Ionic rare earth ore tailing sandy land soil improvement structure and improvement method

Abstract

The invention relates to an ion type rare earth ore tailing sandy land soil improvement structure and an improvement method, and belongs to the technical field of ecological restoration. The ion type rare earth ore tailing sandy land soil improvement structure sequentially comprises a humus layer, a surface soil layer and a subsoil layer. The subsoil layer comprises rare earth ore tailing sandy land soil and a slow-release modifier; the surface soil layer comprises the rare earth ore tailing sandy land soil, a slow-release modifier and a quick-acting modifier; the slow-release improver comprises agricultural and forestry wastes, and the quick-acting improver comprises livestock and poultry manure, lime and a compound fertilizer. According to ecological function characteristics of the soil, aiming at physical characteristics and nutrient content of the soil and specific rare earth and aluminum toxicity pollution of a mining area, the soil layer is remolded by using different dosages and different types of improvers, so that the restoration of a local damaged soil ecological system is accelerated, and the ecological function restoration of the soil in the rare earth ore tailing sand land is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of ecological restoration, and in particular relates to a soil improvement structure and an improvement method for ionic rare earth mine tailings. Background Art

[0002] The soil in abandoned mining areas is characterized by compacted surface soil and loss of stratification, and the function of the soil ecosystem is seriously degraded. At present, researchers have developed different high-efficiency repair modifiers, microbial agents and other contaminated soil repair agents, which have good repair effects. However, the existing technology does not reshape the soil profile. Directly using modifiers to improve the surface soil and planting tolerant plants such as Miscanthus, Chinese milk vetch, and sea buckthorn may only result in short-term greening, and cannot restore the ecological functions of the mining area soil in the long term. It is difficult to rebuild the soil ecosystem, which affects the ecological restoration of the entire mining area and leads to reclamation failure.

[0003] At present, some people have conducted in-depth research on soil profile reconstruction for soil reclamation in mining areas. For example, patent CN108668553A discloses a reclamation method for heavy metal tailings reservoirs in the Custer area, which includes the following steps: (1) leveling the dry beach of the tailings reservoir in the mining area; (2) digging trenches in a mesh form on the dry beach treated in step (1); (3) evenly laying the soil that can be planted in the trench dug in step (2) by transporting the soil out; (4) covering the soil surface with a layer of plant litter; (5) planting plants; (6) after the plants grow steadily, a relatively complete ecosystem can be formed. Although this method can effectively control the heavy metal pollution of the tailings reservoir and repair the ecological environment of the tailings reservoir, it adopts the imported soil method of "layered stripping and staggered backfilling", which consumes huge manpower and material resources and is costly.

[0004] Therefore, there is an urgent need to find an ecological restoration method that is low in cost, consumes less manpower and material resources, and can be widely used in mine reclamation. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems existing in the above-mentioned prior art and to provide a soil improvement structure and improvement method for ionic rare earth mine tailings.

[0006] The present invention is achieved through the following technical solutions:

[0007] In the first aspect, the present invention provides an ionic rare earth tailings soil improvement structure, which includes a humus layer, a topsoil layer, and a subsoil layer in sequence; the subsoil layer includes rare earth tailings soil and a slow-release improver; the topsoil layer includes the rare earth tailings soil, a slow-release improver, and a quick-acting improver; the slow-release improver includes agricultural and forestry waste, and the quick-acting improver includes livestock and poultry manure, lime, and compound fertilizer.

[0008] In order to restore the normal ecosystem function of the soil in the mining area and rebuild the local ecosystem in the mining area, the present invention adopts a method of imitating a natural soil profile to improve the soil. The present invention adopts different types of improvers to improve and reconstruct the soil profile in the mining area. The improved structure includes a humus layer, a topsoil layer, and a subsoil layer from top to bottom, wherein the humus layer can provide a habitat for soil animals; the topsoil layer and the subsoil layer are improved by using improvers, and the quick-acting improver has the characteristics of high organic matter and nutrient content and easy decomposition, can quickly release nutrient elements in the soil to be used by plants and microorganisms, and has a rapid improvement effect; the slow-release improver includes agricultural and forestry wastes, and the slow-release improver has the characteristics of high carbon content and low nutrient content, slow nutrient decomposition efficiency, can release nutrients for a long time, can effectively reduce the loss of nutrient elements, and has a lasting improvement effect. The use of slow-release improvers and quick-acting improvers to improve the soil in the mine tailings land can make the topsoil layer contain higher water content, organic matter and rich nutrients, which is beneficial to the germination of plant seeds and the growth of seedlings; the use of slow-release improvers to improve the soil in the mine tailings land can make the subsoil layer have sufficient water content, compactness and continuous nutrient supply, providing space for the development of a large number of plant roots; below the subsoil layer is the tailings soil, which is not fully matured into soil and has large particle size, and can provide support for the upper soil improvement structure of the present invention.

[0009] The soil improvement structure of the present invention uses the ecological restoration theory, is based on the advocated "waste recycling system", and greenly recycles local industrial and agricultural waste to develop improvers, providing a low-cost, low-consumption, green, environmentally friendly, and non-secondary pollution mining area soil profile reconstruction method, which can initially restore the basic ecosystem functions (nutrient provision, water and fertilizer conservation, and physical support) of contaminated soil and promote future soil utilization transformation.

[0010] Preferably, the humus layer includes plant residues, and the plant residues include at least one of straw and plant litter; specifically, the plant residues include at least one of plant litter collected in a natural environment and artificially harvested straw; the thickness of the humus layer does not exceed 5 cm; more preferably, the thickness of the humus layer is 1 cm-3 cm.

[0011] Preferably, in the topsoil layer, the slow-release improver is added in an amount of 1wt%-5wt%, and the quick-acting improver is added in an amount of 2wt%-7wt%.

[0012] More preferably, in the topsoil layer, the slow-release improver is added in an amount of 1wt%-3wt%, and the quick-acting improver is added in an amount of 5wt%-7wt%.

[0013] Preferably, the thickness of the topsoil layer does not exceed 15 cm; more preferably, the thickness of the topsoil layer is 5 cm-15 cm.

[0014] Preferably, the topsoil layer is obtained by improving the soil of the rare earth mine tailings with the slow-release improver and the quick-acting improver. Specifically, the topsoil layer is obtained by mixing the slow-release improver and the quick-acting improver with the soil of the rare earth mine tailings.

[0015] Preferably, in the subsoil layer, the slow-release modifier is added in an amount of 1wt%-5wt%.

[0016] More preferably, in the subsoil layer, the slow-release modifier is added in an amount of 1 wt% to 3 wt%.

[0017] Preferably, the thickness of the subsoil layer does not exceed 30 cm; more preferably, the thickness of the subsoil layer is 15 cm-30 cm.

[0018] Preferably, the agricultural and forestry waste includes at least one of dead branches and leaves, wood chips and straw.

[0019] Preferably, the preparation method of the sustained-release improver comprises: drying and grinding the agricultural and forestry waste. More preferably, the ground agricultural and forestry waste is passed through a 10-mesh sieve to obtain the sustained-release improver.

[0020] Preferably, the subsoil layer is obtained by improving the soil of the rare earth mine tailings with the slow-release modifier. Specifically, the subsoil layer is obtained by mixing the slow-release modifier with the soil of the rare earth mine tailings.

[0021] Preferably, the mass ratio of livestock and poultry manure, lime and compound fertilizer in the quick-acting improver is (300-500):(1-1.2):2; more preferably, the mass ratio of livestock and poultry manure, lime and compound fertilizer in the quick-acting improver is (300-500):1:2.

[0022] Preferably, the preparation method of the quick-acting improver comprises: uniformly mixing the livestock and poultry manure, lime and compound fertilizer according to the mass ratio to obtain the quick-acting improver.

[0023] The quick-acting improver and the slow-release improver of the present invention have excellent improvement effects, strong soil quality improvement effects, low cost, ecological environmental protection and no pollution, and effectively recycle and utilize local industrial and agricultural waste. Specifically, the addition amount of the slow-release improver and the addition amount of the quick-acting improver described in the present invention is a proportion of the soil quality.

[0024] The present invention selects local organic wastes such as livestock and poultry manure and agricultural and forestry wastes that are convenient and easily available as soil conditioners, thereby realizing the recycling of wastes. The quick-acting conditioner can improve the fertility of the surface soil, so that the soil in the mining area has the nutrients required for plant growth, and provides a way to eliminate the acidification of the soil in the mine tailings area; the slow-release conditioner can allow the soil in the mining area to maintain a high organic matter content for a long time, and the improvement effect is long-lasting. In addition, the organic matter that is not easy to decompose will slowly promote the stability of aggregates for a long time, providing assistance for the reconstruction of the physical structure of the soil in the mine tailings area.

[0025] Preferably, the livestock and poultry manure is dried and sterilized; and the lime can be industrial lime.

[0026] Preferably, the compound fertilizer comprises nitrogen, phosphorus and potassium fertilizers.

[0027] Preferably, the improved structure further comprises hemp crops planted on the humus layer.

[0028] Furthermore, hemp crops that are tolerant to rare earth metal pollution, grow fast, and have high economic value can be selected and planted on the humus layer, which can further improve the soil, enhance the function of the soil ecosystem in the mine tailings, enhance the physical structure of the soil through the physical action of plant roots and secretions, promote the dissolution of mineral nutrients such as phosphorus and potassium, promote microbial reproduction, promote the formation of soil aggregates, and enhance the soil's anti-erosion ability and self-recovery ability. At the same time, the application of the soil conditioner of the present invention and the planting of plants also have a synergistic effect, which is helpful for controlling soil pollution in mine tailings and preventing the loss of rare earth elements.

[0029] Preferably, the hemp crops include at least one of ramie, jute, ramie, flax, sisal and hemp; the planting density is 3-5 plants / m 2 .

[0030] Preferably, the planting is carried out by sowing in a square shape with equal spacing, with a spacing of 60 cm, and watering and cultivating every other day.

[0031] In a second aspect, the present invention provides a method for preparing the above-mentioned ionic rare earth mine tailings soil improvement structure, comprising the following steps:

[0032] (1) leveling the soil of the rare earth mine tailings, and evenly mixing the slow-release modifier with the soil of the rare earth mine tailings to obtain a soil precursor;

[0033] (2) Spreading a quick-acting improver on the surface of the soil precursor obtained in step (1), and mixing it evenly with a certain thickness of the soil precursor to obtain a topsoil layer, and the remaining soil precursor forms a subsoil layer;

[0034] (3) Spreading plant residues on the surface of the topsoil layer obtained in step (2) to obtain a humus layer.

[0035] The improvement method of the present invention is simple and easy to operate. It uses tailings soil as raw material. According to the ecological function characteristics of the soil, it targets the physical properties of the soil, the nutrient content, and the rare earth and aluminum toxicity pollution unique to the mining area. It does not require the introduction of new soil. Different types of improvers in different doses are used to reshape the soil layer, accelerate the recovery of the local damaged soil ecosystem, and achieve the recovery of the ecological function of the mine tailings soil.

[0036] Preferably, in step (1), the method of leveling the rare earth tailings land includes but is not limited to deep digging and shallow padding, deep plowing and turning the soil. Leveling the soil surface can loosen the soil density and aggregate structure, and reshape the micro-topography of the mine tailings land.

[0037] Preferably, when the slow-release modifier is mixed with the soil in step (1), the thickness of the turned soil does not exceed 45 cm.

[0038] Preferably, when the slow-release modifier is mixed with a certain thickness of subsoil layer in step (2), the thickness of the certain thickness of subsoil layer does not exceed 15 cm.

[0039] Preferably, the improvement method further comprises step (4): planting hemp crops on the surface of the humus layer obtained in step (3).

[0040] Specifically, before the step (1), the soil fertility, basic physical and chemical properties, and soil pollution status of the ionic rare earth mine tailings land can also be measured to clarify the initial soil condition. The test indicators of the soil fertility and basic physical and chemical properties include: soil layer thickness, pH, bulk density, water holding capacity, organic matter content, particle size, nutrient elements (nitrogen, phosphorus, potassium, sulfur and other macroelements, boron, copper, zinc, manganese and other trace elements), soil cation content; the test indicators of soil pollution status include: the total amount of rare earth elements and their effective content, the total amount of aluminum elements and their effective content.

[0041] Specifically, after step (4), the improved soil can also be investigated, the thickness of the effective soil layer can be measured, and the rhizosphere soil, non-rhizosphere soil and blank plot soil can be collected. According to the requirements of "Quality Grade of Cultivated Land (GB / T 33469-2016)" and "Technical Guidelines for Restoration of Ecological Functions of Soils in Ionic Rare Earth Mining Areas (T / CI 017-2023)", the soil fertility index and soil pollution index can be measured to judge the soil quality restoration effect. The soil fertility index includes: pH, bulk density, water holding capacity, organic matter content, particle size, nutrient element content (nitrogen, phosphorus, potassium, sulfur and other macro-elements, boron, copper, zinc, manganese and other trace elements), cation concentration; the soil pollution index includes: the total amount of rare earth elements (REEs) and their effective content, the total amount of aluminum and its effective content.

[0042] Furthermore, the hemp crops can be harvested regularly to realize plant resource recycling, and can also realize crop cycle planting and restoration, further restoring the ecological function of the soil.

[0043] The present invention improves soil according to soil physical properties, nutrient content and rare earth and aluminum toxicity pollution unique to mining areas, and is particularly suitable for ionic rare earth mine tailings areas.

[0044] The present invention has the following beneficial effects:

[0045] (1) The present invention provides a soil improvement structure and method for ionic rare earth mine tailings, which does not use foreign soil sources and completely utilizes the soil from the abandoned mining area for transformation, with low cost;

[0046] (2) The present invention reshapes the soil layer with different types of modifiers in different doses according to the characteristics of soil ecological functions, soil physical properties, nutrient content and rare earth and aluminum toxicity pollution unique to the mining area, accelerates the restoration of the local damaged soil ecosystem, and realizes the restoration of the ecological function of the soil in the mine tailings area;

[0047] (3) The present invention uses locally available industrial, agricultural and forestry wastes to prepare soil conditioners with excellent improvement effects, strong soil quality improvement effects and low costs, including quick-acting conditioners with rapid nutrient release and simple plant absorption, and slow-release conditioners with long-lasting fertilizer effects and slow nutrient release. Long-term artificial cultivation is not required, and the natural development of the soil is used to promote the recovery of soil ecosystem functions.

[0048] (4) The present invention can further select hemp crops with large biomass, fast growth rate, developed root system, strong tolerance and economic benefits. The rapid growth can achieve a short-term regreening effect on the ground, providing a habitat for small animals on the ground; the developed root system can promote the formation of soil aggregates through physical and chemical effects, improve the self-recovery ability of the soil, and provide nutrients and habitats for underground microbial communities and protozoa;

[0049] (5) After the restoration of the ionic rare earth mine tailings land by the present invention, the soil physical structure is significantly enhanced (bulk density is reduced, clay content is increased, and sand content greater than 5 mm is reduced), the water and fertilizer retention capacity is enhanced, the organic matter content is significantly increased, acidification and aluminum toxicity are alleviated, the effective state of rare earth metals is significantly reduced, the soil profile is significantly stratified, and the soil quality basically meets the requirements of "Quality Grades of Cultivated Land (GB / T 33469-2016)" and "Technical Guidelines for Restoration of Soil Ecological Functions in Ionic Rare Earth Mining Areas (T / CI 017-2023)", laying a solid foundation for the subsequent reclamation of mine tailings land. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a schematic diagram of a specific process of the improved method of Example 1 of the present invention;

[0051] Figure 2 A schematic diagram of the survey of the ionic rare earth mine tailings conditions in step (1) of the improved method of Example 1;

[0052] Figure 3 The ionic rare earth tailings land after the landform remodeling in step (2) of the improved method of Example 1;

[0053] Figure 4 It is a cross-sectional schematic diagram of the soil improvement structure of the ionic rare earth mine tailings in Example 1;

[0054] Figure 5 It is a cross-sectional schematic diagram of the soil improvement structure of the ionic rare earth mine tailings in Example 2;

[0055] Figure 6 This is a cross-sectional schematic diagram of the soil improvement structure of the ionic rare earth mine tailings field of Comparative Example 1;

[0056] Figure 7 This is a cross-sectional schematic diagram of the soil improvement structure of the ionic rare earth mine tailings field of Comparative Example 2;

[0057] Figure 8 A schematic diagram of collecting soil samples for monitoring the restoration quality of soil after soil improvement according to the present invention;

[0058] Fig. 9 The soil profiles of the improved soil of Example 1 and Comparative Example 3 after one year of reclamation and the unrepaired tailings land are shown in Figure 1, wherein (a) is the profile of the improved soil of Comparative Example 3 after one year of reclamation, (b) is the profile of the improved soil of Example 1 after one year of reclamation, and (c) is the soil profile of the unrepaired tailings land;

[0059] Fig.10 This is a diagram showing the effect of planting ramie in improved soil according to Example 1;

[0060] Fig.11 This is a diagram showing the effect of planting ramie in improved soil according to Example 2;

[0061] Fig.12 This is a diagram showing the effect of ramie planting in improved soil of Example 3;

[0062] Fig.13 This is a statistical diagram of the difference in ramie planting biomass between Example 1 and Example 2. DETAILED DESCRIPTION

[0063] To better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be understood by those skilled in the art that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0064] Unless otherwise specified, the experimental methods used in the examples are all conventional methods; the materials, reagents, etc. used, unless otherwise specified, can be obtained from commercial channels.

[0065] In a specific implementation case of the present invention, an abandoned tailings site of an ionic rare earth mine in Dingnan County, Ganzhou City, Jiangxi Province was selected as the object of the invention implementation.

[0066] In a specific implementation case of the present invention, the preparation method of the quick-acting improver is: livestock and poultry manure (specifically pigs, cattle, and chickens) is collected from local livestock farms in Dingnan County, Ganzhou City, Jiangxi Province, and high-temperature fermentation, deodorization, disinfection, and drying are performed to remove pathogenic bacteria and microorganisms in the livestock and poultry manure, and local industrial lime and agricultural nitrogen, phosphorus, and potassium fertilizers sold in the local market are mixed, and the mixture is prepared after evenly mixing.

[0067] In a specific implementation case of the present invention, the preparation method of the sustained-release modifier is: collecting sawdust sold by a local wood processing plant in Dingnan County, Ganzhou City, Jiangxi Province, collecting dead branches and leaves from natural forests with good growth in the surrounding areas of mines, collecting local agricultural waste orange stalks, drying them, and then grinding and sieving them.

[0068] In the specific implementation case of the present invention, ramie seeds were purchased from the Ramie Research Institute of the Chinese Academy of Agricultural Sciences.

[0069] Example 1

[0070] In the specific implementation of the technical solution of the present invention, according to Figure 1 The specific implementation process is as follows:

[0071] A method for improving soil in ionic rare earth mine tailings, comprising the following steps:

[0072] (1) We selected ionic rare earth mine tailings with different abandonment times (1, 3, 6, and 10 years) in Dingnan County, Ganzhou City, Jiangxi Province as the survey objects and compared them with the surrounding unmined natural vegetation growth areas. The survey schematic diagram is shown in the figure below. Figure 2 As shown, soil was collected from tailings land and natural vegetation growth area, and crushed stone, gravel and plant residues were picked out after air drying, ground and sieved (10 mesh and 100 mesh), and the physical and chemical properties of the soil were measured to clarify the obstacle factors for soil reclamation in ionic rare earth mine tailings land;

[0073] (2) Improve the tailings of the ionic rare earth mine that has been abandoned for 6 years. Use light excavators and bulldozers to dig deep and fill shallow, level the uneven terrain with gullies and hills formed after mining; deep plowing and turning the soil to break up the hardened soil on the surface of the ionic rare earth mine tailings, loosen the soil density and aggregate structure; the ionic rare earth mine tailings after landform reshaping Figure 3 ;

[0074] (3) Take livestock and poultry manure from local animal husbandry sites, perform high-temperature fermentation, deodorization, disinfection, sterilization, and drying treatments; mix the livestock and poultry manure with local industrial lime and commercially available nitrogen, phosphorus, and potassium fertilizers at a mass ratio of 400:1:2 to prepare a quick-acting improver; take sawdust sold by a local wood processing plant, dead branches and leaves from natural forests around the mining area, and agricultural waste citrus stalks, grind them, pass through a 10-mesh sieve, and mix them evenly to prepare a slow-release improver;

[0075] (4) The slow-release improver was evenly spread on the soil surface of the mining area at a ratio of 2%, and a tractor was used to mix a 40 cm soil layer to form a soil precursor with improved soil structure; then the quick-acting improver was spread on the surface of the soil precursor at a ratio of 5%, and a tractor was used to mix a 10 cm soil layer to form a topsoil layer with improved soil structure, and the remaining 30 cm of soil precursor was used as the subsoil layer with improved soil structure; then plant residues such as orange stalks and plant litter were spread with a thickness of 3 cm to form a humus layer with improved soil structure; an improved soil structure with a depth of 43 cm was obtained, and the cross-sectional schematic diagram of the soil is shown as follows: Figure 4 As shown;

[0076] (5) The ramie seeds were sterilized with 10% hydrogen peroxide solution for 20 minutes, and then washed with pure water for germination. After germination, well-developed seeds were selected for sowing. The seeds were sown in squares and at equal intervals, with a sowing interval of 60 cm and a planting density of 3-5 plants / m 2 , water and cultivate every other day;

[0077] (6) One year after planting, observe soil improvement.

[0078] Example 2

[0079] The soil improvement method for ionic rare earth mine tailings provided in this embodiment is different from that in embodiment 1 only in step (4), and the other steps are the same; step (4) of the improvement method in this embodiment is: the slow-release improver is evenly spread on the soil surface of the mining area at a ratio of 5%, and a tractor is used to mix a 40 cm soil layer to form a soil precursor with improved soil structure; then the quick-acting improver is spread on the surface of the soil precursor at a ratio of 2%, and a tractor is used to mix a 10 cm soil layer to form a topsoil layer with improved soil structure, and the remaining 30 cm of soil precursor is used as the subsoil layer of the improved soil structure; then, plant residues such as orange stalks and plant litter are spread with a thickness of 3 cm to form a humus layer with improved soil structure; an improved soil structure with a depth of 43 cm is obtained, and the cross-sectional schematic diagram of the soil is shown as follows: Figure 5 shown.

[0080] Example 3

[0081] The soil improvement method for ionic rare earth mine tailings provided in this embodiment is different from that in embodiment 1 only in step (4), and the other steps are the same; step (4) of the improvement method in this embodiment is: a slow-release improver is evenly spread on the soil surface of the mining area at a ratio of 2%, and a tractor is used to mix a 25 cm soil layer to form a soil precursor with an improved soil structure; then a quick-acting improver is spread on the surface of the soil precursor at a ratio of 5%, and a tractor is used to mix a 5 cm soil layer to form a topsoil layer with an improved soil structure, and the remaining 20 cm of soil precursor is used as a subsoil layer with an improved soil structure; then, plant residues such as orange stalks and plant litter are spread with a thickness of 1 cm to form a humus layer with an improved soil structure; an improved soil structure with a depth of 26 cm is obtained.

[0082] Comparative Example 1

[0083] This comparative example provides a method for improving soil in an ionic rare earth mine tailings area. Compared with Example 1, the only difference is that steps (3) and (4) are different, and the other steps are the same; step (3) of the improvement method of this comparative example is: taking livestock and poultry manure from a local animal husbandry site, performing high-temperature fermentation, deodorization, disinfection, sterilization, and drying treatment; mixing the livestock and poultry manure with local industrial lime and commercially available nitrogen, phosphorus, and potassium fertilizers in a mass ratio of 400:1:2 to prepare a quick-acting improver;

[0084] Step (4) is: spreading the quick-acting improver at a ratio of 7% evenly on the soil surface of the mining area, using a tractor to mix a 40 cm soil layer to form a topsoil layer with improved soil structure; then spreading 3 cm thick orange stalks, plant litter and other plant residues to form a humus layer with improved soil structure; an improved soil structure with a depth of 43 cm is obtained, and the cross-sectional schematic diagram of the soil is as follows Figure 6 shown.

[0085] Comparative Example 2

[0086] This comparative example provides a method for improving soil in an ionic rare earth mine tailings area. Compared with Example 1, the only difference is that steps (3) and (4) are different, and the other steps are the same; step (3) of the improvement method of this comparative example is: taking sawdust sold by a local wood processing plant, dead branches and leaves of natural forests around the mining area, and agricultural waste citrus stalks, grinding them, passing through a 10-mesh sieve, and mixing them evenly to prepare a slow-release improver;

[0087] Step (4) is: evenly spread the slow-release improver at a ratio of 3% on the surface of the soil in the mining area, use a tractor to mix a 40 cm soil layer to form a subsoil layer with improved soil structure; then spread 3 cm thick orange stalks, plant litter and other plant residues to form a humus layer with improved soil structure; an improved soil structure with a depth of 43 cm is obtained, and the cross-sectional schematic diagram of the soil is as follows Figure 7 shown.

[0088] Comparative Example 3

[0089] The soil improvement method for ionic rare earth mine tailings provided in this comparative example is different from that in Example 1 only in step (4), and the other steps are the same; step (4) of the improvement method in this comparative example is: a quick-acting improver is evenly spread on the soil surface of the mining area at a ratio of 5%, and a tractor is used to mix a 40 cm soil layer to form a soil precursor with an improved soil structure; then a slow-release improver is spread on the surface of the soil precursor at a ratio of 2%, and a tractor is used to mix a 10 cm soil layer to form a topsoil layer with an improved soil structure, and the remaining 30 cm of soil precursor is used as a subsoil layer with an improved soil structure; then, plant residues such as orange stalks and plant litter are spread with a thickness of 3 cm to form a humus layer with an improved soil structure; an improved soil structure with a depth of 43 cm is obtained.

[0090] The present invention carries out physical and chemical property detection on the soil of ionic rare earth mine tailings with different abandonment years. The test results show that the clay content of the soil of ionic rare earth mine tailings is much lower than that of the soil of the surrounding normal vegetation area, the soil bulk density is significantly higher than that of the surrounding normal vegetation area, and the soil organic matter content is also much lower than that of the surrounding normal vegetation area; the soil conductivity, ammonium nitrogen and alkaline nitrogen content of the tailings abandoned for 1 year are much higher than those of the soil of the surrounding normal vegetation area, while the soil of the tailings abandoned for 3 to 10 years are much lower than those of the surrounding normal vegetation area. It is speculated that the use of high-concentration leaching agents and the leaching of metals at the beginning of mining activities make the initial soil conductivity, ammonium nitrogen and alkaline nitrogen content far exceed the normal soil content. Then, with the abandonment of the mining area, the poor physical structure of the tailings land caused ionic metals, ammonium nitrogen and alkaline nitrogen to enter the surrounding water bodies along with the loss of water and soil. We infer that in the early stage of tailings land abandonment, due to the high concentration of ionic metals, ammonium nitrogen and alkaline nitrogen, plants could not survive. High concentration of pollution was the main obstacle to the reclamation of tailings land soil in the early stage. And the soil of the tailings land after mining, due to the destruction of physical structure and soil stratification, the organic matter was greatly lost. As the abandonment time increases, the physical and chemical properties become worse and worse, making it difficult for plants to colonize. The extremely low content of organic matter and poor soil physical structure are the main obstacles to the reclamation of tailings land soil in the later stage.

[0091] Therefore, through the analysis of soil physical and chemical properties and comparative analysis with the surrounding unmined normal vegetation areas, it was found that the physical and chemical properties of soil in ionic rare earth mine tailings with different abandonment times (1 to 10 years) did not improve significantly, and the main obstacles to its vegetation reclamation are: low clay content, high sand content (>5mm), large bulk density, extremely poor physical structure, and lack of organic matter in the tailings soil; extremely high ammonia nitrogen and metal concentrations in the early tailings, and poor nutrients in the later tailings.

[0092] Collect improved soil samples according to Figure 8Soil samples and blank soil samples were collected from the repaired plots, and the physical and chemical properties of the soil in the ionic rare earth tailings field improved by the improved method step (4) of Example 1 and Comparative Examples 1-3 were tested. The test method is as follows:

[0093] Test density: ring knife method;

[0094] Soil particle size (sand, silt, clay): hydrometer method;

[0095] pH: potentiometric method;

[0096] EC: electrode method;

[0097] CEC: hexaamminecobalt trichloride extraction-spectrophotometry;

[0098] Extractable metals: CaCl2 extraction method;

[0099] TC, TN: dry combustion method (Vario EL Cube);

[0100] The test results are shown in Table 1.

[0101] Table 1 Physical and chemical properties of the soil in the ionic rare earth mine tailings after improvement by the improvement methods of Example 1 and Comparative Examples 1-3

[0102]

[0103] It can be seen from Table 1 that the soil pH of the ionic rare earth mine tailings area is 4.45, the concentrations of EC, CEC, and extractable nutrient elements are low, the fertility is weak, the bulk density is large, the content of powder and clay particles with a diameter of less than 0.05mm is high, the soil compaction problem is prominent, and the concentrations of extractable aluminum and rare earth elements are high, which are highly toxic and completely unsuitable for plant colonization.

[0104] In Example 1, after the soil profile was reconstructed, the bulk density, soil particle size and pH of the topsoil and subsoil layers were significantly improved, the total carbon, total nitrogen, EC, CEC and nutrient content of the topsoil layer were significantly higher than those of the unrestored soil, and the soil fertility was significantly enhanced, which met the requirements of the "Quality Grades of Cultivated Land (GB / T 33469-2016)" and the "Technical Guidelines for Restoration of Soil Ecological Functions in Ionic Rare Earth Mining Areas (T / CI 017-2023) requires that, at the same time, the content of effective rare earth elements and aluminum in the soil are significantly reduced (>90%), the pollution situation is significantly improved, and the quick-acting improver can effectively fix toxic elements such as rare earth and aluminum to prevent them from being lost from the tailings soil; since the subsoil layer is applied with a slow-release improver, the content of EC, CEC and extractable elements has not changed significantly, and the downward trend of the content of effective rare earth elements and aluminum in the soil is not as significant as that in the topsoil layer, but the soil bulk density is significantly reduced, and the proportion of soil powder (0.002-0.05mm) is significantly increased, providing sufficient space for the growth and colonization of plant roots, and the application of slow-release improvers can not only effectively absorb the nutrients lost by the quick-acting improvers with soil and water loss, but also the strong durability of the improvement is also conducive to the succession and formation of the soil profile in the natural succession process after restoration, and promote the development and transformation of the soil of the polluted plot to natural soil.

[0105] In Comparative Example 3, although the physical and chemical properties of the topsoil and subsoil layers after the soil profile was reconstructed were significantly improved compared with the unrepaired soil, they did not conform to the OABC layer structure of the natural soil profile, but were similar to the soil improved by the improvers in Comparative Examples 1 and 2. In addition, since the subsoil layer was improved entirely with quick-acting improvers, the EC value was significantly improved, and it was unable to absorb the nutrients of the upper layer with soil and water loss like the subsoil layer in Example 1, which easily caused a large loss of soil elements, resulting in poor long-term reclamation effect.

[0106] According to the method in Table 1, the fertility index of the soil in the ionic rare earth mine tailings land after one year of reclamation by the improved method in Example 1 and Comparative Examples 1-2 was tested, and the test results are shown in Table 2.

[0107] Table 2 Fertility index of the soil in the ionic rare earth mine tailings land after one year of reclamation by the improved method of Example 1 and Comparative Example 1-2

[0108]

[0109]

[0110] It can be seen from Tables 1 and 2 that, compared with the traditional method of simply adding different types of amendments, after the soil profile of the contaminated plot is reconstructed by simulating natural soil profiles, the humus layer and the topsoil layer can provide the necessary nutrients for plant colonization in a short period of time. After the subsoil layer is improved with slow-release amendments, the soil bulk density is effectively reduced in the early stage of reclamation, which promotes the colonization of plant roots. One year after the reclamation period, the soil still has good physical and chemical properties, which proves that the subsoil layer can still effectively absorb the nutrients of the topsoil layer with soil erosion under the influence of natural climate such as rain erosion, and the small-particle organic matter released over a long period of time can effectively promote the root customization of plants and inhibit the activation of toxic elements (aluminum and rare earths).

[0111] The soil profiles of Example 1, Comparative Example 3 and the unrepaired tailings land were observed one year after reclamation. The results showed that Fig. 9 and Table 3, where compaction: 0, loose; 1, weakly compacted; 2, moderately compacted; 3, strongly compacted.

[0112] Table 3 Description of soil profiles of Example 1, Comparative Example 3 and unrepaired tailings land

[0113]

[0114]

[0115] Fig. 9 The soil profiles of Comparative Example 3 (a) and Example 1 (b) of the present invention and the unrepaired tailings land (c) after one year of reclamation are shown in FIG. Fig. 9 As shown in Table 3, there is no obvious stratification in the soil section of the unrepaired tailings land ( Fig. 9 c), which is consistent with the characteristics of the tailings soil being destroyed by mining activities and the characteristics of soil structure and stratification; and after one year of soil profile remodeling and reclamation, Example 1 ( Fig. 9 b) The surface soil and deep soil of the improved plots are significantly stratified, and the soil fertility is effectively restored. At the same time, a large number of roots can be observed to be distributed in the pores of the soil, proving that after the soil profile of the tailings land is reconstructed by this method, the water and fertilizer retention capacity is enhanced, and it can effectively provide space for ramie planting. Ramie planting can strengthen the ecological succession of the soil and promote the development and transformation of the soil of the polluted plot to natural soil. While in comparative example 3 ( Fig. 9 The soil profile of a) has significantly fewer ramie roots and is still in a relatively compact state with no significant stratification.

[0116] Fig.10 This is a picture showing the effect of ramie in the improved soil of Example 1 after one year of planting. Fig.11 This is the effect diagram of ramie planted in the improved soil of Example 2 after one year. Fig.12This is the effect diagram of ramie planted in the improved soil of Example 3 after one year. Fig.13 The difference statistical diagram of ramie planting biomass between Example 1 and Example 2 is shown in FIG. Figure 10-13 It can be seen that the ramie planting effects of Examples 2 and 3 are not good, and the ramie planting effect in Example 1 is better. When ramie is planted in the soil reconstructed in Example 1, the biomass is significantly higher than that in Example 2.

[0117] In summary, the soil profile reconstructed by the method of the present invention can effectively provide growth space and required nutrients for plant colonization, and due to the application of modifiers, the content of effective toxic elements (aluminum, rare earth) is significantly reduced, so that the reclamation effect is significantly enhanced.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A soil improvement structure for ionic rare earth mine tailings, characterized in that: The improved structure includes a humus layer, a topsoil layer, and a subsoil layer in sequence; the subsoil layer includes soil from rare earth mine tailings and a slow-release improver; the topsoil layer includes soil from rare earth mine tailings, a slow-release improver, and a quick-acting improver; the slow-release improver includes agricultural and forestry waste, and the quick-acting improver includes livestock and poultry manure, lime, and compound fertilizer.

2. The ionic rare earth mine tailings soil improvement structure according to claim 1, characterized in that: In the topsoil layer, the slow-release improver is added in an amount of 1wt%-5wt%, and the quick-acting improver is added in an amount of 2wt%-7wt%.

3. The ionic rare earth mine tailings soil improvement structure according to claim 1, characterized in that: In the subsoil layer, the slow-release modifier is added in an amount of 1wt%-5wt%.

4. The ionic rare earth mine tailings soil improvement structure according to claim 1, characterized in that: The mass ratio of the livestock and poultry manure, lime and compound fertilizer in the quick-acting improver is (300-500):(1-1.2):

2.

5. The ionic rare earth mine tailings soil improvement structure according to claim 1, characterized in that: The humus layer includes plant residues, and the plant residues include at least one of straw and plant litter.

6. The ionic rare earth mine tailings soil improvement structure according to claim 1, characterized in that: The agricultural and forestry waste includes at least one of dead branches and leaves, wood chips and straw.

7. The ionic rare earth mine tailings soil improvement structure according to claim 1, characterized in that: The thickness of the humus layer does not exceed 5 cm; and / or, the thickness of the topsoil layer does not exceed 15 cm; and / or, the thickness of the subsoil layer does not exceed 30 cm.

8. The ionic rare earth mine tailings soil improvement structure according to claim 1, characterized in that: The improved structure also includes hemp crops planted on the humus layer.

9. A method for preparing the ionic rare earth mine tailings soil improvement structure according to any one of claims 1 to 8, characterized in that: The following steps are involved: (1) leveling the soil of the rare earth mine tailings, and evenly mixing the slow-release modifier with the soil of the rare earth mine tailings to obtain a soil precursor; (2) Spreading a quick-acting improver on the surface of the soil precursor obtained in step (1), and mixing it evenly with a certain thickness of the soil precursor to obtain a topsoil layer, and the remaining soil precursor forms a subsoil layer; (3) Spreading plant residues on the surface of the topsoil layer obtained in step (2) to obtain a humus layer.

10. The method for preparing the ionic rare earth mine tailings soil improvement structure according to claim 9, characterized in that: The method further comprises the step (4): planting hemp crops on the surface of the humus layer obtained in the step (3).

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