A Pollution Control and Vegetation Restoration Structure and Method for a Historic Metal Tailings Pond

Abstract

The present invention discloses a structure and method for treating pollution and restoring vegetation in historical legacy metal tailing ponds. The structure includes a coarse gravel layer, a water-retaining and stable soil layer, a biodegradable layer, a vegetation growth soil layer, and a fine gravel layer laid sequentially from bottom to top on the surface of the tailing pond. The method includes the laying of each layer and the steps of oxygen and moisture barrier. The fine gravel layer serves to reduce the evaporation of moisture in the vegetation growth soil layer and promote lateral drainage. The biodegradable layer serves to consume the diffused oxygen and increase the nutrients in the vegetation growth soil layer. The water-retaining and stable soil layer not only has a high saturated moisture content, can block the penetration of oxygen and water, but also can stabilize heavy metals and prevent the leaching and migration of heavy metals. The present invention can effectively prevent the contact between sulfide mineral tailings and oxygen and water, control the oxidation of sulfides and the generation of acid mine drainage from the source, and can make the vegetation growth soil layer in an independent environment free from pollution threats, continuously maintaining good plant growth conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of pollution control and mine ecological restoration, and specifically relates to a pollution control and vegetation restoration structure and method for historical legacy metal tailing ponds. Background Art

[0002] According to the data in the "Annual Report on the Prevention and Control of Environmental Pollution by Solid Wastes in Large and Medium-sized Cities across the Country in 2020" released by the Ministry of Ecology and Environment of China, the annual output of tailings from 196 key surveyed industrial enterprises is as high as 1.03 billion tons, while the comprehensive utilization rate is only 27%.

[0003] The "Technical Specification for Mine Ecological Environment Protection and Ecological Restoration and Governance" requires that the soil covering thickness for vegetation restoration after closing the pond should not be less than 10 cm; the "Quality Control Standard for Land Reclamation" requires that the tailing pond should be covered with more than 50 cm of soil when reclaimed, and an isolation layer should be set if there is pollution. The surface should be covered with soil when closing the pond, and the thickness is determined according to the particle size of the solid waste and the types of plants to be planted. According to the research by expert Romano Connie G of the University of Waterloo in Canada, when using a single material for covering (such as soil), for a 1 m covering thickness within a 100-year simulation time, the oxidation rate is only reduced by about 75%. However, the "Quality Control Standard for Land Reclamation" in China only requires covering more than 0.5 m of soil for the closing and reclamation of tailing ponds, and cannot significantly prevent the generation of acidic mine wastewater pollution. The sulfides therein will continuously undergo oxidation reactions under the action of oxygen and water, generating an acidic wastewater. Taking pyrite as an example, its main oxidation process is as follows:

[0004] FeS 2 + 7 / 2O 2 + H 2 O → Fe 2+ + 2SO 4 2- + 2H +

[0005] Fe 2+ + 1 / 4O 2 + H + → Fe 3+ + 1 / 2H 2 O

[0006] Fe 3+ + 3H 2 O → Fe(OH) 3 + 3H +

[0007] FeS 2 + 14Fe 3+ + 8H 2 O → 15Fe2+ + 2SO 4 2- + 16H +

[0008] FeS 2 + 15 / 4O 2 + 1 / 2H 2 O → Fe 3+ + 2SO 4 2- + H +

[0009] This kind of wastewater has a low pH (2 - 4), high concentrations of heavy metals and sulfates, and can cause acidification and heavy metal pollution to the groundwater, surface water and soil around the mining area. Therefore, for general tailing ponds, especially those left over from history, the vegetation restored during the closure of the ponds can only maintain the effect for a few years, and the surrounding soil and vegetation will gradually become polluted and die.

[0010] Therefore, it is a technical problem to carry out source pollution control and vegetation restoration for the metal tailing ponds left over from history. For this reason, it is very necessary to study a simple - operation, low - cost and long - effective pollution control and vegetation restoration structure and method for the metal tailing ponds left over from history. Summary of the Invention

[0011] The first object of the present invention is to provide a pollution control and vegetation restoration structure for metal tailing ponds left over from history.

[0012] The second object of the present invention is to provide a method for using the pollution control and vegetation restoration structure for metal tailing ponds left over from history.

[0013] The first object of the present invention is achieved as follows: it includes a coarse gravel layer, a water - retaining and stable soil layer, a biodegradable layer, a vegetation - growing soil layer and a fine gravel layer laid on the surface of the tailing pond from bottom to top in sequence. The particle size of the soil in the water - retaining and stable soil layer is smaller than that of the gravel in the coarse gravel layer.

[0014] Preferably, the fineness modulus of the coarse gravel layer is 2.5 - 3.5, and the thickness of the coarse gravel layer is 15 - 20 cm.

[0015] Preferably, the water - retaining and stable soil layer is obtained by uniformly mixing fly ash, red mud and sieved fine soil in a mass ratio of 10:1 - 5:10, and the thickness of the water - retaining and stable soil layer is 10 - 15 cm.

[0016] Preferably, the biodegradable layer is one or more of crushed straws, sawdust, and pulp, and the thickness of the biodegradable layer is 5 - 10 cm.

[0017] Preferably, the vegetation growth soil layer is the native soil around the tailings pond or the artificially configured soil after improvement, and the thickness of the vegetation growth soil layer is 10-20 cm.

[0018] Preferably, the particle size of the fine gravel layer is 0.1-0.5 mm, and the thickness of the fine gravel layer is 2-5 cm.

[0019] Preferably, after sowing seeds or transplanting seedlings in the vegetation growth soil layer, the fine gravel layer is laid.

[0020] The second object of the present invention is achieved as follows, including the following steps:

[0021] S1. Lay the coarse gravel layer, water retention and stability soil layer, biodegradable layer, vegetation growth soil layer and fine gravel layer in sequence;

[0022] S2. A capillary barrier effect is formed at the interface between the coarse gravel layer and the water retention and stability soil layer, so that the water retention and stability soil layer maintains a high water saturation degree and blocks the downward infiltration of water; during the biodegradation process, the biodegradable layer consumes the oxygen diffused from the upper layer, blocks the downward diffusion of oxygen, and at the same time provides nutrients for the plants planted in the vegetation growth soil layer; the plant roots distributed in the vegetation growth soil layer intercept water and reduce the downward infiltration of water; the fine gravel layer reduces the evaporation of water in the vegetation growth soil layer, enhances the lateral drainage, reduces the scouring effect of rainwater on the vegetation growth soil layer, and reduces the downward infiltration of water.

[0023] Compared with the prior art, the present invention has the following technical effects:

[0024] 1. The present invention adopts the principle of capillary barrier covering and blocking. When two particle layers with different particle sizes are in contact, due to the difference in unsaturated hydraulic properties, the vertical water flow between the two layers is often restricted, thus generating a capillary barrier effect, keeping a high saturation degree in the water retention and stability soil layer, and preventing oxygen and water from contacting sulfides;

[0025] 2. The present invention uses the biodegradable layer as an organic reaction barrier. During the biodegradation process, it can not only consume the oxygen diffused from the upper layer, but also provide nutrients for the vegetation growth in the upper layer;

[0026] 3. The present invention uses the three-layer structure of the vegetation growth soil layer, the biodegradable layer and the water retention and stability soil layer to block and consume water and oxygen layer by layer, greatly weakening the permeability of oxygen and water, solving the oxidation of sulfides from the source and preventing the generation of acidic mine wastewater;

[0027] 4. The fly ash and red mud in the water retention and stability soil layer of the present invention are alkaline. For the tailings ponds with historical legacy and already acidified pollution, their leachate can help neutralize the acidic substances in the tailings and stabilize the heavy metals with the risk of migration and diffusion;

[0028] 5. The fine gravel layer of the present invention can not only shield the soil layer for vegetation growth, reduce the evaporation of soil moisture, but also increase lateral drainage, reduce the scouring of rainwater on the lower layer and the infiltration of rainwater into the deep tailings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic structural diagram of the present invention;

[0030] In the figure: 1 - coarse gravel layer, 2 - water-retaining and stable soil layer, 3 - biodegradable layer, 4 - soil layer for vegetation growth, 5 - fine gravel layer, 6 - tailings pond. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The present invention will be further described below in conjunction with the drawings, but the present invention is not limited in any way. Any transformation or replacement based on the teachings of the present invention falls within the protection scope of the present invention.

[0032] Example 1

[0033] As shown in the Figure 1 drawing, for the pollution control and vegetation restoration of a sulfur-containing tailings pond according to the present invention, it includes a coarse gravel layer 1, a water-retaining and stable soil layer 2, a biodegradable layer 3, a soil layer for vegetation growth 4, and a fine gravel layer 5 laid in sequence from bottom to top on the surface of the tailings pond. Both the coarse gravel layer 1 and the fine gravel layer 5 are made of sand and gravel. The particle size of the coarse gravel layer 1 has a fineness modulus of 2.5 - 3.5 and a thickness of 20 cm. The particle size of the fine gravel layer 5 is 0.1 - 0.5 mm and the thickness is 2 cm. The water-retaining and stable soil layer 2 is obtained by uniformly mixing fly ash, red mud, and sieved fine soil in a mass ratio of 10:1:10. The water-retaining and stable soil layer 2 is sieved through a 80-mesh sieve and has a thickness of 10 cm. The biodegradable layer 3 is crushed straw with a thickness of 5 cm. The soil layer for vegetation growth 4 is the surrounding native soil with a thickness of 10 cm. The soil layer for vegetation growth 4 is planted with Indigofera amblyantha, Medicago sativa, Robinia pseudoacacia, and Juncus alatus.

[0034] Example 2

[0035] As shown in the Figure 1As shown in the figure, for the pollution control and vegetation restoration of a sulfur-containing tailings reservoir according to the present invention, it includes a coarse gravel layer 1, a water-retaining and stable soil layer 2, a biodegradable layer 3, a vegetation growth soil layer 4, and a fine gravel layer 5 laid in sequence from bottom to top on the surface of the tailings reservoir. Both the coarse gravel layer 1 and the fine gravel layer 5 are selected from waste soil and rock. The fineness modulus of the coarse gravel layer 1 is 2.5 - 3.5, and the thickness is 15 cm. The particle size of the fine gravel layer 5 is 0.1 - 0.5 mm, and the thickness is 3 cm. The water-retaining and stable soil layer 2 is obtained by uniformly mixing fly ash, red mud, and sieved fine soil in a mass ratio of 10:3:10. The water-retaining and stable soil layer 2 passes through an 80-mesh sieve, and the thickness of the water-retaining and stable soil layer 2 is 15 cm. The biodegradable layer 3 is sawdust, and the thickness is 8 cm. The vegetation growth soil layer 4 is artificially improved soil, and the thickness is 15 cm. The vegetation growth soil layer 4 is planted with Indigofera amblyantha, alfalfa, Robinia pseudoacacia, and Juncus przewalskii var. przewalskii.

[0036] Example 3

[0037] As shown in the attached Figure 1 As shown in the figure, for the pollution control and vegetation restoration of a sulfur-containing tailings reservoir according to the present invention, it includes a coarse gravel layer 1, a water-retaining and stable soil layer 2, a biodegradable layer 3, a vegetation growth soil layer 4, and a fine gravel layer 5 laid in sequence from bottom to top on the surface of the tailings reservoir. Both the coarse gravel layer 1 and the fine gravel layer 5 are selected from construction waste. The fineness modulus of the coarse gravel layer 1 is 2.5 - 3.5, and the thickness is 15 cm. The particle size of the fine gravel layer 5 is 0.1 - 0.5 mm, and the thickness is 5 cm. The water-retaining and stable soil layer 2 is obtained by uniformly mixing fly ash, red mud, and sieved fine soil in a mass ratio of 10:5:10. The water-retaining and stable soil layer 2 passes through an 80-mesh sieve, and the thickness of the water-retaining and stable soil layer 2 is 15 cm. The biodegradable layer 3 is pulp, and the thickness is 10 cm. The vegetation growth soil layer 4 is artificially improved soil, and the thickness is 20 cm. The vegetation growth soil layer 4 is planted with Indigofera amblyantha, alfalfa, Robinia pseudoacacia, and Juncus przewalskii var. przewalskii.

[0038] Example 4

[0039] As shown in the attached Figure 1As shown in the figure, for the pollution control and vegetation restoration of a sulfur-containing tailings pond according to the present invention, it includes a coarse gravel layer 1, a water-retaining and stable soil layer 2, a biodegradable layer 3, a vegetation growth soil layer 4, and a fine gravel layer 5 laid successively from bottom to top on the surface of the tailings pond. The coarse gravel layer 1 and the fine gravel layer 5 are both obtained by mixing sand, waste soil and rock, and construction waste in a mass ratio of 1:1:1. The fineness modulus of the coarse gravel layer 1 is 2.5 - 3.5, and the thickness is 17.5 cm. The particle size of the fine gravel layer 5 is 0.1 - 0.5 mm, and the thickness is 3.5 cm. The water-retaining and stable soil layer 2 is obtained by uniformly mixing fly ash, red mud and sieved fine soil in a mass ratio of 10:3:10. The water-retaining and stable soil layer 2 passes through a 80-mesh sieve, and the thickness of the water-retaining and stable soil layer 2 is 12.5 cm. The biodegradable layer 3 is obtained by mixing crushed straw, sawdust and pulp in a mass ratio of 1:1:1, and the thickness is 7.5 cm. The vegetation growth soil layer 4 is artificially improved soil, and the thickness is 15 cm. The vegetation growth soil layer 4 is planted with Indigofera amblyantha, Medicago sativa, Robinia pseudoacacia, and Juncus alatus. A certain tailings pond was treated according to Example 4, and the leachate of the tailings pond was detected. The detection results are shown in Table 1;

[0040] Table 1 Detection Results of Tailings Pond Leachate

[0041]

[0042] Note: The simulation method refers to the analysis method of Connie G. Romano et al.: The cumulative mass curve of sulfate is extrapolated to the cumulative mass after 100 years, that is, the cumulative mass of the 1200th cycle is calculated by the fitting formula of the existing cumulative curve; thus, the pollution inhibition efficiency in a longer simulation interval is calculated.

[0043] It can be seen from the above experimental data that after applying the method of this patent, the content of sulfate in the wastewater (mg / L) after 12 months of treatment is significantly reduced; the oxidation rate of sulfide minerals (i.e., the amount of sulfate generated) is reduced by 93.2% after 100 years of simulation, showing obvious pollution control effect. After investigation, after applying the method of this patent, the vegetation coverage rate in the second year is higher than 90%.

Claims

1. A pollution control and vegetation restoration structure for historical legacy metal tailing ponds, characterized in that it includes a coarse gravel layer (1), a water-retaining and stable soil layer (2), a biodegradable layer (3), a vegetation growth soil layer (4), and a fine gravel layer (5) laid successively from bottom to top on the surface of the tailing pond. The soil particle size of the water-retaining and stable soil layer is smaller than the gravel particle size of the coarse gravel layer; The water-retaining and stable soil layer (2) is obtained by uniformly mixing fly ash, red mud, and sieved fine soil in a mass ratio of 10:1 to 5:10, and the thickness of the water-retaining and stable soil layer (2) is 10 - 15 cm; The biodegradable layer (3) is one or more of crushed straws, sawdust, and pulp, and the thickness of the biodegradable layer (3) is 5 - 10 cm; The method for the pollution control and vegetation restoration structure of the historical legacy metal tailing pond includes the following steps: S1. Lay the coarse gravel layer (1), the water-retaining and stable soil layer (2), the biodegradable layer (3), the vegetation growth soil layer (4), and the fine gravel layer (5) successively; S2. A capillary barrier effect is formed at the interface between the coarse gravel layer (1) and the water-retaining and stable soil layer (2), so that the water-retaining and stable soil layer (2) maintains a high water saturation degree, blocking the downward infiltration of water; the biodegradable layer (3) consumes the oxygen diffused from the upper layer during the biodegradation process, blocking the downward diffusion of oxygen, and at the same time providing nutrients for the plants planted in the vegetation growth soil layer (4); the plant roots distributed in the vegetation growth soil layer (4) intercept water, reducing the downward infiltration of water; the fine gravel layer (5) reduces the water evaporation of the vegetation growth soil layer (4), enhances the lateral drainage, reduces the scouring effect of rainwater on the vegetation growth soil layer (4), and reduces the downward infiltration of water; The fineness modulus of the coarse gravel layer (1) is 2.5 - 3.5, and the thickness of the coarse gravel layer (1) is 15 - 20 cm; The particle size of the fine gravel layer (5) is 0.1 - 0.5 mm, and the thickness of the fine gravel layer (5) is 2 - 5 cm.

2. The pollution control and vegetation restoration structure for the historical legacy metal tailing pond according to claim 1, characterized in that the vegetation growth soil layer (4) is the native soil around the tailing pond or the artificially configured soil after improvement, and the thickness of the vegetation growth soil layer (4) is 10 - 20 cm.

3. The pollution control and vegetation restoration structure for the historical legacy metal tailing pond according to claim 1, characterized in that after sowing seeds or transplanting seedlings in the vegetation growth soil layer (4), the fine gravel layer (5) is laid.

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