Desert soil salt-resistant water-retaining material, preparation method thereof and salt-resistant water-retaining method using the same

Abstract

This application relates to the field of degraded soil improvement and remediation technology, and particularly to a desert soil salt-barrier and water-retaining material, its preparation method, and a method for salt-barrier and water-retaining using the desert soil salt-barrier and water-retaining material. The material comprises coal gangue and industrial gypsum solid waste; the coal gangue includes organic matter and clay minerals, with the organic matter comprising less than 30% of the coal gangue mass and the clay minerals comprising more than 50% of the coal gangue mass; the industrial gypsum solid waste is hemihydrate gypsum obtained by drying and dehydrating desulfurized gypsum, with a purity of not less than 90%, and the mass ratio of coal gangue to hemihydrate gypsum is (80~100):(10~20); the pH value of the desert soil salt-barrier and water-retaining material is weakly acidic to neutral. Therefore, the raw materials for this material can be sourced locally, resulting in low production costs. Furthermore, this material not only retains water but also effectively inhibits topsoil alkali return, enhancing the soil's buffering capacity against salinity and alkali.

Description

Technical Field

[0001] This application relates to the field of degraded soil improvement and remediation technology, and in particular to a desert soil salt-barrier and water-retaining material, its preparation method, and a method for salt-barrier and water-retaining using the desert soil salt-barrier and water-retaining material. Background Technology

[0002] Saline soil is widely distributed in the arid northwest region. It is a hard, compacted layer formed by soluble salts such as sodium chloride and sodium sulfate, mainly appearing from the surface to a soil depth of 100 cm. The presence of underlying saline soil layers in desert areas triggers a series of water and salt transport disorders: on the one hand, irrigation water infiltration erodes the saline soil layer, leading to soil collapse and a significant reduction in water resource utilization; on the other hand, intense evaporation causes salts to migrate upwards with water, ultimately leading to salt accumulation and alkali reversion in the topsoil. These water and salt transport disorders are the core reason why desert soil restoration and greening projects in this region require large investments but yield poor results. Traditional methods such as soil replacement or the use of soil conditioners cannot fundamentally solve this problem.

[0003] In related technologies, not only can coal gangue, carboxymethyl cellulose, and magnesium phosphate cement be used to make water-retaining materials, which can be calcined and activated to improve water retention, but also multi-layered structures can be constructed, with an impermeable layer, a salt barrier layer, a membrane layer, and a planting layer arranged sequentially from bottom to top. Straw, bentonite, diatomaceous earth, and activated silica can also be pressed into partitions. Furthermore, cement and alkaline soil stabilizers can be added to coal gangue to create impermeable materials. However, while water-retaining materials composed of coal gangue, carboxymethyl cellulose, and magnesium phosphate cement can improve water retention, they cannot solve the core problem of salt barrier. Multi-layered improvement systems can achieve salt and alkali barrier effects, but the process is complex and the material cost is high. The preparation of straw-based partitions not only faces the problem of difficult raw material acquisition but also suffers from excessively high process costs. Coal gangue-based impermeable materials not only have high preparation costs, but their alkaline components can further exacerbate soil salinization. Summary of the Invention

[0004] This application is made in view of the above-mentioned issues.

[0005] According to one aspect of this application, a desert soil salt-barrier and water-retaining material is provided, comprising: Coal gangue and industrial gypsum solid waste; the coal gangue includes organic matter and clay minerals, wherein the mass of the organic matter is less than 30% of the mass of the coal gangue, and the mass of the clay minerals is greater than 50% of the mass of the coal gangue; the industrial gypsum solid waste is hemihydrate gypsum obtained by drying and dehydrating desulfurized gypsum, wherein the purity of the hemihydrate gypsum is not less than 90%, and the mass ratio of the coal gangue to the hemihydrate gypsum is (80~100):(10~20); the pH value of the desert soil salt-proof and water-retaining material is weakly acidic to neutral.

[0006] Compared with existing technologies, the desert soil salt-barrier and water-retaining material provided in this application includes coal gangue and industrial gypsum solid waste. The coal gangue is solid waste from coal mining and washing, and the hemihydrate gypsum is derived from desulfurized gypsum through drying and dehydration. Both are industrial wastes, requiring no additional procurement costs, thus achieving near-zero raw material costs. Furthermore, this type of industrial solid waste is abundant around coal and power industries in the arid saline-alkali soil distribution areas of Northwest China, allowing for local supply and significantly reducing the additional costs of raw material transportation and storage, ensuring the feasibility of large-scale application of the material.

[0007] The coal gangue in this application includes organic matter and clay minerals, with the organic matter comprising less than 30% of the coal gangue mass and the clay minerals comprising more than 50% of the coal gangue mass. The industrial gypsum solid waste is hemihydrate gypsum obtained by drying and dehydrating desulfurized gypsum, with a purity of not less than 90%. The low organic matter content prevents material structure damage and performance degradation caused by organic matter decomposition. The high proportion of clay minerals, with their layered structure and large specific surface area, can form a large number of pores to store water and adsorb and retain salt ions through ion exchange, thus solidifying the foundation for water retention and salt barrier. The dried hemihydrate gypsum with a purity of not less than 90% is used as a cementing component and is mixed with coal gangue in a mass ratio of (80~100):(10~20). It can react under the action of irrigation water infiltration or natural precipitation to form a stable cementing structure, improve the overall strength of the material, and further enhance the barrier effect against salt ions. Hemihydrate gypsum and its hydration product, dihydrate gypsum, have poor impermeability. Excessive admixture can lead to excessive volume expansion, damaging the salt-barrier waterproofing layer structure and causing cracks. Insufficient admixture prevents the hydration products from fully filling the voids between coal gangue particles, hindering the formation of a continuous cementitious skeleton. This results in a significant decrease in the compaction density and an abnormally high porosity, reducing the material's mechanical strength and making it prone to cracking and collapse under desert winds and rainfall. It also damages the water-retaining structure of the pores, causing rapid water leakage and a significant decrease in water retention. Furthermore, insufficient admixture greatly reduces the material's ability to retain salt ions, failing to effectively prevent the upward migration of salt from the underground salt bed layer and inhibiting topsoil efflorescence, essentially rendering the salt barrier function ineffective. Furthermore, coal gangue itself is weakly acidic and contains sulfides, which produce acid upon oxidation. When combined with hemihydrate gypsum, the material becomes weakly acidic to neutral overall. This acid-base property can neutralize the alkaline environment in desert saline soil areas and effectively inhibit the re-alkaliing of topsoil. In addition, the high proportion of clay minerals in coal gangue has ion exchange properties, and the hydrated hemihydrate gypsum can also retain salt ions through ion adsorption. The two work together to enhance the soil's buffering capacity against salinity and alkali, thus solving the core problem of disordered water and salt transport in desert soil from a chemical mechanism perspective.

[0008] Therefore, the raw materials for the desert soil salt-retaining and water-conserving material provided in this application can be sourced locally, resulting in lower production costs. Furthermore, this material not only retains water but also effectively inhibits topsoil efflorescence, enhancing the soil's buffering capacity against salinity and alkali.

[0009] According to another aspect of this application, a method for preparing a desert soil salt-barrier and water-retaining material is provided, comprising: The desulfurized gypsum is dried and dehydrated to obtain hemihydrate gypsum; the purity of the hemihydrate gypsum is not less than 90%. Coal gangue and hemihydrate gypsum are crushed and sieved in a mass ratio of (80~100):(10~20) to obtain desert soil salt-resistant and water-retaining material; the pH value of the desert soil salt-resistant and water-retaining material is weakly acidic to neutral; the coal gangue includes organic matter and clay minerals, the mass of the organic matter is less than 30% of the mass of the coal gangue, and the mass of the clay minerals is greater than 50% of the mass of the coal gangue.

[0010] According to another aspect of this application, a method for salt and water isolation and retention using the above-mentioned desert soil salt-isolation and water-retention material is provided, comprising: The topsoil of the desert soil is stripped to the pre-designed construction surface, and the desert soil salt-proof and water-retaining material is laid on the pre-designed construction surface and compacted to form a salt-proof and water-retaining layer. The topsoil is backfilled onto the salt-barrier and water-retaining layer.

[0011] Compared with the prior art, the beneficial effects of the preparation method of the desert soil salt-barrier and water-retaining material and the salt-barrier and water-retaining method using the desert soil salt-barrier and water-retaining material provided in this application are the same as the beneficial effects of the desert soil salt-barrier and water-retaining material mentioned above, and will not be repeated here.

[0012] It should be understood that both the foregoing general description and the following detailed description are exemplary and intended to provide further illustration of the claimed technology. Attached Figure Description

[0013] The above and other objects, features, and advantages of this application will become more apparent from the more detailed description of the embodiments of this application in conjunction with the accompanying drawings. The accompanying drawings are used to provide a further understanding of the embodiments of this application and form part of the specification. They are used together with the embodiments of this application to explain this application and do not constitute a limitation thereof. In the accompanying drawings, the same reference numerals generally represent the same components or steps.

[0014] Figure 1 A flowchart illustrating the preparation method of the desert soil salt-barrier and water-retaining material according to an embodiment of this application is shown; Figure 2 A flowchart of a salt-barrier and water-retaining method using desert soil salt-barrier and water-retaining materials, according to an embodiment of this application, is shown. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this application more apparent, exemplary embodiments according to this application will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments of this application. It should be understood that this application is not limited to the exemplary embodiments described herein.

[0016] Saline soil is widely distributed in the arid northwest of my country. It is a hard, compacted layer formed by soluble salts such as sodium chloride and sodium sulfate, mainly appearing from the surface to a soil depth of 100 cm. The presence of underlying saline soil layers in desert areas triggers a series of water and salt transport disorders: on the one hand, irrigation water infiltration can dissolve the saline soil layer, leading to soil collapse and a significant reduction in water resource utilization; on the other hand, intense evaporation can cause salts to migrate upwards with water, ultimately leading to salt accumulation and alkalinity in the topsoil. These water and salt transport disorders are the core reason why desert soil restoration and greening projects in this region require large investments but yield poor results. Traditional methods such as soil replacement or the use of soil conditioners cannot fundamentally solve this problem.

[0017] In related technologies, not only can coal gangue, carboxymethyl cellulose, and magnesium phosphate cement be used to make water-retaining materials, which can be calcined and activated to improve water retention, but also multi-layered structures can be constructed, with an impermeable layer, a salt barrier layer, a membrane layer, and a planting layer arranged sequentially from bottom to top. Straw, bentonite, diatomaceous earth, and activated silica can also be pressed into partitions. Furthermore, cement and alkaline soil stabilizers can be added to coal gangue to create impermeable materials. However, while water-retaining materials composed of coal gangue, carboxymethyl cellulose, and magnesium phosphate cement can improve water retention, they cannot solve the core problem of salt barrier. Multi-layered improvement systems can achieve salt and alkali barrier effects, but the process is complex and the material cost is high. The preparation of straw-based partitions not only faces the problem of difficult raw material acquisition but also suffers from excessively high process costs. Coal gangue-based impermeable materials not only have high preparation costs, but their alkaline components can further exacerbate soil salinization.

[0018] To address the aforementioned problems, this application provides a desert soil salt-barrier and water-retaining material. The raw materials for this material can be sourced locally, resulting in low production costs. Furthermore, this material not only retains water but also effectively inhibits topsoil alkali return, enhancing the soil's buffering capacity against salinity and alkali. This desert soil salt-barrier and water-retaining material comprises coal gangue and industrial gypsum solid waste. The coal gangue includes organic matter and clay minerals, with the organic matter comprising less than 30% of the coal gangue's mass and the clay minerals comprising more than 50% of the coal gangue's mass. The industrial gypsum solid waste is hemihydrate gypsum obtained by drying and dehydrating desulfurized gypsum, with a purity of not less than 90%. The mass ratio of coal gangue to hemihydrate gypsum is (80~100):(10~20). The pH value of the desert soil salt-barrier and water-retaining material is weakly acidic to neutral.

[0019] It is understandable that the arid region described in this application has virtually no groundwater replenishment, relying instead on top-down irrigation water or natural precipitation. When irrigation water infiltrates or natural precipitation occurs, the raw materials in this application can react to form a stable cementitious structure. Furthermore, the coal gangue contained in this material is solid waste from coal mining and washing, and the hemihydrate gypsum is derived from desulfurized gypsum through drying and dehydration. Both are industrial wastes, requiring no additional procurement costs, thus achieving near-zero raw material costs. Simultaneously, such industrial solid wastes are abundant around coal and power industries in the arid saline-alkali soil distribution areas of Northwest China, allowing for local supply and significantly reducing the additional costs of raw material transportation and storage, ensuring the feasibility of large-scale application of the material.

[0020] The coal gangue in this application includes organic matter and clay minerals, with the organic matter comprising less than 30% of the coal gangue mass and the clay minerals comprising more than 50% of the coal gangue mass. The industrial gypsum solid waste is hemihydrate gypsum obtained by drying and dehydrating desulfurized gypsum, with a purity of not less than 90%. The low organic matter content prevents material structure damage and performance degradation caused by organic matter decomposition. The high proportion of clay minerals, with their layered structure and large specific surface area, can form a large number of pores to store water and adsorb and retain salt ions through ion exchange, thus solidifying the foundation for water retention and salt barrier. The desulfurized gypsum dried hemihydrate gypsum with a purity of not less than 90% is used as a cementing component. When mixed with coal gangue at a mass ratio of (80~100):(10~20), it can react under the action of irrigation water infiltration or natural precipitation to form a stable cementing structure, improving the overall strength of the material and further enhancing the barrier effect against salt ions. Hemihydrate gypsum and its hydration product, dihydrate gypsum, have poor impermeability. Excessive admixture can lead to excessive volume expansion, causing structural damage to the salt-barrier waterproofing layer, such as cracks. Insufficient admixture prevents the hydration products from fully filling the voids between coal gangue particles, hindering the formation of a continuous cementitious skeleton. This results in a significant decrease in the compaction density and an abnormally high porosity, reducing the material's mechanical strength and making it prone to cracking and collapse under desert winds and rainfall. It also damages the water-retaining structure of the pores, leading to rapid water leakage and a significant decrease in water retention. Furthermore, insufficient admixture greatly reduces the material's ability to retain salt ions, failing to effectively prevent the upward migration of salt from the underground salt bed layer with water, making it difficult to suppress surface alkali return, and essentially rendering the salt barrier function ineffective. Furthermore, coal gangue itself is weakly acidic and contains sulfides, which produce acid upon oxidation. When combined with hemihydrate gypsum, the material becomes weakly acidic to neutral overall. This acid-base property can neutralize the alkaline environment in desert saline soil areas and effectively inhibit the re-alkaliing of topsoil. In addition, the high proportion of clay minerals in coal gangue has ion exchange properties, and the hydrated hemihydrate gypsum can also retain salt ions through ion adsorption. The two work together to enhance the soil's buffering capacity against salinity and alkali, thus solving the core problem of disordered water and salt transport in desert soil from a chemical mechanism perspective.

[0021] In one alternative embodiment, the clay minerals in this application include at least one of kaolinite, chlorite, illite, montmorillonite, and illite-montmorillonite mixed-layer minerals. First, these clay minerals provide water storage space and lock in moisture through capillary action, forming the physical basis for the water retention performance of desert soil salt-barrier and water-retaining materials. Furthermore, the bonding and interweaving between the clay mineral particles provide structural support for the coal gangue and hemihydrate gypsum composite system, enhancing the overall compressive and weathering resistance of the material and ensuring its structural stability in desert environments. Second, they all contain exchangeable cations (such as potassium, sodium, calcium, and magnesium ions), which can undergo ion exchange reactions with salt ions in desert soil, trapping salt ions in the mineral layers or pores, preventing salt from migrating upwards with water and causing topsoil alkali return. Simultaneously, the adsorbed salt ions can reduce the salt concentration in the soil solution, enhancing the soil's salt-alkali buffering capacity. Moreover, these clay minerals are all hydrous silicate substances, and their chemical properties are compatible with the hydration environment of hemihydrate gypsum. They will not react adversely with the hydration product of hemihydrate gypsum, gypsum dihydrate. On the contrary, they can promote the hydration reaction of gypsum through the active sites on the mineral surface, and strengthen the interfacial bond between coal gangue and hemihydrate gypsum.

[0022] In one alternative embodiment, the hemihydrate gypsum in this application includes at least one of α-hemihydrate gypsum and β-hemihydrate gypsum. The effect is optimal when only α-hemihydrate gypsum is used. Both α-hemihydrate gypsum and β-hemihydrate gypsum can generate dihydrate gypsum crystals during hydration, which interweave with clay minerals in coal gangue to form a continuous cementitious skeleton. This not only improves the compressive strength and weathering resistance of the material, but also optimizes the water storage structure by filling pores through crystal growth. Simultaneously, the hydration products can adsorb salt ions to assist in salt separation. However, α-hemihydrate gypsum is a short columnar crystal prepared by crystallization of salt solution under normal pressure or by high-pressure steam. It has higher crystallinity and more complete grains. The structural density formed after hydration is far superior to the needle-like crystal structure of β-hemihydrate gypsum. This not only significantly improves the mechanical strength of the material, but also forms a more uniform microporous network, greatly enhancing water retention efficiency and salt ion retention capacity. β-hemihydrate gypsum, as a dried product of desulfurization gypsum in power plants, has basic cementing and auxiliary salt-barrier and water-retaining effects, but its crystal structure is loose and its material performance is weaker than that of α-hemihydrate gypsum. Therefore, when only α-hemihydrate gypsum is used, the material can achieve the best state in terms of structural stability, water retention efficiency and salt barrier effect, making it more suitable for the stringent requirements of desert soil salt pan management.

[0023] In an alternative embodiment, the permeability coefficient k of the desert soil salt-barrier and water-retaining material in this application is less than 1×10 when the compaction degree reaches 95%. -5The extremely low permeability coefficient (cm / s) signifies excellent seepage prevention and water-blocking properties, effectively slowing the infiltration rate of irrigation water or natural precipitation, reducing water loss into the underground saline-alkali soil layer, and simultaneously creating a stable water storage space within the material layer. This improves water resource utilization in desert soil areas and solves the problems of poor water retention and easy water leakage in desert soil. On the other hand, the slow infiltration of water significantly reduces the erosion effect on the saline-alkali soil layer, preventing soil structure damage due to erosion and collapse. It also blocks the upward migration of underground salt ions with the infiltrated water flow, inhibiting topsoil salt accumulation and alkali return from the source of water and salt transport, alleviating the core contradiction of disordered water and salt transport in desert soil. Furthermore, this permeability coefficient matches a compaction degree of 95%, ensuring the density and structural stability of the material layer, enabling it to adapt to the harsh environment of desert areas. The low permeability also creates a physical salt-barrier and water-retaining barrier, synergistically enhancing the desert soil remediation effect with the material's chemical ion exchange for salt barrier and the water-retaining effect of clay mineral pores.

[0024] In one alternative approach, the mass of organic matter in this embodiment is less than 10% of the mass of the coal gangue. During the decomposition of organic matter, acidic or alkaline substances may be generated. Controlling its content to below 10% can maintain the acid-base compatibility between the material and the desert soil and saline soil layers, ensure the normal progress of the hemihydrate gypsum hydration reaction and the efficient functioning of the clay mineral ion exchange function. In addition, the oxidative decomposition of organic matter will also consume oxygen in the material layer and release harmful substances. A low proportion of organic matter can reduce such negative effects, reduce the interference with the soil ecology of the desert soil area, and at the same time avoid the degradation of the material's water retention and salt barrier performance caused by the decomposition of organic matter, so that the material remains effective in desert soil remediation for a long time.

[0025] This application also provides a method for preparing a desert soil salt-barrier and water-retaining material, which can produce a desert soil salt-barrier and water-retaining material with both water retention and inhibition of topsoil alkali return with a simple process and low preparation cost. Figure 1 A flowchart illustrating a method for preparing a desert soil salt-barrier and water-retaining material according to an embodiment of this application is shown. Figure 1 As shown, the preparation method includes: S101: Hemihydrate gypsum is obtained by drying and dehydrating desulfurized gypsum.

[0026] For example, the purity of the hemihydrate gypsum in this application embodiment is not less than 90%. Hemihydrate gypsum (CaSO4·1 / 2H2O) is a dehydration product of dihydrate desulfurization gypsum (CaSO4·2H2O) produced by flue gas desulfurization in coal-fired power plants, which is then dried (160-180℃). It is a cementing material with adhesive properties. During the hydraulic process, it undergoes slight volume expansion, which can further promote the compaction of coal gangue powder / fine particles. Therefore, hemihydrate gypsum can be used as an auxiliary material for coal gangue-based salt-barrier and water-retaining layers to enhance impermeability.

[0027] S102: Coal gangue and hemihydrate gypsum are crushed and sieved in a mass ratio of (80~100):(10~20) to obtain desert soil salt-proof and water-retaining material.

[0028] For example, the coal gangue in this application embodiment includes organic matter and clay minerals, wherein the mass of the organic matter is less than 30% of the mass of the coal gangue, and the mass of the clay minerals is greater than 50% of the mass of the coal gangue.

[0029] For example, in the embodiments of this application, the crushing and screening of coal gangue must balance impermeability and economic cost. Specifically, according to crushing theory, crushing is the process of reducing particle size by overcoming the cohesive force of the material with external force. Increased material fineness significantly increases system energy consumption costs. FC Bond proposed the work index to characterize the unit energy consumption (kW·h / t) required to crush or grind a unit mass of material to 80% particle size through a 100μm sieve. This index correlates crushing power consumption with material particle size parameters using the Bond formula, allowing for a quantitative assessment of ore crushability and grindability. Assuming a coal gangue particle size of 50mm from a coal washing plant, the energy consumption per ton was calculated using the Bond formula to crush to below 2mm and below 1mm. It was found that a 1mm reduction in output particle size increased energy consumption costs by more than 50%.

[0030] The Bond formula is as follows: .

[0031] When performing particle size conversion, during feeding, 50mm ≈ F 80 =70000μm (empirical coefficient × 1.4). In Product 1, 100% passing through a 2mm sieve ≈ P 80 =2800μm. In Product 2, 100% passed through a 1mm sieve ≈P 80 =1400μm. Work index of hard kaolin: Wi=10kWh / t (median, measured range 8~12kWh / t). Table 1 shows the work index of different equipment during crushing and screening.

[0032] Table 1

[0033] Therefore, from a technical and economic perspective, the fineness of coal gangue should not be reduced indefinitely in order to improve the seepage prevention effect of the salt-barrier and water-retaining layer. Instead, a feasible approach is to incorporate powdered hemihydrate gypsum with cohesive properties to fill the pores of the coal gangue powder, thereby improving the density of the structure and its tensile and shear strength.

[0034] Based on this, the sieve used in the sieving process in this application embodiment has a mesh size of 2mm to 3mm, and the particle size of the desert soil salt-retaining and water-conserving material is greater than 0 and less than or equal to 2mm.

[0035] For example, 80-100 parts of coal gangue serve as the main substrate, providing a skeletal support for the material. The clay minerals it contains can establish a foundation for water retention and salt barrier properties through their porosity and ion exchange capabilities. 10-20 parts of hemihydrate gypsum serve as a cementing component. This avoids the problems of excessive dosage leading to increased material costs or an overly dense structure affecting water retention pores, while also preventing insufficient dosage from failing to form a continuous cementitious skeleton. The gypsum dihydrate crystals generated through the hydration reaction can tightly bind the coal gangue particles, while simultaneously filling the skeletal pores and optimizing the water storage structure. During the crushing process, the coal gangue and hemihydrate gypsum are thoroughly refined and uniformly mixed, increasing their contact area and promoting a more complete hydration reaction of the hemihydrate gypsum. This allows the hydration products to be evenly distributed within the coal gangue skeleton, resulting in a uniformly structured material. Simultaneously, the fine particles generated during crushing and grinding increase the specific surface area of ​​the material, enhancing the ion exchange capacity and pore water storage efficiency of the clay minerals. Ultimately, the prepared material possesses both a stable physical structure and highly efficient salt barrier and water retention functions.

[0036] For example, the pH value of the desert soil salt-retaining and water-retaining material in the embodiments of this application is weakly acidic to neutral.

[0037] This application also provides a method for salt and water isolation and retention using desert soil salt-isolation and water-retention materials, which can isolate and retain desert soil at a lower cost. Figure 2 A flowchart illustrating a salt-barrier and water-retaining method using desert soil salt-barrier and water-retaining materials, according to an embodiment of this application, is shown. Figure 2 As shown, the salt-barrier and water-retaining structure includes: S201: Strip the topsoil of the desert soil to the pre-designed construction surface, lay desert soil salt-proof and water-retaining material on the pre-designed construction surface and compact it to form a salt-proof and water-retaining layer.

[0038] For example, this step includes: if the depth of the saline soil layer in the desert soil is less than 1 meter, peeling off the topsoil of the desert soil to expose the upper surface of the saline soil layer, laying the desert soil salt-barrier and water-retaining material on the upper surface of the saline soil layer and compacting it to form a salt-barrier and water-retaining layer. First, peeling off the topsoil to the upper surface of the saline soil layer can directly eliminate the interference of the transition layer between the loose surface soil and the saline soil layer, allowing the salt-barrier and water-retaining material to directly contact the saline soil layer, avoiding the problem of loose material laying and water and salt flow due to the presence of the transition layer, and building a stable construction base for the salt-barrier and water-retaining layer. Secondly, laying and compacting this material on the surface of the saline soil layer creates a physical seepage barrier due to its extremely low permeability coefficient. This barrier prevents irrigation water or natural rainfall from directly infiltrating and contacting the saline soil layer, significantly reducing the erosive effect of water and preventing soil collapse caused by erosion, thus protecting the stability of the desert soil's geological structure. Furthermore, this barrier cuts off the upward migration pathway of salt in the saline soil layer with water, inhibiting the accumulation of salt and alkali on the surface soil caused by upward salt movement at its source. Simultaneously, the compacted salt-barrier and water-retaining layer, relying on its own cementitious structure and the ion exchange properties of clay minerals, can both store water to improve the water resource utilization rate of desert soil and adsorb and retain a small amount of infiltrated salt ions, further enhancing the salt barrier effect. Ultimately, through the synergistic effect of physical barrier and chemical adsorption, the problem of disordered water and salt transport in shallowly buried saline soil layers in desert soil is solved.

[0039] For example, this step further includes: if the depth of the saline layer in the desert soil is greater than 1 meter, stripping the topsoil of the desert soil to a depth of 1 meter, laying the desert soil salt-barrier and water-retaining material at the 1-meter depth and compacting it to form a salt-barrier and water-retaining layer. For desert soil areas where the saline layer is deeper than 1 meter, the operation of stripping the topsoil to a depth of 1 meter and laying and compacting the salt-barrier and water-retaining material to form a salt-barrier and water-retaining layer is a targeted treatment measure tailored to the geological characteristics of this type of desert soil, playing a key role in terms of construction feasibility, water and salt regulation, and the practicality of ecological restoration. First, when the saline layer is buried deeper than 1 meter, continuing to strip it to the upper surface of the saline layer would significantly increase the amount of topsoil stripping work and construction costs, and might also damage the original soil structure of the desert soil due to excessive excavation. Stripping to a depth of 1 meter not only controls construction costs and difficulty but also precisely intercepts the migration of salt ions in that area. Secondly, a salt-barrier and water-retaining material is laid and compacted at a depth of 1 meter. Utilizing the material's low permeability coefficient, a physical barrier against water and salt is formed. This reduces the infiltration of irrigation or rainfall into deeper soil layers, storing water in the topsoil layer above 1 meter, thus improving water resource utilization. It also prevents salt from migrating upwards from deeper soil layers to the topsoil, avoiding salt accumulation and alkali reversion. Simultaneously, the compacted material layer, relying on the ion exchange properties of clay minerals, adsorbs and retains salt ions within the 1-meter soil layer, further enhancing the salt barrier effect. Furthermore, this construction method avoids touching the deep salt bed layer, minimizing disturbance to the underground soil and reducing the risk of soil structure damage caused by construction. This creates a stable soil environment for subsequent desert soil restoration and vegetation planting, balancing treatment effectiveness with engineering practicality.

[0040] For example, the thickness of the salt-barrier and water-retaining layer in this application embodiment is 30cm to 60cm. First, 30cm as the lower limit of thickness ensures that the salt-barrier and water-retaining material forms a continuous and dense barrier layer. If the thickness is less than 30cm, the material layer is easily damaged by natural forces such as wind erosion and freeze-thaw cycles in desert areas, and cannot effectively block the upward migration of salt from the saline soil layer. At the same time, insufficient water storage space will also lead to a significant decrease in water retention capacity, making it difficult to meet the basic water requirements for vegetation growth. The upper limit of 60cm thickness allows the material layer to have sufficient pore space to store more water, enhancing its adaptability to the arid desert environment. It also extends the path of salt migration through sufficient thickness, and with the ion exchange effect of clay minerals, it can more fully intercept salt ions, strengthen the salt barrier effect, and avoid the problems of excessive raw material consumption and increased construction costs due to excessive thickness, as well as the problems of poor soil permeability and impaired plant root respiration caused by excessively thick material layers. In addition, the thickness range of 30cm to 60cm matches the depth of desert topsoil stripping. Whether it is laid directly on the surface of the salt rock layer when it is shallowly buried or laid at a depth of 1 meter when it is deeply buried, the salt-barrier and water-retaining layer of this thickness can form a stable structural connection with the surrounding soil layer. It is not easy to crack or shift due to changes in soil stress, thus ensuring the long-term effectiveness of the salt-barrier and water-retaining function.

[0041] S202: Backfill the topsoil onto the salt-proof and water-retaining layer.

[0042] To verify the effectiveness of the preparation method of the desert soil salt-retaining and water-conserving material provided in the embodiments of this application, the following are examples.

[0043] Example 1 The first step involves drying and dehydrating the desulfurized gypsum to obtain hemihydrate gypsum. The hemihydrate gypsum is a dehydrated product of dihydrate desulfurized gypsum produced from flue gas desulfurization in coal-fired power plants, further dried at 160℃, with a purity of 91%.

[0044] The second step involves crushing and sieving the pretreated coal gangue and hemihydrate gypsum in a mass ratio of 80:20 to obtain a desert soil salt-resistant and water-retaining material. The organic matter in the coal gangue comprises 25% of its mass, and the clay minerals comprise 75%. A cone crusher is used for crushing, and a 2mm mesh is used for sieving.

[0045] Example 2 The first step involves drying and dehydrating the desulfurized gypsum to obtain hemihydrate gypsum. The hemihydrate gypsum is a dehydrated product of dihydrate desulfurized gypsum produced from flue gas desulfurization in coal-fired power plants, further dried at 160℃, with a purity of 92%.

[0046] The second step involves crushing and sieving the pretreated coal gangue and hemihydrate gypsum in a mass ratio of 85:15 to obtain a desert soil salt-resistant and water-retaining material. The organic matter in the coal gangue comprises 25% of its mass, and the clay minerals comprise 75%. A cone crusher is used for crushing, and a 2.5mm mesh is used for sieving.

[0047] Example 3 The first step involves drying and dehydrating the desulfurized gypsum to obtain hemihydrate gypsum. The hemihydrate gypsum is a dehydrated product of dihydrate desulfurized gypsum produced from flue gas desulfurization in coal-fired power plants, further dried at 160℃, with a purity of 95%.

[0048] The second step involves crushing and sieving the pretreated coal gangue and hemihydrate gypsum in a mass ratio of 100:10 to obtain a desert soil salt-resistant and water-retaining material. The organic matter in the coal gangue comprises 25% of its mass, and the clay minerals comprise 75%. A cone crusher is used for crushing, and a 3mm mesh is used for sieving.

[0049] The methods for determining the clay mineral content and organic matter content of coal gangue are as follows: (1) Coal gangue is crushed and ground to 200 mesh, and low-temperature coal gangue ash is obtained by oxygen plasma oxygen low-temperature ashing method; (2) XRD detection is performed on the low-temperature ash to obtain the mineral composition spectrum; (3) Based on the mass of low-temperature ash, the percentage of clay mineral mass is calculated using XRD analysis software such as Siroquant; (4) Organic matter content = 100% - low-temperature ash yield (%). The low-temperature ashing operation is carried out in accordance with GB / T 7560-2001 "Determination of Minerals in Coal".

[0050] To better demonstrate the performance of the embodiment, the above-mentioned desert soil salt-barrier and water-retaining material is laid on the upper surface of the salt rock layer when the depth of the salt rock layer is less than 1 meter, forming a 60cm salt-barrier and water-retaining layer.

[0051] Next, the compaction degree and corresponding permeability coefficient of the salt-barrier and water-retaining layers in Examples 1 to 3 were tested. The compaction degree was determined according to the ring cutter method in GB50202-2018 "Code for Acceptance of Construction Quality of Building Foundations and Substructures". The permeability coefficient k was determined using an environmental soil and rock flexible wall permeameter. The permeation sample diameter was 10 cm, the height was 10 cm, and the confining pressure was set to 20 kPa.

[0052] Table 2 shows the performance parameters of the salt-barrier and water-retaining layers made of desert soil salt-barrier and water-retaining materials in Examples 1 to 3.

[0053] Table 2

[0054] As shown in Table 2, the salt-barrier and water-retaining layers made of desert soil salt-barrier and water-retaining materials in Examples 1 to 3 of this application can effectively block the upward movement of salt in the salt rock layer and reduce the downward infiltration and erosion of water with low cost and simple process.

[0055] The above description is merely a specific embodiment of this application. Obviously, various modifications and combinations can be made without departing from the spirit and scope of this application. Accordingly, this specification and accompanying drawings are merely exemplary descriptions of this application as defined by the appended claims, and are considered to cover any and all modifications, variations, combinations, or equivalents within the scope of this application. Clearly, those skilled in the art can make various alterations and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and modifications of this application fall within the scope of the claims of this application and their equivalents, the intent of this application includes these modifications and modifications. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the protection scope of this application. Therefore, the protection scope of this application should be determined by the protection scope of the stated claims. It should also be noted that in the apparatus and method of this application, the components or steps can be disassembled and / or recombined. These disassemblies and / or recombinations should be considered equivalent solutions of this application. The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use this application. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other aspects without departing from the scope of this application. Therefore, this application is not intended to be limited to the aspects shown herein, but rather to be applied within the widest scope consistent with the principles and novel features disclosed herein. The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of this application to the forms disclosed herein. Although several exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

Claims

1. A desert soil salt-barrier and water-retaining material, characterized in that, include: Coal gangue and industrial gypsum solid waste; the coal gangue includes organic matter and clay minerals, wherein the mass of the organic matter is less than 30% of the mass of the coal gangue, and the mass of the clay minerals is greater than 50% of the mass of the coal gangue; the industrial gypsum solid waste is hemihydrate gypsum obtained by drying and dehydrating desulfurized gypsum, wherein the purity of the hemihydrate gypsum is not less than 90%, and the mass ratio of the coal gangue to the hemihydrate gypsum is (80~100):(10~20); the pH value of the desert soil salt-proof and water-retaining material is weakly acidic to neutral.

2. The desert soil salt-barrier and water-retaining material according to claim 1, characterized in that, The hemihydrate gypsum includes at least one of α-hemihydrate gypsum and β-hemihydrate gypsum.

3. The desert soil salt-barrier and water-retaining material according to claim 1, characterized in that, The permeability coefficient k of the desert soil salt-barrier and water-retaining material is less than 1×10 when the compaction degree reaches 95%. -5 cm / s.

4. The desert soil salt-barrier and water-retaining material according to claim 1, characterized in that, The mass of the organic matter is less than 10% of the mass of the coal gangue.

5. A method for preparing a desert soil salt-barrier and water-retaining material according to any one of claims 1 to 4, characterized in that, include: The desulfurized gypsum is dried and dehydrated to obtain hemihydrate gypsum; the purity of the hemihydrate gypsum is not less than 90%. Coal gangue and hemihydrate gypsum are crushed and sieved in a mass ratio of (80~100):(10~20) to obtain desert soil salt-resistant and water-retaining material; the pH value of the desert soil salt-resistant and water-retaining material is weakly acidic to neutral; the coal gangue includes organic matter and clay minerals, the mass of the organic matter is less than 30% of the mass of the coal gangue, and the mass of the clay minerals is greater than 50% of the mass of the coal gangue.

6. The method for preparing desert soil salt-barrier and water-retaining material according to claim 5, characterized in that, The sieve used in the sieving process has a mesh size of 2mm to 3mm, and the particle size of the desert soil salt-retaining and water-conserving material is greater than 0 and less than or equal to 2mm.

7. A method for salt-barrier and water-retaining using the desert soil salt-barrier and water-retaining material according to any one of claims 1 to 6, characterized in that, include: The topsoil of the desert soil is stripped to the pre-designed construction surface, and the desert soil salt-proof and water-retaining material is laid on the pre-designed construction surface and compacted to form a salt-proof and water-retaining layer. The topsoil is backfilled onto the salt-barrier and water-retaining layer.

8. The salt-barrier water-retaining method according to claim 7, characterized in that, The topsoil of the stripped desert soil is brought to a pre-designed construction surface, and the desert soil salt-barrier and water-retaining material is laid on the pre-designed construction surface and compacted to form a salt-barrier and water-retaining layer, including: If the depth of the saline soil layer in the desert soil is less than 1 meter, the topsoil of the desert soil is stripped away to expose the upper surface of the saline soil layer. The desert soil salt-barrier and water-retaining material is then laid on the upper surface of the saline soil layer and compacted to form a salt-barrier and water-retaining layer.

9. The salt-barrier and water-retaining method according to claim 8, characterized in that, The process of stripping the topsoil of the desert soil to a predetermined construction surface, laying the desert soil salt-barrier and water-retaining material on the predetermined construction surface and compacting it to form a salt-barrier and water-retaining layer, also includes: If the depth of the saline soil layer in the desert soil is greater than 1 meter, the topsoil of the desert soil is stripped down to a depth of 1 meter, and the desert soil salt-barrier and water-retaining material is laid at the 1-meter depth and compacted to form a salt-barrier and water-retaining layer.

10. The salt-barrier and water-retaining method according to claim 7, characterized in that, The thickness of the salt-barrier and water-retaining layer is 30cm to 60cm.

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