Composite flocculant, preparation method and application thereof

Abstract

The present application provides a composite flocculant, a preparation method thereof and an application thereof. The composite flocculant is a ceramsite-based composite material comprising a magnetic Fe3O4 core, an aluminum salt intermediate layer and a rare earth outer layer, and the rare earth is a lanthanide element. The magnetic Fe3O4 core in the composite flocculant of the present invention has a high saturation magnetization intensity, which can realize the rapid separation of the flocculant from water; at the same time, Fe3O4 can block the erosion of competitive ions such as Cl ‑ , SO4² ‑ in the aqueous phase on the aluminum salt and rare earth lanthanum, reducing the dissolution of active components; the aluminum salt intermediate layer promotes flocculation, and the lanthanum ions (La³ + ) in the rare earth outer layer react with phosphate (PO4³ ‑ ) to generate LaPO4 precipitate to improve the phosphorus removal effect. The components act synergistically to efficiently remove pollutants in water and significantly improve water quality.

Description

Technical Field

[0001] This application relates to the technical field of water pollution treatment, and particularly relates to a composite flocculant, a preparation method thereof, and an application thereof. Background Art

[0002] Phosphorus-containing wastewater can cause eutrophication of water bodies. Therefore, effectively reducing phosphorus in water bodies is of great significance for preventing and controlling water body eutrophication. Currently, common phosphorus removal methods mainly include adsorption method, membrane separation method, chemical precipitation method, biological method, crystallization method, etc. Different phosphorus removal methods are applicable to the treatment of different water qualities. In the process of treating eutrophic water bodies, the chemical precipitation method and the crystallization method will consume a large amount of chemical reagents and simultaneously generate precipitates that are difficult to treat. The membrane separation method and the biological method are greatly affected by environmental conditions, while the adsorption method has the advantages of simple operation, good and stable phosphorus removal effect, less sludge production, and low operating cost. Commonly used adsorbents mainly include zeolite, chitosan, diatomite, activated carbon, etc. Among them, zeolite, as a mineral with a framework structure, has a large specific surface area and a rich pore structure. Its cations will not change the basic framework of zeolite during ion exchange reactions and can have good adsorption and ion exchange effects with cations in the environment, and is widely used in water treatment; chitosan is a polymer obtained by deacetylating chitin widely existing in nature. Due to its similar structure to cellulose and the presence of acetamide groups, this structure makes chitosan have good adsorption function and is also very conducive to the modification of materials. However, the adsorption capacities of traditional adsorbents are relatively low, and it is difficult to meet the requirements for sewage treatment up to standard by using a single adsorbent. Therefore, it is necessary to develop a new type of flocculant with high phosphorus removal ability. Summary of the Invention

[0003] This application is made in view of the above problems, and its purpose is to provide a composite flocculant, a preparation method thereof, and an application thereof.

[0004] Specifically, in the first aspect of this application, a composite flocculant is provided. The composite flocculant is a ceramsite-based composite material comprising a magnetic Fe3O4 core, an aluminum salt intermediate layer, and a rare earth outer layer, and the rare earth is a lanthanide element;

[0005] The composite flocculant includes the following components in parts by mass: 100-120 parts of silicon-aluminum-based ceramsite, 8-10 parts of polyaluminum chloride, 8-10 parts of lanthanum salt, 12-18 parts of iron source, 10-15 parts of polyacrylamide, 1-5 parts of silane coupling agent, and 0.2-0.6 part of citric acid.

[0006] Preferably, the particle size of the silicon-aluminum-based ceramsite is 2-4 mm, and the molar ratio of SiO2 to Al2O3 is 2-4:1.

[0007] Preferably, the iron source includes iron salt and ferrous salt;

[0008] And / or, the molar ratio of the ferric salt to the ferrous salt is 2-3:1.

[0009] The second aspect of the present application provides a method for preparing the composite flocculant, comprising the following steps:

[0010] S1: Calcining the silicon-aluminum-based ceramsite to form a honeycomb-like porous structure;

[0011] S2: Immersing the calcined silicon-aluminum-based ceramsite in a polyaluminum chloride solution, performing ultrasonic treatment, and then drying to form PAC@ceramsite;

[0012] S3: Reacting the PAC@ceramsite by immersing it in a lanthanum salt solution to generate La-PAC@ceramsite, and then calcining the La-PAC@ceramsite;

[0013] S4: Immersing the La-PAC@ceramsite in an iron source to form a nano-Fe3O4 layer on the surface of the La-PAC@ceramsite, and then treating the Fe3O4 / La-PAC@ceramsite with a silane coupling agent to obtain silicon-modified Fe3O4 / La-PAC@ceramsite;

[0014] S5: Mixing the silicon-modified Fe3O4 / La-PAC@ceramsite in step S4 with polyacrylamide and spray-drying into porous particles;

[0015] S6: Immersing the porous particles in a citric acid solution and drying to obtain the composite flocculant.

[0016] Preferably, the calcination temperature in step S1 is 800-850 °C;

[0017] And / or, the calcination time is 2-3 h.

[0018] Preferably, the ultrasonic treatment time in step S2 is 1-2 h, and drying is performed at 70-90 °C.

[0019] Preferably, the pH of the reaction of immersing the PAC@ceramsite in the lanthanum salt solution in step S3 is 8-9;

[0020] The reaction temperature of immersing the PAC@ceramsite in the lanthanum salt solution is 60-70 °C;

[0021] The reaction time of immersing the PAC@ceramsite in the lanthanum salt solution is 2-3 h;

[0022] The calcination temperature of the La-PAC@ceramsite in step S3 is 400-500 °C;

[0023] The calcination time of the La-PAC@ceramsite in step S3 is 1-2 h.

[0024] Preferably, in step S4, the La-PAC@ceramsite is immersed in the iron source, and the pH is adjusted to 9-11;

[0025] and / or, the temperature of the hydrothermal reaction is 60-70 °C;

[0026] and / or, the time of the hydrothermal reaction is 5-6 h.

[0027] Preferably, the atmosphere of the calcination in step S4 is a protective atmosphere;

[0028] and / or, the protective atmosphere includes a nitrogen or noble gas atmosphere;

[0029] and / or, the calcination in step S4 includes a first-stage calcination and a second-stage calcination;

[0030] and / or, the temperature of the first-stage calcination is 450-500 °C;

[0031] and / or, the time of the first-stage calcination is 1-2 h;

[0032] and / or, the temperature of the second-stage calcination is 650-700 °C;

[0033] and / or, the time of the second-stage calcination is 30-40 min.

[0034] Preferably, the drying temperature in step S6 is 60-70 °C, and the drying time is 1-3 h.

[0035] The third aspect of the present application provides an application of the composite flocculant in water pollution treatment.

[0036] The present invention has the following beneficial effects:

[0037] (1) The composite flocculant of the present invention comprises a magnetic Fe3O4 core, an aluminum salt intermediate layer and a rare earth outer layer of a ceramsite-based composite material, and the rare earth is a lanthanide element. Among them, the magnetic Fe3O4 core has a high saturation magnetization intensity, which can realize the rapid separation of the flocculant from water; at the same time, Fe3O4 can block the erosion of competitive ions such as Cl - and SO4² - in the aqueous phase on the aluminum salt and rare earth lanthanum, reducing the dissolution of active components; the aluminum salt intermediate layer promotes flocculation, and the lanthanum ions (La 3+ ) in the rare earth outer layer react with phosphate (PO4 3- ) to form LaPO4 precipitate to improve the phosphorus removal effect. The components act synergistically to efficiently remove pollutants in water and significantly improve water quality.

[0038] (2) In the composite flocculant of the present invention, taking the silicon-aluminum-based ceramsite as the carrier, polyaluminum chloride is loaded on its surface, which can rapidly flocculate and capture suspended phosphorus. At the same time, the silicon-aluminum-based ceramsite is modified with lanthanum salt, and La³ + acts synergistically with polyaluminum chloride to efficiently remove heavy metal ions in water, significantly improve the flocculation effect, and reduce the treatment cost; the nano-Fe3O4 layer generated by the iron source in the silicon-aluminum-based ceramsite enhances the magnetism and adsorption capacity of the composite flocculant, enabling rapid recovery of the medicament and reducing secondary pollution; the treatment with citric acid solution further optimizes the surface properties of the flocculant, improves its adaptability and stability in complex water quality, and ensures long-term and efficient sewage treatment effect.

[0039] (3) Through specific preparation steps, the present invention effectively combines various components such as silicon-aluminum-based ceramsite, polyaluminum chloride, and lanthanum nitrate to form a composite flocculant with excellent performance. This composite flocculant not only has high flocculation and phosphorus removal capabilities, but also can remove heavy metal ions in water, and has strong magnetism and adsorption capacity, is easy to recover, and reduces the risk of secondary pollution.

[0040] (4) The composite flocculant of the present invention has broad application prospects in water pollution treatment. Whether in domestic sewage, industrial wastewater or agricultural wastewater treatment, this composite flocculant can exert its unique advantages, providing strong technical support for water pollution control. At the same time, the use of this composite flocculant can effectively reduce the treatment cost and improve the treatment efficiency, which is of great significance for promoting the in-depth development of water pollution control work. Description of the Drawings

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present drawings or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present drawings. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0042] Figure 1 It is the total phosphorus removal rate of the flocculant in the examples and comparative examples.

[0043] The realization, functional features and advantages of the present drawings will be further described in combination with the embodiments with reference to the drawings. Detailed Embodiments

[0044] In order to make the objectives, technical solutions and advantages of the present application more clear and understandable, the present application will be described and explained below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application. Based on the embodiments provided in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0045] Obviously, the following description is only some examples or embodiments of the present application. For those of ordinary skill in the art, without creative efforts, the present application can also be applied to other similar scenarios. In addition, it can also be understood that although the efforts made in this development process may be complex and lengthy, for those of ordinary skill in the art related to the content disclosed in the present application, some design, manufacturing or production changes based on the technical content disclosed in the present application are only conventional technical means and should not be understood as the content disclosed in the present application being insufficient.

[0046] If there is no special indication, the "including" and "comprising" mentioned in the present application mean open-ended, and can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or only the components listed can be included or comprised.

[0047] If there is no special indication, in the present application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0048] An embodiment of the first aspect of the present application provides a composite flocculant, which comprises a magnetic Fe3O4 core, an aluminum salt intermediate layer and a rare earth outer layer of a ceramsite-based composite material, and the rare earth is a lanthanide element. Among them, the magnetic Fe3O4 core has a high saturation magnetization intensity, which can realize the rapid separation of the flocculant from water; at the same time, Fe3O4 can block the erosion of competitive ions such as Cl - 、SO4² - in the water phase on the aluminum salt and rare earth lanthanum, reducing the dissolution of active components; the aluminum salt intermediate layer promotes flocculation, and the lanthanum ions (La³ + in the rare earth outer layer react with phosphate (PO4³ - ) to generate LaPO4 precipitate to improve the phosphorus removal effect. The components work together to efficiently remove pollutants in water and significantly improve water quality.

[0049] In an embodiment of the present invention, the composite flocculant comprises the following components in parts by mass: 100-120 parts of silicon-aluminum-based ceramsite, 8-10 parts of polyaluminum chloride, 8-10 parts of lanthanum salt, 12-18 parts of iron source, 10-15 parts of polyacrylamide, 1-5 parts of silane coupling agent, and 0.2-0.6 parts of citric acid.

[0050] The silicon-aluminum-based ceramsite is purchased from Zhejiang Green Beauty New Environmental Protection Technology Co., Ltd. The silicon-aluminum-based ceramsite has SiO2 and Al2O3 as the core components and is made from aluminosilicate minerals or industrial solid wastes (such as fly ash and coal gangue). The ratio of Al2O3 to SiO2 is controlled between 1:2-4. The specific surface area of the silicon-aluminum-based ceramsite > 7x10 4 cm 2 / g, and the porosity > 40%; the silicon-aluminum-based ceramsite plays a core skeleton role in the composite flocculant, enhancing the flocculation effect; the mass fraction of the silicon-aluminum-based ceramsite is any value or any combination of values among 100, 105, 110, 115, and 120 parts.

[0051] The polyaluminum chloride is self-produced by Hengyang Jianheng Industry Co., Ltd. Polyaluminum chloride is an inorganic polymer polyvalent ion polymeric electrolyte coagulant. It is an intermediate hydrolysis product between aluminum trichloride and aluminum hydroxide. Due to the bridging effect of hydroxide ions and the polymerization of polyvalent ions, an inorganic polymer water treatment agent with a relatively large molecular weight and a relatively high charge is formed. The mass fraction of alumina (AL2O3) in the polyaluminum chloride is 28%, the basicity is 85%, and the mass fraction of water-insoluble matter is 0.4%. In the embodiments of the present invention, its mass fraction is any value among 8, 9, and 10 parts; polyaluminum chloride has an efficient flocculation effect and can quickly form large flocs.

[0052] The lanthanum salt is lanthanum nitrate, which can effectively improve the sedimentation performance of the flocculant; its mass fraction is any value among 8, 9, and 10 parts.

[0053] The iron source includes ferric salt and ferrous salt, and the molar ratio of the ferric salt to the ferrous salt is 2-3:1; further, the ferric salt is FeCl3·6H2O, and the ferrous salt is FeCl2·4H2O. FeCl3·6H2O and FeCl2·4H2O are purchased from Shanghai Huayi Fine Chemical Co., Ltd. The mass fraction of the FeCl3·6H2O / FeCl2·4H2O mixture is any value or combination among 12, 14, 16, and 18 parts.

[0054] The polyacrylamide is self-produced by Hengyang Jianheng Industry Co., Ltd., which is white powder or small granular substance, and the effective ingredient content is greater than 99%. The molecular weight of the polyacrylamide is 4 million - 7 million; in the embodiments of the present invention, its mass fraction is any value among 10, 12, 14, and 15 parts.

[0055] The silane coupling agent is KH-550, CAS No.: 919-30-2; and its mass fraction is any value among 1, 3, and 5 parts.

[0056] The concentration of the citric acid solution is 0.1-0.3 mol / L, which optimizes the surface charge distribution of the flocculant and improves the flocculation efficiency. Citric acid is used to optimize the flocculation effect; and its mass fraction is any value among 0.2, 0.4, and 0.6 parts. The components act synergistically to significantly improve the flocculation effect and stability.

[0057] In the composite flocculant of the present invention, silicoaluminate ceramsite is used as a carrier, and polyaluminum chloride is loaded on its surface, which can rapidly flocculate and capture suspended phosphorus. At the same time, lanthanum nitrate is used to modify the silicoaluminate ceramsite, and La³ + acts synergistically with polyaluminum chloride to efficiently remove heavy metal ions in water, significantly improve the flocculation effect, and reduce the treatment cost; the nano-Fe3O4 layer formed by the FeCl3·6H2O / FeCl2·4H2O mixed solution in the silicoaluminate ceramsite enhances the magnetism and adsorption capacity of the composite flocculant, enabling rapid recovery of the medicament and reducing secondary pollution; the treatment with the citric acid solution further optimizes the surface properties of the flocculant, improves its adaptability and stability in complex water quality, and ensures long-term and efficient sewage treatment effects.

[0058] In the embodiment of the present invention, the particle size of the silicoaluminate ceramsite is 2-4 mm, and the ratio of SiO2 to Al2O3 is 2-4:1, ensuring that it has a higher specific surface area and stronger adsorption capacity during the flocculation process.

[0059] In the embodiment of the present invention, the total iron concentration in the FeCl3·6H2O / FeCl2·4H2O mixed solution is 0.12 mol / L, and the molar ratio of FeCl3·6H2O to FeCl2·4H2O is 2-3:1, ensuring that the mixed solution exerts the best synergistic effect during the flocculation process.

[0060] The embodiment of the second aspect of the present application provides a preparation method of the composite flocculant described above, including the following steps:

[0061] S1: Calcining the silicoaluminate ceramsite to form a honeycomb-like porous structure;

[0062] S2: Immersing the calcined silicoaluminate ceramsite in a polyaluminum chloride solution, performing ultrasonic treatment, and then drying to form PAC@ceramsite;

[0063] S3: Immersing PAC@ceramsite in a lanthanum salt solution for reaction to generate La-PAC@ceramsite;

[0064] S4: Immerse the La-PAC@ceramsite in an iron source for hydrothermal reaction. After the reaction is completed, calcine it to form Fe3O4 / La-PAC@ceramsite, and then treat the Fe3O4 / La-PAC@ceramsite with a silane coupling agent; silicon-modified Fe3O4 / La-PAC@ceramsite is prepared.

[0065] S5: Mix the silicon-modified Fe3O4 / La-PAC@ceramsite in step S4 with polyacrylamide and spray-dry it into porous particles.

[0066] S6: Immerse the porous particles in a citric acid solution and dry them to obtain a composite flocculant.

[0067] In the embodiment of the present invention, in step S1, a silicon-aluminum-based ceramsite with a particle size of 2-4 mm is selected, soaked in 10% HNO3 for 2 h to remove impurities, rinsed with water until neutral, and dried. Calcined in a high-temperature furnace at 800-850 °C for 2-3 h to form a honeycomb-like porous structure with a specific surface area > 300 m² / g.

[0068] In step S2, the concentration of the polyaluminum chloride solution is 10-15%, the ultrasonic treatment time is 1-2 h, and it is dried to constant weight at 70-90 °C to ensure uniform loading of polyaluminum chloride. Immerse the calcined silicon-aluminum-based ceramsite in a polyaluminum chloride (PAC) solution. The polyaluminum chloride solution is prepared by dissolving polyaluminum chloride in 10 times the amount of deionized water to fill the pores of the ceramsite with PAC and provide initial flocculation ability.

[0069] In step S3, the concentration of the lanthanum nitrate solution is 0.5-1 mol / L, preferably 0.2 mol / L. Dropwise add ammonia water to adjust the pH to 8.5 and stir at 60-70 °C for 2.5-3 h. La³ + Complexes with the hydroxyl groups in PAC to generate La-PAC@ceramsite, and the La loading is about 8 wt%. Then calcine the La-PAC@ceramsite at 400-500 °C for 1-2 h to stably anchor La³ + In the form of LaO(OH) on the surface of the ceramsite. La³ + Provides high-density adsorption sites and enhances the chemical precipitation ability for PO4³ -

[0070] In step S4, immerse the La-PAC@ceramsite in a mixed solution of FeCl3·6H2O / FeCl2·4H2O, dropwise add NaOH to adjust the pH to 10, carry out hydrothermal reaction at 60-70 °C for 5-6 h, and form a nano-Fe3O4 layer on the surface to form Fe3O4 / La-PAC@ceramsite. Under a N2 atmosphere, calcine the Fe3O4 / La-PAC@ceramsite at 450-500 °C for 1-2 h, and then raise the temperature to 650-700 °C and calcine for 30-40 min to avoid oxidation of Fe3O4.

[0071] ​The surface of Fe3O4 / La-PAC@ceramsite was treated with silane coupling agent (KH-550) to improve hydrophobicity and reduce the aggregation of the agent itself.

[0072] In step S5, the modified Fe3O4 / La-PAC@ceramsite is mixed with polyacrylamide in a ratio of 10:1, the spray drying temperature is 150-180°C, and the particles are spray dried into 1-3 mm particles.

[0073] In step S6, the porous particles are immersed in the citric acid solution for 2 hours, the drying temperature is 60-70°C, and the drying time is 1-3 hours.

[0074] The working principle of the composite flocculant of the present invention is: polyaluminium chloride quickly neutralizes the surface charge of the colloid to form flocs that encapsulate phosphorus particles; La³ + Reacts with dissolved phosphorus to form LaPO4 precipitation, further reducing the phosphorus content in water, La³ + It works together with polyaluminium chloride to efficiently remove heavy metal ions; the nano-Fe3O4 layer enhances magnetism and adsorption, drives the entire particle to settle under the magnetic field, shortens the separation time, and achieves rapid recovery of the reagent; citric acid optimizes surface properties, improves adaptability and stability, and ensures long-term and efficient sewage treatment.

[0075] The third aspect of the present application provides an application of the composite flocculant in water pollution treatment. The specific operation is: add the composite flocculant to the water to be treated at 5-10g / m³, stir and mix for 10-15 minutes, let it settle for 30-60 minutes, observe the clarity of the water quality, and detect the concentration of phosphorus and heavy metal ions to ensure that the discharge meets the standards. It is suitable for various scenarios such as industrial wastewater and domestic sewage, significantly improving treatment efficiency and reducing operating costs.

[0076] Example 1

[0077] A composite flocculant comprises the following components in parts by mass: 100 parts of silica-aluminum-based ceramsite, 9 parts of polyaluminum chloride, 9 parts of lanthanum nitrate, 14 parts of FeCl3·6H2O / FeCl2·4H2O mixed solution, 12 parts of polyacrylamide, 2 parts of silane coupling agent KH-550, and 0.4 parts of citric acid.

[0078] Example 2

[0079] This embodiment is substantially the same as Embodiment 1, except that the mass fraction of polyaluminium chloride is 10 parts.

[0080] Example 3

[0081] This embodiment is substantially the same as embodiment 1, except that the mass fraction of lanthanum nitrate is 10 parts.

[0082] Example 4

[0083] This example is basically the same as Example 1, except that the mass fraction of the FeCl3·6H2O / FeCl2·4H2O mixture is 17 parts.

[0084] Example 5

[0085] This example is basically the same as Example 1, except that the mass fraction of the FeCl3·6H2O / FeCl2·4H2O mixture is 12 parts.

[0086] Example 6

[0087] This example is basically the same as Example 1, except that the mass fraction of polyacrylamide is 14 parts.

[0088] Example 7

[0089] This example is basically the same as Example 1, except that the mass fraction of citric acid is 0.5 part.

[0090] Example 8

[0091] A preparation method of a composite flocculant includes the following steps:

[0092] S1: Select silicon-aluminum-based ceramsite with a particle size of 2 - 4 mm, soak it in 10% HNO3 for 2 h to remove impurities, rinse it with clear water until neutral, dry it, and calcine it in a high-temperature furnace at 800 °C for 3 h to form a honeycomb-like porous structure with a specific surface area > 300 m² / g;

[0093] S2: Immerse the calcined silicon-aluminum-based ceramsite in a 12% polyaluminum chloride solution, perform ultrasonic treatment for 1.5 h, and dry it at 80 °C to constant weight to form PAC@ceramsite;

[0094] S3: Immerse PAC@ceramsite in a 0.2 mol / L lanthanum nitrate solution, add ammonia water to adjust the pH to 8.5, stir at 60 °C for 3 h, and La³ + Complexes with the hydroxyl groups in PAC to generate La-PAC@ceramsite, and then calcine La-PAC@ceramsite at 450 °C for 1.5 h to stably anchor La³ + In the form of LaO(OH) on the surface of the ceramsite;

[0095] S4: Immerse La-PAC@ceramsite into the mixed solution of FeCl3·6H2O / FeCl2·4H2O, add NaOH dropwise to adjust the pH to 10, and carry out hydrothermal reaction at 60 °C for 6 h to form a nano-Fe3O4 layer on the surface of La-PAC@ceramsite. Calcinate Fe3O4 / La-PAC@ceramsite at 450 °C for 1 h under N2 atmosphere, then raise the temperature to 650 °C and calcinate for 30 min, and then treat Fe3O4 / La-PAC@ceramsite with silane coupling agent KH-550;

[0096] S5: Mix the modified Fe3O4 / La-PAC@ceramsite in step S4 with polyacrylamide at a ratio of 10:1, and spray-dry at 160 °C to form 1-3 mm porous particles;

[0097] S6: Immerse the porous particles into the citric acid solution for 2 h, and dry at 60 °C to constant weight to obtain the composite flocculant.

[0098] Example 9

[0099] This example is basically the same as Example 8, except that in step S1, it is calcined in a high-temperature furnace at 850 °C for 2 h.

[0100] Example 10

[0101] This example is basically the same as Example 8, except that in step S2, the concentration of the polyaluminum chloride solution is adjusted to 15%.

[0102] Example 11

[0103] This example is basically the same as Example 8, except that in step S3, it is stirred at 70 °C for 3 h.

[0104] Example 12

[0105] This example is basically the same as Example 8, except that in step S4, the hydrothermal reaction is carried out at 70 °C for 5 h.

[0106] Example 13

[0107] This example is basically the same as Example 8, except that in step S5, the spray-drying temperature is 170 °C.

[0108] Comparative Example 1

[0109] This comparative example is basically the same as Example 8, except that step S3 is removed and the composite flocculant does not contain rare earth materials.

[0110] Comparative Example 2

[0111] This comparative example is basically the same as Example 8, except that step S4 is removed and the composite flocculant does not contain the nano-Fe3O4 layer.

[0112] Comparative Example 3

[0113] This comparative example is basically the same as Example 8, except that the order of steps S3 and S2 is reversed, and lanthanum nitrate is loaded first and then PAC treatment is carried out.

[0114] Comparative Example 4

[0115] This comparative example is basically the same as Example 8, except that in step S4, Fe3O4 / La-PAC@ceramsite is calcined at 700 °C for 1 h.

[0116] Experimental cases

[0117] The composite flocculants prepared in Examples 8-13 and Comparative Examples 1-4 were respectively applied to the wastewater treatment in the secondary sedimentation tank of a sewage treatment plant in a certain city in Hunan Province. The initial TP concentration was 18.53 mg / L, the dosage was 70 mg / L, and the reaction time was 40 min. The total phosphorus removal effect was detected, and the results are shown in Table 1.

[0118] Table 1 Water treatment results of the composite flocculants prepared in Examples 8-13 and Comparative Examples 1-4

[0119]

[0120] It can be seen from Example 8 and Comparative Example 1 that when the composite flocculant does not contain rare earth materials, the total phosphorus removal rate drops significantly to 79.11%, indicating that rare earth materials play a key role in improving the flocculation effect. This may be because rare earth materials can enhance the adsorption capacity of the flocculant and promote the rapid precipitation of phosphorus, thus significantly improving the total phosphorus removal rate. When the composite flocculant does not contain rare earth materials, the deep precipitation mechanism of LaPO4 is lacking, resulting in difficulty in completely removing phosphate ions. PAC can only remove colloidal phosphorus and cannot desorb H2PO4 - , while rare earth materials can effectively remove H2PO4 in the solution by forming stable LaPO4 precipitation - , making up for the deficiency of PAC and improving the overall flocculation effect. In addition, the lack of the La layer leads to an increase in the dissolution of Al³ + under acidic conditions (pH < 6), and the stability of the flocculant decreases, affecting the flocculation effect.

[0121] It can be seen from Example 8 and Comparative Example 2 that after removing the nano-Fe3O4 layer, the total phosphorus removal rate drops to 84.94%. This may be because Fe3O4 has a high saturation magnetization intensity, enabling rapid separation of the flocculant from water. In addition, the nano-Fe3O4 magnetic core also protects the aluminum salt and rare earth layers from hydraulic shear damage, allowing the flocculant to be recycled. Moreover, Fe3O4 can combine with PO4³ - through ligand exchange to form FePO4 precipitate, enhancing the phosphorus removal effect. Its excellent magnetic and adsorption properties contribute to improving the efficiency of the flocculant and further optimizing the wastewater treatment effect.

[0122] It can be seen from Example 8 and Comparative Example 3 that when lanthanum nitrate is loaded first and then PAC treatment is carried out during the preparation of the composite flocculant, the total phosphorus removal rate drops to 87.91%. This shows that the step sequence has a significant impact on the flocculation effect. The reasons may be as follows: The La layer is covered by PAC, shielding the active sites and reducing the formation efficiency of LaPO4, thereby affecting the phosphorus removal effect; The PAC layer on the outside causes the LaO(OH) structure to be loose, reducing the phosphorus adsorption capacity and affecting the flocculation effect. Adjusting the preparation sequence to ensure that the La layer contacts the phosphate ions first to form stable LaPO4 precipitate is an effective way to improve the total phosphorus removal rate; In addition, loading lanthanum nitrate first and then carrying out PAC treatment may lead to structural collapse and the shedding of the La layer, affecting the stability and efficiency of the flocculant and further reducing the total phosphorus removal rate. Therefore, PAC treatment should be carried out first and then lanthanum nitrate should be loaded.

[0123] It can be seen from Example 8 and Comparative Example 4 that when Fe3O4 / La-PAC@ceramsite is calcined at 700°C for 1 h, Fe3O4 will be oxidized to Fe2O3, resulting in the total phosphorus removal rate dropping to 89.91%. The reasons may be as follows: The oxidation of Fe3O4 to Fe2O3 (losing magnetism) causes the flocculant to be unable to be separated quickly, affecting the treatment efficiency; The surface activity of Fe2O3 decreases and the adsorption sites decrease, further weakening the phosphorus removal effect. See Figure 1 .

[0124] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same structure and the same function and effect as the technical idea within the technical scope of this application are included in the technical scope of this application. In addition, within the scope of not departing from the main idea of this application, various deformations that those skilled in the art can think of are applied to the embodiments, and other ways constructed by combining some components of the embodiments are also included in the scope of this application.

Claims

1. A composite flocculant, characterized in that, The composite flocculant is a ceramsite-based composite material comprising a magnetic Fe3O4 core, an aluminum salt intermediate layer and a rare earth outer layer, and the rare earth is a lanthanide element; The raw materials for preparing the composite flocculant include the following components in parts by mass: 100-120 parts of silicon-aluminum-based ceramsite, 8-10 parts of polyaluminum chloride, 8-10 parts of lanthanum salt, 12-18 parts of iron source, 10-15 parts of polyacrylamide, 1-5 parts of silane coupling agent, and 0.2-0.6 parts of citric acid.

2. The composite flocculant according to claim 1, characterized in that, The iron source includes iron salt and ferrous salt; And / or, the molar ratio of the iron salt to the ferrous salt is 2-3:

1.

3. A preparation method of the composite flocculant according to any one of claims 1-2, characterized in that, It includes the following steps: S1: Calcining the silicon-aluminum-based ceramsite to form a honeycomb-like porous structure; S2: Immersing the calcined silicon-aluminum-based ceramsite in a polyaluminum chloride solution, performing ultrasonic treatment, and then drying to form PAC@ceramsite; S3: Immersing PAC@ceramsite in a lanthanum salt solution for reaction to generate La-PAC@ceramsite, and then calcining La-PAC@ceramsite; S4: Immersing La-PAC@ceramsite in an iron source for hydrothermal reaction, and after the reaction is completed, calcining to form Fe3O4 / La-PAC@ceramsite, and then treating Fe3O4 / La-PAC@ceramsite with a silane coupling agent; obtaining silicon-modified Fe3O4 / La-PAC@ceramsite; S5: Mixing the silicon-modified Fe3O4 / La-PAC@ceramsite in step S4 with polyacrylamide and spray-drying into porous particles; S6: Immersing the porous particles in a citric acid solution and drying to obtain the composite flocculant.

4. The preparation method of the composite flocculant according to claim 3, characterized in that, The temperature of the calcination in step S1 is 800-850 °C; And / or, the time of the calcination is 2-3 h.

5. The preparation method of the composite flocculant according to claim 3, wherein, The time of the ultrasonic treatment in step S2 is 1-2 h, and drying is performed at 70-90 °C.

6. The preparation method of the composite flocculant according to claim 3, wherein, The pH of the reaction of immersing PAC@ceramsite in a lanthanum salt solution in step S3 is 8-9; The temperature of the reaction of immersing PAC@ceramsite in a lanthanum salt solution is 60-70 °C; The time of the reaction of immersing PAC@ceramsite in a lanthanum salt solution is 2 h-3 h; The temperature of the calcination of La-PAC@ceramsite in step S3 is 400-500 °C; The time of the calcination of La-PAC@ceramsite in step S3 is 1-2 h.

7. The preparation method of the composite flocculant according to claim 3, characterized in that, In step S4, La-PAC@ceramsite is immersed in an iron source and the pH is adjusted to 9-11; And / or, the temperature of the hydrothermal reaction is 60-70 °C; And / or, the time of the hydrothermal reaction is 5-6 h.

8. The preparation method of the composite flocculant according to claim 3, wherein The atmosphere of the calcination in step S4 is a protective atmosphere; And / or, the protective atmosphere includes a nitrogen or rare gas atmosphere; And / or, the calcination in step S4 includes a first-stage calcination and a second-stage calcination; And / or, the temperature of the first-stage calcination is 450-500 °C; And / or, the time of the first-stage calcination is 1-2 h; And / or, the temperature of the second-stage calcination is 650-700 °C; And / or, the time of the second-stage calcination is 30-40 min.

9. Application of the composite flocculant according to any one of claims 1-2 in water pollution treatment.

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