Ecological restoration and water retention technology for coal gangue waste mine

Abstract

The invention discloses a coal gangue abandoned mine ecological restoration water retention technology, and belongs to the technical field of environmental protection. According to the remediation technology, after the surface soil of the mine is loosened, the alkaline waste and the heavy metal adsorbent are firstly added for neutralization and adsorption pretreatment, and then the composite soil conditioner is continuously added to sequentially cover and construct the improved composite layer soil in a gradient manner; the composite soil conditioner comprises fly ash, steel slag, local clay, straw fibers, water-retaining slow-release microcapsules, charcoal, papermaking white mud and humus soil, high-resistance vegetation is transplanted on the obtained improved composite layer soil, meanwhile, a microbial agent is inoculated, and remediation is completed after the soil is maintained to be stable. According to the method, multiple technical processes are integrated and matched and cooperated with one another, the purpose of long-acting water retention is finally achieved through the combined action of multiple remediation mechanisms of materials, vegetation and microorganisms, and compared with a traditional mine remediation technology, the method is better in stability and longer in acting time and has a good application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental protection, and in particular relates to an ecological restoration and water conservation technology for abandoned coal gangue mines. Background Art

[0002] Coal gangue is solid mining waste generated during coal mining and washing and processing. Due to its low comprehensive utilization rate, these coal gangues continue to accumulate and eventually form abandoned mines, which not only occupies a large amount of land resources, but also causes serious pollution and damage to the ecological environment.

[0003] The ecological restoration of abandoned gangue mines faces many challenges, among which poor water retention capacity is a key issue. Gangue itself has a loose structure and large pores, and lacks the water and fertilizer retention capacity of soil, which makes it difficult for vegetation to grow, further exacerbating soil erosion and ecological deterioration. Traditional mine restoration technology is insufficient for the ecological restoration of abandoned gangue mines. For example, simple vegetation coverage is difficult to fundamentally solve the problem of rapid water loss; although plant varieties that are acid-resistant and drought-resistant and adapted to the environment of gangue mines have been selected as much as possible, the growth of these plants still faces challenges. The special properties of gangue, such as high acidity, low fertility, and unstable structure, make the growth rate of vegetation slow and the survival rate low, making it difficult to play an effective restoration role. The improvement effect of simply introducing microorganisms on mine restoration is limited, and due to the poor stability of gangue soil, the harsh environment of gangue, such as high acidity and high concentration of heavy metals, will inhibit the survival and reproduction of microorganisms, and the external environmental factors of the mine will also interfere with the structure of the microbial community.

[0004] Therefore, it is of great significance to develop an efficient, environmentally friendly and economical ecological restoration and water conservation technology for abandoned coal gangue mines to improve the long-term water and fertilizer conservation capacity of abandoned coal gangue mines. Summary of the invention

[0005] In response to the problems raised in the background technology, the purpose of the present invention is to provide a technology for ecological restoration and water conservation in abandoned coal gangue mines, by making full use of alkaline industrial waste for neutralization pretreatment, followed by gradient covering to construct an improved composite layer of soil, and finally transplanting a high-resistant vegetation combination and inoculating microbial agents, so that the harsh ecological environment of abandoned coal gangue mines can be restored.

[0006] The present invention provides a technology for ecological restoration and water conservation of abandoned coal gangue mines, comprising the following steps: Step 1: Crush, plow and loosen the surface soil of the abandoned coal gangue mine. After the surface treatment, evenly sprinkle the alkaline waste and heavy metal adsorbent on the surface, and repeatedly plow until it is uniform; Step 2: Continue to add composite soil conditioner to the mine surface soil treated in step 1, and gradually cover it to construct an improved composite layer of soil; The improved composite soil layer includes a water-retaining bottom layer, an anti-corrosion slow-release middle layer, and an organic surface layer, and the composite soil conditioner includes fly ash, steel slag, local clay, straw fiber, water-retaining slow-release microcapsules, biochar, papermaking white mud, and humus soil; Step 3: Transplant highly resistant vegetation on the improved composite soil layer obtained in step 2, inoculate microbial agents at the same time, and maintain until stable.

[0007] Furthermore, in step one, a jaw crusher and a rotary tiller are used to crush and till the surface soil of the mine, with a treatment depth of 30-50 cm; firstly, the debris is removed and the surface soil is pretreated, which can ensure the uniformity of the coal gangue matrix and provide a good foundation for subsequent repair.

[0008] Furthermore, the alkaline waste material in step 1 includes any one or more of steel slag, red mud, eggshell powder, and urban sludge. The acidity of the soil in abandoned coal gangue mines is relatively high. The present invention uses steel slag, red mud, etc. as neutralizing materials: steel slag is industrial waste slag from steel smelting, mainly containing calcium oxide, magnesium oxide and other components, which can effectively neutralize the acidity of the soil in coal gangue mines, and its mineral phases of dicalcium silicate and tricalcium silicate can also slowly release alkaline substances to achieve the effect of long-term and deep pH regulation. Red mud is an industrial waste generated in the production process of alumina, mainly containing iron oxide, aluminum oxide and other components, which can also play a role in neutralizing acidic soil. The silicate minerals in red mud can also promote the formation of soil aggregates and improve water and fertilizer retention. Eggshell powder can slowly release calcium ions to neutralize soil acidity, maintain soil pH stability for a long time, and provide a good environment for the deep growth of vegetation roots in the later stage. The organic matter rich in urban sludge can not only improve soil structure and increase the content of nutrient elements, but also cooperate to alleviate the salinity and alkalinity of red mud. The present invention combines the above-mentioned industrial waste slag and domestic waste, which can not only neutralize the acidic soil of the mine at a low cost, but also recycle various industrial and domestic waste materials, and is also conducive to the long-term growth of subsequent vegetation. The present invention preferably uses a combination of 45% steel slag, 20% red mud, 10% eggshell powder, and 25% urban sludge as alkaline waste in terms of mass ratio. In a specific implementation case, the urban sludge used has a pH of 8.6-8.8, a moisture content of 70%-76%, and an organic matter content of 50%-55% (dry basis).

[0009] Furthermore, the heavy metal adsorbent in step 1 is composed of rice husk biochar and bentonite in a mass ratio of 10:(1-3). Rice husk biochar can effectively adsorb cadmium, lead, etc. in the soil, and bentonite can significantly enhance the cation exchange capacity and promote the enrichment capacity of heavy metals in the soil. The present invention uses the above-mentioned heavy metal adsorbent to preliminarily adsorb and solidify heavy metals in soil and alkaline waste, which is beneficial to the rapid growth and development of vegetation and bacteria in the later stage, and can improve the restoration rate of mine ecology.

[0010] Furthermore, the preparation method of the water-retaining sustained-release microcapsules described in step 2 is: taking acrylic acid, acrylamide, and potassium humate and dissolving them in deionized water, dripping sodium hydroxide solution in an ice water bath, then adding an initiator and a cross-linking agent and stirring to obtain a prepolymer solution, slowly dripping the prepolymer solution into a composite solution of chitosan and sodium montmorillonite, reacting in a water bath at 50-60°C after ultrasonication, and finally centrifuging, washing, and drying to obtain microcapsules; wherein the mass ratio of chitosan to sodium montmorillonite is (1-2):1, the mass ratio of acrylic acid, acrylamide, and potassium humate is 15:5:3, the initiator is potassium persulfate, and the cross-linking agent is N,N′-methylenebisacrylamide.

[0011] Further, the specific method of constructing the improved composite layer soil by gradient covering in sequence in step 2 is: fly ash, steel slag, and local clay are mixed evenly, and then added to the mine soil after neutralization and adsorption treatment, and the soil is evenly plowed as a water-retaining bottom layer; then straw fibers are embedded in the water-retaining bottom layer in a grid shape to construct a straw fiber grid, and then a suspension of water-retaining slow-release microcapsules is evenly sprayed to obtain an anti-corrosion slow-release middle layer; finally, biochar, papermaking white mud, and humus soil are mixed and evenly covered on the surface of the anti-corrosion slow-release middle layer to construct an organic surface layer. After neutralization and adsorption treatment, the present invention mixes fly ash, steel slag, local clay and coal gangue matrix as a water-retaining bottom layer. Fly ash can reduce matrix density, increase water holding capacity and supplement phosphorus and potassium nutrients. Steel slag helps to improve structural strength and impermeability. The mixture of the two can further improve the structural strength of coal gangue mine soil; the water-retaining bottom layer can be used as the base layer for mine soil repair, enhance deep water retention, and provide a transition buffer for the deep growth of vegetation roots in the later stage. On the basis of the water-retaining bottom layer, the present invention uses straw fiber and fly ash mixed in a grid-like manner to embed into the water-retaining bottom layer, further enhancing the shear strength and overcoming the problem of loose gangue structure leading to soil erosion; unlike most current polymer water-retaining materials, which have the problem of gradually weakening water-retaining capacity with the increase of use time and decomposition or loss in gangue soil, the present invention also prepares a slow-release microcapsule, which has excellent water-retaining and heavy metal adsorption functions, and can achieve the effect of long-term balanced soil regulation. Finally, the present invention covers the mixture of biochar, papermaking white mud, and humus soil as an organic surface layer. Biochar has high porosity and adsorption, can significantly improve the soil water-retaining capacity, fix nutrients and reduce leaching, papermaking white mud can enhance the surface impermeability and cohesion, humus soil is rich in organic matter, provides nutrients to promote microbial activity; the construction of the organic surface layer provides a sufficient nutrient basis for the rapid growth and development of subsequent vegetation strains. After the soil is improved by traditional restoration schemes, it may be damaged due to continued weathering of coal gangue, rain erosion and other reasons, resulting in reduced water retention capacity; by constructing the above-mentioned improved composite layer soil, the present invention improves the structure of the soil in abandoned coal gangue mines, effectively improves its water retention performance and stability, improves its anti-erosion ability, reduces evaporation, and lays a foundation for the subsequent stable and rapid growth of vegetation and fungi.

[0012] Furthermore, in the water-retaining bottom layer, the mass ratio of fly ash, steel slag and local clay is 1:(2-3):(3-5), and the thickness of the water-retaining bottom layer is 25-30 cm; in the anti-corrosion slow-release middle layer, the straw fiber grid spacing is 20×20 cm; in the organic surface layer, the mass ratio of biochar, papermaking white mud and humus is (20-30):(10-20):1, and the thickness of the organic surface layer is 5-10 cm.

[0013] Furthermore, the highly resistant vegetation described in step 3 includes southeastern sedum, sea buckthorn, and pennisetum, which are interplanted in rows at (40-60):3:(2-5). Southeastern sedum is a heavy metal hyperaccumulator that can further absorb heavy metals; sea buckthorn is drought-resistant and barren-resistant, and its well-developed root system can fix nitrogen and improve soil fertility, alleviating the problem of poor substrates such as fly ash and steel slag; pennisetum grows fast and has a deep root system, and its root distribution level is different from that of sea buckthorn. It can also be combined with a straw fiber grid to synergize with sea buckthorn to improve erosion resistance and prevent soil erosion; the present invention transplants southeastern sedum, sea buckthorn, and pennisetum in a complementary manner, further strengthening the soil fixation and repair effects, and can regulate the microclimate, reduce water consumption, and promote organic matter circulation.

[0014] Furthermore, the microbial agent in step 3 includes arbuscular mycorrhizal fungi, sulfate-reducing bacteria, Pseudomonas, and Frankia, and the ratio of their usage is (3-5):1:(1-2):(2-3); wherein the arbuscular mycorrhizal fungi are propagated in the rhizosphere of the clover host, and the spore suspension (density is about 60 / mL) is collected, and the concentration of the sulfate-reducing bacteria liquid is about 3×10 8 CFU / mL, the concentration of Pseudomonas liquid is 2×10 7 CFU / mL, the concentration of Frankia solution is 8×10 6 CFU / mL. Arbuscular mycorrhizal fungi can coexist with vegetation to promote nutrient absorption; sulfate-reducing bacteria can assist in the treatment of heavy metals; Pseudomonas has the ability to degrade organic matter and fix heavy metals; Frankia can coexist with vegetation to fix nitrogen and promote vegetation growth.

[0015] The beneficial effects of the present invention are: Based on the limitations of existing coal gangue abandoned mine restoration technology, the present invention integrates a variety of technical processes including neutralization adsorption, soil improvement, vegetation transplantation, microbial inoculation, etc., which match and cooperate with each other, and finally achieve the purpose of long-term water retention through the multiple restoration mechanisms of materials-vegetation-microorganisms. The present invention has low raw material and process costs, and at the same time recycles a variety of industrial and domestic waste materials. Compared with traditional mine restoration technology, it has better stability, longer-lasting effect, and good application prospects. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the embodiments. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0018] Example 1 A technology for ecological restoration and water conservation of abandoned coal gangue mines, comprising the following steps: 1. Select an abandoned coal gangue mine area with a slope less than 25°, and use a jaw crusher and a rotary tiller to crush and plow the surface soil after removing impurities (the treatment depth is 50 cm); after pre-treating the surface soil, evenly sprinkle alkaline waste (45% steel slag, 20% red mud, 10% eggshell powder, 25% urban sludge) and heavy metal adsorbent (rice husk biochar: bentonite = 10:2) on the surface (the addition amount is 120 kg / mu of alkaline waste and 20 kg / mu of heavy metal adsorbent), and repeatedly plow with a rotary tiller until it is uniform.

[0019] 2. Add 1 part of chitosan to 50 parts of 1% acetic acid solution and stir evenly. Add 0.8 parts of sodium montmorillonite to 50 parts of deionized water and disperse by ultrasonic. Mix the two evenly to obtain a wall material composite liquid. Add 15 parts of acrylic acid, 5 parts of acrylamide and 3 parts of potassium humate to 80 parts of deionized water, drip 20 parts of 10% sodium hydroxide solution under ice water bath, add 0.2 parts of potassium persulfate and 0.1 parts of N,N′-methylenebisacrylamide and stir evenly to obtain a prepolymer liquid. Slowly drip the prepolymer liquid into the wall material composite liquid, ultrasonicate for 15 min, react in a constant temperature water bath at 55°C for 4 h, centrifuge, wash, dry and grind to obtain water-retaining sustained-release microcapsules. Fly ash, steel slag and local clay were mixed evenly (mass ratio of 1:2.5:4), then added to the mine soil after neutralization and adsorption treatment, and tilled evenly to serve as a water-retaining bottom layer (30 cm); corn straw fiber (5-10 mm) and fly ash were mixed in a ratio of 3:1 and embedded in the water-retaining bottom layer in a grid shape (spacing 20×20 cm) to construct a straw fiber grid, and then the suspension of the above-mentioned water-retaining slow-release microcapsules was evenly sprayed (microcapsule dosage 15 kg / mu) to obtain an anti-corrosion slow-release middle layer; finally, biochar, papermaking white mud and humus soil were mixed (mass ratio 25:15:1) and evenly covered on the surface of the anti-corrosion slow-release middle layer to construct an organic surface layer (10 cm).

[0020] 3. Transplant southeastern sedum, seabuckthorn, and pennisetum (mixed between rows at 5,000 plants / mu, 300 plants / mu, and 300 bushes / mu) on the improved composite soil, and inoculate microbial agents (0.5 kg / m 3 , arbuscular mycorrhizal fungi suspension, sulfate-reducing bacteria solution, Pseudomonas solution, and Frankia solution in a volume ratio of 4:1:1.2:2.5) and cured until stable.

[0021] The initial soil data were tested and compared with the soil data after treatment. The results are shown in Table 1.

[0022] Table 1 Mine soil testing data

[0023] Example 2 A technology for ecological restoration and water conservation of abandoned coal gangue mines, comprising the following steps: 1. Select an abandoned coal gangue mine area with a slope less than 25°, and use a jaw crusher and a rotary tiller to crush and plow the surface soil after removing impurities (the treatment depth is 40 cm); after pre-treating the surface soil, sprinkle alkaline waste (50% steel slag, 20% red mud, 10% eggshell powder, 20% urban sludge) and heavy metal adsorbent (rice husk biochar: bentonite = 10:1) evenly on the surface (the addition amount is 120 kg / mu of alkaline waste and 20 kg / mu of heavy metal adsorbent), and use a rotary tiller to repeatedly plow until it is uniform.

[0024] 2. Add 1 part of chitosan to 50 parts of 1% acetic acid solution and stir evenly. Add 0.5 parts of sodium montmorillonite to 50 parts of deionized water and disperse by ultrasonic. Mix the two evenly to obtain a wall material composite liquid. Add 15 parts of acrylic acid, 5 parts of acrylamide and 3 parts of potassium humate to 80 parts of deionized water, drip 20 parts of 10% sodium hydroxide solution under ice water bath, add 0.2 parts of potassium persulfate and 0.1 parts of N,N′-methylenebisacrylamide and stir evenly to obtain a prepolymer liquid. Slowly drip the prepolymer liquid into the wall material composite liquid, ultrasonicate for 15 min, react in a constant temperature water bath at 55°C for 4 h, centrifuge, wash, dry and grind to obtain water-retaining sustained-release microcapsules. Fly ash, steel slag and local clay were mixed evenly (mass ratio of 1:2:5), then added to the mine soil after neutralization and adsorption treatment, and tilled evenly to serve as a water-retaining bottom layer (25 cm); corn straw fiber (5-10 mm) and fly ash were mixed in a ratio of 3:1 and embedded in the water-retaining bottom layer in a grid shape (spacing 20×20 cm) to construct a straw fiber grid, and then the suspension of the above-mentioned water-retaining slow-release microcapsules was evenly sprayed (microcapsule dosage 15 kg / mu) to obtain an anti-corrosion slow-release middle layer; finally, biochar, papermaking white mud and humus soil were mixed (mass ratio 20:20:1) and evenly covered on the surface of the anti-corrosion slow-release middle layer to construct an organic surface layer (10 cm).

[0025] 3. Transplant southeastern sedum, seabuckthorn, and pennisetum (4,000 plants / mu, 300 plants / mu, and 500 bushes / mu inter-row mixed planting) on ​​the improved composite soil, and inoculate microbial agents (0.5 kg / m 3 , arbuscular mycorrhizal fungi suspension, sulfate-reducing bacteria solution, Pseudomonas solution, and Frankia solution in a volume ratio of 4:1:1.6:2.4) and cured until stable.

[0026] The initial soil data were tested and compared with the soil data after treatment. The results are shown in Table 2.

[0027] Table 2 Mine soil testing data

[0028] Example 3 A technology for ecological restoration and water conservation of abandoned coal gangue mines, comprising the following steps: 1. Select an abandoned coal gangue mine area with a slope less than 25°, and use a jaw crusher and a rotary tiller to crush and plow the surface soil after removing impurities (the treatment depth is 45 cm); after pre-treating the surface soil, sprinkle alkaline waste (50% steel slag, 15% red mud, 10% eggshell powder, 25% urban sludge) and heavy metal adsorbent (rice husk biochar: bentonite = 10:3) evenly on the surface (the addition amount is 120 kg / mu of alkaline waste and 20 kg / mu of heavy metal adsorbent), and use a rotary tiller to repeatedly plow until it is uniform.

[0029] 2. Add 1 part of chitosan to 50 parts of 1% acetic acid solution and stir evenly. Add 1 part of sodium montmorillonite to 50 parts of deionized water and disperse by ultrasonic. Mix the two evenly to obtain a wall material composite liquid. Add 15 parts of acrylic acid, 5 parts of acrylamide and 3 parts of potassium humate to 80 parts of deionized water, drip 20 parts of 10% sodium hydroxide solution under ice water bath, add 0.2 parts of potassium persulfate and 0.1 parts of N,N′-methylenebisacrylamide and stir evenly to obtain a prepolymer liquid. Slowly drip the prepolymer liquid into the wall material composite liquid, ultrasonicate for 15 min, react in a constant temperature water bath at 55°C for 4 h, centrifuge, wash, dry and grind to obtain water-retaining sustained-release microcapsules. Fly ash, steel slag and local clay were mixed evenly (mass ratio of 1:3:3), then added to the mine soil after neutralization and adsorption treatment, and evenly plowed to serve as a water-retaining bottom layer (30 cm); corn straw fiber (5-10 mm) and fly ash were mixed in a ratio of 3:1 and embedded in the water-retaining bottom layer in a grid shape (spacing 20×20 cm) to construct a straw fiber grid, and then the suspension of the above-mentioned water-retaining slow-release microcapsules was evenly sprayed (microcapsule dosage 18 kg / mu) to obtain an anti-corrosion slow-release middle layer; finally, biochar, papermaking white mud and humus soil were mixed (mass ratio of 30:10:1) and evenly covered on the surface of the anti-corrosion slow-release middle layer to construct an organic surface layer (8 cm).

[0030] 3. Transplant southeastern sedum, seabuckthorn, and pennisetum (mixed between rows at 6,000 plants / mu, 300 plants / mu, and 200 clumps / mu) on the improved composite soil, and inoculate microbial agents (0.5 kg / m 3 , arbuscular mycorrhizal fungi suspension, sulfate-reducing bacteria solution, Pseudomonas solution, and Frankia solution in a volume ratio of 5:1:1:2) and cured until stable.

[0031] The initial soil data was tested and compared with the soil data after treatment. The results are shown in Table 3.

[0032] Table 3 Mine soil testing data

[0033] Comparative Example 1 Refer to the step parameters of Example 1, except that in step 2, sodium montmorillonite is not used to prepare water-retaining sustained-release microcapsules.

[0034] The initial soil data was tested and compared with the soil data after treatment. The results are shown in Table 4.

[0035] Table 4 Mine soil testing data

[0036] Comparative Example 2 Refer to the step parameters of Example 1, except that in step 3, the volume ratio of the arbuscular mycorrhizal fungus suspension, sulfate-reducing bacteria solution, Pseudomonas solution, and Frankia solution is adjusted to 1:1:1:1.

[0037] The initial soil data was tested and compared with the soil data after treatment. The results are shown in Table 5.

[0038] Table 5 Mine soil testing data

[0039] According to the test results of the above-mentioned Examples 1-3, the mine restoration technology of the present invention has a strong ability to retain water and fertilizer. Through the joint action of the multiple restoration mechanisms of materials, vegetation and microorganisms, the soil restoration of abandoned coal gangue mines is basically completed after a short period of treatment: the heavy metal content is greatly reduced, the content of nutrients such as nitrogen, phosphorus and potassium is significantly increased, and it has excellent long-term water retention capacity, which ensures the stability of mine soil and can effectively reduce the cumbersome maintenance costs in the later stage. Comparing the data of Example 1 with Comparative Example 1, it can be seen that the water-retaining slow-release microcapsules prepared by the present invention can play a stable and long-term water-retaining role, and will not gradually weaken the water-retaining capacity due to other factors such as the outside world. Compared with most existing polymer water-retaining materials, the improvement effect is significant; comparing the data of Example 1 with Comparative Example 2, it can be seen that the combination and proportion of microbial strains selected by the present invention have a significant effect on the synergistic restoration effect of materials, vegetation and microorganisms. The raw materials and process costs of the technology of the present invention are low, and a variety of industrial and living wastes are recycled and utilized as resources. Compared with traditional mine restoration technology, it has better stability, longer-lasting and good application prospects.

[0040] The embodiments described above only express several preferred embodiments of the present invention, and the descriptions thereof are relatively specific and detailed, but are not intended to limit the present invention. It should be noted that for those skilled in the art, the present invention may also have various changes and modifications, and any modifications, equivalent substitutions, improvements, etc. made within the concept and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A technology for ecological restoration and water conservation of abandoned coal gangue mines, characterized in that: The steps include: Step 1: Crush, plow and loosen the surface soil of the abandoned coal gangue mine. After the surface treatment, evenly sprinkle the alkaline waste and heavy metal adsorbent on the surface, and repeatedly plow until it is uniform; Step 2: Continue to add composite soil conditioner to the mine surface soil treated in step 1, and gradually cover it to construct an improved composite layer of soil; The improved composite soil layer includes a water-retaining bottom layer, an anti-corrosion slow-release middle layer, and an organic surface layer, and the composite soil conditioner includes fly ash, steel slag, local clay, straw fiber, water-retaining slow-release microcapsules, biochar, papermaking white mud, and humus soil; Step 3: Transplant highly resistant vegetation on the improved composite soil layer obtained in step 2, inoculate microbial agents at the same time, and maintain until it is stable.

2. The water conservation technology for ecological restoration of abandoned coal gangue mines according to claim 1 is characterized in that: In step 1, a jaw crusher and a rotary tiller are used to crush and till the surface soil of the mine, with a processing depth of 30-50 cm.

3. The water conservation technology for ecological restoration of abandoned coal gangue mines according to claim 1 is characterized in that: The alkaline waste material in step 1 includes any one or more of steel slag, red mud, eggshell powder, and municipal sludge.

4. The water conservation technology for ecological restoration of abandoned coal gangue mines according to claim 1 is characterized in that: The heavy metal adsorbent in step 1 is composed of rice husk biochar and bentonite in a mass ratio of 10:(1-3).

5. The water conservation technology for ecological restoration of abandoned coal gangue mines according to claim 1 is characterized in that: The preparation method of the water-retaining sustained-release microcapsules in step 2 is as follows: acrylic acid, acrylamide and potassium humate are dissolved in deionized water, sodium hydroxide solution is dripped into the solution under ice water bath, then initiator and cross-linking agent are added and stirred to obtain prepolymer solution, the prepolymer solution is slowly dripped into the composite solution of chitosan and sodium montmorillonite, reacted in a water bath at 50-60°C after ultrasonic treatment, and finally centrifuged, washed and dried to obtain microcapsules; wherein the mass ratio of chitosan to sodium montmorillonite is (1-2):

1.

6. The water conservation technology for ecological restoration of abandoned coal gangue mines according to claim 1, characterized in that: The specific method of constructing the improved composite layer soil by gradient covering in sequence in step 2 is: fly ash, steel slag and local clay are mixed evenly, and then added to the mine soil after neutralization and adsorption treatment, and the soil is evenly plowed as a water-retaining bottom layer; straw fibers are then embedded in the water-retaining bottom layer in a grid shape to construct a straw fiber grid, and then a suspension of water-retaining slow-release microcapsules is evenly sprayed to obtain a corrosion-resistant slow-release middle layer; finally, biochar, papermaking white mud and humus soil are mixed and evenly covered on the surface of the corrosion-resistant slow-release middle layer to construct an organic surface layer.

7. The water conservation technology for ecological restoration of abandoned coal gangue mines according to claim 6 is characterized in that: In the water-retaining bottom layer, the mass ratio of fly ash, steel slag and local clay is 1:(2-3):(3-5), and the thickness of the water-retaining bottom layer is 25-30 cm; in the anti-corrosion slow-release middle layer, the straw fiber grid spacing is 20×20 cm; in the organic surface layer, the mass ratio of biochar, papermaking white mud and humus soil is (20-30):(10-20):1, and the thickness of the organic surface layer is 5-10 cm.

8. The water conservation technology for ecological restoration of abandoned coal gangue mines according to claim 1, characterized in that: The highly resistant vegetation described in step three includes Sedum austriatum, Hippophae rhamnoides and Pennisetum truncatum, which are interplanted in the ratio of (40-60):3:(2-5).

9. The technology for ecological restoration and water conservation of abandoned coal gangue mines according to claim 1, characterized in that: The microbial agent in step 3 includes arbuscular mycorrhizal fungi, sulfate-reducing bacteria, Pseudomonas, and Frankia, and the usage ratio is (3-5):1:(1-2):(2-3).

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