Sponge water retention structure based on coal-based solid waste as well as construction method and application of sponge water retention structure

Abstract

The invention belongs to the field of resource utilization of coal-based solid waste, and particularly relates to a sponge water retention structure based on coal-based solid waste and a construction method and application of the sponge water retention structure. The sponge water retention structure comprises at least one water retention interlayer made of a coal-based solid waste material; the water retention interlayer is horizontally embedded into the soil of the plough layer, the thickness of the water retention interlayer is a preset thickness, and the embedding depth is a preset depth; the coal-based solid waste material is selected from one or more of coal gangue, desulfurized gypsum and gasified slag. The sponge water retention structure provided by the invention has good water retention and salt resistance effects.

Description

Technical Field

[0001] This invention belongs to the field of resource utilization of coal-based solid waste, specifically relating to a sponge water-retaining structure based on coal-based solid waste, its construction method, and its application. Background Technology

[0002] Due to hydrogeological limitations, groundwater levels are deep in many areas, making extraction and utilization difficult and costly, thus hindering their use as a reliable source of agricultural irrigation water. Against this backdrop, the soil's moisture retention capacity becomes a core factor determining vegetation survival, crop yield, and ecosystem stability.

[0003] Traditional farmland water conservation techniques, such as mulching, water-saving irrigation, and the application of organic fertilizers or polymeric water-retaining agents, while effective to some extent, still have significant limitations in the extremely arid environment of western China. For example, surface mulching mainly inhibits surface evaporation and has limited effect on retaining deep soil moisture; frequent water-saving irrigation relies on a stable water source and is energy-intensive; conventional water-retaining materials may be costly, have environmental risks due to degradation products, or experience a decline in effectiveness over long-term use. Therefore, there is an urgent need to explore new methods and materials that are locally sourced, low-cost, environmentally friendly, and can significantly enhance the "water storage and supply" capacity of the topsoil.

[0004] In recent years, the resource utilization of coal-based solid waste (such as fly ash and coal gangue) has received widespread attention. These materials, due to their unique pore structure and surface characteristics, often exhibit good adsorption properties and a certain water-holding capacity. If such large quantities of industrial solid waste awaiting treatment can be functionally modified or structurally designed to transform them into water-retaining materials suitable for soil improvement in arid regions, it would not only achieve "treating harm with waste" but also open up new avenues for water conservation in agriculture.

[0005] Relevant patent documents retrieved: This invention, published in China (CN120787540A) on October 17, 2025, discloses an ecological restoration method for waste dumps using directional porous soil constructed from coal-based solid waste. The method includes: S1: mixing coal-based solid waste in a specific mass ratio; S2: mixing organic matter in a specific mass ratio; S3: mixing S2 with bacterial solution; S4: compounding S3 with S1; S5: mixing the mixture obtained in S4 with aluminum powder and calcium hydroxide; S6: fermenting and drying S5, while simultaneously screening the particle size range to obtain a porous medium; S7: drilling holes on the surface of the waste dump and filling the holes with the porous medium; S8: compounding switchgrass and Apocynum venetum in a specific ratio; S9: planting plants in the holes of S7; and S10: monitoring at a certain period. This invention achieves a comprehensive improvement in the efficiency of coal-based solid waste resource utilization and the quality of mining area ecological restoration by regulating the particle size and mineral composition of coal-based solid waste, constructing porous media pores in a directional manner, and coupling soil-vegetation systems. Relevant non-patent literature retrieved: The journal or book title is "China Coal," and the article title is "Preparation and Characterization of Coal-Based Solid Waste Biological Water-Retaining Agents," volume number 2025.11.011. This article aims to improve the water retention performance of soil water-retaining agents in northern sand control belts and promote the recycling of coal-based solid waste resources and sustainable environmental development. Using coal gangue, coal slime, lignite, and other raw materials from mining areas in this region, and selecting previously preserved coal-activated microorganisms as research objects, the water absorption ratio was used as an indicator. Through strain screening, single-factor experiments, and mixing experiments, the formulation of water-retaining agents was optimized. This research provides support for its application in soil water retention and resource recycling.

[0006] The prior art represented by the aforementioned documents has at least the following unresolved technical problems or defects: The effectiveness of the aforementioned literature in water retention and salt inhibition in the soil tillage layer still needs improvement, and the cost is relatively high, making it unsuitable for large-scale use.

[0007] In solving the above problems or overcoming the above defects, the present invention has encountered the following difficulties and obstacles: (1) The sources of solid waste such as coal gangue, desulfurization gypsum, and gasification slag are complex and the composition fluctuates greatly, which may lead to differences in performance between batches and affect the stability of the interlayer; (2) If the particle size distribution after crushing and screening does not reach the optimized range (such as too many coarse particles leading to excessive pores, and too many fine particles leading to decreased permeability), it will affect the balance between water retention and salt conduction functions; (3) When excavating the profile in the field, it is necessary to disturb the original soil structure, resulting in uneven interlayer depth and affecting the stability of the water transport path. Summary of the Invention

[0008] The purpose of this invention is to provide a combination of a sponge water-retaining structure based on coal-based solid waste, its construction method and application, and related technologies, to solve the technical problems of reduced soil moisture and increased soil alkalization in the arid Northwest region.

[0009] Terminology Explanation: Unless otherwise defined, all technical terms in this document have the same meanings as commonly understood by one of ordinary skill in the art to which the subject matter of the claims pertains. Unless otherwise stated, all patents, patent inventions, and publications cited in this document are incorporated herein by reference in their entirety. If multiple definitions exist for terms in this document, the definitions in this chapter shall prevail.

[0010] It should be understood that the above brief description and the following detailed description are exemplary and for illustrative purposes only, and do not limit the subject matter of the invention in any way. In this invention, the singular is used in conjunction with the plural unless otherwise specifically stated. It should also be noted that, unless otherwise stated, the use of “or” or “or” means “and / or”. Furthermore, the use of the term “comprising” and other forms such as “including,” “containing,” and “contains” are not limiting.

[0011] The definition of the standard chemical terminology can be found in the reference "Resource Utilization Technology of Coal-based Solid Waste (Second Edition)".

[0012] The term "coal-based solid waste" refers to the general term for solid waste generated during coal mining, washing, processing and combustion, mainly including coal gangue, fly ash, slag and coal gasification slag.

[0013] The term "coal gangue" refers to solid waste generated during coal mining and washing. It is mainly composed of rocks such as sandstone and shale, has a low carbon content, and is usually blackish-gray in color.

[0014] The term "desulfurization gypsum" refers to a byproduct of flue gas desulfurization processes in industrial plants such as coal-fired power plants. Its main component is calcium sulfate dihydrate, which is highly pure and low in impurities, making it an important industrial raw material. It is widely used in building materials, agriculture, and engineering.

[0015] The term "gasification slag" refers to the solid waste generated during the coal gasification process, which mainly consists of unburned coal particles and ash.

[0016] The term "fragmentation" refers to the process of using external force to overcome the cohesive forces between solid waste particles, causing large pieces of solid waste to break into smaller pieces.

[0017] The term "sieving" refers to separating materials based on their particle size by passing them through sieves with different aperture sizes.

[0018] On the one hand, the present invention provides a sponge water-retaining structure based on coal-based solid waste, wherein the water-retaining structure includes at least one water-retaining layer made of coal-based solid waste material; the water-retaining layer is horizontally embedded in the topsoil, with a predetermined thickness and a predetermined burial depth; the coal-based solid waste material is selected from one or more of coal gangue, desulfurization gypsum, and gasification slag.

[0019] Preferably, the component content of the coal-based solid waste is as follows:

[0020] Preferably, the thickness of the water-retaining barrier is 1-10cm, more preferably 2-5cm.

[0021] Preferably, the water-retaining barrier is buried at a depth of 5-30cm from the ground surface, more preferably 3-15cm.

[0022] Preferably, the water-retaining structure includes two water-retaining layers arranged vertically to form a double-layer sponge water-retaining structure.

[0023] More preferably, the upper partition is buried at a depth of 2-5cm and a thickness of 1-3cm; the lower partition is buried at a depth of 8-12cm and a thickness of 2-6cm.

[0024] Preferably, when the coal-based solid waste material is desulfurized gypsum, it is used to improve soil alkalinity and reduce sodium adsorption ratio (SAR).

[0025] Preferably, when the coal-based solid waste material is coal gangue, it is used to provide excellent water absorption and retention properties.

[0026] Secondly, the present invention provides a method for constructing the above-mentioned sponge water-retaining structure, comprising the following steps: (1) The coal-based solid waste is crushed and screened to obtain coal-based solid waste material with a predetermined particle size; (2) In the soil area to be treated, excavate a soil profile to a predetermined depth; (3) At a predetermined depth in the soil profile, a layer of coal-based solid waste material prepared in step (1) is evenly laid to form a water-retaining barrier layer; (4) Backfill the original soil or imported soil on top of the laid water-retaining layer until the ground surface is reached, and compact it slightly.

[0027] Preferably, the pH, TDS, particle size, volume, and saturated moisture content of the coal-based solid waste material are as follows:

[0028] Thirdly, this invention provides the application of the above-mentioned sponge water-retaining structure in ecological restoration or saline-alkali land improvement in arid and semi-arid regions.

[0029] The present invention has the following beneficial effects: (1) Turning waste into treasure and making resources: This invention uses coal-based solid waste as the main material, which is low cost and realizes the high added value of industrial solid waste resource utilization, which has both environmental protection and economic value.

[0030] (2) Structured water retention with long-lasting effect: Unlike simple material mixing, this invention constructs a "soil-sponge" composite structure by setting up physical barriers. This structure can quickly absorb water and slow down infiltration during the watering stage, and can slowly replenish the upper soil layer as a water source during the evaporation stage, while blocking salt below or in the barriers, thereby maintaining a high effective water content and a low salt concentration in the crop root zone (especially 0-15cm) for a long time.

[0031] (3) The double-layer structure has obvious advantages: the double-layer design can form a tiered effect of "water retention-salt inhibition-water retention". The upper layer can inhibit surface evaporation and intercept the upward movement of salt; the lower layer can further retain water and supply the deep roots of crops. The soil moisture content between the two layers is significantly improved.

[0032] (4) Promotes crop growth: Experiments have shown that, under simulated drought conditions, soils with the structure of this invention have significantly better seedling emergence rate and later growth of crops such as alfalfa than untreated soils, verifying its actual agronomic benefits. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the soil column used in the leaching test in Example 1 of the present invention.

[0034] Figure 2 This is a schematic diagram of different treatment structures in the pot experiment of Embodiment 2 of the present invention.

[0035] Figure 3 This is a comparison chart of infiltration time (a), infiltration rate (b), and leachate volume (c) for different soil columns in Example 1.

[0036] Figure 4 This is a distribution map of water storage in soil profiles for different treatments in Example 1. Figure 5 This is a pH distribution map of soil profiles under different treatments in Example 1. Figure 6 This is a distribution map of sodium adsorption ratio (SAR) in soil profiles of different treatments in Example 1. Figure 7 This is a distribution map of electrical conductivity (EC) in soil profiles for different treatments in Example 1. Figure 8 The soil EC value and water content (a) and ion concentration (b) in Example 1 are shown in Figure 1. 2+ c is Na + d is HCO3 - Correlation analysis diagram of ). Figure 9 This is a comparison chart of soil evaporation rates under different treatments in Example 2. Figure 10 This is a comparison chart of soil water storage in different soil layers under different treatments in Example 2 (different letters indicate significant differences between different treatments in the same soil layer). P <0.05). Figure 11 This is a comparison chart of soil pH, SAR, and EC values ​​for different treatments in soil layers in Example 2 (different letters indicate significant differences between different treatments in the same soil layer). P <0.05). Figure 12 The seedling emergence rate of different treatments 5 days after sowing in Example 2 is shown. Figure 13 The growth charts for alfalfa treated with CK, T3, T6, and T7 are shown one month after sowing in Example 2. Detailed Implementation

[0037] The present invention will be described below through specific embodiments to make the technical solution of the present invention easier to understand and master. However, the present invention is not limited thereto. The described embodiments are only some embodiments of the present invention, and not all embodiments.

[0038] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, which should be understood to include values ​​close to them. For numerical ranges, one or more new numerical ranges can be obtained by combining the endpoint values ​​of the ranges, the endpoint values ​​of the ranges with individual point values, and individual point values ​​with each other, and these numerical ranges should be considered as specifically disclosed herein. Unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “described” as used herein include both singular and plural indicators. Numerical ranges expressed by endpoints include all numerical values ​​and fractions within the corresponding range, as well as the expressed endpoints.

[0039] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort should fall within the scope of protection of this invention. Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; the reagents and materials described, unless otherwise specified, are commercially available.

[0040] The component contents of the coal-based solid waste used in this invention are shown in Table 1 below: Table 1

[0041] The pH, TDS, particle size, volume, and saturated moisture content of the coal-based solid waste material used in this invention are shown in Table 2 below: Table 2

[0042] Example 1 This embodiment uses a soil column simulation test to verify the water retention and salt barrier effects of different coal-based solid waste materials as interlayers.

[0043] Materials: The experimental soil was saline-alkali soil from the Zhundong region of Xinjiang Uygur Autonomous Region. Coal-based solid waste materials included desulfurization gypsum (FGDG), coal gangue (CG), and gasification slag (GS), the chemical composition and physical properties of which are shown in Tables 1 and 2. The lumpy materials were ground and passed through a 40-mesh sieve for later use.

[0044] Experimental Design: Five treatment groups were set up, including a control (CK, no interlayer), Flue Gas Desulfurization Gypsum (FGDG, single-layer), Coal Gangue (CG), Gasified Slag (GS), and a double-layer desulfurization gypsum (D-FGDG, double-layer) interlayer. Each treatment was replicated three times. A soil column with an inner diameter of 6 cm and a height of 40 cm was used for the experiment. From bottom to top, the soil column consisted of a 5 cm soil layer, a 5 cm solid waste interlayer, and a 25 cm soil layer (e.g., ...). Figure 1The amount of water used for soil and coal-based solid waste samples was calculated based on the filling height and bulk density. The water volume was the saturated water content of the soil layer at a height of 30cm (saturated water content was 22.74%, and the water volume for each soil column was 337.32g).

[0045] Sample collection and index testing: Soil samples were collected on day 5 (after leaching) and day 30 (after evaporation), at depths of 0-5, 5-10, 10-15, 15-20, 20-25, and 25-30 cm.

[0046] During the leaching stage, wetting peaks and infiltration rates were recorded for different soil columns. After sample collection, water content and salinity were measured.

[0047] Moisture content: determined by drying method. Weigh 10g of sample and place it in an aluminum box, put it in an oven, and dry it at 105-110℃ until constant weight. Take it out and cool it in a desiccator for about 20 minutes, then weigh it immediately. Repeat the process until the difference between two replicates is no more than 3 mg.

[0048]

[0049] In the formula, m0 is the mass of the empty aluminum box (g), m1 is the mass of the wet soil + aluminum box (g), and m2 is the mass of the dry soil + aluminum box (g).

[0050] Salinity and alkalinity indicators: After air drying indoors and passing through a 2 mm sieve, soil pH and electrical conductivity were measured. First, 10 g of soil sample was weighed, added to 50 ml of deionized water, shaken for 30 minutes, and then filtered to obtain an extract with a soil-to-water ratio of 1:5. Then, the pH was measured using a Mettler Toledo benchtop pH meter (FE-28, Switzerland). Electrical conductivity was measured using a Mettler Toledo benchtop conductivity meter (FE-38, Switzerland). Soil water-soluble potassium (K) was measured using inductively coupled plasma atomic emission spectrometry (Inductively Coupled Plasma Atomic Emission Spectrometry, Leeman, USA). + Na + Ca 2+ and Mg 2+ The sodium adsorption ratio (SAR) is calculated using formula (2).

[0051]

[0052]

[0053] Results Analysis (1) Effects on soil column infiltration rate and soil moisture content The water absorption mechanisms of different coal-based solid waste materials are different. Desulfurized gypsum mainly relies on its internal porous structure for physical adsorption; coal gangue is due to the strong adsorption and lattice binding of clay minerals (such as kaolinite) it contains; gasification slag mainly depends on physical adsorption due to its huge surface area and rich pore structure, as well as chemical adsorption of surface hydrophilic groups.

[0054] As Figure 3 shown, the infiltration time order of different treated soils is: FGDG < D-FGDG < GS < CK < CG, and the leaching completion time order is FGDG < D-FGDG < CK < GS < CG. Among them, the infiltration time and leaching completion time of the desulfurized gypsum (FGDG) treatment are the shortest, shortening 28.2% and 41.5% of the time compared with the CK treatment. Followed by the double-layer desulfurized gypsum (D-FGDG) treatment. In terms of infiltration rate, compared with the CK treatment, the infiltration rates of the FGDG, GS, and D-FGDG treatments increased significantly by 39.7%, 21.7%, and 33.4% respectively, while the CG treatment decreased by 71.2%. Ca in desulfurized gypsum 2+ has hydrophilicity, which can promote the flocculation of soil colloids, thus improving the soil structure and increasing the water infiltration rate. Due to the large particle size and low water absorption of the gasification slag treatment (Table 2), it can also increase the soil infiltration rate. Coal gangue has developed pores itself, and after physical grinding, its surface area can be increased. When the particle size becomes smaller, its surface free energy increases and its activity increases, so it has high water absorption performance and can intercept water at the interlayer to reduce the infiltration time and infiltration rate.

[0055] Compared with the CK treatment, the leachate volumes of the coal-based solid waste treatments decreased by 50.5%, 88.2%, 26.6%, and 23.2% respectively, indicating that more water in the coal-based solid waste treatments was retained in the soil column. From the soil profile water storage of different treatments ( Figure 4As can be seen, coal-based solid waste treatment can significantly increase the water content of different soil layers, and it still has a significant water retention effect with increasing evaporation time. The interlayers of FGDG, CG, and GS are distributed in the 25-30cm depth. As shown in the figure, the water content of this soil layer treated with coal-based solid waste is significantly higher than that of the control (CK) treatment. After 5 days of evaporation, compared with the CK treatment, the soil water storage of FGDG, CG, and GS increased by 21.1%, 26.5%, and 7.1% in the 0-25cm soil layer, respectively; by 16.9%, 34.0%, and 25.8% in the 25-30cm soil layer, respectively; and by a decreasing trend in the 30-35cm soil layer, decreasing by 0.5%, 9.5%, and 17.4%, respectively. After 30 days of evaporation, compared with the control (CK) treatment, the soil water storage capacity of FGDG, CG, and GS increased by 26.9%, 31.6%, and 26.7% in the 0-25cm soil layer, respectively; by 58.3%, 106.8%, and 29.5% in the 25-30cm soil layer; and by 33.6%, 35.0%, and 13.5% in the 30-35cm soil layer. In the initial stage of evaporation, more water was retained in and above the coal-based solid waste interlayer. As the evaporation time increased, the water retained in the coal-based solid waste interlayer replenished the upper and lower soil layers, thus increasing the soil moisture content. The coal gangue (CG) treatment showed the best water retention effect, followed by the desulfurized gypsum (FGDG) treatment. In the D-FGDG treatments, the interlayers were located at 15-17.5cm and 27.5-30cm, respectively. Figure 4 It can be clearly seen that the water content above and below the interlayer and between the two interlayers is higher than that at the interlayer, indicating that the double-layer treatment can not only replenish water, but also increase the soil water content between the interlayers through the barrier effect.

[0056] (2) Impact on soil salinity index like Figure 5 The figure shows the pH of soil profiles treated with different coal-based solid waste interlayers. Compared with the control (CK) treatment, the FGDG and D-FGDG treatments significantly reduced the soil profile pH. The GS treatment showed no significant difference in soil pH compared to the CK treatment. The CG treatment showed an increasing trend in the 0-20cm soil layer compared to the CK treatment. After 5 days of evaporation, compared with the CK treatment, the FGDG treatment reduced soil pH by 0.2 units in the 0-25cm soil layer and by 0.6 units in the 25-30cm soil layer; the FGDG and CG treatments reduced pH by 0.4 and 0.2 units, respectively, in the 30-35cm soil layer. After 30 days of evaporation, the FGDG treatment reduced soil pH by 0.2 units; the FGDG, CG, and GS treatments reduced pH by 0.7, 0.1, and 0.1 units, respectively, in the 25-30cm soil layer; and the FGDG and CG treatments reduced pH by 0.5 and 0.3 units, respectively, in the 30-35cm soil layer.

[0057] Figure 6Sodium adsorption ratio (SAR) in soil profiles treated with different coal-based solid waste interlayers is shown. Compared with the control (CK) treatment, the desulfurized gypsum treatment significantly reduced soil SAR, the GS treatment showed no significant difference in soil SAR compared with CK, while the CG treatment showed a significantly higher soil SAR than CK in the 25-30 cm interlayer. After 5 days of evaporation, compared with CK, in the 0-25 cm soil layer, the SAR of FGDG and GS treatments decreased by 43.0% and 2.4%, respectively, while the CG treatment increased by 17.7%; in the 25-30 cm soil layer, the SAR of FGDG and GS treatments decreased by 76.0% and 20.0%, respectively, while the CG treatment increased by 231.3%; in the 30-35 cm soil layer, the SAR of FGDG treatment decreased by 50.1%, while the CG and GS treatments increased by 61.7% and 15.5%, respectively. After 30 days of evaporation, compared with the control (CK) treatment, in the 0-25cm soil layer, the soil SAR of the FGDG, CG, and GS treatments decreased by 34.6%, 0.8%, and 11.3%, respectively; in the 25-30cm soil layer, FGDG reduced the SAR by 70.6%, while CG and GS treatments increased it by 245.7% and 14.6%, respectively; in the 30-35cm soil layer, FGDG and GS treatments reduced the SAR by 62.9% and 1.4%, respectively, while CG increased it by 15.6%. The overall soil profile SAR of the D-FGDG treatment was lower than that of the CK treatment and also lower than that of the FGDG treatment.

[0058] As soil depth increases, the pH and SAR of soil treated with desulfurized gypsum gradually decrease, which is related to the Ca content in the desulfurized gypsum. 2+ It is related to the migration of Ca. 2+ Able to replace Na on soil colloids + and CO3 in the soil 2- and HCO3 - The reaction forms CaCO3 precipitate, which significantly reduces soil pH and sodium adsorption ratio. Figure 8 d in Ca 2+ and HCO3 - The significant negative correlation also proves the above point.

[0059] Figure 7 The electrical conductivity (EC) of soil profiles under different coal-based solid waste interlayer treatments is shown. Coal-based solid waste interlayer treatments increased soil EC values, with the desulfurized gypsum treatment showing the largest increase. Compared to the control (CK) treatment, after 5 days of evaporation, the overall soil EC values ​​of the FGDG and D-FGDG treatments increased by 206.5% and 344.4%, respectively; after 30 days of evaporation, the increases were 172.4% and 213.0%, respectively. The increase in soil EC values ​​was related to soil moisture content and calcium content. 2+ and Na + Correlation analysis showed a significant positive correlation between soil EC values ​​and these three indicators. Increased soil moisture content promotes salt dissolution, thereby increasing soil EC values. Coal-based solid waste contains a certain amount of Ca. 2+ Especially in desulfurized gypsum, this will increase the amount of exogenous Ca. 2+ This leads to an increase in soil EC values; while Na + The increase is mainly due to leaching and dissolution of the solution and Ca. 2+ The increase is due to the replacement of organic matter. Although the treatment of coal-based solid waste interlayers increases the soil EC value, it is mainly located in the interlayer, and the D-FGDG treatment, which has the highest increase, has an average EC value of less than 1300 µS / cm, which is sufficient for the growth of most crops and will not affect plant growth.

[0060] Example 2 Based on the water retention effect of double-layer sponge layer experiments, this embodiment addresses the problems of salt accumulation and low soil moisture content in arid areas of Northwest China by conducting pot experiments. The double-layer structure is used to adjust the water and salt distribution in the soil profile, forming a high-water, low-salt layer on the soil surface that is conducive to crop growth.

[0061] Experimental treatments: The experimental site was located in the outdoor greenhouse of the laboratory at the Tsinghua University Research Center for Ecological Restoration and Carbon Sequestration of Saline-Alkali Land. A total of 8 treatments were set up (e.g., ...). Figure 2 As shown in the figure, the treatments are as follows: T1 (single-layer FGDG, 3cm depth, 2cm thickness), T2 (single-layer FGDG, 3cm depth, 5cm thickness), T3 (double-layer FGDG, 3cm depth, 2cm thickness, 10cm depth, 5cm thickness), T4 (double-layer FGDG, surface layer thickness 2cm, 10cm depth, 5cm thickness), T5 (double-layer FGDG, 3cm depth, 2cm thickness, 10cm depth, 2cm thickness), T6 (double-layer coal gangue, 3cm depth, 2cm thickness, 10cm depth, 5cm thickness), and T7 (double-layer coal gangue, 3cm depth, 2cm thickness, 10cm depth, 2cm thickness), with each treatment repeated three times. To simulate arid climate, the experiment was conducted in summer on August 4, 2025, and the plants were placed in a greenhouse to increase soil evaporation. The experiment used transparent flower pots with a diameter of 10cm and a height of 30cm. On the first day of potting, water was added only according to the field water holding capacity of the soil in the control treatment (12.46%). After 10 days of evaporation, alfalfa was sown, with 10 seeds per pot. At the same time, water was added according to the field water holding capacity of the top 3cm of soil. Subsequent irrigation was carried out after the crops emerged. If wilting occurred, irrigation was carried out according to the field water holding capacity of the top 3cm of soil.

[0062] Sample collection and index testing The flowerpots were weighed on days 3, 6, 8, 10, and 15 of the experiment to determine soil moisture evaporation. Soil samples were collected on August 19, 15 days after the start of the experiment, at depths of 0-5, 5-10, 10-15, and 15-20 cm. The collected samples were then tested for salinity and alkalinity using the same method as in Example 1.

[0063] Results Analysis (1) Effects on soil evaporation and moisture content like Figure 9 As shown, compared with the CK treatment, the cumulative soil moisture evaporation of the T2 (FGDG single layer, 3cm depth, 5cm thickness), T3 (FGDG double layer, 3cm depth, 2cm thickness, 10cm depth, 5cm thickness), T4 (FGDG double layer, surface layer thickness 2cm, 10cm depth, 5cm thickness), T5 (FGDG double layer, 3cm depth, 2cm thickness, 10cm depth, 2cm thickness), T6 (coal gangue double layer, 3cm depth, 2cm thickness, 10cm depth, 5cm thickness), and T7 (coal gangue double layer, 3cm depth, 2cm thickness, 10cm depth, 2cm thickness) treatments were significantly reduced, by 15.0%, 15.9%, 6.4%, 33.6%, and 21.7%, respectively. Moreover, the moisture evaporation of the coal gangue treatment was lower than that of the desulfurization gypsum treatment.

[0064] Figure 10 Soil water storage in different soil layers was measured for different treatments. Compared with the control (CK) treatment, in the 0-5cm soil layer, except for the T4 treatment (FGDG double-layer, surface thickness 2cm, depth 10cm, thickness 5cm), the soil water storage increased in all other treatments, with the T7 treatment showing the largest increase at 54.2%, followed by the T6 treatment; in the 5-10cm soil layer, only the T7 treatment showed an increase in soil water storage of 3.8%; in the 10-15cm soil layer, except for the T1 treatment, the soil water storage increased in all other treatments, with the T6 treatment showing the largest increase at 117.0%; in the 15-20cm soil layer, the soil water storage in all treatments was lower than that in the CK treatment, with the T6 treatment showing the largest decrease at 34.8%. Regarding the overall water storage in the potted plants, except for the T1 and T4 treatments, the total water storage in all other treatments was higher than that in the CK treatment, with the T2, T3, T6, and T7 treatments showing significant differences, corresponding to changes in cumulative evaporation.

[0065] The soil moisture content at a depth of 15-20 cm was lower in all interlayer treatments than in the control (CK) treatment, which is related to the interlayer treatments above the 15 cm soil layer. Among the different interlayer treatments, treatment T6 had the lowest soil evaporation and the highest water storage, which is related to the strong water absorption of coal gangue. Treatments T2 and T3 in the desulfurization gypsum treatment also showed good evaporation reduction and water retention effects.

[0066] (2) Impact on soil salinity index like Figure 11As shown in Figure a, all desulfurized gypsum interlayer treatments significantly reduced soil pH, with treatment T3 showing the largest reduction of 0.8 units. The soil pH of the coal gangue interlayer treatment did not differ significantly from the control (CK). In the 0-10cm soil layer, all coal-based solid waste interlayer treatments significantly reduced soil SAR. Compared to the CK treatment, in the 0-5cm soil layer, the soil SAR of treatments T1-T7 decreased by 80.9%, 48.1%, 83.6%, 85.2%, 68.6%, 41.4%, and 24.8%, respectively; in the 5-10cm soil layer, the soil SAR of treatments T1-T7 decreased by 84.7%, 80.8%, 86.6%, 78.5%, 87.1%, 38.6%, and 31.4%, respectively. In the 10-20cm soil layer, the soil SAR of the desulfurized gypsum interlayer treatment was significantly lower than that of the CK treatment, while the soil SAR of the coal gangue interlayer treatment was higher than that of the CK treatment, with treatment T6 showing a significant difference. In terms of the overall reduction in SAR of the soil profile, the T3 treatment showed the largest reduction, at 80.0%. The effect of desulfurized gypsum on improving soil pH and SAR in the pot experiment was consistent with that in the leaching experiment.

[0067] Desulfurized gypsum interlayer treatment effectively reduced soil alkalization index, but simultaneously increased soil EC value, which is related to the dissolution of desulfurized gypsum. Coal gangue interlayer treatment reduced soil EC values ​​in the 0-5cm and 15-20cm soil layers, but increased EC values ​​in the 5-15cm soil layer, which is related to the location of the coal gangue interlayer in this soil layer. From the overall soil profile, the soil EC values ​​of treatments T1-T5 were significantly higher than those of the control (CK) treatment, while there was no significant difference in soil EC values ​​between treatments T6 and T7. Table 3 shows the ion concentrations in different soil layers for different treatments. All coal-based solid waste interlayer treatments increased soil water-soluble potassium (K). + The ion content showed the largest overall increase in the T6 treatment, which is related to the K content in coal gangue. + High content is related. Coal-based solid waste interlayer treatment can reduce soil Na content by 0-5 cm. + The Na content in the soil was significantly different between treatment T4 and control (CK). Across the entire soil profile, treatments T1, T3, T4, and T5 showed significantly different Na content. + The content of Na in the T6 treatment was lower than that in the CK treatment. + The content was significantly higher than the control treatment by 38.1%. Compared with the CK treatment, the water-soluble Ca content in each soil layer of treatments T1-T5 was significantly higher. 2+ The content of all treatments increased significantly, with the T3 treatment showing the largest increase; the T6 and T7 treatments reduced the water-soluble Ca content in the 0-5 cm and 15-20 cm soil layers, respectively. 2+ The content increased by 5-15 cm of water-soluble Ca. 2+ The content was not statistically significant. Water-soluble Mg in different soil layers was also observed. 2+ Content and water-soluble Ca 2+The content changes showed a consistent trend. Treatments T1-T3 reduced water-soluble HCO3 in different soil layers. - The content of water-soluble HCO3 in the soil layer was reduced by 5-20 cm after treatments T4 and T5. - Content, but water-soluble HCO3 content varies between different treatments. - The content difference was not significant.

[0068] Table 3. Soil water-soluble ion concentrations in different soil layers under different treatments.

[0069] Note: Different letters in the table represent significant differences between different treatments in the same soil layer. P <0.05).

[0070] (3) Impact on crop growth To simulate arid climate, on the first day of potted plant cultivation, water was added only according to the field water holding capacity of the soil in the control treatment (12.46%). After 10 days of evaporation, alfalfa was sown, and water was added at the same time according to the field water holding capacity of the top 3cm of soil. Five days after sowing, the emergence rates of treatments T6 and T7 were 25% and 35%, respectively, while no seedlings emerged in the other treatments. Subsequently, seedlings also emerged in treatment T3. This indicates that under arid conditions, treatments T3 (FGDG double-layer, 3cm depth, 2cm thickness, 10cm depth, 5cm thickness), T6 (coal gangue double-layer, 3cm depth, 2cm thickness, 10cm depth, 5cm thickness), and T7 (coal gangue double-layer, 3cm depth, 2cm thickness, 10cm depth, 2cm thickness) have good water retention effects and can ensure crop emergence.

[0071] In summary, all coal-based solid waste treatments can achieve water retention, with coal gangue interlayer treatment showing the best water retention effect and desulfurization gypsum treatment showing the best alkali reduction effect. Although coal-based solid waste interlayer treatment can increase soil salinity, this salinity will not affect crop growth. Furthermore, double-layer desulfurization gypsum treatment can replenish moisture between the upper and lower layers and maintain moisture in the space between the layers.

[0072] Based on the desulfurized gypsum and coal gangue interlayer materials screened by leaching test, the water retention and alkali reduction effects of the two materials under different interlayer treatments were compared and analyzed. It was found that the two materials had better water retention and alkali reduction effects when interlayer treatments were set with "depth of 3cm and thickness of 2cm" and "depth of 10cm and thickness of 5cm", respectively.

[0073] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A sponge-like water-retaining structure based on coal-based solid waste, characterized in that, The water-retaining structure includes at least one water-retaining layer made of coal-based solid waste material; the water-retaining layer is horizontally embedded in the topsoil, with a predetermined thickness and a predetermined burial depth; the coal-based solid waste material is selected from one or more of coal gangue, desulfurization gypsum, and gasification slag.

2. The sponge water-retaining structure according to claim 1, characterized in that, The component contents of the coal-based solid waste are as follows:

3. The sponge water-retaining structure according to claim 1, characterized in that, The thickness of the water-retaining barrier is 1-10cm.

4. The sponge water-retaining structure according to claim 1, characterized in that, The water-retaining barrier is buried at a depth of 5-30cm from the ground surface.

5. The sponge water-retaining structure according to claim 1, characterized in that, The water-retaining structure includes two water-retaining layers, an upper layer and a lower layer, forming a double-layer sponge water-retaining structure.

6. The sponge water-retaining structure according to claim 5, characterized in that, The upper partition is buried at a depth of 2-5cm and a thickness of 1-3cm; the lower partition is buried at a depth of 8-12cm and a thickness of 2-6cm.

7. The method for constructing the sponge water-retaining structure according to any one of claims 1-6, characterized in that, Includes the following steps: (1) The coal-based solid waste is crushed and screened to obtain coal-based solid waste material with a predetermined particle size; (2) In the soil area to be treated, excavate a soil profile to a predetermined depth; (3) At a predetermined depth in the soil profile, a layer of coal-based solid waste material prepared in step (1) is evenly laid to form a water-retaining barrier layer; (4) Backfill the original soil or imported soil on top of the laid water-retaining layer until the ground surface is reached, and compact it.

8. The construction method according to claim 7, characterized in that, The pH, TDS, particle size, volume, and saturated moisture content of the coal-based solid waste material are shown below:

9. The application of the sponge water-retaining structure according to any one of claims 1-6 in ecological restoration or saline-alkali land improvement in arid and semi-arid regions.

10. The application according to claim 9, characterized in that, When the coal-based solid waste material is desulfurized gypsum, it can be used to prepare a sponge-like water-retaining structure that improves soil alkalinity and reduces sodium adsorption ratio; when the coal-based solid waste material is coal gangue, it can be used to prepare a sponge-like water-retaining structure that provides excellent water absorption performance.

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