Study on Applicable Technology of Geological Environment Protection and Governance in Ordos Energy Base

I. Study on Applicable Technologies of Geological Environment Protection and Governance in Coal Development

It is necessary to select the appropriate geological environment protection and treatment technology for coal development according to the main geological environment problems existing in different types of mining areas and the local climate, landform and economic conditions. For example, on the basis of extensive data collection and investigation, we found that the main geological environment problems in Daliuta mining area are: first, land subsidence and ground fissures; The second is the accumulation and spontaneous combustion of coal gangue hill; The third is the destruction of water resources. Tongchuan mining area not only has problems such as land subsidence, ground fissures, coal gangue hill and water pollution, but also faces the transformation of coal resource-exhausted cities. Taking the land subsidence, ground fissures, coal gangue accumulation, water resources destruction and the transformation of coal-exhausted cities in Daliuta mining area of Tongchuan mining area as examples, this paper probes into the applicable technologies of geological environment protection and governance in coal development in two key areas.

(a) the applicable technology of land subsidence and ground fissure treatment

1. Land use distribution in mining area

Daliuta area is located at the junction of Mu Us Sandy Land and Loess Plateau, and belongs to loess hilly area and loess hilly area covered with yellow sand. The average agricultural population in Daliuta Town is 14.2 people /km2, cultivated land (irrigated land and Sichuan land)15mu /km2, and mountainous area18mu /km2, which is a sparsely populated area. 70.5% of the land area is grass irrigated land, sandy land and bedrock area, and the subsidence area formed by fully mechanized mining is completely subsidence area, which is difficult to distinguish from the original hilly landform. The key to control land subsidence in these areas is to backfill large ground fissures.

At the same time, the destructive effect of subsidence on cultivated land and the management and restoration of cultivated land in subsidence areas can not be ignored. According to SPOT5-5 satellite remote sensing image and field investigation (Xu, 2006) on July 3, 2005, the cultivated land area in Daliuta mining area accounts for 15.8% of the total cultivated land area, of which dry land accounts for 6.6% and irrigated land accounts for 9.2%. The dry land is distributed on the beach between sand dunes, terraces, low hills and valley plains, covering an area of 24.84km2 The main crops are corn, millet, millet, potato and sunflower. Irrigation land is mainly distributed in Wulanmulun River and Shuiyuan Valley. Such as Shuanggou, Muhegou, Huojimiangou, Haojiagou and Halagou. The main crops are corn, millet, millet, potatoes, millet, vegetables, melons, medicinal firewood and other plants, covering an area of 9.24km2 Although these agricultural land accounts for a small proportion in the whole mining area, it is the basis for local farmers to survive. Therefore, the destruction of cultivated land needs to be dealt with emphatically.

2. Applicable technologies for land subsidence and ground fissure treatment.

According to the topography and land use of Daliuta mining area, large cracks can be simply filled in grass irrigated land, sandy land and bedrock area, and the collapsed pits can be naturally stable and naturally integrated with the local hilly landform as long as they do not affect coal mining and do not need special treatment.

For agricultural land, it is necessary to apply some engineering control technologies combined with biological control technologies to restore the use of cultivated land. In view of the fact that the coal gangue in Daliuta mining area contains a certain amount of heavy metals and fluoride, it can not be used for filling and reclamation of collapsed pits. Therefore, the collapsed cultivated land in Daliuta mining area can be reclaimed by the simple method of deep digging and shallow cushion, and it is suitable for restoring cultivated land after land leveling. Combined with simple, cheap and effective biological reclamation technologies such as mud pump reclamation technology or acid-base neutralization method and green manure method, the bulk density, porosity, water content and infiltration, organic matter content and nutrient content of reclaimed soil are suitable for improving land productivity.

(2) Applicable technologies for coal gangue hill control.

1. Properties and existing problems of coal gangue in mining area

All coal seams in Shendong mining area belong to low metamorphic coal, and the coal and rock types belong to semi-bright, semi-dark and dim briquette. Its composition is bright coal and dark coal, with a small amount of vitrinite and silk coal, and the total organic matter is over 98%, which is flammable. The harmful components in coal are low, mostly ultra-low ash, ultra-low sulfur, ultra-low phosphorus and high calorific value coal. Coal gangue and selected coal gangue are composed of black coal gangue, mainly containing rocks with false roof and false bottom in coal seam. Mining gangue mixed with coal increases the flammability of gangue. The higher the degree of mechanization, the more coal gangue is added. Therefore, even if the sulfur content in the gangue is low and the gangue is mixed with combustible coal, the spontaneous combustion of the gangue hill is inevitable if the external conditions permit. Before the investigation area, there was spontaneous combustion of gangue in the waste dump of Daliuta Coal Mine in Liuta.

When coal gangue is stored in the yard, it is easy to produce wind erosion dust in windy weather, and its dust raising conditions mainly depend on its particle size, surface moisture content and wind speed. According to meteorological statistics, the annual average wind speed in this area is 1.7m/s, and it is windy in spring. The frequency of wind speed exceeding 4.8m/s in a year is about 5.53%, which shows that the gangue hill can reduce dust under certain conditions.

In addition, coal gangue contains a certain amount of heavy metals and fluoride. If it is piled up at will and no measures are taken for reclamation, it will pollute the soil environment.

2. Applicable technologies for comprehensive management of coal gangue hill.

Prevention is the top priority of spontaneous combustion in coal gangue hill. In view of the high mechanization degree of coal preparation in Daliuta mining area, the most effective measure to prevent spontaneous combustion of coal gangue is to effectively remove the coal chips or coal blocks mixed into it. In addition, in view of the possibility of heavy metal pollution of coal gangue in mining area, it is effective to adopt the methods of layered accumulation, covering soil reclamation and greening. According to the different fire areas, the severity of spontaneous combustion, geographical environment and construction conditions, a reasonable and effective control scheme for spontaneous combustion of coal gangue hill is selected. From the engineering practice at home and abroad, the comprehensive measures of grouting method, supplemented by surface sealing, compaction and injection of foam extinguishing agent are mature and effective technologies to control spontaneous combustion of waste hills at present.

In recent years, in order to improve efficiency, reduce cost and reduce pollution, Daliuta mining area has considered and implemented underground treatment technology of gangue residues in the mine design and construction stage, and digested and treated all the gangue underground (Julia, 2002).

Underground waste rock and slag treatment is to discharge the waste rock and slag produced in the production process to the nearby lane, waste rock lane, construction lane and other abandoned lanes with mine forklifts and trackless rubber-tyred vehicles, supplemented by other safety auxiliary measures.

(1) Use adhesive tape to treat the gangue in the construction stage of roadway extension, roadway mouth and roadway head chamber.

According to the amount of gangue discharge, the underground gangue discharge chamber is excavated in the permanent coal pillar reserved nearby, and the original abandoned roadway in the mine is fully utilized as far as possible.

(2) Treatment of gangue or other structures in the process of coal seam thinning.

According to the design, a 15m roadway should be opened every 50m between two adjacent drift. In addition to the roadway that must be reserved in the production process, other roadways can be used as gangue discharge roadways. If the reserved roadway is still insufficient to discharge gangue, according to the need, dig a roadway with the same cross section and a depth of about 8m in the coal pillar of the nearby roadway. For some abandoned construction lanes, it is also used as a gangue dump lane. When discharging gangue, in the case of less gangue, the mine forklift shovel directly to the gangue discharge lane; When there are a lot of gangue, dump the gangue to the gangue discharge lane with a trackless rubber-tyred vehicle, and then pile it with a mine forklift to maximize the use of the gangue discharge lane.

In order to prevent spontaneous combustion of gangue, retaining walls are built in all gangue discharge lanes. In the gangue lane filled with broken coal, the surface of gangue should be covered with tight loess; In order to prevent the secondary pollution of gangue, a water-resisting layer should be set up; The driveway entrance is permanently sealed to prevent spontaneous combustion.

The underground treatment technology of coal gangue slag is adopted to reduce the cost of tons of coal without occupying land, and to prevent the pollution of toxic and harmful substances in coal gangue to the environment and water body under weathering and leaching; Put an end to spontaneous combustion of coal gangue, reduce the content of toxic and harmful substances such as sulfide in the air, and achieve good economic and ecological environmental benefits.

(3) Applicable technologies for comprehensive utilization of water resources in mining areas

1. Hydrogeological conditions and water resources destruction in mining areas

The mining area is located at the junction of Mu Us Sandy Land and Loess Plateau in northern Shaanxi, with high terrain in the northwest and low terrain in the southeast. There are sand dunes, sand dunes and beaches in the west and north, and loess hilly areas in the east and southeast. The groundwater types in the mining area can be divided into three types: loose rock pore water-bearing rock group, burnt rock fracture water-bearing rock group and Jurassic clastic rock pore water-bearing rock group. The water-bearing strata affected by coal development mainly include the quaternary upper Pleistocene Salawusu formation aquifer and burnt rock aquifer.

Due to the development of coal resources, the destruction of water resources in this area is all-round: surface subsidence and ground fissures caused by underground coal mining have changed the geotechnical structure of unsaturated zone, and mine drainage has changed the recharge, diameter and drainage conditions of groundwater, resulting in a series of problems such as aquifer drainage, groundwater level decline, surface water drying up and water quality deterioration, thus affecting the total amount and quality of available water resources in mining areas. The aeolian sand aquifer is most affected in the mining area, and the aquifer in some areas has been drained, and the original aquifer has become a deep vadose zone. Under the current conditions, the influence range of groundwater in this area is controlled by the scale of natural aquifers, ranging from several hundred meters to several kilometers. On the west side of Wulanmulun River, due to the small scale of aeolian sand and loess aquifer, the influence scope is small; On the east side of Wulanmulun River, especially in the area of Aobao Shili, the aquifer is large, and mining has a great impact on groundwater (Xu, 2006).

2. Applicable technologies for comprehensive utilization of water resources in mining areas

Under the effective management of Shendong Coal Company, Daliuta Mining Area has basically realized the resource utilization of mine water. The specific measures are to adopt advanced technology to treat domestic sewage, and at the same time, combining the characteristics of mine water, goaf and its fillings, focus on developing the filtration and purification technology of mine water goaf, and successfully implement it in Daliuta Mine Field, which has achieved objective economic, environmental and ecological benefits.

Although Daliuta mining area has successfully realized the comprehensive utilization of mine water, the loss of water resources has become an increasingly serious deficit because the mining area is located in the arid desert area of northwest China, with less precipitation and more evaporation, and the natural shortage of water resources, coupled with the problem of water resources destruction caused by coal development, and other ways need to be considered for comprehensive and effective utilization of water resources in the mining area.

In view of this situation, scholars at home and abroad have turned to the study of soil water utilization. However, these studies are all in the basic theoretical research stage, including: the study on the influence of subsidence on soil moisture, the study on the mechanism of soil moisture migration in subsidence areas, and the study on soil water pollution caused by mining. At present, there is no research on improving soil water use efficiency in subsidence areas. From 2005 to 2007, the National Natural Science Foundation's general project "Study on Water Migration Mechanism in the Aerated Zone under Mining Subsidence" (project number: 40472 124) carried out the research on water migration and ecological environment in the unsaturated zone in Shenfu Dongsheng coal mining subsidence area, and achieved some preliminary results, which provided theoretical basis and technical support for the protection and comprehensive utilization of soil water resources in coal mining areas. On this basis, the comprehensive utilization of soil water in coal mining subsidence area is further discussed, and the protection and treatment scheme suitable for the comprehensive utilization of soil water in Daliuta mining area is put forward, which makes a certain contribution to saving ecological water in mining area.

(d) technologies suitable for the transformation of coal-exhausted cities

1. Development Status of Mining Cities

Tongchuan Mining Bureau is a large coal enterprise developed on the basis of 65438-0955 in Laotongguan Coal Mine. There are 3,004 registered employees1person, 3,269 retirees1person, and about 216,000 employees' families. Because most of the production mines were built in the late 1950s and put into operation in the early 1960s, the coal reserves, mine field scope, production capacity and service life of the mines were all limited by the geological conditions and mining conditions at that time. Since 1980s, nine pairs of mines have been scrapped and closed, reducing the design capacity by 3.96 million tons. At present, the approved production capacity of 8 pairs of mines in the world is 9.65 million t/a, and there are no associated mines. Some mines in the eastern region are exhausted, with heavy burden and high production cost, and are applying for the closure and bankruptcy project of national resource-exhausted mines. The problem of production development is increasingly prominent, and the survival and development of enterprises are facing severe challenges.

2. Appropriate technologies for the transformation of resource-exhausted mining cities

Referring to the experience of transformation of resource-exhausted cities at home and abroad, we believe that the following points are very important for the successful transformation of Tongchuan mining city.

(1) Promote its economic transformation with vigorously developing alternative industries as the core.

Specifically: fully tap the utilization potential of existing coal resources; Strengthen the comprehensive utilization and reuse of associated resources and wastes to reduce the waste of resources; Actively apply for the continuation of the mine, extend the mining period of coal resources and extend the mining time; According to its own functional orientation, characteristics and market demand, we should develop alternative industries (such as tourism) as soon as possible and finally form a diversified industrial structure.

(2) Promote social transformation focusing on promoting employment and improving social security.

Specific measures include: training the skills of laid-off workers; Support the development of small and medium-sized enterprises; Encourage self-employment; Establish and improve the social security mechanism.

(3) Promote the environmental transformation of mining cities with the goal of changing the environment.

Specific measures include: transforming abandoned mines and open pit mines into mine parks according to local conditions, so as to improve the living environment of mining cities and promote the development of tourism in mining cities.

Second, research on geological environment protection and treatment technology in petroleum development.

There are a large number of petroleum pollutants in the development zone of Ordos Oilfield, mainly in the form of oily sewage, crude oil and waste gas-containing mud. This means that if measures are not taken in time, oil pollution will become the main pollution mode in this area, the pollution degree will further deepen and the ecological environment will further deteriorate. According to the previous research results and the conclusion of this study, the direct pollution of oily sewage, crude oil and mud containing waste gas to local groundwater does not exist, and the pollution to surface water is relatively small, but the pollution to soil is very serious. The protection and management of soil ecological environment is of great significance to people's survival and life, and should be paid universal attention to. According to the soil properties and pollution situation in loess area, combined with the comprehensive factors such as geology, climate and urban planning in this area, bioremediation technology can be considered. Through analysis, investigation and testing, it is found that there are a large number of microbial flora in loess soil, which provides innate conditions for using microorganisms to repair oily soil.

Therefore, based on this fact, through the breakthrough and demonstration of soil pollution caused by crude oil landing, the microbial in-situ remediation experiment of soil in this area was carried out to explore the feasible methods of ecological restoration in loess area.

(a) The factors that should be considered in the remediation of oil-contaminated soil in loess area.

In northern Shaanxi and eastern Gansu, soil oil pollution is more serious, and due to the development of oil industry and the increase of oil consumption, soil oil pollution will become more and more common and serious. In view of the above analysis, the following factors should be considered in the remediation of soil oil pollution in loess area: ① climatic characteristics, geological structure and soil types of contaminated sites; (2) According to the different types, quantities and properties of pollutants, adopt appropriate remediation technologies; (3) the effect, time, difficulty and cost of restoration; ④ The selected method should be suitable for local economic development and urban planning; ⑤ Try to adopt technologies with low cost, no pollution, high efficiency and strong operability; ⑥ Develop new technologies according to local conditions.

(B) the choice of repair methods

For the loess area, the soil is easy to adsorb petroleum pollutants. On the one hand, from the nature of petroleum pollutants, petroleum is a kind of macromolecular hydrophobic viscous substance, so petroleum molecules can easily reach the soil surface and attach to the surface of soil particles, while petroleum pollutants attached to the surface of soil particles are more likely to attach to more petroleum pollutants; At the same time, oil is lighter than water, and the oil in water is mainly dissolved phase and emulsified oil, which has good dispersibility and is easy to be captured and adsorbed by soil particle colloid. Moreover, the solubility of oil in water is low. According to the empirical law of adsorption, the lower the solubility, the greater the adsorption capacity. Finally, the oil in water exists in the form of tiny particles in the turbulent state of water, and its adsorption mechanism is not only the adsorption of oil molecules with particles under the action of intermolecular force and charge force, but also the adhesion of the whole oil particles to particles, so that oil can reach adsorption equilibrium at a high speed in a short time, which is also the characteristic of oil adsorption; On the other hand, from the nature of loess, the adsorption speed of porous media mainly depends on the external diffusion speed and interstitial diffusion speed of particles. The diffusion rate outside particles is directly proportional to the dissolution concentration, the surface area of adsorbent and the particle size of adsorbent, while the diffusion rate of voids is usually inversely proportional to the higher power of adsorbent particle size. However, loess is mainly composed of silt (0.05~0.005mm), which has a small particle size, a large external area and a small diffusion distance within the particle, resulting in a faster adsorption speed. It is precisely because of these characteristics in the loess area that an efficient, economical and ecologically affordable clean technology is needed to repair the oil-polluted soil in the loess area. Natural attenuation is a new cleaning technology developed on the basis of biodegradation, and it is the development of traditional biological treatment methods. Compared with physical and chemical remediation of contaminated soil, microbial remediation can accelerate the rate of natural biodegradation by optimizing environmental factors, which is undoubtedly an efficient, economical and ecologically affordable clean technology and the most vital method to control oil pollution.

To sum up, it is more suitable to use microbial technology to repair oil-contaminated soil in loess area at present.