A modified biochar and a preparation method and application thereof

Abstract

The application discloses modified biochar as well as a preparation method and application thereof, mixes biomass and sepiolite powder, obtains mixed solid matters through ball milling; adds the obtained mixed solid matters into water, carries out ultrasonic treatment, obtains biomass / sepiolite mixed slurry; carries out microwave heating on the obtained biomass / sepiolite mixed slurry, carries out reaction, and obtains the modified biochar. The modified biochar provided by the application realizes the synergistic effect of the biochar and the sepiolite by microwave co-pyrolysis, and the sepiolite is closely combined with the biochar to prepare a composite material. Compared with traditional biochar, the modified biochar improves the lead removal effect of water bodies and soil, has a lower lead leaching risk, and simultaneously, the preparation method and cost are improved, and the modified biochar can be used as an adsorbent for treating lead-containing wastewater and a lead pollution soil passivator.

Description

TECHNICAL FIELD

[0001] The present application relates to a heavy metal pollution treatment technology, and in particular to a modified biochar and a preparation method and application thereof. BACKGROUND

[0002] Rapid industrialization and urbanization inevitably lead to serious heavy metal pollution, which threatens the ecological system and human health. Lead is a common heavy metal and also one of the main heavy metal pollutants in China. Lead has high toxicity and carcinogenicity, enters the human body through water and food chains, and causes symptoms of acute or chronic poisoning of the respiratory tract, digestive, nervous, blood, urinary and immune systems, and even death. Lead is mainly produced from flue gas, wastewater and solid waste generated by industry, agriculture and mining, and if not properly discharged, it will directly pollute the atmosphere, hydrosphere and pedosphere. At the same time, heavy metals in the atmosphere and wastewater can also be transferred and accumulated in the soil through precipitation, which not only reduces soil quality, microbial activity and crop productivity, but also endangers ecological safety and human health.

[0003] At present, various technologies have been developed to treat lead pollution. For water body lead pollution, technologies such as chemical precipitation, flotation, ion exchange, solvent extraction, etc. are used; for soil lead pollution, technologies such as soil replacement, chemical leaching, super-accumulating plant extraction, etc. are used. Biochar is a carbonaceous organic matter prepared by pyrolysis of biomass under anaerobic or limited oxygen conditions in a closed system. Due to its negative surface charge, charge density, high porosity and large specific surface area, it is considered to be a low-cost material with sufficient applicability and selectivity, which can be used to remove lead from water bodies or passivate soil. Compared with other technologies, the use of biochar has the advantages of simplicity, low cost and safety, making it the most promising solution to lead pollution at present.

[0004] Although biochar is currently the main material for heavy metal pollution remediation, it has the limitation of low adsorption capacity, so it is usually necessary to optimize its preparation method or modify it to improve its adsorption performance. At present, the preparation and modification methods of biochar are mainly tube furnace pyrolysis and solvent modification. However, tube furnace pyrolysis has the technical defects of uneven heating of raw materials and harsh oxygen-limited conditions; solvent modification requires the preparation of biochar products before modification, which is energy-consuming and complicated. Therefore, it is urgent to develop new biochar preparation and modification technologies to improve its adsorption performance for lead. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the deficiencies and defects mentioned in the above background technology, and to provide a modified biochar and a preparation method and application thereof to improve its adsorption performance for lead.

[0006] To solve the above technical problems, the technical solution proposed by the present application is:

[0007] A method for preparing a modified biochar, comprising the following steps:

[0008] (1) mixing biomass with sepiolite powder at a mass ratio of 1-4:1, and ball milling to obtain a mixed solid;

[0009] (2) adding the mixed solid obtained in step (1) into water, and performing ultrasonic treatment to obtain a biomass / sepiolite mixed slurry;

[0010] (3) performing microwave heating on the biomass / sepiolite mixed slurry obtained in step (2), maintaining the temperature at 100-600°C to perform reaction, and obtaining the modified biochar.

[0011] As a further improvement, the biomass in step (1) is a lignocellulose-based straw material.

[0012] As a further improvement, the ball milling speed in step (1) is 400-600 rpm, and the time is 5-20 minutes.

[0013] As a further improvement, the liquid-solid ratio of the mixed solid to water in step (2) is 2-10:1, and the ultrasonic treatment time is 10-30 minutes.

[0014] As a further improvement, the microwave power in step (3) is 300-800 W, and the reaction time is 0.5-8 hours.

[0015] As a further improvement, the temperature in step (3) is 300-500°C, the microwave power is 400-650 W, and the reaction time is 0.5-3 hours.

[0016] The present application also provides a modified biochar prepared by the method, wherein sepiolite particles are attached to the surface of the biochar.

[0017] The present application also provides the use of the modified biochar prepared by the method in removing lead from water bodies or passivating lead in soil.

[0018] As a further improvement, for a water body containing lead, 0.1-0.5 g of the modified biochar is added for every 50 mg of lead; for soil containing lead, 5-15 g of the modified biochar is added for every 50 mg of lead.

[0019] As a further improvement, for a water body containing lead, the reaction conditions are: pH 3-6, and the reaction time at room temperature is more than 2 hours; for soil containing lead, the reaction conditions are: maintaining the soil moisture content at 30-50%, and aging at room temperature for more than 15 days.

[0020] The present application prepares a composite material by closely combining sepiolite and biochar, which improves the micro-morphology of biochar by microwave pyrolysis to provide good reaction point for lead adsorption, and further improves the lead removal effect by the synergistic effect of sepiolite, thereby solving the technical problem of low lead adsorption capacity of biochar material.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] 1. The modified biochar provided by the present application is heated inside and outside at the same time by microwave pyrolysis, which improves the specific surface area and pore volume of biochar, and significantly improves the lead removal and lead passivation performance of water and soil compared with direct pyrolysis, and the microwave pyrolysis only requires a lower pyrolysis temperature and does not require inert gas assistance, thereby reducing production costs.

[0023] 2. The modified biochar provided by the present application is modified by co-pyrolysis with sepiolite; on the one hand, the addition of sepiolite can accelerate the pyrolysis of biomass, increase the degree of aromatic condensation of biochar, and reduce the oxidation of biochar, thereby improving the stability of the obtained biochar; on the other hand, sepiolite has good heavy metal adsorption capacity as a clay mineral, and sepiolite particles adhere to the surface of biochar at high temperature to play a modification role, and the biochar / sepiolite synergistic effect can further improve the lead removal and lead passivation effect.

[0024] 3. The present application co-pyrolyzes sepiolite and biochar by one-step method, reduces the use of acid, alkali and organic solvent in traditional solvent modification, simplifies the preparation process of modified biochar, saves energy and reduces production costs. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0026] Figure 1 is a scanning electron microscope image of the modified biochar prepared in Example 1;

[0027] Figure 2 is a scanning electron microscope image of the modified biochar prepared in Example 2 after adsorbing lead;

[0028] Figure 3 is an X-ray energy spectrum analysis diagram of the modified biochar prepared in Example 2 after adsorbing lead;

[0029] Figure 4 is a scanning electron microscope image of the modified biochar prepared in Example 3;

[0030] Figure 5 is the result of the modified biochar prepared in Example 4 for lead removal experiment (influence of pyrolysis temperature on removal rate);

[0031] Figure 6 is the result of the modified biochar prepared in Example 5 for lead removal experiment (influence of microwave power on removal rate);

[0032] Figure 7 is the result of the modified biochar prepared in Example 6 for lead removal experiment (influence of pyrolysis time on removal rate);

[0033] Figure 8 is the proportion of each form of lead in the soil during the aging of the soil in the application example;

[0034] Figure 9 is the comparison of the lead removal effect of the biochar prepared in the comparative example and the modified biochar prepared in Example 3. DETAILED DESCRIPTION

[0035] In order to facilitate the understanding of the present application, the present application will be described in more detail and in a more complete and specific manner below in conjunction with the accompanying drawings and preferred embodiments, but the scope of protection of the present application is not limited to the following specific embodiments.

[0036] Unless otherwise defined, all the professional terms used herein have the same meaning as generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing the specific embodiments and are not intended to limit the scope of protection of the present application.

[0037] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0038] Biochar material is an important means for heavy metal pollution remediation. Although biochar is applied in various fields of heavy metal remediation due to its low raw material cost, environmental friendliness and simple operation, its preparation cost, cycle and lead removal effect still have room for improvement. Therefore, effective biochar synthesis routes need to be explored from the aspects of preparation means and modification methods to simplify the preparation steps, optimize the preparation cost, form larger specific surface area and more abundant porous structure, and further improve the lead removal performance.

[0039] In some specific embodiments, the modified biochar provided by the present application comprises biomass and sepiolite solid powder in a mass ratio of (1-4): 1. The sepiolite powder is uniformly and closely combined with the biochar, and the sepiolite particles are attached to the surface of the biochar.

[0040] Traditional biochar preparation uses tubular furnace pyrolysis, that is, using electric heating wire to heat, and heating biomass. In the whole process, heat is transferred from the furnace body to the biomass through heat conduction, heat convection and heat radiation, and the heating process of the biomass is from outside to inside. Therefore, temperature gradient is inevitably generated, leading to uneven heating and affecting the quality of biochar. At the same time, tubular furnace pyrolysis requires high pyrolysis temperature, long pyrolysis time and inert gas assistance, which increases the preparation cost and cycle. Modification of biochar is the mainstream method to improve the lead removal performance of biochar at present, but the traditional solvent modification method needs to prepare original carbon first and then modify, which consumes high energy and has complicated steps. Based on the above two technical defects, the modified biochar is prepared by using microwave co-pyrolysis method. On the one hand, the pyrolysis temperature and time of biochar are significantly reduced by microwave pyrolysis characteristics, and the production cost is reduced, and the heating process is more uniform, which is beneficial to the formation of loose and porous structure of biochar; on the other hand, sepiolite and biochar are co-pyrolyzed by one-step method, which reduces the use of acid, alkali and organic solvent in the traditional solvent modification method, simplifies the preparation process of modified biochar, saves energy and reduces production cost. At the same time, sepiolite is a cheap and easily available clay mineral, and its surface has a large number of negative charges, which has strong adsorption capacity for lead, and can play a synergistic effect with biochar to further improve the lead removal performance of modified biochar.

[0041] In some specific embodiments, the preparation method of the modified biochar of the present application adopts microwave co-pyrolysis method, and the specific steps are as follows:

[0042] (1) mixing biomass and sepiolite powder in a mass ratio of 1-4:1, ball milling to obtain a mixed solid.

[0043] Preferably, the biomass adopts lignocellulose-based straw material.

[0044] In some specific embodiments, the specific surface area of the biomass is between 1-30 m 2 / g, the pore volume is between 0.1-0.15 cm 3 / g, the pore size is between 2-5 nm, and the particle size range is between 100-200 mesh.

[0045] In some specific embodiments, the specific surface area of the sepiolite solid powder is 20-110 m 2 / g, the pore volume is 0.05-0.2 cm 3 / g, the pore size is 10-20 nm, and the particle size range is between 100-200 mesh.

[0046] Preferably, ball milling is carried out at a speed of 400-600 revolutions per minute, and the ball milling time is 5-20 minutes.

[0047] (2) adding the mixed solid obtained in step (1) into water, and performing ultrasonic oscillation to obtain a biomass / sepiolite mixed slurry.

[0048] Preferably, the mixed solid is added into deionized water at a liquid-solid ratio of 2-10:1 (w / w), and ultrasonic oscillation is performed for 10-30 minutes.

[0049] (3) performing microwave heating on the biomass / sepiolite mixed slurry obtained in step (2) to maintain a temperature of 100-600°C (preferably 300-500°C), drying and grinding after reaction to obtain the modified biochar.

[0050] Preferably, the reaction time is 0.5-8 hours, more preferably 0.5-3 hours, and more preferably 2 hours. Preferably, the microwave power is 300-800 W, and more preferably 400-650 W.

[0051] The modified biochar provided by the present application is applied to removal of lead in water bodies and passivation of lead in soil.

[0052] In some specific embodiments, for a water body containing lead elements of 50-200 mg / L, the modified biochar provided by the present application is added, so that 0.1-0.5 g of the modified biochar is added for each 50 mg of lead, and the reaction condition is pH of 3-6, room temperature (for example, 15-35°C) and reaction time of 2 hours or more; for soil containing lead elements of 50-200 mg / kg, the modified biochar provided by the present application is added, so that 5-15 g of the modified biochar is added for each 50 mg of lead, and the reaction condition is to maintain the water content of the soil at 30-50% (wt) and to age at room temperature for 15 days or more.

[0053] In some specific embodiments, solid-liquid separation is performed on the mixture after reaction, for example, centrifugation or suction filtration, so as to recover the modified biochar.

[0054] The inventors have prepared and modified biochar by using various heating methods including tube furnace pyrolysis and microwave pyrolysis, and experiments show that the adsorption capacity of the modified biochar prepared by microwave co-pyrolysis for lead in water bodies and the passivation capacity of the modified biochar for lead in soil are significantly higher than those of the biochar prepared by tube furnace pyrolysis; at the same time, the inventors have also confirmed that the microwave pyrolysis parameters and the ratio of biomass to sepiolite have a complex effect on the modified biochar, and in different pyrolysis temperatures, different microwave powers, different pyrolysis times and different sepiolite addition ratios, a relatively obvious phenomenon of improved treatment effect is shown in discrete multiple regions.

[0055] The removal efficiency of the modified biochar prepared by the present application for lead in water bodies can reach 97%, the proportion of weak acid extractable lead in lead-contaminated soil can be reduced by 62% within 15 days, and a stable passivation effect can be maintained within 60 days.

[0056] The application adopts a one-step method to prepare modified biochar, and realizes the synergistic effect of biochar and sepiolite by microwave co-pyrolysis to tightly combine sepiolite and biochar to prepare a composite material. Compared with traditional biochar, the lead removal effect of water and soil is improved, the lead leaching risk is lower, and the preparation method and cost are improved, which can be used as an adsorbent for treating lead-containing wastewater and a passivator for lead-contaminated soil.

[0057] The lead removal rate determination and calculation method in the embodiment of the application is as follows:

[0058] 2 groups of 10 250mL lead-containing solutions with an initial concentration of 200mg / L were prepared, and the solution was prepared by Pb(NO3)2. 0.1g of modified biochar was added respectively, and the oscillation reaction was carried out in a constant temperature shaker at 25 DEG C, the rotation speed was 180r / min, after 8h of reaction, static sinking, after filtration with 0.22mu m water phase filter membrane, the supernatant was determined by inductively coupled plasma emission spectrometer, and the lead removal rate was calculated.

[0059] Example 1

[0060] The modified biochar preparation method of the embodiment adopts a microwave co-pyrolysis method, and the specific steps are as follows:

[0061] (1) 0.8g of giant reed straw powder passing through a 100 mesh sieve and 0.2g of sepiolite powder passing through a 200 mesh sieve were weighed, and ball milling was carried out at a speed of 400r / min for 5min. Then the solid mixture was added into a 50mL beaker, 10mL of deionized water was added, and ultrasonic oscillation was carried out for 10min;

[0062] The specific surface area of the biomass (giant reed straw powder) is 15.14m 2 / g, the pore volume is 0.064cm 3 / g, and the particle size range is 100 mesh sieve; the specific surface area of the sepiolite solid powder is 38.77m 2 / g, and the pore volume is 0.093cm 3 / g;

[0063] (2) the mixed slurry was added into a JUPITER-B microwave digestion instrument matched with a sample dissolving cup, the sample dissolving cup was covered with a sealing cup cover, and was loaded into a reaction tank rack after being covered with a protective outer cover, and was tightened with a 2N torque wrench, and was placed in the microwave digestion instrument, and temperature and pressure probes were connected; the microwave digestion instrument was set, the microwave power was kept at 600W and the reaction time was kept at 2h, the temperature was set at 300 DEG C, and after setting the parameters, the program was run, the protection door was closed, and the program was run; after the reaction was completed, the mixed slurry was taken out after natural cooling to room temperature;

[0064] (3) the mixed slurry obtained in step (2) was dried at 80 DEG C and ground to obtain the modified biochar.

[0065] The modified biochar prepared in the embodiment comprises biomass and sepiolite solid powder in a mass ratio of 4:1. An electron microscope photograph is shown in Figure 1 The sepiolite is closely combined with the biochar, and sepiolite particles are attached to the surface of the biochar. The specific surface area of the modified biochar is 56.24 m 2 / g, and the pore volume is 0.31 cm 3 / g.

[0066] Embodiment 2

[0067] The modified biochar prepared in the embodiment comprises biomass and sepiolite solid powder in a mass ratio of 4:1. An electron microscope photograph is shown in

[0068] (1) 0.5 g of giantreed straw powder passing through a 200-mesh sieve and 0.5 g of sepiolite powder passing through a 100-mesh sieve were weighed and ball-milled at a speed of 400 r / min for 5 minutes. Then the solid mixture was added into a 50-mL beaker, 10 mL of deionized water was added, and ultrasonic oscillation was performed for 10 minutes;

[0069] The specific surface area of the biomass (giantreed straw powder) is 21.17 m 2 / g, the pore volume is 0.13 cm 3 / g, and the particle size range is 200-mesh sieve. The specific surface area of the sepiolite solid powder is 31.75 m 2 / g, and the pore volume is 0.17 cm 3 / g.

[0070] (2) The mixed slurry was added into a sample dissolving cup matched with the JUPITER-B microwave digestion instrument, the sample dissolving cup was covered with a sealing cup cover, and was loaded into a reaction tank rack after being covered with a protective outer cover, and was twisted tightly with a 2N torque wrench. The temperature probe and pressure probe were connected. The microwave digestion instrument was set, the microwave power was kept at 600 W, the reaction time was kept at 1 h, the temperature was set at 600℃, and the parameters were set after the program was run. The protection door was closed, and the program was run. After the reaction was completed, the mixed slurry was taken out after natural cooling to room temperature;

[0071] (3) The mixed slurry obtained in step (2) was dried at 80℃ and ground to obtain the modified biochar.

[0072] The modified biochar prepared in the embodiment comprises biomass and sepiolite solid powder in a mass ratio of 4:1. An electron microscope photograph is shown in 2 / g, and the pore volume is 0.41 cm 3 / g. Figure 2 is a scanning electron microscope photograph after lead attachment, and the modified biochar presents an irregular fragment structure, and the sepiolite is uniformly combined with the biochar; Figure 3is the X-ray energy spectrum analysis chart after adsorbing lead. From the X-ray energy spectrum analysis results of the selected points, it can be seen that lead has been successfully adsorbed on the surface of the modified biochar.

[0073] Example 3

[0074] The modified biochar preparation method of the embodiment adopts a microwave co-pyrolysis method, and the specific steps are as follows:

[0075] (1) 0.6 g of giant reed straw powder passing through a 200 mesh sieve and 0.4 g of sepiolite powder passing through a 200 mesh sieve are weighed, and ball milled at a speed of 400 revolutions per minute for 5 minutes. Then the solid mixture is added to a 50 mL beaker, 10 mL of deionized water is added, and ultrasonic oscillation is performed for 10 minutes;

[0076] The specific surface area of the biomass (giant reed straw powder) is 25.62 m 2 / g, the pore volume is 0.097 cm 3 / g, and the particle size range is 200 mesh sieve; the specific surface area of the sepiolite solid powder is 37.85 m 2 / g, and the pore volume is 0.21 cm 3 / g;

[0077] (2) The mixed slurry is added to the sample dissolving cup matched with the JUPITER-B microwave digestion instrument, the sample dissolving cup is covered with a sealing cup cover, and then the protective outer cover is covered and loaded into the reaction tank rack. The 2N torque wrench is tightened, and the temperature probe and pressure probe are connected. The microwave digestion instrument is set, the microwave power is kept at 800 W, the reaction time is set at 0.5 h, the temperature is set at 400℃, and the parameters are set. After running the program, close the protection door and run the program; after the reaction is completed, it is naturally cooled to room temperature, and the mixed slurry is taken out;

[0078] (3) The mixed slurry obtained in step (2) is dried at 80℃ and ground to obtain the modified biochar.

[0079] The modified biochar prepared in this embodiment includes biomass and sepiolite solid powder in a mass ratio of 1.5:1. The electron microscope photo is shown in Figure 4 , the sepiolite is closely combined with the biochar, and the sepiolite particles are attached to the surface of the biochar; the specific surface area of the modified biochar is 115.35 m 2 / g, and the pore volume is 0.52 cm 3 / g.

[0080] Example 4

[0081] The modified biochar preparation method of the embodiment adopts a microwave co-pyrolysis method, and the specific steps are as follows:

[0082] (1) Take 0.6g of giant reed straw powder sieved through a 200-mesh sieve and 0.4g of sepiolite powder sieved through a 200-mesh sieve, and ball mill at a speed of 400rpm for 5 minutes. Then add the solid mixture into a 50mL beaker, add 10mL of deionized water, and ultrasonically shake for 10 minutes;

[0083] (2) Put the mixed slurry into a sample dissolving cup matched with the JUPITER-B microwave digestion instrument, put on the sealing cup cover, put on the protective outer cover, and then put into the reaction tank rack, and tighten with a 2N torque wrench. Put it into the microwave digestion instrument, connect the temperature probe and pressure probe. Set the microwave digestion instrument to maintain a microwave power of 800W and a reaction time of 0.5h, and set the temperature to 100℃, 200℃, 300℃, 400℃, 500℃, and 600℃, respectively. Set the parameters and run the program, close the protection door, and run the program. After the reaction is completed, naturally cool to room temperature, and take out the mixed slurry;

[0084] (3) Dry and grind the mixed slurry obtained in step (2) at 80℃ to obtain the modified biochar.

[0085] The above prepared groups of modified biochar were subjected to lead removal reaction experiments to test their water body lead removal capacity, and the steps were as follows:

[0086] 0.1g of modified biochar was added to a conical flask containing 250mL of lead-containing solution with an initial concentration of 200mg / L, and the shaking reaction was carried out in a 25℃ constant temperature shaker at a speed of 180rpm. After 8h of reaction, the supernatant was filtered with a 0.22μm water phase filter membrane, and the lead concentration was measured by inductively coupled plasma emission spectrometer, and the lead removal rate was calculated.

[0087] The results are shown in Table 1. Figure 5 The lead removal reaction experiment showed that the pyrolysis temperature had a significant effect on the water body lead removal effect. High and low temperatures were not conducive to the improvement of the lead removal capacity of the modified biochar. The best reaction temperature was 400℃, and the better reaction temperature range was 300℃ to 500℃.

[0088] Example 5

[0089] The modified biochar preparation method of this example is the same as that of Example 4, except that the reaction temperature in step (2) is kept at 400℃ and the reaction time is 0.5h, and the microwave power is set to 300W, 400W, 500W, 600W, 700W, and 800W, respectively

[0090] The above prepared groups of modified biochar were subjected to lead removal reaction experiments to test their water body lead removal capacity, and the results are shown in Table 2. Figure 6The results of the lead removal reaction experiment show that the optimal microwave power is 600 W, and the microwave with appropriate power is conducive to the development of the pore structure of the biochar and the enhancement of the adsorption capacity of the biochar. However, when the power is too high, the structural strength of the obtained biochar is reduced, and the pore structure collapses, which is not conducive to subsequent use.

[0091] Example 6

[0092] The preparation method of the modified biochar in this example is the same as that in Example 4, except that the reaction temperature in step (2) is maintained at 400°C, the microwave power is set to 600 W, and the pyrolysis time is set to 0.5 h, 1 h, 2 h, 4 h, and 6 h, respectively.

[0093] The above-prepared groups of modified biochar were subjected to lead removal reaction experiments to test their water body lead removal capacity, and the results are shown in Figure 7 The results of the lead removal reaction experiment show that the optimal pyrolysis time is 2 h, and the lead removal capacity increases first and then decreases with the extension of the preparation reaction time.

[0094] Application Example

[0095] Different lead-contaminated soils (all taken from lead-contaminated farmland in Wancheng County, Changsha City) with a lead concentration of 223.3 mg / g were taken. The soil samples were air-dried, ground, and passed through a 100-mesh sieve. 1000 g of soil was taken in a 2L flowerpot, and the modified biochar prepared in Example 3 was added and mixed uniformly. The mixture was aged at room temperature for 60 days, and the soil moisture content was maintained at 30-50% and stirred regularly during the aging period. The soil was dried, ground, and passed through a 200-mesh sieve at 7, 15, 30, and 60 days, respectively. The BCR extraction method was used to determine the proportion of each form of lead in the soil during the aging period, and the results are shown in Figure 7

[0096] As can be seen from Figure 8 , with the extension of the aging time, the proportion of acid-extractable lead (weakly acid-soluble lead) in the soil decreases first and then remains stable, i.e., the bioavailability of lead decreases. The passivation effect reaches the best at 15 days of aging, and then remains basically stable until 60 days.

[0097] Comparative Example

[0098] (a) The preparation method of the modified biochar in this comparative example is the same as that in Example 3, except that no deionized water is added in step (1), and the pyrolysis is performed in a tube furnace at 400°C for 0.5 h in step (2);

[0099] (b) The preparation method of the biochar in this comparative example is the same as that in Example 3, except that no sepiolite is added in step (1).

[0100] (c) The preparation method in this comparative example is the same as that in Example 3, except that no biomass is added in step (1).

[0101] ​The two prepared biochar were applied to water body to remove lead, and the results, as shown in Figure 9 Figure 3, show that the material prepared in Example 3 has obvious advantages in lead removal effect at different lead concentrations, compared with unmodified biochar, biochar prepared by tubular furnace pyrolysis, and microwave-activated sepiolite.

[0102] The above is only the preferred embodiment of the present application, and does not limit the present application in any form. Therefore, any simple modification, equivalent change and modification of the above embodiment according to the technical essence of the present application, without departing from the technical scheme of the present application, shall fall within the protection scope of the technical scheme of the present application.

Claims

1. A method of producing a modified biochar, characterized by, The method comprises the following steps: (1) mixing biomass and sepiolite powder at a mass ratio of 1-4:1, and ball milling to obtain a mixed solid; the biomass is a lignocellulose-based straw material; (2) adding the mixed solid obtained in step (1) into water, and performing ultrasonic treatment to obtain a biomass / sepiolite mixed slurry; (3) performing microwave heating on the biomass / sepiolite mixed slurry obtained in step (2), maintaining the temperature at 300-500 DEG C to perform reaction, and obtaining the modified biochar; the power of the microwave is 400-650 W; In the modified biochar, sepiolite particles are attached to the surface of the biochar.

2. The method of producing a modified biochar according to claim 1, characterized in that, In step (1), the ball milling speed is 400-600 rpm, and the time is 5-20 minutes.

3. The method of claim 1, wherein the modified biochar is produced by, In step (2), the liquid-solid ratio of the mixed solid to water is 2-10:1, w / w, and the ultrasonic treatment time is 10-30 minutes.

4. The method of producing a modified biochar according to claim 1, wherein, In step (3), the reaction time is 0.5-8 hours.

5. The method of claim 4, wherein the modified biochar is prepared by, In step (3), the reaction time is 0.5-3 hours.

6. Application of the modified biochar prepared by the method of any one of claims 1-5 in removing lead in water or passivating lead in soil.

7. Use according to claim 6, characterized in that, For lead-containing water, the modified biochar is added, so that 0.1-0.5 g of the modified biochar is added for every 50 mg of lead; for lead-containing soil, the modified biochar is added, so that 5-15 g of the modified biochar is added for every 50 mg of lead.

8. Use according to claim 7, characterized in that, For lead-containing water, the reaction conditions are: pH is 3-6, and the reaction time at room temperature is more than 2 h; for lead-containing soil, the reaction conditions are: the water content of the soil is maintained at 30-50%, and the aging time at room temperature is more than 15 days.

Images