A coal gangue-based improved soil and its preparation method

Abstract

This invention relates to the field of solid waste resource utilization technology, and discloses a coal gangue-based improved soil and its preparation method. The coal gangue-based improved soil comprises the following raw materials: coal gangue, sand, and fermentation inoculants; the fermentation inoculants include Bacillus subtilis SHBCC D11446, arbuscular mycorrhizal fungi SHBCC D24696, Trichoderma viride SHBCC D10197, and Bacillus belye GS02 with accession number CCTCC NO: M 2025531. This invention enables more complete utilization of phosphorus, potassium, nitrogen, and organic matter in coal gangue, and the resulting coal gangue-based improved soil has a high nutrient content and a low content of available heavy metals. It also avoids excessive increases in alkalinity and salinity caused by the introduction of coal gangue, thus enabling the improved soil to effectively promote plant growth.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization technology, and in particular to a coal gangue-based improved soil and its preparation method. Background Technology

[0002] Coal gangue is a type of solid waste generated during coal mining and washing. It is a dark gray rock with a low carbon content and harder than coal, formed alongside coal seams during coal formation. The chemical composition of coal gangue is complex, mainly consisting of inorganic and organic matter. The inorganic components primarily consist of oxides of silicon, aluminum, calcium, magnesium, and iron, such as SiO2, Al2O3, Fe2O3, CaO, and MgO. It also contains some rare metal elements, such as gallium, vanadium, titanium, and cobalt. These elements exist in complex compound forms within coal gangue, offering various possibilities for its comprehensive utilization.

[0003] Currently, the main uses of coal gangue include the production of building materials, power generation, coal and pyrite recovery, land reclamation and backfilling, and the preparation of chemical products. However, there are certain technical limitations, and the utilization rate of coal gangue is generally around 60-70%, which is relatively low. For example, in patent CN118620630A, coal gangue and coal-to-oil residue are mixed and then subjected to acid treatment and roasting. Then, it is mixed with polyacrylamide, water, monomers, and initiators and subjected to polymerization, settling, solid-liquid separation, and drying. Finally, it is mixed with polyethylene terephthalate, ammonium bicarbonate solution, and crosslinking agent and subjected to crosslinking, solid-liquid separation, and drying. The resulting modified coal gangue can be used for soil improvement. This patent reduces the risk of heavy metal leaching from coal gangue by coating the surface of coal gangue with a polymer with a three-dimensional network structure. However, coal gangue contains a lot of phosphorus and potassium elements that are difficult for plants to absorb and utilize. The method of this patent cannot effectively utilize these elements. In addition, the roasting process will also cause the loss of organic matter in the coal gangue. Summary of the Invention

[0004] To address the aforementioned technical problems—namely, the low utilization rate of coal gangue in existing methods for preparing improved soil, making it difficult to fully utilize the organic matter and elements such as phosphorus and potassium—this invention provides a coal gangue-based improved soil and its preparation method. This invention enables more complete utilization of phosphorus, potassium, and organic matter in coal gangue, and the resulting coal gangue-based improved soil has a high nutrient content and a low content of available heavy metals. Simultaneously, it avoids the excessive increase in alkalinity and salinity caused by the introduction of coal gangue, thus enabling the improved soil to effectively promote plant growth.

[0005] The specific technical solution of this invention is as follows: In a first aspect, the present invention provides a coal gangue-based improved soil, comprising the following raw materials: coal gangue, sand, and fermentation inoculants; wherein the fermentation inoculants include Bacillus subtilis SHBCC D11446, Rhizophagus irregularis SHBCC D24696, Trichoderma viride SHBCCCD10197, and Bacillus velezensis GS02 with accession number CCTCC NO: M 2025531.

[0006] The information of each strain in the fermentation agent used in this invention is as follows: (1) Bacillus velezensis GS02 is a new strain isolated from soil by our team. Its preservation information is as follows: Name of depositary institution: China Center for Type Culture Collection (CCTCC); Address of the depositary institution: Wuhan University, Wuhan, China; Deposit date: March 20, 2025; Accession number: CCTCC NO: M 2025531.

[0007] (2) Bacillus subtilis SHBCC D11446 can be purchased from the Shanghai Center for Microbial Culture Collection (SHBCC). The information about this strain in SHBCC is as follows: Strain number: SHBCC D11446; Other numbers: AS1.421; Chinese name: Bacillus subtilis SHBCC D11446 AS1.421.

[0008] (3) Arbuscular mycorrhizal fungus SHBCC D24696 can be purchased from the Shanghai Center for Microbial Culture Collection (SHBCC). Information about this strain in SHBCC is as follows: Strain number: SHBCC D24696; Other number: PL112; Chinese name: Arbuscular mycorrhizal PL112 SHBCC D24696=PL112; Latin name: Rhizophagus irregularis PL112.

[0009] (4) *Trichoderma viride* SHBCC D10197 can be purchased from the Shanghai Center for Microbial Culture Collection (SHBCC). Information about this strain in SHBCC is as follows: Strain number: SHBCC D10197; Other numbers: NBRC 30546 = ATCC26802; Chinese name: Trichoderma viride.

[0010] Among the aforementioned fermentation agents, *Bacillus velezensis* GS02, during the mixed fermentation of raw materials such as coal gangue and sand, can immobilize heavy metals, reduce the content of available heavy metals, and increase the content of organic matter, total nitrogen, available phosphorus, and available potassium. Simultaneously, it can reduce the increase in soil alkalinity and salinity after the introduction of coal gangue. However, current research on *Bacillus velezensis* has not reported any strains possessing these combined functions.

[0011] This invention combines Bacillus belye GS02 with Bacillus subtilis SHBCC D11446, arbuscular mycorrhizal fungi SHBCC D24696, and Trichoderma viride SHBCC D10197. The four strains can produce a synergistic effect, achieving better fermentation results in the coal gangue-based improved soil. This results in higher organic matter, total nitrogen, available phosphorus, and available potassium content, as well as lower available heavy metal content. It also avoids the excessive increase in alkalinity and salinity of the improved soil caused by the introduction of coal gangue. This not only makes the improved soil more suitable for plant cultivation and effectively promotes plant growth, but also improves the utilization rate of coal gangue, allowing for more complete utilization of phosphorus, potassium, and organic matter.

[0012] Furthermore, after being fermented with the microbial agent described in this invention, the nutrients in coal gangue are activated, resulting in higher levels of organic matter, available phosphorus, and readily available potassium. However, while the microbial agent can reduce soil compaction to some extent, it cannot completely solve the problem of soil compaction when coal gangue is used as planting soil. Sandy soil, on the other hand, has low organic matter content, lacks clay minerals, has low cation exchange capacity (CEC), and poor fertilizer retention capacity, but it has weak cohesion and good aeration. This invention combines coal gangue and sandy soil to improve the soil structure of coal gangue-based improved soil, giving it better aeration while maintaining a higher nutrient content.

[0013] Preferably, the coal gangue includes small-diameter coal gangue, medium-diameter coal gangue, and large-diameter coal gangue in a mass ratio of 30-50:30-40:15-30; the small-diameter coal gangue has a particle size of no more than 2 mm, the medium-diameter coal gangue has a particle size of 2-6 mm (excluding 2 mm and 6 mm), and the large-diameter coal gangue has a particle size of 6-10 mm (including 6 mm and 10 mm).

[0014] Small-diameter coal gangue (d≤2mm) has a strong water retention effect on plant roots; medium-diameter coal gangue (2mm<d<6mm) combines water retention and air permeability; and large-diameter coal gangue (6mm≤d≤10mm) can provide both air permeability and dust control and sand fixation. This invention uses a compound of these three types of coal gangue in a certain proportion, making the coal gangue-based improved soil more suitable for plant growth.

[0015] Preferably, the ratio of viable counts of Bacillus subtilis SHBCC D11446, arbuscular mycorrhizal fungi SHBCC D24696, Trichoderma viride SHBCC D10197, and Bacillus belyi GS02 is 1000:0.8-1.2:0.1-0.3:100-300.

[0016] Preferably, the mass of the fermentation agent is 0.1 to 1.5% of the mass of the coal gangue.

[0017] Preferably, the coal gangue-based improved soil also includes the following raw materials: water-retaining agent and organic fertilizer.

[0018] Furthermore, the water-retaining agent includes at least one of sodium polyacrylate, diatomaceous earth, and perlite; the organic fertilizer includes at least one of manure, green manure, compost, and commercial fertilizer; and the mass of both the water-retaining agent and the organic fertilizer is 0.1% to 1% of the mass of coal gangue.

[0019] Preferably, the sand has a particle size of less than 2 mm and the sand accounts for 30-70% of the total mass of all raw materials.

[0020] Secondly, the present invention provides a method for preparing the coal gangue-based improved soil, comprising: mixing all raw materials and fermenting them to obtain coal gangue-based improved soil.

[0021] Preferably, the moisture content is adjusted to 15-25% before fermentation; the fermentation temperature is 20-37°C and the time is 10-30 days.

[0022] Preferably, the preparation steps of the fermentation agent include: inoculating Bacillus subtilis SHBCC D11446 and Bacillus belye GS02 into TSB medium, and inoculating arbuscular mycorrhizal fungi SHBCC D24696 and Trichoderma viride SHBCCCD10197 into PDA medium, and after scaling up the culture, centrifuging the fermentation broth at high speed, discarding the supernatant, collecting the mycelial sludge, mixing the mycelial sludge with a protectant, and freeze-drying to obtain mycelial powder of the four strains; mixing the mycelial powder of the four strains to obtain the fermentation agent.

[0023] Preferably, the process of mixing all raw materials includes the following steps: after preparing the fermentation agent into a bacterial solution, it is mixed with coal gangue, water-retaining agent and organic fertilizer are added, and after mixing evenly, it is mixed with sand.

[0024] Furthermore, the method for preparing the fermentation agent into a bacterial solution is as follows: the fermentation agent and water are mixed at a mass ratio of 0.7 to 1.2:9.

[0025] Furthermore, before mixing the bacterial solution with the coal gangue, the coal gangue is first crushed to a particle size of no more than 10 mm. Then, through sorting and screening, the crushed coal gangue is divided into three categories: a particle size of no more than 2 mm, a particle size of 2-6 mm (excluding 2 mm and 6 mm), and a particle size of 6-10 mm (including 6 mm and 10 mm). These categories are then mixed in a mass ratio of 30-50:30-40:15-30.

[0026] Compared with the prior art, the present invention has the following advantages: (1) This invention uses a specific fermentation agent to mix and ferment raw materials including coal gangue and sand. The four strains of bacteria contained in the fermentation agent can produce a synergistic effect, thereby immobilizing heavy metals to a greater extent, activating phosphorus and potassium elements, increasing organic matter and total nitrogen content, and avoiding excessive increase in alkalinity and salt content of the improved soil caused by the introduction of coal gangue. This not only enables the improved soil to effectively promote plant growth, but also improves the utilization rate of coal gangue, so that the phosphorus, potassium elements and organic matter in it can be more fully utilized.

[0027] (2) The present invention uses three types of coal gangue with different particle sizes (d≤2mm, 2mm<d<6mm and 6mm≤d≤10mm) to improve the soil, which can make the soil more water-retaining and breathable, thus providing a more suitable soil environment for plant growth.

[0028] (3) This invention can not only realize the large-scale and full-quantity resource utilization of coal gangue, but also solve the various environmental pollution problems caused by coal gangue accumulation, thereby creating new economic growth points and providing strong technical support for solving the coal gangue treatment problem in coal mining areas. Detailed Implementation

[0029] The present invention will be further described below with reference to embodiments.

[0030] General Implementation Examples First, the present invention relates to a coal gangue-based improved soil, comprising the following raw materials: coal gangue, sand, and fermentation inoculants; wherein the fermentation inoculants include Bacillus subtilis SHBCC D11446, Rhizophagus irregularis SHBCC D24696, Trichoderma viride SHBCCCD10197, and Bacillus velezensis GS02 with accession number CCTCC NO: M 2025531.

[0031] In some specific embodiments, the coal gangue includes small-diameter coal gangue, medium-diameter coal gangue, and large-diameter coal gangue in a mass ratio of 30-50:30-40:15-30; the small-diameter coal gangue has a particle size of no more than 2 mm, the medium-diameter coal gangue has a particle size of 2-6 mm (excluding 2 mm and 6 mm), and the large-diameter coal gangue has a particle size of 6-10 mm (including 6 mm and 10 mm).

[0032] In some specific embodiments, the ratio of viable counts of Bacillus subtilis SHBCC D11446, arbuscular mycorrhizal fungi SHBCC CD24696, Trichoderma viride SHBCC D10197, and Bacillus belyi GS02 is 1000:0.8-1.2:0.1-0.3:100-300.

[0033] In some specific embodiments, the mass of the fermentation agent is 0.1 to 1.5% of the mass of the coal gangue.

[0034] In some specific embodiments, the particle size of the sand is less than 2 mm, and the mass of the sand accounts for 30-70% of the total mass of all raw materials.

[0035] In some specific embodiments, the coal gangue-based improved soil further includes the following raw materials: a water-retaining agent and organic fertilizer. The water-retaining agent includes at least one of sodium polyacrylate, diatomaceous earth, and perlite, with a mass of 0.1-1% of the coal gangue mass. The organic fertilizer includes at least one of manure, green manure, compost, and commercial fertilizer, with a mass of 0.1-1% of the coal gangue mass.

[0036] Second, the present invention relates to a method for preparing the coal gangue-based improved soil, comprising: mixing all raw materials and fermenting them to obtain coal gangue-based improved soil.

[0037] In some specific embodiments, the moisture content is adjusted to 15-25% before fermentation; the fermentation temperature is 20-37°C and the time is 10-30 days.

[0038] In some specific embodiments, the preparation steps of the fermentation agent include: inoculating Bacillus subtilis SHBCCD11446 and Bacillus belye GS02 into TSB medium, and inoculating arbuscular mycorrhizal fungi SHBCCD24696 and Trichoderma viride SHBCC D10197 into PDA medium, and scaling up the culture at 25-30℃ and 100-130 rpm / min for 20-24 h, centrifuging the fermentation broth at high speed, discarding the supernatant, collecting the mycelial sludge, mixing the mycelial sludge with a protectant, and freeze-drying to obtain mycelial powder of the four strains; mixing the mycelial powder of the four strains to obtain the fermentation agent.

[0039] In some specific embodiments, the process of mixing all raw materials includes the following steps: after preparing the fermentation agent into a bacterial solution, it is mixed with coal gangue, water-retaining agent and organic fertilizer are added, and after being mixed evenly, it is mixed with sand.

[0040] In the above specific embodiments, the following options or preferred methods may be used: The method for preparing fermentation inoculum into a bacterial solution is as follows: the fermentation inoculum and water are mixed at a mass ratio of 0.7 to 1.2:9; Before mixing the bacterial solution with the coal gangue, the coal gangue is first crushed to a particle size of no more than 10 mm. Then, through sorting and screening, the crushed coal gangue is divided into three categories: a particle size of no more than 2 mm, a particle size of 2-6 mm (excluding 2 mm and 6 mm), and a particle size of 6-10 mm (including 6 mm and 10 mm). These are then mixed in a mass ratio of 30-50:30-40:15-30. Specific Implementation The present invention will now be described through specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Variations and advantages that can be conceived by those skilled in the art without departing from the spirit and scope of the inventive concept are included in the present invention, and the scope of protection of the present invention is defined by the appended claims and any equivalents thereof.

[0042] Example 1: Effects of microbial inoculants on the physicochemical properties of coal gangue-based improved soil 1.1 Preparation of fermentation inoculum The TSB culture medium is prepared as follows: 17.0g tryptone, 3.0g yeast extract, 5.0g sodium chloride, 2.5g dipotassium hydrogen phosphate, and 2.5g glucose are added to a final volume of 1000mL with distilled water. The pH is adjusted to 7.1-7.5, and the medium is sterilized at 121℃ for 30min.

[0043] The PDA culture medium is prepared as follows: 5g potato extract powder, 20g glucose, 15g agar, and dilute to 1000mL with distilled water. Sterilize at 121℃ for 30min.

[0044] Bacillus subtilis SHBCC D11446 and Bacillus bereaves GS02 were inoculated into TSB medium, while arbuscular mycorrhizal fungi SHBCC D24696 and Trichoderma viride SHBCC D10197 were inoculated into PDA medium. The cultures were incubated at 28°C and 120 rpm / min for 24 h. The fermentation broth was then centrifuged at high speed (10000×g, 10 min), the supernatant was discarded, and the mycelial sludge was collected. This sludge was mixed with a protectant (a reconstituted solution of 15% (w / v) skim milk powder) and freeze-dried to obtain mycelial powders of four strains: SHBCC D11446, SHBCC D24696, SHBCC D10197, and GS02.

[0045] Take SHBCC D11446 microbial powder, SHBCC D24696 microbial powder and SHBCC D10197 microbial powder, mix them in a live cell ratio of 1000:0.8:0.1 to obtain fermentation agent GN3.

[0046] Take SHBCC D11446 microbial powder, SHBCC D24696 microbial powder, SHBCC D10197 microbial powder and GS02 microbial powder, and mix them in a live cell count ratio of 1000:0.8:0.1:100 to obtain the fermentation agent GN4-min.

[0047] Take SHBCC D11446 microbial powder, SHBCC D24696 microbial powder, SHBCC D10197 microbial powder and GS02 microbial powder, and mix them in a live cell ratio of 1000:1.2:0.3:300 to obtain the fermentation agent GN4-max.

[0048] 1.2 Strain Antagonism Experiment The LB medium is prepared as follows: 10g tryptone, 5g yeast extract, 10g sodium chloride, and 15g / L agar are added to a final volume of 1000mL with distilled water and sterilized at 121℃ for 30min. The PDA medium is prepared as follows: 5g potato extract powder, 20g glucose, and 15g agar are added to a final volume of 1000mL with distilled water and sterilized at 121℃ for 30min. Before solidification, equal volumes of the LB and PDA media are mixed. After solidification, the LB / PDA composite medium is obtained.

[0049] Bacillus subtilis SHBCC D11446 and Bacillus belye GS02 were streaked in pairs with arbuscular mycorrhizal fungi SHBCC CD24696 and Trichoderma viride SHBCC D10197 on LB / PDA composite medium, with the streaks not intersecting. The mixtures were incubated at 30°C for 4 days. The following criteria were used to determine if there was antagonism between the strains: if a sterile zone formed at the intersection of the two strains, it indicated that an inhibition zone had been formed, and the two strains were antagonistic and could not be combined; if no sterile zone was formed, it indicated that the two strains were not antagonistic and could be combined. The results (Table 1) show that there was no antagonism between the strains, and they did not interfere with each other or affect the growth of the fungi; therefore, they can be mixed as a compound inoculum.

[0050] Table 1 Results of strain antagonism experiment SHBCC D11446 - - - SHBCC D24696 - - - SHBCC D10197 - - - GS02 - - - Note: "+" indicates a positive result and has an antagonistic effect; "-" indicates a negative result and has no antagonistic effect.

[0051] 1.3 Preparation of coal gangue-based improved soil After crushing the coal gangue to a particle size of no more than 10 mm, it is sorted and screened to select small-sized coal gangue (d≤2 mm), medium-sized coal gangue (2 mm<d<6 mm), and large-sized coal gangue (6 mm≤d≤10 mm). These are then mixed in a mass ratio of 4:4:3 to obtain a coal gangue mixture.

[0052] SHBCC D11446 bacterial powder, SHBCC D24696 bacterial powder, SHBCC D10197 bacterial powder, GS02 bacterial powder, fermentation inoculant GN3, fermentation inoculant GN4-min and fermentation inoculant GN4-max were mixed with water at a mass ratio of 1:9 to obtain bacterial solution.

[0053] At a mass ratio of 1:10, each bacterial solution was sprayed separately into the coal gangue mixture and stirred evenly to obtain mixture A. Perlite water-retaining agent and commercial organic fertilizer (Changchun Xinyangguang Organic Fertilizer Co., Ltd.) were added to mixture A, with each added at 0.1% of the coal gangue mixture's mass. The mixture was stirred evenly to obtain mixture B. Mixture B and sand were mixed at a mass ratio of 7:3 and stirred evenly to obtain mixture C. The moisture content of mixture C was adjusted to 20%, and fermented at 25℃ for 10 days. During this period, a film was used to reduce moisture loss, resulting in improved coal gangue-based soil. The control group (CK) used an equal mass of water instead of the bacterial solution.

[0054] 1.4 Testing of the physical and chemical properties of coal gangue-based improved soil Sandy soil and coal gangue-based improved soil prepared from each group were taken, and their pH, electrical conductivity (EC), organic matter content, total nitrogen content, available phosphorus content, available potassium content and available heavy metal content were determined. The results are shown in Tables 2 and 3.

[0055] Table 2. Test results of physicochemical properties of coal gangue-based improved soil. Table 3. Results of detection of available heavy metal content in coal gangue-based improved soil. According to Tables 2 and 3, it can be seen that: (1) Compared with the CK group, the improved soil prepared by the GS02 group has a pH and EC value closer to that of sandy soil, higher content of organic matter, total nitrogen, available phosphorus and available potassium, and lower content of available heavy metals. This indicates that the strain can improve the excessive alkalinity and salt content of coal gangue, and has the functions of activating phosphorus and potassium elements, fixing nitrogen, and passivating heavy metal elements.

[0056] (2) Compared with single-strain fermentation agents using four strains and GN3, the improved soil prepared by the GN4-min and GN4-max groups has lower alkalinity, EC value, and available heavy metal content, as well as higher organic matter, total nitrogen, available phosphorus, and available potassium content. This indicates that the four strains in the fermentation agent of this invention can produce a synergistic effect, achieving better fermentation results, resulting in higher nutrient content in the coal gangue-based improved soil, and reducing the risk of soil heavy metal pollution to a greater extent.

[0057] Example 2: Performance of improved soil with different amounts of coal gangue added 2.1 Preparation of coal gangue-based improved soil Following the method described in Example 1, four types of single-strain bacterial powders were prepared. Then, SHBCC D11446 bacterial powder, SHBCC CD24696 bacterial powder, SHBCC D10197 bacterial powder, and GS02 bacterial powder were mixed at a live cell count ratio of 1000:1:0.2:200 to obtain the fermentation agent GN4-mid.

[0058] After crushing the coal gangue to a particle size of no more than 10 mm, it is sorted and screened to select small-sized coal gangue (d≤2 mm), medium-sized coal gangue (2 mm<d<6 mm), and large-sized coal gangue (6 mm≤d≤10 mm). These are then mixed in a mass ratio of 4:4:3 to obtain a coal gangue mixture.

[0059] Fermentation agent GN4-mid and water were mixed at a mass ratio of 1:9 to obtain a bacterial solution. The bacterial solution was sprayed onto the coal gangue mixture at a mass ratio of 1:100, and then tilled and mixed evenly to obtain mixture A. Perlite water-retaining agent and commercial organic fertilizer (Changchun Xinyangguang Organic Fertilizer Co., Ltd.) were added to mixture A, with each added at 0.1% of the coal gangue mixture mass. The mixture was then tilled and mixed evenly to obtain mixture B. In groups #1 to #3, mixture B was mixed with sand at mass ratios of 3:7, 1:1, and 7:3, respectively, and then tilled and mixed evenly to obtain mixture C. The moisture content of mixture C was adjusted to 20%, and then fermented at 25℃ for 10 days. During this period, a film was used to reduce moisture loss, resulting in coal gangue-based improved soil #1 to #3.

[0060] 2.2 Testing of the physical and chemical properties of coal gangue-based improved soil Multiple sampling was used to obtain coal gangue-based improved soil samples from groups #1 to #3. The pH, electrical conductivity (EC), organic matter content, total nitrogen content, available phosphorus content, available potassium content, and available heavy metal content were measured. The results are shown in Tables 4 and 5.

[0061] Table 4. Test results of physicochemical properties of coal gangue-based improved soil Table 5. Results of detection of available heavy metal content in coal gangue-based improved soil. According to Tables 4 and 5, it can be seen that the pH and EC values ​​of the coal gangue-based improved soils prepared in groups #1 to #3 are still close to those of sandy soils, while the organic matter content, total nitrogen content, and available potassium content have been significantly improved. Moreover, the contents of each available heavy metal in the improved soils are lower than the soil pollution risk values ​​for agricultural land.

[0062] 2.3 Alfalfa Planting Experiment The coal gangue-based improved soils prepared in groups #1 to #3 were used as experimental groups, and sandy soils were used as control groups. Blank controls CK1 to CK3 were also set up (the coal gangue-based improved soils of CK1 to CK3 were prepared according to groups #1 to #3, and the only difference between them and groups #1 to #3 was that no fermentation agent GN4-mid was added). Alfalfa was used as the indicator crop. The sowing density of each group was the same. After shallow covering with soil, a field experiment was conducted for 30 days. Plant samples from each group were taken at multiple points, and plant height, root length and fresh weight were measured. The results are shown in Table 6.

[0063] Table 6 Results of Alfalfa Growth Monitoring According to Table 6, it can be seen that: (1) When the improved soil of group #1 to #3 is used, the average plant height and average fresh weight of alfalfa are significantly increased compared with sandy soil, indicating that the coal gangue-based improved soil prepared by the method of the present invention can promote plant growth.

[0064] (2) When using the improved soil from groups #1 to #3, the average plant height, average root length, and average fresh weight of alfalfa were significantly increased compared to the corresponding blank controls (CK1 to CK3). This indicates that fermentation treatment with the fermentation agent of this invention can make the improved soil more suitable for plant growth.

[0065] 2.4 Buckwheat Planting Experiment The coal gangue-based improved soils prepared in groups #1 and #2 were used as experimental groups, and blank controls CK1 and CK2 were set up (the coal gangue-based improved soils of CK1 and CK2 were prepared according to groups #1 and #2 respectively, and the only difference from groups #1 and #2 was that the fermentation inoculant GN4-mid was not added). Buckwheat was used as the indicator crop, and the sowing density of each group was the same. After shallow covering with soil, a field experiment was carried out for 30 days. Plant samples from each group were taken at multiple points, and plant height, root length and fresh weight were measured. The results are shown in Table 7.

[0066] Table 7 Results of Buckwheat Growth Monitoring Table 7 shows that when using the improved soil from groups #1 and #2, the average plant height, average root length, and average fresh weight of buckwheat were significantly increased compared to the corresponding blank controls (CK1 and CK2). This indicates that fermentation treatment using the fermentation agent of this invention can make the improved soil more suitable for plant growth.

[0067] Example 3: The Influence of Coal Gangue Particle Size on Improved Soil Properties 3.1 Preparation of coal gangue-based improved soil Following the method described in Example 1, four types of single-strain bacterial powders were prepared. Then, SHBCC D11446 bacterial powder, SHBCC CD24696 bacterial powder, SHBCC D10197 bacterial powder, and GS02 bacterial powder were mixed at a live cell count ratio of 1000:1:0.2:200 to obtain the fermentation agent GN4-mid.

[0068] After crushing the coal gangue to a particle size of no more than 10 mm, it is sorted and screened to select small-sized coal gangue (d≤2 mm), medium-sized coal gangue (2 mm<d<6 mm), and large-sized coal gangue (6 mm≤d≤10 mm). These are then mixed in a mass ratio of 4:4:3 to obtain a coal gangue mixture.

[0069] After preparing the fermentation agent GN4-mid according to the method in Example 2, it was mixed with water at a mass ratio of 1:9 to obtain a bacterial solution. The bacterial solution was sprayed onto the coal gangue mixture at a mass ratio of 1:100, and then tilled and mixed evenly to obtain mixture A. Perlite water-retaining agent and commercial organic fertilizer (Changchun Xinyangguang Organic Fertilizer Co., Ltd.) were added to mixture A, with each added at 0.1% of the mass of the coal gangue mixture. The mixture was then tilled and mixed evenly to obtain mixture B. In groups #1 to #3, mixture B was mixed with sand at a mass ratio of 7:3, and then tilled and mixed evenly to obtain mixture C. After adjusting the moisture content of mixture C to 20%, it was fermented at 25℃ for 10 days, during which time covering with a film was used to reduce moisture loss, resulting in coal gangue-based improved soil #3.

[0070] In the above process, the coal gangue mixture is replaced with small-sized coal gangue (d≤2mm), medium-sized coal gangue (2mm<d<6mm), and large-sized coal gangue (6mm≤d≤10mm) of equal mass, while the other raw materials and steps remain unchanged, to obtain coal gangue-based improved soil #4 to #6 respectively.

[0071] 3.2 Alfalfa Planting Experiment The coal gangue-based improved soil prepared in groups #3 to #6 was used as the experimental group. Alfalfa was used as the indicator crop. The sowing density of each group was the same. After shallow covering, a field experiment was conducted for 30 days. Plant samples from each group were taken at multiple points to measure plant height, root length and fresh weight. The results are shown in Table 8.

[0072] Table 8 Results of Alfalfa Growth Monitoring #3 Coal gangue mixture 5.85 10.03 0.38 #4 Small-diameter coal gangue 2.32 5.42 0.11 #5 Medium-sized coal gangue 2.85 5.35 0.121 #6 Large-diameter coal gangue 2.47 4.96 0.09 Table 8 shows that the difference between groups #4-#6 and #3 lies in the particle size of the coal gangue used. Compared to groups #4-#6, the improved soil from group #3 resulted in increased average plant height, average root length, and average fresh weight of alfalfa. This indicates that the use of three different particle sizes of coal gangue (d≤2mm, 2mm<d<6mm, and 6mm≤d≤10mm) in this invention can provide a more suitable soil environment for plant growth.

[0073] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. Unless otherwise specified, the raw materials and equipment used in this invention are conventional in the art and can be obtained through conventional commercial means; unless otherwise specified, the methods used in this invention are conventional methods in the art.

[0074] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing coal gangue-based improved soil, characterized in that, include: After mixing all raw materials, the moisture content is adjusted to 15-25%, and fermented at 20-37℃ for 10-30 days to obtain coal gangue-based improved soil. The raw materials include coal gangue, sand, fermentation inoculant, water-retaining agent, and organic fertilizer. The fermentation inoculant includes Bacillus subtilis (Bt) with a bacterial count ratio of 1000:0.8-1.2:0.1-0.3:100-300. Bacillus subtilis SHBCC D11446, Arbuscular mycorrhizal fungi ( Rhizophagus irregularis SHBCC D24696, Trichoderma viride ( Trichoderma viride Bacillus belye (SHBCC D10197 and CCTCC NO: M 2025531) Bacillus velezensis GS02.

2. The preparation method according to claim 1, characterized in that, The coal gangue includes small-diameter coal gangue, medium-diameter coal gangue, and large-diameter coal gangue with a mass ratio of 30~50:30~40:15~30.

3. The preparation method according to claim 2, characterized in that, The small-diameter coal gangue has a particle size of no more than 2 mm, the medium-diameter coal gangue has a particle size of 2-6 mm, and the large-diameter coal gangue has a particle size of 6-10 mm.

4. The preparation method according to claim 1, characterized in that, The mass of the fermentation agent is 0.1-1.5% of the mass of coal gangue.

5. The preparation method according to claim 1, characterized in that, The water-retaining agent includes at least one of sodium polyacrylate, diatomaceous earth, and perlite.

6. The preparation method according to claim 1, characterized in that, The organic fertilizer includes at least one of manure, green manure, compost, and commercial fertilizer.

7. The preparation method according to claim 1, characterized in that, The water-retaining agent and organic fertilizer are both 0.1-1% of the mass of coal gangue.

8. The preparation method according to claim 1, characterized in that, The sand has a particle size of less than 2 mm and its mass accounts for 30-70% of the total mass of all raw materials.

9. The preparation method according to claim 1, characterized in that, The process of mixing all raw materials includes the following steps: after preparing the fermentation agent into a bacterial solution, it is mixed with coal gangue, water-retaining agent and organic fertilizer are added, and after mixing evenly, it is mixed with sand.

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