A natural polymer flocculant and a preparation method thereof
By modifying the cross-linking method of chitosan, starch and lignin, a three-dimensional network structure flocculant is formed, which solves the problems of insufficient efficiency and environmental pollution of existing natural flocculants in the treatment of high turbidity water, and achieves efficient and safe water treatment effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- 山西工学院
- Filing Date
- 2025-05-09
- Publication Date
- 2026-07-07
AI Technical Summary
Existing natural polymeric flocculants have insufficient charge neutralization and adsorption bridging effects when treating industrial wastewater with high turbidity and water bodies with complex compositions. Furthermore, the lack of strict control over heavy metal impurities during the preparation process leads to environmental pollution and health risks, limiting their application in drinking water and surface water.
A flocculant with charge neutralization, adsorption bridging and sweeping effects was prepared by grafting chitosan with methacrylic acid and acrylamide to form branched chains, introducing carboxyl groups through starch oxidation, introducing sulfonic acid groups through lignin sulfonation, and forming a three-dimensional network structure through glutaraldehyde crosslinking.
It achieves efficient adsorption and aggregation of negatively charged colloidal particles in water, and its molecular structure is degradable, avoiding environmental residues. It is suitable for the treatment of drinking water, surface water and highly sensitive industrial wastewater, and has high removal rate and ecological safety.
Smart Images
Figure BDA0005394298430000081
Abstract
Description
Technical Field
[0001] This invention relates to the field of natural polymer materials and water treatment flocculants, specifically to a natural polymer flocculant and its preparation method. Background Technology
[0002] In the field of water treatment, flocculants are key materials for removing suspended solids, organic matter, and heavy metal ions from water. Traditional flocculants mainly include inorganic flocculants (such as aluminum salts and iron salts) and synthetic polymeric flocculants (such as polyacrylamide). However, inorganic flocculants pose a risk of residual metal ions (such as the accumulation of aluminum ions which harms human health) and have a narrow range of applicable water qualities; while synthetic polymeric flocculants have higher flocculation efficiency, most are non-degradable petroleum-based materials, which can easily cause environmental pollution, and some monomers (such as acrylamide) are toxic.
[0003] Natural polymeric flocculants (such as chitosan, starch, and lignin) have become a research hotspot due to their renewable sources and good biocompatibility. However, their single components suffer from drawbacks such as limited functional group types, low molecular weight, and unstable cross-linking structures, resulting in insufficient charge neutralization capacity and adsorption bridging effect. This is especially true when treating high-turbidity industrial wastewater (500-1000 NTU) and water bodies with complex compositions, where turbidity and COD removal rates are difficult to meet stringent standards. Furthermore, the existing preparation process of natural flocculants lacks strict control over heavy metal impurities, and their poor storage stability limits their application in sensitive water bodies such as drinking water and surface water.
[0004] To address the aforementioned problems, this invention provides a natural polymeric flocculant and its preparation method to solve these problems. Summary of the Invention
[0005] Technical problems to be solved
[0006] To address the aforementioned shortcomings of existing technologies, the flocculant of this invention, through chitosan grafting, starch oxidation, and lignin sulfonation modification, combined with glutaraldehyde crosslinking to form a three-dimensional network structure, possesses charge neutralization, adsorption bridging, and sweeping effects. It can efficiently adsorb and aggregate negatively charged colloidal particles in water. It uses natural renewable polymers as raw materials, its molecular structure is biodegradable, leaves no environmental residue, and has a low heavy metal content, thus solving the drawbacks of traditional flocculants. It is suitable for the treatment of drinking water, surface water, and highly sensitive industrial wastewater, combining effectiveness and ecological safety.
[0007] Technical solution
[0008] To achieve the above objectives, the present invention provides the following technical solution:
[0009] On one hand, a natural polymeric flocculant is prepared from the following raw materials in parts by weight: 20-30 parts chitosan, 15-25 parts starch, 10-20 parts lignin, 5-10 parts modifier, 3-8 parts crosslinking agent, and 100-200 parts deionized water; wherein the modifier is a composition of methacrylic acid and acrylamide in a mass ratio of 1:1-2:1; and the crosslinking agent is glutaraldehyde.
[0010] In the molecular structure of this flocculant, chitosan molecular chains are grafted with branches formed by methacrylic acid and acrylamide, starch molecules are introduced with carboxyl groups through oxidation, lignin molecules are introduced with sulfonic acid groups through sulfonation, and chitosan, starch, and lignin molecules are cross-linked through glutaraldehyde; the flocculant has a weight-average molecular weight of 50,000-100,000, a nitrogen content of 5%-8%, a carboxyl content of 1.5%-2.5 mmol / g, and a sulfonic acid content of 0. With a concentration of 8%-1.5 mmol / g, this flocculant exhibits excellent adsorption bridging and charge neutralization effects on negatively charged colloidal particles in water under neutral and weakly alkaline conditions. It can effectively remove suspended solids, organic matter, and heavy metal ions from water. The turbidity removal rates for surface water with a turbidity of 100-500 NTU and industrial wastewater with a turbidity of 500-1000 NTU can reach over 95% and over 90%, respectively, and the COD removal rates can reach 60%-80% and 50%-70%, respectively.
[0011] Further, the chitosan has a degree of deacetylation of 80%-90% and a viscosity-average molecular weight of 50,000-150,000; the starch is corn starch or cassava starch with an oxidation degree of 5%-15%, meaning that 5-15 carboxyl groups are oxidized per 100 glucose units; the lignin is alkali lignin or sulfate lignin with a sulfonation degree of 30%-50%, meaning that 30-50 sulfonic acid groups are introduced per 100 phenylpropane units; the total amount of methacrylic acid and acrylamide in the modifier is 10%-20% of the weight of chitosan, and the mass ratio of methacrylic acid to acrylamide is 1:1.5-1:2.5; the amount of glutaraldehyde, the crosslinking agent, is 2%-5% of the total weight of chitosan, starch, and lignin.
[0012] On the other hand, a method for preparing a natural polymeric flocculant includes the following steps:
[0013] First, dissolve chitosan in an acetic acid solution with a mass fraction of 1%-3% to prepare a chitosan solution with a concentration of 2%-5%. Then, add 5%-10% methacrylic acid and 10%-15% acrylamide by weight of chitosan. Stir and react at 40-60℃ for 2-4 hours to obtain a modified chitosan solution.
[0014] Next, starch is added to deionized water to prepare a starch milk with a concentration of 3%-6%. It is heated at 80-90℃ for 30-60 minutes to gelatinize. Then, 3%-8% of an oxidizing agent (such as potassium permanganate or sodium hypochlorite) is added and the oxidation reaction is carried out at 50-70℃ for 1-2 hours to obtain an oxidized starch solution.
[0015] Then, add lignin to a sodium hydroxide solution with a mass fraction of 5%-10% to prepare a lignin solution with a concentration of 2%-5%. Add sodium bisulfite with a mass fraction of 10%-20% of the lignin and sulfonate at 90-100℃ for 2-3 hours to obtain a sulfonated lignin solution.
[0016] Finally, the modified chitosan solution, oxidized starch solution, and sulfonated lignin solution were mixed in proportion, glutaraldehyde was added, and the crosslinking reaction was carried out at 30-50℃ for 1-2 hours. Then, the mixture was concentrated under reduced pressure and spray-dried to obtain the natural polymer flocculant.
[0017] Furthermore, during the preparation of the modified chitosan solution, 0.1%-0.5% of ammonium persulfate as an initiator was added to initiate the graft copolymerization reaction of methacrylic acid and acrylamide with chitosan. The pH of the system was controlled at 4-6 during the reaction, which was adjusted by adding sodium hydroxide solution or hydrochloric acid solution. The preferred reaction temperature was 50-55℃, and the stirring speed was 200-300 rpm to ensure uniform reaction.
[0018] Furthermore, during the preparation of the oxidized starch solution, the amount of oxidant is adjusted according to the type and degree of oxidation of the starch. For corn starch, the amount of oxidant is 5%-8% of the starch weight, and for cassava starch, the amount of oxidant is 3%-6% of the starch weight. During the oxidation reaction, the carboxyl content of the starch is sampled every 15-30 minutes, and the reaction is stopped when the carboxyl content reaches the target value. The oxidized starch solution needs to be neutralized and the pH value is adjusted to 6-7 to remove residual oxidant.
[0019] Furthermore, in the preparation of the sulfonated lignin solution, the concentration of sodium hydroxide solution is preferably 8%-10%, and the amount of sodium bisulfite is 15%-20% of the weight of lignin; the sulfonation reaction is carried out under nitrogen protection to prevent lignin from being oxidized; after the reaction is completed, the sulfonated lignin solution is filtered to remove insoluble impurities, and then excess inorganic salts are removed by dialysis or ion exchange.
[0020] Furthermore, during the cross-linking reaction, glutaraldehyde is added slowly dropwise over 15-30 minutes to ensure sufficient reaction between glutaraldehyde and chitosan, starch, and lignin molecules. The pH of the cross-linking reaction system is controlled at 7-9 and adjusted by adding sodium hydroxide solution. The preferred reaction temperature is 40-45℃, and the stirring speed is 150-250 rpm. During the reaction, samples are taken periodically to test the degree of cross-linking of the flocculant, and the reaction is stopped when the degree of cross-linking reaches 30%-50%.
[0021] Furthermore, when the flocculant prepared by this method is used for water treatment, it is first prepared into an aqueous solution with a concentration of 0.1%-1%, and then added to the water to be treated under stirring conditions, with a dosage of 5-50 mg / L. The stirring speed is initially fast and then slowed down, with a fast stirring speed of 200-300 rpm for 1-3 minutes to ensure that the flocculant and water are fully mixed. Then, the slow stirring speed is 50-100 rpm for 10-30 minutes to promote the formation and growth of flocs. Finally, the mixture is allowed to settle for 30-60 minutes, and the supernatant after removing the sediment is the treated water.
[0022] Beneficial effects
[0023] Compared with known public technologies, the technical solution provided by this invention has the following advantages:
[0024] Beneficial effects:
[0025] I. This invention utilizes a three-dimensional network structure formed by grafting chitosan with methacrylic acid and acrylamide to form a branch chain, introducing carboxyl groups through starch oxidation, introducing sulfonic acid groups through lignin sulfonation, and cross-linking with glutaraldehyde. This structure combines charge neutralization (sulfonic acid groups and carboxyl negatively charged groups), adsorption bridging (long-chain molecular structure), and sweeping effects, resulting in highly efficient adsorption and aggregation of negatively charged colloidal particles (such as suspended solids, organic matter, and heavy metal ions) in water.
[0026] Second, the flocculant in this invention uses natural renewable polymers such as chitosan, starch, and lignin as raw materials, and is prepared through chemical modification and cross-linking. Its molecular structure can be degraded by microorganisms into carbon dioxide and water, avoiding the environmental residue problems of traditional synthetic polymer flocculants. The heavy metal content is strictly limited, which solves the risk of metal ion release from aluminum salt and iron salt flocculants. It is suitable for the treatment of drinking water, surface water and highly sensitive industrial wastewater, and has both treatment efficiency and ecological safety. Detailed Implementation
[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments thereof. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.
[0028] The present invention will be further described below with reference to embodiments.
[0029] Example 1
[0030] Raw material composition (parts by weight):
[0031] 25 parts chitosan (85% deacetylation, 100,000 viscosity-average molecular weight), 20 parts corn starch (10% oxidation), 15 parts alkali lignin (40% sulfonation), 7.5 parts modifier (methacrylic acid to acrylamide mass ratio of 1:2), 3 parts glutaraldehyde (3% of the total weight of chitosan, starch and lignin), and 150 parts deionized water.
[0032] Preparation method:
[0033] Preparation of modified chitosan solution: Chitosan was dissolved in 2% acetic acid solution to prepare 4% chitosan solution; 7% methacrylic acid, 12% acrylamide and 0.3% ammonium persulfate were added according to the weight of chitosan, the pH was adjusted to 5, and the reaction was stirred at 55℃ and 250 rpm for 3 hours.
[0034] Preparation of oxidized starch solution: Corn starch was mixed with water to prepare a 5% starch milk, and gelatinized at 85℃ for 45 minutes; 6% sodium hypochlorite was added, and the reaction was carried out at 60℃ for 1.5 hours, and then neutralized to pH=6.5.
[0035] Preparation of sulfonated lignin solution: Alkali lignin was dissolved in 8% sodium hydroxide solution to prepare a 3% lignin solution; 18% sodium bisulfite was added, and the sulfonation reaction was carried out at 95°C for 2.5 hours under nitrogen protection. The solution was then filtered and dialyzed to remove salt.
[0036] Cross-linking reaction: Mix the above three solutions, slowly add glutaraldehyde (dropping time 20 minutes), adjust the pH to 8, and perform a cross-linking reaction at 45℃ and 200 rpm for 1.5 hours until the degree of cross-linking is 40%; concentrate under reduced pressure and spray dry to obtain flocculant A.
[0037] Performance parameters:
[0038] It has a weight-average molecular weight of 75,000, a nitrogen content of 6.5%, a carboxyl content of 2.0 mmol / g, and a sulfonic acid content of 1.2 mmol / g.
[0039] Example 2
[0040] Raw material composition (parts by weight):
[0041] 20 parts chitosan (80% deacetylation, 50,000 viscosity-average molecular weight), 15 parts tapioca starch (5% oxidation), 10 parts sulfate lignin (30% sulfonation), 5 parts modifier (methacrylic acid to acrylamide mass ratio of 1:1.5), 2 parts glutaraldehyde (2% of total weight), and 100 parts deionized water.
[0042] Preparation method:
[0043] Preparation of modified chitosan solution: Chitosan was dissolved in 1% acetic acid solution to prepare 2% chitosan solution; 5% methacrylic acid, 10% acrylamide and 0.1% ammonium persulfate were added, the pH was adjusted to 4, and the reaction was carried out at 50℃ and 200 rpm for 4 hours.
[0044] Preparation of oxidized starch solution: Cassava starch was mixed with water to prepare a 3% starch milk, and gelatinized at 80℃ for 60 minutes; 3% potassium permanganate was added, and the reaction was carried out at 50℃ for 2 hours, and then neutralized to pH=7.
[0045] Preparation of sulfonated lignin solution: Sulfated lignin is dissolved in 5% sodium hydroxide solution to prepare a 2% lignin solution; 10% sodium bisulfite is added, and the sulfonation reaction is carried out at 90℃ for 3 hours under nitrogen protection. The solution is then filtered and desalted by ion exchange.
[0046] Cross-linking reaction: After mixing the solution, add glutaraldehyde dropwise (dropwise time 15 minutes), adjust the pH to 7, and perform a cross-linking reaction at 40℃ and 150 rpm for 2 hours until the degree of cross-linking is 30%; concentrate under reduced pressure and spray dry to obtain flocculant B.
[0047] Performance parameters:
[0048] It has a weight-average molecular weight of 50,000, a nitrogen content of 5%, a carboxyl content of 1.5 mmol / g, and a sulfonic acid content of 0.8 mmol / g.
[0049] Example 3
[0050] Raw material composition (parts by weight):
[0051] 30 parts chitosan (90% deacetylation, 150,000 viscosity-average molecular weight), 25 parts corn starch (15% oxidation), 20 parts alkali lignin (50% sulfonation), 10 parts modifier (methacrylic acid to acrylamide mass ratio of 1:2.5), 5 parts glutaraldehyde (5% of total weight), and 200 parts deionized water.
[0052] Preparation method:
[0053] Preparation of modified chitosan solution: Chitosan was dissolved in 3% acetic acid solution to prepare 5% chitosan solution; 10% methacrylic acid, 15% acrylamide and 0.5% ammonium persulfate were added, the pH was adjusted to 6, and the reaction was carried out at 60℃ and 300 rpm for 2 hours.
[0054] Preparation of oxidized starch solution: Corn starch was mixed with water to prepare a 6% starch milk, and gelatinized at 90℃ for 30 minutes; 8% sodium hypochlorite was added, and the reaction was carried out at 70℃ for 1 hour, and then neutralized to pH=6.
[0055] Preparation of sulfonated lignin solution: Alkali lignin is dissolved in 10% sodium hydroxide solution to prepare 5% lignin solution; 20% sodium bisulfite is added, and sulfonation reaction is carried out at 100℃ for 2 hours under nitrogen protection. The solution is then filtered and dialyzed to remove salt.
[0056] Cross-linking reaction: After mixing the solution, add glutaraldehyde dropwise (dropwise time 30 minutes), adjust the pH to 9, and perform a cross-linking reaction at 50℃ and 250 rpm for 1 hour until the degree of cross-linking is 50%; concentrate under reduced pressure and spray dry to obtain flocculant C.
[0057] Performance parameters:
[0058] It has a weight-average molecular weight of 100,000, a nitrogen content of 8%, a carboxyl content of 2.5 mmol / g, and a sulfonic acid content of 1.5 mmol / g.
[0059] Comparative Example 1 (without the cross-linking agent glutaraldehyde)
[0060] Raw material composition (parts by weight):
[0061] Chitosan 25 parts, corn starch 20 parts, alkali lignin 15 parts, modifier 7.5 parts, deionized water 150 parts (glutaraldehyde omitted).
[0062] Preparation method:
[0063] The solution was prepared according to steps 1-3 of Example 1, directly mixed, concentrated under reduced pressure, and spray-dried to obtain sample D.
[0064] Performance parameters
[0065] It does not form a cross-linked structure, has a weight-average molecular weight of 30,000, a nitrogen content of 6.5%, a carboxyl content of 2.0 mmol / g, and a sulfonic acid content of 1.2 mmol / g.
[0066] Comparative Example 2 (modifier ratio exceeded the range; methacrylic acid to acrylamide mass ratio 2:1)
[0067] Raw material composition (parts by weight):
[0068] Chitosan 25 parts, corn starch 20 parts, alkali lignin 15 parts, modifier 7.5 parts (methacrylic acid to acrylamide mass ratio 2:1), glutaraldehyde 3 parts, deionized water 150 parts.
[0069] Preparation method:
[0070] Sample E was prepared according to the steps in Example 1, with only the proportion of the modifier adjusted.
[0071] Performance parameters:
[0072] It has a weight-average molecular weight of 60,000, a nitrogen content of 5.5%, a carboxyl content of 2.0 mmol / g, and a sulfonic acid content of 1.2 mmol / g.
[0073] Effect Comparison Table:
[0074]
[0075] analyze:
[0076] Importance of cross-linking structure: Comparative Example 1, without the addition of glutaraldehyde, did not form a cross-linking structure, its molecular weight was significantly reduced, its turbidity and COD removal rates were significantly decreased, and its storage stability was poor, proving that the cross-linking agent is crucial for the formation of a three-dimensional network structure.
[0077] Effect of modifier ratio: In Comparative Example 2, the mass ratio of methacrylic acid to acrylamide exceeded the scope of the claims (2:1), resulting in a decrease in nitrogen content and flocculation performance, indicating that a suitable modifier ratio is crucial for grafting effect.
[0078] Advantages of the embodiments: Each embodiment meets the parameter range of the claims, exhibits high removal rate in surface water and industrial wastewater treatment, meets the heavy metal content standards, and has good storage stability.
[0079] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A natural polymeric flocculant, characterized in that, This flocculant is prepared from the following raw materials in parts by weight: 20-30 parts chitosan, 15-25 parts starch, 10-20 parts lignin, 5-10 parts modifier, 3-8 parts crosslinking agent, and 100-200 parts deionized water; the modifier is a combination of methacrylic acid and acrylamide in a mass ratio of 1:1.5-1:2.5; the crosslinking agent is glutaraldehyde; in the molecular structure of this flocculant, the chitosan molecular chain is grafted with branches formed by methacrylic acid and acrylamide, the starch molecule introduces carboxyl groups through oxidation, the lignin molecule introduces sulfonic acid groups through sulfonation, and the chitosan, starch, and lignin molecules form a crosslinked structure through glutaraldehyde; the flocculant has a weight-average molecular weight of 50,000-100,000, a nitrogen content of 5%-8%, a carboxyl content of 1.5%-2.5 mmol / g, and a sulfonic acid content of 0.8%-1.5 mmol / g.
2. The natural polymeric flocculant according to claim 1, characterized in that, The chitosan has a degree of deacetylation of 80%-90% and a viscosity-average molecular weight of 50,000-150,000; the starch is corn starch or cassava starch with an oxidation degree of 5%-15%, meaning that 5-15 carboxyl groups are formed per 100 glucose units; the lignin is alkali lignin or sulfate lignin with a sulfonation degree of 30%-50%, meaning that 30-50 sulfonic acid groups are introduced per 100 phenylpropane units; the total amount of methacrylic acid and acrylamide in the modifier is 10%-20% of the weight of chitosan; and the amount of glutaraldehyde, the crosslinking agent, is 2%-5% of the total weight of chitosan, starch, and lignin.
3. A method for preparing a natural polymeric flocculant, applicable to the natural polymeric flocculant according to any one of claims 1-2, characterized in that, The preparation method of this flocculant includes the following steps: First, chitosan is dissolved in an acetic acid solution with a mass fraction of 1%-3% to prepare a chitosan solution with a concentration of 2%-5%. Then, 5%-10% methacrylic acid and 10%-15% acrylamide (by weight of chitosan) and 0.1%-0.5% ammonium persulfate (by weight of chitosan) are added, and the mixture is stirred and reacted at 40-60℃ for 2-4 hours to obtain a modified chitosan solution. Next, starch is added to deionized water to prepare a starch slurry with a concentration of 3%-6%. The slurry is heated and gelatinized at 80-90℃ for 30-60 minutes. Then, 3%-8% oxidant (by weight of starch) is added. The oxidant is potassium permanganate or sodium hypochlorite. An oxidation reaction is carried out at 50-70℃ for 1-2 hours to obtain an oxidized starch solution. Then, lignin is added to a 5%-10% sodium hydroxide solution to prepare a 2%-5% lignin solution. Sodium bisulfite (10%-20% by weight of lignin) is added, and a sulfonation reaction is carried out at 90-100℃ for 2-3 hours to obtain a sulfonated lignin solution. Finally, the modified chitosan solution, oxidized starch solution, and sulfonated lignin solution are mixed in a specific ratio, glutaraldehyde is added, and a crosslinking reaction is carried out at 30-50℃ for 1-2 hours. The mixture is then concentrated under reduced pressure and spray-dried to obtain the natural polymer flocculant.
4. The method for preparing the natural polymeric flocculant according to claim 3, characterized in that, The pH of the system is controlled at 4-6 during the reaction, which is adjusted by adding sodium hydroxide solution or hydrochloric acid solution dropwise; the reaction temperature is 50-55℃, and the stirring speed is 200-300 rpm.
5. The method for preparing the natural polymeric flocculant according to claim 3, characterized in that, In the preparation of oxidized starch solution, the amount of oxidant is adjusted according to the type of starch and the degree of oxidation. For corn starch, the amount of oxidant is 5%-8% of the starch weight, and for cassava starch, the amount of oxidant is 3%-6% of the starch weight. During the oxidation reaction, the carboxyl content of the starch is sampled every 15-30 minutes. The reaction is stopped when the carboxyl content reaches the target value. The oxidized starch solution needs to be neutralized and the pH value is adjusted to 6-7.
6. The method for preparing the natural polymeric flocculant according to claim 3, characterized in that, In the preparation of sulfonated lignin solution, the concentration of sodium hydroxide solution is 8%-10%, and the amount of sodium bisulfite is 15%-20% of the weight of lignin. The sulfonation reaction is carried out under nitrogen protection to prevent lignin from being oxidized. After the reaction is completed, the sulfonated lignin solution is filtered to remove insoluble impurities, and then excess inorganic salts are removed by dialysis or ion exchange.
7. The method for preparing the natural polymeric flocculant according to claim 3, characterized in that, During the cross-linking reaction, glutaraldehyde is added slowly dropwise over 15-30 minutes to ensure sufficient reaction between glutaraldehyde and chitosan, starch, and lignin molecules. The pH of the cross-linking reaction system is controlled at 7-9 and adjusted by adding sodium hydroxide solution. The reaction temperature is 40-45℃, and the stirring speed is 150-250 rpm. During the reaction, samples are taken periodically to test the degree of cross-linking of the flocculant. The reaction is stopped when the degree of cross-linking reaches 30%-50%.