A composite flocculant with high dehydration efficiency and its preparation method

Abstract

This invention relates to the field of flocculation materials technology, specifically to a high-dehydration-efficiency composite flocculation material and its preparation method, prepared from the following raw materials: modified guar gum, aminated plasma-activated mesoporous biochar nanoparticles, silane coupling agent, and β-cyclodextrin-encapsulated slow-release phytic acid chelating agent. This invention, by limiting the specific compounding ratio of modified guar gum, plasma-aminated mesoporous biochar, silane coupling agent, and slow-release phytic acid chelating agent, and by employing a dedicated raw material preparation and organic-inorganic composite molding process, relies on the complementary functions of each component and the synergistic effect of process conditions to simultaneously solve the problems existing in current sediment flocculation and dehydration from three dimensions: colloidal stabilization mechanism, floc skeleton structure, and metal ion interference inhibition. Compared to traditional ordinary biochar-based composite flocculation materials, the composite flocculation material of this invention can significantly reduce the water content of sediment after dehydration and increase the floc settling rate.

Description

Technical Field

[0001] This invention relates to the field of flocculation materials technology, specifically to a composite flocculation material with high dehydration efficiency and its preparation method. Background Technology

[0002] Ecological dredging operations in shallow lakes generate a large amount of sediment with high water content. The sediment is rich in negatively charged colloidal particles, dissolved organic matter, and trace metal ions. The colloids maintain a stable dispersion state by electrostatic repulsion and hydration film. Sediment dewatering and volume reduction is a key step in the dredging process. The utilization of dewatered sediment cakes for agricultural resource utilization is the mainstream disposal method for reducing and recycling sediment. However, the flocculants currently used for sediment dewatering have several technical defects and are difficult to adapt to the complex sediment treatment needs of shallow lakes.

[0003] Currently, commonly used dewatering agents in engineering projects are mainly divided into two categories: aluminum-based inorganic flocculants and ordinary natural polymeric flocculants. Among aluminum-based flocculants, PAC is the most widely used. Although this agent can achieve basic flocculation and sedimentation, long-term addition will cause aluminum enrichment in the mud cake. When the mud cake is used in farmland, it is easy to cause soil acidification and aluminum toxicity accumulation. There are strict controls and restrictions on the application of aluminum-admixed dewatering mud cake in farmland in various regions, which greatly reduces the channels for the resource utilization of bottom sediment. At the same time, aluminum salt agents require a large dosage, resulting in high treatment costs. They also have poor adaptability to lake bottom sediments with large differences in organic matter and colloid content. When the composition of bottom sediment and water quality fluctuate, the dewatering effect will fluctuate significantly, and the moisture content of the mud cake will be unstable.

[0004] Conventional natural polymeric flocculants often use raw materials such as guar gum and starch. These have few active groups in their molecular chains, enabling only weak charge neutralization. They cannot effectively strip the hydration film on the surface of colloidal particles, making it difficult to remove bound water from the sludge. The resulting flocs are loose and porous with many water-holding spaces, leading to a high moisture content in the dewatered sludge cake and increasing the land cost for sludge transportation and storage. Existing polymeric flocculants combined with biochar use only a simple physical blending process. The interfacial bonding between the organic polymer and biochar powder is weak, making phase separation easy to occur during flocculation. Furthermore, the biochar used is not plasma-activated or amino-grafted, resulting in insufficient pore size and surface active sites, limiting its adsorption capacity for ultrafine colloids and organic matter. The system lacks a slow-release chelating component, allowing trace metal cations in the sediment to continuously consume the polymeric flocculant's active sites, interfering with the flocculation reaction. This results in a short effective action period and limited overall dewatering improvement.

[0005] In summary, existing sediment dewatering flocculants suffer from several problems, including aluminum salt residue limiting their agricultural use, weak dewatering capacity of ordinary polymers, poor adsorption performance of biochar, interference from metal ions in flocculation, and poor compatibility between organic and inorganic components. There is an urgent need to develop corresponding composite flocculants to solve these industry problems. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a composite flocculant with high dehydration efficiency.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A composite flocculant with high dehydration efficiency is prepared from the following raw materials in parts by weight: 26-32 parts modified guar gum, 10-14 parts aminated plasma pre-activated mesoporous biochar nanoparticles, 1.5-2.2 parts silane coupling agent, and 0.6-0.9 parts β-cyclodextrin-encapsulated slow-release phytic acid chelating agent. The particle size of the aminated plasma pre-activated mesoporous biochar nanopowder is 60–100 nm. The β-cyclodextrin-encapsulated sustained-release phytic acid chelating agent is a solid inclusion complex prepared from phytic acid and β-cyclodextrin.

[0008] As a further technical solution, the preparation method of the β-cyclodextrin-encapsulated sustained-release phytic acid chelating agent is as follows: phytic acid and β-cyclodextrin are added to a mixture of anhydrous ethanol and deionized water in a molar ratio of 1:1.5 to prepare a 50% (w / w) ethanol-water solution system. The mixture is stirred at 40°C and 180 r / min for 4 h to encapsulate the phytic acid. The mixture is then freeze-dried at -45°C and -0.04 to -0.06 MPa, pulverized, and passed through a 100-mesh sieve to obtain the sustained-release chelating agent powder.

[0009] As a further technical solution, the preparation process of the plasma pre-activated aminated mesoporous biochar nanopowder uses 100 parts by weight of wheat straw char as a basis, CO2 activation gas flow rate of 0.8 L / min, dilute nitric acid etching solid-liquid mass ratio of 1:12, and KH-550 addition of 6-7 parts.

[0010] As a further technical solution, the preparation steps of the plasma-activated aminated mesoporous biochar nanopowder are as follows: S1 Carbonization and Pore Forming: Wheat straw was carbonized at 500℃ for 2 hours under a protective atmosphere of nitrogen flow rate of 0.3L / min and oxygen volume fraction of ≤1%; the carbonized product was heated to 700℃ at a heating rate of 8℃ / min and activated at a constant temperature of CO2 atmosphere for 1.5 hours; after activation, it was cooled, ball-milled to a particle size of 60-100nm, and washed with water to remove ash. S2 plasma pre-activation: Water-washed biochar powder is spread in a uniform layer with a thickness of 0.8–1.2 mm and a density of 0.6 g / cm³. 2 The load-bearing density was placed in the plasma chamber and continuously processed for 12 minutes under the conditions of atmospheric pressure ±5kPa, argon flow rate 0.5L / min, and discharge power 120W. S3 Water Washing and Neutralization: After plasma treatment, the powder is washed with water until the pH of the effluent stabilizes at 6.5–7.5; S4 Vacuum Pre-Dehydration: The neutralized wet powder is vacuum dried at 80℃ until the moisture content is ≤0.8%; S5 Low-Temperature Etching: Pre-dried powder is mixed with 7% dilute nitric acid at a solid-liquid ratio of 1:12, stirred and etched at 25℃ and 200r / min for 2 hours, then washed with water again until neutral and dehydrated a second time. S6 Aminografted: Dehydrated powder was dispersed in anhydrous ethanol system, KH-550 was added, and the mixture was refluxed at 82℃ for 2 hours. After filtration and drying, aminated plasma-activated mesoporous biochar nanoparticles were obtained.

[0011] As a further technical solution, after the CO2 atmosphere constant temperature activation process is completed, high-purity nitrogen gas with a flow rate of 0.5L / min is continuously introduced to purge for 60 minutes, so that the material can be naturally cooled to room temperature under air-isolated conditions.

[0012] As a further technical solution, the composite flocculant is used for the dewatering treatment of bottom sediment in shallow lakes. When used, it is prepared as a deionized water solution with a mass fraction of 0.8% and added to the mud at a dosage of 0.3% based on the dry weight of the bottom sediment.

[0013] As a further technical solution, the preparation process of the modified guar gum, based on 100 parts by weight of guar gum dry powder, includes the following amounts of each modifying agent: 2.5-3.5 parts by weight of 30% hydrogen peroxide aqueous solution, 20-23 parts by weight of 3-chloro-2-hydroxypropyltrimethylammonium chloride, 7-9 parts by weight of maleic anhydride, and 5-6 parts by weight of dodecyl glycidyl ether.

[0014] As a further technical solution, the preparation steps of the modified guar gum are as follows: a. Oxidative degradation pretreatment: Guar gum powder was prepared into an aqueous suspension with a mass fraction of 4%, and hydrogen peroxide aqueous solution was added dropwise at 35℃ and 150r / min with a single addition not exceeding 0.5% of the total mass of the system for oxidative degradation. b. Cation grafting crosslinking: The pH of the system was adjusted to 8.2 by micro-adjusting with 20% sodium hydroxide aqueous solution, with a single drop volume ≤ 0.3% of the total mass of the system. 3-chloro-2-hydroxypropyltrimethylammonium chloride was added, and the reaction was carried out at a constant temperature of 55°C in a sealed environment for 3 hours. c-carboxyl hydrophobic modification and crosslinking: The pH of the system was adjusted to 7.2 by micro-adjustment with 10% dilute hydrochloric acid, with a single drop volume ≤ 0.3% of the total mass of the system. Maleic anhydride and dodecyl glycidyl ether were added simultaneously, and the reaction was carried out at 55℃ for 1.5h. Post-treatment: The product was washed three times with anhydrous ethanol, and the solid phase was separated by alcohol precipitation. The product was then vacuum dried at 40℃ and -0.07MPa for 8 hours to obtain modified guar gum.

[0015] A method for preparing a composite flocculant with high dehydration efficiency includes the following steps: S1. Preparation of plasma-preactivated aminated mesoporous biochar nanopowder; S2. Organic-inorganic covalent composite molding: Weigh each solid raw material according to weight parts, add modified guar gum to deionized water to prepare an aqueous solution with a mass fraction of 8% to 12%, and stir at 52 to 58℃ and 120 r / min until completely dissolved; add dropwise a 10% mass fraction silane coupling agent anhydrous ethanol solution, and premix at a constant temperature for 15 min; add dropwise anhydrous ethanol suspension of aminated plasma pre-activated mesoporous biochar with a solid content of 10% to 14%, and disperse using 300W ultrasonication for 45 to 55 min, while stirring at 300 r / min simultaneously; add β-cyclodextrin to encapsulate and slow-release phytic acid chelating agent, adjust the speed to 80 r / min, and stir at a constant temperature of 52 to 58℃ for chelation stabilization for 2 h; after natural cooling to room temperature, vacuum dry at 45 to 50℃ and -0.07 to -0.08 MPa for 10 hours, pulverize and pass through a 120-mesh standard sieve to obtain a powdered composite flocculant material.

[0016] As a further technical solution, the silane coupling agent is KH-550.

[0017] Compared with the prior art, the beneficial effects of the present invention are: This invention uses modified guar gum as the organic flocculant matrix. First, the molecular chain length is controlled through oxidative degradation, and then cationic groups, carboxyl groups, and hydrophobic long chains are introduced for multiple modifications. Due to the high-density cationic sites on the guar gum molecular chain, the negative charge on the surface of the sediment colloidal particles can be rapidly neutralized, breaking the stable colloidal dispersion system. Simultaneously grafted hydrophobic alkyl chains can disrupt the hydration film on the surface of the colloidal particles, converting bound water inside the particles into free water, reducing the water-holding capacity of the sediment at the microscopic level, and solving the defects of ordinary virgin guar gum, such as weak charge neutralization and poor ability to remove bound water.

[0018] This invention utilizes plasma-preactivated aminated mesoporous biochar nanoparticles as an inorganic adsorption framework. First, high-temperature CO2 activation constructs a rich mesoporous structure. Then, plasma etching increases surface porosity and active sites. Finally, amino grafting modification is completed. Plasma treatment widens the pore channels of the biochar and increases its specific surface area. The amino groups endow the powder with positively charged adsorption capacity, enabling it to capture nanoscale fine colloids and free organic matter in water. Combined with low-temperature etching using dilute nitric acid, ash impurities on the carbon surface are further removed, preventing pore blockage. Compared to unactivated ordinary biochar, this significantly increases the colloidal adsorption capacity, overcoming the limitation of single polymers in retaining ultrafine suspended matter.

[0019] This invention adds silane coupling agent KH-550 as an interfacial linking medium. One end of the silane molecule undergoes a condensation reaction with the hydroxyl groups on the surface of biochar, while the other end forms a covalent bond with the modified guar gum polymer chain, achieving a stable combination of organic polymer and inorganic biochar powder and preventing phase separation during the flocculation process. β-cyclodextrin encapsulates and slowly releases phytic acid chelating agent, which encapsulates phytic acid molecules through cyclodextrin cavities, enabling the slow release of chelated components. This continuously complexes metal ions in the sediment that interfere with flocculation, preventing the rapid consumption of polymeric cationic groups by metal cations, extending the effective action time of the agent, and solving the problems of metal ion interference in flocculation and low agent utilization in conventional systems.

[0020] In this invention, modified guar gum first undergoes charge neutralization to achieve initial agglomeration of large colloidal particles, forming a basic floc network. Aminated plasma-activated biochar nanoparticles are embedded within the floc network, serving as a rigid support framework to fill the floc pores, reducing internal water storage cavities, and simultaneously allowing for rapid drainage of internal free water via mesoporous channels. A silane coupling agent firmly binds the organic and inorganic components, preventing floc breakage during external stirring and filtration dehydration, maintaining a complete and permeable structure. A β-cyclodextrin-released phytic acid chelating agent continuously complexes metal ions within the system, eliminating charge interference and ensuring the continued activity of the modified guar gum cationic groups and biochar amino sites, preventing premature failure of the flocculation system. The phytic acid-chelated metal complexes can be adsorbed and fixed by the biochar mesopores, simultaneously achieving stable solidification of heavy metals in the sediment and reducing filtrate pollutant emissions. The segmented stirring, ultrasonic, and low-temperature drying processes of the entire preparation process provide a stable environment for the synergistic reaction of each component.

[0021] In summary, this invention addresses the problems of existing sediment flocculation and dewatering processes by limiting the specific compounding ratio of modified guar gum, plasma-aminated mesoporous biochar, silane coupling agent, and slow-release phytic acid chelating agent, along with a dedicated raw material preparation and organic-inorganic composite molding process. Relying on the complementary functions of each component and the synergistic effect of process conditions, it simultaneously solves the problems of existing sediment flocculation and dewatering from three dimensions: colloidal stabilization mechanism, floc skeleton structure, and metal ion interference inhibition. Compared to traditional ordinary biochar compound flocculants, the composite flocculant of this invention can significantly reduce the water content of sediment after dewatering, improve floc settling rate, sludge cake permeability, and organic matter retention rate. The sludge cake structure is stable and has a low compression rate, significantly reducing the land occupation and transportation costs for subsequent sediment treatment. The low dosage of the agents and the absence of high salt residue prevent secondary salinization of the sediment. The slow-release chelating components simultaneously fix trace heavy metals in the sediment, reducing the risk of leachate pollution.

[0022] Instruction manual illustrations Figure 1 This is a schematic diagram comparing the organic matter retention rates of an example and a comparative example of a composite flocculant with high dehydration efficiency. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] This invention provides a composite flocculant with high dehydration efficiency, prepared from the following raw materials in parts by weight: 26-32 parts modified guar gum, 10-14 parts aminated plasma-activated mesoporous biochar nanoparticles, 1.5-2.2 parts silane coupling agent, and 0.6-0.9 parts β-cyclodextrin-encapsulated slow-release phytic acid chelating agent; the particle size of the aminated plasma-activated mesoporous biochar nanoparticles is 60-100 nm; the β-cyclodextrin-encapsulated slow-release phytic acid chelating agent is a solid inclusion complex prepared from phytic acid and β-cyclodextrin.

[0025] β-Cyclodextrin encapsulation of sustained-release phytic acid chelating agent: In this invention, the β-cyclodextrin-encapsulated sustained-release phytic acid chelating agent is preferably a solid inclusion complex prepared by phytic acid and β-cyclodextrin in a molar ratio of 1:1.5. The preferred preparation method of the β-cyclodextrin-encapsulated sustained-release phytic acid chelating agent is as follows: phytic acid and β-cyclodextrin are added to a mixed solution of anhydrous ethanol and deionized water in a volume ratio of 1:1 at a molar ratio of 1:1. This is used to prepare a 50% (w / w) ethanol-water solution system. The mixture is stirred at 40°C and 180 r / min for 4 h to encapsulate the phytic acid; then, it is freeze-dried at -45°C and -0.04 to -0.06 MPa, pulverized, and passed through a 100-mesh sieve to obtain the sustained-release chelating agent powder.

[0026] Amination plasma pre-activated mesoporous biochar nanoparticles: In this invention, the particle size of the aminated plasma-activated mesoporous biochar nanoparticles is preferably 60–100 nm, more preferably 70–90 nm. Based on 100 parts by weight of wheat straw charcoal, the preferred process parameters are: CO2 activation gas flow rate 0.8 L / min, dilute nitric acid etching solid-liquid mass ratio 1:12, and KH-550 addition amount 6–7 parts, more preferably 6.5 parts.

[0027] The preferred preparation steps for the aminated plasma-activated mesoporous biochar nanopowder are as follows: S1 Carbonization and Pore Forming: Wheat straw is carbonized at 500℃ for 2 hours under a protective atmosphere of nitrogen flow rate of 0.3L / min and oxygen volume fraction ≤1%; the carbonized product is heated to 700℃ at a heating rate of 8℃ / min and activated at a constant temperature in a CO2 atmosphere for 1.5 hours; after activation, it is cooled down, ball-milled to a particle size of 60-100nm, and washed with water to remove ash; after the CO2 atmosphere constant temperature activation process is completed, it is preferable to continuously purge with high-purity nitrogen at a flow rate of 0.5L / min for 60 minutes to allow the material to cool naturally to room temperature under air-isolated conditions.

[0028] S2 plasma pre-activation: Water-washed biochar powder is spread in a uniform layer with a thickness of 0.8–1.2 mm and a density of 0.6 g / cm³. 2 The load-bearing density is placed in the plasma chamber and continuously processed for 12 minutes under the conditions of atmospheric pressure ±5kPa, argon flow rate 0.5L / min, and discharge power 120W; the flat layer thickness is preferably 1.0mm.

[0029] S3 Water Washing and Neutralization: After plasma treatment, the powder is washed with water until the pH of the effluent is stable at 6.5-7.5, more preferably at 7.0.

[0030] S4 Vacuum Pre-Dehydration: The neutralized wet powder is vacuum dried at 80℃ until the moisture content is ≤0.8%.

[0031] S5 Low-Temperature Etching: Pre-dried powder is mixed with 7% dilute nitric acid at a solid-liquid ratio of 1:12, stirred and etched at 25℃ and 200r / min for 2 hours, then washed with water again until neutral and dehydrated a second time.

[0032] S6 Aminografted: Dehydrated powder was dispersed in anhydrous ethanol system, KH-550 was added, and the mixture was refluxed at 82℃ for 2 hours. After filtration and drying, aminated plasma-activated mesoporous biochar nanoparticles were obtained.

[0033] Modified guar gum: Based on 100 parts by weight of guar gum powder, the preferred amount of modifying agent is: 2.5-3.5 parts by weight of 30% hydrogen peroxide aqueous solution, 20-23 parts by weight of 3-chloro-2-hydroxypropyltrimethylammonium chloride, 7-9 parts by weight of maleic anhydride, and 5-6 parts by weight of dodecyl glycidyl ether; more preferably, 3 parts by weight of hydrogen peroxide aqueous solution, 21.5 parts by weight of 3-chloro-2-hydroxypropyltrimethylammonium chloride, 8 parts by weight of maleic anhydride, and 5.5 parts by weight of dodecyl glycidyl ether.

[0034] The preferred preparation steps for the modified guar gum are as follows: a. Oxidative degradation pretreatment: Guar gum powder was prepared into an aqueous suspension with a mass fraction of 4%, and hydrogen peroxide aqueous solution was added dropwise at 35℃ and 150r / min with a single addition not exceeding 0.5% of the total mass of the system for oxidative degradation. b. Cation grafting crosslinking: The pH of the system was adjusted to 8.2 by micro-adjusting with 20% sodium hydroxide aqueous solution, with a single drop volume ≤ 0.3% of the total mass of the system. 3-chloro-2-hydroxypropyltrimethylammonium chloride was added, and the reaction was carried out at a constant temperature of 55°C in a sealed environment for 3 hours. c-carboxyl hydrophobic modification and crosslinking: The pH of the system was adjusted to 7.2 by micro-adjustment with 10% dilute hydrochloric acid, with a single drop volume ≤ 0.3% of the total mass of the system. Maleic anhydride and dodecyl glycidyl ether were added simultaneously, and the reaction was carried out at 55℃ for 1.5h. Post-treatment: The product was washed three times with anhydrous ethanol, and the solid phase was separated by alcohol precipitation. The product was then vacuum dried at 40℃ and -0.07MPa for 8 hours to obtain modified guar gum.

[0035] Preparation process of composite flocculants: The preferred method for preparing the composite flocculant of the present invention includes the following steps: S1. Preparation of plasma-preactivated aminated mesoporous biochar nanopowder; S2. Organic-inorganic covalent composite molding: Weigh each solid raw material according to weight parts, add modified guar gum to deionized water to prepare an aqueous solution with a mass fraction of 8% to 12%, preferably 10%, and stir at 52 to 58°C and 120 r / min until completely dissolved, preferably at 55°C; add a 10% mass fraction of anhydrous ethanol solution of silane coupling agent, and premix and stir at a constant temperature for 15 min; add an anhydrous ethanol suspension of aminated plasma-activated mesoporous biochar with a solid content of 10% to 14%, preferably 12%, at a uniform rate. The mixture was ultrasonically dispersed at 300W for 45–55 min, preferably 50 min, while simultaneously stirred at 300 rpm. A β-cyclodextrin-encapsulated slow-release phytic acid chelating agent was added, and the stirring speed was adjusted to 80 rpm. The mixture was then stirred and stabilized at a constant temperature of 52–58°C for 2 h. After natural cooling to room temperature, the mixture was vacuum-dried at 45–50°C and -0.07–-0.08 MPa for 10 h, preferably 48°C and -0.075 MPa. The resulting powdered composite flocculant was then pulverized and passed through a 120-mesh standard sieve. KH-550 is preferred as the silane coupling agent.

[0036] The composite flocculant of the present invention is preferably used for the dewatering treatment of bottom sediment in shallow lakes. When using it, it is prepared as a deionized water solution with a mass fraction of 0.8% and added to the mud at a dosage of 0.3% based on the dry weight of the bottom sediment.

[0037] The following are specific examples: Example 1: Step 1: Preparation of β-cyclodextrin-encapsulated sustained-release phytic acid chelating agent: Phytic acid and β-cyclodextrin were mixed at a molar ratio of 1:1.5, and a mixture of anhydrous ethanol and deionized water at a volume ratio of 1:1 was added to prepare a 50% ethanol-water solution system. The mixture was stirred at 40°C and 180 r / min for 4 h to encapsulate the phytic acid chelating agent. The mixture was then freeze-dried at -45°C and -0.04 MPa, pulverized, and passed through a 100-mesh sieve to obtain β-cyclodextrin-encapsulated slow-release phytic acid chelating agent powder.

[0038] Step 2: Preparation of aminated plasma-activated mesoporous biochar nanopowder: Based on 100 parts by weight of wheat straw charcoal, add 6 parts of KH-550.

[0039] S1 Carbonization and Pore Forming: Wheat straw was carbonized at 500℃ for 2 hours under a protective atmosphere of nitrogen flow rate 0.3L / min and oxygen volume fraction ≤1%; the carbonized product was heated to 700℃ at a heating rate of 8℃ / min and activated at a constant temperature of CO2 gas flow rate of 0.8L / min for 1.5 hours; after activation, high-purity nitrogen gas was continuously purged at a rate of 0.5L / min for 60 minutes, and the mixture was allowed to cool naturally to room temperature in the absence of air; the mixture was then ball-milled to a particle size of 60nm and washed with water to remove ash.

[0040] S2 plasma pre-activation: After water washing, the biochar powder is laid in a 0.8mm thick layer with a concentration of 0.6g / cm³. 2 The load-bearing density is laid in the plasma cavity, and the plasma is continuously processed for 12 minutes at atmospheric pressure -5 kPa, argon flow rate 0.5 L / min, and discharge power 120 W.

[0041] S3 Water Washing and Neutralization: The plasma-treated powder is continuously washed with water until the pH of the effluent stabilizes at 6.5.

[0042] S4 Vacuum Pre-Dehydration: Neutralized wet powder is vacuum dried at 80℃ until the moisture content is ≤0.8%.

[0043] S5 Low-temperature etching: Pre-dried powder was mixed with 7% dilute nitric acid at a solid-liquid mass ratio of 1:12, and etched at 25℃ and 200r / min for 2 hours with stirring. After washing with water until neutral, it was dehydrated a second time. S6 Amine grafting: Dehydrated powder was dispersed in anhydrous ethanol system, 6 parts of KH-550 were added, and the mixture was refluxed at 82℃ for 2 hours. After filtration and drying, 60nm amination plasma-activated mesoporous biochar nanoparticles were obtained.

[0044] Step 3: Preparation of modified guar gum: Based on 100 parts by weight of guar gum powder, the amount of modifying reagent added is as follows: 2.5 parts of 30% hydrogen peroxide aqueous solution, 20 parts of 3-chloro-2-hydroxypropyltrimethylammonium chloride, 7 parts of maleic anhydride, and 5 parts of dodecyl glycidyl ether.

[0045] a. Oxidative degradation pretreatment: Prepare a 4% aqueous suspension of guar gum powder, stir at 35℃ and 150r / min, and add hydrogen peroxide aqueous solution dropwise in portions, with each addition not exceeding 0.5% of the total mass of the system, to complete the oxidative degradation; b. Cation grafting crosslinking: Adjust the pH of the system to 8.2 with a small amount of 20% sodium hydroxide aqueous solution, with a single drop volume ≤ 0.3% of the total mass of the system, add 20 parts of 3-chloro-2-hydroxypropyltrimethylammonium chloride, and react at a constant temperature of 55℃ in a sealed environment for 3 hours; c. Carboxyl hydrophobic modification and crosslinking: The pH of the system was adjusted to 7.2 by micro-adjustment with 10% dilute hydrochloric acid, with a single drop volume ≤ 0.3% of the total mass of the system. 7 parts maleic anhydride and 5 parts dodecyl glycidyl ether were added simultaneously, and the reaction was carried out at 55℃ for 1.5 h. d. Post-treatment: The product was washed 3 times with anhydrous ethanol, the solid phase was separated by alcohol precipitation, and the product was dried under vacuum at 40℃ and -0.07MPa for 8 h to obtain modified guar gum.

[0046] Step 4: Organic-inorganic covalent composite molding to prepare composite flocculants: Raw material weight ratio: 26 parts modified guar gum, 10 parts aminated plasma pre-activated mesoporous biochar nanoparticles, 1.5 parts KH-550 silane coupling agent, and 0.6 parts β-cyclodextrin-encapsulated sustained-release phytic acid chelating agent.

[0047] Add 26 parts of modified guar gum to deionized water to prepare an 8% aqueous solution, and stir at 52℃ and 120r / min until completely dissolved; Add dropwise a 10% KH-550 anhydrous ethanol solution and premix at 52℃ for 15 min. A suspension of 10% aminated biochar in anhydrous ethanol was added dropwise at a uniform rate, and ultrasonic dispersion was performed at 300W for 45 minutes while stirring at 300r / min. Add 0.6 parts of β-cyclodextrin to encapsulate the sustained-release phytic acid chelating agent, adjust the speed to 80 r / min, and stir at 52℃ for 2 hours to stabilize the chelation. The system was naturally cooled to room temperature, then vacuum dried at 45℃ and -0.07MPa for 10 hours. After pulverization, it was passed through a 120-mesh standard sieve to obtain a powdered composite flocculant with high dehydration efficiency.

[0048] Material usage instructions: When used for dewatering the bottom sediment of shallow lakes, the composite flocculant material of this embodiment is prepared into a deionized water solution with a mass fraction of 0.8%, and then uniformly mixed into the slurry at a dosage of 0.3% based on the dry weight of the bottom sediment.

[0049] Example 2: Step 1: Preparation of β-cyclodextrin-encapsulated sustained-release phytic acid chelating agent: The same preparation process as in Example 1 was used, except that the vacuum degree of subsequent freeze-drying was adjusted to -0.06 MPa, and all other process parameters were completely consistent, to obtain β-cyclodextrin-encapsulated sustained-release phytic acid chelating agent powder.

[0050] Step 2: Preparation of aminated plasma-activated mesoporous biochar nanopowder: Based on 100 parts by weight of wheat straw charcoal, add 7 parts of KH-550.

[0051] S1 Carbonization and Pore Forming: Wheat straw was carbonized at 500℃ for 2 hours under a protective atmosphere of nitrogen flow rate 0.3L / min and oxygen volume fraction ≤1%; the carbonized product was heated to 700℃ at a heating rate of 8℃ / min and activated at a constant temperature of CO2 gas flow rate of 0.8L / min for 1.5 hours; after activation, high-purity nitrogen gas was continuously purged at a rate of 0.5L / min for 60 minutes, and the mixture was allowed to cool naturally to room temperature in the absence of air; the mixture was ball-milled to a particle size of 100nm and washed with water to remove ash.

[0052] S2 plasma pre-activation: After water washing, the biochar powder is laid in a 1.2mm thick layer with a concentration of 0.6g / cm³. 2 The load-bearing density is laid in the plasma cavity, and the plasma is continuously processed for 12 minutes at atmospheric pressure +5 kPa, argon flow rate 0.5 L / min, and discharge power 120 W.

[0053] S3 Water Washing and Neutralization: The plasma-treated powder is continuously washed with water until the pH of the effluent stabilizes at 7.5.

[0054] S4 Vacuum Pre-Dehydration: Neutralized wet powder is vacuum dried at 80℃ until the moisture content is ≤0.8%.

[0055] S5 Low-temperature etching: Pre-dried powder was mixed with 7% dilute nitric acid at a solid-liquid mass ratio of 1:12, and etched at 25℃ and 200r / min for 2 hours with stirring. After washing with water until neutral, it was dehydrated a second time. S6 Amine grafting: Dehydrated powder was dispersed in anhydrous ethanol system, 7 parts of KH-550 were added, and the mixture was refluxed at 82℃ for 2 hours. After filtration and drying, 100nm amination plasma-activated mesoporous biochar nanoparticles were obtained.

[0056] Step 3: Preparation of modified guar gum: Based on 100 parts by weight of guar gum powder, the amount of modifying reagent added is as follows: 3.5 parts of 30% hydrogen peroxide aqueous solution, 23 parts of 3-chloro-2-hydroxypropyltrimethylammonium chloride, 9 parts of maleic anhydride, and 6 parts of dodecyl glycidyl ether.

[0057] a. Oxidative degradation pretreatment: Prepare a 4% aqueous suspension of guar gum powder, stir at 35℃ and 150r / min, and add hydrogen peroxide aqueous solution dropwise in portions, with each addition not exceeding 0.5% of the total mass of the system, to complete the oxidative degradation; b. Cation grafting crosslinking: Adjust the pH of the system to 8.2 with a small amount of 20% sodium hydroxide aqueous solution, with a single drop volume ≤ 0.3% of the total mass of the system, add 23 parts of 3-chloro-2-hydroxypropyltrimethylammonium chloride, and react at a constant temperature of 55℃ in a sealed environment for 3 hours; c-carboxyl hydrophobic modification and crosslinking: The pH of the system was adjusted to 7.2 by micro-adjusting with 10% dilute hydrochloric acid, with a single drop volume ≤ 0.3% of the total mass of the system. Simultaneously, 9 parts of maleic anhydride and 6 parts of dodecyl glycidyl ether were added, and the reaction was carried out at a constant temperature of 55℃ for 1.5h. Post-treatment: The product was washed three times with anhydrous ethanol, the solid phase was separated by alcohol precipitation, and the product was dried under vacuum at 40℃ and -0.07MPa for 8 hours to obtain modified guar gum.

[0058] Step 4: Organic-inorganic covalent composite molding to prepare composite flocculants: Raw material weight ratio: 32 parts modified guar gum, 14 parts aminated plasma pre-activated mesoporous biochar nanoparticles, 2.2 parts KH-550 silane coupling agent, and 0.9 parts β-cyclodextrin-encapsulated sustained-release phytic acid chelating agent.

[0059] Add 32 parts of modified guar gum to deionized water to prepare a 12% aqueous solution, and stir at 58℃ and 120r / min until completely dissolved; Add dropwise a 10% KH-550 anhydrous ethanol solution and premix at 58℃ for 15 min. A suspension of 14% aminated biochar in anhydrous ethanol was added dropwise at a uniform rate, and ultrasonic dispersion was performed at 300W for 55 minutes while stirring at 300r / min. Add 0.9 parts of β-cyclodextrin to encapsulate the sustained-release phytic acid chelating agent, adjust the speed to 80 r / min, and stir at 58℃ for 2 hours to stabilize the chelation. The system was naturally cooled to room temperature, then vacuum dried at 50℃ and -0.08MPa for 10 hours. After pulverization, it was passed through a 120-mesh standard sieve to obtain a powdered composite flocculant with high dehydration efficiency.

[0060] Material usage instructions: The operating parameters are the same as in Example 1.

[0061] Example 3: Step 1: Preparation of β-cyclodextrin-encapsulated sustained-release phytic acid chelating agent: Using the same preparation process as in Example 1, the freeze-drying vacuum degree was controlled at -0.05 MPa, and the other process parameters remained unchanged, to obtain β-cyclodextrin-encapsulated sustained-release phytic acid chelating agent powder.

[0062] Step 2: Preparation of aminated plasma-activated mesoporous biochar nanopowder: Based on 100 parts by weight of wheat straw charcoal, the amount of KH-550 added is 6.5 parts.

[0063] S1 Carbonization and Pore Forming: Wheat straw was carbonized at 500℃ for 2 hours under a protective atmosphere of nitrogen flow rate 0.3L / min and oxygen volume fraction ≤1%; the carbonized product was heated to 700℃ at a heating rate of 8℃ / min and activated at a constant temperature of CO2 gas flow rate of 0.8L / min for 1.5 hours; after activation, high-purity nitrogen gas was continuously purged at a rate of 0.5L / min for 60 minutes, and the mixture was allowed to cool naturally to room temperature in the absence of air; the mixture was then ball-milled to a particle size of 80nm and washed with water to remove ash.

[0064] S2 plasma pre-activation: After water washing, the biochar powder is laid in a 1.0mm thick layer with a concentration of 0.6g / cm³. 2 The load-bearing density is laid in the plasma cavity, and the plasma is continuously processed for 12 minutes at atmospheric pressure of 0 kPa, argon flow rate of 0.5 L / min, and discharge power of 120 W.

[0065] S3 Water Washing and Neutralization: The plasma-treated powder is continuously washed with water until the pH of the effluent stabilizes at 7.0.

[0066] S4 Vacuum Pre-Dehydration: Neutralized wet powder is vacuum dried at 80℃ until the moisture content is ≤0.8%.

[0067] S5 Low-Temperature Etching: Pre-dried powder and 7% dilute nitric acid are mixed at a solid-liquid mass ratio of 1:12, stirred and etched at 25℃ and 200r / min for 2 hours, washed with water until neutral, and then dehydrated a second time.

[0068] S6 Aminografted: Dehydrated powder was dispersed in anhydrous ethanol system, 6.5 parts of KH-550 were added, and the mixture was refluxed at 82℃ for 2 hours. After filtration and drying, 80 nm amination plasma pre-activated mesoporous biochar nanoparticles were obtained.

[0069] Step 3: Preparation of modified guar gum: Based on 100 parts by weight of guar gum powder, the amount of modifying reagent added is as follows: 3 parts of 30% hydrogen peroxide aqueous solution, 21.5 parts of 3-chloro-2-hydroxypropyltrimethylammonium chloride, 8 parts of maleic anhydride, and 5.5 parts of dodecyl glycidyl ether.

[0070] a. Oxidative degradation pretreatment: Prepare a 4% aqueous suspension of guar gum powder, stir at 35℃ and 150r / min, and add hydrogen peroxide aqueous solution dropwise in portions, with each addition not exceeding 0.5% of the total mass of the system, to complete the oxidative degradation; b. Cationic grafting crosslinking: The pH of the system was adjusted to 8.2 by micro-adjusting with 20% sodium hydroxide aqueous solution, with a single drop volume ≤ 0.3% of the total system mass. 21.5 parts of 3-chloro-2-hydroxypropyltrimethylammonium chloride were added, and the reaction was carried out at 55℃ in a sealed environment for 3 hours. c. Carboxyl hydrophobic modification crosslinking: The pH of the system was adjusted to 7.2 by micro-adjusting with 10% dilute hydrochloric acid, with a single drop volume ≤ 0.3% of the total system mass. 8 parts of maleic anhydride and 5.5 parts of dodecyl glycidyl ether were added simultaneously, and the reaction was carried out at 55℃ in a sealed environment for 1.5 hours. d. Post-treatment: The product was washed three times with anhydrous ethanol, the solid phase was separated by alcohol precipitation, and the product was dried under vacuum at 40℃ and -0.07MPa for 8 hours to obtain modified guar gum.

[0071] Step 4: Organic-inorganic covalent composite molding to prepare composite flocculants: Raw material weight ratio: 29 parts modified guar gum, 12 parts aminated plasma pre-activated mesoporous biochar nanoparticles, 1.8 parts KH-550 silane coupling agent, and 0.75 parts β-cyclodextrin-encapsulated sustained-release phytic acid chelating agent.

[0072] Add 29 parts of modified guar gum to deionized water to prepare a 10% aqueous solution, and stir at 55℃ and 120r / min until completely dissolved; Add dropwise a 10% KH-550 anhydrous ethanol solution and premix at 55℃ for 15 min. A suspension of 12% aminated biochar in anhydrous ethanol was added dropwise at a uniform rate, and ultrasonic dispersion was performed at 300W for 50 minutes while stirring at 300r / min. Add 0.75 parts of β-cyclodextrin to encapsulate the sustained-release phytic acid chelating agent, adjust the speed to 80 r / min, and stir at 55℃ for 2 hours to stabilize the chelation. The system was naturally cooled to room temperature, then vacuum dried at 48℃ and -0.075MPa for 10 hours. After pulverization, it was passed through a 120-mesh standard sieve to obtain a powdered composite flocculant with high dehydration efficiency.

[0073] Material usage instructions: The operating parameters are the same as in Example 1.

[0074] Comparative Example 1: The overall preparation process is completely consistent with Example 3, except for the adjustment of raw material components: the aminated plasma-activated mesoporous biochar nanoparticles are removed, the modified guar gum is added to 41 parts, 1.8 parts of silane coupling agent and 0.75 parts of β-cyclodextrin-encapsulated slow-release phytic acid chelating agent are added. The remaining preparation processes, reaction temperatures, stirring speeds, ultrasonic times, vacuum drying parameters, and sieve mesh sizes are all consistent with Example 3. The application conditions are the same as in the example, with the bottom sediment dosage and solution concentration remaining unchanged.

[0075] Comparative Example 2: The overall preparation process is completely consistent with that of Example 3. The raw material components are: β-cyclodextrin inclusion complex with slow-release phytic acid chelating agent is removed, modified guar gum is adjusted to 29.75 parts, aminated biochar powder is 12 parts, and silane coupling agent is 1.8 parts. All preparation process parameters are exactly the same as those of Example 3, with no other changes.

[0076] Comparative Example 3: The raw material ratio is exactly the same as in Example 3. The only difference is that the S2 plasma pre-activation step is removed from the biochar powder preparation process. The remaining carbonization, etching, and amino grafting processes remain unchanged. The final biochar powder does not have a plasma pore-forming activated structure. The composite flocculant forming, drying, and sieving processes are the same as in Example 3.

[0077] Comparative Example 4: The raw material ratio is exactly the same as that in Example 3 by weight. The modified guar gum is replaced with virgin guar gum dry powder that has not undergone oxidation, cationic, or carboxyl hydrophobic modification. The preparation process of the remaining biochar powder, silane coupling agent, chelating agent, and all process parameters of the composite molding are the same as those in Example 3.

[0078] test: The test used the same sediment material: sediment from the same shallow lake dredging site, with an initial moisture content of 87.2%, an organic matter content of 11.6%, and a suspended colloidal particle content of 32.4%. Each sample was tested in parallel three times, and the arithmetic mean was taken as the final test data.

[0079] Experiment 1: Moisture content and cake compressibility of bottom sediment after dewatering. Test method: Sample preparation: All examples and comparative examples of flocculant materials were uniformly prepared into a 0.8% deionized water solution by mass fraction. The solution was added to 1000g of wet bottom mud at a dosage of 0.3% of the dry weight of the bottom mud. The mixture was stirred at 200r / min for 5min with an electric stirrer and allowed to stand for flocculation and sedimentation for 30min. Solid-liquid separation: A vacuum filtration device was used to collect the mud cake by filtration under a negative pressure of 0.05 MPa for 10 minutes. Moisture content test: Weigh the mud cake after filtration, mass m1, and dry it at a constant temperature of 105℃ in a forced-air drying oven until constant weight m2. The formula for calculating the moisture content of the bottom mud is: Moisture content = (m1-m2) / m1×100%; Cake compressibility test: Take an equal amount of flocculated cake and place it in a standard consolidation apparatus. Apply a constant pressure of 0.1 MPa and hold for 20 minutes. Record the cake thickness before and after compression. Compressibility = (initial thickness - thickness after compression) / initial thickness × 100%; Instruments and equipment: digital display electric stirrer, vacuum filtration unit, 101 type forced air drying oven, electronic analytical balance (accuracy 0.0001g), standard geosynthetic consolidation apparatus, digital display thickness gauge.

[0080] Table 1. Results of sediment dewatering moisture content and mud cake compression rate tests The moisture content of all three sets of examples after dehydration was less than 42.1%, and the compressibility of the mud cake was controlled within 11.3%. Comparative Example 1 lacks ammoniated plasma-activated biochar, which lacks a mesoporous adsorption carrier and cannot adsorb and capture fine colloidal particles. The flocculated flocs are loose with many water-holding pores, resulting in a significant increase in the moisture content of the mud cake and a significant increase in compression deformation. Comparative Example 2: Without slow-release phytic acid chelating agent, metal ions in the sediment could not be chelated and stabilized, the charge neutralization of colloidal particles was incomplete, fine suspended matter was difficult to aggregate and settle, the content of free bound water was high, and the dehydration effect was significantly reduced. Comparative Example 3 biochar was not pre-activated by plasma, resulting in a significant reduction in specific surface area and number of mesopores, insufficient adsorption capacity, poor floc density, and weaker dehydration performance compared to all examples. Comparative Example 4 uses unmodified virgin guar gum, which lacks cationic graft groups and hydrophobic modification structures. It has weak charge neutralization ability and poor hydrophobic dehydration effect. The bound water inside the mud cake cannot be effectively removed, and the moisture content and compressibility deteriorate simultaneously.

[0081] Experiment 2: Flocculation sedimentation rate and supernatant turbidity test: Test method: Preparation of flocculation system: Take 1L of homogeneous lake bottom sediment slurry, add each group of flocculant solutions respectively, stir at 200r / min for 5min and then transfer to a 1000mL standard sedimentation cylinder; Settling rate determination: Record the time required for the floc interface to settle from the 1000mL mark to the 200mL mark on the graduated cylinder, and calculate the settling height per unit time to characterize the settling rate; Turbidity of supernatant: After settling and standing for 30 minutes, the upper 2 / 3 of the supernatant was collected and the turbidity was measured using a portable turbidimeter, in NTU. Instruments and equipment: 1000mL standard sedimentation cylinder, digital display stirrer, WGZ-200 portable turbidimeter, stopwatch.

[0082] Table 2. Results of flocculation sedimentation rate and supernatant turbidity detection In the examples, the settling rate was higher than 2.8 cm / min, the turbidity of the supernatant was lower than 7.2 NTU, the flocs were fully aggregated, the settling speed was fast, and the water clarity was high; Comparative Example 1: The non-ammonized mesoporous biochar nanoparticles lack a nano-adsorption framework, and the fine colloids cannot aggregate to form large flocs, resulting in slow sedimentation and a large number of suspended particles remaining, which leads to a sharp increase in turbidity. Comparative Example 2 lacks a slow-release phytic acid chelating agent, so heavy metals and colloidal stabilizers in the sediment cannot be complexed and removed. Colloidal particles remain in a stable dispersed state, making it difficult to flocculate and agglomerate, and the turbidity of the supernatant is significantly higher. Comparative Example 3: Ordinary biochar has fewer mesoporous structures, insufficient adsorption sites, smaller floc size, lower sedimentation rate than the Example, and more residual suspended matter in the supernatant. Comparative Example 4 showed that the original guar gum had insufficient charge modification and weak charge neutralization ability, which could not quickly neutralize the negative charge of the sediment colloid. As a result, the floc formation rate was slow, the particles were small, the settling efficiency was low, and the turbidity was poor.

[0083] Experiment 3: Test of the permeability and organic matter retention rate of bottom mud cake: Test method: Mud cake preparation: The same flocculation and filtration process as in Experiment 1 was used to collect an equal amount of intact mud cake; Permeability coefficient test: The saturated permeability coefficient of the mud cake was determined using a geotextile permeameter and the constant head method, which characterizes the ease with which water passes through the mud cake; Organic matter retention rate test: The organic matter content of the original bottom mud before flocculation and the organic matter content of the supernatant after filtration were tested respectively. Retention rate = (original mud organic matter - supernatant organic matter) / original mud organic matter × 100%; Instruments and equipment: constant head geotextile permeameter, total organic carbon (TOC) analyzer, forced-air drying oven, electronic balance.

[0084] Table 3. Results of mud cake permeability coefficient and organic matter retention rate. The three sets of examples have high mud cake permeability coefficient, low water penetration resistance, and organic matter retention rate of over 94%, which can effectively fix organic pollutants in bottom sediment and simultaneously improve dewatering efficiency. Comparative Example 1: The mesoporous framework of non-ammonized biochar resulted in dense blockage inside the flocculated mud cake, fewer water permeable channels, a significant reduction in permeability coefficient, and the inability to adsorb and retain organic colloids, leading to a significant decrease in retention rate. Comparative Example 2 lacks a slow-release phytic acid chelating agent, so small molecule organic colloids cannot be complexed and fixed, a large amount of organic matter is lost with the filtrate, the retention rate is low, and fine organic particles clog the pores of the mud cake, reducing permeability. Comparative Example 3 biochar was not plasma activated, resulting in insufficient adsorption capacity, weak retention of small organic molecules, fewer micropores inside the mud cake, and lower water permeability than the Example. Comparative Example 4: Unmodified guar gum has poor hydrophobic properties. After flocculation, the mud cake has many hydrophilic groups, the pores are filled with bound water, resulting in high permeation resistance. In addition, it lacks a cross-linking network to fix organic matter, resulting in poor retention.

[0085] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not describe all details exhaustively, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification.

Claims

1. A composite flocculant with high dewatering efficiency, characterized in that, It is prepared from the following raw materials in parts by weight: 26-32 parts modified guar gum, 10-14 parts aminated plasma pre-activated mesoporous biochar nanoparticles, 1.5-2.2 parts silane coupling agent, and 0.6-0.9 parts β-cyclodextrin-encapsulated sustained-release phytic acid chelating agent; The particle size of the aminated plasma pre-activated mesoporous biochar nanopowder is 60–100 nm. The β-cyclodextrin-encapsulated sustained-release phytic acid chelating agent is a solid inclusion complex prepared from phytic acid and β-cyclodextrin.

2. The composite flocculant with high dehydration efficiency according to claim 1, characterized in that, The preparation method of the β-cyclodextrin-encapsulated sustained-release phytic acid chelating agent is as follows: phytic acid and β-cyclodextrin are added to a mixture of anhydrous ethanol and deionized water in a molar ratio of 1:1.5 to prepare a 50% (w / w) ethanol-water solution system. The mixture is stirred at 40°C and 180 r / min for 4 h to encapsulate the phytic acid. The mixture is then freeze-dried at -45°C and -0.04 to -0.06 MPa, pulverized, and passed through a 100-mesh sieve to obtain the sustained-release chelating agent powder.

3. The composite flocculant with high dewatering efficiency according to claim 1, characterized in that, The preparation process of plasma pre-activated aminated mesoporous biochar nanopowder uses 100 parts by weight of wheat straw char as a basis, CO2 activation gas flow rate of 0.8 L / min, dilute nitric acid etching solid-liquid mass ratio of 1:12, and KH-550 addition of 6-7 parts.

4. The composite flocculant with high dewatering efficiency according to claim 3, characterized in that, The specific steps for preparing the plasma-preactivated aminated mesoporous biochar nanopowder are as follows: S1 Carbonization and Pore Forming: Wheat straw was carbonized at 500℃ for 2 hours under a protective atmosphere of nitrogen flow rate of 0.3L / min and oxygen volume fraction of ≤1%; the carbonized product was heated to 700℃ at a heating rate of 8℃ / min and activated at a constant temperature of CO2 atmosphere for 1.5 hours; after activation, it was cooled, ball-milled to a particle size of 60-100nm, and washed with water to remove ash. S2 plasma pre-activation: Water-washed biochar powder is spread in a uniform layer with a thickness of 0.8–1.2 mm and a density of 0.6 g / cm³. 2 The load-bearing density was placed in the plasma chamber and continuously processed for 12 minutes under the conditions of atmospheric pressure ±5kPa, argon flow rate 0.5L / min, and discharge power 120W. S3 Water Washing and Neutralization: After plasma treatment, the powder is washed with water until the pH of the effluent stabilizes at 6.5–7.5; S4 Vacuum Pre-Dehydration: The neutralized wet powder is vacuum dried at 80℃ until the moisture content is ≤0.8%; S5 Low-Temperature Etching: Pre-dried powder is mixed with 7% dilute nitric acid at a solid-liquid ratio of 1:12, stirred and etched at 25℃ and 200r / min for 2 hours, then washed with water again until neutral and dehydrated a second time. S6 Aminografted: Dehydrated powder was dispersed in anhydrous ethanol system, KH-550 was added, and the mixture was refluxed at 82℃ for 2 hours. After filtration and drying, aminated plasma-activated mesoporous biochar nanoparticles were obtained.

5. The composite flocculant with high dewatering efficiency according to claim 4, characterized in that, After the CO2 atmosphere constant temperature activation process is completed, high-purity nitrogen gas with a flow rate of 0.5L / min is continuously introduced to purge for 60 minutes, allowing the material to cool naturally to room temperature under air-isolated conditions.

6. The composite flocculant with high dewatering efficiency according to claim 1, characterized in that, The composite flocculant is used for the dewatering treatment of bottom sediment in shallow lakes. When used, it is prepared as a deionized water solution with a mass fraction of 0.8% and added to the slurry at a dosage of 0.3% based on the dry weight of the bottom sediment.

7. The composite flocculant with high dewatering efficiency according to claim 1, characterized in that, The preparation process of the modified guar gum, based on 100 parts by weight of guar gum dry powder, includes the following amounts of each modifying agent: 2.5-3.5 parts by weight of 30% hydrogen peroxide aqueous solution, 20-23 parts by weight of 3-chloro-2-hydroxypropyltrimethylammonium chloride, 7-9 parts by weight of maleic anhydride, and 5-6 parts by weight of dodecyl glycidyl ether.

8. The composite flocculant with high dewatering efficiency according to claim 7, characterized in that, The specific steps for preparing the modified guar gum are as follows: a. Oxidative degradation pretreatment: Guar gum powder was prepared into an aqueous suspension with a mass fraction of 4%, and hydrogen peroxide aqueous solution was added dropwise at 35℃ and 150r / min with a single addition not exceeding 0.5% of the total mass of the system for oxidative degradation. b. Cation grafting crosslinking: The pH of the system was adjusted to 8.2 by micro-adjusting with 20% sodium hydroxide aqueous solution, with a single drop volume ≤ 0.3% of the total mass of the system. 3-chloro-2-hydroxypropyltrimethylammonium chloride was added, and the reaction was carried out at a constant temperature of 55°C in a sealed environment for 3 hours. c-carboxyl hydrophobic modification and crosslinking: The pH of the system was adjusted to 7.2 by micro-adjustment with 10% dilute hydrochloric acid, with a single drop volume ≤ 0.3% of the total mass of the system. Maleic anhydride and dodecyl glycidyl ether were added simultaneously, and the reaction was carried out at 55℃ for 1.5h. Post-treatment: The product was washed three times with anhydrous ethanol, and the solid phase was separated by alcohol precipitation. The product was then vacuum dried at 40℃ and -0.07MPa for 8 hours to obtain modified guar gum.

9. A method for preparing a composite flocculant with high dehydration efficiency according to any one of claims 1-8, characterized in that, Includes the following steps: S1. Preparation of plasma-preactivated aminated mesoporous biochar nanopowder; S2. Organic-inorganic covalent composite molding: Weigh each solid raw material according to weight parts, add modified guar gum to deionized water to prepare an aqueous solution with a mass fraction of 8% to 12%, and stir at 52 to 58℃ and 120 r / min until completely dissolved; add dropwise a 10% mass fraction silane coupling agent anhydrous ethanol solution, and premix at a constant temperature for 15 min; add dropwise anhydrous ethanol suspension of aminated plasma pre-activated mesoporous biochar with a solid content of 10% to 14%, and disperse using 300W ultrasonication for 45 to 55 min, while stirring at 300 r / min simultaneously; add β-cyclodextrin to encapsulate and slow-release phytic acid chelating agent, adjust the speed to 80 r / min, and stir at a constant temperature of 52 to 58℃ for chelation stabilization for 2 h; after natural cooling to room temperature, vacuum dry at 45 to 50℃ and -0.07 to -0.08 MPa for 10 hours, pulverize and pass through a 120-mesh standard sieve to obtain a powdered composite flocculant material.

10. The preparation method according to claim 9, characterized in that, The silane coupling agent is KH-550.

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