A high-efficiency flocculation and low-ecological risk composite flocculation material and a preparation method thereof

Abstract

The application discloses a kind of high-efficiency flocculation, low ecological risk composite flocculation material and preparation method thereof, and relates to the technical field of water treatment flocculation material, comprising the following steps: agricultural waste biochar is oxidized and activated, and activated biochar with carboxyl and hydroxyl on the surface is obtained;Then activated biochar is compounded with attapulgite, and iron salt and ferrous salt are introduced for in-situ coprecipitation to obtain a magnetic mineral composite carrier.Chs is dissolved in weakly acidic aqueous solution, and glycidyltrimethylammonium chloride is added for quaternary ammonium reaction to obtain quaternary ammonium chs solution.Cationic starch is added to deionized water for gelatinization to obtain cationic starch gelatinization liquid, and the quaternary ammonium chs solution and cationic starch gelatinization liquid are mixed to obtain a natural polymer composite solution;The application uses activated biochar and attapulgite as a composite skeleton, and activated biochar has a porous structure and oxygen-containing functional groups, which can adsorb organic colloids and fine suspended particles.

Description

Technical Field

[0001] This invention relates to the field of water treatment flocculation materials technology, specifically to a high-efficiency flocculation, low-ecological-risk composite flocculation material and its preparation method. Background Technology

[0002] Flocculation and sedimentation is a commonly used solid-liquid separation technology in water supply treatment, sewage treatment, industrial wastewater pretreatment, and eutrophication control of lakes. Traditional flocculants mainly include aluminum salts, iron salts, polyaluminum chloride, polyferric sulfate, polyacrylamide, and their modified products. These flocculants have advantages such as convenient addition, rapid effect, and low cost, but some problems still exist in practical applications: On the one hand, single inorganic salt flocculants mainly rely on charge neutralization and double-layer compression, resulting in limited floc strength and sedimentation velocity significantly affected by water quality fluctuations; furthermore, excessive addition may lead to increased metal ion residues in the effluent. On the other hand, while some synthetic polymeric flocculants have strong bridging effects, their non-degradability, potential residual monomers, and the subsequent sludge disposal pressure limit their application in the treatment of ecologically sensitive water bodies.

[0003] In recent years, natural polymeric flocculants have attracted attention. Naturally sourced materials such as chitosan, starch, cellulose, and tannic acid have advantages such as wide availability, biodegradability, and low toxicity. However, when used directly as flocculants, they also have drawbacks, including significant pH-dependent solubility, limited molecular chain utilization efficiency, insufficient floc density, difficulty in recovery, and poor water stability. Simply mixing natural polymers with mineral powders can improve adsorption and sedimentation performance to some extent, but the lack of stable bonding between components leads to component loss in water, resulting in unstable long-term treatment effects. Summary of the Invention

[0004] The purpose of this invention is to provide a high-efficiency, low-ecological-risk composite flocculant and its preparation method. By constructing a magnetic biochar / attapulgite composite framework, a tannic acid-iron coordination layer, and a natural polymer low-degree cross-linked network, the material simultaneously possesses the capabilities of adsorption and capture, charge neutralization, polymer bridging, complexation phosphorus removal, mineral-assisted sedimentation, and magnetic response recovery. This improves the removal efficiency of suspended particles, organic colloids, and phosphorus-containing pollutants, while reducing the dissolution of flocculant components and the risk of ecotoxicity.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a high-efficiency flocculation, low-ecological-risk composite flocculation material, comprising the following steps: Agricultural waste biochar is oxidized and activated to obtain activated biochar with carboxyl and hydroxyl groups on the surface; then the activated biochar is combined with attapulgite and iron salts and ferrous salts are introduced for in-situ co-precipitation to obtain a magnetic mineral composite carrier.

[0006] Chitosan was dissolved in a weakly acidic aqueous solution, and glycidyltrimethylammonium chloride was added to carry out a quaternization reaction to obtain a quaternized chitosan solution.

[0007] Cationic starch is added to deionized water and gelatinized to obtain a cationic starch gelatinized solution. The quaternized chitosan solution is mixed with the cationic starch gelatinized solution to obtain a natural polymer composite solution.

[0008] Tannic acid solution and ferric salt solution are added to the magnetic mineral composite carrier dispersion to form a tannic acid-iron coordination layer on the surface of the magnetic mineral composite carrier, thus obtaining a coordination-modified carrier.

[0009] A natural polymer composite solution is added to a coordination-modified carrier dispersion, and then genipin is added for low-degree cross-linking. After solid-liquid separation, washing, drying and pulverization, a high-efficiency flocculation and low-ecological-risk composite flocculant material is obtained.

[0010] Furthermore, the preparation steps of the activated biochar are as follows: One or more of corn stalks, rice husks, bamboo shavings, or wood shavings are placed under an inert atmosphere and pyrolyzed at 450-650℃ for 1.5-3 hours to obtain biochar. The biochar is then added to a 5-15% hydrogen peroxide solution and stirred at 50-70℃ and 300-500 r / min for 2-4 hours. After filtration, the biochar is washed with deionized water until neutral and then vacuum dried at 60-80℃ for 6-10 hours to obtain activated biochar.

[0011] Furthermore, the preparation steps of the magnetic mineral composite carrier are as follows: Activated biochar and attapulgite were added to deionized water and stirred for 30-60 minutes at 20-30℃ and 600-800 r / min to obtain a carrier suspension. Ferric chloride hexahydrate and ferrous chloride tetrahydrate were added to the carrier suspension and stirred for 20-40 minutes under nitrogen protection. Then, ammonia was added dropwise to adjust the pH to 9.0-10.5, and the reaction was continued at 60-80℃ for 1-2 hours. The mixture was then magnetically separated, washed, and dried to obtain a magnetic mineral composite carrier.

[0012] Furthermore, the ratio of activated biochar, attapulgite, ferric chloride hexahydrate, ferrous chloride tetrahydrate, and deionized water is 8-12g: 15-25g: 6-9g: 3-5g: 400-600mL.

[0013] Furthermore, the preparation steps of the quaternized chitosan solution are as follows: Chitosan with a degree of deacetylation of 80-95% is added to an aqueous solution of acetic acid with a mass fraction of 1.0-2.0%, and stirred at 25-35℃ until dissolved. Then glycidyltrimethylammonium chloride is added, and the mixture is reacted at 55-70℃ for 4-8 hours. The pH is adjusted to 6.0-7.0 to obtain a quaternized chitosan solution.

[0014] Furthermore, the ratio of chitosan, aqueous acetic acid solution, and glycidyltrimethylammonium chloride used is 6-10g: 300-500mL: 8-16g.

[0015] Furthermore, the preparation steps of the natural polymer composite solution are as follows: Cationic starch is added to deionized water and gelatinized at 80-90℃ for 30-50 min. After cooling to 40-50℃, quaternized chitosan solution is added and stirred at 400-600 r / min for 30-60 min to obtain a natural polymer composite solution.

[0016] Furthermore, the ratio of cationic starch, deionized water, and quaternized chitosan solution is 10-18g: 200-300mL: 250-450mL.

[0017] Furthermore, the preparation steps of the coordination-modified support are as follows: The magnetic mineral composite carrier was ultrasonically dispersed in deionized water for 10-20 min to obtain a carrier dispersion with a mass concentration of 30-60 g / L. Tannic acid solution was added to the carrier dispersion and stirred for 20-40 min. Then, ferric chloride solution was added dropwise to adjust the pH to 6.5-7.5. The mixture was stirred for 1-2 h at 20-30 °C to obtain a coordination-modified carrier with a tannic acid-iron coordination layer on its surface.

[0018] Furthermore, the mass ratio of the magnetic mineral composite carrier, tannic acid, and ferric chloride is 100:6-15:2-6.

[0019] Furthermore, the specific steps of the low-degree crosslinking are as follows: The natural polymer composite solution was added dropwise to the coordination-modified carrier dispersion and stirred for 1-2 hours at 25-35℃ and 500-700 r / min. Then, genipin ethanol solution was added and the reaction was continued at 35-45℃ for 2-4 hours. After the reaction was completed, the solid was separated by magnetic separation or centrifugation. The obtained solid was washed 2-4 times with deionized water, vacuum dried at 50-70℃ for 8-12 hours, pulverized and passed through an 80-120 mesh sieve to obtain a high-efficiency flocculation and low ecological risk composite flocculant material.

[0020] Furthermore, the mass ratio of the coordination-modified carrier, the solids in the natural polymer composite solution, and genipin is 100:20-45:0.5-2.5.

[0021] Furthermore, the composite flocculant material comprises a magnetic mineral composite carrier, a tannic acid-iron coordination layer, quaternized chitosan, cationic starch, and a genipin cross-linking structure, forming a multi-level synergistic flocculation system. Among these, attapulgite and biochar provide adsorption sites and sedimentation frameworks, iron oxide provides magnetic response recovery capabilities, the tannic acid-iron coordination layer provides phenolic hydroxyl complexation sites, quaternized chitosan and cationic starch provide charge neutralization and polymer bridging effects, and the genipin cross-linking structure is used to reduce the dissolution of natural polymer components in water.

[0022] Furthermore, the particle size of the composite flocculant is 80-200μm, the saturation magnetization is 8-25 emu / g, and the dosage is 20-120mg / L when used in water bodies with a pH of 5-9. The composite flocculant is used for the flocculation treatment of suspended solids containing kaolin, humic acid, algal cells, colloidal particles in dyeing and printing wastewater, or phosphorus-containing wastewater. After flocculation, solid-liquid separation can be achieved through sedimentation, filtration, or separation assisted by an external magnetic field.

[0023] This invention also provides a high-efficiency flocculation and low-ecological-risk composite flocculation material, which is prepared by any of the above preparation methods; the composite flocculation material uses magnetic biochar / attapulgite as an inorganic-carbon-based composite skeleton, tannic acid-iron coordination layer as surface complexing layer, quaternized chitosan and cationic starch as degradable flocculation functional layers, and forms a low-degree cross-linked network through genipin.

[0024] Compared with existing technologies, this invention provides a high-efficiency, low-ecological-risk composite flocculant and its preparation method, which has the following beneficial effects: This invention uses activated biochar and attapulgite as a composite framework. Activated biochar has a porous structure and oxygen-containing functional groups, which can adsorb organic colloids and fine suspended particles; attapulgite has a mineral framework and a sedimentation-aiding effect, which can improve the density and sedimentation speed of flocs. The combination of the two can improve the problem of loose flocs and slow sedimentation of single natural polymer flocculants.

[0025] Magnetic magnetite (Fe3O4) is formed on the surface of activated biochar / attapulgite through in-situ co-precipitation of ferric and ferrous salts, endowing the material with magnetic recovery capabilities. After flocculation, the flocs can be separated and recovered through sedimentation, filtration, or external magnetic field assistance, which helps reduce the pressure of subsequent sludge disposal.

[0026] A tannic acid-iron coordination layer was constructed on the surface of a magnetic mineral composite carrier. The phenolic hydroxyl groups in tannic acid can form a stable coordination structure with iron ions, and at the same time, they can adsorb or complex phosphate, organic colloids and some metal ions, thereby improving the adaptability of the composite flocculant to complex polluted water bodies.

[0027] Quaternized chitosan and cationic starch were used as the functional layer for natural polymer flocculants. Quaternized chitosan still has good cationic properties in neutral and weakly alkaline water, which can enhance the charge neutralization effect; cationic starch has a long-chain bridging effect, and when combined with quaternized chitosan, it can enhance the capture and scavenging effect on colloidal particles.

[0028] Genipin is used for low-degree crosslinking, which is more suitable for low-ecological-risk water treatment scenarios compared to conventional highly toxic crosslinking agents. Low-degree crosslinking can reduce the dissolution of natural polymer components in water while retaining the extension ability of polymer chain segments, giving the material both stability and flocculation activity. Attached Figure Description

[0029] Figure 1 The image shows a scanning electron microscope image of the composite flocculant prepared in Example 2.

[0030] Figure 2 The image shows a scanning electron microscope image of the composite flocculant prepared in Comparative Example 2.

[0031] Figure 3 The images show the actual results of luminescent bacteria detection in the supernatant after treatment in Example 2 and Comparative Example 6.

[0032] Figure 4 The bar chart shows the luminescence inhibition rate of the supernatant after treatment in Example 2 and Comparative Example 6. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] Please see Figures 1-4 This invention provides a technical solution for a high-efficiency, low-ecological-risk composite flocculant and its preparation method: Unless otherwise stated, all reagents used in the following examples are commercially available products, and the water used is deionized water. The degree of deacetylation of the chitosan is 80-95%, the cationic starch is commercially available water treatment grade cationic starch, and the attapulgite is water treatment attapulgite that has been crushed and passed through a 200-mesh sieve. pH adjustment is performed using hydrochloric acid or ammonia.

[0035] Example 1 A method for preparing a high-efficiency, low-ecological-risk composite flocculant material includes the following steps: S1: Corn stalks were placed under a nitrogen atmosphere and pyrolyzed at 450℃ for 1.5h to obtain biochar; the biochar was added to a 5% hydrogen peroxide solution and stirred at 50℃ and 300r / min for 2h; after filtration, it was washed with deionized water until neutral and dried under vacuum at 60℃ for 6h to obtain activated biochar.

[0036] S2: Add 8g of activated biochar and 15g of attapulgite to 400mL of deionized water and stir for 30min at 20℃ and 600r / min to obtain a carrier suspension; add 6g of ferric chloride hexahydrate and 3g of ferrous chloride tetrahydrate to the carrier suspension and stir for 20min under nitrogen protection, then add ammonia water dropwise to adjust the pH to 9.0, and continue the reaction at 60℃ for 1h. Magnetic separation, washing and drying are performed to obtain a magnetic mineral composite carrier.

[0037] S3: Add 6g of chitosan with a degree of deacetylation of 80% to 300mL of acetic acid aqueous solution with a mass fraction of 1.0%, stir at 25℃ until dissolved, then add 8g of glycidyltrimethylammonium chloride, react at 55℃ for 4h, adjust the pH to 6.0, and obtain quaternized chitosan solution.

[0038] S4: Add 10g of cationic starch to 200mL of deionized water, gelatinize at 80℃ for 30min, cool to 40℃ and add 250mL of quaternized chitosan solution, stir at 400r / min for 30min to obtain a natural polymer composite solution.

[0039] S5: The magnetic mineral composite carrier was added to deionized water and ultrasonically dispersed for 10 min to obtain a carrier dispersion with a mass concentration of 30 g / L; tannic acid solution was added to the carrier dispersion and stirred for 20 min, then ferric chloride solution was added dropwise to adjust the pH to 6.5, and stirring was continued at 20℃ for 1 h to obtain the coordination modified carrier; wherein, the mass ratio of magnetic mineral composite carrier, tannic acid and ferric chloride was 100:6:2.

[0040] S6: The natural polymer composite solution was added dropwise to the coordination-modified carrier dispersion and stirred for 1 hour at 25°C and 500 r / min. Then, genipin ethanol solution was added, and the reaction was continued at 35°C for 2 hours. After the reaction was completed, the solid was magnetically separated, washed twice with deionized water, vacuum dried at 50°C for 8 hours, pulverized, and passed through an 80-mesh sieve to obtain a high-efficiency flocculation and low-ecological-risk composite flocculant. The mass ratio of solids to genipin in the coordination-modified carrier, natural polymer composite solution, and genipin was 100:20:0.5.

[0041] Example 2 A method for preparing a high-efficiency, low-ecological-risk composite flocculant material includes the following steps: S1: Rice husks were placed under a nitrogen atmosphere and pyrolyzed at 550℃ for 2.2h to obtain biochar; the biochar was added to a 10% hydrogen peroxide solution and stirred at 60℃ and 400r / min for 3h. After filtration, the biochar was washed with deionized water until neutral and dried under vacuum at 70℃ for 8h to obtain activated biochar.

[0042] S2: Add 10g activated biochar and 20g attapulgite to 500mL of deionized water and stir for 45min at 25℃ and 700r / min to obtain a carrier suspension; add 7.5g ferric chloride hexahydrate and 4g ferrous chloride tetrahydrate to the carrier suspension and stir for 30min under nitrogen protection, then add ammonia water dropwise to adjust the pH to 9.8, and continue the reaction at 70℃ for 1.5h. Magnetic separation, washing and drying are performed to obtain a magnetic mineral composite carrier.

[0043] S3: Add 8g of chitosan with a degree of deacetylation of 88% to 400mL of acetic acid aqueous solution with a mass fraction of 1.5%, stir at 30℃ until dissolved, then add 12g of glycidyltrimethylammonium chloride, react at 63℃ for 6h, adjust the pH to 6.5, and obtain quaternized chitosan solution.

[0044] S4: Add 14g of cationic starch to 250mL of deionized water, gelatinize at 85℃ for 40min, cool to 45℃ and add 350mL of quaternized chitosan solution, stir at 500r / min for 45min to obtain a natural polymer composite solution.

[0045] S5: The magnetic mineral composite carrier was added to deionized water and ultrasonically dispersed for 15 min to obtain a carrier dispersion with a mass concentration of 45 g / L; tannic acid solution was added to the carrier dispersion and stirred for 30 min, then ferric chloride solution was added dropwise to adjust the pH to 7.0, and stirring was continued at 25℃ for 1.5 h to obtain the coordination-modified carrier; wherein, the mass ratio of magnetic mineral composite carrier, tannic acid and ferric chloride was 100:10:4.

[0046] S6: The natural polymer composite solution was added dropwise to the coordination-modified carrier dispersion and stirred for 1.5 h at 30 °C and 600 r / min. Then, genipin ethanol solution was added and the reaction was continued at 40 °C for 3 h. After the reaction was completed, the solid was magnetically separated, washed three times with deionized water, vacuum dried at 60 °C for 10 h, pulverized and passed through a 100-mesh sieve to obtain a high-efficiency flocculation and low-ecological-risk composite flocculant. The mass ratio of solids to genipin in the coordination-modified carrier, natural polymer composite solution and S6 was 100:32:1.5.

[0047] Example 3 A method for preparing a high-efficiency, low-ecological-risk composite flocculant material includes the following steps: S1: Bamboo chips were placed under a nitrogen atmosphere and pyrolyzed at 650℃ for 3 hours to obtain biochar; the biochar was added to a 15% hydrogen peroxide solution and stirred at 70℃ and 500r / min for 4 hours. After filtration, the biochar was washed with deionized water until neutral and dried under vacuum at 80℃ for 10 hours to obtain activated biochar.

[0048] S2: Add 12g activated biochar and 25g attapulgite to 600mL of deionized water and stir for 60min at 30℃ and 800r / min to obtain a carrier suspension; add 9g ferric chloride hexahydrate and 5g ferrous chloride tetrahydrate to the carrier suspension and stir for 40min under nitrogen protection, then add ammonia water dropwise to adjust the pH to 10.5, and continue the reaction at 80℃ for 2h. Magnetic separation, washing and drying are performed to obtain a magnetic mineral composite carrier.

[0049] S3: Add 10g of chitosan with a degree of deacetylation of 95% to 500mL of acetic acid aqueous solution with a mass fraction of 2.0%, stir at 35℃ until dissolved, then add 16g of glycidyltrimethylammonium chloride, react at 70℃ for 8h, adjust the pH to 7.0, and obtain quaternized chitosan solution.

[0050] S4: Add 18g of cationic starch to 300mL of deionized water, gelatinize at 90℃ for 50min, cool to 50℃ and add 450mL of quaternized chitosan solution, stir at 600r / min for 60min to obtain a natural polymer composite solution.

[0051] S5: The magnetic mineral composite carrier was added to deionized water and ultrasonically dispersed for 20 min to obtain a carrier dispersion with a mass concentration of 60 g / L; tannic acid solution was added to the carrier dispersion and stirred for 40 min, then ferric chloride solution was added dropwise to adjust the pH to 7.5, and stirring was continued at 30℃ for 2 h to obtain the coordination modified carrier; wherein, the mass ratio of magnetic mineral composite carrier, tannic acid and ferric chloride was 100:15:6.

[0052] S6: The natural polymer composite solution was added dropwise to the coordination-modified carrier dispersion and stirred for 2 hours at 35℃ and 700 r / min. Then, genipin ethanol solution was added, and the reaction was continued at 45℃ for 4 hours. After the reaction was completed, the solid was magnetically separated, washed four times with deionized water, vacuum dried at 70℃ for 12 hours, pulverized, and passed through a 120-mesh sieve to obtain a high-efficiency flocculation and low-ecological-risk composite flocculant. The mass ratio of solids to genipin in the coordination-modified carrier, natural polymer composite solution, and genipin was 100:45:2.5.

[0053] Comparative Example 1 Based on Example 2, the hydrogen peroxide activation treatment step in step S1 was omitted, that is, the biochar obtained from rice husk pyrolysis was directly used in the subsequent preparation, and the remaining steps and parameters were the same as in Example 2.

[0054] Comparative Example 2 Based on Example 2, the 20g of attapulgite in step S2 was replaced with 20g of activated biochar, and the remaining steps and parameters were the same as in Example 2.

[0055] Comparative Example 3 Based on Example 2, ferric chloride hexahydrate and ferrous chloride tetrahydrate in step S2 are omitted, and in-situ coprecipitation magnetization treatment is not performed. The remaining steps and parameters are the same as in Example 2.

[0056] Comparative Example 4 Based on Example 2, the tannic acid in step S5 was omitted, and only ferric chloride solution was added for treatment. The remaining steps and parameters were the same as in Example 2.

[0057] Comparative Example 5 Based on Example 2, the quaternized chitosan solution obtained in step S3 was replaced with an unquaternized chitosan acetic acid solution with the same solid content, and the remaining steps and parameters were the same as in Example 2.

[0058] Comparative Example 6 Based on Example 2, the genipin in step S6 was replaced with an equal mass of glutaraldehyde, and the remaining steps and parameters were the same as in Example 2.

[0059] Performance testing The performance of the composite flocculants prepared in Examples 1-3 and Comparative Examples 1-6 was tested.

[0060] I. Simulated Wastewater Configuration Deionized water was used to prepare a simulated complex polluted water body, in which kaolin was used to provide suspended particles, humic acid was used to simulate natural organic colloids, and potassium dihydrogen phosphate was used to provide phosphate pollutants. The initial turbidity of the simulated wastewater was 500 NTU, the suspended solids concentration was 320 mg / L, the COD was 120 mg / L, the total phosphorus concentration was 2.00 mg / L, and the pH was 7.0 ± 0.2.

[0061] II. Flocculation Treatment Methods Take 1000 mL of simulated wastewater and place it in a beaker. Add composite flocculant at a dosage of 80 mg / L. First, stir rapidly at 250 rpm for 2 min, then stir slowly at 60 rpm for 10 min. After standing and settling for 15 min, take the supernatant about 2 cm below the liquid surface for testing. Each test was repeated 3 times, and the average value was taken.

[0062] III. Testing Methods 1. Turbidity removal rate: The turbidity before and after treatment was determined according to the turbidity-related methods in GB / T 5750.4-2023 "Standard Examination Methods for Drinking Water - Part 4: Sensory Characteristics and Physical Indicators", and the turbidity removal rate was calculated using the following formula: Turbidity removal rate (%) = (turbidity before treatment - turbidity after treatment) / turbidity before treatment × 100%.

[0063] 2. Suspended solids removal rate: The concentration of suspended solids before and after treatment was determined according to GB / T 11901-1989 "Determination of suspended solids in water quality by gravimetric method", and the suspended solids removal rate was calculated.

[0064] 3. COD removal rate: COD before and after treatment was determined according to HJ 828-2017 "Determination of Chemical Oxygen Demand in Water - Dichromate Method", and the COD removal rate was calculated.

[0065] 4. Total phosphorus removal rate: The total phosphorus concentration before and after treatment was determined according to GB / T 11893-1989 "Determination of total phosphorus in water quality by ammonium molybdate spectrophotometric method", and the total phosphorus removal rate was calculated.

[0066] 5. Acute toxicity of water: The luminescence inhibition rate of the supernatant after flocculation treatment on luminescent bacteria was tested according to GB / T 15441-1995 "Determination of acute toxicity of water by luminescent bacteria method". The lower the luminescence inhibition rate, the lower the acute ecological risk.

[0067] 6. Leaching safety: The solids obtained after flocculation and separation were leached in accordance with HJ / T 299-2007 "Leaching Toxicity of Solid Waste - Leaching Method - Sulfuric Acid and Nitric Acid Method". The total iron concentration in the leachate was determined in accordance with GB / T 5750.6-2023 "Standard Examination Methods for Drinking Water - Part 6: Metals and Metalloids".

[0068] 7. Magnetic Recovery Rate: The flocculated system containing flocs was placed under an external magnetic field of 0.4T for 3 minutes. The magnetically responsive flocs were collected, dried, and weighed. The magnetic recovery rate was calculated based on the ratio of the recovered solid mass to the theoretically added solid mass. This item serves as a supplementary evaluation indicator for the material recovery performance.

[0069] 8. Reusability: The flocculant material after magnetic recovery was washed with deionized water and then used for the same simulated wastewater treatment. This was repeated 5 times, and the turbidity removal rate was recorded on the 5th use.

[0070] Table 1 Table 2 As shown in Tables 1 and 2, Examples 1-3 all exhibited high turbidity removal rates, suspended solids removal rates, COD removal rates, and total phosphorus removal rates, indicating that the present invention can achieve good flocculation treatment effects. Among them, Example 2 showed the best overall performance, with a turbidity removal rate of 98.4%, a suspended solids removal rate of 97.8%, a COD removal rate of 68.9%, a total phosphorus removal rate of 88.7%, a sedimentation time to supernatant clarity of 6.5 min, a magnetic recovery rate of 94.3%, and a turbidity removal rate still maintained at 95.1% even after the fifth use.

[0071] In Comparative Example 1, the oxidation-activation step was omitted, resulting in a reduction in oxygen-containing functional groups on the surface of the biochar. This decreased the biochar's binding capacity with the tannic acid-iron coordination layer and the natural polymer layer, and consequently reduced its ability to adsorb organic colloids and trap fine particles. Consequently, the COD and total phosphorus removal rates were lower than in Example 2, and the turbidity removal rate also decreased significantly after the fifth use. This indicates that biochar oxidation activation can improve the interfacial bonding capacity and pollutant adsorption capacity of the composite carrier.

[0072] Comparative Example 2 replaced attapulgite with an equal amount of activated biochar. Lacking the mineral rod-like framework and sedimentation-aiding structures, the material exhibited reduced floc density and a longer sedimentation time to supernatant clarity, increasing from 6.5 min in Example 2 to 15.3 min. Both turbidity removal rate and suspended solids removal rate decreased. This demonstrates that attapulgite is not merely a simple filler but plays a crucial role in floc framework formation and rapid sedimentation.

[0073] Comparative Example 3, which did not undergo in-situ co-precipitation magnetization treatment, resulted in a material with virtually no magnetic recovery capability, exhibiting a magnetic recovery rate of only 8.6%. The turbidity removal rate significantly decreased after the fifth use. Although its acute toxicity was low, the lack of magnetic recovery capability and active sites for iron oxides resulted in significantly insufficient material reusability and total phosphorus removal capacity. This indicates that the magnetic iron(III) oxide formed by in-situ co-precipitation makes a significant contribution to material recovery and stable use.

[0074] Comparative Example 4, which removed tannic acid and retained only ferric chloride, failed to form a stable tannic acid-iron coordination layer. This resulted in a decrease in the material's ability to complex and capture organic colloids and phosphates, with COD removal rates and total phosphorus removal rates decreasing to 49.6% and 66.9%, respectively. This indicates that the tannic acid-iron coordination layer can significantly enhance the synergistic removal capacity of composite flocculants for complex pollutants.

[0075] In Comparative Example 5, replacing quaternized chitosan with unquaternized chitosan resulted in a decrease in cationic charge density and a weakening of charge neutralization under neutral conditions. This also affected polymer bridging and scavenging effects, leading to lower levels of turbidity removal, suspended solids removal, COD removal, and total phosphorus removal compared to other groups. This indicates that quaternization modification of chitosan improves the applicability of flocculants in neutral water bodies.

[0076] In Comparative Example 6, genipin was replaced with glutaraldehyde. The initial flocculation performance of the material remained good, but the luminescence inhibition rate of the supernatant against luminescent bacteria increased to 31.7% after treatment, which was significantly higher than the 5.6% in Example 2. This indicates that using genipin for low-degree crosslinking can reduce potential ecological risks while maintaining flocculation effects, making it suitable for low-ecological-risk water treatment applications.

[0077] In summary, this invention achieves a comprehensive effect of efficient flocculation, rapid sedimentation, magnetic response recovery, reuse, and low acute ecological risk through the synergistic effect between activated biochar, attapulgite, magnetic iron oxide, tannic acid-iron coordination layer, quaternized chitosan, cationic starch, and genipin low-degree cross-linked network.

[0078] Although the present invention has been described in conjunction with specific embodiments, the above embodiments do not constitute a limitation on the scope of protection of the present invention. Those skilled in the art can make conventional adjustments or equivalent substitutions to the specific raw material types, process parameters, and application water bodies without departing from the principles and spirit of the present invention, and all such adjustments and substitutions should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a high-efficiency flocculating, low-ecological risk composite flocculating material, characterized in that, Includes the following steps: Agricultural waste biochar is oxidized and activated to obtain activated biochar with carboxyl and hydroxyl groups on the surface; then the activated biochar is combined with attapulgite and iron salts and ferrous salts are introduced for in-situ co-precipitation to obtain a magnetic mineral composite carrier. Chitosan was dissolved in a weakly acidic aqueous solution, and glycidyltrimethylammonium chloride was added to carry out a quaternization reaction to obtain a quaternized chitosan solution. Cationic starch is added to deionized water and gelatinized to obtain cationic starch gelatinized solution. The quaternized chitosan solution is mixed with the cationic starch gelatinized solution to obtain a natural polymer composite solution. Tannic acid solution and ferric salt solution are added to the magnetic mineral composite carrier dispersion to form a tannic acid-iron coordination layer on the surface of the magnetic mineral composite carrier, thereby obtaining a coordination-modified carrier. A natural polymer composite solution is added to a coordination-modified carrier dispersion, and then genipin is added for low-degree cross-linking. After solid-liquid separation, washing, drying and pulverization, a high-efficiency flocculation and low-ecological-risk composite flocculant material is obtained.

2. A process for the preparation of a high-efficiency flocculating, low-ecological risk composite flocculating material according to claim 1, characterized in that, The preparation steps of the activated biochar are as follows: One or more of corn stalks, rice husks, bamboo shavings, or wood shavings are placed under an inert atmosphere and pyrolyzed at 450-650℃ for 1.5-3 hours to obtain biochar. The biochar is then added to a 5-15% hydrogen peroxide solution and stirred at 50-70℃ and 300-500 r / min for 2-4 hours. After filtration, the biochar is washed with deionized water until neutral and then vacuum dried at 60-80℃ for 6-10 hours to obtain activated biochar.

3. The process for the preparation of a high-efficiency flocculating, low-ecological risk composite flocculating material according to claim 1, characterized in that, The preparation steps of the magnetic mineral composite carrier are as follows: Activated biochar and attapulgite were added to deionized water and stirred for 30-60 minutes at 20-30℃ and 600-800r / min to obtain a carrier suspension. Ferric chloride hexahydrate and ferrous chloride tetrahydrate were added to the carrier suspension and stirred for 20-40 min under nitrogen protection. Then, ammonia was added dropwise to adjust the pH to 9.0-10.

5. The reaction was continued at 60-80℃ for 1-2 h. The mixture was then magnetically separated, washed, and dried to obtain a magnetic mineral composite carrier. The ratio of activated biochar, attapulgite, ferric chloride hexahydrate, ferrous chloride tetrahydrate, and deionized water is 8-12g: 15-25g: 6-9g: 3-5g: 400-600mL.

4. The process for the preparation of a high-efficiency flocculating, low-ecological risk composite flocculating material according to claim 1, characterized in that, The preparation steps of the quaternized chitosan solution are as follows: Chitosan with a degree of deacetylation of 80-95% is added to an aqueous solution of acetic acid with a mass fraction of 1.0-2.0%, and stirred at 25-35℃ until dissolved. Then glycidyltrimethylammonium chloride is added, and the mixture is reacted at 55-70℃ for 4-8 hours. The pH is adjusted to 6.0-7.0 to obtain a quaternized chitosan solution. The ratio of chitosan, aqueous acetic acid solution, and glycidyltrimethylammonium chloride used is 6-10g: 300-500mL: 8-16g.

5. The method for preparing a high-efficiency flocculation, low-ecological-risk composite flocculation material according to claim 1, characterized in that, The preparation steps of the natural polymer composite solution are as follows: Cationic starch is added to deionized water and gelatinized at 80-90℃ for 30-50 min. After cooling to 40-50℃, quaternized chitosan solution is added and stirred at 400-600 r / min for 30-60 min to obtain a natural polymer composite solution. The ratio of cationic starch, deionized water and quaternized chitosan solution is 10-18g: 200-300mL: 250-450mL.

6. The method for preparing a high-efficiency flocculation, low-ecological-risk composite flocculation material according to claim 1, characterized in that, The preparation steps of the coordination-modified support are as follows: The magnetic mineral composite carrier was ultrasonically dispersed in deionized water for 10-20 min to obtain a carrier dispersion with a mass concentration of 30-60 g / L. Tannic acid solution was added to the carrier dispersion and stirred for 20-40 min. Then, ferric chloride solution was added dropwise to adjust the pH to 6.5-7.

5. The mixture was stirred at 20-30℃ for 1-2 h to obtain a coordination-modified carrier with a tannic acid-iron coordination layer on its surface. The mass ratio of the magnetic mineral composite carrier, tannic acid, and ferric chloride is 100:6-15:2-6.

7. The process for the preparation of a high-efficiency flocculating, low-ecological risk composite flocculating material according to claim 1, characterized in that, The specific steps for the low-degree crosslinking are as follows: The natural polymer composite solution was added dropwise to the coordination-modified carrier dispersion and stirred for 1-2 hours at 25-35℃ and 500-700 r / min. Then, genipin ethanol solution was added and the reaction was continued at 35-45℃ for 2-4 hours. After the reaction was completed, the solid was separated by magnetic separation or centrifugation. The obtained solid was washed 2-4 times with deionized water, vacuum dried at 50-70℃ for 8-12 hours, pulverized and passed through an 80-120 mesh sieve to obtain a high-efficiency flocculation and low ecological risk composite flocculant material. The mass ratio of the coordination-modified carrier, solids in the natural polymer composite solution, and genipin is 100:20-45:0.5-2.

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8. The process for the preparation of a high-efficiency flocculating, low-ecological risk composite flocculating material according to claim 1, characterized in that, The composite flocculant material contains a multi-level synergistic flocculant system formed by magnetic mineral composite carrier, tannic acid-iron coordination layer, quaternized chitosan, cationic starch and genipin cross-linking structure. Among them, attapulgite and biochar provide adsorption sites and sedimentation framework, iron oxide provides magnetic response recovery capability, tannic acid-iron coordination layer provides phenolic hydroxyl complexation sites, quaternized chitosan and cationic starch provide charge neutralization and polymer bridging effect, and genipin cross-linking structure is used to reduce the dissolution of natural polymer components in water.

9. The process for the preparation of a high-efficiency flocculating, low-ecological risk composite flocculating material according to claim 1, characterized in that, The composite flocculant has a particle size of 80-200μm, a saturation magnetization of 8-25 emu / g, and a dosage of 20-120mg / L when used in water bodies with a pH of 5-9. The composite flocculant is used for the flocculation treatment of kaolin suspended solids, humic acid, algal cells, colloidal particles in dyeing and printing wastewater, or phosphorus-containing wastewater. After flocculation, solid-liquid separation can be achieved through sedimentation, filtration, or separation assisted by an external magnetic field.

10. A high-flocculating, low-ecological risk composite flocculating material, characterized in that, Prepared by the preparation method according to any one of claims 1-9; The composite flocculant uses magnetic biochar / attapulgite as an inorganic-carbon-based composite framework, tannic acid-iron coordination layer as a surface complexing layer, quaternized chitosan and cationic starch as degradable flocculant functional layers, and forms a low-degree cross-linked network through genipin.

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