Vermiculite magnetic modified biomass charcoal as well as preparation method and application thereof

Abstract

The invention relates to the technical field of biomass charcoal, in particular to vermiculite magnetic modified biomass charcoal as well as a preparation method and application thereof, and the vermiculite magnetic modified biomass charcoal is obtained by mixing magnetic modified biomass charcoal with expanded vermiculite and carrying out anaerobic heating and ball milling; the mass of the vermiculite accounts for 1%-20% of the mass of the magnetic modified biomass charcoal; the magnetic modified biomass charcoal is obtained by mixing magnetite turbid liquid with a biomass raw material and then carrying out anaerobic pyrolysis. By adopting the vermiculite magnetic modified biomass charcoal, the remediation performance on heavy metals in soil can be effectively improved, the whole preparation process is simple, and the preparation cost is low.

Description

Technical Field

[0001] The invention relates to the technical field of biomass carbon, and in particular to a vermiculite magnetic modified biomass carbon and a preparation method and application thereof. Background Art

[0002] There are various types of heavy metal pollution in soil, which varies with regional changes, and it is a big challenge for the development of governance work. Among them, the problem of combined pollution of cadmium and arsenic is more prominent, which can affect the quality of crops and enter the human body through the food chain and accumulate, threatening human health. Due to the almost opposite chemical behaviors of cadmium and arsenic in the soil, their joint governance is difficult. The reduction of cadmium's migration ability requires the reduction of soil Eh or the increase of pH, but the reduction of arsenic's migration ability requires the increase of soil Eh or the decrease of pH. Therefore, researchers need to find a remediation method that can effectively control cadmium and arsenic combined pollution and is environmentally friendly.

[0003] Biochar is a material widely used in the remediation of heavy metals. However, its adsorption performance is relatively limited. Most of its surfaces are negatively charged, so it can adsorb cationic heavy metals well, but its adsorption capacity for anionic heavy metals, such as As, is relatively weak, and there is a problem that it is not easy to recycle after use.

[0004] Magnetite has a good ability to adsorb and fix As in the soil, and can combine with As in the soil through electrostatic adsorption, chelation, etc. Therefore, the magnetic iron oxide is attached to prepare magnetic modified biochar, which greatly increases the adsorption and fixation ability of As, and can be separated by an external magnetic field. However, the magnetic modified magnetite has a weak adsorption capacity for Cd in the soil, and it contains a high iron content. Long-term use will affect the soil nutrient balance, which is not conducive to the growth of crops. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a vermiculite magnetic modified biochar and a preparation method and application thereof, which can effectively improve the adsorption and fixation effect of As and Cd.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] The first aspect of the present invention provides a vermiculite magnetic modified biomass charcoal, wherein the vermiculite magnetic modified biomass charcoal is obtained by mixing the magnetic modified biomass charcoal with vermiculite, heating the mixture at 200°C to 220°C for 1h to 1.5h under anaerobic conditions, and then ball milling the mixture;

[0008] The mass of the vermiculite accounts for 1% to 20% of the mass of the magnetically modified biochar;

[0009] The magnetic modified biomass charcoal is obtained by mixing a magnetite suspension with a biomass raw material in a mass volume ratio of 1kg:10L-12L and subjecting the mixture to anaerobic pyrolysis.

[0010] The present invention mixes vermiculite with magnetically modified biochar, and can improve the adsorption capacity of Cd by controlling the addition amount of vermiculite. The vermiculite is mixed with the magnetically modified biochar in an addition amount of 1% to 20% of the mass of the magnetically modified biochar, and the highest adsorption condition for Cd is ensured while the voids of the magnetically modified biochar are not blocked. This is mainly because too much vermiculite addition will block the voids of the magnetically modified biochar, thereby affecting the adsorption capacity for Cd. As is adsorbed by the magnetically modified biochar, so that the obtained vermiculite magnetically modified biochar can have a good adsorption effect on both As and Cd heavy metals in the soil, and compared with single biochar, the vermiculite magnetically modified biochar has a better adsorption effect.

[0011] In another preferred embodiment, the vermiculite is expanded vermiculite with a particle size less than 2 mm.

[0012] In another preferred embodiment, the particle size of the vermiculite magnetically modified biochar is 10 μm to 100 μm.

[0013] In another preferred embodiment, the magnetite suspension is composed of Fe in FeSO4. 2+ and Fe in FeCl3 3+ It is obtained by co-precipitation in water, wherein the molar ratio of FeSO4 to FeCl3 is 1:1.8-2, and the initial concentration of FeSO4 is 0.09 mol / L-1.1 mol / L.

[0014] In another preferred embodiment, the biomass raw material is plant straw, and the plant straw is plant straw with a length of less than 0.5 cm after drying and crushing.

[0015] The second aspect of the present invention provides a method for preparing the vermiculite magnetic modified biochar, comprising the following steps:

[0016] Mix FeSO4 and FeCl3 in a molar ratio of 1:1.8-2, and coprecipitate in water to obtain a magnetite suspension;

[0017] The rice straw and the magnetite suspension are mixed in a mass volume ratio of 1 kg: 10 L to 12 L, the pH is adjusted to 11 to 12, stirred and reacted in a water bath at 60° C. to 65° C. for 2 h to 2.5 h, allowed to stand, and filtered to obtain a mixture;

[0018] Anaerobic pyrolysis of the mixture at 370° C. to 430° C. for 2 h to 2.5 h to obtain the magnetically modified biochar;

[0019] The magnetically modified biomass charcoal is mixed with expanded vermiculite, heated at 200° C. to 220° C. for 1 h to 1.5 h under anaerobic conditions, and ball-milled to obtain the vermiculite magnetically modified biomass charcoal.

[0020] In another preferred embodiment, the ball milling time is 1 h to 1.5 h.

[0021] The third aspect of the present invention provides the use of the vermiculite magnetic modified biomass charcoal in the preparation of soil heavy metal passivators.

[0022] In another preferred embodiment, the heavy metals are Cd and As.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The vermiculite magnetic modified biochar in the present invention has a good adsorption effect on heavy metals in the soil and is easy to recycle after use. By adding 1% to 20% of the mass of the magnetic modified biochar, the adsorption capacity for Cd can be improved, and the magnetic modified biochar is then used to adsorb As, so that the obtained vermiculite magnetic modified biochar can have a good adsorption effect on both As and Cd heavy metals in the soil, and compared with single biochar, the vermiculite magnetic modified biochar has a better adsorption effect.

[0025] The preparation cost of vermiculite magnetic modified biochar is low, which is similar to the preparation cost of biochar. It has extremely high economic feasibility and can be applied on a large scale. The cost is relatively low. It can reduce the risk of heavy metal pollution in the soil while improving soil fertility and properties. It can reduce the cost of soil remediation and agricultural production and increase farmers' economic benefits. The repaired soil is freeze-dried and then separated with a magnet, with a recovery rate of about 40% to 50%. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The figure is the structural characterization result of V-MBC; a is the X-ray diffraction spectrum of V-MBC and the standard XRD of magnetite and silicon-containing minerals, and b is the Fourier infrared spectrum of V-MBC. V-MBC represents vermiculite magnetic modified biochar.

[0027] Figure 2 The figure shows the effect of the initial pH of the solution on the removal rate of Cd(Ⅱ) and As(Ⅲ) by V-MBC; wherein, a is the effect of the removal rate of Cd(Ⅱ), and b is the effect of the removal rate of As(Ⅲ).

[0028] Figure 3 Figure 1 is the adsorption kinetic analysis result diagram of V-MBC for Cd(Ⅱ) and As(Ⅲ); wherein, a is the adsorption kinetic analysis result diagram of Cd(Ⅱ), and b is the adsorption kinetic analysis result diagram of As(Ⅲ).

[0029] Figure 4 Figure 3 is the isothermal adsorption curve of V-MBC for Cd(Ⅱ) and As(Ⅲ); where a is the isothermal adsorption curve of Cd(Ⅱ), and b is the isothermal adsorption curve of As(Ⅲ).

[0030] Figure 5 This is a diagram showing the dynamic changes of soil pH with different V-MBC addition amounts and PBC within 21 days, where PBC represents biochar.

[0031] Figure 6 This is a graph showing the changes in soil soluble organic carbon after 21 days of soil incubation.

[0032] Figure 7 This is the graph showing the changes in available Cd content in the soil after 21 days of soil cultivation.

[0033] Figure 8 This is the graph showing the changes in available As content in the soil after 21 days of soil cultivation. DETAILED DESCRIPTION

[0034] The following will be combined with the specific implementation of the present invention to clearly and completely describe the technical solution in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] The methods described in the embodiments of the present invention are conventional methods unless otherwise specified. The materials, reagents, etc. used can be obtained from commercial sources unless otherwise specified.

[0036] At present, the adsorption performance of biochar is relatively limited. Its surface is negatively charged and can adsorb cationic heavy metals well, but its adsorption capacity for anionic heavy metal As is relatively weak, and there is a problem that it is not easy to recycle after use. Magnetite can combine with As in soil and water bodies through electrostatic adsorption, chelation, etc. Therefore, magnetic iron oxides are attached to prepare magnetically modified biochar, and they can be separated by an external magnetic field. The magnetically modified magnetite has a weak adsorption capacity for Cd in the soil, and after magnetic modification, the higher iron content will affect the soil nutrient balance and crop growth when the material is applied at a high rate.

[0037] Vermiculite is a complex iron and magnesium hydrous silicate mineral, which can also improve acidic soils when applied. Vermiculite is abundant and cheap in my country. It can be used as a soil conditioner to improve soil structure and has a certain adsorption capacity for heavy metal ions. It has advantages such as large specific surface area and strong cation exchange capacity, and is a substance that can effectively adsorb heavy metals.

[0038] At present, most of the research on modified biochar materials in the remediation of heavy metal pollution is concentrated in water bodies, and there is a lack of research on remediation in actual soil environments. Xu Shuang's research found that the absorption of heavy metals in water bodies by modified biochar is much better than that of original biochar, and magnetic modification has become a hot research topic because it has recycling advantages that other biochars do not have. In addition to the lack of research on the remediation of actual heavy metal-contaminated soil environments, the modification of biochar also has problems such as poor adsorption effect, cumbersome remediation procedures, high costs, and modification methods that are not green and environmentally friendly and prone to secondary pollution.

[0039] In order to solve these problems and better play the role of biochar, the present invention combines biochar, magnetite and vermiculite to obtain a material that can simultaneously repair soil cadmium and arsenic complex pollution, so as to overcome the defects of insufficient repair capacity of existing materials and the impact on soil nutrient balance and crop growth, and verify its repair ability in soil.

[0040] The biomass raw materials in the following examples are rice straw from Lianyungang, Jiangsu, which are obtained by crushing and passing through a 100-mesh sieve. Expanded vermiculite was purchased from Huacaishi flagship store.

[0041] The following is a detailed description of a vermiculite magnetic modified biochar and its preparation method and application.

[0042] Example 1

[0043] A method for preparing vermiculite magnetic modified biochar comprises the following steps:

[0044] S1. Dissolve FeSO4·7H2O and FeCl3·6H2O in water to produce a coprecipitation reaction to obtain a magnetite suspension; wherein the initial concentration of FeSO4 is 0.1 mol / L, and the initial concentration of FeCl3 is 0.2 mol / L.

[0045] S2. Mix rice straw and magnetite suspension in a mass volume ratio of 1 g:10 mL, add 10 mol / L NaOH dropwise into the mixed solution and stir, adjust the pH to 11, stir in a 60°C water bath for 1 h, let stand for 24 h, filter and vacuum freeze-dry to obtain a mixture.

[0046] S3. Place the mixture in an atmosphere furnace with N2 atmosphere, perform anaerobically pyrolysis at 400°C for 2 hours, take it out after cooling, and obtain magnetically modified biochar; add expanded vermiculite at 1% of the mass of the magnetically modified biochar, anaerobically heat at 200°C for 1 hour, and grind it in a ball mill for 1 hour to obtain vermiculite magnetically modified biochar material with a particle size of 100 μm.

[0047] Example 2

[0048] A method for preparing vermiculite magnetic modified biochar comprises the following steps:

[0049] S1. Dissolve FeSO4·7H2O and FeCl3·6H2O in water to produce a coprecipitation reaction to obtain a magnetite suspension; wherein the initial concentration of FeSO4 is 0.1 mol / L, and the initial concentration of FeCl3 is 0.2 mol / L.

[0050] S2. Mix rice straw and magnetite suspension in a mass volume ratio of 1 g:10 mL, add 10 mol / L NaOH dropwise into the mixed solution and stir, adjust the pH to 11, stir in a 60°C water bath for 1 h, let stand for 24 h, filter and vacuum freeze-dry to obtain a mixture.

[0051] S3. Place the mixture in an atmosphere furnace with N2 atmosphere, perform anaerobically pyrolysis at 400°C for 2 hours, take it out after cooling, add 5% of the mixture by mass of expanded vermiculite, anaerobically heat at 200°C for 1 hour, and grind it in a ball mill for 1 hour to obtain vermiculite magnetic modified biomass carbon material with a particle size of 80 μm.

[0052] Example 3

[0053] A method for preparing vermiculite magnetic modified biochar comprises the following steps:

[0054] S1. Dissolve FeSO4·7H2O and FeCl3·6H2O in water to cause a coprecipitation reaction to obtain a magnetite suspension; wherein the initial concentration of FeSO4 is 0.1 mol / L, and the initial concentration of FeCl3 is 0.2 mol / L.

[0055] S2. Mix rice straw and magnetite suspension in a mass volume ratio of 1 g:10 mL, add 10 mol / L NaOH dropwise into the mixed solution and stir, adjust the pH to 11, stir in a 60°C water bath for 1 h, let stand for 24 h, filter and vacuum freeze-dry to obtain a mixture.

[0056] S3. Place the mixture in an atmosphere furnace with N2 atmosphere, perform anaerobically pyrolysis at 400°C for 2 hours, take it out after cooling, and obtain magnetically modified biochar; add expanded vermiculite at a mass percentage of 10% of the mass of the magnetically modified biochar, heat it anaerobically at 200°C for 1 hour, and grind it in a ball mill for 1.5 hours to obtain vermiculite magnetically modified biochar material with a particle size of 50 μm.

[0057] Example 4

[0058] A method for preparing vermiculite magnetic modified biochar comprises the following steps:

[0059] S1. Dissolve FeSO4·7H2O and FeCl3·6H2O in water to produce a coprecipitation reaction to obtain a magnetite suspension; wherein the initial concentration of FeSO4 is 0.1 mol / L, and the initial concentration of FeCl3 is 0.2 mol / L.

[0060] S2. Mix rice straw and magnetite suspension in a mass volume ratio of 1 g:10 mL, add 10 mol / L NaOH dropwise into the mixed solution and stir, adjust the pH to 11, stir in a 60°C water bath for 1 h, let stand for 24 h, filter and vacuum freeze-dry to obtain a mixture.

[0061] S3. Place the mixture in an atmosphere furnace with N2 atmosphere, perform anaerobically pyrolysis at 400°C for 2 hours, take it out after cooling, and obtain magnetically modified biochar; add expanded vermiculite with a mass percentage of 20% of the magnetically modified biochar, anaerobically heat at 200°C for 1 hour, and grind it in a ball mill for 1.5 hours to obtain vermiculite magnetically modified biochar material with a particle size of 10 μm.

[0062] 1. Effect of preparation conditions on adsorption of vermiculite magnetic modified biochar materials

[0063] The vermiculite magnetic modified biomass carbon materials obtained in Examples 1 to 4 were cleaned with deionized water and used as a control group. After the adsorption experiment, the heavy metal content of the solution was measured to obtain the optimal preparation conditions. The treatment numbers are as follows: 0% A, 1% A, 5% A, 10% A, 20% A, 0% B, 1% B, 5% B, 10% B, 20% B, where the numbers represent the mass percentage of vermiculite added, A represents without deionized water washing, and B represents with deionized water washing.

[0064] The conditions of the adsorption experiment were: 25°C, initial Cd(Ⅱ) and As(Ⅲ) concentrations of 30 mg·L -1 and 10mg·L -1, pH 7, equilibrium time 24 hours. The results are shown in Table 1. With the increase of the proportion of vermiculite added, the removal rates of Cd(Ⅱ) and As(Ⅲ) of the materials showed a trend of first increasing and then slightly decreasing. Excessive vermiculite addition will cause the pores of biochar to be blocked, resulting in a decrease in adsorption capacity. After washing with deionized water, the removal rates of Cd(Ⅱ) of the materials with the same amount of vermiculite added were significantly lower than those of the materials not washed with deionized water. When the vermiculite addition was 1% and 10%, the removal rate of As(Ⅲ) of the materials before and after washing with deionized water was not significantly affected. When the vermiculite addition was 0%, 5% and 20%, the removal rate of As(Ⅲ) of the materials not washed with deionized water was significantly higher than that of the materials washed with deionized water. Therefore, taking the group without deionized water washing as the sample, when the vermiculite addition amount was 5%, the removal rate of Cd(Ⅱ) reached the highest point; when the vermiculite addition amount was 10%, the removal rate of As(Ⅲ) reached the highest point. Considering the removal rate of the two elements and the utilization rate of the materials, the vermiculite-magnetic modified biochar without deionized water washing and with a vermiculite addition mass ratio of 5% was selected as the best material for subsequent experiments.

[0065] Table 1 Effect of V-MBC in different treatment groups on Cd and As removal efficiency

[0066]

[0067]

[0068] Note: The same lowercase letters represent significant differences among treatments (p<0.05)

[0069] 2. Single factor adsorption test

[0070] 1) Effect of initial solution pH on removal rate

[0071] Prepare 10 mg / L As solution with initial pH of 2, 4, 6, 8, 10, and 12. Weigh 25 mg1 of the vermiculite magnetic modified biochar in Example 2 into a dry and clean 50 mL centrifuge tube, add 25 mL of As solution with different pH values, and set 3 replicates for each treatment. Oscillate and adsorb at 25 ° C for 24 hours, filter through a 0.45 μm needle-type microporous filter membrane, and store in a 10 mL centrifuge tube. Determine the concentration of As(Ⅲ) in the solution.

[0072] Prepare 30 mg / L Cd solution with initial pH of 2, 3, 4, 5, 6, 7, and 8. Weigh 25 mg of the vermiculite magnetic modified biochar in Example 2 into a dry and clean 50 mL centrifuge tube, add 25 mL of Cd solution with different pH values, and set three replicates for each treatment. Oscillate and adsorb at 25 ° C for 24 h, filter through a 0.45 μm needle-type microporous filter membrane, store in a 10 mL centrifuge tube, and measure the Cd concentration in the solution.

[0073] The pH value of 6, which had the highest removal rate for Cd and As, was selected as the optimal adsorption condition for subsequent experiments.

[0074] 2) Adsorption kinetics

[0075] Weigh 25 mg of the vermiculite magnetic modified biochar in Example 2 into a dry and clean 50 mL centrifuge tube, add 25 mL of 10 mg / L As solution at pH 6, and set 3 replicates for each treatment. After 1 h, 2 h, 4 h, 8 h, 12 h, 16 h, 24 h, and 48 h adsorption intervals at 25 ° C and pH 6, the results were measured after filtration through a 0.45 μm needle-type microporous filter membrane.

[0076] Weigh 25 mg of the vermiculite magnetic modified biochar in Example 2 into a dry and clean 50 mL centrifuge tube, add 25 mL of 30 mg / L Cd solution, and set 3 replicates for each treatment. At 25°C and pH 6, the adsorption intervals were 30 s, 60 s, 120 s, 300 s, 600 s, 1200 s, 1800 s, 3600 s, and 7200 s, respectively, and then filtered through a 0.45 μm needle-type microporous filter membrane for determination.

[0077] The pseudo-first-order kinetic equation is shown in formula (1), and the pseudo-second-order kinetic equation is shown in formula (2):

[0078] dq t / d t =K1(q e -q t ) Formula (1);

[0079] dq t / d t =K2(q e -q t ) 2 Formula (2).

[0080] In the formula, q e represents the adsorption capacity of V-MBC at the adsorption equilibrium time, in mg / g; q t represents the adsorption capacity of V-MBC at adsorption time t, in mg / g; K1 represents the adsorption rate constant of the pseudo-first-order kinetic equation; K2 represents the adsorption rate constant of the pseudo-second-order kinetic equation.

[0081] 3) Isothermal adsorption

[0082] The concentrations of As solution were set to 0.5 mg / L, 1 mg / L, 2.5 mg / L, 5 mg / L, 10 mg / L, 15 mg / L, and 20 mg / L. Weigh 25 mg of the vermiculite magnetic modified biochar in Example 2 into a dry and clean 50 mL centrifuge tube, add 25 mL of As solution of different concentrations, and set 3 replicates for each treatment. Oscillating adsorption was performed at 25 ° C and pH 6 for 24 h, and the results were determined after filtration through a 0.45 μm needle-type microporous filter membrane.

[0083] Set the concentrations of Cd solution to 1 mg / L, 2.5 mg / L, 5 mg / L, 10 mg / L, 20 mg / L, 40 mg / L, 60 mg / L, 100 mg / L, and 200 mg / L. Weigh 25 mg of different materials into a dry and clean 50 mL centrifuge tube, add 25 mL of Cd solution of different concentrations, and set 3 replicates for each treatment. Oscillating adsorption was performed at 25 ° C and pH 6 for 24 hours, and the samples were filtered through a 0.45 μm needle-type microporous filter membrane before determination.

[0084] The Langmuir equation is shown in equation (3), and the Freundlich equation is shown in equation (4):

[0085] qe=q m K L c e / (1+K L c e ) Formula (3);

[0086] qe=K F c e 1 / n Formula (4).

[0087] Where, qe is the equilibrium adsorption capacity, the unit is μg / g; q m is the maximum adsorption capacity, in mg / g; c e is the equilibrium adsorption concentration in mg / L, K L represents the adsorption rate constant of the Langmuir model, K F represents the adsorption rate constant of the Freundlich model; n is the adsorption index, and its value reflects the intensity of the adsorption reaction or the heterogeneity of the adsorption.

[0088] 3. Soil culture test

[0089] Soil samples were collected from paddy soil in agricultural land around a mining area in Zhejiang Province, and were air-dried, ground and sieved through a 2 mm sieve for cultivation experiments.

[0090] Add 100g of air-dried soil to a 150ml beaker and evenly mix with different mass percentages of passivator materials, add 100ml of ultrapure water, and keep the soil flooded by 2cm to 3cm. The experiment set up five treatments, namely, a blank control group, a vermiculite-magnetic modified biochar in Example 2 with an addition of 1%, a vermiculite-magnetic modified biochar in Example 2 with an addition of 3%, an original biochar with an addition of 1%, and an original biochar with an addition of 3%, respectively marked as CK, VMBC1%, VMBC3%, PBC1% and PBC3%, and each treatment was set up with three replicates. During the culture period, weigh and add water every day to ensure that the water-soil ratio is consistent. The soil pH value was measured in situ on the 0th, 4th, 7th, 11th, 14th, 18th, and 21st days of culture. After the culture was completed, soil samples were collected and naturally air-dried. Take part of the soil and pass it through a 10-mesh sieve to determine the pH value of the soil before and after culture. Part of the soil was sieved through a 100-mesh sieve to determine its soluble carbon (DOC) content and the effective content of heavy metals Cd and As. The prepared materials were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy.

[0091] 4. Results

[0092] 1) Structural characterization

[0093] The relevant characterization experiments were carried out using 5% A. Figure 1 a in the figure shows the X-ray diffraction spectrum of the material V-MBC. According to the standard powder diffraction card, the two peaks at 35.4° and 62.5° in the spectrum are the characteristic peaks of magnetite crystals. The results show that magnetite is successfully attached to the surface of V-MBC. The peaks at 35.5°, 43.1°, 57.0°, and 62.6° in the spectrum are the characteristic peaks of silicon-containing minerals, indicating that vermiculite is also successfully attached to the surface of V-MBC. Through spectrum analysis, the characteristic peaks of magnesium ferrite and iron silicide can also be interpreted, but compared with magnetite and silicon-containing minerals, their content is very small. The infrared spectrum of vermiculite-magnetic modified biochar material is shown in the figure below. Figure 1 As shown in b in the figure. It can be observed in the spectrum that at 3428cm -1 A more obvious absorption peak appears at 1621cm, which is due to the adsorption of water molecules between the vermiculite layers, resulting in the stretching vibration of the -OH group. -1 The absorption peak at 1007cm is due to the absorption of water molecules between vermiculite layers and the bending absorption of OH. -1 The absorption peak at 443cm is due to the stretching vibration of Si-O in the silicon oxide formed after the material is modified by vermiculite. The appearance of the above peaks can fully prove that the vermiculite has been attached to the magnetic modified biomass carbon material. -1 The characteristic peaks appearing at are Fe-O in Fe3O4 and Fe in high spin state. 3+The characteristic peak of stretching vibration of 3130cm -1 and 1400cm -1 The peak band at is due to the attachment of Fe3O4, which introduces a large number of hydroxyl groups and aromatic ring compounds onto the surface of the material, resulting in the bending vibration of CH and CO. The presence of these functional groups ensures that the material can effectively adsorb Cd and As.

[0094] 2) Single factor adsorption test

[0095] Effect of initial solution pH on removal efficiency

[0096] like Figure 2 The figure shows the effect of the initial pH of the solution on the removal rate of Cd and As by the vermiculite-magnetic modified biochar material. The adsorption of Cd and A by the material is affected by pH, but it can maintain a relatively stable removal rate within a certain pH range, indicating that the material has a certain stability. Among them, the removal rate of As by the material is greatly affected by the initial pH of the solution. The removal rate of Cd by V-MBC generally shows a trend of first increasing and then tending to equilibrium with the increase of the initial pH of the solution; the removal rate of As by the increase of the initial pH of the solution generally shows a trend of first increasing, tending to equilibrium in the middle, and then decreasing. When the pH is 5, the removal effect of V-MBC on Cd (Ⅱ) is the best, with a maximum removal rate of 49.23%. When the pH is 6. The removal effect of V-MBC on As (Ⅲ) is the best, with a maximum removal rate of 56.03%. Considering the removal rates of the two elements comprehensively, pH 6 is selected as the optimal adsorption condition for the material application and applied to subsequent adsorption tests.

[0097] Adsorption kinetics

[0098] like Figure 3 The figure shows the adsorption kinetic curves of V-MBC for Cd and As. The adsorption of these two heavy metals, Cd(Ⅱ) and As(Ⅲ), by V-MBC can be divided into two stages. For Cd(Ⅱ), the adsorption rate was relatively fast in the first 300s, and the adsorption equilibrium was reached in 1200s; for As, the adsorption rate was relatively fast in the first 12h, and the adsorption equilibrium was reached in 12h. Table 2 shows the adsorption kinetic fitting parameters of V-MBC for Cd and As. It can be seen from the table that the R values ​​of the pseudo-first-order kinetic model and the pseudo-second-order kinetic model for Cd adsorption by V-MBC are 2 are 0.9398 and 0.9488 respectively, and the theoretical equilibrium adsorption capacity qe is 18.80 mg·g -1 and 19.96 mg g -1 The R values ​​of pseudo-first-order kinetic model and pseudo-second-order kinetic model for As adsorption by V-MBC 2 are 0.9724 and 0.9680 respectively, and the theoretical equilibrium adsorption capacity qe is 3.91 mg·g-1 and 4.18 mg·g -1 .

[0099] Table 2 Fitting parameters of adsorption kinetics of Cd and As by vermiculite magnetic modified biochar

[0100]

[0101] Isothermal adsorption

[0102] Figure 4 Table 3 shows the isothermal adsorption curves of V-MBC for Cd and As adsorption. Both the Langmuir model and the Freundlich model can fit the isothermal adsorption process of V-MBC materials for these two heavy metals well. Table 3 shows the adsorption thermodynamic fitting parameters of V-MBC for Cd and As adsorption. As can be seen from Table 3, the correlation coefficient R between the Langmuir model and the Freundlich model for V-MBC for Cd adsorption is 2 are 0.9951 and 0.9979 respectively, and the maximum adsorption capacity qm is 188.52 mg·g -1 The correlation coefficient R between the Langmuir model and the Freundlich model for As adsorption by V-MBC 2 are 0.9984 and 0.9979 respectively, and the maximum adsorption capacity qm is 23.63 mg·g -1 The adsorption preference coefficients 1 / n of the material for Cd and As are 0.7922 and 0.8950, respectively.

[0103] Table 3 Thermodynamic fitting parameters of adsorption of Cd and As by vermiculite magnetic modified biochar

[0104]

[0105] 3) Vermiculite-magnetic modified biochar soil cultivation application test

[0106] Dynamic changes in soil pH

[0107] like Figure 5As shown in the figure, during the 21-day cultivation, the soil pH showed an upward trend with the increase of cultivation time and tended to balance after 11 days of cultivation. After cultivation, the pH increased by 1.04 to 2.85 units, and the final regional equilibrium value was between 7.34 and 7.72. Compared with the blank control group, the addition of vermiculite-magnetic modified biochar and original biochar caused the soil pH to show an upward trend, and the rising speed was fast at first and then slow. In the early stage of cultivation, the effect of original biochar on soil pH was significantly higher than that of vermiculite-magnetic modified biochar, and increased with the increase of addition amount. At the end of the cultivation period, the pH of each group remained relatively stable, ranging from 7.40 to 7.60, and there was no significant difference with the pH of the control group (P>0.05). Among them, the group with vermiculite-magnetic modified biochar as the passivator was slightly lower than the blank group and the original biochar group. The vermiculite-magnetic modified biochar material had little effect on pH during the whole process.

[0108] Changes in soil soluble carbon (DOC) content

[0109] like Figure 6 As shown in the results, compared with the blank control group, the DOC of the soil added with VMBC material increased after 21 days of cultivation, the DOC of V-MBC1% increased by 8.48%, and the DOC of V-MBC3% increased significantly by 24.13% (P<0.05); while the DOC content of the soil added with PBC1% and PBC3% did not change significantly compared with the blank control at different addition amounts. Compared with the addition of PBC, the DOC content of the soil added with VMBC material increased by 18.70% to 43.47%. The results show that the effect of these two passivation materials on the improvement of soil DOC content is vermiculite magnetic modified biochar > original biochar.

[0110] Changes in the availability of heavy metals in soil after the addition of vermiculite-modified biochar

[0111] like Figure 7 As shown in the results, compared with the blank control group, after 21 days of cultivation, the effective Cd content in the soil treated with different passivators showed a downward trend. Among them, the effective Cd content in the soil with VMBC material added was significantly reduced (P<0.05), decreasing by 11.06% and 22.62%, respectively; while the effective Cd content in the soil with 1% PBC decreased by 5.52%, and the effective Cd content in the soil with 3% addition decreased significantly by 10.81%. With the increase in the addition amount of the two passivators, the effectiveness of Cd in the soil gradually decreased. The effective Cd content in the soil decreased by 8.61% to 29.29% before and after cultivation.

[0112] like Figure 8As shown in the results, compared with the blank control group, after 21 days of cultivation, the available As content in the soil treated with different passivators was significantly reduced (P<0.05). The available As content in the soil with the addition of vermiculite magnetic modified biochar decreased by 10.13% and 27.90%, respectively; while the available As content in the soil with the addition of original biochar decreased by 11.81% and 9.65%, respectively. The effectiveness of As in the soil decreased with the increase of the amount of vermiculite added, but increased with the increase of the amount of PBC material added. The available As content in the soil decreased by 10.26% to 35.29% before and after cultivation.

[0113] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0114] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A vermiculite magnetic modified biochar, characterized in that: The vermiculite magnetic modified biomass charcoal is obtained by mixing the magnetic modified biomass charcoal with vermiculite, heating at 200° C. to 220° C. for 1 h to 1.5 h under anaerobic conditions, and then ball milling. The mass of the vermiculite accounts for 1% to 20% of the mass of the magnetically modified biochar; The magnetic modified biomass charcoal is obtained by mixing a magnetite suspension with a biomass raw material in a mass volume ratio of 1kg:10L-12L and subjecting the mixture to anaerobic pyrolysis.

2. The vermiculite magnetic modified biochar according to claim 1, characterized in that: The vermiculite is expanded vermiculite with a particle size less than 2 mm.

3. The vermiculite magnetic modified biochar according to claim 2, characterized in that: The particle size of the vermiculite magnetic modified biomass charcoal is 10 μm to 100 μm.

4. The vermiculite magnetic modified biochar according to claim 3, characterized in that: The magnetite suspension is composed of Fe in FeSO4 2+ and Fe in FeCl3 3+ It is obtained by co-precipitation in water, wherein the molar ratio of FeSO4 to FeCl3 is 1:1.8-2, and the initial concentration of FeSO4 is 0.09 mol / L-1.1 mol / L.

5. The vermiculite magnetic modified biochar according to claim 4, characterized in that: The biomass raw material is plant straw.

6. A method for preparing vermiculite magnetic modified biochar according to claim 5, characterized in that: The following steps are involved: Mix FeSO4 and FeCl3 in a molar ratio of 1:1.8-2, and coprecipitate in water to obtain a magnetite suspension; The rice straw and the magnetite suspension are mixed in a mass volume ratio of 1 kg: 10 L to 12 L, the pH is adjusted to 11 to 12, stirred and reacted in a water bath at 60° C. to 65° C. for 2 h to 2.5 h, allowed to stand, and filtered to obtain a mixture; Anaerobic pyrolysis of the mixture at 370° C. to 430° C. for 2 h to 2.5 h to obtain the magnetically modified biochar; The magnetically modified biomass charcoal is mixed with expanded vermiculite, heated at 200° C. to 220° C. for 1 h to 1.5 h under anaerobic conditions, and ball-milled to obtain the vermiculite magnetically modified biomass charcoal.

7. The method for preparing vermiculite magnetic modified biochar according to claim 6, characterized in that: The ball milling time is 1 h to 1.5 h.

8. Use of the vermiculite magnetic modified biochar according to any one of claims 1 to 5 in the preparation of a soil heavy metal passivator.

9. The use according to claim 8, characterized in that: The heavy metals are Cd and As.

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