A salt-tolerant composite catalyst based on organic sludge and red mud, and a preparation method and application thereof

Abstract

The application provides a salt-tolerant composite catalyst based on organic sludge and red mud, a preparation method and application thereof, and belongs to the field of advanced oxidation treatment of industrial wastewater; the salt-tolerant composite catalyst is prepared by mixing, pyrolyzing, shaping and secondary solidifying 50-70 parts of sludge powder and 30-50 parts of dried red mud; the organic sludge has an organic matter content of greater than or equal to 45%, the red mud has an iron oxide content of greater than or equal to 20%, the salt-tolerant composite catalyst is a porous particle with a size of 1-5 mm, has a "carbon shell-metal shell" structure and a micropore-mesopore-macropore gradient pore channel, a specific surface area of greater than or equal to 150 m 2 / g, and a particle compressive strength of greater than or equal to 15 N. The salt-tolerant composite catalyst realizes the synergistic resource utilization of organic sludge and red mud, has excellent salt tolerance, high catalytic activity and good stability, can be adapted to an engineering continuous flow process, has a remarkable effect when used for treating high-salinity and refractory organic wastewater with a salinity of 0.5%-5%, and has both environmental and economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of advanced oxidation treatment technology for industrial wastewater, specifically relating to a salt-tolerant composite catalyst prepared by synergistic preparation of organic sludge and red mud, its preparation method, and its application. Background Technology

[0002] The rapid development of industries such as dyeing and printing, pharmaceuticals, and fine chemicals has led to a year-on-year increase in the discharge of recalcitrant organic wastewater. This type of wastewater is complex in composition, highly toxic, and has poor biodegradability, making it difficult to achieve discharge standards using traditional biological treatment and physicochemical methods. High-salt recalcitrant organic wastewater (such as polyester dyeing wastewater, pesticide intermediate production wastewater, and chlor-alkali chemical wastewater) contains high concentrations of Cl-. - SO4 2- The presence of anions further increases the difficulty of processing: salt ions are prone to side reactions with free radicals in advanced oxidation systems, consuming active species. The salting-out effect can also cause blockage of catalyst pores and loss of active components, leading to rapid decline in the activity of traditional catalysts in high-salt systems and a significant increase in metal dissolution rate, which cannot meet the needs of engineering applications.

[0003] Advanced oxidation techniques based on persulfate activation, such as persulfate monosulfate (PMS) and persulfate disulfate (PDS), can generate sulfate radicals (·SO4). - High-performance catalysts (with an oxidation-reduction potential of 2.5-3.1V) and hydroxyl radicals (·OH, with an oxidation-reduction potential of 2.8V) can efficiently degrade recalcitrant organic pollutants in water, making them a current research hotspot and mainstream technology in the field of water treatment. The core of this technology lies in the development of high-performance catalysts. Reducing preparation costs while ensuring catalyst efficiency and stability is crucial for the industrial application of this technology. The "waste-to-waste" concept provides a solution for low-cost catalyst preparation—utilizing industrial solid waste to prepare catalysts can both reduce costs and achieve resource utilization of solid waste, aligning with the green development strategy.

[0004] However, existing technologies for preparing persulfate-activated catalysts from solid waste still have many shortcomings: The use of single raw materials and the lack of exploration of synergistic effects: Existing technologies mostly use single types of solid waste as raw materials, ignoring the complementary and synergistic effects of solid wastes with different properties. This leads to problems such as insufficient active sites and poor structural stability in the prepared catalysts. Among them, industrial carbon-rich organic sludge is rich in elements such as carbon and nitrogen, making it an excellent precursor for carbon-based catalytic materials. However, its pyrolysis products alone have low mechanical strength and lack metallic active components. Red mud is rich in metal oxides such as iron, aluminum, and titanium, and has the potential to serve as active centers for heterogeneous catalysts. However, when used directly, it has a low specific surface area, the active components are encapsulated in the crystal lattice, and its strong alkalinity easily leads to pH imbalance in water bodies. Currently, there is no technology to scientifically combine these two complementary solid wastes to prepare high-performance catalysts.

[0005] Lack of engineering adaptation design: Most existing catalysts are in powder form, which are easy to lose and difficult to recover in actual water treatment projects, and can also cause secondary pollution. They are also unable to adapt to continuous flow treatment processes and lack integrated design from preparation to molding and reactor application, making it difficult to meet the needs of continuous and stable treatment of industrial wastewater.

[0006] Insufficient catalyst stability and narrow applicability: Some waste residue-based catalysts have high metal leaching rates, which leads to both catalytic activity attenuation and secondary water pollution; the catalytic activity of most catalysts is highly dependent on the pH of the reaction system, and their activity decreases significantly under neutral or weakly alkaline conditions. In high-salt systems, the corrosion of salt ions will further aggravate deactivation, limiting their applicability.

[0007] Therefore, developing a composite catalyst that utilizes organic sludge and red mud to prepare a mixture with high catalytic activity, high stability, wide pH adaptability, and excellent salt tolerance, and is adaptable to continuous flow engineering processes, is of great significance for promoting the industrialization of advanced persulfate oxidation technology and the resource utilization of solid waste. Summary of the Invention

[0008] This invention addresses the problems of existing technologies by providing a salt-tolerant composite catalyst based on the synergistic preparation of organic sludge and red mud, along with its preparation method and applications.

[0009] To achieve the above objectives, the technical solution adopted in this application is as follows: In a first aspect, a salt-tolerant composite catalyst based on the synergistic preparation of organic sludge and red mud is prepared by mixing, pyrolysis, molding, and secondary solidification of the following raw materials in parts by weight: 50-70 parts of sludge powder and 30-50 parts of dried red mud; wherein the organic content of the industrial carbon-rich organic sludge is ≥45%, preferably 48%-55%; the sludge powder is obtained by drying and crushing the industrial carbon-rich organic sludge; the industrial carbon-rich organic sludge includes one or more of municipal sewage anaerobic digestion sludge, dyeing and printing sludge, and pharmaceutical bacterial residue; the content of iron oxides (calculated as Fe2O3) in the dried red mud is ≥20%; The salt-resistant composite catalyst consists of porous particles with a particle size of 1 mm-5 mm and a specific surface area ≥150 m². 2 / g, particle compressive strength ≥15N; the preferred particle size of the salt-resistant composite catalyst is 2mm-3mm, and the specific surface area is 180m². 2 / g-250m 2 / g, with a bulk density of 0.6g / cm². 3 -0.9g / cm 3 The metal leaching rate, calculated as Fe, is ≤0.5 mg / L.

[0010] Preferably, the salt-tolerant composite catalyst has a gradient composite structure of carbon shell and metal shell, wherein the carbon shell is a porous carbon matrix derived from the pyrolysis of industrial carbon-rich organic sludge, and the metal shell is Fe formed by reduction from dried red mud. 0 The catalyst is composed of iron-based active materials, mainly Fe3O4; the metal shell is tightly wrapped by a carbon shell; the pore structure of the catalyst is a gradient pore structure with micropores, mesopores and macropores, wherein the micropore diameter is <2nm, the mesopore diameter is 2-50nm, and the macropore diameter is >50nm.

[0011] Secondly, a method for preparing a salt-tolerant composite catalyst based on the synergistic preparation of organic sludge and red mud, the specific steps of which are as follows: S1: Raw material pretreatment: Industrial carbon-rich organic sludge and red mud are dried to constant weight at 105±5℃, crushed and passed through a 100-mesh standard sieve to obtain sludge powder and dried red mud. The criterion for drying to constant weight is that the difference in mass between two consecutive weighings is ≤0.5%. S2: Ingredients and blending: Weigh out the corresponding mass parts of sludge powder and dried red mud according to the ratio of 50-70 parts of industrial carbon-rich organic sludge and 30-50 parts of dried red mud in a 1:1 ratio, add deionized water, the amount of deionized water added is 10%-15% of the total dry basis mass, knead at room temperature for 20-30 minutes to form a uniform plastic wet material. S3: Place the wet plastic material in an inert atmosphere tube furnace, heat it to 350-450℃ at a heating rate of 5℃ / min, and hold it for 30-60min; then heat it to 750-900℃ at a heating rate of 5℃ / min and hold it for 60-120min. S4: Post-treatment: After the pyrolysis product is naturally cooled to room temperature, it is rinsed 2-3 times with 0.1-0.2M dilute hydrochloric acid for 10-20 minutes each time, and then repeatedly rinsed with deionized water until the pH of the eluent is 6.5-7.5. It is then dried in an oven at 105±5℃ to constant weight to obtain composite catalyst powder. S5: Molding: Place the composite catalyst powder in a mixer and start mechanical mixing at a speed of 30-40 r / min. Slowly add a binder solution accounting for 5%-10% of the mass of the composite catalyst powder at a dropping rate of 5-10 mL / min. Mix until the material forms a granulation masterbatch that can be formed into a ball by hand and easily dispersed by kneading. Place the masterbatch in a rolling granulator to obtain spherical particles. S6: Secondary curing: Place the spherical particles in an oven at 120±5℃ and dry for 2-4 hours. Then place them in a muffle furnace and heat them to 400-500℃ at a heating rate of 5℃ / min in an air atmosphere. Hold for 30 minutes and cool to obtain a salt-resistant composite catalyst.

[0012] In addition, the salt-tolerant composite catalyst of this application can also be prepared by extrusion.

[0013] Preferably, in step S3, the inert atmosphere is nitrogen or argon, and the gas flow rate is 50-100 mL / min; in step S5, the binder is one of a sodium carboxymethyl cellulose solution or a sodium alginate solution with a mass concentration of 5%-10%.

[0014] Thirdly, the application of a salt-tolerant composite catalyst prepared based on the synergistic preparation of organic sludge and red mud in the continuous flow process for activating persulfate treatment of recalcitrant organic wastewater in industry.

[0015] As a preferred embodiment, the specific operation method is as follows: The salt-tolerant composite catalyst is filled into a fixed bed or moving bed reactor. The industrial organic wastewater to be treated is mixed with persulfate in a certain proportion and then continuously passed through the catalyst bed in an upflow or downflow manner. Under the catalytic action of the catalyst, the persulfate is activated into a strong oxidizing free radical, which degrades the recalcitrant organic pollutants in the wastewater. The concentration of the persulfate is 0.5-5 mM, the hydraulic residence time of the wastewater in the catalyst bed is 10-60 min, and the ratio of the catalyst filling volume to the wastewater treatment flow rate is 1:2 to 1:10, that is, the wastewater treatment flow rate corresponding to each liter of catalyst is 2-10 L / h.

[0016] Preferably, the persulfate is permonosulfate or perdisulfate; the industrial recalcitrant organic wastewater includes dyeing and printing wastewater, pharmaceutical wastewater, and comprehensive wastewater from chemical industrial parks; the salinity of the high-salt recalcitrant organic wastewater in the industrial recalcitrant organic wastewater is 5000-50000 mg / L (calculated as NaCl), the COD concentration in the wastewater is 100-1000 mg / L, and the color is 50-1000 times; when treating high-salt recalcitrant organic wastewater with a salinity ≥10000 mg / L, the persulfate dosage is 3-4 mM, the hydraulic retention time is 30-50 min, and the ratio of catalyst filling volume to wastewater treatment flow rate is 1:2 to 1:5.

[0017] Preferably, the pH of the reaction system is 3-11, requiring no additional pH adjustment; the reaction temperature is room temperature (15-35℃), requiring no additional heating or cooling.

[0018] Fourthly, an industrial wastewater treatment system is provided for the application of the salt-tolerant composite catalyst according to any one of claims 5-8 in a continuous flow process to activate persulfate for the treatment of recalcitrant organic wastewater in the industry. The system comprises a raw water tank, a booster pump, a dosing device, a static mixer, a reactor, and an effluent tank connected in sequence, and further includes a backwashing device connected to the reactor. The reactor is a fixed-bed or moving-bed reactor, and its interior is filled with the salt-tolerant composite catalyst according to any one of claims 1-2. The dosing device is used to add persulfate solution to the raw water and to fully mix the persulfate solution with the raw water through the static mixer. The backwashing device is used to periodically backwash and regenerate the composite catalyst in the reactor.

[0019] Preferably, the backwash water of the backwashing device is treated effluent that meets the standards, the backwashing flow rate is 2-5 m / h, the backwashing time is 5-10 min, and the backwashing cycle is 24-72 h.

[0020] Compared with the prior art, the advantages and positive effects of the present invention are as follows: This application discloses a salt-tolerant composite catalyst prepared by synergistic synthesis of organic sludge and red mud, its preparation method, and its application. The catalyst utilizes the complementary components of organic sludge and red mud to generate a strong synergistic effect. The organic sludge provides the catalyst with a carbon source, nitrogen source, and pore-forming template, while the reducing gas generated by its pyrolysis removes Fe from the red mud. 3+ Reduced to highly active Fe 2+ Or Fe; red mud provides the catalyst with metal active centers and rigid framework support. Through synergistic pyrolysis, metal species are anchored in the carbon matrix to form a "carbon shell-metal shell" structure, which not only solves the problems of insufficient active sites and poor mechanical strength of single sludge-based carbon materials, but also overcomes the defects of low specific surface area and difficulty in releasing active components of single red mud; The prepared salt-resistant composite catalyst forms a gradient channel of micropores, mesopores, and macropores. Combined with molding and secondary curing processes, the catalyst particles have a compressive strength of ≥15N and can be directly filled into fixed bed / moving bed reactors to withstand the hydraulic impact under continuous flow conditions. This completely solves the technical bottlenecks of traditional powder catalysts, such as easy loss, difficulty in recovery, and inability to adapt to continuous flow processes. The alkaline buffering capacity of red mud and the coating effect of the carbon layer enable the catalyst to maintain high catalytic activity in a wide pH range of 3-11 without the need for additional pH adjustment, thus reducing operating costs. The physical confinement and chemical bonding of the carbon layer to the active metal components (forming CM bonds, where M is Fe, Al, etc.) ensures that the iron ion dissolution rate is ≤0.5mg / L, far below the national standard limit (0.8mg / L), avoiding secondary pollution of water bodies and improving the long-term stability of the catalyst. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a flowchart illustrating the preparation process of a salt-tolerant composite catalyst based on the synergistic preparation of organic sludge and red mud according to this application. Figure 2 This is a report on the performance test results of the finished composite catalyst S1 from Example 1; Figure 3 This is a graph showing the change in iron ion dissolution concentration in simulated effluent water after 37 days of continuous operation of the finished composite catalyst S1 from Example 1. Figure 4 This is a comparison chart showing the degradation effects of the finished composite catalyst S1 from Example 1 on Acid Red B COD, TOC, and UV254 over 24 hours. Figure 5 The graph shows the degradation effect of the finished composite catalyst S1 from Example 1 on different wastewaters. Figure 6 This is a diagram showing the granulation process of the finished composite catalyst S1 in Example 1; Figure 7 One of the actual product images of the finished composite catalyst S1 from Example 1; Figure 8 The second image shows the finished composite catalyst S1 product from Example 1. Figure 9 This application describes an industrial wastewater treatment system. Detailed Implementation

[0023] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0024] Numerous specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways than those described herein, and therefore the invention is not limited to the specific embodiments disclosed in the following specification.

[0025] Example 1, as Figure 1 , Figure 6 , Figure 7 , Figure 8 As shown in Example 1, a salt-tolerant composite catalyst prepared based on the synergistic preparation of organic sludge and red mud is described in the following specific preparation method: S1: Raw material pretreatment: Take municipal sewage anaerobic digestion sludge (organic matter content 52%) and red mud from the alumina plant (Fe2O3 content 28%), dry them in an oven at 105℃ to constant weight, crush them in a planetary ball mill and pass them through a 100-mesh standard sieve to obtain sludge powder and dried red mud. S2: Ingredients and blending: Weigh 60 parts of sludge powder and 40 parts of dried red mud, add 12% of deionized water by total dry weight, place in a kneader and knead at room temperature for 25 minutes to form a uniform plastic wet material. S3: Pyrolysis: Place the wet plastic material into an inert atmosphere tube furnace, introduce nitrogen gas (flow rate 80 mL / min), raise the temperature to 400℃ at 5℃ / min, hold for 45 min; continue to raise the temperature to 800℃ at 5℃ / min, hold for 90 min; S4: Post-treatment: After the pyrolysis product is naturally cooled to room temperature, it is rinsed twice with 0.1M dilute hydrochloric acid for 15 minutes each time, and then rinsed with deionized water until the pH of the eluent is 7.0. It is then dried in an oven at 105℃ to constant weight to obtain composite catalyst powder. S5: Molding: Place the composite catalyst powder in a mixer at a speed of 40 r / min, slowly add 8% sodium carboxymethyl cellulose, and mix until the material forms a granulation masterbatch that can be formed into a ball by hand and easily dispersed by kneading; place the masterbatch in a rolling granulator to granulate and obtain shaped wet granules with a particle size of 3-5 mm. S6: Secondary curing: The molded wet particles are placed in an oven at 120°C and dried for 3 hours. Then, they are placed in a muffle furnace and heated to 450°C at 5°C / min in an air atmosphere. The temperature is maintained for 30 minutes. After cooling, the finished composite catalyst S1 of Example 1 is obtained.

[0026] The performance of the finished composite catalyst S1 from Example 1 was tested, and the results are as follows: Figure 2 , Figure 3 As shown: Specific surface area 202m² 2 / g, bulk density 0.75g / cm³ 3 The particle compressive strength is 136.5 N, and the metal leaching rate (Fe) is 0.02 mg / L, which meets the performance index requirements of this invention.

[0027] Comparative Example 1: Preparation of a single sludge-based carbon catalyst: Using only 100 parts of dyeing and printing sludge as raw material, the remaining preparation steps were exactly the same as in Example 1, yielding the single sludge-based carbon catalyst D1 of Comparative Example 1. Performance test results showed a specific surface area of ​​120 m². 2 / g, bulk density 0.58g / cm³ 3 The particle compressive strength is 18N, the metal dissolution rate (Fe) is 0.1mg / L (the metal content itself is low), there are insufficient catalytic active sites and poor mechanical strength.

[0028] Comparative Example 2, Preparation of a single red mud-based catalyst: Using only 100 parts of red mud as raw material, the low-temperature carbonization stage was omitted during the preparation process. The temperature was directly increased to 800℃ at 5℃ / min and held for 90min. The remaining steps were exactly the same as in Example 1, yielding the single red mud-based catalyst D2 of Comparative Example 2. Performance testing results showed a specific surface area of ​​65 m². 2 / g, bulk density 1.2g / cm³ 3 The particle compressive strength is 130N, the metal leaching rate (Fe) is 1.2mg / L, the specific surface area is low, the metal leaching rate is high, and the environmental safety is poor.

[0029] An application experiment was conducted on the composite catalyst S1 from Example 1 for treating high-salt dyeing and printing wastewater: Experimental setup: A continuous flow fixed bed treatment system was constructed, including a raw water tank, a peristaltic pump (lift pump), a dosing tank (dosing device), a static mixer, a fixed bed reaction column, an outlet water tank, and a backwashing device; the reaction column was filled with 50 mL of the composite catalyst S1 prepared in Example 1.

[0030] Simulated wastewater: High-salt dyeing wastewater was prepared, containing 100 mg / L of Acid Red b dye and a COD concentration of approximately 250 mg / L. NaCl was added to adjust the salinity to 15000 mg / L, and the original water pH was approximately 7.5.

[0031] Operating parameters: Water is fed in via upflow, with a hydraulic retention time of 45 min; sodium persulfate (PDS) solution is added, with a PDS concentration of 3.5 mM in the feed water; reaction temperature is 25℃, and pH is not adjusted; backwashing cycle is 18 h, backwashing flow rate is 3 m / h, and backwashing time is 8 min.

[0032] Experimental results: such as Figure 4 As shown, the system ran continuously for 24 hours, with samples taken every 2 hours. The effluent decolorization rate remained stable at over 95%, and the COD removal rate remained stable at over 89%, indicating that the catalyst maintained high efficiency and stable catalytic activity even in a high-salt system.

[0033] Comparative Experiment: Under the same experimental conditions as the application experiment of the composite catalyst S1 in treating high-salt dyeing wastewater, S1 was replaced with equal volumes of D1 from Comparative Example 1 and D2 from Comparative Example 2. The results are as follows: Catalyst D1: The initial effluent decolorization rate was 65%, which dropped to below 40% after 3 hours of operation. The COD removal rate was 45% initially, but dropped to below 20% later. This was because the single sludge-based carbon catalyst had insufficient metal active sites, resulting in a rapid decline in catalytic activity.

[0034] Catalyst D2: The overall effluent decolorization rate is only 35%-40%, the COD removal rate is ≤30%, and the effluent iron ion concentration reaches 1.0-1.2mg / L, which is close to the national standard limit. This is because the single red mud-based catalyst has a small specific surface area, the active components are difficult to release, the catalytic performance is poor, and the metal dissolution rate is high.

[0035] Adaptability experiments were conducted on the composite catalyst S1 of Example 1 for different wastewater types. Catalyst S1 was applied to treat pharmaceutical wastewater (COD concentration 500 mg / L) and comprehensive wastewater from a chemical industrial park (COD concentration 800 mg / L, containing phenols and anilines, which are difficult to degrade organic matter). The hydraulic retention time was adjusted to 40 min, the PDS dosage was 3 mM, and the remaining experimental conditions were the same as in Example 2.

[0036] Experimental results: such as Figure 5 As shown, after 12 hours of continuous operation, the COD removal rate of pharmaceutical wastewater is ≥80%, and the COD removal rate of comprehensive wastewater from the chemical industrial park is ≥75%, indicating that the composite catalyst of the present invention has good adaptability to various types of recalcitrant organic wastewater in industry.

[0037] As can be seen, the salt-tolerant composite catalyst prepared by the co-production of organic sludge and red mud in this invention uses industrial solid waste as raw material, resulting in low cost and achieving "waste treatment with waste." The catalyst possesses high catalytic activity, excellent salt tolerance and structural stability, wide pH adaptability, low metal leaching rate, and high environmental friendliness. This catalyst is in granular form and can be directly filled into fixed-bed / moving-bed reactors, perfectly adapting to continuous flow industrial wastewater treatment processes. The associated wastewater treatment system is simple to operate, has low operating costs, and the catalyst is regenerable and reusable.

[0038] like Figure 9 As shown, the catalyst and treatment system of the present invention can efficiently treat various recalcitrant organic wastewaters from dyeing, printing and dyeing, pharmaceutical, and chemical industrial parks. It is especially suitable for the deep treatment of high-salinity recalcitrant organic wastewater with a salinity of 0.5%-5%, and has broad industrial application prospects in the field of industrial wastewater treatment. At the same time, it can realize the resource utilization of organic sludge and red mud, and has environmental, economic and social benefits.

[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A salt-tolerant composite catalyst prepared based on the synergistic preparation of organic sludge and red mud, characterized in that, The product is prepared by mixing, pyrolysis, molding, and secondary solidification of the following raw materials in parts by weight: 50-70 parts sludge powder and 30-50 parts dried red mud; wherein the organic content of the industrial carbon-rich organic sludge is ≥45%; the sludge powder is obtained by drying and crushing the industrial carbon-rich organic sludge; the industrial carbon-rich organic sludge includes one or more of municipal sewage anaerobic digestion sludge, dyeing and printing sludge, and pharmaceutical bacterial residue; the iron oxide content of the dried red mud is ≥20%. The salt-resistant composite catalyst consists of porous particles with a particle size of 1 mm-5 mm and a specific surface area ≥150 m². 2 / g, particle compressive strength ≥15N.

2. The salt-tolerant composite catalyst prepared based on the synergistic preparation of organic sludge and red mud according to claim 1, characterized in that, The salt-tolerant composite catalyst has a gradient composite structure of carbon shell and metal shell, wherein the carbon shell is a porous carbon matrix derived from the pyrolysis of industrial carbon-rich organic sludge, and the metal shell is Fe formed by reduction from dried red mud. 0 The catalyst is composed of iron-based active materials, mainly Fe3O4; the metal shell is tightly wrapped by a carbon shell; the pore structure of the catalyst is a gradient pore structure with micropores, mesopores and macropores, wherein the micropore diameter is <2nm, the mesopore diameter is 2-50nm, and the macropore diameter is >50nm.

3. A method for preparing a salt-tolerant composite catalyst based on the synergistic preparation of organic sludge and red mud according to any one of claims 1 or 2, characterized in that, The specific steps are as follows: S1: Raw material pretreatment: Industrial carbon-rich organic sludge and red mud are dried to constant weight at 105±5℃, crushed and passed through a 100-mesh standard sieve to obtain sludge powder and dried red mud. S2: Ingredients and blending: Weigh out the corresponding mass parts of sludge powder and dried red mud according to the ratio of 50-70 parts of industrial carbon-rich organic sludge and 30-50 parts of dried red mud in a 1:1 ratio, add deionized water, the amount of deionized water added is 10%-15% of the total dry basis mass, knead at room temperature for 20-30 minutes to form a uniform plastic wet material. S3: Place the wet plastic material in an inert atmosphere tube furnace, heat it to 350-450℃ at a heating rate of 5℃ / min, and hold it for 30-60min; then heat it to 750-900℃ at a heating rate of 5℃ / min and hold it for 60-120min. S4: Post-treatment: After the pyrolysis product is naturally cooled to room temperature, it is rinsed 2-3 times with 0.1-0.2M dilute hydrochloric acid for 10-20 minutes each time, and then repeatedly rinsed with deionized water until the pH of the eluent is 6.5-7.

5. It is then dried in an oven at 105±5℃ to constant weight to obtain composite catalyst powder. S5: Molding: Place the composite catalyst powder in a mixer and start mechanical mixing at a speed of 30-40 r / min. Slowly add a binder solution accounting for 5%-10% of the mass of the composite catalyst powder at a dropping rate of 5-10 mL / min. Mix until the material forms a granulation masterbatch that can be formed into a ball by hand and easily dispersed by kneading. Place the masterbatch in a rolling granulator to obtain spherical particles. S6: Secondary curing: Place the spherical particles in an oven at 120±5℃ and dry for 2-4 hours. Then place them in a muffle furnace and heat them to 400-500℃ at a heating rate of 5℃ / min in an air atmosphere. Hold for 30 minutes and cool to obtain a salt-resistant composite catalyst.

4. The salt-tolerant composite catalyst prepared based on the synergistic preparation of organic sludge and red mud according to claim 3, characterized in that, In step S3, the inert atmosphere is nitrogen or argon, and the gas flow rate is 50-100 mL / min; in step S5, the binder is one of sodium carboxymethyl cellulose solution or sodium alginate solution with a mass concentration of 5%-10%.

5. The application of a salt-tolerant composite catalyst prepared based on the synergistic preparation of organic sludge and red mud, as described in claim 1 or 2, in the continuous flow process for activating persulfate treatment of recalcitrant organic wastewater in industry.

6. The application of the salt-tolerant composite catalyst prepared based on the synergistic preparation of organic sludge and red mud according to claim 5 in the continuous flow process for activating persulfate treatment of recalcitrant organic wastewater in industry, characterized in that, The specific operation method is as follows: The salt-resistant composite catalyst is filled into a fixed bed or moving bed reactor. The industrial organic wastewater to be treated is mixed with persulfate in a certain proportion and then continuously passed through the catalyst bed in an upflow or downflow manner. The mass concentration of the persulfate is 0.5-5 mM, the hydraulic residence time of the wastewater in the catalyst bed is 10-60 min, and the ratio of catalyst filling volume to wastewater treatment flow rate is 1:2 to 1:10, that is, the wastewater treatment flow rate corresponding to each liter of catalyst is 2-10 L / h.

7. The application of the salt-tolerant composite catalyst prepared based on the synergistic preparation of organic sludge and red mud according to claim 5 in the continuous flow process for activating persulfate treatment of recalcitrant organic wastewater in industry, characterized in that, The persulfate is either permonosulfate or perdisulfate; the recalcitrant industrial organic wastewater includes dyeing and printing wastewater, pharmaceutical wastewater, and comprehensive wastewater from chemical industrial parks. The salinity of the high-salt recalcitrant organic wastewater in the industrial recalcitrant organic wastewater is 5000-50000 mg / L (calculated as NaCl), the COD concentration in the wastewater is 100-1000 mg / L, and the color is 50-1000 times. When treating high-salt recalcitrant organic wastewater with a salinity ≥10000 mg / L, the persulfate dosage is 3-4 mM, the hydraulic retention time is 30-50 min, and the ratio of catalyst filling volume to wastewater treatment flow rate is 1:2 to 1:

5.

8. The salt-tolerant composite catalyst prepared based on the synergistic preparation of organic sludge and red mud according to claim 7, characterized in that, The pH of the reaction system is 3-11, and no additional pH adjustment is required; the reaction temperature is room temperature (15-35℃), and no additional heating or cooling is required.

9. An industrial wastewater treatment system for implementing the application of the salt-tolerant composite catalyst according to any one of claims 5-8 in a continuous flow process to activate persulfate for the treatment of recalcitrant organic wastewater in industry, characterized in that, The reactor comprises, in sequence, a raw water tank, a booster pump, a dosing device, a static mixer, a reactor, and an outlet water tank, and further includes a backwashing device connected to the reactor; the reactor is a fixed-bed or moving-bed reactor, and its interior is filled with a salt-tolerant composite catalyst as described in any one of claims 1-2; the dosing device is used to add persulfate solution to the raw water and to fully mix the persulfate solution with the raw water through the static mixer; the backwashing device is used to periodically backwash and regenerate the composite catalyst in the reactor.

10. The industrial wastewater treatment system according to claim 9, characterized in that, The backwash water of the backwashing device is treated effluent that meets the standards. The backwashing flow rate is 2-5 m / h, the backwashing time is 5-10 min, and the backwashing cycle is 24-72 h.

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