Preparation method of trace element and positive charge modified yak manure biochar

Abstract

The invention relates to the technical field of biochar, and particularly discloses a preparation method of trace element and positive charge modified yak dung biochar, through modification of trace elements of boron, molybdenum, manganese, zinc and selenium and modification by combining with glycine positive charges, the prepared biochar can significantly enhance the binding capacity with plant root systems, improve the water and fertilizer retention performance of soil, and improve the water and fertilizer retention performance of the soil. The method is suitable for soil remediation and improvement in the northwest Sichuan plateau area.

Description

Technical Field

[0001] The present invention relates to the technical field of biochar, in particular to a method for preparing yak dung biochar modified with trace elements and positive charges. Background Art

[0002] In the highland pastoral areas of northwestern Sichuan, where forest resources are scarce and coal is scarce and expensive, many herders rely on yak dung as a fuel. Dried or oven-dried yak dung, produced from the excrement of yaks after consuming pasture, is rich in nitrogen and carbon. It has a low ignition point and ignites easily in the low-oxygen environment of the plateau. It also produces no odor and burns gently. However, most tent stoves in these pastoral areas lack chimneys, resulting in smoke and fine particulate matter (PM 2.5) produced during yak dung combustion, which seriously impacts the health of herders and the atmospheric environment of the plateau. Therefore, it is crucial to change the way yak dung is used and utilize it in new technologies, rather than combustion.

[0003] With the rapid development of industrialization and urbanization, soil pollution and degradation are becoming increasingly serious. Traditional soil remediation methods are often costly, time-consuming, and ineffective. Biochar, as an environmentally friendly soil conditioner, has attracted widespread attention due to its excellent adsorption properties and soil-improving effects. However, existing biochar applications in soil remediation and grassland restoration still have certain limitations, such as insufficient adsorption properties and poor stability.

[0004] At present, yak dung biomass carbonization treatment is gradually being accepted and favored by people as a new environmentally friendly treatment method. Due to regional environmental factors, the heavy metal content in yak dung biochar is much lower than that of other types of biochar. It is more suitable to be applied to the soil as a fertilizer to supplement nutrients in the soil, enhance soil fertility, and promote the growth of forage. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing yak dung biochar modified with trace elements and positive charges, so as to solve the problems of insufficient adsorption performance and poor stability of existing biochar, enhance the binding ability of biochar with plant roots, improve the water and fertilizer retention performance of the soil, and increase the biomass of forage grass.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: The preparation method of yak dung biochar modified with trace elements and positive charge is as follows: Step (1): drying, grinding and sieving yak dung to obtain pretreated yak dung; Step (2): adding boric acid, ammonium molybdate, manganese sulfate, zinc sulfate, and sodium selenate to deionized water, stirring evenly to obtain a trace element mixed solution, adding calcium hydroxide solution to the trace element mixed solution, stirring evenly, allowing to stand, filtering out the precipitate, and drying to obtain a trace element additive; Step (3): mixing the pretreated yak dung with the trace element additive, stirring for 1 to 2 hours to obtain trace element modified yak dung, and pyrolyzing the trace element modified yak dung under nitrogen protection to obtain trace element modified yak dung biochar; Step (4): mixing the trace element modified yak dung biochar with glycine, reacting at 80-100° C. for 1-2 h, and drying after the reaction to obtain the trace element and positive charge modified yak dung biochar.

[0007] As a limitation of the present invention, in step (2), the mass ratio of boric acid, ammonium molybdate, manganese sulfate, zinc sulfate, and sodium selenate is (5-7):(9-11):(3-5):1:(0.04-0.06).

[0008] As a limitation of the present invention, in step (3), the mass of the trace element additive accounts for 1% to 5% of the total mass of the pretreated yak dung.

[0009] As a limitation of the present invention, the mass ratio of the trace element modified yak dung biochar to glycine is 1:(5-10).

[0010] As a limitation of the present invention, during the pyrolysis treatment, the pyrolysis temperature is controlled at 400-600° C. and the pyrolysis time is 2-6 hours.

[0011] As a limitation of the present invention, step (3) is specifically: The pretreated yak dung was mixed with a trace element additive and stirred for 1 to 2 hours to obtain trace element modified yak dung. The trace element modified yak dung, attapulgite and potassium dihydrogen phosphate were mixed under nitrogen protection and pyrolyzed to obtain trace element modified yak dung biochar.

[0012] As a limitation of the present invention, the mass ratio of trace element modified yak dung, attapulgite, and potassium dihydrogen phosphate is (5-10):(0.5-1.5):(1-3).

[0013] As a limitation of the present invention, step (4) is specifically: The yak dung is mixed with sawdust, and Bacillus subtilis and Trichoderma harzianum are added to the compost, and the compost is aerobically fermented for 50 to 70 days, and the compost is turned over every 8 to 12 days. After the fermentation is completed, the fermentation product is dried and crushed to obtain composted yak dung. The trace element modified yak dung biochar was mixed with composted yak dung, and the mixture was fully ball-milled. After the ball-milling was completed, the mixture was mixed with glycine and reacted for 1 to 2 hours. After the reaction was completed, the mixture was dried to obtain the trace element and positive charge modified yak dung biochar.

[0014] The trace element and positive charge modified yak dung biochar is obtained according to any one of the preparation methods described above.

[0015] As a limitation of the present invention, the trace element and positive charge modified yak dung biochar can be used for soil remediation, with an amount of 0.5 to 2.0 kg per square meter of soil.

[0016] Compared with the prior art, the present invention has the following beneficial effects: Yak dung biochar, enriched with trace elements, can replenish those deficient in the soil and promote grass growth. The addition of attapulgite effectively increases the biochar's specific surface area, average pore size, and total pore volume, facilitating the biochar's attachment of nutrients such as potassium dihydrogen phosphate and trace elements that promote grass growth. Adding composted yak dung improves the biochar's fertility. Glycine-modified biochar has a positive surface charge and stronger adsorption properties, effectively absorbing heavy metals and organic pollutants from the soil. Ball milling enriches the biochar's pore structure, enhancing its adsorption and ion exchange capacity. The modified biochar is stable, resistant to decomposition, and can persist in the soil for a long time, continuously exerting its ameliorative effects. This biochar preparation method is simple, low-cost, and easy to mass-produce and apply. DETAILED DESCRIPTION

[0017] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0018] Yak dung was collected from the cattle shed of the Ruoergai Alpine Wetland Ecological Station in Hongyuan County, Aba Prefecture, Sichuan Province. Attapulgite (200 mesh) was provided by Huachuan Mineral Products Processing Plant in Lingshou County. Bacillus subtilis inoculant (5×10 7 CFU / g), Trichoderma harzianum agent (1×10 8 CFU / g) was provided by Jiangsu Pengyao Lianye Biological.

[0019] Example 1: Preparation method of yak dung biochar modified with trace elements and positive charge, specifically: Step 1: Yak dung pretreatment 1000 g of fresh yak dung was dried, ground and passed through a 100-mesh sieve to obtain pretreated yak dung.

[0020] Step 2: Depositing trace elements Add 6 g of boric acid, 10 g of ammonium molybdate, 4 g of manganese sulfate, 1 g of zinc sulfate, and 0.05 g of sodium selenate to 100 ml of deionized water, stir evenly to obtain a trace element mixed solution, add 100 ml of 0.02 mol / L calcium hydroxide solution to the trace element mixed solution, stir evenly, let stand, filter out the precipitate, and dry to obtain a trace element additive.

[0021] Step 3: Preparation of trace element modified yak dung biochar The pretreated yak dung was mixed with the trace element additive and stirred for 1 hour to obtain trace element modified yak dung. The trace element modified yak dung was pyrolyzed under nitrogen as a protective gas to obtain trace element modified yak dung biochar, wherein the mass of the trace element additive accounted for 3% of the total mass of the pretreated yak dung, the pyrolysis temperature was 500°C, and the pyrolysis time was 2 hours.

[0022] Step 4: Preparation of trace element and positive charge modified yak dung biochar Glycine was mixed with deionized water to prepare a 1 mol / L glycine solution. The trace element modified yak dung biochar was immersed in the glycine solution for modification. The ratio of trace element modified yak dung biochar to glycine was 1:5. The pH was maintained at 8 and the reaction was carried out for 2 h. After the reaction was completed, it was dried at 400 °C for 0.5 h to obtain trace element and positive charge modified yak dung biochar.

[0023] Example 2: Preparation method of yak dung biochar modified with trace elements and positive charge, specifically: Step 1: Yak dung pretreatment 1000 g of fresh yak dung was dried, ground and passed through a 100-mesh sieve to obtain pretreated yak dung.

[0024] Step 2: Depositing trace elements Add 6 g of boric acid, 10 g of ammonium molybdate, 4 g of manganese sulfate, 1 g of zinc sulfate, and 0.05 g of sodium selenate to 100 ml of deionized water, stir evenly to obtain a trace element mixed solution, add 100 ml of 0.02 mol / L calcium hydroxide solution to the trace element mixed solution, stir evenly, let stand, filter out the precipitate, and dry to obtain a trace element additive.

[0025] Step 3: Preparation of trace element modified yak dung biochar The pretreated yak dung was mixed with the trace element additive and stirred for 1 hour to obtain trace element modified yak dung. The trace element modified yak dung was pyrolyzed under nitrogen as a protective gas to obtain trace element modified yak dung biochar, wherein the mass of the trace element additive accounted for 1% of the total mass of the pretreated yak dung, the pyrolysis temperature was 500°C, and the pyrolysis time was 2 hours.

[0026] Step 4: Preparation of trace element and positive charge modified yak dung biochar Glycine was mixed with deionized water to prepare a 1 mol / L glycine solution. The trace element modified yak dung biochar was immersed in the glycine solution for modification. The ratio of trace element modified yak dung biochar to glycine was 1:5. The pH was maintained at 8 and the reaction was carried out for 2 h. After the reaction was completed, it was dried at 400 °C for 0.5 h to obtain trace element and positive charge modified yak dung biochar.

[0027] Example 3: Preparation method of yak dung biochar modified with trace elements and positive charge, specifically: Step 1: Yak dung pretreatment 1000 g of fresh yak dung was dried, ground and passed through a 100-mesh sieve to obtain pretreated yak dung.

[0028] Step 2: Depositing trace elements Add 6 g of boric acid, 10 g of ammonium molybdate, 4 g of manganese sulfate, 1 g of zinc sulfate, and 0.05 g of sodium selenate to 100 ml of deionized water, stir evenly to obtain a trace element mixed solution, add 100 ml of 0.02 mol / L calcium hydroxide solution to the trace element mixed solution, stir evenly, let stand, filter out the precipitate, and dry to obtain a trace element additive.

[0029] Step 3: Preparation of trace element modified yak dung biochar The pretreated yak dung was mixed with the trace element additive and stirred for 1 hour to obtain trace element modified yak dung. The trace element modified yak dung was pyrolyzed under nitrogen as a protective gas to obtain trace element modified yak dung biochar, wherein the mass of the trace element additive accounted for 5% of the total mass of the pretreated yak dung, the pyrolysis temperature was 500°C, and the pyrolysis time was 2 hours.

[0030] Step 4: Preparation of trace element and positive charge modified yak dung biochar Glycine was mixed with deionized water to prepare a 1 mol / L glycine solution. The trace element modified yak dung biochar was immersed in the glycine solution for modification. The ratio of trace element modified yak dung biochar to glycine was 1:5. The pH was maintained at 8 and the reaction was carried out for 2 h. After the reaction was completed, it was dried at 400 °C for 0.5 h to obtain trace element and positive charge modified yak dung biochar.

[0031] Example 4: Preparation method of yak dung biochar modified with trace elements and positive charge, specifically: Step 1: Yak dung pretreatment 1000 g of fresh yak dung was dried, ground and passed through a 100-mesh sieve to obtain pretreated yak dung.

[0032] Step 2: Depositing trace elements Add 6 g of boric acid, 10 g of ammonium molybdate, 4 g of manganese sulfate, 1 g of zinc sulfate, and 0.05 g of sodium selenate to 100 ml of deionized water, stir evenly to obtain a trace element mixed solution, add 100 ml of 0.02 mol / L calcium hydroxide solution to the trace element mixed solution, stir evenly, let stand, filter out the precipitate, and dry to obtain a trace element additive.

[0033] Step 3: Preparation of trace element modified yak dung biochar The pretreated yak dung was mixed with a trace element additive and stirred for 1 hour to obtain trace element modified yak dung. The trace element modified yak dung was mixed with 200 g of attapulgite, 400 g of potassium dihydrogen phosphate and 200 g of deionized water, stirred evenly, and naturally dried at room temperature to obtain mixed biochar. Under nitrogen protection, the mixed biochar was pyrolyzed to obtain trace element modified yak dung biochar. The pyrolysis temperature was 500°C and the pyrolysis time was 2 h.

[0034] Step 4: Prepare the composted yak dung Yak dung and sawdust were mixed in a mass ratio of 2.5:1, and 0.05% of the total mass of yak dung and sawdust Bacillus subtilis and 0.05% of the total mass of Trichoderma harzianum were added. The compost was aerobically fermented for 60 days, and the pile was turned over every 10 days. After the fermentation was completed, the fermentation product was dried and crushed to obtain composted yak dung.

[0035] Step 5: Preparation of trace element and positive charge modified yak dung biochar Glycine was mixed with deionized water to prepare a 1 mol / L glycine solution. The trace element modified yak dung biochar and composted yak dung were mixed in a mass ratio of 5:1 and fully ball milled. The ball milling time was 6 h, the ball milling speed was 550 rpm, the grinding ball diameter was 5 mm, and the grinding direction was reversed every 30 min during grinding. After ball milling, the biochar was modified by soaking in a glycine solution. The ratio of trace element modified yak dung biochar to glycine was 1:5. The pH of the glycine solution was maintained at 8. The reaction was carried out for 2 h. After soaking, it was dried at 400 °C for 0.5 h to obtain trace element and positive charge modified yak dung biochar.

[0036] Based on Example 1, control experiments were carried out, specifically Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4, as described below: Comparative Example 1: This comparative example involves a method for preparing yak dung biochar modified with trace elements and positive charges. The only difference from Example 1 is that manganese sulfate and zinc sulfate are not added. Specifically: Step 1: Yak dung pretreatment 1000 g of fresh yak dung was dried, ground and passed through a 100-mesh sieve to obtain pretreated yak dung.

[0037] Step 2: Depositing trace elements Add 6 g of boric acid, 10 g of ammonium molybdate, and 0.05 g of sodium selenate to 100 ml of deionized water and stir evenly to obtain a trace element mixed solution. Add 100 ml of 0.02 mol / L calcium hydroxide solution to the trace element mixed solution, stir evenly, let stand, filter out the precipitate, and dry to obtain a trace element additive.

[0038] Step 3: Preparation of trace element modified yak dung biochar The pretreated yak dung was mixed with the trace element additive and stirred for 1 hour to obtain trace element modified yak dung. The trace element modified yak dung was pyrolyzed under nitrogen as a protective gas to obtain trace element modified yak dung biochar, wherein the mass of the trace element additive accounted for 3% of the total mass of the pretreated yak dung, the pyrolysis temperature was 500°C, and the pyrolysis time was 2 hours.

[0039] Step 4: Preparation of trace element and positive charge modified yak dung biochar The trace element modified yak dung biochar was modified by soaking it in a glycine solution. The ratio of trace element modified yak dung biochar to glycine was 1:5. The pH was maintained at 8 and the reaction was carried out for 2 hours. After the reaction was completed, it was dried at 400°C for 0.5 hour to obtain trace element and positive charge modified yak dung biochar.

[0040] Comparative Example 2: This comparative example relates to a method for preparing yak dung biochar modified with trace elements and positive charges. The only difference from Example 1 is that boric acid and ammonium molybdate are not added. Specifically: Step 1: Yak dung pretreatment 1000 g of fresh yak dung was dried, ground and passed through a 100-mesh sieve to obtain pretreated yak dung.

[0041] Step 2: Depositing trace elements Add 4 g of manganese sulfate, 1 g of zinc sulfate, and 0.05 g of sodium selenate to 100 ml of deionized water and stir evenly to obtain a trace element mixed solution. Add 100 ml of 0.02 mol / L calcium hydroxide solution to the trace element mixed solution, stir evenly, let stand, filter out the precipitate, and dry to obtain a trace element additive.

[0042] Step 3: Preparation of trace element modified yak dung biochar The pretreated yak dung was mixed with the trace element additive and stirred for 1 hour to obtain trace element modified yak dung. The trace element modified yak dung was pyrolyzed under nitrogen as a protective gas to obtain trace element modified yak dung biochar, wherein the mass of the trace element additive accounted for 3% of the total mass of the pretreated yak dung, the pyrolysis temperature was 500°C, and the pyrolysis time was 2 hours.

[0043] Step 4: Preparation of trace element and positive charge modified yak dung biochar The trace element modified yak dung biochar was modified by soaking it in a glycine solution. The ratio of trace element modified yak dung biochar to glycine was 1:5. The pH was maintained at 8 and the reaction was carried out for 2 hours. After the reaction was completed, it was dried at 400°C for 0.5 hour to obtain trace element and positive charge modified yak dung biochar.

[0044] Comparative Example 3: This comparative example relates to a method for preparing yak dung biochar modified with trace elements and positive charges. The only difference from Example 1 is that sodium selenate is not added. Specifically: Step 1: Yak dung pretreatment 1000 g of fresh yak dung was dried, ground and passed through a 100-mesh sieve to obtain pretreated yak dung.

[0045] Step 2: Depositing trace elements Add 6 g of boric acid, 10 g of ammonium molybdate, 4 g of manganese sulfate, and 1 g of zinc sulfate to 100 ml of deionized water, stir evenly to obtain a trace element mixed solution, add 100 ml of 0.02 mol / L calcium hydroxide solution to the trace element mixed solution, stir evenly, let stand, filter out the precipitate, and dry to obtain a trace element additive.

[0046] Step 3: Preparation of trace element modified yak dung biochar The pretreated yak dung was mixed with the trace element additive and stirred for 1 hour to obtain trace element modified yak dung. The trace element modified yak dung was pyrolyzed under nitrogen as a protective gas to obtain trace element modified yak dung biochar, wherein the mass of the trace element additive accounted for 3% of the total mass of the pretreated yak dung, the pyrolysis temperature was 500°C, and the pyrolysis time was 2 hours.

[0047] Step 4: Preparation of trace element and positive charge modified yak dung biochar The trace element modified yak dung biochar was modified by soaking it in a glycine solution. The ratio of trace element modified yak dung biochar to glycine was 1:5. The pH was maintained at 8 and the reaction was carried out for 2 hours. After the reaction was completed, it was dried at 400°C for 0.5 hour to obtain trace element and positive charge modified yak dung biochar.

[0048] Comparative Example 4: This comparative example relates to a method for preparing yak dung biochar. The only difference from Example 1 is that the yak dung biochar is not modified with glycine. Specifically: Step 1: Yak dung pretreatment 1000 g of fresh yak dung was dried, ground and passed through a 100-mesh sieve to obtain pretreated yak dung.

[0049] Step 2: Depositing trace elements Add 6 g of boric acid, 10 g of ammonium molybdate, 4 g of manganese sulfate, 1 g of zinc sulfate, and 0.05 g of sodium selenate to 100 ml of deionized water, stir evenly to obtain a trace element mixed solution, add 100 ml of 0.02 mol / L calcium hydroxide solution to the trace element mixed solution, stir evenly, let stand, filter out the precipitate, and dry to obtain a trace element additive.

[0050] Step 3: Preparation of trace element modified yak dung biochar The pretreated yak dung was mixed with the trace element additive and stirred for 1 hour to obtain trace element modified yak dung. The trace element modified yak dung was pyrolyzed under nitrogen as a protective gas to obtain trace element modified yak dung biochar, wherein the mass of the trace element additive accounted for 3% of the total mass of the pretreated yak dung, the pyrolysis temperature was 500°C, and the pyrolysis time was 2 hours.

[0051] Detection experiment: Yak dung biochar samples were prepared according to the processes in Example 1, Example 2, Example 3, Example 4, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4.

[0052] Surface potential test: The yak dung biochar sample was crushed and moistened with deionized water. After filtering out excess water, 1 g of the sample was placed in a glass sample tank. The sample was pressed tightly with a stopper and sealed. The surface potential of the yak dung biochar was measured. The electrolyte solution was a 0.001 mol / L potassium chloride solution.

[0053] Soil fertility test: The experimental soil was collected from the alpine grassland of Hongyuan County, Aba Prefecture, Sichuan Province. The experimental soil was sieved through a 2mm sieve and air-dried. A certain amount of air-dried soil sample was weighed and placed in a flower pot. A total of 45 flower pots were filled and divided into 9 groups of 5 pots each. 8 of these groups were randomly selected and mixed with different yak dung biochar samples in the flower pots at a rate of 1kg / m 2 The remaining group served as a control, adding an equal amount of experimental soil to the test sample. Grass seeds from the same batch and specifications were selected for seedling cultivation. Then, the same number of grass seedlings with consistent growth were transplanted into each pot. The grass was watered and pest-treated according to the normal grass growth cycle. Once grass growth stabilized, changes in grass biomass were measured in each group, using the control group's grass biomass as a benchmark. Soil samples were taken from each group and the control group, and rainfall was simulated using an infiltrator. Changes in soil water retention capacity were measured in each group, using the control group's soil water retention capacity as a benchmark.

[0054] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Surface potential (mV) +25 +23 +27 +31 +21 +19 +24 -5 Forage biomass (%) +31 +25 +36 +43 +23 +21 +26 +17 Soil water retention capacity (%) +30 +28 +32 +35 +23 +22 +25 +13 Conclusion: According to the test data, it can be seen that the surface potential, forage biomass and soil water retention capacity of the trace element and positively charged modified trace element yak dung biochar prepared in Example 1 are better than those of Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4.

[0055] It can be seen from Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 that depositing multiple trace elements is beneficial to promoting the growth of forage grass.

[0056] It can be seen from Example 1 and Comparative Example 4 that the yak dung biochar was not modified with glycine. The yak dung biochar was negatively charged and had a low surface potential. It was easy to react with anions in the soil and had a weak binding ability with the root system, which was not conducive to the absorption of trace elements by forage.

[0057] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

Claims

1. A method for preparing yak dung biochar modified with trace elements and positive charge, characterized in that: Specifically: Step (1): drying, grinding and sieving fresh yak dung to obtain pretreated yak dung; Step (2): adding boric acid, ammonium molybdate, manganese sulfate, zinc sulfate, and sodium selenate to deionized water, stirring evenly to obtain a trace element mixed solution, adding calcium hydroxide solution to the trace element mixed solution, stirring evenly, standing, filtering out the precipitate, and drying to obtain a trace element additive; Step (3): mixing the pretreated yak dung with the trace element additive, stirring for 1 to 2 hours to obtain trace element modified yak dung, and pyrolyzing the trace element modified yak dung under nitrogen protection to obtain trace element modified yak dung biochar; Step (4): mixing the trace element modified yak dung biochar with glycine, reacting at 80-100° C. for 1-2 hours, and drying after the reaction is completed to obtain the trace element and positive charge modified yak dung biochar.

2. The method for preparing the trace element and positive charge modified yak dung biochar according to claim 1, characterized in that: In step (2), the mass ratio of boric acid, ammonium molybdate, manganese sulfate, zinc sulfate and sodium selenate is (5-7):(9-11):(3-5):1:(0.04-0.06).

3. The method for preparing the trace element and positive charge modified yak dung biochar according to claim 1, characterized in that: In step (3), the mass of the trace element additive accounts for 1% to 5% of the total mass of the pretreated yak dung.

4. The method for preparing the trace element and positive charge modified yak dung biochar according to claim 1, characterized in that: The mass ratio of trace element modified yak dung biochar and glycine is 1:(5-10).

5. The method for preparing the trace element and positive charge modified yak dung biochar according to claim 1, characterized in that: In step (3), the pyrolysis temperature during pyrolysis treatment is 400-600° C., and the pyrolysis time is 2-6 hours.

6. The method for preparing the trace element and positive charge modified yak dung biochar according to claim 1, characterized in that: Step (3) is as follows: The pretreated yak dung was mixed with a trace element additive and stirred for 1 to 2 hours to obtain trace element modified yak dung. Under nitrogen protection, the trace element modified yak dung, attapulgite and potassium dihydrogen phosphate were mixed and pyrolyzed to obtain trace element modified yak dung biochar.

7. The method for preparing the trace element and positive charge modified yak dung biochar according to claim 6, characterized in that: The mass ratio of trace element modified yak dung, attapulgite and potassium dihydrogen phosphate is (5-10):(0.5-1.5):(1-3).

8. The method for preparing the trace element and positive charge modified yak dung biochar according to claim 1, characterized in that: Step (4) is as follows: The yak dung is mixed with sawdust, and Bacillus subtilis and Trichoderma harzianum are added to the compost, and the compost is aerobically fermented for 50 to 70 days, and the compost is turned over every 8 to 12 days. After the fermentation is completed, the fermentation product is dried and crushed to obtain composted yak dung; The trace element modified yak dung biochar was mixed with composted yak dung, and fully ball-milled. After the ball-milling, it was mixed with glycine and reacted for 1 to 2 hours. After the reaction was completed, it was dried to obtain the trace element and positive charge modified yak dung biochar.

9. The trace element and positive charge modified yak dung biochar obtained by the preparation method according to any one of claims 1 to 8.

10. The trace element and positive charge modified yak dung biochar according to claim 9, characterized in that: The trace element and positive charge modified yak dung biochar can be used for soil remediation, with a dosage of 0.5 to 2.0 kg per square meter of soil.