Catalyst for treating coking wastewater by activating persulfate and preparation method thereof

Abstract

The invention relates to the technical field of sewage treatment, in particular to a catalyst for treating coking wastewater by activating persulfate and a preparation method of the catalyst. The preparation method of the catalyst comprises the following steps: adding a molybdenum source, a reducing agent and a dispersing agent into a charcoal precursor solution containing fine coal gasification slag, and then carrying out hydrothermal reaction to obtain a mixed solution; the mixed solution is dried, calcined and pyrolyzed to obtain magnetic biochar; the magnetic biochar is subjected to microwave treatment to obtain the catalyst. The coal gasification fine slag is used as a raw material to prepare the catalyst, so that solid waste reduction and resource reutilization can be effectively realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sewage treatment, in particular to a catalyst for activating persulfate to treat coking wastewater and a preparation method thereof. BACKGROUND

[0002] Coking wastewater is a typical refractory wastewater containing aromatic compounds and heterocyclic compounds. At present, A / O, A2 / O and A / O2 processes are commonly used to treat coking wastewater, but the COD and colority of the treated water cannot meet the requirements of the Standard for Pollutant Discharge of Coking Chemical Industry (GB16171-2012). Some biologically refractory organic pollutants such as polycyclic aromatic hydrocarbons, amines, alkyl phenols and pyridines remain in the biochemical treated water of coking wastewater, which still poses a risk to the environment. Therefore, it is necessary to further treat coking wastewater. At present, the methods for advanced treatment of coking wastewater include coagulation, adsorption, advanced oxidation and reverse osmosis treatment technology. Among them, the advanced oxidation technology based on persulfate (PMS) oxidation is a deep treatment technology that has emerged in recent years. Under normal circumstances, PMS can be activated by heating, ultraviolet irradiation and transition metal ions to generate sulfate radicals and hydroxyl radicals, so as to achieve efficient removal of organic pollutants. However, the above methods for activating sulfate radicals have problems such as high cost, high energy consumption and the possibility of secondary pollution caused by transition metal ions. Therefore, how to improve the activation efficiency of PMS while reducing energy consumption and avoiding environmental pollution is an important problem faced by the application of PMS activators. SUMMARY

[0003] The purpose of the present application is to provide a catalyst for activating persulfate to treat coking wastewater and a preparation method thereof, so as to solve the problems existing in the prior art and achieve the requirements of the Standard for Pollutant Discharge of Coking Chemical Industry (GB16171-2012) for the quality of coking wastewater, with the characteristics of high removal efficiency, economic efficiency and resource recycling of solid waste.

[0004] To achieve the above purpose, the present application provides the following solutions:

[0005] One of the technical solutions of the present application is a preparation method of a catalyst for activating persulfate to treat coking wastewater, comprising the following steps:

[0006] Step 1: adding a molybdenum source (sodium molybdate), a reducing agent (thiourea) and a dispersing agent (ethylene glycol) into a biochar precursor solution containing coal gasification fine slag, and then performing a hydrothermal reaction to obtain a mixed solution;

[0007] Step 2: drying and calcining the mixed solution to obtain magnetic biochar;

[0008] Step 3: the magnetic biochar is treated by microwave to obtain the catalyst.

[0009] Further, in step 1, the straw powder and the coal gasification fine slag are mixed with water (stirring for 12-24 h) to obtain the biochar precursor solution containing the coal gasification fine slag.

[0010] Pre-blending the straw powder and the coal gasification fine slag in the solvent to prepare the precursor solution can realize uniform mixing of the two, and at the same time, it is helpful for the coal gasification fine slag to be doped in the pores of the straw powder, so as to increase the specific surface area of the final product and enrich the pore structure.

[0011] Further, in step 1, the hydrothermal reaction conditions are 100-180℃ for 6-14 h.

[0012] The hydrothermal reaction conditions defined in the application help the molybdenum to be fully reacted with the reducing agent, so as to generate specific active sites on the surface of the biochar, and the activation of PMS is better.

[0013] Further, in step 1, the straw powder is obtained by drying and grinding crop straw as raw material; further, the crop straw is dried at 80-120℃ for 20-26 h to obtain dehydrated straw, and the dehydrated straw is put into a mortar and ground, and then sieved through a 50-120 mesh sieve to obtain the straw powder.

[0014] Further, in step 1, the amount ratio of the straw powder, the coal gasification fine slag and water is (8-15) g:(3-8) g:(5-30) mL.

[0015] Further, in step 1, the amount ratio of the sodium molybdate, the biochar precursor solution containing the coal gasification fine slag, the thiourea and the ethanedioic acid glycol ester is (0.3-2.5) g:(20-50) mL:(1.5-3.5) g:(0.5-3.0) g.

[0016] Further, in step 2, the drying is vacuum drying at 100-180℃ for 3-8 h.

[0017] Further, in step 2, the calcination pyrolysis conditions are: nitrogen atmosphere, heating at 3-8℃ / min to 500-800℃ for pyrolysis for 50-140 min.

[0018] Further, in step 3, the microwave treatment specifically includes: microwave irradiation reaction at a temperature of 150-250℃ and a power of 500-2000W for 4-10 min, and stirring every 30-60 s during the reaction.

[0019] The catalyst prepared by the above preparation method is the second technical scheme of the application.

[0020] The third technical solution of the present application is the application of the above-mentioned catalyst in the treatment of coking wastewater by activating persulfate.

[0021] Further, the mass ratio of the catalyst and the persulfate is (0.5-3) : (4-22).

[0022] Further, the ratio of the catalyst and the coking wastewater is (0.5-3) g : (400-1000) mL.

[0023] The fourth technical solution of the present application is the application of the above-mentioned catalyst in the treatment of refractory organic wastewater.

[0024] The present application discloses the following technical effects:

[0025] Biochar (BC) is a porous, carbon-rich, and cost-effective carbon-based activated material prepared by pyrolysis of biomass waste. The persistent free radicals, defect sites, nitrogen doping, and abundant oxygen-containing functional groups present in biochar all contribute to the activation of PMS to produce strong oxidizing free radicals. Considering cost, solid waste recycling, and effectiveness, BC is a very promising PMS heterogeneous catalyst. However, BC alone is not sufficient to efficiently activate PMS. The present application selects coal gasification fine slag, biomass raw material (straw powder), sodium molybdate, thiourea, and ethylene glycol to prepare a molybdenum-doped magnetic biochar through hydrothermal reaction and calcination pyrolysis, and then activates it through microwave treatment to prepare a catalyst for activated persulfate treatment of coking wastewater. Sodium molybdate is reduced by the reducing agent thiourea to form molybdenum disulfide with good plasticity, which forms a nanosheet layer structure. Under the action of the dispersing agent ethylene glycol, the nanosheet layer structure of molybdenum disulfide is uniformly distributed on the surface of the coal gasification slag particles, forming a nanosheet layer three-dimensional composite catalyst material. The high specific surface area of the nanosheet layer of molybdenum disulfide and the small resistance of the biochar provide more reaction sites for efficient catalytic reaction of persulfate. The tetravalent molybdenum ion is efficiently reduced to divalent ion on the surface of the coal gasification slag particles and continuously participates in the reaction. Therefore, the biochar catalyst prepared by the present application can effectively improve the reduction efficiency of metal ions in the electro-persulfate activation system, thereby improving the treatment effect of coking wastewater. In addition to acting as a reducing agent, thiourea also plays the role of a dispersing auxiliary solvent. Under the synergistic action of ethylene glycol and thiourea, the uniform dispersion of the coal gasification slag particles can be ensured, thereby achieving uniform reaction contact, increasing the specific surface area and reaction channels.

[0026] The present application uses rural waste straw and coal gasification fine slag as raw materials to prepare the catalyst, which can effectively realize solid waste reduction and resource recycling.

[0027] The preparation of the biochar precursor of the present application is simple and convenient, and does not require the addition of metal reagents, thereby avoiding secondary pollution.

[0028] The microwave chemical reaction is used in the preparation process of the biochar, special effects of microwave electromagnetic field are cooperated with special heating mode to realize integrated heating, so that the product is not easy to agglomerate and exposes more active sites, thereby effectively improving the activation effect of biochar on persulfate and improving the coking wastewater treatment effect.

[0029] The final drying process of the product adopts microwave drying, greatly shortens time, and has the characteristics of high efficiency, product optimization, energy saving and environmental protection.

[0030] Based on the magnetic characteristics of the coal gasification slag, the biochar prepared by the application has magnetism and can be recycled and reused multiple times. 2 The specific surface area of the final product is 2500-3800 cm 3 / g, the hydrophilic angle is 60-90°, the porosity is 60-95%, the average pore size is 1.2-4.8 μm, and the pore volume is 0.4-0.85 cm / g.

[0031] The advanced oxidation technology of the magnetic biochar for activating persulfate has a wide application range and can also be used for treating other refractory organic wastewater, such as other wastewater in the chemical industry, such as coal chemical wastewater.

[0032] After the coking wastewater treated by biochemical treatment is activated by the catalyst to activate persulfate for deep treatment, the effluent quality can reach the sewage discharge standard of COD≤80 mg / L, ammonia nitrogen≤10 mg / L and total nitrogen≤50 mg / L, and the effluent can be directly used as production recycled water, which not only protects the ecological environment, saves water and reduces treatment cost, but also has important practical significance for the sustainable development of coking enterprises.

[0033] The application discloses a kind of magnetic biochar materials for coking wastewater deep treatment, using microwave radiation to microwave chemical reaction of magnetic biochar, it can be catalytic reaction with persulfate and produce strong oxidizing free radicals to realize effective treatment to coking wastewater. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0035] Figure 1 The electron microscope scanning image of the magnetic biochar to be treated prepared in Example 1 of the present application;

[0036] Figure 2Scanning electron microscope image of magnetic biochar prepared for Example 1 of the present invention;

[0037] Figure 3 Graph of results of repeated treatment of coking wastewater using magnetic biochar in Example 4 of the present invention;

[0038] Figure 4 Graph of metal ion leaching results of repeated treatment of coking wastewater using magnetic biochar in Example 4 of the present invention. DETAILED DESCRIPTION

[0039] Various exemplary embodiments of the present invention will now be described in detail, which should be considered to be illustrative of the present invention and should not be considered to limit the scope of the present invention, and are understood to be a description of certain aspects, features and embodiments of the present invention.

[0040] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. Additionally, for a range of values of a parameter, unless otherwise stated, the inclusion of either a lower or an upper limit of a range is specifically asserted. The exclusion of either a lower or an upper limit of a range is specifically asserted. The combination of an inclusion and exclusion of either a lower or an upper limit is specifically asserted. The scope of the present invention is not intended to be limited to a single aspect, aspect, feature, or implementation.

[0041] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although preferred methods and materials are described, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned herein are incorporated by reference to disclose and describe the methods and / or materials in connection with which the documents are cited. In case of conflict between the present specification and any document incorporated by reference, the present specification will control.

[0042] Various modifications and changes can be made to the specific embodiments of the present invention described herein without departing from the scope or spirit of the present invention. Other embodiments of the present invention will be apparent to those of ordinary skill in the art from the description and examples that follow. The description and examples are illustrative of the present invention and are not intended to limit the scope of the present invention in any manner.

[0043] With respect to the use of "comprising", "including", "containing", "having" and "by" in this specification, these terms are used in their open-ended sense, that is, meaning "including, but not limited to".

[0044] The microwave chemical reactor used in the present embodiment was purchased from Gugyi Huayi Instrument.

[0045] The coal gasification fine slag used in the present embodiment has a specific surface area of 300 cm 2 / g, the hydrophilic angle is 60°, and the porosity is 30-45%, and the water content is 30%.

[0046] The straw used in the embodiment of the present application is wheat straw.

[0047] The raw materials used in the embodiment of the present application are all commercially available products.

[0048] The coking wastewater used in the experiment verification in the embodiment of the present application is coking wastewater after biochemical treatment, and the pollutant composition and concentration are as follows: total nitrogen 200 mg / L, ammonia nitrogen concentration 80 mg / L, and COD value 400 mg / L.

[0049] The persulfate used in the embodiment of the present application is a commercially available PMS.

[0050] The room temperature in the embodiment of the present application is 25±2℃.

[0051] The COD removal rate, ammonia nitrogen removal rate, total nitrogen removal rate, specific surface area, hydrophilic angle, porosity, average pore size, and pore volume in the embodiment of the present application are detected by using the prior art method, and the detailed process does not affect the understanding of the effect of the present application, and is not described here.

[0052] Example 1

[0053] Step 1: 100g of straw was placed in an oven and dried at 100℃ for 22h to obtain dehydrated straw, which was ground in a mortar and sieved through a 100 mesh sieve after grinding;

[0054] Step 2: 15g of dehydrated straw after sieving, 3g of coal gasification fine slag, and 25mL of deionized water were added to prepare a mixed solution, which was stirred for 12h to obtain a biochar precursor solution;

[0055] Step 3: sodium molybdate 0.5g, biochar precursor solution 20ml, thiourea 1.5g, and ethanedioic acid glycol ester 1.5g were mixed for hydrothermal reaction (temperature 100℃, time 8h), and then placed in an oven and vacuum dried at 100℃ for 3h, and cooled to room temperature to obtain a biochar precursor;

[0056] Step 4: the biochar precursor was placed in a tube furnace and heated to 500℃ in a nitrogen atmosphere, and pyrolysis was carried out for 50min at a heating rate of 8℃ / min to obtain a magnetic biochar to be treated sample. The surface electron microscope scanning image of the magnetic biochar to be treated sample is shown in Figure 1 Further detection shows that the specific surface area is 1200cm 2 / g, the hydrophilic angle is 60°, the porosity is 75%, the average pore size is 0.18μm, and the pore volume is 0.20cm 3 / g.

[0057] Step 5: Place the magnetic biochar sample in a microwave chemical reactor for microwave chemical reaction at 150℃ and 500W for 5 minutes, stirring every 30 seconds during the reaction. Then, microwave dry at 100℃ for 20 minutes to obtain magnetic biochar. The electron microscope scanning image of the obtained magnetic biochar surface is shown below. Figure 2 As shown. Comparison Figure 1 and Figure 2 It can be seen that the surface morphology of the magnetic biochar undergoes significant changes through microwave chemical reaction. Under the simultaneous action of microwave radiation and pyrolysis, the particle size of the magnetic biochar decreases, and the particles become loose. This structure helps to expose more abundant catalytic PMS reaction active sites, greatly improving the treatment effect on coking wastewater. Further testing revealed that its specific surface area is 3000 cm². 2 / g, hydrophilic angle 90°, porosity 95%, average pore size 3.6μm, pore volume 0.65cm³. 3 / g.

[0058] Step 6: Add 1g of magnetic biochar granules to 850mL of biochemically treated coking wastewater, and add 9g of commercial PMS to the biochemically treated coking wastewater. React for 20 minutes with stirring. Results show that the COD removal rate of the coking wastewater is 93%, the ammonia nitrogen removal rate is 91%, and the total nitrogen removal rate is 88.5%. This indicates that the magnetic biochar-catalyzed PMS prepared in this invention can generate strong oxidizing sulfate radicals for efficient and deep treatment of coking wastewater.

[0059] Example 2

[0060] Step 1: Place 50g of straw in an oven and dry it at 100℃ for 22 hours to obtain dehydrated straw. Grind the straw in a mortar and pass it through a 100-mesh sieve.

[0061] Step 2: Take 10g of sieved dehydrated straw, 5g of coal gasification fine slag, add 30mL of deionized water to prepare a mixed solution, stir for 15h to obtain a biochar precursor solution;

[0062] Step 3: 0.3g of sodium molybdate, 22ml of biochar precursor solution, 1.7g of thiourea and 1.8g of ethylene oxalate were mixed and subjected to hydrothermal reaction (temperature 110℃, time 10h). Then, the mixture was placed in an oven and vacuum dried at 100℃ for 3h. After cooling to room temperature, the biochar precursor was obtained.

[0063] Step 4: The biochar substrate was placed in a tube furnace and heated to 500℃ in a nitrogen atmosphere for 50 min, with a heating rate of 8℃ / min, to obtain a magnetic biochar sample. Further analysis showed its specific surface area to be 1300 cm². 2 / g, the hydrophilic angle is 65°, the porosity is 75%, the average pore size is 0.19 μm, and the pore volume is 0.25 cm 3 / g.

[0064] Step 5: The magnetic biochar to be treated sample is placed in a microwave chemical reactor for microwave chemical reaction, the temperature is 180℃, the power is 1000W, the microwave radiation reaction is 5min, and stirring is performed every 40 seconds during the reaction; then microwave drying is performed at 150℃ for 10min, to obtain the magnetic biochar. Further detection shows that the specific surface area of the magnetic biochar is 2800cm 2 / g, the hydrophilic angle is 90°, the porosity is 90%, the average pore size is 3.1 μm, and the pore volume is 0.60 cm 3 / g.

[0065] Step 6: 1.2g of magnetic biochar particles are placed into 900mL of coking wastewater after biochemical treatment, 9.5g of commercial PMS is added into the coking wastewater after biochemical treatment, and the reaction is performed for 20min under stirring. The results show that the removal rates of COD, ammonia nitrogen and total nitrogen of the coking wastewater are 94.2%, 91.5% and 86.3% respectively. It is shown that the magnetic biochar prepared in the application can produce strong oxidizing sulfate radicals by catalyzing PMS, and the coking wastewater can be efficiently and deeply treated.

[0066] Example 3

[0067] Step 1: 40g of straw is placed in an oven and dried at 100℃ for 28h to obtain dehydrated straw, which is ground in a mortar and then sieved through a 100 mesh sieve;

[0068] Step 2: 18g of the sieved dehydrated straw, 6g of coal gasification fine slag and 30mL of deionized water are mixed to prepare a mixed solution, and stirring is performed for 18h to obtain a biochar precursor solution;

[0069] Step 3: sodium molybdate 0.5g, biochar precursor solution 25ml, thiourea 2.2g and ethanedioic acid glycol ester 1.5g are mixed for hydrothermal reaction (temperature 115℃, time 12h), and then vacuum drying is performed at 100℃ for 3h in an oven, and the biochar precursor is obtained after cooling to room temperature;

[0070] Step 4: the biochar precursor is placed in a tube furnace, heated to 500℃ in a nitrogen atmosphere, and pyrolysis is performed for 50min at a heating rate of 8℃ / min, to obtain the magnetic biochar to be treated sample. Further detection shows that the specific surface area of the magnetic biochar to be treated sample is 1400cm 2 / g, the hydrophilic angle is 68°, the porosity is 70%, the average pore size is 0.20 μm, and the pore volume is 0.26 cm 3 / g.

[0071] Step 5: The magnetic biochar to be treated is placed in a microwave chemical reactor, and microwave radiation is performed at a temperature of 150℃ and a power of 1500W for 5min, with stirring every 30s; then the magnetic biochar is obtained by microwave drying at 150℃ for 2min. Further detection shows that the specific surface area of the magnetic biochar is 2900cm 2 / g, the hydrophilic angle is 90°, the porosity is 92%, the average pore size is 3.4μm, and the pore volume is 0.63cm 3 / g.

[0072] Step 6: 1.5g of magnetic biochar particles are placed in 950mL of coking wastewater treated by biochemical method, and 10g of commercial PMS is added to the above-mentioned coking wastewater treated by biochemical method, and the reaction is performed under stirring for 30min. The results show that the removal rate of COD of the coking wastewater is 96%, the removal rate of ammonia nitrogen is 92%, and the removal rate of total nitrogen is 85%. It is shown that the magnetic biochar prepared in the present application can produce strong oxidizing sulfate radicals by catalyzing PMS, so as to realize efficient and deep treatment of coking wastewater.

[0073] Example 4

[0074] The same as example 1, except that the following steps are further included:

[0075] Step 7: The magnetic biochar of step 6 is recovered by a magnet, and then deionized water is used for washing for 10min, and then the coking wastewater treatment process of step 6 is repeated, and the reuse effect of the magnetic biochar is counted, and the results are shown in Figure 3 , Figure 3 It is shown that the magnetic biochar prepared in the present application can efficiently treat wastewater for a long time, and the removal rate of COD can remain stable in the continuous wastewater treatment for 10 times. The magnetic biochar prepared in the present application realizes solid waste reduction and resource recycling, and can be reused for multiple times, so as to efficiently and stably treat coking wastewater.

[0076] The concentration of metal ions (molybdenum ions) in the coking wastewater treated for 10 times is determined, and the results are shown in Figure 4 , Figure 4 It is shown that the leaching of molybdenum ions does not exceed 1mg / L in the 10 times of recycling, which meets the coking wastewater discharge standard GB 16171-2012.

[0077] Comparative Example 1

[0078] The same as example 1, except that the coal gasification fine slag in step 2 is omitted.

[0079] Comparative Example 2

[0080] The same as example 1, except that the sodium molybdate in step 3 is omitted.

[0081] Comparative Example 3

[0082] The same as example 1, except that step 5 is omitted.

[0083] The specific surface area (cm2 / g), hydrophilic angle (°), porosity (%) and coking wastewater COD removal rate (%) of the product prepared in the comparative example were detected by the same method as in example 1. 2 / g), hydrophilic angle (°), porosity (%) and coking wastewater COD removal rate (%) were obtained, and the results were statistically analyzed with table 1.

[0084] Table 1 Performance of the catalyst prepared in the comparative example

[0085] Specific surface area Hydrophilic angle Porosity COD % Comparative Example 1 1800 80 80％ 80 Comparative Example 2 2000 85 75％ 85 Comparative Example 3 1200 60 75％ 70

[0086] In subsequent experiments, the parameters in the preparation process of the catalyst for activating persulfate to treat coking wastewater were further experimentally verified, and the results showed that the catalyst prepared under the following parameter conditions could achieve similar technical effects to the above-mentioned examples of the application, and the following preferred parameter ranges were obtained:

[0087] A preparation method of a catalyst for activating persulfate to treat coking wastewater, comprising the following steps:

[0088] Step 1: adding sodium molybdate, thiourea and ethylene glycol to a biochar precursor solution containing coal gasification fine slag (obtained by mixing straw powder and coal gasification fine slag with water) to obtain a mixed solution after hydrothermal reaction;

[0089] Step 2: the mixed solution is dried and calcined pyrolysis to obtain magnetic biochar;

[0090] Step 3: the magnetic biochar is treated by microwave to obtain the catalyst.

[0091] In step 1: the hydrothermal reaction conditions are 100-180℃ for 6-14h; the amount ratio of the straw powder, the coal gasification fine slag and water is (8-15)g:(3-8)g:(5-30)mL; the amount ratio of the sodium molybdate, the biochar precursor solution containing coal gasification fine slag, the thiourea and the ethylene glycol is 0.3-2.5g:20-50mL:1.5-3.5g:0.5-3.0g.

[0092] In step 2: the drying is vacuum drying at 100-180℃ for 3-8h; the calcination pyrolysis conditions are nitrogen atmosphere, heating to 500-800℃ at 3-8℃ / min for pyrolysis for 50-140min.

[0093] The microwave treatment in step 3 specifically includes: microwave irradiation under the conditions of temperature 150-250 DEG C, power 500-2000 W for 4-10 min, stirring every 30-60 s, and then microwave drying at 60-150 DEG C for 0.5-20 min.

[0094] When the prepared catalyst is used to treat coking wastewater, the mass ratio of the catalyst to persulfate is (0.5-3) :(4-22), and the ratio of the catalyst to the coking wastewater is (0.5-3) g :(400-1000) mL.

[0095] The above-described embodiments are only used to describe the preferred modes of the present application, and are not used to limit the scope of the present application, and various modifications and improvements to the technical solutions of the present application made by those skilled in the art without departing from the design spirit of the present application shall fall within the protection scope of the present application defined by the claims.

Claims

1. A method for preparing a catalyst for activating persulfate to treat coking wastewater, characterized in that, Includes the following steps: Step 1: Add a molybdenum source, reducing agent and dispersant to a biochar precursor solution containing coal gasification fine slag, and then carry out a hydrothermal reaction to obtain a mixed solution; Step 2: The mixed solution is dried and then calcined and pyrolyzed to obtain magnetic biochar; Step 3: The magnetic biochar is microwave-treated to obtain the catalyst.

2. The preparation method according to claim 1, characterized in that, In step 1: straw powder and coal gasification fine residue are mixed with water to obtain the biochar precursor solution containing coal gasification fine residue; And / or, the molybdenum source is sodium molybdate, the reducing agent is thiourea, and the dispersant is ethylene oxalate; And / or, the hydrothermal reaction conditions are: 100-180℃, 6-14h.

3. The preparation method according to claim 2, characterized in that, The straw powder is obtained by drying and grinding agricultural crop straw. And / or, the ratio of the straw powder, the coal gasification slag and water is (8-15)g∶(3-8)g∶(5-30)mL; And / or, the ratio of sodium molybdate, the biochar precursor solution containing coal gasification fine slag, the thiourea and the ethylene oxalate is (0.3-2.5)g:(20-50)mL:(1.5-3.5)g:(0.5-3.0)g.

4. The preparation method according to claim 1, characterized in that, In step 2: The drying process involves vacuum drying at 100-180℃ for 3-8 hours. And / or, the calcination pyrolysis conditions are: nitrogen atmosphere, heating at 3-8℃ / min to 500-800℃ for pyrolysis for 50-140min.

5. The preparation method according to claim 1, characterized in that, In step 3, the microwave treatment specifically includes: microwave radiation reaction for 4-10 minutes at a temperature of 150-250℃ and a power of 500-2000W, with stirring every 30-60 seconds during the process.

6. A catalyst prepared by the method according to any one of claims 1-5.

7. The application of the catalyst according to claim 6 in the treatment of coking wastewater by activating persulfate.

8. The application according to claim 7, characterized in that, The mass ratio of the catalyst to persulfate is (0.5-3):(4-22).

9. The application according to claim 7, characterized in that, The ratio of the catalyst to the coking wastewater is (0.5-3) g : (400-1000) mL.

10. The application of the catalyst according to claim 6 in recalcitrant organic wastewater.

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