A lanthanum-based composite phosphorus removal material and its preparation and removal methods

Abstract

This invention relates to a lanthanum-based composite phosphorus removal material and its preparation and removal methods, belonging to the field of water treatment. It solves at least one of the following problems existing in lanthanum-based phosphorus removal materials: the difficulty in balancing high adsorption capacity and structural stability, the difficulty in balancing excellent adsorption performance and simple preparation processes, and the difficulty in synergistically achieving high phosphorus removal efficiency and easy material recycling and regeneration. A method for preparing a lanthanum-based composite phosphorus removal material, using lanthanum nitrate hexahydrate and citric acid as the lanthanum source and carbon source respectively, includes the following steps: co-dissolving lanthanum nitrate hexahydrate and citric acid in water; stirring and mixing under heating conditions until a viscous liquid is formed; calcining the viscous liquid; and grinding the calcined product. This invention achieves high adsorption capacity, high selectivity, and rapid adsorption of phosphates in water, with stable structure, reduced production costs and process complexity, and excellent recycling and regeneration capabilities.

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] Based on the above analysis, the present invention aims to provide a lanthanum-based composite phosphorus removal material and its preparation method and phosphorus removal method, in order to solve at least one of the following problems existing in lanthanum-based phosphorus removal materials: it is difficult to balance high adsorption capacity and structural stability, it is difficult to balance excellent adsorption performance and simple preparation process, and it is difficult to coordinate efficient phosphorus removal effect with easy material recycling and regeneration.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] This invention provides a method for preparing a lanthanum-based composite phosphorus removal material, using lanthanum nitrate hexahydrate and citric acid as the lanthanum source and carbon source, respectively, comprising the following steps:

[0008] S1. Dissolve lanthanum nitrate hexahydrate and citric acid together in water;

[0009] S2. Stir and mix under heating conditions until a viscous liquid is formed;

[0010] S3. Calcine the viscous liquid at a temperature of 200~400℃ for 1~5 hours.

[0011] S4. Grind the calcined product to obtain the lanthanum-based composite phosphorus removal material.

[0012] Further, in step S1, the molar ratio of lanthanum nitrate hexahydrate to citric acid is 1:0.25 to 1:1.25.

[0013] Furthermore, in step S2, the stirring and mixing under heating conditions adopts a stepped heating and stirring method: first, stirring is carried out at 60~80℃ for preliminary mixing, and then the temperature is raised to 110~130℃ for high-temperature mixing.

[0014] Further, in step S1, the molar ratio of lanthanum nitrate hexahydrate to citric acid is 1:0.5 to 1:1.

[0015] Furthermore, in step S3, the calcination temperature is 240~360℃, and the calcination time is 1~3h.

[0016] Further, step S1 includes: first dissolving lanthanum nitrate hexahydrate in water to form a lanthanum nitrate solution with a concentration of 0.1~0.5 mol / L; then adding citric acid in molar ratio and mixing thoroughly.

[0017] Furthermore, the initial mixing time is 30 minutes or more; and / or, the high-temperature mixing time is 30 minutes or more.

[0018] This invention provides a lanthanum-based composite phosphorus removal material, prepared according to the aforementioned method.

[0019] This invention provides a phosphorus removal method, comprising the following steps:

[0020] The lanthanum-based composite phosphorus removal material obtained by the preparation method or the lanthanum-based composite phosphorus removal material described above is directly added to the water to be treated.

[0021] Furthermore, a regenerator is used to desorb and regenerate the lanthanum-based composite phosphorus removal material after phosphorus adsorption.

[0022] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0023] (1) To address the problem of "difficulty in balancing high adsorption capacity and structural stability", the preparation method of this invention constructs a rigid porous carbon framework by in-situ carbonization of citric acid at low temperature. This framework acts as a stable nanoreactor, firmly confining and dispersing highly active nano-lanthanum species (active components) on the outer surface and in 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. Compared with the adsorption capacity of existing phosphorus removal materials (generally lower than 80 mg P / g), this invention has a higher adsorption capacity. At the same time, in terms of "capacity retention rate in multiple adsorption-regeneration cycles", one of the core indicators for measuring long-term structural stability, the lanthanum-based composite phosphorus removal material obtained by this invention has a capacity retention rate comparable to or even better than that of existing technologies, indicating that the lanthanum-based composite phosphorus removal material of this invention has good long-term structural stability.

[0024] (2) To address the problem of "difficulty in balancing excellent adsorption performance with a simple preparation process," the preparation method of this invention utilizes a "one-pot method" and a "one-step low-temperature calcination" as its core processes. Compared with existing technologies that rely on expensive raw materials and / or complex processes to achieve high phosphorus adsorption capacity, this invention has the advantages of a simpler process and lower cost. This method uses citric acid as both a carbon precursor and a complexing agent, simultaneously completing the formation of the carbon matrix and the in-situ fixation 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 scaled-up process, thereby achieving excellent adsorption performance while reducing production costs and process complexity.

[0025] (3) To address the problem of the difficulty in synergistically achieving efficient phosphorus removal and easy material recycling, the preparation method of this invention imparts suitable macroscopic morphology and mechanical strength to the material by controlling the calcination process. The resulting composite material can achieve rapid and thorough desorption and regeneration through alkali treatment after adsorption. More importantly, its unique carbon-based lanthanum species composite structure can effectively resist the chemical impact of the regeneration environment, ensuring that lanthanum species are not lost and adsorption sites do not collapse. It can maintain stable high adsorption performance even after multiple adsorption-desorption cycles, thus solving the engineering application bottleneck of the difficulty in synergistically achieving efficient phosphorus removal and easy recycling.

[0026] (4) In some preferred embodiments, the present invention 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.

[0027] (5) In some specific embodiments, the preparation method of the present invention and the performance indicators of the lanthanum-based composite phosphorus removal material obtained therefrom are as follows:

[0028] a) Initial high adsorption capacity and P removal rate: reflect the stable construction and efficient exposure of active sites;

[0029] The lanthanum-based composite phosphorus removal material obtained in this invention exhibits a phosphorus adsorption capacity (P adsorption capacity) > 80 mg P / g, and a phosphorus removal rate > 60% for simulated wastewater with an initial concentration of 50 mg P / L. When the process parameters are further optimized (molar ratio of lanthanum hexahydrate to citric acid is 1:0.5~1:1, calcination temperature is 240~360℃, and 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 optimal synthesis conditions, such as a molar ratio of lanthanum 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 its peak, with a P adsorption capacity as high as 124.25 mg P / g and a P removal rate as high as 99.4% for simulated wastewater with an initial concentration of 50 mg P / L.

[0030] b) High selective removal rate in complex water bodies: confirming the robustness of the "endosphere complexation" mechanism;

[0031] In actual wastewater, even if multiple coexisting anions (such as...) exist... Despite the competition from other materials, the lanthanum-based composite phosphorus removal material of this invention can still maintain a phosphate removal rate of over 99%.

[0032] c) High capacity retention after multiple cycles: This directly demonstrates the overall structure's durability and excellent regenerative capabilities;

[0033] After five cycles of "adsorption-alkali desorption" regeneration, the P adsorption capacity retention rate of the lanthanum-based composite phosphorus removal material of the present invention is still as high as 81.7% or more.

[0034] The above performance indicators systematically demonstrate that the lanthanum-based composite phosphorus removal material provided by this invention has excellent adsorption capacity, outstanding structural stability and regeneration and recycling capacity, providing a solid guarantee for its large-scale application in actual water purification.

[0035] (6) Compared with existing lanthanum-based phosphorus removal composite materials, the lanthanum-based composite phosphorus removal material prepared by this invention achieves multiple structural breakthroughs:

[0036] In terms of site distribution, it breaks through the traditional limitation of "easy aggregation of surface load", and realizes the uniform dispersion of lanthanum species (active components) at the atomic level inside and outside the carbon framework, which significantly improves site utilization.

[0037] In terms of structural stability, it overcomes the weakness of traditional "physical bonding is easy to lose". By loading lanthanum species in situ onto a nanoporous carbon matrix, an integrated stable structure is constructed, which significantly reduces the dissolution of active components.

[0038] In terms of mass transfer and selectivity, it solves the problem of "easy pore blockage and poor anti-interference" of traditional materials. By utilizing the in-situ formed through-level multi-level pores and the specific internal sphere complexation mechanism, it achieves rapid transport and highly selective capture of phosphate ions.

[0039] This integrated loose porous carbon matrix + lanthanum species nanoscale composite structure, characterized by "uniform dispersion, in-situ loading, and rapid mass transfer," successfully solves the core contradictions of traditional materials, such as "hidden active sites, unstable binding, and hindered mass transfer," endowing the material with comprehensive advantages of high adsorption capacity, high selectivity, high stability, and easy regeneration.

[0040] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0041] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0042] Figure 1 The images shown are SEM images of the lanthanum-based composite phosphorus removal material of Example 3 of this invention before and after phosphorus adsorption (a, b, c before adsorption; d, e, f after adsorption).

[0043] Figure 2 The images show the EDS diagrams of the lanthanum-based composite phosphorus removal material before and after phosphorus adsorption in Example 3 of this invention (a before adsorption, b after adsorption).

[0044] Figure 3 This is a TEM image of the lanthanum-based composite phosphorus removal material of Example 3 of the present invention;

[0045] Figure 4The images show the XRD patterns of the lanthanum-based composite phosphorus removal material before and after phosphorus adsorption in Example 3 of this invention.

[0046] Figure 5 The images shown are FTIR images of the lanthanum-based composite phosphorus removal material before and after phosphorus adsorption in Example 3 of this invention.

[0047] Figure 6 The XPS full spectrum of the lanthanum-based composite phosphorus removal material before and after phosphorus adsorption in Example 3 of this invention is shown below.

[0048] Figure 7 The 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.

[0049] 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;

[0050] 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;

[0051] 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;

[0052] 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;

[0053] 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;

[0054] Figure 13 The figure shows the kinetics of phosphorus adsorption by the lanthanum-based composite phosphorus removal material in Example 3 of this invention.

[0055] 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;

[0056] 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.

[0057] 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;

[0058] 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;

[0059] 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;

[0060] 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

[0061] 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.

[0062] In the prior art, citric acid is mainly used as a complexing agent, solvent, or fuel in the preparation of lanthanum-based composite materials. 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. It is completely decomposed in the subsequent high-temperature calcination process (such as above 550°C) and is not retained in the final product (such as lanthanum cerate, lanthanum oxide, etc.). In addition, most of the lanthanum-based composite materials involving citric acid in the prior art are used to prepare catalysts, which are completely different from the application scenarios of the present invention.

[0063] Unlike existing technologies, this invention breaks with convention by innovatively using citric acid as both a key reactant and a carbon source. By controlling a relatively low calcination temperature (e.g., 200-400°C), citric acid is incompletely decomposed and transformed in situ into an amorphous nanoporous carbon matrix (carbon substrate). Simultaneously, the lanthanum source is decomposed and synthesized into lanthanum species during this process, which are then generated in situ and uniformly doped and loaded onto the outer surface and porous structure of the carbon substrate, ultimately forming a novel "carbon-based + lanthanum species" composite material. This transformation of citric acid from a "temporary worker" to a "building skeleton," and the fundamental change in the product structure from a pure inorganic phase to an inorganic / organic carbon composite, significantly improves the loading and dispersion uniformity of lanthanum species. It also fully utilizes the synergistic effect between the adsorption capacity of the carbon substrate and the specific adsorption of lanthanum species, achieving superior results in adsorption capacity, rate, and material structural stability compared to existing technologies through a simpler and more economical preparation process. The specific technical solution of this invention is as follows:

[0064] In a first aspect, the present invention provides a method for preparing a lanthanum-based composite phosphorus removal material, using lanthanum nitrate hexahydrate and citric acid as the lanthanum source and carbon source, respectively, comprising the following steps:

[0065] S1. Dissolve lanthanum nitrate hexahydrate and citric acid together in water;

[0066] S2. Stir and mix under heating conditions until a viscous liquid is formed;

[0067] S3. Calcine the viscous liquid at a temperature of 200~400℃ for 1~5 hours.

[0068] S4. Grind the calcined product to obtain the lanthanum-based composite phosphorus removal material.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] The third contradiction in the preparation of existing lanthanum-based phosphorus removal materials is that many existing nanoscale lanthanum-based materials have problems such as difficulty in solid-liquid separation and low recovery rate due to their small particle size and low density. Moreover, the regeneration process easily damages their structure, leading to a sharp decline in adsorption capacity.

[0075] To address the challenge of synergistically achieving efficient phosphorus removal and easy material recyclability, this invention employs a controlled calcination process to impart suitable macroscopic morphology and mechanical strength to the material. The resulting composite material can be rapidly and thoroughly desorbed and regenerated after adsorption via alkali treatment. More importantly, its unique carbon-based lanthanum species composite structure effectively resists the chemical shocks of the regeneration environment, ensuring no loss of lanthanum species and no collapse of adsorption sites. It maintains stable high performance even after multiple adsorption-desorption cycles, fundamentally solving the engineering application bottleneck of the difficulty in synergistically achieving efficient phosphorus removal and easy recyclability.

[0076] Specifically, in step S1, the molar ratio of lanthanum nitrate hexahydrate to citric acid is 1:0.25 to 1:1.25.

[0077] For example, the molar ratio of 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.

[0078] Preferably, in step S1, the molar ratio of lanthanum nitrate hexahydrate to citric acid is 1:0.5 to 1:1; more preferably, it is 1:0.7 to 1:0.8.

[0079] For example, 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.

[0080] 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.

[0081] It should be noted that this invention aims to construct an amorphous carbon framework with high specific surface area and abundant pores by synergistically controlling the molar ratio, calcination temperature, and time, and to achieve in-situ uniform anchoring of nanoscale lanthanum species (lanthanum oxide and / or lanthanum hydroxide) on the outer surface and pore structure of the carbon framework. Controlling the molar ratio of lanthanum nitrate hexahydrate to citric acid to 1:0.5~1:1 (more preferably 1:0.7~1:0.8) can balance the construction of the carbon framework and the dispersion of lanthanum species—an excessively high molar ratio (too little citric acid relative to lanthanum nitrate) will lead to an incomplete carbon framework and lanthanum species agglomeration, while an excessively low molar ratio (too little lanthanum nitrate relative to citric acid) will result in an excessively thick carbon framework layer and pore blockage. Controlling the calcination conditions to 240–360℃ for 1–3 h (more preferably 280–360℃ for 1.5–2.5 h) allows for optimal partial carbonization of citric acid and ensures the complete conversion of the lanthanum source into highly active nano-lanthanum species. Too low a calcination temperature or too short a time leads to insufficient precursor decomposition (citric acid and lanthanum nitrate fail to fully decompose and transform, resulting in a porous and fragile carbon framework, and lanthanum species fail to completely convert into active lanthanum oxides and / or lanthanum hydroxides, leading to low material adsorption activity). Too high a calcination temperature or too long a time causes carbon framework collapse and lanthanum species sintering (the carbon framework becomes excessively graphitized, reducing porosity; simultaneously, lanthanum species undergo excessive sintering, transforming from highly active nanoparticles into large-sized crystals, significantly reducing specific surface area and active sites, thus decreasing adsorption performance). The synergistic optimization of these parameters achieves an ideal combination of nanoscale "porous carbon matrix" and "highly dispersed lanthanum active sites," which is key to obtaining excellent adsorption performance, structural stability, and regeneration capability. Imbalance in any single parameter may lead to a decrease in material performance.

[0082] Specifically, in step S2, the stirring and mixing under heating conditions adopts a stepped heating and stirring method: first, stirring is carried out at 60~80℃ for preliminary mixing, and then the temperature is raised to 110~130℃ for high-temperature mixing.

[0083] It should be noted that the stepped heating and stirring process employed in this invention achieves precise control of the precursor structure through staged temperature control. In the low-temperature stage of 60-80℃, the solution maintains good fluidity, allowing lanthanum nitrate hexahydrate and citric acid molecules to mix thoroughly and undergo pre-complexation, forming a uniform precursor complex network. This effectively avoids component segregation and premature hydrolysis and precipitation of lanthanum ions caused by rapid water evaporation and excessively high local concentrations due to excessively high temperatures. In the high-temperature stage of 110-130℃, the system experiences a rapid increase in viscosity due to rapid water evaporation, driving the precursor complex to transform from a solution to a three-dimensional network gel, stabilizing and solidifying the molecular-level homogeneity into a gel structure. This staged temperature control method ensures the uniform distribution of active components at the molecular scale, laying a better foundation for the formation of an ideal porous carbon matrix-lanthanum species composite nanostructure during subsequent calcination.

[0084] For example, the initial mixing temperature is 60°C, 65°C, 70°C, 75°C, or 80°C. The initial mixing time is 30 minutes or more, such as 30 minutes, 40 minutes, 50 minutes, or 60 minutes; for example, the initial mixing time is 30 minutes to 40 minutes.

[0085] For example, the temperature is increased to the initial mixing temperature at a rate of 5~10℃ / min.

[0086] For example, the stirring speed during the initial mixing is 240~320 rpm; for example, 260 rpm, 280 rpm, 300 rpm.

[0087] For example, the temperature of the high-temperature mixture is 110°C, 115°C, 120°C, 125°C, or 130°C.

[0088] For example, the high-temperature mixing time is 30 minutes or more, for example, 30 to 60 minutes, until a viscous liquid is formed, and then step S3 is continued.

[0089] For example, the temperature is increased to the temperature of the high-temperature mixture at a rate of 5~10℃ / min.

[0090] For example, the stirring speed during high-temperature mixing is 240~320 rpm; for example, 260 rpm, 280 rpm, 300 rpm.

[0091] Specifically, step S1 includes: first dissolving lanthanum nitrate hexahydrate in water to form a lanthanum nitrate solution with a concentration of 0.1~0.5 mol / L; then adding citric acid by molar ratio and mixing thoroughly.

[0092] For example, in step S1, lanthanum nitrate hexahydrate is dissolved in water, and the concentration of the resulting lanthanum nitrate solution is 0.1 mol / L, 0.14 mol / L, 0.16 mol / L, 0.18 mol / L, 0.20 mol / L, 0.30 mol / L, 0.40 mol / L, or 0.50 mol / L.

[0093] Preferably, in step S1, a lanthanum nitrate solution with a concentration of 0.1~0.2 mol / L is formed.

[0094] For example, in step S1, lanthanum nitrate hexahydrate is dissolved in water and stirred at 240-320 rpm for at least 60 minutes to ensure that lanthanum nitrate hexahydrate is fully dissolved in water.

[0095] For example, in step S1, citric acid is added in a molar ratio, and the thorough mixing includes: ultrasonic treatment at a power of 100~500W for more than 10 minutes to ensure that lanthanum nitrate hexahydrate and citric acid are thoroughly mixed and co-soluble in water.

[0096] Specifically, in step S3, the calcination atmosphere is air.

[0097] Specifically, in step S3, the temperature is increased to the calcination temperature at a rate of 5~10℃ / min.

[0098] Specifically, in step S3, the calcination is carried out in a tubular furnace.

[0099] Specifically, in step S4, the grinding method is manual grinding.

[0100] Specifically, in step S4, the grinding medium is an agate grinding ball.

[0101] Specifically, in step S4, the grinding is carried out at room temperature in air.

[0102] Preferably, in step S4, the parameters of the product after grinding are required to be as follows:

[0103] Specific surface area: Grinding should not significantly damage the inherent porous structure of the material, and the specific surface area of ​​the material after grinding should be maintained in the range of 20-90 m² / g.

[0104] Secondly, the present invention provides a lanthanum-based composite phosphorus removal material prepared according to the preparation method described in the first aspect. Specifically, the lanthanum-based composite phosphorus removal material is a nanoporous carbon-supported lanthanum composite material, comprising:

[0105] Amorphous nanoporous carbon matrix;

[0106] And active components embedded in situ in the nanoporous carbon matrix;

[0107] The active component includes lanthanum oxide. and / or lanthanum hydroxide .

[0108] It is understood that the lanthanum-based composite phosphorus removal material is formed by reacting lanthanum nitrate hexahydrate with citric acid as a precursor; wherein,

[0109] Citric acid pyrolysis forms an amorphous nanoporous carbon matrix, and lanthanum nitrate is converted into lanthanum oxide. and / or lanthanum hydroxide Lanthanum species are used as active components, which are loaded in the nanoporous carbon matrix in an in-situ intercalation manner.

[0110] Compared with existing lanthanum-based composite phosphorus removal materials, the lanthanum-based composite phosphorus removal material prepared in this invention achieves a fundamental structural breakthrough and possesses significant advantages:

[0111] First, regarding the construction and distribution of active sites, traditional supported materials (such as lanthanum supported on activated carbon, zeolite, etc.) mainly achieve binding through physical impregnation or mixing. Lanthanum species tend to agglomerate on the surface of the support and block the pores, resulting in uneven site distribution and low utilization. However, this invention achieves maximum exposure and efficient utilization of active sites by in-situ co-carbonization of citric acid and lanthanum source, enabling lanthanum species to be uniformly embedded at the molecular / nanoscale and in-situ loaded in the entire system (including the outer surface and internal pores) of the three-dimensional porous carbon framework.

[0112] Secondly, regarding the stability of the material structure, the physical adsorption or weak bonding between lanthanum and the support in traditional materials is prone to failure under hydraulic erosion and acid-base changes, leading to the dissolution and loss of active components. However, the integrated stable "carbon-lanthanum" structure formed by this invention anchors the active sites in the entire 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.

[0113] Furthermore, in terms of mass transfer pathways and selectivity, the pores of traditional materials are easily blocked due to loading, resulting in low mass transfer efficiency, and their surface sites are easily interfered with by coexisting anions. The three-dimensional interconnected multi-level channels generated in situ in this invention provide a "highway" for the rapid diffusion of phosphate ions, and the highly exposed lanthanum sites achieve adsorption by forming highly specific "inner sphere complexes" (La–O–P bonds), making them almost unaffected by other anions in complex water bodies, exhibiting excellent selectivity.

[0114] It should be noted that the microstructure of the lanthanum-based composite phosphorus removal material exhibits a loose and porous structure with a high specific surface area of ​​≥20m² / g, and a multi-level porous structure with both micropores and mesopores.

[0115] Specifically, the specific surface area of ​​the lanthanum-based composite phosphorus removal material is 20~90 m² / g.

[0116] For example, the specific surface area of ​​the phosphorus removal material is 25m² / g, 30m² / g, 40m² / g, 50m² / g, 60m² / g, 70m² / g, 80m² / g, or 85m² / g.

[0117] Specifically, the average pore size of the lanthanum-based composite phosphorus removal material is 5~20 nm.

[0118] For example, the average pore size of the lanthanum-based composite phosphorus removal material is 5 nm, 10 nm, 15 nm, or 20 nm.

[0119] Specifically, the lanthanum-based composite phosphorus removal material contains 30-80% lanthanum by mass and 5-35% carbon by mass.

[0120] For example, the mass percentage of lanthanum in the lanthanum-based composite phosphorus removal material is 30.75%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%.

[0121] For example, the mass percentage of carbon in the lanthanum-based composite phosphorus removal material is 5%, 10%, 15%, 20%, 25%, 30%, or 35%.

[0122] Specifically, the lanthanum-based composite phosphorus removal material has a hierarchical pore structure with both micropores and mesopores, wherein the micropore diameter is less than 2 nm and the mesopore diameter is 2-50 nm. For example, the mesopore diameters are 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, and 50 nm.

[0123] Specifically, the lanthanum-based composite phosphorus removal material has a phosphorus adsorption capacity greater than 80 mg P / g and a phosphorus removal rate greater than 60%.

[0124] In some preferred embodiments, the phosphorus adsorption capacity of the lanthanum-based composite phosphorus removal material is greater than 90 mg P / g, and the phosphorus removal rate is greater than 70%.

[0125] In some preferred embodiments, the lanthanum-based composite phosphorus removal material has a phosphorus adsorption capacity greater than 120 mg P / g and a phosphorus removal rate greater than 99%.

[0126] Specifically, after five adsorption-alkali regeneration cycles, the phosphorus adsorption capacity retention rate of the lanthanum-based composite phosphorus removal material is above 81.7%.

[0127] In some embodiments, the lanthanum-based composite phosphorus removal material is prepared by calcination using lanthanum nitrate hexahydrate as the lanthanum source and citric acid as the carbon source; wherein,

[0128] The pyrolysis of citric acid forms the amorphous nanoporous carbon matrix, and the conversion of lanthanum nitrate hexahydrate forms the active component.

[0129] The conditions for the calcination process include: calcination temperature of 200~400℃ and calcination time of 1~5h.

[0130] For example, 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.

[0131] Preferably, 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.

[0132] In some embodiments, the molar ratio of lanthanum nitrate hexahydrate to citric acid is 1:0.25 to 1:1.25.

[0133] For example, the molar ratio of 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.

[0134] Preferably, the molar ratio of lanthanum nitrate hexahydrate to citric acid is 1:0.5 to 1:1; more preferably, it is 1:0.7 to 1:0.8.

[0135] In some embodiments, the calcination process targets a viscous precursor obtained by initially mixing lanthanum nitrate hexahydrate with citric acid at 60-80°C and then at a high temperature of 110-130°C. Exemplarily, the initial mixing temperature is 60°C, 65°C, 70°C, 75°C, or 80°C. The initial mixing time is ≥30 min, such as 30 min, 40 min, 50 min, or 60 min; for example, the initial mixing time is 30 min to 40 min.

[0136] For example, the temperature is increased to the initial mixing temperature at a rate of 5~10℃ / min.

[0137] For example, the stirring speed during the initial mixing is 240~320 rpm.

[0138] For example, the temperature of the high-temperature mixture is 110°C, 115°C, 120°C, 125°C, or 130°C.

[0139] For example, the high-temperature mixing time is 30 minutes or more, for example, 30 to 60 minutes, until a viscous liquid is formed, and then step S3 is continued.

[0140] For example, the temperature is increased to the temperature of the high-temperature mixture at a rate of 5~10℃ / min.

[0141] For example, the stirring speed during high-temperature mixing is 240~320 rpm.

[0142] Thirdly, the present invention provides a phosphorus removal method, comprising the following steps:

[0143] Adsorption step: The lanthanum-based composite phosphorus removal material obtained by the preparation method described in the first aspect or the lanthanum-based composite phosphorus removal material described in the second aspect is directly added to the water to be treated. During 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 in the lanthanum-based composite phosphorus removal material and the chemical adsorption of lanthanum species, thus obtaining the lanthanum-based composite phosphorus removal material after phosphorus adsorption.

[0144] Regeneration step: The lanthanum-based composite phosphorus removal material after phosphorus adsorption is desorbed and regenerated using a regenerating agent to achieve reuse.

[0145] Optionally, the regenerant includes strong alkaline solutions (such as NaOH solution, KOH solution) and strong alkaline salt solutions (such as sodium carbonate solution, sodium bicarbonate solution).

[0146] Preferably, in the regeneration step, the regenerator is a NaOH solution.

[0147] 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.

[0148] Specifically, the amount of NaOH solution used is based on the liquid-to-solid ratio, with 40-80 mL of NaOH solution used per gram of the adsorbed lanthanum-based composite phosphorus removal material.

[0149] Specifically, the desorption and regeneration temperature is 15~30℃, and the time is 8~12h.

[0150] In one embodiment, the regeneration step specifically includes the following steps:

[0151] S1. Separation and washing: The lanthanum-based composite phosphorus removal material (hereinafter referred to as saturated material) after being saturated with adsorbed phosphorus compounds (such as phosphates) is separated from the aqueous phase (e.g., by sedimentation, centrifugation or filtration) and gently washed with deionized water to remove impurities and residual phosphorus solution adhering to the surface of the adsorbed saturated material.

[0152] S2, Desorption reaction: The washed saturated material is immersed in the regenerator solution and the desorption reaction is carried out in a constant temperature shaker or stirred reactor to obtain a mixture of desorbed lanthanum-based composite phosphorus removal material and desorption liquid (the regenerator is converted into desorption liquid after adsorbing phosphorus-containing substances).

[0153] Reaction conditions: At 15~30℃, the reaction is carried out by shaking or stirring at 240~320 rpm for 8~12 hours to ensure that phosphorus-containing compounds (such as phosphates) are fully desorbed;

[0154] 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).

[0155] S4. Drying: Place the desorbed lanthanum-based composite dephosphorizing material, which has been washed to neutral, in an oven at 60~105℃ and dry for 4~12 hours to obtain regenerated lanthanum-based composite dephosphorizing material, which can then be reused in the dephosphorization process.

[0156] It is understood that the "adsorption capacity" or "P adsorption capacity" mentioned in this invention are standard performance indicators in the field, specifically referring to the maximum mass of phosphorus that a unit mass (per gram) of phosphorus removal material can adsorb when adsorption reaches equilibrium. This value mainly characterizes the inherent limiting adsorption capacity of the material itself and is not significantly related to the initial concentration of phosphorus in the water to be treated. Therefore, it provides a unified and comparable benchmark for comparing the performance of different phosphorus removal materials.

[0157] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and comparative examples.

[0158] Example 1

[0159] This embodiment provides a method for preparing a lanthanum-based composite phosphorus removal material, using lanthanum nitrate hexahydrate and citric acid as the lanthanum source and carbon source, respectively, including the following steps:

[0160] S1. Dissolve lanthanum nitrate hexahydrate and citric acid together in water;

[0161] First, dissolve 5 mmol of lanthanum nitrate hexahydrate (La(NO3)3·6H2O) in 30 ml of deionized water and stir at 240 rpm for 60 min to ensure that the lanthanum nitrate hexahydrate is fully dissolved in the water to form a lanthanum nitrate solution with a concentration of 0.167 mol / L.

[0162] Weigh out the appropriate amount of citric acid according to the molar ratio of lanthanum nitrate hexahydrate to citric acid of 1:0.25 and add it to the lanthanum nitrate solution. Sonicate the solution at 100W for 10 minutes to ensure that the lanthanum nitrate hexahydrate and citric acid are fully mixed and co-soluble in water.

[0163] S2. Stir and mix under heating conditions until a viscous liquid is formed;

[0164] Increase the temperature at a rate of 10℃ / min to the initial mixing temperature of 80℃, and stir at 240 rpm for 30 min; then increase the temperature at a rate of 10℃ / min to the high-temperature mixing temperature of 120℃, and continue stirring at 240 rpm for 30 min until a viscous liquid is formed (the volume of the viscous liquid is 2 ml).

[0165] S3. Calcine the viscous liquid at a temperature of 200~400℃ for 1~5 hours.

[0166] The viscous liquid was poured into a crucible and placed in a tube furnace. It was then calcined in air atmosphere, with the temperature increased at a rate of 10℃ / min to the calcination temperature of 320℃. The calcination time was 2 hours.

[0167] S4. Grind the calcined product to obtain the lanthanum-based composite phosphorus removal material.

[0168] The calcined product was manually ground in air at room temperature using agate grinding balls as the grinding medium. The specific surface area of ​​the lanthanum-based composite dephosphorization material after grinding was controlled within the range of 20~90 m² / g.

[0169] 20 mg of the lanthanum-based composite phosphorus removal material obtained in the above steps was added to a sample solution with an initial phosphorus concentration of 50 mg / L. The mixture was reacted in a shaker at 240 rpm and 25°C for 24 h. Afterward, 2 mL of the supernatant was filtered through a 0.45 μm filter membrane, and the phosphorus concentration was determined using a UV spectrophotometer according to the national standard GB / T 18114.10-2010. The lanthanum-based composite phosphorus removal material obtained in this example exhibited a phosphorus adsorption capacity of 87.125 mg P / g and a phosphorus removal rate as high as 69.7%.

[0170] The difference between Examples 2-5 and Comparative Examples 1-2 and Example 1 is the molar ratio of lanthanum nitrate hexahydrate to citric acid; the other steps and parameters are the same as in Example 1.

[0171] The difference between Examples 6-10 and Comparative Examples 3-5 and Example 3 is the calcination temperature; the other steps and parameters are the same as in Example 3.

[0172] The difference between Examples 11-13 and Comparative Examples 6-7 and Example 3 is the calcination time; the other steps and parameters are the same as in Example 3.

[0173] The difference between Examples 14-17 and Example 3 lies in the process parameters listed in Table 5 below; the remaining steps and parameters are the same as in Example 3.

[0174] Through testing and characterization, the lanthanum-based composite phosphorus removal materials described in Examples 1 to 17 are nanoporous carbon-supported lanthanum composite materials, comprising: an amorphous nanoporous carbon matrix; and an active component in situ embedded in the nanoporous carbon matrix; wherein the active component comprises lanthanum oxide. and / or lanthanum hydroxide The lanthanum-based composite phosphorus removal materials described in Examples 1 to 17 have a multi-level porous structure with both micropores and mesopores, wherein the micropore diameter is less than 2 nm and the mesopore diameter is 2-50 nm.

[0175] Table 1. Structure and composition parameters of the lanthanum-based composite phosphorus removal materials in the examples.

[0176]

[0177] Table 2. Process parameter variables and phosphorus removal performance of the examples and comparative examples (Group 1)

[0178]

[0179] Table 3. Process parameter variables and phosphorus removal performance of the examples and comparative examples (Group 2)

[0180]

[0181] Table 4. Process parameter variables and phosphorus removal performance of the examples and comparative examples (Group 3)

[0182]

[0183] Table 5. Process parameter variables and phosphorus removal performance of the examples (Group 4)

[0184]

[0185] In the above embodiments, the phosphorus-containing sample solution (sample solution with initial phosphorus concentration) used in the test was prepared with potassium dihydrogen phosphate (KH2PO4). Specifically, 0.2195 g of KH2PO4 was weighed and placed in 100 mL of ultrapure water. After magnetic stirring for 1 h to ensure complete dissolution, it was transferred to a 1 L volumetric flask, ultrapure water was added to make up to volume and shaken well to obtain a 50 mg / L phosphate standard sample stock solution (i.e., the sample solution with initial phosphorus concentration).

[0186] Example 18

[0187] This embodiment provides a phosphorus removal method, including the following steps:

[0188] Adsorption step: The lanthanum-based composite phosphorus removal material obtained 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 phosphorus-containing compounds in the water are removed by the combined action of the physical adsorption of the nanoporous carbon matrix in the lanthanum-based composite phosphorus removal material and the chemical adsorption of lanthanum species, and the phosphorus-adsorbed lanthanum-based composite phosphorus removal material is obtained.

[0189] Regeneration step: The lanthanum-based composite phosphorus removal material after phosphorus adsorption is desorbed and regenerated using a 4 mol / L NaOH solution to achieve reuse; the amount of NaOH solution used is based on the liquid-to-solid ratio, with 40 mL of NaOH solution used per gram of lanthanum-based composite phosphorus removal material after phosphorus adsorption.

[0190] Specifically, the regeneration step includes the following steps:

[0191] S1. Separation and washing: The lanthanum-based composite phosphorus removal material (hereinafter referred to as saturated material) after phosphorus adsorption is separated from the aqueous phase (e.g., by sedimentation, centrifugation or filtration) and washed lightly with deionized water to remove impurities and residual phosphorus solution adhering to the surface of the adsorbed saturated material.

[0192] 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).

[0193] 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;

[0194] 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).

[0195] 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.

[0196] 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.

[0197] Application Example 1

[0198] 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.

[0199] Table 6. Wastewater composition from a wastewater treatment plant in Baotou

[0200]

[0201] Table 7. Phosphorus content of wastewater from a wastewater treatment plant in Baotou after adsorption treatment.

[0202]

[0203] Figure 1Images a, b, and c are SEM images of the lanthanum-based composite phosphorus removal material before adsorption. It can be seen that the synthesized lanthanum-based composite phosphorus removal material is loose and porous, with a relatively regular and uniform shape. Images e, d, and f are SEM images of the lanthanum-based composite phosphorus removal material after P adsorption. It can be seen that there are many granular objects on the surface of the lanthanum-based composite phosphorus removal material, indicating that P in the solution was successfully adsorbed and lanthanum phosphate crystals were formed.

[0204] Figure 2 a is the EDS diagram of the lanthanum-based composite phosphorus removal material before adsorption. It can be seen that the lanthanum-based composite phosphorus removal material is composed of three elements: C, O and La. Figure 2 b is the EDS diagram of the lanthanum-based composite phosphorus removal material after P adsorption. A strong P element signal can be seen, and the P element content after adsorption is 7.3%, which proves that the lanthanum-based composite phosphorus removal material successfully adsorbed P.

[0205] Figure 3 The image shows a TEM image of the synthesized lanthanum-based composite phosphorus removal material. It can be seen that the synthesized lanthanum-based composite phosphorus removal material is loose and porous, with a relatively regular and uniform shape, and is composed of C, O, and La elements.

[0206] Figure 4 The images show the XRD patterns of the lanthanum-based composite phosphorus removal material before and after P adsorption. It can be seen that after phosphate adsorption, 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°, and 53.4°.

[0207] Figure 5 These are the FTIR spectra of the lanthanum-based composite phosphorus removal material before and after P adsorption. It can be seen that before adsorption, the phosphorus concentration is 3441.3 cm⁻¹. -1 and 1384.19cm -1 The peak values ​​at 845 cm⁻¹ correspond to the O–H tensile and bending vibrations of M–OH (M represents lanthanum-based composite phosphorus removal material), respectively. -1 The peak at 3441.3 cm⁻¹ represents La-O. However, after phosphate is adsorbed, the peak at 3441.3 cm⁻¹... -1 Moved to 3440cm -1 The peak intensity decreased, and at 1384.19 cm⁻¹ -1 The disappearance of the peak indicates that M-OH participated in the phosphate adsorption process. After adsorbing the pericarpate, the peak at 1056.52 cm⁻¹... -1 615.28cm -1 and 541.76cm -1 Three new peaks appeared nearby, corresponding to the bending vibration of OPO and the asymmetric tensile vibration of PO, respectively. Meanwhile, at 845 cm⁻¹... -1The disappearance of the peak indicates that phosphate ions are adsorbed onto La2O3-C through ligand exchange, and the adsorption result may lead to the formation of La–O–PO3.

[0208] Figure 6 Figures 7 and 8 show the XPS spectra of the lanthanum-based composite phosphorus removal material before and after P adsorption. Figure 6 XPS full spectra before and after adsorption show a new peak at 133.15 eV (P2p) after adsorption, indicating that phosphate ions are adsorbed onto the adsorbent surface. Compared to the standard P2p spectrum of pure KH₂PO₄ (134.0 eV), the binding energy shift is lower. The results indicate that a complex is formed between the lanthanum-based composite phosphorus removal material and phosphate ions, as shown in the La₃d spectrum (…). Figure 7 Before phosphorus adsorption, the binding energies were 852.1 eV and 835.2 eV, respectively. After phosphorus adsorption, the binding energies became 852.8 eV and 835.4 eV, respectively. It can be observed that after phosphorus adsorption, the La3d binding energy shifts towards increasing. This is because after adsorption, a strongly electronegative PO-La bond is formed, which reduces the electron density, thus leading to an increase in the La3d electron binding energy. It is also possible that electrons transfer from the valence band of the ligand atom to the 4f orbital of the La atom, indicating the formation of a lanthanide complex. Therefore, it can be inferred that the adsorption process of phosphate is mainly chemisorption. Figure 8 The narrow spectrum shows that the binding energy of P 2p is about 133.15 eV, which is not the binding energy of P in KH2PO4. This indicates that after the P atom is adsorbed by the composite material, it forms a new chemical bond with the La atom in it.

[0209] Figure 12 The table shows the adsorption isotherm of phosphate by the lanthanum-based composite phosphorus removal material at room temperature (25℃). It can be seen that the equilibrium amount of phosphate adsorbed by the lanthanum-based composite phosphorus removal material gradually increases with increasing phosphate concentration. The experimental data were fitted using the Langmuir and Freundlich models, and the results are shown in Table 8.

[0210] Table 8 Linear fitting parameters of the isothermal adsorption model

[0211]

[0212] Table 8 shows that the correlation coefficient (R²) of the Langmuir model is... 2 =0.986) is higher than the Freundlich model (R 2=0.74), indicating that the Langmuir model is more suitable for describing the isothermal adsorption process of phosphate by the lanthanum-based composite phosphorus removal material. Therefore, the adsorption of phosphate by the lanthanum-based composite phosphorus removal material is monolayer adsorption, and the adsorption process of phosphate involves both chemisorption and physisorption. The maximum adsorption capacity 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.

[0213] Figure 13 The figure shows the adsorption kinetics fitting curves of lanthanum-based composite phosphorus removal material for phosphate. As can be seen from the figure, the adsorption rate of the lanthanum-based composite phosphorus removal material is relatively fast in the initial stage, gradually reaching adsorption equilibrium within 4 hours, with a maximum adsorption capacity of 124.25 mg / g. The adsorption kinetic characteristics of the composite material were analyzed using pseudo-first-order and pseudo-second-order kinetic models.

[0214] Table 9 Fitting parameters for the dynamic model

[0215]

[0216] from Figure 13 As shown in Table 9, the correlation coefficient R of the quasi-second-order dynamics model is... 2 The adsorption capacity calculated by the pseudo-first-order kinetic model is higher than that of the pseudo-second-order adsorption kinetic model, and the equilibrium adsorption capacity (125 mg / g) calculated by the pseudo-second-order adsorption kinetic model is very close to the maximum adsorption capacity obtained experimentally. Therefore, the adsorption process of phosphate by the lanthanum-based composite phosphorus removal material conforms to the pseudo-second-order kinetic model, indicating that the adsorption process of phosphate by the lanthanum-based composite phosphorus removal material is mainly chemical adsorption. It is believed that the adsorption of phosphorus by the lanthanum-based composite phosphorus removal material mainly relies on La 3+ Chemical effects on the complexation of phosphate ions.

[0217] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a lanthanum-based composite phosphorus removal material, characterized in that, Using lanthanum nitrate hexahydrate and citric acid as the lanthanum source and carbon source, respectively, the following steps are included: S1. Dissolving lanthanum nitrate hexahydrate and citric acid in water, including first dissolving lanthanum nitrate hexahydrate in water to form a lanthanum nitrate solution with a concentration of 0.1~0.5 mol / L; then adding citric acid in a molar ratio and mixing thoroughly; wherein the molar ratio of lanthanum nitrate hexahydrate to citric acid is 1:0.3~1:1.2; S2. Stir and mix under heating conditions, using a stepped heating and stirring method: first stir at 60~80℃ for preliminary mixing, then raise the temperature to 110~130℃ for high-temperature mixing until a viscous liquid is formed; the preliminary mixing time is more than 30 minutes, and the high-temperature mixing time is more than 30 minutes. S3. The viscous liquid is calcined at a temperature of 240~360℃ for 1~3 hours; the calcination atmosphere is air. S4. Grind the calcined product to obtain the lanthanum-based composite phosphorus removal material; The lanthanum-based composite phosphorus removal material is a nanoporous carbon-supported lanthanum composite material, comprising: an amorphous nanoporous carbon matrix, and an active component in situ embedded in the nanoporous carbon matrix; The active component is a nanoscale lanthanum species, comprising lanthanum oxide (La₂O₃) and lanthanum hydroxide (La(OH)₃); in the lanthanum-based composite phosphorus removal material, the mass percentage of lanthanum is 30-80%, and the mass percentage of carbon is 5-35%. The lanthanum-based composite phosphorus removal material has a phosphorus adsorption capacity greater than 80 mg P / g and a phosphorus removal rate greater than 60%; after 5 adsorption cycles... After alkali regeneration cycle, the phosphorus adsorption capacity retention rate of the lanthanum-based composite phosphorus removal material is above 81.7%; the lanthanum-based composite adsorption material achieves a phosphate removal rate of over 99% in actual wastewater at pH 6.

1.

2. The preparation method according to claim 1, characterized in that, In step S1, the molar ratio of lanthanum nitrate hexahydrate to citric acid is 1:0.35 to 1:1.

15.

3. The preparation method according to claim 1, characterized in that, In step S2, the stirring and mixing under heating conditions adopts a stepped heating and stirring method: first, stirring is carried out at 65~75℃ for preliminary mixing, and then the temperature is raised to 115~125℃ for high-temperature mixing.

4. The preparation method according to claim 1, characterized in that, In step S1, the molar ratio of lanthanum nitrate hexahydrate to citric acid is 1:0.5 to 1:

1.

5. The preparation method according to claim 1, characterized in that, In step S3, the calcination temperature is 280~360℃ and the calcination time is 1.5~2.5h.

6. The preparation method according to claim 1, characterized in that, Step S1 includes: first dissolving lanthanum nitrate hexahydrate in water to form a lanthanum nitrate solution with a concentration of 0.1~0.2 mol / L; then adding citric acid by molar ratio and mixing thoroughly.

7. The preparation method according to claim 1, characterized in that, The initial mixing time is 30 min to 40 min; and / or the high-temperature mixing time is 30 min to 60 min.

8. A lanthanum-based composite phosphorus removal material, characterized in that, Prepared by the method according to any one of claims 1 to 7.

9. A phosphorus removal method, characterized in that, Includes the following steps: The lanthanum-based composite phosphorus removal material obtained by any one of claims 1-7 or the lanthanum-based composite phosphorus removal material of claim 8 is directly added to the water to be treated.

10. The phosphorus removal method according to claim 9, characterized in that, A regenerator was used to desorb and regenerate the lanthanum-based composite phosphorus removal material after phosphorus adsorption.

Images