CN111974395B - A red mud-based heterogeneous catalyst, its preparation method, and its pollutant degradation method - Google Patents

Abstract

The invention discloses a red mud-based heterogeneous catalyst, a preparation method and a pollutant degradation method, belonging to the technical field of heterogeneous catalysts, and solves the problems of high cost and low degradation efficiency of catalysts used for degradation of organic pollutants in the prior art. The red mud heterogeneous catalyst is prepared by carbonizing red mud and biomass, and the mass ratio of red mud to biomass is 5:1-1:2. The preparation method is uniformly mixing red mud and biomass; heating and carbonizing the mixture, and sequentially cooling, washing and drying the reaction product to obtain the red mud heterogeneous catalyst. In the degradation method, the red mud heterogeneous catalyst, the organic pollutant aqueous solution and the oxidant are mixed, and the mixture is stirred and reacted, so that the organic pollutants in the organic pollutant aqueous solution are degraded. The above-mentioned red mud-based heterogeneous catalyst, its preparation method and the pollutant degradation method can be used for the degradation of organic pollutants.

Description

A red mud-based heterogeneous catalyst, its preparation method, and its pollutant degradation method

technical field

The invention belongs to the technical field of heterogeneous catalysts, and in particular relates to a red mud-based heterogeneous catalyst, a preparation method, and a pollutant degradation method.

Background technique

Red mud is a strong alkaline solid waste produced by the alumina industry. Every ton of alumina produced will produce 1.0 to 2.5 tons of red mud. The stock of red mud in my country is about 400 to 800 million tons. Red mud has fine particles, strong alkalinity and heavy metal content, which is harmful to the environment. From the perspective of resources, red mud contains valuable metals such as iron, aluminum, titanium, and rare earths. However, the grades of the above metals are low, and the economics of recycling are poor. The development of high-value functional materials is of great significance to the comprehensive utilization of red mud.

Utilizing the physical and chemical properties of red mud, such as containing metal elements and large specific surface area, high value-added functional materials such as adsorbents and catalysts can be prepared. The red mud is modified to prepare adsorbents for the adsorption of heavy metal ions in wastewater and soil. The strong alkalinity of red mud can be used to adsorb sulfur dioxide in industrial waste gas, and red mud can also be used as a carrier to load active components to adsorb harmful substances in tail gas. The use of red mud as a catalyst or catalyst support for biomass pyrolysis to produce biomass energy has also been extensively studied.

Industrial wastewater and urban wastewater contain a large amount of organic pollutants. Organic pollutants cause great harm to the ecological environment and human health due to their characteristics of refractory degradation and high toxicity. The reaction between catalysts and oxidants produces active free radicals with strong oxidative properties, which can effectively degrade organic pollutant molecules. However, the existing catalysts for the degradation of organic pollutants have high cost and low degradation efficiency.

Contents of the invention

In view of the above analysis, the present invention aims to provide a red mud-based heterogeneous catalyst and its preparation method and pollutant degradation method, which solves the problems of high cost and low degradation efficiency of catalysts used in the degradation of organic pollutants in the prior art.

The purpose of the present invention is mainly achieved through the following technical solutions:

The invention provides a red mud heterogeneous catalyst, which is prepared by carbonizing red mud and biomass. The mass content of iron oxide in the red mud is 10%-30%, and the mass ratio of red mud to biomass is 5:1-1:2.

Further, the biomass is lignocellulosic waste biomass.

Further, the biomass is straw, sawdust, fallen leaves, bagasse, coconut shell and/or livestock manure, and the total mass content of lignin, cellulose and hemicellulose in the biomass exceeds 70%.

The present invention also provides a preparation method of red mud heterogeneous catalyst, comprising the following steps:

Step 1: Mix red mud and biomass evenly to obtain a mixture;

Step 2: heating the mixture, and performing a carbonization reaction under an inert atmosphere to obtain a reaction product;

Step 3: cooling, washing and drying the reaction product in sequence to obtain a red mud heterogeneous catalyst.

Further, the inert atmosphere is nitrogen or argon, and the inert atmosphere mainly prevents the reduced iron phase from being oxidized during the carbonization process.

Further, in the above step 1, the particle size of the red mud is 0.125-0.25 mm, and the particle size of the biomass is 0.125-0.25 mm.

Further, in the above step 1, uniformly mixing the red mud and the biomass includes the following steps: adding the biomass to the red mud several times, and sieving the mixture of the biomass and the red mud after adding the biomass each time, so that the red mud and the biomass are evenly mixed.

Further, the aperture of the sieve is larger than the particle diameter of the biomass and the particle diameter of the red mud, so that all the biomass particles and the red mud particles pass through the mesh, and during the sieving process, the red mud particles and the biomass particles pass randomly, so that the red mud and the biomass are evenly mixed.

Further, the mass of biomass added each time gradually decreased.

Further, uniformly mixing the red mud and the biomass includes the following steps: divide the biomass into 10 times, and the mass of the biomass added each time is 19%, 17%, 15%, 13%, 11%, 9%, 7%, 5%, 3% and 1% of the total mass of the biomass, first, mix the red mud and 19% of the biomass and sieve, mix the under-screen mixture with 17% of the biomass and sieve again, repeat the above steps until all the biomass is added to the red mud.

Further, in the above step 2, the heating temperature is 600-1000° C., and the heating rate is 5-10° C./min.

Further, for hydrogen peroxide or peracetic acid system, above-mentioned step 2 comprises the following steps:

Step 21: Raise the temperature to 150-250°C at a heating rate of 5-10°C/min, heat the mixture once, and keep it warm for 1-2 hours. At this stage, the pyrolysis of biomass produces acidic products that can neutralize the alkalinity of red mud;

Step 22: Raise the temperature to 800-1000°C at a heating rate of 5-10°C/min, heat the mixture after the first heating, and keep it warm for 1-2 hours. At this stage, the biomass is mainly carbonized into porous biochar with a benzene ring structure, and the iron oxide in the red mud is reduced to a low-priced iron phase.

Further, for persulfate system, above-mentioned step 2 comprises the following steps:

Raise the temperature to 800-1000°C at a heating rate of 8-10°C/min, heat and maintain the mixture, and keep it warm for 2-4 hours, so that more iron oxide in the red mud is reduced to a low-priced iron phase at high temperature.

Further, in the above step 3, the cleaning includes the following steps: sequentially cleaning the cooled reaction product with a cleaning solvent and deionized water.

Further, the cleaning solvent is one or more of methanol, ethanol, and acetone mixed in any proportion.

The present invention also provides a pollutant degradation method, comprising the steps of:

Step a: mixing red mud heterogeneous catalyst, organic pollutant aqueous solution and oxidizing agent;

Step b: performing a stirring reaction on the mixture obtained in step a, so that the organic pollutants in the organic pollutant aqueous solution are degraded.

Further, the above-mentioned oxidizing agent is hydrogen peroxide, peracetic acid or persulfate.

Further, the persulfate is ammonium persulfate, potassium persulfate, sodium persulfate or potassium persulfate.

Further, the organic pollutants include pesticides, antibiotics, dyes, polychlorinated biphenyls and/or phenolic compounds, and the concentration of the organic pollutants in the organic pollutant aqueous solution is 10-200 mg/L.

Further, the above step a includes the following steps: adding the heterogeneous red mud catalyst to the aqueous solution of organic pollutants, stirring for 10-60 minutes, and adding an oxidant to the heterogeneous red mud catalyst and the aqueous solution of organic pollutants.

Further, the red mud heterogeneous catalyst is used in an amount of 0.5-5 g per liter of the organic pollutant aqueous solution.

Further, the oxidizing agent is hydrogen peroxide, and the amount of hydrogen peroxide is 0.02-0.2 mol per liter of the organic pollutant aqueous solution.

Further, hydrogen peroxide is added step by step.

Further, part of the hydrogen peroxide is first added to the heterogeneous red mud catalyst and the aqueous solution of organic pollutants, and then the remaining hydrogen peroxide is added to the heterogeneous red mud catalyst and the aqueous solution of organic pollutants.

Further, the oxidizing agent is peracetic acid, and the dosage of peracetic acid is 0.5-5.0 mmol per liter of organic pollutant aqueous solution.

Further, peracetic acid is added step by step.

Further, part of the peracetic acid is firstly added to the heterogeneous red mud catalyst and the aqueous solution of organic pollutants, and then the remaining hydrogen peroxide is added to the heterogeneous red mud catalyst and the aqueous solution of organic pollutants.

Further, the oxidizing agent is persulfate, and the dosage of persulfate is 0.1-2.0 mmol per liter of organic pollutant aqueous solution.

Further, in the above step b, the stirring reaction time is 20-200 min.

Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

a) The red mud heterogeneous catalyst provided by the present invention is prepared by co-carbonization reaction using industrial waste residue (red mud) and waste biomass as raw materials. Specifically, the iron ions in iron oxide, the main component of red mud, are ferric ions, and the catalytic activity of ferric ions is low. During the co-carbonization of red mud and biomass, biomass carbonization can reduce some of the ferric ions in iron oxide to low-valence iron ions, thereby improving the catalytic activity of red mud and obtaining red mud heterogeneous catalysts.

b) The red mud heterogeneous catalyst provided by the present invention uses waste materials (red mud and waste biomass) as raw materials. Therefore, the above red mud heterogeneous catalyst has the characteristics of low cost and environmental friendliness.

c) The preparation method of the red mud heterogeneous catalyst provided by the present invention can increase the contact probability of the biomass and the red mud by adding the biomass into the red mud several times, thereby promoting the uniform mixing of the two.

d) The pollutant degradation method provided by the present invention utilizes low-valent iron in the red mud heterogeneous catalyst to react with an oxidizing agent to generate strong oxidizing hydroxyl radicals or sulfate radicals, thereby oxidizing and degrading organic pollutants in water. The degradation of organic pollutants by free radicals is non-selective, and strong oxidizing free radicals can basically degrade most of the organic pollutants, and the degree of mineralization of organic pollutants is relatively large.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and appended drawings.

Description of drawings

The drawings are for the purpose of illustrating specific embodiments only and are not to be considered as limitations of the invention, and like reference numerals refer to like parts throughout the drawings.

Fig. 1 is the scanning electron micrograph of the red mud heterogeneous catalyst that the embodiment 1 of the present invention makes;

Fig. 2 is the infrared spectrogram of the red mud heterogeneous catalyst prepared in Example 1 of the present invention;

Fig. 3 is the rhodamine b dye degradation ultraviolet-visible spectrogram of embodiment 6 of the present invention;

Fig. 4 is the ultraviolet-visible spectrogram of methylene blue dye degradation in Example 6 of the present invention.

Detailed ways

The preferred embodiments of the present invention will be specifically described below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with Embodiment 1 of the present invention to explain the principles of the present invention.

The invention provides a red mud heterogeneous catalyst, which is prepared by carbonizing red mud and biomass. The mass content of iron oxide in the red mud is 10%-30%, and the mass ratio of red mud to biomass is 5:1-1:2.

It should be noted that biomass refers to lignocellulosic waste biomass, such as straw, sawdust, fallen leaves, bagasse, coconut shell and/or livestock manure, and the total mass content of lignin, cellulose and hemicellulose in waste biomass exceeds 70%.

Compared with the prior art, the red mud heterogeneous catalyst provided by the present invention uses industrial waste residue (red mud) and waste biomass as raw materials and is prepared by co-carbonization reaction. Specifically, the iron ions in iron oxide, the main component of red mud, are ferric ions, and the catalytic activity of ferric ions is low. During the co-carbonization of red mud and biomass, biomass carbonization can reduce some of the ferric ions in iron oxide to low-valence iron ions, thereby improving the catalytic activity of red mud and obtaining red mud heterogeneous catalysts.

Taking the reaction of iron ions and hydrogen peroxide as an example, as shown in the reaction formula, the reaction rate of ferrous ions and hydrogen peroxide is three orders of magnitude higher than that of ferric ions.

Fe ²⁺ +H ₂ O ₂ →Fe ³⁺ +OH ^- + OH, k＝76M ^-1 S ^-1

Fe ³⁺ +H ₂ O ₂ →Fe ²⁺ +H ⁺ + OOH, k＝0.02M ^-1 S ^-1

In addition, since the above-mentioned red mud heterogeneous catalyst uses waste materials (red mud and waste biomass) as raw materials, the above-mentioned red mud heterogeneous catalyst has the characteristics of low cost and environmental friendliness.

The present invention also provides a preparation method of red mud heterogeneous catalyst, comprising the following steps:

Step 1: Mix red mud and biomass evenly to obtain a mixture;

Step 2: heating the mixture, and performing a carbonization reaction under an inert atmosphere (for example, nitrogen or argon), to obtain a reaction product;

Step 3: cooling, washing and drying the reaction product in sequence to obtain a red mud heterogeneous catalyst.

The reaction formula involved in the above-mentioned preparation method is as follows:

C+Fe ₂ O ₃ →Fe ₃ O ₄ +CO

CO+3Fe ₂ O ₃ →2Fe ₃ O ₄ +CO ₂

C+Fe ₃ O ₄ →3Fe ⁰ +4CO

Compared with the prior art, the beneficial effect of the preparation method of the red mud heterogeneous catalyst provided by the present invention is basically the same as that of the above-mentioned red mud heterogeneous catalyst, and will not be repeated here.

In order to improve the catalytic activity of the red mud heterogeneous catalyst, in the above step 1, the particle size of the red mud is 0.125-0.25 mm, and the particle size of the biomass is 0.125-0.25 mm. This is because the particle size of red mud and biomass is too large, and the specific surface area of the two is small, which will reduce the contact between red mud and biomass, and the carbonization reaction is insufficient. Moreover, using larger particles of red mud and biomass as raw materials, the specific surface area of the prepared red mud heterogeneous catalyst is relatively small, and the catalytic activity is low; while the particle size of red mud and biomass is too small, the particle size of the prepared red mud heterogeneous catalyst is too small, which will lead to difficulties in the separation and recovery of the red mud heterogeneous catalyst during use. Limiting the particle size of red mud and biomass within the above range can further increase the adequacy of the carbonization reaction of red mud and biomass on the basis of ensuring that the red mud heterogeneous catalyst can be effectively separated and recovered, and improve the catalytic activity of the red mud heterogeneous catalyst.

In order to realize the uniform mixing of red mud and biomass, in the above step 1, uniform mixing of red mud and biomass includes the following steps: adding biomass to red mud several times, and sieving the mixture of biomass and red mud after adding biomass each time, so that red mud and biomass are evenly mixed. By adding the biomass to the red mud several times, the contact probability of the biomass and the red mud can be increased, thereby promoting the uniform mixing of the two.

It should be noted that after each addition of biomass, the mixture of biomass and red mud is sieved. The sieve aperture is larger than the particle size of biomass and red mud, so that all biomass particles and red mud particles pass through the sieve holes. During the sieving process, red mud particles and biomass particles pass through randomly, so that the red mud and biomass are mixed evenly.

In order to further improve the mixing uniformity of red mud and biomass, according to the sequence of biomass addition, the quality of biomass added each time was gradually reduced. This is because, at the initial stage of mixing, the content of red mud in the mixture is high, and the addition of biomass can contact with most of the red mud to achieve uniform mixing. As the mixing progresses, the quality of the mixture increases, and the content of red mud in the mixture decreases, reducing the amount of biomass added each time, which can further improve the mixing uniformity of red mud and biomass on the basis of ensuring the mixing efficiency.

Exemplarily, the uniform mixing of red mud and biomass includes the following steps: divide the biomass into 10 times, and the mass of biomass added each time is 19%, 17%, 15%, 13%, 11%, 9%, 7%, 5%, 3% and 1% of the total mass of biomass. First, mix the red mud and 19% of the biomass, and add it to a 60-mesh sieve (the mesh size is 0.25mm) for a sieve. The mixed materials were added to a 60-mesh sieve (0.25 mm in mesh size) for secondary sieving, and the above steps were repeated until all the biomass was added to the red mud, thereby obtaining a uniformly mixed mixture of red mud and biomass.

In order to control the reaction rate of the carbonization reaction, in the above step 2, the heating temperature is 600-1000° C., and the heating rate is 5-10° C./min.

It should be noted that the above red mud heterogeneous catalyst is mainly used for the degradation of organic pollutants. During the degradation process of organic pollutants, it needs to cooperate with hydrogen peroxide, peracetic acid or persulfate to generate free radicals. For subsequent applications (hydrogen peroxide or peracetic acid), different carbonization processes are required in step 2.

Specifically, for hydrogen peroxide or peracetic acid system, above-mentioned step 2 comprises the following steps:

Step 21: Raise the temperature to 150-250°C at a heating rate of 5-10°C/min, heat the mixture once, and keep it warm for 1-2 hours. At this stage, the pyrolysis of biomass produces acidic products that can neutralize the alkalinity of red mud;

Step 22: Raise the temperature to 800-1000°C at a heating rate of 5-10°C/min, heat the mixture after the first heating, and keep it warm for 1-2 hours. At this stage, the biomass is mainly carbonized into porous biochar with a benzene ring structure, and the iron oxide in the red mud is reduced to a low-valent iron phase (ferric oxide or zero-valent iron).

For persulfate system, above-mentioned step 2 comprises the following steps:

Raise the temperature to 800-1000°C at a heating rate of 8-10°C/min, heat and maintain the mixture, and keep it warm for 2-4 hours, so that more iron oxide in the red mud is reduced to a low-valent iron phase (ferric oxide or zero-valent iron) at high temperature.

In order to remove biomass pyrolysis products and soluble salts (for example, sodium salts) remaining on the surface of the prepared red mud heterogeneous catalyst, in the above step 3, the cleaning includes the following steps: sequentially using a cleaning solvent and deionized water to clean the cooled reaction product, and the cleaning solvent is one or more of methanol, ethanol, and acetone mixed in any proportion.

The present invention also provides a pollutant degradation method, comprising the steps of:

Step a: mixing the red mud heterogeneous catalyst, an aqueous solution of organic pollutants, and an oxidizing agent, wherein the oxidizing agent is one of hydrogen peroxide, peracetic acid, and persulfate (for example, ammonium persulfate, potassium persulfate, sodium persulfate, potassium persulfate);

Step b: performing a stirring reaction on the mixture obtained in step a, so that the organic pollutants in the organic pollutant aqueous solution are degraded.

Compared with the prior art, the beneficial effect of the pollutant degradation method provided by the present invention is basically the same as that of the above-mentioned red mud heterogeneous catalyst, which will not be repeated here.

It should be noted that the above pollutant degradation method utilizes the low-valent iron in the red mud heterogeneous catalyst to react with the oxidant to generate strong oxidizing hydroxyl radicals or sulfate radicals, thereby oxidatively degrading organic pollutants in water. Free radicals are non-selective for the degradation of organic pollutants. Strong oxidizing free radicals can basically degrade most organic pollutants, and the mineralization degree of organic pollutants is relatively large.

For example, the organic pollutants include pesticides, antibiotics, dyes, polychlorinated biphenyls and/or phenolic compounds, and the concentration of the organic pollutants in the organic pollutant aqueous solution is 10-200 mg/L.

For the mixing sequence of the red mud heterogeneous catalyst, the organic pollutant aqueous solution and the oxidant, specifically, the above step a includes the following steps: adding the red mud heterogeneous catalyst to the organic pollutant aqueous solution, stirring for 10-60 minutes, and adding the oxidant to the red mud heterogeneous catalyst and the organic pollutant aqueous solution. This is because the red mud heterogeneous catalyst has a large specific surface area and contains porous biochar, which can adsorb organic pollutants, and the adsorption can effectively promote surface catalytic degradation of organic pollutants.

As for the dosage of the red mud heterogeneous catalyst, specifically, the dosage of the red mud heterogeneous catalyst is 0.5-5 g per liter of the organic pollutant aqueous solution. This is because the amount of heterogeneous red mud catalyst used is too small, the catalytic effect is poor, and the amount of heterogeneous red mud catalyst used is large, which will consume part of the active free radicals, which will also reduce the catalytic efficiency, and the large amount of heterogeneous red mud catalyst will increase the process cost.

Exemplarily, the oxidizing agent is hydrogen peroxide, and the amount of hydrogen peroxide used is 0.02-0.2 mol per liter of the organic pollutant aqueous solution. This is because the consumption of hydrogen peroxide is small, and the catalytic effect is poor, and the consumption of hydrogen peroxide is large, and self-decomposition into water and oxygen will occur, which cannot produce substantial catalytic effect.

In order to further increase the amount of hydrogen peroxide, hydrogen peroxide is added step by step. Specifically, part of the hydrogen peroxide (for example, 60% of the total mass of hydrogen peroxide) is added to the red mud heterogeneous catalyst and the aqueous solution of organic pollutants, and then the remaining hydrogen peroxide is added to the heterogeneous red mud catalyst and the aqueous solution of organic pollutants, thereby improving the utilization rate of hydrogen peroxide.

For oxidant is peracetic acid, in every liter of organic pollutant aqueous solution, the consumption of peracetic acid is 0.5～5.0mmol, and the consumption of peracetic acid is little, and catalytic effect is poor, and the consumption of peracetic acid is many, and side reaction will occur and cause the utilization efficiency of peracetic acid to be low.

Similarly, in order to improve the utilization rate of peracetic acid, peracetic acid is added step by step. Specifically, first part of peracetic acid (for example, 60% of the total mass of hydrogen peroxide) is added to the heterogeneous red mud catalyst and the aqueous solution of organic pollutants, and then the remaining hydrogen peroxide is added to the heterogeneous catalyst of red mud and the aqueous solution of organic pollutants, thereby improving the utilization rate of peracetic acid.

It should be noted that the oxidant (hydrogen peroxide or peracetic acid) is added step by step. First, part of the oxidant (high concentration and/or large amount of addition) is added to the red mud heterogeneous catalyst and the aqueous solution of organic pollutants, and then the remaining hydrogen peroxide (low concentration and/or small amount of addition) is added to the red mud heterogeneous catalyst and the aqueous solution of organic pollutants. Due to the high initial concentration of organic pollutants in the solution, more oxidants are needed to react to generate active free radicals for oxidative degradation. After a certain degree of reaction, the concentration of organic pollutants is significantly reduced, and then add low concentration or small amount of oxidants to fully degrade the residual organic pollutants in the solution. Adding the oxidant step by step can improve the utilization rate of the oxidant and reduce the impact of the residual oxidant in the solution on the water quality after the reaction.

For example, to degrade the same amount of organic pollutants, in the prior art, the oxidant is added in one step, and the amount of oxidant is 100ml. The oxidant is added step by step in the present invention, only 80ml is needed. The specific addition method is: first add 60% of the total mass of the oxidant (that is, 48ml) to the red mud heterogeneous catalyst and the aqueous solution of organic pollutants, and then add 40% of the remaining total mass of the oxidant (that is, 32ml) to the red mud heterogeneous catalyst and the aqueous solution of organic pollutants, so as to complete the step by step of the oxidant add.

If the oxidant is persulfate, the dosage of persulfate is 0.1-2.0 mmol per liter of organic pollutant aqueous solution. This is because the consumption of persulfate is small, the catalytic effect is poor, and the consumption of persulfate is large, side reactions will occur, resulting in low utilization efficiency of persulfate.

In order to further improve the degradation of organic pollutants, in the above step b, the stirring reaction time is 20-200 min. Limiting the stirring reaction time within the above-mentioned range can appropriately shorten the stirring reaction time on the basis of ensuring sufficient degradation of organic pollutants, thereby reducing the operating cost of the process.

Example 1

The red mud heterogeneous catalyst used in this embodiment has a particle size of 0.125mm and a biomass particle size of 0.15mm. The preparation method of the red mud heterogeneous catalyst is as follows:

Step 1: uniformly mix red mud and biomass to obtain a mixture, the mass ratio of red mud and biomass is 5:1;

Step 2: Raise the temperature to 200°C at a heating rate of 5°C/min, heat the mixture once, and keep it warm for 1h; raise the temperature to 1000°C at a heating rate of 10°C/min, heat the mixture after the first heating, and keep it warm for 1.5h to obtain the reaction product;

Step 3: cooling the reaction product in sequence, washing with ethanol and deionized water, and drying to obtain a red mud heterogeneous catalyst. The yield of the catalyst is 83.67%, and the particle size of the catalyst is 0.125-0.15mm. The catalyst has a large specific surface area and porous structure (see Figure 1). The infrared spectrum analysis of the catalyst shows that the biochar is rich in oxygen-containing functional groups (see Figure 2). The large specific surface area and oxygen-containing functional groups can promote the surface adsorption of organic pollutants.

Example 2

The red mud heterogeneous catalyst used in this embodiment has a particle size of 0.15 mm and a biomass particle size of 0.25 mm. The preparation method of the red mud heterogeneous catalyst is as follows:

Step 1: uniformly mix red mud and biomass to obtain a mixture, the mass ratio of red mud and biomass is 1:1;

Step 2: Raise the temperature to 250°C at a heating rate of 10°C/min, heat the mixture once, and keep it warm for 1.5h; raise the temperature to 800°C at a heating rate of 8°C/min, heat the mixture after the first heating, and keep it warm for 2h to obtain the reaction product;

Step 3: cooling the reaction product in sequence, washing with methanol and deionized water, and drying to obtain a red mud heterogeneous catalyst. The yield of the catalyst is 67.48%, and the particle size of the catalyst is 0.125-0.15mm.

Example 3

The red mud heterogeneous catalyst used in this embodiment has a particle size of 0.25 mm and a biomass particle size of 0.125 mm. The preparation method of the red mud heterogeneous catalyst is as follows:

Step 1: Mix red mud and biomass evenly to obtain a mixture, the mass ratio of red mud and biomass is 1:2;

Step 2: Raise the temperature to 150°C at a heating rate of 7°C/min, heat the mixture once, and keep it for 2 hours; raise the temperature to 920°C at a heating rate of 5°C/min, heat the mixture after the first heating, and keep it for 1 hour to obtain a reaction product;

Step 3: cooling the reaction product in sequence, washing with ethanol and deionized water, and drying to obtain a red mud heterogeneous catalyst. The yield of the catalyst is 58.34%, and the particle diameter of the catalyst is 0.125-0.15mm.

Example 4

The red mud heterogeneous catalyst used in this embodiment has a particle size of 0.23 mm and a biomass particle size of 0.20 mm. The preparation method of the red mud heterogeneous catalyst is as follows:

Step 1: uniformly mix red mud and biomass to obtain a mixture, the mass ratio of red mud and biomass is 3:1;

Step 2: heating up to 980°C at a heating rate of 8°C/min, heating and maintaining the mixture, and keeping it warm for 2 hours to obtain a reaction product;

Step 3: cooling the reaction product in sequence, washing with ethanol and deionized water, and drying to obtain a red mud heterogeneous catalyst. The yield of the catalyst is 81.64%, and the particle size of the catalyst is 0.2-0.23mm.

Example 5

The red mud heterogeneous catalyst used in this embodiment has a particle size of 0.2 mm and a biomass particle size of 0.15 mm. The preparation method of the red mud heterogeneous catalyst is as follows:

Step 1: uniformly mix red mud and biomass to obtain a mixture, the mass ratio of red mud and biomass is 2:1;

Step 2: heat up to 800°C at a heating rate of 10°C/min, heat and maintain the mixture, and keep it warm for 1 hour to obtain a reaction product;

Step 3: cooling the reaction product in sequence, washing with ethanol and deionized water, and drying to obtain a red mud heterogeneous catalyst. The yield of the catalyst is 57.66%, and the particle size of the catalyst is 0.15-0.2 mm.

Example 6

The pollutant degradation method of the present embodiment adopts the red mud heterogeneous catalyst of embodiment 1, and the pollutant degradation method comprises the following steps:

Step a: first add part of the hydrogen peroxide to the red mud heterogeneous catalyst and the organic pollutant aqueous solution, and then add the remaining hydrogen peroxide to the red mud heterogeneous catalyst and the organic pollutant aqueous solution. For each liter of the organic pollutant aqueous solution, the amount of the red mud heterogeneous catalyst is 1 g, and the amount of hydrogen peroxide is 0.05 mol;

Step b: Stirring and reacting the mixture obtained in step a for 50 minutes, so that the organic pollutants in the organic pollutant aqueous solution are degraded. Among them, acid orange dye (concentration is 10mg/L) degradation rate is 90.46%; rhodamine b dye (concentration is 10mg/L) degradation rate is 98.79%; methylene blue dye (concentration is 10mg/L) degradation rate is 99.77%; total organic carbon removal rate is greater than 78.4%. The maximum characteristic adsorption peaks of acid orange, rhodamine b, and methylene blue dyes decreased significantly, indicating that the dye molecules were degraded (see Figures 3-4).

Example 7

The pollutant degradation method of the present embodiment adopts the red mud heterogeneous catalyst of embodiment 1, and the pollutant degradation method comprises the following steps:

Step a: first add part of the hydrogen peroxide to the red mud heterogeneous catalyst and the organic pollutant aqueous solution, and then add the remaining hydrogen peroxide to the red mud heterogeneous catalyst and the organic pollutant aqueous solution. For each liter of the organic pollutant aqueous solution, the amount of the red mud heterogeneous catalyst is 4.5g, and the amount of hydrogen peroxide is 0.18mol;

Step b: Stirring and reacting the mixture obtained in step a for 150 min, so that the organic pollutants in the organic pollutant aqueous solution are degraded. The degradation rate of tetracycline (concentration is 10 mg/L) is 89.86%, the degradation rate of carbamazepine (concentration is 10 mg/L) is 86.54%; the degradation rate of methylene blue dye (concentration is 200 mg/L) is 86.12%; the total organic carbon removal rate is greater than 50.8%.

Example 8

The pollutant degradation method of the present embodiment adopts the red mud heterogeneous catalyst of embodiment 2, and the pollutant degradation method comprises the following steps:

Step a: first add part of peracetic acid to the red mud heterogeneous catalyst and the organic pollutant aqueous solution, and then add the remaining hydrogen peroxide to the red mud heterogeneous catalyst and the organic pollutant aqueous solution. For each liter of the organic pollutant aqueous solution, the amount of the red mud heterogeneous catalyst is 3.2 g, and the amount of peracetic acid is 0.8 mol;

Step b: Stirring and reacting the mixture obtained in step a for 200 min, so that the organic pollutants in the organic pollutant aqueous solution are degraded. Tetracycline (concentration is 10mg/L) degradation rate is 87.24%, 4-chlorobiphenyl (concentration is 10mg/L) degradation rate is 91.24%; Rhodamine b dye (concentration is 40mg/L) degradation rate is 95.75%; Total organic carbon removal rate is greater than 65.8%.

Example 9

The pollutant degradation method of the present embodiment adopts the red mud heterogeneous catalyst of embodiment 2, and the pollutant degradation method comprises the following steps:

Step a: first add part of peracetic acid to the red mud heterogeneous catalyst and the organic pollutant aqueous solution, and then add the remaining hydrogen peroxide to the red mud heterogeneous catalyst and the organic pollutant aqueous solution. For each liter of the organic pollutant aqueous solution, the amount of the red mud heterogeneous catalyst is 2.0 g, and the amount of peracetic acid is 4.5 mol;

Step b: Stirring and reacting the mixture obtained in step a for 30 minutes, so that the organic pollutants in the organic pollutant aqueous solution are degraded. Ofloxacin (concentration is 20mg/L) degradation rate is 96.47%; Ciprofloxacin (concentration is 10mg/L) degradation rate is 98.47%; Phenol (concentration is 50mg/L) degradation rate is 95.44%; Tribromophenol (concentration is 10mg/L) degradation rate is 92.15%;

Example 10

The pollutant degradation method of the present embodiment adopts the red mud heterogeneous catalyst of embodiment 5, and the pollutant degradation method comprises the following steps:

Step a: mix the red mud heterogeneous catalyst, the organic pollutant aqueous solution and sodium persulfate, the amount of the red mud heterogeneous catalyst is 4.1 g, and the amount of peracetic acid is 0.2 mol in every liter of the organic pollutant aqueous solution;

Step b: Stirring and reacting the mixture obtained in step a for 100 min, so that the organic pollutants in the organic pollutant aqueous solution are degraded. The degradation rate of methylene blue (80mg/L) was 98.27%; the degradation rate of atrazine (10mg/L) was 96.49%; the degradation rate of phenol (20mg/L) was 99.34%; the total organic carbon removal rate was greater than 72.14%.

Example 11

The pollutant degradation method of the present embodiment adopts the red mud heterogeneous catalyst of embodiment 5, and the pollutant degradation method comprises the following steps:

Step a: mix the red mud heterogeneous catalyst, the organic pollutant aqueous solution and ammonium persulfate, the amount of the red mud heterogeneous catalyst is 3.5 g, and the amount of peracetic acid is 1.6 mol per liter of the organic pollutant aqueous solution;

Step b: Stirring and reacting the mixture obtained in step a for 150 min, so that the organic pollutants in the organic pollutant aqueous solution are degraded. Rhodamine b (concentration is 30mg/L) degradation rate is 95.77%; Carbamazepine (concentration is 20mg/L) degradation rate is 87.99%; 4-chlorobiphenyl (concentration is 20mg/L) degradation rate is 92.67%; Total organic carbon removal rate is greater than 62.94%.

The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily imagined by those skilled in the art within the technical scope disclosed in the present invention shall be covered within the scope of protection of the present invention.

Claims (6)

1. The preparation method of the red mud heterogeneous catalyst used for degrading organic pollutants and matched with a hydrogen peroxide or peracetic acid system is characterized by comprising the following steps:

step 1: adding biomass into red mud for multiple times, and sieving a mixture of the biomass and the red mud after each time of adding the biomass to uniformly mix the red mud and the biomass to obtain a mixture;

the mass content of ferric oxide in the red mud is 10% -30%, and the mass ratio of the red mud to the biomass is 5:1-1:2;

the pore diameter of the sieved sieve is larger than the particle diameter of the biomass and the particle diameter of the red mud, so that all the biomass particles and the red mud particles pass through the sieve pores, and in the sieving process, the red mud particles and the biomass particles randomly pass through, so that the red mud and the biomass are uniformly mixed;

step 2: the carbonization process is as follows: heating to 150-250 ℃ at a heating rate of 5-10 ℃/min, heating the mixture once, and preserving heat for 1-2 h, wherein the acid product generated by biomass pyrolysis can neutralize the alkalinity of red mud;

heating to 800-1000 ℃ at a heating rate of 5-10 ℃/min, carrying out secondary heating on the mixture after primary heating, and preserving heat for 1-2 hours, carbonizing biomass into porous biochar with benzene ring structure, and reducing ferric oxide in red mud into a low-valence iron phase to obtain a reaction product;

step 3: cooling, cleaning and drying the reaction product in sequence to obtain a red mud heterogeneous catalyst;

the biomass is lignocellulose waste biomass, and the total mass content of lignin, cellulose and hemicellulose in the waste biomass exceeds 70%;

iron ions in ferric oxide which is a main component of the red mud are ferric ions, and in the process of the co-carbonization of the red mud and biomass, the biomass carbonization reduces the ferric ions in part of the ferric oxide into iron ions in a low valence state;

in the step 1, the particle size of the red mud is 0.125-0.25 mm, and the particle size of the biomass is 0.125-0.25 mm.

2. The method for preparing the heterogeneous catalyst of red mud for degrading organic pollutants, which is used in combination with hydrogen peroxide or peroxyacetic acid system according to claim 1, wherein in the step 1, the red mud and biomass are uniformly mixed, and the method comprises the following steps: the biomass is divided into 10 times, the mass of the biomass added each time is 19%, 17%, 15%, 13%, 11%, 9%, 7%, 5%, 3% and 1% of the total mass of the biomass in sequence, firstly, the red mud and 19% of the biomass are mixed and screened, the undersize mixture and 17% of the biomass are mixed and screened again, and the steps are repeated until the biomass is fully added into the red mud.

3. A method for degrading pollutants, characterized in that the red mud heterogeneous catalyst prepared by the preparation method of claim 1 or 2 is adopted, and the degradation method comprises the following steps:

step a: mixing a red mud heterogeneous catalyst, an organic pollutant aqueous solution and an oxidant;

step b: and c, stirring the mixture obtained in the step a for reaction so that the organic pollutants in the organic pollutant aqueous solution are degraded.

4. The pollutant degradation method according to claim 3, wherein the amount of the red mud heterogeneous catalyst used is 0.5-5 g per liter of the organic pollutant aqueous solution.

5. A contaminant degradation method according to claim 3, wherein the oxidizing agent is hydrogen peroxide or peracetic acid.

6. The pollutant degradation method according to claim 5, wherein the oxidant is hydrogen peroxide, and the amount of hydrogen peroxide is 0.02-0.2 mol per liter of the organic pollutant aqueous solution;

or the oxidant is peracetic acid, and the consumption of the peracetic acid in each liter of the organic pollutant aqueous solution is 0.5-5.0 mmol.