Reconstructed soil with multi-layer structure and application of reconstructed soil in ecological restoration of mining area

Abstract

The invention belongs to the technical field of soil reconstruction, and particularly relates to reconstructed soil of a multi-layer structure and application of the reconstructed soil in ecological restoration of a mining area. The reconstructed soil with the multi-layer structure sequentially comprises a surface layer, a barrier layer and a filling layer from top to bottom, the surface layer comprises low-carbon coal gangue and surface soil, the carbon content of the low-carbon coal gangue is smaller than 4 wt%, the particle size of the low-carbon coal gangue is smaller than or equal to 2 mm, and the mass ratio of the low-carbon coal gangue to the surface soil is (1-2): (1-2); the blocking layer comprises fly ash and cement, and the mass ratio of the fly ash to the cement is smaller than or equal to 1.8: 1; the filling layer comprises waste coal gangue. The water retention capacity and the structural stability of the reconstructed soil are remarkably improved. According to the reconstructed soil of the multi-layer structure, mine area waste is effectively utilized, the environmental burden is reduced, and an economical and feasible solution is provided for ecological restoration.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil reconstruction, and in particular relates to a reconstructed soil with a multi-layer structure and its application in ecological restoration of mining areas. Background Art

[0002] Coal mining has stripped away surface vegetation and topsoil, forming a large number of abandoned mine sites. The main problems of these abandoned sites include: 1. Severe shortage of topsoil resources: The amount of topsoil stripped during mining is not enough to cover the reclamation area, resulting in insufficient soil thickness during reclamation. 2. Poor physical and chemical properties of the soil: lack of organic matter, low nutrient content, unstable soil structure, and poor water and fertilizer retention capacity. 3. Difficulty in vegetation restoration: The number of plant species suitable for growth is limited, the survival rate is low, and ecological restoration is difficult. 4. Difficulty in handling solid waste: Coal mining produces a large amount of coal gangue, fly ash and other coal industry solid waste, which is difficult to handle.

[0003] In the process of land reclamation and ecological restoration, the main challenges are how to effectively improve the water retention of reconstructed soil, improve soil structure, promote vegetation growth and recovery, and dissolve coal gangue, fly ash and other coal industry solid waste. Some existing soil improvement methods and materials, such as directly covering the topsoil, adding organic fertilizers or using certain chemical improvers, are not ideal in the special environment of coal mining areas, and also ignore the treatment of coal gangue, fly ash and other coal industry solid waste. The main reasons are: insufficient topsoil resources, unable to achieve large-scale coverage; organic fertilizers are difficult to maintain fertility under conditions of drought and high evaporation; chemical improvers may cause secondary pollution to the environment and are costly; coal industry solid waste has a complex composition, in addition to containing a large amount of carbon, silicon, aluminum, iron, calcium and other major elements, it also contains trace amounts of toxic heavy metal elements such as arsenic, mercury, lead, chromium, cadmium, etc., which are difficult to handle. Summary of the invention

[0004] The purpose of the present invention is to provide a multi-layered reconstructed soil and its application in ecological restoration of mining areas. The multi-layered reconstructed soil provided by the present invention can significantly improve the water retention performance and structural stability of the soil, reduce the environmental burden, and provide an economically feasible method for ecological restoration.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a multi-layer structured reconstructed soil, which comprises, from top to bottom, a surface layer, a barrier layer and a filling layer;

[0007] The surface layer includes low-carbon coal gangue and surface soil, the low-carbon coal gangue is coal gangue with a carbon content of less than 4wt%, the particle size of the low-carbon coal gangue is ≤2mm, and the mass ratio of the low-carbon coal gangue to the surface soil is (1-2): (1-2);

[0008] The barrier layer comprises fly ash and cement, and the mass ratio of the fly ash to the cement is ≤1.8:1;

[0009] The filling layer includes waste coal gangue.

[0010] Preferably, the mass ratio of the low-carbon coal gangue to the surface soil is 1:1.

[0011] Preferably, the thickness of the surface layer is 30 to 70 cm.

[0012] Preferably, the thickness of the surface layer is 40 to 60 cm.

[0013] Preferably, the mass ratio of fly ash to cement is (1.2-1.8):1.

[0014] Preferably, the mass ratio of fly ash to cement is 1.5:1.

[0015] Preferably, the thickness of the barrier layer is 15 to 25 cm.

[0016] Preferably, the thickness of the barrier layer is 20 cm.

[0017] Preferably, the thickness of the filling layer is 20 to 50 cm.

[0018] The present invention provides the application of the reconstructed soil with a multi-layer structure described in the above technical solution in ecological restoration of mining areas.

[0019] The present invention provides a reconstructed soil with a multi-layer structure, which includes, from top to bottom, a surface layer, a barrier layer and a filling layer; the surface layer includes low-carbon coal gangue and surface soil, the low-carbon coal gangue is coal gangue with a carbon content of less than 4wt%, the particle size of the low-carbon coal gangue is ≤2mm, and the mass ratio of the low-carbon coal gangue to the surface soil is (1-2):(1-2); the barrier layer includes fly ash and cement, and the mass ratio of the fly ash to the cement is ≤1.8:1; the filling layer includes waste coal gangue. The present invention optimizes the mass ratio of low-carbon coal gangue to surface soil, combines the barrier layer design of fly ash and cement, and uses waste coal gangue from mining stripping as a filling layer, while eliminating waste coal gangue, fly ash and coal industry solid waste, and significantly improves the water retention and structural stability of the reconstructed soil. The multi-layered reconstructed soil provided by the present invention not only effectively eliminates coal industry solid waste and reduces environmental burden, but also provides an economically feasible solution for ecological restoration. By improving the physical and chemical properties and water retention capacity of the soil, the present invention provides a solid foundation for ecological restoration and vegetation reconstruction in mining areas. In summary, the multi-layered reconstructed soil provided by the present invention has the following technical effects:

[0020] The surface structure of the multi-layered reconstructed soil provided by the present invention serves to plant vegetation. The surface structure of the present invention contains low-carbon coal gangue. The porosity and water absorption of the low-carbon coal gangue enable it to effectively absorb and retain moisture and reduce water loss. On this basis, the present invention controls the mass ratio of low-carbon coal gangue to surface soil to (1-2): (1-2), thereby forming a surface layer with a stable porous structure, increasing the porosity and water holding capacity of the soil, and significantly improving the water retention performance of the reconstructed soil; and the mixing of low-carbon coal gangue in the surface structure can also dissolve a certain amount of coal gangue.

[0021] Moreover, the barrier layer structure of the multi-layered reconstructed soil provided by the present invention serves to prevent the spontaneous combustion of the waste coal gangue in the bottom filling layer, making the structure of the filling layer more stable. At the same time, the barrier layer includes fly ash, which is a kind of solid waste in the coal industry. The addition of fly ash to the barrier layer also eliminates part of the fly ash to a certain extent.

[0022] Furthermore, the filling layer structure of the multi-layered reconstructed soil provided by the present invention functions to dissolve waste coal gangue while stabilizing the underground structure of the multi-layered reconstructed soil.

[0023] In summary, the present invention reconstructs the multi-layer structure of the soil, including a surface layer, a barrier layer and a filling layer, and forms an organic whole through a three-layer structure, wherein the barrier layer is composed of a mixture of fly ash and cement, which can effectively prevent the rapid infiltration of water and keep the upper soil moist, so that the distribution of water in the vertical direction of the reconstructed soil can be more uniform. The filling layer of the present invention uses waste coal gangue naturally accumulated from mining strippings. The physical properties of the waste coal gangue make it excellent in load-bearing and support. Therefore, the present invention not only eliminates the solid waste of the coal industry in the mining area, but also provides good physical support and enhances the stability of the soil structure.

[0024] The multi-layered reconstructed soil provided by the present invention uses mining area materials (such as low-carbon coal gangue, waste coal gangue and topsoil), which not only reduces material costs but also improves the adaptability and ecological restoration capacity of the soil, and is suitable for ecological restoration in mining areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the relative water retention rate at 5 cm under different watering conditions in the embodiments and comparative examples;

[0026] Figure 2 is the relative water retention rate at 25 cm under different watering conditions in the embodiments and comparative examples;

[0027] Figure 3 It is the relative water retention rate under different watering conditions in the embodiments and comparative examples. DETAILED DESCRIPTION

[0028] The present invention provides a multi-layer structured reconstructed soil, which comprises, from top to bottom, a surface layer, a barrier layer and a filling layer;

[0029] The surface layer includes low-carbon coal gangue and surface soil, the low-carbon coal gangue is coal gangue with a carbon content of less than 4wt%, the particle size of the low-carbon coal gangue is ≤2mm, and the mass ratio of the low-carbon coal gangue to the surface soil is (1-2): (1-2);

[0030] The barrier layer comprises fly ash and cement, and the mass ratio of the fly ash to the cement is ≤1.8:1;

[0031] The filling layer includes waste coal gangue.

[0032] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well known to those skilled in the art.

[0033] The reconstructed soil of the multilayer structure provided by the present invention includes a surface layer. In the present invention, the surface layer includes low-carbon coal gangue and surface soil. The surface layer is preferably composed of a mixture of the low-carbon coal gangue and surface soil. The low-carbon coal gangue is a coal gangue with a carbon content of less than 4wt%. The particle size of the low-carbon coal gangue is ≤2mm. The present invention preferably crushes the low-carbon coal gangue to a particle size of ≤2mm before use. The surface soil is preferably surface soil in a mining area. The mass ratio of the low-carbon coal gangue to the surface soil is preferably (1-2): (1-2), more preferably 1:1. The thickness of the surface layer is preferably 30-70cm, more preferably 40-60cm, and in the embodiment it can be 60cm, 50cm or 40cm.

[0034] The multi-layered reconstructed soil provided by the present invention includes a barrier layer arranged on the lower surface of the surface layer. In the present invention, the barrier layer includes fly ash and cement. The fly ash is preferably industrial-grade fly ash. The cement is preferably ordinary Portland cement. The barrier layer is preferably composed of a mixture of the fly ash and cement. The mass ratio of the fly ash to the cement is ≤1.8:1, preferably (1.2-1.8):1, and more preferably 1.5:1. The thickness of the barrier layer is preferably 15-25 cm, and more preferably 20 cm.

[0035] The multi-layered reconstructed soil provided by the present invention includes a filling layer arranged on the lower surface of the barrier layer. In the present invention, the filling layer includes waste gangue. The waste gangue is preferably naturally accumulated gangue from mining strippings. The present invention has no special requirements on the particle size of the waste gangue. The present invention uses the waste gangue as the filling layer of the multi-layered reconstructed soil, which can help to eliminate the waste gangue in the mining area. The thickness of the filling layer is preferably 20 to 50 cm, more preferably 30 to 40 cm.

[0036] The method for preparing the reconstructed soil with a multilayer structure described in the above technical solution provided by the present invention comprises the following steps:

[0037] The filling layer, the barrier layer and the surface layer are prepared in sequence from bottom to top to obtain the reconstructed soil with the multi-layer structure.

[0038] In the present invention, the method for preparing the filling layer preferably comprises: filling the bottom of the reconstructed soil of the multi-layer structure with waste coal gangue to obtain the filling layer.

[0039] In the present invention, the method for preparing the barrier layer preferably comprises: mixing the fly ash, cement and water to obtain a barrier layer mixture; and laying the barrier layer mixture on the upper surface of the filling layer to obtain the barrier layer.

[0040] In the present invention, the preparation method of the surface layer comprises: mixing the low-carbon coal gangue and the surface soil to obtain a surface layer mixture; and laying the surface layer mixture on the upper surface of the barrier layer to obtain the surface layer. The low-carbon coal gangue and the surface soil are preferably mixed on a canvas, and the specific implementation method of mixing the low-carbon coal gangue and the surface soil is preferably: mixing from bottom to top by manual turning. The number of repetitions of mixing the low-carbon coal gangue and the surface soil is preferably ≥5 times, until the low-carbon coal gangue and the surface layer are evenly mixed.

[0041] The present invention provides the application of the reconstructed soil with a multi-layer structure described in the above technical solution in ecological restoration of mining areas.

[0042] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0043] Example 1

[0044] The experimental process of this embodiment includes:

[0045] (1) Experimental example

[0046] The experiment of this embodiment has 9 experimental groups, which are divided into three control groups:

[0047] The first group (low-carbon coal gangue: surface soil mass ratio = 1:1):

[0048] Experimental group 1: surface thickness 60 cm, experimental group 2: surface thickness 50 cm, experimental group 3: surface thickness 40 cm;

[0049] The second largest group (low carbon gangue: surface soil mass ratio = 2:1):

[0050] Experimental group 4: surface thickness 60 cm, experimental group 5: surface thickness 50 cm, experimental group 6: surface thickness 40 cm;

[0051] The third group (low-carbon coal gangue: surface soil mass ratio = 1:2):

[0052] Experimental group 7: surface thickness 60 cm, experimental group 8: surface thickness 50 cm, experimental group 9: surface thickness 40 cm;

[0053] (2) Test plan

[0054] In each experimental group, probe measuring points were set at 5 cm and 25 cm from the topsoil to test its humidity;

[0055] (3) Watering gradient setting

[0056] Set six watering amount gradients of 10mL, 20mL, 50mL, 75mL, 100mL, and 200mL, monitor the humidity every two hours, and observe the humidity changes.

[0057] Comparative Example 1

[0058] In this comparative example, pure surface soil is used instead of the mixture of low-carbon coal gangue and surface soil in Example 1 as the surface experimental control group:

[0059] Control group 10: surface thickness 60 cm, control group 11: surface thickness 50 cm, control group 12: surface thickness 40 cm;

[0060] (2) Test plan

[0061] In each experimental group, probe measuring points were set at 5 cm and 25 cm from the topsoil to test its humidity;

[0062] (3) Watering gradient setting

[0063] Set six watering amount gradients of 10mL, 20mL, 50mL, 75mL, 100mL, and 200mL, monitor the humidity every two hours, and observe the humidity changes.

[0064] Experimental Results

[0065] The calculation of relative water retention rate is to compare the water retention capacity of different soil samples under the same conditions, especially when the initial water content is different. In combination with the present invention, the relative water retention rate can be calculated by formula 1:

[0066]

[0067] In Formula 1: W is the actual water content of the soil, usually referring to the soil water content measured under specific conditions (such as after watering); Wd is the actual water content of the soil before watering, and 1 hour before watering is selected as this value in the experiment.

[0068] Due to the large differences in the initial humidity of different experimental groups, in order to make the results comparable, the humidity at 1 hour before watering, 1 hour after watering, 6 hours after watering, 12 hours after watering, and 18 hours after watering at 5 cm and 25 cm from the soil surface under different watering amounts are selected, and the outliers are removed (as time increases, without watering, the relative water retention rate exceeds 50% or the change amount exceeds ±20% or is significantly abnormal compared with other groups), and their relative water retention rates are calculated. The relative water retention rates at 5 cm and 25 cm from the soil surface are averaged to obtain the schematic diagram of "relative water retention rate under different watering amounts".

[0069] The results are as Figure 1 、 Figure 2 、and Figure 3 shown. Among them: Figure 1 is the relative water retention rate at 5 cm under different watering amounts in the examples and comparative examples; Figure 2 is the relative water retention rate at 25 cm under different watering amounts in the examples and comparative examples; Figure 3 is the relative water retention rate under different watering amounts in the examples and comparative examples.

[0070] According to Figure 1 to Figure 3 the experimental data analysis, in the surface structure of the reconstructed soil with a multi-layer structure provided by the present invention: for the mass ratio of coal gangue to surface soil = 1:1 and 1:2, better water retention performance is shown. In comparison, the water retention performance of coal gangue: surface soil is 1:1 > 1:2 > 2:1.

[0071] Under the same watering amount, the relative water retention rate of the soil at 5 cm from the surface in the 1:1 ratio group is mostly higher than that of other ratios. At 25 cm from the surface, each of the three ratios has its own advantages, but the overall relative water retention rate of the 1:1 ratio is in a relatively high range; among the relative water retention rates obtained by averaging the values at 5 cm and 25 cm from the surface, the 1:1 ratio is higher than other ratios under different watering amounts.

[0072] As the watering amount increases, the relative water retention rate of the 1:1 ratio group increases more stably.

[0073] (2) Influence of surface layer thickness

[0074] By comparing the experimental groups with different surface layer thicknesses:

[0075] The surfaces with thicknesses of 60 cm and 50 cm show better water retention effects. In comparison, the water retention effect is 50 cm thickness surface > 60 cm thickness surface > 40 cm thickness surface.

[0076] A thicker surface layer is conducive to even distribution of moisture.

[0077] The difference in humidity values ​​between probes at different depths is small, indicating a more uniform moisture distribution.

[0078] It can be seen from the above results that compared with the prior art, the advantages of the present invention are:

[0079] Improved water retention performance: Under the condition of watering 200mL (simulating extreme precipitation): compared with the relative water retention rate of using a single surface soil cover (control group 10) in Comparative Example 1, the optimal reconstruction scheme in Example 1 (experimental group 1) increased by 42.031%, 77.080%, 7.068%, and 22.994% after watering for 1h, 6h, 12h, and 18h, respectively; Under the condition of watering 10mL (simulating light rain): compared with the relative water retention rate of using a single surface soil cover (control group 10) in Comparative Example 1, the optimal reconstruction scheme in Example 1 (experimental group 1) increased by 139.532%, 63.346%, 91.097%, and 17.235% after watering for 1h, 6h, 12h, and 18h, respectively.

[0080] Among them, the average relative water retention rate at 200mL-5cm and 25cm of watering: the data of experimental group 1 after watering for 1h, 6h, 12h and 18h ​​were: 13.944%, 8.261%, 3.981%, 3.296% respectively; the data of control group 10 after watering for 1h, 6h, 12h and 18h ​​were: 9.817%, 4.665%, 3.718%, 2.680% respectively.

[0081] The average relative water retention rate at 5cm and 25cm after watering with 10mL of water: the data of experimental group 1 after watering for 1h, 6h, 12h and 18h ​​were: 0.148%, -0.932%, -0.152%, -1.525% respectively; the data of control group 10 after watering for 1h, 6h, 12h and 18h ​​were: -0.374%, -0.570%, -1.710%, -1.843% respectively.

[0082] The moisture distribution in the surface structure of the multi-layered reconstructed soil provided by the present invention is more uniform: the moisture gradient in the vertical direction is smaller.

[0083] The reconstructed soil structure of the multi-layer structure provided by the present invention has good structural stability: it maintains a stable water retention effect under different watering amounts.

[0084] The multi-layered reconstructed soil provided by the present invention can effectively digest the solid waste of the coal industry: the surface layer digests the low-carbon coal gangue, the barrier layer digests the fly ash, and the filling layer digests a large amount of coal gangue.

[0085] It can be seen from the above embodiments that the present invention proposes a multi-layer structure of reconstructed soil with strong water retention performance in response to the special needs of mining areas. The present invention significantly improves the water retention performance and structural stability of the soil by optimizing the mixing ratio of low-carbon coal gangue and surface soil in the surface structure, combining the barrier layer design of fly ash and cement, and using mining strippings, i.e., waste coal gangue, as a filling layer. The reconstructed soil with a multi-layer structure provided by the present invention not only effectively utilizes mining waste and reduces the environmental burden, but also provides an economically feasible solution for ecological restoration. By improving the physical and chemical properties and water retention capacity of the soil, the present invention provides a solid foundation for ecological restoration and vegetation reconstruction in mining areas.

[0086] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A multi-layered reconstructed soil, characterized in that: From top to bottom, it includes: surface layer, barrier layer and filling layer; The surface layer includes low-carbon coal gangue and surface soil, the low-carbon coal gangue is coal gangue with a carbon content of less than 4wt%, the particle size of the low-carbon coal gangue is ≤2mm, and the mass ratio of the low-carbon coal gangue to the surface soil is (1-2): (1-2); The barrier layer comprises fly ash and cement, and the mass ratio of the fly ash to the cement is ≤1.8:1; The filling layer includes waste coal gangue.

2. The multi-layered reconstructed soil according to claim 1, characterized in that: The mass ratio of the low-carbon coal gangue to the surface soil is 1:

1.

3. The multi-layered reconstructed soil according to claim 1 or 2, characterized in that: The thickness of the surface layer is 30 to 70 cm.

4. The multi-layered reconstructed soil according to claim 3, characterized in that: The thickness of the surface layer is 40 to 60 cm.

5. The multi-layered reconstructed soil according to claim 1, characterized in that: The mass ratio of fly ash to cement is (1.2-1.8):

1.

6. The multi-layered reconstructed soil according to claim 6, characterized in that: The mass ratio of fly ash to cement is 1.5:

1.

7. The multi-layered reconstructed soil according to claim 1, 5 or 6, characterized in that: The thickness of the barrier layer is 15 to 25 cm.

8. The multi-layered reconstructed soil according to claim 7, characterized in that: The thickness of the barrier layer is 20 cm.

9. The multi-layered reconstructed soil according to claim 1, characterized in that: The thickness of the filling layer is 20 to 50 cm.

10. Use of the multi-layered reconstructed soil according to any one of claims 1 to 9 in ecological restoration of mining areas.

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