A method for treating wastewater from an aluminium mill

Abstract

The application discloses a method for treating wastewater in an aluminum profile factory, and belongs to the field of wastewater treatment. The method can significantly improve flocculation efficiency and floc settling performance through the synergistic effect of charge neutralization, bridging flocculation, chelation crosslinking and physical enhancement by preparing a composite flocculant. In addition, the method can achieve better treatment effect by combining the multiple effects of physical pore adsorption, chemical complexation and ion exchange of the modified adsorbent on the residual metal ions after flocculation, and has a significant adsorption purification effect. In addition, the treatment agent used by the application is biodegradable and friendly, and will not cause secondary pollution, and has good industrialization popularization value.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, and more specifically, to a method for treating wastewater in an aluminum profile factory. Background Technology

[0002] During the production of aluminum profiles, processes such as degreasing, alkaline etching, pickling, oxidation, coloring, and sealing all generate a large amount of cleaning wastewater. This type of wastewater has a complex composition, typically containing high concentrations of heavy metal ions such as aluminum, fluoride, nickel, and chromium ions, and is either acidic or alkaline. If discharged directly without effective treatment, it will cause serious harm to the ecological environment and human health.

[0003] Currently, the mainstream treatment process for wastewater from aluminum profile factories follows a "neutralization and adjustment - coagulation and sedimentation - solid-liquid separation" technical route. However, traditional treatment methods have many shortcomings: on the one hand, wastewater quality fluctuates greatly, and conventional flocculants have unstable removal effects on different pollutants; on the other hand, a single adsorbent material is difficult to simultaneously and efficiently remove multiple ionic pollutants, and adsorbent regeneration is difficult and prone to secondary pollution. Therefore, developing a method that can efficiently and stably treat comprehensive wastewater from aluminum profile factories is of significant practical importance.

[0004] Several treatment solutions for aluminum profile wastewater have been disclosed in existing technologies. For example, Chinese patent CN116514306A discloses a method for treating wastewater from an aluminum profile production line. This involves discharging alkaline and acidic wastewater into a collection tank, allowing it to settle, adding a treatment agent, and then filtering it through a sand-carbon mixture before reuse. The treatment agent in this method includes a composite material of Mg(OH)2 nanosheets coated on the surface of spherical Fe3O4 and a tantalum pentachloride ion hybrid microporous material. Although this method achieves wastewater recycling, its treatment agent preparation process is complex and costly, and its ability to remove fluoride ions and organic pollutants from the wastewater is limited, making it difficult to meet increasingly stringent emission standards. Another example is Chinese patent CN101293717A, which discloses a wastewater treatment and recycling technology for aluminum profile manufacturing enterprises. This technology categorizes wastewater into three types—chromium-containing wastewater, high-fluoride wastewater, and low-fluoride wastewater—for separate treatment based on the different pollutants. In this method, most of the fluoride and aluminum in the high-fluoride wastewater are removed by coagulation and sedimentation, followed by secondary treatment using a combination of modified activated carbon and modified zeolite. Although this technology classifies and treats different pollutants, the process is lengthy, requires significant equipment investment, and is complex to operate and manage. Furthermore, the classified and diverted treatment mode places high demands on the wastewater collection system, making it unsuitable for the actual production conditions of small and medium-sized aluminum profile plants.

[0005] To address the shortcomings of the existing technology, this invention provides a method for treating wastewater from an aluminum profile factory. By optimizing the flocculant compound system and adsorbent materials, the method achieves efficient, economical, and stable treatment of wastewater from the aluminum profile factory. Summary of the Invention

[0006] In view of this, in order to solve one of the above-mentioned technical problems, the present invention provides a method for treating wastewater in an aluminum profile factory, the specific technical solution of which is as follows: A method for treating wastewater in an aluminum profile factory, the method comprising the following steps: S1. pH adjustment: Collect the wastewater from the aluminum profile factory into the equalization tank, add pH adjuster under stirring conditions, and adjust the pH of the wastewater to 6.5~8.5; S2. First flocculation and sedimentation: Add composite flocculant to the wastewater flocculation treatment tank after pH adjustment, stir and treat under the first stirring condition, then let it stand to settle, and separate the supernatant and sludge. S3. Adsorption treatment: The supernatant obtained in step S2 is sent to the adsorption treatment tank, and modified adsorbent is added for adsorption treatment; S4. Second flocculation and fine treatment: The effluent after adsorption treatment is sent into the fine treatment tank, the composite flocculant is added, and the mixture is stirred under the second stirring condition. After settling, the supernatant is taken. S5. The supernatant obtained in step S4 is filtered through sand filtration and microfiltration membrane filtration before being discharged or reused; The preparation method of the composite flocculant is as follows: Hydroxypropyltrimethylammonium chloride chitosan and sodium alginate were dissolved in deionized water and stirred in a water bath at 40-60°C to obtain mixed solution A. Polyaluminum ferric sulfate and polyacrylamide were dissolved in deionized water and stirred to obtain mixed solution B; Disperse nano-silica in anhydrous ethanol and ultrasonically disperse for 15-30 min to obtain a nano-silica dispersion. Under stirring conditions, mixed solution B is slowly added to mixed solution A, followed by nano-silica dispersion. Stirring is continued for 30-60 minutes, and then spray-dried to obtain the composite flocculant.

[0007] Furthermore, the raw materials for preparing the composite flocculant include the following parts by weight: 20-25 parts of hydroxypropyltrimethylammonium chloride chitosan, 20-40 parts of sodium alginate, 8-15 parts of polyaluminum ferric sulfate, 7-9 parts of polyacrylamide, and 7-9 parts of nano silica.

[0008] Furthermore, the particle size of the nano-silica is 50~80nm.

[0009] Furthermore, in step S2, the amount of the composite flocculant added is 50~200 mg / L.

[0010] Further, in step S2, the reaction is stirred at a speed of 80~150 r / min for 30~60 min, and then allowed to stand and precipitate for 30~60 min.

[0011] Further, in step S3, the method for preparing the modified adsorbent is as follows: (S3-a) Place diatomaceous earth in a muffle furnace and heat it to 400-600℃ at a heating rate of 5-10℃ / min. Calcine for 3-5 hours. After cooling, grind it through a 200-mesh sieve to obtain pretreated diatomaceous earth. (S3-b) The pretreated diatomaceous earth is added to a sulfuric acid solution with a mass concentration of 10%~20% and a solid-liquid ratio of 1g:(10~15)mL. The mixture is stirred and acidified for 1~3h under a water bath at 60~80℃. After filtration and washing until neutral, the mixture is dried to obtain acidified modified diatomaceous earth. (S3-c) Dissolve chitosan in acetic acid solution with a volume fraction of 1%~3% to prepare a chitosan solution with a mass concentration of 1.5%~3.0%; dissolve sodium alginate in deionized water to prepare a sodium alginate solution with a mass concentration of 1.0%~2.5%; add acidified modified diatomaceous earth to the chitosan solution with a solid-liquid ratio of 1g:(5~10)mL, stir for 30~60min, then slowly add sodium alginate solution, and continue stirring for 1~2h to obtain a composite gel system; (S3-d) The composite gel system is added dropwise to a calcium chloride solution with a mass concentration of 2%~5%, and crosslinked and cured at room temperature for 2~4 hours to form gel microspheres; (S3-e) The gel microspheres are washed with deionized water 3 to 5 times and dried to obtain the modified adsorbent.

[0012] Further, in step S3, the amount of the modified adsorbent added is 1g:(20~35)mL; the adsorption treatment time is 1~2h.

[0013] Further, in step S4, the reaction is stirred at a speed of 60~100 r / min for 10~20 min, and then allowed to stand and precipitate for 40~60 min.

[0014] Furthermore, in step S4, the amount of the composite flocculant added is 20~80 mg / L.

[0015] Furthermore, the weight ratio of chitosan to sodium alginate is 1:(0.3~2).

[0016] Compared with existing technologies, its beneficial effects include: 1. This invention, through the preparation of a composite flocculant, significantly improves flocculation efficiency and floc settling performance through the synergistic effects of charge neutralization, bridging flocculation, chelation crosslinking, and physical enhancement. Furthermore, this invention achieves better treatment results by using staged flocculation, enhancing floc rigidity with nano-silica, and forming a network sweeping structure with chitosan and sodium alginate polymer chains, generating large, dense flocs with fast settling speeds.

[0017] 2. The modified adsorbent prepared in this invention involves first calcining diatomaceous earth at high temperature to open its internal pores and remove organic impurities, then acidifying it with sulfuric acid to etch the pore structure and increase the number of acidic adsorption sites on the surface; subsequently, chitosan-sodium alginate cross-linked gel microspheres are loaded to introduce a large number of chelating functional groups. The modified adsorbent simultaneously possesses multiple functions including physical pore adsorption, chemical complexation, and ion exchange, effectively adsorbing residual metal ions after flocculation, and exhibiting significant adsorption and purification effects.

[0018] 3. The treatment agent used in this invention is biodegradable and will not cause secondary pollution, thus possessing good industrial application value. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to its embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of the invention.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0021] An embodiment of the present invention provides a method for treating wastewater in an aluminum profile factory, the method comprising the following steps: S1. pH adjustment: Collect the wastewater from the aluminum profile factory into the equalization tank, add pH adjuster under stirring conditions, and adjust the pH of the wastewater to 6.5~8.5; S2. First flocculation and sedimentation: Add composite flocculant to the wastewater flocculation treatment tank after pH adjustment, stir and treat under the first stirring condition, then let it stand to settle, and separate the supernatant and sludge. S3. Adsorption treatment: The supernatant obtained in step S2 is sent to the adsorption treatment tank, and modified adsorbent is added for adsorption treatment; S4. Second flocculation and fine treatment: The effluent after adsorption treatment is sent into the fine treatment tank, the composite flocculant is added, and the mixture is stirred under the second stirring condition. After settling, the supernatant is taken. S5. The supernatant obtained in step S4 is filtered through sand filtration and microfiltration membrane filtration before being discharged or reused; The preparation method of the composite flocculant is as follows: Hydroxypropyltrimethylammonium chloride chitosan and sodium alginate were dissolved in deionized water and stirred in a water bath at 40-60°C to obtain mixed solution A. Polyaluminum ferric sulfate and polyacrylamide were dissolved in deionized water and stirred to obtain mixed solution B; Disperse nano-silica in anhydrous ethanol and ultrasonically disperse for 15-30 min to obtain a nano-silica dispersion. Under stirring conditions, mixed solution B is slowly added to mixed solution A, followed by the addition of nano-silica dispersion. Stirring continues for 30-60 minutes, and the mixture is then spray-dried to obtain the composite flocculant. In the composite flocculant prepared by this invention, hydroxypropyltrimethylammonium chloride chitosan carries a positive charge and can efficiently capture negatively charged colloidal particles and metal complex ions in wastewater through charge neutralization. Polyacrylamide plays a bridging flocculation role, accelerating floc growth. Polyaluminum ferric sulfate combines the flocculation advantages of both aluminum and iron salts, maintaining high flocculation activity over a wide pH range. Sodium alginate contains a large number of carboxyl groups, which can chelate and crosslink with polyvalent metal ions, enhancing the network structure and sedimentation performance of the flocs. Nano-silica, as an inorganic reinforcing component, can improve the density and mechanical strength of the flocs.

[0022] In one embodiment, the raw materials for preparing the composite flocculant include the following parts by weight: 20-25 parts of hydroxypropyltrimethylammonium chloride chitosan, 20-40 parts of sodium alginate, 8-15 parts of polyaluminum ferric sulfate, 7-9 parts of polyacrylamide, and 7-9 parts of nano silica.

[0023] In one embodiment, the particle size of the nano-silica is 50-80 nm.

[0024] In one embodiment, in step S2, the amount of the composite flocculant added is 50~200 mg / L.

[0025] In one embodiment, in step S2, the reaction is stirred at a speed of 80~150 r / min for 30~60 min, and then allowed to stand and precipitate for 30~60 min.

[0026] In one embodiment, in step S3, the modified adsorbent is prepared by: (S3-a) Place diatomaceous earth in a muffle furnace and heat it to 400-600℃ at a heating rate of 5-10℃ / min. Calcine for 3-5 hours. After cooling, grind it through a 200-mesh sieve to obtain pretreated diatomaceous earth. (S3-b) The pretreated diatomaceous earth is added to a sulfuric acid solution with a mass concentration of 10%~20% and a solid-liquid ratio of 1g:(10~15)mL. The mixture is stirred and acidified for 1~3h under a water bath at 60~80℃. After filtration and washing until neutral, the mixture is dried to obtain acidified modified diatomaceous earth. (S3-c) Dissolve chitosan in acetic acid solution with a volume fraction of 1%~3% to prepare a chitosan solution with a mass concentration of 1.5%~3.0%; dissolve sodium alginate in deionized water to prepare a sodium alginate solution with a mass concentration of 1.0%~2.5%; add acidified modified diatomaceous earth to the chitosan solution with a solid-liquid ratio of 1g:(5~10)mL, stir for 30~60min, then slowly add sodium alginate solution, and continue stirring for 1~2h to obtain a composite gel system; (S3-d) The composite gel system is added dropwise to a calcium chloride solution with a mass concentration of 2%~5%, and crosslinked and cured at room temperature for 2~4 hours to form gel microspheres; (S3-e) The gel microspheres are washed with deionized water 3 to 5 times and dried to obtain the modified adsorbent.

[0027] In this invention, the modified adsorbent uses diatomaceous earth that has undergone high-temperature calcination and acidification modification, resulting in a significantly increased specific surface area and more surface active sites. The chitosan-sodium alginate composite coating layer is rich in amino and carboxyl functional groups, enabling efficient adsorption of heavy metal ions through coordination complexation and ion exchange. The egg-box structure formed by the crosslinking of sodium alginate and calcium chloride has a three-dimensional network porous morphology, which is beneficial for the diffusion and adsorption of pollutant molecules. The freeze-drying process preserves the porous structure of the gel microspheres, avoiding the pore collapse caused by traditional heat drying. This invention differs from existing adsorbents that use a composite of quaternized fibers and modified diatomaceous earth.

[0028] In one embodiment, in step S3, the amount of the modified adsorbent added is 1g:(20~35)mL; the adsorption treatment time is 1~2h.

[0029] In one embodiment, in step S4, the reaction is stirred at a speed of 60-100 r / min for 10-20 min, and then allowed to stand and precipitate for 40-60 min.

[0030] In one embodiment, in step S4, the amount of composite flocculant added is 20~80 mg / L.

[0031] In one embodiment, the weight ratio of chitosan to sodium alginate is 1:(0.3~2).

[0032] This invention employs a biological-inorganic composite flocculant for segmented flocculation, combined with adsorption treatment by a modified adsorbent, followed by fine filtration through sand filtration and microfiltration to treat aluminum profile wastewater. The synergistic effect results in a significant comprehensive treatment effect, making it suitable for industrial applications of comprehensive aluminum profile wastewater treatment.

[0033] The implementation schemes of the present invention will now be described in detail with reference to specific embodiments.

[0034] Example 1: The preparation method of the composite flocculant in this embodiment is as follows: According to the weight parts, 20 parts of hydroxypropyltrimethylammonium chloride chitosan and 25 parts of sodium alginate were dissolved in 60 parts of deionized water and stirred under a water bath at 60°C to obtain mixed solution A. Dissolve 11 parts of polyaluminum ferric sulfate and 9 parts of polyacrylamide in 30 parts of deionized water, stir to dissolve, and obtain mixed solution B; Eight parts of nano-silica were dispersed in 10 parts of anhydrous ethanol and ultrasonically dispersed for 15 min to obtain a nano-silica dispersion. Under stirring conditions, mixed solution B was slowly added to mixed solution A, followed by the addition of nano-silica dispersion. Stirring was continued for 45 minutes, and the mixture was then spray-dried to obtain the composite flocculant.

[0035] The preparation method of the modified adsorbent in this embodiment is as follows: (S3-a) Place the diatomaceous earth in a muffle furnace and heat it to 500°C at a heating rate of 10°C / min. Calcine for 3 hours, cool, and then grind it through a 200-mesh sieve to obtain pretreated diatomaceous earth. (S3-b) The pretreated diatomaceous earth was added to a 10% sulfuric acid solution with a solid-liquid ratio of 1g:10mL. The mixture was stirred and acidified in a water bath at 75℃ for 2 hours. After filtration and washing until neutral, the mixture was dried to obtain acidified modified diatomaceous earth. (S3-c) Chitosan was dissolved in a 1% (v / v) acetic acid solution to prepare a 3.0% (w / w) chitosan solution; sodium alginate was dissolved in deionized water to prepare a 2% (w / w) sodium alginate solution; acidified modified diatomaceous earth was added to the chitosan solution at a solid-liquid ratio of 1 g:10 mL, and after stirring for 40 min, sodium alginate solution was slowly added dropwise, and stirring was continued for 1 h to obtain a composite gel system; and the weight ratio of chitosan to sodium alginate was 1:0.7. (S3-d) The composite gel system was added dropwise to a 3% calcium chloride solution and crosslinked and cured at room temperature for 3 hours to form gel microspheres; (S3-e) The gel microspheres were washed five times with deionized water and dried to obtain the modified adsorbent; This embodiment describes a method for treating wastewater in an aluminum profile factory, the method comprising the following steps: S1. pH adjustment: Collect the wastewater from the aluminum profile factory into the equalization tank, add pH adjuster under stirring conditions, and adjust the pH of the wastewater to 7.0; S2. First flocculation and sedimentation: Add 150 mg / L of composite flocculant to the wastewater flocculation treatment tank after pH adjustment, stir at 100 r / min for 45 min, then let it stand and settle for 60 min, and separate the supernatant and settled sludge. S3. Adsorption treatment: The supernatant obtained in step S2 is sent to the adsorption treatment tank, and modified adsorbent is added at a ratio of 1g:30mL for adsorption treatment for 2h. S4. Second flocculation and fine treatment: The effluent after adsorption treatment is sent to the fine treatment tank, and the composite flocculant is added at a dosage of 50 mg / L. The mixture is stirred at 100 r / min for 15 min, then allowed to stand and settle for 45 min. The supernatant is then taken. S5. The supernatant obtained in step S4 is filtered through sand filtration and microfiltration membrane filtration before being discharged or reused.

[0036] Example 2: The preparation method of the composite flocculant in this embodiment is as follows: According to the weight parts, 22 parts of hydroxypropyltrimethylammonium chloride chitosan and 23 parts of sodium alginate were dissolved in 60 parts of deionized water and stirred under a water bath at 60°C to obtain mixed solution A. Dissolve 12 parts of polyaluminum ferric sulfate and 8 parts of polyacrylamide in 30 parts of deionized water, stir to dissolve, and obtain mixed solution B; 99 parts of nano-silica were dispersed in 10 parts of anhydrous ethanol and ultrasonically dispersed for 20 min to obtain a nano-silica dispersion. Under stirring conditions, mixed solution B was slowly added to mixed solution A, followed by the addition of nano-silica dispersion. Stirring was continued for 50 minutes, and the mixture was then spray-dried to obtain the composite flocculant.

[0037] The preparation method of the modified adsorbent in this embodiment is as follows: (S3-a) Place the diatomaceous earth in a muffle furnace and heat it to 500°C at a heating rate of 10°C / min. Calcine for 3 hours, cool, and then grind it through a 200-mesh sieve to obtain pretreated diatomaceous earth. (S3-b) The pretreated diatomaceous earth was added to a 10% sulfuric acid solution with a solid-liquid ratio of 1g:10mL. The mixture was stirred and acidified in a water bath at 75℃ for 2 hours. After filtration and washing until neutral, the mixture was dried to obtain acidified modified diatomaceous earth. (S3-c) Chitosan was dissolved in a 1% (v / v) acetic acid solution to prepare a 3.0% (w / w) chitosan solution; sodium alginate was dissolved in deionized water to prepare a 2% (w / w) sodium alginate solution; acidified modified diatomaceous earth was added to the chitosan solution at a solid-liquid ratio of 1 g:10 mL, and after stirring for 40 min, sodium alginate solution was slowly added dropwise, and stirring was continued for 1 h to obtain a composite gel system; and the weight ratio of chitosan to sodium alginate was 1:0.7. (S3-d) The composite gel system was added dropwise to a 3% calcium chloride solution and crosslinked and cured at room temperature for 3 hours to form gel microspheres; (S3-e) The gel microspheres were washed five times with deionized water and dried to obtain the modified adsorbent; This embodiment describes a method for treating wastewater in an aluminum profile factory, the method comprising the following steps: S1. pH adjustment: Collect the wastewater from the aluminum profile factory into the equalization tank, add pH adjuster under stirring conditions, and adjust the pH of the wastewater to 7.0; S2. First flocculation and sedimentation: Add 160 mg / L of composite flocculant to the wastewater flocculation treatment tank after pH adjustment, stir and react at 100 r / min for 40 min, then let it stand and settle for 60 min, and separate the supernatant and settled sludge. S3. Adsorption treatment: The supernatant obtained in step S2 is sent to the adsorption treatment tank, and modified adsorbent is added at a ratio of 1g:30mL for adsorption treatment for 2h. S4. Second flocculation and fine treatment: The effluent after adsorption treatment is sent to the fine treatment tank, and the composite flocculant is added at a dosage of 50 mg / L. The mixture is stirred at 100 r / min for 15 min, then allowed to stand and settle for 45 min. The supernatant is then taken. S5. The supernatant obtained in step S4 is filtered through sand filtration and microfiltration membrane filtration before being discharged or reused.

[0038] Example 3: The preparation method of the composite flocculant in this embodiment is as follows: According to the weight parts, 23 parts of hydroxypropyltrimethylammonium chloride chitosan and 22 parts of sodium alginate were dissolved in 60 parts of deionized water and stirred under a water bath at 60°C to obtain mixed solution A. Dissolve 11 parts of polyaluminum ferric sulfate and 9 parts of polyacrylamide in 30 parts of deionized water, stir to dissolve, and obtain mixed solution B; Nine parts of nano-silica were dispersed in 10 parts of anhydrous ethanol and ultrasonically dispersed for 20 min to obtain a nano-silica dispersion. Under stirring conditions, mixed solution B was slowly added to mixed solution A, followed by the addition of nano-silica dispersion. Stirring was continued for 50 minutes, and the mixture was then spray-dried to obtain the composite flocculant.

[0039] The preparation method of the modified adsorbent in this embodiment is as follows: (S3-a) Place the diatomaceous earth in a muffle furnace and heat it to 500°C at a heating rate of 10°C / min. Calcine for 3 hours, cool, and then grind it through a 200-mesh sieve to obtain pretreated diatomaceous earth. (S3-b) The pretreated diatomaceous earth was added to a 10% sulfuric acid solution with a solid-liquid ratio of 1g:10mL. The mixture was stirred and acidified in a water bath at 75℃ for 2 hours. After filtration and washing until neutral, the mixture was dried to obtain acidified modified diatomaceous earth. (S3-c) Chitosan was dissolved in a 1% (v / v) acetic acid solution to prepare a 3.0% (w / w) chitosan solution; sodium alginate was dissolved in deionized water to prepare a 2% (w / w) sodium alginate solution; acidified modified diatomaceous earth was added to the chitosan solution at a solid-liquid ratio of 1 g:10 mL, and after stirring for 40 min, sodium alginate solution was slowly added dropwise, and stirring was continued for 1 h to obtain a composite gel system; and the weight ratio of chitosan to sodium alginate was 1:0.7. (S3-d) The composite gel system was added dropwise to a 3% calcium chloride solution and crosslinked and cured at room temperature for 3 hours to form gel microspheres; (S3-e) The gel microspheres were washed five times with deionized water and dried to obtain the modified adsorbent; This embodiment describes a method for treating wastewater in an aluminum profile factory, the method comprising the following steps: S1. pH adjustment: Collect the wastewater from the aluminum profile factory into the equalization tank, add pH adjuster under stirring conditions, and adjust the pH of the wastewater to 7.0; S2. First flocculation and sedimentation: Add 180 mg / L of composite flocculant to the wastewater flocculation treatment tank after pH adjustment, stir and react at 100 r / min for 40 min, then let it stand and settle for 60 min, and separate the supernatant and settled sludge. S3. Adsorption treatment: The supernatant obtained in step S2 is sent to the adsorption treatment tank, and modified adsorbent is added at a ratio of 1g:30mL for adsorption treatment for 2h. S4. Second flocculation and fine treatment: The effluent after adsorption treatment is sent to the fine treatment tank, and the composite flocculant is added at an addition amount of 60 mg / L. The mixture is stirred at a speed of 100 r / min for 15 min, then allowed to stand and settle for 40 min. The supernatant is then taken. S5. The supernatant obtained in step S4 is filtered through sand filtration and microfiltration membrane filtration before being discharged or reused.

[0040] Comparative Example 1: The difference between Comparative Example 1 and Example 3 is that no nano-silica is added during the preparation of the composite flocculant in Comparative Example 1, while the rest is the same as in Example 3.

[0041] Comparative Example 2: The difference between Comparative Example 2 and Example 3 is that hydroxypropyltrimethylammonium chloride chitosan and sodium alginate are not added during the preparation of the composite flocculant in Comparative Example 2, while the rest is the same as in Example 3.

[0042] Comparative Example 3: Compared with Example 3, Comparative Example 3 differs in that, in the preparation process of the composite flocculant in Comparative Example 3, hydroxypropyltrimethylammonium chloride chitosan, sodium alginate, polyaluminum ferric sulfate, polyacrylamide and nano silica are directly mixed, and the resulting mixture is used as the composite flocculant.

[0043] Comparative Example 4: The difference between Comparative Example 4 and Example 3 is that the modified adsorbent in Comparative Example 4 uses raw diatomaceous earth, that is, the diatomaceous earth is only crushed through a 200-mesh sieve and has not undergone other treatments. Otherwise, it is the same as Example 3.

[0044] Comparative Example 5: Compared with Example 3, Comparative Example 5 differs in that the diatomaceous earth in the preparation method of the modified adsorbent in Comparative Example 5 is only subjected to high-temperature calcination and sulfuric acid acidification (i.e., only steps S3-a and S3-b are completed), and the chitosan-sodium alginate cross-linking coating is not performed (steps S3-c to S3-e are omitted). The acidified modified diatomaceous earth is directly used as the adsorbent, and the rest is the same as in Example 3.

[0045] Comparative Example 6: The difference between Comparative Example 6 and Example 3 is that Comparative Example 6 did not undergo a second flocculant treatment (i.e., step S4), but otherwise it was the same as Example 3.

[0046] The effects were verified by the methods of Examples 1-3 and Comparative Examples 1-6. Table 1 below shows the water quality of the experimental water; Table 2 shows the experimental results.

[0047] Table 1: Water quality of experimental water

[0048] Table 2: Experimental Results

[0049] Analysis of the data in Table 2 shows that this invention achieves efficient and stable purification of comprehensive wastewater from aluminum profile factories through the synergistic effect of multiple mechanisms, including charge neutralization, bridging flocculation, chelation crosslinking, physical reinforcement, and pore adsorption. Compared with Example 3, the composite flocculant in Comparative Example 1 did not contain nano-silica during preparation. Due to the lack of nano-silica as an inorganic reinforcing component to support the floc skeleton and increase density, it could not effectively increase the density and mechanical strength of the flocs, resulting in loose, brittle flocs and deteriorated settling performance. This indicates that nano-silica can strengthen the floc structure and accelerate solid-liquid separation by enhancing the physical reinforcement effect. The composite flocculant in Comparative Example 2 did not contain hydroxypropyltrimethylammonium chloride chitosan and sodium alginate during preparation, leading to a weakened charge neutralization effect with metal complex ions. It also lacked the chelation crosslinking effect of carboxyl groups with multivalent metal ions, failing to form a large and dense floc network structure, resulting in a flocculation effect inferior to Example 3. The treatment effect of Comparative Example 3 (simple mixing of components) was also significantly worse than that of Example 3, indicating that the preparation process of the present invention, through solution compounding combined with spray drying, can fully disperse and combine the components at the molecular level, which helps to provide flocculation effect. In the adsorption treatment step of Comparative Example 4, unmodified raw diatomaceous earth was used instead of the modified adsorbent of the present invention. Since the natural pores of raw diatomaceous earth are severely blocked by impurities, have a small specific surface area, and lack effective active adsorption sites on the surface, its adsorption capacity for residual metal ions in wastewater is extremely limited, resulting in a treatment effect that is not as good as that of Example 3. This shows that the series of modification treatments of the present invention, including high-temperature calcination to unclog the internal pores, sulfuric acid acid etching to increase adsorption sites, and subsequent cross-linking coating to introduce chemical complexation function, can significantly improve the adsorption treatment effect. In the preparation process of the modified adsorbent in Comparative Example 5, only diatomaceous earth was subjected to high-temperature calcination and sulfuric acid acidification, but the chitosan-sodium alginate cross-linking coating step was completely omitted (i.e. steps S3-c to S3-e were not performed). Since acidification modification can only optimize the physical pore structure of diatomaceous earth and increase some inorganic acidic sites, it lacks the three-dimensional network porous structure constructed by chitosan-sodium alginate cross-linked gel microspheres and a large number of amino and carboxyl functional groups, and cannot effectively exert chemical adsorption effects such as coordination complexation and ion exchange, resulting in an incomprehensible adsorption effect.The wastewater treatment method in Comparative Example 6 omits the second flocculation fine treatment step (i.e., step S4). After adsorption treatment, the wastewater is directly subjected to sand filtration and microfiltration membrane filtration. Since a small amount of fine suspended particles and destabilized colloids that have not been completely flocculated remain in the effluent after adsorption treatment, the composite flocculant lacks the further charge neutralization and bridging sweeping effect of these residues during the second flocculation process. As a result, these fine pollutants cannot be effectively flocculated and settled, leading to all indicators being significantly worse than those in Example 3. This shows that in the staged flocculation process adopted in this invention, the second flocculation fine treatment is not a redundant repetitive operation, but a crucial step in the final purification of the effluent after the first flocculation to remove the main pollutants and the adsorption treatment to remove dissolved ions. This ensures that the final effluent water quality meets the standards and effectively reduces the pollution load and membrane clogging risk of the subsequent membrane filtration system.

[0050] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0051] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for treating wastewater in an aluminum profile factory, characterized in that, The method includes the following steps: S1. pH adjustment: Collect the wastewater from the aluminum profile factory into the equalization tank, add pH adjuster under stirring conditions, and adjust the pH of the wastewater to 6.5~8.5; S2. First flocculation and sedimentation: Add composite flocculant to the wastewater flocculation treatment tank after pH adjustment, stir and treat under the first stirring condition, then let it stand to settle, and separate the supernatant and precipitated sludge. S3. Adsorption treatment: The supernatant obtained in step S2 is sent to the adsorption treatment tank, and a modified adsorbent is added for adsorption treatment; S4. Second flocculation and fine treatment: The effluent after adsorption treatment is sent to the fine treatment tank, the composite flocculant is added, and the mixture is stirred under the second stirring condition. Then, it is allowed to settle and the supernatant is taken. S5. The supernatant obtained in step S4 is filtered through sand filtration and microfiltration membrane filtration before being discharged or reused; The preparation method of the composite flocculant is as follows: Hydroxypropyltrimethylammonium chloride chitosan and sodium alginate were dissolved in deionized water and stirred in a water bath at 40-60°C to obtain mixed solution A. Polyaluminum ferric sulfate and polyacrylamide were dissolved in deionized water and stirred to obtain mixed solution B; Disperse nano-silica in anhydrous ethanol and ultrasonically disperse for 15-30 min to obtain a nano-silica dispersion. Under stirring conditions, mixed solution B is slowly added to mixed solution A, followed by nano-silica dispersion. Stirring is continued for 30-60 minutes, and then spray-dried to obtain the composite flocculant.

2. The method according to claim 1, characterized in that, The raw materials for preparing the composite flocculant include the following parts by weight: 20-25 parts of hydroxypropyltrimethylammonium chloride chitosan, 20-40 parts of sodium alginate, 8-15 parts of polyaluminum ferric sulfate, 7-9 parts of polyacrylamide, and nano silica.

3. The method according to claim 2, characterized in that, The particle size of the nano-silica is 50~80nm.

4. The method according to claim 2, characterized in that, In step S2, the amount of the composite flocculant added is 50~200 mg / L.

5. The method according to claim 1, characterized in that, In step S2, the reaction is stirred at a speed of 80~150 r / min for 30~60 min, and then allowed to stand and precipitate for 30~60 min.

6. The method according to claim 1, characterized in that, In step S3, the modified adsorbent is prepared by: (S3-a) Place diatomaceous earth in a muffle furnace and heat it to 400-600℃ at a heating rate of 5-10℃ / min. Calcine for 3-5 hours. After cooling, grind it through a 200-mesh sieve to obtain pretreated diatomaceous earth. (S3-b) The pretreated diatomaceous earth is added to a sulfuric acid solution with a mass concentration of 10%~20% and a solid-liquid ratio of 1g:(10~15)mL. The mixture is stirred and acidified for 1~3h under a water bath at 60~80℃. After filtration and washing until neutral, the mixture is dried to obtain acidified modified diatomaceous earth. (S3-c) Dissolve chitosan in acetic acid solution with a volume fraction of 1%~3% to prepare a chitosan solution with a mass concentration of 1.5%~3.0%; dissolve sodium alginate in deionized water to prepare a sodium alginate solution with a mass concentration of 1.0%~2.5%; add acidified modified diatomaceous earth to the chitosan solution with a solid-liquid ratio of 1g:(5~10)mL, stir for 30~60min, then slowly add sodium alginate solution, and continue stirring for 1~2h to obtain a composite gel system; (S3-d) The composite gel system is added dropwise to a calcium chloride solution with a mass concentration of 2%~5%, and crosslinked and cured at room temperature for 2~4 hours to form gel microspheres; (S3-e) The gel microspheres are washed with deionized water 3 to 5 times and dried to obtain the modified adsorbent.

7. The method according to claim 1, characterized in that, In step S3, the amount of modified adsorbent added is 1g:(20~35)mL; the adsorption treatment time is 1~2h.

8. The method according to claim 1, characterized in that, In step S4, the reaction is stirred at a speed of 60~100 r / min for 10~20 min, and then allowed to stand and precipitate for 40~60 min.

9. The method according to claim 1, characterized in that, In step S4, the amount of composite flocculant added is 20~80 mg / L.

10. The method according to claim 6, characterized in that, The weight ratio of chitosan to sodium alginate is 1:(0.3~2).

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