Low-temperature high-efficiency phosphorus removal composite agent for severe cold regions and preparation method thereof

Abstract

This invention discloses a low-temperature, high-efficiency phosphorus removal composite agent for frigid regions and its preparation method, belonging to the technical field of water treatment and environmental functional materials. The composite agent is composed of 50-60 parts of iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan, 15-20 parts of a low-temperature activating component, 10-15 parts of a crystallization inducer, and 10-15 parts of an adsorption-enhancing carrier. The components of this invention synergistically form a cascade synergistic chain of "rapid adsorption-micro-area precipitation-induced crystallization-carrier dispersion," achieving highly efficient phosphorus removal in near-freezing-point water bodies. It also allows for magnetic separation and recovery, reducing phosphorus removal costs and making it suitable for wastewater treatment in frigid regions.

Description

Technical Field

[0001] This invention relates to the field of water treatment and environmental functional materials technology, and in particular to a low-temperature, high-efficiency phosphorus removal composite agent for frigid regions and its preparation method. Background Technology

[0002] Phosphorus is one of the key limiting nutrients leading to eutrophication of water bodies. Currently, commonly used phosphorus removal methods mainly include biological methods, chemical precipitation methods, and adsorption methods. Among them, biological phosphorus removal operates stably under normal temperature conditions, but in cold winter regions (where water temperatures are often below 10℃, or even close to freezing point), the metabolic activity of microorganisms decreases significantly, and the phosphorus uptake capacity of polyphosphate-accumulating bacteria is greatly weakened, resulting in a sharp decrease in biological phosphorus removal efficiency, making it difficult to meet discharge standards. Chemical precipitation methods (such as adding aluminum salts, iron salts, or calcium salts) are less affected by low temperatures, but to achieve ideal phosphorus removal results, excessive amounts of metal salts are often required, which not only increases the cost of reagents but also generates a large amount of chemical sludge, leading to secondary pollution and sludge disposal problems.

[0003] Adsorption methods have attracted widespread attention due to their ease of operation, low sludge production, and ability to recover phosphorus. However, existing adsorption materials face many challenges in low-temperature environments: On the one hand, the adsorption process of conventional adsorbents (such as activated alumina, zeolite, modified clay, etc.) is mostly physical adsorption or ion exchange. At low temperatures, the diffusion rate of phosphate ions decreases and the adsorption kinetics slow down, resulting in a significant decrease in adsorption capacity and removal rate. On the other hand, although some metal-based adsorbents can form inner spherical complexes with phosphate ions, the chemical bonding effect weakens under low-temperature conditions, and the adsorption equilibrium time is prolonged. In addition, currently reported magnetic adsorption materials mostly focus on room-temperature adsorption performance and magnetic separation and recovery capabilities, lacking specific designs for low-temperature water bodies. Crystallization for phosphorus removal generally requires high supersaturation and suitable temperature conditions. Homogeneous nucleation is difficult at low temperatures, and crystal growth is slow, limiting the direct application of precipitation methods in cold regions.

[0004] In conclusion, developing a composite treatment agent that can efficiently and rapidly remove phosphorus in low-temperature water bodies in frigid regions, while also possessing the potential for magnetic separation and recovery as well as phosphorus resource utilization, is of great significance for solving the problem of winter wastewater treatment in northern and high-altitude areas of my country. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a low-temperature, high-efficiency phosphorus removal composite agent for frigid regions and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A low-temperature, high-efficiency phosphorus removal composite agent for frigid regions is made of the following components by weight: 50-60 parts of iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan, 15-20 parts of low-temperature activating component, 10-15 parts of crystallization inducer, and 10-15 parts of adsorption enhancement carrier.

[0007] Preferably, the preparation method of the iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan is as follows: Step 1. Dissolve hexadecyltrimethylammonium bromide and urea in deionized water to prepare a 1-2 wt% aqueous solution. Add Fe3O4 nanoparticles and ultrasonically disperse them for 20-30 minutes in an ultrasonic device with a power of 100-300W and a frequency of 30-40kHz to obtain mixture A. Add tetraethyl orthosilicate and 3-aminopropyltriethoxysilane to mixture A and stir the mixture at 50-60℃ and 300-500rpm for 6-8 hours. After the reaction is complete, separate the microspheres using a strong magnet and carefully pour the mixture onto a plate. The supernatant was washed 2-3 times with deionized water and 2-3 times with anhydrous ethanol. It was then vacuum dried at 50-60℃ for 12-15 h. The dried product was dispersed in an acidic ethanol solution (ethanol: concentrated hydrochloric acid = 50:1, v / v) and stirred under reflux at 50-60℃ for 6-12 h. The extraction was repeated 2-3 times. The product was then washed with deionized water until neutral, washed twice with anhydrous ethanol, and vacuum dried at 50-60℃ for 12-15 h to obtain aminated magnetic mesoporous silica microspheres (M-MSN-NH2). Step 2. Dissolve ferric sulfate nonahydrate, aluminum sulfate octadecahydrate, and magnesium sulfate heptahydrate in deionized water to prepare a mixed aqueous solution with a total metal concentration of 0.1-0.5 mol / L. Add the M-MSN-NH2 prepared in Step 1, stir at 200-300 rpm for 15-30 min, adjust the pH to 4.0-5.0 with 1-2% dilute acetic acid solution or dilute sodium hydroxide solution, and stir and load at 50-60℃ for 6-12 h. Then add urea, slowly raise the temperature to 90-100℃ at a rate of 3-5℃ / min, and react for 2-4 h. After the reaction is complete, separate the microspheres using a strong magnet, carefully pour off the supernatant, wash 2-3 times with deionized water and 2-3 times with anhydrous ethanol, and vacuum dry at 50-60℃ for 12-24 h to obtain iron-aluminum-magnesium modified magnetic mesoporous silica microspheres (FeAlMg-M-MSN). Step 3. Dissolve quaternized chitosan in a 2-3% acetic acid aqueous solution to prepare a 1.5-2.5 wt% quaternized chitosan solution. Add zirconium oxychloride octahydrate and stir at 300-500 rpm for 1-2 hours to obtain mixture B. Then add FeAlMg-M-MSN obtained in Step 2 and stir at 200-300 rpm for 15-30 minutes. Adjust the pH to 4.5-5.0 with 1-2% dilute acetic acid solution or dilute sodium hydroxide solution. Slowly add 50% glutaraldehyde aqueous solution in an ice-water bath at 0-4℃ and react for 4-6 hours. After the reaction is complete, separate the microspheres with a strong magnet, carefully pour off the supernatant, wash with deionized water 2-3 times, wash with anhydrous ethanol 2-3 times, and freeze-dry for 24-48 hours to obtain iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan (FeAlMg-M-MSN@Zr-QCS).

[0008] In step 1, hexadecyltrimethylammonium bromide (CTAB) is used as a structure-directing agent, dissolved in water with urea to form a micelle template; Fe3O4 nanoparticles are uniformly dispersed under ultrasonic assistance, followed by the addition of tetraethyl orthosilicate (TEOS) and 3-aminopropyltriethoxysilane (APTES) under weakly alkaline conditions (urea hydrolysis provides OH-). - TEOS and APTES undergo sol-gel condensation on the surface of CTAB micelles, forming a mesoporous silica shell that simultaneously encapsulates the Fe3O4 core. APTES introduces amino groups (-NH2) to functionalize the material. After the reaction, the CTAB template is removed by acidic ethanol reflux extraction to obtain aminated magnetic mesoporous silica microspheres (M-MSN-NH2) with an ordered mesoporous structure. In step 2, M-MSN... -NH2 dispersed in Fe-containing 3+ Al 3+ Mg 2+ The mixed solution is adjusted to pH 4.0-5.0 to protonate the amino group and adsorb metal ions through electrostatic interactions or weak coordination; then urea is added and the temperature is slowly raised to 90-100℃, where the urea undergoes thermal hydrolysis to produce OH-. - This process causes metal ions to precipitate uniformly in the mesoporous channels and on the surface, forming hydroxides or hydroxyl oxides. This avoids localized overconcentration and achieves uniform loading of Fe, Al, and Mg. After precipitation, washing and drying yield iron-aluminum-magnesium modified magnetic mesoporous silica microspheres (FeAlMg-M-MSN). In step 3, quaternized chitosan (QCS) dissolves in dilute acetic acid. The positively charged quaternary ammonium groups and unreacted hydroxyl and amine groups on its molecular chain can react with Zr. 4+(From zirconium oxychloride octahydrate) undergoes coordination chelation to form a stable QCS-Zr complex; after adding FeAlMg-M-MSN, glutaraldehyde is slowly added dropwise under ice-water bath conditions. The aldehyde group of glutaraldehyde undergoes a Schiff base crosslinking reaction with the amino group on the QCS molecular chain, stably coating or crosslinking the QCS-Zr complex onto the FeAlMg-M-MSN surface, while Zr... 4+ It is also fixed in the cross-linked network, and freeze-drying maintains the loose and porous structure of the material, ultimately resulting in a composite adsorbent material with strong magnetic responsiveness and a surface rich in quaternary ammonium groups and metal adsorption sites.

[0009] Preferably, in step 1, the molar ratio of hexadecyltrimethylammonium bromide to urea is 1:1-2.

[0010] Preferably, in step 1, the Fe3O4 nanoparticles have a particle size of 10-30 nm, and the mass ratio of Fe3O4 nanoparticles to hexadecyltrimethylammonium bromide is 1:4-5.

[0011] Preferably, in step 1, the mass ratio of tetraethyl orthosilicate, 3-aminopropyltriethoxysilane, and Fe3O4 nanoparticles is 2.0-2.5:0.30-0.35:1.

[0012] Preferably, in step 2, the molar ratio of iron, aluminum, and magnesium in ferric sulfate nonahydrate, aluminum sulfate octadecahydrate, and magnesium sulfate heptahydrate is 1:0.3-0.5:0.1-0.2.

[0013] Preferably, in step 2, the ratio of aminated magnetic mesoporous silica microspheres to the metal mixed aqueous solution is 5-10 g: 1 L.

[0014] Preferably, in step 2, the mass ratio of urea to aminated magnetic mesoporous silica microspheres is 1-3:1.

[0015] Preferably, in step 3, the mass ratio of quaternized chitosan to zirconium oxychloride octahydrate is 4-6:1.

[0016] Preferably, in step 3, the ratio of iron-aluminum-magnesium modified magnetic mesoporous silica microspheres to mixed solution B is 2-4 g: 1 L.

[0017] Preferably, in step 3, the mass ratio of glutaraldehyde to iron-aluminum-magnesium modified magnetic mesoporous silica microspheres is 0.1-0.5:1.

[0018] Preferably, the low-temperature activation component is a mixture of magnesium salt and pH buffer at a mass ratio of 1:0.5-0.8; wherein the magnesium salt is magnesium chloride hexahydrate or magnesium sulfate heptahydrate, and the pH buffer is a mixture of sodium bicarbonate and sodium carbonate at a mass ratio of 1-3:1.

[0019] Preferably, the crystallization inducer is composed of nano-calcium carbonate with a particle size of 50-200 nm and magnesium silicate in a mass ratio of 1:0.3-0.6.

[0020] Preferably, the adsorption-enhancing carrier is activated attapulgite with a specific surface area ≥300 m². 2 / g.

[0021] A method for preparing a low-temperature, high-efficiency phosphorus removal composite agent for frigid regions includes the following steps: S1. Preparation of iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan; S2. Preparation of low-temperature activation component: Weigh magnesium salt and pH buffer, put them into a high-speed mixer, and mix for 20-30 minutes at room temperature and 300-500 rpm to obtain low-temperature activation component mixed powder; S3. Preparation of crystallization inducer: Weigh nano-calcium carbonate and magnesium silicate, put them into a high-speed mixer, and mix for 40-60 minutes at 30-45℃ and 800-1000 rpm to obtain crystallization inducer powder; S4. Preparation of adsorption enhancement carrier: Weigh the raw attapulgite ore, crush it to 200-300 mesh, activate it at 120-180℃ for 2-4 hours, cool it and pass it through a 200-300 mesh sieve to obtain the adsorption enhancement carrier. S5. Compounding: Weigh iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan, low-temperature activating components, crystallization inducing agents, and adsorption enhancing carriers, put them into a three-dimensional mixer, stir and mix at 30-45℃ and 200-400rpm for 20-40min, then vacuum dry at 40-50℃ for 12-24h, grind and pass through a 100-150 mesh sieve to obtain a low-temperature high-efficiency phosphorus removal composite agent for frigid regions.

[0022] Preferably, the mechanism of action of the low-temperature high-efficiency phosphorus removal composite agent for frigid regions in this invention is explained as follows: First, using iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan (FeAlMg-M-MSN@Zr-QCS) as the main adsorbent, rapid dispersion and magnetic separation recovery are achieved by utilizing the high specific surface area of ​​mesoporous silica and the magnetic Fe3O4 core. The surface-modified quaternized chitosan retains its positive charge at low temperatures, capturing negatively charged phosphate ions through electrostatic attraction. Simultaneously, zirconium (Zr... 4+ ), iron (Fe) 3+ ), aluminum (Al) 3+ ), magnesium (Mg) 2+ Metal ions such as phosphate provide abundant coordination sites, forming stable inner spherical complexes with phosphate, which can maintain strong chemical affinity even when the water temperature is close to the freezing point; Secondly, the magnesium salts and pH buffers in the low-temperature activation components slowly dissolve in low-temperature water, releasing Mg. 2+ It also maintains a slightly alkaline environment, primarily promoting the reaction of phosphate and Mg. 2+ Combined, and under seed induction, magnesium phosphate precipitates are formed. Simultaneously, if NH4 is present in the water... + It can also synergistically generate magnesium ammonium phosphate, compensating for the slow chemical reaction kinetics at low temperatures; the nano-calcium carbonate (50-200nm) and magnesium silicate in the crystallization induction agent act as seed crystals, significantly reducing the nucleation energy barrier of calcium phosphate or magnesium phosphate crystallization, inducing heterogeneous nucleation of phosphate on the seed crystal surface, accelerating crystal growth, and avoiding the problem of difficult homogeneous nucleation at low temperatures. Among them, magnesium silicate has a layered structure similar to magnesium phosphate and can serve as a low-energy-barrier heterogeneous nucleation template; the adsorption enhancement carrier (activated attapulgite, specific surface area ≥300m²) 2 The composite agent ( / g) not only directly adsorbs phosphate ions through its layered chain structure and surface hydroxyl groups, but also acts as a dispersion matrix to prevent the main adsorbent from agglomerating and increase the collision efficiency between the composite agent and phosphorus. Under low temperature conditions, each component forms a cascade synergistic chain of "rapid adsorption - micro-area precipitation - induced crystallization - carrier dispersion": the main adsorbent rapidly enriches phosphate ions, the low temperature activates the components to increase local supersaturation, the crystallization inducer promotes the formation of crystal nuclei, and finally stabilizes phosphorus into insoluble crystalline precipitate. At the same time, the magnetic core can realize the convenient recovery and regeneration of the composite agent, thus maintaining efficient and long-lasting phosphorus removal performance in cold environments.

[0023] Compared with the prior art, the beneficial effects of the present invention are: 1. Low-temperature high-efficiency adsorption performance: Ferro-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan serves as the main adsorbent, combining the high specific surface area of ​​mesoporous silica, the rapid magnetic separation characteristics of the magnetic Fe3O4 core, and the positive charge retained by quaternized chitosan at low temperatures. Furthermore, the introduction of Zr... 4+ Fe 3+ Al 3+ Mg 2+ The presence of various metal ions provides abundant coordination sites, enabling it to efficiently capture phosphate ions in near-freezing water through electrostatic attraction and internal spherical complexation, overcoming the drawback of conventional adsorbents whose activity decreases significantly at low temperatures.

[0024] 2. Synergistic effect of low-temperature activation and induced crystallization: The low-temperature activation components (magnesium salt and pH buffer) in the compound can slowly release Mg²⁺ in low-temperature water. + It maintains a slightly alkaline environment and works synergistically with crystallization inducers (nano-calcium carbonate and magnesium silicate) to significantly reduce the nucleation energy barrier of phosphate crystallization. It induces heterogeneous nucleation of phosphate ions on the seed surface and rapidly transforms them into insoluble magnesium ammonium phosphate or magnesium phosphate precipitate, effectively compensating for the problems of slow chemical reaction kinetics and difficulty in homogeneous nucleation under low temperature conditions.

[0025] 3. Dispersion and Adsorption Enhancement: The adsorption enhancement carrier uses activated attapulgite soil (specific surface area ≥ 300 m²). 2 / g), its layered chain structure and abundant surface hydroxyl groups not only have a strong phosphate adsorption capacity, but also can serve as a dispersion matrix to effectively prevent the main adsorbent from agglomerating, greatly improving the collision efficiency and space utilization of the composite agent and phosphorus, and further enhancing the overall effect of low-temperature phosphorus removal.

[0026] 4. Cascaded synergy and convenient recovery: Under low-temperature conditions, each component forms a cascaded synergistic chain of "rapid adsorption - micro-area precipitation - induced crystallization - carrier dispersion", which realizes rapid enrichment of phosphorus, local supersaturation enhancement, stable crystallization transformation and convenient separation. At the same time, the magnetic core (Fe3O4) in the material can be rapidly recovered and regenerated through a strong magnet, which significantly reduces operating costs and meets the long-term use needs of extremely cold regions.

[0027] 5. Environmental friendliness and process feasibility: The preparation method of this composite agent is mild, and the raw materials include natural minerals (attapulgite, calcium carbonate, magnesium silicate) and bio-based materials (chitosan). It has good environmental compatibility, avoids the risk of secondary pollution, and the preparation process is simple to operate and easy to scale up. It provides an efficient, economical and sustainable phosphorus removal solution for low-temperature wastewater treatment in cold regions during winter. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0029] Preparation Example 1: The preparation method of iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan is as follows: Step 1. Dissolve 4.5g of hexadecyltrimethylammonium bromide and 1.11g of urea in 369mL of deionized water to prepare a 1.5wt% aqueous solution. Add 1.0g of Fe3O4 nanoparticles (20nm particle size) and ultrasonically disperse in an ultrasonic device with a power of 200W and a frequency of 35kHz for 25min to obtain mixture A. Add 2.25g of tetraethyl orthosilicate and 0.325g of 3-aminopropyltriethoxysilane to mixture A and stir at 55℃ and 400rpm for 7h. After the reaction is completed, separate the microspheres with a strong magnet, decant the supernatant, wash three times with deionized water and three times with anhydrous ethanol, and vacuum dry at 55℃ for 13h. Disperse the dried product in an acidic ethanol solution (ethanol: concentrated hydrochloric acid = 50:1). In v / v), the mixture was stirred and refluxed at 55°C for 8 hours, and the extraction was repeated twice. Then, it was washed with deionized water until neutral, washed twice with anhydrous ethanol, and dried under vacuum at 55°C for 13 hours to obtain aminated magnetic mesoporous silica microspheres. Step 2. Dissolve 54.37g of ferric sulfate nonahydrate, 25.79g of aluminum sulfate octadecahydrate and 7.15g of magnesium sulfate heptahydrate in deionized water to prepare 1L of mixed aqueous solution with a total metal concentration of 0.3mol / L. Add 7.5g of the aminated magnetic mesoporous silica microspheres prepared in Step 1, stir at 250rpm for 20min, adjust the pH to 4.5 with 1.5% dilute acetic acid, stir and load at 55℃ for 8h, add 15g of urea, raise the temperature to 95℃ at 4℃ / min, and react for 3h. After the reaction is completed, separate the microspheres with a strong magnet, pour off the supernatant, wash with deionized water 3 times and anhydrous ethanol 3 times in sequence, and vacuum dry at 55℃ for 18h to obtain iron-aluminum-magnesium modified magnetic mesoporous silica microspheres. Step 3. Dissolve 20g of quaternized chitosan in 1L of 2.5% acetic acid aqueous solution to prepare a 2.0wt% quaternized chitosan solution. Add 4g of zirconium oxychloride octahydrate and stir at 400rpm for 1.5h to obtain mixture B. Add 3g of iron-aluminum-magnesium modified magnetic mesoporous silica microspheres prepared in step 2 and stir at 250rpm for 20min. Adjust the pH to 4.8 with 1.5% dilute acetic acid. Slowly add 1.8g of 50% glutaraldehyde aqueous solution in an ice-water bath at 2℃ and react for 5h. After the reaction is completed, separate the microspheres with a strong magnet, pour off the supernatant, wash three times with deionized water and three times with anhydrous ethanol, and freeze-dry for 36h to obtain iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan.

[0030] Preparation Example 2: The preparation method of iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan is as follows: Step 1. Dissolve 4.0 g of hexadecyltrimethylammonium bromide and 0.66 g of urea in 461 mL of deionized water to prepare a 1.0 wt% aqueous solution. Add 1.0 g of Fe3O4 nanoparticles (10 nm in diameter) and ultrasonically disperse the solution for 20 min in an ultrasonic device with a power of 100 W and a frequency of 30 kHz to obtain mixture A. Add 2.0 g of tetraethyl orthosilicate and 0.30 g of 3-aminopropyltriethoxysilane to mixture A and stir the mixture at 50 °C and 300 rpm for 6 h. After the reaction is complete, separate the microspheres using a strong magnet, decant the supernatant, wash twice with deionized water and twice with anhydrous ethanol, and vacuum dry at 50 °C for 12 h. Disperse the dried product in an acidic ethanol solution (ethanol: concentrated hydrochloric acid = 50:1). In v / v), the mixture was stirred and refluxed at 50°C for 6 hours, and the extraction was repeated twice. Then, it was washed with deionized water until neutral, washed twice with anhydrous ethanol, and dried under vacuum at 50°C for 12 hours to obtain aminated magnetic mesoporous silica microspheres. Step 2. Dissolve 20.08 g of ferric sulfate nonahydrate, 7.14 g of aluminum sulfate octadecahydrate and 1.76 g of magnesium sulfate heptahydrate in deionized water to prepare 1 L of mixed aqueous solution with a total metal concentration of 0.1 mol / L. Add 5.0 g of the aminated magnetic mesoporous silica microspheres prepared in Step 1, stir at 200 rpm for 15 min, adjust the pH to 4.0 with 1% dilute acetic acid, stir and load at 50 °C for 6 h, add 5.0 g of urea, raise the temperature to 90 °C at 3 °C / min, and react for 2 h. After the reaction is completed, separate the microspheres with a strong magnet, pour off the supernatant, wash twice with deionized water and twice with anhydrous ethanol, and vacuum dry at 50 °C for 12 h to obtain iron-aluminum-magnesium modified magnetic mesoporous silica microspheres. Step 3. Dissolve 15g of quaternized chitosan in 1L of 2.0% acetic acid aqueous solution to prepare a 1.5wt% quaternized chitosan solution. Add 3.75g of zirconium oxychloride octahydrate and stir at 300rpm for 1h to obtain mixture B. Add 2.0g of iron-aluminum-magnesium modified magnetic mesoporous silica microspheres prepared in step 2 and stir at 200rpm for 15min. Adjust the pH to 4.5 with 1% dilute acetic acid. Slowly add 2.0g of 50% glutaraldehyde aqueous solution in an ice-water bath at 0℃ and react for 4h. After the reaction is completed, separate the microspheres with a strong magnet, pour off the supernatant, wash twice with deionized water and twice with anhydrous ethanol, and freeze-dry for 24h to obtain iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan.

[0031] Preparation Example 3: The preparation method of iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan is as follows: Step 1. Dissolve 5.0 g of hexadecyltrimethylammonium bromide and 1.65 g of urea in 326 mL of deionized water to prepare a 2.0 wt% aqueous solution. Add 1.0 g of Fe3O4 nanoparticles (30 nm in diameter) and ultrasonically disperse the solution for 30 min in an ultrasonic device with a power of 300 W and a frequency of 40 kHz to obtain mixture A. Add 2.5 g of tetraethyl orthosilicate and 0.35 g of 3-aminopropyltriethoxysilane to mixture A and stir the mixture at 60 °C and 500 rpm for 8 h. After the reaction is complete, separate the microspheres using a strong magnet, decant the supernatant, wash the mixture three times with deionized water and three times with anhydrous ethanol, and vacuum dry it at 60 °C for 15 h. Disperse the dried product in an acidic ethanol solution (ethanol: concentrated hydrochloric acid = 50:1). In v / v), the mixture was stirred and refluxed at 60°C for 12 h, and the extraction was repeated 3 times. Then, it was washed with deionized water until neutral, washed twice with anhydrous ethanol, and dried under vacuum at 60°C for 15 h to obtain aminated magnetic mesoporous silica microspheres. Step 2. Dissolve 82.64 g of ferric sulfate nonahydrate, 49.00 g of aluminum sulfate octadecahydrate and 14.50 g of magnesium sulfate heptahydrate in deionized water to prepare 1 L of mixed aqueous solution with a total metal concentration of 0.5 mol / L. Add 10.0 g of the aminated magnetic mesoporous silica microspheres prepared in Step 1, stir at 300 rpm for 30 min, adjust the pH to 5.0 with 2% dilute acetic acid, stir and load at 60 °C for 12 h, add 30 g of urea, raise the temperature to 100 °C at 5 °C / min, and react for 4 h. After the reaction is completed, separate the microspheres with a strong magnet, pour off the supernatant, wash with deionized water 3 times and anhydrous ethanol 3 times in sequence, and vacuum dry at 60 °C for 24 h to obtain iron-aluminum-magnesium modified magnetic mesoporous silica microspheres. Step 3. Dissolve 25g of quaternized chitosan in 1L of 3.0% acetic acid aqueous solution to prepare a 2.5wt% QCS solution. Add 4.17g of zirconium oxychloride octahydrate and stir at 500rpm for 2h to obtain mixture B. Add 4.0g of iron-aluminum-magnesium modified magnetic mesoporous silica microspheres prepared in Step 2 and stir at 300rpm for 30min. Adjust the pH to 5.0 with 2% dilute acetic acid. Slowly add 0.8g of 50% glutaraldehyde aqueous solution in an ice-water bath at 4℃ and react for 6h. After the reaction is completed, separate the microspheres with a strong magnet, pour off the supernatant, wash three times with deionized water and three times with anhydrous ethanol, and freeze-dry for 48h to obtain iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan.

[0032] Comparative Preparation Example 1: The preparation method of magnetic mesoporous silica@zirconium-quaternized chitosan is as follows: Step 1. Dissolve 4.5 g of hexadecyltrimethylammonium bromide and 1.11 g of urea in 369 mL of deionized water to prepare a 1.5 wt% aqueous solution. Add 1.0 g of Fe3O4 nanoparticles (20 nm in diameter) and ultrasonically disperse the solution for 25 min in an ultrasonic device with a power of 200 W and a frequency of 35 kHz to obtain mixture A. Add 2.25 g of tetraethyl orthosilicate and 0.325 g of 3-aminopropyltriethoxysilane to mixture A and stir the mixture at 55 °C and 400 rpm for 7 h. After the reaction is complete, separate the microspheres using a strong magnet, decant the supernatant, wash the mixture three times with deionized water and three times with anhydrous ethanol, and vacuum dry it at 55 °C for 13 h. The dried product was dispersed in an acidic ethanol solution (ethanol: concentrated hydrochloric acid = 50: 1 v / v), stirred and refluxed at 55°C for 8 h, and the extraction was repeated twice. Then, it was washed with deionized water until neutral, washed twice with anhydrous ethanol, and vacuum dried at 55°C for 13 h to obtain aminated magnetic mesoporous silica microspheres. Step 2. Dissolve 20g of quaternized chitosan in 1L of 2.5% acetic acid aqueous solution to prepare a 2.0wt% quaternized chitosan solution. Add 4g of zirconium oxychloride octahydrate and stir at 400rpm for 1.5h to obtain mixture B. Add 3g of the aminated magnetic mesoporous silica microspheres prepared in Step 1 and stir at 250rpm for 20min. Adjust the pH to 4.8 with 1.5% dilute acetic acid. Slowly add 1.8g of 50% glutaraldehyde aqueous solution in an ice-water bath at 2℃ and react for 5h. After the reaction is complete, separate the microspheres using a strong magnet, decant the supernatant, wash three times with deionized water and three times with anhydrous ethanol, and freeze-dry for 36h to obtain magnetic mesoporous silica@zirconium-quaternized chitosan.

[0033] Comparative Preparation Example 2: The preparation method of iron-aluminum-magnesium modified magnetic mesoporous silica microspheres is as follows: Step 1. Dissolve 4.5g of hexadecyltrimethylammonium bromide and 1.11g of urea in 369mL of deionized water to prepare a 1.5wt% aqueous solution. Add 1.0g of Fe3O4 nanoparticles (20nm particle size) and ultrasonically disperse in an ultrasonic device with a power of 200W and a frequency of 35kHz for 25min to obtain mixture A. Add 2.25g of tetraethyl orthosilicate and 0.325g of 3-aminopropyltriethoxysilane to mixture A and stir at 55℃ and 400rpm for 7h. After the reaction is completed, separate the microspheres with a strong magnet, decant the supernatant, wash three times with deionized water and three times with anhydrous ethanol, and vacuum dry at 55℃ for 13h. Disperse the dried product in an acidic ethanol solution (ethanol: concentrated hydrochloric acid = 50:1). In v / v), the mixture was stirred and refluxed at 55°C for 8 hours, and the extraction was repeated twice. Then, it was washed with deionized water until neutral, washed twice with anhydrous ethanol, and dried under vacuum at 55°C for 13 hours to obtain aminated magnetic mesoporous silica microspheres. Step 2. Dissolve 54.37g of ferric sulfate nonahydrate, 25.79g of aluminum sulfate octadecahydrate and 7.15g of magnesium sulfate heptahydrate in deionized water to prepare 1L of mixed aqueous solution with a total metal concentration of 0.3mol / L. Add 7.5g of the aminated magnetic mesoporous silica microspheres prepared in Step 1, stir at 250rpm for 20min, adjust the pH to 4.5 with 1.5% dilute acetic acid, stir and load at 55℃ for 8h, add 15g of urea, raise the temperature to 95℃ at 4℃ / min, and react for 3h. After the reaction is completed, separate the microspheres with a strong magnet, pour off the supernatant, wash with deionized water 3 times and anhydrous ethanol 3 times in sequence, and vacuum dry at 55℃ for 18h to obtain iron-aluminum-magnesium modified magnetic mesoporous silica microspheres. Comparative Preparation Example 3: The preparation method of aminated magnetic mesoporous silica microspheres is as follows: Step 1. Dissolve 4.5g of hexadecyltrimethylammonium bromide and 1.11g of urea in 369mL of deionized water to prepare a 1.5wt% aqueous solution. Add 1.0g of Fe3O4 nanoparticles (20nm particle size) and ultrasonically disperse in an ultrasonic device with a power of 200W and a frequency of 35kHz for 25min to obtain mixture A. Add 2.25g of tetraethyl orthosilicate and 0.325g of 3-aminopropyltriethoxysilane to mixture A and stir at 55℃ and 400rpm for 7h. After the reaction is completed, separate the microspheres with a strong magnet, decant the supernatant, wash three times with deionized water and three times with anhydrous ethanol, and vacuum dry at 55℃ for 13h. Disperse the dried product in an acidic ethanol solution (ethanol: concentrated hydrochloric acid = 50:1). In a v / v mixture, the mixture was stirred and refluxed at 55°C for 8 hours, and the extraction was repeated twice. Then, it was washed with deionized water until neutral, washed twice with anhydrous ethanol, and dried under vacuum at 55°C for 13 hours to obtain aminated magnetic mesoporous silica microspheres.

[0034] Example 1: A low-temperature high-efficiency phosphorus removal composite agent for frigid regions, made from the following components by mass percentage: 56 parts of iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan, 18 parts of low-temperature activating component, 14 parts of crystallization inducer, and 12 parts of adsorption enhancement carrier.

[0035] A method for preparing a low-temperature, high-efficiency phosphorus removal composite agent for frigid regions includes the following steps: S1. Weigh 56g of the preparation of iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan from Example 1; S2. Preparation of low-temperature activation component: Weigh 11.25g magnesium sulfate heptahydrate, 4.5g sodium bicarbonate and 2.25g sodium carbonate, put them into a high-speed mixer, mix at room temperature and 400rpm for 25min to obtain low-temperature activation component mixed powder; S3. Preparation of crystallization inducer: Weigh 10g of 100nm nano calcium carbonate and 4g of magnesium silicate, put them into a high-speed mixer, and mix for 50min at 40℃ and 900rpm to obtain crystallization inducer powder; S4. Preparation of adsorption enhancement carrier: Weigh 12g of attapulgite ore, crush it to 250 mesh, activate it at 150℃ for 3h, cool it and pass it through a 250 mesh sieve to obtain the adsorption enhancement carrier. S5. Compounding: Iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan, low-temperature activating components, crystallization inducers, and adsorption enhancement carriers are put into a three-dimensional mixer and stirred at 40℃ and 300rpm for 30min. Then, the mixture is vacuum dried at 45℃ for 18h, ground, and passed through a 120-mesh sieve to obtain a low-temperature high-efficiency phosphorus removal compound for frigid regions.

[0036] Example 2: A low-temperature high-efficiency phosphorus removal composite agent for frigid regions, made from the following components by mass percentage: 50 parts of iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan, 20 parts of low-temperature activating component, 15 parts of crystallization inducer, and 15 parts of adsorption enhancement carrier.

[0037] A method for preparing a low-temperature, high-efficiency phosphorus removal composite agent for frigid regions includes the following steps: S1. Weigh 50g of the preparation of iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan as shown in Example 2; S2. Preparation of low-temperature activation component: Weigh 13.25g magnesium chloride hexahydrate, 5.06g sodium bicarbonate and 1.69g sodium carbonate, put them into a high-speed mixer, mix at room temperature and 500rpm for 20min to obtain low-temperature activation component mixed powder; S3. Preparation of crystallization inducer: Weigh 11.25g of 50nm nano calcium carbonate and 3.75g of magnesium silicate, put them into a high-speed mixer, and mix for 40min at 35℃ and 1000rpm to obtain crystallization inducer powder; S4. Preparation of adsorption enhancement carrier: Weigh 15g of attapulgite ore, crush it to 200 mesh, activate it at 120℃ for 4h, cool it and pass it through a 200-mesh sieve to obtain the adsorption enhancement carrier. S5. Compounding: Iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan, low-temperature activating components, crystallization inducers, and adsorption enhancement carriers are put into a three-dimensional mixer and stirred at 35℃ and 400rpm for 25min. Then, the mixture is vacuum dried at 40℃ for 24h, ground, and passed through a 100-mesh sieve to obtain a low-temperature high-efficiency phosphorus removal compound for frigid regions.

[0038] Example 3: A low-temperature high-efficiency phosphorus removal composite agent for frigid regions, made from the following components by mass percentage: 60 parts of iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan, 20 parts of low-temperature activating component, 10 parts of crystallization inducer, and 10 parts of adsorption enhancement carrier.

[0039] A method for preparing a low-temperature, high-efficiency phosphorus removal composite agent for frigid regions includes the following steps: S1. Weigh 60g of the preparation example 3 to prepare iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan; S2. Preparation of low-temperature activation component: Weigh 11.25g magnesium chloride hexahydrate, 4.375g sodium bicarbonate and 4.375g sodium carbonate, put them into a high-speed mixer, mix at room temperature and 300rpm for 30min to obtain low-temperature activation component mixed powder; S3. Preparation of crystallization inducer: Weigh 6.25g of 200nm nano calcium carbonate and 3.75g of magnesium silicate, put them into a high-speed mixer, and mix at 45℃ and 800rpm for 60min to obtain crystallization inducer powder; S4. Preparation of adsorption enhancement carrier: Weigh 10g of attapulgite ore, crush it to 300 mesh, activate it at 180℃ for 2h, cool it and pass it through a 300-mesh sieve to obtain the adsorption enhancement carrier. S5. Compounding: Iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan, low-temperature activating components, crystallization inducers, and adsorption enhancement carriers are put into a three-dimensional mixer and stirred at 45℃ and 200rpm for 40min. Then, the mixture is vacuum dried at 50℃ for 12h, ground, and passed through a 150-mesh sieve to obtain a low-temperature high-efficiency phosphorus removal compound for frigid regions.

[0040] Comparative Example 1: Based on Example 1, the difference is that the low-temperature activation component is missing, and the rest is the same as Example 1.

[0041] Comparative Example 2: Based on Example 1, the difference is that the proportion of the low-temperature activation component is too low, only 8 parts, while the rest is the same as in Example 1.

[0042] Comparative Example 3: Based on Example 1, the difference is that the crystallization inducing agent is missing, otherwise it is the same as Example 1.

[0043] Comparative Example 4: Based on Example 1, the difference is that the adsorption enhancement carrier was not activated and had a specific surface area of ​​only 120 m². 2 / g, the rest is the same as in Example 1.

[0044] Comparative Example 5: Based on Example 1, the difference is that the iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan was replaced with the magnetic mesoporous silica@zirconium-quaternized chitosan prepared in Comparative Preparation Example 1, and the rest is the same as Example 1.

[0045] Comparative Example 6: Based on Example 1, the difference is that the iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan was replaced with the iron-aluminum-magnesium modified magnetic mesoporous silica microspheres prepared in Comparative Preparation Example 2, and the rest is the same as Example 1.

[0046] Comparative Example 7: Based on Example 1, the difference is that the iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan was replaced with the aminated magnetic mesoporous silica microspheres prepared in Comparative Preparation Example 3, and the rest is the same as in Example 1.

[0047] Performance testing: 1. Total phosphorus (TP) removal rate test: Referring to GB / T 11893-1989 standard, phosphorus-containing simulated wastewater (initial TP concentration set at 5.0 mg / L, pH=7.0) was prepared in a (2±1)℃ low temperature constant temperature bath. 0.5 g of samples from Examples 1-3 and Comparative Examples 1-7 were weighed and added to 1 L of simulated wastewater. The mixture was stirred at 200 r / min for 30 min, then allowed to stand for 60 min. The supernatant was filtered through a 0.45 μm filter membrane. The residual TP concentration in the filtrate was determined by potassium persulfate digestion-ammonium molybdate spectrophotometry. Each group of samples was measured in parallel 3 times. The average TP removal rate was calculated as follows: Removal rate (%) = (initial concentration - residual concentration) / initial concentration × 100%.

[0048] 2. Low-temperature storage performance degradation rate test: Samples from Examples 1-3 and Comparative Examples 1-7 were sealed in polyethylene bottles and stored in a low-temperature freezer at (-20±1)℃ for 30 days. The TP removal rate of the samples was determined before and after storage according to the above-mentioned "Total Phosphorus (TP) Removal Rate Test" method (the test temperature was still 2℃). Low-temperature storage performance degradation rate (%) = (Removal rate before storage - Removal rate after storage) / Removal rate before storage × 100%. The lower the degradation rate, the better the low-temperature storage stability.

[0049] 3. Sludge moisture content test: Take 1.0g of samples from Examples 1-3 and Comparative Examples 1-7 and add them to 1L of phosphorus-containing simulated wastewater (initial TP=5.0mg / L). Stir at 2℃ and 200r / min for 30min. After standing for 60min, use a strong magnet to adsorb and separate the magnetic flocs. Collect the bottom sludge and place it in a weighing bottle that has been pre-weighed. Dry it in an oven at 105℃ until it reaches constant weight. Calculate the moisture content: Moisture content (%) = (Wet sludge mass - Dry sludge mass) / Wet sludge mass × 100%. Take the average value of 3 tests for each group.

[0050] 4. Flocculation settling velocity test: Referring to GB / T 16881-2008, at 2℃, add 0.5g of sample to 1L of phosphorus-containing simulated wastewater (initial TP=5.0mg / L), stir rapidly at 200r / min for 2min, then stir slowly at 50r / min for 10min. Then transfer the mixture to a 1L graduated cylinder and let it settle. Record the time (s) required for the floc interface to descend from the liquid surface to the 500mL mark on the graduated cylinder. At the same time, observe the overall settling of the flocs within 5min after the start of settling. Each group is tested 3 times. The average settling velocity (mm / s) is calculated as (height from the liquid surface to the 500mL mark, in mm) / time (s). The height is converted according to the actual size of the graduated cylinder. The faster the settling velocity, the better the solid-liquid separation performance.

[0051] 5. Magnetic Separation and Recovery Performance Test: Under low temperature conditions of (2±1)℃, 0.5g of samples from Examples 1-3 and Comparative Examples 1-7 were weighed and dispersed in 1L of phosphorus-containing simulated wastewater (initial TP=5.0mg / L, pH=7.0). The mixture was stirred at 200r / min for 30min to allow for sufficient adsorption. Subsequently, the magnetic separation device (neodymium magnet with surface magnetic induction intensity ≥0.3T) was tightly attached to the outer wall of the container, and magnetic separation was performed under static conditions. The time from the initial application of the magnetic field to the complete adsorption of magnetic microspheres in the solution to the container wall was recorded. The time required for no visible black particles to be observed in the supernatant (magnetic separation time, unit: s) was measured. Then, under the condition of maintaining the magnetic field, the supernatant was poured off, and the microspheres adsorbed by the magnet were recovered. The recovered product was washed three times with deionized water and dried under vacuum at 55℃ to constant weight. The recovered mass was weighed, and the magnetic separation recovery rate was calculated according to the following formula: Recovery rate (%) = (dried mass after recovery / initial mass of added sample) × 100%. Each group of samples was measured in parallel three times, and the average value was taken. At the same time, the turbidity (NTU) of the supernatant after magnetic separation was measured using a UV-Vis spectrophotometer (600 nm wavelength) to characterize the thoroughness of magnetic separation. The shorter the magnetic separation time, the higher the recovery rate, and the lower the turbidity of the supernatant, the better the magnetic separation recovery performance.

[0052] Table 1. Performance Test Results

[0053] Data Analysis: Example 1 achieved a total phosphorus removal rate of 91.2%, a low-temperature storage attenuation rate of only 4.8%, a sludge moisture content of 72.5%, a floc settling velocity of 0.70 mm / s, a magnetic separation time of 40 s, a recovery rate of 67.6%, and a supernatant turbidity of 2.8 NTU. This formulation fully embodies the synergistic effect of "rapid adsorption-micro-area sedimentation-induced crystallization-carrier dispersion": the main adsorbent FeAlMg-M-MSN@Zr-QCS efficiently captures phosphate at low temperatures through quaternary ammonium positive charge and multi-metal inner sphere complexation; the low-temperature activating component (Mg... 2+ +HCO 3- Release Mg 2+ It maintains a slightly alkaline environment, which, together with the crystallization inducer (nano CaCO3 + magnesium silicate), significantly reduces the crystallization energy barrier, enabling phosphate to be rapidly converted into dense magnesium ammonium phosphate / calcium phosphate crystals. The activated attapulgite not only adsorbs phosphorus itself, but also prevents the main adsorbent from agglomerating and improves collision efficiency. The above mechanisms result in thorough phosphorus removal, dense sludge (low moisture content), and rapid sedimentation. At the same time, the magnetic core ensures rapid magnetic separation and high recovery rate, and excellent low-temperature storage stability.

[0054] Example 2 showed a total phosphorus removal rate of 90.1%, a decay rate of 5.0%, a sludge moisture content of 74.1%, a settling velocity of 0.65 mm / s, a magnetic separation time of 42 s, a recovery rate of 66.9%, and a supernatant turbidity of 3.5 NTU. Compared to Example 1, the proportions of the main adsorbent, activating component, and crystallization inducer were slightly adjusted (50 parts main adsorbent, 20 parts low-temperature activating component, 15 parts crystallization inducer, and 15 parts carrier). Overall performance remained high. The slightly lower total phosphorus removal rate was due to a decrease in the proportion of the main adsorbent, but the increased proportions of the low-temperature activating component and crystallization inducer still ensured effective precipitation and crystallization. The slightly lower magnetic separation recovery rate was related to a slight increase in agglomeration caused by the increased proportion of the adsorption-enhancing carrier, but overall, it still met the application requirements for extremely cold regions.

[0055] Example 3 showed a total phosphorus removal rate of 90.6%, a decay rate of 4.9%, a sludge moisture content of 73.8%, a settling velocity of 0.67 mm / s, a magnetic separation time of 41 s, a recovery rate of 67.2%, and a supernatant turbidity of 3.2 NTU. This formulation had the highest proportion of primary adsorbent (60 parts), but a relatively low proportion of crystallization inducer (10 parts), resulting in a slightly lower removal rate than Example 1. This indicates that the content of crystallization inducer is equally crucial for the complete conversion of phosphate at low temperatures. However, due to the strong adsorption capacity of the primary adsorbent, it still maintained good phosphorus removal efficiency and settling performance, good low-temperature storage stability, and excellent magnetic separation performance.

[0056] Comparative Example 1, lacking the low-temperature activation component, saw its total phosphorus removal rate drop to 64.5%, its attenuation rate increase to 12.3%, its sludge moisture content reach as high as 85.6%, and its settling velocity be only 0.32 mm / s. This was due to the absence of Mg... 2+ Without pH buffers, a locally supersaturated slightly alkaline environment cannot be formed at low temperatures. Phosphate ions mainly rely on electrostatic attraction and coordination adsorption of the main adsorbent, lacking precipitation and crystallization transformation. Therefore, the phosphorus removal effect decreases, and the generated flocs are mostly adsorbent particles and a small amount of loose precipitate. They have strong water retention and slow settling. When stored at low temperatures, the lack of inorganic salt buffer protection leads to more significant degradation in material performance. The magnetic separation performance is still acceptable (recovery rate 65.8%, turbidity 6.5 NTU), but the turbidity of the supernatant increases, indicating that some fine particles have not been effectively aggregated.

[0057] In Comparative Example 2, the proportion of the low-temperature activation component was too low (only 8 parts), resulting in a total phosphorus removal rate of 73.2%, a decay rate of 9.6%, a sludge moisture content of 80.3%, and a settling velocity of 0.42 mm / s. Although a certain amount of Mg was present... 2+The pH buffer was used, but it was insufficient to establish a sufficiently high supersaturation at low temperatures, resulting in incomplete crystallization. The performance was improved compared to Comparative Example 1, but it was still far lower than that of Examples 1-3. This indicates that the dosage of the low-temperature activating component needs to reach more than 10 parts to effectively promote precipitation and crystallization. Other indicators, such as magnetic separation recovery rate of 66.3% and turbidity of 5.1 NTU, were slightly better than Comparative Example 1, but overall, they still did not meet the requirements for efficient phosphorus removal.

[0058] Comparative Example 3 lacked a crystallization inducer, resulting in a total phosphorus removal rate of 68.9%, a decay rate of 11.5%, a sludge moisture content of 89.2%, and a settling velocity of only 0.23 mm / s. It had the highest sludge moisture content and slowest settling velocity among all samples. Although the low-temperature activation component could provide Mg... 2+ The pH was adjusted, but due to the lack of nano-calcium carbonate and magnesium silicate as seed crystals, phosphate could only nucleate homogeneously at low temperatures. The nucleation energy barrier was high, and crystal growth was slow, resulting in a large number of amorphous fine precipitates. These precipitates had strong water retention, were difficult to settle, and easily penetrated the filter membrane, leading to high residual phosphorus. The magnetic separation recovery rate was 65.1%, but the turbidity of the supernatant was as high as 7.3 NTU, indicating that a large number of non-magnetic fine particles were not captured. This verifies the key role of crystallization inducers in "heterogeneous nucleation" at low temperatures.

[0059] Comparative Example 4 used unactivated attapulgite soil (specific surface area only 120 m²). 2 The total phosphorus removal rate was 71.6%, the attenuation rate was 8.9%, the sludge moisture content was 79.5%, the settling velocity was 0.47 mm / s, the magnetic separation time was extended to 52 s, the recovery rate was 64.2%, and the turbidity was 6.0 NTU. Insufficiently activated attapulgite had weak adsorption capacity and poor dispersion of the main adsorbent, leading to the aggregation of some of the main adsorbent, reducing the effective collision efficiency and phosphorus adsorption capacity. Simultaneously, the unactivated carrier did not bind firmly to the magnetic particles, causing some fine particles to detach during magnetic separation, resulting in prolonged magnetic separation time, decreased recovery rate, and increased turbidity. This confirms the auxiliary synergistic effect of the high specific surface area of ​​the adsorption-enhancing carrier and activation treatment on low-temperature phosphorus removal.

[0060] Comparative Example 5, where the main adsorbent was replaced with iron-, aluminum-, and magnesium-free modified magnetic mesoporous silica@zirconium-quaternized chitosan (i.e., containing only Zr-QCS), achieved a total phosphorus removal rate of 66.3%, a decay rate of 10.8%, a sludge moisture content of 83.7%, and a settling velocity of 0.27 mm / s. (Fe was missing.) 3+ Al 3+ Mg 2+ Metal coordination sites, relying solely on the positive charge of the quaternary ammonium group and Zr 4+Partial coordination effect, adsorption capacity and affinity decrease significantly at low temperature. At the same time, the lack of precipitation contribution from metal ions means that the electrostatic attraction of organic quaternary ammonium salts alone cannot effectively induce subsequent crystallization, resulting in low phosphorus removal rate, loose sludge, and acceptable magnetic separation performance (recovery rate 66.0%). However, the turbidity of the supernatant is 6.8 NTU, indicating that multi-metal co-doping is crucial for low-temperature phosphorus removal.

[0061] Comparative Example 6 replaced the main adsorbent with iron-aluminum-magnesium modified magnetic mesoporous silica microspheres (i.e., FeAlMg-M-MSN, without Zr-QCS coating) that lacked quaternized chitosan and zirconium cross-linking layers. The total phosphorus removal rate was 57.8%, the decay rate was 14.2%, the sludge moisture content was 84.9%, the settling velocity was 0.25 mm / s, the magnetic separation recovery rate plummeted to 59.5%, and the supernatant turbidity reached as high as 12.4 NTU. Although this material has certain metal adsorption sites, it lacks the positively charged surface of quaternized chitosan and the cross-linking protective layer, resulting in slow adsorption kinetics at low temperatures, easy particle aggregation, and easy detachment of the metal layer. Small fragments detached during magnetic separation caused low recovery rate and high turbidity. The performance deteriorated severely after low-temperature storage, indicating that the Zr-QCS cross-linking network not only provides positive charge but also plays a stabilizing and protective role for the magnetic core and metal layer.

[0062] Comparative Example 7 used only aminated magnetic mesoporous silica microspheres (M-MSN-NH2), without any metal loading, quaternized chitosan, low-temperature activating components, or crystallization inducers. Relying solely on the weak protonation adsorption of phosphate by amino groups, the total phosphorus removal rate was only 43.5%, with a high attenuation rate of 18.5%. The sludge moisture content was 86.3%, the settling velocity was the slowest (0.15 mm / s), and although the magnetic separation time was short (36 s), the recovery rate was only 62.8%, and the supernatant turbidity was the highest (15.6 NTU). This material almost lost its phosphorus removal capacity at low temperatures, and after freeze-thaw cycles, the pores collapsed and the amino groups oxidized, leading to a sharp decline in performance. During magnetic separation, a large number of nano-sized particles could not be effectively captured, causing secondary pollution. This comparative example, as the most basic control, reversely verified that the multi-level functionalization modification of the main adsorbent, the low-temperature activating components, and the crystallization inducers are all indispensable core elements for efficient low-temperature phosphorus removal in frigid regions.

[0063] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A low-temperature, high-efficiency phosphorus removal compound agent for frigid regions, characterized in that, It includes the following components by weight: 50-60 parts of iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan, 15-20 parts of low-temperature activation component, 10-15 parts of crystallization inducer, and 10-15 parts of adsorption enhancement carrier.

2. The low-temperature high-efficiency phosphorus removal composite agent for frigid regions according to claim 1, characterized in that, The preparation method of the iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan is as follows: Step 1. Dissolve hexadecyltrimethylammonium bromide and urea in deionized water to prepare a 1-2 wt% aqueous solution. Add Fe3O4 nanoparticles and ultrasonically disperse them for 20-30 min in an ultrasonic device with a power of 100-300 W and a frequency of 30-40 kHz to obtain mixture A. Add tetraethyl orthosilicate and 3-aminopropyltriethoxysilane to mixture A and stir the mixture at 50-60℃ and 300-500 rpm for 6-8 h. After the reaction is complete, let... The microspheres were separated using a strong magnet. The supernatant was carefully poured off and the microspheres were washed 2-3 times with deionized water and 2-3 times with anhydrous ethanol. The microspheres were then vacuum dried at 50-60°C for 12-15 hours. The dried product was dispersed in an acidic ethanol solution and refluxed at 50-60°C for 6-12 hours. The extraction was repeated 2-3 times. The microspheres were then washed with deionized water until neutral and washed twice with anhydrous ethanol. The microspheres were then vacuum dried at 50-60°C for 12-15 hours to obtain aminated magnetic mesoporous silica microspheres. Step 2. Dissolve ferric sulfate nonahydrate, aluminum sulfate octadecahydrate, and magnesium sulfate heptahydrate in deionized water to prepare a metal mixed aqueous solution with a total metal concentration of 0.1-0.5 mol / L. Add the aminated magnetic mesoporous silica microspheres prepared in Step 1, stir at 200-300 rpm for 15-30 min, adjust the pH to 4.0-5.0 with 1-2% dilute acetic acid solution or dilute sodium hydroxide solution, and stir and load at 50-60℃ for 6-12 h. Then add urea, slowly raise the temperature to 90-100℃ at a rate of 3-5℃ / min, and react for 2-4 h. After the reaction is complete, separate the microspheres with a strong magnet, carefully pour off the supernatant, wash with deionized water 2-3 times, wash with anhydrous ethanol 2-3 times, and vacuum dry at 50-60℃ for 12-24 h to obtain iron-aluminum-magnesium modified magnetic mesoporous silica microspheres. Step 3. Dissolve quaternized chitosan in a 2-3% acetic acid aqueous solution to prepare a 1.5-2.5 wt% quaternized chitosan solution. Add zirconium oxychloride octahydrate and stir at 300-500 rpm for 1-2 hours to obtain mixture B. Then add the iron-aluminum-magnesium modified magnetic mesoporous silica microspheres obtained in Step 2 and stir at 200-300 rpm for 15-30 minutes. Adjust the pH to 4.5-5.0 with 1-2% dilute acetic acid solution or dilute sodium hydroxide solution. Slowly add 50% glutaraldehyde aqueous solution in an ice-water bath at 0-4℃ and react for 4-6 hours. After the reaction is complete, separate the microspheres with a strong magnet, carefully pour off the supernatant, wash with deionized water 2-3 times, wash with anhydrous ethanol 2-3 times, and freeze-dry for 24-48 hours to obtain iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan.

3. The low-temperature high-efficiency phosphorus removal composite agent for frigid regions according to claim 2, characterized in that, In step 1, the molar ratio of hexadecyltrimethylammonium bromide to urea is 1:1-2; the Fe3O4 nanoparticles have a particle size of 10-30 nm, and the mass ratio of Fe3O4 to hexadecyltrimethylammonium bromide is 1:4-5; the mass ratio of tetraethyl orthosilicate, 3-aminopropyltriethoxysilane to Fe3O4 nanoparticles is 2.0-2.5:0.30-0.35:1; the acidic ethanol solution is prepared by mixing ethanol and concentrated hydrochloric acid at a volume ratio of 50:

1.

4. The low-temperature high-efficiency phosphorus removal composite agent for frigid regions according to claim 2, characterized in that, In step 2, the molar ratio of iron, aluminum, and magnesium in ferric sulfate nonahydrate, aluminum sulfate octadecahydrate, and magnesium sulfate heptahydrate is 1:0.3-0.5:0.1-0.2; the amount ratio of the aminated magnetic mesoporous silica microspheres to the metal mixed aqueous solution is 5-10 g:1 L; and the mass ratio of urea to the aminated magnetic mesoporous silica microspheres is 1-3:

1.

5. The low-temperature high-efficiency phosphorus removal composite agent for frigid regions according to claim 2, characterized in that, In step 3, the mass ratio of quaternized chitosan to zirconium oxychloride octahydrate is 4-6:1; the ratio of the amount of iron-aluminum-magnesium modified magnetic mesoporous silica microspheres to mixed solution B is 2-4 g:1 L; and the mass ratio of glutaraldehyde to iron-aluminum-magnesium modified magnetic mesoporous silica microspheres is 0.1-0.5:

1.

6. The low-temperature high-efficiency phosphorus removal composite agent for frigid regions according to claim 1, characterized in that, The low-temperature activation component is composed of magnesium salt and pH buffer in a mass ratio of 1:0.5-0.8; the magnesium salt is magnesium chloride hexahydrate or magnesium sulfate heptahydrate, and the pH buffer is composed of sodium bicarbonate and sodium carbonate in a mass ratio of 1-3:

1.

7. The low-temperature high-efficiency phosphorus removal composite agent for frigid regions according to claim 1, characterized in that, The crystallization inducer is composed of nano-calcium carbonate with a particle size of 50-200nm and magnesium silicate in a mass ratio of 1:0.3-0.

6.

8. The low-temperature high-efficiency phosphorus removal composite agent for frigid regions according to claim 1, characterized in that, The adsorption-enhancing support is activated attapulgite having a specific surface area of > 300 m 2 / g.

9. A method for preparing a low-temperature, high-efficiency phosphorus removal composite agent for frigid regions as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Preparation of iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan; S2. Preparation of low-temperature activation component: Weigh magnesium salt and pH buffer, put them into a high-speed mixer, and mix for 20-30 minutes at room temperature and 300-500 rpm to obtain low-temperature activation component mixed powder; S3. Preparation of crystallization inducer: Weigh nano-calcium carbonate and magnesium silicate, put them into a high-speed mixer, and mix for 40-60 minutes at 30-45℃ and 800-1000 rpm to obtain crystallization inducer powder; S4. Preparation of adsorption enhancement carrier: Weigh the raw attapulgite ore, crush it to 200-300 mesh, activate it at 120-180℃ for 2-4 hours, cool it and pass it through a 200-300 mesh sieve to obtain the adsorption enhancement carrier. S5. Compounding: Weigh iron-aluminum-magnesium modified magnetic mesoporous silica@zirconium-quaternized chitosan, low-temperature activating components, crystallization inducing agents, and adsorption enhancing carriers, put them into a three-dimensional mixer, stir and mix at 30-45℃ and 200-400rpm for 20-40min, then vacuum dry at 40-50℃ for 12-24h, grind and pass through a 100-150 mesh sieve to obtain a low-temperature high-efficiency phosphorus removal composite agent for frigid regions.

Images