Resource and environmental issues, soil and water conservation issues are the themes of world development in the 21st century. China is a country with relatively scarce land resources, but the destruction of land resources caused by the exploitation of mineral resources and irrational use has been expanding at an alarming rate for a long time. There are more than 8,000 state-owned mining enterprises in China and more than 230,000 individual mines. According to statistics, the total destroyed land area of ​​the national mining area reached 2.88 million hm 2 , and the annual growth rate was about 4.67 million hm 2 . Among them, non-ferrous metals industrial solid waste each year up to 60 million t, the cumulative stock pile has reached 1 billion t, occupation of land of more than 70,000 hm 2. It has caused huge economic losses to our country. Therefore, the ecological restoration of mine abandoned land is of great significance for protecting cultivated land resources, alleviating the contradiction between people and land in China, achieving sustainable development and building a harmonious society.
I. Significance of carrying out research on ecological restoration of mine abandoned land
Mine abandoned land will have a serious impact on the environment in the surrounding area. Uncovered loose deposits under the influence of wind and water, soil erosion is intensified, land is desertified, dust is polluted by the wind during high winds, affecting crop growth and human health. When heavy rains, it will accumulate a large amount of sediment to block rivers and damage water conservancy facilities. In addition, mine waste often contains various pollutants, which will invade the surface and groundwater, causing pollution of soil and water resources, resulting in soil quality degradation, crop yield reduction, ecological balance being destroyed or even endangering human survival and health. According to relevant information, the pollution of solid waste can last for 500 years, and the untreated tailings pollutants can reach more than 100 years. More information shows that the annual economic loss caused by solid waste pollution in China More than 9 billion yuan, indirect losses of about 30 billion yuan. Therefore, the ecological restoration of mining wasteland is not only a current work to protect and improve the human environment, but also a great cause for the benefit of future generations. It is especially important for the current situation that China has a small area of ​​cultivated land per capita.
Second, the research status of ecological restoration of mine abandoned land in China
The problem of environmental pollution and ecological damage caused by the exploitation of mineral resources is one of the important contents of environmental protection that people are currently paying close attention to. Since the reform and opening up, due to the rapid development of the economy, the demand for industrial raw materials and energy has increased, and the rational exploitation of mine resources has played an important role in revitalizing the local economy. However, the mining production process is another process that destroys the ecological environment. The problems such as landform changes, soil erosion, atmospheric and water pollution, ecological imbalances, agricultural production damage and even social disputes have been seriously affected. Life has undermined the sustainable development of the economy.
The research work on the comprehensive management technology of mine soil erosion in modern China began in the late 1950s and early 1960s and was carried out spontaneously with the development of the national economy and socialist construction. In the 1980s, many mining areas have successively carried out some comprehensive management techniques for soil erosion in mines, and accumulated a lot of valuable experience. In the 1970s, coal mining areas of the eastern plains sporadically carry out ecological restoration of land subsidence, land and water for ecological restoration after construction, planting rice and wheat, such as planting lotus or fish. Since the 1980s, China's mine water and soil loss comprehensive treatment technology has made great progress, but in general, the deterioration of the mining environment has not been effectively curbed. In October 1988, the promulgation of China's "Land Reclamation Regulations" made the comprehensive management of soil erosion in China's mines into the legal track, and the speed and quality of mine wasteland restoration have been greatly improved. From 1989 to 1991, the National Land Department carried out 23 land ecological restoration test sites in Hebei, Jiangsu, Anhui, Shanxi, Hunan, Liaoning and other provinces. By the end of 1992, the ecologically restored land reached 33,000 hm 2 , 1994. national and Jiangsu Tongshan in Huaibei, Anhui, Hebei Tangshan created three comprehensive ecological restoration demonstration project. The local mining areas and local land management departments have also established many demonstration bases for ecological restoration in order to obtain a large number of experiences in ecological restoration and to promote ecological restoration theory and technical achievements. In the early 1980s, the ecological restoration rate of abandoned mines was 0.7% to 1%. The ecological restoration rate in the late 1980s was about 2%, and the ecological restoration rate in the 1990s was 13.33%. China's theoretical research on the ecological restoration of abandoned land began in the 1980s and began to take shape after the 1990s.
In the past ten years, the research on the ecological restoration of mine abandoned land has developed by leaps and bounds. The main research institutions are: China University of Mining and Technology, Shanxi Agricultural University, Sun Yat-sen University and Hong Kong Baptist University. The two major research areas are: ecological restoration theory and technology research with the purpose of land use as the representative of China University of Mining and Technology and Shanxi Agricultural University; and the study of Sun Yat-sen University and Hong Kong Baptist University Representatives, theoretical research and technical research with the main purpose of the non-ferrous metal mine abandoned land as the research object, the control of environmental pollution and the restoration of natural ecosystems. In terms of coal mines, China University of Mining and Technology has proposed some new technologies for the mechanism of mining subsidence and its ecological restoration.
Third, the characteristics of magnesium mine wasteland
In recent years, with economic development, many rural areas, especially the rapid development of industrial zones in Liaoning Province magnesite, calcined magnesite ore dust emissions increasing, especially in the coastal areas of soil salinization serious, large precipitation conditions The hard-to-recover magnesium ore mining area has a great impact on the surrounding environment, making the research on the reclaiming technology of the magnesite meteorite in the coastal area become a major research hotspot and difficult problem in recent years. When magnesite dust enters the soil, soil productivity decreases and soil quality deteriorates. After the dust pollution of soil, the soil will cause a series of changes, such as reducing the effectiveness of soil phosphorus elements and trace elements, plant nutrients in the soil ratio imbalance, dust contaminated soil soil properties also deteriorate the dispersibility of the soil particles Reinforcement, structural damage, reduced porosity, and decreased permeability, thus affecting the growth of plants in the soil, slowing the rate of photosynthesis and the magnitude of Hill's reaction, resulting in large-scale reduction of farmland and even wasteland, resulting in huge economic losses. Long-term inhalation of dust can cause a variety of diseases that endanger human health and life.
Fourth, the status quo of research on magnesium ore abandoned land at home and abroad
At home and abroad for research mine coal, iron ore and other recovery techniques relatively high, but research on pollution and restoration of magnesite is still in the preliminary stages of understanding, from the 1930s, some of the soil of foreign workers began to magnesian base Soil research, Caboun et al. (1996) studied the effects of magnesite dust pollution in the Jelsava-Lubenic region of Slovakia. The results showed that in areas highly contaminated with magnesite dust, the removal of dust re-contamination still prevented plants from surviving. Going down, but the turf covering can prevent the penetration of pollutants into the soil, which can be a powerful way to prevent magnesite dust pollution. Josh: (1997) soil, air and water at three locations around the contaminated area of ​​the magnesite calcination plant in the Kuman hlmalaya district of India, contaminated by the magnesite calcination plant, and affected by mining, surrounding areas, uncontaminated pine forests The situation was studied and the results showed that the soil and water pH were alkaline in the contaminated area of ​​the magnesite calcining plant, and the soil organic carbon content and nitrogen content were very low, and only some shrubs could be grown.
In recent years, some scholars in China have also studied the improvement of the utilization of magnesium alkalized soil. According to Liu Xianglai (1985), studies on magnesium alkalized soil suggest that the damage of magnesium alkalization land does not depend on water solubility. The absolute content of magnesium, depending on the ratio of water-soluble magnesium to calcium, potted and field trials show that practical excess calcium phosphate farmyard manure is an effective measure to improve magnesium alkalized soil. According to Du Baolin (1990), the study on the magnesia alkaline soil in the Hexi Corridor suggests that in addition to the improved ways and measures for the general salinized soil, measures should be added: (1) Calcium modifiers such as practical gypsum and superphosphate. Increase the content of water-soluble calcium ions in the soil and coordinate the ratio of calcium to magnesium. (2) Practical humic acid and other improvers, activate calcium in the soil, increase calcium ions in the soil solution, and lower the pH. (3) A large number of green manures are planted, and the organic acids produced by the decomposing of green manure can also activate soil calcium, lower the pH value, and increase soil nutrients.
Theoretical and technical research on ecological restoration of abandoned mines in non-ferrous metal mines has also achieved a series of results under the years of research at Sun Yat-Sen University and Hong Kong Baptist University. The main limiting factors affecting plant settlement in tailings and its improvement measures are proposed: through ecological survey and experimental means, a variety of plant species that can be used for tailings ecological restoration are selected; and a fast and accurate prediction method for tailings acidification is developed. The corresponding acidification measures are proposed; the process and mechanism of natural settlement of tailings plants are discussed in depth; the effects of legumes and mycorrhiza and introduction of soil seed bank on vegetation restoration of tailings wasteland are studied; the study of heavy metals in vegetation reconstruction Migration and accumulation laws; research on the treatment of metal mine wastewater by constructed wetlands has also made great progress. It can be seen that the ecological restoration work of abandoned land in mining areas has attracted more attention in recent years, and the ecological restoration rate has also increased at a faster rate. However, there is still a big gap compared with foreign countries. At present, the ecological restoration rate of abandoned land in developed countries has reached more than 75%, and the quality of ecological restoration is also high.
V. Discussion and outlook
Before the 1980s, the theoretical and practical work of comprehensive management of soil erosion in mines in China was basically afforestation or field-building in various mining areas. The main purpose was to improve the environment, maintain mine safety and ease the pressure on land demand. The involvement of theoretical work. Undoubtedly, these early ecological restoration practices have accumulated some valuable experience. After the 1980s, with the intervention of larger-scale theories and policies, the situation has changed a lot.
From the current ecological restoration situation in China, the following theoretical and technical problems need to be solved: combining the local socio-economic, natural landscape, climatic conditions and the physical and chemical properties of abandoned land to determine the target of comprehensive soil erosion control (end use) And processes; research on the natural succession process and mechanism of ecosystems in mine abandoned land; according to China's national conditions, carry out high-quality, high-yield, high-efficiency, three-dimensional agriculture, comprehensive ecological restoration and ecological environment reconstruction; research on topsoil recovery technology; Research on the theoretical system and method of ecological restoration of abandoned land; reconstruction of the dynamics and stability of the ecosystem: reconstruction of the safety of the ecosystem; establishment of a technical benefit evaluation system for the comprehensive management of mine water and soil loss; establishment of a demonstration base for comprehensive management of mine water and soil loss.
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