Lanthanum-based composite phosphorus removal material as well as preparation method and phosphorus removal method thereof

Abstract

The invention relates to a lanthanum-based composite phosphorus removal material as well as a preparation method and a phosphorus removal method thereof, and belongs to the field of water treatment. At least one of the problems that high adsorption capacity and structural stability of an existing lanthanum-based phosphorus removal material are difficult to consider, excellent adsorption performance and a simple preparation process are difficult to balance, and efficient phosphorus removal effect and easy recycling and regeneration of the material are difficult to cooperate and the like is solved. The invention relates to a preparation method of a lanthanum-based composite phosphorus removal material, which takes lanthanum nitrate hexahydrate and citric acid as a lanthanum source and a carbon source respectively, and comprises the following steps: dissolving the lanthanum nitrate hexahydrate and the citric acid in water; stirring and mixing under a heating condition until viscous liquid is formed; calcining the viscous liquid; and grinding the calcined product. According to the invention, high adsorption capacity, high selectivity and rapid adsorption of phosphate in a water body are realized, the structure is stable, the production cost and the process complexity are reduced, and the material has excellent recovery and regeneration capability.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a lanthanum-based composite phosphorus removal material and its preparation and removal methods. Background Technology

[0002] Phosphorus is a key limiting factor causing eutrophication in water bodies. Among current phosphorus removal methods, adsorption is of great interest due to its ease of operation. Among numerous adsorption materials, lanthanum-based materials stand out due to their high affinity for phosphates, environmental friendliness, and ability to form stable adsorption solutions. Its precipitation properties make it a highly promising phosphorus removal adsorbent.

[0003] Currently researched lanthanum-based phosphorus removal materials mainly include the following categories: lanthanum-based perovskite materials (such as...) , etc.), lanthanide hydroxides (such as...) Nanosheets, porous Lanthanum is commonly prepared via MOF precursor conversion or co-precipitation methods, as well as through lanthanum-based composite oxides / hydroxides (such as La-Mn, La-Fe bimetallic materials) and lanthanum-based supported materials (such as lanthanum-loaded carbon nanotubes and lanthanum-loaded film materials). Furthermore, studies have also supported active lanthanum components on diatomaceous earth, alumina, and magnetic materials. Alternatively, lanthanum-based adsorbents can be placed on carriers such as cellulose to achieve material immobilization, magnetic separation, or improved dispersibility; or by constructing lanthanum-based MOFs (metal-organic frameworks) or introducing intermediate layers such as polydopamine (PDA), efforts can be made to improve the specific surface area, adsorption capacity, and stability of the material; some studies have also directly added powdered lanthanum-based adsorbents to biological treatment systems such as A / A / O to explore the synergistic effect of biological phosphorus removal and chemical adsorption.

[0004] Although lanthanum-based adsorbents have shown promising application prospects in phosphorus removal, existing technologies still face several challenges. For example, there is a trade-off between adsorption capacity and stability: high lanthanum loading typically leads to high adsorption capacity, but often comes with a high risk of active component leaching and loss, as well as poor material structural stability, potentially causing secondary pollution and shortening material lifespan. Other issues include the complexity and cost of preparation processes: the preparation of many high-performance composite materials (such as MOFs and PDA-modified materials) involves complex processes, expensive reagents, or harsh conditions, hindering their large-scale production and practical application. Finally, there is the issue of non-recyclability: the regeneration process for some lanthanum-based materials after phosphorus adsorption is complex, and the regenerated material exhibits a significant decline in performance. Summary of the Invention

[0005] In view of the above analysis, the present application aims to provide a lanthanum-based composite phosphorus removal material, a preparation method thereof and a phosphorus removal method, to solve at least one of the problems that the existing lanthanum-based phosphorus removal material is difficult to balance high adsorption capacity and structural stability, excellent adsorption performance and simple preparation process, efficient phosphorus removal effect and easy recycling and regeneration of the material.

[0006] The object of the present application is achieved by the following technical solutions: The present application provides a preparation method of a lanthanum-based composite phosphorus removal material, taking lanthanum nitrate hexahydrate and citric acid as the lanthanum source and carbon source, respectively, comprising the following steps: S1, dissolving lanthanum nitrate hexahydrate and citric acid in water together; S2, stirring and mixing under heating conditions until a viscous liquid is formed; S3, calcining the viscous liquid, the calcination temperature is 200-400℃, and the calcination time is 1-5h; S4, grinding the calcined product to obtain the lanthanum-based composite phosphorus removal material.

[0007] Further, in step S1, the molar ratio of lanthanum nitrate hexahydrate to citric acid is 1:0.25-1:1.25.

[0008] Further, in step S2, the stirring and mixing under heating conditions adopts stepwise heating and stirring: first stirring and mixing at 60-80℃ for preliminary mixing, and then heating to 110-130℃ for high-temperature mixing.

[0009] Further, in step S1, the molar ratio of lanthanum nitrate hexahydrate to citric acid is 1:0.5-1:1.

[0010] Further, in step S3, the calcination temperature is 240-360℃, and the calcination time is 1-3h.

[0011] Further, step S1 comprises: first dissolving lanthanum nitrate hexahydrate in water to form a lanthanum nitrate solution with a concentration of 0.1-0.5mol / L; then adding citric acid according to the molar ratio and mixing thoroughly.

[0012] Further, the time for preliminary mixing is more than 30min; and / or, the time for high-temperature mixing is more than 30min.

[0013] The present application provides a lanthanum-based composite phosphorus removal material prepared according to the preparation method.

[0014] The present application provides a phosphorus removal method, comprising the following steps: The lanthanum-based composite phosphorus removal material obtained by the preparation method or the lanthanum-based composite phosphorus removal material is directly put into the water to be treated.

[0015] Further, the lanthanum-based composite phosphorus removal material after adsorbing phosphorus is desorbed and regenerated by using a regenerant.

[0016] Compared with the prior art, the present application can achieve at least one of the following beneficial effects: (1) For the problem of "high adsorption capacity and structural stability difficult to be considered", the preparation method of the present application constructs a rigid porous carbon skeleton through in-situ carbonization of citric acid at low temperature. The skeleton as a stable nano-reactor firmly limits and disperses the high-activity nano-lanthanum species (active component) on the outer surface and pores of the carbon skeleton, which avoids the dissolution and agglomeration of the active component and maintains the structural integrity of the material as a whole, so as to realize the consideration of high adsorption capacity and long-term structural stability. Compared with the adsorption capacity of the existing phosphorus removal materials (generally less than 80 mg P / g), the present application has higher adsorption capacity. At the same time, in terms of "capacity retention rate in multiple adsorption-regeneration cycles", which is one of the core indicators for measuring long-term structural stability, the lanthanum-based composite phosphorus removal material obtained by the present application has a multiple adsorption-regeneration capacity retention rate comparable to or even better than the prior art, indicating that the lanthanum-based composite phosphorus removal material of the present application has good long-term structural stability.

[0017] (2) For the problem of "balancing excellent adsorption performance and simple preparation process", the preparation method of the present application uses "one-pot method" and "one-step low-temperature calcination" core process. Compared with the scheme in the prior art which relies on expensive raw materials and / or complex process to achieve high phosphorus adsorption capacity, the present application has the advantages of simpler process and lower cost. The method uses citric acid as a carbon precursor and a complexing agent at the same time, and synchronously completes the formation of the carbon matrix and the in-situ fixation of the lanthanum species in the low-temperature calcination step, which simplifies the preparation of complex inorganic lanthanum species / organic carbon composite into a continuous, controllable and easy-to-scale process, so as to obtain excellent adsorption performance while reducing production cost and process complexity.

[0018] (3) For the problem of "high-efficiency phosphorus removal effect and easy recycling and regeneration of the material difficult to be coordinated", the preparation method of the present application gives the material suitable macroscopic morphology and mechanical strength by regulating the calcination process. The obtained composite material can be quickly and completely desorbed and regenerated by alkali treatment after adsorption. More importantly, the unique carbon matrix-lanthanum species composite structure can effectively resist the chemical shock of the regeneration environment, ensure that the lanthanum species do not lose and the adsorption sites do not collapse, and still maintain stable high adsorption performance after multiple adsorption-desorption cycles, solving the engineering application bottleneck of the difficulty in coordinating high-efficiency phosphorus removal and easy recycling and regeneration.

[0019] (4) In some preferred embodiments, the present application further optimizes the porous structure, lanthanum species dispersion and surface chemical properties of the obtained lanthanum-based composite phosphorus removal material by controlling the key preparation process parameters within a specific range, thereby significantly improving its adsorption performance and structural stability.

[0020] (5) In some specific embodiments, the performance indicators of the preparation method of the present application and the lanthanum-based composite phosphorus removal material obtained thereby are as follows: a) Initial high adsorption capacity and P removal rate: reflecting the stable construction and efficient exposure of active sites; The phosphorus adsorption capacity (P adsorption capacity) of the lanthanum-based composite phosphorus removal material obtained in the embodiments of the present application is >80 mg P / g, and the phosphorus removal rate for simulated wastewater with an initial concentration of 50 mg P / L is >60%. When the process parameters are further optimized (the molar ratio of lanthanum nitrate hexahydrate to citric acid is 1:0.5~1:1, the calcination temperature is 240~360℃, and the calcination time is 1~3h), the P adsorption capacity of the lanthanum-based composite phosphorus removal material is >90 mg P / g, and the phosphorus removal rate for simulated wastewater with an initial concentration of 50 mg P / L is >70%. Under the optimal synthesis conditions, such as a molar ratio of lanthanum nitrate hexahydrate to citric acid of 1:0.75, a calcination temperature of 320℃, and a calcination time of 2h, the performance of the obtained lanthanum-based composite phosphorus removal material reaches a peak, with a P adsorption capacity as high as 124.25 mg P / g and a P removal rate for simulated wastewater with an initial concentration of 50 mg P / L as high as 99.4%.

[0021] b) High selective removal rate in complex water bodies: confirming the stability of the "inner sphere complexation" mechanism; In actual wastewater, even in the presence of multiple coexisting anions (such as ), the phosphorus removal rate of the lanthanum-based composite phosphorus removal material described in the present application can still remain above 99%.

[0022] c) High capacity retention rate after multiple cycles: directly proving the durability of the overall structure and excellent regeneration ability; After 5 cycles of "adsorption-alkali desorption" regeneration, the P adsorption capacity retention rate of the lanthanum-based composite phosphorus removal material described in the present application is still as high as 81.7% and above; The above performance indicators systematically prove that the lanthanum-based composite phosphorus removal material provided by the present application has excellent adsorption capacity, outstanding structural stability and regeneration cycle ability, providing a solid guarantee for its large-scale application in actual water purification.

[0023] (6) Compared with existing lanthanum-based phosphorus removal composite materials, the lanthanum-based composite phosphorus removal material prepared by the present application achieves multiple breakthroughs in structure: In terms of site distribution, it breaks through the traditional "surface load easy agglomeration" limitation, realizes the atomic level uniform dispersion of lanthanum species (active component) inside and outside the carbon skeleton, and significantly improves the site utilization rate; In terms of structural stability, it overcomes the traditional "physical combination easy loss" weakness, builds an integrated stable structure by loading lanthanum species in situ to nanoporous carbon matrix, and significantly reduces the dissolution of active components; In terms of mass transfer and selectivity, it solves the traditional material "pore easy to block, poor anti-interference" problem, uses the in-situ formed through multi-level pore and specific inner sphere complex mechanism to realize the rapid transport and high selectivity capture of phosphate; This "uniform dispersion, in-situ loading, rapid mass transfer" integrated loose porous carbon matrix + lanthanum species nanoscale composite structure successfully solves the core contradiction of "hidden active site, unstable combination, mass transfer blocked" in traditional materials, and gives the material the comprehensive advantages of high adsorption capacity, high selectivity, high stability and easy regeneration.

[0024] In the present application, the above technical solutions can be combined with each other to realize more preferred combination schemes. Other features and advantages of the present application will be described in the subsequent specification, and some advantages will become apparent from the specification, or will be understood by implementing the present application. The purpose and other advantages of the present application can be achieved and obtained from the specific embodiments described in the specification and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0025] The accompanying drawings are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the principles of the application. Figure 1 SEM images of the lanthanum-based composite phosphorus removal material of embodiment 3 of the present application before and after adsorbing phosphorus (a, b, c before adsorption; d, e, f after adsorption); Figure 2 EDS images of the lanthanum-based composite phosphorus removal material of embodiment 3 of the present application before and after adsorbing phosphorus (a before adsorption, b after adsorption); Figure 3 TEM image of the lanthanum-based composite phosphorus removal material of embodiment 3 of the present application; Figure 4 XRD images of the lanthanum-based composite phosphorus removal material of embodiment 3 of the present application before and after adsorbing phosphorus; Figure 5 FTIR images of the lanthanum-based composite phosphorus removal material of embodiment 3 of the present application before and after adsorbing phosphorus; Figure 6 XPS full spectrum images of the lanthanum-based composite phosphorus removal material of embodiment 3 of the present application before and after adsorbing phosphorus; Figure 7The image shows the La 3d spectra of the lanthanum-based composite phosphorus removal material before and after phosphorus adsorption in Example 3 of this invention. Figure 8 This is the P 2p spectrum of the lanthanum-based composite phosphorus removal material after phosphorus adsorption in Example 3 of the present invention; Figure 9 This is a comparison chart of the phosphorus adsorption performance of lanthanum-based composite phosphorus removal materials synthesized with different molar ratios in the embodiments of the present invention; Figure 10 This is a comparison chart of the phosphorus adsorption performance of lanthanum-based composite phosphorus removal materials synthesized at different calcination temperatures in the embodiments of the present invention; Figure 11 This is a comparison chart of the phosphorus adsorption performance of lanthanum-based composite phosphorus removal materials synthesized at different calcination times in the embodiments of the present invention; Figure 12 This is the adsorption isotherm diagram of phosphorus adsorption by the lanthanum-based composite phosphorus removal material in Example 3 of the present invention; Figure 13 The figure shows the kinetics of phosphorus adsorption by the lanthanum-based composite phosphorus removal material in Example 3 of this invention. Figure 14 The figure shows the experimental results of the cyclic regeneration of the lanthanum-based composite phosphorus removal material in Example 3 of this invention; Figure 15 This is the EDS image of the lanthanum-based composite phosphorus removal material of Comparative Example 1 of the present invention before phosphorus adsorption. Figure 16 This is an EDS image of the lanthanum-based composite phosphorus removal material in Example 1 of the present invention before phosphorus adsorption; Figure 17 This is an EDS image of the lanthanum-based composite phosphorus removal material before phosphorus adsorption in Example 2 of the present invention; Figure 18 This is an EDS image of the lanthanum-based composite phosphorus removal material in Example 4 of the present invention before phosphorus adsorption; Figure 19 This is an EDS image of the lanthanum-based composite phosphorus removal material in Example 5 of the present invention before phosphorus adsorption. Detailed Implementation

[0026] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0027] In the prior art, citric acid is mainly used as a complexing agent, a solvent or a fuel in the preparation process of lanthanum-based composites, and its core role is to ensure the uniform distribution of metal ions through complexation in the precursor stage, or to provide reaction energy in the combustion method, and to be completely decomposed in the subsequent high-temperature calcination (such as above 550℃) process, and not to remain in the final product (such as lanthanum cerate, lanthanum oxide, etc.); in addition, the lanthanum-based composites involving citric acid in the prior art are mostly used for preparing catalysts, which are completely different from the application scenarios of the present application.

[0028] Unlike the prior art, the concept of the present application breaks this convention and innovatively uses citric acid as a key reactant and a carbon source. By controlling a relatively low calcination temperature (such as 200~400℃), citric acid is not completely decomposed and is in-situ converted into an amorphous nanoporous carbon matrix (carbon matrix); at the same time, the lanthanum source is decomposed and combined into lanthanum species in this process, and is in-situ generated and uniformly doped in the outer surface and loose porous structure of the carbon matrix, and finally forms a brand-new "carbon matrix + lanthanum species" composite material. This role transformation of citric acid from a "temporary worker" to a "building skeleton", as well as the fundamental change in the product structure from a pure inorganic phase to an inorganic / organic carbon composite, significantly improves the loading amount and dispersion uniformity of lanthanum species, and fully utilizes the synergistic effect between the adsorption capacity of the carbon matrix and the specific adsorption of the lanthanum species, to achieve more simple and more economical preparation process, and achieves more excellent effects than the prior art in terms of adsorption capacity, rate and material structure stability. The specific technical solutions of the present application are as follows: In a first aspect, the present application provides a preparation method of a lanthanum-based composite phosphorus removal material, using lanthanum nitrate hexahydrate and citric acid as the lanthanum source and the carbon source, respectively, comprising the following steps: S1, dissolving lanthanum nitrate hexahydrate and citric acid in water together; S2, stirring and mixing under heating conditions until a viscous liquid is formed; S3, calcining the viscous liquid, the calcination temperature is 200~400℃, and the calcination time is 1~5h; S4, grinding the calcined product to obtain the lanthanum-based composite phosphorus removal material.

[0029] Based on the above scheme, the main difference between the preparation method of this invention and the prior art lies in the following: It abandons the traditional approach of completely decomposing citric acid at high temperatures, instead utilizing it as an in-situ carbon source and structure-directing agent. Through low-temperature calcination at 200-400℃, the carbonization of citric acid and the in-situ loading of lanthanum species are achieved, thereby constructing a composite structure with nanoporous amorphous carbon as the substrate (carbon matrix) and lanthanum oxide / lanthanum hydroxide highly dispersed within the carbon matrix. This method not only significantly improves the utilization efficiency and dispersion uniformity of lanthanum, but also utilizes the synergistic effect between the physical adsorption of the carbon matrix and the chemical capture of lanthanum active sites to achieve high adsorption capacity, high selectivity, and rapid adsorption of phosphates in water.

[0030] One of the contradictions facing existing lanthanum-based phosphorus removal materials and their preparation is that achieving high adsorption capacity requires creating high specific surface area and a large number of highly active amorphous lanthanum sites (e.g., lanthanum hydroxide gel). However, these metastable structures spontaneously transform to a stable state in aqueous phase, leading to adsorption site failure and structural disintegration. On the other hand, pursuing structural stability (such as the stable lattice of perovskites) would encapsulate the active sites inside the crystal, resulting in a situation where "lanthanum is present but ineffective." Furthermore, traditional supported materials have always been constrained by the difficulty of reconciling high loading capacity with uniform dispersion and strong binding force, making it difficult to simultaneously achieve both adsorption capacity and structural stability.

[0031] To address the challenge of balancing high adsorption capacity with structural stability, this invention constructs a rigid porous carbon framework through in-situ carbonization of citric acid at low temperatures. This framework acts as a stable nanoreactor, firmly confining and dispersing highly active nano-lanthanum species (active components) on the outer surface and within the pores of the carbon framework. This avoids the dissolution and aggregation of active components while maintaining the overall structural integrity of the material, thus achieving a balance between high adsorption capacity and long-term structural stability.

[0032] The second contradiction in the preparation of existing lanthanum-based phosphorus removal materials is that, in order to achieve high performance, existing technologies often rely on complex hydrothermal synthesis, template methods, or multi-step loading processes, which are cumbersome and costly; while simple co-precipitation methods are difficult to control the material structure and performance, resulting in mediocre adsorption capacity and selectivity.

[0033] To address the challenge of balancing superior adsorption performance with a simplified preparation process, this invention revolutionizes the complex process by employing a "one-pot method" and a "one-step low-temperature calcination" core technology. This method utilizes citric acid as both a carbon precursor and a complexing agent, simultaneously achieving the formation of the carbon matrix / carbon substrate and the in-situ immobilization of lanthanum species during the low-temperature calcination step. This simplifies the preparation of complex inorganic lanthanum species / organic carbon complexes into a continuous, controllable, and easily scalable process, thereby achieving excellent adsorption performance while reducing production costs and process complexity.

[0034] The third contradiction in the preparation of existing lanthanum-based phosphorus removal materials: many existing nanoscale lanthanum-based materials have the problems of difficult solid-liquid separation, low recovery rate, and easy structural damage in the regeneration process, resulting in rapid decay of adsorption capacity.

[0035] To solve the problem of the difficulty in coordinating the high-efficiency phosphorus removal effect and the easy recovery and regeneration of the material, the application gives the material appropriate macroscopic morphology and mechanical strength by regulating the calcination process. The obtained composite material can realize rapid and complete desorption regeneration through alkali treatment after adsorption. More importantly, the unique carbon substrate-lanthanum species composite structure can effectively resist the chemical shock of the regeneration environment, ensure that the lanthanum species does not lose and the adsorption site does not collapse, and still maintain stable high performance after multiple adsorption-desorption cycles, thereby fundamentally solving the engineering application bottleneck of the difficulty in coordinating the high-efficiency phosphorus removal and the easy recovery and regeneration.

[0036] Specifically, in step S1, the molar ratio of the lanthanum nitrate hexahydrate to citric acid is 1:0.25 to 1:1.25.

[0037] Illustratively, the molar ratio of the lanthanum nitrate hexahydrate to citric acid is 1:0.25, 1:0.3, 1:0.35, 1:0.4, 1:0.45, 1:0.5, 1:0.55, 1:0.6, 1:0.65, 1:0.68, 1:0.7, 1:0.73, 1:0.75, 1:0.77, 1:0.8, 1:0.85, 1:0.9, 1:0.95, 1:1, 1:1.05, 1:1.1, 1:1.15, 1:1.2, or 1:1.25.

[0038] Preferably, in step S1, the molar ratio of the lanthanum nitrate hexahydrate to citric acid is 1:0.5 to 1:1; more preferably, 1:0.7 to 1:0.8.

[0039] Illustratively, in step S3, the calcination temperature is 200℃, 220℃, 240℃, 260℃, 280℃, 300℃, 310℃, 320℃, 330℃, 340℃, 360℃, 380℃, or 400℃; and the calcination time is 1h, 1.5h, 1.8h, 1.9h, 2h, 2.1h, 2.2h, 2.5h, 3h, 4h, or 5h.

[0040] Preferably, in step S3, the calcination temperature is 240-360℃, and the calcination time is 1-3h. More preferably, the calcination temperature is 280-360℃, and the calcination time is 1.5-2.5h.

[0041] It should be noted that the present application aims to build an amorphous carbon skeleton with high specific surface area and rich pores and realize in-situ uniform anchoring of nanoscale lanthanum species (lanthanum oxide and / or lanthanum hydroxide) on the outer surface and pore structure of the carbon skeleton by synergistically controlling the molar ratio, calcination temperature and time. Controlling the molar ratio of lanthanum nitrate hexahydrate to citric acid at 1:0.5-1:1 (more preferably 1:0.7-1:0.8) can balance the carbon skeleton construction and lanthanum species dispersion - too high molar ratio (too little citric acid relative to lanthanum nitrate) will lead to incomplete carbon skeleton and lanthanum species agglomeration, and too low molar ratio (too little lanthanum nitrate relative to citric acid) will cause the carbon skeleton layer to be too thick and the pores to be blocked. Controlling the calcination conditions at 240-360℃ for 1-3h (more preferably 280-360℃ for 1.5-2.5h) can make citric acid achieve the best partial carbonization and make the lanthanum source fully convert into high-activity nanometer lanthanum species - too low calcination temperature or too short time will lead to insufficient decomposition of the precursor (citric acid and lanthanum nitrate cannot be fully decomposed and converted, the carbon skeleton is loose and fragile, and the lanthanum species cannot be fully converted into active lanthanum oxide and / or lanthanum hydroxide, resulting in low adsorption activity of the material); too high calcination temperature or too long time will cause the carbon skeleton to collapse and the lanthanum species to sinter (the carbon skeleton will be excessively graphitized, the porosity will decrease; at the same time, the lanthanum species will be excessively sintered, from high-activity nanoparticles to large-size crystals, the specific surface area and active sites will be greatly reduced, and the adsorption performance will decrease). The synergistic optimization of the above parameters realizes the ideal combination of nanoscale "porous carbon matrix" and "highly dispersed lanthanum active sites", which is the key to obtaining excellent adsorption performance, stable structure and regeneration capacity. Any imbalance of a single parameter may cause the performance of the material to decrease.

[0042] Specifically, in step S2, the stirring and mixing under heating conditions adopt stepwise heating and stirring: first stirring and mixing at 60-80℃ for preliminary mixing, and then heating and stirring at 110-130℃ for high-temperature mixing.

[0043] It should be noted that the stepwise heating and stirring process adopted by the present application realizes precise control of the precursor structure by controlling the temperature in stages. At the low temperature stage of 60-80℃, the solution maintains good fluidity, so that the lanthanum nitrate hexahydrate and citric acid molecules are fully mixed and pre-complexed to form a uniform precursor complex network, effectively avoiding the segregation of components and the premature hydrolysis and precipitation of lanthanum ions caused by rapid evaporation of water and local high concentration due to too high temperature. At the high temperature stage of 110-130℃, the system promotes rapid water evaporation to sharply increase the viscosity, driving the precursor complex to complete the transition from solution to three-dimensional network gel, and stabilizing the molecular-level uniformity into a gel structure. This segmented temperature control method ensures the uniform distribution of active components at the molecular scale, laying a better foundation for forming ideal porous carbon matrix-lanthanum species composite nanostructure in the subsequent calcination process.

[0044] Exemplarily, the temperature of the preliminary mixing is 60℃, 65℃, 70℃, 75℃, 80℃. The time of the preliminary mixing is 30min or more, such as 30min, 40min, 50min, 60min; for example, the time of the preliminary mixing is 30min-40min.

[0045] Exemplarily, the temperature is increased to the temperature of the preliminary mixing at a rate of 5-10℃ / min.

[0046] Exemplarily, the stirring speed during the preliminary mixing is 240-320rpm; for example, 260rpm, 280rpm, 300rpm.

[0047] Exemplarily, the temperature of the high-temperature mixing is 110℃, 115℃, 120℃, 125℃, 130℃.

[0048] Exemplarily, the time of the high-temperature mixing is 30min or more, such as 30-60min, until a viscous liquid is formed, and then step S3 is continued.

[0049] Exemplarily, the temperature is increased to the temperature of the high-temperature mixing at a rate of 5-10℃ / min.

[0050] Exemplarily, the stirring speed during the high-temperature mixing is 240-320rpm; for example, 260rpm, 280rpm, 300rpm.

[0051] Specifically, step S1 comprises: first dissolving lanthanum nitrate hexahydrate in water to form a lanthanum nitrate solution with a concentration of 0.1-0.5mol / L; and then adding citric acid according to a molar ratio and mixing thoroughly.

[0052] Exemplarily, in step S1, the lanthanum nitrate solution formed by dissolving lanthanum nitrate hexahydrate in water has a concentration of 0.1mol / L, 0.14mol / L, 0.16mol / L, 0.18mol / L, 0.20mol / L, 0.30mol / L, 0.40mol / L, 0.50mol / L.

[0053] Preferably, in step S1, the lanthanum nitrate solution has a concentration of 0.1-0.2mol / L.

[0054] Exemplarily, in step S1, the lanthanum nitrate hexahydrate is dissolved in water, and stirred at a speed of 240-320rpm for 60min or more to ensure that the lanthanum nitrate hexahydrate is fully dissolved in water.

[0055] Exemplarily, in step S1, the citric acid is added according to a molar ratio, and the thorough mixing comprises: ultrasonic treatment for 10min or more under a power of 100-500W to ensure that the lanthanum nitrate hexahydrate and the citric acid are fully mixed and co-dissolved in water.

[0056] Specifically, in step S3, the atmosphere for calcination is air.

[0057] Specifically, in step S3, the temperature is raised to the calcination temperature at a rate of 5-10℃ / min.

[0058] Specifically, in step S3, the calcination is performed in a tube furnace.

[0059] Specifically, in step S4, the grinding is performed manually.

[0060] Specifically, in step S4, the grinding medium is agate grinding ball.

[0061] Specifically, in step S4, the grinding is performed at room temperature in air.

[0062] Preferably, in step S4, the parameters of the product after grinding are as follows: Specifically, the specific surface area of the material should not be significantly damaged by grinding, and the specific surface area of the material after grinding should be maintained in the range of 20-90m² / g.

[0063] In a second aspect, the present application provides a lanthanum-based composite phosphorus removal material prepared by the preparation method according to the first aspect. Specifically, the lanthanum-based composite phosphorus removal material is a nano-porous carbon-supported lanthanum composite material, which comprises: an amorphous nano-porous carbon matrix; and an active component in-situ embedded in the nano-porous carbon matrix; wherein the active component comprises lanthanum oxide and / or lanthanum hydroxide .

[0064] It can be understood that the lanthanum-based composite phosphorus removal material is formed by reaction of lanthanum nitrate hexahydrate and citric acid as precursors; wherein, the amorphous nano-porous carbon matrix is formed by pyrolysis of citric acid, and lanthanum species in the form of lanthanum oxide and / or lanthanum hydroxide are formed by conversion of lanthanum nitrate, and the active component is loaded in the nano-porous carbon matrix in an in-situ embedded manner.

[0065] Compared with existing lanthanum-based composite phosphorus removal materials, the lanthanum-based composite phosphorus removal material prepared by the present application has achieved a fundamental breakthrough in structure and has built significant advantages: Firstly, in the construction and distribution of active sites, the traditional supported materials (such as lanthanum supported on activated carbon, zeolite, etc.) mainly realize the combination through physical impregnation or mixing, and the lanthanum species is easy to agglomerate on the surface of the carrier and block the pore, resulting in uneven distribution of sites and low utilization rate; while the present application makes the lanthanum species uniformly embedded and in-situ supported in the whole system of three-dimensional porous carbon skeleton (including the outer surface and internal pores) in a molecular level / nanoscale through in-situ co-carbonization of citric acid and lanthanum source, realizing the maximum exposure and efficient utilization of active sites.

[0066] Secondly, in the stability of material structure, the physical adsorption or weak bonding between lanthanum and the carrier in traditional materials is easy to fail in hydraulic flushing and acid-base changes, resulting in the loss of active components; while the "carbon-lanthanum" integrated stable structure formed by the present application anchors the active sites in the whole rigid carbon network through in-situ loading, which not only significantly improves the mechanical strength of the material, but also fundamentally solves the problems of active component loss and secondary pollution.

[0067] Thirdly, in the mass transfer path and selectivity, the pore of traditional materials is easy to be blocked due to loading, and the surface sites are easy to be disturbed by coexisting anions; the three-dimensional through multi-level pores generated in-situ by the present application provide a "highway" for the rapid diffusion of phosphate, and the highly exposed lanthanum sites realize adsorption by forming a specific "inner sphere complex" (La-O-P bond), which almost does not interfere with other anions in complex water bodies, showing excellent selectivity.

[0068] It should be noted that the micro-morphology of the lanthanum-based composite phosphorus removal material presents a loose porous structure, has a high specific surface area, and has a multi-level pore structure with micropores and mesopores coexisting.

[0069] Specifically, the specific surface area of the lanthanum-based composite phosphorus removal material is 20-90 m² / g.

[0070] For example, the specific surface area of the phosphorus removal material is 25 m² / g, 30 m² / g, 40 m² / g, 50 m² / g, 60 m² / g, 70 m² / g, 80 m² / g, or 85 m² / g.

[0071] Specifically, the average pore size of the lanthanum-based composite phosphorus removal material is 5-20 nm.

[0072] For example, the average pore size of the lanthanum-based composite phosphorus removal material is 5 nm, 10 nm, 15 nm, or 20 nm.

[0073] Specifically, the mass percentage of lanthanum element in the lanthanum-based composite phosphorus removal material is 30-80%, and the mass percentage of carbon element is 5-35%.

[0074] Exemplarily, the lanthanum-based composite phosphorus removal material has a mass percentage of lanthanum element of 30.75%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%.

[0075] Exemplarily, the lanthanum-based composite phosphorus removal material has a mass percentage of carbon element of 5%, 10%, 15%, 20%, 25%, 30%, 35%.

[0076] Specifically, the lanthanum-based composite phosphorus removal material has a multi-level pore structure with coexisting micropores and mesopores, wherein the micropore diameter is less than 2 nm, and the mesopore diameter is 2-50 nm. For example, the mesopore diameter is 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, or 50 nm.

[0077] Specifically, the lanthanum-based composite phosphorus removal material has a phosphorus adsorption capacity of greater than 80 mg P / g and a phosphorus removal rate of greater than 60%.

[0078] In some preferred embodiments, the lanthanum-based composite phosphorus removal material has a phosphorus adsorption capacity of greater than 90 mg P / g and a phosphorus removal rate of greater than 70%.

[0079] In some more preferred embodiments, the lanthanum-based composite phosphorus removal material has a phosphorus adsorption capacity of greater than 120 mg P / g and a phosphorus removal rate of greater than 99%.

[0080] Specifically, after 5 cycles of adsorption-alkali regeneration, the lanthanum-based composite phosphorus removal material has a phosphorus adsorption capacity retention rate of greater than 81.7%.

[0081] In some embodiments, the lanthanum-based composite phosphorus removal material is prepared by a calcination process using lanthanum nitrate hexahydrate as a lanthanum source and citric acid as a carbon source; wherein, the citric acid is pyrolyzed to form the amorphous nanoporous carbon matrix, and the lanthanum nitrate hexahydrate is converted to form the active component; The calcination process has a calcination temperature of 200-400°C and a calcination time of 1-5 h.

[0082] Exemplarily, the calcination temperature is 200°C, 220°C, 240°C, 260°C, 280°C, 300°C, 310°C, 320°C, 330°C, 340°C, 360°C, 380°C, or 400°C; and the calcination time is 1 h, 1.5 h, 1.8 h, 1.9 h, 2 h, 2.1 h, 2.2 h, 2.5 h, 3 h, 4 h, or 5 h.

[0083] Preferably, the calcination temperature is 240-360°C, and the calcination time is 1-3 h. More preferably, the calcination temperature is 280-360°C, and the calcination time is 1.5-2.5 h.

[0084] In some embodiments, the molar ratio of the lanthanum nitrate hexahydrate to citric acid is 1:0.25-1:1.25.

[0085] For example, the molar ratio of the lanthanum nitrate hexahydrate to citric acid is 1:0.25, 1:0.3, 1:0.35, 1:0.4, 1:0.45, 1:0.5, 1:0.55, 1:0.6, 1:0.65, 1:0.68, 1:0.7, 1:0.73, 1:0.75, 1:0.77, 1:0.8, 1:0.85, 1:0.9, 1:0.95, 1:1, 1:1.05, 1:1.1, 1:1.15, 1:1.2, 1:1.25.

[0086] Preferably, the molar ratio of the lanthanum nitrate hexahydrate to citric acid is 1:0.5-1:1; more preferably, 1:0.7-1:0.8.

[0087] In some embodiments, the object of the calcination process is a viscous precursor obtained by preliminarily mixing the lanthanum nitrate hexahydrate and citric acid at 60-80°C and high-temperature mixing at 110-130°C. For example, the temperature of the preliminary mixing is 60°C, 65°C, 70°C, 75°C, 80°C. The time of the preliminary mixing is ≥30 min, such as 30 min, 40 min, 50 min, 60 min; for example, the time of the preliminary mixing is 30-40 min.

[0088] For example, the temperature is raised to the temperature of the preliminary mixing at a rate of 5-10°C / min.

[0089] For example, the stirring speed during the preliminary mixing is 240-320 rpm.

[0090] For example, the temperature of the high-temperature mixing is 110°C, 115°C, 120°C, 125°C, 130°C.

[0091] For example, the time of the high-temperature mixing is ≥30 min, such as 30-60 min, until a viscous liquid is formed, and then step S3 is continued.

[0092] For example, the temperature is raised to the temperature of the high-temperature mixing at a rate of 5-10°C / min.

[0093] For example, the stirring speed during the high-temperature mixing is 240-320 rpm.

[0094] In a third aspect, the present application provides a method for removing phosphorus, comprising the following steps: The lanthanum-based composite phosphorus removal material obtained by the preparation method of the first aspect or the lanthanum-based composite phosphorus removal material of the second aspect is directly put into water to be treated. In the adsorption process, the water flows through the lanthanum-based composite phosphorus removal material, and the phosphorus-containing compounds in the water are removed by the combined action of the physical adsorption of the nanoporous carbon matrix and the chemical adsorption of the lanthanum species in the lanthanum-based composite phosphorus removal material, to obtain a lanthanum-based composite phosphorus removal material after adsorbing phosphorus; The regeneration step: using a regenerant to desorb and regenerate the lanthanum-based composite phosphorus removal material after adsorbing phosphorus; to realize repeated use.

[0095] Optionally, the regenerant includes a strong alkali solution (such as NaOH solution, KOH solution), a strong alkali salt solution (such as sodium carbonate solution, sodium bicarbonate solution).

[0096] Preferably, in the regeneration step, the regenerant is a NaOH solution.

[0097] Specifically, the concentration of the NaOH solution is 2-6 mol / L. Preferably, the concentration of the NaOH solution is 3-5 mol / L, for example, 4 mol / L.

[0098] Specifically, the amount of the NaOH solution is 40-80 mL per gram of the lanthanum-based composite phosphorus removal material after adsorption, calculated by the liquid-solid ratio.

[0099] Specifically, the temperature of the desorption regeneration is 15-30°C, and the time is 8-12 hours.

[0100] In an embodiment, the regeneration step specifically includes the following steps: S1, separation and washing: the lanthanum-based composite phosphorus removal material saturated with phosphorus-containing compounds (such as phosphate) (referred to as saturated material) is separated from the water phase (for example, by sedimentation, centrifugation or filtration), and is washed with deionized water to remove impurities and residual phosphorus solution attached to the surface of the saturated material after adsorption; S2, desorption reaction: the washed saturated material is immersed in a regenerant solution, and a desorption reaction is carried out in a constant temperature oscillator or a stirring reactor, to obtain a mixture of the desorbed lanthanum-based composite phosphorus removal material and the desorption liquid (the regenerant after adsorbing phosphorus-containing substances is converted into the desorption liquid); Reaction conditions: oscillation or stirring reaction at 15-30°C and a rotation speed of 240-320 rpm for 8-12 hours, to ensure that the phosphorus-containing compounds (such as phosphate) are fully desorbed; S3, separation and washing again: after the end of the desorption reaction, the desorbed lanthanum-based composite phosphorus removal material and the desorption liquid are separated (for example, by centrifugation or suction filtration), and the desorbed lanthanum-based composite phosphorus removal material is repeatedly washed with deionized water until the washing liquid is neutral (pH ~ 7) to completely remove the residual regenerant and the desorbed phosphorus-containing substances (such as phosphate ions); S4, drying: the desorbed lanthanum-based composite phosphorus removal material washed to neutral is placed in an oven at 60-105°C for 4-12 hours to obtain the regenerated lanthanum-based composite phosphorus removal material, which can be reused for the phosphorus removal process.

[0101] It can be understood that the "adsorption capacity" or "P adsorption capacity" mentioned in the present application is a standard performance index in the art, which specifically refers to the maximum mass of phosphorus that can be adsorbed by unit mass (1 gram) of the phosphorus removal material when the adsorption reaches equilibrium. This value mainly represents the inherent limit adsorption capacity of the material itself, and is not much related to the initial concentration of phosphorus in the water to be treated, thus providing a unified and comparable benchmark for performance comparison between different phosphorus removal materials.

[0102] The technical solutions of the present application are further described in detail below in combination with specific examples and comparative examples.

[0103] Example 1 The present embodiment provides a preparation method of a lanthanum-based composite phosphorus removal material, taking lanthanum nitrate hexahydrate and citric acid as the lanthanum source and the carbon source, respectively, which comprises the following steps: S1, dissolving lanthanum nitrate hexahydrate and citric acid in water together; First, 5 mmol of lanthanum nitrate hexahydrate (La(NO3)3·6H2O) is dissolved in 30 ml of deionized water, stirred at 240 rpm for 60 min to ensure that the lanthanum nitrate hexahydrate is fully dissolved in water to form a lanthanum nitrate solution with a concentration of 0.167 mol / L; Then, the corresponding amount of citric acid is weighed according to the molar ratio of lanthanum nitrate hexahydrate to citric acid of 1:0.25 and added to the lanthanum nitrate solution, and ultrasonic treatment is performed at a power of 100 W for 10 min to ensure that the lanthanum nitrate hexahydrate and the citric acid are fully mixed and dissolved in water; S2, stirring and mixing under heating conditions until a viscous liquid is formed; The temperature is raised to 80°C at a rate of 10°C / min, and stirred at 240 rpm for 30 min; then the temperature is raised to 120°C at a rate of 10°C / min, and continues to be stirred at 240 rpm for 30 min, until a viscous liquid is formed (the volume of the viscous liquid is 2 ml); S3, calcining the viscous liquid at a calcination temperature of 200-400°C for 1-5h; The viscous liquid is poured into a crucible and placed in a tube furnace for calcination under an air atmosphere, with a temperature rise of 10℃ / min to a calcination temperature of 320℃, and a calcination time of 2h; S4, grinding the calcined product to obtain the lanthanum-based composite phosphorus removal material.

[0104] The calcined product is ground at room temperature in air using manual grinding, with a grinding medium of agate grinding balls, and the specific surface area of the ground lanthanum-based composite phosphorus removal material is controlled to be in the range of 20-90m² / g.

[0105] Take 20 mg of the lanthanum-based composite phosphorus removal material obtained in the above step and add it to a sample solution with an initial phosphorus concentration of 50mg / L. After 24h of reaction in a shaker at a speed of 240 rpm and a temperature of 25℃, take 2mL of the supernatant, filter it through a 0.45μm filter membrane, and then measure the phosphorus concentration according to the national standard method GB / T 18114.10-2010 using an ultraviolet spectrophotometer. The P adsorption capacity of the lanthanum-based composite phosphorus removal material obtained in this example is 87.125mg P / g, and the P removal rate is as high as 69.7%.

[0106] Examples 2-5 and Comparative Examples 1-2 differ from Example 1 in the molar ratio of lanthanum nitrate hexahydrate to citric acid, and the remaining steps and parameters are the same as in Example 1.

[0107] Examples 6-10 and Comparative Examples 3-5 differ from Example 3 in the calcination temperature, and the remaining steps and parameters are the same as in Example 3.

[0108] Examples 11-13 and Comparative Examples 6-7 differ from Example 3 in the calcination time, and the remaining steps and parameters are the same as in Example 3.

[0109] Examples 14-17 differ from Example 3 in the process parameters listed in Table 5 below, and the remaining steps and parameters are the same as in Example 3.

[0110] After testing and characterization, the lanthanum-based composite phosphorus removal material described in Examples 1-17 is a nanoporous carbon-supported lanthanum composite material, which includes: an amorphous nanoporous carbon matrix; and an active component embedded in situ in the nanoporous carbon matrix; wherein the active component contains lanthanum oxide and / or lanthanum hydroxide . The lanthanum-based composite phosphorus removal material described in Examples 1-17 has a hierarchical pore structure with both micropores and mesopores, wherein the micropore size is less than 2nm and the mesopore size is 2-50nm.

[0111] Table 1 Structure and composition parameters of the lanthanum-based composite phosphorus removal material of the examples

[0112] Table 2 Process parameter variables and phosphorus removal performance of examples and comparative examples (first group)

[0113] Table 3 Process parameter variables and phosphorus removal performance of examples and comparative examples (second group)

[0114] Table 4 Process parameter variables and phosphorus removal performance of examples and comparative examples (third group)

[0115] Table 5 Process parameter variables and phosphorus removal performance of examples (fourth group)

[0116] The phosphorus-containing sample solution (sample solution with initial phosphorus concentration) used in the above examples for testing was prepared using potassium dihydrogen phosphate (KH2PO4). Specifically, 0.2195 g of KH2PO4 was weighed into 100 mL of ultrapure water, and after magnetic stirring for 1 h to ensure complete dissolution, it was transferred to a 1 L volumetric flask, diluted to volume with ultrapure water, and shaken to obtain a 50 mg / L phosphate standard sample stock solution (i.e., a sample solution with initial phosphorus concentration).

[0117] Example 18 The present embodiment provides a method for removing phosphorus, comprising the following steps: The adsorption step: the lanthanum-based composite phosphorus removal material prepared by the preparation method described in Example 3 is directly put into the water to be treated, and the water flows through the lanthanum-based composite phosphorus removal material. The physical adsorption of the nanoporous carbon matrix and the chemical adsorption of the lanthanum species in the lanthanum-based composite phosphorus removal material work together to remove phosphorus-containing compounds in the water, and the lanthanum-based composite phosphorus removal material after adsorbing phosphorus is obtained. The regeneration step: the lanthanum-based composite phosphorus removal material after adsorbing phosphorus is desorbed and regenerated by using a 4 mol / L NaOH solution to realize repeated use; the amount of NaOH solution used is 40 mL per gram of lanthanum-based composite phosphorus removal material after adsorbing phosphorus, based on the liquid-solid ratio.

[0118] Specifically, the regeneration step specifically comprises the following steps: S1, separation and washing: the lanthanum-based composite phosphorus removal material after adsorbing phosphorus (referred to as saturated material) is separated from the water phase (for example, by sedimentation, centrifugation or filtration), and then washed with deionized water to remove impurities and residual phosphorus solution attached to the surface of the saturated material after adsorption; S2. Desorption reaction: The washed saturated material is immersed in a 4 mol / L NaOH solution and the desorption reaction is carried out in a constant temperature shaker or stirred reactor to obtain a mixture of desorbed material (i.e., desorbed lanthanum-based composite phosphorus removal material) and desorption liquid (the regenerator is converted into desorption liquid after adsorbing phosphorus-containing substances). Desorption reaction conditions: The reaction is carried out at 15~30℃ with shaking or stirring at 320 rpm for 8 hours to ensure that phosphorus-containing compounds (such as phosphates) are fully desorbed; S3. Separation and Washing: After the desorption reaction is completed, the desorbed lanthanum-based composite phosphorus removal material is separated from the desorption solution (e.g., by centrifugation or filtration), and the desorbed lanthanum-based composite phosphorus removal material is repeatedly washed with deionized water until the washing solution is neutral (pH~7) to thoroughly remove residual regenerator and desorbed phosphorus-containing substances (such as phosphate ions). S4. Drying: Place the desorbed lanthanum-based composite dephosphorizing material, which has been washed to neutral, in an oven at 60°C and dry for 12 hours to obtain regenerated lanthanum-based composite dephosphorizing material, which can then be reused in the dephosphorization process.

[0119] Depend on Figure 14 It can be seen that the adsorption performance of the lanthanum-based composite phosphorus removal material in this embodiment of the invention decreases slightly with the increase of the number of recycling cycles. However, the adsorption capacity after the first regeneration is almost unaffected. After five recycling cycles, the adsorption capacity of the lanthanum-based composite phosphorus removal material in this embodiment of the invention still maintains 81.7% of the first adsorption capacity, and the desorption efficiency does not change significantly. The same desorption-regeneration experiment was performed on other embodiments. After five "adsorption-alkali desorption" regeneration cycles, the P adsorption capacity retention rate of the lanthanum-based composite phosphorus removal material in this embodiment of the invention is still as high as 81.7% or higher. This indicates that the lanthanum-based composite adsorbent material in this embodiment of the invention has excellent recyclability and can be reused multiple times and recover phosphates through alkali regeneration.

[0120] Application Example 1 Actual wastewater was collected from a wastewater treatment plant in Baotou. The wastewater composition is shown in Table 6, with a phosphate content of 3.5 mgP / L. The lanthanum-based composite adsorbent material prepared in Example 1 was used for treatment. 50 mL of wastewater was taken for the experiment, and 5 mg of the lanthanum-based composite adsorbent material prepared in Example 1 was added. After stirring and shaking for 5 minutes, 2 mL of the supernatant was taken and filtered through a 0.45 μm filter membrane. The phosphate content was then measured, and the phosphate concentration was <0.01 mgP / L. Under the interference of other ions, the lanthanum-based composite adsorbent material prepared in this embodiment of the invention achieved a phosphate removal rate of over 99%, and the treated wastewater met international standards for phosphorus treatment.

[0121] Table 6. Wastewater composition from a wastewater treatment plant in Baotou

[0122] Table 7 Phosphorus content of sewage treated by adsorption in a sewage treatment plant in Baotou

[0123] Figure 1 Fig. 7 is SEM images of the lanthanum-based composite phosphorus removal material before adsorption of P. It can be seen that the synthesized lanthanum-based composite phosphorus removal material is loose and porous, and the shape is relatively regular and uniform. Fig. 8 is SEM images of the lanthanum-based composite phosphorus removal material after adsorption of P. It can be seen that there are many granular objects on the surface of the lanthanum-based composite phosphorus removal material, indicating that the P in the solution is successfully adsorbed, and lanthanum phosphate crystals are formed.

[0124] Figure 2 Fig. 9 is an EDS image of the lanthanum-based composite phosphorus removal material before adsorption of P. It can be seen that the lanthanum-based composite phosphorus removal material is composed of C, O and La elements. Figure 2 Fig. 10 is an EDS image of the lanthanum-based composite phosphorus removal material after adsorption of P. It can be seen that there is a strong P element signal, and the content of P element after adsorption is 7.3%, which proves that the lanthanum-based composite phosphorus removal material successfully adsorbs P.

[0125] Figure 3 Fig. 11 is a TEM image of the synthesized lanthanum-based composite phosphorus removal material. It can also be seen that the synthesized lanthanum-based composite phosphorus removal material is loose and porous, the shape is relatively regular and uniform, and is composed of C, O and La elements.

[0126] Figure 4 Fig. 12 is an XRD pattern of the lanthanum-based composite phosphorus removal material before and after adsorption of P. It can be seen that after adsorption of phosphate, characteristic diffraction peaks belonging to LaPO4(JCPDS #73-0188) appear at 2θ = 14.5°, 22.7°, 25.2°, 28.7°, 31.0°, 41.4°, 48.0°, 53.4°.

[0127] Figure 5 Fig. 13 is an FTIR spectrum of the lanthanum-based composite phosphorus removal material before and after adsorption of P. It can be seen that before adsorption, the peak values at 3441.3 cm -1 and 1384.19 cm -1 correspond to O-H stretching vibration and bending vibration of M-OH (M represents the lanthanum-based composite phosphorus removal material), and the peak at 845 cm -1 represents La-O. After adsorption of phosphate, the peak at 3441.3 cm -1 moves to 3440 cm -1 , the peak intensity decreases, and the peak at 1384.19 cm -1 disappears, indicating that M-OH participates in the phosphate adsorption process. After adsorption of phosphate, the peaks at 1056.52 cm -1 and 615.28 cm -1and 541.76 cm -1 Three new peaks appeared, corresponding to the bending vibration of O-P-O and asymmetric stretching vibration of P-O. Meanwhile, the peak at 845 cm -1 disappeared, indicating that phosphate was adsorbed on La2O3-C through ligand exchange, and the adsorption results might lead to the formation of La–O–PO3.

[0128] Figure 6 , 7, 8 are XPS spectra of lanthanum-based composite phosphorus removal materials before and after adsorbing P. Figure 6 From the XPS full spectra before and after adsorption, it can be seen that a new peak appeared at 133.15 eV (P2p) after adsorption, indicating that phosphate ions were adsorbed on the surface of the adsorbent. Compared with the standard P2p spectrum of pure KH2PO4 (134.0 eV), the binding energy was lower. The results showed that a complex was formed between the lanthanum-based composite phosphorus removal material and the phosphate ion. The La3d spectrum (Fig. 7) showed that the binding energies were 852.1 eV and 835.2 eV before adsorbing phosphorus, and 852.8 eV and 835.4 eV after adsorbing phosphorus. It can be found that the La3d binding energy moved in the direction of increasing after adsorbing phosphorus. This is because the formation of P-O-La bond with strong electronegativity after adsorption will reduce the electron density, thus leading to the increase of La3d electron binding energy. It may also be due to the transfer of electrons from the valence band of the ligand atoms to the 4f orbitals of La atoms, indicating the formation of a lanthanum-based complex. Therefore, it can be inferred that the adsorption process of phosphate is mainly chemical adsorption. From the narrow spectrum in Fig. 8, it can be found that the binding energy of P 2p is about 133.15 eV, which is not the binding energy of P in KH2PO4, indicating that the P atom is adsorbed by the composite material and produces a new chemical bond with the La atom. Figure 7 Figure 8

[0129] Figure 12 is the adsorption isotherm of lanthanum-based composite phosphorus removal material for phosphate at room temperature (25℃), it can be seen that the equilibrium amount of lanthanum-based composite phosphorus removal material adsorbing phosphate gradually increases with the increase of phosphate concentration. The test data was fitted by using Langmuir model and Freundlich model, and the results are shown in Table 8.

[0130] Table 8 Linear fitting parameters of isothermal adsorption model

[0131] From Table 8, it can be seen that the correlation coefficient (R 2 =0.986) of Langmuir model is higher than that of Freundlich model (R 2 ​​=0.74), indicating that the Langmuir model is more suitable for describing the isothermal adsorption process of the lanthanum-based composite phosphorus removal material to phosphate, therefore, the adsorption of the lanthanum-based composite phosphorus removal material to phosphate is monolayer adsorption, and the process of adsorbing phosphate includes chemical adsorption and physical adsorption. The maximum adsorption amount calculated by the Langmuir equation is 142.65 mg / g, indicating that the lanthanum-based composite phosphorus removal material is a phosphorus removal adsorption material with good application potential.

[0132] Figure 13 is the adsorption kinetics fitting curve of the lanthanum-based composite phosphorus removal material to phosphate, as shown in the figure, the adsorption rate of the lanthanum-based composite phosphorus removal material is relatively fast in the initial stage, and gradually reaches adsorption equilibrium within 4h, and the maximum adsorption amount is 124.25 mg / g. The adsorption kinetics characteristics of the composite material are analyzed by using the pseudo-first-order and pseudo-second-order kinetic models.

[0133] Table 9 Kinetic model fitting parameters

[0134] From Figure 13 and Table 9, the correlation coefficient R 2 of the pseudo-second-order kinetic model is higher than that of the pseudo-first-order kinetic model, and the equilibrium adsorption amount (125 mg / g) calculated by the pseudo-second-order adsorption kinetics model is very close to the maximum adsorption amount obtained by the test, therefore, the adsorption process of the lanthanum-based composite phosphorus removal material to phosphate conforms to the pseudo-second-order kinetic model, indicating that the adsorption process of the lanthanum-based composite phosphorus removal material to phosphate is mainly chemical adsorption, and it is considered that the adsorption of the lanthanum-based composite phosphorus removal material to phosphorus mainly relies on the chemical action of La 3+ complexing with phosphate ions.

[0135] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A method for preparing a lanthanum-based composite phosphorus removal material, characterized in that, A lanthanum-based composite phosphorus removal material is prepared by using lanthanum nitrate hexahydrate and citric acid as a lanthanum source and a carbon source, respectively, including the following steps: S1, dissolving lanthanum nitrate hexahydrate and citric acid in water; S2, stirring and mixing under heating conditions until a viscous liquid is formed; S3, calcining the viscous liquid, the calcination temperature being 200-400℃ and the calcination time being 1-5h; S4, grinding the calcined product to obtain the lanthanum-based composite phosphorus removal material.

2. The production method according to claim 1, characterized by, In step S1, the molar ratio of the lanthanum nitrate hexahydrate to the citric acid is 1:0.25-1:1.

25.

3. The preparation method according to claim 1, characterized in that, In step S2, the stirring and mixing under heating conditions are performed by using a stepwise heating stirring method: first stirring and mixing at 60-80℃ for preliminary mixing, and then heating to 110-130℃ for high-temperature mixing.

4. The method of claim 1, wherein, In step S1, the molar ratio of the lanthanum nitrate hexahydrate to the citric acid is 1:0.5-1:

1.

5. The preparation method according to claim 1, characterized in that, In step S3, the calcination temperature is 240-360℃ and the calcination time is 1-3h.

6. The method of claim 1, wherein, In step S1, the lanthanum nitrate hexahydrate is first dissolved in water to form a lanthanum nitrate solution with a concentration of 0.1-0.5mol / L, and then the citric acid is added according to the molar ratio and mixed thoroughly.

7. The preparation method according to claim 3, characterized in that, The time for the preliminary mixing is more than 30min, and / or the time for the high-temperature mixing is more than 30min.

8. A lanthanum-based composite phosphorus removal material, characterized by, The preparation method is prepared according to any one of claims 1-7.

9. A method of removing phosphorus, characterized by, including the following steps: The lanthanum-based composite phosphorus removal material prepared by the preparation method of any one of claims 1-7 or the lanthanum-based composite phosphorus removal material of claim 8 is directly put into water to be treated.

10. The method of claim 9, wherein, The lanthanum-based composite phosphorus removal material after adsorbing phosphorus is desorbed and regenerated by using a regenerant.

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