Compound coal gangue, coal gangue ecological soil for improving soil salinization, and preparation method and application thereof

Abstract

The present application relates to the technical field of soil improvement, and particularly relates to a compound coal gangue for improving soil salinization, coal gangue ecological soil and a preparation method and application thereof. The compound coal gangue for improving light and moderate salinized soil comprises the following components: 70-80% of coal gangue with a particle size of 2.095mm<3.353mm, 15-20% of coal gangue with a particle size of 0.69mm<2.095mm, and 10-15% of coal gangue with a particle size of less than 0.69mm. The compound coal gangue for improving heavy salinized soil comprises the following components: 50-60% of coal gangue with a particle size of 1.004mm<2.095mm, 35-40% of coal gangue with a particle size of 0.506mm<1.004mm, and 5-10% of coal gangue with a particle size of less than 0.506mm. The compound coal gangue is prepared into coal gangue ecological soil, thereby realizing directional and efficient improvement of light, moderate and heavy salinized soil.

Description

Technical Field

[0001] This invention relates to the field of soil improvement technology, and in particular to a compound coal gangue and coal gangue ecological soil for improving soil salinization, as well as their preparation methods and applications. Background Technology

[0002] Current saline-alkali land management technologies mainly revolve around physical, chemical, biological, and integrated approaches. Physical measures, such as underground drainage and sand-topped soil, directly regulate water and salt movement through engineering methods, but rely on large amounts of freshwater and are prone to secondary salinization. Chemical amendments, such as gypsum and humic acid, can neutralize alkalinity, but are costly, have unstable effects, and may cause secondary pollution. Biological treatments, such as planting salt-tolerant crops and using microbial agents, are eco-friendly, but have long improvement cycles and limited effectiveness on severely saline-alkali land. These technologies generally suffer from fragmented application: management measures often target single problems, such as reducing salinity or increasing fertility, lacking synergy; and they over-rely on external resources, such as freshwater, chemical reagents, and microbial agents, leading to high costs and poor sustainability. For example, while flood irrigation can suppress salt in the short term, it raises the groundwater level and causes salinization, while microbial agents have low survival rates in extreme saline-alkali environments and their functions are difficult to sustain.

[0003] The existing technologies for treating saline-alkali land using coal gangue, a major industrial solid waste, mainly revolve around the following core directions: (1) Microbial-coal gangue composite technology: By screening salt-alkali tolerant functional microorganisms, they are combined with coal gangue to form composite microbial agents. The role of microorganisms is to activate the nutrients in coal gangue, secrete organic acids to neutralize alkalinity, and improve the soil micro-ecological environment. (2) Coal gangue-based material preparation and application system: Coal gangue is processed into forms that are easy to transport and apply, focusing on engineering and large-scale treatment application schemes. For example, coal gangue is made into powder and transported remotely to the treatment area by pneumatic pipeline, or made into a solid-liquid mixture and spread on the surface by special vehicles, such as trenching spreaders. (3) Coal gangue composite amendment / conditioner: Coal gangue is compounded with other industrial and agricultural wastes, such as phosphogypsum, straw, livestock and poultry manure, wood ash, etc., as well as chemical additives, such as organic acids, humic acid, water-retaining agents, etc. Multifunctional soil conditioners are prepared by physical, chemical or biological fermentation methods, aiming to solve the physical structure, chemical properties and fertility problems of saline-alkali land at the same time. (4) Structural application of coal gangue: Coal gangue is used as a layer in the soil profile and combined with other materials, such as microbial inoculum layer, straw layer, silt layer, etc., to construct a multi-layer soil conditioner structure, so as to achieve the synergistic effect of physical barrier, chemical improvement and biological remediation.

[0004] Although these technologies have made progress in resource utilization, they are still generally limited by: (1) the inherent defects of coal gangue materials: the stability of the mineral phase makes it difficult to release nutrients, and it is necessary to break the stable structure through complex activation methods, which increases the cost and process complexity; at the same time, the water retention and fertilizer retention are poor and there is a risk of heavy metals. Direct application may aggravate water stress and cause secondary pollution, so additional amendments or passivation treatment are required. (2) the constraints of extreme saline-alkali environment on the technical effect: extreme environment leads to low survival rate of microorganisms, and the activity of bacterial agents is easily reduced by high salinity and alkali stress, affecting the stability of the improvement effect, and specific bacterial strains need to be screened; moreover, surface improvement is prone to salt return, and deep salt rises with water evaporation, making the treatment effect difficult to last. Although multi-layer structures can be constructed, the amount of engineering work is large. (3) the process complexity and high cost caused by achieving effective improvement: the complex pretreatment process increases the cost, the high energy consumption of high temperature calcination restricts the promotion of technology; long-distance transportation and component fluctuations further increase the difficulty of implementation, the high cost of the supply chain and the difference in raw materials lead to unstable product quality.

[0005] Based on this, the present invention is proposed. Summary of the Invention

[0006] The core difference between this invention and existing technologies lies in its abandonment of the pursuit of a single, universal coal gangue amendment, and the proposal of a systematic solution based on the degree of salinization, from material design to engineering application. On the one hand, through differentiated coal gangue particle size distribution, combined with bio-activation and organic fermentation processes, the pore structure is precisely controlled to prepare specialized ecological soils suitable for targeted improvement of light, medium, and severe saline-alkali land. On the other hand, differentiated treatment strategies are implemented to address the core obstacles of different degrees of salinization: for light and medium saline-alkali land, the focus is on breaking down the physical barriers of "soil compaction and poor permeability," while for severe saline-alkali land, the core is to block the continuous transport of capillary water. This forms a complete, graded treatment technology system from material preparation to engineering application.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a compound coal gangue for improving soil salinization, including compound coal gangue for improving mildly to moderately salinized soil or compound coal gangue for improving severely salinized soil. The compound coal gangue for improving mildly to moderately saline-alkali soils comprises the following components in percentage: 70-80% coal gangue with a particle size of 2.095mm < ≤ 3.353mm, 15-20% coal gangue with a particle size of 0.69mm < ≤ 2.095mm, and 10-15% coal gangue with a particle size of ≤ 0.69mm; The compound coal gangue for improving severely saline-alkali soil includes the following components in percentage: 50-60% coal gangue with a particle size of 1.004mm < ≤ 2.095mm, 35-40% coal gangue with a particle size of 0.506mm < ≤ 1.004mm, and 5-10% coal gangue with a particle size of ≤ 0.506mm.

[0008] The present invention also provides the application of the aforementioned compound coal gangue in the preparation of products for improving soil salinization.

[0009] This invention also provides an activated coal gangue for improving soil salinization, comprising the following components: The aforementioned compound coal gangue and colloidal Bacillus bacterial solution; The mass-to-volume ratio of the compound coal gangue and colloidal Bacillus bacterial solution is 100kg: 5~20L; The initial viable cell concentration of the Bacillus subtilis culture is ≥5×10⁻⁶. 5 CFU / mL; The described gelatinous Bacillus is gelatinous Bacillus LT1906, with the Latin name: Paenibacillus mucilaginous It is deposited at the China General Microbiological Culture Collection Center, located at No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing, Institute of Microbiology, Chinese Academy of Sciences, on December 9, 2020, with accession number CGMCC No. 21337.

[0010] This invention also provides a method for preparing activated coal gangue to improve soil salinization, comprising the following steps: The compounded coal gangue was mixed with a bacterial solution of Bacillus subtilis and kept at 15-40°C for 24-72 hours to obtain activated coal gangue.

[0011] The present invention also provides the application of the activated coal gangue or the activated coal gangue prepared by the preparation method described above in the improvement of soil salinization.

[0012] This invention also provides an ecological soil for improving soil salinization caused by coal gangue, comprising the following components: Activate coal gangue and organic fermentation materials; The activated coal gangue is the activated coal gangue described above or the activated coal gangue prepared by the preparation method described above.

[0013] Preferably, the method for preparing the organic fermentation material is as follows: Mix straw and cow dung at a mass ratio of 2-4:1 to obtain a material to be fermented; adjust the moisture content of the material to be fermented to 35-45% and the carbon-nitrogen ratio to 25-30:1, and ferment for 30-50 days to obtain organic fermented material.

[0014] This invention also provides a method for preparing coal gangue ecological soil to improve soil salinization, comprising the following steps: A layer of activated coal gangue is laid in a 7-9cm layer, and organic fermented material is laid in a 19-21cm layer. A total of 5-7 layers are laid and kept at 50℃ or above for 15-20 days to obtain coal gangue ecological soil. Intermittent ventilation is used during ventilation, with ventilation lasting 15-20 minutes and stopping for 30-40 minutes, operating in cycles. The ventilation rate is controlled at 0.1-0.2 m³ / t. h.

[0015] The present invention also provides the application of any of the coal gangue ecological soils described herein or the coal gangue ecological soils prepared by the preparation method described in claim 8 in improving soil salinization.

[0016] The present invention also provides a method for improving soil salinization, comprising the following steps: Coal gangue ecological soil is applied or laid in saline-alkali soil; The application rate of coal gangue ecological soil in slightly saline-alkali land is 3-5 t / mu; The application rate of coal gangue ecological soil in moderately saline-alkali land is 6-8 tons per mu; The thickness of the ecological soil paving for coal gangue in severely saline-alkali land is 50-80 cm.

[0017] The present invention has the following advantages: (i) Differentiated coal gangue particle size distribution directionally regulates pore structure, providing an ideal soil physical framework for coal gangue ecological soil.

[0018] The structure and function of coal gangue ecological soil are highly dependent on the scientific design of its particle size distribution. By differentiating the particle size distribution, the pore structure of the ecological soil can be directionally controlled.

[0019] To address the core contradiction in improving mild to moderate saline-alkali land—the difficulty of simultaneously achieving aeration and water permeability while retaining water and fertilizer—this study focuses on regulating the pore structure by constructing a high non-capillary porosity. A gradation design primarily using 2.095–3.353 mm coal gangue particles (70–80%) significantly increases the non-capillary porosity (pore size > 0.1 mm) of the coal gangue ecological soil, a crucial channel for aeration and water permeability, achieving a non-capillary porosity of 25–35%. When mixed with mild to moderate saline-alkali soil, these abundant large pores effectively break down the sticky and compacted physical structure of the soil, creating space for rapid water infiltration, salt leaching, and root respiration. Simultaneously, the inclusion of fine particles (<0.69 mm, 10–15%) increases capillary porosity and specific surface area, enhancing water retention capacity and thus contributing to water and fertilizer retention.

[0020] To address the core challenge of "easy salt reversion" in the improvement of severely saline-alkali land, the pore structure is regulated by blocking the continuous transport of capillary water. A gradation design primarily using coal gangue particles of 1.004~2.095mm (50~60%) and 0.506~1.004mm (35~40%), with the introduction of a small portion of fine particles smaller than 0.506mm (5~10%), while avoiding the introduction of coarse particles larger than 2.095mm, can significantly increase the proportion of large-diameter capillary pores with an equivalent pore size in the range of 0.02~0.06mm. Within this pore size range, the capillary action that retains and transports water is weaker, and the interconnectivity between them is poor, making it difficult for water to form a stable lateral or upward flow. On the other hand, the proportion of small-diameter capillary pores with an equivalent pore size in the range of 0.002mm~0.02mm is controlled at a low level. The interconnectivity between these capillary pores is greatly reduced, making it impossible to form an efficient capillary water transport network, and capillary water cannot move continuously within it. When a 50cm thick layer of coal gangue ecological soil is applied to severely saline-alkali land, it forms a "blocking layer," thereby cutting off the core channel through which deep, high-concentration salt solutions migrate upwards via capillary action. This addresses the technical shortcomings of existing methods, which rely on simply covering coal gangue and other waste materials without scientific pore design, failing to effectively cut off the upward flow of deep salts via capillary action and resulting in poor treatment of salt return in severely saline-alkali land.

[0021] (ii) Microbial activation and organic fermentation material enhancement provide a stable aggregate structure for coal gangue ecological soil.

[0022] The specific preserved Bacillus subtilis LT1906 (CGMCC No. 21337) was used to activate the mineral structure of coal gangue. Its secreted organic acids and bioenzymes can activate aluminosilicate minerals, promoting the directional dissolution of elements such as calcium, potassium, phosphorus, and magnesium from the mineral lattice. This not only solves the problem of nutrient fixation and utilization in coal gangue but also provides a mineral surface rich in active sites for the subsequent aggregation and bonding of coal gangue particles with organic matter.

[0023] Neither a single physical grading nor biological activation can easily form a long-term stable fertile soil structure. Another major advantage of this technology is that the active organic matters such as humic acid and amino acids generated from the transformation of organic substances bind to the active sites exposed on the surface of the biologically activated coal gangue mineral particles. At the same time, the dominant microbial flora established during the fermentation process and the extracellular polymers secreted by them can, like biological glue, cement the coal gangue particles and the organic matter together. The three work together to finally construct a stable aggregate structure of "coal gangue particle-organic matter-microorganism", fundamentally overcoming the core technical bottlenecks of poor structure, ineffective nutrients and single function in the utilization of coal gangue. The coal gangue ecological soil based on differential grading can synchronously optimize the physical structure, water migration and nutrient supply of the soil, create a rhizosphere environment with coordinated water, air and fertilizer for crop growth, and is a high-performance soil substitute product with excellent physical and chemical properties and biological activity, having broad application prospects in the fields of ecological restoration and green agriculture.

[0024] (III) Differential improvement and grading process measures to promote the reconstruction of the saline-alkali soil ecosystem.

[0025] This technology implements differential treatment for different degrees of saline-alkalinity, proposes a three-level improvement process for light, medium and heavy saline-alkali soils, and combines it with an open-channel salt drainage project to form a closed-loop improvement system. For light saline-alkali soil, the application rate is 3-5 t / mu, and the coal gangue ecological soil for light and medium saline-alkali improvement is shallowly rotary mixed in; for medium saline-alkali soil, the application rate is 6-8 t / mu, and the coal gangue ecological soil for light and medium saline-alkali improvement is shallowly rotary mixed in; for heavy saline-alkali soil, 50-80 cm of coal gangue ecological soil for heavy saline-alkali improvement is covered on the surface, and at the same time, a "field" - shaped open-channel salt drainage system is constructed.

[0026] This technical solution overcomes the shortcomings of the existing technology: (1) Solving the problem of salt return in heavy saline-alkali soil: "covering soil to raise the ground" combined with open channels forms a three-dimensional salt drainage network of "vertical barrier-horizontal drainage", effectively controlling the groundwater level and transporting and draining salts, and solving the historical problems of surface improvement effect and serious salt return in traditional methods; (2) Improving the engineering feasibility: The solution has specific parameters for ditch depth, slope, cushion layer, etc., ensuring the effectiveness and durability of the project, and is more operable and popularizable than some complex multi-layer structure construction processes; (3) Abandoning the "one-size-fits-all" application rate and mode: The differential application plan ensures the optimal allocation and economy of resources. For light and medium saline-alkali soils, the plough layer structure is quickly optimized, and for heavy saline-alkali soils, the technical path of "ecological soil preparation-covering soil to raise the ground-open-channel salt drainage" combines three in one, enabling salt control, soil fertility improvement and ecological reconstruction to be carried out simultaneously, not only completing the improvement of the physical and chemical properties of the soil, but also realizing the reconstruction of the entire soil ecosystem.

[0027] Depository Instructions

[0028] The described gelatinous Bacillus is gelatinous Bacillus LT1906, with the Latin name: Paenibacillus mucilaginous It is deposited at the China General Microbiological Culture Collection Center, located at No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing, Institute of Microbiology, Chinese Academy of Sciences, on December 9, 2020, with accession number CGMCC No. 21337. Detailed Implementation

[0029] This invention also provides a method for improving soil salinization, specifically including the following steps: The steps for improving slightly saline-alkali soil (water-soluble salt content 1~3g / kg, pH<8.5) are as follows: First, use a rotary tiller to loosen the surface layer of the saline-alkali land to a depth of 10~15cm. Then, evenly spread the coal gangue ecological soil prepared by compounding coal gangue for improving slightly to moderately saline-alkali soil at an application rate of 3~5t / mu, mix it with the original soil layer by rotary tillage, and irrigate it fully in one go using sprinkler irrigation or flood irrigation. When the soil moisture is suitable, subsequent planting operations can be carried out.

[0030] The method for improving moderately saline-alkali soil (water-soluble salt content 3~5g / kg, pH 8.5≤9.0) is as follows: First, use a rotary tiller to cultivate the saline-alkali land to a depth of 15~20cm and remove impurities. Then, evenly spread the coal gangue ecological soil prepared by compounding coal gangue to improve mildly to moderately saline-alkali soil at an application rate of 6~8t / mu, mix it with the original soil layer by rotary tillage, and irrigate it fully in one go using sprinkler irrigation or flood irrigation. When the soil moisture is suitable, subsequent planting operations can be carried out.

[0031] The method for improving severely saline-alkali soil (water-soluble salt content 5~10g / kg, pH 9.0≤9.5) is as follows: First, dig a grid-shaped open ditch network. The longitudinal main ditch (edge ​​of the plot) is 80~100cm wide, and the ditch depth is adjusted according to the groundwater level (1.5~1.8m when the groundwater level is <1.5m; 1.0~1.2m when the groundwater level is 1.5~2.5m; 0.8~1.0m when the groundwater level is >2.5m), with a ditch wall slope of 1:1.2. The transverse branch ditches (inside the plot) are spaced 50m apart, 60~80cm wide, and 20cm lower than the longitudinal main ditch. After clearing debris from the surface of the saline-alkali land and leveling the land, a layer of coal gangue ecological soil, prepared by using compound coal gangue to improve severely saline-alkali soil, is laid on the surface of the saline-alkali soil. The thickness of the layer is 50-80cm. A laser leveling machine is used to level the soil and ensure a smooth connection at the edge of the open channel.

[0032] In this invention, the preparation method of the *Bacillus subtilis* LT1906 bacterial culture is as follows: The preserved LT1906 strain is inoculated into a seed culture medium (sucrose 5–10 g / L, K₂HPO₄ 0.1–0.2 g / L, MgSO₄·7H₂O 0.1–0.2 g / L, FeCl₃ 0.002–0.005 g / L, CaCO₃ 0.2–0.5 g / L, (NH₄)₂SO₄ 0.2–0.5 g / L, pH 7.0–7.5, sterilized) and cultured at 30°C and 160 rpm for 48 hours to obtain the LT1906 seed culture; the seed culture is then transferred at an inoculation rate of 10% (v / v) to a fermentation culture medium (sucrose 5–10 g / L, K₂HPO₄ 0.1–0.2 g / L, MgSO₄·7H₂O 0.1–0.2 g / L). The LT1906 bacterial culture was obtained by culturing in a sterilized solution (containing FeCl3 0.002~0.005 g / L, CaCO3 0.2~0.5 g / L, pH 7.0~7.5) at 30℃ and 160 rpm for 48 hours. The culture had a viscosity of over 2 mPa·s due to the secretion of extracellular polysaccharides.

[0033] The following detailed description of the solutions provided by the present invention, in conjunction with the embodiments, should not be construed as limiting the scope of protection of the present invention.

[0034] In this embodiment of the invention, the seed culture medium for preparing Bacillus subtilis LT1906 bacterial culture, using water as a solvent, comprises the following components at the following concentrations: sucrose 8 g / L, K2HPO4 0.2 g / L, MgSO4·7H2O 0.1 g / L, FeCl3 0.003 g / L, CaCO3 0.3 g / L, (NH4)2SO4 0.3 g / L, pH 7.2.

[0035] In this embodiment of the invention, the fermentation medium for preparing the Bacillus subtilis LT1906 bacterial culture, using water as a solvent, comprises the following components at the following concentrations: sucrose 8 g / L, K2HPO4 0.2 g / L, MgSO4·7H2O 0.1 g / L, FeCl3 0.003 g / L, CaCO3 0.3 g / L, pH 7.2.

[0036] In this embodiment of the invention, the preparation method of Bacillus subtilis LT1906 bacterial culture is as follows: the preserved LT1906 strain is inoculated into a seed culture medium and cultured at 30°C and 160 rpm for 48 hours to obtain LT1906 seed culture; the seed culture is transferred to a fermentation culture medium at an inoculation rate of 10% (v / v) and cultured at 30°C and 160 rpm for 48 hours to obtain Bacillus subtilis LT1906 bacterial culture.

[0037] The viable cell concentration of the prepared Bacillus subtilis LT1906 bacterial suspension was 1×10⁻⁶. 6 CFU / mL.

[0038] Example 1

[0039] Preparation of Coal Gangue Ecological Soil for Improving Mild to Moderately Saline-Alkaline Soils

[0040] This embodiment provides a method for preparing eco-soil from coal gangue to improve mild to moderate soil salinization: waste coal gangue is crushed and then sieved through a three-layer sieve with apertures of 3.353mm, 2.095mm, and 0.69mm from top to bottom. The coal gangue is then blended according to the following proportions: 75% of the coal gangue has a particle size of 2.095mm < 3.353mm, 15% has a particle size of 0.69mm < 2.095mm, and 10% has a particle size of ≤ 0.69mm, to obtain blended coal gangue.

[0041] Each ton of compounded coal gangue was mixed with 50L of Bacillus subtilis LT1906 bacterial solution and kept at 25℃ for 48h to obtain activated coal gangue.

[0042] Mix corn stalks and cow manure crushed to 2cm in a 3:1 mass ratio to obtain the material to be fermented. Adjust the moisture content to 40% and the carbon-nitrogen ratio to 28:1. Use intermittent aeration. On the 16th day of fermentation, the material temperature reaches 50℃. Maintain the high temperature above 50℃ for 15 days to obtain the organic fermented material.

[0043] Six layers were laid, consisting of an 8cm layer of activated coal gangue and a 20cm layer of organic fermentation material (alternating layers of activated coal gangue and organic fermentation material). The pile was trimmed every three layers to ensure stability, until the pile measured 22 m × 8 m × 1.3 m. Intermittent ventilation was used, with a 15-minute ventilation cycle followed by a 30-minute ventilation stop, maintaining a ventilation rate of 0.1 m³ / t. h. On the second day, the temperature reached 50℃. On the fifth day, a tracked turner was used to turn the pile to ensure uniform mixing of the materials. After maintaining the temperature above 50℃ for 15 days, coal gangue ecological soil with improved mild to moderate salinization was obtained.

[0044] Physical structure assessment (Table 1) revealed that a gradation design primarily using 2.095–3.353 mm particles (75%) achieved a non-capillary porosity of 32.5% in the coal gangue ecological soil. This high non-capillary porosity creates crucial pathways for water infiltration, salt leaching, and root respiration, ensuring aeration and permeability in mild to moderate saline-alkali soils and preventing compaction. Simultaneously, the addition of fine particles (≤0.69 mm) and the integration of organic matter enhanced capillary porosity, enabling the ecological soil to retain water while maintaining permeability. After fermentation and aggregate structure reconstruction, the bulk density was optimized to 1.05 g / cm³, which is beneficial for root growth; the content of water-stable aggregates (<0.25 mm) reached 30.22%, demonstrating erosion resistance.

[0045] Table 1 Physical structure of coal gangue ecological soil for improving mildly to moderately saline-alkali soil

[0046] The coal gangue ecological soil prepared through the synergistic process of "microbial activation + organic fermentation" exhibits fundamentally improved chemical and nutrient properties (Table 2). It displays a near-neutral pH, low salinity, and abundant organic matter, with both total and available nutrient content meeting or exceeding the standards for moderately fertile soils. This optimized nutrient system not only directly supplies nutrients for plant growth but also reduces nutrient loss through its strong fertilizer retention capacity, thus laying a solid chemical foundation for improving mildly to moderately saline-alkali land and promoting vegetation restoration.

[0047] Table 2 Chemical and nutrient properties of coal gangue ecological soil for improving mildly to moderately saline-alkali soil

[0048] The coal gangue raw materials used must be tested in advance to ensure that their heavy metal content meets the standards. The total heavy metal content of the coal gangue ecological soil (Table 3) meets the risk screening value specified in the "GB 15618-2018 Soil Environmental Quality Standard for Agricultural Land Soil Pollution Risk Control". To assess the environmental risk under rainwater runoff, leaching experiments were conducted using the "Coal and Coal Gangue Leaching Test Method" (GB / T 34230-2017), and the heavy metal concentration in the leachate met the Class V water standard limit of the "Surface Water Environmental Quality Standard" (GB 3838-2002).

[0049] Table 3. Environmental safety and risk control indicators for improved coal gangue ecological soil in mildly to moderately saline-alkali soils.

[0050] Example 2

[0051] Preparation of Coal Gangue Ecological Soil for Improving Severely Saline-Alkaline Soil

[0052] This embodiment provides a method for preparing improved coal gangue ecological soil for severely salinized soil: The specific steps are the same as in Example 1, except that when preparing the compounded coal gangue, the waste coal gangue is crushed and then sieved through a three-layer screen with apertures of 2.095mm, 1.004mm, and 0.506mm from top to bottom. The coal gangue is then compounded according to the following proportions: 55% of the coal gangue has a particle size of 1.004mm < 2.095mm, 35% has a particle size of 0.506mm < 1.004mm, and 10% has a particle size of ≤ 0.506mm, to obtain the compounded coal gangue.

[0053] Compared to Example 1, the proportion of intermediate particle size (0.506~2.095mm) was significantly increased. By avoiding the introduction of coarse particles (>2.095mm) and finely controlling the proportion of fine particles (≤0.506mm), the proportion of small-diameter capillary pores (0.002mm~0.02mm) that contribute most to salt uptake was controlled to below 5% (Table 4), thus failing to form an efficient capillary water transport network. With the main equivalent pore size adjusted to 0.02~0.06mm, the capillary force was weak and the interconnectivity between pores was poor, preventing continuous capillary water transport. This structure makes the 50cm thick ecological soil cover an effective salt-blocking layer. Simultaneously, by combining organic additives and biological activation, it possesses a high content of water-stable aggregates and a low bulk density, ensuring the long-term stability of the structure. The total nutrient and available nutrient contents meet or exceed the standards for medium-fertility soils (Table 5), and the total heavy metal content and leachate concentration meet the corresponding standards (Table 6).

[0054] Table 4 Physical structure of coal gangue ecological soil for improving severely saline-alkali soil

[0055] Table 5 Chemical and nutrient properties of coal gangue ecological soil for improving severely saline-alkali soil

[0056] Table 6. Environmental safety and risk control indicators for improved coal gangue ecological soil in severely saline-alkali soil.

[0057] Application Example 1

[0058] This embodiment provides an application of coal gangue ecological soil for improving mildly salinized soil. The application was implemented in Daying Village, Zangzhai Township, Ying County, Shuozhou City, Shanxi Province. The target plot is located on the southeast side of the village, west of the Hanyuan Railway, with longitude g113.04012782 and latitude 39.59581197 (GCJ-02 coordinate system). The water-soluble salt content of the soil in this plot was measured to be 2.8 g / kg by gravimetric method and the pH value was measured to be 8.4 by potentiometric method, which determined it to be mildly saline-alkali land. The specific improvement method is as follows: (1) A large rotary tiller was selected and its blade shaft speed was set to 250 rpm to perform shallow rotary tillage operation with a depth of 15 cm on the surface to loosen the topsoil. (2) A centrifugal fertilizer spreader was used to spread the coal gangue ecological soil prepared in Example 1 for improving mildly to moderately salinized soil at an application rate of 3t / mu. (3) After spreading the ecological soil, perform rotary tillage again at the same depth of 15cm to fully and evenly mix the ecological soil with the original saline-alkali soil to form a homogeneous improved tillage layer. (4) Use flood irrigation to irrigate fully in one go, and use the high non-capillary pore channels of the coal gangue ecological soil to leach the surface soluble salts down to below the tillage layer. (5) Allow the soil to drain naturally after irrigation, and test the improved soil and carry out subsequent planting operations when the soil moisture is suitable.

[0059] Soil samples from 0-20cm depth were taken to test the improvement effect. After improvement, the soil pH value approached neutral, the salinity and exchangeable sodium content were lower, and the organic matter was abundant (Table 7). The significantly improved soil properties are attributed to two factors: firstly, the high non-capillary porosity of the coal gangue ecological soil (32.5%) created a key channel for salt leaching, which, combined with the watering leaching step, effectively reduced surface salinity; secondly, the addition of fine particles and the composite of organic matter increased capillary porosity, enabling the improved soil to retain water while maintaining good aeration and permeability. The bulk density was optimized from 1.6g / cm³ to 1.12g / cm³, which is beneficial to root growth. In summary, the improved soil has enhanced aeration, permeability, water and fertilizer retention capacity, reduced salinity, a more suitable pH, and sufficient nutrients, laying a good soil foundation for vegetation restoration and crop planting.

[0060] Table 7. Soil nutrients, salinity, and physical properties before and after improvement of mildly saline-alkali land.

[0061] Application Example 2

[0062] This embodiment provides an application of coal gangue ecological soil in improving moderately saline-alkali soil. This application is implemented in Daying Village, Cangzhai Township, Ying County, Shuozhou City, Shanxi Province. The target plot is located on the southeast side of the village and west of the Hanyuan Railway, with longitude g113.04021394 and latitude 39.59564888 (GCJ-02 coordinate system). Through the gravimetric method, the soil water-soluble salt content of this plot is measured to be 4.2 g / kg, and the pH value is measured to be 8.8 by the potentiometric method, which is determined to be moderately saline-alkali land. The specific improvement method is the same as that of Application Example 1, except that: the operation depth of the rotary tiller is 20 cm, and the application rate of coal gangue ecological soil for improving moderately saline-alkali soil is 6 t / mu.

[0063] Take soil samples from 0 to 20 cm to detect the improvement effect (Table 8). After improvement, the soil has good ventilation and water permeability, water and fertilizer retention capabilities, significantly reduced salinity, suitable pH, and sufficient nutrients, laying a solid foundation for vegetation restoration and crop planting in moderately saline-alkali land.

[0064] Table 8 Soil nutrients, salinity, and physical indicators before and after the improvement of moderately saline-alkali land

[0065] Application Example 3

[0066] This embodiment provides an application of coal gangue ecological soil in improving severely saline-alkali soil. This application is implemented in Daying Village, Cangzhai Township, Ying County, Shuozhou City, Shanxi Province. The target plot is located on the southeast side of the village and west of the Hanyuan Railway, with longitude g113.04362978 and latitude 39.59413598 (GCJ-02 coordinate system). Through the gravimetric method, the soil water-soluble salt content of this plot is measured to be 8.5 g / kg, and the pH value is measured to be 9.4 by the potentiometric method, which is determined to be severely saline-alkali land. The specific improvement method is as follows: (1) Construct an open-channel salt drainage system: Excavate a "field" - shaped open ditch network. The longitudinal main ditch is located at the edge of the plot, with a ditch width of 100 cm, a ditch depth of 1.8 m, and a ditch wall slope of 1:1.2; the transverse branch ditches are located inside the plot, with a ditch width of 80 cm, a ditch depth of 2.0 m, and a spacing of 50 m. (2) Cover with coal gangue ecological soil: Clean the surface layer debris and level the land. Lay the coal gangue ecological soil for improving severely saline-alkali soil on the surface of the target plot, with a laying thickness of 50 cm, and level it with a laser land grader to ensure smooth connection with the edge of the open channel.

[0067] Nutrient, salinity, and physical properties were tested using 0-20cm samples of the original saline-alkali soil and the overlying coal gangue ecological soil (Table 9). This comprehensive treatment scheme, through a three-dimensional design combining vertical blocking with an ecological soil cover layer and horizontal drainage via an open channel network, achieved a rapid decrease in salinity within one month and established a stable physicochemical barrier within 3-12 months. The key lies in the durability of the porous structure of the coal gangue ecological soil and the continuous maintenance of the open channel salt drainage system. This improvement scheme successfully reconstructed severely saline-alkali land into usable land with controlled salinity, loose structure, and improved fertility, providing a reliable technical path to solve the cyclical problem of "treatment-salinization" in severely saline-alkali land.

[0068] Table 9. Soil nutrients, salinity, and physical properties before and after improvement of severely saline-alkali land.

[0069] As can be seen from the above embodiments, the present invention provides a compound coal gangue for improving soil salinization, coal gangue ecological soil, its preparation method, and its application. The compound coal gangue for improving mildly to moderately salinized soil comprises the following components in percentage: 70-80% coal gangue with a particle size of 2.095mm < ≤ 3.353mm, 15-20% coal gangue with a particle size of 0.69mm < ≤ 2.095mm, and 10-15% coal gangue with a particle size of ≤ 0.6mm; the compound coal gangue for improving severely salinized soil comprises the following components in percentage: 50-60% coal gangue with a particle size of 1.004mm < ≤ 2.095mm, 35-40% coal gangue with a particle size of 0.506mm < ≤ 1.004mm, and 5-10% coal gangue with a particle size of ≤ 0.506mm. The compounded coal gangue of this invention is used to prepare coal gangue ecological soil with precise control of pore structure, realizing the targeted and efficient improvement of light, medium and heavy saline-alkali land.

[0070] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A compound coal gangue for improving soil salinization, characterized in that, This includes compound coal gangue for improving mildly to moderately salinized soils or compound coal gangue for improving severely salinized soils. The compound coal gangue for improving mildly to moderately saline-alkali soils comprises the following components in percentage: 70-80% coal gangue with a particle size of 2.095mm < ≤ 3.353mm, 15-20% coal gangue with a particle size of 0.69mm < ≤ 2.095mm, and 10-15% coal gangue with a particle size of ≤ 0.69mm; The compound coal gangue for improving severely saline-alkali soil includes the following components in percentage: 50-60% coal gangue with a particle size of 1.004mm < ≤ 2.095mm, 35-40% coal gangue with a particle size of 0.506mm < ≤ 1.004mm, and 5-10% coal gangue with a particle size of ≤ 0.506mm.

2. The application of the compound coal gangue as described in claim 1 in the preparation of products for improving soil salinization.

3. An activated coal gangue for improving soil salinization, characterized in that, It includes the following components: The compound coal gangue and colloidal Bacillus bacterial solution as described in claim 1; The mass-to-volume ratio of the compound coal gangue and colloidal Bacillus bacterial solution is 100kg: 5~20L; The initial viable cell concentration of the Bacillus subtilis culture is ≥5×10⁻⁶. 5 CFU / mL; The described gelatinous Bacillus is gelatinous Bacillus LT1906, with the Latin name: Paenibacillus mucilaginosus It is deposited at the China General Microbiological Culture Collection Center, located at No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing, Institute of Microbiology, Chinese Academy of Sciences, on December 9, 2020, with accession number CGMCC No. 21337.

4. A method for preparing activated coal gangue to improve soil salinization, characterized in that, Includes the following steps: The compounded coal gangue as described in claim 1 is mixed with a bacterial solution of Bacillus subtilis and kept at 15-40°C for 24-72 hours to obtain activated coal gangue.

5. The application of the activated coal gangue according to claim 3 or the activated coal gangue prepared by the preparation method according to claim 4 in improving soil salinization.

6. A type of ecological soil made from coal gangue to improve soil salinization, characterized in that, It includes the following components: Activate coal gangue and organic fermentation materials; The activated coal gangue is the activated coal gangue as described in claim 3 or the activated coal gangue prepared by the preparation method described in claim 4.

7. The coal gangue ecological soil according to claim 6, characterized in that, The method for preparing the organic fermentation material is as follows: Mix straw and cow dung at a mass ratio of 2-4:1 to obtain a material to be fermented; adjust the moisture content of the material to be fermented to 35-45% and the carbon-nitrogen ratio to 25-30:1, and ferment for 30-50 days to obtain organic fermented material.

8. A method for preparing coal gangue ecological soil to improve soil salinization, characterized in that, Includes the following steps: A layer of activated coal gangue is laid in a 7-9cm layer, and organic fermented material is laid in a 19-21cm layer. A total of 5-7 layers are laid and kept at 50℃ or above for 15-20 days to obtain coal gangue ecological soil. Intermittent ventilation is used during ventilation, with ventilation lasting 15-20 minutes and stopping for 30-40 minutes, operating in cycles. The ventilation rate is controlled at 0.1-0.2 m³ / t. h.

9. The application of the coal gangue ecological soil according to any one of claims 6 to 7 or the coal gangue ecological soil prepared by the preparation method according to claim 8 in improving soil salinization.

10. A method for improving soil salinization, characterized in that, Includes the following steps: Coal gangue ecological soil is applied or laid in saline-alkali soil; The application rate of coal gangue ecological soil in slightly saline-alkali land is 3-5 t / mu; The application rate of coal gangue ecological soil in moderately saline-alkali land is 6-8 tons per mu; The thickness of the ecological soil paving for coal gangue in severely saline-alkali land is 50-80 cm.

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