Farmland restoration and pollution prevention and control in mineral grain complex

China Mining Industries and Food a vast area, only coal resource and resource distribution complex area of arable land accounted for over 40% of the total arable land, of which coal resources and maintain complex area of cultivated land resources by more than 10% of the country's arable land The cumulative production of raw coal accounts for 58% of the country's total output, and grain production accounts for 45% of the country's total grain output. At the same time, due to mining activities, a large area of ​​surface subsidence has been caused, which has reduced the shortage of farmland and cultivated land. According to estimates, the subsidence caused by the underground mining of 10,000 tons of raw coal is as low as 0.033 hm ² and more than 0.533 hm ² , with an average of 0.2-0.33 hm ² . It is expected that the subsidence will increase by about 2×10 ⁴ hm ² per year. Coal mining causes the plain to become a rugged and collapsed area, fertile farmland becomes a swamp; coal gangue dust flies, mine wastewater, exhaust gas seepage, seriously polluting farmland. Among the many coal mining disturbances, the damage to the land is the most direct and the largest. Among them, coal mining, destruction of farmland and its environmental problems are particularly prominent, not only seriously affecting the economic development of the Ministry of Economy and Trade, but also triggered a series of social problems and contradictions, which have seriously affected the sustainable development of the mining area. The farmland restoration and pollution prevention and control work carried out in China's mineral grain complex has played an important role in national food security and ecological security of mining areas.

1. Farmland restoration project and solid waste treatment in mining area

At present, the main measures for the restoration of farmland in China's coal mining areas are filling and reclamation and non-filling and reclamation. Through the management, a large number of farmland have been restored and the national food security has been guaranteed.

(1) Direct farmland restoration technology

When the damage to the damaged farmland is low, the direct use or natural recovery and utilization mode is generally adopted to restore the farmland utilization. It is mainly divided into the direct use method of the stagnant water area and the direct use method of the unsteady submerged area. For mining areas with a large degree of damage, hidden dangers of geological disasters, and lack of filling materials, the land dressing and utilization method (including land leveling and terrace repair method, dumping yard renovation method, tailings renovation method), and land use and drainage Farmland restoration is carried out by law, land excavation and shallow pad shallow utilization method. The non-filling restoration project of farmland has the advantages of low reclamation cost, high ecological diversity and low secondary pollution, but also defects such as soil compaction, extensive land use, low economic benefit and long recovery period. Since the non-filling recovery project of farmland is mainly the use of construction machinery, its reclamation effect mainly depends on the land reclamation machinery, the timing of reclamation, the purpose of reclamation and the planning of reclamation.

(2) Using solid waste to fill farmland restoration technology

At present, the accumulated coal gangue reaches 15 to 2 billion tons, and there are about 850 coal gangue mountains, occupying more than 6,700 hm2 of soil. According to the National Development and Reform Commission and the State Environmental Protection Administration's "Notice on Printing and Distributing the Energy Saving and Emission Reduction Work of the Coal Industry", by the end of the "Eleventh Five-Year Plan", the comprehensive utilization rate of solid waste such as coal gangue and slime was 43% in 2005. Increase to 70%. The use of solid waste from coal gangue, ash fly ash, garbage and other mining areas to fill the subsidence, slope, water, joints and pits caused by mining can not only restore the use of farmland, but also reduce the occupation of solid waste. Land, keep the ecological environment healthy. The main types of farmland filling and recovery technologies include fly ash filling, coal gangue filling and river and lake silt filling.

1. Fill the coal gangue to restore the farmland. Use of coal gangue of subsidence area populated farmland reclamation, reduce waste rock area, restore the value of mining subsidence of land use, but should pay attention gangue heavy metal pollution of farmland soils.

2. Fill the fly ash to restore the farmland. The fly ash is directly filled into the subsidence farmland, and the land is leveled. Compared with agricultural soil, fly ash reclaimed soil has many physical and chemical properties. Soil organic matter, total nitrogen, available phosphorus and other soil nutrient contents are low, pH value is greater than 8, and alkalinity is too strong. It is necessary to adjust soil pH and increase organic matter. Make improvements. The total potassium content and available potassium content of the reclaimed soil are sufficient, and no special potassium supplement is needed.

3. Fill the sludge to restore the farmland. Mainly use reservoir sediment, lake mud and lime, bentonite , zeolite mixed farmland to reclaim or improve soil. Nitrogen, phosphorus and other organic matter are present in the sludge. The main limiting factors for agricultural use are toxic heavy metals and pathogenic bacteria. The application of fly ash, reservoir sludge and sludge in appropriate proportions has a positive effect on improving soil fertility.

Second, the restoration of farmland landscape in the mining area

The understanding of farmland landscape reconstruction in China's coal mining areas is still relatively limited and insufficient attention. Practice has proved that the restoration of modern farmland landscape in the direction of ecological agriculture can coordinate regional social, economic and ecological benefits and ensure the sustainable social and economic development of coal mining areas.

(1) Rehabilitation of farmland landscape pattern

Restoration of farmland landscape in mining area is a systematic project. Rationally organizing farmland landscape pattern can coordinate the relationship between farmland production and sustainable use of farmland, effectively prevent pollution spread, maintain farmland biodiversity, and prevent pests and diseases. According to the theory of shadow ecology, landscape coordination is needed in the construction of farmland restoration projects in the mining area. The internal focus should be on the coordination of farmland patches and corridors. The exterior should be coordinated with the surrounding landscape through corridor construction. Strengthen the internal organization and coordination of the farmland landscape in the mining area, the coordination of the external organization of the farmland landscape and the coordination of the rural residential area landscape; adopt the scientific development concept and comprehensively plan the farmland restoration project; adjust the local characteristics of the farmland landscape according to local conditions.

(2) Rehabilitation of farmland intensive use mode

The change of agricultural production mode will inevitably lead to the evolution of the landscape pattern of reclaimed farmland in the mining area, and the most important change is the corridor structure. Some of the fixed open channels in the reclamation farmland irrigation system will gradually disappear, and will be replaced by underground water pipes, sprinkler irrigation, drip irrigation, micro irrigation and other water-saving facilities; some of the field roads for small farm implements and human and animal services will be reclaimed as farmland. Field roads will be expanded and adapted to large-scale agricultural machinery operations, forming large-scale farmland patches. At the same time, according to the principle of “integration, coordination, circulation (benign) and regeneration” of ecology, through the diversification of biological populations in the mining area, diversification of agricultural industry, improvement of species niche, establishment of food chain, improvement of green vegetation coverage, efficient and rational use of light , warm, water, and soil resources, promote a virtuous cycle of materials, reduce waste emissions, and achieve simultaneous economic and environmental benefits in mining areas and sustainable use of resources. For example, in the Huaibei mining area, due to the relatively high underground phreatic level, there is perennial or seasonal water accumulation in the deep part of the subsidence after coal mining subsidence, adding water ecosystems and increasing ecological landscape heterogeneity. In the reclamation, a highly efficient base pond farmland ecosystem can be established by using a deep-deep process. Generally, fish and ducks (goose) can be cultured in a three-dimensional manner on the surface of the water. Ducks (goose) can provide oxygen for fish in the water and provide high-quality bait, while the water surface provides a clean environment for ducks (goose). The three-dimensional intensive utilization mode of “there are fruits in the garden, chickens under the trees, fish in the pond, ducks on the water surface (goose)” is established, which can establish a benign material and energy circulation system and play the overall function of the reclamation farmland ecosystem.

3. Mechanical use and environmental protection measures for farmland restoration projects

The use of machinery for excavation of topsoil in mining areas, excavation and transportation of fillings, land leveling and loosening can shorten farmland recovery time and reduce reclamation costs. At present, the machinery used to restore farmland in the mining area mainly includes excavators, bulldozers, towed scrapers, and mud pumps .

(1) Excavators and bulldozers (also known as towed scrapers) are reclaimed. The land reclamation speed using the machine is fast, and it is easy to re-fill the mature soil as the topsoil layer to ensure that the soil structure damage after re-cultivation is small. However, it is necessary to drain and drill wells in the water storage area to reduce the phreatic level.

(2) Mud pump reclamation. The use of the machine is prone to the loss of nutrients in the soil, the mixing of the upper and lower soil layers of the reclaimed soil, the large moisture content of the reclaimed soil, the difficulty in discharging, the salinization of the soil, the destruction of soil microorganisms and soil animals. It is necessary to excavate the drainage ditch to reduce the groundwater level and to drain the excess water in the soil; improve the mud pump reclamation process, layer and layer filling, and quickly discharge the soil moisture in the filling area; pre-separate the excavation depth area and the superficial topsoil, And proper storage, after the soil in the reconstructed area is basically discharged, cover the surface of the reclaimed farmland; plant green manure on the cultivated land after reclamation to consume the excess water in the lower layer and supplement the soil nutrients.

(3) Bulldozer reclamation. This mechanical construction generally has problems of mixing soil and soil and soil compaction. Need to pay attention to topsoil selection, stripping and backfilling.

Whether filling or refilling, due to mechanical disturbances or the characteristics of the filling during the reclamation process, the original structure of the farmland soil is destroyed, and the reclaimed soil is porous, structural, and arable. The physicochemical properties such as fertility have undergone major changes. The amount of nutrients available for crops in reclaimed soil is less, and the fertility of soil is much lower than that of ordinary farmland. Corresponding measures are needed to improve and fertilize the soil and improve the fertility of the reclaimed land. However, the retanning machine also has a negative effect in the process of use, the most common is the problem of reclaimed soil compaction.

4. Farmland pollution-free filling and dynamic filling

(1) Pollution-free filling and reclamation technology

In general, the content of Cd, Cu, Se and Hg in coal shale exceeds the soil background value, and the contents of B, Cd, Pb, Cu, Se, Zn, Hg, F and Ni in fly ash also exceed the standard. Therefore, coal research stone, The characteristics of fly ash itself and the content of harmful elements have the potential for environmental hazards. Hu Zhenqi et al. believe that the impact of reclaiming on coal mining and fly ash filling coal mining subsidence is mainly the impact of reclamation and the impact after reclamation; the environmental impact during reclamation is mainly in solid waste transportation. The environmental impacts on the atmosphere and along the line and the water pollution in the fly ash hydraulic transport; the environmental impact after reclamation is mainly the impact on groundwater, soil and growing vegetation. The main measures to prevent the contamination of farmland and the spread of pollution are to increase the isolation layer (soil or other materials) to reduce the leaching of heavy metals, to add gangue and fly ash to lower the pH value, and to inoculate the mycorrhiza to reduce the thickness of the soil.

(2) Dynamic filling and reclamation technology

A key issue in abandoned land and mining areas is the lack or complete lack of topsoil for reclamation. In the mining area with a higher underground phreatic level, when it is re-suppressed, it will often form a large area of ​​water accumulation area, which needs to be drained. It is constructed by digging deep pad shallow process, easy to mix the soil layer, and the soil quality after long-term submersion. It is also not good, the texture is sticky, the fertility is low, and it needs to be improved. Therefore, with the "full and effective combination of mining and reclamation, that is, the integration of mining reclamation" as the core, mining and reclamation can effectively reduce the investment in reclamation, shorten the reclamation cycle, and increase the benefits of reclamation. The technical process of dynamic filling and reclamation of farmland is as follows: mining subsidence prediction, topsoil stripping, coal research stone (fly ash, mine solid waste, etc.) filling pre-reconstructed subsidence farmland, covering soil and leveling, planting.

When using dynamic subsidence to reclaim farmland, it is necessary to determine the reclamation time reasonably. Without accurate mining plan, mining subsidence is not expected to proceed. At the same time, according to the requirements of ecological reclamation, it is first necessary to pre-separate the topsoil according to the mining schedule, and then fill it, and finally cover the soil and level it.

V. Quality control measures for reclamation farmland ecological reconstruction

Reconstruction of farmland ecological reconstruction Because of the heavy construction and light quality of the land reclamation project in the mining area, the planning and design, topsoil stripping, property rights allocation and other links cannot be completely integrated with ecological reconstruction, resulting in uncoordinated landscape pattern and environmental restoration. The long period, poor biodiversity and lack of aesthetic value are ultimately manifested by low productivity and instability in farmland. Therefore, the following remedies are required.

(1) Gradually adjust the landscape pattern of farmland in accordance with the requirements of agricultural modernization. Compared with the farmland landscape before the subsidence, the scale of the field is small, the area ratio of the patch surface of the farmland is unreasonable, and the landscape pattern has obvious “functional depreciation”, which makes the landscape after ecological reconstruction. The pattern lags behind the times and cannot meet the requirements of agricultural modernization. Therefore, in the future, necessary interventions must be taken to optimize and adjust the reconstructed farmland landscape pattern.

(2) Adding organic fertilizer and improving the substrate conditions of the farmland. Since the reclamation project started after the surface subsidence, the soil moisture and soil bulk density increased under the erosion and submersion of the topsoil, and the soil fertility decreased, especially in the reclamation project. Reconstruction technology makes the soil after reclamation solid, the physical properties of the soil are low, and the reclaimed soil takes a long time to recover. Of course, improving ground power is also a common task for all land development and reclamation. It is necessary to increase the application of organic fertilizer, improve soil performance and improve the substrate level of farmland after completion of the project.

(3) Bring into play the function of property rights allocation and improve the intensive utilization level of farmland. From the perspective of farmland landscape pattern, it is impossible to integrate with the surrounding farmland pattern. The higher the administrative level, the more obvious the performance, and the function of property rights allocation resources cannot be fully utilized. In addition, it reflects the old property rights system and limits the role of macroscopic allocation of farmland landscape pattern. Therefore, on the one hand, we should make full use of the public interest of property rights to bind private and collective property rights, use planning methods on a macro level, rationally allocate resources, and coordinate the reclamation farmland with the surrounding environment; on the other hand, we should make full use of the property rights division function. To make full use of the functions of property rights allocation resources and improve the intensive use of farmland.

(4) Rationally arranging plant layouts to increase the aesthetic value and biodiversity of farmland landscapes. Most of the mining reclamation projects only focus on the project layout, the shelter forest structure is single, there is no spatial level of the three-dimensional use of the landscape, over-emphasizing the hardening of the roads in the field, ignoring the simplicity of the color of the farmland corridors, it is difficult to increase the aesthetic value and biodiversity of the farmland landscape. Sex. The crop rotation system under the planned economic system has maintained the ground force to a certain extent, reducing the occurrence of pests and diseases and the spread of farmland weeds. Under the market economic system, challenges have been put forward for farmland rotation, but the rational distribution of plants should be ignored to prevent weeds, pests and diseases, and the agricultural soil industrialization should be strengthened while maintaining the sustainability of farmland soil.

(5) Develop water-saving agriculture and strengthen the sustainable use of farmland.

The shortage of water resources is global. Although the water in the subsidence area has been reclaimed after the reclamation of the mining area, it has overcome the leakage of the open channel. However, the irrigation method has adopted the water irrigation, and the waste of water resources is still serious. The quality of agricultural products. Therefore, the development of water-saving agriculture and the improvement of the competitiveness of agricultural products are also the guarantee for the continued use of farmland.

Conclusion

Farmland restoration and pollution prevention in the mineral grain complex area is an important task of land reclamation in China, which is directly related to national food security and ecological security of mining areas. The recovery technology of farmland in the mining area is non-filling and reclamation. It has the advantages of low cost, high ecological diversity and small secondary pollution. However, it has defects such as soil compaction and extensive land use. Secondly, it can reduce the waste pressure by filling and reclamation. It occupies land and pollutes the environment, but there are problems such as poor soil quality and even potential heavy metal pollution. Regardless of the type of reclamation technology, the use of machinery generally has soil compaction problems, and corresponding measures are needed to improve and fertilize the soil. It is necessary to actively promote the pollution-free filling and dynamic filling technology of farmland. At the same time, in accordance with the concept of intensive land use, in the process of land reclamation in the mining area, through the rational use of mining solid waste for filling, optimizing the landscape structure of reclaimed farmland, and establishing three-dimensional ecological agriculture, it can effectively reduce land pressure and improve land use. Rate, farmland intensification and ecological quality. However, the promotion of farmland restoration and pollution prevention technologies requires the state and local governments to formulate relevant industrial policies, promote mining enterprises to assume social responsibilities, and consciously recuperate, and establish a guarantee system for comprehensively carrying out land reclamation in mining areas.