Red mud-based multifunctional water treatment agent and preparation method thereof

Abstract

The invention 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 and control, function enhancement, slow-release carrier forming and the like, and by introducing a modified polyacrylamide functional additive and a compound flocculant, the removal capacity of the treatment agent on heavy metal ions, organic pollutants and high-hardness ions is effectively improved; sodium alginate-polyvinyl alcohol is adopted to construct an ionic crosslinking type slow release system, so that the combination of long-acting release and broad-spectrum purification functions is realized. Compared with the prior art, the method has the advantages that resource utilization of the red mud waste is achieved, and the prepared water treatment agent has the remarkable advantages of being stable in structure, high in adaptability, high in 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, the pollution of water resources is becoming increasingly serious. The treatment of various industrial wastewater and domestic sewage has become an important issue that needs to be solved urgently. In order to improve the treatment effect of wastewater, it is often necessary to use efficient water treatment agents for flocculation, sedimentation and other treatments to remove suspended matter, heavy metal ions, organic matter and other pollutants in the water. However, most traditional flocculants rely on the production of chemical raw materials, with high production costs. At the same time, the by-products such as waste residues and waste liquids produced are prone to secondary pollution and have a negative impact on the environment.

[0003] As one of the important industrial sectors in my country, the aluminum industry produces a large amount of red mud waste in the process of extracting alumina. Red mud has a high alkali content, and its main components are iron oxide, aluminum oxide, silicon oxide, etc. If it cannot be used reasonably, it will lead to large-scale stacking and occupying land, and even cause serious soil and groundwater pollution problems. Therefore, how to achieve the comprehensive utilization of red mud resources efficiently and economically has become an important research topic in the industry.

[0004] In recent years, research on red mud in the field of water treatment has gradually increased. Red mud has certain adsorption properties because it is rich in metal oxides and has a high specific surface area. It can be used as a low-cost water treatment material to remove heavy metal ions, organic pollutants, etc. in 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, polyaluminum ferric oxide, etc., 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] The patent with 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 materials, then adding alkaline substances to adjust to weak acidity, and finally obtaining a powdered water treatment agent by spray drying. Although this method realizes the preliminary utilization of elements such as aluminum and iron in red mud and prepares a water treatment agent with certain performance, 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, and it is difficult to meet the diversified needs of complex water quality. In addition, this method only prepares powdered preparations by spray drying, which has problems such as easy dust generation and uncontrollable dissolution rate, and is 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 the existing technology, thereby broadening its application scope in the field of water treatment and improving environmental and economic benefits. Summary of the invention

[0007] The purpose of the present invention is to provide a red mud-based multifunctional water treatment agent and a preparation method thereof, aiming to solve the problems of single treatment effect, high secondary pollution risk and poor morphological adaptability in the preparation process of the existing red mud-based water treatment agent. The present invention not only focuses on how to reasonably and effectively utilize the red mud waste residue of the aluminum plant to reduce environmental pollution, but also strives to improve the treatment performance of the red mud-based water treatment agent, expand its application range, adapt to different water quality conditions, and provide 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: The first aspect of the present invention provides 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 treatment to separate the dealkalized red mud and the filtrate; (2) drying and crushing the dealkalized red mud to obtain dry powdered red mud; (3) adding water to the dry red mud powder and stirring under heating conditions to obtain a red mud suspension; (4) adding hydrochloric acid solution dropwise to the red mud suspension, stirring for reaction, and filtering the reactants to remove insoluble matter after the reaction is completed 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 a 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; Wherein, the functional additive is modified polyacrylamide, and the compound flocculant is compounded by polyaluminium chloride ferric, polydimethyldiallylammonium chloride and polyaluminium silicate sulfate; (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, the stirring reaction is continued for 30-60 minutes, and the obtained product is dried to obtain the red mud-based multifunctional water treatment agent.

[0009] Furthermore, the alkaline substances in the filtrate obtained in step (1) are recovered after precipitation and concentration processes, thereby realizing resource recycling.

[0010] Further, in step (2), the de-alkalized red mud is dried until the moisture content of the red mud is less than 2%, and the particle size of the pulverized dry red mud after crushing is less than 50 μm.

[0011] Further, in step (3), the mass ratio of the pulverized dry red mud to water is 1:3 - 6, the heating temperature is 60 - 80°C, the stirring speed is 300 - 500 revolutions per minute, and the stirring time is 30 - 60 minutes.

[0012] Further, in step (4), the concentration of the hydrochloric acid solution is 10 - 20%, the mass ratio of the hydrochloric acid solution to the pulverized dry red mud is 2 - 5:1, the reaction temperature is controlled at 50 - 60°C, and the reaction time is 1 - 2 hours.

[0013] Further, the alkali in step (5) is one or more of sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, and sodium bicarbonate.

[0014] Further, in step (6), the addition amounts of the functional additive and the compound flocculant are independently 5 - 15% of the mass of the water treatment agent stock solution.

[0015] Further, the preparation method of the functional additive in step (6) includes the following steps: (a) Chitosan is added to an aqueous acetic acid solution, and stirred to obtain a chitosan solution. Nanometer montmorillonite is dispersed in deionized water to obtain a nanometer montmorillonite dispersion; (b) The chitosan solution and the nanometer montmorillonite dispersion are mixed, heated, and acrylamide monomer, ammonium persulfate, and N,N'-methylenebisacrylamide are added under stirring, and the reaction is carried out for 3 - 5 hours, then epichlorohydrin is added, and the reaction is continued for 1 - 3 hours; (c) After the reaction is completed, the reactant is filtered, the solid product is dried and ground, and sieved through a 60-mesh sieve to obtain the functional additive.

[0016] Further, in step (a), the concentration of the aqueous acetic acid solution is 1 - 3%, the mass-to-volume ratio of chitosan to the aqueous acetic acid solution is 1:30 - 50, and the stirring time is 3 - 6 hours; the mass-to-volume ratio of the nanometer montmorillonite to deionized water is 1:15 - 30.

[0017] Further, taking the mass portion of chitosan as 1 portion, the mass portions of nanometer montmorillonite, acrylamide monomer, ammonium persulfate, N,N'-methylenebisacrylamide, and epichlorohydrin are respectively 0.8 - 2 portions, 1.5 - 3 portions, 0.015 - 0.03 portions, 0.008 - 0.015 portions, and 0.2 - 0.5 portions.

[0018] Further, the heating temperature in step (b) is 40-60°C.

[0019] The functional additive of the present invention uses polyacrylamide as the matrix and is modified by introducing chitosan, nano-montmorillonite and epichlorohydrin. Polyacrylamide can provide a flocculation bridging effect in the system, which can flocculate fine particles, colloidal impurities, etc. into larger particles to achieve rapid sedimentation and separation. The chitosan molecule structure is rich in amino and hydroxyl functional groups, which can chelate heavy metal ions in water bodies, such as Pb 2+ , Cd 2+ , Cr 3+ , etc., to achieve efficient removal; nano-montmorillonite has a layered structure and an extremely high specific surface area, and can enrich pollutants such as dyes, organic matters, oils, etc. in its interlayer structure, enhancing the adsorption broad spectrum; epichlorohydrin contains active epoxy groups and chloromethyl groups in its molecule, and undergoes ring-opening reactions with functional groups such as hydroxyl (-OH) and amino (-NH 2 ) on the polymer main chain to form ether bonds or amine-ether bonds, thus bridging between molecules and significantly enhancing the thermal stability, shear stability and swelling resistance of the polymer, making it not easily degraded or inactivated in water treatment applications. Further, this functional additive can also form a good composite with the subsequent slow-release carrier, ensuring its stable and continuous release ability in actual use, thereby extending its treatment efficiency and life cycle in water bodies. Compared with traditional single-polymer flocculants, the functional additive system of the present invention constructs a stable three-dimensional cross-linked structure, has excellent pH stability, thermal stability and shear tolerance, and can maintain good effects in environments with acid-base fluctuations or high flow rates. In addition, this additive has high compatibility with the red mud-based brine water treatment system, neither causing precipitation side reactions nor synergistically enhancing its treatment effect, and is particularly suitable for complex scenarios of heavy metal wastewater, oily wastewater and high-turbidity industrial wastewater.

[0020] Further, the mass ratio of polyaluminum ferric chloride, poly(dimethyldiallylammonium chloride), and polyaluminum silicate sulfate in the compound flocculant in step (6) is (4-6):(2-4):1.

[0021] The compound flocculant of the present invention realizes a multi-mechanism synergistic flocculation treatment effect by scientifically combining inorganic polymers, organic polymers and composite flocculation materials. The Al 3+ and Fe 3+It has strong charge neutralization ability, 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 products has good bridging adsorption function, which can effectively promote the formation of flocs. Poly(dimethyldiallylammonium chloride) has a large number of cationic groups on its chain, which can further neutralize negatively charged organic substances and suspended impurities in water, and bridge and entangle between particles through the long-chain structure, enhancing the integrity and adhesion of flocs, and is especially suitable for the efficient treatment of oily wastewater and dye wastewater. Polyaluminum silicate sulfate constructs a porous network during the flocculation process, improving the density and sedimentation rate of flocs, and having good adsorption ability for fine particles, thereby improving the clarity and stability of the effluent. The three flocculants complement each other in the ratio, can significantly improve the flocculation efficiency and the broad spectrum of water quality adaptation, and have good treatment effects on high-turbidity, high-hardness, heavy metal-containing and complex organic wastewater.

[0022] The composite water treatment agent of the present invention can adapt 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 addition amount of nano-montmorillonite can be appropriately increased in the functional additives, so as to enhance the dispersion stability and pretreatment ability for Ca 2+ 、Mg 2+ , reduce the flocculation hindrance, and improve the flocculation efficiency and sedimentation performance in hard water. For oily wastewater, the proportion of poly(dimethyldiallylammonium chloride) can be appropriately increased, or the addition amount of chitosan can be appropriately increased in the functional additives, so as to enhance the ability to encapsulate and aggregate oil pollutants, improve the strength of the floc structure, and achieve the efficient removal and separation of emulsified oil. For heavy metal-containing wastewater, the proportion of polyaluminum ferric chloride can be appropriately increased, and the strong charge neutralization ability and multidentate coordination ability of polyaluminum ferric chloride can be used to form stable precipitates or complexes with heavy metal ions, so that the heavy metals are precipitated from the water body, thereby achieving efficient removal.

[0023] 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.

[0024] Furthermore, in step (7), the concentration of the calcium chloride solution is 1 - 3%, and the mass ratio of the mixed solution to the calcium chloride solution is 1:1.5 - 3.

[0025] Furthermore, the drying in step (7) is hot air drying, vacuum freeze drying or spray drying.

[0026] The composite water treatment agent prepared in the present invention is subjected to shaping treatment through a slow-release technology, achieving long-term controlled release during the dosing process. This slow-release carrier system is based on the composite structure of sodium alginate and polyvinyl alcohol, and realizes ionic cross-linking through a calcium chloride solution to construct a stable three-dimensional gel network. Sodium alginate has excellent film-forming and gelling abilities, and its molecular structure is rich in carboxylate groups (-COO - Na + ), and will undergo ion exchange after contacting with calcium ions (Ca 2+ ), quickly forming an insoluble cross-linked structure, thereby constructing a preliminary gel skeleton. Polyvinyl alcohol is introduced as a polymer assistant 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 anti-hydrolysis, anti-swelling and controlled release capabilities. Calcium chloride solution, as a cross-linking agent, provides a stable Ca 2+ source, enabling sodium alginate to gel quickly and achieve structural setting. The entire system has a dense structure and uniform pores, which can effectively embed the active components in the water treatment agent and achieve slow and continuous release after being added to the water body. Compared with traditional instant-release powders or liquids, the carrier of the present invention not only significantly extends the action time of the water treatment agent and reduces the dosing frequency, but also has good environmental friendliness and biodegradability.

[0027] The second aspect of the present invention provides a red mud-based multifunctional water treatment agent prepared by the above preparation method.

[0028] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: By introducing a functional additive synergistically modified by chitosan, nano-montmorillonite and epichlorohydrin, the present invention enhances the chelating and adsorption abilities of the water treatment agent for heavy metals, oils and organic pollutants. At the same time, by compounding polyaluminum ferric chloride, poly(dimethyldiallylammonium chloride) and polyaluminum silicate sulfate to form a synergistic flocculation system, the coagulation and sedimentation efficiency of complex pollutants in the water body is significantly improved. In addition, through the slow-release carrier constructed by sodium alginate and polyvinyl alcohol, the active components of the treatment agent are stably embedded by using Ca 2+ ion cross-linking technology, realizing the function of continuous release and long-term action in water, and avoiding the problems of rapid dissolution and failure of traditional powder or liquid dosage forms. The water treatment agent prepared in the present invention has good applicability, safety and environmental friendliness, and is particularly suitable for treating high-difficulty industrial wastewater, such as heavy metal wastewater, oily wastewater and high-hardness water. Specific embodiments

[0029] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Unless otherwise specified, the raw materials used in the examples are all common commercially available products. The following is an exemplary description: Chitosan was purchased from Xi'an Qiyue Biotechnology Co., Ltd. with a particle size of 100-150 nm.

[0031] Nano-montmorillonite was purchased from Jiangsu Huabo Nanomaterial Technology Co., Ltd. with a particle size of 50-150 nm.

[0032] Polyaluminium ferric chloride was purchased from Henan Hengyuan Water Treatment Materials Co., Ltd.

[0033] Polydimethyldiallylammonium chloride was purchased from Shandong Huatai Petrochemical Group Co., Ltd.

[0034] Polyaluminium silicate sulfate was purchased from Henan Hengyuan Water Treatment Materials Co., Ltd.

[0035] Sodium alginate was purchased from Qingdao Mingyue Seaweed Group Co., Ltd.

[0036] Polyvinyl alcohol was purchased from Anhui Wanwei High-tech Materials Co., Ltd.

[0037] Cationic polyacrylamide was purchased from Henan Hengyuan Water Treatment Materials Co., Ltd.

[0038] Aluminum sulfate was purchased from Jiangsu Huatai Chemical Co., Ltd.

[0039] Nonionic polyacrylamide was purchased from Henan Hengyuan Water Treatment Materials Co., Ltd.

[0040] Lime milk was purchased from Henan Hengyuan Water Treatment Materials Co., Ltd.

[0041] Polyethyleneimine was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0042] Example 1 This embodiment provides a method for preparing a functional additive, comprising the following steps: (a) 5 g of chitosan was weighed and added to 200 mL of 2% acetic acid aqueous 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; (b) Mix the chitosan solution with the nano-montmorillonite dispersion, place it in a water bath and heat it to 50 °C. While stirring, sequentially add 10 g of acrylamide monomer, 0.2 g of ammonium persulfate, and 0.1 g of N,N'-methylenebisacrylamide, and react for 4 hours. Subsequently, add 1 g of epichlorohydrin and continue to react for 2 hours; (c) After the reaction, cool the system to room temperature, take out the solid by vacuum filtration, place it in a hot air drying oven at 70 °C and dry for 12 hours. After grinding, pass it through a 60-mesh sieve to obtain a light yellow functional additive powder for standby.

[0043] Example 2 This example provides a preparation method of a red mud-based multifunctional water treatment agent, including the following steps: The red mud used is the red mud generated during the alumina production process of Chalco Guangxi Branch. Its main components (wt%) are shown in Table 1: Table 1:

[0044] (1) Place the red mud slurry in a plate and frame filter press, filter it under a pressure of 1.0 MPa for 60 minutes to separate the de-alkalized red mud and the filtrate. The filtrate is subjected to precipitation and concentration treatment to recover the alkaline components therein, and the de-alkalized red mud is reserved for standby; (2) Put the de-alkalized red mud into a microwave drying oven and continuously dry it at 70 °C until the moisture content is lower than 2%. The drying time is about 3 hours. Subsequently, use a high-speed rotary crusher to crush it, and adjust the crushing time to 30 minutes to obtain dry red mud with an average particle size of less than 50 μm; (3) Add the dry red mud to deionized water at a mass ratio of 1:3, transfer it to a closed stainless steel stirring tank, stir at 70 °C, control the stirring speed at 400 rpm, and stir for 45 minutes to form a uniform red mud suspension; (4) Slowly drip a 15% hydrochloric acid solution into the above red mud suspension. The mass ratio of the hydrochloric acid solution to the dry red mud is 3:1. Stir while dripping, keep the reaction temperature at 55 °C, control the reaction time at 1.5 hours. After the reaction, cool the system to room temperature, and remove the insoluble matter by vacuum filtration to obtain a transparent chloride salt solution; (5) Slowly drip a 10% sodium hydroxide solution into the above chloride salt solution, control the dripping speed at 10 mL per minute, the stirring speed at 300 rpm, adjust the pH to 4.5, and stir at a constant temperature for 30 minutes to obtain the original solution of the water treatment agent; (6) Add a functional additive and a compound flocculant to the above original solution of the water treatment agent, stir and mix for 40 minutes to obtain a composite water treatment agent; Among them, the functional additive is prepared according to the method of Example 1, and the addition amount of the functional additive is 10% of the mass of the original solution of the water treatment agent; The compound flocculant is a mixture of polyaluminum ferric chloride, poly(dimethyldiallylammonium chloride), and polyaluminum silicate sulfate with a mass ratio of 6:3:1; (7) Add sodium alginate to deionized water, stir at 60 °C in a water bath for 1 hour to obtain a 0.025 g / mL sodium alginate solution; separately, add polyvinyl alcohol to deionized water, heat and stir at 90 °C until completely dissolved to obtain a 0.025 g / mL polyvinyl alcohol solution, and mix the two in a mass ratio of 1:1 to obtain a composite carrier solution; Slowly add the composite water treatment agent to the composite carrier solution. The mass ratio of the composite water treatment agent to the composite carrier solution is 1:2. Stir while adding, and maintain the stirring time for 45 minutes to obtain a uniformly mixed solution; Prepare a 2% mass concentration calcium chloride solution separately, add it to the above mixed solution. The mass ratio of the mixed solution to the calcium chloride solution is 1:2, and carry out a cross-linking reaction at room temperature for 45 minutes to form gel particles; Scoop out the cross-linked gel particles with a filter screen, place them in a hot air drying oven, and dry at 60 °C for 18 hours to obtain a dry granular red mud-based multifunctional water treatment agent product.

[0045] Example 3 This example provides a preparation method of a red mud-based multifunctional water treatment agent. The difference from Example 2 is that the mass ratio of polyaluminum ferric chloride, poly(dimethyldiallylammonium chloride), and polyaluminum silicate sulfate is 4:4:1.

[0046] Example 4 This example provides a preparation method of a red mud-based multifunctional water treatment agent. The difference from Example 2 is that in step (a) of the preparation process of the functional additive, 10 g of nano-montmorillonite is added to 100 mL of deionized water.

[0047] Comparative Example 1 This comparative example provides a preparation method of a red mud-based multifunctional water treatment agent. The difference from Example 2 is that the functional additive is replaced with cationic polyacrylamide powder.

[0048] Comparative Example 2 This comparative example provides a preparation method of a red mud-based multifunctional water treatment agent. The difference from Example 2 is that the functional additive is replaced with polyethyleneimine.

[0049] Comparative Example 3 This comparative example provides a preparation method of a red mud-based multifunctional water treatment agent. The difference from Example 2 is that the compound flocculant is replaced with a mixture of aluminum sulfate, non-ionic polyacrylamide, and lime milk with a mass ratio of 5:3:1.

[0050] Comparative Example 4 This comparative example provides a preparation method of a red mud-based multifunctional water treatment agent, which is different from Example 2 in that the mass ratio of polyaluminum chloride ferric, poly(dimethyldiallylammonium chloride), and polyaluminum silicate sulfate is 1:4:5.

[0051] Comparative Example 5 This comparative example provides a preparation method of a red mud-based multifunctional water treatment agent, which is different from Example 2 in that in step (7), sodium alginate is replaced by gelatin, and polyvinyl alcohol is replaced by hydroxypropyl methylcellulose.

[0052] Application Example The water treatment agents prepared in Examples 2-4 and Comparative Examples 1-5 were subjected to water treatment effect tests. The test water sample was simulated wastewater, and the pollutant contents are shown in Table 2: Table 2:

[0053] Test method: Take 8 portions of equal amounts of simulated wastewater, and add equal amounts of the water treatment agents prepared in Examples 2-4 and Comparative Examples 1-5 respectively. Stir rapidly (300 rpm) for 1 minute, stir slowly (100 rpm) for 10 minutes, and take the supernatant after standing and settling for 30 minutes. Detect the pollutant contents of the supernatant respectively. The results are shown in Table 3: Table 3:

[0054] 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. In Comparative Example 1, cationic polyacrylamide was used as a functional additive, lacking the heavy metal chelation and broad-spectrum adsorption functions of chitosan and montmorillonite, resulting in limited removal ability for various pollutants. In Comparative Example 2, polyethyleneimine was used 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 deteriorated significantly. In Comparative Example 3, the compound flocculant was replaced by aluminum sulfate + non-ionic polyacrylamide + lime milk. The floc structure formed by this compound flocculant is loose, resulting in a significant deterioration of the effect. In Comparative Example 4, the ratio of poly(dimethyldiallylammonium chloride) and polyaluminum silicate sulfate is much higher than that of polyaluminum chloride ferric, resulting in excessive charge neutralization and insufficient structural compactness, making it difficult to achieve synergistic removal of complex pollutants. In Comparative Example 5, the slow-release carrier was replaced by gelatin + hydroxypropyl methylcellulose. Since the gel network formed by it is unstable and easily disintegrates rapidly, it cannot maintain a uniform release of active ingredients for a long time, resulting in a decrease in the overall treatment efficiency.

[0055] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope 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 treatment to separate the dealkalized red mud and the filtrate; (2) drying and crushing the dealkalized red mud to obtain dry powdered red mud; (3) adding water to the dry red mud powder and stirring under heating conditions to obtain a red mud suspension; (4) adding hydrochloric acid solution dropwise to the red mud suspension, stirring for reaction, and filtering the reactants to remove insoluble matter after the reaction is completed 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 a 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; in, The functional additive is modified polyacrylamide, and the compound flocculant is compounded from polyaluminium ferric chloride, polydimethyldiallylammonium chloride and polyaluminium silicate sulfate; (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, the stirring reaction is continued for 30-60 minutes, and the obtained product is dried to obtain the red mud-based multifunctional water treatment agent.

2. The preparation method according to claim 1, characterized in that: 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, characterized in that: The added amounts of the functional additive and the compound flocculant in step (6) are independently 5-15% of the mass of the water treatment agent stock solution.

4. The preparation method according to claim 1, characterized in that: The method for preparing the functional additive in step (6) comprises the following steps: (a) adding chitosan to an acetic acid aqueous 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 under 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 ground, and passed through a 60-mesh sieve to obtain the functional additive.

5. The preparation method according to claim 4, characterized in that: The concentration of the acetic acid aqueous solution in step (a) 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; the mass volume ratio of the nano-montmorillonite to deionized water is 1:15-30.

6. The preparation method according to claim 4, characterized in that: Based on 1 part by mass of chitosan, the parts by mass 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.

7. The preparation method according to claim 1, characterized in that: The mass ratio of polyaluminium chloride ferric, polydimethyldiallylammonium chloride and polyaluminium silicate sulfate in the composite flocculant in step (6) is (4-6):(2-4):

1.

8. The preparation method according to claim 1, characterized in that: 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.

9. The preparation method according to claim 1, characterized in that: 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.

10. A red mud-based multifunctional water treatment agent, characterized in that: The method is prepared by any one of claims 1 to 9.

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