Flocculating agent for treating papermaking wastewater

Abstract

The invention relates to the technical field of wastewater treatment, in particular to a flocculating agent for treating papermaking wastewater. The problem that fine suspended solids (SS) and soluble lignin derivatives in the papermaking wastewater cannot be simultaneously removed by a traditional flocculant is solved. The flocculant comprises a component A and a component B, the component A comprises a zirconium-silicate-chitosan copolymer and modified chitosan quaternary ammonium salt, soluble lignin is captured by utilizing zirconium site specificity on polyzirconium silicate, and the flocculant is endowed with extremely high positive charge density and chelation function; the component A comprises a component A and a component B, the component B comprises an amphoteric starch grafted copolymer and a nano composite material, during use, the component A is firstly added to capture chromaticity and neutralize SS, then the component B is added, the component A and the SS are bridged by using anion and cation groups of the amphoteric starch grafted copolymer, and the nano composite material is used for net capture and weight increment; through the synergistic effect of multiple modified substances, the turbidity, chromaticity and COD of the papermaking wastewater are synchronously and efficiently removed.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a flocculant for treating papermaking wastewater. Background Technology

[0002] The paper industry is an important global industry, but its production process generates a large amount of wastewater. Paper wastewater (especially chemical pulping and intermediate stage water) has a complex composition of pollutants, which is usually characterized by high chemical oxygen demand (COD), high suspended solids (SS) and high color.

[0003] In existing technologies, flocculation and sedimentation is one of the most commonly used and economical pretreatment or advanced treatment methods for papermaking wastewater. However, papermaking wastewater contains not only a large amount of anionic fine suspended solids (such as short fibers, inorganic fillers such as calcium carbonate or kaolin fragments), but also a large amount of dissolved organic matter (DOM), especially lignin and its derivatives (such as lignin sulfonates). These soluble lignins are the main source of the wastewater's high color and are themselves anionic polymers. In wastewater, soluble anionic lignin and anionic fine suspended solids have a synergistic stabilizing effect. On the one hand, soluble lignin adsorbs onto the surface of fine suspended solids, enhancing their surface negative charge and hydration layer, leading to increased electrostatic repulsion between colloidal particles, making the system extremely stable and difficult to settle; on the other hand, fine suspended solids also provide a dispersion carrier for soluble lignin. Traditional flocculants, such as polyaluminum chloride (PAC) or cationic polyacrylamide (CPAM), have shown significant shortcomings in treating this type of wastewater.

[0004] While inorganic flocculants such as PAC can remove some suspended solids through charge neutralization, they are very ineffective at removing soluble lignin. To remove color, extremely high dosages are required, resulting in a large amount of chemical sludge and low effluent pH. Organic flocculants such as CPAM mainly rely on adsorption bridging, which has a good effect on removing suspended solids, but they can hardly remove soluble lignin. Even when PAC and CPAM are used in combination, they often cannot efficiently "capture" soluble lignin and "net" fine suspended solids simultaneously due to their single function, resulting in high dosage, high total treatment cost, and difficulty in consistently meeting effluent quality standards, especially the requirements for reclaimed water reuse.

[0005] Therefore, developing a novel flocculant capable of simultaneously and efficiently removing anionic fine suspended solids and soluble lignin derivatives from papermaking wastewater is a pressing technical challenge in this field. To address this, a flocculant for treating papermaking wastewater is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a flocculant for treating papermaking wastewater.

[0007] To achieve the above objectives, the present invention provides the following technical solution: Unless otherwise specified, all parts in this invention are parts by weight; all chitosan used in this invention is the same type of chitosan.

[0008] This invention provides a flocculant for treating papermaking wastewater, the flocculant comprising component A and component B; Component A is a composite coagulant; the composite coagulant includes a zirconium-silicate-chitosan copolymer and a modified chitosan quaternary ammonium salt; the raw materials for preparing the modified chitosan quaternary ammonium salt include chitosan, glycidyltrimethylammonium chloride, disodium ethylenediaminetetraacetate, and carbodiimide; Component B is a composite flocculant; the composite flocculant includes amphoteric starch graft copolymers and nanocomposite materials; The nanocomposite material includes sodium bentonite, acrylamide, and the cationic monomer diallyl dimethyl ammonium chloride.

[0009] Preferably, the zirconium-silicate-chitosan copolymer is prepared by the following steps: 100 parts of a sodium silicate solution with a modulus of 3.3 (containing 25% SiO2) are added to 1100 parts of deionized water and stirred. The mixture is heated to 30°C, and 20 wt% sulfuric acid solution is added dropwise to adjust the pH to 4.5, thus obtaining an activated silica sol. 50 parts of zirconium oxychloride are dissolved in 100 parts of deionized water to prepare a zirconium solution. The zirconium solution is then added dropwise to the activated silica sol, maintaining the pH between 4.0 and 4.5 (adjusted with sodium hydroxide solution) during the addition process. After the reaction was completed, the temperature was raised to 60℃ for 2 hours and then cooled to room temperature to obtain a polyzirconia intermediate. 10 parts of chitosan (viscosity 100-200 mPa·s, degree of deacetylation 90%) were added to 400 parts of deionized water, 1 wt% acetic acid was added to completely dissolve it, and 1 part of silane coupling agent KH-560 was added. The mixture was stirred at 45℃ for 30 minutes to obtain a chitosan solution. The polyzirconia intermediate was added to the chitosan solution and reacted at 50℃ for 2-3.5 hours. After cooling, a zirconium-silicate-chitosan copolymer was obtained.

[0010] Preferably, the modified chitosan quaternary ammonium salt is prepared by the following steps: 20 parts of chitosan are dissolved in 400 parts of 2wt% acetic acid solution, 30 parts of glycidyltrimethylammonium chloride are added, and the mixture is reacted at 70°C for 5-7 hours to obtain a chitosan quaternary ammonium salt solution; 10 parts of disodium ethylenediaminetetraacetate and 5 parts of carbodiimide (specifically EDC) are added, and the mixture is reacted at room temperature for 6 hours to graft disodium ethylenediaminetetraacetate onto the chitosan quaternary ammonium salt; after purification using a dialysis bag, the mixture is freeze-dried to obtain the modified chitosan quaternary ammonium salt.

[0011] Preferably, component A is prepared by mixing 100 parts of zirconium-silicate-chitosan copolymer and 2-5 parts of modified chitosan quaternary ammonium salt, and then adding 600 parts of deionized water and 5 parts of stabilizer sorbitol.

[0012] Preferably, the amphoteric starch graft copolymer is prepared by the following steps: 100 parts of cassava starch are added to 500 parts of deionized water, sodium hydroxide is added to adjust the pH to 11, 20 parts of cationic etherifying agent 3-chloro-2-hydroxypropyltrimethylammonium chloride (CMA) are added, and the mixture is reacted at 45°C for 4 hours. After washing, neutralization, and drying, cationic starch is obtained. 50 parts of cationic starch are added to 500 parts of deionized water, and the mixture is heated to 90°C for gelatinization. After cooling to 70°C, nitrogen gas is introduced to remove oxygen for 30 minutes to obtain a gelatinized liquid. 10 parts of acrylic acid monomer are taken, and sodium hydroxide solution is added dropwise under ice bath to adjust the neutralization degree to 60%-80%. After mixing with 1 part of ammonium persulfate initiator, the mixture is added dropwise to the gelatinized liquid and reacted for 2-4 hours. After cooling, the mixture is washed with ethanol, dried, and pulverized to obtain the amphoteric starch graft copolymer.

[0013] Preferably, the nanocomposite material is prepared by the following steps: 12-20 parts of sodium-based bentonite are added to 1000 parts of deionized water, and the mixture is stirred at high speed at 2000 rpm for 2 hours. Then, 15 parts of acrylamide and 10 parts of cationic monomer dimethyl diallyl ammonium chloride (DMDAAC) are added, nitrogen gas is introduced to remove oxygen for 30 minutes, 0.2 parts of ammonium persulfate initiator are added, and the mixture is heated to 65°C and reacted for 5 hours to carry out in-situ intercalation polymerization to obtain the nanocomposite material.

[0014] Preferably, component B is prepared by mixing 15-30 parts of amphoteric starch graft copolymer and 10 parts of nanocomposite material, and then compounding in 1200 parts of deionized water.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention utilizes a zirconium-silicate-chitosan copolymer as the core coagulation component. By leveraging the strong specific complexing affinity of zirconium ions for oxygen-containing groups such as phenolic hydroxyl and carboxyl groups in the molecular structure of lignin and its derivatives, it can precisely capture soluble organic pigments in wastewater that are difficult to remove through traditional charge neutralization and transform them into insoluble complexes. Simultaneously, the polysilicic acid framework provides a stable inorganic core for this complexation, enhancing the rigidity of the microflocs, while the chitosan segments improve the dispersion efficiency of the agent in the aqueous phase. This multi-site complexation mechanism overcomes the shortcomings of conventional aluminum and iron salt coagulants, such as weak lignin adsorption capacity and high dosage, and solves the problem of high color and difficult degradation of papermaking wastewater.

[0016] 2. This invention, by introducing modified chitosan quaternary ammonium salt, endows the flocculant with extremely high positive charge density and chelating function. The high density of positive charge can rapidly compress the electric double layer on the surface of fine fibers and inorganic fillers in papermaking wastewater, greatly weakening the electrostatic repulsion between colloids and causing suspended particles to quickly destabilize and aggregate. In addition, the modified chitosan quaternary ammonium salt, as a dispersant and charge enhancer, can assist the zirconium-silicate-chitosan copolymer in better dispersion and action in water.

[0017] 3. This invention utilizes the unique structure of amphoteric starch graft copolymers to play a crucial "targeted bridging" role in the flocculation process. Because this component contains both cationic and anionic groups, it can not only continue to adsorb residual anionic impurities in wastewater through its cationic groups, but also utilize its anionic side chains to undergo secondary chemical bonding and electro-adsorption with the previously formed positively charged zirconium-lignin complex. This unique "molecular stitching" mechanism tightly connects the originally dispersed, fine, and loosely structured microflocs into a stable macromolecular network structure through chemical bonds and physical adsorption, effectively preventing the flocs from breaking down and disintegrating under strong water flow disturbance, thus laying a solid structural foundation for subsequent efficient solid-liquid separation.

[0018] 4. This invention solves the technical problem of light and difficult-to-settle flocs in papermaking wastewater by introducing bentonite / cationic polyacrylamide intercalated nanocomposite materials. This composite material has a unique "core-shell" structure, with high-density bentonite sheets as the "weighting core" and surface-grafted long-chain polymers as the "net-catching arms." In the later stages of the flocculation reaction, the extended polymer chains can rapidly capture all suspended micro-flocs in the system, and the gravity of the weighting core drives the flocs to settle quickly, shortening the settling time and increasing the hydraulic load of the settling tank.

[0019] 5. This invention employs a unique sequential dosing strategy for components A and B, achieving efficient stepwise removal of complex pollutants from papermaking wastewater. Component A is added first, focusing on the "chemical capture" of dissolved organic matter and the destabilization of colloids, while component B is added later, focusing on the "physical trapping" of flocs and promoting sedimentation. This stepwise synergistic mechanism avoids competition and interference between multiple functions (such as charge neutralization and adsorption bridging) of a single agent in a complex system, ensuring that each modified substance can exert its maximum efficiency at the optimal reaction stage, thus solving the problem of simultaneous removal of suspended solids (SS) and soluble lignin. Attached Figure Description

[0020] Figure 1 The graphs show the test results of color removal rate and COD removal rate in Examples 1-5 of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0022] Please see Figure 1This invention provides a flocculant for treating papermaking wastewater, the technical solution of which is as follows: Example 1 100 parts of a sodium silicate solution with a modulus of 3.3 (containing 25% SiO2) were added to 1100 parts of deionized water and stirred. The mixture was heated to 30°C, and the pH was adjusted to 4.5 by adding 20 wt% sulfuric acid solution dropwise to obtain an activated silica sol. 50 parts of zirconium oxychloride were dissolved in 100 parts of deionized water to prepare a zirconium solution. This zirconium solution was added dropwise to the activated silica sol, maintaining the pH between 4.0 and 4.5 (adjusted with sodium hydroxide solution) during the addition. After the addition was complete, the temperature was raised to 60°C. The reaction was carried out for 2 hours and then cooled to room temperature to obtain a polyzirconia intermediate. 10 parts of chitosan (viscosity 100-200 mPa·s, degree of deacetylation 90%) were added to 400 parts of deionized water, 1 wt% acetic acid was added to completely dissolve it, and 1 part of silane coupling agent KH-560 was added. The mixture was stirred at 45°C for 30 minutes to obtain a chitosan solution. The polyzirconia intermediate was added to the chitosan solution and reacted at 50°C for 2 hours. After cooling, a zirconium-silicate-chitosan copolymer was obtained.

[0023] 20 parts of chitosan were dissolved in 400 parts of 2wt% acetic acid solution, and 30 parts of glycidyltrimethylammonium chloride were added. The mixture was reacted at 70℃ for 5 h to obtain a chitosan quaternary ammonium salt solution. 10 parts of disodium ethylenediaminetetraacetate and 5 parts of carbodiimide (specifically EDC) were added, and the mixture was reacted at room temperature for 6 h. After purification using a dialysis bag, the mixture was freeze-dried to obtain the modified chitosan quaternary ammonium salt.

[0024] After mixing 100 parts of zirconium-silicate-chitosan copolymer and 2 parts of modified chitosan quaternary ammonium salt, 600 parts of deionized water and 5 parts of stabilizer sorbitol were added to obtain a composite coagulant, which is component A. 100 parts of cassava starch were added to 500 parts of deionized water, and sodium hydroxide was added to adjust the pH to 11. 20 parts of cationic etherifying agent 3-chloro-2-hydroxypropyltrimethylammonium chloride (CMA) were added, and the mixture was reacted at 45°C for 4 hours. After washing, neutralization, and drying, cationic starch was obtained. 50 parts of cationic starch were added to 500 parts of deionized water, and the mixture was heated to 90°C for gelatinization. The temperature was then lowered to 70°C, and nitrogen gas was introduced to remove oxygen for 30 minutes to obtain a gelatinized liquid. 10 parts of acrylic acid monomer were taken, and sodium hydroxide solution was added dropwise under ice bath to adjust the neutralization degree to 60%. The mixture was mixed with 1 part of ammonium persulfate initiator and added dropwise to the gelatinized liquid for 2 hours. After cooling, the mixture was washed with ethanol, dried, and pulverized to obtain an amphoteric starch graft copolymer.

[0025] 12 parts of sodium-based bentonite were added to 1000 parts of deionized water and stirred at 2000 rpm for 2 hours. Then, 15 parts of acrylamide and 10 parts of cationic monomer diallyl dimethyl ammonium chloride (DMDAAC) were added. Nitrogen gas was introduced to remove oxygen for 30 minutes. Then, 0.2 parts of ammonium persulfate initiator were added and the mixture was heated to 65°C and reacted for 5 hours to obtain the nanocomposite material.

[0026] A composite flocculant, component B, was obtained by mixing 15 parts of amphoteric starch graft copolymer and 10 parts of nanocomposite material and then compounding it in 1200 parts of deionized water.

[0027] The flocculant consists of component A and component B.

[0028] Examples 2-5

[0029] The preparation method and parameters of Example 1 are as follows, with specific differences shown in Table 1. In Table 1, reaction time 1 is the reaction time when the polyzirconium silicate intermediate is added to the chitosan solution; reaction time 2 is the reaction time when preparing the chitosan quaternary ammonium salt solution; and reaction time 3 is the reaction time when the neutralized acrylic monomer and initiator are mixed and added dropwise to the gelatinized liquid during the preparation of the amphoteric starch graft copolymer.

[0030] Table 1 Specific preparation parameters for Examples 2-5

[0031] Comparative Example 1

[0032] The preparation method and parameters of Example 1 are the same, except that after the polyzirconium silicate intermediate is prepared, it is not grafted onto the chitosan molecular chain, but chitosan is added separately to component A.

[0033] Comparative Example 2

[0034] The preparation method and parameters of Example 1 are the same, except that zirconium-silicate-chitosan copolymer was not added to component A.

[0035] Comparative Example 3

[0036] The preparation method and parameters were the same as in Example 1, except that disodium ethylenediaminetetraacetate was not grafted onto the chitosan quaternary ammonium salt.

[0037] Comparative Example 4

[0038] The preparation method and parameters are the same as in Example 1, except that no modified chitosan quaternary ammonium salt is added to component A.

[0039] Comparative Example 5

[0040] The preparation method and parameters were the same as in Example 1, except that the cassava starch was not cationized or modified with acrylic acid grafting.

[0041] Comparative Example 6

[0042] The preparation method and parameters of Example 1 were used, except that the cassava starch was not cationicized when preparing the amphoteric starch graft copolymer.

[0043] Comparative Example 7

[0044] The preparation method and parameters of Example 1 are the same, except that the amphoteric starch graft copolymer was not added to component B.

[0045] Comparative Example 8

[0046] The preparation method and parameters of Example 1 are the same, except that sodium-based bentonite is physically mixed with polyacrylamide-cationic monomer copolymer generated separately, which is used as component B.

[0047] Comparative Example 9

[0048] The preparation method and parameters of Example 1 were used, except that no nanocomposite material was added to component B.

[0049] Comparative Example 10

[0050] The preparation method and parameters are the same as in Example 1, except that the flocculant in this application only includes component A.

[0051] Comparative Example 11

[0052] The preparation method and parameters are the same as in Example 1, except that the flocculant in this application only includes component B.

[0053] Comparative Example 12

[0054] Only 400 mg / L PAC and 5 mg / L CPAM were used in combination.

[0055] Experimental Example

[0056] 1000 mL of papermaking wastewater with the following characteristics was collected: turbidity 350 NTU, color 600 times, COD 850 mg / L, and pH 7.5. The wastewater was added to a beaker and placed on a six-piece stirrer at 200 rpm. Component A was added at a concentration of 150 mg / L, and the mixture was stirred for 2 minutes. The stirring speed was then reduced to 60 rpm, and component B was added at a concentration of 30 mg / L, followed by stirring for 5 minutes. Stirring was stopped, and the mixture was allowed to settle for 10 minutes. The supernatant was then collected for analysis. For Comparative Example 12, PAC was first added to the wastewater, and the mixture was stirred at 200 rpm for 2 minutes. The stirring speed was then reduced to 60 rpm, and CPAM was added, followed by stirring for 5 minutes. Subsequent steps were the same. The results are shown in Table 2 and... Figure 1 As shown.

[0057] Table 2 Wastewater treatment effect test of Examples 1-5 and Comparative Examples 1-12

[0058] From Table 2 and Figure 1 As can be seen, in Examples 1-5, the zirconium-silicate-chitosan copolymer and modified chitosan quaternary ammonium salt in component A are key to achieving efficient capture of anionic pollutants. They enhance charge neutralization and pollutant selectivity through organic-inorganic synergy and chelation-adsorption synergy, respectively. The amphoteric starch graft copolymer and nanocomposite material in component B enhance bridging aggregation and adsorption capacity, which is the core for achieving rapid sedimentation of flocs. The two-stage synergistic effect of "charge neutralization-bridging aggregation" between components A and B, as well as the structural complementarity of each modified component, makes the turbidity removal rate, color removal rate and COD removal rate of the examples significantly better than those of the comparative examples and traditional agents. In particular, the removal effect on anionic fine suspended matter and soluble lignin derivatives is outstanding, with a turbidity removal rate of 95.3%-97.3%, a color removal rate of 93.6%-94.5%, and a COD removal rate of 85.0%-86.2%.

[0059] In Comparative Example 1, after preparing the polyzirconium silicate intermediate, it was not grafted onto the chitosan molecular chain. Although component A still contained polyzirconium silicate and chitosan, the color removal rate decreased compared to Example 1, indicating that the grafting process is crucial. Grafting prevents phase separation between inorganic and organic components, and utilizes the chitosan chains to "extend" Zr sites into the water, improving capture efficiency. In contrast, during physical mixing, PZS is prone to self-aggregation and deactivation, failing to exert a synergistic effect. In Comparative Example 2, without the addition of the zirconium-silicate-chitosan copolymer to component A, the color removal rate was significantly reduced. This fully demonstrates that the zirconium-silicate-chitosan copolymer is the key active ingredient for removing soluble lignin (color). Without the specific complexation of Zr sites, ordinary flocculants cannot capture soluble organic matter.

[0060] After chitosan quaternary ammonium salt is grafted with disodium ethylenediaminetetraacetate, it can remove Fe complexed with lignin derivatives in papermaking wastewater through chelation. 3+ Ca2 + Metal ions disrupt the stable structure of lignin, making it more easily adsorbed. In Comparative Example 3, disodium ethylenediaminetetraacetate was not grafted onto the chitosan quaternary ammonium salt, making it difficult for the lignin derivative to destabilize, resulting in lower data than in Example 1. In Comparative Example 4, no modified chitosan quaternary ammonium salt was added to component A, and all indicators decreased, indicating that this substance provided the necessary positive charge density, assisting in the destabilization of the colloid.

[0061] In Comparative Example 5, the cassava starch was not cationized or modified with acrylic acid grafting. Unmodified starch has no charge and cannot adsorb micro-flocs, thus losing its bridging function and reducing the turbidity removal rate. In Comparative Example 6, the cassava starch was not cationized during the preparation of the amphoteric starch graft copolymer, resulting in only anionic modification. The effect was not as good as in Example 1, confirming the necessity of the amphoteric structure: cationic groups capture residual anionic suspended matter, and anionic groups "chemically stitch" with Zr in component A. The absence of the cationic portion weakens the ability to capture fine suspended solids (SS). In Comparative Example 7, no amphoteric starch graft copolymer was added to component B, resulting in the lack of an "intermediate bridging agent." The tiny flocs were difficult to aggregate into large particles, leading to turbidity in the supernatant.

[0062] In Comparative Example 8, sodium-based bentonite was physically mixed with a separately polymerized polyacrylamide-cationic monomer copolymer as component B. Using physical mixing, the bentonite maintained its original agglomerated state, with most adsorption sites encapsulated within the agglomerates, preventing effective contact with anionic fine suspended matter and soluble lignin derivatives. Furthermore, the synergistic effect between the polymer and bentonite was absent, the bridging effect was weakened, and the floc structure was loose with slow sedimentation. In Comparative Example 9, no nanocomposite material was added to component B, and there was no "weighting agent." The flocs were light and the solid-liquid separation was incomplete.

[0063] In Comparative Examples 10 and 11, the effects of using component A alone or component B alone were far lower than those of using them in combination. When using A alone, the resulting microflocs were too small to settle (low turbidity removal rate); when using B alone, due to the lack of charge neutralization and specific complexation, the negatively charged lignin and SS remained unstable, making it difficult to form effective flocs. This demonstrates the indivisibility of the sequential addition of components A and B in this invention. In Comparative Example 12, the combined use of 400 mg / L PAC and 5 mg / L CPAM showed some effect on turbidity with conventional reagents, but its removal capacity for color and COD was far lower than that of this invention.

[0064] 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 flocculant for treating papermaking wastewater, characterized in that: the flocculant comprises component A and component B; the component A is a composite coagulant; the composite coagulant comprises a zirconium-silicate-chitosan copolymer and a modified chitosan quaternary ammonium salt; the modified chitosan quaternary ammonium salt is prepared from chitosan, glycidyltrimethylammonium chloride, disodium ethylenediaminetetraacetate and carbodiimide; the component B is a composite flocculant; the composite flocculant comprises an amphoteric starch graft copolymer and a nanocomposite; the nanocomposite is prepared from sodium-based bentonite, acrylamide and diallyldimethylammonium chloride. The zirconium-silicate-chitosan copolymer is prepared by the following steps: adding a sodium silicate solution into deionized water and stirring, adjusting the pH value after heating, and obtaining an activated silicic acid sol; adding a zirconium solution dropwise into the activated silicic acid sol, heating and curing the reaction after the dropwise addition is completed, and cooling to room temperature to obtain a zirconium polysilicate intermediate; adding chitosan into the deionized water, adding acetic acid, adding a silane coupling agent, and stirring to obtain a chitosan solution; adding the zirconium polysilicate intermediate into the chitosan solution for reaction, and cooling to obtain the zirconium-silicate-chitosan copolymer. The modified chitosan quaternary ammonium salt is prepared by the following steps: dissolving the chitosan in an acetic acid solution, adding the glycidyltrimethylammonium chloride for reaction to obtain a chitosan quaternary ammonium salt solution, adding the disodium ethylenediaminetetraacetate and the carbodiimide for reaction at room temperature, and freeze-drying after purification to obtain the modified chitosan quaternary ammonium salt. The component A is obtained by mixing the zirconium-silicate-chitosan copolymer and the modified chitosan quaternary ammonium salt, and then adding deionized water and sorbitol for compounding. The amphoteric starch graft copolymer is prepared by the following steps: adding cassava starch into deionized water, adjusting the pH value, adding a cationic etherifying agent for reaction, washing, neutralizing, and drying to obtain cationic starch; adding the cationic starch into the deionized water, heating and gelatinizing; cooling, purging oxygen with nitrogen, adding acrylic acid monomer and ammonium persulfate for reaction, washing and drying after cooling, and crushing to obtain the amphoteric starch graft copolymer.

2. The flocculating agent for treating papermaking wastewater according to claim 1, characterized by: The nanocomposite is prepared by the following steps: adding the sodium-based bentonite into deionized water and stirring, adding the acrylamide and the diallyldimethylammonium chloride, purging oxygen with nitrogen, and adding ammonium persulfate for reaction to obtain the nanocomposite.

3. The flocculating agent for treating papermaking wastewater according to claim 1, characterized by: The component B is obtained by mixing the amphoteric starch graft copolymer and the nanocomposite, and then compounding in deionized water.

4. The flocculating agent for treating papermaking wastewater according to claim 1, characterized by: ​ 5. The flocculating agent for treating papermaking wastewater according to claim 1, characterized by: ​ 6. The flocculating agent for treating papermaking wastewater according to claim 1, characterized by: ​ 7. The flocculating agent for treating papermaking wastewater according to claim 1, characterized by: ​

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