A composite flocculant for wastewater from tea filter paper making and its preparation method

Abstract

This invention discloses a composite flocculant for wastewater from tea filter paper production and its preparation method. The composite flocculant comprises a prepolymerized titanium salt coagulant and a boric acid-functionalized lignin-based polymer. The prepolymerized titanium salt coagulant is prepared by controlling the alkalinity, and the boric acid-functionalized lignin-based polymer uses lignin as a backbone, grafted with cationic monomers and C... 14 -C 18 This composite flocculant comprises long-chain alkyl hydrophobic monomers and monomers containing arylboronic acid groups. Through a unique coupling mechanism, it utilizes the coagulation and charge neutralization effects of titanium salts and the adsorption bridging effects of lignin polymers, combined with the reversible cross-linking of boric acid groups and vicinal diols in polysaccharides, to achieve highly efficient and synergistic removal of fine fibers, colloidal particles, and dissolved organic matter from white water used in tea filter paper production. At dosages of 15-45 mg / L, it exhibits excellent performance in turbidity removal, COD removal, and suspended solids removal, making it particularly suitable for treating wastewater from tea filter paper production.

Description

Technical Field

[0001] This invention relates to the field of flocculant technology, and in particular to a composite flocculant for wastewater from tea filter paper making and its preparation method. Background Technology

[0002] Tea filter paper is a special paper product that comes into direct contact with food. It is typically produced using a wet papermaking process, where the paper is formed through the synergistic action of wet-end chemicals in pulping, papermaking, sizing, retention aids, and filtration aids. This production process generates a large amount of white water and mixed wastewater, which contains suspended solids such as fine fibers and fillers, as well as complex organic components such as sizing agents, dispersants, retention aid residues, and dissolved and colloidal substances (DCS). As papermaking systems become increasingly closed-loop and recirculating, the proportion of white water reuse is constantly increasing. Dissolved and colloidal substances are more likely to accumulate in the system, thus interfering with the retention of fine particles and the filtration process, weakening the expected function of polyelectrolyte additives, and causing problems such as decreased paper machine operational stability. On the other hand, alkyl ketene dimers and alkenyl succinic anhydrides commonly used in alkaline sizing systems can easily enter the white water loop and form hydrophobic residues if they are not fully retained or undergo hydrolysis. This can lead to viscous deposits, spot defects, and negative interactions with wet-end chemicals, thereby exacerbating the difficulty of white water treatment.

[0003] For the treatment of white water and wastewater from papermaking, existing technologies mostly employ a combination of physicochemical and biochemical methods, with coagulation and flocculation being widely used due to their short process and strong adaptability. Commonly used inorganic coagulants include polyaluminum chloride, polyferric sulfate, and their compound systems, combined with cationic polyacrylamide and other polymeric flocculants to achieve charge neutralization, entrapment, and adsorption bridging. However, aluminum salt coagulants may leave aluminum ion residues in the treated effluent, and aluminum ions are considered to have a potential link to nervous system diseases, posing a safety hazard for the treatment of wastewater from the production of food contact materials such as tea filter paper. In recent years, titanium-based coagulants have attracted attention due to their wide dosage and pH adaptability under certain conditions, good floc properties, no aluminum residue risk, and resource utilization potential. Meanwhile, to reduce the environmental burden of petrochemical-based polymeric flocculants and enhance their green attributes, research and application of modified flocculants prepared using lignin, a byproduct of papermaking, are increasing. Common methods include introducing cationic groups to increase charge density and enhance the adsorption and neutralization capacity for colloids and fine particles.

[0004] However, existing coagulation and flocculation systems still have limitations in scenarios involving high circulation, high concentrations of dissolved and colloidal substances, and hydrophobic residues of sizing agents in white water from tea filter paper production. On one hand, the removal efficiency of conventional inorganic salts for dissolved and colloidal substances and hydrophobic colloids is easily affected by water quality fluctuations, often requiring higher dosages and generating more sludge. On the other hand, traditional cationic polymeric or lignin-based flocculants mainly rely on charge neutralization and adsorption bridging mechanisms, offering limited synergistic control over systems containing polysaccharide-containing dissolved organic matter and hydrophobic residues of sizing agents, making it difficult to simultaneously meet the requirements of floc strength, shear stability, and rapid sedimentation separation. The starch, carboxymethyl cellulose, hemicellulose, and other polysaccharide components remaining in papermaking white water contain abundant vicinal diol structures. Utilizing these endogenous components to participate in the construction of the flocculation network holds promise for achieving more efficient pollutant removal.

[0005] Therefore, there is an urgent need to develop a novel composite flocculant that can achieve synergistic effects of multiple flocculation mechanisms under complex composition conditions of papermaking white water, adapt to water quality fluctuations, and improve solid-liquid separation efficiency, so as to meet the process requirements of white water purification and recycling in tea filter paper making. Summary of the Invention

[0006] To address the aforementioned problems in the existing technology, this invention provides a composite flocculant for tea filter paper wastewater and its preparation method. By constructing a multi-mechanism synergistic system of "inorganic coagulation—organic multi-point adsorption bridging—reversible dynamic cross-linking—hydrophobic association and trapping," it improves the comprehensive removal capacity of fine fibers, colloidal particles, dissolved and colloidal substances, and hydrophobic residues of sizing agents in white water, enhances floc strength and sedimentation separation efficiency, and strengthens adaptability to water quality fluctuations.

[0007] To achieve the above objectives, the present invention adopts the following technical solution.

[0008] The first aspect of this invention provides a composite flocculant for wastewater from tea filter paper making, comprising the following components by weight: 70-90 parts of prepolymerized titanium salt coagulant, 10-30 parts of boric acid functionalized lignin-based polymer, 0.5-5 parts of coagulant aid, 0.1-2 parts of pH adjuster, and 0.1-1 parts of stabilizer.

[0009] The boric acid-functionalized lignin-based polymer uses lignin as a backbone and is grafted with cationic monomers and C. 14 -C 18 The long-chain alkyl and arylboronic acid groups, wherein the mass ratio of the cationic monomer to lignin is (0.5-3.0):1, and the C 14 -C 18 The mass ratio of long-chain alkyl hydrophobic monomer to lignin is (0.2-1.2):1, and the mass ratio of monomer containing arylboronic acid group to lignin is (0.15-0.8):1.

[0010] Further, the prepolymerized titanium salt coagulant is one or more combinations of polytitanium sulfate, polytitanium chloride, and polyhydroxytitanium complex, with an alkalinity of 1.8-2.2 and a titanium content of 8-15 wt% based on TiO2. The prepolymerized titanium salt coagulant is an inorganic polymeric coagulant prepared by controlling the degree of hydrolysis and polymerization of titanium salt, and its alkalinity is defined as OH... - With Ti 4+ The molar ratio is [not specified]. When the alkalinity is controlled within the range of 1.8-2.2, the proportion of medium and large polymer species in the titanium salt hydrolysis products is relatively high. These polymer species have high positive charge density and large molecular size, which can effectively neutralize negatively charged colloidal particles in wastewater and promote floc formation through adsorption bridging and scavenging. Compared with traditional aluminum and iron salt coagulants, prepolymerized titanium salt coagulants have advantages such as no aluminum residue risk, high floc density, good settling performance, and a wide applicable pH range, making them more suitable as inorganic coagulation skeleton components in composite systems. In addition, the titanium-containing sludge produced can be calcined to recover titanium dioxide, which has resource utilization value.

[0011] Furthermore, the lignin is one or more combinations of alkali lignin, lignin sulfonate, papermaking black liquor lignin, and enzymatically hydrolyzed lignin, with a weight-average molecular weight of 5000-50000 Da. Lignin is a natural polymer formed by phenylpropane structural units linked by ether and carbon-carbon bonds. Its molecular structure contains abundant active groups such as phenolic hydroxyl groups, alcoholic hydroxyl groups, carboxyl groups, and methoxy groups, which can serve as a backbone material for graft copolymerization reactions. Notably, the phenolic hydroxyl groups in lignin molecules, especially the catechol-type structures, have the ability to coordinate with the surface of Ti(IV) or titanium oxides. The phenolic hydroxyl groups in lignin molecules can interact with the hydrolysis products of titanium salts, which is beneficial for forming an organic-inorganic composite structure. Choosing lignin with a weight-average molecular weight of 5000-50000 Da ensures sufficient molecular chain length to provide multiple grafting sites while avoiding problems such as poor solubility and reduced reactivity caused by excessively large molecular weights.

[0012] Furthermore, the cationic monomer is one or more combinations of dimethyl diallyl ammonium chloride, methacryloyloxyethyl trimethyl ammonium chloride, and acryloyloxyethyl trimethyl ammonium chloride. After the cationic monomer is grafted onto the lignin backbone, it provides a positive charge to the polymer, enabling it to adsorb, neutralize, and bridge negatively charged fine fibers, colloidal particles, and dissolved and colloidal substances in the wastewater at multiple points through electrostatic attraction.

[0013] Furthermore, the C 14 -C 18 The long-chain alkyl hydrophobic monomer is one or more combinations of tetradecyl methacrylate, hexadecyl methacrylate, and octadecyl methacrylate. Choose C.14 -C 18 The hydrophobic monomers with alkyl chain lengths are based on the chemical structure characteristics of sizing agent residues in the white water used for tea filter paper making. The alkyl chain length of alkyl ketene dimers is typically C0. 16 -C 18 The alkyl chain length of alkenyl succinic anhydride is typically C. 16 -C 20 By using hydrophobic monomers with alkyl chain lengths similar to those of the sizing agent, stronger intermolecular associations can be formed through hydrophobic interactions, thereby improving the collection efficiency of sizing agent residues and their hydrolysis byproducts.

[0014] Furthermore, the monomer containing the arylboronic acid group is one or more combinations of 3-acrylamidophenylboronic acid, 4-vinylphenylboronic acid, and 3-methylacrylamidophenylboronic acid. The arylboronic acid group is the key functional group for achieving the dynamic covalent cross-linking flocculation mechanism of this invention. Phenylboronic acid and its derivatives can form reversible borate ester bonds with compounds containing vicinal diol structures in aqueous solution. This reaction is significantly pH-dependent, with neutral to weakly alkaline conditions favoring the formation and maintenance of the borate ester cross-linking structure, while under acidic conditions, the borate ester bonds hydrolyze and break. The starch, carboxymethyl cellulose, hemicellulose, and other polysaccharide components remaining in the white water from tea filter paper production contain abundant vicinal diol structures and can serve as natural substrates for the borate ester cross-linking reaction. When boric acid-functionalized lignin-based polymers are added to papermaking white water, their arylboronic acid groups can undergo in-situ cross-linking reactions with the polysaccharide components in the wastewater, forming a dynamic cross-linked network structure. This transforms dissolved polysaccharide organic matter into settleable flocs, significantly improving the removal efficiency of dissolved and colloidal substances, while also enhancing the floc network strength and shear stability. The mass ratio of monomers containing arylboronic acid groups to lignin is controlled at (0.15-0.8):1, corresponding to an arylboronic acid group content of 0.2-1.0 mmol / g. Within this range, the polymer has sufficient cross-linking site density to form an effective flocculation network.

[0015] Furthermore, the boric acid-functionalized lignin-based polymer has a cationicity of 15-40%, a hydrophobic monomer grafting rate of 3-15%, an arylboronic acid group content of 0.2-1.0 mmol / g, and a weight-average molecular weight of 80,000-1,800,000 Da. These parameter ranges were determined through comprehensive optimization, and the synergistic effect of each parameter achieves optimal flocculation performance.

[0016] Furthermore, the coagulant aid is one or more combinations of polyaluminum chloride, polyferric sulfate, modified bentonite, and polysilicic acid. The addition of the coagulant aid can further enhance the flocculation effect. Polyaluminum chloride and polyferric sulfate can form a composite inorganic coagulation system with prepolymerized titanium salts. Modified bentonite can serve as a skeleton material for flocs to increase floc density, and polysilicic acid can form polysilicic acid-metal salt complexes with metal ions to enhance adsorption bridging.

[0017] Furthermore, the pH adjuster is one or more combinations of sodium hydroxide, calcium hydroxide, sodium carbonate, and sulfuric acid. The pH adjuster is used to adjust the pH value of the composite flocculant to a suitable range to ensure the stability of the prepolymerized titanium salt and the solubility of the boric acid-functionalized lignin-based polymer.

[0018] Furthermore, the stabilizer is one or more combinations of polyethylene glycol, sodium carboxymethyl cellulose, xanthan gum, and disodium EDTA. The addition of the stabilizer prevents instability phenomena such as precipitation, stratification, or gelation of the composite flocculant during storage. Polyethylene glycol and xanthan gum primarily provide stability through rheological regulation and steric hindrance, with minimal impact on the coagulation activity of titanium salts; sodium carboxymethyl cellulose combines rheological stability with weak complexing effects; disodium EDTA, as a chelating agent, can balance stability requirements with the maintenance of titanium salt coagulation activity by controlling its dosage.

[0019] A second aspect of the present invention provides a method for preparing the above-mentioned composite flocculant for papermaking wastewater from tea filter paper, comprising the following steps.

[0020] Step S1, Preparation of prepolymerized titanium salt coagulant: The titanium salt solution is neutralized with alkali solution to an alkalinity of 1.8-2.2 under stirring, and aged at 50-70℃ for 2-6 hours to obtain the prepolymerized titanium salt coagulant. The titanium salt is titanium sulfate, titanium oxysulfate, or titanium tetrachloride, and the alkali solution is sodium hydroxide solution or ammonia water with a concentration of 1-5 mol / L and a dropping rate of 5-20 mL / min. Slow dropping of the alkali solution and appropriate aging at a suitable temperature help control the hydrolysis and polymerization rate of the titanium salt, obtaining a prepolymerized titanium salt product with a uniform molecular weight distribution and a suitable degree of polymerization. Too rapid a dropping rate can lead to localized over-alkaliization and the formation of titanium hydroxide precipitation, while too slow a dropping rate results in low production efficiency.

[0021] Step S2, Preparation of boric acid-functionalized lignin-based polymer: Lignin is dissolved in an alkaline aqueous solution with pH 9-12, and cationic monomers and C are added. 14 -C 18A long-chain alkyl hydrophobic monomer, a monomer containing an arylboronic acid group, and an initiator are reacted at 55-85℃ for 4-10 hours under nitrogen protection. The resulting product is purified by dialysis and dried to obtain a boric acid-functionalized lignin-based polymer. The lignin concentration is 3-10 wt%, and the initiator is one or a combination of potassium persulfate and ammonium persulfate, used at 0.5-3% of the total monomer mass. Potassium persulfate and ammonium persulfate are water-soluble initiators suitable for aqueous phase initiation. Alkaline conditions favor the dissolution of lignin and the activation of phenolic hydroxyl groups, creating favorable conditions for free radical graft copolymerization. Nitrogen protection eliminates dissolved oxygen in the system, preventing oxygen from inhibiting the free radical polymerization reaction.

[0022] Step S3, preparation of composite flocculant: dissolve boric acid functionalized lignin-based polymer in water to prepare a 0.5-3 wt% solution, add prepolymerized titanium salt coagulant, coagulant aid, pH adjuster and stabilizer under stirring conditions, stir at 30-50℃ for 30-90 minutes to obtain composite flocculant for tea filter paper wastewater.

[0023] Furthermore, the phenolic hydroxyl groups in lignin molecules, especially the catechol-type structures, have the ability to coordinate with Ti(IV) ions or the surface of titanium oxides. This coordination interaction is beneficial to the formation of an organic-inorganic composite structure during the preparation of composite flocculants, thereby enhancing the synergistic effect of the two components.

[0024] A third aspect of this invention provides the application of the aforementioned composite flocculant for tea filter paper wastewater in the treatment of white water from tea filter paper production, wherein the dosage of the composite flocculant is 15-45 mg / L. The composite flocculant of this invention is particularly suitable for papermaking white water systems containing residual polysaccharide additives and with high loadings of dissolved colloidal substances. Under conventional mixing, reaction, and sedimentation process conditions, it can achieve rapid flocculation and sedimentation of pollutants in white water and clarify the effluent, facilitating subsequent reuse or achieving compliant discharge.

[0025] Compared with the prior art, the present invention provides a composite flocculant for wastewater from tea filter paper making and its preparation method, which has the following beneficial effects: (1) In this invention, a prepolymerized titanium salt coagulant is used in combination with boric acid functionalized lignin-based polymer. The titanium salt is used to rapidly destabilize colloidal particles through charge neutralization. At the same time, the lignin polymer achieves adsorption bridging through the adsorption of cationic groups and the hydrophobic effect of long-chain alkyl groups. The synergistic effect of the two significantly improves the flocculation efficiency.

[0026] (2) The white water used in tea filter paper production contains a large amount of polysaccharides such as cellulose and hemicellulose. In this invention, arylboronic acid groups are introduced into the lignin polymer. Boric acid forms a reversible borate bond with the vicinal diol structure in the polysaccharide molecule, thereby achieving specific capture of dissolved and colloidal polysaccharides.

[0027] (3) The flocs formed by this invention are dense and have a moderate particle size. The settling velocity can reach 2.1-2.8 cm / min, and the residual turbidity is as low as 49-88 NTU, which is significantly better than conventional flocculants. Rapid settling helps to shorten the water treatment cycle, improve the equipment treatment capacity, and reduce operating costs.

[0028] (4) This invention uses lignin as one of the main raw materials. Lignin is derived from a by-product of the papermaking industry, and is inexpensive and widely available. Titanium salt is used as the main coagulation component, which has lower biotoxicity and environmental risk compared with traditional aluminum salt coagulants. When non-aluminum salts such as polyferric sulfate, polysilicic acid, and modified bentonite are selected as coagulant aids, the risk of aluminum residue can be further reduced. It is suitable for the treatment of wastewater related to food contact materials with strict requirements for aluminum residue. The lignin-based component has good environmental friendliness, and titanium-containing sludge has the potential for resource utilization, which meets the development requirements of clean production and circular economy in the papermaking industry. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] In this invention, all weight parts are based on the mass of the active ingredients of each component, wherein the prepolymerized titanium salt coagulant is calculated as TiO2, and the boric acid functionalized lignin-based polymer is calculated on a dry basis. In actual use, each component can be added in solution or solid form. Example 1

[0031] S1. Preparation of prepolymerized titanium salt coagulant: Take 100 mL of titanium oxysulfate (TiOSO4) solution (concentration of 150 g / L based on TiO2), and slowly add sodium hydroxide solution (2 mol / L) under stirring to alkalize, controlling the degree of alkalinity (n(OH)). - The ratio of Ti to TiO2 is 2.0. During the alkalization process, the solution gradually changes from transparent to milky white. After alkalization, it is aged at 60°C for 4 hours to obtain a prepolymerized titanium salt coagulant with a concentration of 80 g / L based on TiO2.

[0032] S2. Preparation of boric acid-functionalized lignin-based polymers: Ten parts of lignin (alkali lignin, molecular weight approximately 10,000 Da) were dissolved in an aqueous sodium hydroxide solution at pH 10.5 to prepare a 6 wt% solution. Then, 20 parts of a cationic monomer (methacryloyloxyethyltrimethylammonium chloride, DMC) and 8 parts of C were added sequentially to the solution.16 Long-chain alkyl hydrophobic monomer (hexadecyl methacrylate), 5 parts of monomer containing arylboronic acid groups (4-vinylphenylboronic acid). C 16 Long-chain alkyl hydrophobic monomers were pre-dissolved in a small amount of ethanol and then added. 1.5 parts of initiator (a 1:1 mixture of potassium persulfate and ammonium persulfate, amounting to 1.5% of the total monomer mass) were added. The reaction was carried out at 70°C for 7 hours under nitrogen protection. After the reaction, the product was dialyzed in deionized water for 72 hours using a dialysis bag (molecular weight cutoff 8000-14000 Da), with the water changed every 12 hours. After dialysis, the product was freeze-dried to obtain boric acid-functionalized lignin-based polymers.

[0033] The performance indicators of the polymer were determined as follows: cationicity 27%, hydrophobic monomer grafting rate 9%, arylboronic acid group content 0.6 mmol / g, and weight average molecular weight 940,000 Da.

[0034] S3. Preparation of composite flocculant: A 1 wt% solution of boric acid-functionalized lignin-based polymer was prepared by dissolving boric acid-functionalized lignin-based polymer in deionized water. Under stirring conditions, 80 parts by weight of prepolymerized titanium salt coagulant, 20 parts by weight of boric acid-functionalized lignin-based polymer, 3 parts by weight of coagulant aid (polyaluminum chloride, Al2O3 content 10%), 1 part by weight of pH adjuster (sodium hydroxide, to adjust the system pH to 8.0), and 0.5 parts by weight of stabilizer (a mixture of polyethylene glycol 4000 and xanthan gum in a 1:1 mass ratio) were added. The mixture was stirred at 40℃ for 60 minutes to obtain a composite flocculant for tea filter paper wastewater.

[0035] Wastewater treatment applications: Take 1000 mL of white wastewater (pH 7.2, turbidity 850 NTU, COD 1450 mg / L, suspended solids content 1850 mg / L) from a tea filter paper manufacturing enterprise. Add 30 mg / L of the composite flocculant prepared in Example 1 under rapid stirring (300 r / min) at room temperature. After rapid stirring for 2 minutes, change to slow stirring (50 r / min) for 15 minutes. After standing and settling for 30 minutes, take the supernatant to determine the treatment effect. Example 2

[0036] The difference from Example 1 is: The basicity of S1 is 1.9, the aging temperature is 55℃, and the aging time is 3 hours; S2 contains 10 parts lignin, 15 parts cationic monomer, and C. 14 Six parts of long-chain alkyl hydrophobic monomer (tetradecyl methacrylate), three parts of monomer containing arylboronic acid group, lignin solution concentration of 5 wt%, pH of 10, reaction temperature of 65℃, reaction time of 6 hours. The properties of the boric acid-functionalized lignin-based polymer are as follows: cationicity 22%, hydrophobic monomer grafting rate 7%, arylboronic acid group content 0.4 mmol / g, and weight-average molecular weight 650,000 Da. S3 contains 75 parts of prepolymerized titanium salt coagulant, 25 parts of boric acid functionalized lignin-based polymer, 2.5 parts of coagulant aid, 1 part of pH adjuster, and 0.5 parts of stabilizer (sodium carboxymethyl cellulose). The dosage of composite flocculant for wastewater treatment is 25 mg / L. Example 3

[0037] The difference from Example 1 is: The basicity of S1 is 2.1, the aging temperature is 65℃, and the aging time is 5 hours; S2 contains 10 parts lignin, 25 parts cationic monomer, and C. 18 10 parts of long-chain alkyl hydrophobic monomer (octadecyl methacrylate), 7 parts of monomer containing arylboronic acid group, lignin solution concentration of 7 wt%, pH of 11, reaction temperature of 75℃, reaction time of 8 hours. The properties of the boric acid-functionalized lignin-based polymer are as follows: cationicity 33%, hydrophobic monomer grafting rate 12%, arylboronic acid group content 0.8 mmol / g, and weight-average molecular weight 1.25 million Da. S3 contains 85 parts of prepolymerized titanium salt coagulant, 15 parts of boric acid functionalized lignin-based polymer, 4 parts of coagulant aid, 1.5 parts of pH adjuster, and 0.8 parts of stabilizer (polyethylene glycol 4000). The dosage of composite flocculant for wastewater treatment is 35 mg / L. Example 4

[0038] The difference from Example 1 is: The basicity of S1 is 1.8, the aging temperature is 50℃, and the aging time is 2 hours; S2 contains 10 parts lignin, 5 parts cationic monomer, and C. 14 Four parts of long-chain alkyl hydrophobic monomers, two parts of monomers containing arylboronic acid groups, lignin solution concentration of 3 wt%, pH of 9, reaction temperature of 55℃, reaction time of 4 hours, and initiator dosage of 0.5% of total monomer mass; The properties of the boric acid-functionalized lignin-based polymer are as follows: cationicity 16%, hydrophobic monomer grafting rate 4%, arylboronic acid group content 0.25 mmol / g, and weight-average molecular weight 90,000 Da. S3 contains 70 parts of prepolymerized titanium salt coagulant, 30 parts of boric acid functionalized lignin-based polymer, 0.5 parts of coagulant aid, 0.1 parts of pH adjuster, and 0.1 parts of stabilizer (xanthan gum). The dosage of composite flocculant for wastewater treatment is 15 mg / L. Example 5

[0039] The difference from Example 1 is: The basicity of S1 is 2.2, the aging temperature is 70℃, and the aging time is 6 hours; S2 contains 10 parts lignin, 30 parts cationic monomer, and C. 18 The reaction mixture consisted of 12 parts of long-chain alkyl hydrophobic monomers, 8 parts of monomers containing arylboronic acid groups, a lignin solution concentration of 10 wt%, a pH of 12, a reaction temperature of 85℃, a reaction time of 10 hours, and an initiator amount of 3% of the total monomer mass. The properties of the boric acid-functionalized lignin-based polymer are as follows: cationicity 38%, hydrophobic monomer grafting rate 14%, arylboronic acid group content 0.95 mmol / g, and weight-average molecular weight 1.7 million Da. S3 contains 90 parts of prepolymerized titanium salt coagulant, 10 parts of boric acid functionalized lignin-based polymer, 5 parts of coagulant aid, 2 parts of pH adjuster, and 1 part of stabilizer (disodium ethylenediaminetetraacetate). The dosage of composite flocculant for wastewater treatment is 45 mg / L. Comparative Example 1

[0040] Using only 80 parts of prepolymerized titanium salt coagulant (prepared by the same method as S1 in Example 1), 3 parts of coagulant aid, 1 part of pH adjuster and 0.5 parts of stabilizer, without adding boric acid functionalized lignin-based polymer, other conditions are the same as in Example 1. Comparative Example 2

[0041] In step S2, no monomers containing arylboronic acid groups are added; only 10 parts of lignin, 20 parts of cationic monomer, and C are used. 16 Eight parts of long-chain alkyl hydrophobic monomers were used, with other conditions the same as in Example 1. The resulting lignin-based polymer had a cationicity of 26%, a hydrophobic monomer grafting rate of 8.5%, an arylboronic acid group content of 0 mmol / g, and a weight-average molecular weight of 880,000 Da. Other steps were the same as in Example 1. Comparative Example 3

[0042] Commercially available polyaluminum chloride (30% Al2O3 content) was used, with an addition amount of 30 mg / L based on Al2O3. The treatment conditions were the same as in Example 1. Comparative Example 4

[0043] Commercially available cationic polyacrylamide (25% cationicity, 8 million Da molecular weight) was used at a dosage of 5 mg / L, and the treatment conditions were the same as in Example 1. Performance testing methods

[0044] 1. Turbidity removal rate test: In accordance with GB / T 13200-1991 "Determination of turbidity in water", the turbidity of the water samples before and after treatment was measured using a turbidity meter, and the removal rate was calculated.

[0045] 2. COD removal rate test: COD of water samples before and after treatment was determined according to HJ 828-2017 "Determination of Chemical Oxygen Demand in Water - Dichromate Method", and the removal rate was calculated.

[0046] 3. Suspended solids removal rate test: The suspended solids content of water samples before and after treatment was determined according to GB / T 11901-1989 "Determination of suspended solids in water by gravimetric method", and the removal rate was calculated.

[0047] 4. Flocculation Settling Velocity Test: Immediately after flocculation treatment, transfer the mixture to a 500 mL graduated cylinder (liquid level 30 cm). After stopping stirring, start timing and observe the time required for the floc-supernatant interface to descend 10 cm from the liquid surface. Calculate the settling velocity (cm / min). Settling velocity = 10 cm / settling time (min).

[0048] 5. Residual turbidity test: After standing for 30 minutes to settle, take the supernatant and measure the residual turbidity (NTU). Test Results

[0049] Comparative and example data: .

[0050] pH range test results (Example 1): .

[0051] Results Analysis and Explanation Example 1, using the optimal median values ​​of each parameter range, achieved the best overall treatment effect, with a turbidity removal rate of 94.2%, a COD removal rate of 76.5%, a suspended solids removal rate of 92.8%, a fast floc settling speed (2.8 cm / min), and low residual turbidity (49 NTU), proving the effectiveness of the optimal implementation method.

[0052] Examples 2 and 3 achieved good processing results under different parameter combinations. Although slightly lower than Example 1, they were still significantly better than the comparative examples, proving the stability and adjustability of the technical solution.

[0053] Examples 4 and 5 respectively verified the lower and upper limits of the range of the claim parameters. Although the processing effect was reduced, it remained within an acceptable range and was significantly better than the comparative example, proving the rationality of the scope of protection of the claim.

[0054] Comparative Example 1, without the addition of boric acid-functionalized lignin-based polymers, relied solely on prepolymerized titanium salt coagulants, resulting in a turbidity removal rate of only 72.4%, a COD removal rate of only 51.2%, slow floc settling speed (1.6 cm / min), and high residual turbidity (235 NTU). This demonstrates the crucial role of boric acid-functionalized lignin-based polymers in the composite flocculation system.

[0055] Comparative Example 2 used an unfunctionalized lignin-based polymer, which was an improvement over Comparative Example 1, but the turbidity removal rate (85.3%) and COD removal rate (62.8%) were still significantly lower than those of Examples 1-5, demonstrating the importance of arylboronic acid functionalization, especially the dynamic crosslinking effect on polysaccharide-type dissolved organic matter.

[0056] Comparative Example 3 used conventional polyaluminum chloride, and Comparative Example 4 used conventional cationic polyacrylamide. The treatment effects of both were significantly lower than those of the embodiments of the present invention, which proves the technical advantages of the "coagulation-bridging-dynamic crosslinking" coupling mechanism of the present invention.

[0057] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A composite flocculant for wastewater from tea filter paper making, characterized in that, It includes the following components by weight: 70-90 parts of prepolymerized titanium salt coagulant, 10-30 parts of boric acid functionalized lignin-based polymer, 0.5-5 parts of coagulant aid, 0.1-2 parts of pH adjuster, and 0.1-1 parts of stabilizer; The boric acid-functionalized lignin-based polymer uses lignin as a backbone and is grafted with cationic monomers and C. 14 -C 18 The long-chain alkyl and arylboronic acid groups, wherein the mass ratio of the cationic monomer to lignin is (0.5-3.0):1, and the C 14 -C 18 The mass ratio of long-chain alkyl hydrophobic monomer to lignin is (0.2-1.2):1, and the mass ratio of monomer containing arylboronic acid group to lignin is (0.15-0.8):

1.

2. The composite flocculant for tea filter paper wastewater according to claim 1, characterized in that, The prepolymerized titanium salt coagulant is one or more of polytitanium sulfate, polytitanium chloride, and polyhydroxytitanium complex, with an alkalinity of 1.8-2.2 and a titanium content of 8-15 wt% based on TiO2.

3. The composite flocculant for tea filter paper wastewater according to claim 1, characterized in that, The lignin is one or more of alkali lignin, lignin sulfonate, papermaking black liquor lignin, and enzymatically hydrolyzed lignin, with a weight-average molecular weight of 5000-50000 Da.

4. The composite flocculant for papermaking wastewater from tea filter paper according to claim 1, characterized in that, The cationic monomer is one or more combinations of dimethyl diallyl ammonium chloride, methacryloyloxyethyltrimethylammonium chloride, and acryloyloxyethyltrimethylammonium chloride; the C 14 -C 18 The long-chain alkyl hydrophobic monomer is one or more of tetradecyl methacrylate, hexadecyl methacrylate, and octadecyl methacrylate; the monomer containing arylboronic acid group is one or more of 3-acrylamidophenylboronic acid, 4-vinylphenylboronic acid, and 3-methacrylamidophenylboronic acid.

5. The composite flocculant for tea filter paper wastewater according to claim 1, characterized in that, The boric acid-functionalized lignin-based polymer has a cationicity of 15-40%, a hydrophobic monomer grafting rate of 3-15%, an arylboronic acid group content of 0.2-1.0 mmol / g, and a weight-average molecular weight of 80,000-1,800,000 Da.

6. The composite flocculant for papermaking wastewater from tea filter paper according to claim 1, characterized in that, The coagulant is one or more of polyaluminum chloride, polyferric sulfate, modified bentonite, and polysilicic acid; the pH adjuster is one or more of sodium hydroxide, calcium hydroxide, sodium carbonate, and sulfuric acid; and the stabilizer is one or more of polyethylene glycol, sodium carboxymethyl cellulose, xanthan gum, and disodium EDTA.

7. A method for preparing a composite flocculant for papermaking wastewater from tea filter paper as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Neutralize the titanium salt solution with alkali solution to an alkalinity of 1.8-2.2 under stirring, and age it at 50-70℃ for 2-6 hours to obtain a prepolymerized titanium salt coagulant. S2. Dissolve lignin in an alkaline aqueous solution with pH 9-12, and add cationic monomers and C. 14 -C 18 Long-chain alkyl hydrophobic monomers, monomers containing arylboronic acid groups, and initiators are reacted at 55-85℃ for 4-10 hours under nitrogen protection. After dialysis purification and drying, boric acid functionalized lignin-based polymers are obtained. S3. Dissolve boric acid functionalized lignin-based polymer in water to prepare a 0.5-3 wt% solution. Add prepolymerized titanium salt coagulant, coagulant aid, pH adjuster and stabilizer under stirring conditions. Stir for 30-90 minutes at 30-50℃ to obtain a composite flocculant for tea filter paper wastewater.

8. The preparation method according to claim 7, characterized in that, The titanium salt mentioned in step S1 is titanium sulfate, titanium oxysulfate, or titanium tetrachloride, and the alkaline solution is either sodium hydroxide solution or ammonia water, with a concentration of 1-5 mol / L and a dropping rate of 5-20 mL / min.

9. The preparation method according to claim 7, characterized in that, In step S2, the lignin concentration is 3-10 wt%, and the initiator is one or a combination of potassium persulfate and ammonium persulfate, with an amount of 0.5-3% of the total mass of the monomers.

10. The application of the composite flocculant for tea filter paper making wastewater as described in any one of claims 1-6 in the treatment of white water in tea filter paper making, characterized in that, The dosage of the composite flocculant is 15-45 mg / L.