WO2024251202A1 - Method for preparing porous carbon material by means of red mud modification and use of porous carbon material - Google Patents

Abstract

Disclosed in the present application are a method for preparing a porous carbon material by means of red mud modification and the use of the porous carbon material. The method comprises: subjecting red mud to drying, grinding, acid leaching, washing, filtering and washing to obtain a neutral red mud slurry, crushing and carbonizing waste plastic bottles, mixing same with the red mud slurry, performing magnetic stirring to realize thorough mixing, and drying and activating the formed red mud-carbon material mixture, so as to obtain a porous carbon material. In the present application, by means of simple carbonization and activation methods, industrial solid waste, i.e., red mud, and plastic are converted into an adsorptive material, coordinated gas-solid treatment is achieved, and a new idea is provided for resource utilization of the red mud; compared with a traditional adsorbent, the porous carbon material, which is prepared from carbonized plastic doped with red mud, in the present application has a better pore structure and selectivity; moreover, PFCs can be enriched into a high-concentration gas after adsorption-desorption, and a certain economic value is obtained, such that environment-friendly utilization of waste from the aluminum industry is achieved, the environment treatment cost is reduced, and the aims of pollution reduction, carbon reduction and synergistic interaction are achieved.

Description

A method for preparing porous carbon material by modifying red mud and its application

This application claims the priority of the Chinese patent application filed with the China Patent Office on June 6, 2023, with application number CN202310669230.6 and invention name “A method and application of preparing porous carbon materials by modifying red mud”, the entire contents of which are incorporated by reference in this application.

Technical Field

The present application belongs to the technical field of solid waste resource utilization, and specifically relates to a method for preparing porous carbon materials by modifying red mud and its application.

Background Art

Red mud is a major solid waste generated during the production of alumina. Depending on the quality of alumina and the production process, red mud can be divided into Bayer red _mud , sintering red _mud and combined red mud. Red mud contains a large amount of metal oxides such as _Fe2O3 , _Al2O3 and _TiO2 , and has the potential to become an effective material for treating atmospheric pollutants. The traditional method of treating red mud is mainly stockpiling, which not only occupies land resources, but also the heavy metals in the red mud will penetrate into the ground through surface water and rainwater leaching, polluting the surrounding soil and causing soil salinization. At the same time, small particles on the surface of red mud will also diffuse into the air, causing air pollution. Therefore, improving its comprehensive utilization rate is the key to solving the problem of large-scale accumulation of red mud.

As an organic polymer material, plastic is widely used in industrial production and daily life because of its convenience, low cost, lightness, high strength and corrosion resistance. However, plastic is prone to aging and damage during use, has a short service life, and is difficult to degrade in the natural environment. If untreated waste plastic is directly discharged into the environment, it will cause white pollution and trigger a serious ecological crisis. At present, the main methods for treating plastics include landfill, incineration and pyrolysis. Although landfill is the simplest method, it requires a lot of land resources; and the incineration process will produce a large amount of harmful gases, which will cause secondary pollution if leaked into the air.

Industrial waste gas has a great destructive effect on the environment and can easily bring great inconvenience to people's lives. In the electrolytic aluminum industry, the largest source of pollution is the flue gas emitted by the electrolytic cell, such as dust, _{perfluorocarbons} (PFCs, mainly _CF4 and _C2F6 ), _CO2, etc. Among them, PFCs, as strong greenhouse gases, have a long life and a high global warming potential. The global warming potential is thousands or even tens of thousands of times that of _CO2 . When discharged into the environment, it is easy to cause global warming, leading to problems such as melting glaciers, rising sea levels, and land desertification.

At present, the emission reduction technologies for PFCs are mainly combustion, cracking, catalysis and adsorption. Among them, adsorption is considered to be a promising technology for capturing PFCs due to its low energy consumption, low cost and easy management. Among the multi-adsorbents, porous carbon materials are widely used due to their low preparation cost, large specific surface area, developed pore structure, good chemical and mechanical stability, and relatively easy regeneration. Although in the traditional preparation of porous carbon materials, a certain amount of pore structure can be obtained by treating carbon materials with physical or chemical activation methods, physical activation requires very high temperatures and a long time, and the increase in the specific surface area of the activated carbon materials is relatively limited. The carbon materials after chemical activation need to be cleaned to remove the activator residues in the pores, which further increases the cost of the reaction.

At present, the treatment of red mud and waste plastics in China in terms of adsorbents mainly focuses on using acid and alkali to treat red mud or activating agents to treat waste plastics to prepare adsorbents. The materials prepared in this way cannot fully utilize the metal oxides, specific surface area and pore structure contained therein, making it difficult to achieve efficient adsorption and purification performance, and it is difficult to achieve the goal of solid waste resource utilization.

Summary of the invention

The present application provides a method for preparing porous carbon materials by combining red mud with plastic modification and for adsorbing and treating fluorine-containing gases. The method adopts a catalytic activation method, utilizes the abundant metal _oxides such as _Fe2O3 in red mud to dope with carbon materials, and then activates them to increase the surface active points of the micropores inside the carbon materials, so that the micropores are transformed into mesopores, thereby improving the adsorption effect of the porous carbon adsorbent and achieving the effect of purifying the fume of electrolytic aluminum.

At the same time, in order to alleviate the problem of low utilization rate of red mud and plastics, the present application uses red mud and waste plastic bottles as raw materials, and through simple carbonization and activation, the prepared porous carbon adsorbent has better adsorption properties, which can not only remove PFCs in the flue gas of electrolytic aluminum, but also reduce the pollution of red mud to the environment and realize the resource utilization of red mud. At the same time, it realizes the environmentally friendly utilization of waste within the aluminum industry, reduces the cost of environmental governance, and achieves the purpose of synergistic efficiency improvement of pollution reduction and carbon reduction.

The technical solution of this application is as follows:

A method for preparing porous carbon material by modifying red mud, the specific steps are as follows:

(1) grinding red mud dried at 100-115° C. to constant weight and passing through a 100-mesh sieve to obtain red mud powder, adding a 0.05 mol/L citric acid solution to the red mud powder, stirring the mixture under magnetic stirring at room temperature for 20-30 min, filtering the mixture and washing the mixture with deionized water until the pH value is neutral, thereby obtaining a neutral red mud slurry;

(2) crushing the collected waste plastic bottles into small pieces and carbonizing them to obtain a carbon material; mixing the carbon material with a neutral red mud slurry to obtain a mixture, wherein the mixing is performed by magnetic stirring at room temperature for 2-4 hours;

(3) The mixture is vacuum dried, the obtained dried product is calcined and activated, and after cooling to room temperature, a red mud-based porous carbon material is obtained.

Preferably, the citric acid in the citric acid solution in step (1) accounts for 1-10% of the mass of the red mud powder.

Preferably, the main component of the waste plastic bottles in step (2) is polyethylene (PE).

Preferably, the carbonization in step (2) is: heating to 450-600°C at a heating rate of 5°C/min and calcining for 3h under _N2 atmosphere.

Preferably, in step (2), the mass ratio of the carbon material to the red mud powder is 1:2-4.

Preferably, the rotation speed of the magnetic stirring in step (1) and step (2) is independently 300-500 rpm; and the equipment for magnetic stirring is a magnetic stirrer.

Preferably, the vacuum drying temperature in step (3) is 60-80° C., and the vacuum drying time is 12 h.

Preferably, the calcination activation in step (3) is: heating to 500-800°C at a heating rate of 5°C/min under _N2 atmosphere and calcining for 3h.

The present application also provides an application of the red mud-based porous carbon material prepared by the method described in the above technical scheme for adsorbing and treating fluorine-containing gases, and the application is: placing the red mud-based porous carbon material in a fixed bed reactor, pretreating it at 300°C for 2h under a _N2 atmosphere, passing fluorine-containing gas after cooling to 120°C, and performing adsorption purification. After the red mud-based porous carbon material is saturated with adsorption, heating it to 150°C for desorption, collecting the desorbed gas, and using the red mud-based porous carbon material again as an adsorption material after desorption to adsorb and purify the fluorine-containing gas.

Preferably, the fluorine-containing gas includes 2% C ₂ F ₆ , 2% CF ₄ , 2% CO ₂ , and 94% N ₂ .

Preferably, the flow rate of the fluorine-containing gas is 200 mL/min.

Preferably, the desorption is _N2 purging desorption; and the desorption time is 3h.

Preferably, the adsorption amount of perfluorocarbon by the red mud-based porous carbon material is 1.75 mmol/g, 2.15 mmol/g, 2.45 mmol/g, 2.48 mmol/g, 2.34 mmol/g, 2.54 mmol/g or 1.90 mmol/g.

Preferably, the fluorine-containing gas is aluminum electrolysis fume.

The beneficial effects of this application are as follows:

(1) The present application uses red mud loaded carbonized plastic to prepare porous carbon materials for adsorbing and treating PFCs in electrolytic aluminum flue gas. Compared with adsorption materials prepared using red mud or waste plastic alone, this has better effects, not only improving the PFCs removal rate, but also reducing the generation of HF and _CO2 gases, thus providing a new method for the resource utilization of red mud.

(2) After the porous carbon material prepared in the present application adsorbs PFCs, high-concentration PFCs can be obtained through adsorption-desorption, which can reduce the energy consumption of subsequent treatments such as plasma decomposition and thermal catalysis.

(3) This application converts waste plastic bottles into carbon materials as carriers, and then loads the metal oxides in red mud It increases the surface area of the material and the selectivity of the gas, alleviating the impact of waste plastics on the environment.

(4) The present application utilizes the method of “treating waste with waste”, which not only improves the utilization rate of red mud and plastics, but also reduces process costs and reduces pollution to the environment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a process flow chart of red mud modification to prepare porous carbon materials for treating fluorine-containing gases.

DETAILED DESCRIPTION

In conjunction with the following examples, the present application is further described in detail. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. The reagents or instruments used in the examples that do not indicate the manufacturer can all be conventional products that can be purchased commercially.

The red mud used in the examples of the present application comes from an aluminum company in Wenshan City, Yunnan Province.

Example 1

A method for preparing porous carbon materials by modifying red mud and its application in adsorbing and treating fluorine-containing gases, as shown in FIG1 , has the following specific steps:

(1) Red mud from an aluminum company in Wenshan City, Yunnan Province was placed in an oven at 100°C and dried to constant weight, and then ground to pass through a 100-mesh sieve to obtain red mud powder for use; then an appropriate amount of the red mud powder was taken into a beaker, and a citric acid solution was added for acid treatment, wherein the citric acid in the citric acid solution accounted for 1% of the mass of the red mud powder to remove alkali metals and adhesive components in the red mud, and the red mud was placed in a magnetic stirrer and stirred at room temperature for 20 minutes at a speed of 300 rpm, and then filtered and washed with deionized water until the pH was neutral to obtain a red mud slurry for use;

(2) crushing the collected polyethylene plastic bottles into small pieces, placing them in a tube furnace, heating them to 450°C at a heating rate of 5°C/min under a _N2 atmosphere, and calcining them for 3 h to obtain a carbon material;

(3) The carbon material obtained in step (2) is added to the red mud slurry in a mass ratio of 1:2 with the red mud powder obtained in step (1) and mixed. The mixture is placed in a magnetic stirrer and stirred at room temperature for 2 h at a rotation speed of 300 rpm. After being fully mixed, the formed mixture is placed in a vacuum drying oven at 60°C for 12 h to remove moisture. The dried mixture is then placed in a tubular furnace under a _N2 atmosphere and heated to 500°C at a heating rate of 5°C/min and calcined for 3 h. After the calcination temperature is cooled to room temperature, a red mud-based porous carbon material is obtained.

The red mud-based porous carbon material was placed in a fixed bed reactor and pretreated at 300°C for 2 h under N ₂ atmosphere. After cooling to 120°C, a fluorine-containing mixed gas (2% C ₂ F ₆ , 2% CF ₄ , 2% CO ₂ , 94% N ₂ ) was introduced at a gas flow rate of 200 mL/min. The outlet gas was tested for PFCs using a flue gas analyzer. When the outlet concentration was the same as the inlet concentration and no longer changed, adsorption saturation was achieved. Then the fixed bed reactor was placed in a fixed bed reactor and the adsorption was carried out. The temperature of the reactor was raised to 150°C, and _N2 was purged and desorbed for 3 hours. The desorbed PFCs were detected by a flue gas analyzer. The adsorption amount of PFCs by the carbon material adsorbent was 1.75 mmol/g. It was also found that the desorbed carbon material was still very effective in purifying fluorine-containing gases when used as an adsorption material again.

Example 2

A method for preparing porous carbon materials by modifying red mud and its application in adsorbing and treating fluorine-containing gases, the specific steps are as follows:

(1) Red mud from an aluminum company in Wenshan City, Yunnan Province was placed in an oven at 100°C and dried to constant weight, and then ground to pass through a 100-mesh sieve to obtain red mud powder for use; then an appropriate amount of the red mud powder was taken into a beaker, and a 0.05 mol/L citric acid solution was added for acid treatment, wherein the citric acid in the citric acid solution accounted for 5% of the mass of the red mud powder to remove alkali metals and adhesive components in the red mud, and the red mud was placed in a magnetic stirrer and stirred at room temperature for 20 minutes at a speed of 300 rpm, and then filtered and washed with deionized water until the pH was neutral to obtain a red mud slurry for use;

(2) crushing the collected polyethylene plastic bottles into small pieces, placing them in a tube furnace under a _N2 atmosphere, heating them to 525°C at a heating rate of 5°C/min for 3 h to obtain a carbon material;

(3) The carbon material obtained in step (2) is added to the red mud slurry in a mass ratio of 1:2 with the red mud powder obtained in step (1), and the mixture is placed in a magnetic stirrer and stirred at room temperature for 2 h at a rotation speed of 300 rpm. After being fully mixed, the formed mixture is placed in a vacuum drying oven at 60°C for 12 h to remove moisture. The dried mixture is then placed in a tubular furnace under a _N2 atmosphere, heated to 500°C at a heating rate of 5°C/min, and calcined for 3 h. After the calcination temperature is cooled to room temperature, a red mud-based porous carbon material is obtained.

The red mud-based porous carbon material was placed in a fixed bed reactor and pretreated at 300° _C for 2h under _N2 atmosphere. After cooling to 120°C, a fluorine-containing mixed gas (2% _C2F6 , 2% _CF4 , 2% _CO2 , 94% _N2 ) was introduced at a gas flow rate of 200mL/min for an adsorption experiment. The outlet gas was detected for PFCs using a flue gas analyzer. When the outlet concentration was the same as the inlet concentration and no longer changed, adsorption saturation was reached. The temperature of the fixed bed reactor was then raised to 150°C, and _N2 was purged and desorbed for 3h. The desorbed PFCs were detected by the flue gas analyzer. The adsorption amount of PFCs by the carbon material adsorbent was 2.15mmol/g. It was also found that the desorbed carbon material was still very effective as an adsorbent material for purifying fluorine-containing gases.

Example 3

A method for preparing porous carbon materials by modifying red mud and its application in adsorbing and treating fluorine-containing gases, the specific steps are as follows:

(1) Red mud from an aluminum company in Wenshan City, Yunnan Province was placed in an oven and dried at 100°C to constant weight. The red mud powder is ground and passed through a 100-mesh sieve to obtain a red mud powder for use; then an appropriate amount of the red mud powder is taken into a beaker, and a citric acid solution with a concentration of 0.05 mol/L is added for acid treatment, wherein the citric acid in the citric acid solution accounts for 10% of the mass of the red mud powder, and the alkali metal and adhesive components in the red mud are removed, and the red mud is placed in a magnetic stirrer and stirred at room temperature for 20 minutes at a speed of 300 rpm, and then filtered and washed with deionized water until the pH is neutral to obtain a red mud slurry for use;

(2) crushing the collected polyethylene plastic bottles into small pieces, placing them in a tube furnace under a _N2 atmosphere, heating them to 600°C at a heating rate of 5°C/min and calcining them for 3 h to obtain a carbon material;

(3) The carbon material obtained in step (2) is added to the red mud slurry in a mass ratio of 1:2 with the red mud powder obtained in step (1), and the mixture is placed in a magnetic stirrer and stirred at room temperature for 2 h at a rotation speed of 300 rpm. After being fully mixed, the formed mixture is placed in a vacuum drying oven at 60°C for 12 h to remove moisture. The dried mixture is then placed in a tubular furnace under a _N2 atmosphere, heated to 500°C at a heating rate of 5°C/min, and calcined for 3 h. After the calcination temperature is cooled to room temperature, a red mud-based porous carbon material is obtained.

The red mud-based porous carbon material was placed in a fixed bed reactor and pretreated at 300° _C for 2h under _N2 atmosphere. After cooling to 120°C, a fluorine-containing mixed gas (2% _C2F6 , 2% _CF4 , 2% _CO2 , 94% _N2 ) was introduced at a gas flow rate of 200mL/min for an adsorption experiment. The outlet gas was detected for PFCs using a flue gas analyzer. When the outlet concentration was the same as the inlet concentration and no longer changed, adsorption saturation was reached. The temperature of the fixed bed reactor was then raised to 150°C, and _N2 was purged and desorbed for 3h. The desorbed PFCs were detected by the flue gas analyzer. The adsorption amount of PFCs by the carbon material adsorbent was 2.45mmol/g. It was also found that the desorbed carbon material was still very effective as an adsorbent material for purifying fluorine-containing gases.

Example 4

A method for preparing porous carbon materials by modifying red mud and its application in adsorbing and treating fluorine-containing gases, the specific steps are as follows:

(1) Red mud from an aluminum company in Wenshan City, Yunnan Province was placed in an oven at 110° C. and dried to constant weight, and then ground to pass through a 100-mesh sieve to obtain red mud powder for use; then an appropriate amount of the red mud powder was taken into a beaker, and a 0.05 mol/L citric acid solution was added for acid treatment, wherein the citric acid in the citric acid solution accounted for 5% of the mass of the red mud powder to remove alkali metals and adhesive components in the red mud, and the red mud was placed in a magnetic stirrer and stirred at room temperature for 25 minutes at a speed of 400 rpm, and then filtered and washed with deionized water until the pH was neutral to obtain a red mud slurry for use;

(2) crushing the collected polyethylene plastic bottles into small pieces, placing them in a tube furnace under a _N2 atmosphere, heating them to 600°C at a heating rate of 5°C/min and calcining them for 3 h to obtain a carbon material;

(3) The carbon material obtained in step (2) is added to the red mud slurry in a mass ratio of 1:3 to the red mud powder obtained in step (1), and the mixture is placed in a magnetic stirrer and stirred at room temperature for 3 hours at a rotation speed of 400 rpm. After sufficient mixing, the formed mixture is placed in a vacuum drying oven at 70°C for 12 hours to remove moisture. The dried mixture is then placed in a tubular furnace under a _N2 atmosphere, and the temperature is increased to 500°C at a heating rate of 5°C/min and calcined for 3 hours. After the calcination temperature is cooled to room temperature, a red mud-based porous carbon material is obtained.

The red mud-based porous carbon material was placed in a fixed bed reactor and pretreated at 300° _C for 2h under _N2 atmosphere. After cooling to 120°C, a fluorine-containing mixed gas (2% _C2F6 , 2% _CF4 , 2% _CO2 , 94% _N2 ) was introduced at a gas flow rate of 200mL/min for an adsorption experiment. The outlet gas was detected for PFCs using a flue gas analyzer. When the outlet concentration was the same as the inlet concentration and no longer changed, adsorption saturation was reached. The temperature of the fixed bed reactor was then raised to 150°C, and _N2 was purged and desorbed for 3h. The desorbed PFCs were detected by the flue gas analyzer. The adsorption amount of PFCs by the carbon material adsorbent was 2.48mmol/g. It was also found that the desorbed carbon material was still very effective as an adsorbent material for purifying fluorine-containing gases.

Example 5

A method for preparing porous carbon materials by modifying red mud and its application in adsorbing and treating fluorine-containing gases, the specific steps are as follows:

(1) Red mud from an aluminum company in Wenshan City, Yunnan Province was placed in an oven at 110° C. and dried to constant weight, and then ground to pass through a 100-mesh sieve to obtain red mud powder for use; then an appropriate amount of the red mud powder was taken into a beaker, and a 0.05 mol/L citric acid solution was added for acid treatment, wherein the citric acid in the citric acid solution accounted for 5% of the mass of the red mud powder to remove alkali metals and adhesive components in the red mud, and the red mud was placed in a magnetic stirrer and stirred at room temperature for 25 minutes at a speed of 400 rpm, and then filtered and washed with deionized water until the pH was neutral to obtain a red mud slurry for use;

(2) crushing the collected polyethylene plastic bottles into small pieces, placing them in a tube furnace under a _N2 atmosphere, heating them to 600°C at a heating rate of 5°C/min and calcining them for 3 h to obtain a carbon material;

(3) The carbon material obtained in step (2) is added to the red mud slurry in a mass ratio of 1:4 to the red mud powder obtained in step (1), and the mixture is placed in a magnetic stirrer and stirred at room temperature for 3 h at a rotation speed of 400 rpm. After sufficient mixing, the formed mixture is placed in a vacuum drying oven at 70°C for 12 h to remove moisture. The dried mixture is then placed in a tubular furnace under a _N2 atmosphere, and the temperature is increased to 500°C at a heating rate of 5°C/min and calcined for 3 h. After the calcination temperature is cooled to room temperature, a red mud-based porous carbon material is obtained.

The red mud-based porous carbon material was placed in a fixed bed reactor and pretreated at 300°C for 2 h under N ₂ atmosphere. After cooling to 120°C, a fluorine-containing mixed gas (2% C ₂ F ₆ , 2% CF ₄ , 2% CO ₂ , 94% N ₂ ) was introduced. The rate was 200mL/min, and the adsorption experiment was carried out. The outlet gas was detected for PFCs using a flue gas analyzer. When the outlet concentration was the same as the inlet concentration and no longer changed, the adsorption saturation was reached. Then the temperature of the fixed bed reactor was increased to 150°C, and _N2 was purged and desorbed for 3 hours. The desorbed PFCs were detected by the flue gas analyzer. The adsorption amount of PFCs by the carbon material adsorbent was 2.34mmol/g. At the same time, it was found that the desorbed carbon material was still very effective as an adsorption material for purifying fluorine-containing gases.

Example 6

A method for preparing porous carbon materials by modifying red mud and its application in adsorbing and treating fluorine-containing gases, the specific steps are as follows:

(1) Red mud from an aluminum company in Wenshan City, Yunnan Province was placed in an oven at 115°C and dried to constant weight, and then ground to pass through a 100-mesh sieve to obtain red mud powder for use; then an appropriate amount of the red mud powder was taken into a beaker, and a citric acid solution with a concentration of 0.05 mol/L was added for acid treatment, wherein the citric acid in the citric acid solution accounted for 5% of the mass of the red mud powder to remove alkali metals and adhesive components in the red mud, and the red mud was placed in a magnetic stirrer and stirred at room temperature for 30 minutes at a speed of 500 rpm, and then filtered and washed with deionized water until the pH was neutral to obtain a red mud slurry for use;

(2) crushing the collected polyethylene plastic bottles into small pieces, placing them in a tube furnace under a _N2 atmosphere, heating them to 600°C at a heating rate of 5°C/min and calcining them for 3 h to obtain a carbon material;

(3) The carbon material obtained in step (2) is added to the red mud slurry in a mass ratio of 1:3 with the red mud powder obtained in step (1) and mixed. The mixture is placed in a magnetic stirrer at room temperature for 4 hours at a rotation speed of 500 rpm. After sufficient mixing, the formed mixture is placed in a vacuum drying oven at 80°C for 12 hours to remove moisture. The dried mixture is then placed in a tubular furnace under a _N2 atmosphere and heated to 650°C at a heating rate of 5°C/min and calcined for 3 hours. After the calcination temperature is cooled to room temperature, a red mud-based porous carbon material is obtained.

The red mud-based porous carbon material was placed in a fixed bed reactor and pretreated at 300° _C for 2h under _N2 atmosphere. After cooling to 120°C, a fluorine-containing mixed gas (2% _C2F6 , 2% _CF4 , 2% _CO2 , 94% _N2 ) was introduced at a gas flow rate of 200mL/min for an adsorption experiment. The outlet gas was detected for PFCs using a flue gas analyzer. When the outlet concentration was the same as the inlet concentration and no longer changed, adsorption saturation was reached. The temperature of the fixed bed reactor was then raised to 150°C, and _N2 was purged and desorbed for 3h. The desorbed PFCs were detected by the flue gas analyzer. The adsorption amount of PFCs by the carbon material adsorbent was 2.54mmol/g. It was also found that the desorbed carbon material was still very effective as an adsorbent material for purifying fluorine-containing gases.

Example 7

A method for preparing porous carbon material by modifying red mud and its application in adsorbing and treating fluorine-containing gas, comprising the following steps: The steps are as follows:

(1) Red mud from an aluminum company in Wenshan City, Yunnan Province was placed in an oven at 115°C and dried to constant weight, and then ground to pass through a 100-mesh sieve to obtain red mud powder for use; then an appropriate amount of the red mud powder was taken into a beaker, and a citric acid solution with a concentration of 0.05 mol/L was added for acid treatment, wherein the citric acid in the citric acid solution accounted for 5% of the mass of the red mud powder to remove alkali metals and adhesive components in the red mud, and the red mud was placed in a magnetic stirrer and stirred at room temperature for 30 minutes at a speed of 500 rpm, and then filtered and washed with deionized water until the pH was neutral to obtain a red mud slurry for use;

(2) crushing the collected polyethylene plastic bottles into small pieces, placing them in a tube furnace under a _N2 atmosphere, heating them to 600°C at a heating rate of 5°C/min and calcining them for 3 h to obtain a carbon material;

(3) The carbon material obtained in step (2) is added to the red mud slurry in a mass ratio of 1:3 with the red mud powder obtained in step (1), and the mixture is placed in a magnetic stirrer and stirred at room temperature for 4 hours at a rotation speed of 500 rpm. After being fully mixed, the formed mixture is placed in a vacuum drying oven at 80°C for 12 hours to remove moisture. The dried mixture is then placed in a tubular furnace under a _N2 atmosphere, and the temperature is increased to 800°C at a heating rate of 5°C/min and calcined for 3 hours. After the calcination temperature is cooled to room temperature, a red mud-based porous carbon material is obtained.

The red mud-based porous carbon material was placed in a fixed bed reactor and pretreated at 300° _C for 2h under _N2 atmosphere. After cooling to 120°C, a fluorine-containing mixed gas (2% _C2F6 , 2% _CF4 , 2% _CO2 , 94% _N2 ) was introduced at a gas flow rate of 200mL/min for an adsorption experiment. The outlet gas was detected for PFCs using a flue gas analyzer. When the outlet concentration was the same as the inlet concentration and no longer changed, adsorption saturation was reached. The temperature of the fixed bed reactor was then raised to 150°C, and _N2 was purged and desorbed for 3h. The desorbed PFCs were detected by the flue gas analyzer. The adsorption amount of PFCs by the carbon material adsorbent was 1.90mmol/g. It was also found that the desorbed carbon material was still very effective as an adsorbent material for purifying fluorine-containing gases.

Comparative Example 1

The red mud slurry prepared in Example 6 was filtered and placed in a vacuum drying oven at 80°C for 12h, then placed in a tubular furnace under N2 atmosphere, heated to 600°C at a heating rate of 5°C/min and calcined for 3h to obtain a red mud-based adsorbent, which was placed in a fixed bed reactor and pretreated at 300°C for _2h under N2 atmosphere. After cooling to 120°C, a fluorine-containing mixed gas (2% _C2F6 , 2% _CF4 , 2% _CO2 , 94% _N2 ) was introduced at a gas flow rate of 200mL/min to perform an adsorption experiment. The outlet gas was tested for PFCs using a flue gas analyzer. When the outlet concentration was the same as the inlet concentration and no longer changed, adsorption saturation was reached. Then the temperature of the fixed bed reactor was raised to 150°C, and _N2 was purged for desorption for 3h. The desorbed PFCs were tested by the flue gas analyzer, and the adsorption amount of PFCs by the red mud-based adsorbent was 1.12mmol/g.

Comparative Example 2

The carbon material prepared in Example 6 was mixed with KOH with a concentration of 0.05 mol/L in a mass ratio of 1:3. The mixture was placed in a magnetic stirrer and stirred at room temperature for 1 h at a speed of 500 rpm. After being fully mixed, it was placed in a vacuum drying oven at 80°C for 12 h to remove moisture. The dried mixture was then placed in a tubular furnace under _N2 atmosphere and heated to 650°C at a heating rate of 5°C/min for 3 h. After the calcination temperature was cooled to room temperature, a porous carbon material was obtained. The material was placed in a fixed bed reactor and pretreated at 300°C for 2 h under _N2 atmosphere. After cooling to 120°C, a fluorine _- containing mixed gas (2% _C2F6 , 2% _CF4 , 2% _CO2 , 94% _N2 ) was introduced at a gas flow rate of 200 mL/min to conduct an adsorption experiment. The outlet gas was tested for PFCs using a flue gas analyzer. When the outlet concentration was the same as the inlet concentration and no longer changed, adsorption saturation was reached. The temperature of the fixed bed reactor was then raised to 150°C and N2 was conducted. ₂ After purging and desorption for 3 hours, the desorbed PFCs were detected by flue gas analyzer, and the adsorption amount of PFCs by porous carbon material was 1.35mmol/g.

In Example 1, Example 2, and Example 3, the effect of carbonization temperature on the performance of the adsorbent was considered, and 600°C was determined to be the optimal carbonization temperature of the carbon material; in Example 3, Example 4, and Example 5, the effect of the amount of red mud powder added on the performance of the adsorbent was considered. As the amount of red mud added increased, the adsorption effect of PFCs increased, but the adsorption effects of the carbon material and red mud powder mass ratios of 1:3 and 1:4 were similar, and considering the economic effect, 1:3 was the optimal mass ratio; in Example 4, Example 6, and Example 7, the effect of activation temperature on the performance of the adsorbent was considered. As the temperature increased, the adsorption effect of PFCs decreased, because too high a temperature would cause the micropore volume and total specific surface area to decrease, which was not conducive to the adsorption of PFCs. Therefore, when the carbonization temperature was 600°C, the mass ratio of carbon material to red mud powder was 1:3, and the activation temperature was 650°C, that is, Example 6, the pore structure of the prepared red mud-based porous carbon adsorbent was richer, and the adsorption effect of PFCs was the best.

Although the above-mentioned embodiment provides a detailed description of the present application, it is only a part of the embodiments of the present application rather than all the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present application.

Claims (14)

A method for preparing porous carbon material by modifying red mud, characterized in that the specific steps are as follows: (1) grinding red mud dried at 100-115° C. to constant weight and passing through a 100-mesh sieve to obtain red mud powder, adding a 0.05 mol/L citric acid solution to the red mud powder, stirring the mixture under magnetic stirring at room temperature for 20-30 min, filtering the mixture and washing the mixture with deionized water until the pH value is neutral, thereby obtaining a neutral red mud slurry; (2) crushing the collected waste plastic bottles into small pieces for carbonization to obtain a carbon material; mixing the carbon material with a neutral red mud slurry to obtain a mixture, wherein the mixing is performed by magnetic stirring at room temperature for 2-4 hours; (3) The mixture is vacuum dried, the obtained dried product is calcined and activated, and after cooling to room temperature, a red mud-based porous carbon material is obtained. The method according to claim 1, characterized in that the citric acid in the citric acid solution in step (1) accounts for 1-10% of the mass of the red mud powder. The method according to claim 1 is characterized in that the main component of the waste plastic bottles in step (2) is polyethylene. The method according to claim 1 is characterized in that the carbonization in step (2) is: heating to 450-600°C at a heating rate of 5°C/min and calcining for 3h under _N2 atmosphere. The method according to claim 1, characterized in that in step (2), the mass ratio of the carbon material to the red mud powder is 1:2-4. The method according to claim 1, characterized in that the rotation speed of the magnetic stirring in step (1) and step (2) is independently 300-500 rpm. The method according to claim 1 is characterized in that the vacuum drying temperature in step (3) is 60-80°C and the vacuum drying time is 12 hours. The method according to claim 1 is characterized in that the calcination activation in step (3) is: heating to 500-800°C at a heating rate of 5°C/min and calcining for 3h under _N2 atmosphere. The application of the red mud-based porous carbon material prepared by the method according to any one of claims 1 to 8 for adsorbing and treating fluorine-containing gases, the application being: placing the red mud-based porous carbon material in a fixed bed reactor, pretreating it at 300°C for 2h under a _N2 atmosphere, passing a fluorine-containing gas after cooling to 120°C for adsorption and purification, and after the red mud-based porous carbon material is saturated with adsorption, heating it to 150°C for desorption, collecting the desorbed gas, and using the desorbed red mud-based porous carbon material again as an adsorbent material to adsorb and purify the fluorine-containing gas. The use according to claim 9, characterized in that the fluorine-containing gas comprises 2% C ₂ F ₆ , 2% CF ₄ , 2% CO ₂ , and 94% N ₂ . The use according to claim 9 or 10, characterized in that the flow rate of the fluorine-containing gas is is 200mL/min. The use according to claim 9 is characterized in that the desorption is _N2 purge desorption; and the desorption time is 3 hours. The use according to claim 9 is characterized in that the adsorption amount of perfluorocarbon by the red mud-based porous carbon material is 1.75 mmol/g, 2.15 mmol/g, 2.45 mmol/g, 2.48 mmol/g, 2.34 mmol/g, 2.54 mmol/g or 1.90 mmol/g. The use according to claim 9 is characterized in that the fluorine-containing gas is electrolytic aluminum fume.