 2 is only that phytic acid solution was not used to activate and modify the bamboo powder during the preparation process, and the finally prepared product is named BC-400-0.

[0036] Product Characterization

[0037] The surface morphologies of the biochar materials prepared in Example 2 and Comparative Example 1 were preliminarily characterized using a scanning electron microscope (SEM). As Figure 2 (a) shows, the surface of BC-400-0 prepared in Comparative Example 1 is relatively rough, and the layered collapse results in a loose structure. In contrast, the surface of BC-400-PO prepared in Example 2 4 shows a macroporous structure and is densely covered with microporous structures, as shown in Figure 2 (b) and 2(c). This indicates that PA modification has a significant effect on the morphology and pore structure of biochar, effectively catalyzing and accelerating the decomposition and dehydration reactions of biomass. Figure 2 (d) shows the SEM mapping image of BC-400-PO 4 , showing the uniform distribution of carbon, oxygen, and phosphorus elements on the bulk surface. The elemental weight percentage values are presented in Table 1. This observation confirms the successful synthesis of BC-400-PO 4 .

[0038] Table 1 Weight percentages of C, O, and P elements in BC-400-0, BC-350-PO 4 , BC-400-PO 4 and BC-450-PO 4

[0039]

[0040] Next, the functional groups of the biochar materials prepared in the above examples and comparative examples were analyzed using Fourier transform infrared spectroscopy (FT-IR). As Figure 3 (a) shows, the broadband from 2800 cm -1 to 3000 cm -1 can be attributed to the stretching vibration of aromatic framework C-H. The peak corresponding to the stretching vibration of the P=O bond appears at 1177 cm-​1， The stretching vibration peak of the P-O bond in P-O-H appears at 1030 cm -1 . These findings indicate that the phosphorus in BC-X-PO 4 mainly exists in the form of dihydrogen phosphate and monohydrogen phosphate. When comparing BC-400-0 with the acid-modified biochar BC-350-PO 4 , BC-400-PO 4 and BC-450-PO 4 , the intensities of the oxygen-containing functional groups C=O (at 1580 cm -1 ) and C-O (at 1100 cm -1 ) do not change significantly. However, in the spectra of the acid-modified biochar, a shoulder peak at 1100 cm -1 is detected. This shoulder peak may be attributed to the ionization-related P + -O - in phosphate esters and the symmetric vibration within the polyphosphate chain.

[0041] The surface elemental composition and functional groups of the biochar were analyzed by XPS. As Figure 3 (b) shows, the prepared BC-X-PO 4 biochar exhibits signals of C 1s, O 1s, and P 2p, confirming that BC-X-PO 4 is mainly composed of C, O, and P elements.

[0042] Figure 4 (a) shows the N 2 adsorption-desorption isotherm of BC-X-PO4, and the pore structure parameters are presented in Table 2. The adsorption-desorption isotherm shows typical type-IV curve characteristics, with an obvious hysteresis loop in the high-pressure range of 0.25 < P / P 0 < 1.0. This phenomenon is mainly attributed to the rich mesoporous structure of the material. The specific surface areas of BC-350-PO 4 , BC-400-PO 4 and BC-450-PO 4 are 374.6 m 2 / g, 967.8 m 2 / g, and 623.8 m 2 / g, respectively. The micropore surface areas are 346.4 m 2 / g, 824.2 m 2 / g, and 577.1 m 2 / g, respectively, and the external surface areas are 28.2 m 2 / g, 143.6 m 2 / g, and 46.6 m 2 / g. As the carbonization temperature increased from 350 °C to 450 °C, the specific surface area, micropore surface area, and external surface area initially increased and then decreased. Compared with the unacidified biochar, the acidified biochar showed an increase in specific surface area, micropore surface area, and external surface area. As can be seen from the pore size distribution diagram in Figure 4 (b), the micropore size of the material was mainly concentrated in the range of 0 to 5 nm. The average pore diameters of BC-350-PO 4 , BC-400-PO 4 and BC-450-PO 4 were 2.1 nm, 2.2 nm, and 2.1 nm respectively, and the average mesopore diameters were 3.6 nm, 3.0 nm, and 3.2 nm respectively. Compared with the unacidified biochar BC-400-0 (average pore diameter of 2.3 nm and average mesopore diameter of 4.5 nm), the average pore diameter and mesopore diameter of the acidified biochar both decreased. This performance improvement was attributed to the introduction of additional oxygen-containing functional groups. At the same time, due to the modification process, the surface area and pore volume increased significantly, providing more reaction sites. This further verified the fact that phosphorylation was successful. In summary, the synthesis method adopted in the present invention produced phosphorus-doped porous biochar with a large specific surface area and a layered pore structure. It can be inferred that phytic acid not only catalyzed the conversion of biomass into biochar with a high surface area and good pore structure, but also participated in the construction of the final functionalized biochar.

[0043] Table 2 Basic physical properties of BC-400-0, BC-350-PO 4 , BC-400-PO 4 and BC-450-PO 4

[0044]

[0045] Experimental tests

[0046] Next, batch experiments were carried out to explore the uranium(VI) adsorption performance of the biochars prepared in each example and comparative example. As shown in Figure 5 (a), the uranium(VI) adsorption capacity of the biochar varied significantly with the different amounts of doped phosphorus (P). At a solid-liquid ratio of 0.06 g / L, the removal efficiency of uranium(VI) by the unacidified biochar BC-400-0 was only 41%. At the same time, the uranium(VI) adsorption capacity of the biochar was also affected by the carbonization temperature, showing a certain degree of temperature dependence. Biochars BC-350-PO 4 , BC-400-PO 4 and BC-450-PO 4The uranium removal efficiencies reached 93%, 98% and 85% respectively. These results indicate that the adsorption performance of porous phosphorus-doped biochar for uranium(VI) is significantly higher than that of pure biochar. This can be attributed to the following factors: First, the porous material introduces more abundant reaction sites through phosphorus doping. These sites promote the interaction between the material surface and uranium(VI) ions. Second, the uraniumophilic groups formed during the doping process effectively enhance the binding ability to uranium(VI), resulting in a significant increase in the adsorption efficiency.

[0047] Figure 5 (b) shows the effect of the solid-liquid ratio on the adsorption performance. With the increase in the concentration of BC-400-PO 4 , the removal rate of uranium(VI) gradually increases. When the solid-liquid ratio reaches 0.06 g / L, the removal rate of BC-400-PO 4 for uranium(VI) reaches 97.9%. However, with the further increase in the dose of BC-400-PO 4 , the uranium(VI) removal efficiency remains unchanged while the adsorption capacity decreases. Therefore, in subsequent experiments, 0.06 g / L was selected as the optimal adsorbent dose of BC-400-PO 4 .

[0048] When the pH value increases from 2 to 6, the uranium removal efficiency of BC-400-PO 4 increases from 45% to 99%, and the uranium adsorption efficiency gradually rises and reaches stability when the solution pH value reaches 7, as shown in Figure 5 (c). Figure 5 (d) shows the electrostatic interaction between the negatively charged adsorbent surface and positively and negatively charged uranium ions, including (UO 2 ) 2 (OH) 2 2+ , UO 2 (OH) + , UO 2 2+ , (UO 2 ) 3 (OH) 5+ , (UO 2 ) 3 (OH) 7- , (UO 2 )(OH) 3- . Phytic acid (PA) usually exists as a negatively charged substance in a wide pH range. This is due to the dissociation of -PO 4 , which enhances its hydrophilicity. The Zeta potential change trend of BC-400-PO 4 is as shown in Figure 5(e). When pH < 2, due to surface protonation and the inhibition of surface phosphate group ionization, BC-400-PO 4 has a positively charged surface. As the pH value increases from 2 to 7, the surface potential of the adsorbent gradually turns negative due to the ionization of phosphate groups. When the pH value increases from 2 to 5, the negative charges on the surface of BC-400-PO 4 attract the positive charges of (UO 2 ) 2 (OH) 2 2 +, UO 2 (OH)+, UO 2 2 +,(UO 2 ) 3 (OH) 5 +, resulting in electrostatic attraction between the surface of BC-400-PO 4 and U(VI). When the pH value further increases to 6, the negative charges on the surface of BC-400-PO 4 are enhanced, thus enhancing the electrostatic adsorption of uranium on BC-400-PO 4 , resulting in a rapid increase in uranium removal efficiency. When the pH value rises to 7, U(VI) mainly exists in a negatively charged state in the form of UO 2 (OH) 3- and so on. At the same time, the surface of BC-400-PO 4 is still negatively charged. Therefore, the electrostatic repulsion between the two increases, and then the adsorption efficiency decreases. These results indicate that the introduction of PA can effectively reduce the positive charges on the surface of biochar, which is beneficial to the absorption of U(VI) from aqueous solutions. Therefore, the adsorption of uranium on BC-400-PO 4 is more likely to occur under weakly acidic conditions, enabling the effective removal of uranium in the solution. The optimal solution pH value is 6. In addition, Figure 5 (f) clearly shows that in 0.50 mol / L NaCl solution, the uranium removal efficiency of BC-400-PO 4 can still reach 87.9%. This indicates that the ionic strength has little effect on the uranium adsorption capacity of the material.

[0049] Figure 6 (a) shows the relationship between uranium removal efficiency and adsorption time. The adsorption rate of BC-400-PO 4 for U(VI) is initially rapid and then slows down. Within the first 20 minutes, the adsorption rate increases sharply, decreases from 20 minutes to 60 minutes, and then changes in a stable and slow manner, reaching adsorption equilibrium within 200 minutes. The adsorption rate is controlled by the concentration of the adsorbate and the unoccupied adsorption sites. BC-400-PO 4The rapid adsorption of uranium within the initial 30 minutes can be attributed to the large number of unoccupied adsorption sites present in the solution. However, as the unoccupied adsorption sites are gradually consumed and the uranium concentration in the solution decreases, the adsorption rate will gradually decline. Therefore, 240 minutes was selected as the reaction time in subsequent experiments.

[0050] Pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models were used to fit the adsorption process of BC-400-PO 4 for uranium. As Figure 6 (b) shows, the adsorption of BC-400-PO 4 for uranium follows the PSO kinetic model. The correlation coefficient of the PSO kinetic model is 0.9954, which is much higher than that of the PFO kinetic model (R 2 = 0.9867). The adsorption kinetics is closer to the pseudo-second-order model, indicating that the adsorption process of BC-400-PO 4 for U(VI) is mainly dominated by chemisorption. Subsequently, the Langmuir and Freundlich isothermal adsorption models were used to fit and analyze the removal of U(VI). As can be seen from Figure 6 (c), compared with the Langmuir model (R 2 = 0.9135), the adsorption of BC-400-PO 4 for U(VI) is more in line with the Freundlich isothermal adsorption model (R 2 = 0.9979). The theoretical maximum adsorption capacity is 624.81 mg / g, which is very close to the experimental value (556.8 mg / g), indicating that the adsorption of uranium(VI) on BC-400-PO 4 occurs mainly through a multi-layer adsorption mode.

[0051] Temperature is also a key factor affecting the adsorption performance of adsorbents. The standard Gibbs free energy is an important parameter used to evaluate the thermodynamic potential for the formation of substances from elements in their most stable states under standard conditions. For a spontaneous reaction, the change in Gibbs free energy between reactants and products is negative, and the corresponding enthalpy value (ΔH) increases. The change in the standard Gibbs free energy of the reaction (ΔG) tends to become more negative at higher temperatures. The value of ΔS can indicate whether the adsorption process is controlled by the binding effect or the dissociation effect. For an endothermic adsorption process, the value of ΔH is positive, while for an exothermic adsorption process, the value of ΔH is negative. Figure 7 (a) shows the curve of BC-400-PO 4 removing U(VI) as a function of temperature. According to the results presented in the figure, as the temperature increases, the adsorption capacity of BC-400-PO 4 for U(VI) gradually increases. Using adsorption thermodynamics to fit BC-400-PO 4Data on the effect of U(VI) removal as a function of temperature ( Figure 7 (b)), and the relevant parameters were obtained, as shown in Table 3. The results showed that the enthalpy change ΔH was greater than 0, indicating that the adsorption of U(VI) by BC-400-PO 4 was endothermic. The entropy change ΔS was greater than 0, indicating that the reaction was spontaneous. ΔG was less than 0, indicating that the reaction proceeded in the forward direction. In the forward reaction, as the temperature increased, heating could promote the reaction. Therefore, the results showed that the adsorption of U(VI) by BC-400-PO 4 was a spontaneous and endothermic reaction.

[0052] Table 3 Thermodynamic fitting data for the absorption of U(VI) by BC-400-PO 4 and BC-400-0

[0053]

[0054] Actual uranium(VI)-containing wastewater represents a complex environment in which many heavy metal ions coexist. Therefore, to study the selective adsorption ability of BC-400-PO 4 for uranium(VI), Ca 2+ , Mg 2+ , Cu 2+ , Cd 2+ , Mn 2+ and Zn 2+ were selected for interference ion selectivity experiments, and the concentration ratio of these ions to uranium(VI) was 1:1. As Figure 7 (c) shows, even in a complex ionic environment, BC-400-PO 4 still showed excellent removal effect on uranium(VI). The significant selectivity of BC-400-PO 4 for uranium(VI) strongly indicated that the synergistic effect between -PO 4 and BC-400-PO 4 could enhance the specific selectivity for uranium(VI) more effectively than the individual biochar components, thus demonstrating that BC-400-PO 4 had good selectivity. Slight interference of Cu 2+ was observed, which might be due to the formation of copper phosphate between the surface phosphate groups and copper ions. However, the Q e value of uranium(VI) was much higher than that of other competing metal ions.

[0055] Reusability is an important indicator for evaluating the practical application of new adsorbents. Therefore, BC-400-PO 4As an adsorbent, the reusability of phosphorus-doped porous biochar was investigated. The regeneration of the adsorbent was accomplished by washing the saturated adsorbent with 0.1 mol / L hydrochloric acid solution. During this process, the adsorbed uranium(VI) was released from the adsorption sites, thus regenerating the adsorbent. As Figure 7 (d) shows, BC-400-PO 4 had a uranium(VI) desorption rate of nearly 100% after the first use, meaning that almost all of the adsorbed uranium had been released from BC-400-PO 4 . In addition, BC-400-PO 4 could undergo at least 5 adsorption-desorption cycles without reducing the desorption efficiency and adsorption efficiency. Five consecutive adsorption-desorption cycles could regenerate BC-400-PO 4 -U, achieving a uranium removal efficiency of 90.6% and a desorption efficiency of 91.9%. This indicates that the surface structure and properties of BC-400-PO 4 were stable and not easily damaged. Therefore, BC-400-PO 4 exhibited good reusability and economic practicality, which was beneficial for its application in the actual environment, reflecting excellent environmental friendliness and economic benefits.

[0056] Through dynamic adsorption experiments on a fixed-bed column, the potential application of BC-400-PO 4 in treating uranium-containing nuclear wastewater was verified. The actual wastewater came from a tailings wastewater treatment plant with a pH value of 5.8. As Figure 8 (a) and 8(b) show, a fixed-bed column device was used to treat the actual low-concentration uranium wastewater. 0.12 g of the adsorbent was used, and the flow rate of the peristaltic pump was set at 1.5 mL / min. The experimental results demonstrated its remarkable adsorption efficiency. Specifically, when treating an 8 L wastewater sample, the U(VI) concentration in the solution was effectively reduced from 0.456 mg / L to 0.082 mg / L. In addition, the filtration continued until the wastewater volume reached 10 L, and the U(VI) concentration in the wastewater tended to be stable without significant fluctuations. This phenomenon indicated that the BC-400-PO 4 adsorbent had reached its saturated adsorption capacity. It could be easily regenerated by eluting with diluted hydrochloric acid (0.1 M) and could be directly used for the next adsorption cycle. These results show that phosphorus-doped porous biochar has good potential in the practical application of treating uranium-containing nuclear wastewater.

[0057] Next, SEM, FT-IR, and XPS were used to study the adsorption mechanism of uranium on phosphorus-doped porous biochar. As Figure 9 (a) shows, after uranium adsorption, BC-400-PO 4 (BC-400-PO 4In the SEM mapping image analysis of BC-400-PO(-U), the distributions of C, O, P, and U elements are uniform. On the other hand, in the FT-IR spectrum of BC-400-PO 4 -U, a new peak is observed at 910 cm-1( Figure 9 (b)), which is attributed to the O=U=O stretching vibration. In addition, the XPS survey spectrum of BC-400-PO 4 -U shows a strong U 4f signal, as Figure 9 (c) shows. Meanwhile, the high-resolution U 4f XPS spectrum of BC-400-PO 4 -U shows signals of U(VI) element at binding energies of 393.03 eV (U 4f5 / 2) and 382.14 eV (U 4f7 / 2), as Figure 9 (d) shows, confirming that uranium is adsorbed on the surface of BC-400-PO 4 . The high-resolution O 1s XPS spectrum of BC-400-PO 4 -U shows a new peak at a binding energy of 530.03 eV, which is attributed to the U=O bond, as Figure 9 (f) shows. These results verify the efficient adsorption of uranium on BC-400-PO4.

[0058] Based on the specific changes in the FT-IR and XPS spectra of BC-400-PO 4 before and after uranium adsorption, the specific adsorption mechanism can be analyzed. Specifically, the FT-IR spectrum of BC-400-PO 4 -U shows that the stretching vibration peaks of P-O and P=O shift from 1030 cm-1 and 1178 cm-1 to 1031 cm-1 and 1203 cm-1 respectively, as Figure 9 (b) shows. The blue shift of the P-O stretching frequency indicates that when uranium is adsorbed on BC-400-PO 4 , the electron density of the P-O and P=O bonds increases. This result indicates that the ionization of the P-O-H group and the coordination of phosphate with uranyl occur during the adsorption process. On the other hand, the O 1s binding energies of C-O, P-O, and P=O species shift from 533.56 eV, 532.26 eV, and 531.63 eV to 532.32 eV, 531.50 eV, and 530.61 eV respectively. As for the P 2p peak, it can be observed that the peak located in phosphate shifts to pyrophosphate( Figure 9 (e) and 9(f)), and the binding energy of P 2p shifts from 133.39 eV (P2p 1 / 2 ) and 132.87 eV (P 2p 3 / 2 ) to 133.28 eV (P 2p 1 / 2 ) and 132.48 eV (P 2p 3 / 2 ). All these XPS results indicate that there is a chemical interaction between uranyl ions and -PO 4 grafted freely on the surface of BC-400-PO 4 groups.

[0059] Therefore, the possible mechanism of U(VI) adsorption can be inferred as follows: (1) Coordination occurs between U(VI) and the P=O oxygen atoms in BC-400-PO 4 by filling the empty orbitals of U(VI) with the lone pair electrons of the neutral P=O groups. (2) Electrostatic interaction occurs between the negatively charged surface and a specific form of U(VI) present in the aqueous medium.

[0060] To make it easier for those of ordinary skill in the art to understand the improvements of the present invention over the prior art, some of the drawings and descriptions of the present invention have been simplified, and the above embodiments are preferred implementation schemes of the present invention. In addition, the present invention can also be implemented in other ways. Any obvious replacement without departing from the concept of the technical solution of the present invention is within the protection scope of the present invention.

Claims

1. A method for preparing phytic acidified porous biochar material based on bamboo powder, characterized in that: The bamboo powder is mixed with a phytic acid solution, and then heated and dried to allow the phytic acid to react chemically with the bamboo powder, and then subjected to a high-temperature carbonization treatment to obtain the phytic acid-treated porous biochar material based on the bamboo powder.

2. A method for preparing phytic acidified porous biochar material based on bamboo powder, characterized in that: The specific steps include: (1) Raw material selection and pretreatment: bamboo powder is selected as the basic raw material, and it is crushed and sieved to obtain bamboo powder with uniform particle size; (2) Activation modification: The pretreated bamboo powder is mixed with a phytic acid solution, and then immersed and stirred to allow the phytic acid to fully penetrate and adsorb on the surface of the bamboo powder. The phytic acid and the bamboo powder are then heated and dried to allow a chemical reaction to occur, thereby forming a phytic acid-treated porous biochar material. (3) High temperature synthesis: The obtained phytic acid porous biochar material is carbonized under high temperature conditions to obtain the phytic acid porous biochar material based on bamboo powder.

3. The method for preparing the phytated porous biochar material based on bamboo powder according to claim 2, characterized in that: In step (1), high-quality bamboo is selected as the basic raw material, and the bamboo is cut and crushed to obtain fine bamboo powder. The bamboo powder is then dried at 80° C. to a constant weight to ensure that the moisture is completely removed. The dried bamboo powder is then sieved to obtain bamboo powder with uniform particle size.

4. The method for preparing the phytated porous biochar material based on bamboo powder according to claim 2, characterized in that: In step (2), bamboo powder and 85% phytic acid solution are weighed and mixed in a mass ratio of 1:

2. The bamboo powder and the phytic acid solution are fully stirred to ensure that the two are completely blended. Then, the mixture is stirred at 25° C. at a speed of 180 rpm for 24 hours to ensure uniform mixing.

5. The method for preparing the phytic acidified porous biochar material based on bamboo powder according to claim 4, characterized in that: In step (2), the stirred mixture is dried at 80°C for 10 hours to further remove moisture, and then the dried mixture is transferred to a muffle furnace for pyrolysis under air-ventilated conditions, starting from room temperature and heated to a target temperature of 400°C at a heating rate of 5°C / min, and maintained at 400°C for 1 hour to ensure that the pyrolysis process is fully carried out.

6. The method for preparing the phytated porous biochar material based on bamboo powder according to claim 5, characterized in that: In step (2), after the pyrolysis is completed, the mixture is allowed to cool naturally to room temperature, the carbonized material is collected, and washed with ultrapure water to remove excess free acid and other inorganic substances. The washing process is continued until the pH value of the filtrate reaches 6-7.

7. The method for preparing the phytated porous biochar material based on bamboo powder according to claim 2, characterized in that: In step (3), the washed carbonized material is dried at 80° C., and the dried carbonized material is sieved again using an 80-mesh sieve to obtain the final phytic acid-treated porous biochar material based on bamboo powder.

8. A phytic acidified porous biochar material based on bamboo powder, characterized in that: The compound is prepared by the preparation method according to any one of claims 1 to 7.

9. An application of the phytated porous biochar material based on bamboo powder according to claim 8, characterized in that: Used to remove radioactive U(VI) from wastewater.

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