Compound ecological soil based on coal gangue biochar and preparation method thereof

Abstract

The present application relates to solid resource utilization technical field, specifically to a kind of compound ecological soil based on coal gangue biochar and preparation method thereof.The present application overcomes the technical problem that the acid resistance of mine soil to be repaired is poor, resulting in low soil fertility.The present application grinds and dries coal gangue raw material, and activates to obtain coal gangue biochar;part of coal gangue biochar is fermented with organic fertilizer inoculated with fermentation agent by aerobic composting to obtain carbon-based organic fertilizer;vacuum negative pressure is used to make the remaining coal gangue biochar adsorb composite active bacteria liquid under negative pressure, spray sodium alginate solution to obtain biological microcapsule material;finally, mine soil to be repaired, carbon-based organic fertilizer, biological microcapsule material and calcined oyster shell powder are step by step compounded to obtain compound ecological soil.The present application significantly improves the acid and alkali impact resistance and persistent fertility of ecological soil by constructing physical aggregate, double-effect acid and alkali buffer system and microcapsule long-acting ecological network.

Description

Technical Field

[0001] This invention relates to the field of solid resource utilization technology, specifically to a compound ecological soil based on coal gangue biochar and its preparation method. Background Technology

[0002] With the continuous development of global mineral resources, mining subsidence areas and abandoned mining sites have caused serious land degradation and ecological damage. How to restore these abandoned mining areas to arable land with agricultural production capacity has become a focus in the fields of ecology and soil engineering. In recent years, the use of industrial waste (such as coal gangue) to prepare biochar, and using it as a core matrix, supplemented with soil, organic fertilizer, and microbial agents to prepare compound ecological soil, has been considered a highly promising technological approach. This technology not only achieves the resource utilization of large quantities of solid waste, but its products can also effectively improve soil physicochemical properties, regulate soil porosity, and sequestrate carbon and reduce emissions.

[0003] Although compounded ecological soil based on coal gangue biochar has many theoretical advantages, existing compounding technologies still face core problems in actual harsh mine remediation projects. Mining areas (especially coal mining areas) are often accompanied by severe acidic mine wastewater pollution, resulting in an extreme and fluctuating acidity of the soil environment. Conventional biochar has limited buffering capacity and is prone to structural collapse or surface passivation in complex soil environments, making it unable to maintain long-term stability. This leads to extremely low survival rates of microorganisms in extreme environments, and organic nutrients are easily lost under rainwater erosion, making it impossible to provide long-term and continuous nutrient supply for plants (such as remediation pioneer plants or crops), and making it difficult to truly meet the standards for reclamation into arable land.

[0004] To this end, a compound ecological soil based on coal gangue biochar and its preparation method are proposed. Summary of the Invention

[0005] The purpose of this invention is to design a compound ecological soil based on coal gangue biochar and its preparation method.

[0006] To achieve the above objectives, the present invention provides the following technical solution: Unless otherwise specified, all the following parts are by weight.

[0007] This invention provides a method for preparing a compound ecological soil based on coal gangue biochar, comprising the following steps: Coal gangue raw materials are crushed, dried and activated to obtain coal gangue biochar; part of the coal gangue biochar and organic fertilizer are aerobically composted and fermented to produce carbon-based organic fertilizer; the remaining coal gangue biochar is negatively pressure adsorbed with compound live bacteria liquid and sprayed with sodium alginate to obtain bio-microcapsule material; finally, the mine soil to be remediated, carbon-based organic fertilizer, bio-microcapsule material and calcined oyster shell powder are compounded in steps to obtain compound ecological soil.

[0008] Preferably, the preparation method of coal gangue biochar is as follows: 200 parts of coal gangue raw material (silicon oxide content 58%-62%; aluminum oxide content 22%-24%; fixed carbon content 7%-10%; the remaining components include small amounts of metal oxides such as iron oxide, calcium oxide, and magnesium oxide) are crushed by a crusher and then mechanically sieved to extract particles with particle sizes in the ranges of 0.1-0.5 mm and 1-2 mm; the particles are fed into a drying kiln and dried at 105℃ until the moisture content is <1%, obtaining dried raw material; the dried raw material is fed into a program-controlled temperature rotary pyrolysis furnace and heated to 280-320℃ at a heating rate of 10℃ / min, at which time a small amount of air is introduced into the furnace (controlled by temperature). With an oxygen concentration of 1%-2%, the material is kept at a temperature of 1 hour. Through micro-oxygen activation, a large number of carboxyl and hydroxyl groups are generated on the surface of the biochar. After the first stage, the oxygen is cut off, and high-purity nitrogen is introduced at a flow rate of 1 L / min to quickly purge the furnace cavity, replacing the residual oxygen in the furnace and switching to an oxygen-free state. Under nitrogen protection, the temperature is raised to 450℃-550℃ at a heating rate of 20℃ / min and held at this temperature for 1 hour. After pyrolysis, heating is stopped, and under the condition of continuous nitrogen supply protection, the material is cooled to room temperature through an oxygen-free discharge system. Mechanical screening is then performed to remove particles with a particle size greater than 2 mm, resulting in coal gangue biochar (with an average pore size concentrated in 2-50 nm).

[0009] Preferably, the preparation method of carbon-based organic fertilizer is as follows: 18-22 parts of coal gangue biochar and 200 parts of organic fertilizer (crushed livestock and poultry manure or plant straw with an organic matter content ≥45%) are put into a trough mixer for preliminary mixing. Simultaneously, 0.5-1 parts of aerobic composting fermentation agent are inoculated into the material, and the total moisture content of the mixture is controlled at 55%-60% by spraying clean water. The mixture is stirred evenly to obtain a homogeneous mixture. The mixture is then transferred to a fermentation tank, piled up, and the pile height is controlled at 1.1-1.5 meters. m, utilize fermentation microorganisms to naturally raise the temperature to 60℃ (during this high temperature period, use a turning machine to mechanically turn the pile every 2-3 days, or turn the pile immediately to supplement oxygen when the core temperature exceeds 60℃), maintain this high temperature for 7 days for composting fermentation, and the total fermentation cycle is 15-20 days; when the pile temperature naturally drops to close to the ambient temperature, and the material turns blackish-brown, has no foul odor and is accompanied by a fresh earthy fragrance, it is judged to be fully decomposed. Finally, spread the decomposed material naturally in a ventilated place to reduce its moisture content to below 30%, and obtain carbon-based organic fertilizer.

[0010] The preferred method for preparing the aerobic composting fermentation agent is as follows: *Bacillus subtilis*, *Bacillus thermophilus*, and *Bacillus spp.* (all commercially available) are inoculated into liquid culture medium and fermented for 40 hours at 37°C (55°C for *Bacillus thermophilus*), an aeration rate of 1:1 vvm, and a constant pH of 7.0 until the spore formation rate is ≥85%. *Aspergillus niger* and *Saccharomyces cerevisiae* are inoculated into liquid culture medium and fermented for 60 hours at 30°C and an aeration rate of 1:0.8 vvm. After fermentation, the fermentation broth is collected. 35 parts of the *Bacillus subtilis* fermentation broth, 25 parts of the *Bacillus thermophilus* fermentation broth, 20 parts of the *Aspergillus niger* fermentation broth, 15 parts of the *Bacillus spp.* fermentation broth, and 5 parts of the *Saccharomyces cerevisiae* fermentation broth are mixed evenly in a sterile tank to obtain a compound live bacteria solution. 125 parts of wheat bran, 75 parts of soybean meal powder, and 37.5 parts of rice husk powder are then mixed. The mixture is added to a mixer and stirred evenly, then sent to a high-temperature steam sterilizer and sterilized at 121℃ and 0.1MPa for 45 minutes, then cooled to room temperature. Next, 12-13 parts of sodium humate powder (as a dormancy protectant) are added and dry-mixed evenly in the mixer to obtain solid dry material. A high-speed mixer is started to evenly spray the compound live bacteria solution onto the solid dry material. The mixed material is then spread evenly in a sterile fermentation tray, with a thickness controlled at 5-7cm, and sent to a temperature- and humidity-controlled fermentation chamber. The ambient temperature is controlled at 32℃, and the relative humidity is maintained at 85%. Solid-state shallow fermentation is carried out for 4 days, with manual or mechanical turning once a day to replenish oxygen. After solid-state fermentation, the material is sent to a fluidized bed dryer, with the inlet air temperature controlled at ≤45℃ for low-temperature drying. Drying is stopped when the material moisture content drops to 10%, and then the material is pulverized through an 80-mesh sieve to obtain aerobic composting fermentation inoculant.

[0011] Preferably, the preparation method of the bio-microcapsule material is as follows: 10 parts of a compound live bacteria solution (the same compound live bacteria solution prepared during the preparation of aerobic composting fermentation inoculant) are dispersed in 25 parts of sterile physiological saline, and mixed evenly at a low temperature of 5°C to obtain a microbial inoculant suspension; 75-85 parts of coal gangue biochar are placed in a vacuum impregnation tank, and a vacuum is drawn to -0.09 MPa and maintained for 15 minutes to exhaust the gas in the mesopores (2-50 nm) of the biochar using negative pressure; under vacuum, the microbial inoculant suspension is drawn in through the side inlet pipe of the impregnation tank using the internal and external pressure difference, and the variable frequency stirring is turned on, controlling the speed to 35 rpm. Stir at 25 rpm for 10 minutes (to prevent damage to the biochar pore framework) to force the microbial agent suspension into and adsorb it into the pores of the coal gangue biochar. Slowly introduce sterile air into the tank to release the vacuum and restore atmospheric pressure. Then, spray 100 parts of a 2% sodium alginate aqueous solution evenly into the tank and continue stirring at 25 rpm for 20-30 minutes. After that, remove the formed material and send it to a low-temperature vacuum drying oven. Dry it under the condition that the inlet air temperature is ≤35℃ until the moisture content of the material drops below 15%. After that, remove it and seal it in a cool, dry place to obtain the bio-microcapsule material.

[0012] The preferred method for preparing the compounded ecological soil is as follows: Take 800 portions of mine soil to be remediated, air-dry or sun-dry it, then crush it using a soil crusher and pass it through a vibrating screen with a 5mm aperture to remove stones, plant roots, and large particles to obtain the mine matrix; use a variable frequency high-speed / low-speed mixer for stepwise compounding, adding the mine matrix and carbon-based organic fertilizer together into the mixer, turning on the high-frequency spindle, and mixing at a high shear speed of 80 rpm for 3 minutes. During the first minute of mixing, spray an appropriate amount of water evenly into the mixer through a misting system to dynamically adjust the overall moisture content of the mixture to 2%. 5%-30% This step aims to break the compact structure of the original soil. With the help of the capillary force and high shear collision of water, organic matter and mineral particles are recombined to initially construct an artificial soil aggregate structure with a particle size between 2-5mm. After high-speed granulation, without stopping the machine, add bio-microcapsule material and 13-17 parts of calcined oyster shell powder to the mixer (with the water spraying step continuing). Quickly adjust the mixer speed to 30 rpm and tumble and mix for 12 minutes until the entire material is homogenized. After compounding, unload the material from the mixer and let it stand and mature in a cool and ventilated place for 24-48 hours to obtain compounded ecological soil.

[0013] Preferably, the preparation method of calcined oyster shell powder is as follows: waste natural oyster shells are collected, repeatedly rinsed with deionized water, and after cleaning, they are sent to an oven and dried at 105°C to obtain dried oyster shells; the dried oyster shells are fed into a jaw crusher for coarse crushing to obtain oyster shell fragments with an average particle size of 2 cm; the oyster shell fragments are loaded into a refractory crucible and sent into a muffle furnace, and calcined at 800°C at a heating rate of 5°C / min for 2 hours under normal pressure air atmosphere; after calcination, the material is naturally cooled to room temperature with the furnace, and then fed into a pulverizer for grinding and passed through a 200-mesh sieve to obtain calcined oyster shell powder.

[0014] Another aspect of the present invention provides a compound ecological soil based on coal gangue biochar, the raw materials for which include coal gangue raw materials, organic fertilizer, aerobic composting fermentation agent, compound live bacteria liquid, sodium alginate, mine soil to be restored and calcined oyster shell powder.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes aerobic composting fermentation agents in a specific aerobic composting process to inoculate coal gangue biochar with organic acids released during the later stages of fermentation, thereby exposing more adsorption sites on its porous framework. Simultaneously, the biochar's well-developed mesoporous structure chemically immobilizes a large amount of easily vaporized and volatilized ammonia during fermentation, forming a carbon-based organic fertilizer rich in stable mineral nutrients. When compounded with ecological soil, the biochar's high specific surface area and the organic-inorganic complex form a long-lasting ion exchange network, effectively locking in key nutrients such as nitrogen, phosphorus, and potassium. This significantly reduces nutrient leaching caused by rainwater runoff in mines, achieving on-demand, slow-release nutrient supply and solving the problems of "low fertilizer efficiency, rapid loss, and difficulty in retention" after traditional fertilization of mine soils.

[0016] This invention utilizes vacuum negative pressure to drive sodium alginate solution to penetrate deep into the mesopores of coal gangue biochar and encapsulate functional bacteria. In the subsequent compounding stage, oyster shell powder calcined at 800℃ is rich in highly active calcium oxide, which rapidly undergoes a hydration reaction after being added to the soil matrix, releasing free Ca2+. 2+ These exogenous highly active Ca 2+ It can penetrate and drive the guluronic acid in sodium alginate to undergo specific chelation, and construct a gel structure with a three-dimensional network skeleton in situ; at the same time, the trace amount of endogenous active ash on the surface of biochar provides auxiliary anchoring points, and finally forms a dense and tough flexible solidified coating with strong acid impact resistance, providing protection for microorganisms under extreme stress such as acidic wastewater in mines.

[0017] This invention addresses the technical challenge of mine soils undergoing remediation being highly susceptible to erosion by strongly acidic mine wastewater or drastic fluctuations in localized alkalinity. It constructs a highly efficient dual-effect acid-resistant buffering system composed of biochar with rich surface functional groups and calcined oyster shell powder. In the first stage, the coal gangue biochar undergoes micro-aerobic activation, generating a large number of oxygen-containing functional groups such as carboxyl and hydroxyl groups on its surface, exhibiting excellent proton exchange and complexation buffering capabilities. Combined with calcined oyster shell powder, when the remediated soil encounters acid erosion, the active calcium oxide in the oyster shell powder can rapidly neutralize the acid, while the porous calcium carbonate and biochar functional groups provide long-term pH buffering and balancing, thereby maintaining the soil pH within a suitable range over a long period. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the preparation process of the compounded ecological soil of this invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] For details, please refer to [link / reference]. Figure 1 This invention provides a compound ecological soil based on coal gangue biochar and its preparation method, the technical solution of which is as follows: Example 1 Bacillus subtilis, Bacillus thermophilus, and Bacillus mucilaginosus were inoculated into liquid culture medium and fermented for 40 hours at 37℃ (55℃ for Bacillus thermophilus), an aeration rate of 1:1 vvm, and a constant pH of 7.0 until the spore formation rate was ≥85%. Aspergillus niger and Saccharomyces cerevisiae were inoculated into liquid culture medium and fermented for 60 hours at 30℃ and an aeration rate of 1:0.8 vvm. After fermentation, the fermentation broth was collected. 35 parts of Bacillus subtilis fermentation broth, 25 parts of Bacillus thermophilus fermentation broth, 20 parts of Aspergillus niger fermentation broth, 15 parts of Bacillus mucilaginosus fermentation broth, and 5 parts of Saccharomyces cerevisiae fermentation broth were mixed evenly in a sterile tank to obtain a compound live bacteria solution. 125 parts of wheat bran, 75 parts of soybean meal powder, and 37.5 parts of rice husk powder were added to a mixer and stirred evenly. The mixture was then placed in a high-temperature steam sterilizer and sterilized at 121°C and 0.1 MPa for 45 minutes, then cooled to room temperature. 12.5 parts of sodium humate powder were then added and mixed thoroughly in a mixer to obtain solid dry material. A high-speed mixer was started to evenly spray the compound live bacteria solution onto the solid dry material. The mixed material was then spread evenly in a sterile fermentation tray, with a thickness controlled at 6 cm. It was then placed in a temperature- and humidity-controlled fermentation chamber, where the ambient temperature was maintained at 32°C and the relative humidity at 85%. Solid-state shallow fermentation was carried out for 4 days, with manual or mechanical turning of the tray once a day to replenish oxygen. After solid-state fermentation, the material was sent to a fluidized bed dryer, with the inlet air temperature controlled at ≤45°C, for low-temperature drying. Drying was stopped when the material moisture content dropped to 10%. The material was then pulverized through an 80-mesh sieve to obtain aerobic composting fermentation inoculant.

[0021] Waste natural oyster shells were collected, repeatedly rinsed with deionized water, and then dried in an oven at 105°C to obtain dried oyster shells. The dried oyster shells were then fed into a jaw crusher for coarse crushing to obtain oyster shell fragments with an average particle size of 2 cm. The oyster shell fragments were then placed in a refractory crucible and fed into a muffle furnace. Under normal atmospheric pressure, the temperature was increased to 800°C at a heating rate of 5°C / min and calcined for 2 hours. After calcination, the material was allowed to cool naturally to room temperature in the furnace. The material was then fed into a pulverizer for grinding and passed through a 200-mesh sieve to obtain calcined oyster shell powder.

[0022] 200 portions of coal gangue raw material were crushed by a crusher and then mechanically screened to extract particles with diameters in the ranges of 0.1-0.5 mm and 1-2 mm. The particles were then fed into a drying kiln and dried at 105℃ until the moisture content was <1%, yielding dried raw material. This dried raw material was then fed into a program-controlled temperature rotary pyrolysis furnace and heated to 300℃ at a rate of 10℃ / min. A small amount of air (oxygen concentration controlled at 1%-2%) was introduced into the furnace, and the temperature was maintained for 1 hour. This marked the end of the first stage. Afterwards, the oxygen supply is cut off, and high-purity nitrogen is introduced at a flow rate of 1L / min to quickly purge the furnace cavity, replacing the residual oxygen in the furnace and switching to an oxygen-free state. Under nitrogen protection, the temperature is raised to 500℃ at a heating rate of 20℃ / min and held at this temperature for 1 hour. After pyrolysis is completed, heating is stopped, and under the condition of continuous nitrogen supply protection, the material is cooled to room temperature through the discharge system in an oxygen-free environment. Mechanical screening is then performed to remove particles with a particle size greater than 2mm, yielding coal gangue biochar. Take 20 parts of coal gangue biochar and 200 parts of organic fertilizer (crushed livestock and poultry manure or plant straw with an organic matter content ≥45%) and put them into a trough mixer for initial mixing. At the same time, inoculate the material with 0.8 parts of aerobic composting fermentation agent and dynamically adjust the moisture content of the mixture by spraying clean water to control it at 58%. Mix evenly to obtain a mixture. Transfer the mixture to a fermentation tank, build a pile, and control the pile height at 1.3m. Utilize the fermentation microorganisms to naturally raise the temperature to 60℃ (during this high temperature period, use a turning machine to mechanically turn the pile every 2-3 days, or turn the pile immediately to supplement oxygen when the core temperature exceeds 60℃). Maintain this high-temperature composting fermentation for 7 days, with a total fermentation cycle of 18 days. When the pile temperature naturally drops to close to the ambient temperature, and the material turns blackish-brown, has no foul odor, and is accompanied by a fresh earthy fragrance, it is judged to be fully decomposed. Finally, spread the decomposed material out naturally in a ventilated place to reduce its moisture content to below 30%, thus obtaining carbon-based organic fertilizer. Ten parts of a compound live bacteria solution were dispersed in 25 parts of sterile physiological saline and mixed evenly at 5°C to obtain a microbial agent suspension. Eighty parts of coal gangue biochar were placed in a vacuum impregnation tank, and a vacuum was drawn to -0.09 MPa and maintained for 15 minutes to purge the gas from the mesopores of the coal gangue biochar using negative pressure. Under vacuum, the microbial agent suspension was drawn in through the side inlet pipe of the impregnation tank using the internal and external pressure difference. A variable frequency stirrer was turned on, and the speed was controlled at 35 rpm. Vacuum stirring was maintained for 10 minutes to allow the microorganisms to disperse. The biological agent suspension was forcibly injected and adsorbed into the pores of coal gangue biochar; sterile air was slowly introduced into the tank to release the vacuum and restore the pressure to normal; then 100 parts of a 2% sodium alginate aqueous solution were evenly sprayed into the tank, and stirring was continued at 25 rpm for 25 minutes. After the stirring was completed, the formed material was removed and sent to a low-temperature vacuum drying oven, where it was dried under the condition that the inlet air temperature was ≤35℃ until the moisture content of the material dropped to below 15%. After removal, it was sealed and stored in a cool and dry place to obtain the biological microcapsule material. 800 portions of mine soil to be remediated were taken, and after natural air drying or sun drying, they were crushed using a soil crusher and passed through a vibrating screen with a 5mm aperture to obtain the mine matrix. A variable frequency high-speed / low-speed mixer was used for stepwise compounding. The mine matrix and carbon-based organic fertilizer were put into the mixer together, and the high-frequency spindle was turned on to mix at a high shear speed of 80 rpm for 3 minutes. During the first minute of mixing, an appropriate amount of water was evenly sprayed into the mixer through a misting system to dynamically adjust the overall moisture content of the mixture to 28%. After high-speed granulation, without stopping the machine, bio-microcapsule material and 15 portions of calcined oyster shell powder were added to the mixer. The mixer speed was quickly adjusted to 30 rpm and tumbling was carried out for 12 minutes. After compounding, the material was unloaded from the mixer and left to stand and mature in a cool and ventilated place for 36 hours to obtain the compounded ecological soil.

[0023] Examples 2-5 refer to the parameter conditions in Example 1, with specific differences shown in Table 1.

[0024] Table 1 Parameters and conditions for Examples 1-5 Dosage of sodium humate powder / portions 12.5 12 12 13 13 Laying thickness / cm 6 5 7 5 7 Temperature in the first stage of coal gangue biochar preparation / ℃ 300 280 290 310 320 Temperature in the second stage of coal gangue biochar preparation / ℃ 500 450 480 520 550 Dosage / parts of coal gangue biochar used in the preparation of carbon-based organic fertilizer 20 18 19 21 22 Dosage / parts of aerobic composting fermentation inoculant 0.8 0.5 1 0.5 1 Height of the stack / m 1.3 1.1 1.2 1.4 1.5 Total fermentation cycle / day 18 15 15 20 20 Amount / parts of coal gangue biochar used in the preparation of bio-microcapsule materials 80 75 78 82 85 Stirring time / min 25 20 30 20 30 Overall moisture content / % 28 25 25 30 30 Dosage / parts of calcined oyster shell powder 15 13 14 16 17 resting and ripening time / h 36 24 30 42 48 Comparative Example 1 follows the same parameters and conditions as in Example 1, except that the first stage of micro-oxygen activation at 300°C is not performed in the preparation process of coal gangue biochar. Instead, the temperature is directly raised to 500°C and held for 2 hours under nitrogen protection at the same heating rate. The remaining steps remain unchanged.

[0025] Comparative Example 2 follows the same parameters and conditions as in Example 1, except that the organic fertilizer is separately added with microbial agents for aerobic composting fermentation. After fermentation and maturation, it is then physically mixed with 20 parts of coal gangue biochar at room temperature to obtain a mixture that replaces the carbon-based organic fertilizer in subsequent compounding.

[0026] Comparative Example 3 follows the same parameters and conditions as in Example 1, except that no vacuuming operation is performed during the preparation of the bio-microcapsule material. Instead, the composite live bacteria suspension is directly stirred with coal gangue biochar for 10 minutes under normal pressure, followed by spraying with sodium alginate solution and drying.

[0027] Comparative Example 4 follows the same parameters and conditions as in Example 1, except that in the preparation process of the bio-microcapsule material, although vacuum adsorption of bacterial liquid was performed, sodium alginate aqueous solution was not sprayed afterward, and low-temperature drying was carried out directly.

[0028] Comparative Example 5 uses the same parameters and conditions as in Example 1, except that instead of calcined oyster shell powder, an equal amount of natural raw oyster shell powder that has only been washed and crushed through a 200-mesh sieve is added during compounding.

[0029] Comparative Example 6 follows the same parameters and conditions as in Example 1, except that during the preparation of the compound ecological soil, all materials are simultaneously added to the mixer and stirred at a high shear speed of 80 rpm for 15 minutes.

[0030] Comparative Example 7 follows the same parameters and conditions as in Example 1, except that the high-speed, high-shear section (first 3 minutes) of the compounded ecological soil does not use a misting spray system to spray water, and the materials are mixed in a dry state. The subsequent frequency conversion stirring steps are the same.

[0031] Experiment Example 1: Soil Fertility Test The soil composition of Examples 1-5 and Comparative Examples 1-7 was tested, and the results are shown in Tables 2-3.

[0032] Table 2 Soil fertility of Examples 1-5 and Comparative Examples 1-7 Example 1 7.15 66.5 0.32 132.5 42.1 Example 2 6.95 64.2 0.35 121.0 38.5 Example 3 7.22 65.8 0.31 128.4 40.2 Example 4 6.88 63.1 0.38 115.6 36.8 Example 5 7.05 65.0 0.34 125.2 39.4 Comparative Example 1 6.35 58.2 0.52 82.4 28.5 Comparative Example 2 6.72 55.4 0.44 81.3 31.2 Comparative Example 3 6.85 61.2 0.41 102.5 33.6 Comparative Example 4 6.78 50.5 0.45 96.8 30.4 Comparative Example 5 5.65 62.1 0.58 105.2 26.8 Comparative Example 6 6.62 52.2 0.49 85.6 29.1 Comparative Example 7 6.70 54.3 0.51 88.0 27.5 Table 3 Soil fertility of Examples 1-5 and Comparative Examples 1-7 Example 1 218.4 248.5 135.2 315.1 Example 2 202.3 244.1 131.8 303.2 Example 3 211.0 246.8 133.5 306.5 Example 4 195.8 241.2 129.4 301.4 Example 5 206.5 245.1 132.6 309.8 Comparative Example 1 152.6 210.5 112.4 260.5 Comparative Example 2 165.4 202.1 115.8 272.4 Comparative Example 3 178.2 225.4 121.0 289.6 Comparative Example 4 169.5 218.7 118.2 281.3 Comparative Example 5 182.4 220.6 120.5 145.2 Comparative Example 6 148.5 195.2 108.6 225.8 Comparative Example 7 155.0 198.8 110.3 258.1 As shown in Tables 2 and 3, Examples 1-5 of the present invention all exhibited extremely excellent fertility indicators. Specifically, the compound ecological soil prepared in Example 1 maintained a stable pH value within the optimal slightly alkaline microenvironment for crop growth, had high organic matter content, low salt content, and demonstrated good overall retention and slow-release capabilities for water-soluble nitrogen, available phosphorus, readily available potassium, and trace elements. Examples 2-5, with reasonable adjustments within a certain parameter range, showed slight fluctuations in various physicochemical indicators due to minor adjustments in process parameters, but the overall soil fertility remained good. This fully demonstrates that the compound ecological soils of Examples 1-5 can overcome the dual core challenges of high acid-base impact and extreme nutrient deficiency in mine soils.

[0033] The difference in Comparative Example 1 lies in the absence of the first-stage 300℃ micro-aerobic activation process. Because the coal gangue biochar failed to accumulate a large number of oxygen-containing functional groups such as carboxyl and hydroxyl groups in situ, its cation exchange capacity dropped significantly, greatly weakening its ability to complex and retain mineral nutrients (such as water-soluble nitrogen and available potassium), resulting in severe nutrient leaching and loss. The difference in Comparative Example 2 lies in changing the co-fermentation process of biochar and fertilizer to separate fermentation followed by physical mixing. In the aerobic composting process lacking biochar intervention, the large amount of ammonia released during the high-temperature fermentation period could not be captured and adsorbed in situ by the porous framework of the biochar, causing a large amount of the core nitrogen source to volatilize with the gas, resulting in the most severe loss of water-soluble nitrogen. Furthermore, the biochar failed to undergo micro-pore expansion and surface activation by organic acids during fermentation, leading to poorer stability in its recombination with organic matter. The difference in Comparative Example 3 lies in the absence of a vacuum negative pressure process during the preparation of the bio-microcapsule material. Under normal pressure, the well-developed mesopores of biochar are filled with gas, forming strong capillary resistance. This prevents the functional composite live bacteria solution from penetrating deep into the pores, causing it to remain loosely on the outer surface of the biochar. Microorganisms are easily killed or washed away and inactivated, resulting in a decline in biological fertility indicators. The difference in Comparative Example 4 lies in the absence of a sodium alginate spraying step after the microcapsules adsorb the bacterial solution. Although a vacuum is used to press some bacteria into the pores, the lack of a flexible semi-permeable membrane barrier formed by sodium alginate means that the loaded composite live bacteria are directly exposed to the complex external mineral remediation matrix. They are easily detached from the pores by water leaching, leading to the failure of microbial colonization.

[0034] The difference in Comparative Example 5 lies in the use of natural raw oyster shell powder instead of calcined oyster shell powder in the compounding process. The microstructure of natural raw oyster shells is highly dense, with the calcium carbonate inside tightly encapsulated by large-molecule keratin, resulting in an extremely sluggish proton response and a complete lack of highly active calcium oxide. The raw shell powder cannot effectively neutralize or build a high-efficiency buffer, causing the pH value of the ecological soil to drop. This low pH environment then triggers the chemical fixation of phosphorus. Simultaneously, due to the lack of high-temperature phase transition release, the release of effective calcium plummets. The difference in Comparative Example 6 lies in the use of a high-shear mixing rate of 80 rpm throughout the compounding process. The continuous high-intensity mechanical shearing and collision for 15 minutes not only tore and destroyed the sodium alginate shell upon which the bio-microcapsule material depended, leading to the exposure and death of a large number of the internally loaded functional bacteria, but also pulverized the artificial soil aggregate structure that had just been constructed. The ecological soil structure completely degraded into fine powder, causing the complete collapse of the soil's water and fertilizer retention barrier, resulting in extremely severe nutrient leaching and loss. The difference in Comparative Example 7 lies in the absence of the atomized spray water conditioning process in the compound granulation stage, resulting in dry mixing. Due to the lack of crucial water introduction, the material particles cannot undergo physical recombination through liquid bridging force, water capillary pull, and the swelling and cohesion of macromolecular organic matter. This prevents the ecological soil from developing an artificial aggregate structure with intermediate pores, and the material remains in a loose and fragmented state. Due to the lack of a stable physical aggregate structure to encapsulate and retain nutrients, readily available nutrients such as water-soluble nitrogen and available phosphorus are severely lost with water, the substrate salinity rebounds, and both physical and chemical fertility become ineffective.

[0035] Experiment Example 2: Acid Resistance Test Weigh 1 kg each of the compound ecological soils prepared in Examples 1-5 and Comparative Examples 1-7, and pack them into a special plexiglass leaching column with an inner diameter of 10 cm and a height of 40 cm, and compact them evenly. Prepare a high-concentration simulated acidic mine wastewater with deionized water, and adjust its composition to: 2.5 mmol / L H2SO4, 1.0 mmol / L FeSO4, and 0.5 mmol / L... Al2(SO4)3 was used, with pH controlled at 3.0. Simulated acidic wastewater was continuously pumped into the top of each leaching column using a multi-channel peristaltic pump at a constant flow rate of 5 mL / min, with a total of 3000 mL pumped into each group. After leaching, each soil column was air-dried at 30℃ to 60% of its maximum water holding capacity, and then placed in a constant temperature and humidity chamber for incubation for 7 days to allow the soil microenvironment to return to chemical and biological equilibrium. Soil samples were collected from the core layer (10-15 cm deep) of each soil column, and the contents of pH, organic matter, water-soluble nitrogen, available phosphorus, and available potassium in the soil after acid shock were measured. The results are shown in Table 4.

[0036] Table 4 Soil fertility after acid shock in Examples 1-5 and Comparative Examples 1-7 Example 1 6.62 62.5 110.2 36.8 185.4 Example 2 6.38 59.8 98.5 32.1 168.0 Example 3 6.68 61.9 106.1 34.5 176.5 Example 4 6.25 58.0 92.4 29.8 159.2 Example 5 6.45 60.5 102.3 33.1 172.3 Comparative Example 1 4.65 45.2 41.3 12.5 82.6 Comparative Example 2 5.21 42.6 32.5 15.4 95.1 Comparative Example 3 5.42 55.1 68.4 20.2 118.3 Comparative Example 4 5.35 53.8 62.1 18.6 112.2 Comparative Example 5 4.15 56.4 55.8 10.2 105.4 Comparative Example 6 5.10 35.2 34.8 11.0 72.6 Comparative Example 7 5.18 38.6 38.0 12.3 78.4 As shown in Table 4, the compound ecological soils described in Examples 1-5 of this invention exhibited strong acid buffering capacity and fertility retention effect after being subjected to leaching impact from high-concentration acidic mine wastewater. The soil pH values ​​in Examples 1-5 all formed a solid defensive barrier and did not suffer devastating acidification. At the same time, the organic matter, water-soluble nitrogen, available phosphorus, and available potassium in each group remained at high levels. This proves that the stepwise compounding system of this invention forms a profound synergistic stress resistance mechanism through its internal microphysical structure, fast-acting-long-acting chemical buffer pool, and biological protection network, endowing the ecological soil with acid erosion resistance and long-lasting fertility retention performance.

[0037] In Comparative Example 1, the biochar failed to accumulate a large number of oxygen-containing functional groups such as carboxyl and hydroxyl groups in situ during pyrolysis, resulting in a sharp drop in its charge exchange and chemical adsorption capacity for hydrogen ions. Under the severe impact of strong acid wastewater, the soil pH value rapidly declined, and the acidic environment further triggered intense chemical exchange and leaching of mineral nutrients, causing a sharp drop in water-soluble nitrogen and available potassium. This confirms that the microaerobic activation stage plays a core role in constructing a high cation exchange capacity acid-resistant and fertilizer-retaining framework. In Comparative Example 2, organic fertilizer was fermented separately and then physically mixed with biochar. In the aerobic composting process without the in-situ intervention of biochar, the large amount of ammonia released during the high-temperature fermentation period lost the opportunity to be captured and retained by the porous structure of biochar, resulting in a large amount of the core nitrogen source volatilizing with the gas upon heating. At the same time, the biochar failed to undergo microscopic complexation and activation by organic acids during fermentation, making its integrated structure with organic matter extremely prone to loosening and collapse. Under the leaching and washing of acidic liquid, its water-soluble nitrogen index dropped severely, and organic matter was also severely lost. In Comparative Example 3, under normal pressure, the gas barrier effect prevented the composite active bacterial solution from being targeted and penetrating deep into the pores within the well-developed mesopores of biochar, causing it to loosely adhere to the outer surface of the biochar. When faced with the dynamic penetration of high-concentration acidic mine wastewater, the microorganisms, lacking the deep protection of the porous framework, were directly exposed to the antagonistic toxicity of strong acid and harmful metal ions (iron and aluminum), resulting in large-scale inactivation or elution of the bacterial community. Consequently, the subsequent dynamic phosphorus and potassium solubilization and fertilizer retention metabolism of the functional bacterial community were lacking, and the available phosphorus and readily available potassium indicators of the ecological soil showed a significant decline. In Comparative Example 4, although the bacterial solution entered some pores through the vacuum, the lack of a flexible semi-permeable membrane barrier formed by sodium alginate solution allowed the external strongly acidic wastewater to directly penetrate and diffuse into the pores without hindrance. When subjected to prolonged stress at extremely low pH, the microorganisms in the micropores suffered severe damage due to the lack of local microenvironmental isolation and protection, directly leading to the death of a large number of bacteria and colonization failure. The long-term biochemical fertility cycle maintained by the bacterial community was completely damaged, resulting in a significant decline in the final retention of water-soluble nitrogen and available phosphorus.

[0038] Comparative Example 5, when faced with a sudden surge of highly acidic mine wastewater, was completely unable to neutralize or buffer the impact. This led to a catastrophic acidification of the microenvironment within the soil column, resulting in a decrease in pH. The acidic environment, in turn, triggered severe chemical fixation of phosphorus, leading to a reduction in its available phosphorus levels. Comparative Example 6 pulverized the sodium alginate shell of the bio-microcapsule material, causing complete exposure of the internally loaded functional microbial community. The artificial soil aggregate structure was broken down, and the macroscopic physical structure of the ecological soil degraded into fine powder, causing it to lose its physical barrier against water and nutrients. Under leaching impact, the entire system suffered erosion and loss, resulting in a significant decrease in organic matter and available potassium. In Comparative Example 7, due to the lack of crucial water introduction, the material particles were completely unable to undergo physical recombination through liquid bridging forces, water capillary pull, and the swelling and cohesive forces of macromolecular organic matter. This resulted in the ecological soil being unable to develop an artificial aggregate structure capable of encapsulating nutrients, and the material remained in an extremely loose and isolated fragmented state. When faced with large-volume acid leaching, due to the lack of a stable physical aggregate structure to encapsulate and retain nutrients, water-soluble nitrogen and available phosphorus were lost with the water, and soil fertility was greatly reduced.

[0039] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing compound ecological soil based on coal gangue biochar, characterized in that, The method includes the following steps: Coal gangue raw material is crushed, dried and activated to obtain coal gangue biochar; the first batch of coal gangue biochar and organic fertilizer are aerobically composted and fermented to produce carbon-based organic fertilizer; the second batch of coal gangue biochar is negatively pressure adsorbed with composite live bacteria liquid and sprayed with sodium alginate to obtain bio-microcapsule material; the mine soil to be restored, the carbon-based organic fertilizer, the bio-microcapsule material and calcined oyster shell powder are compounded in steps to obtain the compound ecological soil.

2. The method for preparing a compound ecological soil based on coal gangue biochar according to claim 1, characterized in that, The preparation method of the coal gangue biochar is as follows: the coal gangue raw material is crushed, sieved, and dried to obtain dry raw material; the dry raw material is sent into a pyrolysis furnace, heated to 280-320℃, and oxygen is introduced for heat preservation; then the oxygen in the furnace is replaced with nitrogen, and the temperature is raised to 450℃-550℃ for heat preservation; after pyrolysis is completed, it is cooled to room temperature, sieved, and the coal gangue biochar is obtained.

3. The method for preparing a compound ecological soil based on coal gangue biochar according to claim 1, characterized in that, The preparation method of the carbon-based organic fertilizer is as follows: take the first part of the coal gangue biochar and mix it with the organic fertilizer, inoculate with aerobic composting fermentation agent, control the moisture content of the material at 55%-60%, and obtain a mixture; transfer the mixture to a fermentation tank, build a pile, control the pile height at 1.1-1.5m, and the total fermentation cycle is 15-20 days; after the pile temperature naturally decreases and the composting is completed, spread it out naturally to dry, and obtain the carbon-based organic fertilizer.

4. The method for preparing a compound ecological soil based on coal gangue biochar according to claim 3, characterized in that, The preparation method of the aerobic composting fermentation agent is as follows: Bacillus subtilis, Bacillus stearothermophilus, Bacillus mucilaginosus, Aspergillus niger, and Saccharomyces cerevisiae are inoculated into liquid culture medium respectively. After fermentation, the fermentation liquid is collected and mixed to obtain a compound live bacteria liquid. Wheat bran, soybean meal powder, and rice husk powder are stirred evenly, sterilized, and sodium humate powder is added to obtain solid dry material. The compound live bacteria liquid is sprayed onto the solid dry material, mixed, and spread evenly in a sterile fermentation pan for fermentation. After fermentation, the material is dried, crushed, and sieved to obtain the aerobic composting fermentation agent.

5. The method for preparing a compound ecological soil based on coal gangue biochar according to claim 1, characterized in that, The preparation method of the bio-microcapsule material is as follows: the composite live bacteria liquid is dispersed in sterile physiological saline to obtain a microbial agent suspension; the gas in the second part of the coal gangue biochar is vented under negative pressure, and the microbial agent suspension is drawn in by the pressure difference. After stirring, sterile air is introduced into the tank to normal pressure, and then sodium alginate aqueous solution is sprayed into the tank. After stirring, vacuum drying is performed to obtain the bio-microcapsule material.

6. The method for preparing a compound ecological soil based on coal gangue biochar according to claim 1, characterized in that, The preparation method of the compound ecological soil is as follows: take the soil to be restored from the mine, air dry and crush it to obtain the mine matrix; mix the mine matrix and the carbon-based organic fertilizer, adjust the overall moisture content to 25%-30%, then add the biological microcapsule material and the calcined oyster shell powder and stir; after compounding, unload and let stand for 24-48 hours to obtain the compound ecological soil.

7. A compound ecological soil based on coal gangue biochar, characterized in that, The raw materials for preparation include coal gangue, organic fertilizer, aerobic composting fermentation agent, compound live bacteria liquid, sodium alginate, mine soil to be restored, and calcined oyster shell powder; the compound ecological soil is prepared by any one of the preparation methods of claims 1-6.

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