A matrix material for modifying and reconstructing water-retaining layers in cold mining areas and its preparation method

Abstract

This invention relates to the fields of mine ecological restoration and solid waste resource utilization, specifically to a matrix material for modifying and reconstructing water-retaining layers in high-altitude and cold mining areas and its preparation method. The water-retaining layer modification and reconstruction matrix material comprises coal gangue and superabsorbent polymer (SAP); wherein the gradation of the coal gangue is A:B:C:D:E = (1-3):(1-3):(1-3):(1-3):(1-3); based on the total mass of the water-retaining layer modification and reconstruction matrix material, the content of SAP is greater than 0 and less than or equal to 0.4%. This invention improves water retention and accelerates ecological restoration in mining areas by adding SAP and determining the gradation of the coal gangue to reconstruct the water-retaining layer.

Description

Technical Field

[0001] This invention relates to the fields of mine ecological restoration and solid waste resource utilization, specifically to a matrix material for modifying and reconstructing water-retaining layers in high-altitude and cold mining areas and its preparation method. Background Technology

[0002] Coal gangue is a solid waste inevitably generated during coal mining and processing. Its production volume is enormous, and long-term stockpiling not only occupies a large amount of land but also pollutes the surrounding environment. Currently, the main measure for ecological restoration of coal gangue piles is direct soil covering for vegetation restoration and reconstruction. However, due to the harsh site conditions in high-altitude mining areas and the high cost of soil covering, as well as the risk of secondary damage to the extraction area, it is considered to directly apply coal gangue as a matrix filling material for exposed sites in mining areas. This approach can achieve resource utilization of waste and significantly reduce restoration costs. While coal gangue is a primary material for ecological restoration in mining areas, it is rich in nutrients and can provide a good habitat for microbial metabolism. However, when used alone, its large particles can lead to poor structure, affecting permeability and water and fertilizer retention capacity, which in turn hinders water transport by plant roots. Therefore, it is necessary to mix coal gangue with other exogenous substances for rational utilization. Summary of the Invention

[0003] This invention provides a matrix material for modifying and reconstructing water-retaining layers in high-altitude and cold mining areas and its preparation method. By adding superabsorbent resin and determining the gradation of coal gangue, the water-retaining layer in the mining area is reconstructed, thereby improving water retention and accelerating the ecological restoration of the mining area.

[0004] A water-retaining layer modified and reconstructed matrix material includes coal gangue and superabsorbent resin; wherein the gradation of the coal gangue is A:B:C:D:E=(1-3):(1-3):(1-3):(1-3):(1-3); A, B, C, D, and E are the particle size gradient of the coal gangue, A: 2-5mm, B: 1-2mm, C: 0.5-1mm, D: 0.25-0.5mm, E: 0.1-0.25mm;

[0005] Based on the total mass of the modified and reconstructed matrix material of the water-retaining layer, the mass fraction of the superabsorbent resin is greater than 0 and less than or equal to 0.4%.

[0006] Studies have found that controlling the gradation of coal gangue and the content of superabsorbent polymers can increase saturated water content, capillary water content, and field water holding capacity, thus meeting the requirements for substrate planting.

[0007] According to an embodiment of the present invention, the preferred gradation of the coal gangue is A:B:C:D:E = (1-3):(2-3):(1-2):(2-3):(1-3).

[0008] According to an embodiment of the present invention, the preferred gradation of the coal gangue is A:B:C:D:E = (1.8-2.2):(1.8-2.2):(1.8-2.2):(1.8-2.2):(1.8-2.2).

[0009] According to a specific embodiment of the present invention, the gradation of the coal gangue is A:B:C:D:E = 3:3:1:2:1, or A:B:C:D:E = 2:2:2:2:2, or A:B:C:D:E = 1:2:1:3:3.

[0010] According to an embodiment of the present invention, the bulk density of the coal gangue is 1.3 g / cm³. 3 -1.6g / cm 3 For example, 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 In some preferred embodiments, the concentration is 1.3 g / cm³. 3 -1.4g / cm 3 .

[0011] According to embodiments of the present invention, based on the total mass of the modified and reconstructed matrix material of the water-retaining layer, the mass fraction of the superabsorbent resin is 0.05%-0.4%, specifically, for example, 0.05%, 0.1%, 0.2%, 0.3%, and 0.4%. In some preferred embodiments, it is 0.3%-0.4%.

[0012] According to an embodiment of the present invention, the water absorption ratio of the superabsorbent resin is ≥350, for example, 350-500.

[0013] According to a specific embodiment of the present invention, the water absorption ratio of the superabsorbent resin is 350-390, for example 386.

[0014] According to an embodiment of the present invention, the monomer of the superabsorbent resin is potassium polyacrylate.

[0015] According to an embodiment of the present invention, the particle size of the superabsorbent resin is 0.45-0.90 mm.

[0016] According to a specific embodiment of the present invention, the superabsorbent resin is of model SDK324SOCO-SAP.

[0017] According to a specific embodiment of the present invention, the water-retaining layer modified and reconstructed matrix material includes coal gangue and superabsorbent resin; wherein, the gradation of the coal gangue is A:B:C:D:E = 2:2:2:2:2, or A:B:C:D:E = 3:3:1:2:1; and the bulk density of the coal gangue is 1.3 g / cm³. 3 -1.4g / cm3 Based on the total mass of the modified and reconstructed matrix material of the water-retaining layer, the mass fraction of the superabsorbent resin is 0.3%-0.4%.

[0018] According to a preferred embodiment of the present invention, the water-retaining layer modified and reconstructed matrix material includes coal gangue and superabsorbent resin; wherein the gradation of the coal gangue is A:B:C:D:E = 2:2:2:2:2; and the bulk density of the coal gangue is 1.3 g / cm³. 3 Based on the total mass of the modified and reconstructed matrix material of the water-retaining layer, the mass fraction of the superabsorbent resin is 0.3%.

[0019] The gradation of the coal gangue mentioned above refers to the mass ratio of each particle size gradient.

[0020] The present invention also provides a method for preparing the above-mentioned water-retaining layer modified and reconstructed matrix material, including mixing the components according to the proportions.

[0021] This invention relates to a water-retaining layer modified and reconstructed matrix material suitable for harsh, high-altitude mining areas. This invention is the first to apply superabsorbent polymer (SOCO-SAP) to coal gangue matrices of different grades and determines the optimal dosage that affects plant growth. This water-retaining layer modified and reconstructed matrix material requires no addition of fertilizers or other functional materials, offering advantages in both process and economy. It can solve the ecological restoration problem in high-altitude, soilless mining areas and simultaneously enable the resource utilization of large quantities of coal gangue solid waste. Attached Figure Description

[0022] Figure 1 This is a comparison of the water absorption ratio after freezing and freeze-thaw cycles in Experiment Example 1 of this invention.

[0023] Figure 2 The XRD analysis results of coal gangue in Experiment Example 2 of this invention are shown. Detailed Implementation

[0024] The following examples are for illustrative purposes only and are not intended to limit the scope of the invention. Where specific techniques or conditions are not specified in the examples, they should be performed according to the techniques or conditions described in the literature in this field, or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased from legitimate channels.

[0025] In the following examples, A, B, C, D, and E represent the particle size gradient of coal gangue: A: 2-5 mm (gravel), B: 1-2 mm (very coarse gravel), C: 0.5-1 mm (coarse sand), D: 0.25-0.5 mm (medium gravel), and E: 0.1-0.25 mm (fine gravel).

[0026] In the following examples, the superabsorbent polymer is model SDK324 SOCO-SAP, purchased from Qingdao SOCO New Materials Co., Ltd. (SOCO), with a water absorption ratio ≥350 (actually measured as 386), and the monomer is potassium polyacrylate. It appears as white fine sand crystals with a particle size of 0.45-0.90 mm.

[0027] The following embodiments describe a method for preparing a water-retaining layer modified and reconstructed matrix material, including mixing the components according to the specified proportions.

[0028] Example 1

[0029] This embodiment provides a water-retaining layer modified and reconstructed matrix material, comprising coal gangue and superabsorbent resin; wherein the gradation of the coal gangue is A:B:C:D:E = 2:2:2:2:2; and the bulk density of the coal gangue is 1.3 g / cm³. 3 Based on the total mass of the modified and reconstructed matrix material of the water-retaining layer, the mass fraction of the superabsorbent resin is 0.3%.

[0030] Example 2

[0031] This embodiment provides a water-retaining layer modified and reconstructed matrix material, comprising coal gangue and superabsorbent resin; wherein the gradation of the coal gangue is A:B:C:D:E = 2:2:2:2:2; and the bulk density of the coal gangue is 1.3 g / cm³. 3 Based on the total mass of the modified and reconstructed matrix material of the water-retaining layer, the mass fraction of the superabsorbent resin is 0.4%.

[0032] Example 3

[0033] This embodiment provides a water-retaining layer modified and reconstructed matrix material, comprising coal gangue and superabsorbent resin; wherein the gradation of the coal gangue is A:B:C:D:E = 3:3:1:2:1; and the bulk density of the coal gangue is 1.3 g / cm³. 3 Based on the total mass of the modified and reconstructed matrix material of the water-retaining layer, the mass fraction of the superabsorbent resin is 0.3%.

[0034] Example 4

[0035] This embodiment provides a water-retaining layer modified and reconstructed matrix material, comprising coal gangue and superabsorbent resin; wherein the gradation of the coal gangue is A:B:C:D:E = 3:3:1:2:1; and the bulk density of the coal gangue is 1.3 g / cm³. 3 Based on the total mass of the modified and reconstructed matrix material of the water-retaining layer, the mass fraction of the superabsorbent resin is 0.4%.

[0036] Example 5

[0037] This embodiment provides a water-retaining layer modified and reconstructed matrix material, comprising coal gangue and superabsorbent resin; wherein the gradation of the coal gangue is A:B:C:D:E = 2:2:2:2:2; and the bulk density of the coal gangue is 1.4 g / cm³. 3 Based on the total mass of the modified and reconstructed matrix material of the water-retaining layer, the mass fraction of the superabsorbent resin is 0.3%.

[0038] Example 6

[0039] This embodiment provides a water-retaining layer modified and reconstructed matrix material, comprising coal gangue and superabsorbent resin; wherein the gradation of the coal gangue is A:B:C:D:E = 2:2:2:2:2; and the bulk density of the coal gangue is 1.4 g / cm³. 3 Based on the total mass of the modified and reconstructed matrix material of the water-retaining layer, the mass fraction of the superabsorbent resin is 0.4%.

[0040] Example 7

[0041] This embodiment provides a modified and reconstructed matrix material for a water-retaining layer, comprising coal gangue and superabsorbent resin; wherein the gradation of the coal gangue is A:B:C:D:E = 3:3:1:2:1; and the bulk density of the coal gangue is 1.4 g / cm³. 3 Based on the total mass of the modified and reconstructed matrix material of the water-retaining layer, the mass fraction of the superabsorbent resin is 0.3%.

[0042] Example 8

[0043] This embodiment provides a modified and reconstructed matrix material for a water-retaining layer, comprising coal gangue and superabsorbent resin; wherein the gradation of the coal gangue is A:B:C:D:E = 3:3:1:2:1; and the bulk density of the coal gangue is 1.4 g / cm³. 3 Based on the total mass of the modified and reconstructed matrix material of the water-retaining layer, the mass fraction of the superabsorbent resin is 0.4%.

[0044] Experiment 1: Screening of water-retaining materials

[0045] The basic information of the tested water-retaining materials is shown in Table 1.

[0046] Table 1 Basic Information of Water-Retaining Materials Tested

[0047]

[0048]

[0049] SOCO1 is equivalent to SDK324 SOCO-SAP.

[0050] 1) Water absorption ratio after freezing and freeze-thaw cycles

[0051] When selecting water-retaining materials, the focus is on the application of SAP in high-altitude and cold mining areas, especially the changes in the water absorption performance of the material at low temperatures. Therefore, this experiment uses both dry freeze-thaw and wet freeze-thaw methods.

[0052] Freeze-dry method: Weigh 1g of the test material into an empty beaker, label it, place it in a freezer (-25℃), freeze it continuously for 30 days, and then determine its water absorption ratio.

[0053] Wet freezing method: Weigh 1g of the test material and place it in a beaker with 50mL of deionized water, label it, and place it in a freezer (-25℃). Thaw it once every 3 days, repeating the process 2, 4, 6, and 8 times, and then measure its water absorption ratio.

[0054] 2) Effects of freezing and freeze-thaw cycles on SAP water absorption ratio

[0055] Under 30 days of freezing and 8 freeze-thaw cycles, SOCO2, BK, and HDB, these three SAPs showed low water absorption ratio degradation rates and performed well. Figure 1 The water absorption ratios of JDL1, JDL2, SNF, HRD, and SOCO1 decreased by 4.53%–17.90% compared to the control, while DM and WT decreased by 3.54%–7.47%. Overall, the SAPs with potassium polyacrylate and acrylamide-inorganic mineral composites as their main components exhibited relatively strong resistance to low-temperature freezing and freeze-thaw cycles, especially SOCO2, BK, and HDB, which still maintained good water absorption capacity after 30 days of freezing and 8 repeated freeze-thaw cycles.

[0056] Although JDL1 and JDL2 have high water absorption rates under unfrozen conditions, considering the ambient temperature of the study area, SOCO materials are relatively stable. SOCO1 with a smaller particle size was chosen for the experiment. SOCO2, with its larger water absorption and expansion volume, is more suitable for field use. Therefore, considering the experimental design (such as the water content of the ring sampler, infiltration, and pot experiments), as well as the material's water absorption performance, stability, and material state (some SAPs, while having strong water absorption and retention, also have strong binding properties, resulting in smaller pores in the substrate and inhibiting plant growth), SOCO1 was selected. The specific choice between large and small particles depends on the substrate application. In terms of material stability, SOCO2 > SOCO1.

[0057] Experiment 2

[0058] Moisture is crucial for the restoration and reconstruction of mining area ecosystems. Superabsorbent polymer (SAP) is a discovered and widely used water-retaining material with excellent flocculation properties, enabling soil to maintain good permeability, reducing soil erosion, and inhibiting soil moisture evaporation. While effectively improving the rhizosphere water environment of crops, providing plants with the necessary water, and increasing crop yield, SAP can also improve soil physical structure, promote soil aggregate formation, and enhance soil aeration. Previous studies have been limited to one or a few aspects of SAP's role in soil improvement, windbreak and sand fixation, and improving afforestation survival rates. However, there are few reports on the use of SAP alone in coal gangue matrix as a functional material for constructing a water-retaining layer and restoring vegetation in high-altitude mining areas.

[0059] The coal gangue used in this experiment was taken from Well No. 7 of the Juhugeng Mining Area in the Muli Coalfield, Tianjun County, Xining City, Qinghai Province. Before the experiment, XRD and XRF tests were performed on the retrieved coal gangue, and water-retaining materials were selected.

[0060] XRD testing conditions: Coal gangue powder was passed through a 200-mesh sieve, ground evenly, and then a suitable amount was compacted with a glass plate. The testing conditions were: both the divergence slit (DS) and scattering slit (SS) of the aperture system were 1°; the scanning speed was 8° / min; and the scanning range was 5-80°. The test results are shown in [the table / document / reference needed]. Figure 2 .

[0061] Test results: The main mineral components of coal gangue are quartz, plagioclase, muscovite and chlorite, accounting for 60.8%, 17.2%, 10.5% and 9.90% respectively.

[0062] XRF detection conditions: After the sample was naturally air-dried, 1 kg was quartered, ground in an agate mortar and pestle, and passed through a 10-mesh (2 mm) sieve. 100 g was then quartered again and ground through a 200-mesh (75 μm) sieve. After the sample was mixed thoroughly, 4 g of the sample was placed in a sample container, with a sample thickness of 5 mm.

[0063] Test results: The coal gangue contained 58.14% SiO2, 23.59% Al2O3, and 8.12% Fe2O3, and also contained small amounts of K2O, MgO, CaO, Na2O, and T. i O2, P2O5, SO3, see Table 2 for details.

[0064] Table 2 XRF Analysis Results of Coal Gangue

[0065]

[0066] Experiment 1 involved repeated water absorption and freeze-thaw tests on various water-retaining materials. Considering factors such as water absorption rate, water absorption ratio, material properties, and economy, the super absorbent polymer (SAP) with the best performance was selected. The model was SDK324SOCO-SAP (hereinafter referred to as SAP) for this experiment (see Table 1 for details). It was purchased from Qingdao Soco New Materials Co., Ltd. (SOCO). The water absorption ratio was ≥350 (measured at 386), which is superior to traditional water-retaining materials. The monomer is potassium polyacrylate. It appears as white fine sand crystals with a particle size of 0.45-0.90 mm. It has strong gel properties, which can enhance the permeability of the soil. It has a three-dimensional network structure and contains a large number of hydrophilic groups on the polymer chain. When water molecules come into contact with the hydrophilic groups, they can enter the matrix and store water by means of the water potential difference formed by the difference in water potential gradient inside and outside the network structure. It can absorb water and swell while keeping water from flowing out. Compared to traditional absorbent materials, SAP absorbs water through both physical and chemical means. Once absorbed, it is not easily released even under pressure, repeatedly cycling through a process of "absorbing water when available and releasing water when needed," while also inhibiting moisture evaporation. SAP is non-toxic and non-corrosive, biodegradable into carbon dioxide and water, and beneficial and harmless to plants and soil. Using SAP water-retaining agents within appropriate limits will effectively enhance the water retention performance of coal gangue matrix.

[0067] (1) The coal gangue was dried, crushed, and sieved. Based on the USDA soil grading standards, the coal gangue was sieved into five particle size gradients: A: 2-5mm (gravel), B: 1-2mm (very coarse gravel), C: 0.5-1mm (coarse sand), D: 0.25-0.5mm (medium gravel), and E: 0.1-0.25mm (fine gravel). Coal gangue of different particle size gradients was mixed in a certain proportion. To facilitate the application of coal gangue in land reclamation, this experimental example used a dry mixing method. The sieved coal gangue was designed with three gradations: A:B:C:D:E, with mass ratios of 3:3:1:2:1 (sandy), 2:2:2:2:2 (loamy), and 1:2:1:3:3 (clayy), respectively. The bulk density was controlled to be 1.3 g / cm³. 3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 The saturated water content (SWC), capillary water content (FC), and field water holding capacity (CM) of coal gangue were measured under 60 different gradations with SAP mass fractions of 0%, 0.1%, 0.2%, 0.3%, and 0.4%, respectively, to reveal the influence of the three factors on the variation law of coal gangue water content.

[0068] (2) Based on the above experimental results, with a bulk density of 1.3 g / cm³, SAP was added to three different grades of coal gangue at mass fractions of 0%, 0.1%, 0.2%, 0.3%, and 0.4%, respectively. One-dimensional vertical constant head infiltration tests were conducted, with each test repeated three times, for a total of 45 soil columns. Simultaneously, soil moisture monitoring station data were used to measure the changes in internal moisture content of the soil columns. The effect of different SAP application rates on the infiltration performance of coal gangue with different gradations was observed.

[0069] (3) Prepare the above 15 substrates according to the specified ratios (bulk density set at 1.3 g / cm³). 3 A potted plant experiment was conducted with SAP (0%-0.4%) to observe the plant growth of different grades of coal gangue substrate. The biomass of Leymus chinensis in different grades of coal gangue substrate was compared and analyzed to screen the optimal substrate ratio for the construction of water-retaining layers in cold mining areas.

[0070] 3. Test Procedure

[0071] (1) According to different proportions, the required coal gangue and superabsorbent polymer (SAP) are thoroughly mixed and then packed into 100cm containers. 3 The ring cutters were compacted with a tamper to the designed bulk density. The filled ring cutters were then placed in a water tank, arranged neatly with a certain distance between each cutter. Water was then added to the tank until the water level was slightly lower than the height of the ring cutters, allowing the coal gangue inside to become saturated. After 12 hours of saturation, the ring cutters were removed, excess water was wiped off the outer wall with a paper towel, and they were weighed to obtain the saturated moisture content. The ring cutters were then placed in sand for 2 hours and weighed again to obtain the capillary moisture content. Finally, the ring cutters were placed on fresh dry sand for 48 hours and weighed again; this was the field moisture content. Each sample was repeated three times, and the average value was taken.

[0072] (2) The infiltration device is made of PVC soil column barrel with a wall thickness of 3mm, a diameter of 15cm, and a height of 50cm. The bottom of the soil column is evenly covered with small holes of 5mm diameter to facilitate uniform water absorption. The outer wall of the soil column is attached with graduated strips. The filling height is 35cm, and the water head is controlled at 5cm. During filling, the adjacent layers are roughened. The inner wall of the soil column is evenly coated with Vaseline to prevent preferential flow. At the same time, holes are drilled on the outer wall of the soil column at 10cm, 20cm, and 30cm to facilitate the insertion of sensors. After the sensors are inserted, the gaps in the side holes are sealed with glass glue to prevent water leakage, so as to measure the change law of volumetric moisture content of coal gangue at different heights, and to reveal the infiltration change law of using different mass fractions of SAP under different graded coal gangue. The test ends when the water infiltrates to the bottom of the soil column, and the water supply from the Marshall bottle is stopped. The wetting front and cumulative infiltration readings were recorded using a timing method that started with frequent readings and gradually decreased infiltration. For the first 20 minutes, the readings were recorded every 1 minute; from 20 to 60 minutes, the readings were recorded every 2 minutes; and after 60 minutes, the readings were recorded every 5 minutes until the infiltration test was completed.

[0073] (3) After uniformly mixing the prepared coal gangue and superabsorbent polymer (SAP), the bulk density is controlled to be 1.3 g / cm³. 3 Flower pots were filled with plants that were 15cm high, with a top diameter of 15cm and a bottom diameter of 13cm. There were 15 different ratios, with three replicates for each ratio, resulting in a total of 45 potted plants. 0.5g of crested wheatgrass seeds were evenly sown in each pot. Planting took place on July 1, 2023, and the plants were harvested on October 1, 2023. The aboveground and underground biomass was then observed.

[0074] 4. Test Results

[0075] (1) Effects of different reconstruction factors on the moisture content of coal gangue

[0076] The average saturated moisture content of coal gangue at five different SAP mass fractions were 21.26%, 24.96%, 25.97%, 28.28%, and 30.41%, respectively; the average capillary moisture content was 12.58%, 13.64%, 13.66%, 15.66%, and 17.50%, respectively; and the field capacity was 7.39%, 7.52%, 7.71%, 8.91%, and 10.63%, respectively. The study shows that the average moisture content of coal gangue is positively correlated with the SAP mass fraction, and that SAP mass fractions of 0.3% and 0.4% have the best effect. Analysis of variance showed that there was a significant difference between the amount of SAP used and the change in moisture content (p<0.05), indicating that the mass fraction of SAP is one of the main factors affecting the change in moisture content of coal gangue. The average saturated moisture content corresponding to the four bulk densities was 36.23%, 35.90%, 32.32%, and 29.97%, respectively; the average capillary moisture content was 17.28%, 15.62%, 12.88%, and 12.65%, respectively; and the average field capacity was 10.54%, 10.21%, 7.38%, and 5.60%, respectively. It is evident that the average moisture content is negatively correlated with the bulk density. Analysis of variance shows that the differences in moisture content of coal gangue under different bulk densities are significant (P<0.05), indicating that changes in bulk density affect the moisture content of coal gangue. Under the three gradations of sandy, loamy, and clayey types, the average saturated moisture contents are 26.14%, 26.18%, and 26.22%, respectively; the average capillary moisture contents are 11.49%, 14.71%, and 17.62%, respectively; and the average field capacity are 6.13%, 8.52%, and 10.64%, respectively. Analysis of variance also shows that the particle size distribution of coal gangue affects the change in its moisture content (P<0.05), and the moisture content gradually increases with the increase of the proportion of fine particles, showing a significant correlation.

[0077] To better explore the combined effects of SAP mass fraction, bulk density, and coal gangue particle size distribution on coal gangue moisture content, saturated moisture content, capillary moisture content, and field capacity were used as dependent variables, and SAP mass fraction (X1), bulk density (X2), and coal gangue particle size distribution (X3) as independent variables. Stepwise regression analysis was used to establish models of the effects of saturated moisture content (SWC), capillary moisture content (FC), and field capacity (CM) under different reconstruction methods. The variable introduction models satisfying the condition (P<0.05) are shown in Table 3. Generally, the magnitude of the direct path coefficient determines the degree of response of the independent variable to the dependent variable; the larger the coefficient, the greater the degree of response. The study shows that although SAP mass fraction, bulk density, and coal gangue particle size distribution all affect saturated moisture content, there are significant differences in the degree of response. SAP mass fraction and bulk density have higher direct path coefficients and have the greatest impact on saturated moisture content. For capillary water content and field water holding capacity, the three factors have relatively small differences in their influence, specifically in the order of bulk density > coal gangue particle size distribution > SAP mass fraction.

[0078] Table 3. Influence coefficients of different reconstruction factors on the moisture content of coal gangue.

[0079]

[0080]

[0081] (2) The influence of SAP on the variation law of wet front of gangue in different grades of coal

[0082] A wetting front is a distinct interface formed between the moistened leading edge of the soil and the dry soil layer during water infiltration. The migration speed of the wetting front indicates the water-holding capacity of coal gangue; the faster the migration speed, the stronger the permeability and the weaker the water-holding capacity. The depth of the wetting front increases with time. In the initial stage of infiltration, the wetting front curve is steeper, gradually flattening and eventually stabilizing as infiltration time increases. The time taken for the wetting front to reach the bottom of the soil column differs for the five mass fractions, and the migration time of the wetting front is significantly positively correlated with the SAP mass fraction. With the increase of SAP usage, the wetting front advancement rate gradually slows down. This is mainly because the unique three-dimensional network structure of SAP contains a large number of hydrophilic groups. When water molecules come into contact with the hydrophilic groups, they can enter the coal gangue interior and store water by utilizing the potential difference formed by the different water potential gradients inside and outside the network structure, thus inhibiting the advancement speed of the wetting front. The effect of SAP varies depending on the gradation of coal gangue. In a sandy gradation, the infiltration process without SAP took only 115 minutes. The infiltration time was slightly longer with 0.1% and 0.2% SAP, at 140 and 155 minutes respectively, while the infiltration times were 335 and 340 minutes with 0.3% and 0.4% SAP, respectively. In a loamy gradation, the trend was similar to that of sandy gradation, with the infiltration processes of 0.3% and 0.4% SAP being almost synchronous. This indicates that SAP works best when used in appropriate amounts, while excessively high or low amounts do not achieve optimal results. The infiltration times were 270 and 335 minutes respectively. The infiltration times were 350 min, 710 min, and 740 min, respectively. Under the slightly cohesive gradation, the infiltration time without SAP was 520 min. SAP concentrations of 0.1% and 0.2% increased this to 670 min and 740 min, respectively. SAP concentrations of 0.3% and 0.4% significantly inhibited water infiltration, increasing the time from 520 min to 1560 min and 1980 min, respectively. This indicates that the addition of different SAP concentrations inhibits the infiltration capacity of coal gangue to varying degrees, effectively retaining moisture. Furthermore, the higher the SAP concentration, the stronger the inhibition of coal gangue infiltration, suggesting that SAP can delay water infiltration and prolong the infiltration duration. At the same SAP concentration, the time taken for the wetting front to reach the bottom of the soil column consistently increased from shortest to longest in the order of slightly sandy < slightly loamy < slightly cohesive.

[0083] (3) The effect of SAP on the cumulative infiltration amount and infiltration rate of coal gangue of different grades

[0084] Cumulative infiltration refers to the total amount of water passing through a unit area within a certain period. For ease of experimental observation, the change in water depth in a Marble bottle is used to represent the cumulative infiltration of coal gangue. The cumulative infiltration without SAP, from largest to smallest, is: loamy > clayey > sandy, at 16.8 cm, 15.6 cm, and 13.5 cm respectively. The cumulative infiltration of coal gangue with SAP added is consistently greater than that of the control group and is positively correlated with the SAP mass fraction. Under a sandy gradation, the cumulative infiltration with SAP mass fractions of 0.1%-0.4% is 14.0 cm, 14.9 cm, 15.4 cm, and 17.0 cm, respectively; under a loamy gradation, the cumulative infiltration at the four mass fractions is 17.0 cm, 17.1 cm, 17.5 cm, and 18.0 cm, respectively; and under a clayey gradation, the corresponding cumulative infiltration is 15.9 cm, 16.7 cm, 17.0 cm, and 17.5 cm, respectively. Meanwhile, it can be found that the cumulative infiltration of coal gangue under the action of 0.1% and 0.2% SAP is less than that of pure coal gangue. 0.3% and 0.4% SAP make coal gangue absorb more water, while inhibiting water infiltration, so that its water retention performance can be maximized, and the infiltration time is the longest.

[0085] The amount of water passing through a cross-section per unit time is called the infiltration rate of coal gangue, which is an important indicator in the infiltration process. In the initial infiltration stage, due to the dry surface of the coal gangue and its strong water adsorption capacity, the infiltration rate curve is relatively steep. As the infiltration time increases, gravity becomes the dominant factor in the infiltration process. Different amounts of SAP (superoxide dismutase) added cause the infiltration rate to vary over time, eventually stabilizing in the later stages of infiltration. At the end of the infiltration test, the average infiltration rates of SAP from 0% to 0.4% under the three gradations were as follows: 0.46 cm / min, 0.36 cm / min, 0.37 cm / min, 0.18 cm / min, and 0.18 cm / min for sandy gradation; 0.20 cm / min, 0.18 cm / min, 0.17 cm / min, 0.08 cm / min, and 0.07 cm / min for loamy gradation; and 0.11 cm / min, 0.07 cm / min, 0.07 cm / min, 0.04 cm / min, and 0.03 cm / min for viscous gradation. The addition of SAP significantly inhibited the water infiltration rate of coal gangue of different gradations. This is mainly because the addition of SAP changed the pore characteristics of coal gangue, which significantly reduced the infiltration rate. In particular, the effect of SAP at a mass fraction of 0.3% was close to 0.4%.

[0086] (4) The effect of SAP on the volumetric moisture content variation characteristics of gangue of different grades at different depths

[0087] During the infiltration process, the volumetric moisture content of coal gangue at different depths was measured over time using a soil moisture monitoring station under the influence of SAP (Soil Moisture Precipitation). Without SAP, the initial volumetric moisture content increased with depth for all three gradations. At different depths, the initial volumetric moisture content consistently ranked as follows: loamy > clayey > sandy. Under the sandy gradation, the volumetric moisture contents at 10cm, 20cm, and 30cm depths were 23.5%, 56.6%, and 62.5%, respectively. Under the loamy and clayey gradations, the initial moisture contents at different depths were 31.1%, 65.0%, and 72.0%, and 31.0%, 64.5%, and 71.9%, respectively, showing an increase compared to the sandy gradation. The moisture content tended to its maximum value when the wetting front passed the sensor, and then stabilized when the wetting front passed all sensors to the bottom. After infiltration, the moisture content at 20cm and 30cm depths was higher than that at 10cm depth, indicating that the lower part of the coal gangue had better water retention properties, providing the necessary moisture for plant growth and promoting water transport in plant roots. The increases in volumetric moisture content at different depths with SAP concentrations of 0.1% and 0.2% were relatively small for the three gradations, but the effects were better with 0.3% and 0.4% SAP concentrations, increasing the volumetric moisture content at different depths by about 10% compared to 0% SAP, with no significant difference between the two. This suggests that with appropriate application, SAP can improve water transport in coal gangue while also saving costs.

[0088] (5) Effects of SAP on the growth of creeping bentgrass in coal gangue matrix of different grades

[0089] Biomass results from the *Leymus chinensis* planting experiment using different mass fractions of SAP under three different substrate gradations showed that the trends of aboveground fresh weight, aboveground dry weight, underground fresh weight, and underground dry weight were basically the same, all significantly higher than those of pure coal gangue matrix. Under the three substrate gradations, the biomass exhibited with increasing SAP application was (soil-oriented > sandy-oriented > clay-oriented). Under a slightly soil-balanced substrate, with SAP application rates ranging from 0.1% to 0.4%, the aboveground fresh weight and aboveground dry weight increased by 5.44, 8.11, 18.22, 17.78 and 7.00, 8.83, 22.67, 17.00 times, respectively, compared to pure coal gangue substrate. The underground fresh weight and underground dry weight increased by 5.14, 9.14, 25.43, 22.86 and 5.80, 12.00, 27.60, 24.60 times, respectively, compared to pure coal gangue substrate. The addition of SAP altered the biomass distribution pattern of *Leymus chinensis* seedlings, leading to increased underground biomass as the plant allocates more resources to the root system to adapt to the environment. This increase in underground biomass may be an important adaptation of the plant to the ecological environment. This further demonstrates that under a slightly soil-balanced substrate, a SAP mass fraction of 0.3% resulted in the highest biomass, representing the best combination for substrate improvement and meeting planting requirements. The next best values ​​were 0.4%, 0.2%, 0.1%, and 0%. When the amount of SAP used is the same, although the viscous gradation has good water retention, the excessive moisture inside the substrate may hinder the water transport of plant roots, resulting in slightly worse vegetation performance compared to the loamy and sandy gradations.

[0090] (6) Summary

[0091] 1. Under soil and clayey gradations, with a bulk density of 1.3 g / cm3 or 1.4 g / cm3 and an SAP application rate of 0.3% or 0.4%, the saturated water content, capillary water content, and field water holding capacity are superior to other reconstruction methods.

[0092] 2. SAP inhibits the infiltration capacity of coal gangue to varying degrees, delays water infiltration, prolongs the infiltration duration, and effectively retains moisture. Within the range of 0%-0.4%, the higher the dosage, the stronger the inhibition of coal gangue infiltration. Under the same mass fraction, the time taken for the wetting front to reach the bottom of the soil column by SAP is always from shortest to longest: sandy < loamy < clayey.

[0093] 3. The cumulative infiltration rate of coal gangue under the action of 0.1% and 0.2% SAP is only slightly increased compared with pure coal gangue. 0.3% and 0.4% SAP allow coal gangue to absorb more water, thus maximizing its water retention capacity. At the same time, it significantly inhibits the water infiltration rate, especially at a mass fraction of 0.3%, where the effect is close to that of 0.4%.

[0094] 4. Under the soil-graded conditions, with an SAP mass fraction of 0.3% and a bulk density of 1.3 g / cm3, the germination time of Leymus chinensis is early, the number of germinations is high, and the dry weight accumulation is high. This ratio can significantly improve the water retention of coal gangue matrix, and the germination and growth of Leymus chinensis are the best, which can meet the planting requirements.

[0095] In summary, based on the results of water content, infiltration, and pot experiments, it is recommended that a bulk density of 1.3 g / cm³, a soil-based gradation (2:2:2:2:2), and a SAP mass fraction of 0.3% be the preferred choice for both effectiveness and economy as a substrate material preparation technology for modifying and reconstructing water-retaining layers in high-altitude and cold mining areas. Secondly, a bulk density of 1.3 g / cm³, a soil-based or sand-based gradation (3:3:1:2:1), and a SAP usage of 0.3% or 0.4% are recommended as the main substrate ratios for water-retaining layer reconstruction. These gradation combinations have good water content, infiltration performance, and water retention performance, but their vegetation cover is slightly weaker than the former. Overall, they are better than other gradations and can accelerate the ecological restoration of mining areas.

[0096] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A matrix material for modifying and reconstructing water-retaining layers in cold mining areas, characterized in that, It is composed of coal gangue and superabsorbent resin; wherein, the gradation of the coal gangue is A:B:C:D:E=2:2:2:2:2; A, B, C, D, and E are the particle size gradient of the coal gangue, A: 2-5mm, B: 1-2mm, C: 0.5-1mm, D: 0.25-0.5mm, E: 0.1-0.25mm; The coal gangue has a bulk density of 1.3 g / cm 3 ; Based on the total mass of the modified and reconstructed matrix material of the water-retaining layer, the mass fraction of the superabsorbent resin is 0.3%. The superabsorbent resin has a water absorption ratio of ≥350; The monomer of the superabsorbent resin is potassium polyacrylate; The superabsorbent resin has a particle size of 0.45-0.90 mm.

2. The water-retaining layer modified and reconstructed matrix material according to claim 1, characterized in that, The superabsorbent polymer is designated as SDK324 SOCO-SAP.

3. The method for preparing the water-retaining layer modified and reconstructed matrix material according to any one of claims 1-2, characterized in that, This includes mixing the components according to the specified proportions.

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