Green ecological composite coagulant and preparation method thereof

Abstract

This invention discloses a green and eco-friendly composite coagulant and its preparation method. The coagulant comprises the following raw materials in weight percentages: 20-40% modified fly ash, 10-40% modified bentonite, 5-15% modified talc, 5-15% modified chitosan, and 5-15% modified plant polysaccharides. This green and eco-friendly composite coagulant, through organic-inorganic hybridization and multi-dimensional molecular-level modification, possesses synergistic advantages such as high-efficiency coagulation, targeted adsorption, and rigid framework construction. Its significant beneficial effects include: achieving green ecology and resource utilization of solid waste; targeted destabilization and rapid phosphorus removal; powerful complex breaking and deep mineralization of heavy metals; and overcoming the bottleneck of sludge dewatering limits.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a composite water treatment agent and its preparation method that can be used for three core water treatment processes: removal of suspended solids and phosphorus from municipal sewage, targeted treatment of industrial heavy metal wastewater, and deep dewatering and conditioning of sludge with high water content. Background Technology

[0002] With the accelerated pace of global industrialization and urbanization, aquatic environments are facing unprecedented and complex pollution challenges. Modern wastewater treatment is no longer limited to the traditional reduction of chemical oxygen demand (COD) and biochemical oxygen demand (BOD), but has gradually evolved into comprehensive treatment projects targeting complex pollution systems. These complex pollution systems typically include fine suspended solids that are difficult to settle naturally, high concentrations of phosphorus that lead to eutrophication, heavy metal ions with high ecotoxicity and accumulative properties, and large quantities of colloidal residual sludge that is extremely difficult to dewater at the end of wastewater treatment.

[0003] In the coagulation and flocculation reaction stages of conventional water treatment, existing commercially available agents and treatment processes reveal numerous insurmountable technical bottlenecks. Traditional inorganic coagulants (such as polyaluminum chloride PAC and polyferric sulfate PFS) mainly rely on the hydrolysis products of aluminum and iron ions for charge neutralization and double-layer compression. However, the flocs generated by such inorganic coagulants generally have a loose structure, extremely high water content, and very limited ability to specifically remove dissolved heavy metal ions and low concentrations of total phosphorus. On the other hand, simple organic polymeric flocculants (such as polyacrylamide PAM series), although possessing excellent molecular chain bridging and sweeping capabilities, lack chemical adsorption and targeted chelation functions. When faced with complex industrial wastewater (especially electroplating and smelting wastewater containing high concentrations of organic complexing agents), PAM is often ineffective. More seriously, polyacrylamide carries potential neurotoxicity and environmental biotoxicity risks due to acrylamide monomer residues during degradation, severely limiting its large-scale application in ecologically sensitive areas.

[0004] In specific application areas, the pain points of existing technologies are particularly prominent. First, in the field of phosphorus removal from municipal wastewater, conventional aluminum or iron salt phosphorus removal agents not only require extremely high dosages but also lead to the generation of large amounts of difficult-to-treat chemical sludge. Furthermore, free aluminum ions may be discharged with the effluent, introducing a serious risk of secondary pollution. Second, in the field of heavy metal treatment in industrial wastewater, traditional hydroxide alkaline precipitation methods are completely ineffective against heavy metal ions in a strongly complexed state (such as those complexed with EDTA or citric acid), easily resulting in severely excessive levels of heavy metals in the effluent.

[0005] Finally, in the field of sludge conditioning and dewatering, because the residual sludge contains a large number of extracellular polymeric substances (EPS) formed by the cross-linking of proteins and polysaccharides, a large amount of water is firmly bound within the gel network, becoming highly bound water. Conventional agents (such as simple PAC or PAM) can only cause surface flocculation and cannot form effective rigid dewatering channels inside the sludge. This results in a generally high moisture content (usually greater than 80%) in the sludge cake after pressing by a plate and frame filter press. The sludge cake is viscous and colloidal, which is not only difficult to peel off from the filter cloth, but also greatly increases the energy consumption and treatment costs of subsequent long-distance transportation, landfill, and incineration.

[0006] To address these comprehensive challenges, developing a novel, multifunctional, eco-friendly composite water treatment agent with targeted adsorption capabilities has become a crucial area for breakthrough in the environmental protection industry. In recent years, academia has attempted to introduce natural polymers such as chitosan or inorganic minerals such as fly ash into water treatment systems. However, research shows that natural materials or large quantities of industrial solid waste that have not undergone targeted, in-depth chemical and physical modification have significant performance defects. For example, natural chitosan is insoluble in neutral water, fly ash has a small specific surface area and lacks active sites, and talc's strong hydrophobicity prevents it from being uniformly dispersed in aquatic sludge. If these unmodified substrates are directly and simply physically mixed, not only will no synergistic effect be produced, but the extremely poor compatibility between them will lead to a precipitous decline in flocculation performance. Therefore, it is essential to start from the perspective of molecular design and supramolecular self-assembly, and to deeply customize the modification of the physicochemical defects of each raw material in order to develop truly eco-friendly composite coagulants that can meet the stringent requirements of municipal, industrial, and sludge treatment fields.

[0007] Therefore, overcoming the shortcomings of existing water treatment agents, such as limited functionality, poor environmental adaptability, and susceptibility to secondary pollution, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] To address the technical shortcomings of existing water treatment agents, such as limited functionality, poor environmental adaptability, and susceptibility to secondary pollution, this invention provides a multifunctional ecological composite coagulant and its preparation method that combines efficient coagulation, targeted adsorption, and rigid framework construction. This coagulant is prepared using natural renewable materials (plant polysaccharides, chitosan) and inexpensive inorganic minerals and solid waste (bentonite, talc, fly ash) as basic raw materials through precise multidimensional physicochemical modification and supramolecular self-assembly composite processes.

[0009] To address the aforementioned problems, the present invention provides a green and eco-friendly composite coagulant, characterized in that it comprises the following raw materials in weight percentages: 20-40% modified fly ash, 10-40% modified bentonite, 5-15% modified talc, 5-15% modified chitosan, and 5-15% modified plant polysaccharides.

[0010] Preferably, the modified fly ash is fly ash that has undergone acid activation modification.

[0011] Preferably, the modified bentonite is sodium-based bentonite modified from calcium-based bentonite.

[0012] Preferably, the modified talc is a hydrophilic talc modified from natural hydrophobic talc.

[0013] Preferably, the modified chitosan is obtained by quaternization and targeted functional group grafting modification of natural chitosan.

[0014] Preferably, the modified plant polysaccharide is derived from extracts of agricultural and forestry waste.

[0015] This invention also provides a method for preparing a green and eco-friendly composite coagulant, comprising the following steps: Step 1: Add deionized water to the reactor equipped with an adjustable high-speed shear emulsifier head, and slowly drip 0.1M hydrochloric acid solution into the deionized water to adjust the pH value of the water to a stable 6.0 and maintain a slightly acidic environment. Step 2: Weigh each raw material according to the ratio of the green ecological composite coagulant, add the modified chitosan and modified plant polysaccharide into the reaction vessel, heat the reaction vessel, maintain the temperature at 50°C, and make the main stirring shaft continuously stir at 400 rpm for 1.5 hours to carry out the reaction and form a high molecular flocculent interpenetrating network structure in the solution. Step 3: After confirming that the polymer flocculation interpenetrating network structure is matured and stable without particle precipitation, the high-speed shear emulsifier head is rapidly increased to a high speed of 9000 rpm, and then modified talc, modified bentonite and modified fly ash are sequentially sprayed into the reactor; maintain high-speed shear for 40 minutes to obtain inorganic-organic composite hybrid slurry; Step 4: The inorganic-organic composite slurry is fed into a drying tower by a high-pressure pump for drying. The inlet temperature of the hot air in the drying tower is controlled at 170°C and the outlet exhaust temperature is controlled at 85°C to obtain the green ecological composite coagulant.

[0016] Preferably, the modification method of the modified fly ash is as follows: the original fly ash is mixed with a hydrochloric acid or sulfuric acid solution with a concentration of 1M-3M at a solid-liquid mass ratio of 1:5-1:10. The mixed slurry is placed in a shaking reactor and continuously stirred and activated at a speed of 50-100 rpm for 24 hours under constant temperature of 80℃. The solid and liquid are separated by high-speed centrifugation, and the solid obtained by separation is repeatedly washed with double-distilled water until the supernatant is neutral. The supernatant is then dried at 105℃ for 24 hours to prepare acid-activated fly ash with well-developed pores.

[0017] Preferably, the modification method of the modified bentonite is as follows: Raw calcium-based bentonite powder is dispersed in water, and sodium carbonate is added. Sodiumization treatment is carried out by stirring at a temperature of 60-90℃ to prepare a highly dispersed sodium-based bentonite slurry with a mass fraction of 3%-5%.

[0018] A separate aqueous solution of aluminum salt was prepared, and an aqueous solution of sodium hydroxide was slowly added dropwise to the aqueous solution of aluminum salt under strong stirring, controlling a specific OH / Al molar ratio of 2.0-2.5. The solution was then aged at room temperature for 24 hours to obtain a hydroxyl aluminum pillar solution rich in Al13 polymer.

[0019] A composite modified solution is formed by slowly adding an aqueous iron salt solution dropwise to the aluminum hydroxide pillar solution. A zirconium salt aqueous solution is prepared by mixing zirconium oxychloride with distilled water. The sodium-based bentonite slurry is heated to 60-80°C, and under continuous vigorous stirring, the composite modified solution and the zirconium salt aqueous solution are slowly added sequentially, allowing the interlayer ion exchange and assembly reaction to continue for 2-3 hours to obtain the modified slurry.

[0020] The modified slurry is pressure filtered, the filter cake is collected and washed with water to remove impurity ions, and finally the filter cake is dried, depolymerized and dispersed to obtain modified bentonite.

[0021] Preferably, the modification method of the modified talc is as follows: 200-mesh natural hydrophobic talc powder is placed in a stirred ball mill and pulverized and activated at high speed for 4 to 10 hours; after the surface contact angle of the natural hydrophobic talc powder is significantly reduced, it is taken out and ultrasonically dispersed in a mixed solvent of ethanol and purified water (volume ratio of about 9:1). A slightly acidic aminosilane coupling agent accounting for 1%-3% of the mass of talc powder is added dropwise under high-speed stirring to obtain a mixed solution. The mixed solution is heated to 70-80°C and refluxed and stirred for 3 hours; the reaction solution is taken out and filtered to separate solid and liquid. The solid is repeatedly washed with anhydrous ethanol and dried in an 80°C forced-air drying oven to constant weight. It is then pulverized and sieved to obtain hydrophilic modified talc.

[0022] Preferably, the modification method of the modified chitosan is as follows: Natural chitosan powder with a deacetylation degree greater than 85% is dispersed in isopropanol solvent at a mass fraction of 5-10%, and a concentrated sodium hydroxide solution is slowly added dropwise for swelling and alkalization treatment; then glycidyltrimethylammonium chloride solution is added, and a quaternization reaction is carried out at a constant temperature of 60-80℃ for 3-5 hours.

[0023] After washing and purifying the reaction product with ethanol, the product is dissolved at a mass fraction of 2-5% in an alkaline aqueous solution with a pH of 11-13. Carbon disulfide (CS2) and a trace amount of epichlorohydrin crosslinking agent are then slowly added dropwise under vigorous stirring. The molar ratio of natural chitosan to CS2 ranges from 1:1 to 3:1; the molar ratio of natural chitosan to epichlorohydrin crosslinking agent ranges from 0.05:1 to 0.2:1.

[0024] The residual free amino groups on the natural chitosan chain undergo a nucleophilic addition reaction with carbon disulfide to generate a multifunctional modified chitosan derivative that simultaneously possesses positive charge and heavy metal-specific chelating ability.

[0025] Preferably, the modification method of the modified plant polysaccharide is as follows: Plant polysaccharides extracted from agricultural and forestry waste are prepared into an aqueous solution with a mass fraction of 5%-10%. This aqueous solution is pumped into a microfluidic homogenizer and continuously circulated 3-5 times under a working pressure of 100-150 MPa. The aqueous solution is then transferred to a reaction vessel, and solid NaOH is added as a catalyst. The mixture is heated to 75°C and magnetically stirred to ensure complete activation and dissolution. The system temperature is then lowered to 40-60°C, and a cationic etherifying reagent is slowly added dropwise. After continuous reaction at a constant temperature for 2-4 hours, the reaction solution is poured into a large amount of anhydrous ethanol for alcohol precipitation. A large amount of white flocculent precipitate is collected, filtered, washed multiple times, and vacuum dried and ground at 65°C to obtain a highly active quaternized ammonium plant polysaccharide modified product.

[0026] The green and eco-friendly composite coagulant of this invention, through organic-inorganic hybridization and multidimensional molecular-level modification, possesses synergistic advantages such as high-efficiency coagulation, targeted adsorption, and rigid framework construction, mainly reflected in the following four aspects: 1. Green ecology and solid waste resource utilization: Using natural polymers (chitosan, plant polysaccharides) and inorganic minerals / solid waste (fly ash, bentonite, talc) as base materials, it is not only environmentally friendly, free from secondary pollution and toxic residues, but also realizes high-value-added utilization of bulk industrial solid waste.

[0027] 2. Targeted Destabilization and Rapid Phosphorus Removal: Utilizing the specially introduced active metal sites in the pores of bentonite and fly ash, phosphate ions are specifically chemically immobilized, i.e., targeted destabilization of dissolved phosphate ions in water. Simultaneously, combined with the netting and sweeping effect of long-chain polymer components, and using inorganic microparticles as counterweight cores, deep purification of turbidity and total phosphorus is achieved through ultra-gravity rapid co-sedimentation.

[0028] 3. Powerful Complex Breaking and Deep Mineralization of Heavy Metals: Faced with complex industrial wastewater, the high-density grafted functional groups on modified chitosan can forcefully break the binding of organic complexing agents, specifically targeting and chelating heavy metal ions such as Pb²⁺, Cu²⁺, and Cd²⁺. Combined with the gelation and gravity sedimentation of the system, secondary release of heavy metals can be completely avoided.

[0029] 4. Breaking through the bottleneck of sludge dewatering limits: The electrostatic interaction of cationic macromolecules powerfully tears apart extracellular polymers (EPS) formed by the cross-linking of proteins and polysaccharides in the sludge, releasing bound water. Simultaneously, extremely hard fly ash microspheres act as internal pressure-bearing fulcrums (pipeline effect), combined with hydrophilic talc sheets after polarity reversal as drainage guides (interlayer channel effect). This triple synergistic mechanism of "breaking through-flocculation-skeleton construction" can maintain the microscopic drainage channels without collapsing under extremely high mechanical pressure, successfully reducing the sludge moisture content to the drying limit of below 55%.

[0030] This invention discloses a novel green and eco-friendly composite coagulant prepared primarily from natural plant polysaccharides, bentonite, talc, power plant fly ash, and marine bio-based chitosan. It also proposes a refined preparation process for this green and eco-friendly composite coagulant based on multi-dimensional molecular-level modification, as well as innovative application methods for this coagulant in three core water treatment fields: suspended solids and phosphorus removal in municipal sewage, targeted treatment of industrial heavy metal wastewater, and deep dewatering and conditioning of high-moisture sludge. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to embodiments. It should be understood that the following specific embodiments are only used to explain the invention and do not constitute a limitation thereof.

[0032] This invention provides a green and eco-friendly composite coagulant, comprising the following raw materials in weight percentages: 20-40% modified fly ash, 10-40% modified bentonite, and 5-15% modified talc. Modified chitosan 5-15%, modified plant polysaccharides 5-15%. Among them: The modified fly ash is acid-activated modified fly ash. The modified bentonite is sodium-based bentonite modified from calcium-based bentonite. The modified talc is hydrophilic talc modified from natural hydrophobic talc through mechanical activation. The modified chitosan is obtained by quaternization and targeted functional group grafting modification of natural chitosan. The modified plant polysaccharide is obtained by modification from agricultural and forestry waste extracts.

[0033] Depending on the needs, different raw material ratios (weight percentages) can be used to prepare green and eco-friendly composite coagulants, such as, but not limited to, the formulations of the seven examples given in Table 1 below: Table 1

[0034] This invention also provides a method for preparing the green and ecological composite coagulant. The coagulant of this invention is prepared according to the raw material ratio shown in Example 1 of Table 1, and the steps are as follows: Step 1: Add 1000 mL of ultrapure deionized water to a large glass reactor equipped with a constant temperature jacket and an adjustable high-speed shear emulsification head. Slowly drip 0.1M hydrochloric acid solution into the deionized water to adjust the pH of the water to a stable 6.0 and maintain a slightly acidic environment.

[0035] Step 2: Weigh all raw materials according to the raw material ratio in Example 1, in grams.

[0036] 5 grams of modified chitosan and 15 grams of modified plant polysaccharide powder were simultaneously and uniformly added to the reactor. The water bath heating system was turned on to rapidly raise the temperature inside the reactor and maintain it at 50°C. The main stirring shaft was set to a speed of 400 rpm. Under mild conditions of moderate shear force, the reaction was continuously stirred and maintained for 1.5 hours. During this period, the two polymer active long chains with different spatial conformations and charge densities fully extended and intertwined under the drive of slightly acidic conditions and thermal energy. Through the intermolecular hydrogen bond network and strong electrostatic attraction, a uniform and highly resilient "polymer flocculation interpenetrating network structure" was spontaneously and gradually formed in the solution.

[0037] Step 3: After confirming that the polymer flocculation interpenetrating network structure has matured and stabilized without particle precipitation, the high-speed shear emulsifying head built into the reactor is rapidly increased to an extremely high speed of 9000 rpm to form a powerful vortex system within the reactor. Using a double-helix metering feeder, 15 grams of modified talc, 30 grams of modified bentonite, and 35 grams of modified fly ash powder are sequentially and continuously sprayed into the reactor at a uniform speed. Under the extremely high hydrodynamic shear stress and microscale ultra-strong mixing action of the 9000 rpm high-speed shear emulsifying head, the agglomerates of inorganic mineral particles are forcibly torn apart into monomers. The free and extended organic polymer interpenetrating chains, like countless "microscopic ropes," are extremely firmly wrapped, entangled, and anchored deep within the pores and surface of the porous fly ash and bentonite, as well as between the talc layers, through multiple forces such as hydrogen bonds, dipole moments, and electrostatic adsorption. This shear-composite self-assembly process under extremely high-speed conditions was strictly maintained for 40 minutes, ultimately forming a dark brown, viscous, and microstructure-stable inorganic-organic composite slurry in the reactor.

[0038] Step 4: To prevent macroscopic phase separation of the slurry's composite structure, the obtained self-assembled viscous inorganic-organic composite slurry is immediately and under high pressure pumped into the atomizing disc of a large industrial-grade centrifugal spray dryer using a screw pump. The inlet temperature of the drying tower's hot air is strictly controlled within a safe range of 170℃ and the outlet exhaust temperature is 85℃ to prevent polymer coking and carbonization. Within milliseconds of contact with the high-temperature hot air, the slurry droplets flowing through the atomizing disc undergo intense three-dimensional contraction of their microscopic interpenetrating structure and instantaneously solidify and lock into shape, forming a large number of light brown powders with spherical microstructures, uniform particle size distribution, and excellent free flowability. The powder at the bottom of the drying chamber is collected by a cyclone separator, and after natural cooling, the multifunctional green ecological composite coagulant product of Example 1 is obtained, which is then packaged and sealed for storage.

[0039] The raw materials used in preparing the coagulant of this invention require specialized modification. The modification processes for each raw material are as follows: The modification method for the modified fly ash is as follows: solid waste generated from coal-fired power plants can be used as raw material for modification treatment. First, the raw fly ash is mixed with a 1M-3M hydrochloric acid or sulfuric acid solution at a solid-liquid mass ratio of 1:5-1:10. Then, the mixed slurry is placed in a shaking reactor and continuously stirred and activated at 50-100 rpm for 24 hours under constant temperature of 80℃. After activation, the solid and liquid are separated by high-speed centrifugation, and the separated solid is repeatedly washed with double-distilled water until the supernatant is neutral. The supernatant is then dried at 105℃ for 24 hours to prepare acid-activated fly ash with well-developed pores.

[0040] The modification method of the modified bentonite is as follows: First, the raw calcium-based bentonite powder is dispersed in water, and sodium carbonate is added and stirred at 60-90℃ for sodium treatment to prepare a highly dispersed sodium-based bentonite slurry with a mass fraction of 3%-5%. An aluminum salt aqueous solution is prepared separately, and sodium hydroxide aqueous solution is added dropwise to the aluminum salt aqueous solution at a very slow rate under strong stirring, controlling a specific OH / Al molar ratio of 2.0-2.5, and aged at room temperature for 24 hours to obtain a hydroxyl aluminum pillar solution rich in Al13 polymer. An iron salt (such as FeCl3) aqueous solution is slowly added dropwise to the hydroxyl aluminum pillar solution to form a composite modification solution. Zirconium oxychloride (ZrOCl2) and distilled water are prepared to form a zirconium salt aqueous solution. The sodium-based bentonite slurry is then heated to 60-80℃, and under continuous strong stirring, the composite modification solution and the zirconium salt aqueous solution are slowly added sequentially, continuously carrying out interlayer ion exchange and assembly reactions for 2-3 hours. After the reaction is complete, the modified slurry is subjected to high-pressure filtration, the filter cake is collected and washed with water to remove impurity ions, and finally the filter cake is dried, depolymerized and dispersed to obtain a highly active zirconium / iron / aluminum cross-linked bentonite phosphorus removal adsorbent, thus obtaining modified bentonite.

[0041] The modification method of the modified talc is as follows: natural hydrophobic talc powder with a fineness of 200 mesh is placed in a stirred ball mill with a cooling jacket and high-hardness zirconium oxide filling grinding media. The rotation speed is set to 500-2000 rpm, and high-intensity mechanical pulverization and activation treatment is continuously carried out for 4 to 10 hours until a significant decrease in its surface contact angle is detected, gradually activating the surface hydroxyl groups.

[0042] After mechanical activation, the talc powder is ultrasonically dispersed in a mixed solvent of ethanol and purified water (ethanol to purified water volume ratio approximately 9:1) at a dosage of 5-15% by mass. To promote hydrolysis, the pH of the mixed solvent is adjusted to 4.0-5.5 beforehand using glacial acetic acid. An aminosilane coupling agent, accounting for 1%-3% of the talc powder mass, is added dropwise under vigorous stirring to obtain a mixed solution. The entire system is then heated to 70-80℃ and refluxed with stirring for approximately 3 hours. After the reaction, the reaction solution is filtered to separate the solid and liquid phases. The solid is repeatedly washed with anhydrous ethanol to remove non-reacted adsorbed silane monomers. Finally, it is dried in an 80℃ forced-air drying oven to constant weight, pulverized, and sieved to obtain a two-dimensional hydrophilic modified talc framework substrate with strong hydrophilicity and high surface activity, thus obtaining modified talc.

[0043] The modification method of the modified chitosan is as follows: Natural chitosan powder with a deacetylation degree greater than 85% was dispersed in isopropanol solvent at a mass fraction of 5-10%, and a concentrated sodium hydroxide solution was slowly added dropwise for swelling and alkalization treatment; then glycidyltrimethylammonium chloride (GTMAC) solution was added, and the quaternization reaction was carried out at a constant temperature of 60-80℃ for 3-5 hours to obtain the reaction product.

[0044] The reaction product was purified by washing with ethanol, and then dissolved at a mass fraction of 2-5% in an alkaline aqueous solution with a pH of 11-13. Carbon disulfide (CS2) and a trace amount of epichlorohydrin crosslinking agent were slowly added dropwise under vigorous stirring. The molar ratio of natural chitosan to CS2 ranged from 1:1 to 3:1; the molar ratio of natural chitosan to epichlorohydrin crosslinking agent ranged from 0.05:1 to 0.2:1. The residual free amino groups on the natural chitosan chains underwent a nucleophilic addition reaction with carbon disulfide, ultimately generating a multifunctional modified chitosan derivative possessing both a permanent positive charge and extremely strong heavy metal-specific chelating ability.

[0045] The modification of the plant polysaccharides employs a process that deeply couples physical and chemical processes: Plant polysaccharides extracted from agricultural and forestry waste were prepared into an aqueous solution with a mass fraction of 5%-10%. This aqueous solution was pumped into a microfluidic homogenizer and continuously circulated 3-5 times under extremely high working pressure of 100-150 MPa to thoroughly complete the physical degradation of macromolecules and expose surface-active groups. After physical activation, the aqueous solution was transferred to a reaction vessel, and solid NaOH was added as a catalyst. The mixture was heated to 75°C and magnetically stirred to ensure complete activation and dissolution. The temperature of the aqueous solution system was then lowered to 40-60°C, and a cationic etherifying agent (such as 3-chloro-2-hydroxypropyltrimethylammonium chloride or a similar quaternizing agent) was slowly added dropwise. The reaction was carried out continuously at a constant temperature for 2-4 hours. After the reaction was completed, the viscous reaction solution was poured into a large amount of anhydrous ethanol for alcohol precipitation, resulting in a large amount of white flocculent precipitate. After filtration, multiple washings, and vacuum drying and grinding at 65°C, a highly active quaternized plant polysaccharide modified product was obtained, thus yielding the modified plant polysaccharide.

[0046] The green and eco-friendly composite coagulant of this invention, through organic-inorganic hybridization and multi-dimensional molecular-level modification, possesses synergistic advantages such as high-efficiency coagulation, targeted adsorption, and rigid framework construction. It has the following beneficial effects: 1. Green ecology and solid waste resource utilization: Using natural polymers (chitosan, plant polysaccharides) and inorganic minerals / solid waste (fly ash, bentonite, talc) as base materials, it is not only environmentally friendly, free from secondary pollution and toxic residues, but also realizes high-value-added utilization of bulk industrial solid waste.

[0047] 2. Targeted Destabilization and Rapid Phosphorus Removal: Utilizing the active metal sites specifically introduced into the pores of bentonite and fly ash, phosphate ions are specifically chemically immobilized. Simultaneously, combined with the netting and sweeping effect of long-chain polymer components, and using inorganic microparticles as a counterweight core, ultra-gravity rapid co-sedimentation and deep purification of turbidity and total phosphorus are achieved.

[0048] 3. Powerful Complex Breaking and Deep Mineralization of Heavy Metals: Faced with complex industrial wastewater, the high-density grafted functional groups on modified chitosan can forcefully break the binding of organic complexing agents, specifically targeting and chelating heavy metal ions such as Pb²⁺, Cu²⁺, and Cd²⁺. Combined with the gelation and gravity sedimentation of the system, secondary release of heavy metals can be completely avoided.

[0049] 4. Breaking through the bottleneck of sludge dewatering limits: The electrostatic interaction of cationic macromolecules powerfully tears apart extracellular polymers (EPS) formed by the cross-linking of proteins and polysaccharides in the sludge, releasing bound water. Simultaneously, extremely hard fly ash microspheres act as internal pressure-bearing fulcrums (pipeline effect), combined with hydrophilic talc sheets after polarity reversal as drainage guides (interlayer channel effect). This triple synergistic mechanism of "breaking through-flocculation-skeleton construction" can maintain the microscopic drainage channels without collapsing under extremely high mechanical pressure, successfully reducing the sludge moisture content to the drying limit of below 55%.

[0050] The above description is merely a specific embodiment of the present invention. It should be noted that any modifications, equivalent substitutions, and variations made within the spirit and framework of the present invention should be included within the protection scope of the present invention.

Claims

1. A green ecological composite coagulant, characterized in that, The raw materials include the following weight percentages: modified fly ash 20-40%, modified bentonite 10-40%, and modified talc 5-15%. Modified chitosan 5-15%, modified plant polysaccharide 5-15%.

2. The green and ecological composite coagulant as described in claim 1, characterized in that, The modified fly ash is fly ash that has been modified by acid activation; The modified bentonite is sodium-based bentonite modified from calcium-based bentonite.

3. The green and eco-friendly composite coagulant as described in claim 1, characterized in that, The modified talc is a hydrophilic talc modified from natural hydrophobic talc.

4. The green and eco-friendly composite coagulant as described in claim 1, characterized in that, The modified chitosan is obtained by quaternization and targeted functional group grafting modification of natural chitosan; the modified plant polysaccharide is obtained by modification of agricultural and forestry waste extracts.

5. A method for preparing a green and eco-friendly composite coagulant as described in any one of claims 1 to 4, comprising the following steps: Step 1: Add deionized water to the reactor equipped with an adjustable high-speed shear emulsifier head, and slowly drip 0.1M hydrochloric acid solution into the deionized water to adjust the pH value of the water to a stable 6.0 and maintain a slightly acidic environment. Step 2: Weigh each raw material according to the ratio of the green ecological composite coagulant, and then put the modified chitosan and modified plant polysaccharide into the reaction vessel. Heat the reaction vessel and maintain the temperature at 50°C. Stir the main stirring shaft continuously at 400 rpm for 1.5 hours to carry out the reaction and form a high molecular flocculent interpenetrating network structure in the solution. Step 3: After confirming that the polymer flocculent interpenetrating network structure is matured and stable without particle precipitation, the high-speed shear emulsifying head is rapidly raised to a high-speed rotation of 9000 rpm, and then modified talc, modified bentonite and modified fly ash are sprayed into the reactor in sequence; maintain high-speed shearing for 40 minutes to obtain inorganic-organic composite hybrid slurry; Step 4: The inorganic-organic composite slurry is fed into a drying tower by a high-pressure pump for drying. The inlet temperature of the hot air in the drying tower is controlled at 170°C and the outlet exhaust temperature is controlled at 85°C to obtain the green ecological composite coagulant.

6. The preparation method according to claim 5, characterized in that, The modification method of the modified fly ash includes: Fly ash was mixed with a 1M-3M hydrochloric acid or sulfuric acid solution at a solid-liquid mass ratio of 1:5-1:

10. The mixture was placed in a shaking reactor and continuously stirred at 50-100 rpm for 24 hours under constant temperature of 80℃. The solid and liquid were separated by high-speed centrifugation, and the solid obtained was repeatedly washed with double-distilled water until the supernatant was neutral. The supernatant was then dried at 105℃ for 24 hours to prepare acid-activated fly ash with well-developed pores.

7. The preparation method according to claim 5, characterized in that, The modification method of the modified bentonite includes: Calcium-based bentonite powder is dispersed in water, sodium carbonate is added, and the mixture is stirred at 60-90℃ to carry out sodium treatment, thereby preparing a highly dispersed sodium-based bentonite slurry with a mass fraction of 3%-5%. A separate aqueous solution of aluminum salt was prepared, and an aqueous solution of sodium hydroxide was slowly added dropwise to the aqueous solution of aluminum salt under strong stirring, controlling a specific OH / Al molar ratio of 2.0-2.5, and aged at room temperature for 24 hours to obtain a hydroxyl aluminum pillar solution rich in Al13 polymer; A composite modified solution is formed by slowly adding an aqueous iron salt solution to the aluminum hydroxide pillar solution; a zirconium salt aqueous solution is prepared by mixing zirconium oxychloride with distilled water; the sodium-based bentonite slurry is heated to 60-80°C, and the composite modified solution and zirconium salt aqueous solution are slowly added sequentially under continuous strong stirring, and the interlayer ion exchange and assembly reaction is carried out for 2-3 hours to obtain the modified slurry. The modified slurry is pressure filtered, the filter cake is collected and washed with water to remove impurity ions, and finally the filter cake is dried, depolymerized and dispersed to obtain modified bentonite.

8. The preparation method according to claim 5, characterized in that, The modification method of the modified talc includes: 200-mesh natural hydrophobic talc powder is placed in a stirred ball mill and pulverized and activated for 4 to 10 hours at a set speed. After the surface contact angle of the natural hydrophobic talc powder is significantly reduced, it is removed and ultrasonically dispersed in a mixed solvent of ethanol and purified water at a dosage of 5-15% by mass. The pH value of the mixed solvent needs to be adjusted to 4.0-5.5 beforehand using glacial acetic acid. A slightly acidic aminosilane coupling agent of 1%-3% by mass of talc powder is added dropwise under high-speed stirring to obtain a mixed solution. The mixed solution is heated to 70-80℃ and refluxed and stirred for 3 hours. The reaction solution is removed and filtered to separate the solid and liquid. The solid is repeatedly washed with anhydrous ethanol and dried in an 80℃ forced-air drying oven to constant weight. It is then pulverized and sieved to obtain hydrophilic modified talc.

9. The preparation method according to claim 5, characterized in that, The modification formula for the modified chitosan includes: Natural chitosan powder with a deacetylation degree greater than 85% is dispersed in isopropanol solvent at a mass fraction of 5-10%, and a concentrated sodium hydroxide solution is slowly added dropwise for swelling and alkalization treatment; then glycidyltrimethylammonium chloride solution is added, and a quaternization reaction is carried out at a constant temperature of 60-80℃ for 3-5 hours. After washing and purifying the reaction product with ethanol, the product is dissolved in an alkaline aqueous solution with a pH of 11-13 at a mass fraction of 2-5%. Carbon disulfide and a trace amount of epichlorohydrin crosslinking agent are slowly added dropwise under high-speed stirring. The molar ratio of natural chitosan to carbon disulfide ranges from 1:1 to 3:1, and the molar ratio of natural chitosan to epichlorohydrin crosslinking agent ranges from 0.05:1 to 0.2:

1. The residual free amino groups on the natural chitosan chain undergo a nucleophilic addition reaction with carbon disulfide to generate a multifunctional modified chitosan derivative that simultaneously possesses positive charge and heavy metal-specific chelating ability.

10. The preparation method according to claim 5, characterized in that, The modification method of the modified plant polysaccharide is as follows: Plant polysaccharides extracted from agricultural and forestry waste were prepared into an aqueous solution with a mass fraction of 5%-10%. This aqueous solution was pumped into a microfluidic homogenizer and continuously circulated 3-5 times under a working pressure of 100-150 MPa. The aqueous solution was then transferred to a reaction vessel, and solid NaOH was added as a catalyst. The mixture was heated to 75°C and magnetically stirred to ensure complete activation and dissolution. The temperature of the reaction vessel system was then lowered to 40-60°C, and a cationic etherification reagent was slowly added dropwise. After continuous reaction at a constant temperature for 2-4 hours, the reaction solution was poured into a large amount of anhydrous ethanol for alcohol precipitation. A large amount of white flocculent precipitate was obtained, which was then filtered, washed multiple times, and vacuum dried and ground at 65°C to obtain a highly active quaternized ammonium plant polysaccharide modified product.

Images