A lanthanum-iron bimetallic synergistically modified biochar-based composite material and a preparation method and application thereof

Abstract

This invention discloses a lanthanum-iron bimetallic synergistic modified biochar-based composite material, its preparation method, and its application, belonging to the field of wastewater treatment technology. This invention utilizes zinc chloride to pretreat livestock and poultry manure, followed by a single high-temperature calcination to obtain pore-forming modified biochar. Then, lanthanum and iron salts are loaded onto the biochar using an equal-volume impregnation method, followed by a second high-temperature calcination to obtain the lanthanum-iron bimetallic synergistic modified biochar-based composite material. Through the synergistic effect of zinc chloride pore-forming pretreatment, carbothermal reduction, and lanthanum / iron bimetallic induction, high-density, high-stability oxygen vacancies are generated on the surface and within the pores of the biochar. Simultaneously, the lanthanum-iron bimetallic material is anchored to the carbon framework via Fe-O-C and La-O-C chemical bonds, forming a perovskite-type LaFeO3 crystal phase. This enhances the adsorption capacity, selectivity, and adsorption rate for phosphates, strengthens the mechanical strength and chemical stability of the material, and can be used for the efficient treatment of phosphorus-containing wastewater.

Description

Technical Field

[0001] This invention belongs to the technical field of wastewater treatment, specifically relating to a lanthanum-iron bimetallic synergistic modified biochar-based composite material, its preparation method, and its application. Background Technology

[0002] With the rapid development of industrial and agricultural production and the acceleration of urbanization, large amounts of nitrogen and phosphorus pollutants are discharged into natural water bodies, leading to increasingly serious eutrophication problems. Eutrophication can trigger a series of environmental disasters, including massive algal blooms, a sharp decline in dissolved oxygen, water quality deterioration, and the collapse of aquatic ecosystems. Among these, phosphate is usually the main limiting factor in eutrophication. Therefore, how to efficiently and economically remove phosphate from water has become a research hotspot in the fields of water treatment and environmental remediation.

[0003] Currently, the main methods for removing phosphates from water bodies include biological methods, chemical precipitation, and adsorption. Biological methods are complex to operate and sensitive to changes in water quality; chemical precipitation produces large amounts of chemical sludge, easily causing secondary pollution, and has high operating costs. In contrast, adsorption is considered one of the most promising phosphorus removal technologies due to its simple operation, low cost, recyclable adsorbents, and environmental friendliness.

[0004] Phosphorus exists primarily in water as phosphate anions. Its efficient removal relies mainly on sufficient positively charged sites, active metal centers, or exchangeable ligands on the adsorbent surface. This allows for the directional transfer of phosphate from the liquid phase to the solid phase through electrostatic attraction, surface complexation, or ligand exchange. Therefore, the key to adsorption technology lies in endowing the adsorbent surface with strong affinity and high selectivity for phosphate. Currently, among materials used for phosphorus removal, Guo et al. prepared FeBT and ZrBT adsorbents by modifying bentonite with iron and zirconium. Although zirconium-modified bentonite still exhibits some phosphate adsorption capacity under the interference of coexisting ions, its maximum phosphate adsorption capacity is only 4.29 mg P / g, indicating a generally low adsorption capacity. Chen et al., in their review, pointed out that while synthetic adsorbents such as polymer-based organic resins and metal-organic framework materials have high adsorption capacities and good selectivity, their high preparation costs and complex synthesis processes make them economically unfeasible for large-scale wastewater treatment. Therefore, there is an urgent need to develop novel phosphorus removal adsorbents that combine high adsorption capacity, good economic efficiency, and environmental friendliness.

[0005] In recent years, biochar has attracted widespread attention as a novel environmental functional material. Biochar is a carbon-rich solid material formed by the pyrolysis and carbonization of biomass (such as agricultural waste, forestry byproducts, and livestock manure) under oxygen-limited or anoxic conditions. It possesses advantages such as large specific surface area, well-developed pore structure, abundant surface functional groups, wide availability of raw materials, and low cost, showing great potential in soil improvement, carbon sequestration, and water pollutant removal. However, the surface of raw biochar is usually negatively charged and lacks functional sites specifically for adsorbing phosphates. Therefore, its adsorption capacity for anionic phosphates is often very limited, exhibiting low adsorption capacity and slow adsorption rate, making it difficult to meet the needs of practical applications. To address this deficiency, targeted modification of biochar through metal loading is an effective way to improve its adsorption performance. The reasons include: (1) the loaded metal ions can significantly improve the adsorption affinity and selectivity of phosphates through ligand exchange, electrostatic adsorption or the formation of internal spherical complexes; (2) the oxygen vacancies on the surface of metal oxides can serve as Lewis acid sites, and can specifically coordinate with phosphate ions through Lewis acid-base interactions, thereby enhancing the adsorption capacity. However, the metal oxide or hydroxide loading modification method for biochar has the problems of complex preparation process and low adsorption capacity. First, the traditional co-precipitation method directly loads metal oxides or hydroxides, which easily leads to severe aggregation of metal oxide or hydroxide particles on the surface and in the pores of biochar, reducing the exposure of effective adsorption sites and making it difficult to further improve the adsorption capacity. Second, in the conventional pyrolysis and metal loading process, the generation of oxygen vacancies is often random and insufficient.

[0006] Therefore, there is an urgent need to develop a novel biochar-based adsorbent that can both prevent metal particle aggregation and effectively regulate and increase oxygen vacancies. This is of great significance for breaking through existing technological bottlenecks and achieving efficient removal of phosphates. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a lanthanum-iron bimetallic synergistic modified biochar-based composite material, its preparation method and application, so as to solve the problems mentioned in the background art or achieve better technical effects.

[0008] In order to solve the above-mentioned technical problems, the inventors derived the technical solution of the present invention through practice and summary. The present invention discloses a lanthanum-iron bimetallic synergistic modified biochar-based composite material, wherein the composite material is composed of a modified biochar matrix and lanthanum-iron bimetallic oxide loaded on the surface.

[0009] The modified biochar matrix is ​​livestock and poultry manure biochar modified by zinc chloride pore-forming.

[0010] The lanthanum-iron bimetallic oxide is anchored to the surface and pores of the biochar carbon framework by Fe-OC and La-OC chemical bonding, forming a perovskite-type LaFeO3 crystal phase.

[0011] The molar ratio of lanthanum to iron in the composite material is 1~2:1~4.

[0012] Furthermore, the molar ratio of lanthanum to iron in the composite material is 1:3.

[0013] Furthermore, in any of the above-mentioned methods for preparing lanthanum-iron bimetallic synergistic modified biochar-based composite materials, a high-density and high-stability oxygen vacancies are generated on the surface and in the pores of biochar through the synergistic effect of zinc chloride pore-forming pretreatment, carbothermal reduction, and lanthanum and iron bimetallic induction. At the same time, lanthanum-iron bimetallic materials are anchored to the carbon skeleton by Fe-OC and La-OC chemical bonding, forming a lanthanum-iron bimetallic synergistic modified biochar-based composite material containing perovskite-type LaFeO3 crystal phase.

[0014] Furthermore, the preparation method of the lanthanum-iron bimetallic synergistic modified biochar-based composite material includes the following steps:

[0015] S1: After air-drying, removing impurities, and sieving livestock and poultry manure, pre-treatment with zinc chloride solution is carried out to obtain ZnBC precursor;

[0016] S2: The ZnBC precursor obtained in S1 is subjected to a first high-temperature calcination under an inert atmosphere to obtain the pyrolysis product;

[0017] S3: The pyrolysis product obtained in S2 is soaked in acid to remove residual zinc ions and ash, washed until neutral, dried, ground and sieved to obtain pore-forming modified biochar.

[0018] S4: Using the impregnation method, a mixed impregnation solution of lanthanum salt and iron salt is prepared based on the saturated water absorption rate of the pore-forming modified biochar obtained in S3. The impregnation solution is added to the pore-forming modified biochar to ensure that the solution is completely absorbed. After aging, lanthanum and iron-loaded modified biochar is obtained.

[0019] S5: After drying the lanthanum and iron-loaded modified biochar obtained in S4, it is subjected to a second high-temperature calcination under an inert atmosphere. After cooling, the lanthanum-iron bimetallic synergistic modified biochar-based composite material is obtained.

[0020] Furthermore, in S1, the concentration of the zinc chloride solution is 1~3 mol / L, and the liquid-to-solid ratio is 3~8:1 mL / g.

[0021] Furthermore, in S2 and S5, the inert atmosphere is nitrogen or argon, and the flow rate is 30~100mL / min; the heating rate of the first high-temperature calcination and the second high-temperature calcination is 3~10℃ / min, the calcination temperature is 500~700℃, and the holding time is 1~4h.

[0022] Furthermore, in S4, the lanthanum salt is lanthanum nitrate hexahydrate, and the iron salt is ferric chloride hexahydrate; the total cation concentration in the mixed impregnation solution is 0.5~2M.

[0023] Furthermore, the application of any of the above-described lanthanum-iron bimetallic synergistic modified biochar-based composite materials in the removal of phosphates from water.

[0024] Furthermore, the application of the lanthanum-iron bimetallic synergistic modified biochar-based composite material in the removal of phosphate from water involves adding the composite material to phosphate-containing wastewater and performing adsorption by stirring or shaking under conditions of pH=4~10 and temperature of 15~45℃.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) The present invention first uses zinc chloride to pretreat animal manure (such as cow manure). The biochar formed by calcining the animal manure after zinc chloride modification can significantly increase the oxygen-containing functional groups on the biochar and expand the specific surface area of ​​the biochar. Then, lanthanum / iron metal elements are introduced by equal volume impregnation to change the surface negative charge characteristics of the biochar, thereby significantly improving the ability to capture phosphate ions through electrostatic attraction.

[0027] (2) The present invention uses an equal-volume impregnation method to replace the traditional co-precipitation method. First, the saturated water absorption rate of zinc chloride modified biochar is determined. Then, the volume of metal salt solution that is just completely absorbed by the biochar is precisely prepared according to the water absorption rate. The impregnation solution is evenly sprayed on the surface of the biochar so that the metal ions are always constrained in the pore structure of the biochar during the drying and calcination process, avoiding migration and agglomeration caused by excessive solvent. This is conducive to the high dispersion of lanthanum / iron bimetallic oxide on the surface of biochar, thereby introducing more positively charged adsorption sites on the surface of biochar and enhancing the adsorption capacity of biochar for phosphate.

[0028] (3) In this invention, the biomass is first pretreated by impregnation with zinc chloride solution combined with high-temperature calcination in an inert atmosphere. On the one hand, zinc chloride induces the development of the pore structure of biochar, and on the other hand, the oxygen-containing functional groups remaining after pyrolysis provide an oxygen source for oxygen vacancies. Secondly, lanthanum / iron metal salt precursors are loaded onto the surface of modified biochar and composite materials are synthesized by secondary high-temperature calcination. During the synthesis process, the carbothermic reduction of metal oxides is achieved by utilizing the reducing properties of the biochar carbon matrix, and lattice oxygen is removed to form oxygen vacancies. At the same time, by means of the electronic interaction between lanthanum and iron, the valence state transition of iron ions and lattice distortion induce a large number of interfacial oxygen vacancies, and lanthanum can effectively inhibit iron agglomeration, significantly improving the density and stability of oxygen vacancies.

[0029] (4) The core of the oxygen vacancy generation in this invention is the synergistic effect of zinc chloride modification pretreatment, biochar carbothermal reduction, and lanthanum / iron bimetal induction: The well-developed channels and oxygen-containing functional groups formed in the biochar after zinc chloride modification pretreatment provide a dense reaction interface for the carbothermal reduction stage, making the lanthanum / iron bimetal precursor highly dispersed in the channel, strengthening the contact between the carbon matrix and the metal oxide, and reacting with oxygen in the adjacent metal oxide lattice, such as hydroxyl oxygen-containing functional groups combining with the oxygen in the adjacent metal oxide lattice and removing it in the form of water molecules, thereby generating oxygen vacancies in the lattice. During the carbothermal reduction process, the electronic transition of iron ions and the lattice distortion of iron oxides are fully excited, promoting the reaction process of adjacent oxygen-containing functional groups in the carbon matrix to capture lattice oxygen in the iron oxide (removed in the form of water molecules), thereby inducing a large number of interfacial oxygen vacancies at the bimetal-carbon interface; at the same time, the unique electronic structure of lanthanum inhibits iron agglomeration throughout the carbothermal reduction and oxygen vacancy generation process, so that the lanthanum-iron bimetal remains in a highly dispersed state. Compared with other methods, this method generates high oxygen vacancy density and strong stability, has a simple process, does not require the addition of additional reducing agents or other reagents, and greatly reduces costs.

[0030] (5) By loading lanthanum salt and iron salt, the present invention utilizes the synergistic anchoring and enhancement effect of lanthanum oxide and iron oxide on the carbon skeleton of biochar (Fe-OC and La-OC double chemical bonding), which significantly improves the mechanical strength and chemical stability of biochar and extends the effective service life of the adsorbent. Attached Figure Description

[0031] Figure 1 This is a process flow diagram for preparing the lanthanum-iron bimetallic synergistic modified biochar-based composite material of the present invention;

[0032] Figure 2 The image shows the XRD pattern of the lanthanum-iron bimetallic synergistic modified biochar-based composite material of the present invention. Detailed Implementation

[0033] To make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to specific examples.

[0034] Unless otherwise specified, all raw materials or reagents used in the following examples are commercially available products.

[0035] A method for preparing a lanthanum-iron bimetallic synergistic modified biochar-based composite material, such as... Figure 1 As shown, the steps are as follows:

[0036] (1) Air dry the livestock and poultry manure (such as cow manure) naturally, remove visible impurities, and pass it through a 100-mesh sieve for later use;

[0037] (2) Add a 2 mol / L ZnCl2 solution to the livestock and poultry manure obtained in step (1) at a liquid-to-solid ratio of 5:1 (mL / g), stir magnetically for 2 h, sonicate for 30 min, then let the mixture stand for 24 h, and then place it in a vacuum drying oven at 60 °C to dry to constant weight to obtain ZnBC precursor.

[0038] This step uses zinc chloride to create pores in biochar, and then uses a vacuum filtration method to determine its saturated water absorption rate in order to determine the volume of the metal salt solution to be used for modification. This avoids problems such as metal aggregation, reduction of active sites, and high reagent costs caused by excessive metal salts in conventional volume impregnation modification.

[0039] Determination of saturated water absorption rate by vacuum filtration: After drying the pore-modified biochar to constant weight, accurately weigh 5g, recorded as m1, and place it in a beaker. Add pure water to soak it, ensuring the liquid level is at least 3cm above the biochar. Stir with a glass rod until all the biochar is submerged in the water, then place it in a vacuum drying oven. Evacuate to -0.09 MPa and maintain for 30 minutes to use negative pressure to encourage water molecules to enter the micropores. After restoring to normal pressure, soak for another 2 hours. Then, place qualitative filter paper in a Buchner funnel, moisten it with a small amount of water, and turn on the vacuum pump... Adjust the pressure to -0.01~-0.02MPa to ensure the filter paper adheres tightly. Transfer the saturated biochar along with the supernatant water into the funnel. Rinse the beaker with a small amount of water and transfer the water in. Maintain this vacuum level and filter until no more droplets fall continuously from the neck of the funnel. Remove the biochar and weigh it to obtain a saturated wet weight of 14.86g, which is recorded as m2. The saturated water absorption rate is calculated as (m2-m1) / m1×100%, which is equal to 1.97g·H2O / g·C. Take 2g·H2O / g·C, or it can be written as 2mL / g.

[0040] (3) The ZnBC precursor obtained in step (2) was placed in a tube furnace under a nitrogen atmosphere for calcination. The nitrogen flow rate was 50 mL / min, and the temperature was increased to 600℃ at a rate of 5℃ / min. The pyrolysis was carried out at a constant temperature for 2~3 h, and then naturally cooled to room temperature to obtain the pyrolysis product.

[0041] (4) Soak the pyrolysis product obtained in step (3) in 1 mol / L hydrochloric acid solution for 2-3 hours to remove residual Zn. 2+ The ash was then washed with pure water until neutral, dried under vacuum at 60°C to constant weight, and ground through a 100-mesh sieve to obtain pore-shaped modified biochar.

[0042] (Biomasses are pretreated by impregnation with zinc chloride solution combined with high-temperature calcination in an inert atmosphere. On the one hand, zinc chloride induces the development of biochar pore structure, and on the other hand, the oxygen-containing functional groups remaining after pyrolysis provide an oxygen source for oxygen vacancies.)

[0043] (5) Different proportions of La / Fe were loaded onto the pore-forming modified biochar obtained in step (4) using the equal-volume impregnation method; specifically:

[0044] Based on the saturated water absorption rate of biochar (2 mL / g), calculate the required volume of impregnation solution according to the biochar mass (volume = biochar mass × 2 mL / g); prepare a mixed solution with a total cation concentration of 1 M; calculate the amounts of lanthanum nitrate hexahydrate and ferric chloride hexahydrate according to the set La / Fe molar ratio (1~2:1~4); dissolve them in pure water and bring the volume to the calculated volume; add the prepared impregnation solution dropwise to the biochar while stirring rapidly until the mixture is homogeneous and the solution is completely absorbed by the biochar; age at room temperature for 12~24 h.

[0045] (6) The lanthanum / iron-loaded modified biochar obtained by impregnation in step (5) is dried and then placed in a tube furnace. The nitrogen flow rate is 50 mL / min, and the temperature is raised to 600℃ at a rate of 5℃ / min. The temperature is kept constant for 2 hours for pyrolysis and secondary high-temperature calcination. After natural cooling, the lanthanum-iron bimetallic synergistic modified biochar-based composite material is obtained.

[0046] (By utilizing the reducing properties of biochar carbon matrix, carbothermic reduction of metal oxides was achieved, resulting in the removal of lattice oxygen and the formation of oxygen vacancies; simultaneously, through the electronic interaction between lanthanum and iron, the valence state transition of iron ions and lattice distortion induced the generation of a large number of interfacial oxygen vacancies, and lanthanum can effectively inhibit iron agglomeration, significantly improving the density and stability of oxygen vacancies;)

[0047] This invention utilizes the synergistic effect of zinc chloride modification pretreatment, biochar carbothermal reduction, and lanthanum / iron bimetallic induction to generate oxygen vacancy density with strong stability. The process is simple, requires no additional reducing agents, and significantly reduces costs. Simultaneously, the synergistic anchoring and strengthening effect of lanthanum oxide and iron oxide on the carbon skeleton of biochar (Fe-OC and La-OC double chemical bonding) significantly improves the mechanical strength and chemical stability of biochar, extending the effective service life of the entire composite material system.

[0048] Example 1

[0049] A method for preparing a lanthanum-iron bimetallic synergistic modified biochar-based composite material, comprising the following steps:

[0050] (1) Air dry the livestock and poultry manure (such as cow manure) naturally, remove visible impurities, and pass it through a 100-mesh sieve for later use;

[0051] (2) Add a 2 mol / L ZnCl2 solution to the livestock and poultry manure obtained in step (1) at a liquid-to-solid ratio of 5:1 (mL / g), stir magnetically for 2 h, sonicate for 30 min, then let the mixture stand for 24 h, and dry it in a vacuum drying oven at 60 °C to constant weight to obtain ZnBC precursor.

[0052] (3) The ZnBC precursor obtained in step (2) was placed in a tube furnace under a nitrogen atmosphere for calcination. The nitrogen flow rate was 50 mL / min, the temperature was increased to 600℃ at a rate of 5℃ / min, and the pyrolysis was carried out at a constant temperature for 2 hours. The product was then naturally cooled to room temperature to obtain the pyrolysis product.

[0053] (4) Soak the pyrolysis product obtained in step (3) in 1 mol / L hydrochloric acid solution for 2 h to remove residual Zn. 2+ The ash was removed, and the mixture was washed with pure water until neutral. It was then vacuum dried at 60°C to constant weight and ground through a 100-mesh sieve to obtain modified biochar.

[0054] (5) Load La / Fe onto the modified biochar obtained in step (4) using the equal volume impregnation method; specifically: weigh 10g of the modified biochar obtained in step (4), and calculate the required impregnation liquid volume as 20mL based on its saturated water absorption rate of 2mL / g; weigh the corresponding mass of lanthanum nitrate hexahydrate (La(NO3)3·6H2O) and ferric chloride hexahydrate (FeCl3·6H2O) according to the total cation concentration of 1M and the La / Fe molar ratio of 1:1, dissolve them in pure water and make up to 20 mL; add the prepared impregnation liquid dropwise to the biochar, while stirring rapidly until the solution is completely absorbed and mixed evenly, and age at room temperature for 12~24h;

[0055] (6) The lanthanum / iron-loaded modified biochar obtained by impregnation in step (5) is dried and then placed in a tube furnace. The nitrogen flow rate is 50 mL / min, and the temperature is raised to 600℃ at a rate of 5℃ / min. The temperature is kept constant for 2 hours for pyrolysis and secondary high-temperature calcination. After natural cooling, the lanthanum-iron bimetallic synergistic modified biochar-based composite material is obtained.

[0056] Example 2

[0057] Unlike Example 1, only the La / Fe molar ratio of the impregnation solution in step (5) is changed to 1:2, and the other steps are the same as in Example 1.

[0058] Example 3

[0059] Unlike Example 1, only the La / Fe molar ratio of the impregnation solution in step (5) is changed to 1:3, and the other steps are the same as in Example 1.

[0060] Example 4

[0061] Unlike Example 1, only the La / Fe molar ratio of the impregnation solution in step (5) is changed to 1:4, and the other steps are the same as in Example 1.

[0062] Example 5

[0063] Unlike Example 1, only the La / Fe molar ratio of the impregnation solution in step (5) is changed to 2:1, and the other steps are the same as in Example 1.

[0064] The XRD pattern of the lanthanum-iron bimetallic synergistic modified biochar-based composite material prepared in the above embodiments is shown in the figure. Figure 2 As shown in the figure, before the adsorption reaction, the La / Fe@BC composite materials with different molar ratios exhibit obvious characteristic diffraction peaks at positions such as 2θ=23.1°, 32.5°, 40.1°, 46.7°, and 58.2°. This is in high agreement with the standard PDF card (PDF#75-0439) of LaFeO3, indicating that La and Fe were successfully loaded onto the biochar matrix during pyrolysis and formed a stable perovskite oxide crystal phase (LaFeO3).

[0065] Comparative Example 1

[0066] Unlike Example 3, the biochar was not pretreated with zinc chloride and was directly loaded with lanthanum / iron metal salt precursors. The composite material was then synthesized through a second high-temperature calcination.

[0067] The specific preparation process is as follows:

[0068] (1) Air dry the livestock and poultry manure (such as cow manure) naturally, remove visible impurities, and pass it through a 100-mesh sieve for later use;

[0069] (2) The cow dung in step (1) was placed in a tube furnace under a nitrogen atmosphere for calcination. The nitrogen flow rate was 50 mL / min, and the temperature was raised to 600℃ at a rate of 5℃ / min. The pyrolysis was carried out at a constant temperature for 2 hours and then naturally cooled to room temperature to obtain the pyrolysis product.

[0070] (3) The pyrolysis product obtained in step (2) was soaked in 1 mol / L hydrochloric acid solution for 2 h to remove ash, then washed with pure water until neutral, dried under vacuum at 60 °C to constant weight, and ground through a 100-mesh sieve to obtain biochar.

[0071] (4) La / Fe is loaded onto the biochar obtained in step (3) using the equal volume impregnation method. Specifically, 10g of biochar is weighed, and the required impregnation liquid volume is calculated to be 20mL based on its saturated water absorption rate of 2mL / g. According to the total cation concentration of 1M and the La / Fe molar ratio of 1:1, the corresponding masses of lanthanum nitrate hexahydrate (La(NO3)3·6H2O) and ferric chloride hexahydrate (FeCl3·6H2O) are weighed, dissolved in pure water and diluted to 20mL. The prepared impregnation liquid is added dropwise to the biochar, and the mixture is stirred rapidly until the solution is completely absorbed and mixed evenly. The mixture is aged at room temperature for 24h.

[0072] (5) The lanthanum / iron biochar obtained by impregnation in step (4) is dried and then placed in a tube furnace. The nitrogen flow rate is 50 mL / min, and the temperature is raised to 600℃ at a rate of 5℃ / min. The mixture is kept at a constant temperature for 2 hours and then naturally cooled to room temperature to obtain the lanthanum-iron bimetallic synergistic modified biochar-based composite material.

[0073] Comparative Example 2

[0074] Unlike Example 3, lanthanum / iron bimetallic synergistic modification was not used (only lanthanum was used for loading, and the corresponding iron loading was 0).

[0075] The specific preparation process is as follows:

[0076] (1) Air dry the livestock and poultry manure (such as cow manure) naturally, remove visible impurities, and pass it through a 100-mesh sieve for later use;

[0077] (2) Add a 2 mol / L ZnCl2 solution to the livestock and poultry manure obtained in step (1) at a liquid-to-solid ratio of 5:1 (mL / g), stir magnetically for 2 h, sonicate for 30 min, let the mixture stand for 24 h, and then dry it in a vacuum drying oven at 60 °C to constant weight to obtain ZnBC precursor.

[0078] (3) The precursor obtained in step (2) was placed in a tube furnace under a nitrogen atmosphere for calcination. The nitrogen flow rate was 50 mL / min, the temperature was increased to 600℃ at a rate of 5℃ / min, and the pyrolysis was carried out at a constant temperature for 2 hours. The product was then naturally cooled to room temperature to obtain the pyrolysis product.

[0079] (4) Soak the pyrolysis product obtained in step (3) in 1 mol / L hydrochloric acid solution for 2 h to remove residual Zn. 2+ The ash was removed, and the mixture was washed with pure water until neutral. It was then vacuum dried at 60°C to constant weight and ground through a 100-mesh sieve to obtain modified biochar.

[0080] (5) Load La onto the biochar obtained in step (4) using the equal volume impregnation method; specifically: weigh 10g of biochar, calculate the required impregnation liquid volume as 20mL based on its saturated water absorption rate of 2mL / g; weigh the corresponding mass of lanthanum nitrate hexahydrate (La(NO3)3·6H2O) according to the total cation concentration of 1M, dissolve it in pure water and make up to 20mL; add the prepared impregnation liquid dropwise to the biochar, while stirring rapidly until the solution is completely absorbed and mixed evenly, and age at room temperature for 12~24h;

[0081] (6) The lanthanum-loaded biochar obtained by impregnation in step (5) is dried and then placed in a tube furnace. The nitrogen flow rate is 50 mL / min, and the temperature is raised to 600℃ at a rate of 5℃ / min. The mixture is kept at a constant temperature for 2 hours and then naturally cooled to room temperature to obtain the lanthanum-modified biochar-based composite material.

[0082] Comparative Example 3

[0083] Unlike the best embodiment, lanthanum / iron bimetallic synergistic modification was not used (only iron was used for loading).

[0084] The specific preparation process is as follows:

[0085] (1) Air dry the livestock and poultry manure (such as cow manure) naturally, remove visible impurities, and pass it through a 100-mesh sieve for later use;

[0086] (2) Add a 2 mol / L ZnCl2 solution to the livestock and poultry manure obtained in step (1) at a liquid-to-solid ratio of 5:1 (mL / g), stir magnetically for 2 h, sonicate for 30 min, let the mixture stand for 24 h, and then dry it in a vacuum drying oven at 60 °C to constant weight to obtain ZnBC precursor.

[0087] (3) The precursor obtained in step (2) was placed in a tube furnace under a nitrogen atmosphere for calcination. The nitrogen flow rate was 50 mL / min, the temperature was increased to 600℃ at a rate of 5℃ / min, and the pyrolysis was carried out at a constant temperature for 2 hours. The product was then naturally cooled to room temperature to obtain the pyrolysis product.

[0088] (4) The pyrolysis product obtained in step (3) was soaked in 1 mol / L hydrochloric acid solution for 2 h to remove residual Zn2+ and ash, then washed with pure water until neutral, dried under vacuum at 60℃ to constant weight, and ground through a 100-mesh sieve to obtain modified biochar.

[0089] (5) Load Fe onto the biochar obtained in step (4) using the equal volume impregnation method; specifically: weigh 10g of biochar, calculate the required impregnation liquid volume as 20mL based on its saturated water absorption rate of 2mL / g; weigh the corresponding mass of ferric chloride hexahydrate (FeCl3·6H2O) according to the total cation concentration of 1M, dissolve it in pure water and make up to 20mL; add the prepared impregnation liquid dropwise to the biochar, while stirring rapidly until the solution is completely absorbed and mixed evenly, and age at room temperature for 12~24h;

[0090] (6) The iron-loaded biochar obtained by impregnation in step (5) is dried and then placed in a tube furnace. The nitrogen flow rate is 50 mL / min, and the temperature is raised to 600℃ at a rate of 5℃ / min. The mixture is kept at a constant temperature for 2 hours and then naturally cooled to room temperature to obtain the iron-modified biochar-based composite material.

[0091] Comparative Example 4

[0092] Unlike the preferred embodiment, the strategy for lanthanum / iron bimetallic synergistic modification loading is changed, and the equal-volume impregnation method of the present invention is not used, but the traditional co-precipitation method is used instead.

[0093] The specific preparation process is as follows:

[0094] (1) Air dry the livestock and poultry manure (such as cow manure) naturally, remove visible impurities, and pass it through a 100-mesh sieve for later use;

[0095] (2) Add a 2 mol / L ZnCl2 solution to the livestock and poultry manure obtained in step (1) at a liquid-to-solid ratio of 5:1 (mL / g), stir magnetically for 2 h, sonicate for 30 min, let the mixture stand for 24 h, and then dry it in a vacuum drying oven at 60 °C to constant weight to obtain ZnBC precursor.

[0096] (3) The precursor obtained in step (2) was placed in a tube furnace under a nitrogen atmosphere for calcination. The nitrogen flow rate was 50 mL / min, the temperature was increased to 600℃ at a rate of 5℃ / min, and the pyrolysis was carried out at a constant temperature for 2 hours. The product was then naturally cooled to room temperature to obtain the pyrolysis product.

[0097] (4) Soak the pyrolysis product obtained in step (3) in 1 mol / L hydrochloric acid solution for 2 h to remove residual Zn. 2+ The ash was removed, and the mixture was washed with pure water until neutral. It was then vacuum dried at 60°C to constant weight and ground through a 100-mesh sieve to obtain modified biochar.

[0098] (5) Fe was loaded onto the biochar obtained in step (4) using the equal volume impregnation method. Specifically, 10 g of biochar was weighed and dispersed in 50 mL of pure water, and ultrasonically treated for 10 min to make it uniformly suspended. According to the total cation concentration of 1 M and the La / Fe molar ratio of 1:1, the corresponding masses of lanthanum nitrate hexahydrate (La(NO3)3·6H2O) and ferric chloride hexahydrate (FeCl3·6H2O) were weighed and dissolved in 50 mL of pure water to prepare a mixed salt solution. The salt solution was slowly added to the biochar suspension, and after stirring for 30 min, 1 M NaOH solution was added dropwise under vigorous stirring until the pH reached 10~11, generating La / Fe hydroxide coprecipitate. Stirring was continued for 1 h, and the mixture was aged at room temperature for 12 h. The precipitate was separated by centrifugation and washed with pure water until no Cl was found. - (Tested with AgNO3);

[0099] (6) The iron-loaded biochar obtained by impregnation in step (5) is dried and then placed in a tube furnace. The nitrogen flow rate is 50 mL / min, and the temperature is raised to 600℃ at a rate of 5℃ / min. The mixture is kept at a constant temperature for 2 hours and then naturally cooled to room temperature to obtain the iron-modified biochar-based composite material.

[0100] Example 6

[0101] The modified biochar-based composite materials prepared in Examples 1-5 and Comparative Examples 1-4 were used as adsorbents for the adsorption and removal of phosphate in waste liquid. The test method was as follows: the concentration of the remaining phosphate in the solution was determined by ammonium molybdate spectrophotometry to calculate the adsorption amount.

[0102] First, prepare several 100 mL phosphate aqueous solutions with an initial concentration of 50 mg / L. Take 0.2 g of the composite materials prepared in Examples 1-5 and Comparative Examples 1-4 and add them to the corresponding phosphate aqueous solutions. The reaction conditions are 25℃, pH=7±0.1, and shaking and mixing at 150 rpm. Samples are taken at 5, 10, 20, 30, 60, 90, 120, 180 and 240 minutes, respectively, and passed through a 0.45 μm needle filter. Then, the phosphate concentration is measured. The test results are shown in Table 1 below.

[0103] Table 1. Composite materials prepared in Examples 1-5 and Comparative Examples 1-4

[0104] The efficiency of phosphate adsorption at different times

[0105]

[0106] The adsorption kinetics results in Table 1 show that Example 3 (La / Fe = 1:3) exhibits the best bimetallic synergistic effect, with Fe... 3+ La enhances pore structure stability and provides some active sites. 3+By enhancing phosphate binding through specific coordination, the two work synergistically to promote intraparticle diffusion, resulting in the maximum adsorption capacity. In contrast, in the comparative example, the lack of ZnCl2 activation led to poor internal pore connectivity, the lack of synergistic effect from single-metal modification, and the tendency of co-precipitation to clog pores, all of which significantly inhibited intraparticle diffusion, resulting in a decrease in the equilibrium removal rate.

[0107] Example 7

[0108] 0.2g of the composite materials prepared in Examples 1-5 and Comparative Examples 1-4 were added to 100mL of phosphorus solutions with concentrations of 10, 20, 30, 40, 50, 80, 100 and 150mg / L, respectively. The mixture was shaken and mixed at 25℃, pH=7±0.1 and 150rpm for 1440 minutes. Samples were then taken, passed through a 0.45μm needle filter, and the phosphate concentration was measured. The test results are shown in Table 2 below.

[0109] Table 2. Composite materials prepared in Examples 1-5 and Comparative Examples 1-4

[0110] Adsorption efficiency in phosphate solutions with different initial concentrations

[0111]

[0112] The adsorption isotherm results in Table 2 show that Example 3 (La / Fe = 1:3) exhibits a significantly higher adsorption capacity for phosphate than other examples and all comparative examples, reaching an equilibrium adsorption capacity of 40.46 mg / g at an initial concentration of 150 mg / L, making it the optimal material ratio. Compared to other examples deviating from the 1:3 ratio, the Fe in Example 3... 3+ The introduction of [a specific ingredient] not only optimized the pore structure of biochar and increased its specific surface area and oxygen vacancy density, but also [achieved better results] through interaction with La. 3+ The synergistic effect of the two metals enhanced the coordination ability of surface hydroxyl groups and the full exposure of phosphate-specific binding sites. However, excessive La easily caused agglomeration that obscured active sites, and excessive Fe competed for adsorption sites, both weakening the bimetallic synergistic adsorption effect and leading to a decline in the performance of the other examples. Compared with the comparative examples, Example 3, after ZnCl2 activation and equal-volume impregnation, not only solved the problems of low porosity and insufficient exposure of active sites in the unactivated material (Comparative Example 1), but also overcame the defects of lack of synergistic effect and weak phosphate binding ability in the single-metal modified materials (Comparative Examples 2 and 3), while avoiding the disadvantages of metal agglomeration, pore blockage and poor stability of active sites in the co-precipitation method (Comparative Example 4), thus exhibiting the best adsorption performance. Figure 2As can be seen, after the adsorption of phosphate (La / Fe@BC-1 / 3+P), several typical new diffraction peaks were observed in the figure. Specifically, the diffraction peaks located near 21.5°, 26.8°, 28.5°, and 30.9° are attributed to the formation of LaPO4 (PDF#46-1326); at the same time, characteristic diffraction peaks of FePO4 (PDF#30-0659) appeared at positions such as 36.7° and 39.1°, indicating that a chemical precipitation reaction occurred, that is, phosphate compounds were formed in La / Fe@BC-1 / 3.

[0113] Example 8

[0114] 0.2g of the composite materials prepared in Examples 1-5 and Comparative Examples 1-4 were added to 100mL of phosphorus solutions with different initial concentrations. The solutions were shaken and mixed at 25℃, 35℃ and 45℃, pH=7±0.1 and 150rpm for 1440 minutes, respectively. Samples were then taken, passed through a 0.45μm needle filter, and the phosphate concentration was measured. The test results are shown in Tables 3 and 4 below.

[0115] Table 3. Adsorption efficiency of the composite materials prepared in Examples 1-5 and Comparative Examples 1-4 at 35°C

[0116]

[0117] Table 4. Adsorption efficiency of the composite materials prepared in Examples 1-5 and Comparative Examples 1-4 at 45°C.

[0118]

[0119] The thermodynamic experimental results in Tables 2, 3, and 4 show that the adsorption of phosphate by all materials is an endothermic process, and the adsorption capacity increases with increasing temperature. Example 3 (La / Fe = 1:3) exhibits the most significant temperature response, consistently demonstrating the best performance at all temperatures. Furthermore, the overall adsorption performance of the examples is significantly superior to the comparative examples. This is because the optimal bimetallic ratio in Example 3 constructs both an efficient mass transfer channel and provides highly active adsorption sites. Heating accelerates phosphate ion diffusion and enhances the endothermic coordination reaction between La / Fe and phosphate, resulting in the most significant performance improvement. Examples deviating from the optimal ratio and the comparative examples (unactivated, single-metal modified, and co-precipitated materials) show weaker temperature responses and limited adsorption performance improvements due to weak synergistic effects, high mass transfer resistance, or insufficient active sites.

[0120] Example 9

[0121] 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 and 5 g of the composite materials prepared in Examples 1-5 and Comparative Examples 1-4 were respectively added to 100 mL of a 50 mg / L phosphorus solution. The reaction conditions were 25 °C, pH=7±0.1, and shaking and mixing at 150 rpm for 1440 minutes. The mixture was then passed through a 0.45 μm needle filter, and the phosphate concentration was measured. The test results are shown in Table 5 below.

[0122] Table 5 Preparation of Examples 1-5 and Comparative Examples 1-4

[0123] Phosphate concentration of composite materials at different dosages

[0124]

[0125] The results of the dosage experiments in Table 5 show that the phosphate removal efficiency of all materials increases with increasing dosage, and then tends to stabilize. Example 3 (La / Fe=1:3) exhibits the best phosphate removal effect, achieving high efficiency even at low dosages, and its performance at all dosages is significantly better than other examples and comparative examples. This is because the optimal bimetallic ratio in Example 3 provides the material with a high density of active sites, providing sufficient phosphate binding sites even at low dosages, resulting in a rapid increase in removal rate with increasing dosage. In contrast, examples and comparative examples deviating from the optimal ratio have lower active site density or insufficient exposure, leading to slower improvement in removal efficiency and overall phosphate removal efficiency far lower than that of Example 3.

[0126] Example 10

[0127] 0.2 g of the composite material was added to 100 ml of phosphorus solutions with a concentration of 50 mg / L and pH values ​​of 3, 4, 5, 6, 7, 8, 9, 10 and 11. The reaction conditions were 25 °C, pH=7±0.1, and shaking and mixing at 150 rpm for 1440 minutes. The mixture was then passed through a 0.45 μm needle filter, and the phosphate concentration was measured. The test results are shown in Table 6 below.

[0128] Table 6 Preparation of Examples 1-5 and Comparative Examples 1-4

[0129] Phosphate concentration of composite materials at different pH values

[0130]

[0131] The pH effect results in Table 6 show that the phosphate removal rate of all materials exhibits an optimal trend under neutral conditions and decreases under acidic and alkaline conditions, with the best adsorption performance at pH=7. Example 3 (La / Fe=1:3) demonstrated the best removal effect across the entire pH range, and its resistance to pH interference was significantly better than other examples and comparative examples. This is because the optimal bimetallic ratio in Example 3 endows the material with abundant surface hydroxyl sites and a moderate zero-charge point, which reduces H+ ions under acidic conditions. + The competitive adsorption further reduces the OH content in the alkaline environment. - The interference and the repulsion of phosphate by the surface negative charge can maintain high activity of adsorption sites over a wide pH range; however, the synergistic effect of the examples that deviate from the optimal ratio is weakened, the surface charge regulation ability is insufficient, and the performance degradation is more obvious under acid and alkaline conditions; the comparative examples have weak resistance to pH interference due to low density or insufficient exposure of active sites, and the overall phosphorus removal performance is poor.

[0132] Example 11

[0133] 0.2 g of the composite material was added to 100 mL of a 50 mg / L phosphorus solution, and Cl was added separately. - NO3 - SO4 2- CO3 2- The phosphate concentration of HA (humic acid) was set to 10, 20, 50, and 100 mg / L. The reaction conditions were 25℃, pH=7±0.1, and shaking and mixing at 150 rpm for 1440 minutes. The mixture was then passed through a 0.45 μm needle filter and the phosphate concentration was measured. The test results are shown in Tables 7-11 below.

[0134] Table 7 Preparation of Examples 1-5 and Comparative Examples 1-4

[0135] Composite materials with different concentrations of Cl - Adsorption efficiency under ion doping

[0136]

[0137] Table 8 Preparation of Examples 1-5 and Comparative Examples 1-4

[0138] Composite materials at different concentrations of NO3 - Adsorption efficiency under ion doping

[0139]

[0140] Table 9 Preparation of Examples 1-5 and Comparative Examples 1-4

[0141] Composite materials with different concentrations of SO4 2- Adsorption efficiency under ion doping

[0142]

[0143] Table 10 Preparation of Examples 1-5 and Comparative Examples 1-4

[0144] Composite materials at different concentrations of CO3 2- Adsorption efficiency under ion doping

[0145]

[0146] Table 11 Preparation of Examples 1-5 and Comparative Examples 1-4

[0147] Adsorption efficiency of composite materials under different concentrations of HA ion doping

[0148]

[0149] The experimental results of coexisting ions and humic acid (HA) in Tables 7-11 show that the phosphate adsorption performance of all materials decreases with increasing concentrations of coexisting ions and HA, with the interference intensity in the following order: CO3. 2- >HA>SO4 2- >Cl - NO3 - Example 3 (La / Fe=1:3) exhibited the best anti-interference capability. This is due to CO3... 2- It competes with phosphate for La / Fe active sites and readily forms precipitates with metal ions, thus exhibiting the strongest inhibition of specific adsorption; HA reduces adsorption performance through both surface complexation and pore blockage, with interference being secondary; SO4 2- Similar to phosphate structures, there is some competitive adsorption; while Cl - and NO3 - The competition with phosphate is the weakest, resulting in the least impact. The optimal bimetallic ratio in Example 3 endows the material with abundant specific La-P coordination sites, exhibiting strong repulsion against weakly competing ions, while the high density of active sites effectively buffers SO42-. 2- Competitive adsorption and pore-blocking effect of HA, only at high concentrations of CO3 2- Slight performance degradation occurred under certain conditions; the synergistic effect was weakened in examples deviating from the optimal ratio, and there were insufficient specific adsorption sites, which were affected by HA and SO4. 2- The interference was more pronounced; the comparative samples, due to their low active site density and high proportion of non-specific adsorption, had the weakest anti-interference ability, especially at high concentrations of CO3. 2- The performance degradation is most significant under HA conditions.

[0150] The iron-modified biochar-based composite material prepared in this invention exhibits significantly improved selective adsorption performance. By modifying biochar with a lanthanum / iron bimetallic compound, and utilizing the strong affinity of lanthanum for phosphate and the electronic regulation and structural optimization functions of iron, multi-metal synergistic specific adsorption sites are constructed on the biochar surface, significantly enhancing its selective adsorption of phosphorus. Iron doping alters the electronic structure of lanthanum, facilitating the formation of stable inner-sphere complexes between phosphate and lanthanum. Simultaneously, the introduction of iron significantly increases the porosity of the material, providing more active sites for phosphate mass transfer and binding.

[0151] Significantly enhanced adsorption capacity: Excessive volume impregnation (conventional method) easily leads to localized supersaturated solution precipitation, causing metal particle agglomeration in traditional modification. The equal-volume impregnation method uniformly disperses the metal salt solution within the pore space of the biochar. Therefore, it effectively reduces the agglomeration effect of metal particles in traditional biochar bimetallic modification, maximizing the exposure of effective active sites per unit mass of adsorbent and improving the adsorption capacity.

[0152] Enhanced Adsorption Activity: By designing a "pretreatment-impregnation-secondary calcination" process route and precisely controlling the pyrolysis atmosphere, a high concentration of oxygen vacancies was induced on the metal oxide surface, overcoming the uncontrollable state of random oxygen vacancy generation. This leads to the conclusion that oxygen vacancies, as highly active centers, significantly enhance the intrinsic affinity of individual adsorption sites for phosphate and their interaction with the electron cloud, achieving deep removal capabilities even in low-concentration phosphorus environments.

[0153] Structural durability and long service life: Zinc chloride pretreatment activates the carbon framework and promotes the intercalation of metals into the carbon matrix during secondary calcination. Simultaneously, high temperature induces the formation of robust La-OC and Fe-OC chemical bonds. Therefore, the relationship between the metal oxide and the support is no longer a simple physical deposition, but rather a chemically anchored integral structure. Consequently, this material possesses excellent mechanical strength to resist water erosion, significantly extending the effective replacement cycle of the adsorbent and reducing long-term operating costs.

Claims

1. A lanthanum-iron bimetallic synergistic modified biochar-based composite material, characterized in that, The composite material consists of a modified biochar matrix and lanthanum-iron bimetallic oxide supported on the surface; The modified biochar matrix is ​​animal fecal biochar modified by zinc chloride pore-forming. The lanthanum-iron bimetallic oxide is anchored to the surface and pores of the biochar carbon framework by Fe-OC and La-OC chemical bonding, forming a perovskite-type LaFeO3 crystal phase. The molar ratio of lanthanum to iron in the composite material is 1~2:1~4.

2. The lanthanum-iron bimetallic synergistic modified biochar-based composite material according to claim 1, characterized in that, The molar ratio of lanthanum to iron in the composite material is 1:

3.

3. A method for preparing the lanthanum-iron bimetallic synergistic modified biochar-based composite material as described in claim 1 or 2, characterized in that, Through the synergistic effect of zinc chloride pore-forming pretreatment, carbothermal reduction, and lanthanum-iron bimetallic induction, high-density and high-stability oxygen vacancies are generated on the surface and in the pores of biochar. At the same time, lanthanum-iron bimetallic compounds are anchored to the carbon skeleton by Fe-OC and La-OC chemical bonding, forming a lanthanum-iron bimetallic synergistic modified biochar-based composite material containing perovskite-type LaFeO3 crystal phase.

4. The preparation method of the lanthanum-iron bimetallic synergistic modified biochar-based composite material according to claim 3, characterized in that, The steps are as follows: S1: After air-drying, removing impurities, and sieving livestock and poultry manure, pre-treatment with zinc chloride solution is carried out to obtain ZnBC precursor; S2: The ZnBC precursor obtained in S1 is subjected to a first high-temperature calcination under an inert atmosphere to obtain the pyrolysis product; S3: The pyrolysis product obtained in S2 is soaked in acid to remove residual zinc ions and ash, washed until neutral, dried, ground and sieved to obtain pore-forming modified biochar. S4: Using the impregnation method, a mixed impregnation solution of lanthanum salt and iron salt is prepared based on the saturated water absorption rate of the pore-forming modified biochar obtained in S3. The impregnation solution is added to the pore-forming modified biochar to ensure that the solution is completely absorbed. After aging, lanthanum and iron-loaded modified biochar is obtained. S5: After drying the lanthanum and iron-loaded modified biochar obtained in S4, it is subjected to a second high-temperature calcination under an inert atmosphere. After cooling, the lanthanum-iron bimetallic synergistic modified biochar-based composite material is obtained.

5. The preparation method of the lanthanum-iron bimetallic synergistic modified biochar-based composite material according to claim 4, characterized in that, In S1, the concentration of the zinc chloride solution is 1~3 mol / L, and the liquid-to-solid ratio is 3~8:1 mL / g.

6. The method for preparing the lanthanum-iron bimetallic synergistic modified biochar-based composite material according to claim 4, characterized in that, In S2 and S5, the inert atmosphere is nitrogen or argon, and the flow rate is 30~100mL / min.

7. The method for preparing the lanthanum-iron bimetallic synergistic modified biochar-based composite material according to claim 4, characterized in that, The heating rate for the first and second high-temperature calcinations is 3~10℃ / min, the calcination temperature is 500~700℃, and the holding time is 1~4h.

8. The method for preparing the lanthanum-iron bimetallic synergistic modified biochar-based composite material according to claim 4, characterized in that, In S4, the lanthanum salt is lanthanum nitrate hexahydrate, and the iron salt is ferric chloride hexahydrate; the total cation concentration in the mixed impregnation solution is 0.5~2M.

9. The application of the lanthanum-iron bimetallic synergistic modified biochar-based composite material according to claim 1 or 2 in the removal of phosphate from water.

10. The application of the lanthanum-iron bimetallic synergistic modified biochar-based composite material according to claim 9 in the removal of phosphate from water, characterized in that, The composite material was added to phosphate-containing wastewater and adsorbed by stirring or shaking under conditions of pH=4~10 and temperature of 15~45℃.

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