CN116237048B - Preparation method and application of magnetic nitrided biochar catalytic material based on steel rolling pickling waste liquid - Google Patents

Abstract

The invention discloses a preparation method of a magnetic nitriding biochar catalytic material based on steel rolling pickling waste liquid, which comprises the following steps: pyrolyzing the mixed powder of urea and corncob under the protection of nitrogen, and cooling to obtain black nitriding biochar powder; adding an oxidant into the steel rolling pickling waste liquid, adjusting the molar ratio of Fe ³⁺ to Fe ²⁺ to obtain yellow green pickling waste liquid, adding black nitriding biochar powder, and uniformly stirring to obtain mixed liquid of nitriding biochar and pickling waste liquid; adding a precipitant into the mixed liquid until the pH value reaches 7-13, stopping stirring to ensure that Fe ₃O₄ crystals are completely developed, and finally performing magnetic separation to obtain the black magnetic nitriding biochar catalytic material. The prepared magnetic nitriding biochar material is applied to the treatment process of organic wastewater, plays a synergistic effect of nano-scale Fe ₃O₄ and the biochar material modified by nitrogen, realizes the green development goal of treating waste with waste, and has higher economic value and social value.

Description

A method for preparing magnetic nitrided biochar catalytic material based on steel mill pickling wastewater and its application

Technical Field

The invention belongs to the technical field of resource conservation and environmental governance, and relates to a method for preparing a magnetic nitrided biochar catalytic material based on steel rolling pickling waste liquid, and application of the catalytic material in wastewater containing organic pollutants such as tetracycline.

Background Art

Steel mill pickling waste liquid is waste acid liquid generated during the rolling process of steel components. It is a kind of hazardous industrial wastewater that is difficult to treat and highly corrosive. It contains a large amount of iron ions and a small amount of other metal ions such as zinc, calcium, magnesium, and manganese. It is a valuable secondary resource. Traditional treatment methods such as neutralization and precipitation can achieve harmless treatment of pickling waste liquid, but it will produce a large amount of iron-containing sludge, which not only poses a risk of secondary pollution, but also causes a waste of iron resources. At present, although pickling sludge can be returned to the steel smelting process as a sintering or pelletizing ingredient after treatment, it has certain significance in terms of resource recycling, but the level of high-value utilization of valuable materials such as iron elements still needs to be improved.

Nano Fe ₃ O ₄ is an emerging magnetic material. It is widely used in water treatment due to its unique structural characteristics and excellent magnetic properties. It shows excellent adsorption or catalytic effects in removing heavy metals and organic matter. However, the traditional preparation method of nano Fe ₃ O ₄ relies on the use of pure iron salt reagents such as FeCl ₂ and FeSO ₄ , which has high production and use costs, severely limiting its large-scale application in industry. If the large amount of iron in the steel mill pickling waste liquid is utilized as the raw material for the production of nano Fe ₃ O ₄ , it can not only realize the green and low-cost preparation of nano Fe ₃ O ₄ materials, but also explore a path for high-value resource utilization based on the harmless treatment of pickling waste liquid.

However, nano-Fe ₃ O ₄ often has the problem of agglomeration due to its small particle size, which reduces the specific surface area of the material and also affects the number of active sites in the reaction process. If nano-Fe ₃ O ₄ is compounded with other materials or its surface is modified, its ability to remove and degrade industrial pollutants can be further improved.

In view of this, the present invention is proposed.

Summary of the invention

The technical problem solved by the present invention is to provide a method for preparing a magnetic nitrided biochar catalytic material based on steel mill pickling waste liquid and its application, and the main purposes are three points: (1) to provide a new idea for the harmless treatment of steel mill pickling waste liquid; (2) to recycle the iron ions in the steel mill pickling waste liquid, thereby saving resources and reducing the preparation cost of _{Fe3O4 materials} ; (3) to improve the agglomeration phenomenon of nano _{- Fe3O4} , and give play to the synergistic effect of nitrided biochar materials and nano _{- Fe3O4} in the treatment of organic wastewater.

In order to solve the above technical problems, the present invention provides the following technical solutions:

A method for preparing a magnetic nitrided biochar catalytic material based on steel rolling pickling waste liquid, the method comprising the following steps:

(1) dissolving urea in deionized water, adding corncob powder, and stirring to obtain a turbid mixed solution of urea and corncob;

(2) placing the turbid liquid in step (1) in a constant temperature water bath for stirring, and then drying and grinding in sequence to obtain a mixed powder of urea and corn cob;

(3) placing the mixed powder obtained in step (2) in a tubular furnace, pyrolyzing it under the protection of nitrogen, and obtaining black nitrided biochar powder after cooling;

(4) washing the black nitrided biochar powder obtained in step (3), filtering and separating the powder, drying and grinding the powder for later use;

(5) adding an oxidant to the steel rolling pickling waste liquid, adjusting the molar ratio of Fe ³⁺ to Fe ²⁺ , obtaining a yellow-green pickling waste liquid, adding the black nitrided biochar powder obtained in step (4) to the yellow-green pickling waste liquid, stirring evenly to obtain a mixed liquid of the nitrided biochar and the pickling waste liquid;

(6) stirring the mixed liquid obtained in step (5) at a certain temperature, adding a precipitant until the pH value reaches 7 to 13, and then stopping, so that Fe ³⁺ and Fe ²⁺ undergo a co-precipitation reaction, and Fe ₃ O ₄ nanoparticles are generated on the surface and inside of the nitrided biochar;

(7) In the absence of protective gas, the mixed liquid obtained in step (6) is transferred into a stirrer at a higher temperature to allow the Fe ₃ O ₄ crystals to fully develop, and a black paste-like liquid is obtained after stirring;

(8) The black paste obtained in step (7) is subjected to magnetic separation, and the obtained precipitate is washed, dried and ground in sequence to obtain a black magnetic nitrided biochar catalytic material.

In recent years, biochar materials have received great attention as active catalysts in the field of water environment management. The raw materials are widely available and cheap, and they have a large specific surface area, rich pore structure and diverse surface groups. They are sustainable green catalytic materials. When used as a carrier to fix and disperse nanoparticles of other catalysts, the resulting composite material can combine the advantages of biochar and metal degradation of organic matter, increase the active sites for the generation of free radicals and electron transfer, increase the reaction rate of the entire system, reduce the leaching of metal catalysts, and improve the material's reusability. In addition, the introduction of nitrogen atoms can significantly change the physical and chemical properties of carbon materials and enhance their catalytic activity. Nitrogen atoms with higher electronegativity can induce electrons to transfer from neighboring carbon atoms to themselves, thereby changing the charge density of local carbon atoms, making the charge distribution of adjacent carbon atoms different, improving the transfer efficiency of electrons, and breaking the chemical inertness of the material itself.

The present invention uses steel rolling pickling waste liquid and cheap and easily available urea and corn cobs as raw materials, and adopts a chemical co-precipitation method to load the generated nano _Fe3O4 particles on the skeleton of nitrided biochar. The prepared magnetic nitrided biochar material can be used as a persulfate activator in the degradation process of high- _{concentration} tetracycline wastewater, and has the advantages of low raw material cost, efficient and stable catalytic process, and easy recycling.

Preferably, in step (1), the mass ratio of urea to corn cob powder is (1-4):1, wherein the urea is a nitrogen source and the corn cob powder is a carbon source.

Preferably, in step (2), the temperature of the constant temperature water bath is 20-30°C, the stirring speed is 500-700 r/min, the stirring time is 4-6 hours, the drying temperature is 70-80°C, and the drying time is 8-12 hours. The functions of stirring and the constant temperature water bath are to quickly and fully impregnate the urea into the biomass.

Preferably, in step (3), the temperature is raised to the pyrolysis temperature at a rate of 4 to 6°C/min, the pyrolysis temperature is 500 to 900°C, and the pyrolysis time is 1 to 1.5 hours.

Preferably, in step (4), the black powder obtained in step (3) is ultrasonically cleaned in dilute sulfuric acid and anhydrous ethanol for 30 minutes to remove ash, tar and other substances, washed with deionized water, filtered and separated, and then dried and ground for later use.

Preferably, in step (5), the oxidant is H ₂ O ₂ . At a certain temperature, the redox potential value of the pickling waste liquid is linearly related to the molar ratio of different iron ions. By adjusting the redox potential of the pickling waste liquid between 471-491 mV, n(Fe ³⁺ ):n(Fe ²⁺ ) is (1-1.8):1. The mass ratio of the generated Fe ₃ O ₄ to the added nitrided biochar is 1:(0.25-5).

According to the above reaction equation, the molar ratio of Fe ³⁺ to Fe ²⁺ ions in the coprecipitation reaction is 2:1. Divalent iron is easily oxidized under the condition of no protective gas, so n(Fe ³⁺ ):n(Fe ²⁺ ) is limited to (1-1.8):1.

Preferably, in step (6), the mixed liquid obtained in step (5) is heated to 45-55°C, and a precipitant is quickly added until the pH value reaches 5, and Fe2 ⁺ begins to precipitate. The precipitant is added dropwise to reduce the co-precipitation reaction rate, so that Fe3 ⁺ and Fe2 ⁺ slowly react on the surface of the nitrided biochar to generate nano-sized _Fe3O4 with uniform particle size _. The addition of the precipitant is stopped after the pH value reaches 7-13. Preferably, the precipitant is a 2 mol/L NaOH solution.

Preferably, in step (7), the stirrer speed is 500-1000 r/min, the stirring temperature is 50-90° C., and the stirring time is 15-120 min, so that Fe ³⁺ and Fe ²⁺ react fully with the alkali source and the Fe ₃ O ₄ crystals develop more perfectly.

Preferably, in step (8), magnetic separation is performed by adsorption using a permanent magnet across the container, and then the water is poured out to achieve separation.

The present invention also provides a magnetic nitrided biochar catalytic material obtained by the preparation method, wherein the material is a composite material of nano Fe ₃ O ₄ and nitrided biochar.

The present invention also provides the use of the magnetic nitrided biochar catalytic material in the treatment of organic wastewater, especially using it as a persulfate activator in the treatment of tetracycline wastewater. The catalytic material has the advantages of large specific surface area, sufficient active sites, high pollutant degradation efficiency, safe and stable catalytic process, easy recycling and reuse, and no secondary pollution.

Compared with the prior art, the present invention has the following beneficial effects:

(1) Nitrided biochar materials were prepared using cheap and readily available corn cobs as raw materials and urea as a nitrogen source for doping and modification. This significantly improved the catalytic performance of the carbon materials and increased the number of reactive sites dominated by edge nitrogen, providing new ideas for the reuse of waste biomass.

(2) The iron ions in the steel mill pickling wastewater were used as the raw material for preparing nano-Fe ₃ O ₄ magnetic particles, so that the nano-Fe ₃ O ₄ was dispersed and loaded on the surface of the nitrided biochar material during the crystallization process. While giving the nitrided biochar material magnetic properties, it also significantly improved the agglomeration problem of nano-Fe ₃ O ₄ .

(3) The prepared magnetic nitrided biochar material is applied to the treatment of organic wastewater, giving full play to the synergistic effect of nano-Fe ₃ O ₄ and nitrogen-modified biochar material, achieving the green development goal of "waste treatment with waste", which has high economic and social value.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

FIG1 is a SEM image of the magnetic nitrided biochar material of Example 1 of the present invention;

FIG2 is a VSM diagram of the magnetic nitrided biochar material of Example 1 of the present invention;

FIG3 is a pore structure diagram of the magnetic nitrided biochar material of Example 1 of the present invention;

FIG4 is a diagram showing the degradation effect of the magnetic nitrided biochar material of Example 1 of the present invention on tetracycline at different pH values;

FIG5 is a diagram showing the degradation effect of the magnetic nitrided biochar material of Example 1 of the present invention after four cycles of use;

FIG6 is a tetracycline degradation curve of magnetic biochar powder with different nitrogen contents in Comparative Example 1 of the present invention.

DETAILED DESCRIPTION

The following will describe the technical solutions and technical problems solved in the embodiments of the present invention in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them.

Example 1

(1) Weigh 3 g of urea into a beaker, add 50 ml of deionized water, and stir in an ultrasonic instrument to dissolve. Weigh 1 g of corncob powder and add it to the dissolved urea solution so that the mass ratio of urea to corncob in the solution is 3:1, and a turbid mixed solution of urea and corncob is obtained.

(2) The urea and corncob mixed turbid liquid was placed in a constant temperature water bath magnetic stirrer at 25°C, stirred at a speed of 600 r/min for 5 hours, taken out and placed in a drying oven at 70°C for 10 hours, and then fully ground for use to obtain a urea and corncob mixed powder.

(3) Add 20 g of corn cob urea mixed powder into a 40 ml corundum crucible and place it in a tubular furnace. Under the protection of nitrogen, heat it to 900 °C at a rate of 5 °C/min, keep it at that temperature for 1 h, and then cool it to room temperature with the furnace to obtain black nitrided biochar powder.

(4) The nitrided biochar powder was ultrasonically cleaned in dilute sulfuric acid and anhydrous ethanol for 30 min to remove ash, tar and other substances, washed with deionized water, filtered and separated, dried and ground for later use.

(5) Add an appropriate amount of H ₂ O ₂ to the steel mill pickling waste liquid, adjust the redox potential to 481 mV, make n(Fe ³⁺ ):n(Fe ^{2 +} ) to 1.4:1, and obtain a yellow-green pickling waste liquid. Add the nitride biochar powder obtained in step (4) to the yellow-green pickling waste liquid, make the mass ratio of the generated Fe ₃ O ₄ to the added nitrided biochar to 1:1, and stir for 1 hour to obtain a mixed liquid of nitrided biochar and pickling waste liquid.

(6) The mixed liquid was heated to 50° C., and 2 mol/L NaOH solution was quickly added to the mixed liquid until the pH value reached 5, and then the solution was slowly added dropwise until the pH value reached 11 and stopped.

(7) The liquid obtained in step (6) is transferred to a stirrer at 50-90° C., the rotation speed is adjusted to 500-1000 r/min, and stirred vigorously for 15-120 min to obtain a black paste-like liquid.

(8) The black paste liquid was cooled to room temperature and then subjected to magnetic separation. The resulting precipitate was repeatedly washed with deionized water for 4-5 times until the washing solution was neutral, and then washed twice with anhydrous ethanol. The precipitate was dried in a vacuum drying oven at 60°C for 10 h and then ground to obtain a black magnetic nitrided biochar catalytic material.

Test Case

The black magnetic nitrided biochar catalytic material prepared in Example 1 was tested by scanning electron microscopy, and it can be seen that Fe ₃ O ₄ spherical particles with a diameter of about 13 nm are attached to the surface and channels of the nitrided biochar, as shown in FIG1 .

The material has a specific surface area of 157.68 ^{m 2} /g, a saturation magnetization of 17.9 emu /g, and a hysteresis loop (VSM) as shown in Figure 2. Figure 3 shows the N ₂ adsorption-desorption isotherm and pore structure of the magnetic nitrided biochar material. The material exhibits a type IV isotherm and an H ₃ type back ring, has a mesoporous structure, a BET specific surface area of 157.68 m ² /g, and a pore size mainly distributed at 2.86-32.13 nm, with an average pore size of 14.26 nm, of which the pores at 2.86-4.25 nm are generated by nano-Fe ₃ O ₄ deposited on the surface of the carbon material, and the remaining pores are generated by the pores of the carbon material and the nano-Fe ₃ O ₄ deposited therein.

Take 200mg/L tetracycline stock solution and dilute it to 50mg/L tetracycline simulated wastewater, take 50ml tetracycline simulated wastewater and place it in a 100ml conical flask, adjust the pH to 3-11 with NaOH _{and H2SO4} , add 1.2g/L magnetic nitrided biochar powder, add sodium persulfate solution to make its concentration 6mmol/L after ultrasonic dispersion for five minutes, place it in a constant temperature oscillating box at 25℃ and set the speed to 180r/min, take samples at regular intervals within 240min of the degradation reaction, and determine the tetracycline concentration after filtering through a 0.45 water filter membrane. The degradation curve of tetracycline under different reaction pH is shown in Figure 4, which shows that the degradation effect is best in neutral water with pH=7, and the degradation efficiency can reach about 92% within 60min. The magnetic nitrided biochar material after the tetracycline degradation reaction was placed in a 0.1 mol/L NaOH solution and stirred for 2 hours. After eluting the tetracycline molecules and degradation intermediates that may be adsorbed on the surface of the material, it was washed to neutrality and dried to wait for the next reuse test. As shown in Figure 5, the TC degradation rate of the material did not change much in the first three cycle tests, and only after the fourth cycle test did the degradation rate drop to 80.8%, indicating that the material has a relatively stable ability to activate persulfate to degrade tetracycline.

Comparative Example 1 (adding different amounts of urea)

Take 200mg/L tetracycline stock solution and dilute it to 50mg/L tetracycline simulated wastewater. Take 50ml tetracycline simulated wastewater and place it in a 100ml conical flask. Adjust the pH to ₇ with NaOH and _H2SO4 , and add 1.2g/L magnetic biochar powder with different nitrogen contents, where the mass ratio of urea to corn cob is (1-4):1. After ultrasonically dispersing the magnetic nitrogenated biochar in the tetracycline simulated wastewater for five minutes, add sodium persulfate solution to make its concentration 6mmol/L, place it in a constant temperature oscillating box at 25℃ and set the speed to 180r/min. Samples are taken at regular intervals within 240min of the degradation reaction, and the tetracycline concentration is determined after filtering through a 0.45 water filter membrane.

The tetracycline degradation curves of magnetic biochar powders with different nitrogen contents are shown in Figure 6. When the mass ratio of urea to corncob is 3:1 and 4:1, the degradation rates of tetracycline by Fe ₃ O ₄ -1N ₃ BC-900 and Fe ₃ O ₄ -1N ₄ BC-900 can reach 92.73% and 94.20% respectively within 30 minutes. However, in the actual preparation process, with the increase of urea content, the yield of carbon materials after high-temperature pyrolysis decreases. From the perspective of tetracycline degradation efficiency and resource conservation, the mass ratio of corncob to urea is considered to be 1:3 as the optimal ratio.

The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims (8)

1. A method for preparing a magnetic nitrided biochar catalytic material based on steel mill pickling wastewater, characterized in that the method comprises the following steps: (1) dissolving urea in deionized water, adding corncob powder, and stirring to obtain a turbid mixed solution of urea and corncob; the mass ratio of the urea to the corncob powder is (1-4):1, wherein the urea is a nitrogen source and the corncob powder is a carbon source; (2) placing the turbid liquid in step (1) in a constant temperature water bath for stirring, and then drying and grinding in sequence to obtain a mixed powder of urea and corn cob; (3) placing the mixed powder obtained in step (2) in a tubular furnace, pyrolyzing it under the protection of nitrogen, and obtaining black nitrided biochar powder after cooling; (4) washing the black nitrided biochar powder obtained in step (3), filtering and separating the powder, drying and grinding the powder for later use; (5) adding an oxidant to the steel mill pickling waste liquid, adjusting the molar ratio of Fe ³⁺ to Fe ²⁺ , obtaining a yellow-green pickling waste liquid, adding the black nitrided biochar powder obtained in step (4) to the yellow-green pickling waste liquid, stirring evenly to obtain a mixed liquid of the nitrided biochar and the pickling waste liquid; the oxidant is H ₂ O ₂ , and the redox potential of the pickling waste liquid is adjusted between 471 and 491 mV to make n(Fe ³⁺ ):n(Fe ²⁺ ) be (1 to 1.8):1; (6) stirring the mixed liquid obtained in step (5) at a certain temperature, adding a precipitant until the pH value reaches 7 to 13, and then stopping, so that Fe ³⁺ and Fe ²⁺ undergo a co-precipitation reaction, and Fe ₃ O ₄ nanoparticles are generated on the surface and inside of the nitrided biochar; (7) In the absence of protective gas, the mixed liquid obtained in step (6) is transferred into a stirrer at a higher temperature to allow the Fe ₃ O ₄ crystals to fully develop, and a black paste-like liquid is obtained after stirring; (8) The black paste obtained in step (7) is subjected to magnetic separation, and the obtained precipitate is washed, dried and ground in sequence to obtain a black magnetic nitrided biochar catalytic material. 2. The method for preparing magnetic nitrided biochar catalytic material based on steel rolling pickling waste liquid according to claim 1 is characterized in that, in step (2), the temperature of the constant temperature water bath is 20-30°C, the stirring speed is 500-700 r/mim, the stirring time is 4-6h, the drying temperature is 70-80°C, and the drying time is 8-12h. 3. The method for preparing a magnetic nitrided biochar catalytic material based on steel rolling pickling waste liquid according to claim 1 is characterized in that in step (3), the temperature is increased to the pyrolysis temperature at a rate of 4 to 6°C/min, the pyrolysis temperature is 500 to 900°C, and the pyrolysis time is 1 to 1.5 hours. 4. The method for preparing a magnetic nitrided biochar catalytic material based on steel rolling pickling waste liquid according to claim 1 is characterized in that, in step (4), the black powder obtained in step (3) is ultrasonically cleaned in dilute sulfuric acid and anhydrous ethanol for 30 minutes, washed with deionized water and separated by suction, and then dried and ground for use. 5. The method for preparing a magnetic nitrided biochar catalytic material based on steel rolling pickling waste liquid according to claim 1 is characterized in that, in step (6), the mixed liquid obtained in step (5) is heated to 45-55°C, a precipitant is quickly added until the pH value reaches 5, and then the precipitant is added dropwise, and the addition of the precipitant is stopped after the pH value reaches 7-13, and the precipitant is a 2 mol/L NaOH solution. 6. The method for preparing magnetic nitrided biochar catalytic material based on steel rolling pickling waste liquid according to claim 1 is characterized in that in step (7), the agitator speed is 500-1000 r/min, the stirring temperature is 50-90°C, and the stirring time is 15-120 min. 7. The magnetic nitrided biochar catalytic material obtained by the preparation method according to any one of claims 1 to 6. 8. Use of the magnetic nitrided biochar catalytic material according to claim 7 in the treatment of organic wastewater.