Efficient composite flocculant and preparation process thereof

Abstract

The invention relates to the technical field of water treatment, and discloses an efficient composite flocculant and a preparation process thereof. The method comprises the following steps: carrying out alkalization copolymerization on an aluminum salt and an iron salt according to a molar ratio of 7: 3 to form an aluminum-iron copolymerization flocculation matrix; the oriented cationic flocculation polymer is formed by copolymerization of acrylamide and methacryloyloxyethyl trimethyl ammonium chloride according to a molar ratio of 6: 4; the silica sol nano bridging layer connects the two layers through chemical bonds to form a core-shell composite structure; and the anti-oxidation interface adaptive component is dispersed in the anti-oxidation interface. According to the invention, the utilization rate of effective components, the storage stability, the oxidation resistance and the broad-spectrum adaptability to special water quality conditions of the flocculant are improved.

Description

Technical Field

[0001] This application relates to the field of water treatment technology, and in particular to a high-efficiency composite flocculant and its preparation process. Background Technology

[0002] With the acceleration of industrialization, water pollution has become increasingly severe. Flocculation technology, as a core process in water treatment, plays an irreplaceable role in wastewater treatment and drinking water purification. Traditional flocculants are mainly divided into two categories: inorganic flocculants and organic flocculants. Inorganic flocculants, such as polyaluminum chloride (PAC) and polyferric sulfate (PFS), destabilize colloidal particles through charge neutralization and net-sweeping mechanisms. Organic polymeric flocculants, such as polyacrylamide (PAM), promote floc formation through the adsorption and bridging effects of long-chain molecules. In recent years, to fully leverage the synergistic advantages of inorganic and organic flocculants, composite flocculants have gradually become a research hotspot. By compounding inorganic components such as aluminum salts and iron salts with cationic polymers, flocculation efficiency can be improved to a certain extent and the application range can be broadened.

[0003] However, existing composite flocculants still have many shortcomings in practical applications. First, traditional composite flocculants mostly use simple physical mixing methods to combine inorganic and organic components. The two components bind randomly in the solution due to electrostatic attraction, causing the highly charged active sites of the inorganic polynuclear polymer to be prematurely neutralized by the organic polymer chains. This results in the neutralized component being partially ineffective before being added to the water. Simultaneously, the uncontrolled entanglement of the organic polymer chains with the inorganic components reduces their ability to fully extend, weakening the adsorption and bridging efficiency. Second, the inorganic and organic components continuously interact during storage, leading to poor product stability, short shelf life, and an inability to control the release sequence of the two components' activity, making it difficult to achieve spatiotemporal synergy between charge neutralization and bridging. In addition, existing flocculants are not adaptable to special water quality conditions. In particular, when treating modified sludge pre-oxidized by ozone micro-nano bubbles, residual oxidizing substances will continue to degrade organic polymer chains. If micro-nano bubbles are encapsulated inside the flocs, they will reduce the density of the flocs and deteriorate the settling performance. Existing technologies lack targeted antioxidant protection mechanisms and bubble interface control methods. Summary of the Invention

[0004] This application provides a high-efficiency composite flocculant and its preparation process, which solves the technical problems of the mutual interference between inorganic and organic components in existing composite flocculants, which leads to premature failure of active components, poor storage stability, and insufficient adaptability to ozone-modified sludge. It improves the utilization rate of effective components, storage stability, antioxidant capacity, and broad-spectrum adaptability to special water quality conditions of the flocculant.

[0005] In a first aspect, this application provides a high-efficiency composite flocculant, comprising: The aluminum-iron copolymer flocculant matrix is ​​composed of a polynuclear hydroxy polymer formed by alkalization copolymerization of aluminum salt and iron salt in an aluminum-iron molar ratio of 7:3, with an alkalinity of 0.55. Directed cationic flocculant polymer, formed by copolymerization of acrylamide and methacryloyloxyethyltrimethylammonium chloride in a molar ratio of 6:4, has a cationicity of 35%-40% and a viscosity-average molecular weight of 5×10⁻⁶. 6 -8×10 6 Da; The silica sol nano-bridging layer is composed of active silica sol particles with a particle size of 5-15nm. It is bonded to the aluminum-iron copolymer flocculant matrix through Si-O-Al and Si-O-Fe bonds, and is combined with the directional cationic flocculant polymer through hydrogen bonds, forming a core-shell composite structure with the aluminum-iron copolymer flocculant matrix as the core, the silica sol nano-bridging layer as the middle layer, and the directional cationic flocculant polymer as the outer layer. Antioxidant interface adaptants, including sodium thiosulfate, L-ascorbic acid and sodium dodecyl sulfonate, are dispersed in the core-shell composite structure.

[0006] Secondly, this application provides a preparation process for a high-efficiency composite flocculant, comprising: S1. Mix aluminum chloride solution and ferric chloride solution at an aluminum-iron molar ratio of 7:3, and perform alkali copolymerization treatment by adding alkaline solution dropwise to obtain the aluminum-iron copolymer flocculent matrix; S2. Acrylamide and methacryloyloxyethyltrimethylammonium chloride are mixed in a molar ratio of 6:4 and grafted copolymerized through a redox initiation system to obtain the directional cationic flocculant polymer. S3. The acidic silica sol crosslinking medium is added to the aluminum-iron copolymer flocculant matrix for dehydration and condensation treatment, and then the directional cationic flocculant polymer is introduced after swelling for hydrogen bonding treatment to obtain a silicon bridge ternary composite flocculant with a core-shell composite structure. S4. Sodium thiosulfate, L-ascorbic acid and sodium dodecyl sulfonate are added to the silicon-bridged ternary composite flocculant for antioxidant and bubble interface adaptation treatment. After vacuum concentration and pH adjustment, the high-efficiency composite flocculant is obtained.

[0007] The technical solution provided in this application achieves spatial isolation and directional bonding at the molecular scale between inorganic electrically neutralizing components and organic bridging components by constructing a core-shell composite structure consisting of an aluminum-iron copolymer flocculant matrix, a directional cationic flocculant polymer, a silica sol nano-bridging layer, and an antioxidant interface adaptable component. Specifically, the 7:3 aluminum-iron molar ratio copolymer flocculant matrix enables Al… 13 High-charge aluminum polymerization morphology and Fe3(OH)4 5The synergistic coexistence of ⁺-type iron polymer forms and the precise control of alkalinity (0.55) ensure the stability of the polynuclear hydroxyl polymer morphology distribution, enabling inorganic components to simultaneously possess strong charge neutralization capabilities and organic complexation and adsorption properties. The directional cationic flocculant polymer, copolymerized with acrylamide and methacryloyloxyethyltrimethylammonium chloride in a 6:4 molar ratio, precisely matches the cationicity to the surface negative charge increment of the ozone-modified sludge, achieving a viscosity-average molecular weight of 5 × 10⁻⁶. 6 -8×10 6 The controlled range of Da ensures that the extension length of the polymer chains matches the spacing between the modified sludge particles, avoiding shear breakage caused by excessively high molecular weight and insufficient bridging caused by excessively low molecular weight. The silica sol nano-bridging layer covalently anchors the silica sol particles to the surface of the inorganic matrix through Si-O-Al and Si-O-Fe bonds, while simultaneously binding with organic polymers through hydrogen bonds. The resulting core-shell composite structure maintains spatial isolation between inorganic and organic components during storage, preventing premature deactivation. After being added to the sludge system, the shielding effect of the silica sol layer gradually weakens with changes in pH and ionic strength, achieving the time-sequential release and synergistic effect of the charge-neutralizing and bridging components. In the antioxidant interface-adaptive components, sodium thiosulfate directly reduces and consumes residual ozone, L-ascorbic acid preferentially captures hydroxyl radicals, and sodium dodecyl sulfonate adsorbs at the bubble interface through its hydrophobic end and electrostatically pairs with quaternary ammonium groups at its hydrophilic end, causing the flocculant to be directionally enriched on the bubble surface. During the flocculation process, the bubbles are squeezed out rather than encapsulated in flocs, fundamentally solving the technical problems of mutual interference between components, poor storage stability, and insufficient adaptability to oxidizing water quality in existing composite flocculants.

[0008] The core-shell composite structure design breaks through the traditional simple physical mixing approach. Through the spatial isolation and directional bonding mechanism achieved by the silica sol nano-bridging layer, it not only ensures the activity stability of the effective components during storage, but more importantly, establishes a time-sequential regulation system for component release, prioritizing charge neutralization over bridging, consistent with the kinetics of colloid destabilization. The introduction of antioxidant interface-adaptive components addresses the dual interference of residual oxidizing substances and micro / nano bubbles in the ozone modification process. Through molecular-level antioxidant protection and interfacial chemical regulation, it extends the effective action time of organic polymers and improves floc density and sedimentation performance through an active bubble removal mechanism. Attached Figure Description

[0009] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1This is a schematic flowchart illustrating the preparation process of the high-efficiency composite flocculant in the embodiments of this application; Figure 2 This is a schematic diagram comparing the performance of flocculants under different water quality conditions in the embodiments of this application. Detailed Implementation

[0011] This application provides a high-efficiency composite flocculant and its preparation process. The terms "first," "second," "third," "fourth," etc. (if present) in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in a sequence other than that illustrated or described herein. Furthermore, the terms "comprising" or "having" and any variations thereof are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0012] For ease of understanding, the specific process of the embodiments of this application is described below. One embodiment of the high-efficiency composite flocculant in this application includes: The aluminum-iron copolymer flocculant matrix is ​​composed of a polynuclear hydroxy polymer formed by alkalization copolymerization of aluminum salt and iron salt in an aluminum-iron molar ratio of 7:3, with an alkalinity of 0.55. Directed cationic flocculant polymer, formed by copolymerization of acrylamide and methacryloyloxyethyltrimethylammonium chloride in a molar ratio of 6:4, has a cationicity of 35%-40% and a viscosity-average molecular weight of 5×10⁻⁶. 6 -8×10 6 Da; The silica sol nano-bridging layer is composed of active silica sol particles with a particle size of 5-15nm. It is bonded to the aluminum-iron copolymer flocculant matrix through Si-O-Al and Si-O-Fe bonds, and is combined with the directional cationic flocculant polymer through hydrogen bonds, forming a core-shell composite structure with the aluminum-iron copolymer flocculant matrix as the core, the silica sol nano-bridging layer as the middle layer, and the directional cationic flocculant polymer as the outer layer. Antioxidant interface-adaptive components, including sodium thiosulfate, L-ascorbic acid and sodium dodecyl sulfonate, are dispersed in the core-shell composite structure.

[0013] In the aluminum-iron copolymer flocculant matrix, the aluminum salt is aluminum chloride, the iron salt is ferric chloride, and the polynuclear hydroxyl polymer includes Al 13 High-charge aluminum polymerization morphology and Fe3(OH)4 5The ⁺-type iron polymerization form has a pH value of 3.8-4.2 for the aluminum-iron copolymer flocculant matrix and a total aluminum-iron metal ion concentration of 0.6-0.8 mol / L.

[0014] Specifically, the 7:3 molar ratio of aluminum to iron in the aluminum-iron copolymer flocculant matrix is ​​designed based on the complementarity of aluminum-based and iron-based flocculants in their flocculation mechanisms. Aluminum-based polynuclear hydroxyl polymer Al 13 It possesses a high positive charge density, and its Keggin structure carries an effective charge of +7 valence, exhibiting outstanding performance in charge neutralization; the iron-based polynuclear hydroxyl polymer Fe3(OH)4 5 ⁺ Due to the stronger coordination and complexation ability of the d-orbital electronic configuration of iron ions, their adsorption affinity for organic debris is significantly better than that of aluminum-based polymers. A basicity of 0.55 is the lowest among Al-based bimetallic systems. 13 and Fe3(OH)4 5 ⁺ The critical condition for the coexistence of two high-charge polynuclear forms to reach peak content is as follows: below this alkalinity, the degree of metal ion hydrolysis and polymerization is insufficient; above this alkalinity, the increased pH of the system will lead to the precipitation of hydroxides. Both situations will weaken the content of effective flocculant components in the flocculant matrix. A pH of 3.8-4.2 and a total metal ion concentration of 0.6-0.8 mol / L are the inherent physicochemical parameters of the aluminum-iron copolymerization system after reaching thermodynamic equilibrium under an alkalinity of 0.55. Within this range, the morphological distribution of polynuclear hydroxy polymers is most stable, and spontaneous further hydrolysis or condensation reactions will not occur.

[0015] The 6:4 molar ratio of acrylamide to methacryloyloxyethyltrimethylammonium chloride in the directional cationic flocculant polymer determines the cationicity of the copolymer to be 35%-40%. This cationicity is based on the characteristic change in the zeta potential of the sludge particles modified by ozone micro-nano bubbles, which shifts negatively from the original -18mV to -25mV to -28mV to -35mV. The positive charge density carried by the directional cationic flocculant polymer with a cationicity of 35%-40% precisely matches the increased surface negative charge of the modified sludge, achieving sufficient charge neutralization without causing colloidal restabilization due to excessive cations. The viscosity-average molecular weight is controlled at 5×10⁻⁶. 6 -8×10 6 The value of Da is determined based on the actual particle size distribution of microbial cell fragments in modified sludge, which is concentrated in the range of 0.5-5 μm. The extension length of the polymer chain corresponding to this molecular weight range is compatible with the interparticle spacing in the above particle size range, which can form an effective adsorption bridging between adjacent particles. At the same time, it avoids the molecular chain from breaking under shear conditions or forming excessively large flocs that encapsulate micro-nano bubbles due to excessively high molecular weight.

[0016] The core technology of the silica sol nano-bridging layer is to spatially isolate and directionally bond the aluminum-iron copolymer flocculant matrix with the directional cationic flocculant polymer at the molecular scale. The surface of the 5-15 nm active silica sol particles is rich in silanol groups. These silanol groups form Si-O-Al and Si-O-Fe covalent bonds with Al-OH and Fe-OH in the aluminum-iron polynuclear hydroxyl polymer through dehydration condensation reactions, anchoring the silica sol particles to the inorganic flocculant matrix surface. Simultaneously, they bind with amide groups on the molecular chains of the directional cationic flocculant polymer through hydrogen bonds, coating the organic polymer components on the outside of the silica sol layer. This core-shell composite structure allows inorganic and organic components to coexist in the same product without mutual interference. During storage, the silica sol interlayer acts as a spatial shield, maintaining the activity of both flocculant components. After addition to the sludge system, the shielding effect of the silica sol layer gradually weakens with changes in system pH and ionic strength, allowing the inorganic neutralizing components and organic bridging components to be released sequentially and synergistically exert their flocculation effect. In the antioxidant interface adaptor components, sodium thiosulfate directly reduces and consumes residual ozone molecules, L-ascorbic acid, as a free radical scavenger, preferentially reacts with hydroxyl radicals to protect organic polymer chains from oxidative degradation, and sodium dodecyl sulfonate is adsorbed on the micro-nano bubble interface through its hydrophobic end and electrostatically paired with the quaternary ammonium groups of the organic components through its hydrophilic end. This allows the flocculant to be directionally enriched at the bubble interface and squeezed out of the bubbles during the flocculation process instead of being encapsulated inside the flocs.

[0017] In one specific embodiment, in the aluminum-iron copolymer flocculant matrix, the aluminum salt is aluminum chloride, the iron salt is ferric chloride, and the polynuclear hydroxyl polymer includes Al 13 High-charge aluminum polymerization morphology and Fe3(OH)4 5 The ⁺-type iron polymerization form has a pH value of 3.8-4.2 for the aluminum-iron copolymer flocculant matrix and a total aluminum-iron metal ion concentration of 0.6-0.8 mol / L.

[0018] In one specific embodiment, the initiator system of the directional cationic flocculant polymer is a redox initiation system composed of ammonium persulfate and sodium bisulfite. The amount of ammonium persulfate is 0.08% of the total mass of the comonomer, the amount of sodium bisulfite is 0.5 times the mass of ammonium persulfate, the copolymerization reaction temperature is 45°C, and the reaction time is 6 hours.

[0019] In one specific embodiment, the molar ratio of SiO2 to metal ions in the aluminum-iron copolymer flocculant matrix in the silica sol nanobridge layer is 0.08-0.12, the SiO2 solid content of the active silica sol particles is 2.8-3.2 g / L, and the surface silanol density is 4.5-5.2 ions / nm².

[0020] In one specific embodiment, the reaction rate constant between L-ascorbic acid and hydroxyl radicals in the antioxidant interface adaptor component is 1.1 × 10¹. 0L / (mol·s), sodium dodecyl sulfonate is adsorbed onto the gas-liquid interface of micro-nano bubbles through its hydrophobic alkyl chain, and the sulfonate group forms an electrostatic pair with the quaternary ammonium cation group of the directional cationic flocculant polymer.

[0021] In one specific embodiment, the effective component content of the high-efficiency composite flocculant is as follows: the total content of Al2O3 and Fe2O3 is greater than or equal to 8.0%, the effective content of directional cationic flocculant is greater than or equal to 0.8%, the SiO2 content is 0.4%-0.6%, the Zeta potential of the high-efficiency composite flocculant is +25 to +32 mV, the pH value is 4.5±0.2, and the density is 1.25-1.30 g / mL.

[0022] In one specific embodiment, aluminum-iron copolymer flocculant matrix uses aluminum chloride and ferric chloride as metal salt raw materials, and the polynuclear hydroxy polymer formed after alkalization copolymerization of the two simultaneously contains Al 13 High-charge aluminum polymerization morphology and Fe3(OH)4 5 ⁺-type iron polymer form, in which Al 13 Fe3(OH)4 is a tetradecaaluminum with a Keggin structure, carrying a +7 effective charge, and is the most potent charge-neutralizing active form among aluminum-based flocculants; 5 ⁺ is a trinuclear iron-hydroxyl polymer, whose unpaired electrons in the 3d orbitals of iron ions endow it with strong complexing and adsorption properties for organic ligands. The pH of this aluminum-iron copolymer flocculant matrix is ​​controlled within the range of 3.8-4.2, and the total aluminum-iron metal ion concentration is maintained at 0.6-0.8 mol / L. Under these conditions, Al... 13 and Fe3(OH)4 5 ⁺ Both polynuclear forms are in a thermodynamically stable range and will not spontaneously transform into low-activity mononuclear ions or amorphous hydroxide precipitates. The synthesis of the directional cationic flocculant polymer uses a redox initiation system composed of ammonium persulfate and sodium bisulfite. The amount of ammonium persulfate is 0.08% of the total mass of the comonomer, and the amount of sodium bisulfite is 0.5 times the mass of ammonium persulfate. This initiator ratio can continuously and stably generate initial free radicals at a low temperature of 45°C, avoiding chain transfer side reactions and excessively wide molecular weight distribution caused by high-temperature initiation. The copolymerization reaction lasts for 6 hours, and the monomer conversion rate reaches more than 95%. The cationicity and molecular weight of the final product are both within the design range.

[0023] In one specific embodiment, the molar ratio of SiO2 in the silica sol nanobridge layer to metal ions in the aluminum-iron copolymer flocculant matrix is ​​controlled within the range of 0.08-0.12. This ratio determines the coverage density of silica sol particles on the surface of the aluminum-iron polynuclear polymer. When the molar ratio is below 0.08, the coverage of silica sol particles on the inorganic matrix surface is incomplete, and some aluminum-iron polynuclear polymers are directly exposed and undergo uncontrolled electrostatic interactions with the organic polymer components, destroying the integrity of the core-shell composite structure. When the molar ratio is above 0.12, excessive silica sol particles form multilayer accumulations on the aluminum-iron matrix surface. An excessively thick silica sol layer is difficult to open due to changes in system pH and ionic strength during application, hindering the timely release of inorganic flocculants. The SiO2 solid content of the active silica sol particles is 2.8-3.2 g / L. This concentration corresponds to a sufficiently large interparticle spacing to maintain good dispersibility and flowability without gelation. A surface silanol density of 4.5-5.2 silanols / nm² is the surface chemical state achieved by silica sol after 90 minutes of curing under acidic conditions at pH 3.0. This density of silanols provides sufficient reaction sites for the formation of Si-O-Al and Si-O-Fe covalent bonds, and also retains a sufficient number of unreacted silanols for subsequent bonding of organic polymer components through hydrogen bonding.

[0024] In one specific embodiment, the total content of Al2O3 and Fe2O3 in the finished high-efficiency composite flocculant is greater than or equal to 8.0%. This content ensures that a single addition provides sufficient metal ion hydrolysis products to neutralize and trap the modified sludge colloidal particles. The effective content of the directional cationic flocculant polymer is greater than or equal to 0.8%, enabling the organic polymer components to establish a sufficient adsorption bridging network between particles during flocculation. The SiO2 content of 0.4%-0.6% corresponds to the appropriate proportion of the silica sol nano-bridging layer in the composite system, satisfying both spatial isolation function and avoiding excessive dilution of the effective flocculant concentration. The zeta potential of the finished product is +25 to +32 mV. This positive potential value matches the negative potential of the ozone-modified sludge particles, which is -28 mV to -35 mV. When the flocculant is added to the modified sludge, the neutralization of positive and negative charges brings the zeta potential of the system close to zero, resulting in the highest colloid destabilization efficiency. A pH of 4.5 ± 0.2 represents the optimal acid-base condition where the stability of the aluminum-iron polynuclear hydroxyl polymer, the protonation degree of the quaternary ammonium groups in the organic components, and the shielding effect of the silica sol layer are all at their best. A density of 1.25-1.30 g / mL indicates that the effective components have been enriched to the industrial application concentration after vacuum concentration. At this density, the product has good flowability, facilitating precise dosing with a metering pump. At the same time, the sufficiently high concentration of effective components allows the on-site dosage to be controlled within the economically reasonable range of 1.0-2.0 mL / L of modified sludge.

[0025] Please see Figure 1 One embodiment of the preparation process of the high-efficiency composite flocculant in this application includes: S1. Mix aluminum chloride solution and ferric chloride solution at an aluminum-iron molar ratio of 7:3, and perform alkali copolymerization treatment by adding alkaline solution dropwise to obtain aluminum-iron copolymer flocculent matrix; In this mixture of aluminum chloride and ferric chloride solutions, aluminum ions exist as [Al(H2O)6]³⁺ and ferric ions as [Fe(H2O)6]³⁺. As the alkali solution is added dropwise, the OH⁻ concentration in the solution increases gradually, with aluminum and ferric ions undergoing three stages: mononuclear hydrolysis, dimer formation, and polynuclear polymerization. The 7:3 molar ratio of aluminum to iron ensures that aluminum ions preferentially form Al₂O₃ during the alkalization process. 13 In Keggin-type polymers, iron ions are induced to form Fe3(OH)4 by the template of aluminum polymers. 5 The trinuclear structure is embedded in the interstitial sites of the aluminum polymer, and the hydrolysis and polymerization processes of the two metals are coupled rather than carried out independently, ultimately forming a polynuclear hydroxyl polymer mixture system of aluminum and iron copolymer. The limitation of the alkaline droplet acceleration rate of 5 mL / min is to avoid the irreversible formation of amorphous hydroxide precipitation due to excessively high local OH⁻ concentration.

[0026] S2. Acrylamide and methacryloyloxyethyltrimethylammonium chloride were mixed in a molar ratio of 6:4 and grafted copolymerized through a redox initiation system to obtain a directional cationic flocculant polymer. In this process, ammonium persulfate undergoes a single-electron transfer reaction under the reduction of sodium bisulfite. The formation rate of sulfate radicals (SO4⁻·) is determined by the concentration ratio of the two initiators and the reaction temperature. At a reaction temperature of 45℃, the thermal decomposition half-life of ammonium persulfate is much longer than that of its redox reaction with sodium bisulfite. The formation of free radicals is dominated by the redox pathway, with a stable formation rate. The chain growth reaction and chain termination reaction reach a dynamic equilibrium, resulting in a narrow molecular weight distribution index of the copolymer. The double bond reactivity of the acrylamide monomer is higher than that of the methacryloyloxyethyltrimethylammonium chloride monomer. After correction for the reactivity ratio, the actual composition ratio of the two monomers in the copolymer chain is close to the feed ratio, thus ensuring that the cationicity of the final product falls within the design range of 35%-40%.

[0027] S3. Add the acidic silica sol crosslinking medium to the aluminum-iron copolymer flocculant matrix for dehydration and condensation treatment, and then introduce the directional cationic flocculant polymer after swelling for hydrogen bonding treatment to obtain a silicon bridge ternary composite flocculant with a core-shell composite structure. In the first stage, after adding the acidic silica sol crosslinking medium to the aluminum-iron copolymer flocculant matrix, the Si-OH on the surface of the silica sol nanoparticles undergoes a dehydration condensation reaction with the Al-OH and Fe-OH on the surface of the aluminum-iron polynuclear hydroxyl polymer under acidic conditions at 40℃. Each condensation reaction removes one molecule of water and forms a Si-O-Al or Si-O-Fe covalent bond. This reaction reaches equilibrium within 60 minutes, at which point the silica sol particles are anchored to the surface of the aluminum-iron polymer through covalent bonds, forming an inorganic-silicon composite. In the second stage, the swelling solution of the directional cationic flocculant polymer is introduced into the inorganic-silicon composite. The NH and C=O in the amide group -CONH2 on the CPAM molecular chain form hydrogen bonds with the remaining Si-OH on the surface of the silica sol particles that did not participate in the condensation reaction. The bond energy of the hydrogen bond is 15-40 kJ / mol, which is weaker than the Si-O-Al covalent bond but sufficient to stably adsorb the organic molecular chain on the outside of the silica sol layer, thereby constructing a core-shell composite structure.

[0028] S4. Sodium thiosulfate, L-ascorbic acid and sodium dodecyl sulfonate were added to the silicon bridge ternary composite flocculant for antioxidant and bubble interface adaptation treatment. After vacuum concentration and pH adjustment, a high-efficiency composite flocculant was obtained.

[0029] Sodium thiosulfate directly eliminates the threat of oxidants by reducing ozone to oxygen, while L-ascorbic acid competitively intercepts free radicals through a rapid reaction with them, thereby blocking the chain degradation reaction of CPAM molecules by free radicals. Sodium dodecyl sulfate has a C1... 12 Alkyl hydrophobic segments spontaneously adsorb at the gas-liquid interface of micro- and nano-bubbles to form a monolayer. The hydrophilic sulfonate groups of these segments face the liquid phase and pair with the quaternary ammonium cation groups on the CPAM chain through electrostatic attraction. This pairing causes the flocculant molecules to oriented and form a dense layer on the bubble surface. During flocculation, as the flocs compact, the bubbles are squeezed and broken out by the dense layer rather than being retained by the loose flocs. Vacuum concentration removes water from the composite solution under low-temperature vacuum conditions, increasing the concentration of effective components to the level required for industrial applications. The pH is adjusted to 4.5 so that all components in the ternary composite structure are simultaneously in their optimal active state.

[0030] Figure 2 This is a schematic diagram comparing the performance of flocculants under different water quality conditions in the embodiments of this application. Figure 2 As shown, the horizontal axis represents five typical water quality types: low-turbidity raw water, high-turbidity raw water, high-organic-content wastewater, dyeing and printing wastewater, and oily wastewater; the vertical axis represents the pollutant removal rate, expressed as a percentage (%). The figure compares the treatment effects of the composite flocculant of this invention, polyaluminum chloride (PAC), and polyacrylamide (PAM) under the same dosing conditions. Figure 2It can be seen that the composite flocculant of the present invention exhibits the best removal effect in all water quality types, with a removal rate of 94.5% in low turbidity raw water, 92.8% in high turbidity raw water, 88.6% in high organic wastewater, 86.3% in dyeing and printing wastewater, and 83.7% in oily wastewater. Compared with traditional PAC flocculants, these figures are improved by 12.2%, 14.3%, 15.4%, 17.4%, and 18.3%, respectively. The improvement is even more significant than that of polyacrylamide (PAM). This fully verifies that the present invention achieves efficient and adaptive removal of pollutants with different characteristics through the synergistic effect of aluminum-iron copolymer flocculant matrix, directional cationic flocculant polymer, silica sol nano-bridging layer, and antioxidant interface adaptable components.

[0031] In one specific embodiment, in step S1, the alkaline solution is a sodium hydroxide solution with a concentration of 2.0 mol / L, the dropping rate is 5 mL / min, the alkalinity is 0.55, the alkalinization reaction temperature is 65°C, the stirring speed is 400 r / min, and after the alkalinization is completed, it is stirred and matured at 150 r / min at 65°C for 2 hours. In step S2, the redox initiation system consists of ammonium persulfate and sodium bisulfite. The amount of ammonium persulfate is 0.08% of the total mass of the comonomer, and the amount of sodium bisulfite is 0.5 times the mass of ammonium persulfate. The reaction temperature is 45℃, the reaction time is 6 hours, and the reaction product is dried at 60℃ for 12 hours and then ground through a 60-mesh sieve to obtain directional cationic flocculant polymer powder.

[0032] Specifically, in step S1, the actual amount of sodium hydroxide added corresponding to an alkalinity of 0.55 is determined by the total concentration and total volume of metal ions in the aluminum-iron mixed solution. The alkalinity is defined as the ratio of the number of moles of OH⁻ added to the theoretical maximum number of moles of OH⁻ required for the hydrolysis of metal ions, i.e., the number of moles of OH⁻ added divided by the sum of three times the number of moles of aluminum and iron ions. The selection of an alkalinization reaction temperature of 65℃ is based on the activation energy requirement of the aluminum-iron bimetallic hydrolysis polymerization reaction. At this temperature, aluminum ions transform from a mononuclear hydrated state to Al⁻. 13 The conversion rate of polynuclear polymerization state is related to the conversion of iron ions from mononuclear hydrated state to Fe3(OH)4. 5The conversion rates of the trinuclear polymer state tend to match, and the polymerization reactions of the two metals proceed synchronously, avoiding the problem of preferential precipitation of iron hydroxide caused by the much faster polymerization rate of iron ions compared to aluminum ions at low temperatures. A stirring speed of 400 r / min maintains high-intensity turbulent mixing during the alkalization stage, ensuring uniform contact between the dripped sodium hydroxide solution and the aluminum-iron mixture within milliseconds, eliminating localized high pH areas around the alkali dripping point. After alkalization, the stirring speed is reduced to 150 r / min for 2 hours of maturation. Low-speed stirring provides mild mass transfer conditions, allowing the formed polynuclear hydroxyl polymer to further develop and refine its polynuclear structure through olation and oxolation reactions. The olation reaction involves the formation of an M-OH-M structure through hydroxyl bridging between metal ions, while the oxolation reaction involves further dehydration of hydroxyl bridges to form a MOM oxygen bridge structure. The advancement of these two reactions gradually increases the structural stability and charge density of the polynuclear polymer to its final steady state.

[0033] In step S2, the amount of ammonium persulfate used is 0.08% of the total mass of the comonomer, which is a low-concentration initiator system. At this dosage, the initial free radical concentration in the system is 10⁻⁻⁶. 7 The concentration is on the order of mol / L, the chain initiation rate is more than two orders of magnitude lower than the chain growth rate, and each active chain can accept a sufficient number of monomer molecules for chain growth before termination, thus achieving 5 × 10⁻⁶ molecules. 6 Up to 8×10 6 The target viscosity-average molecular weight of Da is determined by the amount of sodium bisulfite used, which is 0.5 times the mass of ammonium persulfate. This ratio ensures a slight excess of oxidant over reductant. After the ammonium persulfate is consumed in the reaction with sodium bisulfite, some remains. The remaining ammonium persulfate undergoes slow thermal decomposition at 45°C, continuously replenishing free radicals and maintaining a stable free radical generation rate throughout the 6-hour reaction period, rather than a rapid decline after an initial burst. The reaction product is a hydrous gel copolymer. The drying temperature of 60°C is lower than the thermal degradation initiation temperature of CPAM (usually above 200°C). Drying to constant weight for 12 hours ensures that free and bound water in the gel are fully removed. After grinding, the particle size corresponding to a 60-mesh sieve is no greater than 250 μm. Powder within this particle size range can completely swell and dissolve under stirring conditions for 2 hours when preparing a 2.5% solution in the subsequent step S3. Particles with excessively large particle sizes will result in incomplete swelling, leaving unswelled gel particles in the solution, affecting the uniformity of subsequent hydrogen bonding treatment.

[0034] In one specific embodiment, in step S3, the acidic silica sol crosslinking medium is prepared by acidifying a 0.5 mol / L sodium silicate solution to pH 3.0 with 1.0 mol / L hydrochloric acid and then allowing it to stand and mature at 30°C for 90 minutes. The particle size of the silica sol crosslinking medium is 5-15 nm, and the SiO2 solid content is 2.8-3.2 g / L. The volume ratio of the silica sol crosslinking medium to the aluminum-iron copolymer flocculant matrix is ​​3:10. The dehydration condensation treatment was carried out at a temperature of 40℃, a stirring speed of 200 r / min, and a treatment time of 60 minutes. The directional cationic flocculant polymer was prepared into a 2.5% solution and then added dropwise to the inorganic-silicon composite liquid at a rate of 5 mL / min. The hydrogen bonding coupling treatment was carried out at a temperature of 40℃, a stirring speed of 150 r / min, and a treatment time of 120 minutes.

[0035] Specifically, in step S3, the preparation process of the acidic silica sol crosslinking medium involves acidifying the sodium silicate solution with hydrochloric acid to convert silicate ions into active silica monomers Si(OH)4. Under acidic conditions with a pH of 3.0, the active silica monomers gradually grow into nanoscale sol particles through intermolecular dehydration condensation reactions. After standing and aging at 30°C for 90 minutes, the particles grow to 5-15 nm, and the condensation rate naturally decreases and tends to stabilize. Sol particles in this particle size range have sufficient specific surface area to provide a large number of surface Si-OH reaction sites, and will not cause steric hindrance in the subsequent composite process due to excessive particle size. The volume ratio of 3:10 between silica sol crosslinking medium and aluminum-iron copolymer flocculant matrix is ​​determined based on the ratio between the amount of SiO2 in silica sol and the amount of metal ions in aluminum-iron matrix. At this volume ratio, silica sol particles can form a single layer covering on the surface of aluminum-iron polynuclear polymer rather than multiple layers stacked. The single layer covering can completely establish the silica sol isolation layer without hindering the release of inorganic components after the flocculant is put into use due to excessive layer thickness.

[0036] The dehydration condensation treatment was carried out at 40°C for 60 minutes. This temperature is lower than the morphological transformation temperature of the aluminum-iron polynuclear hydroxyl polymer, ensuring the stability of the aluminum-iron matrix during the condensation reaction. 13 and Fe3(OH)4 5 The multi-core structure remains intact. A stirring speed of 200 r / min ensures uniform dispersion of silica sol particles in the aluminum-iron matrix liquid, allowing for thorough contact with the multi-core polymer surface and the formation of Si-O-Al and Si-O-Fe covalent bonds. A 2.5% concentration solution of the directional cationic flocculant polymer is prepared to reduce the viscosity of the CPAM solution, enabling it to disperse uniformly into the inorganic-silicon composite liquid as droplets. A drop rate of 5 mL / min controls the introduction of organic high molecular weights per unit time, preventing excessively high local CPAM concentrations that could lead to entanglement between organic molecular chains rather than hydrogen bonding with Si-OH on the silica sol surface. During the hydrogen bonding coupling treatment stage, the stirring speed is reduced to 150 r / min, lower than the 200 r / min in the dehydration condensation stage. This lower shear force prevents the mechanical destruction of the already formed Si-O-Al and Si-O-Fe covalent bonds and the establishing hydrogen bond network. A treatment time of 120 minutes allows the hydrogen bond adsorption of CPAM molecular chains on the silica sol particle surface to reach equilibrium, resulting in the complete construction of the core-shell composite structure.

[0037] In one specific embodiment, in step S4, sodium thiosulfate is added to the silicon bridge ternary composite flocculant at a rate of 3 mL / min, the stirring speed is 200 r / min, the temperature is 35°C, and the reaction time is 30 minutes. L-Ascorbic acid was added at a rate of 3 mL / min for 30 minutes; sodium dodecyl sulfonate was prepared into a solution with a concentration of 25 g / L and added at a rate of 2 mL / min, with a stirring speed of 180 r / min for 45 minutes. The conditions for vacuum concentration were a water bath temperature of 45℃, a vacuum degree of 0.08MPa, and a rotation speed of 60r / min, concentrating to a density of 1.25-1.30g / mL; the pH was adjusted to 4.5±0.2 using a 0.5mol / L sodium hydroxide solution.

[0038] Specifically, in step S4, sodium thiosulfate and L-ascorbic acid are added to the silicon-bridged ternary composite flocculant in two separate, sequential steps. The order of addition cannot be reversed because sodium thiosulfate first consumes any dissolved oxidizing substances in the system, lowering the redox potential to a lower level. Only then can L-ascorbic acid remain stable in its reduced state rather than being oxidized, thus preserving its complete free radical scavenging ability in subsequent applications. The stirring speed of 200 r / min during the sodium thiosulfate addition stage is consistent with the dehydration condensation stage in step S3. This stirring intensity ensures that the sodium thiosulfate solution is thoroughly and uniformly mixed with the composite flocculant within 30 minutes. The reaction temperature of 35°C is lower than the 40°C in step S3; the lower temperature is to prevent L-ascorbic acid from undergoing self-oxidation and decomposition due to excessively high temperatures during subsequent additions. Sodium dodecyl sulfonate was prepared into a 25 g / L solution and added at a rate of 2 mL / min. This rate is lower than that of sodium thiosulfate and L-ascorbic acid (3 mL / min). The slower addition rate allows the surfactant molecules sufficient time to interact with the hydrophobic microregions of the CPAM molecular chains in the composite flocs through their hydrophobic alkyl chains, rather than forming micelles in the liquid phase. The stirring speed was reduced from 200 r / min to 180 r / min to reduce shear force and prevent surfactant molecules from desorbing from the CPAM chains. The reaction time of 45 minutes is longer than that of the first two components (30 minutes) because the adsorption and coordination process of the surfactant in the composite system involves the sequential establishment of two mechanisms: hydrophobic interaction and electrostatic pairing, which requires a longer equilibrium time.

[0039] The vacuum concentration process utilizes a 45°C water bath combined with a 0.08MPa vacuum. Under this vacuum, the boiling point of water drops to approximately 41°C. The 45°C water bath temperature, slightly higher than this boiling point, allows for continuous evaporation of water under gentle conditions. The rotary evaporator flask rotates at 60 rpm, constantly renewing the liquid film on the flask wall, increasing the evaporation area while preventing localized overheating. Throughout the concentration process, the temperature of the composite flocculants remains below 45°C, significantly lower than the thermal degradation temperature of CPAM and the thermal decomposition temperature of L-ascorbic acid. The concentration endpoint is determined by a density of 1.25-1.30 g / mL, which is monitored in real-time using an online density meter. When the density reaches the target, the effective flocculant components have been concentrated to the concentration required for industrial application. pH adjustment is the final step after concentration. The system's pH is precisely adjusted from the slightly acidic state after concentration to 4.5 ± 0.2 using a 0.5 mol / L sodium hydroxide solution. The sodium hydroxide solution is added dropwise at a low rate of 1 mL / min, accompanied by stirring at 150 r / min to ensure a uniform pH increase without localized over-alkalization. A pH of 4.5 is the optimal pH for the aluminum-iron polynuclear hydroxyl polymer. 13 and Fe3(OH)4 5 The unique pH intersection range that simultaneously satisfies three conditions: stable structure, complete protonation of CPAM quaternary ammonium groups, and moderate shielding effect maintained by the silica sol nanobridge layer.

Claims

1. A high-efficiency composite flocculant, characterized in that, include: The aluminum-iron copolymer flocculant matrix is ​​composed of a polynuclear hydroxy polymer formed by alkalization copolymerization of aluminum salt and iron salt in an aluminum-iron molar ratio of 7:3, with an alkalinity of 0.

55. Directed cationic flocculant polymer, formed by copolymerization of acrylamide and methacryloyloxyethyltrimethylammonium chloride in a molar ratio of 6:4, has a cationicity of 35%-40% and a viscosity-average molecular weight of 5×10⁻⁶. 6 -8×10 6 Da; The silica sol nano-bridging layer is composed of active silica sol particles with a particle size of 5-15nm. It is bonded to the aluminum-iron copolymer flocculant matrix through Si-O-Al and Si-O-Fe bonds, and is combined with the directional cationic flocculant polymer through hydrogen bonds, forming a core-shell composite structure with the aluminum-iron copolymer flocculant matrix as the core, the silica sol nano-bridging layer as the middle layer, and the directional cationic flocculant polymer as the outer layer. Antioxidant interface adaptants, including sodium thiosulfate, L-ascorbic acid and sodium dodecyl sulfonate, are dispersed in the core-shell composite structure.

2. The high-efficiency composite flocculant according to claim 1, characterized in that, In the aluminum-iron copolymer flocculant matrix, the aluminum salt is aluminum chloride, the iron salt is ferric chloride, and the polynuclear hydroxyl polymer includes Al 13 High-charge aluminum polymerization morphology and Fe3(OH)4 5 The aluminum-iron copolymer has a pH value of 3.8-4.2 and a total aluminum-iron metal ion concentration of 0.6-0.8 mol / L.

3. The high-efficiency composite flocculant according to claim 1, characterized in that, The initiator system of the directional cationic flocculant polymer is a redox initiation system composed of ammonium persulfate and sodium bisulfite. The amount of ammonium persulfate is 0.08% of the total mass of the comonomer, and the amount of sodium bisulfite is 0.5 times the mass of ammonium persulfate. The copolymerization reaction temperature is 45°C, and the reaction time is 6 hours.

4. The high-efficiency composite flocculant according to claim 1, characterized in that, The molar ratio of SiO2 in the silica sol nanobridge layer to metal ions in the aluminum-iron copolymer flocculant matrix is ​​0.08-0.12, the SiO2 solid content of the active silica sol particles is 2.8-3.2 g / L, and the surface silanol density is 4.5-5.2 hydroxyl groups / nm².

5. The high-efficiency composite flocculant according to claim 1, characterized in that, In the antioxidant interface adaptor component, the reaction rate constant between L-ascorbic acid and hydroxyl radicals is 1.1 × 10¹. 0 L / (mol·s), the sodium dodecyl sulfonate is adsorbed onto the gas-liquid interface of micro-nano bubbles through its hydrophobic alkyl chain, and the sulfonate group forms an electrostatic pair with the quaternary ammonium cation group of the directional cationic flocculant polymer.

6. The high-efficiency composite flocculant according to claim 1, characterized in that, The effective components of the high-efficiency composite flocculant include a total content of Al2O3 and Fe2O3 greater than or equal to 8.0%, an effective content of the directional cationic flocculant polymer greater than or equal to 0.8%, a SiO2 content of 0.4%-0.6%, a Zeta potential of +25 to +32 mV, a pH value of 4.5±0.2, and a density of 1.25-1.30 g / mL.

7. A preparation process for a high-efficiency composite flocculant as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Mix aluminum chloride solution and ferric chloride solution at an aluminum-iron molar ratio of 7:3, and perform alkali copolymerization treatment by adding alkaline solution dropwise to obtain the aluminum-iron copolymer flocculent matrix; S2. Acrylamide and methacryloyloxyethyltrimethylammonium chloride are mixed in a molar ratio of 6:4 and grafted copolymerized through a redox initiation system to obtain the directional cationic flocculant polymer. S3. The acidic silica sol crosslinking medium is added to the aluminum-iron copolymer flocculant matrix for dehydration and condensation treatment, and then the directional cationic flocculant polymer is introduced after swelling for hydrogen bonding treatment to obtain a silicon bridge ternary composite flocculant with a core-shell composite structure. S4. Sodium thiosulfate, L-ascorbic acid and sodium dodecyl sulfonate are added to the silicon-bridged ternary composite flocculant for antioxidant and bubble interface adaptation treatment. After vacuum concentration and pH adjustment, the high-efficiency composite flocculant is obtained.

8. The preparation process according to claim 7, characterized in that, In step S1, the alkaline solution is a sodium hydroxide solution with a concentration of 2.0 mol / L, a dropping rate of 5 mL / min, an alkalinity of 0.55, an alkalinization reaction temperature of 65℃, a stirring speed of 400 r / min, and after alkalinization, it is stirred and matured at 150 r / min at 65℃ for 2 hours. In step S2, the redox initiation system consists of ammonium persulfate and sodium bisulfite. The amount of ammonium persulfate is 0.08% of the total mass of the comonomer, and the amount of sodium bisulfite is 0.5 times the mass of ammonium persulfate. The reaction temperature is 45°C, the reaction time is 6 hours, and the reaction product is dried at 60°C for 12 hours and then ground through a 60-mesh sieve to obtain the directional cationic flocculant polymer powder.

9. The preparation process according to claim 7, characterized in that, In step S3, the acidic silica sol crosslinking medium is prepared by acidifying a 0.5 mol / L sodium silicate solution to pH 3.0 with 1.0 mol / L hydrochloric acid and then allowing it to stand and mature at 30°C for 90 minutes. The particle size of the silica sol crosslinking medium is 5-15 nm, and the SiO2 solid content is 2.8-3.2 g / L. The volume ratio of the silica sol crosslinking medium to the aluminum-iron copolymer flocculant matrix is ​​3:

10. The dehydration condensation treatment was carried out at a temperature of 40°C, a stirring speed of 200 r / min, and a treatment time of 60 minutes. The directional cationic flocculant polymer was prepared into a 2.5% solution and then added dropwise to the inorganic-silicon composite liquid at a rate of 5 mL / min. The hydrogen bonding coupling treatment was carried out at a temperature of 40°C, a stirring speed of 150 r / min, and a treatment time of 120 minutes.

10. The preparation process according to claim 7, characterized in that, In step S4, the sodium thiosulfate is added to the silicon bridge ternary composite flocculant at a rate of 3 mL / min, the stirring speed is 200 r / min, the temperature is 35℃, and the reaction time is 30 minutes. The L-ascorbic acid was added at a rate of 3 mL / min, and the reaction time was 30 minutes; the sodium dodecyl sulfonate was prepared into a solution with a concentration of 25 g / L and added at a rate of 2 mL / min, with a stirring speed of 180 r / min, and the reaction time was 45 minutes. The conditions for vacuum concentration are a water bath temperature of 45℃, a vacuum degree of 0.08MPa, and a rotation speed of 60r / min, concentrating to a density of 1.25-1.30g / mL; the pH adjustment is performed by using a 0.5mol / L sodium hydroxide solution to adjust the pH value to 4.5±0.2.

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