Soil conditioner for repairing farmland heavy metal pollution and preparation method thereof

Abstract

The invention provides a soil conditioner for repairing farmland heavy metal pollution and a preparation method of the soil conditioner, and belongs to the technical field of soil conditioning materials.The preparation method comprises the steps of preparing primary modified biochar and preparing secondary modified biochar, and the method for preparing the primary modified biochar comprises the steps that biochar powder is added into a nitric acid solution, water bath is conducted, filtering is conducted, and the secondary modified biochar is obtained; putting a filter cake into a reactor, putting the reactor into a microwave device, adjusting the frequency to be 2.35-2.55 GHz, introducing N2, adjusting the pressure to be 6-8 MPa, reacting for 4-6 minutes, then changing the frequency to be 2.05-2.25 GHz, introducing Cl2, changing the pressure to be 4-6 MPa, reacting for 7-13 minutes, after the reaction is finished, pyrolyzing and cooling a reactant, soaking the reactant in a NaOH solution, filtering and drying to obtain primary modified biochar; the soil conditioner prepared by the invention has a good adsorption effect on heavy metals such as cadmium, mercury, chromium, copper and nickel.

Description

Technical Field

[0001] The invention belongs to the technical field of soil conditioning materials, and in particular relates to a soil conditioner for repairing heavy metal pollution in farmland and a preparation method thereof. Background Art

[0002] Heavy metal pollution in farmland mainly comes from human industrial and agricultural activities, such as mining, leather making, electroplating, fertilizer application, sewage irrigation, etc. The heavy metal pollutants produced will not only lead to crop yield reduction, but also endanger human health through enrichment in the food chain.

[0003] Biochar has a certain adsorption effect on agricultural heavy metal pollutants such as lead, chromium, copper, and cadmium. The main adsorption mechanisms of biochar are: (1) The pores of biochar adsorb heavy metal pollutants through electrostatic forces, π-π bond interactions, van der Waals forces, etc. (2) The presence of K + , Ca 2+ Mg 2+ and Na + Alkali metal ions such as iodine and iodine can adsorb heavy metals through ion exchange. (3) Oxygen-containing functional groups on the surface of biochar, such as carboxyl and hydroxyl (which have a better complexing effect on lead and copper ions), can form stable complexes with heavy metal ions.

[0004] However, (1) during the preparation of biochar, the higher the pyrolysis temperature, the more porous the biochar structure and the stronger the ion exchange effect. Therefore, the total adsorption capacity for heavy metals is greater. However, the higher the pyrolysis temperature, the oxygen-containing functional groups on the surface of biochar are decomposed by heat, and the number and types of them are fewer. Therefore, the types of heavy metals that can be adsorbed are fewer.

[0005] (2) After biochar ages, the pore structure collapses, which will lead to a decrease in the adsorption capacity of biochar and the secondary precipitation of adsorbed heavy metals.

[0006] Patent CN109622592A discloses a method for removing heavy metals from soil based on modified biochar, which is obtained by mixing calcium carbonate with agricultural waste and calcining them. Calcium carbonate can increase the porosity of biochar and improve the adsorption capacity of biochar for heavy metals, but pore adsorption is physical adsorption with a certain reversibility, which easily leads to secondary precipitation of adsorbed heavy metals, and this method does not solve the problem that oxygen-containing functional groups on the surface of biochar decompose as the pyrolysis temperature increases. Summary of the invention

[0007] In view of the problems existing in the prior art, the present invention provides a soil conditioner for repairing heavy metal pollution in farmland and a preparation method thereof, so as to achieve the following invention objectives: (1) increasing the pore structure of biochar and improving the ion exchange effect, while effectively reducing the decomposition of functional groups during the pyrolysis of biochar; (2) improving the adsorption capacity of biochar for various heavy metals; and (3) improving the adsorption capacity of aged biochar for heavy metals.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: A soil conditioner for repairing heavy metal pollution in farmland and a preparation method thereof, comprising the following steps: 1. Preparation of biochar Rinse the corn stalks and dry them naturally until no liquid drips, then cut them into small pieces of 1 to 4 cm, add them to a Na2CO3 solution, soak them for 25 to 35 minutes, take them out and dry them to a moisture content of 10 to 20% to obtain dried corn stalks, put the dried corn stalks into a muffle furnace, heat them to 180 to 230°C at a rate of 3 to 8°C / min in a CO2 environment, continue pyrolysis for 2 to 3 hours, cool them down and take them out to obtain biochar; The mass ratio of the corn stalk to the Na2CO3 solution is 0.8-1.2:18-22; The mass fraction of the Na2CO3 solution is 25-35%; The Na2CO3 solution releases CO2 during the pyrolysis process, which increases the porosity of the biochar; In the CO2 environment, the deoxygenation and dehydrogenation reactions of biochar can be promoted, and the specific surface area and micropore ratio of biochar can be effectively increased; The biochar pyrolysis temperature is 180-230° C., and the pyrolysis temperature is low, so a large number of oxygen-containing functional groups are retained.

[0009] 2. Preparation of primary modified biochar (1) Grind the biochar into biochar powder with a particle size of 0.05-0.3 mm, add the biochar powder into a nitric acid solution, and heat it in a 50-70°C water bath for 0.8-1.2 h, then filter, and rinse the filter cake with deionized water to obtain an intermediate product A; (2) The intermediate product A is evenly spread in the reactor, and the reactor is placed in a microwave device. The microwave frequency of the microwave device is adjusted to 2.35-2.55 GHz, and N2 is introduced into the reactor at a flow rate of 100-300 mL / min. The pressure in the reactor is maintained at 6-8 MPa. After reacting for 4-6 minutes, Cl2 with a concentration of 3-5% is introduced into the reactor at a flow rate of 80-120 mL / min. The microwave frequency is changed to 2.05-2.25 GHz, and the reactor pressure is changed to 4-6 MPa. The reaction is continued for 7-13 minutes. After the reaction is completed, the intermediate product B is obtained; (3) After the muffle furnace is heated to 180-230°C, the intermediate product B is placed in the muffle furnace, and then the temperature is raised to 500-700°C at a rate of 15-25°C / min, and the temperature is maintained at 500-700°C for 10-20 minutes, and then cooled to room temperature. The cooled product is then completely immersed in a NaOH solution for 55-65 minutes, and then filtered. The filter cake is placed in a constant temperature drying oven at 30-50°C and dried for 15-25 minutes to obtain a first modified biochar; In step (1), the mass ratio of biochar powder to nitric acid solution is 0.8-1.2:90-110, and the mass fraction of nitric acid solution is 40-60%; The 3-5% Cl2 in step (2) refers to the concentration of Cl2 in the air; The mass fraction of the NaOH solution in step (3) is 15-25%; The nitric acid solution in step (1) can coarsen the pore structure of the biochar, thereby increasing its adsorption capacity for heavy metals, and at the same time introduce nitro groups into the biochar powder, thereby increasing the reaction activity of the biochar powder; In step (2), the microwave device can convert microwave energy into the internal energy of gas molecules, thereby exciting them, intensifying the intermolecular motion and causing mutual collision. In this process, various electrons, free radicals, excited molecules, atoms, and positive and negative ions are generated; In the step (2), N2 is introduced into the reactor. Under the action of the microwave device, the generated nitrogen anions act as strong nucleophiles and attack the electrophilic functional groups on the surface of the biochar (intermediate product A), such as carboxyl and phenolic hydroxyl groups, to form nitrogen-oxygen-containing functional groups, such as nitro, amine and amide groups. The functional groups are relatively stable and are not easily decomposed at high temperatures, which can improve the complex adsorption effect of heavy metal cadmium. In the step (2), 3-5% Cl2 is introduced into the reactor. Under the action of the microwave device, the generated chlorine anions attack the carbon-carbon double bonds on the surface of the biochar (intermediate product A), breaking the double bonds, thereby introducing C-Cl, which can improve the complex adsorption effect of heavy metals mercury and chromium; The biochar (intermediate product A) is pyrolyzed at a temperature of 180 to 230° C. during preparation, thereby retaining a large amount of carbon-carbon double bonds; In step (3), the biochar (intermediate product B) is pyrolyzed at 500-700° C., which can further increase its porosity and improve its total adsorption capacity for various heavy metals; The soaking in NaOH solution in step (3) can hydrolyze the amine and amide groups generated in step (2) into carboxyl groups, thereby improving the complex adsorption effect of biochar on copper and nickel.

[0010] 3. Preparation of secondary modified biochar (1) Add sodium silicate to deionized water, stir until it is completely dissolved, add n-hexanol, stir evenly, and use HCl solution to adjust the pH to 1.5-2.5 to obtain a sodium silicate solution. The sodium silicate solution is placed in a water bath at 55-65°C for 3.5-4.5 hours, then transferred to a forced air drying oven, dried at 100-120°C for 5-7 hours, transferred to a muffle furnace, calcined at 180-220°C for 1.5-2.5 hours, and ground into a powder with a particle size of 0.1-0.2 mm to obtain a modified silica gel; (2) The primary modified biochar and the modified silica gel are mixed evenly, and then anhydrous ethanol is added and stirred into a paste. After natural drying, the dried product is ground into a powder with a particle size of 0.1 to 0.3 mm to obtain the secondary modified biochar, which is a soil conditioner for repairing heavy metal pollution in farmland; In the step (1), the mass ratio of sodium silicate, deionized water and n-hexanol is 0.8-1.2:15.5-15.6:0.7-0.8; The mass fraction of the HCl solution in step (1) is 15-25%; In the step (2), the mass ratio of the first modified biochar, modified silica gel, and anhydrous ethanol is 0.8-1.2:5-7:2.5-3.5; The addition of n-hexanol in step (1) can make the prepared modified silica gel have more pores and loading points, which can effectively load the prepared modified biochar. The Si in the silica gel and the C in the biochar can combine to form a dense protective structure, thereby improving the stability of the pore structure of the biochar.

[0011] Compared with the prior art, the present invention has the following beneficial effects: 1. The soil conditioner of the present invention has a high adsorption capacity for various heavy metals. The adsorption capacities for heavy metals cadmium, mercury, chromium, copper and nickel are 41-49 mg / g, 30-36 mg / g, 66-74 mg / g, 91-98 mg / g and 73-81 mg / g respectively.

[0012] 2. The soil conditioner of the present invention still has a high adsorption capacity for heavy metals after aging, which can avoid the secondary precipitation of heavy metals, specifically 39-45 mg / g of cadmium, 26-34 mg / g of mercury, 60-70 mg / g of chromium, 80-90 mg / g of copper, and 65-75 mg / g of nickel. DETAILED DESCRIPTION

[0013] Example 1 1. Preparation of biochar Rinse the corn stalks and dry them naturally until no liquid drips, then cut them into small pieces of 2 to 3 cm, add them into a Na2CO3 solution, soak them for 30 minutes, take them out and dry them to 15% moisture content to obtain dried corn stalks, put the dried corn stalks into a muffle furnace, heat them to 200°C at a rate of 5°C / min in a CO2 environment, continue pyrolysis for 2.5 hours, cool them down and take them out to obtain biochar; The mass ratio of the corn stalk to the Na2CO3 solution is 1:20; The mass fraction of the Na2CO3 solution is 30%.

[0014] 2. Preparation of primary modified biochar (1) Grind the biochar into biochar powder with a particle size of 0.1 to 0.2 mm, add the biochar powder into a nitric acid solution, heat it in a 60°C water bath for 1 h, and then filter it. Rinse the filter cake with deionized water to obtain an intermediate product A; (2) The intermediate product A is evenly spread in the reactor, and the reactor is placed in a microwave device. The microwave frequency of the microwave device is adjusted to 2.45 GHz, and N2 is introduced into the reactor at a flow rate of 200 mL / min. The pressure in the reactor is maintained at 7 MPa. After reacting for 5 minutes, Cl2 with a concentration of 4% is introduced into the reactor at a flow rate of 100 mL / min. The microwave frequency is changed to 2.15 GHz, and the reactor pressure is changed to 5 MPa. The reaction is continued for 10 minutes. After the reaction is completed, the intermediate product B is obtained; (3) After the muffle furnace is heated to 200 °C, the intermediate product B is placed in the muffle furnace, and then the temperature is raised to 600 °C at a rate of 20 °C / min. After pyrolysis at 600 °C for 15 min, it is cooled to room temperature, and then the cooled product is completely immersed in a NaOH solution. After soaking for 60 min, it is filtered and the filter cake is placed in a 40 °C constant temperature drying oven and dried for 20 min to obtain a first modified biochar; In step (1), the mass ratio of biochar powder to nitric acid solution is 1:100, and the mass fraction of nitric acid solution is 50%; The 4% Cl2 in step (2) refers to the concentration of Cl2 in the air; The mass fraction of the NaOH solution in step (3) is 20%.

[0015] 3. Preparation of secondary modified biochar (1) Sodium silicate was added to deionized water, stirred to completely dissolve, and then n-hexanol was added. After stirring evenly, the pH was adjusted to 2 using HCl solution to obtain a sodium silicate solution. The sodium silicate solution was placed in a water bath at 60°C for 4 hours, then transferred to a forced air drying oven, dried at 110°C for 6 hours, transferred to a muffle furnace and calcined at 200°C for 2 hours, and then ground into a powder with a particle size of 0.15 mm to obtain a modified silica gel; (2) The primary modified biochar and the modified silica gel are mixed evenly, and then anhydrous ethanol is added and stirred into a paste. After natural drying, the dried product is ground into a powder with a particle size of 0.2 mm to obtain the secondary modified biochar, which is a soil conditioner for repairing heavy metal pollution in farmland; In the step (1), the mass ratio of sodium silicate, deionized water and n-hexanol is 1:15.56:0.73; The mass fraction of the HCl solution in step (1) is 20%; In the step (2), the mass ratio of the first modified biochar, modified silica gel and anhydrous ethanol is 1:6:3.

[0016] Example 2 1. Preparation of biochar After the corn stalks are rinsed and naturally dried until no liquid drips, they are cut into small pieces of 1 to 2 cm, and then added to a Na2CO3 solution and soaked for 25 min. After being taken out, the moisture content is dried to 10% to obtain dried corn stalks. The dried corn stalks are placed in a muffle furnace, and the temperature is raised to 180°C at a rate of 3°C / min in a CO2 environment. The pyrolysis is continued for 2 h, and the biochar is obtained after being cooled. The mass ratio of the corn stalk to the Na2CO3 solution is 0.8:18; The mass fraction of the Na2CO3 solution is 25%.

[0017] 2. Preparation of primary modified biochar (1) Grind the biochar into biochar powder with a particle size of 0.05 to 0.1 mm, add the biochar powder into a nitric acid solution, heat it in a 50°C water bath for 0.8 h, and then filter it. Rinse the filter cake with deionized water to obtain an intermediate product A; (2) The intermediate product A was evenly spread in the reactor, and the reactor was placed in a microwave device. The microwave frequency of the microwave device was adjusted to 2.35 GHz. N2 was introduced into the reactor at a flow rate of 100 mL / min. The pressure in the reactor was maintained at 6 MPa. After reacting for 4 minutes, 3% Cl2 was introduced into the reactor at a flow rate of 80 mL / min. The microwave frequency was changed to 2.05 GHz, and the reactor pressure was changed to 4 MPa. The reaction was continued for 7 minutes. After the reaction was completed, the intermediate product B was obtained. (3) After the muffle furnace is heated to 180°C, the intermediate product B is placed in the muffle furnace, and then the temperature is raised to 500°C at a rate of 15°C / min. After pyrolysis at 500°C for 15 minutes, it is cooled to room temperature, and then the cooled product is completely immersed in a NaOH solution. After soaking for 55 minutes, it is filtered and the filter cake is placed in a 30°C constant temperature drying oven and dried for 15 minutes to obtain a first modified biochar; In step (1), the mass ratio of biochar powder to nitric acid solution is 0.8:90, and the mass fraction of nitric acid solution is 40%; The 3% Cl2 in step (2) refers to the concentration of Cl2 in the air; The mass fraction of the NaOH solution in step (3) is 15%.

[0018] 3. Preparation of secondary modified biochar (1) Add sodium silicate to deionized water, stir until it is completely dissolved, add n-hexanol, stir evenly, and use HCl solution to adjust the pH to 1.5 to obtain a sodium silicate solution. The sodium silicate solution is placed in a water bath at 55°C for 3.5 hours, then transferred to a forced air drying oven, dried at 100°C for 5 hours, transferred to a muffle furnace, calcined at 180°C for 1.5 hours, and ground into a powder with a particle size of 0.1 mm to obtain a modified silica gel; (2) The primary modified biochar and the modified silica gel are mixed evenly, and then anhydrous ethanol is added and stirred into a paste. After natural drying, the dried product is ground into a powder with a particle size of 0.1 mm to obtain the secondary modified biochar, which is a soil conditioner for repairing heavy metal pollution in farmland; In the step (1), the mass ratio of sodium silicate, deionized water and n-hexanol is 0.8:15.5:0.7; The mass fraction of the HCl solution in step (1) is 15%; In the step (2), the mass ratio of the first modified biochar, modified silica gel and anhydrous ethanol is 0.8:5:2.5.

[0019] Example 3 1. Preparation of biochar Rinse the corn stalks and dry them naturally until no liquid drips, then cut them into small pieces of 3 to 4 cm, add them into a Na2CO3 solution, soak them for 35 minutes, take them out and dry them to 20% moisture content to obtain dried corn stalks, put the dried corn stalks into a muffle furnace, heat them to 230°C at a rate of 8°C / min in a CO2 environment, continue pyrolysis for 3 hours, cool them down and take them out to obtain biochar; The mass ratio of the corn stalk to the Na2CO3 solution is 1.2:22; The mass fraction of the Na2CO3 solution is 35%.

[0020] 2. Preparation of primary modified biochar (1) Grind the biochar into biochar powder with a particle size of 0.2 to 0.3 mm, add the biochar powder into a nitric acid solution, heat it in a 70°C water bath for 1.2 h, and then filter it. Rinse the filter cake with deionized water to obtain an intermediate product A; (2) The intermediate product A was evenly spread in the reactor, and the reactor was placed in a microwave device. The microwave frequency of the microwave device was adjusted to 2.55 GHz. N2 was introduced into the reactor at a flow rate of 300 mL / min. The pressure in the reactor was maintained at 8 MPa. After reacting for 6 minutes, 5% Cl2 was introduced into the reactor at a flow rate of 120 mL / min. The microwave frequency was changed to 2.25 GHz, and the reactor pressure was changed to 6 MPa. The reaction was continued for 13 minutes. After the reaction was completed, the intermediate product B was obtained. (3) After the muffle furnace is heated to 230°C, the intermediate product B is placed in the muffle furnace, and then the temperature is raised to 700°C at a rate of 25°C / min. After pyrolysis at 700°C for 20 minutes, the product is cooled to room temperature, and then the cooled product is completely immersed in a NaOH solution. After soaking for 65 minutes, the product is filtered and the filter cake is placed in a 50°C constant temperature drying oven and dried for 25 minutes to obtain a first modified biochar. In step (1), the mass ratio of biochar powder to nitric acid solution is 1.2:110, and the mass fraction of nitric acid solution is 60%; The 5% Cl2 in step (2) refers to the concentration of Cl2 in the air; The mass fraction of the NaOH solution in step (3) is 25%.

[0021] 3. Preparation of secondary modified biochar (1) Add sodium silicate to deionized water, stir until it is completely dissolved, add n-hexanol, stir evenly, and use HCl solution to adjust the pH to 2.5 to obtain a sodium silicate solution. The sodium silicate solution is placed in a water bath at 65°C for 4.5 hours, then transferred to a forced air drying oven, dried at 120°C for 7 hours, transferred to a muffle furnace, calcined at 220°C for 2.5 hours, and ground into a powder with a particle size of 0.2 mm to obtain a modified silica gel; (2) The primary modified biochar and the modified silica gel are mixed evenly, and then anhydrous ethanol is added and stirred into a paste. After natural drying, the dried product is ground into a powder with a particle size of 0.3 mm to obtain the secondary modified biochar, which is a soil conditioner for repairing heavy metal pollution in farmland; In the step (1), the mass ratio of sodium silicate, deionized water and n-hexanol is 1.2:15.6:0.8; The mass fraction of the HCl solution in step (1) is 25%; In the step (2), the mass ratio of the first modified biochar, modified silica gel and anhydrous ethanol is 1.2:7:3.5.

[0022] Comparative Example 1 In order to verify the effect of N2 in step 2, the same soil conditioner and preparation method as in Example 1 were used, except that the introduction of N2 in step 2 was omitted.

[0023] Comparative Example 2 In order to verify the effect of 4% Cl2 in step 2, the same soil conditioner and preparation method as in Example 1 were used, except that the introduction of 4% Cl2 in step 2 was omitted.

[0024] Comparative Example 3 In order to verify the effect of the modified silica gel in step 3, the same soil conditioner and its preparation method as in Example 1 were used, the difference being that step 3 was omitted, and the first modified biochar prepared in step 2 was the soil conditioner.

[0025] Test Example 1 The soil conditioners prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to heavy metal adsorption tests, and the test method was as follows: Prepare 6 portions of 5 heavy metal pollutant solutions containing cadmium ions, mercury ions, chromium ions, copper ions, and nickel ions, 100 mL each, and the concentration is 100 mg / L. Take 5 portions of the soil conditioners prepared in Examples 1 to 3 and Comparative Examples 1 to 3, 0.1 g each, and add them to the corresponding heavy metal pollutant solutions. After stirring evenly, let it stand for 24 hours, use a pipette to draw 10 mL of the heavy metal pollutant solution for atomic absorption spectrometer analysis, and record the concentration of the heavy metal pollutant solution before and after adsorption. The adsorption capacity calculation formula is as follows:

[0026] Wherein: Q is the unit adsorption capacity, mg / g; C0 is the initial concentration of the heavy metal pollutant solution before adsorption, mg / L; C is the concentration of the heavy metal pollutant solution after adsorption, mg / L; V is the volume of the heavy metal pollutant solution, L; W is the amount of the soil conditioner corresponding to Examples 1 to 3 and Comparative Examples 1 to 3, g.

[0027] The test results are shown in Table 1.

[0028] Table 1

[0029] Test Example 2 The soil conditioners prepared in Examples 1 to 3 and Comparative Example 3 were treated by different aging methods and then subjected to heavy metal adsorption tests. The test method is as follows: 1. 6 g of each soil conditioner prepared in Examples 1 to 3 and Comparative Example 3 was mixed with 420 mL of H2O2 (5%) solution, then placed in an uncovered glass bottle, heated in an oven at 80°C, stirred twice a day, and after 2 days, the oven temperature was raised to 105°C for final drying. After drying, each sample was washed with deionized water until the pH value was stable to obtain a soil conditioner simulating natural oxidation aging.

[0030] 2. Add 6 g of the soil conditioner prepared in Examples 1 to 3 and Comparative Example 3 into 10°C water and soak for 12 h, then put it into a water bath and dry it at 60°C for 12 h. Repeat this cycle for 30 days to obtain a soil conditioner that simulates natural dry-wet-cold-hot cycle aging.

[0031] Prepare 4 portions of 5 heavy metal pollutant solutions containing cadmium ions, mercury ions, chromium ions, copper ions, and nickel ions, 100 mL each, and a concentration of 100 mg / L. Take 5 portions of the soil conditioner for simulating natural oxidation aging prepared in Examples 1 to 3 and Comparative Example 3, 0.1 g each, and add them to the heavy metal pollutant solutions. After stirring evenly, let stand for 24 hours, use a pipette to draw 10 mL of the solution for atomic absorption spectrometer analysis, and record the concentration of the heavy metal pollutant solution before and after adsorption. The adsorption capacity calculation formula is the same as that of Test Example 1; The heavy metal adsorption test method of the soil conditioner prepared by Examples 1 to 3 and Comparative Example 3, which simulates natural dry-wet cold-heat cycle aging, is the same as the heavy metal adsorption test method of the soil conditioner simulates natural oxidation aging; The test results are shown in Table 2.

[0032] Table 2

[0033] It can be seen from the results of Test Example 1 that compared with Comparative Example 1, Comparative Example 1 does not introduce nitrogen-containing functional groups, so the adsorption of cadmium, copper and nickel by the soil conditioner prepared in Comparative Example 1 is greatly reduced; since Comparative Example 1 lacks competition from nitrogen-containing functional groups, more C-Cl functional groups are introduced, and the adsorption of mercury and chromium is slightly greater than that of Example 1; Compared with Example 2, Example 1 does not introduce C-Cl functional groups into Example 2, so the adsorption amount of mercury and chromium by the soil conditioner prepared in Example 2 is greatly reduced; Compared with Example 3, Example 1 did not load the modified biochar prepared in Example 3 with modified silica gel, resulting in that the biochar could not be effectively dispersed and the adsorption sites were reduced. Therefore, the adsorption amount of cadmium, mercury, chromium, copper and nickel by the soil conditioner prepared in Example 3 was reduced; It can be seen from the results of Experimental Example 2 that the modified biochar prepared in Comparative Example 3 was not loaded with modified silica gel, and a stable carbon-silicon structure was not formed. The pore structure collapsed after aging, resulting in a significant decrease in the adsorption of cadmium, mercury, chromium, copper and nickel by the aged soil conditioner prepared in Comparative Example 3. The adsorption of cadmium, mercury, chromium, copper and nickel by the aged soil conditioner prepared in Examples 1 to 3 was less than that of the unaged soil conditioner in Examples 1 to 3.

Claims

1. A method for preparing a soil conditioner for repairing heavy metal pollution in farmland, Features: The preparation method includes preparing primary modified biochar and preparing secondary modified biochar; The method for preparing the primary modified biochar is as follows: adding biochar powder to a nitric acid solution, bathing in water for 0.8 to 1.2 hours, filtering, placing the filter cake in a reactor, placing the reactor in a microwave device, adjusting the frequency to 2.35 to 2.55 GHz, and heating N 2 The pressure in the reactor is maintained at 6-8 MPa. After 4-6 minutes of reaction, 3-5% Cl 2 Passing into the reactor, changing the microwave frequency to 2.05-2.25 GHz, changing the reactor pressure to 4-6 MPa, reacting for 7-13 minutes, after the reaction, placing the reactants in a muffle furnace with an initial temperature of 180-230°C, and then heating to 500-700°C at a rate of 15-25°C / min, pyrolyzing for 10-20 minutes, cooling to room temperature, soaking in NaOH solution, filtering, and drying to obtain a first modified biochar; The method for preparing the secondary modified biochar is to uniformly mix the primary modified biochar and modified silica gel, then add anhydrous ethanol, stir into a paste, dry naturally, and grind into powder to obtain the secondary modified biochar.

2. A method for preparing a soil conditioner for repairing heavy metal pollution in farmland according to claim 1, Features: In the step of preparing the first modified biochar, the particle size of the biochar powder is 0.05-0.3 mm, and the temperature of the water bath is 50-70°C.

3. A method for preparing a soil conditioner for repairing heavy metal pollution in farmland according to claim 1, Features: In the step of preparing the modified biochar once, N 2 The flow rate into the reactor is 100-300 mL / min, and the concentration is 3-5% Cl 2 The flow rate into the reactor is 80-120 mL / min.

4. A method for preparing a soil conditioner for repairing heavy metal pollution in farmland according to claim 1, Features: In the step of preparing the modified biochar once, the mass ratio of biochar powder to nitric acid solution is 0.8-1.2:90-110, the mass fraction of nitric acid solution is 40-60%, and the mass fraction of NaOH solution is 15-25%.

5. A method for preparing a soil conditioner for repairing heavy metal pollution in farmland according to claim 1, Features: In the step of preparing the secondary modified biochar, the mass ratio of the primary modified biochar, modified silica gel, and anhydrous ethanol is 0.8-1.2:5-7:2.5-3.

5.

6. A method for preparing a soil conditioner for repairing heavy metal pollution in farmland according to claim 1, Features: The preparation method of the modified silica gel comprises the following steps: adding sodium silicate into deionized water, stirring and dissolving the sodium silicate, adding n-hexanol, stirring evenly, adjusting the pH value to 1.5-2.5 using an HCl solution to obtain a sodium silicate solution, placing the sodium silicate solution in a water bath for 3.5-4.5 hours, drying the solution, transferring the solution to a muffle furnace, calcining the solution at 180-220° C. for 1.5-2.5 hours, and grinding the solution into powder to obtain the modified silica gel.

7. A method for preparing a soil conditioner for repairing heavy metal pollution in farmland according to claim 6, Features: In the preparation method of the modified silica gel, the mass ratio of sodium silicate, deionized water and n-hexanol is 0.8-1.2:15.5-15.6:0.7-0.8, the temperature of the sodium silicate solution water bath is 55-65° C., and the particle size of the modified silica gel is 0.1-0.2 mm.

8. A method for preparing a soil conditioner for repairing heavy metal pollution in farmland according to claim 1, Features: The biochar preparation method comprises washing and drying corn stalks, cutting them into small pieces of 1 to 4 cm, and then 2 CO 3 After soaking in the solution for 25 to 35 minutes, the water content was dried to 10 to 20%, and then placed in a muffle furnace under CO 2 Under the environment, the temperature is raised to 180-230°C at a rate of 3-8°C / min, pyrolyzed for 2-3h, and biochar is obtained after cooling.

9. A method for preparing a soil conditioner for repairing heavy metal pollution in farmland according to claim 8, Features: In the biochar preparation method, corn stalks and Na 2 CO 3 The mass ratio of the solution is 0.8-1.2:18-22, and the Na 2 CO 3 The mass fraction of the solution is 25-35%.

10. A soil conditioner for repairing heavy metal pollution in farmland obtained by the preparation method according to any one of claims 1 to 9.

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