Environmental geological impact assessment and ecological restoration of abandoned mines

1. Various impacts of abandoned mines on the environment

1.1 Destruction of land resources

In the process of mineral resources development, the damage to the land mainly includes: the damage to the land by the mine, the damage to the land by the storage of waste materials, the damage to the land by a series of geological disasters caused by mining, the damage to the road and related mining equipment in the mining area. The loss of cultivated land resources is mainly reflected in the wide range of abandoned cultivated land, and the destruction of cultivated land resources is mainly forest land. The damage of abandoned mines to land resources is also manifested in the high cost, difficulty and long time of restoration.

1.2 Destruction of landform and landscape

In the process of mineral resources development, the damage caused to the surrounding terrain and landscape is mainly manifested in: in order to adapt to the terrain conditions of the open pit, mining road, industrial land and other engineering sites, the construction unit has reformed the original terrain, resulting in a certain degree of damage. At the same time, due to the mining of ore, waste is piled up, and the storage of ore will also bring great pressure to the original terrain, which will have a certain impact on the terrain. For example, the rare earth mining process, the so-called "mountain moving movement", like shaving the head, the top soil and vegetation of the mountain are removed, the surface cultivated soil is excavated, and the bedrock is directly exposed, which causes damage to the mountain vegetation that is difficult to repair.

1.3 Geological disasters in mines

The disasters caused by mining directly or indirectly include collapse, debris flow, cave collapse, landslide, mine water inrush and so on. Landslide, ground collapse and mine water inrush are the most common geological disasters. People should not only suffer from geological disasters caused by improper construction in the mining process, but also suffer from geological disasters caused by improper treatment of slag piles, tailings piles, goaf and other prevention and control measures.

1.4 Aquifer damage

In the process of mining, due to the use of modern mechanical equipment, it will cause serious pollution and damage to the underground water in the mining area, and the loss and imbalance of underground water is the main cause of groundwater loss. Underground aquifers are often connected to underground rivers, and the flow interruption and diversion of underground aquifers will produce devastating blows to underground ecosystems. Due to the insufficient attention and understanding of underground rivers, it is more difficult to damage and repair them, which makes them more ecological and research value.

1.5 Soil and Water pollution

In areas rich in mineral resources, in addition to a large number of ferrous metals, there are also many nonferrous precious metals, which is easy to cause soil and water pollution. Due to the particularity of non-ferrous precious metals, during mining, heavy metal pollution is generally not highly valued, protective measures are not in place, or even no protective measures are taken, which is easy to cause heavy metals and other pollutants to migrate to the surrounding soil and water, causing serious pollution to the surrounding environment.

Rare earth mining environmental problems are particularly serious, rare earth engineering to solve the environmental problems of the initial investment cost is very large, because of this, private development of rare earth often can not meet the environmental requirements. In the suburb of Baotou City, Inner Mongolia Autonomous Region, the rare earth waste slag formed by Baotou Steel rare earth is transported to the tailings dam through the pipeline with the waste liquid, and accumulated over time to form the current capacity of 170 million tons of "rare earth lake", which is seriously polluted. Some parts of Ganzhou have been labeled "unfit for human habitation" because rare earth mining has seriously polluted drinking water and agricultural irrigation water. Rare earth elements are non-essential trace elements for human body, and long-term low dose exposure or intake may have adverse consequences on human health or metabolism in vivo.

2. Comprehensive impact of abandoned mines on the environment

There are three main impacts of abandoned mines on the environment: geology, ecology and environmental pollution. Under complex geological conditions, the existence of landslide and debris flow will lead to the destruction of slope vegetation, and then affect the landform. From the point of view of ecological environment, because forest vegetation and surface vegetation have been damaged to varying degrees, soil erosion has been intensified, which has caused serious impact on the growth and growth environment of animals and plants, which has led to the disappearance of the diversity of plants and animals. In terms of environmental pollution, due to the geological conditions of the mine, it will lead to the increase of water pollution, soil pollution and solid pollution, and long-term infiltration and diffusion will form a wide range of pollution.

2.1 Impact of function zones of abandoned mines on the environment

Abandoned mines generally include slag dumps, mining dumps, tailings dumps and other abandoned lands. Due to different causes, the impact on the environment is also different. This paper discusses its impact on the environment from many aspects.

In mining, low-quality ore is often thrown away directly, resulting in a large amount of waste accumulation. Due to its relatively chaotic geological conditions, the rock layers are very loose, and there is not much organic matter, it is difficult to form rich vegetation on the surface, and therefore, it is more likely to cause soil erosion and uneven settlement. There are a lot of harmful elements in the abandoned mines and tailings abandoned land produced by mining. Some mineral elements, due to long-term exposure and oxidation, will produce spontaneous combustion and explosion risk; At the same time, these harmful substances will also penetrate into the soil with the rain, and then enter the water cycle, which will lead to greater environmental pollution. The environmental problems of the buildings built in the mining process and the abandoned land formed by the leftovers and wastes after mining are mainly manifested as a large amount of land waste and the processing equipment has the capacity of secondary use but is idle and abandoned, forming a new environmental hidden danger.

2.2 Specific harm to the environment caused by abandoned mines

Specifically, the impact of mine abandonment on ecological environment is multifaceted. First, due to the large consumption of abandoned mines, more fertile farmland has become barren. However, the per capita cultivated land resources are low, facing a large number of mines desertification, resulting in a large amount of resource waste. Secondly, the abandonment of mines has caused severe damage to the soil and surface topography, and the drastic movement and deformation of rock strata and upper soil layer caused by mining. Irreparable damage to vegetation and terrain. In addition, it also has a certain impact on the overall balance of regional ecosystems. For example, in the relatively dry areas of Northwest China, vegetation itself has a strong ability to prevent wind and fix sand. The exploitation of mineral resources has led to the intensification of desertification, and has local negative effects on precipitation, temperature and humidity. In the south, open-pit mining of rare earth minerals mixes with rainwater, releasing heavy metals that threaten surrounding rivers and residents.

3. Mine environmental impact assessment

On the whole, the environmental impact assessment of mine is carried out with the disaster body as the object, and with the increasing awareness of environmental protection today, the problem of visual pollution caused by it is getting more and more attention. In recent years, with the frequent occurrence of environmental pollution accidents caused by mining, the pollution risk assessment of soil and groundwater has been paid more and more attention.

3.1 Geological hazard assessment

3.1.1 Overall slope stability assessment

The surrounding mining area generally belongs to the hilly and mountainous landform units, the surface soil cover is very shallow, and some surface bedrock is exposed. Taking the adjacent mining area as an example, several fault zones develop around the mining area, and local bedrock folds and rock joints are relatively developed, but in general, the ratio is relatively stable. Due to the influence of mining, the rock mass will appear large slide, spalling and other bad geological phenomena.

3.1.2 Risk assessment of stope slope

Non-metallic minerals are mostly open-pit mining. Taking the surrounding abandoned mines as an example, the rock joint cracks of the mining site are developed, and there are no obvious geological disasters such as landslide, collapse, ground subsidence, ground cracks and debris flow within the mining area. The slope of the mining site is generally relatively stable, but there are still small pieces of dangerous rock and pumice on the slope and slope of the mining site. There are often small pieces of rubble rolling down the slope, collapse, poor stability.

3.1.3 Stability evaluation of slag dump

The form of slag accumulation is near fan, taking the surrounding abandoned mine as an example, its heap contains a lot of slag and a little soil, with a large height difference; The slope is usually steeper and larger. The compaction degree of waste slag pile is poor, the interior is loose, and the stability is very poor. If there are other inducements such as heavy rain, it is easy to cause geological disasters such as debris flow and landslide.

3.2 Destruction of landform and landscape

Open-pit mining is the most economical mining method, and its special mining method has caused great damage to the terrain and landform of the mining area and its surroundings. The vegetation on the ground has been cut down artificially, forming pits and deposits, which have greatly changed the terrain and caused changes in the mountain form and vegetation. Due to the perennial construction of mining roads and mining areas, the landform and vegetation resources in the mining area have been seriously damaged. However, due to the lack of detailed topographic and geomorphic damage assessment system, it is difficult to evaluate it quantitatively. It is gratifying that in recent years, a number of ecological restoration projects have been carried out in the Yangtze River area, and the vegetation of abandoned mines has been better restored.

3.3 Soil and groundwater pollution risk assessment

At present, soil pollution survey and risk assessment of construction land are mainly used. Due to the lack of relevant laws and regulations on environmental pollution of abandoned mines, there is almost no investigation and risk assessment on environmental pollution of abandoned mines. It is difficult to find the pollution of soil or groundwater in the surrounding farmland by mines, and it can only be found through soil pollution survey or environmental pollution accidents. Therefore, it has become an urgent task to introduce relevant laws, regulations and standards. At present, the pollution status of contaminated farmland or construction land can only be investigated by referring to the evaluation standards related to agricultural land or construction land, but even if the corresponding pollutants are detected, it is difficult to block the pollution source. Because the waste minerals generally have a large area and generally higher terrain, the soil at the foot of the slope is in the upstream of the surface water and groundwater, and it is easy to cause pollutants to migrate to the soil at the foot of the slope along the current, resulting in a large area of soil pollution.

Therefore, the pollution risk assessment of the abandoned mine not only involves the abandoned mine itself, but also includes the surrounding soil and groundwater that it may affect.

4. Restoration measures for abandoned mines

4.1 Control of landslide

In the control of the landslide, we must ensure the stability of the mountain, in order to carry out the control of the landslide, if the stability of the landslide can not be guaranteed; Once a secondary landslide occurs, it will not only affect the treatment process, but also endanger the life and safety of the relevant personnel. In the actual management, we should carefully observe and field survey, and comprehensively consider the surrounding geological conditions, and use the relevant theoretical knowledge of engineering mechanics, mine geological environment, etc., to conduct a comprehensive analysis of relevant data and information; After the discussion, they will work out a new management plan. Finally, the engineering scheme is simulated by using the relevant software to determine the feasibility of the scheme. After the demonstration by experts, the feasibility of the scheme is determined.

4.2 Treatment of abandoned open-pit mines

In the relevant treatment of the abandoned mines, it is difficult to treat the open pit mine. The open-pit mine generally covers a wide area, has a large topographic relief, and has a severe damage to the geological environment, while the natural recovery time is long and the effect is poor. The amount of money needed to repair the huge project is insufficient and the gap is huge. The most economical and effective way to deal with this situation is to fill shallow mines, and then use these shallow soils as farmland and forest land; As for deeper mines, they can be used for aquaculture, but when they are built, protective fences should be built around the mines and warning signs should be set up to avoid accidents.

4.3 Mining area collapse geological control measures

In geological reclamation of landslides, the subsidence of the foundation and the condition of the soil should be fully considered, and the stress analysis should be carried out to avoid sliding and deformation during the filling of slag and pit. Cement mortar is used to fill out the cracking and collapsing position to ensure its bearing capacity and stability and prevent secondary collapse. In filling, appropriate grouting scheme should be adjusted according to the direction and structure of the tunnel, so as to prevent the holes after grouting. Of course, it is the most economical to cover the soil after the natural collapse of the collapse area, but its time span is longer.

4.4 Land reclamation and vegetation reconstruction

Through the rational development of the abandoned mine land, it can be better adapted to the needs of social development, and the local geological environment can be creatively reformed. For example, in low-lying places, the harmful minerals and slag in the mine are removed first, and then the foundation pit is levelled; The bottom of the mine is paved with mud humus suitable for the growth of fish, and it is used as a fish pond for rational use. As for agriculture and forestry, this can be achieved through reasonable sloping land and artificial filling.

In the aspect of vegetation restoration, we should focus on the research from the aspect of breeding. Because the soil of the mine is prone to salinization and lack of nutrient supplement, it is necessary to choose plants that are suitable for arid environment and soil is not fertile. In loose soil areas, by selecting plants with developed roots, the soil can be effectively fixed, which not only increases the survival rate of vegetation but also avoids soil damage. In the desert mining areas in the north, shrubs and other drought-resistant tree species dominate. It is best to test the new varieties that are easy to raise, easy to manage and easy to survive, which can greatly improve the survival rate and recovery efficiency of plants, and greatly reduce the cultivation and cultivation costs of seeds, and achieve better greening effects with the same time and labor costs.

4.5 Suggestions for mine environmental restoration monitoring

It is the basis to accurately grasp the dynamic change of geological environment and its control effect to monitor the indicators that affect the environmental restoration of mining area by using various technical means and methods. Focus on mining area collapse, landslide geological disaster monitoring and land restoration monitoring.

4.6 Comprehensive treatment of abandoned mines

In order to solve the problem of mine environmental damage in a targeted way, the comprehensive treatment method with targeted treatment measures should be adopted.

For example, for a certain abandoned mine, the use of land improvement technology, and strive to completely restore the vegetation on the site. Firstly, in the process of restoring soil capacity, a large amount of guest soil and a large amount of organic matter were mixed in. Improve soil nutrition by increasing the population of microorganisms. Through these measures, the restoration of soil system can be gradually promoted. Only by restoring the vegetation to the best state and providing better living conditions for various organisms can the whole ecosystem of the mining area be gradually improved.

Secondly, in the governance, it is necessary to fully take into account the management requirements of abandoned mines to ensure that greater social and economic benefits are achieved in the governance process. Especially in the future management, it is necessary to fully explore the intrinsic value of the mine, carry out targeted, comprehensive and systematic management, in order to ensure that the future management work can be smooth and orderly.