Method for reclamation of soil substrates and coal gangue landfills

Abstract

The application provides a soil matrix and a method for reclamation of a coal gangue landfill site. The soil matrix comprises, in percentage by weight: 3-5% of coal gangue, 1-3% of fly ash, 0.5-1.5% of coal gasification fine slag, 7-9% of microbial fertilizer and 81.5-88.5% of surface soil in a mining area. Based on the analysis results of the basic physicochemical properties of coal-based solid waste and surface soil in the mining area, the key limiting factors of the physicochemical properties of the coal-based solid waste such as coal gangue, fly ash and coal gasification fine slag and the surface soil are determined, and the soil matrix containing coal-based solid waste is formed by adjusting the components and the ratio. The addition of the fly ash increases the content of alkaline hydrolysis nitrogen and available phosphorus in the surface soil, the addition of the coal gangue mainly increases the content of available potassium and organic matter in the surface soil, the addition of the coal gasification fine slag mainly increases the content of available phosphorus and organic matter in the surface soil, and the addition of the microbial fertilizer increases the nutrient content in the surface soil in the mining area.

Description

Technical Field

[0001] This invention relates to the field of mine ecological restoration technology, and more specifically, to a method for reclamation of soil matrix and coal gangue landfills. Background Technology

[0002] Currently, coal gangue reclamation technology is the most effective coal gangue disposal technology both domestically and internationally. Coal gangue reclamation can effectively reduce the damage of coal gangue piles to the mining area and its surrounding environment, and also has advantages such as mature disposal technology, low cost, and easy supervision.

[0003] However, due to the complex composition of coal gangue, if bottom seepage prevention treatment is not carried out, rainwater erosion after reclamation will produce Pb-containing substances. 2+ Cr 2+ Cd 2+ Hg + Leachate from coal gangue containing heavy metal ions pollutes groundwater and the surrounding environment. Further improvements are needed to the existing coal gangue reclamation process.

[0004] Furthermore, after landfilling coal gangue layers, a certain thickness of soil needs to be laid on top to allow for plant cultivation. However, current technologies mostly involve directly excavating and mining better soil from other regions as the soil layer to be laid on top of the coal gangue layer, which results in high transportation costs. If a soil matrix that can be directly adapted to local conditions using coal gangue and other coal-based solid wastes could be prepared, the reclamation of coal gangue landfills could be achieved more economically and efficiently. Summary of the Invention

[0005] The main objective of this invention is to provide a method for reclamation of soil matrix and coal gangue landfills, in order to solve the problems of poor soil structure, low nutrient levels and poor water retention in mining areas in the prior art.

[0006] To achieve the above objectives, according to one aspect of the present invention, a soil matrix is ​​provided, comprising, by weight percentage: 3-5% coal gangue, 1-3% fly ash, 0.5-1.5% coal gasification slag, 7-9% microbial fertilizer, and topsoil from the mining area.

[0007] Furthermore, the particle size of the coal gangue is less than 1 mm;

[0008] And / or, fly ash is a product of the combustion of coal-based fuels in thermal power plants;

[0009] And / or, the particle size of the coal gasification slag is less than 2 mm;

[0010] And / or, the topsoil of the mining area is the topsoil at a depth of 0 to 20 cm, preferably, the pH value of the topsoil of the mining area is 7.5 to 8.5, and preferably, the particle size of the topsoil of the mining area is less than 2 mm.

[0011] According to another aspect of this application, a method for reclamation of a coal gangue landfill is provided, wherein an impermeable layer, a coal gangue composite filling layer and a soil layer are sequentially arranged from bottom to top at the bottom of the coal gangue landfill, wherein the coal gangue composite filling layer is formed by filling coal gangue and slurry material, and the soil of the soil layer includes any of the above-mentioned soil matrix.

[0012] Furthermore, the impermeable layer includes, from bottom to top, a modified bentonite layer, an HDPE membrane, a sand diversion layer, and a geotextile;

[0013] Preferably, the thickness of the modified bentonite layer is 30-50cm, and preferably, the modified bentonite layer is made of fly ash modified bentonite.

[0014] Preferably, the thickness of the sand diversion layer is 40-60cm;

[0015] Preferably, an HDPE guide pipe is buried in the sandy soil guide layer.

[0016] Furthermore, the method for setting the composite filling layer includes: laying coal gangue, filling the coal gangue with slurry material to form a composite filling layer, wherein the composite filling layer includes a filling layer and a support layer located above the filling layer;

[0017] Preferably, the coal gangue composite filling layer comprises 3 to 5 layers of composite filling layer.

[0018] Furthermore, the thickness of the composite filler layer is 1–2 μm;

[0019] Preferably, the thickness of the filling layer is 50-170 cm and the thickness of the support layer is 30-50 cm.

[0020] Furthermore, the diameter of the coal gangue in the coal gangue composite filling layer is less than or equal to 30 cm.

[0021] Furthermore, by weight, the raw materials of the slurry material include: 5-15 parts sodium alginate, 30-45 parts fly ash, 8-15 parts loess, 2-6 parts hydrotalcite, 3-8 parts bentonite, 50-70 parts modified lignocellulose solution, 2-5 parts sodium bicarbonate, 2-5 parts aluminum sulfate, and 120-200 parts water.

[0022] Preferably, the raw materials for the slurry material include: 5-10 parts sodium alginate, 35-40 parts fly ash, 10-12 parts loess, 3-5 parts hydrotalcite, 5-7 parts bentonite, 55-65 parts modified lignocellulose solution, 3-4 parts sodium bicarbonate, 3-4 parts aluminum sulfate, and 140-180 parts water.

[0023] Furthermore, the slurry material is prepared by the following method:

[0024] Step A1: Mix fly ash with modified lignocellulose solution to obtain a first mixture;

[0025] Step A2: Bentonite is mixed with sodium carbonate and a portion of water to obtain a second mixture, preferably, the portion of water is 10-15 parts by weight;

[0026] Step A3: After mixing the first mixture and the second mixture, the resulting mixture is mixed with sodium alginate, loess, hydrotalcite, bentonite and the remaining water to obtain the third mixture;

[0027] Step A4: Mix the third mixture with aluminum sulfate to obtain a slurry material.

[0028] Furthermore, the thickness of the soil layer is 100-150cm.

[0029] By applying the technical solution of this invention, based on the analysis results of the basic physicochemical properties of coal-based solid waste and topsoil in mining areas, the key limiting factors of the physicochemical properties of coal-based solid waste, such as coal gangue, fly ash, and coal gasification slag, and topsoil are determined. A soil matrix containing coal-based solid waste is formed by adjusting the composition and proportions. Specifically, the addition of fly ash increases the content of available nitrogen and available phosphorus in the topsoil; the addition of coal gangue mainly increases the content of available potassium and organic matter in the topsoil; the addition of coal gasification slag mainly increases the content of available phosphorus and organic matter in the topsoil; and the addition of microbial fertilizer increases the nutrient content in the topsoil of the mining area.

[0030] The physicochemical properties and water and fertilizer retention capacity of this soil matrix meet the technical requirements for greening planting soil indicators, realizing the effective utilization of coal-based solid waste. Using this soil matrix containing coal-based solid waste for landfilling coal gangue can achieve on-site material sourcing and better realize the reclamation of coal gangue landfills. Attached Figure Description

[0031] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0032] Figure 1 A structural schematic diagram of a coal gangue landfill reclamation design according to an embodiment of the present invention is shown.

[0033] The above-mentioned attached drawings include the following reference numerals: 1. impermeable layer; 2. filling layer; 3. support layer; 4. soil layer; 5. vegetation; 6. dam; 7. drainage ditch. Detailed Implementation

[0034] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0035] As analyzed in the background section of this application, existing technologies suffer from poor soil structure, low nutrient levels, and poor water retention in mining areas. Simultaneously, the large amount of coal gangue generated during coal mining and washing processes is difficult to dispose of as solid waste. To address these issues, this application provides a method for reclamation of soil matrix and coal gangue landfills.

[0036] According to a typical embodiment of this application, a soil matrix is ​​provided, comprising, by weight percentage: 3-5% coal gangue, 1-3% fly ash, 0.5-1.5% coal gasification slag, 7-9% microbial fertilizer and mining topsoil.

[0037] Based on the analysis of the basic physicochemical properties of coal-based solid waste and topsoil in mining areas, this application identifies the key limiting factors for the physicochemical properties of coal-based solid waste, fly ash, and coal gasification slag, as well as topsoil. By adjusting the composition and proportions, a soil matrix containing coal-based solid waste is formed. Specifically, the addition of fly ash increases the content of available nitrogen and available phosphorus in the topsoil; the addition of coal gangue mainly increases the content of available potassium and organic matter in the topsoil; the addition of coal gasification slag mainly increases the content of available phosphorus and organic matter in the topsoil; and the addition of microbial fertilizer increases the nutrient content in the topsoil of the mining area.

[0038] The physicochemical properties and water and fertilizer retention capacity of this soil matrix meet the technical requirements for greening planting soil indicators, realizing the effective utilization of coal-based solid waste. Using this soil matrix containing coal-based solid waste for landfilling coal gangue allows for on-site material sourcing and better facilitates the reclamation of coal gangue landfills. To better meet the needs of plant growth and improve the water and fertilizer retention of the soil matrix, in some embodiments of this application, the coal gangue particle size is less than 1 mm. In some embodiments of this application, the coal gangue is selected from the Burtai Coal Preparation Plant.

[0039] Fly ash can be selected from existing technologies without special requirements. For example, fly ash can be a product of coal-based fuel combustion in thermal power plants, which is produced in large quantities and is relatively easy to obtain.

[0040] Microbial fertilizers are used to enrich soil nutrients and can be selected from existing technologies. This application does not have any special requirements for them. For example, microbial fertilizers produced by Shengfeng Horticulture in Xingtai, Hebei Province can be used.

[0041] Preferably, the particle size of the coal gasification slag is less than 2 mm. In some embodiments of this application, the coal gasification slag is selected from the Ordos Coal-to-Oil Plant.

[0042] Furthermore, the topsoil in the mining area is the surface soil at a depth of 0–20 cm. Preferably, the pH value of the topsoil in the mining area is 7.5–8.5, which allows it to better cooperate with other components in the soil matrix and is beneficial to plant growth. To further improve the water and fertilizer retention capacity of the soil matrix, the particle size of the topsoil in the mining area is preferably less than 2 mm.

[0043] The specific preparation method of the above-mentioned soil matrix can refer to the existing technology. For example, the preparation method of the above-mentioned soil matrix is ​​to mix coal gangue, fly ash, coal gasification fine slag, microbial fertilizer and topsoil of the mining area evenly to obtain the soil matrix.

[0044] Those skilled in the art can also add other components to the above-mentioned soil matrix according to specific circumstances to achieve its intended function, and this application does not have any special limitations in this regard.

[0045] In some typical embodiments of this application, the soil matrix comprises, by weight percentage: 3-5% coal gangue, 1-3% fly ash, 0.5-1.5% coal gasification slag, 7-9% microbial fertilizer, and the remainder being topsoil from the mining area.

[0046] In some embodiments of this application, the proportions of coal gangue, fly ash, coal gasification slag, and microbial fertilizer in the soil matrix are 4wt%, 2wt%, 1wt%, and 8wt%, respectively, with the remainder being topsoil from the mining area. This is particularly suitable for plant growth and has good water and fertilizer retention capacity.

[0047] According to another typical embodiment of this application, a method for reclamation of a coal gangue landfill is provided. The method includes sequentially setting an impermeable layer, a coal gangue composite filling layer, and a soil layer from bottom to top at the bottom of the coal gangue landfill. The coal gangue composite filling layer is formed by filling coal gangue and slurry material, and the soil of the soil layer includes the aforementioned soil matrix.

[0048] The method for reclamation of coal gangue landfills disclosed in this application involves setting up an impermeable layer to prevent Pb in the coal gangue from entering the landfill. 2+ Cr 2+ Cd 2+ Hg + Heavy metal ions, under the corrosive action of rainwater and other substances, seep downwards, causing pollution to groundwater and the surrounding environment. Furthermore, in the coal gangue composite filling layer formed by coal gangue and slurry material, the slurry material can bond the coal gangue blocks, improve the connection between coal gangue, increase the density and mechanical strength of the entire coal gangue composite filling layer, and prevent the entry and circulation of oxygen, which helps to reduce the combustibility of coal gangue.

[0049] In some typical embodiments of this application, the impermeable layer includes a modified bentonite layer, an HDPE membrane, a sand diversion layer, and a geotextile arranged sequentially from bottom to top. The impermeable layer with this composition has good impermeability and mechanical properties, which can better meet the impermeability requirements of coal gangue landfills, and has high stability.

[0050] In some preferred embodiments of this application, the thickness of the modified bentonite layer is 30-50 cm; preferably, the modified bentonite layer is made of fly ash modified bentonite, which significantly improves the seepage prevention effect.

[0051] Preferably, the thickness of the sand diversion layer is 40-60cm; preferably, an HDPE diversion pipe is buried in the sand diversion layer to divert the seepage to the diversion ditch, thereby reducing the impact of the seepage on the environment.

[0052] In some typical embodiments of this application, the method for setting the composite filling layer includes: laying coal gangue, filling the coal gangue with slurry material to form a composite filling layer, wherein the composite filling layer includes a filling layer and a support layer above the filling layer; wherein the filling layer is formed by filling coal gangue and slurry material, and the support layer is a relatively dense material layer formed only by slurry material above the filling layer, which has high strength and stability, and can prevent spontaneous combustion of coal gangue and prevent heavy metal leaching and environmental pollution. By adopting the method of sequentially setting multiple composite filling layers, the coal gangue and slurry material in the composite filling layer can be filled more tightly, which can further improve the density and mechanical strength of the coal gangue composite filling layer and reduce the flammability of coal gangue.

[0053] Preferably, the thickness of the composite filler layer is 1–2 m. Preferably, the thickness of the filler layer is 50–170 cm, and the thickness of the support layer is 30–50 cm. In some preferred embodiments of this application, the coal gangue composite filler layer comprises 3–5 layers, exhibiting high strength and achieving good environmental and economic value.

[0054] The filling method of the above-mentioned slurry material can be selected from existing technologies. For example, a mud pump can be used to inject the slurry into the grouting pipeline or the borehole under pressure and inject it into the predetermined grouting position in the predetermined coal gangue layer.

[0055] In some embodiments of this application, in order to further improve the stability of the coal gangue composite filler layer, the diameter of the coal gangue in the coal gangue composite filler layer is less than or equal to 30 cm.

[0056] In some typical embodiments of this application, the raw materials of the slurry material, by weight, include: 5-15 parts sodium alginate, 30-45 parts fly ash, 8-15 parts loess, 2-6 parts hydrotalcite, 3-8 parts bentonite, 50-70 parts modified lignocellulose solution, 2-5 parts sodium bicarbonate, 2-5 parts aluminum sulfate, and 120-200 parts water. The slurry material formed from the above raw materials exhibits excellent water retention, good flame retardant effect, and good permeability to coal gangue layers. It is also stable in performance. Filling the gaps in the coal gangue with this slurry material effectively coats and cross-links the coal gangue, effectively preventing spontaneous combustion of the coal gangue and preventing heavy metal leaching that pollutes the environment. Furthermore, the raw materials for this slurry material are inexpensive and readily available.

[0057] Modified lignocellulose has many active sites, which can form a certain self-crosslinking network structure. When used in combination with sodium alginate, it can greatly improve the toughness and ductility of sodium alginate slurry, thereby greatly improving its water retention performance. Fly ash is activated and crosslinked under the action of alkali, which can not only achieve its own crosslinking network, but also form a crosslinking network with modified lignin, further improving the mechanical properties and water retention performance of the slurry material. Furthermore, the high-valence metal ions such as trivalent iron ions and tetravalent titanium ions precipitated from fully activated fly ash can also crosslink better with sodium alginate and fill into the network skeleton structure. Moreover, after full crosslinking, fly ash has strong adhesion to coal and is easier to fill into coal gangue layers. After the material is formed, it has stable performance, extremely high fire resistance, is not easy to break, and has good flexibility.

[0058] Furthermore, the bentonite in the slurry material is a good water absorbent material. It absorbs water and expands, which will further fill the gaps in the cross-linked network of the slurry and improve the water retention and barrier effect. Moreover, the bentonite modified by sodium bicarbonate in the raw materials can improve its water absorption and is also a good flame retardant material. In addition, loess, hydrotalcite and other materials are also good flame retardant materials. The combination of the three can also greatly improve the flame retardant performance of the filling slurry material.

[0059] Furthermore, although aluminum sulfate in the raw materials acts as a crosslinking agent, it also generates a certain amount of aluminum hydroxide under alkaline conditions. This not only prevents the sodium alginate system from gelling too quickly, but the generated aluminum hydroxide is also a good flame retardant material, which can further improve the flame retardant effect of the slurry material.

[0060] In some preferred embodiments of this application, the raw materials of the slurry material include: 5-10 parts sodium alginate, 35-40 parts fly ash, 10-12 parts loess, 3-5 parts hydrotalcite, 5-7 parts bentonite, 55-65 parts modified lignocellulose solution, 3-4 parts sodium bicarbonate, 3-4 parts aluminum sulfate, and 140-180 parts water. This can better leverage the synergistic effect of the raw materials in the slurry material and further improve the flame retardant and water absorption and retention effects of the slurry material.

[0061] In some embodiments of this application, the modified lignocellulose solution is obtained by enzymatic hydrolysis of lignin in the presence of phenol, a strong alkali, and water. The strong alkali includes, but is not limited to, any one or more of sodium hydroxide and potassium hydroxide.

[0062] Natural lignin is a natural polycyclic aromatic macromolecule composed of hydrophobic nonpolar groups on a phenylpropane skeleton and hydrophilic polar groups such as phenol groups. However, the reactivity of existing natural lignin is significantly insufficient. Based on this, this invention first performs alkaline modification on lignin, increasing its active sites. The modified lignin has more active sites, which can then form a certain self-crosslinking network structure. When used in conjunction with slurry materials containing sodium alginate, it can greatly improve the toughness and ductility of the slurry material, thereby significantly improving its water retention performance and fire-extinguishing properties. Furthermore, during the alkaline modification of lignin, some unreacted sodium hydroxide remains. This unreacted sodium hydroxide is then mixed with fly ash. The unreacted sodium hydroxide from the lignin modification process allows for the initial activation and crosslinking of the fly ash, promoting the full utilization of its functions.

[0063] In some typical embodiments of this application, the preparation method of the modified lignocellulose solution includes: carrying out a modification reaction of enzymatically hydrolyzed lignin, phenol, sodium hydroxide, and water under closed conditions to obtain the modified lignocellulose solution. As a preferred embodiment, based on 100% of the total mass of added raw materials, the amount of enzymatically hydrolyzed lignin added is 20-25 wt%; the mass ratio of phenol to enzymatically hydrolyzed lignin is 0.5-0.6:1; preferably, the mass ratio of sodium hydroxide to lignin is 0.4-0.6:1. To further increase the active sites of the modified lignocellulose, the reaction temperature of the above modification reaction is preferably 60-70°C, and the reaction time is 2-3 hours.

[0064] In some typical embodiments of this application, in order to better leverage the synergistic effect of the various raw materials forming the slurry material, the slurry material is prepared by the following method: Step A1, fly ash is mixed with modified lignocellulose solution to obtain a first mixture, preferably, the mixing time is 3-8 minutes, so that the first mixture is relatively uniform and the fly ash can fully react with the solution in the modified lignocellulose; Step A2, bentonite is mixed with sodium carbonate and a portion of water to obtain a second mixture, preferably, the portion of water is 10-15 parts by weight; Step A3, after mixing the first mixture and the second mixture, the resulting mixture is mixed with sodium alginate, loess, hydrotalcite, bentonite and the remaining water to obtain a third mixture, preferably, the mixing time of the first mixture and the second mixture is 10-25 minutes, more preferably, the mixing time of the resulting mixture after mixing the first mixture and the second mixture with sodium alginate, loess, hydrotalcite, bentonite and the remaining water is 5-10 minutes, which is beneficial to further improve the filling effect of the slurry material; Step A4, the third mixture is mixed with aluminum sulfate to obtain the slurry material.

[0065] Since the modified lignocellulose obtained through strong alkali modification may contain some unreacted alkali residue, it is then mixed with fly ash. The unreacted alkali from the lignin modification process is used to initially activate and crosslink the fly ash. Then, bentonite and sodium bicarbonate are combined. Bentonite can effectively adsorb and slowly release sodium bicarbonate. When mixed with the modified lignin + fly ash system, sodium bicarbonate, being a weak alkali, further promotes the activation and crosslinking of the fly ash. Furthermore, sodium carbonate, produced by the reaction of sodium bicarbonate and sodium hydroxide, further promotes the activation and crosslinking of the fly ash. Through these multiple activation and crosslinking processes, the formation of the fly ash's own crosslinking network and the crosslinking network between fly ash and modified lignin can be better achieved, further improving the mechanical properties and water retention of the slurry material. Moreover, the high-valence metal ions precipitated from the fully activated fly ash, such as ferric ions and tetravalent titanium ions, can also better crosslink with sodium alginate and fill the network framework structure.

[0066] By employing a specific raw material ratio and feeding sequence in a triple-crosslinking system, a filling slurry material is prepared that exhibits excellent water retention, good flame retardancy, and excellent permeability to coal gangue layers. The resulting coal gangue composite filling layer, formed by filling coal gangue with this slurry material, is more stable and reliable. Placing a soil matrix on top of this material satisfies the growth needs of plants and is environmentally friendly.

[0067] In some preferred embodiments of this application, the thickness of the soil layer is 100-150 cm in order to better meet the growth needs of plants.

[0068] In some typical embodiments of this application, a schematic diagram of the design structure for reclamation of coal gangue landfills using the method described in this application is shown below. Figure 1 As shown, a seepage-proof layer 1 is laid at the bottom of the coal gangue landfill. Coal gangue is then laid on the seepage-proof layer 1, and slurry material is filled into the coal gangue to form a filling layer 2. A support layer 3 with a thickness of 30-50 cm is then set on the filling layer 2 to form a composite filling layer. Coal gangue is then laid on the above composite filling layer, and slurry material is filled into the coal gangue to form a filling layer 2. Another support layer 3 with a thickness of 30-50 cm is then set on the filling layer 2 to form another composite filling layer. The preparation of the above composite filling layer is repeated until all coal gangue composite filling layers are completed. The thickness of each coal gangue composite filling layer is 1-2 m. Each composite filling layer includes a filling layer 2 formed by coal gangue and filling slurry material, and a support layer 3 formed only by slurry material above the filling layer. The thickness of the support layer 3 is 30-50 cm. A soil layer 4 is laid on the prepared coal gangue composite backfill layer; green plants 5 are planted on the soil layer 4 to realize the reclamation of the coal gangue landfill; for use needs, a water-blocking dam 6 and a suitable drainage ditch 7 can also be set above the coal gangue landfill according to the terrain.

[0069] The beneficial effects that this application can achieve will be further illustrated below with reference to embodiments and comparative examples.

[0070] Preparation Example 1

[0071] This preparation example provides a filling slurry material comprising the following raw materials in parts by weight: 8 parts sodium alginate, 36 parts fly ash, 11 parts loess, 4 parts hydrotalcite, 6 parts bentonite, 60 parts modified lignocellulose solution, 4 parts sodium bicarbonate, 4 parts aluminum sulfate, and 180 parts water. The modified lignocellulose solution is prepared by the following method: enzymatically hydrolyzed lignin, phenol, sodium hydroxide, and water are reacted under sealed conditions to obtain the modified lignocellulose solution. The total mass of the raw materials added in this step is 100%, and the amount of enzymatically hydrolyzed lignin added is 22 wt%; the mass ratio of phenol to enzymatically hydrolyzed lignin is 0.5:1; the mass ratio of sodium hydroxide to lignin is 0.5:1; the remainder is water; the reaction temperature is 65°C; and the reaction time is 2.5 h.

[0072] The above raw materials were prepared into a slurry material according to the following steps:

[0073] (1) Add fly ash to the modified lignocellulose solution, mix evenly, and stir for 5 minutes to obtain mixture A;

[0074] (2) Mix bentonite, sodium bicarbonate and some water to obtain mixture B; the water added is 13 parts.

[0075] (3) Mix mixture A and mixture B evenly and stir for 15 minutes; then add the remaining raw materials except aluminum sulfate and mix evenly for 7 minutes; finally add aluminum sulfate and mix evenly to obtain the filling slurry material.

[0076] Preparation Example 2

[0077] This preparation example provides a filling slurry material comprising the following raw materials in parts by weight: 5 parts sodium alginate, 40 parts fly ash, 12 parts loess, 3 parts hydrotalcite, 5 parts bentonite, 65 parts modified lignocellulose solution, 3 parts sodium bicarbonate, 3 parts aluminum sulfate, and 160 parts water. The modified lignocellulose solution is prepared by the following method: enzymatically hydrolyzed lignin, phenol, sodium hydroxide, and water are reacted under sealed conditions to obtain the modified lignocellulose solution. The total mass of the raw materials added in this step is 100%, and the amount of enzymatically hydrolyzed lignin added is 20 wt%; the mass ratio of phenol to enzymatically hydrolyzed lignin is 0.6:1; the mass ratio of sodium hydroxide to lignin is 0.6:1; the remainder is water; the reaction temperature is 70°C; and the reaction time is 2 hours.

[0078] The above raw materials were prepared into a slurry material according to the following steps:

[0079] (1) Add fly ash to the modified lignocellulose solution, mix evenly, and mix for 8 minutes to obtain mixture A;

[0080] (2) Mix bentonite, sodium bicarbonate and some water to obtain mixture B; the added water is 11 parts;

[0081] (3) Mix mixture A and mixture B evenly for 25 minutes; then add the remaining raw materials except aluminum sulfate and mix evenly for 5 minutes; finally add aluminum sulfate and mix evenly to obtain the filling slurry material.

[0082] Preparation Example 3

[0083] The only difference from Preparation Example 1 is that, in the preparation of the modified lignocellulose solution, an equal mass of water was used to replace the sodium hydroxide in Example 1.

[0084] Preparation Example 4

[0085] The only difference from Preparation Example 1 is that, in the raw materials for the filling slurry, sodium alginate in Example 1 is replaced by an equal mass of fly ash and modified lignocellulose solution, wherein the mass ratio of fly ash to modified lignocellulose solution is 1:1.66.

[0086] Preparation Example 5

[0087] The only difference from Preparation Example 1 is that, in the raw materials of the filling slurry, equal masses of sodium alginate and modified lignin solution are used instead of fly ash in Example 1, wherein the mass ratio of sodium alginate and modified lignocellulose solution is 1:7.5.

[0088] Preparation Example 6

[0089] The only difference from Preparation Example 1 is that, in the raw materials for filling the slurry, an equal mass of water is used to replace sodium bicarbonate.

[0090] Preparation Example 7

[0091] The only difference from Preparation Example 1 is that the modified lignocellulose solution was replaced with an equal mass of the same enzymatic hydrolyzed lignocellulose aqueous solution (22% by mass) as in Example 1 in the raw materials for filling the slurry.

[0092] Preparation Example 8

[0093] The slurry material used is the same as that used in Preparation Example 1. The only difference is that all the raw materials are directly mixed evenly to obtain the slurry material for filling.

[0094] The performance of the filling slurry material prepared in the above preparation example was tested, and the specific test data are listed in Table 1.

[0095] The determination of flame retardant properties is based on the flame retardant requirements of the Coal Mine Safety Standard: MT113-1995.

[0096] Final setting time: The final setting time of the landfill grout is measured using the resistance method. The inflection point of the resistivity-time curve corresponds to the final setting time. The method for testing the water loss rate of the filling grout is as follows: The filling grout is heated at 100℃ for 1 hour, and the water loss rate (%) is calculated based on the weight difference before and after heating.

[0097] The compressive strength test method is as follows: a standard test block of 10cm×10cm×10cm is prepared according to GB / T50081-2019, and its compressive strength is tested after curing for 7 days.

[0098] Table 1

[0099]

[0100] As can be seen from the results in Table 1, the present invention is based on the mechanism of preventing spontaneous combustion of gangue and dynamic regulation of pore structure. Through reasonable raw material ratio, the prepared gelling material is easy to flow and easy to inject into the grout. It can penetrate into the gaps of the coal gangue layer to form a colloid, which isolates oxygen and prevents spontaneous combustion of the coal gangue layer. It also has good water retention and mechanical strength, and is suitable for filling grout materials for coal gangue layers.

[0101] Preparation Example 9

[0102] The modified bentonite layer in the impermeable layer is made of fly ash-modified bentonite, and its preparation is as follows:

[0103] (1) Under stirring conditions, 500 parts of sodium-based bentonite and 3 parts of N,N-methylenebisacrylamide were dispersed in water and kept at 70°C for 0.5 h to obtain a sodium-based bentonite mixture. 100 parts of an aqueous solution of acrylic acid monomer with a neutralization degree of 60% and 30 parts of 2-acrylamido-2-methylpropanesulfonic acid were added to the sodium-based bentonite mixture, and 2 parts of potassium persulfate were added to adjust the solid content of the mixture to 40 wt%. The reaction was carried out at 70°C for 2 h. After the reaction was completed, the mixture was filtered, washed with water, and vacuum dried to obtain modified sodium-based bentonite.

[0104] (2) Fly ash and sodium hydroxide were mixed at a weight ratio of 1:1 and activated at 550°C for 3 hours. The mixture was then cooled to room temperature and stirred with 5 times its weight of water for 24 hours. The mixture was filtered, washed alternately with dilute acid and water until neutral, and then dried under vacuum to obtain activated fly ash.

[0105] Activated fly ash was added to a 10 wt% ethanol solution of polyethyleneimine (PEI) (weight average molecular weight Mw = 60,000 Daltons), with a weight ratio of activated fly ash to PEI of 2:1. The mixture was stirred at 40°C for 24 h. Subsequently, 5% (by weight) of glutaraldehyde (present in aqueous solution of the activated fly ash) was added, and the reaction was continued at 40°C for another 2 h. After the reaction was complete, the mixture was filtered, washed with water, and vacuum dried to obtain PEI-modified fly ash.

[0106] The modified bentonite from step (1) and the PEI-modified fly ash from step (2) were added to water at a weight ratio of 9:1 and wet-mixed. The mixture was then filtered, washed with water, and vacuum-dried to obtain fly ash-modified bentonite.

[0107] The performance of the fly ash-modified bentonite prepared above was tested, and its permeability coefficient in high-purity water was 1.2 × 10⁻⁶. -13 m / s. Existing coal gangue landfills require a permeability coefficient of less than 1×10⁻⁶ m / s for seepage prevention. -7The modified bentonite layer in the geomembrane of this invention has a very low permeability coefficient (cm / s), providing excellent seepage prevention. Furthermore, in conjunction with the HDPE membrane (high-density polyethylene membrane), sand-soil diversion layer, and geotextile in the geomembrane, it better meets the seepage prevention requirements of coal gangue landfills. In summary, this invention improves existing geomembrane materials, enhances the seepage prevention effect, and meets the usage requirements of coal gangue landfills.

[0108] Preparation Example 10

[0109] A soil matrix containing coal-based solid waste, comprising coal gangue, fly ash, coal gasification slag, microbial fertilizer, and topsoil from the mining area, wherein the proportions of coal gangue, fly ash, coal gasification slag, and microbial fertilizer in the soil matrix are 4%, 2%, 1%, and 8%, respectively, and the remainder is topsoil from the mining area.

[0110] The topsoil from the mining area was selected from the topsoil layer at a depth of 0-20 cm in the demonstration site for the remediation of the Burtai subsidence area, with a pH value of 8.3. The topsoil was ground and then passed through a 2 mm sieve to ensure a particle size of less than 2 mm. The coal gangue was selected from the Burtai coal preparation plant, ground, and then passed through a 1 mm sieve to ensure a particle size of less than 1 mm. The coal gasification slag was selected from the Ordos coal-to-oil plant, ground, and then passed through a 2 mm sieve to ensure a particle size of less than 2 mm. The fly ash was selected from the Shangwan Thermal Power Plant. The microbial fertilizer was selected from Shengfeng Horticulture in Xingtai, Hebei Province. The coal gangue, fly ash, coal gasification slag, microbial fertilizer, and topsoil from the mining area were mixed evenly according to the above proportions to obtain a soil matrix containing coal-based solid waste.

[0111] The improved topsoil in the coal-based solid waste soil matrix of this invention transforms sandy loam into loam-sandy and sandy soil, increasing soil aggregate and improving soil water retention from 3.47% to 16%. The pH value of the coal-based solid waste soil matrix is ​​8.26, and this formulation shows the best effect on improving soil pH. In summary, 8% microbial fertilizer, 4% coal gangue from the Burtai coal preparation plant, 2% fly ash, and 1% coal gasification fine slag have a good effect on improving the topsoil in mining areas and can meet the technical requirements for soil indicators for greening and planting.

[0112] Preparation Example 11

[0113] The difference from Preparation Example 10 is that the proportions of coal gangue, fly ash, coal gasification slag, and microbial fertilizer in the soil matrix are 5%, 1.5%, 1.5%, and 9%, respectively.

[0114] Tests showed that the soil had a water retention capacity of 15.1% and a pH value of 8.63, which met the technical requirements for soil indicators for greening and planting.

[0115] Preparation of Comparative Example 1

[0116] The difference from Preparation Example 10 is that the proportions of coal gangue, fly ash, coal gasification slag, and microbial fertilizer in the soil matrix are 7%, 1.5%, 2%, and 9%, respectively.

[0117] Tests showed that the soil had a water retention capacity of 14.3% and a pH value of 9.2.

[0118] Example 1

[0119] The structure of the coal gangue landfill after the present invention is as follows: Figure 1 As shown, a method for reclamation of a coal gangue landfill includes the following steps:

[0120] (1) An impermeable layer is laid at the bottom of the coal gangue landfill; wherein the impermeable layer comprises, from bottom to top, a modified bentonite layer, a layer of HDPE membrane, a sand diversion layer and a layer of geotextile, wherein the sand diversion layer also contains an HDPE diversion pipe; the material used for the modified bentonite layer is the same as that prepared in Preparation Example 9; the thickness of the modified bentonite layer is 40 cm; the thickness of the sand diversion layer is 60 cm.

[0121] (2) Coal gangue is laid on the impermeable layer, and slurry material is filled in the coal gangue to form a coal gangue composite filling layer; the diameter of the coal gangue in the coal gangue composite filling layer does not exceed 30cm; the filling slurry material is selected from the filling slurry material prepared in Preparation Example 1; the thickness of each layer of coal gangue composite filling layer is 1.5m; a total of 4 layers of coal gangue composite filling layer are prepared; each layer of coal gangue composite filling layer includes a filling layer formed by coal gangue and filling slurry material, and a support layer above the filling layer formed only by slurry material; the thickness of the support layer is 40cm.

[0122] (3) A soil layer is laid on the topmost coal gangue composite backfill layer; the thickness of the soil layer is 150cm; the soil layer uses the soil matrix containing coal-based solid waste prepared in Preparation Example 10, and green plants are planted in the soil layer to realize the reclamation of the coal gangue landfill.

[0123] After six months of storage, the soil within 100m of the above-mentioned reclaimed structure was tested for heavy metal (Cu, Cr, Pb) concentrations, and no significant changes were found in the heavy metal content.

[0124] Example 2

[0125] A method for reclamation of coal gangue landfills is provided, comprising the following steps:

[0126] (1) An impermeable layer is laid at the bottom of the coal gangue landfill; wherein the impermeable layer comprises, from bottom to top, a modified bentonite layer, a layer of HDPE membrane, a sand diversion layer and a layer of geotextile, wherein the sand diversion layer also contains an HDPE diversion pipe; the material used for the modified bentonite layer is the same as that prepared in Preparation Example 9; the thickness of the modified bentonite layer is 30 cm; the thickness of the sand diversion layer is 50 cm.

[0127] (2) Coal gangue is laid on the impermeable layer, and slurry material is filled in the coal gangue to form a coal gangue composite filling layer; the diameter of the coal gangue in the coal gangue composite filling layer does not exceed 30cm; the filling slurry material is selected from the filling slurry material prepared in Preparation Example 2; the thickness of each layer of coal gangue composite filling layer is 2m; a total of 3 layers of coal gangue composite filling layer are prepared; each layer of coal gangue composite filling layer includes a filling layer formed by coal gangue and filling slurry material, and a support layer above the filling layer formed only by slurry material; the thickness of the support layer is 50cm.

[0128] (3) A soil layer is laid on top of the coal gangue composite backfill layer; the thickness of the soil layer is 140cm; the soil layer is selected from the soil matrix containing coal-based solid waste prepared in Preparation Example 10, and green plants are planted in the soil layer to realize the reclamation of the coal gangue landfill.

[0129] After six months of storage, the soil within 100m of the above-mentioned reclaimed structure was tested for heavy metal (Cu, Cr, Pb) concentrations, and no significant changes were found in the heavy metal content.

[0130] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects: Based on the analysis results of the basic physicochemical properties of coal-based solid waste and topsoil in mining areas, the key limiting factors of the physicochemical properties of coal-based solid waste such as coal gangue, fly ash, and coal gasification slag, as well as topsoil, are determined. A soil matrix containing coal-based solid waste is formed by adjusting the composition and ratio. Specifically, the addition of fly ash increases the content of available nitrogen and available phosphorus in the topsoil; the addition of coal gangue mainly increases the content of available potassium and organic matter in the topsoil; the addition of coal gasification slag mainly increases the content of available phosphorus and organic matter in the topsoil; and the addition of microbial fertilizer increases the nutrient content in the topsoil of mining areas. The physicochemical properties and water and fertilizer retention capacity of this soil matrix meet the technical requirements for greening planting soil indicators, realizing the effective utilization of coal-based solid waste. Using this soil matrix containing coal-based solid waste for landfilling coal gangue can achieve on-site material sourcing and better realize the reclamation of coal gangue landfills.

[0131] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for reclamation of coal gangue landfills, characterized in that, At the bottom of the coal gangue landfill, from bottom to top, an impermeable layer, a coal gangue composite filling layer, and a soil layer are sequentially arranged, wherein the coal gangue composite filling layer is formed by filling coal gangue and slurry material. The soil layer comprises a soil matrix, which, by weight percentage, includes: 3-5% coal gangue, 1-3% fly ash, 0.5-1.5% coal gasification slag, 7-9% microbial fertilizer, and topsoil from the mining area; the topsoil is the surface soil layer at a depth of 0-20 cm; the pH value of the topsoil is 7.5-8.5; and the particle size of the topsoil is less than 2 mm. The raw materials for the slurry material include: 5-10 parts sodium alginate, 35-40 parts fly ash, 10-12 parts loess, 3-5 parts hydrotalcite, 5-7 parts bentonite, 55-65 parts modified lignocellulose solution, 3-4 parts sodium bicarbonate, 3-4 parts aluminum sulfate, and 140-180 parts water. The method for preparing the modified lignocellulose solution includes: carrying out a modification reaction of enzymatically hydrolyzed lignin, phenol, sodium hydroxide, and water under closed conditions to obtain a modified lignocellulose solution; based on the total mass of the added raw materials as 100%, the amount of enzymatically hydrolyzed lignin added is 20~25wt%; the mass ratio of phenol to enzymatically hydrolyzed lignin is 0.5~0.6:1; and the mass ratio of sodium hydroxide to lignin is 0.4~0.6:

1. The slurry material is prepared by the following method: Step A1: Mix fly ash with modified lignocellulose solution to obtain a first mixture; Step A2: Bentonite is mixed with sodium bicarbonate and a portion of water to obtain a second mixture, wherein the portion of water is 10-15 parts by weight. Step A3: After mixing the first mixture and the second mixture, the resulting mixture is mixed with sodium alginate, loess, hydrotalcite, bentonite and the remaining water to obtain a third mixture; Step A4: Mix the third mixture with aluminum sulfate to obtain the slurry material.

2. The method for reclamation of coal gangue landfills according to claim 1, characterized in that, The particle size of the coal gangue is less than 1 mm; And / or, the fly ash is a product of the combustion of coal-based fuel in a thermal power plant; And / or, the particle size of the coal gasification slag is less than 2 mm.

3. The method for reclamation of coal gangue landfills according to claim 1, characterized in that, The impermeable layer comprises, from bottom to top, a modified bentonite layer, an HDPE membrane, a sand diversion layer, and a geotextile. The thickness of the modified bentonite layer is 30-50cm, and the modified bentonite layer is made of fly ash modified bentonite. The thickness of the sand diversion layer is 40-60cm; HDPE guide pipes are buried in the sandy soil guide layer.

4. The method for reclamation of coal gangue landfills according to claim 1, characterized in that, The method for setting the composite filling layer includes: laying coal gangue, filling the coal gangue with slurry material to form a composite filling layer, wherein the composite filling layer includes a filling layer and a support layer located above the filling layer; The coal gangue composite filling layer comprises 3 to 5 layers of composite filling layer.

5. The method for reclamation of coal gangue landfills according to claim 4, characterized in that, The thickness of the composite filler layer is 1~2m; The thickness of the filling layer is 50~170cm, and the thickness of the support layer is 30~50cm.

6. The method for reclamation of coal gangue landfills according to any one of claims 1 to 5, characterized in that, The diameter of the coal gangue in the coal gangue composite filling layer is less than or equal to 30 cm.

7. The method for reclamation of coal gangue landfills according to any one of claims 1 to 5, characterized in that, The thickness of the soil layer is 100-150cm.

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