Water treatment agent based on comprehensive utilization of red mud and preparation method thereof

Abstract

The invention belongs to the technical field of water treatment agents, and particularly relates to a water treatment agent based on comprehensive utilization of red mud and a preparation method thereof. The water treatment agent based on comprehensive utilization of red mud is prepared from the following preparation raw materials in parts by weight: 95 to 105 parts of red mud, 25 to 35 parts of dolomite, 10 to 20 parts of diatomite and 5 to 10 parts of sodium polyacrylate. The invention aims to break through the technical bottleneck of a red mud-based water treatment agent through component design and process optimization. The adsorption activity of red mud is activated by introducing dolomite to regulate the alkalinity of a system, mass transfer and dispersity are enhanced by utilizing the high specific surface area of diatomite, and rapid flocculation separation of adsorbed pollutants is realized by virtue of assistance of sodium polyacrylate. All the components form a synergistic removal mechanism aiming at COD, ammonia nitrogen and total phosphorus through pH regulation and control, multi-level adsorption, coprecipitation and flocculation coupling effects, the treatment efficiency and economical efficiency are remarkably improved, and a new way is provided for high-value utilization of the red mud.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment agents, and specifically relates to a water treatment agent based on comprehensive utilization of red mud and a preparation method thereof. Background Art

[0002] As industrial wastewater discharge standards become increasingly stringent, the development of efficient and low-cost water treatment agents has become a research hotspot in the field of environmental engineering. Although traditional water treatment materials have a certain ability to remove pollutants, they have problems such as high raw material costs, single functions, and secondary pollution risks. They are difficult to meet the deep treatment needs of complex wastewater in industrial parks with high COD, high ammonia nitrogen, and high phosphorus.

[0003] Red mud is an alkaline solid waste generated during the production of alumina, with an annual emission of over 150 million tons and a global stockpile of over 4 billion tons. Its main components are SiO 2 、Al 2 O 3 , Fe 2 O 3 , CaO and other metal oxides, in theory, can be used as adsorbents or catalytic carriers for sewage treatment. However, the high alkalinity (pH 10-13), low specific surface area (usually <20 m² / g) and potential leaching risk of heavy metals in red mud severely limit its direct application. Existing red mud resource technology is mostly focused on the field of building materials. When used for water treatment, there are generally problems such as incomplete dealkalization, low utilization rate of active components, and unstable pollutant removal effect.

[0004] The design of existing red mud-based water treatment materials mostly adopts a single modification method, which can partially improve the adsorption performance, but fails to solve the defect of insufficient functional synergy. In addition, the compounding of red mud with auxiliary components such as dolomite and diatomaceous earth lacks systematic pretreatment, resulting in weak interface bonding between components and severe shielding of active sites, making it difficult to exert synergistic effects.

[0005] In response to the above problems, it is urgent to develop a red mud-based multi-effect water treatment agent. Through raw material pretreatment optimization and multi-component functional collaborative design, we can break through the technical bottlenecks of low adsorption capacity and narrow pollutant removal range of traditional materials, and realize large-scale and high-value utilization of red mud. Summary of the invention

[0006] The purpose of the present invention is to provide a water treatment agent based on comprehensive utilization of red mud and a preparation method thereof, which can improve the removal rates of COD, ammonia nitrogen and total phosphorus.

[0007] A water treatment agent based on comprehensive utilization of red mud. The raw materials for preparing the water treatment agent include, by weight, 95-105 parts of pretreated red mud, 25-35 parts of pretreated dolomite, 10-20 parts of pretreated diatomaceous earth and 5-10 parts of sodium polyacrylate.

[0008] The red mud mainly consists of SiO 2 、Al 2 O 3 ,CaO,Fe 2 O 3 wait.

[0009] Preferably, the dolomite has a moisture content of 1.4%-1.45% and a bulk density of 1600-1700 kg / m 3 , mud content ≤0.15%.

[0010] In some preferred embodiments, the dolomite is from the Chenming Yuhua Stone Processing Factory in Liuhe District, Nanjing, and is a dolomite ore.

[0011] The diatomaceous earth is mainly composed of SiO 2 、Al 2 O 3 , Fe 2 O 3 wait.

[0012] Preferably, the relative molecular mass of the sodium polyacrylate is 5 million to 7 million.

[0013] In some preferred embodiments, the sodium polyacrylate comes from Shanghai MacLean Biochemical Technology Co., Ltd.

[0014] By adding appropriate amounts of dolomite, diatomite and sodium polyacrylate to red mud, the prepared water treatment agent can achieve efficient and synergistic removal of pollutants such as COD, ammonia nitrogen and total phosphorus in the water body. This may be because the addition of dolomite can dynamically adjust the pH of the system, which can not only promote the conversion of part of the ammonia nitrogen into ammonia volatilization, but also optimize the adsorption activity of hydroxyl complexes of iron ions, aluminum ions, etc. in red mud, thereby promoting the adsorption of phosphate ions. At the same time, the calcium ions and magnesium ions in dolomite can also react with phosphate ions and ammonium ions after being activated, and simultaneously remove nitrogen and phosphorus. Through the synergy of red mud and diatomite, the high specific surface area and mesoporous structure of diatomite can not only disperse the red mud particles, avoid agglomeration, and increase the adsorption area, but also the silicon hydroxyl groups on the surface adsorb low molecular weight organic matter through hydrogen bonds, thereby achieving the effect of synergistic removal of COD. Sodium polyacrylate assembles red mud, dolomite, and diatomaceous earth particles into a porous complex through bridging, preventing the loss of active components and stabilizing the removal effect of each effective component on pollutants. It also has a certain flocculation effect, aggregating the precipitated particles into large particles and improving the precipitation efficiency. However, red mud is a solid waste with high alkali content, complex mineral composition, and poor dispersion; dolomite is a mineral, and magnesium ions and calcium ions are both in magnesium carbonate and calcium; natural diatomaceous earth contains certain impurities that limit its adsorption performance. If these raw materials are not pretreated, the performance of the prepared water treatment agent will be greatly affected.

[0015] The preparation method of the water treatment agent based on comprehensive utilization of red mud comprises the following steps: S1. Pre-treating red mud, dolomite and diatomite respectively to obtain pre-treated red mud, pre-treated dolomite and pre-treated diatomite; preparing sodium polyacrylate into a sodium polyacrylate aqueous solution with a mass fraction of 8%; S2, mixing the pretreated red mud, pretreated dolomite and pretreated diatomaceous earth uniformly to obtain a mixed dry material; S3. Spray the sodium polyacrylate aqueous solution on the surface of the mixed dry material, make particles with a diameter of 2-4 mm in a disc granulator, and spray dry to a moisture content of ≤1% to obtain a water treatment agent.

[0016] The method for preparing the pretreated red mud comprises the following steps: A1. Dealkalization: The red mud is subjected to three-stage filter pressing and then microwave drying to obtain dealkalized red mud; A2. Acid etching: the dealkalized red mud and the mixed acid solution are mixed, and after ultrasonic reaction, the mixture is washed with deionized water until it is neutral, and vacuum dried at 60°C until the moisture content is ≤3%, thereby obtaining acid-etched red mud; A3. Loading: The acid-etched red mud is immersed in a ferrate solution, shaken at room temperature for 1.5-2.5 hours, and then coated. After filtration at 60°C, vacuum drying is performed to a moisture content of ≤1%, thereby obtaining the pretreated red mud.

[0017] Preferably, in step A1, the three-stage filtration comprises a first stage filtration, a second stage filtration and a third stage filtration.

[0018] Preferably, the first stage filtration is plate and frame filtration, and the specific conditions are: pressure 0.6-0.8 MPa, and the pressure is maintained until the filtrate pH is ≤13.5.

[0019] Preferably, the second stage filtration is vacuum filtration, and the specific conditions are: the vacuum degree is -0.08MPa, and the moisture content is reduced to 45% or below.

[0020] Preferably, the third stage filtration is high-pressure diaphragm filtration, and the specific conditions are: pressure 2.5-3.0 MPa, and diaphragm extrusion to pH ≤ 9.

[0021] Preferably, in step A1, microwave drying includes first-stage microwave drying and second-stage microwave drying.

[0022] Preferably, the conditions of the first stage microwave drying are: power 400-600W, time 5min, temperature 75-85°C.

[0023] Preferably, the conditions for the second stage of microwave drying are: power 200-350W, time 10-20min, temperature 100-110°C.

[0024] Preferably, in step A2, the solid-to-liquid ratio of the dealkalized red mud to the mixed acid solution is 1 g: (5-10) mL.

[0025] Preferably, the concentration of the mixed acid in the mixed acid solution is 0.4-0.6 mol / L.

[0026] Preferably, the mixed acid comprises citric acid and hydrochloric acid.

[0027] Preferably, the molar ratio of citric acid to hydrochloric acid is (2-6):1; more preferably, it is 4:1.

[0028] Preferably, the specific conditions of the ultrasonic reaction are: frequency of 35-45 kHz, power of 150-250 W, temperature of 58-62° C., and time of 1.5-2.5 h.

[0029] Preferably, in step A3, the solid-liquid ratio of the acid-etched red mud and the ferrate solution is 1 g: (10-20) mL.

[0030] Preferably, the concentration of ferrate in the ferrate solution is 1.8-2.2 g / L, and the solvent is a sodium hydroxide aqueous solution with a mass concentration of 4%.

[0031] Preferably, the ferrate includes any one of potassium ferrate and sodium ferrate.

[0032] Preferably, the specific steps of the coating treatment are: adding a sodium alginate aqueous solution with a mass fraction of 2.5%-3.5% and stirring for 30-40 minutes.

[0033] Preferably, the solid-to-liquid ratio of the acid-etched red mud to the sodium alginate aqueous solution with a mass fraction of 2.5%-3.5% is 1 g: (30-40) mL.

[0034] By pretreating red mud, active metal oxides can be released while increasing the specific surface area of ​​red mud, and the removal effect of organic matter can be improved, thereby comprehensively improving the beneficial effect of red mud on sewage treatment. This may be because the three-stage filter press de-alkali process is first used to remove free alkali and bound sodium step by step to avoid excessive acid consumption in subsequent acid etching, and then microwave pulse drying is induced to induce the iron and aluminum oxides in the red mud to change from amorphous to goethite, thereby increasing the specific surface area of ​​red mud and promoting the adsorption of phosphate and organic pollutants; then the amorphous silicate in the red mud is selectively dissolved by mixed acid to form a mesoporous structure, and carboxylic acid groups are grafted to enhance the ion exchange capacity and chelate heavy metal ions at the same time. By optimizing the mixed acid ratio, it is also possible to avoid a single strong acid from destroying the red mud skeleton structure; finally, through the loading of ferrate and the coating of sodium alginate, it can not only promote the degradation of organic matter, but also prevent the rapid decomposition of ferrate ions, increase its action cycle, and thus increase the efficacy of the water treatment agent.

[0035] Preferably, the method for preparing the pretreated dolomite comprises the following steps: crushing the dolomite to a particle size of 5-10 mm, calcining at 650-700° C. for 1.5-2.5 h, and then ball-milling through a 400-mesh sieve to obtain the pretreated dolomite.

[0036] The method for preparing the pretreated diatomite comprises the following steps: B1. Purification: calcine the diatomite at 500-600°C for 1-2h, soak it in an acid solution with a volume concentration of 10%, clean it by ultrasonic for 30-50min, wash it with water until it is neutral, and then dry it to obtain purified diatomite; B2. Modification: After mixing the purified diatomaceous earth and the modifier, adjust the pH to 4-5, age at 58-62℃ for 10-15h, and wash with water until there is no Cl - , calcined at 500-600°C for 1-3h to obtain modified diatomite; B3. Compounding: Mix modified diatomite, mineral powder and fly ash to obtain a solid mixture, add pore-forming agent and deionized water, stir evenly, dry at 100-110° C., and calcine at 700-750° C. for 1-2 hours to obtain the solid mixture.

[0037] Preferably, in step B2, the solid-liquid ratio of the purified diatomaceous earth and the modifier is 1 g: (15-20) mL.

[0038] Preferably, the modifier includes aluminum chloride solution and ferric chloride solution.

[0039] Preferably, in the modifier, the molar ratio of aluminum to iron is 0.2-0.4.

[0040] Preferably, the concentration of the aluminum chloride solution is 0.2-0.4 mol / L; the concentration of the ferric chloride solution is 0.1-0.3 mol / L.

[0041] Preferably, in step B3, the mass ratio of modified diatomaceous earth, mineral powder and fly ash is (2-3):(1-2):1; more preferably, it is 5:3:2.

[0042] Preferably, the pore-forming agent includes one or more of sodium bicarbonate, polyethylene glycol, and starch.

[0043] Preferably, the amount of the pore former added is 5%-10% of the mass of the solid mixture.

[0044] Preferably, the solid-liquid ratio of the solid mixture to deionized water is 1 g: (0.8-1.2) mL.

[0045] By pretreating diatomite, the specific surface area and total pore volume of diatomite can be increased without destroying its structure, thereby greatly improving the adsorption capacity of diatomite, and then improving the adsorption capacity of COD, ammonia nitrogen, etc. in water. This may be because the diatomite is first purified by calcination and then pickling, which not only removes organic impurities and Ca / Fe oxides, improves the purity of silica, but also increases the specific surface area; then by selecting a specific modifier and controlling the molar ratio of the modifier, stable pillaring ions are generated, the interlayer spacing is increased, and the bimetallic pillaring enhances the surface acid sites and ion exchange capacity, greatly improving the adsorption capacity; finally, by compounding mineral powder and fly ash, and selecting polyethylene glycol as a pore-forming agent, a nano-scale through-hole channel is constructed, the mass transfer efficiency and the distribution of active sites are optimized, thereby further improving the adsorption capacity. In the actual operation process, it is necessary to control the order of calcination and pickling during purification. Calcination before pickling can avoid carbonization of organic matter to block the pores, affecting the pore structure and adsorption effect.

[0046] The present invention successfully prepares a water treatment agent by adding auxiliary components to red mud and optimizing the pretreatment of raw materials such as red mud. It can not only remove COD efficiently, but also deeply remove ammonia nitrogen, and achieve the effect of enhanced phosphorus removal, breaking through the technical bottleneck of traditional red mud-based materials with single function and low efficiency. It is particularly suitable for deep treatment of complex wastewater in industrial parks, and has both high efficiency, low cost and environmental friendliness. At the same time, by converting industrial solid waste red mud into high-quality water treatment agent, waste resource utilization is in line with the trend of environmental protection.

[0047] Compared with the prior art, the advantages and beneficial effects of the present invention are: 1. The water treatment agent based on the comprehensive utilization of red mud prepared by the present invention activates the adsorption activity of red mud by introducing dolomite to regulate the alkalinity of the system, utilizes the high specific surface area of ​​diatomaceous earth to enhance mass transfer and dispersibility, and is assisted by sodium polyacrylate to achieve rapid flocculation and separation of adsorbed pollutants. Each component forms a synergistic removal mechanism for COD, ammonia nitrogen, and total phosphorus through pH regulation, multi-level adsorption, coprecipitation, and flocculation coupling, significantly improving the treatment efficiency and economy, and providing a new way for the high-value utilization of red mud.

[0048] 2. The present invention can release active metal oxides while increasing the specific surface area of ​​red mud by pretreating red mud, and at the same time improve the removal effect of organic matter, thereby comprehensively improving the beneficial effects of red mud on sewage treatment.

[0049] 3. The present invention adopts a three-stage filter press de-alkali process to remove free alkali and bound sodium step by step to avoid excessive acid consumption in subsequent acid etching. Microwave pulse drying can induce the iron and aluminum oxides in red mud to transform from amorphous state to goethite, thereby increasing the specific surface area of ​​red mud and promoting the adsorption of phosphate and organic pollutants.

[0050] 4. The present invention can increase the specific surface area and total pore volume of diatomaceous earth by pretreating diatomaceous earth without destroying its structure, thereby greatly improving the adsorption capacity of diatomaceous earth and further improving the adsorption capacity of COD, ammonia nitrogen and the like in water.

[0051] 5. The present invention generates stable pillaring ions by selecting specific modifiers and controlling the molar ratio of the modifiers, thereby increasing the interlayer spacing of diatomite. The bimetallic pillaring enhances the surface acid sites and ion exchange capacity, thereby greatly increasing the adsorption capacity of diatomite. DETAILED DESCRIPTION

[0052] 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.

[0053] The raw materials used in the present invention are all commercially available, specifically: Red mud, main components (w / %): iron oxide, 15.9; aluminum oxide, 22.7; silicon dioxide, 14.3; titanium dioxide, 4.6; calcium oxide, 4.5; magnesium oxide, 2; sodium oxide, 4.2; other substances, the rest. From the aluminum plant of China Aluminum Corporation Henan Branch.

[0054] Dolomite, moisture content is 1.4%-1.45%, bulk density is 1600-1700kg / m 3, mud content ≤0.15%, from Chenming Yuhua Stone Processing Factory in Liuhe District, Nanjing, dolomite ore.

[0055] Diatomaceous earth, main components (w / %): silicon dioxide, 89.01; iron oxide, 3.31; aluminum oxide, 3.1; sodium oxide, 1.87; calcium oxide, 1.07; other substances, the balance. From Sinopharm Chemical Reagent Co., Ltd.

[0056] The relative molecular mass of sodium polyacrylate is 5-7 million, and it comes from Shanghai McLean Biochemical Technology Co., Ltd.

[0057] Mineral powder, grade S105; fly ash, grade one fly ash; both come from Lingshou County Yehui Mineral Products Co., Ltd.

[0058] Example 1 The present embodiment provides a water treatment agent based on comprehensive utilization of red mud. The raw materials for preparing the water treatment agent include, by weight, 100 parts of pretreated red mud, 30 parts of pretreated dolomite, 15 parts of pretreated diatomaceous earth, and 8 parts of sodium polyacrylate.

[0059] The preparation method of the water treatment agent based on comprehensive utilization of red mud comprises the following steps: S1. Prepare sodium polyacrylate into an aqueous solution with a mass fraction of 8% sodium polyacrylate; S2, mixing the pretreated red mud, pretreated dolomite and pretreated diatomaceous earth uniformly to obtain a mixed dry material; S3. Spray the sodium polyacrylate aqueous solution on the surface of the mixed dry material, make particles with a diameter of 2-4 mm in a disc granulator, and spray dry to a moisture content of 0.5% to obtain a water treatment agent.

[0060] The preparation method of the pretreated red mud comprises the following steps: A1. Dealkalization: The red mud is subjected to three-stage filter pressing and then microwave drying to obtain dealkalized red mud; A2. Acid etching: the dealkalized red mud and the mixed acid solution are mixed, and after ultrasonic reaction, the mixture is washed with deionized water until it is neutral, and vacuum dried at 60°C until the moisture content is 2.5%, thereby obtaining acid-etched red mud; A3. Loading: The acid-etched red mud is immersed in a ferrate solution, shaken at room temperature for 2 hours, and then coated. After filtration at 60°C, vacuum drying is performed to a moisture content of 0.5%, thereby obtaining the pretreated red mud.

[0061] In the step A1, the three-stage filtration is a first stage filtration, a second stage filtration and a third stage filtration.

[0062] The first stage filtration is plate and frame filtration, and the specific conditions are: pressure 0.7MPa, and the pressure is maintained until the pH value of the filtrate is 13.

[0063] The second stage filtration is vacuum filtration, and the specific conditions are: the vacuum degree is -0.08MPa, and the moisture content is reduced to 45%.

[0064] The third stage filtration is high-pressure diaphragm filtration, and the specific conditions are: pressure 2.8 MPa, and the diaphragm is squeezed to a pH of 9.

[0065] In the step A1, the microwave drying includes first-stage microwave drying and second-stage microwave drying.

[0066] The conditions of the first stage microwave drying are: power 500W, time 5min, temperature 80°C.

[0067] The conditions of the second stage microwave drying are: power 300 W, time 15 min, temperature 105° C.

[0068] In the step A2, the solid-to-liquid ratio of the dealkalized red mud to the mixed acid solution is 1 g:8 mL.

[0069] The concentration of the mixed acid in the mixed acid solution is 0.5 mol / L.

[0070] The mixed acid is citric acid and hydrochloric acid, and the molar ratio is 4:1.

[0071] The specific conditions of the ultrasonic reaction are: frequency of 40 kHz, power of 200 W, temperature of 60° C., and time of 2 h.

[0072] In the step A3, the solid-to-liquid ratio of the acid-etched red mud to the ferrate solution is 1 g:15 mL.

[0073] The concentration of ferrate in the ferrate solution is 2 g / L, and the solvent is a sodium hydroxide aqueous solution with a mass concentration of 4%.

[0074] The ferrate is potassium ferrate.

[0075] The specific steps of the coating treatment are: adding a 3% sodium alginate aqueous solution by mass and stirring for 35 minutes.

[0076] The solid-to-liquid ratio of the acid-etched red mud to the sodium alginate aqueous solution with a mass fraction of 3% is 1g:35mL.

[0077] The preparation method of the pretreated dolomite comprises the following steps: crushing the dolomite to a particle size of 5-10 mm, calcining at 680° C. for 2 hours, and then ball-milling the dolomite through a 400-mesh sieve to obtain the pretreated dolomite.

[0078] The preparation method of the pretreated diatomaceous earth comprises the following steps: B1. Purification: calcining the diatomite at 550°C for 1.5h, soaking it in an acid solution with a volume concentration of 10%, ultrasonic cleaning it for 40min, washing it with water until it is neutral, and drying it to obtain purified diatomite; B2. Modification: After mixing the purified diatomaceous earth and the modifier, adjust the pH to 4.5, age at 60°C for 12h, and wash with water until there is no Cl - , calcined at 550°C for 2h to obtain modified diatomite; B3. Compounding: Modified diatomaceous earth, mineral powder and fly ash are mixed to obtain a solid mixture, pore-forming agent and deionized water are added and stirred evenly, then the mixture is dried at 105° C. and calcined at 730° C. for 1.5 h to obtain a solid mixture.

[0079] In the step B2, the solid-liquid ratio of the purified diatomaceous earth and the modifier is 1 g:15 mL.

[0080] The modifier is aluminum chloride solution or ferric chloride solution.

[0081] In the modifier, the molar ratio of aluminum to iron is 0.3.

[0082] The concentration of the aluminum chloride solution is 0.3 mol / L; the concentration of the ferric chloride solution is 0.2 mol / L.

[0083] In the step B3, the mass ratio of modified diatomaceous earth, mineral powder and fly ash is 5:3:2.

[0084] The pore-forming agent is sodium bicarbonate.

[0085] The added amount of the pore former is 8% of the mass of the solid mixture.

[0086] The solid-to-liquid ratio of the solid mixture to deionized water is 1 g:1 mL.

[0087] Example 2 The difference between this embodiment and embodiment 1 is that the water treatment agent based on comprehensive utilization of red mud comprises raw materials, by weight, including 105 parts of pretreated red mud, 25 parts of pretreated dolomite, 10 parts of pretreated diatomaceous earth, and 5 parts of sodium polyacrylate.

[0088] Comparative Example 1 The difference between this comparative example and Example 1 is that the water treatment agent based on comprehensive utilization of red mud comprises raw materials, by weight, including 100 parts of red mud, 30 parts of pretreated dolomite, 15 parts of pretreated diatomaceous earth, and 8 parts of sodium polyacrylate.

[0089] Comparative Example 2 The difference between this comparative example and Example 1 is as follows: A1. dealkalization: the red mud is subjected to primary filter pressing and then microwave drying to obtain dealkalized red mud; the primary filter pressing is plate and frame filter pressing, and the specific conditions are: pressure 0.7 MPa, and pressure holding time 1 h.

[0090] Comparative Example 3 The difference between this comparative example and Example 1 is as follows: A1. Dealkalization: red mud is subjected to three-stage filter pressing and then dried to constant weight to obtain dealkalized red mud.

[0091] Comparative Example 4 The difference between this comparative example and Example 1 is as follows: A2, acid etching: the dealkalized red mud and the hydrochloric acid solution are mixed, and after ultrasonic reaction, the mixture is washed with deionized water until it becomes neutral, and vacuum dried at 60° C. until the moisture content is 2.5%, thereby obtaining the acid-etched red mud. The concentration of the hydrochloric acid solution is 0.5 mol / L.

[0092] Comparative Example 5 The difference between this comparative example and Example 1 is that the preparation method of the pretreated red mud comprises the following steps: A1. Dealkalization: The red mud is subjected to three-stage filter pressing and then microwave drying to obtain dealkalized red mud; A2. Acid etching: Mix the dealkalized red mud and the mixed acid solution, wash with deionized water to neutrality after ultrasonic reaction, and vacuum dry at 60°C to a moisture content of 0.5% to obtain the pretreated red mud.

[0093] Comparative Example 6 The difference between this comparative example and Example 1 is as follows: B1. Purification: soak in an acid solution with a volume concentration of 10%, ultrasonically clean for 40 minutes, wash with water until neutral, then dry, and then calcine at 550° C. for 1.5 hours to obtain purified diatomaceous earth.

[0094] Comparative Example 7 The difference between this comparative example and Example 1 is that the preparation method of the pretreated diatomaceous earth comprises the following steps: B1. Purification: calcining the diatomite at 550°C for 1.5h, soaking it in an acid solution with a volume concentration of 10%, ultrasonic cleaning it for 40min, washing it with water until it is neutral, and drying it to obtain purified diatomite; B2. Compounding: Purified diatomite, mineral powder and fly ash are mixed to obtain a solid mixture, pore-forming agent and deionized water are added, stirred evenly, dried at 105°C, and calcined at 730°C for 1.5h to obtain a solid mixture; The mass ratio of the purified diatomite, mineral powder and fly ash is 5:3:2.

[0095] Performance Testing Take 800mL of domestic sewage from the water plant and determine its initial COD, initial ammonia nitrogen content and initial total phosphorus. Prepare the water treatment agent into a solution with a mass concentration of 20%, take 4mL of the solution and put it into 800mL of domestic sewage, mix quickly for 30 seconds, mix slowly for 3 minutes, and take the supernatant after static sedimentation for 10 minutes to determine the COD, ammonia nitrogen and total phosphorus at this time. And calculate the removal rate of the three, the calculation formula is (initial value-post-treatment value) / initial value×100%. The determination of COD, ammonia nitrogen and total phosphorus refers to GB3838-2002 "Water Quality Classification and Limits". The results are shown in Table 1.

[0096] Table 1 Measurement results

[0097] According to statistics, the water treatment agent based on comprehensive utilization of red mud prepared in Examples 1-2 of the present invention is COD degradation rate, ammonia nitrogen removal rate and total phosphorus removal rate are all high. Comparative Example 1 did not pre-treat the red mud; Comparative Example 2 only used a first-stage filter press; Comparative Example 3 did not perform microwave drying after the third-stage filter press, but only ordinary drying treatment; Comparative Example 4 only used hydrochloric acid during acid etching, and did not use citric acid; Comparative Example 5 did not perform step A3 load treatment on the red mud; Comparative Example 6 first acid-leached and then calcined the diatomaceous earth; Comparative Example 7 did not perform step B2 modification treatment on the diatomaceous earth. The COD degradation rate, ammonia nitrogen removal rate and total phosphorus removal rate of the prepared water treatment agent are all insufficient. Therefore, the water treatment agent prepared using the raw materials and methods described in this application can not only increase the pollutant removal range, but also degrade COD and remove ammonia nitrogen and phosphorus at the same time, and the degradation rate and removal rate are both excellent.

[0098] 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 the scope of protection of the present invention.

Claims

1. A water treatment agent based on comprehensive utilization of red mud, characterized in that: The raw materials for its preparation include, by weight, 95-105 parts of pretreated red mud, 25-35 parts of pretreated dolomite, 10-20 parts of pretreated diatomaceous earth, and 5-10 parts of sodium polyacrylate; The method for preparing the pretreated red mud comprises the following steps: A1. Dealkalization: The red mud is subjected to three-stage filter pressing and then microwave drying to obtain dealkalized red mud; A2. Acid etching: the dealkalized red mud and the mixed acid solution are mixed, and after ultrasonic reaction, they are washed with deionized water until neutral, and vacuum dried to obtain acid-etched red mud; A3. Loading: The acid-etched red mud is immersed in a ferrate solution, shaken, coated, and vacuum dried to obtain the product.

2. The water treatment agent based on comprehensive utilization of red mud according to claim 1, characterized in that: In the step A1, the three-stage filtration includes a first stage filtration, a second stage filtration and a third stage filtration.

3. The water treatment agent based on comprehensive utilization of red mud according to claim 2, characterized in that: The first stage filtration is plate and frame filtration, and the specific conditions are: pressure 0.6-0.8MPa, and the pressure is maintained until the filtrate pH is ≤13.5; the second stage filtration is vacuum filtration, and the specific conditions are: vacuum degree is -0.08MPa, and the moisture content is reduced to 45% or below; the third stage filtration is high-pressure diaphragm filtration, and the specific conditions are: pressure 2.5-3.0MPa, and the diaphragm is squeezed to pH≤9.

4. The water treatment agent based on comprehensive utilization of red mud according to claim 2, characterized in that: In the step A1, the microwave drying includes a first stage microwave drying and a second stage microwave drying.

5. The water treatment agent based on comprehensive utilization of red mud according to claim 4, characterized in that: The conditions of the first stage microwave drying are: power 400-600W, time 5min, temperature 75-85°C; the conditions of the second stage microwave drying are: power 200-350W, time 10-20min, temperature 100-110°C.

6. The water treatment agent based on comprehensive utilization of red mud according to claim 1, characterized in that: The method for preparing the pretreated diatomaceous earth comprises the following steps: B1. Purification: calcining the diatomite, soaking it in an acid solution, ultrasonic cleaning it, washing it with water until it is neutral, and drying it to obtain purified diatomite; B2. Modification: After mixing the purified diatomaceous earth and the modifier, adjust the pH to 4-5, age at 58-62℃ for 10-15h, and wash with water until there is no Cl - , calcining to obtain modified diatomaceous earth; B3. Compounding: Mix the modified diatomite, mineral powder and fly ash to obtain a solid mixture, add a pore-forming agent and deionized water, stir evenly, dry and calcine to obtain the solid mixture.

7. The water treatment agent based on comprehensive utilization of red mud according to claim 6, characterized in that: The modifier includes aluminum chloride solution and ferric chloride solution.

8. The water treatment agent based on comprehensive utilization of red mud according to claim 7, characterized in that: In the modifier, the molar ratio of aluminum to iron is 0.2-0.

4.

9. The water treatment agent based on comprehensive utilization of red mud according to claim 1, characterized in that: The preparation method of the pretreated dolomite comprises the following steps: crushing the dolomite to a particle size of 5-10 mm, calcining at 650-700° C. for 1.5-2.5 h, and then ball-milling through a 400-mesh sieve to obtain the pretreated dolomite.

10. A method for preparing a water treatment agent based on comprehensive utilization of red mud according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1. Prepare sodium polyacrylate into an aqueous solution with a mass fraction of 8% sodium polyacrylate; S2, mixing the pretreated red mud, pretreated dolomite and pretreated diatomaceous earth uniformly to obtain a mixed dry material; S3. Spray the sodium polyacrylate aqueous solution on the surface of the mixed dry material, make particles with a diameter of 2-4 mm in a disc granulator, and spray dry to a moisture content of ≤1% to obtain a water treatment agent.

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