Method for preparing bismuth ferrite composite catalytic material by using red mud as well as product and application of bismuth ferrite composite catalytic material

Abstract

The invention discloses a method for preparing a bismuth ferrite composite catalytic material by using red mud as well as a product and application of the bismuth ferrite composite catalytic material. The method comprises the following steps: mixing chlorine salt and red mud, uniformly stirring, adding a hydrochloric acid solution, uniformly stirring, roasting, recovering flue gas generated in the roasting process, and obtaining roasting residues and roasting dust generated by recovering the flue gas after roasting is finished; and mixing the roasted dust and bismuth nitrate, uniformly stirring, adding the calcined residue, uniformly grinding, adding water, stirring, drying the material, and calcining to obtain the bismuth ferrite composite catalytic material. The preparation process is simple, the red mud is used as a main raw material, and full-amount resource utilization of the red mud can be achieved. The prepared composite catalytic material can be used for efficiently purifying landfill leachate, and COD, ammonia nitrogen, total phosphorus and heavy metal pollution are efficiently removed through a photocatalysis mechanism.

Description

Technical Field

[0001] The present invention relates to a method for preparing bismuth ferrite composite catalytic materials using red mud, as well as products and applications thereof, belonging to the field of resource utilization of industrial waste. Background Art

[0002] As a typical multiferroic semiconductor material, bismuth ferrite (BiFeO3) has a unique energy band structure (band gap ~ 2.2 eV), which endows it with excellent visible light response characteristics and shows activities that are difficult to compare with traditional catalysts in the fields of photocatalytic degradation of organic pollutants and Fenton-like advanced oxidation. However, conventional chemical precipitation methods require the use of high-purity iron nitrate (≥99.9%) as the 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 be transformed into bismuth ferrite-based composite catalytic materials, realizing the green preparation of BiFeO3-based composite materials, it has potential advantages such as cost reconstruction advantages and performance synergistic enhancement. Summary of the Invention

[0004] Object of the Invention: The technical problem to be solved by the present invention is to provide a method for preparing bismuth ferrite composite catalytic materials using red mud, as well as products and applications thereof.

[0005] Technical Solution: To solve the above technical problems, the present invention provides a method for preparing bismuth ferrite composite catalytic materials using red mud, including the following steps: (1) Mix a chloride salt and red mud, and stir evenly to obtain chloride red mud; the mass ratio of the chloride salt to red mud is 30 - 60:100; (2) Mix a hydrochloric acid solution and the chloride red mud in step (1), stir evenly, calcine, recover the flue gas generated during the calcination process, and obtain calcined residues and calcined dust generated from the recovered flue gas after the calcination ends; (3) Mix the calcined dust in step (2) and bismuth nitrate, and stir evenly to obtain bismuth-loaded powder; (4) Mix the bismuth-loaded powder in step (3) and the calcined residues in step (2), and grind evenly to obtain bismuth-loaded calcined mixed powder; (5) Mix water and the bismuth-loaded calcined mixed powder, stir, dry the material, and calcine to obtain the bismuth ferrite composite catalytic material; the temperature of the calcination is 750 - 950 °C.

[0006] Among them, the chloride salt in step (1) is any one of ammonium chloride, calcium chloride, or aluminum chloride.

[0007] Among them, the liquid-solid ratio of the hydrochloric acid solution to the chloride red mud in step (2) is 15 - 45:100 mL / g.

[0008] Among them, the mass proportion of hydrochloric acid in the hydrochloric acid solution described in step (2) is 5-25%.

[0009] Among them, the temperature of the roasting described in step (2) is 650-850 °C, and the roasting time is 0.5-4.5 hours.

[0010] Among them, the mass ratio of the roasting dust to bismuth nitrate in step (3) is 40-60:100.

[0011] Among them, the mass ratio of the bismuth-loaded powder to the calcination residue in step (4) is 2.5-17.5:100.

[0012] Among them, the liquid-solid ratio of water to the bismuth-loaded calcined mixed powder in step (5) is 0.4-1.2:1 mL / g.

[0013] Among them, the temperature of the dried material in step (5) is 50-250 °C, and the time is 2-10 hours.

[0014] Among them, in step (5), the calcination time is 0.5-4.5 hours.

[0015] The stirring time described in step (5) is 15-75 minutes.

[0016] The present invention also provides a highly active bismuth ferrite composite catalytic material prepared by the method.

[0017] The present invention also provides the application of the bismuth ferrite composite catalytic material in removing pollutants.

[0018] Among them, the pollutants include one or more of COD, total phosphorus, ammonia nitrogen or mercury ions.

[0019] The present invention also provides the application of the bismuth ferrite composite catalytic material in purifying landfill leachate.

[0020] Reaction mechanism: The neutralized chlorine red mud is calcined. During the calcination process, hydrochloric acid reacts with minerals containing titanium, iron, calcium, etc., promoting the release of titanium, iron, calcium, and other metal elements. The chloride salts further combine with iron and other minor metal elements to form metal chlorides and volatilize synchronously under high-temperature conditions into the flue gas, where they cool and nucleate to form calcination dust. That is, FeCl3 volatilizes first and accumulates in the flue gas particles. When a very small amount of FeCl3 decomposes due to complex factors such as local temperature fluctuations, the generated FeCl2 will also accumulate in the flue gas particles due to factors such as air flow drive and be discharged together with the flue gas particles. The un-volatilized minerals containing titanium, calcium, silicon, etc. are activated by heat and acid excitation to form highly active mineral components. Mix water and the calcined bismuth-loaded mixed powder. During the stirring process, titanium, iron, calcium, and other metal elements undergo hydrolysis, and the formed mixed coprecipitates adsorb and fill in the highly active minerals. The bismuth-loaded raw material is calcined, and the coprecipitates are oxidized to form a mixed catalytic substance mixed with titanium dioxide, bismuth titanate, bismuth ferrite, and other metal oxides. At the same time, during the calcination process, some of the formed mixed catalytic substances further react with the highly active minerals in the calcination residue, and finally a composite catalytic material is formed.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: The preparation process of the present invention is simple, and the main raw material used is red mud, which can realize the full utilization of red mud resources. The prepared composite catalytic material can be used for the efficient purification of landfill leachate, and can efficiently remove COD, ammonia nitrogen, total phosphorus, and heavy metal pollution through a photocatalytic mechanism. Brief description of the drawings

[0022] Figure 1 It is a flow chart of the treatment method of the present invention. Detailed implementation manners

[0023] The technical solution of the present invention will be further described below with reference to the drawings.

[0024] Preparation of landfill leachate and landfill leachate containing mercury: The landfill leachate used in the experiment was taken from Zhuji Sanfeng Environmental Energy Co., Ltd. The COD mass concentration of this batch of landfill leachate was 4152 mg / L, the concentration of total phosphorus was 305 mg / L, and the concentration of ammonia nitrogen was 1075 mg / L. 500 mg of mercury was added to 1 L of landfill leachate and stirred evenly to prepare landfill leachate containing mercury.

[0025] Red mud: Provided by Shandong Zibo Zhengheng Aluminum Co., Ltd., the main detected 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 (inevitable impurities and loss on ignition).

[0026] Example 1 Influence of the mass ratio of chloride salt to red mud on the performance of the prepared bismuth ferrite composite catalytic material Weigh chloride salt and red mud according to the 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, stir evenly to obtain chloride red mud, where the chloride salt is ammonium chloride. Mix hydrochloric acid solution and chloride red mud according to the liquid-solid ratio of 15:100 mL / g, stir evenly to obtain neutralized chloride red mud, where the mass content of hydrochloric acid in the hydrochloric acid solution is 5%. Calcinate the neutralized chloride red mud, recover the flue gas generated during the calcination process, and obtain calcined residue and calcined dust generated from the recovered flue gas after the calcination ends, where the calcination temperature is 650 °C and the calcination time is 0.5 hour. Mix the calcined dust and bismuth nitrate according to the mass ratio of 40:100, stir evenly to obtain bismuth-loaded powder. Mix the bismuth-loaded powder and the calcined residue according to the mass ratio of 2.5:100, grind evenly to obtain bismuth-loaded calcined mixed powder. Mix water and the bismuth-loaded calcined mixed powder according to the liquid-solid ratio of 0.4:1 mL / g, stir for 15 minutes, dry the material to obtain bismuth-loaded raw material, where the drying temperature is 50 °C and the drying time is 10 hours. Calcinate the bismuth-loaded raw material to obtain bismuth ferrite composite catalytic material, where the calcination temperature is 750 °C and the calcination time is 0.5 hour.

[0027] Photocatalytic removal test: Put 1 g of bismuth ferrite composite catalytic material into 1 L of mercury-containing landfill leachate, stir at a speed of 120 rmp while irradiating with an ultraviolet lamp for 120 min, and then centrifuge at a speed of 5000 rpm for solid-liquid separation. Detect the concentrations of different pollutants in the separated liquid and calculate the removal rate. The specific detection and calculation are as follows.

[0028] COD concentration detection and calculation of COD removal capacity: The chemical oxygen demand COD concentration of the leachate is determined according to the national standard "Water Quality - Determination of Chemical Oxygen Demand - Dichromate Method" (HJ828-2017). The COD removal capacity is calculated according to formula (1), where R COD is the COD removal capacity (mg / g), c COD0 and c CODt are the COD concentrations (mg / L) of the domestic waste landfill leachate before and after treatment respectively, m is the mass of the bismuth ferrite composite catalytic material (1 g), and V is the volume of the landfill leachate (1 L).

[0029]

[0030] Total phosphorus concentration detection and calculation of total phosphorus removal capacity: The total phosphorus concentration of the leachate is 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 is calculated according to formula (2), where RTP is the total phosphorus removal capacity (mg / g), c TP0 and c TPt are the total phosphorus concentrations (mg / L) of the domestic waste leachate before and after treatment, respectively. m is the mass of the bismuth ferrite composite catalytic material (1 g), and V is the volume of the waste leachate (1 L).

[0031]

[0032] Ammonia nitrogen concentration detection and ammonia nitrogen removal capacity calculation: The concentration of ammonia nitrogen in the leachate was determined according to the "Water Quality - Determination of Ammonia Nitrogen - Salicylic Acid Spectrophotometry" (HJ 536 - 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 remaining concentration of ammonia nitrogen in the treated leachate (mg / L), m is the mass of the bismuth ferrite composite catalytic material (1 g), and V is the volume of the waste leachate (1 L).

[0033]

[0034] Mercury ion concentration detection and removal capacity calculation: The concentration of mercury ions 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 concentration of mercury ions in the treated leachate (mg / L), m is the mass of the bismuth ferrite composite catalytic material (1 g), and V is the volume of the waste leachate (1 L).

[0035]

[0036] The test results of this example are shown in Table 1.

[0037] Table 1 Influence of the mass ratio of chloride salt and red mud on the performance of the prepared bismuth ferrite composite catalytic material

[0038] As can be seen from Table 1, when the mass ratio of chloride salt to red mud is less than 30:100 (such as in Table 1, when the mass ratio of chloride salt to red mud = 27.5:100, 25:100, 22.5:100 and lower ratios not listed in Table 1), less chloride salt is added, and the reaction between chloride salt and red mud is insufficient during roasting, resulting in a significant decrease in the COD, total phosphorus, ammonia nitrogen, and mercury removal capacities 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 (such as in Table 1, when the mass ratio of chloride salt to red mud = 30:100, 45:100, 60:100), the neutralized chloride red mud is roasted. During the roasting process, hydrochloric acid reacts with minerals containing titanium, iron, calcium, etc., promoting the release of titanium, iron, calcium, and other metal elements. The chloride salt further combines with iron and other trace metal elements to form metal chlorides and simultaneously volatilizes into the flue gas to cool and nucleate to form roasting dust. The unvolatile minerals containing titanium, calcium, silicon, etc. are thermally activated and acid-activated to form highly active mineral components. Finally, the prepared catalyst has a COD removal capacity higher than 2409 mg / g, a total phosphorus removal capacity higher than 185 mg / g, an ammonia nitrogen removal capacity higher than 649 mg / g, and a mercury removal capacity higher than 204 mg / g. When the mass ratio of chloride salt to red mud is greater than 60:100 (such as in Table 1, when the mass ratio of chloride salt to red mud = 65:100, 70:100, 75:100 and higher ratios not listed in Table 1), excessive chloride salt is added, and the reaction between chloride salt and red mud is unbalanced during high-temperature roasting, resulting in a significant decrease in the COD, total phosphorus, ammonia nitrogen, and mercury removal capacities of the prepared catalyst as the mass ratio of chloride salt to red mud further increases. Generally speaking, considering the benefits and costs, when the mass ratio of chloride salt to red mud is equal to 30 - 60:100, it is most beneficial to improve the catalytic performance of the prepared bismuth ferrite composite catalytic material.

[0039] Example 2 Influence of the mass ratio of bismuth-loaded powder to calcination residue on the performance of the prepared bismuth ferrite composite catalytic material Weigh the chloride salt and red mud according to the mass ratio of 60:100 respectively, stir evenly to obtain chloride red mud, where the chloride salt is calcium chloride. Mix the hydrochloric acid solution and chloride red mud according to the liquid-solid ratio of 30:100 mL / g, stir evenly to obtain neutralized chloride red mud, where the mass content of hydrochloric acid in the hydrochloric acid solution is 15%. Calcinate the neutralized chloride red mud, recover the flue gas generated during the calcination process, and obtain calcined residue and calcined dust generated from the recovered flue gas after the calcination ends, where the calcination temperature is 750 °C and the calcination time is 2.5 hours. Mix the calcined dust and bismuth nitrate according to the mass ratio of 50:100, stir evenly to obtain bismuth-loaded powder. Mix the bismuth-loaded powder and calcined residue according to the mass ratios of 1:100, 1.5:100, 2:100, 2.5:100, 10:100, 17.5:100, 20:100, 22.5:100, 25:100 respectively, grind evenly to obtain bismuth-loaded calcined mixed powder. Mix water and bismuth-loaded calcined mixed powder according to the liquid-solid ratio of 0.8:1 mL / g, stir for 45 minutes, dry the material to obtain bismuth-loaded raw material, where the drying temperature is 150 °C and the drying duration is 6 hours. Calcinate the bismuth-loaded raw material to obtain bismuth ferrite composite catalytic material, where the calcination temperature is 850 °C and the calcination time is 2.5 hours.

[0040] 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 the same as in Example 1. The test results of this example are shown in Table 2.

[0041] Table 2 Influence of the mass ratio of bismuth-loaded powder and calcined residue on the performance of the prepared bismuth ferrite composite catalytic material

[0042] As can be seen from Table 2, when the mass ratio of bismuth-loaded powder to calcined residue is less than 2.5:100 (as in Table 2, when the mass ratio of bismuth-loaded powder to calcined residue = 2:100, 1.5:100, 1:100 and lower ratios not listed in Table 2), the addition of bismuth-loaded powder is less, and the reaction between bismuth-loaded powder and calcined residue is insufficient during calcination, resulting in a significant decrease in the COD, total phosphorus, ammonia nitrogen, and mercury removal capacities of the prepared catalyst with the decrease in the mass ratio of bismuth-loaded powder to calcined residue. When the mass ratio of bismuth-loaded powder to calcined residue is equal to 2.5 - 17.5:100 (as in Table 2, when the mass ratio of bismuth-loaded powder to calcined residue = 2.5:100, 10:100, 17.5:100), the mixed water and bismuth-loaded calcined mixed powder are mixed, and titanium, iron, calcium, and other metal elements undergo hydrolysis during stirring, forming a mixed coprecipitate that adsorbs and fills the highly active minerals. The bismuth-loaded raw material is calcined, and the coprecipitate undergoes oxidation to form a mixed catalytic substance mixed with titanium dioxide, bismuth titanate, bismuth ferrite, and other metal oxides. At the same time, some of the mixed catalytic substances formed during the calcination process further react with the highly active minerals in the calcined residue, finally forming a composite catalytic material. Finally, the prepared catalyst has a COD removal capacity higher than 2790 mg / g, a total phosphorus removal capacity higher than 203 mg / g, an ammonia nitrogen removal capacity higher than 701 mg / g, and a mercury removal capacity higher than 220 mg / g. When the mass ratio of bismuth-loaded powder to calcined residue is greater than 17.5:100 (as in Table 2, when the mass ratio of bismuth-loaded powder to calcined residue = 20:100, 22.5:100, 25:100 and higher ratios not listed in Table 2), the addition of bismuth-loaded powder is excessive, and the reaction between bismuth-loaded powder and calcined residue is unbalanced during high-temperature calcination, resulting in a significant decrease in the COD, total phosphorus, ammonia nitrogen, and mercury removal capacities of the prepared catalyst with the further increase in the mass ratio of bismuth-loaded powder to calcined residue. Generally speaking, considering the benefits and costs, when the mass ratio of bismuth-loaded powder to calcined residue is equal to 2.5 - 17.5:100, it is most beneficial to improve the catalytic performance of the prepared bismuth ferrite composite catalytic material.

[0043] Example 3 Influence of Calcination Temperature on the Performance of the Prepared Bismuth Ferrite Composite Catalytic Material Weigh the chloride salt and red mud according to the mass ratio of 60:100 respectively, stir evenly to obtain chloride red mud, where the chloride salt is any one of aluminum chlorides. Mix the hydrochloric acid solution and chloride red mud according to the liquid-solid ratio of 45:100 mL / g, stir evenly to obtain neutralized chloride red mud, where the mass content of hydrochloric acid in the hydrochloric acid solution is 25%. Calcinate the neutralized chloride red mud, recover the flue gas generated during the calcination process, and obtain calcined residue and calcined dust generated from the recovered flue gas after the calcination ends, where the calcination temperature is 850 °C and the calcination time is 4.5 hours. Mix the calcined dust and bismuth nitrate according to the mass ratio of 60:100, stir evenly to obtain bismuth-loaded powder. Mix the bismuth-loaded powder and the calcined residue according to the mass ratio of 17.5:100, grind evenly to obtain bismuth-loaded calcined mixed powder. Mix water and bismuth-loaded calcined mixed powder according to the liquid-solid ratio of 1.2:1 mL / g, stir for 75 minutes, dry the material to obtain bismuth-loaded raw material, where the drying temperature is 250 °C and the drying duration is 2 hours. Calcinate the bismuth-loaded raw material to obtain bismuth ferrite composite catalytic material, where the calcination temperatures are 600 °C, 650 °C, 700 °C, 750 °C, 850 °C, 950 °C, 1000 °C, 1050 °C, 1100 °C, and the calcination time is 4.5 hours.

[0044] The photocatalytic removal test, the detection of COD concentration and the calculation of COD removal capacity, the detection of total phosphorus concentration and the calculation of total phosphorus removal capacity, the detection of ammonia nitrogen concentration and the calculation of ammonia nitrogen removal capacity, and the detection of mercury ion concentration and the calculation of removal capacity are the same as those in Example 1. The test results of this example are shown in Table 3.

[0045] Table 3 Influence of Calcination Temperature on the Performance of the Prepared Bismuth Ferrite Composite Catalytic Material

[0046] As can be seen from Table 3, when the calcination temperature is less than 750 °C (as shown in Table 3, the calcination temperatures are 700 °C, 650 °C, 600 °C, and lower values not listed in Table 3), the calcination temperature is relatively low, and the thermal activation of bismuth-loaded raw materials is insufficient during the calcination process, resulting in a significant decrease in the COD, total phosphorus, ammonia nitrogen, and mercury removal capacities of the prepared catalyst with the decrease in the calcination temperature. When the calcination temperature is equal to 750 - 950 °C (as shown in Table 3, the calcination temperatures are 750 °C, 850 °C, 950 °C), the bismuth-loaded raw materials are calcined, and the coprecipitate is oxidized to form a mixed catalytic substance mixed with titanium dioxide, bismuth titanate, bismuth ferrite, and other metal oxides. At the same time, some of the mixed catalytic substances formed during the calcination process further react with the highly active minerals in the calcination residue to finally form a composite catalytic material. Finally, the prepared catalyst has a COD removal capacity higher than 2980 mg / g, a total phosphorus removal capacity higher than 220 mg / g, an ammonia nitrogen removal capacity higher than 742 mg / g, and a mercury removal capacity higher than 239 mg / g. When the calcination temperature is greater than 950 °C (as shown in Table 3, the calcination temperatures are 1000 °C, 1050 °C, 1100 °C, and higher values not listed in Table 3), due to the overcalcination of the bismuth-loaded raw materials during the high-temperature calcination process and the imbalance of component reactions, the COD, total phosphorus, ammonia nitrogen, and mercury removal capacities of the prepared catalyst all decrease significantly with the further increase in the calcination temperature. Generally speaking, considering the benefits and costs, when the calcination temperature is equal to 750 - 950 °C, it is most beneficial to improve the catalytic performance of the prepared bismuth ferrite composite catalytic material.

[0047] Comparative Example Influence of Different Comparative Processes on the Performance of the Prepared Bismuth Ferrite Composite Catalytic Material Process of the present invention: Weigh chloride salt and red mud according to a mass ratio of 60:100, stir evenly to obtain chlorinated red mud, where the chloride salt is aluminum chloride. Mix hydrochloric acid solution and chlorinated red mud according to a liquid-solid ratio of 45:100 mL / g, stir evenly to obtain neutralized chlorinated red mud, where the mass content of hydrochloric acid in the hydrochloric acid solution is 25%. Calcinate the neutralized chlorinated red mud, recover the flue gas generated during the calcination process, and obtain calcination residue and calcination dust generated from the recovered flue gas after the calcination ends, where the calcination temperature is 750 °C and the calcination time is 2.5 hours. Mix the calcination dust and bismuth nitrate according to a mass ratio of 60:100, stir evenly to obtain bismuth-loaded powder. Mix the bismuth-loaded powder and the calcination residue according to a mass ratio of 17.5:100, grind evenly to obtain bismuth-loaded calcined mixed powder. Mix water and the bismuth-loaded calcined mixed powder according to a liquid-solid ratio of 1.2:1 mL / g, stir for 75 minutes, dry the material to obtain bismuth-loaded raw material, where the drying temperature is 250 °C and the drying duration is 2 hours. Calcinate the bismuth-loaded raw material to obtain a bismuth ferrite composite catalytic material, where the calcination temperature is 950 °C and the calcination time is 4.5 hours.

[0048] Comparative Process 1: Mix hydrochloric acid solution and red mud according to a liquid-solid ratio of 45:100 mL / g, stir evenly to obtain neutralized red mud, where the mass content of hydrochloric acid in the hydrochloric acid solution is 25%. Roast the neutralized red mud, recover the flue gas generated during the roasting process, and obtain calcined residue and roasting dust generated from the recovered flue gas after roasting. The roasting temperature is 750 °C and the roasting time is 2.5 hours. Mix the roasting dust and bismuth nitrate according to a mass ratio of 60:100, stir evenly to obtain bismuth-loaded powder. Mix the bismuth-loaded powder and the calcined residue according to a mass ratio of 17.5:100, grind evenly to obtain bismuth-loaded calcined mixed powder. Mix water and the bismuth-loaded calcined mixed powder according to a liquid-solid ratio of 1.2:1 mL / g, stir for 75 minutes, dry the material to obtain bismuth-loaded raw material, where the drying temperature is 250 °C and the drying duration is 2 hours. Calcinate the bismuth-loaded raw material to obtain bismuth ferrite composite catalytic material, where the calcination temperature is 950 °C and the calcination time is 4.5 hours.

[0049] Comparative Process 2: Weigh chloride salt and red mud respectively according to a mass ratio of 60:100, stir evenly to obtain chloride red mud, where the chloride salt is aluminum chloride. Mix hydrochloric acid solution and chloride red mud according to a liquid-solid ratio of 45:100 mL / g, stir evenly to obtain neutralized chloride red mud, where the mass content of hydrochloric acid in the hydrochloric acid solution is 25%. Mix the neutralized chloride red mud and bismuth nitrate according to a mass ratio of 60:100, stir evenly to obtain bismuth-loaded powder. Mix the bismuth-loaded powder and the calcined residue according to a mass ratio of 17.5:100, grind evenly to obtain bismuth-loaded calcined mixed powder. Mix water and the bismuth-loaded calcined mixed powder according to a liquid-solid ratio of 1.2:1 mL / g, stir for 75 minutes, dry the material to obtain bismuth-loaded raw material, where the drying temperature is 250 °C and the drying duration is 2 hours. Calcinate the bismuth-loaded raw material to obtain bismuth ferrite composite catalytic material, where the calcination temperature is 950 °C and the calcination time is 4.5 hours.

[0050] The photocatalytic removal test, the detection of COD concentration and the calculation of COD removal capacity, the detection of total phosphorus concentration and the calculation of total phosphorus removal capacity, the detection of ammonia nitrogen concentration and the calculation of ammonia nitrogen removal capacity, and the detection of mercury ion concentration and the calculation of removal capacity are the same as those in Example 1. The test results of this comparative example are shown in Table 4.

[0051] Table 4 Influence of Different Comparative Processes on the Performance of the Prepared Bismuth Ferrite Composite Catalytic Material

[0052] 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, It includes the following steps: (1) Mix chloride salts and red mud, stir evenly to obtain chloride red mud; the mass ratio of the chloride salts to the red mud is 30 - 60:100; (2) Mix hydrochloric acid solution and the chloride red mud in step (1), stir evenly, roast, recover the flue gas generated during the roasting process, and obtain calcined residues and roasting dust generated from the recovered flue gas after the roasting ends; (3) Mix the roasting dust in step (2) and bismuth nitrate, stir evenly to obtain bismuth-loaded powder; (4) Mix the bismuth-loaded powder in step (3) and the calcined residues in step (2), grind evenly to obtain bismuth-loaded calcined mixed powder; the mass ratio of the bismuth-loaded powder to the calcined residues is 2.5 - 17.5:100; (5) Mix water and the bismuth-loaded calcined mixed powder, stir, dry the material, and calcine to obtain the bismuth ferrite composite catalytic material; the temperature of the calcination is 750 - 950 °C.

2. The method according to claim 1, wherein The chloride salts in step (1) are any one of ammonium chloride, calcium chloride, or aluminum chloride.

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

4. The method according to claim 1, wherein The mass fraction of hydrochloric acid in the hydrochloric acid solution in step (2) is 5 - 25%.

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

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

100.

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

8. The method according to claim 1, wherein The temperature for drying the material in step (5) is 50 - 250 °C, and the time is 2 - 10 hours.

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

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

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