Neutral high-efficiency sludge dewatering agent with heavy metal deep removal capability and preparation method of neutral high-efficiency sludge dewatering agent

Abstract

The invention discloses a neutral efficient sludge dewatering agent with heavy metal deep removal capacity and a preparation method of the neutral efficient sludge dewatering agent, and belongs to the technical field of sludge drying and dewatering. The preparation method of the neutral efficient sludge dewatering agent comprises the following steps: preparing carboxymethylated poly N-acetyl glucosamine, poly dimethyl diallyl ammonium chloride and acidified modified lignin, preparing iron modified lignin by taking the acidified modified lignin as a raw material; carboxymethylated poly N-acetyl glucosamine and poly dimethyl diallyl ammonium chloride are used as raw materials to prepare a carboxymethylated poly N-acetyl glucosamine / poly dimethyl diallyl ammonium chloride compound, and the iron modified lignin and the carboxymethylated poly N-acetyl glucosamine / poly dimethyl diallyl ammonium chloride compound are roasted and crosslinked. The sludge dewatering agent has the beneficial effects that the prepared sludge dewatering agent is neutral, has multiple synergistic flocculation mechanisms, is excellent in dewatering performance, and also has excellent heavy metal deep removal capability.

Description

Technical Field

[0001] This invention relates to a sludge dewatering agent and its preparation method, specifically to a neutral and highly efficient sludge dewatering agent with deep heavy metal removal capabilities and its preparation method, belonging to the field of sludge drying and dewatering technology. Background Technology

[0002] Given that sludge treatment and disposal costs account for as much as 30%-60% of the total operating costs of wastewater treatment plants, sludge dewatering is a key step in reducing wastewater volume.

[0003] Currently, the mainstream sludge dewatering agents include: polyferric sulfate, ferric chloride, polyacrylamide, chitosan, etc.

[0004] While the aforementioned sludge dewatering agents all have dewatering effects, the dewatering time is relatively long (around 45 minutes) and it is difficult to achieve a sludge cake moisture content below 50%. Furthermore, polyferric sulfate and ferric chloride are both strong acid agents, which will not only severely corrode the treatment system (including: conveying pipelines, pumps, valves, dewatering equipment, especially centrifuges and plate and frame filter presses), but also restrict subsequent sludge disposal methods if the dewatered sludge is planned to be anaerobically digested to produce biogas. In addition, sludge cakes with extreme pH levels can change soil properties and cause land use obstacles. Moreover, when the dewatered filtrate is returned to the front end of the wastewater treatment system, it can also pose potential risks to the biological treatment system.

[0005] In summary, developing neutral and efficient sludge dewatering agents has become an inevitable trend for the industry to move towards refined and green management. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a neutral and highly efficient dehydrating agent with a neutral pH, a short dehydration time (30 min), and the ability to reduce the moisture content of the mud cake to below 50%, as well as its preparation method.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a neutral and highly efficient sludge dewatering agent with deep heavy metal removal capabilities includes the following steps: Step 1: Using polyN-acetylglucosamine as raw material, carboxymethylation modification with chloroacetic acid is carried out to prepare carboxymethylated polyN-acetylglucosamine; Step 2: Polydiallyl ammonium chloride was prepared using dimethyl diallyl ammonium chloride as a monomer and ammonium persulfate as a polymerization initiator; Step 3: Using lignin as raw material, acidify and modify it with sulfuric acid to prepare acid-modified lignin; Step 4: Using the acidified modified lignin obtained in Step 3 as raw material, iron-modified lignin is prepared by iron modification with ferric chloride hexahydrate. Step 5: Using the carboxymethylated polyN-acetylglucosamine prepared in Step 1 and the polydimethyldiallylammonium chloride prepared in Step 2 as raw materials, a compound was prepared to prepare a carboxymethylated polyN-acetylglucosamine / polydimethyldiallylammonium chloride complex. Step 6: Using the iron-modified lignin prepared in Step 4 and the carboxymethylated poly(N-acetylglucosamine) / poly(dimethyldiallylammonium chloride) composite prepared in Step 5 as raw materials, the final product is prepared by calcination and crosslinking.

[0008] Preferably, in step 1, the method for preparing carboxymethylated poly(N-acetylglucosamine) by weight is as follows: (1) Alkalization: Add a mixture of 1 part poly-N-acetylglucosamine and 20 parts isopropanol and water to the reaction vessel, V 异丙醇 V 水 =1:1, then 0.9 parts of sodium hydroxide were dissolved in 5 parts of deionized water and slowly added dropwise to the reaction vessel, and then alkalized by stirring in a 30°C water bath for 1 hour; (2) Etherification: Dissolve 1.1 parts of chloroacetic acid in a mixture of 5 parts of isopropanol and water, V 异丙醇 V 水 =1:1, slowly added dropwise to the alkalized mixture, heated to 60℃, and refluxed for 3 hours; (3) Post-treatment: Cool to room temperature, adjust pH to 7.0, filter, wash the precipitate with 80% ethanol aqueous solution, and dry to constant weight to obtain carboxymethylated polyN-acetylglucosamine.

[0009] Preferably, in step 2, the method for preparing polydimethyldiallylammonium chloride, by weight, is as follows: (1) Loading: Add 10 parts of dimethyl diallyl ammonium chloride and 15 parts of deionized water to the reaction vessel, and purge the oxygen in the reaction vessel with nitrogen gas; (2) Polymerization: Place the reaction vessel in a 60℃ oil bath, dissolve 0.05 parts of ammonium persulfate in a small amount of deionized water and quickly inject it into the reaction vessel, continuously introduce a small amount of nitrogen gas at 60±2℃ for protection, and react at a constant temperature for 8h; (3) Post-treatment: Cool to room temperature, precipitate with acetone and then vacuum dry to obtain polydimethyldiallyl ammonium chloride.

[0010] Preferably, in step 3, the method for preparing acid-modified lignin, by weight, is as follows: (1) Acidification: Add 5 parts of lignin and 50 parts of sulfuric acid solution with a concentration of 1.5 mol / L to the reaction vessel, and stir and reflux in an oil bath at 80°C for 3 hours; (2) Post-treatment: Cool to room temperature, filter, wash the filter cake repeatedly with deionized water until the pH of the filtrate is neutral, dry the filter cake to constant weight, crush and sieve to obtain acidified modified lignin.

[0011] Preferably, in step 4, the method for preparing iron-modified lignin, by weight, is as follows: (1) Fe³⁺ loading: Add 40 parts of deionized water and 2 parts of acidified modified lignin to the reaction vessel, disperse evenly, and slowly add 1 part of ferric chloride hexahydrate. Then place the reaction vessel in a 60℃ water bath and stir for 2 hours. (2) Post-treatment: The reaction system is dried until it is completely solidified and free of moisture, and then ground into a uniform powder to obtain iron-modified lignin.

[0012] Preferably, in step 5, the method for preparing the carboxymethylated poly(N-acetylglucosamine) / poly(dimethyldiallylammonium chloride) complex, by weight, is as follows: (1) Compounding: Mix 1.5 parts of carboxymethylated polyN-acetylglucosamine and 1 part of polydimethyldiallylammonium chloride evenly, add deionized water to make the solid content in the range of 10-20%, stir and react at 50°C for 1 hour to form a uniform viscous slurry; (2) Post-treatment: The reaction system was dried to constant weight to obtain carboxymethylated poly(N-acetylglucosamine) / poly(dimethyldiallylammonium chloride) complex.

[0013] Preferably, in step 6, the method for preparing the final product, by weight, is as follows: (1) Mixing: Thoroughly grind and mix 1 part of iron-modified lignin and 3 parts of carboxymethylated poly(N-acetylglucosamine) / polydimethyldiallylammonium chloride complex; (2) Calcination and crosslinking: The uniformly mixed material is spread evenly in the calciner, with a layer thickness not exceeding 1 cm. The calcination equipment is heated to 190°C at a rate of 5°C / min, and then precisely calcined at this temperature for 30 min. (3) Post-processing: After the time is reached, the roasting equipment is turned off. The material is cooled to below 60°C in the furnace and then ground into fine powder and passed through an 80-100 mesh sieve to obtain the final product.

[0014] A neutral and highly efficient sludge dewatering agent with the ability to deeply remove heavy metals is prepared by any of the methods described above.

[0015] The advantages of this invention are: (1) The aqueous solution (mass concentration of 1.5%) of the sludge dewatering agent provided by the present invention has a pH value in the range of 6-8 and is neutral. When it is added at a dosage of 5‰, it will not corrode the treatment system, restrict the subsequent sludge disposal path, or cause land use obstacles. At the same time, it will not bring potential risks to the biological treatment system. (2) The sludge dewatering agent provided by the present invention has multiple synergistic flocculation mechanisms of enhanced adsorption-bridging, efficient charge neutralization, net sweeping and structural enhancement. The resulting flocs are large in size, compact in structure and high in mechanical strength. The large and dense flocs result in faster settling speed. The solid flocs are not easily damaged during mechanical dewatering, and water is more easily separated from the gaps between the flocs. The powerful net sweeping action squeezes out more water and wraps it in the skeleton. After mechanical dewatering, the moisture content of the sludge cake can be reduced to a lower level. It has excellent dewatering performance and is particularly suitable for deep dewatering of activated sludge with high organic matter content and strong colloidal stability that is difficult to treat.

[0016] Enhanced adsorption-bridging: The three-dimensional network of long molecular chains and modified lignin works together to form a robust floc skeleton, which can effectively capture fine particles and produce larger and denser flocs, thereby promoting the release of water and significantly reducing the moisture content of the mud cake.

[0017] Highly efficient charge neutralization: The grafted strong cationic monomer (dimethyl diallyl ammonium chloride) and inorganic coagulant (ferric chloride) provide a large amount of positive charge, which can quickly neutralize the negatively charged sludge colloidal particles, destroy their stability, and achieve highly efficient depolymerization.

[0018] Netting and sweeping, along with structural reinforcement: The precipitation effect of ferric chloride hydrolysis products combined with the skeletal support of lignin makes the resulting floc structure more robust, with strong shear resistance, and less prone to breakage under the pressure of dewatering machinery (such as plate and frame filter presses).

[0019] (3) The sludge dewatering agent provided by the present invention has excellent deep removal ability of heavy metals. Specifically, the amino and carboxyl groups on poly-N-acetylglucosamine and its carboxymethylated derivatives have a strong complexing and adsorption capacity for heavy metal ions, which helps the sludge dewatering agent provided by the present invention to stabilize the heavy metals in the sludge cake and reduce environmental risks.

[0020] (4) The sludge dewatering agent provided by the present invention integrates multiple functions such as debinding, destabilizing, bridging, structural enhancement, removal of organic matter and heavy metals, and truly achieves multiple effects with one agent, which can significantly simplify the dosing system and operation process.

[0021] (5) The sludge dewatering agent provided by the present invention introduces inexpensive modified lignin as the main coagulant component, and optimizes the dosage of high-priced components (such as poly-N-acetylglucosamine) while ensuring the effect, effectively controlling the raw material cost and having economic potential for large-scale application.

[0022] (6) The core raw materials of the sludge dewatering agent provided by the present invention are derived from aquatic processing waste (shrimp and crab shells) and papermaking by-products (lignin). It is a typical example of turning waste into treasure, which is in line with the principle of circular economy. Furthermore, the agent based on biomass resources has a lower carbon footprint throughout its entire life cycle, which is in line with the concept of green and sustainable development. Detailed Implementation

[0023] The present invention will be described in detail below with reference to specific embodiments.

[0024] I. Preparation of a neutral and highly efficient sludge dewatering agent with deep heavy metal removal capabilities Step 1: Preparation of carboxymethylated poly-N-acetylglucosamine The raw materials used to prepare carboxymethylated polyN-acetylglucosamine, by weight, are: 1 part polyN-acetylglucosamine, 0.9 parts sodium hydroxide, 1.1 parts chloroacetic acid, and 25 parts (V) of a mixture of isopropanol and water. 异丙醇 V 水 =1:1), 5 parts deionized water.

[0025] The method for preparing carboxymethylated poly-N-acetylglucosamine is as follows: (1) Alkalization: Add 1 part of poly-N-acetylglucosamine and 20 parts of isopropanol and water to the reaction vessel (V 异丙醇 V 水 =1:1) and stir to disperse evenly. Then, dissolve 0.9 parts of sodium hydroxide in 5 parts of deionized water and slowly add it dropwise into the reaction vessel over 30 minutes using a dropping funnel. After that, alkalize the mixture by stirring at 300 rpm for 1 hour in a 30°C water bath.

[0026] (2) Etherification: Dissolve 1.1 parts of chloroacetic acid in a mixture of 5 parts of isopropanol and water and slowly add it dropwise to the alkalized mixture. Heat to 60°C and reflux for 3 hours.

[0027] (3) Post-treatment: After the reaction is completed, the reaction system is naturally cooled to room temperature, the pH is adjusted to 7.0 with dilute acetic acid solution, filtered, and then the precipitate is washed 3 times with 80% ethanol aqueous solution (to remove salt and by-products). The filter cake is then dried to constant weight in a vacuum drying oven at 60℃ to obtain carboxymethylated polyN-acetylglucosamine (polymer flocculant).

[0028] Step 2: Preparation of polydimethyldiallylammonium chloride The raw materials used to prepare polydimethyldiallyl ammonium chloride by mass are: 10 parts of dimethyldiallyl ammonium chloride (monomer), 0.05 parts of ammonium persulfate (polymerization initiator), and 15 parts of deionized water.

[0029] The method for preparing polydimethyldiallylammonium chloride is as follows: (1) Loading: Add 10 parts of dimethyl diallyl ammonium chloride and 15 parts of deionized water to the reaction vessel and stir evenly. Then continuously purge high-purity nitrogen gas for 15 minutes to completely remove oxygen from the reaction vessel.

[0030] (2) Polymerization: Place the reaction vessel in a 60°C oil bath, dissolve 0.05 parts of ammonium persulfate in a small amount of deionized water and quickly inject it into the reaction vessel, continuously pass a small amount of nitrogen gas at 60±2°C for protection, and react at a constant temperature for 8 hours (the solution will gradually become viscous).

[0031] (3) Post-processing: After the reaction is completed, the oil bath is removed and the reaction system is naturally cooled to room temperature to obtain a light yellow viscous liquid (solid content is about 40%). After precipitation with acetone, it is vacuum dried to obtain high-purity polydimethyldiallyl ammonium chloride (cationic polymer).

[0032] Step 3: Preparation of acid-modified lignin The raw materials used to prepare acid-modified lignin by mass are: 5 parts lignin and 50 parts sulfuric acid solution with a concentration of 1.5 mol / L.

[0033] The method for preparing acid-modified lignin is as follows: (1) Acidification: Add 5 parts of lignin and 50 parts of sulfuric acid solution with a concentration of 1.5 mol / L to the reaction vessel, and stir and reflux in an oil bath at 80°C for 3 hours.

[0034] (2) Post-processing: After the reaction is completed, the reaction system is naturally cooled to room temperature, filtered, and the filter cake is repeatedly washed with deionized water until the pH of the filtrate is neutral. Then the filter cake is transferred to a watch glass and dried to constant weight in a 105℃ forced-air drying oven. It is then crushed and passed through a 100-mesh sieve to obtain acid-modified lignin (recovery rate >95%).

[0035] After acidification modification, the surface active sites and porosity of lignin increased significantly.

[0036] Step 4: Preparation of iron-modified lignin The raw materials used to prepare iron-modified lignin by mass are: 2 parts acid-modified lignin, 1 part ferric chloride hexahydrate, and 40 parts deionized water.

[0037] The method for preparing iron-modified lignin is as follows: (1) Fe³⁺ loading: Add 40 parts of deionized water to the reaction vessel, add 2 parts of acidified modified lignin while stirring, and after it is evenly dispersed, slowly add 1 part of ferric chloride hexahydrate. Then place the reaction vessel in a 60°C water bath and mechanically stir at 300 rpm for 2 hours.

[0038] (2) Post-treatment: After the reaction is completed, the reaction system is transferred to an evaporating dish and dried in a 105°C forced-air drying oven until it is completely solidified and free of moisture. The dried block is then ground into a uniform brownish-red powder using a mortar and pestle to obtain iron-modified lignin.

[0039] When Fe³⁺ is loaded onto acidified lignin, it forms an inorganic aggregate with coagulation properties—iron-modified lignin.

[0040] Step 5: Preparation of carboxymethylated poly(N-acetylglucosamine) / poly(diallylammonium chloride) complex The raw materials used to prepare the carboxymethylated poly(N-acetylglucosamine) / poly(diallyl ammonium chloride) composite by weight are: 1.5 parts of carboxymethylated poly(N-acetylglucosamine), 1 part of poly(diallyl ammonium chloride), and 8 parts of deionized water.

[0041] The method for preparing carboxymethylated poly(N-acetylglucosamine) / poly(diallyldimethylammonium chloride) complex is as follows: (1) Compounding: Mix 1.5 parts of carboxymethylated polyN-acetylglucosamine and 1 part of polydimethyldiallylammonium chloride evenly, add 8 parts of deionized water (so that the solid content is in the range of 10-20%), stir and react at 50℃ and 200rpm for 1h to form a uniform viscous slurry.

[0042] (2) Post-processing: After the reaction is completed, the reaction system is transferred to an evaporating dish and dried in a 105°C forced-air drying oven to constant weight to obtain carboxymethylated poly(N-acetylglucosamine) / poly(dimethyldiallylammonium chloride) complex.

[0043] When carboxymethylated poly(N-acetylglucosamine) is combined with poly(diallyldimethylammonium chloride), a dual-core polymeric flocculant is formed—a carboxymethylated poly(N-acetylglucosamine) / poly(diallyldimethylammonium chloride) complex.

[0044] Step 6: Prepare the final product The raw materials used to prepare the final product by weight are: 1 part of iron-modified lignin (inorganic aggregate) and 3 parts of carboxymethylated poly(N-acetylglucosamine) / poly(diallyldimethylammonium chloride) complex (organic flocculant).

[0045] The method for preparing the final product is as follows: (1) Mixing: Grind and mix 1 part of iron-modified lignin and 3 parts of carboxymethylated polyN-acetylglucosamine / polydimethyldiallylammonium chloride complex in a mortar (or small mixer) for a long time until the color is uniform and there is no visible color difference or lumps.

[0046] (2) Calcination and crosslinking: Spread the evenly mixed material in the calciner, with a layer thickness not exceeding 1 cm. Heat the calcination equipment to 190°C at a rate of 5°C / min, and calcine precisely at this temperature for 30 min (Note: Observe the color of the material closely. It should turn dark brown or black, but it must never carbonize, turn white, or burn).

[0047] (3) Post-processing: After the time is reached, turn off the roasting equipment, open the furnace door slightly, and let the material cool naturally in the furnace to below 60°C before taking it out. Grind the cooled blocky material into fine powder with a mortar and pestle, and pass it through an 80-100 mesh standard sieve. Continue to grind and sieve the particles that cannot pass through the sieve. (4) Packaging: The sieved uniform powder is put into a sealed bag and stored in a cool and dry place. This is the final product.

[0048] II. Dewatering Effect of Neutral and High-Efficiency Sludge Dewatering Agents with Deep Heavy Metal Removal Capabilities 1. Experimental equipment A hydraulic filter press was used to simulate the effect of a real machine.

[0049] 2. Experimental raw mud Sludge from municipal solid waste and sewage treatment plants was used as the raw sludge for the experiment, and it was prepared with a moisture content of 81.5% or 82.0% for comparative experiments.

[0050] 3. Sludge dewatering agents The sludge dewatering agents used in the experiment included: polyferric sulfate, ferric chloride, polyacrylamide, chitosan, and the sludge dewatering agent prepared in this invention.

[0051] Prepare a 1.5% (w / w) solution of each reagent using deionized water and add it at a dosage of 0.5%. Set up a blank control group without adding any reagent.

[0052] 4. Dehydration effect (1) Effect of reagent type on dehydration efficiency The hydraulic filter press maintained an operating pressure that increased from 0.00 MPa to 5.00 MPa within 45 minutes, using a stacked filtration method. The raw sludge volume was 1 kg. The dewatering efficiency test results of various sludge dewatering agents are shown in Table 1.

[0053] Table 1. Dewatering efficiency test results of various sludge dewatering agents

[0054] As shown in Table 1, the moisture content of the sludge cake in Group 1 is significantly lower than that in other groups, indicating that the dewatering efficiency of the sludge dewatering agent prepared by this invention is significantly better than that of other agents.

[0055] (2) Effect of filtration time on dewatering efficiency The hydraulic filter press maintained an operating pressure that increased from 0.00 MPa to 5.00 MPa within 60 minutes, using a stacked filtration method. The raw sludge volume was 1 kg, and the raw sludge moisture content was 82.0%. In the first 25 minutes, due to the filter cloth wrapping method and equipment limitations, some sludge leakage occurred, and the data obtained was not used as a reference. Starting from the 30th minute, the moisture content was measured every 5 minutes, and the test results are shown in Table 2.

[0056] Table 2. Moisture content test results (%) under different filtration times

[0057] As shown in Table 2, after 30 minutes of filtration, the moisture content of the mud cake in Group 1 reached below 50%, which met the usage requirements. Although other groups also removed a lot of water, the moisture content of the mud cake was still above 59%, which did not meet the usage requirements. As the filtration time increased, the moisture content of the mud cake in each group continued to decrease. After 60 minutes of filtration, except for Group 1, the mud cakes in other groups still did not meet the actual usage requirements of a moisture content below 50%.

[0058] (3) Effect of filter press pressure on dewatering efficiency The hydraulic filter press maintained an operating pressure that increased from 0.00 MPa to 0.50 MPa, 1.00 MPa, 1.50 MPa, 2.00 MPa, 2.50 MPa, 3.00 MPa, 3.50 MPa, 4.00 MPa, 4.50 MPa, 5.00 MPa, or 5.50 MPa within 45 minutes. Filtration was performed using a stacked filtration method. The raw sludge volume was 1 kg, and the raw sludge moisture content was 82.0%. The dewatering efficiency test results of various sludge dewatering agents under different filtration pressures are shown in Tables 3-1 and 3-2.

[0059] Table 3-1 Moisture content test results under different filtration pressures (I) (%)

[0060] Table 3-2 Moisture content test results under different filtration pressures (Part II) (%)

[0061] As shown in Tables 3-1 and 3-2, when the filter press pressure reaches 4.50 MPa, the moisture content of the sludge cake in Group 1 is below 50%, which can meet the usage requirements, while the moisture content of the sludge cake in other groups is still above 56%, which does not yet meet the usage requirements.

[0062] It should be noted that the above embodiments are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of this invention are still within the scope of protection of this invention.

Claims

1. A method for preparing a neutral and highly efficient sludge dewatering agent with deep heavy metal removal capabilities, characterized in that, Includes the following steps: Step 1: Using polyN-acetylglucosamine as raw material, carboxymethylation modification with chloroacetic acid is carried out to prepare carboxymethylated polyN-acetylglucosamine; Step 2: Polydiallyl ammonium chloride was prepared using dimethyl diallyl ammonium chloride as a monomer and ammonium persulfate as a polymerization initiator; Step 3: Using lignin as raw material, acidify and modify it with sulfuric acid to prepare acid-modified lignin; Step 4: Using the acidified modified lignin obtained in Step 3 as raw material, iron-modified lignin is prepared by iron modification with ferric chloride hexahydrate. Step 5: Using the carboxymethylated polyN-acetylglucosamine prepared in Step 1 and the polydimethyldiallylammonium chloride prepared in Step 2 as raw materials, a compound was prepared to prepare a carboxymethylated polyN-acetylglucosamine / polydimethyldiallylammonium chloride complex. Step 6: Using the iron-modified lignin prepared in Step 4 and the carboxymethylated poly(N-acetylglucosamine) / poly(dimethyldiallylammonium chloride) composite prepared in Step 5 as raw materials, the final product is prepared by calcination and crosslinking.

2. The preparation method of the neutral and efficient sludge dewatering agent with deep heavy metal removal capability according to claim 1, characterized in that, In step 1, the method for preparing carboxymethylated poly-N-acetylglucosamine, by weight, is as follows: (1) Alkalization: Add a mixture of 1 part poly-N-acetylglucosamine and 20 parts isopropanol and water to the reaction vessel, V 异丙醇 V 水 =1:1, then 0.9 parts of sodium hydroxide were dissolved in 5 parts of deionized water and slowly added dropwise to the reaction vessel, and then alkalized by stirring in a 30°C water bath for 1 hour; (2) Etherification: Dissolve 1.1 parts of chloroacetic acid in a mixture of 5 parts of isopropanol and water, V 异丙醇 V 水 =1:1, slowly added dropwise to the alkalized mixture, heated to 60℃, and refluxed for 3 hours; (3) Post-treatment: Cool to room temperature, adjust pH to 7.0, filter, wash the precipitate with 80% ethanol aqueous solution, and dry to constant weight to obtain carboxymethylated polyN-acetylglucosamine.

3. The preparation method of the neutral and efficient sludge dewatering agent with deep heavy metal removal capability according to claim 1, characterized in that, In step 2, the method for preparing polydimethyldiallylammonium chloride, by weight, is as follows: (1) Loading: Add 10 parts of dimethyl diallyl ammonium chloride and 15 parts of deionized water to the reaction vessel, and purge the oxygen in the reaction vessel with nitrogen gas; (2) Polymerization: Place the reaction vessel in a 60℃ oil bath, dissolve 0.05 parts of ammonium persulfate in a small amount of deionized water and quickly inject it into the reaction vessel, continuously introduce a small amount of nitrogen gas at 60±2℃ for protection, and react at a constant temperature for 8h; (3) Post-treatment: Cool to room temperature, precipitate with acetone and then vacuum dry to obtain polydimethyldiallyl ammonium chloride.

4. The preparation method of the neutral and efficient sludge dewatering agent with deep heavy metal removal capability according to claim 1, characterized in that, In step 3, the method for preparing acid-modified lignin, by weight, is as follows: (1) Acidification: Add 5 parts of lignin and 50 parts of sulfuric acid solution with a concentration of 1.5 mol / L to the reaction vessel, and stir and reflux in an oil bath at 80°C for 3 hours; (2) Post-treatment: Cool to room temperature, filter, wash the filter cake repeatedly with deionized water until the pH of the filtrate is neutral, dry the filter cake to constant weight, crush and sieve to obtain acidified modified lignin.

5. The preparation method of the neutral and efficient sludge dewatering agent with deep heavy metal removal capability according to claim 1, characterized in that, In step 4, the method for preparing iron-modified lignin, by weight, is as follows: (1) Fe³⁺ loading: Add 40 parts of deionized water and 2 parts of acidified modified lignin to the reaction vessel, disperse evenly, and slowly add 1 part of ferric chloride hexahydrate. Then place the reaction vessel in a 60℃ water bath and stir for 2 hours. (2) Post-treatment: The reaction system is dried until it is completely solidified and free of moisture, and then ground into a uniform powder to obtain iron-modified lignin.

6. The preparation method of the neutral and efficient sludge dewatering agent with deep heavy metal removal capability according to claim 1, characterized in that, In step 5, the method for preparing the carboxymethylated poly(N-acetylglucosamine) / poly(dimethyldiallylammonium chloride) complex, by weight, is as follows: (1) Compounding: Mix 1.5 parts of carboxymethylated polyN-acetylglucosamine and 1 part of polydimethyldiallylammonium chloride evenly, add deionized water to make the solid content in the range of 10-20%, stir and react at 50°C for 1 hour to form a uniform viscous slurry; (2) Post-treatment: The reaction system was dried to constant weight to obtain carboxymethylated poly(N-acetylglucosamine) / poly(dimethyldiallylammonium chloride) complex.

7. The preparation method of the neutral and efficient sludge dewatering agent with deep heavy metal removal capability according to claim 1, characterized in that, In step 6, the method for preparing the final product, by weight, is as follows: (1) Mixing: Thoroughly grind and mix 1 part of iron-modified lignin and 3 parts of carboxymethylated poly(N-acetylglucosamine) / polydimethyldiallylammonium chloride complex; (2) Calcination and crosslinking: The uniformly mixed material is spread evenly in the calciner, with a layer thickness not exceeding 1 cm. The calcination equipment is heated to 190°C at a rate of 5°C / min, and then precisely calcined at this temperature for 30 min. (3) Post-processing: After the time is reached, the roasting equipment is turned off. The material is cooled to below 60°C in the furnace and then ground into fine powder and passed through an 80-100 mesh sieve to obtain the final product.

8. A neutral and highly efficient sludge dewatering agent with deep heavy metal removal capabilities, characterized in that, It is prepared by the method described in any one of claims 1 to 7.

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