Method for preparing composite catalyst by synergistically utilizing red mud and arsenic alkali residues, product and application thereof

Abstract

The invention discloses a method for preparing a composite catalyst by synergistically utilizing red mud and arsenic alkali residues as well as a product and application thereof, and belongs to the field of resource utilization of industrial wastes. The method disclosed by the invention is simple in preparation process, wide in preparation raw material source and capable of realizing full-amount utilization of the red mud and the arsenic alkali residues. Compared with a traditional titanium dioxide and iron arsenate catalyst, the composite catalyst prepared by the method is more excellent in performance, the landfill leachate treatment efficiency can be remarkably improved, and the catalytic removal effect of 2145 mg / g COD, 162 mg / g total phosphorus, 356 mg / g ammonia nitrogen and 122 mg / g mercury can be achieved at most.

Description

Technical Field

[0001] The present invention belongs to the field of resource utilization of industrial waste, and in particular relates to a method for preparing a composite catalyst by collaboratively utilizing red mud and arsenic alkali slag, and a product and application thereof. Background Art

[0002] As typical industrial wastes, red mud and arsenic-alkali slag have significant research value in terms of their environmental hazards and resource utilization potential. As a by-product of alumina production, red mud has a strong alkaline characteristic that causes a significant increase in the soil pH value in the stacking area, forming a large area of ​​alkaline land. The alkalinity of red mud attached liquid far exceeds the suitable range of public water sources, posing a continuous pollution threat to surface water and groundwater systems. Arsenic-alkali slag is a hazardous waste produced in the antimony smelting process, with an arsenic content often exceeding 10%, accompanied by heavy metals such as antimony and lead. Traditional solidification landfill methods are difficult to solve its long-term stability problems, and the infiltration of heavy metals under rainwater erosion poses a potential risk to the ecosystem.

[0003] Although red mud and arsenic alkali slag are industrial wastes, they contain a variety of metal elements and minerals and have certain potential value. The synergistic use of the two to prepare composite catalysts can convert these wastes into catalytically active materials, realize the secondary utilization of resources, and improve resource utilization efficiency. The preparation of traditional catalysts usually consumes a large amount of natural mineral resources. Using red mud and arsenic alkali slag to prepare composite catalysts can reduce dependence on these natural resources and help protect natural resources and the ecological environment.

[0004] Red mud and arsenic alkali slag are industrial wastes with relatively low acquisition costs. Using them as raw materials to prepare composite catalysts can significantly reduce the production cost of catalysts and improve the economy and competitiveness of catalysts in industrial applications. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a method for preparing a composite catalyst by synergistically utilizing red mud and arsenic alkali slag, its product and application.

[0006] Technical solution: The present invention provides a method for preparing a composite catalyst by synergistically utilizing red mud and arsenic alkali slag, comprising the following steps: (1) mixing red mud and arsenic alkali slag and stirring them evenly to obtain alkali mud slag; (2) mixing the sulfuric acid solution and the alkaline sludge, stirring them evenly to obtain acid-loaded sludge; (3) roasting the acid-loaded sludge, and then grinding the roasted slag to obtain roasted powder; (4) mixing the lignin sulfonate and the roasted powder, stirring evenly, and obtaining a roasted sulfonic acid mixed powder; (5) Mixing water and calcined sulfonic acid powder, granulating, and letting it stand to obtain calcined raw granules; placing the calcined raw material in a hydrothermal kettle to perform a hydrothermal reaction on the calcined raw material to obtain a hydrothermal catalytic raw material; and calcining the hydrothermal catalytic raw material to obtain a composite catalyst.

[0007] Furthermore, the mass ratio of the red mud to the arsenic alkali slag in step (1) is 30-60:100.

[0008] Furthermore, the liquid-to-solid ratio of the sulfuric acid solution and the alkali sludge in step (2) is 0.25-0.55:1 mL / g; and the concentration of the sulfuric acid solution is 2-8 M.

[0009] Furthermore, in step (3), the calcination temperature is 450-850° C., the calcination time is 0.5-4.5 hours, and the grinding time is 10-30 minutes.

[0010] Furthermore, the mass ratio of the lignin sulfonate to the roasted powder in step (4) is 0.5-2.5:100.

[0011] Furthermore, the lignin sulfonate in step (4) is any one or more combinations of sodium lignin sulfonate, calcium lignin sulfonate and potassium lignin sulfonate.

[0012] Furthermore, the liquid-to-solid ratio of the water and roasted sulfonic acid mixed powder in step (5) is 0.35-0.65:1 mL / g; the standing time is 0.5-2.5 days; the hydrothermal time is 0.5-4.5 hours, and the hydrothermal temperature is 120-240°C; the roasting temperature is 550-950°C, and the roasting time is 0.5-4.5 hours.

[0013] The invention also provides a composite catalyst prepared by the method.

[0014] The invention also provides application of the composite catalyst in sewage treatment.

[0015] Furthermore, the sewage treatment includes removing one or more of COD, phosphorus, ammonia nitrogen and mercury ions.

[0016] Reaction mechanism: The acid-loaded sludge is roasted, and sulfuric acid reacts with arsenic-alkali slag and red mud under high temperature, promoting the release of trivalent arsenic, trivalent antimony and low-valent selenium in the arsenic-alkali slag and their conversion to pentavalent arsenate, pentavalent antimonate and selenate, promoting the release of iron, titanium and calcium in the red mud. At the same time, under high temperature roasting environment, the unreleased aluminosilicate minerals and calcium-magnesium-containing minerals in the red mud react with sodium carbonate and part of sulfate in the arsenic-alkali slag to form a composite mineral mixture. Mix water and roasted sulfonic acid mixed powder, and the composite mineral mixture in the roasted sulfonic acid mixed powder is self-excited during the static process to form a gel. Lignin sulfonate absorbs some heavy metal elements through ion exchange and is fully wrapped by the gel. Part of iron, titanium, calcium and some heavy metals (lead, copper, nickel) are hydrolyzed and react with arsenate, antimonate and selenate to form a mixed precipitate of arsenate, antimonate and selenate. During the hydrothermal process, iron, titanium and heavy metals are further hydrolyzed, and the amount of mixed precipitates of arsenate, antimonate and selenate is further increased. The gel is hydrothermally hardened, and the mixed precipitates of arsenate, antimonate and selenate and the hydrolysis products of titanium and heavy metals are efficiently fixed. The hydrothermal catalytic raw materials are roasted, and the mixed precipitates of arsenate, antimonate and selenate are partially fused under high temperature, and the hydrolysis products of titanium and heavy metals are dehydrated and mixed to be converted into a mixture of metal oxides.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the preparation process of the present invention is simple, the raw materials are widely available, and the full utilization of red mud and arsenic alkali slag can be achieved. Compared with traditional titanium dioxide and ferric arsenate catalysts, the composite catalyst prepared by the present invention has better performance and can significantly improve the efficiency of landfill leachate treatment, achieving the highest catalytic removal effect of 2145mg / g COD, 162mg / g total phosphorus, 356mg / g ammonia nitrogen, and 122mg / g mercury. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The figure is a flow chart of the processing method of the present invention. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0020] Preparation of landfill leachate and mercury-containing landfill leachate: The landfill leachate used in the experiment was taken from Zhuji Sanfeng Environmental Protection Energy Co., Ltd. The COD mass concentration of this batch of landfill leachate was 4152 mg / L, the total phosphorus concentration was 305 mg / L, and the ammonia nitrogen concentration was 1075 mg / L. 500 mg of mercury was added to 1 L of landfill leachate and stirred evenly to prepare mercury-containing landfill leachate.

[0021] Red mud: provided by Shandong Zibo Zhengheng Aluminum Co., Ltd., the main test components include: 38.52%Fe 2 O3 、27.83%Al 2 O 3 、12.49%SiO 2 、11.36%Na 2 O, 5.61% TiO 2 , 0.57%CaO, 0.34%SO 3 and other components (inevitable impurities and loss on ignition); Arsenic alkali slag: provided by Lengshuijiang Antimony City Environmental Protection Co., Ltd., the main test components include: 56.07% Na 2 CO 3 , 11.65%NaHCO 3 、9.13%Na 3 AsO 4 、4.65%Na 3 SbO 3 4.54%Na 3 AsO 3 , 2.11% NaOH and other ingredients (unavoidable impurities and loss on ignition).

[0022] Example 1 Effect of the mass ratio of red mud to arsenic alkali slag on the performance of the prepared catalyst Red mud and arsenic alkali slag are mixed in a mass ratio of 22.5:100, 25:100, 27.5:100, 30:100, 45:100, 60:100, 65:100, 70:100, and 75:100, and stirred evenly to obtain alkali sludge slag. Sulfuric acid solution and alkali sludge slag are mixed in a liquid-solid ratio of 0.25:1 mL / g, and stirred evenly to obtain acid-loaded sludge slag, wherein the concentration of sulfuric acid solution is 2 M. The acid-loaded sludge slag is roasted, and then the roasted slag is ground to obtain roasted powder, wherein the roasting temperature is 450°C, the roasting time is 0.5 hours, and the grinding time is 10 minutes. Lignin sulfonate and roasted powder are mixed in a mass ratio of 0.5:100, and stirred evenly to obtain roasted sulfonic acid mixed powder, wherein the lignin sulfonate is sodium lignin sulfonate. Water and roasted sulfonic acid mixed powder were mixed at a liquid-solid ratio of 0.35:1 mL / g, granulated, and allowed to stand for 0.5 days to obtain roasted green granules. The roasted raw material was placed in a hydrothermal kettle to perform a hydrothermal reaction on the roasted green granules to obtain a hydrothermal catalytic raw material, wherein the hydrothermal time was 0.5 hours and the hydrothermal temperature was 120°C. The hydrothermal catalytic raw material was roasted to obtain a composite catalyst, wherein the roasting temperature was 550°C and the roasting time was 0.5 hours.

[0023] Photocatalytic removal test: 1g of catalyst was added to 1L of landfill leachate, stirred at 120rpm and irradiated with UV light for 120min, then centrifuged at 5000rpm to separate solid and liquid. The concentration of different pollutants in the separated liquid was tested and the removal rate was calculated. The specific test and calculation are as follows.

[0024] COD concentration detection and calculation of COD removal capacity: The COD concentration of the leachate was determined according to the national standard "Determination of Chemical Oxygen Demand of Water Quality - Dichromate Method" (GB 11914-1989). The COD removal capacity was calculated according to formula (1), where is the COD removal capacity (mg / g), and are the COD concentrations of domestic waste leachate before and after treatment (mg / L), m is the mass of the catalyst (1 g), and V is the volume of the leachate (1 L).

[0025] (1) Total phosphorus concentration detection and total phosphorus removal capacity calculation: The total phosphorus concentration of the leachate was determined according to the standard "Determination of phosphate and total phosphorus in water - continuous flow - ammonium molybdate spectrophotometry" (HJ 670-2013). The total phosphorus removal rate was calculated according to formula (2), where is the total phosphorus removal capacity (mg / g), and are the total phosphorus concentrations of domestic waste leachate before and after treatment (mg / L), m is the mass of the catalyst (1 g), and V is the volume of the leachate (1 L).

[0026] (2) Ammonia nitrogen concentration detection and ammonia nitrogen removal capacity calculation: The ammonia nitrogen concentration of the leachate is determined according to the "Determination of Ammonia Nitrogen in Water Quality - Salicylic Acid Spectrophotometry" (HJ536-2009). The ammonia nitrogen removal capacity is calculated according to formula (3), where is the ammonia nitrogen removal capacity (mg / g), is the initial concentration of ammonia nitrogen in the leachate before treatment (mg / L), is the residual concentration of ammonia nitrogen in the treated leachate (mg / L).

[0027] (3) Mercury ion concentration detection and removal capacity calculation: The mercury ion concentration in the leachate was determined according to the "Water Quality - Determination of Mercury, Arsenic, Selenium, Bismuth and Antimony - Atomic Fluorescence Method" (HJ 694-2014). The mercury ion removal capacity was calculated according to formula (4), where is the mercury ion removal capacity (mg / g), is the initial concentration of mercury ions in the leachate before treatment (mg / L), is the mercury ion concentration in the treated leachate (mg / L), V is the volume of the leachate (1L), m is the mass of waste liquid purifier (1g).

[0028] (4) The test results of this embodiment are shown in Table 1.

[0029] Table 1 Effect of the mass ratio of red mud to arsenic alkali slag on the performance of the prepared catalyst

[0030] It can be seen from Table 1 that when the mass ratio of red mud to arsenic alkali slag is less than 30:100 (such as in Table 1, the mass ratio of red mud to arsenic alkali slag = 27.5:100, 25:100, 22.5:100 and lower ratios not listed in Table 1), less red mud is added, and the red mud and arsenic alkali slag react insufficiently during the roasting process, resulting in the COD, total phosphorus, ammonia nitrogen and mercury removal capacity of the prepared catalyst all significantly decreasing with the decrease of the mass ratio of red mud to arsenic alkali slag. When the mass ratio of red mud to arsenic alkali slag is equal to 30-60:100 (as shown in Table 1, the mass ratio of red mud to arsenic alkali slag = 30:100, 45:100, 60:100), the acid-loaded mud slag is roasted, and sulfuric acid reacts with arsenic alkali slag and red mud under high temperature environment, promoting the release of trivalent arsenic, trivalent antimony and low-valent selenium in arsenic alkali slag and converting them into pentavalent arsenate, pentavalent antimonate and selenate, and promoting the release of iron, titanium and calcium in red mud. At the same time, under high temperature roasting environment, the unreleased aluminosilicate minerals and calcium-magnesium-containing minerals in red mud react with sodium carbonate and part of sulfate in arsenic alkali slag to form a composite mineral mixture. Finally, the prepared COD removal capacity is higher than 1782 mg / g, the total phosphorus removal capacity is higher than 124 mg / g, the ammonia nitrogen removal capacity is higher than 265 mg / g, and the mercury removal capacity is higher than 78 mg / g. When the mass ratio of red mud to arsenic alkali slag is greater than 60:100 (such as in Table 1, the mass ratio of red mud to arsenic alkali slag = 65:100, 70:100, 75:100 and higher ratios not listed in Table 1), excessive red mud is added, and the reaction between red mud and arsenic alkali slag is unbalanced during the roasting process, resulting in a significant decrease in the COD, total phosphorus, ammonia nitrogen and mercury removal capacity of the prepared catalyst as the mass ratio of red mud to arsenic alkali slag further increases. In general, combining benefits and costs, when the mass ratio of red mud to arsenic alkali slag is equal to 30~60:100, it is most conducive to improving the performance of the prepared catalyst.

[0031] Example 2 Effect of the liquid-to-solid ratio of sulfuric acid solution and alkali sludge on the performance of the prepared catalyst Red mud and arsenic alkali slag are mixed in a mass ratio of 60:100, stirred evenly, and alkali sludge slag is obtained. Sulfuric acid solution and alkali sludge slag are mixed in a liquid-solid ratio of 0.1:1mL / g, 0.15:1mL / g, 0.2:1mL / g, 0.25:1mL / g, 0.4:1mL / g, 0.55:1mL / g, 0.6:1mL / g, 0.65:1mL / g, 0.7:1mL / g, stirred evenly, and acid-loaded sludge slag is obtained, wherein the concentration of sulfuric acid solution is 5M. The acid-loaded sludge slag is roasted, and then the roasted slag is ground to obtain roasted powder, wherein the roasting temperature is 650°C, the roasting time is 2.5 hours, and the grinding time is 20 minutes. Lignin sulfonate and roasted powder are mixed in a mass ratio of 1.5:100, stirred evenly, and roasted sulfonic acid mixed powder is obtained, wherein the lignin sulfonate is calcium lignin sulfonate. Water and roasted sulfonic acid mixed powder were mixed at a liquid-solid ratio of 0.5:1 mL / g, granulated, and allowed to stand for 1.5 days to obtain roasted raw granules. The roasted raw material was placed in a hydrothermal kettle for hydrothermal reaction of the roasted raw granules to obtain hydrothermal catalytic raw material, wherein the hydrothermal time was 2.5 hours and the hydrothermal temperature was 180°C. The hydrothermal catalytic raw material was roasted to obtain a composite catalyst, wherein the roasting temperature was 750°C and the roasting time was 2.5 hours.

[0032] The photocatalytic removal test, COD concentration detection and calculation of COD removal capacity, total phosphorus concentration detection and calculation of total phosphorus removal capacity, ammonia nitrogen concentration detection and calculation of ammonia nitrogen removal capacity, and mercury ion concentration detection and removal capacity calculation are all the same as in Example 1. The test results of this example are shown in Table 2.

[0033] Table 2 Effect of liquid-to-solid ratio of sulfuric acid solution and alkali sludge on the performance of the prepared catalyst

[0034] It can be seen from Table 2 that when the liquid-to-solid ratio of sulfuric acid solution and alkali sludge is less than 0.25:1 mL / g (such as in Table 2, the liquid-to-solid ratio of sulfuric acid solution and alkali sludge = 0.2:1 mL / g, 0.15:1 mL / g, 0.1:1 mL / g and lower ratios not listed in Table 2), less sulfuric acid solution is added, and the sulfuric acid solution and alkali sludge do not react fully during the roasting process, resulting in the COD, total phosphorus, ammonia nitrogen and mercury removal capacity of the prepared catalyst being significantly reduced as the liquid-to-solid ratio of sulfuric acid solution and alkali sludge decreases. When the liquid-solid ratio of sulfuric acid solution to alkali sludge is equal to 0.25~0.55:1mL / g (as in Table 2, the liquid-solid ratio of sulfuric acid solution to alkali sludge is 0.25:1mL / g, 0.4:1mL / g, 0.55:1mL / g), the acid-loaded sludge is roasted, and sulfuric acid reacts with arsenic alkali slag and red mud under high temperature environment, promoting the release of trivalent arsenic, trivalent antimony and low-valent selenium in arsenic alkali slag and converting them into pentavalent arsenate, pentavalent antimonate and selenate, and promoting the release of iron, titanium and calcium in red mud. At the same time, under high temperature roasting environment, the unreleased aluminosilicate minerals and calcium-magnesium-containing minerals in red mud react with sodium carbonate and part of sulfate in arsenic alkali slag to form a composite mineral mixture. Finally, the COD removal capacity of the prepared materials is higher than 1873mg / g, the total phosphorus removal capacity is higher than 137mg / g, the ammonia nitrogen removal capacity is higher than 291mg / g, and the mercury removal capacity is higher than 89mg / g. When the liquid-solid ratio of sulfuric acid solution to alkali sludge is greater than 0.55:1mL / g (such as in Table 2, the liquid-solid ratio of sulfuric acid solution to alkali sludge = 0.6:1mL / g, 0.65:1mL / g, 0.7:1mL / g and higher ratios not listed in Table 2), excessive addition of sulfuric acid solution will cause an imbalance in the reaction between sulfuric acid solution and alkali sludge during the roasting process, resulting in a significant decrease in the COD, total phosphorus, ammonia nitrogen and mercury removal capacity of the prepared catalyst as the liquid-solid ratio of sulfuric acid solution to alkali sludge further increases. In general, considering benefits and costs, when the liquid-solid ratio of sulfuric acid solution to alkali sludge is equal to 0.25~0.55:1mL / g, it is most conducive to improving the performance of the prepared catalyst.

[0035] Example 3 Effect of the mass ratio of lignin sulfonate and calcined powder on the performance of the prepared catalyst Red mud and arsenic alkali slag are mixed in a mass ratio of 60:100, stirred evenly, and alkali sludge slag is obtained. Sulfuric acid solution and alkali sludge slag are mixed in a liquid-solid ratio of 0.55:1mL / g, stirred evenly, and acid-loaded sludge slag is obtained, wherein the concentration of sulfuric acid solution is 8M. The acid-loaded sludge slag is roasted, and then the roasted slag is ground to obtain roasted powder, wherein the roasting temperature is 850°C, the roasting time is 4.5 hours, and the grinding time is 30 minutes. Lignin sulfonate and roasted powder are mixed in a mass ratio of 0.25:100, 0.3:100, 0.4:100, 0.5:100, 1.5:100, 2.5:100, 2.75:100, 3:100, 3.25:100, stirred evenly, and roasted sulfonic acid mixed powder is obtained, wherein the lignin sulfonate is potassium lignin sulfonate. Water and roasted sulfonic acid mixed powder were mixed at a liquid-solid ratio of 0.65:1 mL / g, granulated, and allowed to stand for 2.5 days to obtain roasted raw granules. The roasted raw material was placed in a hydrothermal kettle for hydrothermal reaction of the roasted raw granules to obtain hydrothermal catalytic raw material, wherein the hydrothermal time was 4.5 hours and the hydrothermal temperature was 240°C. The hydrothermal catalytic raw material was roasted to obtain a composite catalyst, wherein the roasting temperature was 950°C and the roasting time was 4.5 hours.

[0036] The photocatalytic removal test, COD concentration detection and calculation of COD removal capacity, total phosphorus concentration detection and calculation of total phosphorus removal capacity, ammonia nitrogen concentration detection and calculation of ammonia nitrogen removal capacity, and mercury ion concentration detection and removal capacity calculation are all the same as in Example 1. The test results of this example are shown in Table 3.

[0037] Table 3 Effect of the mass ratio of lignin sulfonate and calcined powder on the performance of the prepared catalyst

[0038] It can be seen from Table 3 that when the mass ratio of lignin sulfonate to roasted powder is less than 0.5:100 (such as in Table 3, the mass ratio of lignin sulfonate to roasted powder = 0.4:100, 0.3:100, 0.25:100 and lower ratios not listed in Table 3), less lignin sulfonate is added, and the reaction of lignin sulfonate and roasted powder is not sufficient during the hydrothermal reaction, resulting in the COD, total phosphorus, ammonia nitrogen and mercury removal capacity of the prepared catalyst significantly decreasing with the decrease of the mass ratio of lignin sulfonate to roasted powder. When the mass ratio of lignin sulfonate to roasted powder is equal to 0.5~2.5:100 (such as in Table 3, the mass ratio of lignin sulfonate to roasted powder = 0.5:100, 1.5:100, 2.5:100), the lignin sulfonate adsorbs some heavy metal elements through ion exchange and is fully wrapped by the gel. Part of iron, titanium, calcium and some heavy metals (lead, copper, nickel) are hydrolyzed and react with arsenate, antimonate and selenate to form mixed precipitates of arsenate, antimonate and selenate. During the hydrothermal process, iron, titanium and heavy metals are further hydrolyzed, and the amount of mixed precipitates of arsenate, antimonate and selenate is further increased. The gel is hydrothermally hardened to achieve efficient fixation of mixed precipitates of arsenate, antimonate and selenate and hydrolysis products of titanium and heavy metals. The hydrothermal catalytic raw material is roasted, and the mixed precipitates of arsenate, antimonate and selenate are partially fused under high temperature. The hydrolysis products of titanium and heavy metals are dehydrated and mixed to form a mixture of metal oxides. Finally, the COD removal capacity of the prepared products is higher than 2017 mg / g, the total phosphorus removal capacity is higher than 147 mg / g, the ammonia nitrogen removal capacity is higher than 318 mg / g, and the mercury removal capacity is higher than 108 mg / g. When the mass ratio of lignin sulfonate to roasted powder is greater than 2.5:100 (such as in Table 3, the mass ratio of lignin sulfonate to roasted powder = 2.75:100, 3:100, 3.25:100 and higher ratios not listed in Table 3), the addition of lignin sulfonate is excessive, and the reaction of lignin sulfonate and roasted powder is unbalanced during the hydrothermal reaction, resulting in the COD, total phosphorus, ammonia nitrogen, and mercury removal capacity of the prepared catalyst significantly decreasing with the further increase of the mass ratio of lignin sulfonate to roasted powder. In general, considering the benefits and costs, when the mass ratio of lignin sulfonate to roasted powder is equal to 0.5~2.5:100, it is most conducive to improving the performance of the prepared catalyst.

[0039] Comparative Example 1 Effects of different preparation processes on the performance of the prepared catalyst The process of the present invention is as follows: red mud and arsenic alkali slag are mixed in a mass ratio of 60:100, stirred evenly, and alkali sludge slag is obtained. Sulfuric acid solution and alkali sludge slag are mixed in a liquid-solid ratio of 0.55:1mL / g, stirred evenly, and acid-loaded sludge slag is obtained, wherein the concentration of sulfuric acid solution is 5M. The acid-loaded sludge slag is roasted, and then the roasted slag is ground to obtain roasted powder, wherein the roasting temperature is 650°C, the roasting time is 4.5 hours, and the grinding time is 30 minutes. Lignin sulfonate and roasted powder are mixed in a mass ratio of 2.5:100, stirred evenly, and roasted sulfonic acid mixed powder is obtained, wherein the lignin sulfonate is potassium lignin sulfonate. Water and roasted sulfonic acid mixed powder are mixed in a liquid-solid ratio of 0.65:1mL / g, granulated, and left to stand for 2.5 days to obtain roasted raw granules. The roasted raw material is placed in a hydrothermal kettle to perform a hydrothermal reaction on the roasted raw granules to obtain a hydrothermal catalytic raw material, wherein the hydrothermal time is 4.5 hours and the hydrothermal temperature is 240°C. The hydrothermal catalytic raw material is calcined to obtain a composite catalyst, wherein the calcination temperature is 950° C. and the calcination time is 4.5 hours.

[0040] Comparative process 1: Red mud and arsenic alkali slag are mixed at a mass ratio of 60:100, stirred evenly, and alkali sludge slag is obtained. Sulfuric acid solution and alkali sludge slag are mixed at a liquid-solid ratio of 0.55:1mL / g, stirred evenly, and acid-loaded sludge slag is obtained, wherein the concentration of sulfuric acid solution is 5M. The acid-loaded sludge slag is roasted, and then the roasted slag is ground to obtain roasted powder, wherein the roasting temperature is 650°C, the roasting time is 4.5 hours, and the grinding time is 30 minutes. Water and roasted powder are mixed at a liquid-solid ratio of 0.65:1mL / g, granulated, and left to stand for 2.5 days to obtain roasted raw granules. The roasted raw material is placed in a hydrothermal kettle to hydrothermally react the roasted raw granules to obtain a hydrothermal catalytic raw material, wherein the hydrothermal time is 4.5 hours and the hydrothermal temperature is 240°C. The hydrothermal catalytic raw material is roasted to obtain a composite catalyst, wherein the roasting temperature is 950°C and the roasting time is 4.5 hours.

[0041] Comparative process 2: Sulfuric acid solution and red mud are mixed at a liquid-solid ratio of 0.55:1 mL / g, stirred evenly, and acid-loaded mud is obtained, wherein the concentration of the sulfuric acid solution is 5 M. The acid-loaded mud is roasted, and the roasted slag is ground to obtain roasted powder, wherein the roasting temperature is 650°C, the roasting time is 4.5 hours, and the grinding time is 30 minutes. Lignin sulfonate and roasted powder are mixed at a mass ratio of 2.5:100, stirred evenly, and roasted sulfonic acid mixed powder is obtained, wherein the lignin sulfonate is potassium lignin sulfonate. Water and roasted sulfonic acid mixed powder are mixed at a liquid-solid ratio of 0.65:1 mL / g, granulated, and left to stand for 2.5 days to obtain roasted raw granules. The roasted raw material is placed in a hydrothermal kettle for hydrothermal reaction of the roasted raw granules to obtain hydrothermal catalytic raw material, wherein the hydrothermal time is 4.5 hours and the hydrothermal temperature is 240°C. The hydrothermal catalytic raw material is calcined to obtain a composite catalyst, wherein the calcination temperature is 950° C. and the calcination time is 4.5 hours.

[0042] The photocatalytic removal test, COD concentration detection and calculation of COD removal capacity, total phosphorus concentration detection and calculation of total phosphorus removal capacity, ammonia nitrogen concentration detection and calculation of ammonia nitrogen removal capacity, and mercury ion concentration detection and removal capacity calculation are all the same as in Example 1. The results of this comparative test are shown in Table 4.

[0043] Table 4 Effects of different preparation processes on the performance of the prepared catalysts

[0044] It can be seen from Table 4 that the COD, total phosphorus, ammonia nitrogen and mercury removal capacity of the catalyst prepared by the process of the present invention is significantly higher than the performance of the catalyst prepared by comparative process 1 and comparative process 2.

[0045] Comparative Example 2 Comparison of performance of different catalysts The process of the present invention is as follows: red mud and arsenic alkali slag are mixed in a mass ratio of 60:100, stirred evenly, and alkali sludge slag is obtained. Sulfuric acid solution and alkali sludge slag are mixed in a liquid-solid ratio of 0.55:1mL / g, stirred evenly, and acid-loaded sludge slag is obtained, wherein the concentration of sulfuric acid solution is 5M. The acid-loaded sludge slag is roasted, and then the roasted slag is ground to obtain roasted powder, wherein the roasting temperature is 650°C, the roasting time is 4.5 hours, and the grinding time is 30 minutes. Lignin sulfonate and roasted powder are mixed in a mass ratio of 2.5:100, stirred evenly, and roasted sulfonic acid mixed powder is obtained, wherein the lignin sulfonate is potassium lignin sulfonate. Water and roasted sulfonic acid mixed powder are mixed in a liquid-solid ratio of 0.65:1mL / g, granulated, and left to stand for 2.5 days to obtain roasted raw granules. The roasted raw material is placed in a hydrothermal kettle to perform a hydrothermal reaction on the roasted raw granules to obtain a hydrothermal catalytic raw material, wherein the hydrothermal time is 0.5 hours and the hydrothermal temperature is 240°C. The hydrothermal catalytic raw material is calcined to obtain a composite catalyst, wherein the calcination temperature is 550° C. and the calcination time is 4.5 hours.

[0046] The photocatalytic removal test, COD concentration detection and calculation of COD removal capacity, total phosphorus concentration detection and calculation of total phosphorus removal capacity, ammonia nitrogen concentration detection and calculation of ammonia nitrogen removal capacity, and mercury ion concentration detection and removal capacity calculation are all the same as in Example 1. The results of this comparative test are shown in Table 5.

[0047] Table 5 Comparison of performance of different catalysts

[0048] It can be seen from Table 5 that the COD, total phosphorus, ammonia nitrogen and mercury removal capacity of the catalyst prepared by the process of the present invention is significantly higher than that of titanium dioxide and ferric arsenate catalysts.

Claims

1. A method for preparing a composite catalyst by synergistically utilizing red mud and arsenic alkali slag, characterized in that: The following steps are involved: (1) mixing red mud and arsenic alkali slag and stirring them evenly to obtain alkali mud slag; (2) mixing the sulfuric acid solution and the alkaline sludge, stirring them evenly to obtain acid-loaded sludge; (3) roasting the acid-loaded sludge, and then grinding the roasted slag to obtain roasted powder; (4) mixing the lignin sulfonate and the roasted powder, stirring evenly, and obtaining a roasted sulfonic acid mixed powder; (5) Mixing water and calcined sulfonic acid powder, granulating, and letting it stand to obtain calcined raw granules; placing the calcined raw material in a hydrothermal kettle to perform a hydrothermal reaction on the calcined raw material to obtain a hydrothermal catalytic raw material; and calcining the hydrothermal catalytic raw material to obtain a composite catalyst.

2. The method for preparing a composite catalyst by synergistically utilizing red mud and arsenic alkali slag according to claim 1, characterized in that: The mass ratio of the red mud to the arsenic alkali slag in step (1) is 30-60:

100.

3. The method for preparing a composite catalyst by synergistically utilizing red mud and arsenic alkali slag according to claim 1, characterized in that: The liquid-to-solid ratio of the sulfuric acid solution and the alkali sludge in step (2) is 0.25-0.55:1 mL / g; the concentration of the sulfuric acid solution is 2-8 M.

4. The method for preparing a composite catalyst by synergistically utilizing red mud and arsenic alkali slag according to claim 1, characterized in that: The calcination temperature in step (3) is 450-850° C., the calcination time is 0.5-4.5 hours, and the grinding time is 10-30 minutes.

5. The method for preparing a composite catalyst by synergistically utilizing red mud and arsenic alkali slag according to claim 1, characterized in that: The mass ratio of the lignin sulfonate to the roasted powder in step (4) is 0.5-2.5:

100.

6. The method for preparing a composite catalyst by synergistically utilizing red mud and arsenic alkali slag according to claim 1, characterized in that: The lignin sulfonate in step (4) is any one or more combinations of sodium lignin sulfonate, calcium lignin sulfonate and potassium lignin sulfonate.

7. The method for preparing a composite catalyst by synergistically utilizing red mud and arsenic alkali slag according to claim 1, characterized in that: The liquid-to-solid ratio of the water and roasted sulfonic acid mixed powder in step (5) is 0.35-0.65:1 mL / g; the standing time is 0.5-2.5 days; the hydrothermal time is 0.5-4.5 hours, and the hydrothermal temperature is 120-240° C.; the roasting temperature is 550-950° C., and the roasting time is 0.5-4.5 hours.

8. The composite catalyst prepared by the method described in any one of claims 1 to 7.

9. Use of the composite catalyst according to claim 8 in sewage treatment.

10. The use according to claim 9, characterized in that: The sewage treatment includes removing one or more of COD, phosphorus, ammonia nitrogen and mercury ions.

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