Method for synergistically removing heavy metals in waste SCR (Selective Catalytic Reduction) catalyst by using red mud-reed biochar

Abstract

The invention provides a method for synergistically removing heavy metals in a waste SCR (Selective Catalytic Reduction) catalyst by using red mud-reed biochar, which comprises the following steps: mixing waste SCR catalyst powder and red mud-reed biochar powder, carrying out immersion cleaning, ultrasonic oscillation and adsorption treatment, carrying out magnetic separation on the biochar adsorbed with the heavy metals, and recovering the SCR catalyst. According to the method, the magnetic biochar is prepared from solid waste materials of red mud and reeds and is applied to heavy metal removal of the waste SCR catalyst, so that the problem of environmental pollution caused by accumulation of the red mud and the reeds is effectively solved, heavy metals on the waste SCR catalyst can be effectively extracted, and the method has great significance in environmental protection and environmental protection. The method has a good development prospect in the field of solid waste recycling.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste resource recovery and utilization, and specifically relates to a method for synergistically removing heavy metals from waste SCR catalysts using red mud-reed biochar. Background Art

[0002] The NH3 selective catalytic reduction technology (NH3-SCR) is the most effective denitrification process for reducing flue gas NO x pollution in current coal-fired power plants. However, during the long-term operation of the denitrification catalyst, heavy metals in the flue gas adhere to the catalyst surface, and long-term accumulation will cause catalyst deactivation. Waste SCR catalysts are resources that can be recycled. Although some conventional recycling methods for waste catalysts can effectively extract heavy metals, there are still certain defects. For example, dissolving heavy metals with acids or alkalis easily produces a large amount of toxic wastewater, causing secondary pollution, while heat treatment methods such as incineration and high-temperature melting consume a large amount of energy and release toxic gases. Therefore, there is an urgent need for a green and environmentally friendly treatment method to separate heavy metal impurities from waste SCR catalysts.

[0003] Red mud is an alkaline waste generated during the production of alumina. With the rapid development of the alumina industry, more than 2 billion tons of red mud are randomly stacked globally. Red mud can be regarded as a material containing valuable mineral elements, including Fe2O3, Al2O3, SiO2, etc. These metal oxides can promote the deep cracking of biomass raw materials during the co-pyrolysis process with biomass raw materials, greatly increasing the specific surface area of the co-pyrolysis products. By carrying out research on waste mixed metal oxides in the field of solid waste recycling and utilization, not only can red mud solid waste be effectively treated, but also "turn waste into treasure and treat waste with waste".

[0004] Reed is an aquatic plant with a wide distribution and high biomass. When harvested in autumn every year, the stems of reeds are left in the fields. If not utilized, it will also cause certain environmental pollution. At the same time, reeds contain a large amount of lignin. When reed straw is pyrolyzed under high-temperature and oxygen-deficient conditions, the reducing gas generated will reduce Fe 3 + in iron salts to Fe 2 + or even Fe 0 , making it magnetic. It can also promote the development of a larger specific surface area and a more abundant pore structure in biochar, which is beneficial as an adsorption material. Summary of the Invention

[0005] To solve the problems existing in the prior art, the present invention provides a method for synergistically removing heavy metals from waste SCR catalysts using red mud and reed biochar. By preparing magnetic biochar from red mud and reed solid waste materials and applying it to the removal of heavy metals from waste SCR catalysts, it not only effectively solves the environmental pollution problem caused by the accumulation of red mud and reeds, but also can effectively extract heavy metals from waste SCR catalysts, showing good development prospects in the fields of environmental protection and solid waste recycling.

[0006] To achieve the above object, the present invention provides the following technical solution: A method for synergistically removing heavy metals from waste SCR catalysts, which involves mixing waste SCR catalyst powder with red mud-reed biochar powder, followed by leaching, ultrasonic oscillation, and adsorption treatment, and then magnetic separation to recover the biochar adsorbed with heavy metals and recycle the SCR catalyst.

[0007] Further, the mixing ratio of the waste SCR catalyst powder to the red mud-reed biochar powder is 0.5 - 1.75:1.

[0008] Further, the mixing ratio of the waste SCR catalyst powder to the red mud-reed biochar powder is 1.75:1.

[0009] Further, mix reed straw powder with pickled red mud powder, and obtain red mud-reed biochar after calcination in an inert atmosphere.

[0010] Further, the mass ratio of the reed straw powder to the pickled red mud powder is 1:1.

[0011] Further, after drying and crushing the red mud, pickle it with a dilute sulfuric acid solution and wash it to neutrality to obtain pickled red mud powder.

[0012] Further, the drying temperature of the red mud is 100°C, the concentration of the dilute sulfuric acid solution is 0.1 mol / L, and the solid-liquid ratio of pickling is 1:5.

[0013] Further, the calcination is carried out by heating at a heating rate of 10°C / min to 500°C - 700°C, calcining for 20 min - 60 min, and then grinding and passing through an 80 - 120 mesh sieve to obtain red mud-reed biochar powder.

[0014] Further, the leaching is carried out using a 0.1 mol / L EDTA solution with a pH value of 2 - 6.

[0015] Further, the leaching is carried out using a 0.1 mol / L EDTA solution with a pH value of 6.

[0016] Furthermore, the ultrasonic power used for ultrasonic oscillation is 0.5 kW. After ultrasonic oscillation for 30 min, the adsorption treatment is carried out for 12 h to 24 h.

[0017] Furthermore, the ultrasonic power used for ultrasonic oscillation is 0.5 kW. After ultrasonic oscillation for 30 min, the adsorption treatment is carried out for 800 min.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects: The present invention provides a method for synergistically removing heavy metals from waste SCR catalysts using red mud - reed biochar. By using two solid wastes, red mud and reed, as raw materials to prepare red mud - reed biochar, it effectively solves the environmental pollution problems caused by the accumulation of red mud and reed, and realizes the resource utilization of solid wastes. On the other hand, during the process of recycling waste SCR catalysts, the present invention can effectively extract heavy metals from the catalysts, avoiding the secondary pollution that may be brought by traditional treatment methods. This concept of "turning waste into treasure and treating waste with waste" meets the requirements of sustainable development, shows good development prospects in the fields of environmental protection and solid waste recycling, and provides an innovative idea and method for solving the problems of solid waste treatment and heavy metal pollution.

[0019] The types and existing forms of heavy metals on waste SCR catalysts are complex and diverse. Generally, they contain various trace heavy metals such as lead, mercury, and arsenic, and the element content of coal types and boiler combustion conditions in different regions will affect the occurrence forms of heavy metals on the catalysts. The red mud - reed biochar prepared by the present invention has a unique structure and properties, which can well cope with this complexity. During the co - pyrolysis of red mud and reed, iron oxides are reduced by reducing gases into magnetic red mud - reed biochar. The various functional groups on it can provide active sites for adsorption reactions, and the porous structure is conducive to promoting the adsorption of reactive ions. This characteristic enables red mud - reed biochar to efficiently adsorb heavy metals with different types and occurrence forms on waste SCR catalysts, and has stronger adaptability and adsorption effect compared with other conventional methods. Therefore, the present invention can more effectively remove heavy metals in the field of recycling waste SCR catalysts, improving the recovery efficiency and quality.

[0020] Compared with conventional methods such as acid-base treatment and heat treatment, the present invention has the advantages of low energy consumption, easy separation, and no secondary pollution. In the process of preparing red mud-reed biochar, the sources of red mud and reed materials are wide and the prices are low, reducing the raw material cost. At the same time, during the co-pyrolysis of red mud and reed to prepare biochar, the generated reducing gas will promote the development of a larger specific surface area and a more abundant pore structure of the biochar, which is not only beneficial to the adsorption of heavy metal ions but also reduces the energy consumption during the preparation process. In addition, the magnetism generated after the reduction of iron oxides in red mud enables the biochar adsorbed with heavy metals to be easily collected and separated from the mixture of waste SCR catalyst and red mud-reed biochar by magnetic separation. This separation and recovery method is simple and efficient, does not involve complex chemical treatment processes, and avoids the generation of secondary pollution. Therefore, the present invention has higher environmental friendliness and economic feasibility in the field of recycling waste SCR catalysts. Brief Description of the Drawings

[0021] Figure 1 SEM morphology diagram of the red mud-reed biochar prepared by the present invention.

[0022] Figure 2 To explore the influence of pH value on the adsorption rate of heavy metals by red mud-reed biochar in Example 1.

[0023] Figure 3 To explore the influence of the dosage of biochar on the adsorption rate of heavy metals by red mud-reed biochar in Example 2.

[0024] Figure 4 To explore the fitting degree between the adsorption curve of red mud-reed biochar with the change of adsorption time and the pseudo-kinetic model in Example 3. Detailed Embodiment

[0025] The present invention will be further described below in conjunction with the drawings and specific embodiments.

[0026] The present invention provides a method for synergistically removing heavy metals from waste SCR catalysts by red mud-reed biochar. The specific process is as follows: (1) Dry and grind the red mud, sieve it through 80-120 mesh, mix it with dilute sulfuric acid solution for pickling, then wash it with deionized water until neutral and dry it; (2) Grind the reed straw and sieve it through 80-120 mesh, grind and mix it with acidified red mud, then in an inert atmosphere environment, heat it to 500°C - 700°C at a heating rate of 10°C / min, calcine it for 20 min - 60 min, and then grind and sieve it through 80 mesh - 120 mesh to obtain red mud-reed biochar powder; (3) After cleaning the ash on the surface of the waste SCR catalyst and grinding it to 80 - 120 mesh to obtain waste SCR catalyst powder, then adjust the pH value of the leaching solution to 2 - 6, and uniformly mix the red mud - reed biochar powder with the waste SCR catalyst powder according to a mass ratio of 0.5 - 1.75:1. Put the mixture into the leaching solution, perform ultrasonic oscillation for 30 min, then carry out adsorption treatment for 12 h - 24 h, and then conduct magnetic separation and filtration.

[0027] Preferably, in step (1), the grinding size of the red mud is 100 mesh, the drying temperature of the red mud is set at 100 °C, the concentration of the dilute sulfuric acid is 0.1 mol / L, and the solid - liquid ratio of the acid pickling is 1:5.

[0028] Preferably, in step (2), the grinding size of the reed is 100 mesh, the mass ratio of red mud to reed is 1:1, the roasting temperature is 600 °C for 30 min, and the size of the red mud - reed biochar obtained after roasting is 100 mesh.

[0029] Preferably, in step (3), the mixing ratio of the red mud - reed biochar to the waste SCR catalyst is 1.75:1, the leaching solution is 0.1 mol / L EDTA solution, and the preferred pH value is 6.

[0030] Preferably, in step (3), the ultrasonic power is 0.5 kW, and after ultrasonic oscillation for 30 min, the adsorption treatment is carried out for 24 h.

[0031] Example 1 This example is about the influence of pH value on the adsorption rate of heavy metals by red mud - reed biochar.

[0032] The present invention provides a method for synergistically removing heavy metals from waste SCR catalysts by red mud - reed biochar. The specific process is as follows: Step S1: Dry and grind 5 g of red mud, pass it through a 100 - mesh sieve, mix it with 0.1 mol / L dilute sulfuric acid solution for acid pickling, and then wash it with deionized water until neutral and dry. Step S2: Grind the dry reed straw and pass it through a 100 - mesh sieve, mix it with the acidified red mud by grinding, and then in an inert atmosphere environment with high - purity nitrogen flowing, heat it to 600 °C at a heating rate of 10 °C / min, and roast it at 600 °C for 30 min to ensure that most of the iron(III) oxide in the red mud is reduced to magnetic iron(II,III) oxide. Step S3: Clean the ash on the surface of the waste SCR catalyst and grind it to 100 mesh to obtain waste SCR catalyst powder. Grind the red mud-reed biochar obtained in Step S2 through a 100-mesh sieve and uniformly mix it with the waste SCR catalyst powder at a mass ratio of 1.75:1. Then, put the mixture into 0.1 mol / L EDTA leaching solutions with pH values of 2, 3, 4, 5, and 6 respectively. After ultrasonic treatment for 30 min, shake and adsorb for 24 h. After completion, use a magnetic adsorption device to collect the biochar adsorbed with heavy metals for magnetic separation and filtration.

[0033] It can be seen from Figure 2 that when the pH value is 2, the minimum adsorption rate is 6%; when the pH value is 6, the maximum adsorption rate reaches 79%.

[0034] Example 2 This example is about the influence of the biochar input amount on the adsorption rate of heavy metals by red mud-reed biochar.

[0035] The present invention provides a method for synergistically removing heavy metals from waste SCR catalysts by red mud-reed biochar. The specific process is as follows: Step S1: Dry and grind 5 g of red mud, pass it through a 100-mesh sieve, mix it with 0.1 mol / L dilute sulfuric acid solution for pickling, and then wash it with deionized water until neutral and dry. Step S2: Grind the dry reed straw and pass it through a 100-mesh sieve, grind and mix it with the acidified red mud. Then, in an inert atmosphere environment with high-purity nitrogen passing through, heat it to 600 °C at a heating rate of 10 °C / min and calcine it at 600 °C for 30 min to ensure that most of the iron(III) oxide in the red mud is reduced to magnetic iron(II,III) oxide. Step S3: Clean the ash on the surface of the waste SCR catalyst and grind it to 100 mesh to obtain waste SCR catalyst powder. Grind the red mud-reed biochar obtained in Step S2 through a 100-mesh sieve and uniformly mix it with the waste SCR catalyst powder according to mass ratios of 0.5:1, 0.75:1, 1:1, 1.25:1, 1.5:1, and 1.75:1. Then, put the mixture into 0.1 mol / L EDTA leaching solution with a pH value of 6. After ultrasonic treatment for 30 min, shake and adsorb for 24 h. After completion, use a magnetic adsorption device to collect the biochar adsorbed with heavy metals for magnetic separation and filtration.

[0036] It can be seen from Figure 3 that when the input amount is 0.5:1, the minimum adsorption rate is 21%; when the input amount is 1.75:1, the maximum adsorption rate reaches 98%. The total adsorption amount of lead shows a trend of first increasing and then decreasing with the increase of the biochar input amount.

[0037] Example 3 This example is to explore the fitting degree of the adsorption rate of the red mud-reed biochar adsorption heavy metal curve with the change of adsorption time.

[0038] The present invention provides a method for synergistically removing heavy metals from waste SCR catalysts by red mud-reed biochar. The specific process is as follows: Step S1: Dry and grind 5 g of red mud, pass it through a 100-mesh sieve, mix it with a 0.1 mol / L dilute sulfuric acid solution for pickling, and then wash it with deionized water until neutral and dry. Step S2: Grind the dry reed straw and pass it through a 100-mesh sieve, grind and mix it with the acidified red mud, and then under an inert atmosphere environment with high-purity nitrogen passing through, heat it to 600 °C at a heating rate of 10 °C / min, and calcine it at 600 °C for 30 min to ensure that most of the iron(III) oxide in the red mud is reduced to magnetic iron(II,III) oxide. Step S3: After cleaning the ash on the surface of the waste SCR catalyst, grind it to 100 meshes to obtain the waste SCR catalyst powder. Grind the red mud-reed biochar obtained in Step S2 through a 100-mesh sieve and uniformly mix it with the waste SCR catalyst powder at a mass ratio of 1.75:1, and then put the mixture into a 0.1 mol / L EDTA leaching solution with a pH value of 6, perform ultrasonic treatment for 30 min, and then oscillate and adsorb for 0, 5 h, 10 h, 15 h, 20 h, 24 h. After completion, use a magnetic separation device to collect the biochar adsorbed with heavy metals for magnetic separation and filtration.

[0039] It can be seen from Figure 4 that when the adsorption time is before 5 h, the adsorption of red mud-reed biochar is more in line with the pseudo-first-order kinetics, indicating that physical adsorption mainly occurs during this period. When the adsorption time exceeds 5 h, the adsorption of red mud-reed biochar has a higher fitting degree with the pseudo-second-order kinetics, indicating that chemical adsorption mainly occurs during this period.

[0040] Example 4: The present invention provides a method for synergistically removing heavy metals from waste SCR catalysts by red mud-reed biochar. The specific process is as follows: Step S1: Place the red mud in an oven, set the temperature to 100 °C, dry for 6 hours, take it out and put it into a ball mill, ball mill it at a rotation speed of 300 r / min for 2 hours, pass it through a 100-mesh sieve to obtain the dried and ground red mud. Mix the red mud obtained in the previous step with a 0.1 mol / L dilute sulfuric acid solution at a solid-liquid ratio of 1:5, stir for 2 hours to complete pickling. Wash the pickled red mud with deionized water repeatedly until the washing liquid is neutral, filter, and place the filter residue in the oven to dry at 110 °C for 8 hours to obtain the acidified red mud.

[0041] Step S2: Cut the reed straws and put them into a ball mill. Ball mill for 2 hours at a speed of 300 revolutions per minute, and then pass through a 100-mesh sieve to obtain the ground reed straws. Step S3: Mix the ground reed straws and acidified red mud evenly at a mass ratio of 1:1. Place them in a muffle furnace, introduce nitrogen to form an inert atmosphere, heat up to 600 °C at a heating rate of 10 °C per minute, and keep roasting for 30 minutes. Put the roasted mixture into a ball mill, ball mill for 2 hours at a speed of 300 revolutions per minute, and then pass through a 100-mesh sieve to obtain the red mud-reed biochar powder.

[0042] Step S4: Rinse the surface ash of the waste SCR catalyst with deionized water, air-dry it naturally, then put it into a ball mill, ball mill for 2 hours at a speed of 300 revolutions per minute, and pass through a 100-mesh sieve to obtain the waste SCR catalyst powder.

[0043] Step S5: Adjust the leaching solution to a 0.1 mol / L EDTA solution with a pH value of 6. Uniformly mix the red mud-reed biochar powder and the waste SCR catalyst powder at a mass ratio of 1.75:1. Put the mixture into the leaching solution, perform ultrasonic oscillation for 30 minutes at a power of 0.5 kW, and carry out static adsorption treatment at room temperature for 15 hours. Perform magnetic separation on the adsorbed mixture to separate out the solid particles, and finally filter to obtain the treated waste SCR catalyst. The carbon morphology structure is as Figure 1 shown. It can be seen that the pore structure is rich, which helps to increase the specific surface area of the material and thus improve its adsorption performance.

[0044] Example 5: The present invention provides a method for synergistically removing heavy metals from waste SCR catalysts by red mud-reed biochar. The specific process is as follows: The particle size of the acidified red mud is 80 mesh, and the particle size of the reed straws is 80 mesh. After mixing, keep roasting at 500 °C for 60 minutes. Grind the roasted mixture and pass through an 80-mesh sieve to obtain the red mud-reed biochar powder.

[0045] The remaining steps are the same as those in Example 4.

[0046] Example 6: The present invention provides a method for synergistically removing heavy metals from waste SCR catalysts by red mud-reed biochar. The specific process is as follows: The particle size of the acidified red mud is 120 mesh, and the particle size of the reed straws is 120 mesh. After mixing, keep roasting at 700 °C for 20 minutes. Grind the roasted mixture and pass through a 120-mesh sieve to obtain the red mud-reed biochar powder.

[0047] The remaining steps are the same as those in Example 4.

[0048] In summary, the present invention utilizes two solid waste materials to prepare magnetic biochar and applies it to the heavy metal removal of waste SCR catalysts. During the co-pyrolysis of red mud and reed, iron oxides are reduced by reducing gases into magnetic red mud-reed biochar. Various functional groups in the red mud-reed biochar can provide active sites for adsorption reactions, and its porous structure is conducive to promoting the adsorption of reactive ions. The types and existing forms of heavy metals on waste SCR catalysts are complex and diverse, generally containing multiple trace heavy metals such as lead, mercury, and arsenic. Moreover, the element content of coal types and boiler combustion conditions in different regions will affect the occurrence form of heavy metals on the catalysts. The magnetic biochar prepared by the present invention can cope with this complexity and meet the adsorption requirements of heavy metals on waste SCR catalysts. In addition, the raw materials used in the present invention are inexpensive, which not only effectively solves the environmental pollution problems caused by the accumulation of red mud and reed, but also can effectively extract heavy metals from waste SCR catalysts, meeting the green environmental protection concept of "turning waste into treasure and treating waste with waste", and having good development prospects in the fields of environmental protection and solid waste recycling and utilization.

[0049] The present invention proposes a method for synergistically removing heavy metals from waste SCR catalysts by red mud-reed biochar. Compared with conventional methods such as acid-base treatment and heat treatment, this method has the advantages of not producing secondary pollution and low energy consumption. The red mud and reed materials used in this method are derived from solid wastes. And during the co-pyrolysis of red mud and reed to prepare red mud-reed biochar, the reducing gases generated thereon will promote the development of a larger specific surface area and a more abundant pore structure of the biochar, which is conducive to the adsorption of heavy metal ions. In addition, the iron oxides in the red mud will generate magnetism after being reduced by reducing gases, which is conducive to the subsequent collection and separation of the biochar adsorbed with heavy metals from the mixture of waste SCR catalysts and red mud-reed biochar, and the separation and recovery are simple without involving secondary pollution problems.

Claims

1. A method for removing heavy metals from waste SCR catalysts by using red mud and reed biochar, characterized in that: The waste SCR catalyst powder is mixed with red mud-reed biochar powder, and after soaking, ultrasonic vibration and adsorption treatment, the biochar that has adsorbed heavy metals is separated by magnetic separation to recover the SCR catalyst.

2. The method for removing heavy metals from waste SCR catalysts by using red mud and reed biochar according to claim 1, characterized in that: The mixing ratio of the waste SCR catalyst powder to the red mud-reed biochar powder is 0.5-1.75:

1.

3. The method for removing heavy metals from waste SCR catalysts by using red mud and reed biochar according to claim 2, characterized in that: The mixing ratio of the waste SCR catalyst powder to the red mud-reed biochar powder is 1.75:

1.

4. The method for removing heavy metals from waste SCR catalysts by using red mud and reed biochar according to claim 1, characterized in that: Reed straw powder and acid-washed red mud powder were mixed in a mass ratio of 1:1, and red mud-reed biochar was obtained after roasting in an inert atmosphere.

5. The method for removing heavy metals from waste SCR catalysts by red mud-reed biochar synergistically according to claim 4, characterized in that: The dried red mud is crushed, and then acid-washed with a dilute sulfuric acid solution until it becomes neutral, thereby obtaining acid-washed red mud powder.

6. The method for removing heavy metals from waste SCR catalysts by using red mud and reed biochar according to claim 4, characterized in that: The roasting is carried out by heating the temperature to 500°C-700°C at a heating rate of 10°C / min, roasting for 20min-60min, and then grinding through a 80-mesh-120-mesh sieve to obtain red mud-reed biochar powder.

7. The method for removing heavy metals from waste SCR catalysts by using red mud and reed biochar according to claim 1, characterized in that: The immersion is carried out using a 0.1 mol / L EDTA solution with a pH value of 2-6.

8. The method for removing heavy metals from waste SCR catalysts by using red mud and reed biochar according to claim 7, characterized in that: The immersion is carried out using a 0.1 mol / L EDTA solution with a pH value of 6.

9. The method for removing heavy metals from waste SCR catalysts by using red mud and reed biochar according to claim 1, characterized in that: The ultrasonic power used in the ultrasonic oscillation is 0.5 kW, and the adsorption treatment is carried out for 12 h to 24 h after the ultrasonic oscillation for 30 min.

10. The method for removing heavy metals from waste SCR catalysts by using red mud and reed biochar according to claim 1, characterized in that: The ultrasonic power used in the ultrasonic oscillation was 0.5 kW, and the adsorption treatment was performed for 800 minutes after the ultrasonic oscillation for 30 minutes.

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