A red mud-based multifunctional water treatment agent and a preparation method thereof

Abstract

The application belongs to the technical field of solid waste resource utilization, and particularly relates to a red mud-based multifunctional water treatment agent and a preparation method thereof. The method comprises the steps of red mud dealkalization, drying and crushing, acid dissolution reaction, pH regulation, function enhancement and slow-release carrier forming, etc. By introducing modified polyacrylamide functional additives and compound flocculants, the removal capacity of the treatment agent for heavy metal ions, organic pollutants and high-hardness ions is effectively improved. A sodium alginate-polyvinyl alcohol ion cross-linking slow-release system is used to realize the combination of long-acting release and broad-spectrum purification functions. Compared with the prior art, the method not only realizes the resource utilization of red mud waste, but also has the advantages of structural stability, strong adaptability, high treatment efficiency and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of solid waste resource utilization, and in particular relates to a red mud-based multifunctional water treatment agent and a preparation method thereof. Background Art

[0002] With the acceleration of industrialization, water pollution is becoming increasingly serious. The treatment of various types of industrial and domestic wastewater has become a critical issue that needs to be addressed urgently. To improve wastewater treatment, high-efficiency water treatment agents are often used for flocculation and sedimentation to remove pollutants such as suspended solids, heavy metal ions, and organic matter. However, traditional flocculants mostly rely on the production of chemical raw materials, which is costly. Furthermore, the resulting byproducts, such as waste residues and waste liquids, can easily cause secondary pollution and have a negative impact on the environment.

[0003] The aluminum industry, one of my country's key industrial sectors, produces large quantities of red mud waste during the extraction of alumina. Red mud has a high alkaline content and its main components are iron oxide, aluminum oxide, and silicon oxide. If not properly utilized, it will lead to large-scale accumulation and occupation of land, and even cause serious soil and groundwater pollution. Therefore, how to efficiently and economically achieve the comprehensive utilization of red mud resources has become a key research topic within the industry.

[0004] In recent years, research on red mud in the field of water treatment has gradually increased. Due to its rich metal oxide content and high specific surface area, red mud has certain adsorption properties and can be used as a low-cost water treatment material to remove heavy metal ions, organic pollutants, etc. from water. In addition, through modification methods such as acid leaching and roasting, red mud can also be prepared into flocculants such as polyaluminum ferric chloride and polyaluminum ferric oxide for wastewater purification. However, the existing technology still has some limitations. For example, the adsorption performance and flocculation effect of red mud are limited by its composition and modification process, and it is not adaptable enough to complex water quality in practical applications.

[0005] Patent application number 202410280828.0 discloses a method for producing water treatment agents using red mud from aluminum plants. The method mainly includes dealkalization treatment of red mud, drying and crushing, heating and dissolving to form a suspension, adding hydrochloric acid to generate chloride material, then adding alkaline substances to adjust to weak acidity, and finally obtaining a powdered water treatment agent by spray drying. Although this method has achieved the preliminary utilization of elements such as aluminum and iron in red mud and prepared a water treatment agent with certain properties, this method relies on the flocculation effect of the iron and aluminum components of the red mud itself, and has weak targeted treatment capabilities for heavy metal ions, organic pollutants and high-hardness water bodies, making it difficult to meet the diversified needs of complex water quality. In addition, this method only prepares powdered preparations through spray drying, which has problems such as easy dust generation and uncontrollable dissolution rate, making it difficult to adapt to practical applications under different working conditions.

[0006] Therefore, there is an urgent need to develop an optimized preparation method for red mud-based water treatment agents, which can ensure the efficient resource utilization of red mud while solving the problems of single function, high risk of secondary pollution and poor morphological adaptability in existing technologies, thereby broadening its application scope in the field of water treatment and improving environmental and economic benefits. Summary of the Invention

[0007] The present invention aims to provide a multifunctional red mud-based water treatment agent and its preparation method, aiming to address the problems of limited treatment efficacy, high risk of secondary pollution, and poor morphological adaptability encountered in the preparation of existing red mud-based water treatment agents. This invention not only focuses on how to rationally and effectively utilize aluminum plant red mud waste to reduce environmental pollution, but also strives to improve the treatment performance of red mud-based water treatment agents, expand their application range, and adapt to different water quality conditions, providing technical support for the sustainable development of the water treatment industry.

[0008] In order to achieve the above object, the present invention provides the following technical solutions:

[0009] The first aspect of the present invention provides a method for preparing a red mud-based multifunctional water treatment agent, comprising the following steps:

[0010] (1) The red mud slurry is subjected to filter pressing to separate the dealkalized red mud and the filtrate;

[0011] (2) Drying and crushing the dealkalized red mud to obtain dry powdered red mud;

[0012] (3) Add water to the dry red mud powder and stir under heating conditions to obtain a red mud suspension;

[0013] (4) Add hydrochloric acid solution dropwise to the red mud suspension, stir and react, and after the reaction is completed, filter the reactant to remove insoluble matter to obtain a chloride solution;

[0014] (5) Add alkali to the chloride salt solution and adjust the pH value of the solution to 4-5 to obtain the water treatment agent stock solution;

[0015] (6) Adding functional additives and compound flocculants to the water treatment agent stock solution to obtain a composite water treatment agent;

[0016] Wherein, the functional additive is modified polyacrylamide, and the compound flocculant is obtained by compounding polyaluminum ferric chloride, polydimethyldiallyl ammonium chloride, and polyaluminum silicate sulfate;

[0017] (7) Sodium alginate and polyvinyl alcohol are dissolved in deionized water respectively, stirred to obtain sodium alginate solution and polyvinyl alcohol solution, the sodium alginate solution and the polyvinyl alcohol solution are mixed to obtain a composite carrier solution, the composite water treatment agent obtained in step (6) is added to the composite carrier solution, stirred for 30-60 minutes to obtain a mixed solution, calcium chloride solution is added to the mixed solution, and the stirring reaction is continued for 30-60 minutes. The obtained product is dried to obtain the red mud-based multifunctional water treatment agent.

[0018] Furthermore, the alkaline substances in the filtrate obtained in step (1) are recovered after precipitation and concentration processes, thereby realizing resource recycling.

[0019] Furthermore, in step (2), the dealkalized red mud is dried until the moisture content of the red mud is less than 2%, and the particle size of the crushed dry powdered red mud is less than 50 μm.

[0020] Furthermore, in step (3), the mass ratio of the dry powdered red mud to water is 1:3-6, the heating temperature is 60-80° C., the stirring speed is 300-500 rpm, and the stirring time is 30-60 minutes.

[0021] Furthermore, the concentration of the hydrochloric acid solution in step (4) is 10-20%, the mass ratio of the hydrochloric acid solution to the dry powdered red mud is 2-5:1, the reaction temperature is controlled at 50-60°C, and the reaction time is 1-2 hours.

[0022] Furthermore, the base in step (5) is one or more of sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, and sodium bicarbonate.

[0023] Furthermore, the addition amount of the functional additive and the compound flocculant in step (6) is independently 5-15% of the mass of the water treatment agent stock solution.

[0024] Furthermore, the preparation method of the functional additive in step (6) comprises the following steps:

[0025] (a) adding chitosan to an aqueous acetic acid solution and stirring to obtain a chitosan solution, and dispersing nano-montmorillonite in deionized water to obtain a nano-montmorillonite dispersion;

[0026] (b) mixing the chitosan solution with the nano-montmorillonite dispersion, heating, adding acrylamide monomer, ammonium persulfate and N,N'-methylenebisacrylamide with stirring, reacting for 3-5 hours, then adding epichlorohydrin and continuing the reaction for 1-3 hours;

[0027] (c) After the reaction is completed, the reactant is filtered, the solid product is dried and then ground, and passed through a 60-mesh sieve to obtain the functional additive.

[0028] Furthermore, in step (a), the concentration of the acetic acid aqueous solution is 1-3%, the mass volume ratio of chitosan to the acetic acid aqueous solution is 1:30-50, the stirring time is 3-6 hours; and the mass volume ratio of the nano-montmorillonite to deionized water is 1:15-30.

[0029] Furthermore, based on 1 part by mass of chitosan, the mass parts of nano-montmorillonite, acrylamide monomer, ammonium persulfate, N,N'-methylenebisacrylamide, and epichlorohydrin are 0.8-2 parts, 1.5-3 parts, 0.015-0.03 parts, 0.008-0.015 parts, and 0.2-0.5 parts, respectively.

[0030] Furthermore, the heating temperature in step (b) is 40-60°C.

[0031] The functional additive of the present invention is based on polyacrylamide and modified by introducing chitosan, nano-montmorillonite and epichlorohydrin. Polyacrylamide can provide flocculation and bridging in the system, flocculating fine particles and colloidal impurities into larger particles, achieving rapid sedimentation and separation. Chitosan is rich in amino and hydroxyl functional groups in its molecular structure, which can chelate heavy metal ions in water, such as Pb, through coordination. 2+ 、Cd 2+ Cr 3+ Nano-montmorillonite, with its layered structure and extremely high specific surface area, can enrich pollutants such as dyes, organic matter, and oils within its interlayer structure, enhancing its broad-spectrum adsorption. Epichlorohydrin molecules contain active epoxy and chloromethyl groups, which react with functional groups such as hydroxyl (-OH) and amino (-NH2) on the polymer backbone to form ether or amine-ether bonds, thus building bridges between molecules. This significantly enhances the polymer's thermal stability, shear stability, and swelling resistance, making it less susceptible to degradation or inactivation in water treatment applications. Furthermore, this functional additive can form a good composite with subsequent sustained-release carriers, ensuring stable and sustained release in actual use, thereby extending its treatment efficiency and lifecycle in water bodies. Compared to traditional single-polymer flocculants, the functional additive system of this invention constructs a stable three-dimensional cross-linked structure with excellent pH stability, thermal stability, and shear tolerance, maintaining good results even in acid-base fluctuations or high-flow environments. In addition, this additive is highly compatible with the red mud-based chloride brine treatment system. It will not trigger precipitation side reactions and can synergistically enhance its treatment effect. It is especially suitable for complex scenarios such as heavy metal wastewater, oily wastewater and high-turbidity industrial wastewater.

[0032] Furthermore, the mass ratio of polyaluminium ferric chloride, polydimethyldiallylammonium chloride and polyaluminium silicate sulfate in the composite flocculant in step (6) is (4-6): (2-4): 1.

[0033] The composite flocculant of the present invention achieves a multi-mechanism synergistic flocculation treatment effect by scientifically combining inorganic polymers, organic polymers and composite flocculation materials. 3+ and Fe 3+ It has a strong charge neutralization ability and can quickly destroy the stability of colloidal particles in water, causing them to coagulate; at the same time, the multi-nuclear hydroxyl complex structure in its hydrolysis product has good bridging adsorption function, which can effectively promote the formation of flocs. Polydimethyldiallylammonium chloride has a large number of cationic groups on its chain, which can further neutralize negatively charged organic matter and suspended impurities in the water, and through the long chain structure, it bridges and entangles between particles, enhancing the integrity and adhesion of the flocs, and is particularly suitable for the efficient treatment of oily wastewater and dye wastewater. Polyaluminum silicate sulfate increases the density and sedimentation rate of the flocs by constructing a porous network during the flocculation process, and at the same time has good adsorption capacity for fine particles, thereby improving the clarity and stability of the effluent. The three flocculants complement each other in the ratio, which can significantly improve the flocculation efficiency and adaptability to the broad spectrum of water quality, and have a good treatment effect on high turbidity, high hardness, and complex wastewater containing heavy metals and organic matter.

[0034] The composite water treatment agent of the present invention can be adapted to different water quality conditions by appropriately adjusting the ratio parameters of functional additives and / or compound flocculants. For example, for high hardness water, the proportion of polyaluminum silicate sulfate can be appropriately increased, or the amount of nano-montmorillonite added in the functional additive can be appropriately increased to enhance the Ca 2+ Mg 2+ The dispersion stability and pretreatment capabilities of polyaluminium chloride can be improved by reducing flocculation barriers and improving flocculation efficiency and sedimentation performance in hard water. For oily wastewater, the proportion of polydimethyldiallylammonium chloride can be appropriately increased, or the amount of chitosan added in the functional additives can be appropriately increased to enhance the ability to encapsulate and aggregate oil pollutants, improve the strength of the floc structure, and achieve efficient removal and separation of emulsified oil. For wastewater containing heavy metals, the proportion of polyaluminium ferric chloride can be appropriately increased. The powerful charge neutralization and multidentate coordination capabilities of polyaluminium ferric chloride can be utilized to form stable precipitates or complexes with heavy metal ions, causing the heavy metals to precipitate and settle from the water, thereby achieving efficient removal.

[0035] Furthermore, in step (7), the mass ratio of sodium alginate to polyvinyl alcohol is 1:0.8-1.2, the concentrations of the sodium alginate solution and the polyvinyl alcohol solution are independently (0.01-0.03) g / mL, and the mass ratio of the composite water treatment agent to the composite carrier solution is 1:1.5-3.

[0036] Furthermore, the concentration of the calcium chloride solution in step (7) is 1-3%, and the mass ratio of the mixed solution to the calcium chloride solution is 1:1.5-3.

[0037] Furthermore, the drying in step (7) is hot air drying, vacuum freeze drying or spray drying.

[0038] The composite water treatment agent prepared in this invention is molded using a sustained-release technology to achieve long-term controlled release during the dosing process. The sustained-release carrier system is based on a composite structure of sodium alginate and polyvinyl alcohol, and is ionically cross-linked by a calcium chloride solution to construct a stable three-dimensional gel network. Sodium alginate has excellent film-forming and gel-forming abilities, and its molecular structure is rich in sodium carboxylate groups (-COO - Na + ), in the presence of calcium ions (Ca 2+ ) will undergo ion exchange upon contact, quickly forming an insoluble cross-linked structure, thereby building a preliminary gel skeleton. Polyvinyl alcohol is introduced as a polymer additive to form an interpenetrating network with sodium alginate, which not only enhances the flexibility and mechanical strength of the gel, but also significantly improves its resistance to hydrolysis, swelling, and controlled release. Calcium chloride solution acts as a cross-linking agent, providing a stable Ca 2+ The carrier is a source of water, rapidly gelling the sodium alginate and achieving structural stability. The dense structure and uniform porosity of the entire system effectively encapsulate the active ingredients in the water treatment agent, enabling slow, sustained release upon addition to the water. Compared to conventional immediate-release powders or liquids, the carrier of this invention not only significantly extends the duration of action of the water treatment agent and reduces dosing frequency, but also exhibits excellent environmental friendliness and biodegradability.

[0039] The second aspect of the present invention provides a red mud-based multifunctional water treatment agent prepared by the above-mentioned preparation method.

[0040] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0041] The present invention enhances the chelating adsorption capacity of the water treatment agent for heavy metals, oils and organic pollutants by introducing functional additives synergistically modified with chitosan, nano-montmorillonite and epichlorohydrin. At the same time, polyaluminium chloride ferric, polydimethyl diallyl ammonium chloride and polyaluminium silicate sulfate are compounded to form a synergistic flocculation system, which significantly improves the coagulation and sedimentation efficiency of complex pollutants in water bodies. In addition, the slow-release carrier constructed by sodium alginate and polyvinyl alcohol is used to form a flocculation system. 2+ Ionic crosslinking technology stably encapsulates the active ingredients of the treatment agent, enabling sustained release and long-lasting action in water, while avoiding the rapid dissolution and loss of effectiveness associated with traditional powdered or liquid formulations. The water treatment agent prepared by this invention exhibits excellent applicability, safety, and environmental friendliness, making it particularly suitable for treating challenging industrial wastewaters, such as heavy metal wastewater, oily wastewater, and high-hardness water. DETAILED DESCRIPTION

[0042] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0043] Unless otherwise specified, the raw materials used in the examples are all common commercially available products. The following is an exemplary description:

[0044] Chitosan was purchased from Xi'an Qiyue Biotechnology Co., Ltd. with a particle size of 100-150 nm.

[0045] Nano-montmorillonite was purchased from Jiangsu Huabo Nanomaterial Technology Co., Ltd. with a particle size of 50-150 nm.

[0046] Polyaluminum ferric chloride was purchased from Henan Hengyuan Water Treatment Materials Co., Ltd.

[0047] Polydimethyldiallylammonium chloride was purchased from Shandong Huatai Petrochemical Group Co., Ltd.

[0048] Polyaluminum silicate sulfate was purchased from Henan Hengyuan Water Treatment Materials Co., Ltd.

[0049] Sodium alginate was purchased from Qingdao Mingyue Seaweed Group Co., Ltd.

[0050] Polyvinyl alcohol was purchased from Anhui Wanwei High-tech Materials Co., Ltd.

[0051] Cationic polyacrylamide was purchased from Henan Hengyuan Water Treatment Materials Co., Ltd.

[0052] Aluminum sulfate was purchased from Jiangsu Huatai Chemical Co., Ltd.

[0053] Non-ionic polyacrylamide was purchased from Henan Hengyuan Water Treatment Materials Co., Ltd.

[0054] Lime milk was purchased from Henan Hengyuan Water Treatment Materials Co., Ltd.

[0055] Polyethyleneimine was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0056] Example 1

[0057] This embodiment provides a method for preparing a functional additive, comprising the following steps:

[0058] (a) 5 g of chitosan was added to 200 mL of 2% acetic acid solution and magnetically stirred for 4 hours to obtain a chitosan solution. 5 g of nano-montmorillonite was added to 100 mL of deionized water and ultrasonically dispersed for 30 minutes to obtain a uniform nano-montmorillonite dispersion.

[0059] (b) The chitosan solution and the nano-montmorillonite dispersion were mixed and heated to 50°C in a water bath. 10 g of acrylamide monomer, 0.2 g of ammonium persulfate, and 0.1 g of N,N'-methylenebisacrylamide were added sequentially with stirring and allowed to react for 4 hours. Subsequently, 1 g of epichlorohydrin was added and the reaction continued for 2 hours.

[0060] (c) After the reaction is completed, the system is cooled to room temperature, the solid is removed by vacuum filtration, and placed in a hot air drying oven at 70°C for 12 hours. After grinding, it is passed through a 60-mesh sieve to obtain a light yellow functional additive powder for later use.

[0061] Example 2

[0062] This embodiment provides a method for preparing a red mud-based multifunctional water treatment agent, comprising the following steps:

[0063] The red mud was produced during the alumina production process of the Guangxi branch of Chinalco. Its main components (wt%) are shown in Table 1:

[0064] Table 1:

[0065]

[0066] (1) The red mud slurry was placed in a plate and frame filter press and filtered at a pressure of 1.0 MPa for 60 minutes to separate the dealkalized red mud and the filtrate. The alkaline components in the filtrate were recovered after precipitation and concentration, and the dealkalized red mud was set aside;

[0067] (2) The dealkalized red mud was placed in a microwave drying oven and dried continuously at 70°C until the moisture content was less than 2%. The drying time was about 3 hours. The red mud was then crushed using a high-speed rotary crusher. The crushing time was adjusted to 30 minutes to obtain dry powdered red mud with an average particle size of less than 50 μm.

[0068] (3) Add dry red mud powder to deionized water at a mass ratio of 1:3, transfer to a closed stainless steel stirring tank, and stir at 70°C with a stirring speed of 400 rpm for 45 minutes to form a uniform red mud suspension;

[0069] (4) Slowly add a 15% hydrochloric acid solution to the above red mud suspension, with a mass ratio of hydrochloric acid solution to dry red mud powder of 3:1, while stirring, the reaction temperature is maintained at 55 ° C, the reaction time is controlled to 1.5 hours, and after the reaction is completed, the system is cooled to room temperature, and the insoluble matter is removed by vacuum filtration to obtain a transparent chloride solution;

[0070] (5) Slowly add 10% sodium hydroxide solution to the above chloride solution, control the drop rate to 10 mL per minute, stir at 300 rpm, adjust the pH to 4.5, and stir at constant temperature for 30 minutes to obtain the water treatment agent stock solution;

[0071] (6) adding functional additives and compound flocculant to the above water treatment agent stock solution, stirring and mixing for 40 minutes to obtain a composite water treatment agent;

[0072] The functional additive was prepared according to the method of Example 1, and the amount of the functional additive added was 10% of the mass of the water treatment agent stock solution;

[0073] The compound flocculant is a mixture of polyaluminium ferric chloride, polydimethyldiallylammonium chloride and polyaluminium silicate sulfate in a mass ratio of 6:3:1;

[0074] (7) Sodium alginate was added to deionized water, stirred in a water bath at 60°C for 1 hour to obtain a 0.025 g / mL sodium alginate solution; polyvinyl alcohol was added to deionized water, heated at 90°C and stirred until completely dissolved to obtain a 0.025 g / mL polyvinyl alcohol solution, and the two were mixed in a mass ratio of 1:1 to obtain a composite carrier solution;

[0075] Slowly add the composite water treatment agent to the composite carrier solution at a mass ratio of 1:2, stirring while adding, and maintain stirring for 45 minutes to obtain a uniform mixed solution;

[0076] A 2% calcium chloride solution was prepared and added to the mixture at a mass ratio of 1:2. The mixture was allowed to cross-link for 45 minutes at room temperature to form gel particles.

[0077] The cross-linked gel particles were scooped out with a filter, placed in a hot air drying oven, and dried at 60° C. for 18 hours to obtain a dry granular red mud-based multifunctional water treatment agent product.

[0078] Example 3

[0079] This embodiment provides a method for preparing a red mud-based multifunctional water treatment agent, which differs from Example 2 in that the mass ratio of polyaluminum ferric chloride, polydimethyldiallylammonium chloride, and polyaluminum silicate sulfate is 4:4:1.

[0080] Example 4

[0081] This embodiment provides a method for preparing a red mud-based multifunctional water treatment agent, which differs from Example 2 in that in step (a) during the preparation of the functional additive, 10 g of nano-montmorillonite is added to 100 mL of deionized water.

[0082] Comparative Example 1

[0083] This comparative example provides a method for preparing a red mud-based multifunctional water treatment agent, which differs from Example 2 in that the functional additive is replaced by cationic polyacrylamide powder.

[0084] Comparative Example 2

[0085] This comparative example provides a method for preparing a red mud-based multifunctional water treatment agent, which differs from Example 2 in that the functional additive is replaced by polyethyleneimine.

[0086] Comparative Example 3

[0087] This comparative example provides a method for preparing a red mud-based multifunctional water treatment agent, which differs from Example 2 in that the compound flocculant is replaced by aluminum sulfate, nonionic polyacrylamide, and lime milk in a mass ratio of 5:3:1.

[0088] Comparative Example 4

[0089] This comparative example provides a preparation method of a red mud-based multifunctional water treatment agent, which differs from Example 2 in that the mass ratio of polyaluminum ferric chloride, polydimethyldiallylammonium chloride, and polyaluminum silicate sulfate is 1:4:5.

[0090] Comparative Example 5

[0091] This comparative example provides a method for preparing a red mud-based multifunctional water treatment agent, which differs from Example 2 in that in step (7), sodium alginate is replaced by gelatin, and polyvinyl alcohol is replaced by hydroxypropyl methylcellulose.

[0092] Application Examples

[0093] The water treatment agents prepared in Examples 2-4 and Comparative Examples 1-5 were tested for water treatment effects. The test water samples were simulated wastewater, and the pollutant contents were as shown in Table 2:

[0094] Table 2:

[0095]

[0096] Test method: Take 8 equal parts of simulated wastewater, add equal parts of the water treatment agents prepared in Examples 2-4 and Comparative Examples 1-5, stir rapidly (300 rpm) for 1 minute, stir slowly (100 rpm) for 10 minutes, let it settle for 30 minutes, take the supernatant, and test the pollutant content of the supernatant. The results are shown in Table 3:

[0097] Table 3:

[0098]

[0099] The above results show that the multifunctional water treatment agent prepared by the present invention has excellent treatment effects on wastewater containing heavy metals, oil and high hardness. Comparative Example 1 uses cationic polyacrylamide as a functional additive, which lacks the heavy metal chelation and broad-spectrum adsorption functions of chitosan and montmorillonite, resulting in limited removal capacity for various pollutants. Comparative Example 2 uses polyethyleneimine as a functional additive, which has a single structure, weak complexing ability, and poor compatibility with the red mud water treatment system, and the effect is significantly worse. The composite flocculant of Comparative Example 3 is replaced by aluminum sulfate + non-ionic polyacrylamide + lime milk. The floc structure formed by this composite flocculant is loose, resulting in a significant deterioration in the effect. In Comparative Example 4, the ratio of polydimethyldiallylammonium chloride and polyaluminum silicate sulfate is much higher than that of polyaluminum ferric chloride, resulting in excessive neutralization of charge and insufficient structural density, making it difficult to achieve synergistic removal of complex pollutants. In comparative example 5, the sustained-release carrier is replaced with gelatin + hydroxypropyl methylcellulose. Since the gel network formed is unstable and easily disintegrates quickly, it is unable to maintain long-term uniform release of the active ingredient, resulting in a decrease in the overall processing efficiency.

[0100] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a red mud-based multifunctional water treatment agent, comprising the following steps: (1) The red mud slurry is subjected to filter pressing to separate the dealkalized red mud and the filtrate; (2) Drying and crushing the dealkalized red mud to obtain dry powdered red mud; (3) Add water to the dry red mud powder and stir under heating conditions to obtain a red mud suspension; (4) Add hydrochloric acid solution dropwise to the red mud suspension, stir and react, and after the reaction is completed, filter the reactant to remove insoluble matter to obtain a chloride solution; (5) Add alkali to the chloride salt solution and adjust the pH value of the solution to 4-5 to obtain the water treatment agent stock solution; (6) Adding functional additives and compound flocculants to the water treatment agent stock solution to obtain a composite water treatment agent; The functional additive is modified polyacrylamide, and the preparation method includes: (a) adding chitosan to an aqueous acetic acid solution and stirring to obtain a chitosan solution, and dispersing nano-montmorillonite in deionized water to obtain a nano-montmorillonite dispersion; (b) mixing the chitosan solution with the nano-montmorillonite dispersion, heating, adding acrylamide monomer, ammonium persulfate and N,N'-methylenebisacrylamide with stirring, reacting for 3-5 hours, then adding epichlorohydrin and continuing the reaction for 1-3 hours; (c) After the reaction is completed, the reactant is filtered, the solid product is dried and then ground, and passed through a 60-mesh sieve to obtain the functional additive; The compound flocculant is prepared by compounding polyaluminium ferric chloride, polydimethyldiallylammonium chloride and polyaluminium silicate sulfate in a mass ratio of (4-6): (2-4):

1. (7) Sodium alginate and polyvinyl alcohol are dissolved in deionized water respectively, stirred to obtain sodium alginate solution and polyvinyl alcohol solution, the sodium alginate solution and the polyvinyl alcohol solution are mixed to obtain a composite carrier solution, the composite water treatment agent obtained in step (6) is added to the composite carrier solution, stirred for 30-60 minutes to obtain a mixed solution, calcium chloride solution is added to the mixed solution, and the stirring reaction is continued for 30-60 minutes. The obtained product is dried to obtain the red mud-based multifunctional water treatment agent.

2. The preparation method according to claim 1, wherein: The concentration of the hydrochloric acid solution in step (4) is 10-20%, the mass ratio of the hydrochloric acid solution to the dry powdered red mud is 2-5:1, the reaction temperature is controlled at 50-60°C, and the reaction time is 1-2 hours.

3. The preparation method according to claim 1, wherein: The amount of the functional additive and the compound flocculant added in step (6) is independently 5-15% of the mass of the water treatment agent stock solution.

4. The preparation method according to claim 3, wherein: In step (a), the concentration of the acetic acid aqueous solution is 1-3%, the mass volume ratio of chitosan to the acetic acid aqueous solution is 1:30-50, the stirring time is 3-6 hours; and the mass volume ratio of the nano-montmorillonite to deionized water is 1:15-30.

5. The preparation method according to claim 4, characterized in that: Based on 1 part by mass of chitosan, the mass parts of nano-montmorillonite, acrylamide monomer, ammonium persulfate, N,N'-methylenebisacrylamide and epichlorohydrin are 0.8-2 parts, 1.5-3 parts, 0.015-0.03 parts, 0.008-0.015 parts and 0.2-0.5 parts respectively.

6. The preparation method according to claim 1, wherein: The mass ratio of sodium alginate to polyvinyl alcohol in step (7) is 1:0.8-1.2, the concentrations of the sodium alginate solution and the polyvinyl alcohol solution are independently (0.01-0.03) g / mL, and the mass ratio of the composite water treatment agent to the composite carrier solution is 1:1.5-3.

7. The preparation method according to claim 1, wherein: The concentration of the calcium chloride solution in step (7) is 1-3%, and the mass ratio of the mixed solution to the calcium chloride solution is 1:1.5-3.

8. A red mud-based multifunctional water treatment agent, characterized in that: The method according to any one of claims 1 to 7 is used for preparation.

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