Preparation method of pokeweed-based modified biochar for adsorbing heavy metal vanadium

Abstract

A preparation method of pokeweed-based modified biochar for adsorbing heavy metal vanadium, comprising: (1) mixing pokeweed powder, NaOH solid and mixed ferric salt solid Fe 2 (SO 4 ) 3 , Fe(NO 3 ) 3 to obtain mixture A; (2) pyrolyzing mixture A in an inert atmosphere, controlling the pyrolysis temperature at 300-800 °C, and cooling to room temperature after pyrolysis to obtain pokeweed-based modified biochar. The biochar obtained by this method achieves the effect of efficiently adsorbing heavy metal vanadium. On the other hand, the raw material used is the plant pokeweed harvested after site remediation, which is easily available, reduces the preparation cost of the adsorbent material, and realizes the resource utilization of solid waste.

Description

Technical Field

[0001] The present invention relates to a preparation method of a heavy metal adsorbent, specifically a preparation method of biochar for adsorbing heavy metal vanadium, belonging to the field of environmental protection. Background Art

[0002] Vanadium is an important metal element in industrial production, known as the "monosodium glutamate of modern industry" and "metal vitamin", and is widely used in important fields such as aviation, energy, and electronic technology, with very important strategic significance. Stone coal is an important and unique vanadium-containing resource in China. At present, vanadium extraction processes such as sodium roasting-chemical leaching, calcification roasting-chemical leaching, and salt-free roasting-chemical leaching are mostly used. During the production process of extracting vanadium from stone coal, vanadium-containing wastewater will be generated. If not properly treated, its discharge will cause great harm to the environment. Once the drinking water is polluted, it will seriously affect the health of residents in the polluted area.

[0003] At present, the main treatment methods for heavy metal-containing wastewater include chemical precipitation method, ion exchange method, adsorption method, etc. The chemical precipitation method has a large consumption of chemicals and will produce a large amount of precipitated sludge; the ion exchange method can effectively separate metal ions from other metal ions, but the cost is too high; the adsorption method has the characteristics of simple operation, low cost, and environmental protection, and has attracted the attention of many researchers. Biochar has the characteristics of a large specific surface area, rich surface functional groups such as carboxyl and hydroxyl groups, making it an excellent heavy metal ion adsorbent. According to different preparation methods, biochar can be divided into pyrolysis carbon and hydrothermal carbon. In recent years, the use of agricultural and forestry waste as raw materials to prepare biochar has attracted great attention. For example: Chinese Patent Application Publication Nos. CN109621900A and CN109621901A disclose a preparation method of modified plant-based biochar. The plant is crushed and dried, then placed in a crucible and buried and compacted with soil, and then the crucible is placed in an electric resistance furnace for high-temperature treatment. After cooling, the soil is removed to obtain the product biochar. This biochar is used to adsorb heavy metal Cd.

[0004] Due to the harm of wastewater containing metal vanadium to the environment, a better treatment method is needed to remove it and purify the environment. Summary of the Invention

[0005] The purpose of the present application is to provide a preparation method of pokeweed-based modified biochar for adsorbing heavy metal vanadium. The biochar obtained by this method achieves the effect of efficiently adsorbing heavy metal vanadium. On the other hand, the raw material used is the plant pokeweed harvested after site remediation. The raw material is easily available, reducing the preparation cost of the adsorbent, and at the same time realizing the resource utilization of solid waste.

[0006] Another purpose of the present application is to treat metal vanadium in wastewater. By using the above-mentioned pokeweed-based modified biochar to treat metal vanadium in wastewater, the removal rate is very high.

[0007] A preparation method of pokeweed-based modified biochar for adsorbing heavy metal vanadium, comprising:

[0008] (1) Mix pokeweed powder, NaOH solid and mixed ferric salt solid Fe 2 (SO 4 ) 3 、Fe(NO 3 ) 3 to obtain mixture A;

[0009] (2) Pyrolyze mixture A in an inert atmosphere, control the pyrolysis temperature at 300 - 800 °C, and cool to room temperature after pyrolysis to obtain pokeweed-based modified biochar. Description of the Drawings

[0010] Figure 1 Figure for comparing the effects of unmodified biochar, modified hydrothermal carbon, and pokeweed-based modified biochar on removing heavy metal vanadium from wastewater

[0011] Figure 2 SEM characterization diagram of pokeweed-based modified biochar

[0012] Figure 3 Infrared spectrum characterization comparison diagram of unmodified biochar, modified hydrothermal carbon, and pokeweed-based modified biochar. Detailed Embodiments

[0013] The following further details the preparation method of a pokeweed-based modified biochar for adsorbing heavy metal vanadium of the present invention. It does not limit the protection scope of this application, and its protection scope is defined by the claims. Certain disclosed specific details provide a comprehensive understanding of each disclosed embodiment. However, those skilled in the relevant art know that the embodiments can also be implemented without one or more of these specific details and by using other materials, etc.

[0014] Unless otherwise required by the context, in the specification and claims, the terms "comprising" and "including" should be understood in an open and inclusive sense, that is, "including, but not limited to".

[0015] As used in the specification, "embodiment", "an embodiment", "another embodiment", or "certain embodiments" etc. refer to the specific features, structures, or characteristics described in relation to the said embodiment being included in at least one embodiment. Therefore, "embodiment", "an embodiment", "another embodiment", or "certain embodiments" do not necessarily all refer to the same embodiment. Moreover, the specific features, structures, or characteristics can be combined in any manner in one or more embodiments. Each feature disclosed in the specification can be replaced by any alternative feature that serves the same, equivalent, or similar purpose. Therefore, unless otherwise specified, the disclosed features are only general examples of equivalent or similar features.

[0016] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The experimental methods without specific conditions noted in the following embodiments are generally in accordance with conventional conditions or the conditions recommended by the manufacturer. Unless otherwise stated, all percentages, ratios, proportions, or parts are by weight.

[0017] The unit in the weight - volume percentage in the present invention is well - known to those skilled in the art. For example, it refers to the weight of the solute in 100 milliliters of the solution.

[0018] In the present invention, the concentration unit "M" of the solution represents mol / L.

[0019] Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to the described content can be applied to the methods of the present invention. The preferred implementation methods and materials described herein are only for demonstration purposes.

[0020] Phytolacca americana is a hyper - accumulator with a large biomass, fast growth rate, wide distribution range, and strong adaptability, and is widely used in the remediation of heavy - metal - contaminated soil / sites. The treatment and disposal of the enriched plants after pollution remediation are particularly important. Improper treatment will become a heavy - metal pollution source of secondary pollution. Incineration and ashing are common methods for biomass reduction treatment, but they are prone to secondary pollution and do not achieve effective resource utilization. The carbonization and reuse of hyper - accumulator plants have become a new way for their resource utilization. Therefore, this application uses the hyper - accumulator Phytolacca americana as a matrix, and prepares a biochar adsorbent for heavy - metal vanadium by adding modifiers and co - pyrolysis treatment. It not only makes reasonable resource utilization of hyper - accumulator plants, but also can greatly increase the specific surface area of the composite adsorbent and increase the adsorption sites to achieve efficient treatment of vanadium - containing wastewater.

[0021] According to the present application, a preparation method of a Phytolacca americana - based modified biochar for adsorbing heavy - metal vanadium includes:

[0022] (1) Mix the pokeweed powder, solid NaOH, and the mixed ferric salt solid Fe 2 (SO 4 ) 3 、Fe(NO 3 ) 3 to obtain mixture A;

[0023] (2) Pyrolyze mixture A in an inert atmosphere, control the pyrolysis temperature at 300 - 800 °C, and cool to room temperature after pyrolysis to obtain pokeweed-based modified biochar.

[0024] In the preparation method of this application, by using the composite modifiers NaOH and mixed iron salts, the adsorption performance of the modified biochar can be significantly improved. NaOH can promote the dissolution and structural destruction of cellulose and lignin components in pokeweed, helping to improve the porosity of the pokeweed powder and increase its specific surface area. In addition, by mixing the above-mentioned ferric salts ferric sulfate and ferric nitrate with pokeweed, and controlling the pyrolysis process to control the formed pyrolysis gas, it is beneficial to improve the pore structure of the biochar and increase the specific surface area, thereby enhancing its adsorption performance. And iron oxides are formed on the biochar to remove metal vanadium ions in water.

[0025] In some embodiments, the mass ratio of solid Fe 2 (SO 4 ) 3 to Fe(NO 3 ) 3 is 2:1 - 3:1.

[0026] The mass ratio of the pokeweed powder to solid NaOH is 1:0.3 - 0.4.

[0027] The mass ratio of the pokeweed powder to the mixed ferric solid is 1:0.5 - 0.7.

[0028] This application controls the dosage of the mixed ferric salts ferric sulfate and ferric nitrate. During the pyrolysis process, by the different generation rates of pyrolysis gases, more gases are generated in a short time at the initial stage of pyrolysis, generating abundant pores on the biochar. In the middle and late stages of pyrolysis, the generated gases further generate more pores on the basis of maintaining the original pore structure, increasing the specific surface area of the biochar. That is, by controlling the emission of pyrolysis gas from the raw materials, the pore structure and pore quantity of the biochar are ensured, the specific surface area is increased, and the adsorption performance of the biochar is enhanced.

[0029] Compared with using a single trivalent iron salt, the biochar prepared by using the above-mentioned mixed trivalent iron salts, especially the pokeweed-based modified biochar prepared by the above-mentioned dosage ratio of the mixed trivalent iron salts, has the characteristics of a more complete pore structure, more abundant pores, and more uniform dispersion of Fe elements.

[0030] In some embodiments, the pyrolysis process in step (2) is divided into a first pyrolysis stage and a second pyrolysis stage.

[0031] The temperature of the first pyrolysis stage is controlled at 320 - 350 °C; the temperature of the second pyrolysis stage is controlled at 600 - 750 °C.

[0032] In the present invention, solid NaOH is directly used, which shows a molten state under pyrolysis treatment at a temperature of 320 - 350 °C. Its reaction activity is higher than that of the NaOH solution used in the impregnated alkali-modified biochar, and it is easier to promote the production of more porous structures in the pokeweed powder, increasing the adsorption sites of the modified biochar; under the condition of 600 - 750 °C, the composite trivalent iron salt forms iron oxides on the surface of the pokeweed powder, and can remove VO 3 - 、VO 4 3- in water (the main valence states of vanadium in aqueous solution usually exist in the form of orthovanadate (VO 4 3- ), metavanadate (VO 3 - ), etc.). At the same time, NaOH will change the occurrence form of Fe on the biochar, and OH - can provide more oxygen-containing functional groups during the Fe loading process, further improving the adsorption activity of the biochar adsorbent for VO 3 - 、VO 4 3- , and realizing its effective adsorption and removal of heavy metal vanadium ions in water.

[0033] In some embodiments, in the first pyrolysis stage, the temperature is raised from room temperature to 320 - 350 °C at a pyrolysis rate of 8 - 12 °C / min.

[0034] In the second pyrolysis stage, the temperature is raised from 320 - 350 °C to 600 - 750 °C at a pyrolysis rate of 8 - 12 °C / min.

[0035] Preferably, in the first pyrolysis stage, the temperature is raised from room temperature to 320 - 350 °C at a pyrolysis rate of 10 °C / min.

[0036] In the second pyrolysis stage, the temperature is raised from 320 - 350 °C to 600 - 750 °C at a pyrolysis rate of 10 °C / min.

[0037] By controlling the heating rate of the pyrolysis process and the two-stage pyrolysis temperature, the pore distribution of the prepared biochar is more uniform, the pore structure is more complete, and the active distribution is increased and more uniform, further improving the removal of VO 3 - 、VO 43- Removal efficiency.

[0038] Preferably, in the first pyrolysis stage, pyrolysis is carried out at a temperature of 320 - 350 °C for 1 - 2 h; in the second pyrolysis stage, pyrolysis is carried out at a temperature of 600 - 750 °C for 1.5 - 3 h.

[0039] Biomass raw materials are one of the main factors determining the physicochemical properties of biochar. Biomass is usually mainly composed of lignin, cellulose, and hemicellulose. Among them, lignin is a natural aromatic compound that acts as an adhesive in plant fibers; cellulose is a glucoside-like compound with a smooth fiber structure on the surface and plays a role in providing the support strength for the tissue as a skeleton; while hemicellulose is a highly branched macromolecular compound composed of different sugars and has an amorphous structure.

[0040] The proportions of the three components of lignin, cellulose, and hemicellulose in different biomasses also vary, which leads to differences in the properties of the biochar prepared by pyrolysis. For different plant species, the structures of these three components are different, and the other chemical components they contain are also different, resulting in great differences in their pyrolysis behaviors.

[0041] The biomass raw material used in this application is Phytolacca americana, which is a perennial herb or shrub. The total amount of its lignin and cellulose is generally above 60%, higher than that of general straw-like biomasses. The biochar prepared by pyrolyzing Phytolacca americana has a higher yield. The modified biochar prepared by mixing with the above-mentioned mixed solid trivalent iron substance and pyrolysis has good adsorption performance for vanadium metal and generates more and more uniform active sites for adsorbing vanadium metal.

[0042] During the pyrolysis process, high-purity nitrogen is introduced to maintain an inert atmosphere in the furnace.

[0043] In some embodiments, the preparation method of Phytolacca americana powder includes rinsing Phytolacca americana to remove surface impurities, drying at room temperature, grinding through a 0.25 mm sieve, and then storing it in a dryer for standby.

[0044] The Phytolacca americana used in this application can be selected from the roots, stems, leaves, etc. of Phytolacca americana growing in various places.

[0045] The raw material of the pokeweed-based biochar prepared in this application is pokeweed, which is usually used as a remediation plant for heavy metal contaminated sites and becomes solid waste after harvesting. Therefore, using harvested pokeweed as the raw material not only reduces the economic cost but also realizes the resource utilization of solid waste. The preparation method is simple. Water is not required during the whole preparation process. Solid NaOH and solid composite ferric salts are directly added and co-pyrolyzed with pokeweed powder, avoiding processes such as solid-liquid separation. At the same time, complex functional material preparation equipment is not needed, which simplifies the material preparation process, has low preparation requirements, and no polluting by-products are generated throughout the process, meeting the concept of green preparation and facilitating industrial application.

[0046] The obtained biochar has a high removal rate for VO 3 - and VO 4 3- in water.

[0047] The preparation method of the pokeweed-based biochar adsorbent of the present invention and its effect on treating vanadium metal will be further described below with specific examples.

[0048] Example 1

[0049] (1) Wash the surface impurities of the pokeweed with water and dry it at room temperature. After grinding it through a 0.25 mm sieve, store it in a dryer for standby;

[0050] (2) Take 10 g of the pokeweed powder from step (1) and pour it into a mortar. Then weigh 3 g of solid NaOH and 5 g of mixed iron salt solid (3.5 g of Fe 2 (SO 4 ) 3 and 1.5 g of Fe(NO 3 ) 3 ) and add them to the mortar. After grinding evenly, pass it through a 0.25 mm sieve;

[0051] (3) Place the mixture powder from step (2) in a vacuum tube furnace for pyrolysis. The heating rate is 10 °C / min. Pyrolyze at 320 °C for 2 h, then continue to heat at 10 °C / min until the temperature reaches 600 °C and pyrolyze for 3 h. High-purity nitrogen is passed through the whole process. After the pyrolysis is completed, cool it to room temperature and take it out to finally obtain the pokeweed-based modified biochar adsorbent.

[0052] Weigh 0.2 g of the biochar adsorbent described in Example 1 and add it to 100 mL of wastewater with vanadium ion concentrations of 50 mg / L and 200 mg / L respectively. Stir and react for 6 h at a shaking speed of 120 rpm. Then take the supernatant and filter it through a 0.45 μm filter membrane. Use an inductively coupled plasma optical emission spectrometer (ICP-OES) to measure the remaining vanadium concentrations in the filtrate, which are 1.78 and 9.74 mg / L respectively. Calculate that the removal rates of the pokeweed-based modified biochar for vanadium ions reach 96.44% and 95.13%.

[0053] Example 2

[0054] (1) Wash the surface impurities of the pokeweed with water, dry it at room temperature, crush it through a 0.25 mm sieve, and store it in a desiccator for later use;

[0055] (2) Take 10 g of the pokeweed powder from step (1) and pour it into a mortar. Then weigh 3.5 g of solid NaOH and 6 g of mixed iron salt solid (4 g of Fe 2 (SO 4 ) 3 and 2Fe(NO 3 ) 3 ) and add them to the mortar. After grinding evenly, pass it through a 0.25 mm sieve;

[0056] (3) Place the mixture powder from step (2) in a vacuum tube furnace for pyrolysis. The heating rate is 10 °C / min. Pyrolyze at 340 °C for 1.5 h, then continue to heat at 10 °C / min until the temperature reaches 700 °C, and pyrolyze for 1.5 h. Pass high-purity nitrogen throughout the process. After pyrolysis, cool it to room temperature and take it out to finally obtain the pokeweed-based modified biochar adsorbent.

[0057] Weigh 0.2 g of the biochar adsorbent described in Example 2 and add it to 100 mL of wastewater with vanadium ion concentrations of 50 mg / L and 200 mg / L respectively. Stir and react for 6 h at a shaking speed of 120 rpm. Then take the supernatant and filter it through a 0.45 μm filter membrane. Use an inductively coupled plasma optical emission spectrometer (ICP-OES) to measure the remaining vanadium concentrations in the filtrate, which are 1.93 and 9.82 mg / L respectively. Calculate that the removal rates of the pokeweed-based modified biochar for vanadium ions reach 96.14% and 95.09%.

[0058] Example 3

[0059] (1) Wash the surface impurities of the pokeweed with water, dry it at room temperature, crush it through a 0.25 mm sieve, and store it in a desiccator for later use;

[0060] (2) Take 10 g of the pokeweed powder from step (1) and pour it into a mortar. Then weigh 4 g of solid NaOH and 7 g of mixed iron salt solid (5 g of Fe2 (SO 4 ) 3 and 2 g of Fe(NO 3 ) 3 ) were added to a mortar, ground evenly and then passed through a 0.25 mm sieve;

[0061] (3) The mixture powder obtained in step (2) was pyrolyzed in a vacuum tube furnace at a heating rate of 10 °C / min, pyrolyzed at 350 °C for 1 h, and then continuously heated at 10 °C / min until the temperature reached 750 °C, and pyrolyzed for 2 h. High-purity nitrogen was passed through the whole process. After pyrolysis, it was cooled to room temperature and taken out. Finally, the pokeweed-based modified biochar adsorbent was obtained.

[0062] Weigh 0.2 g of the biochar adsorbent described in Example 3 and add it to 100 mL of wastewater with vanadium ion concentrations of 50 mg / L and 200 mg / L respectively. Stir and react for 6 h at a shaking speed of 120 rpm. Then take the supernatant and pass it through a 0.45 μm filter membrane. Use an inductively coupled plasma optical emission spectrometer (ICP-OES) to measure the remaining vanadium concentrations in the filtrate to be 2.15 and 9.16 mg / L respectively. It was calculated that the removal rates of the pokeweed-based modified biochar for vanadium ions reached 95.70% and 95.42%.

[0063] Comparative Example 1:

[0064] (1) Wash the surface impurities of the pokeweed with water, dry it at room temperature, crush it and pass it through a 0.25 mm sieve, and then store it in a desiccator for later use;

[0065] (2) Place 10 g of the pokeweed powder obtained in step (1) in a vacuum tube furnace for pyrolysis at a heating rate of 10 °C / min. Pyrolyze at 750 °C for 3 h. High-purity nitrogen was passed through the whole process. After pyrolysis, it was cooled to room temperature and taken out. Finally, the pokeweed-based biochar adsorbent was obtained.

[0066] Weigh 0.2 g of the biochar adsorbent described in the comparative example and add it to 100 mL of wastewater with vanadium ion concentrations of 50 mg / L and 200 mg / L respectively. Stir and react for 6 h at a shaking speed of 120 rpm. Then take the supernatant and pass it through a 0.45 μm filter membrane. Use an inductively coupled plasma optical emission spectrometer (ICP-OES) to measure the remaining vanadium concentrations in the filtrate to be 37.06 and 160.92 mg / L respectively. It was calculated that the removal rates of the unmodified biochar for vanadium ions reached 25.88% and 19.54%.

[0067] Comparative Example 2:

[0068] (1) Wash the surface impurities of the pokeweed with water, dry it at room temperature, crush it and pass it through a 0.25 mm sieve, and then store it in a desiccator for later use;

[0069] (2) Weigh 3 g of NaOH and 4 g of Fe 2 (SO 4 ) 3 and 2 g of Fe(NO 3 ) 3 ) and dissolve them in 50 mL of deionized water. Place 10 g of the pokeweed powder from step (1) into the above solution and stir evenly. Add the obtained suspension into a high-pressure reaction kettle with a polytetrafluoroethylene inner liner, and carry out hydrothermal reaction at 220 °C for 4 h to finally obtain a modified hydrothermal carbon adsorbent.

[0070] Weigh 0.2 g of the hydrothermal carbon adsorbent described in Comparative Example 2 and add them into 100 mL of wastewater with vanadium ion concentrations of 50 mg / L and 200 mg / L respectively. Stir and react at a shaking speed of 120 rpm for 6 h. Then take the supernatant and filter it through a 0.45 μm filter membrane. Use an inductively coupled plasma optical emission spectrometer (ICP-OES) to measure the remaining vanadium concentrations in the filtrate as 30.92 and 140.74 mg / L respectively. Calculate that the removal rates of the modified hydrothermal carbon for vanadium ions reach 38.16% and 29.63%.

[0071] Comparative Example 3:

[0072] (1) Wash the surface impurities of the pokeweed with water and dry it at room temperature. After grinding it through a 0.25 mm sieve, store it in a desiccator for later use;

[0073] (2) Take 10 g of the pokeweed powder from step (1) and pour it into a mortar. Then weigh 4 g of solid NaOH and 5 g of solid ferric chloride and add them to the mortar. After grinding evenly, pass it through a 0.25 mm sieve;

[0074] (3) Place the mixture powder from step (2) in a vacuum tube furnace for pyrolysis. The heating rate is 10 °C / min. Pyrolyze at 350 °C for 1 h, and then continue to heat at 10 °C / min until the temperature reaches 750 °C and pyrolyze for 2 h. Pass high-purity nitrogen throughout the process. After the pyrolysis is completed, cool it to room temperature and take it out to finally obtain a pokeweed-based biochar adsorbent.

[0075] Weigh 0.2 g of the biochar adsorbent described in Comparative Example 3 and add them into 100 mL of wastewater with vanadium ion concentrations of 50 mg / L and 200 mg / L respectively. Stir and react at a shaking speed of 120 rpm for 6 h. Then take the supernatant and filter it through a 0.45 μm filter membrane. Use an inductively coupled plasma optical emission spectrometer (ICP-OES) to measure the remaining vanadium concentrations in the filtrate as 26.325 and 127.16 mg / L respectively. Calculate that the removal rates of the pokeweed-based modified biochar for vanadium ions reach 47.35% and 36.42%.

[0076] Experimental Example 1

[0077] Compare the vanadium removal rates of the modified pokeweed-based biochars in Examples 1, 2, and 3 of the present invention with the unmodified pokeweed-based biochar in Comparative Example 1 and the modified pokeweed-based hydrochar in Comparative Example 2, draw a bar chart of the vanadium removal rates, and analyze the effects of different biochars on vanadium removal. The comparison results are as Figure 1 shown.

[0078] As Figure 1 can be seen, the vanadium removal rates of the modified pokeweed-based biochars prepared by the method of the present invention are all above 95%, while the vanadium removal rate of the unmodified pokeweed-based biochar is only 19.54 - 25.88%, and the vanadium removal rate of the modified pokeweed-based hydrochar prepared at 220°C is also relatively low, being 29.63 - 38.16%. The results prove that the modified pokeweed-based biochar prepared by the method of the present invention has good vanadium adsorption effect.

[0079] Experimental Example 2

[0080] Figure 2 The SEM image of the modified pokeweed-based biochar prepared by the method of Example 1 of the present invention is shown. It can be seen that after the co-pyrolysis of pokeweed powder and the composite modifier, its fiber structure is destroyed, promoting the generation of a large number of porous structures in the pokeweed powder, thereby increasing its adsorption sites; at the same time, iron oxide particles are successfully loaded on the surface of the modified biochar, and vanadium ions can be removed from water through coprecipitation.

[0081] In addition, the specific surface areas and pore volumes of the unmodified biochar, modified pokeweed-based biochar, and modified hydrochar were compared (using the BET specific surface area test method, and the instrument used was a full-automatic nitrogen adsorption specific surface area tester), as shown in Table 1. The results show that the modified pokeweed-based biochar prepared by the method of the present invention has the largest specific surface area and pore volume, thus having stronger adsorption performance.

[0082] Table 1 Specific surface areas, pore diameters, and pore volumes of different biochars

[0083]

[0084]

[0085] Experimental Example 3

[0086] Figure 3 The infrared spectra of the modified pokeweed-based biochar (Example 1) prepared by the method of the present invention were compared with the unmodified biochar (Comparative Example 1) and the modified hydrochar (Comparative Example 2). Compared with the unmodified biochar, functional groups such as -CHOH, C-O, and Fe-O appeared on the surface of the modified biochar obtained by the method of the present application. Therefore, the modified biochar has better adsorption performance for vanadium metal in wastewater.

[0087] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of each raw material of the present invention's product, the addition of auxiliary components, the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. Application of pokeweed-based modified biochar in treating heavy metal vanadium in wastewater, Characterized in that, The preparation method of pokeweed-based modified biochar includes: (1) Mix the pokeweed powder, NaOH solid, and the mixed ferric salt solid Fe 2 (SO 4 ) 3 、Fe(NO 3 ) 3 to obtain mixture A. Among them, the mass ratio of the solid Fe 2 (SO 4 ) 3 to Fe(NO 3 ) 3 is 2:1 to 3:1, the mass ratio of the pokeweed powder to the solid NaOH is 1:0.3 to 0.4, and the mass ratio of the pokeweed powder to the mixed ferric solid is 1:0.5 to 0.7; (2) Pyrolyze the mixture A in an inert atmosphere. The pyrolysis process is divided into a first pyrolysis stage and a second pyrolysis stage. The temperature of the first pyrolysis is controlled at 320-350 °C, and the temperature of the second pyrolysis stage is controlled at 600-750 °C; after pyrolysis, cool to room temperature to obtain pokeweed-based modified biochar.

2. The application according to claim 1, Characterized in that, In the first pyrolysis stage, heat up from room temperature to 320-350 °C at a pyrolysis rate of 8-12 °C / min; In the second pyrolysis stage, heat up from 320-350 °C to 600-750 °C at a pyrolysis rate of 8-12 °C / min.

3. The application according to claim 1, Characterized in that, In the first pyrolysis stage, heat up from room temperature to 320-350 °C at a pyrolysis rate of 10 °C / min; In the second pyrolysis stage, heat up from 320-350 °C to 600-750 °C at a pyrolysis rate of 10 °C / min.

4. The application according to any one of claims 1-3, Characterized in that, The first pyrolysis stage is pyrolyzed at a temperature of 320-350 °C for 1 h to 2 h.

5. The application according to any one of claims 1-3, Characterized in that, The second pyrolysis stage is pyrolyzed at a temperature of 600-750 °C for 1.5 h to 3 h.

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