A method for preparing bismuth ferrite composite catalytic material using red mud, and its product and application

Abstract

The present invention discloses a method for preparing a bismuth ferrite composite catalytic material using red mud, as well as its product and application. The method comprises the following steps: mixing chloride salt and red mud, stirring evenly, adding hydrochloric acid solution, stirring evenly, roasting, recovering the flue gas generated during the roasting process, obtaining calcination residue and roasting dust generated by the recovered flue gas after the roasting is completed; mixing the roasting dust and bismuth nitrate, stirring evenly, adding the calcination residue, grinding evenly, adding water, stirring, drying the material, calcining, and obtaining the bismuth ferrite composite catalytic material. The preparation process of the present invention is simple, and the main raw material used is red mud, which can realize the full resource utilization of red mud. The prepared composite catalytic material can be used for efficient purification of landfill leachate, and realizes efficient removal of COD, ammonia nitrogen, total phosphorus and heavy metal pollution through a photocatalytic mechanism.

Description

Technical Field

[0001] The present invention relates to a method for preparing a bismuth ferrite composite catalytic material by utilizing red mud, and the product and application thereof, belonging to the field of resource utilization of industrial waste. Background Art

[0002] Bismuth ferrite (BiFeO3), a typical multiferroic semiconductor material, possesses excellent visible light response properties due to its unique band structure (band gap of ~2.2 eV). It exhibits activity unmatched by conventional catalysts in applications such as photocatalytic degradation of organic pollutants and Fenton-like advanced oxidation reactions. However, conventional chemical precipitation methods require high-purity ferric nitrate (≥99.9%) as an iron source.

[0003] Red mud is rich in iron oxides. If red mud can be used as an iron source to replace traditional iron salts and converted into bismuth ferrite-based composite catalytic materials, the green preparation of BiFeO3-based composite materials can be achieved, which has potential advantages such as cost reconstruction advantages and synergistic performance enhancement. Summary of the Invention

[0004] Purpose of the invention: The technical problem to be solved by the present invention is to provide a method for preparing bismuth ferrite composite catalytic material using red mud, and its products and applications.

[0005] Technical solution: To solve the above technical problems, the present invention provides a method for preparing a bismuth ferrite composite catalytic material using red mud, comprising the following steps:

[0006] (1) mixing chloride salt and red mud, stirring evenly, and obtaining chloride red mud; wherein the mass ratio of the chloride salt to the red mud is 30-60:100;

[0007] (2) mixing the hydrochloric acid solution and the chlorine red mud described in step (1), stirring them evenly, roasting them, and recovering the flue gas generated during the roasting process, and obtaining a calcined residue and roasting dust generated by the recovered flue gas after the roasting is completed;

[0008] (3) mixing the calcined dust and bismuth nitrate described in step (2) and stirring evenly to obtain bismuth-loaded powder;

[0009] (4) mixing the bismuth-loaded powder described in step (3) and the calcined residue described in step (2), grinding them uniformly to obtain a bismuth-loaded calcined mixed powder;

[0010] (5) Mixing water and the bismuth-loaded calcined mixed powder, stirring, drying the material, and calcining to obtain the bismuth ferrite composite catalytic material; the calcination temperature is 750-950°C.

[0011] Wherein, the chloride salt in step (1) is any one of ammonium chloride, calcium chloride or aluminum chloride.

[0012] Wherein, the liquid-to-solid ratio of the hydrochloric acid solution and the chlorine red mud in step (2) is 15-45:100 mL / g.

[0013] Wherein, the mass proportion of hydrochloric acid in the hydrochloric acid solution in step (2) is 5-25%.

[0014] The calcination temperature in step (2) is 650-850° C., and the calcination time is 0.5-4.5 hours.

[0015] Wherein, the mass ratio of the roasting dust and bismuth nitrate in step (3) is 40~60:100.

[0016] Wherein, the mass ratio of the bismuth-loaded powder to the calcined residue in step (4) is 2.5-17.5:100.

[0017] Wherein, the liquid-to-solid ratio of water and bismuth-loaded calcined mixed powder in step (5) is 0.4-1.2:1 mL / g.

[0018] The drying temperature of the material in step (5) is 50-250° C. and the drying time is 2-10 hours.

[0019] Wherein, in step (5), the calcination time is 0.5 to 4.5 hours.

[0020] The stirring time in step (5) is 15 to 75 minutes.

[0021] The present invention also provides a high-activity bismuth ferrite composite catalytic material prepared by the method.

[0022] The present invention also provides application of the bismuth ferrite composite catalytic material in removing pollutants.

[0023] The pollutants include one or more of COD, total phosphorus, ammonia nitrogen or mercury ions.

[0024] The present invention also provides application of the bismuth ferrite composite catalytic material in purifying landfill leachate.

[0025] Reaction Mechanism: Neutralized chlorine-containing red mud is calcined. During the calcination process, hydrochloric acid reacts with minerals containing titanium, iron, calcium, and other metallic elements, promoting their release. Chloride salts further combine with iron and other minor metallic elements to form metal chlorides, which simultaneously volatilize under high temperature and enter the flue gas, where they cool and nucleate to form calcined dust. FeCl3 volatilizes first and accumulates in flue gas particles. When local temperature fluctuations and other complex factors cause the decomposition of a very small amount of FeCl3, the resulting FeCl2 is also concentrated in the flue gas particles due to airflow and other factors, and is discharged along with the flue gas particles. Unvolatile minerals containing titanium, calcium, and silicon are activated by heat and acid excitation, forming highly active mineral components. Water and the bismuth-loaded calcined powder are mixed. During stirring, titanium, iron, calcium, and other metallic elements hydrolyze, resulting in a mixed co-precipitate that is adsorbed and filled into the highly active minerals. The bismuth-loaded raw material is calcined, and the co-precipitate is oxidized to form a mixed catalytic material mixed with titanium dioxide, bismuth titanate, bismuth ferrite and other metal oxides. At the same time, part of the mixed catalytic material formed during the calcination process further reacts with highly active minerals in the calcination residue to finally form a composite catalytic material.

[0026] Beneficial Effects: Compared with existing technologies, this invention offers the following significant advantages: The preparation process is simple, and the primary raw material used is red mud, enabling full resource utilization of the red mud. The resulting composite catalytic material can be used to efficiently purify landfill leachate, effectively removing COD, ammonia nitrogen, total phosphorus, and heavy metal pollution through a photocatalytic mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Flowchart of the processing method of the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0029] Preparation of landfill leachate and mercury-containing leachate: The landfill leachate used in the experiment was obtained from Zhuji Sanfeng Environmental Protection Energy Co., Ltd. This batch of leachate had a COD concentration of 4152 mg / L, a total phosphorus concentration of 305 mg / L, and an ammonia nitrogen concentration of 1075 mg / L. Mercury-containing leachate was prepared by adding 500 mg of mercury to 1 L of landfill leachate and stirring thoroughly.

[0030] Red mud: provided by Shandong Zibo Zhengheng Aluminum Co., Ltd., the main tested components include: 38.52% Fe2O3, 27.83% Al2O3, 12.49% SiO2, 11.36% Na2O, 5.61% TiO2, 0.57% CaO, 0.34% SO3 and other components (unavoidable impurities and loss on ignition).

[0031] Example 1 Effect of the mass ratio of chloride salt to red mud on the performance of the prepared bismuth ferrite composite catalytic material

[0032] Chloride salt and red mud are weighed in mass ratios of 22.5:100, 25:100, 27.5:100, 30:100, 45:100, 60:100, 65:100, 70:100, and 75:100, respectively, and stirred to obtain chlorine red mud, wherein the chloride salt is ammonium chloride. Hydrochloric acid solution and chlorine red mud are mixed at a liquid-to-solid ratio of 15:100 mL / g and stirred to obtain neutralized chlorine red mud, wherein the hydrochloric acid solution has a hydrochloric acid content of 5% by mass. The neutralized chlorine red mud is roasted, and the flue gas generated during the roasting process is recovered. After the roasting is completed, a calcination residue and roasting dust generated by the recovered flue gas are obtained. The roasting temperature is 650°C, and the roasting time is 0.5 hours. The roasting dust and bismuth nitrate are mixed in a mass ratio of 40:100 and stirred to obtain bismuth-loaded powder. Bismuth-loaded powder and calcined residue were mixed in a mass ratio of 2.5:100 and ground evenly to obtain a bismuth-loaded calcined mixed powder. Water and the bismuth-loaded calcined mixed powder were mixed in a liquid-to-solid ratio of 0.4:1 mL / g, stirred for 15 minutes, and dried to obtain a bismuth-loaded raw meal. The drying temperature was 50°C and the drying time was 10 hours. The bismuth-loaded raw meal was calcined at 750°C for 0.5 hours to obtain a bismuth ferrite composite catalytic material.

[0033] Photocatalytic removal test: 1g of bismuth ferrite composite catalyst was added to 1L of mercury-containing landfill leachate. The mixture was stirred at 120 rpm while irradiated with UV light for 120 minutes. The mixture was then centrifuged at 5000 rpm to separate the solid and liquid. The concentrations of various pollutants in the separated liquid were measured, and the removal rate was calculated. The specific testing and calculations are as follows.

[0034] 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" (HJ828-2017). The COD removal capacity was calculated according to formula (1), where R COD is the COD removal capacity (mg / g), c COD0 and c CODt are the COD concentrations of domestic waste leachate before and after treatment (mg / L), m is the mass of bismuth ferrite composite catalytic material (1 g), and V is the volume of landfill leachate (1 L).

[0035]

[0036] Total phosphorus concentration detection and total phosphorus removal capacity calculation: The total phosphorus concentration of the leachate was determined according to the standard "Water quality - Determination of phosphate and total phosphorus - Continuous flow - ammonium molybdate spectrophotometry" (HJ 670-2013). The total phosphorus removal rate was calculated according to formula (2), where R TP is the total phosphorus removal capacity (mg / g), c TP0 and c TPt are the total phosphorus concentrations of domestic waste leachate before and after treatment (mg / L), m is the mass of bismuth ferrite composite catalytic material (1 g), and V is the volume of landfill leachate (1 L).

[0037]

[0038] Ammonia nitrogen concentration detection and ammonia nitrogen removal capacity calculation: The ammonia nitrogen concentration of the leachate was determined according to the "Water Quality - Determination of Ammonia Nitrogen - Salicylic Acid Spectrophotometric Method" (HJ536-2009). The ammonia nitrogen removal capacity was calculated according to formula (3), where R N is the ammonia nitrogen removal capacity (mg / g), c N0 is the initial concentration of ammonia nitrogen in the leachate before treatment (mg / L), c Nt is the residual concentration of ammonia nitrogen in the treated leachate (mg / L), m is the mass of bismuth ferrite composite catalytic material (1 g), and V is the volume of landfill leachate (1 L).

[0039]

[0040] 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 Spectrometry" (HJ 694-2014). The mercury ion removal capacity was calculated according to formula (4), where R Hg is the mercury ion removal capacity (mg / g), c Hg0 is the initial concentration of mercury ions in the leachate before treatment (mg / L), c Hgt is the mercury ion concentration in the treated leachate (mg / L), m is the mass of bismuth ferrite composite catalytic material (1 g), and V is the volume of landfill leachate (1 L).

[0041]

[0042] The test results of this embodiment are shown in Table 1.

[0043] Table 1 Effect of the mass ratio of chloride salt to red mud on the performance of the prepared bismuth ferrite composite catalytic material

[0044]

[0045] As can be seen from Table 1, when the mass ratio of chloride salt to red mud is less than 30:100 (e.g., in Table 1, the mass ratios of chloride salt to red mud are 27.5:100, 25:100, 22.5:100, and lower ratios not listed in Table 1), less chloride is added, and the chloride salt and red mud do not react fully during the calcination 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 chloride salt to red mud decreases. When the mass ratio of chloride salt to red mud is equal to 30-60:100 (e.g., in Table 1, the mass ratios of chloride salt to red mud are 30:100, 45:100, and 60:100), the neutralized chloride red mud is calcined. During the calcination process, hydrochloric acid reacts with minerals containing titanium, iron, calcium, and other metal elements, promoting the release of titanium, iron, calcium, and other metal elements. Chloride further combines with iron and other minor metal elements to form metal chlorides, which simultaneously volatilize into the flue gas and cool to form nuclei, forming calcined dust. Non-volatilized minerals containing titanium, calcium, and silicon are activated by heat and acid stimulation, forming highly active mineral components. Ultimately, the prepared catalysts achieved COD removal capacities exceeding 2409 mg / g, total phosphorus removal capacities exceeding 185 mg / g, ammonia nitrogen removal capacities exceeding 649 mg / g, and mercury removal capacities exceeding 204 mg / g. When the chloride-to-red mud mass ratio exceeds 60:100 (as shown in Table 1, for chloride-to-red mud mass ratios of 65:100, 70:100, and 75:100, as well as higher ratios not listed in Table 1), excessive chloride addition leads to an imbalance in the chloride-to-red mud reaction during high-temperature calcination. This results in a significant decrease in the COD, total phosphorus, ammonia nitrogen, and mercury removal capacities of the prepared catalysts as the chloride-to-red mud mass ratio increases. In summary, considering the benefits and costs, when the mass ratio of chloride salt to red mud is equal to 30~60:100, it is most conducive to improving the catalytic performance of the prepared bismuth ferrite composite catalytic material.

[0046] Example 2 Effect of the Mass Ratio of Bismuth Support Powder and Calcination Residue on the Performance of the Prepared Bismuth Ferrite Composite Catalytic Material

[0047] Weigh chloride salt and red mud in a mass ratio of 60:100 and stir evenly to obtain chloride red mud, wherein the chloride salt is calcium chloride. Mix hydrochloric acid solution and chloride red mud in a liquid-to-solid ratio of 30:100 mL / g and stir evenly to obtain neutralized chloride red mud, wherein the hydrochloric acid content of the hydrochloric acid solution is 15%. Roast the neutralized chloride red mud, and recover the flue gas generated during the roasting process. After the roasting is completed, a calcination residue and roasting dust generated by the recovered flue gas are obtained. The roasting temperature is 750°C and the roasting time is 2.5 hours. Mix the roasting dust and bismuth nitrate in a mass ratio of 50:100 and stir evenly to obtain bismuth-loaded powder. Bismuth-loaded powder and calcination residue were mixed at mass ratios of 1:100, 1.5:100, 2:100, 2.5:100, 10:100, 17.5:100, 20:100, 22.5:100, and 25:100, respectively, and ground evenly to obtain a bismuth-loaded calcined mixed powder. Water and the bismuth-loaded calcined mixed powder were mixed at a liquid-to-solid ratio of 0.8:1 mL / g, stirred for 45 minutes, and dried to obtain a bismuth-loaded raw meal, wherein the drying temperature was 150°C and the drying time was 6 hours. The bismuth-loaded raw meal was calcined to obtain a bismuth ferrite composite catalytic material, wherein the calcination temperature was 850°C and the calcination time was 2.5 hours.

[0048] The photocatalytic removal test, COD concentration detection and COD removal capacity calculation, total phosphorus concentration detection and total phosphorus removal capacity calculation, ammonia nitrogen concentration detection and ammonia nitrogen removal capacity calculation, 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.

[0049] Table 2 Effect of the mass ratio of bismuth powder and calcined residue on the performance of the prepared bismuth ferrite composite catalytic material

[0050]

[0051] Table 2 shows that when the bismuth support powder / calcined residue mass ratio is less than 2.5:100 (e.g., 2:100, 1.5:100, 1:100, and lower ratios not listed in Table 2), the amount of bismuth support powder added is insufficient, leading to insufficient reaction between the bismuth support powder and the calcined residue during calcination. This results in significant decreases in the COD, total phosphorus, ammonia nitrogen, and mercury removal capacities of the prepared catalysts as the bismuth support powder / calcined residue mass ratio decreases. When the bismuth support powder / calcined residue mass ratio is between 2.5 and 17.5:100 (e.g., 2.5:100, 10:100, and 17.5:100 in Table 2), water and the bismuth support calcined residue mixture are mixed, and titanium, iron, calcium, and other metal elements undergo hydrolysis during stirring, resulting in a mixed coprecipitate that is adsorbed and filled into the highly active mineral. The bismuth-loaded raw meal is calcined, and the co-precipitate undergoes oxidation to form a mixed catalytic material composed of titanium dioxide, bismuth titanate, bismuth ferrite, and other metal oxides. Simultaneously, some of the mixed catalytic material formed during the calcination process reacts with highly active minerals in the calcination residue, ultimately forming a composite catalytic material. Ultimately, the prepared catalysts all achieved COD removal capacities exceeding 2790 mg / g, total phosphorus removal capacities exceeding 203 mg / g, ammonia nitrogen removal capacities exceeding 701 mg / g, and mercury removal capacities exceeding 220 mg / g. When the bismuth support powder / calcined residue mass ratio exceeds 17.5:100 (as shown in Table 2, for ratios of 20:100, 22.5:100, and 25:100, as well as higher ratios not listed in Table 2), excessive bismuth support powder addition leads to an imbalance in the reaction between the bismuth support powder and the calcined residue during high-temperature calcination. This results in a significant decrease in the COD, total phosphorus, ammonia nitrogen, and mercury removal capacity of the prepared catalyst with increasing bismuth support powder / calcined residue mass ratio. Overall, considering both cost and efficiency, a bismuth support powder / calcined residue mass ratio of 2.5 to 17.5:100 is most beneficial for improving the catalytic performance of the prepared bismuth ferrite composite catalyst.

[0052] Example 3 Effect of Calcination Temperature on the Performance of Prepared Bismuth Ferrite Composite Catalytic Material

[0053] Weigh a chloride salt and red mud in a mass ratio of 60:100 and stir evenly to obtain chloride red mud, wherein the chloride salt is any of aluminum chlorides. Mix a hydrochloric acid solution and chloride red mud in a liquid-to-solid ratio of 45:100 mL / g and stir evenly to obtain neutralized chloride red mud, wherein the hydrochloric acid solution has a hydrochloric acid content of 25% by mass. Roast the neutralized chloride red mud, and recover the flue gas generated during the roasting process. After the roasting, a calcination residue and roasting dust generated by the recovered flue gas are obtained. The roasting temperature is 850°C and the roasting time is 4.5 hours. The roasting dust and bismuth nitrate are mixed in a mass ratio of 60:100 and stirred evenly to obtain bismuth-loaded powder. Mix the bismuth-loaded powder and the calcination residue in a mass ratio of 17.5:100 and grind evenly to obtain a bismuth-loaded calcined mixed powder. Water and the bismuth-loaded calcined mixed powder were mixed at a liquid-to-solid ratio of 1.2:1 mL / g, stirred for 75 minutes, and dried to obtain a bismuth-loaded raw meal. The drying temperature was 250°C for 2 hours. The bismuth-loaded raw meal was calcined to obtain a bismuth ferrite composite catalytic material. The calcination temperatures were 600°C, 650°C, 700°C, 750°C, 850°C, 950°C, 1000°C, 1050°C, and 1100°C for 4.5 hours.

[0054] The photocatalytic removal test, COD concentration detection and COD removal capacity calculation, total phosphorus concentration detection and total phosphorus removal capacity calculation, ammonia nitrogen concentration detection and ammonia nitrogen removal capacity calculation, 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.

[0055] Table 3 Effect of calcination temperature on the performance of prepared bismuth ferrite composite catalytic materials

[0056]

[0057] As shown in Table 3, when the calcination temperature is less than 750°C (e.g., calcination temperatures = 700°C, 650°C, 600°C, and lower values not listed in Table 3), the calcination temperature is low, and the thermal activation of the bismuth-loaded raw meal is insufficient during the calcination process, resulting in a significant decrease in the COD, total phosphorus, ammonia nitrogen, and mercury removal capacity of the prepared catalyst as the calcination temperature decreases. When the calcination temperature is equal to 750-950°C (e.g., calcination temperatures = 750°C, 850°C, and 950°C in Table 3), the bismuth-loaded raw meal is calcined, and the coprecipitate undergoes oxidation to form a mixed catalytic material containing titanium dioxide, bismuth titanate, bismuth ferrite, and other metal oxides. Simultaneously, some of the mixed catalytic material formed during the calcination process further reacts with highly active minerals in the calcination residue, ultimately forming a composite catalytic material. Ultimately, the prepared catalysts achieved COD removal capacities exceeding 2980 mg / g, total phosphorus removal capacities exceeding 220 mg / g, ammonia nitrogen removal capacities exceeding 742 mg / g, and mercury removal capacities exceeding 239 mg / g. When the calcination temperature exceeded 950°C (as shown in Table 3, at 1000°C, 1050°C, 1100°C, and other higher values not listed in Table 3), the bismuth-loaded raw meal overburned during high-temperature calcination, leading to an imbalance in the reactions between the components. This resulted in a significant decrease in the COD, total phosphorus, ammonia nitrogen, and mercury removal capacities of the prepared catalysts with increasing calcination temperature. In summary, considering both cost and performance, a calcination temperature between 750°C and 950°C was found to be most beneficial for improving the catalytic performance of the prepared bismuth ferrite composite catalyst.

[0058] Comparative Example Effects of Different Comparative Processes on the Performance of Prepared Bismuth Ferrite Composite Catalytic Materials

[0059] The process of the present invention comprises the following steps: weighing a chloride salt and red mud in a mass ratio of 60:100, stirring evenly, and obtaining chloride red mud, wherein the chloride salt is aluminum chloride. A hydrochloric acid solution and chloride red mud are mixed in a liquid-to-solid ratio of 45:100 mL / g and stirred evenly to obtain neutralized chloride red mud, wherein the mass content of hydrochloric acid in the hydrochloric acid solution is 25%. The neutralized chloride red mud is roasted, and the flue gas generated during the roasting process is recovered. After the roasting is completed, a calcination residue and roasting dust generated by the recovered flue gas are obtained, wherein the roasting temperature is 750°C and the roasting time is 2.5 hours. The roasting dust and bismuth nitrate are mixed in a mass ratio of 60:100, stirred evenly, and obtained a bismuth-loaded powder. The bismuth-loaded powder and the calcination residue are mixed in a mass ratio of 17.5:100, ground evenly, and obtained a bismuth-loaded calcined mixed powder. Water and the bismuth-loaded calcined mixed powder were mixed at a liquid-to-solid ratio of 1.2:1 mL / g, stirred for 75 minutes, and dried to obtain a bismuth-loaded raw meal at a drying temperature of 250°C for 2 hours. The bismuth-loaded raw meal was then calcined at a temperature of 950°C for 4.5 hours to obtain a bismuth ferrite composite catalytic material.

[0060] Comparative Process 1: Hydrochloric acid solution and red mud were mixed at a liquid-to-solid ratio of 45:100 mL / g and stirred to obtain neutralized red mud. The hydrochloric acid solution contained 25% hydrochloric acid by weight. The neutralized red mud was then roasted, and the flue gas generated during the roasting process was recovered. After the roasting, a calcination residue and calcination dust generated by the recovered flue gas were obtained. The roasting temperature was 750°C and the roasting time was 2.5 hours. The calcination dust and bismuth nitrate were mixed at a mass ratio of 60:100 and stirred to obtain bismuth-loaded powder. The bismuth-loaded powder and calcination residue were mixed at a mass ratio of 17.5:100 and ground to obtain a bismuth-loaded calcined mixed powder. Water and the bismuth-loaded calcined mixed powder were mixed at a liquid-to-solid ratio of 1.2:1 mL / g, stirred for 75 minutes, and dried to obtain a bismuth-loaded raw meal. The drying temperature was 250°C and the drying time was 2 hours. The bismuth-loaded raw material is calcined to obtain a bismuth ferrite composite catalytic material, wherein the calcination temperature is 950° C. and the calcination time is 4.5 hours.

[0061] Comparative Process 2: Chloride salt and red mud were weighed in a mass ratio of 60:100 and stirred to obtain chlorine red mud, where the chloride salt was aluminum chloride. Hydrochloric acid solution and chlorine red mud were mixed at a liquid-to-solid ratio of 45:100 mL / g and stirred to obtain neutralized chlorine red mud, where the hydrochloric acid content in the hydrochloric acid solution was 25%. Neutralized chlorine red mud and bismuth nitrate were mixed in a mass ratio of 60:100 and stirred to obtain bismuth-loaded powder. Bismuth-loaded powder and calcination residue were mixed in a mass ratio of 17.5:100 and ground to obtain a bismuth-loaded calcined mixed powder. Water and the bismuth-loaded calcined mixed powder were mixed in a liquid-to-solid ratio of 1.2:1 mL / g, stirred for 75 minutes, and dried to obtain a bismuth-loaded raw meal at a temperature of 250°C for 2 hours. The bismuth-loaded raw meal was calcined to obtain a bismuth ferrite composite catalytic material at a temperature of 950°C for 4.5 hours.

[0062] 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.

[0063] Table 4 Effects of different comparative processes on the performance of the prepared bismuth ferrite composite catalytic materials

[0064]

[0065] As can be seen from Table 4, the COD removal capacity, total phosphorus removal capacity, ammonia nitrogen removal capacity, and mercury removal capacity achieved by the bismuth ferrite composite catalytic material prepared by the process of the present invention are significantly higher than those of comparative process 1 and comparative process 2.

Claims

1. A method for preparing a bismuth ferrite composite catalytic material using red mud, characterized in that: The following steps are involved: (1) mixing chloride salt and red mud, stirring evenly to obtain chloride red mud; the mass ratio of the chloride salt to the red mud is 30-60:100; the chloride salt is any one of ammonium chloride, calcium chloride or aluminum chloride; (2) mixing the hydrochloric acid solution and the chlorine red mud described in step (1), stirring them evenly, roasting them, and recovering the flue gas generated during the roasting process, and obtaining a calcined residue and roasting dust generated by the recovered flue gas after the roasting is completed; (3) mixing the calcined dust and bismuth nitrate described in step (2) and stirring evenly to obtain bismuth-loaded powder; (4) mixing the bismuth-loaded powder described in step (3) and the calcined residue described in step (2), grinding them uniformly to obtain a bismuth-loaded calcined mixed powder; the mass ratio of the bismuth-loaded powder to the calcined residue is 2.5-17.5:100; (5) Mixing water and the bismuth-loaded calcined mixed powder, stirring, drying the material, and calcining to obtain the bismuth ferrite composite catalytic material; the calcination temperature is 750-950°C.

2. The method according to claim 1, characterized in that The liquid-to-solid ratio of the hydrochloric acid solution and the chlorine red mud in step (2) is 15-45:100 mL / g.

3. The method according to claim 1, characterized in that The mass proportion of hydrochloric acid in the hydrochloric acid solution in step (2) is 5-25%.

4. The method according to claim 1, characterized in that The calcination temperature in step (2) is 650-850° C., and the calcination time is 0.5-4.5 hours.

5. The method according to claim 1, characterized in that The mass ratio of the roasting dust and bismuth nitrate in step (3) is 40-60:

100.

6. The method according to claim 1, characterized in that The liquid-to-solid ratio of water to bismuth-loaded calcined mixed powder in step (5) is 0.4-1.2:1 mL / g.

7. The method according to claim 1, characterized in that: The temperature of the drying material in step (5) is 50-250° C. and the time is 2-10 hours.

8. A bismuth ferrite composite catalytic material prepared by the method according to any one of claims 1 to 7.

9. Use of the bismuth ferrite composite catalytic material according to claim 8 in removing pollutants by photocatalysis, characterized in that: The pollutants include one or more of COD, total phosphorus, ammonia nitrogen or mercury ions.

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