Composite flocculant for sludge sedimentation treatment and preparation method thereof

Abstract

The invention discloses a composite flocculant for sludge sedimentation treatment and a preparation method thereof, and belongs to the technical field of sewage treatment.The composite flocculant is specifically prepared from, by weight, 60-80 parts of composite polyamide and 8-21 parts of auxiliary additive, double bonds are modified on polyaluminum ferric silicate, and the composite flocculant serves as a supporting structure of the composite polyamide and also serves as an auxiliary additive. A cation structure is introduced on a polyamide chain segment through free radical addition, a fluorine group on polyamide enhances the stability of the polyamide in a corrosive solution, a siloxane chain segment enhances the compatibility of the polyamide and inorganic sludge, and phosphonium salt, quaternary ammonium salt and polyaluminum ferric silicate cooperate with each other to enhance the flocculation performance. And finally, the composite flocculant with excellent flocculation effect and stability is prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and in particular to a composite flocculant for sludge sedimentation treatment and a preparation method thereof. Background Art

[0002] The application of composite flocculants in sludge sedimentation treatment has experienced significant development. Initially, although single-type flocculants could effectively promote sedimentation, their flocculation effect and stability under complex water conditions were poor, making it difficult to meet the needs of large-scale water treatment. With the emergence of composite flocculants, the combination of different chemical components has improved the flocculation effect, making it more adaptable when treating multiple pollutants.

[0003] In recent years, the technology of composite flocculants has further developed, especially in terms of stability and high efficiency. The new composite flocculants can not only maintain a good flocculation effect under extreme conditions, but also respond to changes in water quality through intelligent adjustment. With the improvement of environmental protection requirements, composite flocculants will play an increasingly important role in the field of sludge treatment in the future. They can not only improve treatment efficiency, but also reduce energy consumption and chemical use, and develop in the direction of high efficiency and stability.

[0004] For example, the prior art CN118791212B discloses a composite flocculant for sludge dewatering, a preparation method and an application thereof, which specifically include the following steps: S1, preparing an inorganic flocculant A: mixing 30-40 parts of a polyferric silicate solution with 10-15 parts of a polydiallyldimethylammonium chloride liquid to obtain an inorganic flocculant A; S2, preparing an organic flocculant B: S201, mixing 15-20 parts of activated carbon with 30-40 parts of wood ash, adding 10-15 parts of cationic polyacrylamide to the first mixture under stirring, and mixing evenly to obtain a first mixture; S202, dissolving 5-15 parts of a composite modifier in deionized water, and adding the first mixture under stirring to obtain an organic flocculant B, so as to solve the problem of low efficiency of using flocculants for sludge dewatering and pollutant removal in related technologies.

[0005] However, the above invention only achieves the effect of sludge dewatering and flocculation by preparing inorganic flocculant A and organic flocculant B and adding them in batches. However, the flocculant is added in batches through organic and inorganic flocculants. The metal hydroxide colloid generated after the inorganic flocculant is dispersed in the water body will preferentially adsorb on the surface of the particles, occupying the active sites that the organic flocculant molecules can originally bind to, resulting in the bridging ability of the organic flocculant being limited, thereby reducing the flocculation efficiency of the organic flocculant, and the timing of addition will affect the flocculation effect of this flocculant. The organic flocculant also lacks a supporting carrier, which leads to its reduced stability and dispersibility in corrosive water bodies. Therefore, the flocculation effect and stability of the existing flocculants need to be further improved. Summary of the Invention

[0006] The object of the present invention is to provide a composite flocculant for sludge sedimentation treatment and a preparation method thereof, so as to solve the technical problem in the prior art that the flocculation effect and stability of flocculants need to be further improved.

[0007] The object of the present invention can be achieved by the following technical solution: A composite flocculant for sludge sedimentation treatment, comprising the following raw materials in parts by weight: 60-80 parts of composite polyamide and 8-21 parts of auxiliary additives;

[0008] The preparation method of the composite polyamide comprises the following steps:

[0009] The hybrid polyamide, micropowder carrier, diallyldimethylammonium chloride and dimethyl sulfoxide are added to the reactor, the temperature of the reactor is increased to 60-80°C, and after stirring for 10-15 minutes, azobisisobutyronitrile is added to the reactor, and the reaction is carried out for 2-4 hours, and the composite polyamide is obtained by post-treatment.

[0010] The reaction principle for preparing composite polyamide is as follows: the double bonds on the hybrid polyurethane, the double bonds on the micropowder carrier and the double bonds on diallyldimethylammonium chloride undergo free radical addition reaction under the catalysis of a free radical initiator to form a spatial segment structure, and finally prepare composite polyamide.

[0011] Furthermore, the auxiliary additives include the following raw materials in parts by weight: 5-8 parts of a sustained-release agent, 1-5 parts of a surfactant, 1-5 parts of a stabilizer, and 1-3 parts of a thickener;

[0012] Furthermore, the corrosion inhibitor is one or both of polyvinyl alcohol and polyacrylamide; the surfactant is one or both of sodium dodecylbenzenesulfonate and hexadecyltrimethylammonium chloride; the stabilizer is one or both of sodium citrate and polyvinylpyrrolidone; and the thickener is one or both of glycerol and sodium carboxymethyl cellulose.

[0013] Furthermore, the amount ratio of the hybrid polyamide, the micropowder carrier, diallyldimethylammonium chloride, dimethyl sulfoxide and azobisisobutyronitrile is 8-10g:1-2g:0.6-0.8g:40-50mL:0.2-0.3g, and the post-treatment includes: after the reactor is cooled to room temperature, the reaction liquid is added to a rotary evaporator with a water bath temperature of 80-100°C, and reduced pressure distillation is performed until no liquid is extracted to obtain a composite polyamide.

[0014] Furthermore, the preparation method of the hybrid polyamide comprises the following steps:

[0015] A1. Add modified polyamide, triethoxysilyl butyraldehyde, 4,4,4-trifluoro-2-butanone, γ-alumina and dimethyl sulfoxide into a reactor, increase the temperature of the reactor to 60-80° C., keep the temperature for reaction for 1-2 hours, and perform post-treatment to obtain chain-extended polyamide;

[0016] A2. Add chain-extended polyamide and dimethyl sulfoxide into a reactor, raise the temperature of the reactor to 60-80°C, keep warm and stir for 10-12 minutes, add allyl bromide into the reactor, keep warm and stir for 6-8 hours, and perform post-treatment to obtain a hybrid polyamide.

[0017] The reaction equation for preparing hybrid polyamide is:

[0018]

[0019] Where: “*” indicates the active linking site of the organic chain segment.

[0020] The reaction principle for preparing hybrid polyamide is as follows: under the catalysis of Lewis acid, triethoxysilylbutyraldehyde is protonated, and the secondary amine group attacks the carbonyl carbon of the triethoxysilylbutyraldehyde to form an unstable imine structure. Under acidic conditions, the α-hydrogen of 4,4,4-trifluoro-2-butanone is deprotonated to form an unstable enol or enol anion structure, thereby attacking the imine structure to prepare the chain-extended polyamide. The tertiary amine group and tertiary phosphorus group on the chain-extended polyamide act as strong nucleophiles, and the lone pair electrons on the nitrogen and phosphorus atoms attack the carbon atom on the allyl bromide. The bromine group on the allyl bromide acts as a leaving group and falls off under the nucleophilic attack to form a bromide ion. After the reaction, a positively charged tetrasubstituted nitrogen cation and phosphorus cation are finally formed, and the hybrid polyamide is finally obtained.

[0021] Furthermore, in step A1, the amount ratio of modified polyamide, triethoxysilylbutyraldehyde, 4,4,4-trifluoro-2-butanone, γ-alumina and dimethyl sulfoxide is 5-6 g:1.1-1.2 g:0.6-0.7 g:0.1-0.2 g:30-36 mL, and the post-treatment includes: after the reactor is cooled to room temperature, the reaction solution is added to a rotary evaporator with a water bath temperature of 80-100° C., and reduced pressure distillation is performed until no liquid is extracted to obtain a chain-extended polyamide;

[0022] Furthermore, in step A2, the ratio of chain-extended polyamide, dimethyl sulfoxide and allyl bromide is 4-5 g:30-32 mL:0.5-0.6 g, and the post-treatment includes: after the reactor is cooled to room temperature, the reaction liquid is added to a rotary evaporator with a water bath temperature of 80-100° C., and the mixture is distilled under reduced pressure until no liquid is extracted to obtain a hybrid polyamide.

[0023] Furthermore, the preparation method of the modified polyamide includes the following steps: adding N,N-dimethylformamide to a reactor and stirring, lowering the temperature of the reactor to 0-5°C, adding bis(4-carboxyphenyl)phenylphosphine oxide to the reactor, keeping warm and stirring for 5-10 minutes, dropwise adding N,N'-dicyclohexylcarbodiimide and N-hydroxysuccinimide to the reactor, keeping warm and stirring for 20-30 minutes, raising the temperature of the reactor to room temperature, continuing to dropwise adding 1,3-propylenediamine to the reactor, keeping warm and stirring for 6-8 hours, and post-treating to obtain the modified polyamide.

[0024] Furthermore, the amount ratio of N,N-dimethylformamide, bis(4-carboxyphenyl)phenylphosphine oxide, N,N'-dicyclohexylcarbodiimide, N-hydroxysuccinimide and 1,3-propylenediamine is 30-40 mL: 4.5-5.5 g: 0.8-1.2 g: 0.3-0.5 g: 0.9-1.1 g, and the post-treatment includes: after the reactor is cooled to room temperature, the reaction liquid is added to a rotary evaporator with a water bath temperature of 80-100°C, and reduced pressure distillation is carried out until no liquid is extracted to obtain a modified polyamide.

[0025] The reaction equation for preparing modified polyamide is:

[0026]

[0027] Where: “*” indicates the active linking site of the organic chain segment.

[0028] The reaction principle for preparing modified polyamide is as follows: N,N'-dicyclohexylcarbodiimide is added to react with carboxyl groups to form an intermediate activated ester, thereby achieving activation of the carboxyl groups on bis(4-carboxyphenyl)phenylphosphine oxide, while N-hydroxysuccinimide enhances the stability of this intermediate product. N,N'-dicyclohexylcarbodiimide and N-hydroxysuccinimide are added to the reactor under low temperature conditions. During this process, the activated carboxyl groups are ready to react with the subsequently added 1,3-propylenediamine to form amide bonds, and finally the modified polyamide is prepared.

[0029] Furthermore, the preparation method of the micropowder carrier comprises the following steps:

[0030] B1. Add propyl orthosilicate and deionized water to a reactor, stir at room temperature for 5-8 minutes, add 30-40 wt% sulfuric acid solution to the reactor, adjust the pH of the system to 3-4, and allow to stand for 1-2 hours to age to obtain an oligomeric silicic acid solution;

[0031] B2. Add ferric sulfate, aluminum sulfate and deionized water to a reactor, raise the temperature of the reactor to 60-80°C, keep stirring for 30-40 minutes, slowly add the oligomeric silicic acid solution to the reactor, keep stirring for 60-80 minutes, cool naturally to room temperature, age naturally for 24-28 hours, and post-treat to obtain a micropowder carrier precursor;

[0032] B3. Add the micropowder carrier precursor, deionized water and anhydrous ethanol into the reactor and stir. Use saturated sodium hydroxide aqueous solution to adjust the pH of the reaction system to 8-9, then increase the temperature of the reactor to 40-60°C, continue to add the modification liquid into the reactor, keep warm and stir for 30-40 minutes, and post-treat to obtain the micropowder carrier.

[0033] The reaction principle for preparing micropowder carriers is as follows: under the catalysis of strong acidic conditions, propyl orthosilicate is hydrolyzed to produce a polysilicic acid structure, and further hydrolyzed with ferric sulfate and aluminum sulfate to produce a gel structure. After low-temperature freezing and drying, a micropowder carrier precursor is obtained. After the micropowder carrier precursor is modified with a silane coupling agent, carbon-carbon double bonds are grafted on its surface to finally prepare a micropowder carrier.

[0034] Furthermore, in step C1, the ratio of propyl silicate to deionized water is 10-12 mL:50-54 mL;

[0035] Furthermore, in step C2, the dosage ratio of ferric sulfate, aluminum sulfate, deionized water and oligosilicic acid solution is 6-8g:4-6g:80-90mL:60-80mL:10-12mL, wherein the modification solution is obtained by mixing 3-(methacryloyloxy)propyltrimethoxysilane and anhydrous ethanol in a dosage ratio of 1-2g:10-12mL, and the post-treatment includes: transferring the aged material to a freezer at a temperature of -20°C and freezing for 12-16h, and then transferring it to a vacuum drying oven and drying it for 36h to obtain a micropowder carrier.

[0036] The present invention also proposes a method for preparing a composite flocculant for sludge sedimentation treatment: adding a composite polyamide, a sustained-release agent, a surfactant and a stabilizer into a stirring tank, heating the stirring tank to 40-60°C, keeping the temperature and stirring until the materials are evenly mixed, continuing to add a thickener into the stirring tank, stopping heating, and continuing stirring until the materials cool to room temperature to obtain a composite flocculant.

[0037] The present invention has the following beneficial effects:

[0038] 1. The polyaluminum ferric silicate component in the composite flocculant prepared by the present invention neutralizes the negative charge on the surface of the sludge colloid through the high positive charge density of aluminum and iron ions, quickly destroying the colloid stability. At the same time, its porous gel structure provides anchor points for the organic polyamide chain to form a three-dimensional cross-linked network. Secondly, the quaternary ammonium salt and phosphate groups introduced by chemical modification of the polyamide chain form a multivalent cation synergistic system with the metal ions in the polyaluminum ferric silicate. The quaternary ammonium salt quickly compresses the colloidal double layer through the strong positive charge, and the phosphate group penetrates the colloidal hydration layer through the three-dimensional space effect. The hydroxyl complex of the aluminum and iron ions further strengthens the adsorption and precipitation effect. The synergistic cooperation of the three significantly enhances the dispersibility of the flocculant. In addition, the rigid skeleton of the polyaluminum ferric silicate limits the disordered extension of the polyamide chain. During the flocculation process, the inorganic core adsorbs the colloid and the organic shell bridges the particles, thereby forming a dense core-shell flocculent structure. The dynamic flexibility of the polyamide chain enhances the capture ability of particles of different particle sizes, thereby improving the flocculation ability of the composite flocculant.

[0039] 2. In the process of preparing the composite flocculant of the present invention, a double bond cross-linking reaction is used to form a stable three-dimensional network structure between the polysilicate aluminum iron powder and the polyamide chain. The rigid skeleton of the powder supports the extension of the polyamide chain, enhances the intermolecular force, and makes the solution have a high surface viscosity, which is easier to adsorb and bridge sludge particles. At the same time, the siloxane groups on the polyamide chain combine with calcium and magnesium ions under alkaline conditions to form a protective layer, preventing the main chain from being destroyed by strong alkali, and maintaining structural stability through dynamic bonding. The strong hydrophobicity and electronegativity of the fluorine group further shield the hydroxide from the erosion of the cationic group, ensuring the charge neutralization ability in an alkaline environment. The three-dimensional cross-linked network also fixes the relative position of the molecular chain through chemical bonds, inhibiting thermal motion under high temperature. The hydrophobic properties of the fluorine group and siloxane jointly reduce moisture penetration and reduce the risk of degradation caused by damp heat, thereby improving the stability of the composite flocculant. DETAILED DESCRIPTION

[0040] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0041] Example 1

[0042] This embodiment provides a method for preparing a micropowder carrier for preparing a composite flocculant for sludge sedimentation treatment, comprising the following steps:

[0043] Step I: Preparation of oligomeric silicic acid solution

[0044] Weigh 100.0 mL of propyl orthosilicate and 500.0 mL of deionized water into a reactor, stir at room temperature for 5 minutes, then add 30 wt % sulfuric acid solution into the reactor, adjust the pH of the system to 3, and allow to stand for 1 hour to age to obtain an oligomeric silicic acid solution.

[0045] Step II: Preparation of micropowder carrier

[0046] Weigh 10.0 g of 3-(methacryloyloxy)propyltrimethoxysilane and 100.0 mL of anhydrous ethanol to obtain a modification solution.

[0047] Weigh: 60.0g ferric sulfate, 40.0g aluminum sulfate and 800.0mL deionized water were added to the reactor, the temperature of the reactor was raised to 60°C, and after stirring for 30 minutes, 600.0mL of oligosilicic acid solution and 100.0mL of modification liquid were slowly added to the reactor, stirred for 60 minutes, cooled naturally to room temperature, and aged naturally for 24 hours. The aged material was transferred to a freezer at -20°C and frozen for 12 hours, and then transferred to a vacuum drying oven and dried for 36 hours to obtain a micropowder carrier precursor.

[0048] Example 2

[0049] This embodiment provides a method for preparing a micropowder carrier for preparing a composite flocculant for sludge sedimentation treatment, comprising the following steps:

[0050] Step I: Preparation of oligomeric silicic acid solution

[0051] Weigh 120.0 mL of propyl orthosilicate and 540.0 mL of deionized water into a reactor, stir at room temperature for 8 minutes, then add 40 wt % sulfuric acid solution into the reactor, adjust the pH of the system to 4, and allow to stand for aging for 2 hours to obtain an oligomeric silicic acid solution.

[0052] Step II: Preparation of micropowder carrier

[0053] Weigh 20.0 g of 3-(methacryloyloxy)propyltrimethoxysilane and mix with 120.0 mL of anhydrous ethanol to obtain a modification solution.

[0054] Weigh: 80.0g of ferric sulfate, 60.0g of aluminum sulfate and 900.0mL of deionized water were added to the reactor, the temperature of the reactor was raised to 80°C, and after stirring for 40 minutes, 800.0mL of oligosilicic acid solution and 120.0mL of modification liquid were slowly added to the reactor, stirred for 80 minutes, cooled naturally to room temperature, and aged naturally for 28 hours. The aged material was transferred to a freezer at -20°C and frozen for 16 hours, and then transferred to a vacuum drying oven and dried for 36 hours to obtain a micropowder carrier precursor.

[0055] Example 3

[0056] This embodiment provides a method for preparing a micropowder carrier for preparing a composite flocculant for sludge sedimentation treatment, comprising the following steps:

[0057] Step I: Preparation of oligomeric silicic acid solution

[0058] Weigh 120.0 mL of propyl orthosilicate and 540.0 mL of deionized water into a reactor, stir at room temperature for 8 minutes, then add 40 wt % sulfuric acid solution into the reactor, adjust the pH of the system to 3, and allow to stand for aging for 2 hours to obtain an oligomeric silicic acid solution.

[0059] Step II: Preparation of micropowder carrier

[0060] Weigh 16.0 g of 3-(methacryloyloxy)propyltrimethoxysilane and 120.0 mL of anhydrous ethanol to obtain a modification solution.

[0061] Weigh: 80.0g of ferric sulfate, 60.0g of aluminum sulfate and 900.0mL of deionized water were added to the reactor, the temperature of the reactor was raised to 70°C, and after stirring for 36 minutes, 720.0mL of oligosilicic acid solution and 120.0mL of modification liquid were slowly added to the reactor, stirred for 70 minutes, cooled naturally to room temperature, and aged naturally for 28 hours. The aged material was transferred to a freezer at -20°C and frozen for 16 hours, and then transferred to a vacuum drying oven and dried for 36 hours to obtain a micropowder carrier precursor.

[0062] Example 4

[0063] This embodiment provides a method for preparing a hybrid polyamide for preparing a composite flocculant for sludge sedimentation treatment, comprising the following steps:

[0064] Step 1: Preparation of modified polyamide

[0065] Weigh: 300.0mL N,N-dimethylformamide was added to the reactor and stirred. After the temperature of the reactor was lowered to 5°C, 45.0g of bis(4-carboxyphenyl)phenylphosphine oxide was added to the reactor. After stirring for 5 minutes, 8.0g of N,N'-dicyclohexylcarbodiimide and 3.0g of N-hydroxysuccinimide were added dropwise to the reactor. After stirring for 20 minutes, the temperature of the reactor was raised to room temperature, and 9.0g of 1,3-propylenediamine was continued to be added dropwise to the reactor. After stirring for 6 hours, the reactor was cooled to room temperature, and the reaction solution was added to a rotary evaporator with a water bath temperature of 80°C, and distilled under reduced pressure until no liquid was recovered to obtain a modified polyamide.

[0066] Step ②, preparation of chain-extended polyamide

[0067] Preparation: 50.0 g of modified polyamide, 11.0 g of triethoxysilylbutyraldehyde, 6.0 g of 4,4,4-trifluoro-2-butanone, 1.0 g of γ-alumina and 300.0 mL of dimethyl sulfoxide were added to a reactor, the reactor temperature was raised to 60°C, and the reaction was kept warm for 2 hours. After the reactor was cooled to room temperature, the reaction liquid was added to a rotary evaporator with a water bath temperature of 80°C, and distilled under reduced pressure until no liquid was extracted to obtain chain-extended polyamide.

[0068] Step ③, preparation of hybrid polyamide

[0069] Weigh: 40.0g of extended chain polyamide and 300.0mL of dimethyl sulfoxide are added to the reactor, the temperature of the reactor is raised to 60°C, and the mixture is stirred at this temperature for 10 minutes. Then, 5.0g of allyl bromide is added to the reactor, and the mixture is stirred at this temperature for 6 hours. After the reactor is cooled to room temperature, the reaction liquid is added to a rotary evaporator with a water bath temperature of 80°C, and distilled under reduced pressure until no liquid is extracted to obtain a hybrid polyamide.

[0070] Example 5

[0071] This embodiment provides a method for preparing a hybrid polyamide for preparing a composite flocculant for sludge sedimentation treatment, comprising the following steps:

[0072] Step 1: Preparation of modified polyamide

[0073] Weigh: 400.0mL N,N-dimethylformamide was added to the reactor and stirred. After the temperature of the reactor was lowered to 0°C, 55.0g of bis(4-carboxyphenyl)phenylphosphine oxide was added to the reactor. After stirring for 10 minutes, 12.0g of N,N'-dicyclohexylcarbodiimide and 5.0g of N-hydroxysuccinimide were added dropwise to the reactor. After stirring for 30 minutes, the temperature of the reactor was raised to room temperature, and 11.0g of 1,3-propylenediamine was continued to be added dropwise to the reactor. After stirring for 8 hours, the reactor was cooled to room temperature, and the reaction solution was added to a rotary evaporator with a water bath temperature of 100°C, and distilled under reduced pressure until no liquid was recovered to obtain a modified polyamide.

[0074] Step ②, preparation of chain-extended polyamide

[0075] Preparation: 60.0 g of modified polyamide, 12.0 g of triethoxysilylbutyraldehyde, 7.0 g of 4,4,4-trifluoro-2-butanone, 2.0 g of γ-alumina and 360.0 mL of dimethyl sulfoxide were added to a reactor, the temperature of the reactor was raised to 80°C, and the reaction was kept warm for 2 hours. After the reactor was cooled to room temperature, the reaction liquid was added to a rotary evaporator with a water bath temperature of 100°C, and distilled under reduced pressure until no liquid was extracted to obtain chain-extended polyamide.

[0076] Step ③, preparation of hybrid polyamide

[0077] Weigh: 50.0g of extended chain polyamide and 320.0mL of dimethyl sulfoxide are added to the reactor, the temperature of the reactor is raised to 80°C, and the mixture is stirred at this temperature for 12 minutes. Then, 6.0g of allyl bromide is added to the reactor, and the mixture is stirred at this temperature for 8 hours. After the reactor is cooled to room temperature, the reaction liquid is added to a rotary evaporator with a water bath temperature of 100°C, and distilled under reduced pressure until no liquid is extracted to obtain a hybrid polyamide.

[0078] Example 6

[0079] This embodiment provides a method for preparing a hybrid polyamide for preparing a composite flocculant for sludge sedimentation treatment, comprising the following steps:

[0080] Step 1: Preparation of modified polyamide

[0081] Weigh: 360.0 mL of N,N-dimethylformamide was added to the reactor and stirred. After the temperature of the reactor was lowered to 3°C, 50.0 g of bis(4-carboxyphenyl)phenylphosphine oxide was added to the reactor. After stirring for 8 minutes, 10.0 g of N,N'-dicyclohexylcarbodiimide and 4.0 g of N-hydroxysuccinimide were added dropwise to the reactor. After stirring for 25 minutes, the temperature of the reactor was raised to room temperature, and 10.0 g of 1,3-propylenediamine was continued to be added dropwise to the reactor. After stirring for 7 hours, the reactor was cooled to room temperature, and the reaction solution was added to a rotary evaporator with a water bath temperature of 90°C, and distilled under reduced pressure until no liquid was recovered to obtain a modified polyamide.

[0082] Step ②, preparation of chain-extended polyamide

[0083] Preparation: 54.0 g of modified polyamide, 11.0 g of triethoxysilylbutyraldehyde, 7.0 g of 4,4,4-trifluoro-2-butanone, 1.6 g of γ-alumina and 320.0 mL of dimethyl sulfoxide were added to a reactor, the temperature of the reactor was raised to 70°C, and the reaction was kept warm for 2 hours. After the reactor was cooled to room temperature, the reaction liquid was added to a rotary evaporator with a water bath temperature of 90°C, and distilled under reduced pressure until no liquid was extracted to obtain chain-extended polyamide.

[0084] Step ③, preparation of hybrid polyamide

[0085] Weigh: 50.0g of extended chain polyamide and 320.0mL of dimethyl sulfoxide are added to the reactor, the temperature of the reactor is raised to 70°C, and the mixture is stirred at this temperature for 12 minutes. Then, 5.4g of allyl bromide is added to the reactor, and the mixture is stirred at this temperature for 7 hours. After the reactor is cooled to room temperature, the reaction liquid is added to a rotary evaporator with a water bath temperature of 90°C, and distilled under reduced pressure until no liquid is extracted to obtain a hybrid polyamide.

[0086] Example 7

[0087] This embodiment provides a method for preparing a composite flocculant for sludge sedimentation treatment, comprising the following steps:

[0088] Step 1: Preparation of composite polyamide

[0089] Weigh: 80.0 g of the hybrid polyamide prepared in Example 4, 10.0 g of the micropowder carrier prepared in Example 1, 6.0 g of diallyldimethylammonium chloride and 400.0 mL of dimethyl sulfoxide were added to the reactor, the temperature of the reactor was raised to 60 ° C, and after stirring for 10 minutes, 2.0 g of azobisisobutyronitrile was added to the reactor, and the reaction was kept warm for 2 hours. After the reactor was cooled to room temperature, the reaction solution was added to a rotary evaporator with a water bath temperature of 80 ° C, and distilled under reduced pressure until no liquid was extracted to obtain a composite polyamide.

[0090] Step 2: Preparation of composite flocculant

[0091] Weigh 60 parts of composite polyamide, 5 parts of polyvinyl alcohol, 1 part of hexadecyltrimethylammonium chloride and 1 part of sodium citrate and add them into a stirring tank. Heat the stirring tank to 40°C, keep stirring until the materials are evenly mixed, then add 1 part of sodium carboxymethyl cellulose into the stirring tank, stop heating, and continue stirring until the materials cool to room temperature to obtain a composite flocculant.

[0092] Example 8

[0093] This embodiment provides a method for preparing a composite flocculant for sludge sedimentation treatment, comprising the following steps:

[0094] Step 1: Preparation of composite polyamide

[0095] Weigh: 100.0 g of the hybrid polyamide prepared in Example 5, 20.0 g of the micropowder carrier prepared in Example 2, 8.0 g of diallyldimethylammonium chloride and 500.0 mL of dimethyl sulfoxide were added to the reactor, the temperature of the reactor was raised to 80° C., and after stirring for 15 minutes, 3.0 g of azobisisobutyronitrile was added to the reactor, and the reaction was kept warm for 4 hours. After the reactor was cooled to room temperature, the reaction solution was added to a rotary evaporator with a water bath temperature of 100° C. and distilled under reduced pressure until no liquid was extracted to obtain a composite polyamide.

[0096] Step 2: Preparation of composite flocculant

[0097] Weigh 80 parts of composite polyamide, 8 parts of polyvinyl alcohol, 5 parts of hexadecyltrimethylammonium chloride and 5 parts of sodium citrate and add them into a stirring tank. Heat the stirring tank to 60°C, keep stirring until the materials are evenly mixed, then add 3 parts of sodium carboxymethyl cellulose into the stirring tank, stop heating, and continue stirring until the materials cool to room temperature to obtain a composite flocculant.

[0098] Example 9

[0099] This embodiment provides a method for preparing a composite flocculant for sludge sedimentation treatment, comprising the following steps:

[0100] Step 1: Preparation of composite polyamide

[0101] Weigh: 90.0 g of the hybrid polyamide prepared in Example 6, 16.0 g of the micropowder carrier prepared in Example 3, 7.2 g of diallyldimethylammonium chloride and 500.0 mL of dimethyl sulfoxide were added to the reactor, the temperature of the reactor was raised to 70 ° C, and after stirring for 15 minutes, 3.0 g of azobisisobutyronitrile was added to the reactor, and the reaction was kept warm for 4 hours. After the reactor was cooled to room temperature, the reaction solution was added to a rotary evaporator with a water bath temperature of 90 ° C, and distilled under reduced pressure until no liquid was extracted to obtain a composite polyamide.

[0102] Step 2: Preparation of composite flocculant

[0103] Weigh 72 parts of composite polyamide, 6 parts of polyvinyl alcohol, 3 parts of hexadecyltrimethylammonium chloride and 3 parts of sodium citrate and add them into a stirring tank. Heat the stirring tank to 50°C, keep stirring until the materials are evenly mixed, then add 2 parts of sodium carboxymethyl cellulose into the stirring tank, stop heating, and continue stirring until the materials cool to room temperature to obtain a composite flocculant.

[0104] Comparative Example 1

[0105] The difference between this comparative example and Example 12 is that, in the process of preparing the hybrid polyamide used, step ② is omitted, and in step ③, an equal amount of modified polyamide is used to replace the hybrid polyamide during the preparation of the hybrid polyamide.

[0106] Comparative Example 2

[0107] The difference between this comparative example and Example 12 is that, in the process of preparing the micropowder carrier used, step III is omitted, and in the process of preparing the composite polyamide, an equal amount of a micropowder carrier precursor is used to replace the micropowder carrier.

[0108] Comparative Example 3

[0109] The difference between this comparative example and Example 12 is that the use of the micropowder carrier is eliminated during the preparation of the composite polyamide.

[0110] Performance testing:

[0111] The apparent viscosity, viscosity in alkaline solution and stability of the composite flocculants prepared in Examples 7-9 and Comparative Examples 1-3 were measured with reference to the standard YS / T 802-2012 "Flocculants for Alumina Production";

[0112] Sludge index test: Pour the treated sludge into a graduated cylinder and let it stand for 20 minutes to obtain a precipitate. Read the volume of the precipitated sludge in the graduated cylinder and record it as V (ml). Take out a petri dish that has been dried to a constant weight and record the mass as m0 (g). Vacuum filter the precipitated sludge, remove the filter cake and place it in a petri dish, dry it to a constant weight, cool it to room temperature, and record the mass as m (g). Calculate the sludge index according to the following formula: Sludge index = V / (m-m0);

[0113] Flocculation rate test: 100 mL of sludge from a municipal sewage treatment plant's thickening tank was measured as the municipal sludge sample, 0.1 g of flocculant was added, and the mixture was rapidly stirred for 1 min, then slowly stirred for 3 min, and allowed to stand for 10 min. 2 mL of supernatant was aspirated with a pipette at 20 mm below the liquid surface in the graduated cylinder, and the absorbance was tested at 550 nm using a spectrophotometer. The flocculation rate = (a0-a) / a0×100%, where a0 is the absorbance value of the original solution of the municipal sludge sample, and a is the absorbance value of the supernatant after flocculant treatment. Specific data are shown in Table 1.

[0114] Table 1 - Performance test data of each sample

[0115]

[0116] Data Analysis:

[0117] Comparative analysis of the data in Table 1 shows that the composite flocculant prepared by the present invention has an apparent viscosity of 825 mPa·s, a viscosity in alkaline solution of 819 mPa·s, is stable for 11 months, and the sludge index of the treated sample is 41.35 mL·g -1 At the same time, the flocculation rate is 99.1%, and all the data are better than the comparative example;

[0118] It is explained that the polyaluminum ferric silicate component in the composite flocculant prepared by the present invention neutralizes the negative charge on the surface of the sludge colloid through the high positive charge density of aluminum and iron ions, quickly destroying the colloid stability. At the same time, its porous gel structure provides anchor points for the organic polyamide chain to form a three-dimensional cross-linked network. Secondly, the quaternary ammonium salt and phosphate groups introduced by chemical modification of the polyamide chain form a multivalent cation synergistic system with the metal ions in the polyaluminum ferric silicate. The quaternary ammonium salt quickly compresses the colloidal double layer through the strong positive charge, and the phosphate group penetrates the colloidal hydration layer through the three-dimensional space effect. The hydroxyl complex of the aluminum and iron ions further strengthens the adsorption and precipitation effect. The synergistic cooperation of the three significantly enhances the dispersibility of the flocculant. In addition, the rigid skeleton of the polyaluminum ferric silicate limits the disordered extension of the polyamide chain. During the flocculation process, the inorganic core adsorbs the colloid and the organic shell bridges the particles, thereby forming a dense core-shell flocculent structure. The dynamic flexibility of the polyamide chain enhances the capture ability of particles of different particle sizes, thereby improving the flocculation ability of the composite flocculant.

[0119] It is explained that in the process of preparing the composite flocculant of the present invention, a double bond cross-linking reaction is used to form a stable three-dimensional network structure between the polysilicate aluminum iron micropowder and the polyamide chain. The rigid skeleton of the micropowder supports the extension of the polyamide chain, enhances the intermolecular force, and makes the solution have a high surface viscosity, which is easier to adsorb and bridge sludge particles. At the same time, the siloxane groups on the polyamide chain combine with calcium and magnesium ions under alkaline conditions to form a protective layer, which prevents the main chain from being destroyed by strong alkali and maintains structural stability through dynamic bonding. The strong hydrophobicity and electronegativity of the fluorine group further shield the corrosion of the cationic group by hydroxide, ensuring the charge neutralization ability in an alkaline environment. The three-dimensional cross-linked network also fixes the relative position of the molecular chain through chemical bonds, inhibiting thermal motion under high temperature. The hydrophobic properties of the fluorine group and siloxane jointly reduce moisture penetration and reduce the risk of degradation caused by wet heat, thereby improving the stability of the composite flocculant.

[0120] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to specific embodiments. Obviously, many modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A composite flocculant for sludge sedimentation treatment, characterized in that: The raw material composition comprises the following parts by weight: 60-80 parts of composite polyamide and 8-21 parts of auxiliary additives; The preparation method of the composite polyamide comprises the following steps: The hybrid polyamide, micropowder carrier, diallyldimethylammonium chloride and dimethyl sulfoxide are added to the reactor, the temperature of the reactor is increased to 60-80°C, and after stirring for 10-15 minutes, azobisisobutyronitrile is added to the reactor, and the reaction is carried out for 2-4 hours, and the composite polyamide is obtained by post-treatment.

2. A composite flocculant for sludge sedimentation treatment according to claim 1, characterized in that: The auxiliary additives include the following raw materials in parts by weight: 5-8 parts of a sustained-release agent, 1-5 parts of a surfactant, 1-5 parts of a stabilizer, and 1-3 parts of a thickener; the usage ratio of the hybrid polyamide, the micropowder carrier, diallyldimethylammonium chloride, dimethyl sulfoxide, and azobisisobutyronitrile is 8-10g:1-2g:0.6-0.8g:40-50mL:0.2-0.3g.

3. A composite flocculant for sludge sedimentation treatment according to claim 1, characterized in that: The preparation method of the hybrid polyamide comprises the following steps: A1. Add modified polyamide, triethoxysilyl butyraldehyde, 4,4,4-trifluoro-2-butanone, γ-alumina and dimethyl sulfoxide into a reactor, increase the temperature of the reactor to 60-80° C., keep the temperature for reaction for 1-2 hours, and perform post-treatment to obtain chain-extended polyamide; A2. Add chain-extended polyamide and dimethyl sulfoxide into a reactor, raise the temperature of the reactor to 60-80°C, keep warm and stir for 10-12 minutes, add allyl bromide into the reactor, keep warm and stir for 6-8 hours, and perform post-treatment to obtain a hybrid polyamide.

4. A composite flocculant for sludge sedimentation treatment according to claim 4, characterized in that: In step A1, the amount ratio of modified polyamide, triethoxysilyl butyraldehyde, 4,4,4-trifluoro-2-butanone, γ-alumina and dimethyl sulfoxide is 5-6g: 1.1-1.2g:0.6-0.7g:0.1-0.2g:30-36mL; in step A2, the usage ratio of chain extended polyamide, dimethyl sulfoxide and allyl bromide is 4-5g:30-32mL:0.5-0.6g.

5. The composite flocculant for sludge sedimentation treatment according to claim 1, characterized in that: The preparation method of the modified polyamide comprises the following steps: adding N,N-dimethylformamide into a reactor and stirring, lowering the temperature of the reactor to 0-5°C, adding bis(4-carboxyphenyl)phenylphosphine oxide into the reactor, keeping warm and stirring for 5-10 minutes, dropwise adding N,N'-dicyclohexylcarbodiimide and N-hydroxysuccinimide into the reactor, keeping warm and stirring for 20-30 minutes, raising the temperature of the reactor to room temperature, continuously adding 1,3-propylenediamine dropwise into the reactor, keeping warm and stirring for 6-8 hours, and performing post-treatment to obtain the modified polyamide.

6. A composite flocculant for sludge sedimentation treatment according to claim 5, characterized in that: The usage ratio of the N,N-dimethylformamide, bis(4-carboxyphenyl)phenylphosphine oxide, N,N'-dicyclohexylcarbodiimide, N-hydroxysuccinimide and 1,3-propylenediamine is 30-40 mL: 4.5-5.5 g: 0.8-1.2 g: 0.3-0.5 g: 0.9-1.1 g.

7. The composite flocculant for sludge sedimentation treatment according to claim 1, characterized in that: The preparation method of the micropowder carrier comprises the following steps: B1. Add propyl orthosilicate and deionized water to a reactor, stir at room temperature for 5-8 minutes, add 30-40 wt% sulfuric acid solution to the reactor, adjust the pH of the system to 3-4, and allow to stand for 1-2 hours to age to obtain an oligomeric silicic acid solution; B2. Add ferric sulfate, aluminum sulfate and deionized water to the reactor, adjust the pH of the reaction system to 8-9 with saturated sodium hydroxide aqueous solution, increase the temperature of the reactor to 60-80°C, keep warm and stir for 30-40 minutes, slowly add oligosilicic acid solution and modification liquid to the reactor, keep warm and stir for 60-80 minutes, cool naturally to room temperature, naturally age for 24-28 hours, and post-treat to obtain the micropowder carrier.

8. The composite flocculant for sludge sedimentation treatment according to claim 7, characterized in that: In step C1, the ratio of propyl silicate to deionized water is 10-12 mL:50-54 mL; in step C2, the ratio of ferric sulfate, aluminum sulfate, deionized water and oligomeric silicic acid solution is 6-8 g:4-6 g:80-90 mL:60-80 mL:10-12 mL, wherein the modification solution is obtained by mixing 3-(methacryloyloxy)propyltrimethoxysilane and anhydrous ethanol in a ratio of 1-2 g:10-12 mL.

9. A method for preparing a composite flocculant for sludge sedimentation treatment according to any one of claims 1 to 8, characterized in that: Add the composite polyamide, sustained-release agent, surfactant and stabilizer into the stirring tank, heat the stirring tank to 40-60°C, keep stirring until the materials are evenly mixed, continue to add the thickener into the stirring tank, stop heating, and continue stirring until the materials cool to room temperature to obtain a composite flocculant.

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