River and lake sediment covering material capable of cooperatively controlling phosphorus and fluorine as well as method and application of river and lake sediment covering material

Abstract

The invention relates to the technical field of environmental engineering and water body remediation, in particular to a river and lake sediment covering material capable of cooperatively controlling phosphorus and fluorine and a method and application thereof. The covering material provided by the invention comprises a base material, an active component and a binder, the matrix material adopts modified clay, is of a porous net structure, and provides stable physical support and adsorption basis; nano-hydroxyapatite and ferric oxide are added into the active component, are dispersed in pores of the matrix and are respectively used for efficiently adsorbing phosphorus and fluorine; the binder is an environment-friendly polymer binder and wraps the surfaces of the matrix and the active component to form a continuous bonding layer, so that the mechanical strength and durability of the material are enhanced. According to the covering material provided by the invention, through specific adsorption of the nano-hydroxyapatite to phosphorus and efficient adsorption of the iron oxide to fluorine, release of phosphorus and fluorine in sediments can be inhibited at the same time, and the problems that a common covering material in the prior art is single in function, low in adsorption capacity and poor in stability are solved.

Description

Technical Field

[0001] This invention relates to the fields of environmental engineering and water remediation technology, specifically to a river and lake sediment cover material that synergistically controls phosphorus and fluoride, its preparation method, and its application. Background Technology

[0002] Eutrophication has become a serious social problem, attracting widespread attention. Eutrophication refers to water pollution caused by excessive levels of nutrients such as nitrogen and phosphorus in water bodies. It leads to cyanobacterial blooms, severely damaging aquatic ecosystems, reducing water body function, and causing mass deaths of fish and other aquatic organisms. Furthermore, the algal toxins and odorous substances produced by cyanobacterial blooms directly affect drinking water safety, ultimately impacting human health and safety. In addition, algae entering drinking water treatment processes can disrupt the normal operation of water purification processes, potentially leading to a significant reduction in water supply. Therefore, addressing the problem of eutrophication is urgently needed.

[0003] Currently, the release of phosphorus and fluoride from river and lake sediments is a significant cause of eutrophication and pollution. Existing covering materials commonly used in technology mainly include single materials such as activated carbon, zeolite, and clay. While these materials can partially control the release of phosphorus or fluoride, they have the following problems: Single function: Existing materials can usually only target one pollutant in phosphorus or fluorine, and cannot achieve synergistic control; Limited adsorption capacity: Traditional materials have low adsorption capacity and are prone to saturation after long-term use, resulting in a decrease in effectiveness; Poor stability: Some materials are easily decomposed or lost in the aquatic environment, affecting the long-term restoration effect.

[0004] The main reasons for these problems are the common use of coating materials with simple composition, unreasonable structural design, and lack of in-depth research on the synergistic mechanism of phosphorus and fluorine.

[0005] Chinese invention patent application CN113415960A (published on September 21, 2021) discloses a multi-objective sediment cover material and its preparation and application methods. The main components of this multi-objective sediment cover material include activated sepiolite and nano-calcium peroxide. The activated sepiolite portion is prepared first, and the nano-calcium peroxide portion is loaded onto the activated sepiolite portion. This invention can improve the redox environment of overlying water and surface sediments, while inhibiting the release of nitrogen, phosphorus, sulfur, organic matter, and heavy metals such as iron and manganese from sediments into the overlying water, providing a new strategy for sediment remediation. However, it does not completely solve the problem of poor stability.

[0006] The paper, titled "Research Progress on Phosphorus Passivation Materials for Lake Sediments," by Ma Xinyu, Yang Pan, Zhang Man, Yang Chunhui, and Yin Hongbin, in *Journal of Lake Science*, 2022, 34(1):1-17, DOI:10.18307 / 2022.0101, mentions that modified clay, as a phosphorus passivation material, can more safely and effectively solve the problem of endogenous phosphorus load in lakes, providing a new approach for sediment remediation. Summary of the Invention

[0007] To address the issues of limited functionality, low adsorption capacity, and poor stability of existing covering materials, this invention provides a synergistic phosphorus and fluoride control covering material for river and lake sediments, comprising: a matrix material, an active component, and a binder. The matrix material is modified clay with a porous network structure, providing stable physical support and adsorption basis; The active components, with the addition of nano-hydroxyapatite and iron oxide, are dispersed in the pores of the matrix for efficient adsorption of phosphorus and fluorine, respectively. The adhesive uses an environmentally friendly polymer adhesive, which coats the surface of the matrix and active components to form a continuous bonding layer, enhancing the mechanical strength and durability of the material.

[0008] This invention also provides a method for preparing a river and lake sediment cover material with synergistic phosphorus and fluoride control, comprising the following steps: Step S1: Prepare modified clay, nano-hydroxyapatite, iron oxide, and environmentally friendly polymer binder; Step S2: Mix modified clay, nano hydroxyapatite, iron oxide, and environmentally friendly polymer binder, granulate, and then dry.

[0009] Step S1 includes: Step S11: Preparation of modified clay: Take natural montmorillonite, soak it in hydrochloric acid solution, stir it 3 times during the process, filter it, wash it with deionized water until the pH of the filtrate is 7, dry it in an oven, crush it and sieve it for later use. Step S12: Preparation of nano-hydroxyapatite: prepared by sol-gel method, dried and set aside for later use; Step S13: Prepare iron oxide: Select nano-grade ferric oxide for later use; Step S14: Prepare an environmentally friendly polymer adhesive for later use.

[0010] Step S2 includes: Step S21: Weigh the raw materials by mass percentage: 70-72% modified clay, 12-15% nano hydroxyapatite, 10-12% iron oxide, and 5-7% environmentally friendly polymer binder (dry weight). Step S22: Pour the modified clay, nano hydroxyapatite, and iron oxide into a high-speed mixer and dry mix them to ensure that the active components are evenly dispersed in the matrix; Step S23: Slowly add the environmentally friendly polymer binder into the mixer and continue stirring to form a uniform paste mixture; Step S24: The paste mixture is transferred to a granulator to form granules with a diameter of 2-3 mm, which are then dried in an oven to obtain the final covering material.

[0011] Furthermore, in step S11, the hydrochloric acid solution is 0.1~0.12 mol / L, the soaking time is 24~25 h, the solid-liquid ratio of natural montmorillonite to hydrochloric acid solution is 1:10, the stirring time is 30~35 min, the oven temperature is 80~82℃, the drying time is 12~12.5 h, and the powder is passed through a 200-mesh sieve.

[0012] Furthermore, the nano-hydroxyapatite prepared in step S12 has a particle size of 50~100nm and a purity of ≥98%; the nano-sized ferric oxide selected in step S13 has a particle size of 100~200nm and a specific surface area of ​​≥50m² / g; the environmentally friendly polymer binder in step S14 can be a polyvinyl alcohol aqueous solution.

[0013] Furthermore, in step S22, the rotation speed of the high-speed mixer for dry mixing is 1500 r / min to 1600 r / min, and the dry mixing time is 10 to 12 min.

[0014] Furthermore, the environmentally friendly polymer binder in step S23 can be a polyvinyl alcohol aqueous solution with a mass fraction of 10-12%, the total liquid-to-solid ratio in the mixer is 1:2, and the stirring time is 20-25 minutes.

[0015] Furthermore, in step S24, the granulator has a pore size of 2mm, the oven temperature is 60~62℃, and the drying time is 6h.

[0016] This invention also provides an application of a synergistic phosphorus and fluoride control river and lake sediment cover material in river and lake sediment remediation.

[0017] Compared with existing technologies, the advantages and effects of this application are as follows: 1. The present invention provides a river and lake sediment covering material for synergistic phosphorus and fluoride control, which can synergistically control phosphorus and fluoride. Through the specific adsorption of phosphorus by nano-hydroxyapatite, a stable precipitate is formed by its chemical affinity with phosphorus. And through the efficient adsorption of fluoride by iron oxide, fluoride ions are exchanged between surface hydroxyl groups and fluoride ions, which solves the defects of the single function of existing materials.

[0018] 2. The present invention provides a synergistic phosphorus and fluoride control material for river and lake sediments, which has a high adsorption capacity. The nanoscale structure of its active components (nano-hydroxyapatite and iron oxide) provides abundant adsorption sites. Combined with the porous structure of modified clay, the material enhances the saturated adsorption capacity for phosphorus to 2 to 3 times that of traditional activated carbon, and enhances the saturated adsorption capacity for fluoride to 1.5 to 2 times that of traditional zeolite, thus extending the service life of the material.

[0019] 3. The river and lake sediment cover material provided by this invention has strong stability. The mechanical strength of the material particles can be enhanced by environmentally friendly polymer binders (such as polyvinyl alcohol and chitosan). It has a low loss rate in dynamic water bodies and does not decompose significantly in water environments with pH 5 to 9. The continuous effect can last for 6 to 12 months, while traditional clay materials only last for 2 to 3 months, ensuring long-term restoration effect.

[0020] 4. The present invention provides a method for preparing and applying a synergistic phosphorus and fluoride control river and lake sediment cover material. The method is simple and highly operable, and all components are environmentally friendly materials. No toxic or harmful substances are released, and no secondary pollution is caused, which meets the environmental protection requirements for water body restoration.

[0021] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the preferred embodiments of this application are described in detail below with reference to the accompanying drawings.

[0022] The above and other objects, advantages and features of this application will become more apparent to those skilled in the art from the following detailed description of specific embodiments in conjunction with the accompanying drawings. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In all drawings, similar elements or parts are generally identified by similar reference numerals. The elements or parts in the drawings are not necessarily drawn to scale.

[0024] in: Figure 1 This is a schematic diagram of the covering material prepared in this application; Figure 2 This is a simulation test diagram of the stability of the covering material prepared in this application; Figure 3 This is a field simulation test diagram of the covering material prepared in this application.

[0025] Among them: 1-modified clay; 2-nano hydroxyapatite; 3-iron oxide; 4-environmentally friendly polymer binder. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. In the following description, specific details such as specific configurations and components are provided merely to help fully understand the embodiments of this application. Therefore, those skilled in the art should understand that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this application. In addition, for clarity and brevity, descriptions of known functions and structures are omitted in the embodiments.

[0027] It should be understood that the phrase "an embodiment" or "this embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of this application. Therefore, "an embodiment" or "this embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments.

[0028] Furthermore, reference numerals and / or letters may be repeated in different examples within this application. Such repetition is for the purpose of simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or settings discussed.

[0029] In this article, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, B exists alone, and A and B exist simultaneously. The term " / and" describes another type of relationship between related objects, indicating that two relationships can exist. For example, A / and B can mean: A exists alone, and A and B exist alone. In addition, the character " / " in this article generally indicates that the related objects before and after it have an "or" relationship.

[0030] In this article, the term "at least one" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, "at least one of A and B" can mean: A exists alone, A and B exist simultaneously, or B exists alone.

[0031] It should also be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion.

[0032] Example 1 This embodiment introduces a river and lake sediment cover material for synergistic phosphorus and fluoride control. Please refer to the schematic diagram of the cover material. Figure 1 This includes the matrix material, active components, and binder; The matrix material uses modified clay 1 as the matrix, which has a porous network structure, providing stable physical support and adsorption basis; The active components are added with nano-hydroxyapatite 2 and iron oxide 3, which are dispersed in the pores of the matrix and used for efficient adsorption of phosphorus and fluorine, respectively. The adhesive uses an environmentally friendly polymer adhesive 4, which coats the surface of the matrix and active components to form a continuous bonding layer, enhancing the mechanical strength and durability of the material.

[0033] Preferably, the active component can be replaced with other materials with similar adsorption properties, such as nano-alumina.

[0034] Preferably, the adhesive can be polyvinyl alcohol or natural polysaccharides instead of polymers.

[0035] The technical effects achieved in this embodiment are as follows: This embodiment provides a synergistic phosphorus and fluoride control material for river and lake sediments. For the first time, it combines "phosphorus-specific adsorbent material + fluoride-efficient adsorbent material + matrix support material" to achieve simultaneous control of phosphorus and fluoride through the synergistic effect between components. This breaks through the limitation of "single component control" in existing materials and fills the technical gap in synergistic phosphorus and fluoride control covering materials. By using modified clay and environmentally friendly polymer binders, the stability and service life of the material are significantly improved.

[0036] Example 2 Based on Example 1, this example provides a method for preparing a synergistic phosphorus and fluoride control material for river and lake sediments under specific conditions, comprising the following steps: Step S1: Prepare modified clay 1, nano hydroxyapatite 2, iron oxide 3, and environmentally friendly polymer binder 4; Step S2: Mix modified clay 1, nano hydroxyapatite 2, iron oxide 3, and environmentally friendly polymer binder 4, granulate, and then dry.

[0037] Step S1 specifically includes: Step S11: Preparation of modified clay 1: Take natural montmorillonite, soak it in 0.1 mol / L hydrochloric acid solution for 24 h (solid-liquid ratio 1:10), stir it 3 times (30 min each time), filter it, wash it with deionized water until the pH of the filtrate is 7, dry it in an oven at 80℃ for 12 h, pulverize it and pass it through a 200 mesh sieve for later use. Step S12: Preparation of nano-hydroxyapatite 2: Prepared by sol-gel method, with particle size controlled at 50~100nm and purity ≥98%, and dried for later use; Step S13: Prepare iron oxide 3: Select nano-sized ferric oxide (α-Fe2O3) with a particle size of 100~200nm and a specific surface area ≥50m². 2 / g, for later use; Step S14: Prepare environmentally friendly polymer adhesive 4: Select a 10% (mass fraction) polyvinyl alcohol (PVA-1788) aqueous solution for later use.

[0038] Step S2 specifically includes: Step S21: Weigh the raw materials by mass percentage: 70% modified clay 1, 15% nano hydroxyapatite 2, 10% iron oxide 3, and 5% environmentally friendly polymer binder 4 (by dry weight). Step S22: Pour modified clay 1, nano hydroxyapatite 2, and iron oxide 3 into a high-speed mixer (speed 1500 r / min) and dry mix for 10 min to ensure that the active components are evenly dispersed in the matrix; Step S23: Slowly add 10% polyvinyl alcohol aqueous solution (total liquid-to-solid ratio 1:2) to the mixer and continue stirring for 20 minutes to form a uniform paste mixture; Step S24: Transfer the paste mixture into a granulator (2mm aperture) to make granules with a diameter of 2-3mm, and dry them in an oven at 60℃ for 6 hours to obtain the final covering material.

[0039] The technical effects achieved in this embodiment are as follows: This embodiment provides a method for preparing a synergistic phosphorus and fluoride control material for river and lake sediments. By selecting nanoscale active components with a specific surface area 10-20 times that of micron-scale materials and optimizing their ratio with the matrix, the active component accounts for 20%-30%, significantly improving the adsorption capacity and adsorption rate of the material and solving the problem of easy saturation of traditional materials. By introducing an environmentally friendly polymer binder, not only is the material's resistance to leaching improved, but also the interfacial interactions between the binder and the matrix and active components, such as hydrogen bonds and van der Waals forces, inhibit the dissolution of active components, solving the defects of easy decomposition and leaching of existing materials. Based on the research on the synergistic release mechanism of phosphorus and fluoride, such as the ion competition effect between the two in sediment pore water, the targeted design of material components avoids adsorption site competition, achieving a synergistic control effect of "1+1>2", providing a new idea for the synergistic remediation of multiple pollutants.

[0040] Example 3 To verify that the covering material has a high adsorption capacity, this embodiment tests the adsorption capacity of the covering materials prepared in Examples 1-2 above: When testing the adsorption capacity of the covering material, the static adsorption method was used. The material was added to simulated wastewater (pH=7) containing phosphorus (initial concentration 50 mg / L) and fluorine (initial concentration 20 mg / L) at a solid-liquid ratio of 1:100. After shaking at 25℃ for 24 hours, the residual concentration was measured.

[0041] The results showed that the material had an adsorption capacity of 65 mg / g for phosphorus and 42 mg / g for fluorine, which verifies that the coating material prepared in this application has a high adsorption capacity.

[0042] This embodiment tests the stability of the covering materials prepared in Examples 1-2 above: The covering material was placed in a circulating water device with a flow rate of 0.8 m / s to simulate a river environment. After five months, the material loss rate was measured to be 2.3%. After soaking in water with pH=6 for five months, the material structure showed no obvious damage, and the adsorption performance retention rate was ≥85%.

[0043] Please refer to the simulation test result graph. Figure 2 This verifies that the covering material prepared in this application has strong stability.

[0044] This embodiment also includes on-site simulation testing of the covering materials prepared in Examples 1-2 above: Covering a sediment column containing phosphorus (8 mg / L in sediment pore water) and fluoride (5 mg / L in pore water) with a 5 cm thick covering material resulted in a significant reduction in phosphorus concentration to 1.2 mg / L and fluoride concentration to 0.8 mg / L in pore water after 5 months, demonstrating a substantial inhibition effect on phosphorus release.

[0045] Please refer to the simulation test result graph. Figure 3 This verifies that the covering material prepared in this application has a significant inhibitory effect on phosphorus and fluorine.

[0046] Example 4 To verify the ecological safety of the covering material, this embodiment conducts experiments on the covering materials prepared in Examples 1-2 above: The experiment involved introducing the covering material prepared in this application into a water body and observing the results. The data showed that within 30 days after the material was introduced, the dissolved oxygen in the water remained stable at 5-7 mg / L, which is within the range suitable for the survival of aquatic organisms. Meanwhile, toxicity tests were conducted on common algae, zooplankton, and benthic organisms in the water. The results showed that the material had no significant impact on the survival rate of these organisms, with the survival rate remaining above 90%.

[0047] This experiment demonstrates that the prepared covering material has good environmental compatibility and ecological safety, avoiding secondary disturbance to the aquatic ecosystem during the restoration process. In addition to not releasing any toxic or harmful substances, the covering material does not change the basic physicochemical properties of the water body in the aquatic environment and does not have a negative impact on the dissolved oxygen content of the water body.

[0048] To verify the suitability of the cover material, this embodiment conducted test experiments on the cover materials prepared in Examples 1-2 above for different sediment types: In clayey sediments, the material can bind tightly with sediment particles to form a stable capping layer, with a binding strength 30% higher than that of traditional materials. In sandy sediments, due to the particle shape of the material and the effect of the binder, it can effectively fill the pores of sandy sediments, reduce the erosion of the capping layer by water flow, and reduce the loss rate by 25% compared with traditional materials. In addition, in high salinity water bodies (salinity 5~10‰), the material's adsorption performance for phosphorus and fluorine only decreases by 5%~8%, far lower than the 15%~20% decrease of traditional materials.

[0049] The test results show that the covering material can maintain good synergistic phosphorus and fluoride control effects under different sedimentation environments and water conditions, and exhibits good adaptability to different types of river and lake sediments.

[0050] This embodiment also calculates the cost-effectiveness of the covering materials prepared in Examples 1-2 above: From the perspective of preparation cost, modified clay, as a matrix material, is widely available and inexpensive, reducing raw material costs by 40% compared to materials with activated carbon as the main matrix. Regarding service life, this covering material exhibits strong stability, with a continuous working time of 6-12 months, while traditional clay materials only last 2-3 months. This means that within the same remediation cycle, using this invention's material can reduce the number of material replacements and lower construction costs. Calculations show that the remediation cost per unit area is reduced by approximately 30% compared to existing technologies. Simultaneously, the material's high adsorption capacity also reduces the amount of material used, further improving its cost-effectiveness and making it more suitable for widespread application in large-scale river and lake sediment remediation projects.

[0051] Example 5 Based on the covering materials prepared in Examples 1-2 above, this example uses a landscape lake in the center of a city as an example to verify the performance of the covering material prepared in this application.

[0052] A scenic lake in the city center has long received rainwater runoff and a small amount of domestic sewage, resulting in severe accumulation of phosphorus and fluoride in the sediments. The total phosphorus concentration in the overlying water remains at 0.8~1.2 mg / L year-round, and the fluoride concentration reaches 1.5~2.0 mg / L. The water transparency is less than 50 cm, and cyanobacterial blooms frequently occur in summer.

[0053] The synergistic phosphorus and fluoride control covering material described in this application was used for remediation. During construction, underwater machinery was used to evenly spread the material on the surface of lakebed sediments, with the covering thickness controlled at 5 cm. Monitoring data 30 days after remediation showed that the total phosphorus concentration in the overlying water decreased to 0.15~0.25 mg / L, the fluoride concentration decreased to 0.3~0.5 mg / L, the phosphorus release inhibition rate reached 83%, and the fluoride release inhibition rate reached 75%; the water transparency increased to 120 cm, and the cyanobacterial biomass decreased by more than 90%. After 12 months of continuous monitoring, even under conditions of large water level fluctuations during the rainy season, the material loss rate was only 3.2%, and the phosphorus and fluoride concentrations in the overlying water remained stable below 0.3 mg / L and 0.6 mg / L, respectively, without any significant rebound.

[0054] This embodiment verifies the long-term synergistic control effect of the covering material on phosphorus and fluoride in static water bodies, and it can resist a certain degree of hydraulic disturbance.

[0055] Example 6 Based on the above embodiments 1-2, this embodiment uses a supporting river channel in an industrial park as an example to verify the performance of the covering material prepared in this application.

[0056] The supporting river channel of an industrial park is affected by the infiltration of industrial wastewater. The phosphorus concentration in the sediment pore water reaches 10~15mg / L and the fluoride concentration reaches 8~12mg / L. The bottom sediment is weakly acidic (pH=5.5~6.0). Traditional covering materials are prone to decomposition and failure under this environment.

[0057] The material prepared in this application was used for remediation, employing a segmented covering process. In turbulent river sections, the covering thickness was increased to 8 cm, and 10% natural polysaccharide binder was added to enhance erosion resistance. Testing on the 60th day after construction showed that the phosphorus concentration in the sediment pore water decreased to 1.2–1.8 mg / L, and the fluoride concentration decreased to 1.0–1.5 mg / L, corresponding to inhibition rates of 88% and 85%, respectively. The material maintained its structural integrity in an acidic environment, retaining 92% of its initial compressive strength. Comparative experiments showed that when using the same amount of single modified clay material, the phosphorus and fluoride inhibition rates were only 45% and 30%, respectively, and the material showed significant disintegration after 3 months.

[0058] This embodiment verifies that the material can still maintain excellent synergistic pollution control performance and structural stability under acidic water and dynamic water flow conditions.

[0059] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Any equivalent substitutions, parameter adjustments, or reasonable changes to the functional implementation methods made by those skilled in the art under the guidance of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A river and lake sediment cover material for synergistic phosphorus and fluoride control, characterized in that, include: Matrix material, active components, and binders; The matrix material is modified clay (1), which has a porous mesh structure; The active components are added with nano-hydroxyapatite (2) and iron oxide (3) and dispersed in the pores of the matrix; The adhesive uses an environmentally friendly polymer adhesive (4) to coat the surface of the matrix and active components, forming a continuous bonding layer.

2. The method for preparing a synergistic phosphorus and fluoride control river and lake sediment cover material according to claim 1, characterized in that, include: Step S1: Prepare modified clay (1), nano hydroxyapatite (2), iron oxide (3), and environmentally friendly polymer binder (4); Step S2: Mix modified clay (1), nano hydroxyapatite (2), iron oxide (3), and environmentally friendly polymer binder (4), granulate, and then dry.

3. The method for preparing a synergistic phosphorus and fluoride control river and lake sediment cover material according to claim 2, characterized in that, Step S1 includes: Step S11: Preparation of modified clay (1): Take natural montmorillonite, soak it in hydrochloric acid solution, stir it 3 times during the process, filter it, wash it with deionized water until the pH of the filtrate is 7, dry it in an oven, crush it and sieve it for later use. Step S12: Preparation of nano-hydroxyapatite (2): Prepared by sol-gel method, dried and ready for use; Step S13: Prepare iron oxide (3): Select nano-grade ferric oxide for later use; Step S14: Prepare environmentally friendly polymer adhesive (4) for later use.

4. A method for preparing a synergistic phosphorus and fluoride control river and lake sediment cover material according to claim 2 or 3, characterized in that, Step S2 includes: Step S21: Weigh the raw materials by mass percentage: modified clay (1) 70~72% (dry weight), nano hydroxyapatite (2) 12~15%, iron oxide (3) 10~12%, and environmentally friendly polymer binder (4) 5~7%; Step S22: Pour the modified clay (1), nano hydroxyapatite (2), and iron oxide (3) into a high-speed mixer for dry mixing, so that the active components are evenly dispersed in the matrix; Step S23: Slowly add the environmentally friendly polymer binder (4) to the mixer and continue stirring to form a uniform paste mixture; Step S24: The paste mixture is transferred to a granulator to form granules with a diameter of 2-3 mm, which are then dried in an oven to obtain the final covering material.

5. The method for preparing a synergistic phosphorus and fluoride control river and lake sediment cover material according to claim 3, characterized in that, In step S11, the hydrochloric acid solution is 0.1~0.12 mol / L, the soaking time is 24~25 h, the solid-liquid ratio of natural montmorillonite to hydrochloric acid solution is 1:10, the stirring time is 30~35 min, the oven temperature is 80~82℃, the drying time is 12~12.5 h, and the powder is passed through a 200 mesh sieve.

6. A method for preparing a synergistic phosphorus and fluoride control river and lake sediment cover material according to claim 3 or 5, characterized in that, The nano-hydroxyapatite (2) prepared in step S12 has a particle size of 50~100nm and a purity of ≥98%; the nano-sized ferric oxide selected in step S13 has a particle size of 100~200nm and a specific surface area of ​​≥50m² / g; the environmentally friendly polymer binder (4) in step S14 is a polyvinyl alcohol aqueous solution.

7. The method for preparing a synergistic phosphorus and fluoride control river and lake sediment cover material according to claim 4, characterized in that, In step S22, the speed of the high-speed mixer for dry mixing is 1500 r / min to 1600 r / min, and the dry mixing time is 10 to 12 min.

8. A method for preparing a synergistic phosphorus and fluoride control river and lake sediment cover material according to claim 4 or 7, characterized in that, The environmentally friendly polymer binder (4) in step S23 can be a polyvinyl alcohol aqueous solution with a mass fraction of 10~12%, the total liquid-to-solid ratio in the mixer is 1:2, and the stirring time is 20~25min.

9. A method for preparing a synergistic phosphorus and fluoride control river and lake sediment cover material according to claim 4 or 7, characterized in that, In step S24, the granulator has a pore size of 2mm, the oven temperature is 60~62℃, and the drying time is 6h.

10. The application of the covering material prepared by the method for preparing a synergistic phosphorus and fluoride control river and lake sediment covering material according to any one of claims 2-9 in the remediation of river and lake sediments.

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