Eco-environmental harm of coal gangue hill

On the one hand, coal gangue piled in the open air occupies a lot of land, on the other hand, it is prone to some physical and chemical reactions, such as spontaneous combustion and dust, which cause serious pollution to the atmosphere and water bodies around the mining area. On the other hand, geological disasters such as collapse and debris flow may occur in coal gangue hill under the action of external force, causing ecological damage and landscape damage, causing social problems, and ultimately endangering the ecological safety and human health in the mining area (Figure 1- 1).

Figure 1- 1 Possible ecological and environmental hazards caused by coal gangue hill

First, the physical hazards of coal gangue hill

1. Occupy land

Coal gangue is the largest solid waste in China's industry at present. According to statistics, there are more than 700 coal gangue hills 1.700 in China's state-owned key coal mines, with an accumulation of more than 50× 1.08t and an area of more than 20000hm2. Moreover, with the exploitation of coal, the amount of coal gangue increases by about 5× 1.08t every year, accounting for about 300~400hm2 of land area, which causes great waste of land resources. Under the basic national conditions of our country with a large population and a small amount of land, the gangue hill occupies a lot of land resources, which intensifies the contradiction between man and land and has an impact on social and economic development. It is necessary to speed up the comprehensive utilization of coal gangue or carry out greening and reclamation, and reduce and eliminate the precious land resources occupied by coal gangue stacking (Figure 1-2).

Figure 1-2 Coal gangue accumulation pressure occupies a lot of land.

2. Dust pollution to the atmospheric environment

Coal gangue is easy to weather in the air, and it will produce dust when it meets the wind. Fine dust particles caused by coal gangue enter human lungs, leading to respiratory tract, lung and other diseases, and even cancer; Larger dust particles enter the eyes, nose, mouth and other organs, which are easy to cause infection, especially the weathered dust often contains heavy metal elements and organic elements harmful to human health. In addition, particles suspended in the atmosphere are likely to cause climate anomalies.

3. Geological disasters caused by coal gangue hill

The natural coal gangue is unstable due to the stacking mode, spontaneous combustion, weathering and other reasons, which is easy to cause geological disasters.

(1) Collapse and landslide of coal gangue hill. Coal gangue piles are mostly formed by natural accumulation, which has the characteristics of large slope and loose internal structure. Moreover, influenced by the spontaneous combustion of coal gangue, coal gangue piles are prone to collapse and landslide. For example, in 1994, a coal gangue hill collapsed in the northern coal well of Zaozhuang Coal Mine, Shandong Province, causing 17 deaths and 7 injuries.

(2) Coal gangue debris flow. Most coal mines in mountainous areas directly dump coal gangue into valleys, and these loose coal gangue become the material source of debris flow. Once strong runoff conditions are formed in the valley due to rainfall, debris flow disasters may be formed. For example, in May 2004, a mudslide occurred in the gangue hill in Wansheng District of Chongqing, causing serious casualties. Five people died, 16 people were missing and 14 houses were buried. In June 2009, a mudslide occurred in Shuangfeng Coal Gangue Mountain in Hechuan, Chongqing, and two villagers were buried and killed.

(3) Coal gangue explosion. Coal gangue hill is made up of coal gangue from coal preparation plant and other coal gangue with certain calorific value and high sulfur content. The calorific value is generally 3350~6280J. This coal gangue hill is heated internally, and with the accumulation of temperature, the highest temperature can reach 800 ~ 1200℃, forming an internal environment with high temperature and high pressure. The surface of weathered coal gangue hill is covered with a layer of fine weathered particles, and the heat and gas inside cannot be emitted. When the Nevas concentration of coal gangue hill reaches a certain level, it is easy to explode, causing geological disasters such as collapse and landslide, which poses a serious threat to the safety of nearby residents.

A large amount of heat energy is released when spontaneous combustion coal gangue hill explodes, and the instantaneous temperature can reach 2300 ~ 2500℃. The high-temperature gangue thrown out by the explosion can cause the surrounding buildings to catch fire, burn the surrounding trees, factory equipment and burn people, and it is also the main heat source of continuous explosion. Figure 1-3 shows that the high-temperature heat wave generated by the explosion of the gangue hill scorched the leaves of trees more than 20 meters away, which shows that the heat generated by the explosion is high and harmful.

Figure 1-3 Harm of high-temperature heat wave produced by the explosion of gangue hill to the environment

Figure 1-4 Destruction of the environment by the dust produced by the explosion in the gangue hill

The explosion of spontaneous combustion gangue hill not only produces high temperature, but also has high explosion pressure. High pressure can make the gas near the explosion source impact outward at a great speed, and its propagation speed can reach 2340m/s, which will cause damage to the buildings and equipment on the ground of the mine. At the same time, the shock wave can raise a lot of gangue dust and make it participate in the explosion, resulting in continuous small explosions of local dust, forming greater destructive power. Shock wave can produce vibration in its action area, making objects loose or even destroyed by vibration. According to the research, when the shock wave acts on buildings in a large area, the overpressure of the wave front is within 20 ~ 30 kPa, which is enough to seriously damage most brick-wood buildings (Figure 1-4, Figure 1-5). When the overpressure exceeds 100kPa, all parts will be destroyed except the solid reinforced concrete building.

Figure 1-5 Houses after Coal Gangue Explosion in Pingdingshan No.4 Coal Mine, May 2005 15.

In May 2005, the coal gangue hill of Henan Pingmei Group collapsed naturally, causing serious damage to surrounding houses and casualties. In addition, in the process of emergency rescue, three more eruptions occurred in the coal gangue hill, resulting in 8 deaths and 122 burns. 1988 an explosion occurred in a garbage dump in Jiaozuo mining area, killing six children. The explosion of gangue hill has always been a common geological disaster in China's coal mines, which has caused great harm and property losses to people in mining areas. On 200 1 May 13, an explosion accident occurred in the gangue hill of Yangquan No.1 Mine, causing1person to die. According to incomplete statistics, there are dozens of geological disasters in waste hills in China every year. It can be seen that the safety status of coal gangue mines in China is not optimistic.

4. Soil erosion in coal gangue hill

The slope of natural coal gangue piles is generally large, and the angle of repose of some coal gangue piles is as high as 40. Due to the large particle size of coal gangue, the weathering degree of surface coal gangue is low at the initial stage of accumulation, and the infiltration capacity of coal gangue hill is strong. With the increase of weathering degree of surface coal gangue, the infiltration capacity gradually decreases, which increases the surface runoff of coal gangue mountain and causes soil erosion. In recent years, coal gangue piles generally need to be compacted. Due to the dense "impermeable layer" formed on the surface of coal gangue hill after mechanical compaction, the topsoil covering it is easy to cause serious soil erosion in rainstorm weather (Figure 1-6).

Figure 1-6 Soil and Water Loss in Yangquan Coal Gangue Mountain

Second, the chemical hazards of coal gangue hill

1. Danger of spontaneous combustion

Because coal gangue hill contains a certain amount of combustible materials such as residual coal, carbonaceous mudstone and waste wood, as well as chemical substances such as pyrite and sulfur which are easy to oxidize and give off heat, coal gangue piled in the open air in the field is prone to spontaneous combustion. Firstly, pyrite (FeS2) in coal gangue generates heat through oxidation. When the temperature reaches the ignition point of combustible materials, it will lead to the spontaneous combustion of combustible materials such as residual coal and carbon, and then lead to the spontaneous combustion of coal gangue hill. After spontaneous COmbustion, the internal temperature of coal gangue can reach 800 ~ 1200℃, and a large number of harmful gases such as co, CO2, SO2, H2S, nitrogen oxides, benzopyrene and so on are generated. Released (table 1-5).

When the oxygen supply is insufficient, the main gases produced are:

Treatment and ecological reconstruction technology of spontaneous combustion coal gangue hill

Treatment and ecological reconstruction technology of spontaneous combustion coal gangue hill

Treatment and ecological reconstruction technology of spontaneous combustion coal gangue hill

When the oxygen supply is sufficient, the oxidation reaction between carbonaceous materials and pyrite is more intense:

Treatment and ecological reconstruction technology of spontaneous combustion coal gangue hill

Treatment and ecological reconstruction technology of spontaneous combustion coal gangue hill

Treatment and ecological reconstruction technology of spontaneous combustion coal gangue hill

At high temperature:

Treatment and ecological reconstruction technology of spontaneous combustion coal gangue hill

Treatment and ecological reconstruction technology of spontaneous combustion coal gangue hill

Table 1-5 Pollution Monitoring Results of Some Spontaneous Combustion Gangue Hills in China Unit: mg/m3.

According to statistics, about 1/3 of more than 700 coal gangue hills belonging to state-owned key coal mines in China are burning. Among them, Shanxi Yangquan Coal Industry Group has accumulated 1× 108t of gangue, and there are more than 20 large and small gangue hills, most of which are spontaneous combustion. Coal gangue will release harmful gases such as SO2, H2S, CO, CO2 and nitrogen oxides during spontaneous combustion, accompanied by a lot of smoke and dust. The spontaneous combustion of coal gangue hill will release CO 10.8g, SO2 6.5g, H2S and nitrogen oxides 2g into the atmosphere per square meter of combustion area every year. A large number of harmful gases such as SO2, H2S, CO, CO2 and nitrogen oxides are released, which not only destroys the mining environment, but also has a great impact on the incidence of acute and chronic diseases of surrounding residents. When coal gangue spontaneously ignites, a large amount of SO2 and nitrogen oxides enter the atmosphere, which is also one of the sources of acid rain. In addition, when coal gangue is piled in the open air, the surface of coal gangue will be weathered into dust. Under the action of wind, the whole mining area will be covered with black coal dust, which will have a serious adverse impact on the surrounding atmospheric environment.

In China, the spontaneous combustion of waste hills in the middle and upper reaches of the Yellow River is serious, such as most waste hills in Ningxia, Wuda Mine in Inner Mongolia, Tongchuan Mine in Shaanxi, Xishan Coal Mine in Taiyuan, Shanxi, Yangquan Coal Industry Group, Jiaozuo in Henan and Pingdingshan, which not only pollutes the atmosphere, but also affects human health. For example, Yangmei Group now has more than 20 waste hills, and the annual waste discharge is about 700× 104t. Due to the accumulation of a large number of washed gangue and some coal in the washed gangue, four super-large gangue piles in No.1 to No.4 mines have successively experienced large-scale spontaneous combustion, which seriously polluted the working environment of gangue discharge and affected the health of gangue discharge workers. Workers at the waste dump site often have symptoms of sulfur dioxide and carbon monoxide poisoning, and are taken to the hospital for emergency treatment. The average COncentration of SO2 is 19mg/m3, and the average concentration of co is 125.9mg/m3. The highest concentrations of SO2 and CO in some areas of gangue hill are 138mg/m3 and 237mg/m3, respectively, which exceeds the national third-class standard of atmospheric environmental quality. For example, the six spontaneous combustion waste hills of Tongchuan Mining Bureau are all high-risk areas of cancer, and the employees who have worked near the waste hills for 5 years all suffer from emphysema. The detection results near the burning area of coal gangue hill in China Wuda Yuejin Coal Preparation Plant show that the average concentration of SO2 is 10.69mg/m3, which is more than 70 times higher than the national standard, while the average concentration of H2S is 1.57mg/m3, which is more than 50 times higher than the national standard/kloc-0.

The spontaneous combustion of coal gangue hill produces a large number of toxic and harmful gases such as carbon monoxide and sulfur dioxide. The spontaneous combustion of a coal gangue hill can last for more than ten to several decades. Due to the long-term release of a large number of toxic and harmful gases, the incidence of respiratory tract in the surrounding area of spontaneous combustion coal gangue hill is obviously higher than that in other areas (Figure 1-7 and Figure 1-8). SO2 and other gases released by spontaneous combustion of coal gangue hill have harmful effects on leaf cells of green plants, leading to chlorophyll death. When the concentration of SO2 exceeds the standard seriously, some sensitive plants will die. See table 1-6 for the pollution concentration of SO2 on green plants.

Figure 1-7 spontaneous combustion of coal gangue hill produces a large number of toxic and harmful gases.

Figure 1-8 spontaneous combustion of Yangquan coal gangue hill

Table1-6 Pollution Damage Concentration of SO2 to Green Plants

sequential

2. Acid water pollution and toxic heavy metal pollution

Weathered coal gangue is not cohesive, mineral particles can move with precipitation, and some components such as toxic elements in weathered coal gangue can penetrate into soil and enter subsurface flow and water system with precipitation. According to the research, the composition and content of chloride ion, bicarbonate ion, magnesium ion, calcium ion, potassium ion and sodium ion in coal gangue are similar to those in inland saline soil, which affects the plant growth on coal gangue hill. Seriously, coal gangue contains many trace heavy metal elements such as polycyclic aromatic hydrocarbons. These toxic heavy metal elements leach into the soil or enter the water area through rainwater, polluting the water environment and soil environment. The degree of pollution depends on the content of these elements, the pH value of coal gangue and the leaching amount. These heavy metal elements are absorbed by crops and enter the human body through the food chain, which is harmful to human health. Metal elements leached from coal gangue include cadmium, lead, mercury, chromium, arsenic, copper, zinc, aluminum and calcium. Their discharge and transfer will pollute the receiving water body (Figure 1-9). Heavy metal ions such as cadmium, lead, mercury, chromium and arsenic are highly toxic and can accumulate in animals and plants in the environment, causing long-term adverse effects on human health, acute and chronic poisoning, causing damage to human liver, kidney, lung and other tissues, and even leading to deformity, canceration and death in severe cases.

Figure 1-9 Acid mine wastewater produced by leaching of coal gangue hill seriously pollutes the surrounding soil and water body.

The sulfur content of coal gangue in many areas of China is relatively high, such as Yangquan coal gangue in Shanxi Province, Nantong coal gangue in Sichuan Province, 18.93%, and Dazhi coal mine in Guizhou Province, which contains 8% ~ 16.08%. Pyrite in coal gangue is oxidized and leached to form acidic water rich in toxic elements such as sulfate, iron and heavy metals. SO2 and CO2 produced by spontaneous combustion in coal gangue hill combine with water molecules, which also easily acidify the soil in coal gangue hill, and the pH value of some soil in coal gangue hill can reach 3. For example, in 2006, Tan Lei River in Gansu was attacked by coal gangue, which threatened the drinking water source of 20,000 people. More than half of the river course has been occupied by a coal gangue hill, which is about 2m wide, 5m high and 200m low 10m long. All the coal gangue at the bottom is soaked in the river, which seriously pollutes the river and the drinking water source.

3. Radioactive pollution of coal gangue to the environment

In the process of long-term accumulation, a large number of radioactive elements are precipitated from coal gangue, which increases the concentration of radioactive elements in the air and causes radiation pollution when it exceeds its background value. The natural radioactive elements in coal gangue are mainly uranium -238, thorium -232, radium -226 and potassium -40. According to the monitoring of Yangquan and other mining areas in Shanxi Province, the natural radioactive core elements in coal gangue are higher than those in raw coal and soil.

According to China's Regulations on Radiological Health Protection, Radiological Health Protection Standard for Building Materials and Radioactive Material Limit of Industrial Waste Residues for Building Materials, combined with the content of radioactive nuclear elements in soil in some parts of the country, it can be considered that coal gangue is not radioactive waste, but general industrial solid waste. Even if 100% coal gangue is used as building materials, it still meets the relevant radioactive limit standards and health protection restrictions.

Third, the destruction of coal gangue hill to the landscape of mining area.

The accumulation of coal gangue hill directly changed the structure and function of the original land, destroyed the original plant ecosystem, and turned the original land into a "stone desert" where nothing grows. In addition, coal gangue is mostly gray-black, and coal gangue hills are mostly tall, and some even reach 100 meters or more. The huge bare black coal gangue hill has become the most important symbol of the coal mining area, which is extremely out of harmony with the natural landscape such as mountains, vegetation and farmland around the mining area. The spontaneous combustion coal gangue hill still emits white smoke, which seriously damages the natural landscape of the mining area (Figure 1- 10).

Figure 1- 10 Destruction of Coal Gangue to Mining Landscape

Wind erosion dust, dust and other particles in coal gangue hill cover buildings, plants, roads, etc., making them lose their original color; Coal gangue dust reduces the cleanliness and illumination of the air; The flowing water and rain of coal gangue washed away the weathering products of coal gangue, which destroyed the water landscape. Dust produced by coal gangue piling and toxic and harmful gases produced by spontaneous combustion have great influence on plant growth, with the leaves of plants turning yellow, the growth rate decreasing and the types of grassland vegetation decreasing, which seriously damages the ecosystem and vegetation landscape of the mining area (Figure1-1).

Figure 1- 1 1 Destruction of Coal Gangue Mountain to Mining Landscape