As China's rapid economic development, the needs of various industries for bauxite resources is increasing. Although the output of bauxite in China has increased year by year in recent years, it still cannot meet the demand for raw materials for the downstream products of bauxite. Taking Chinalco as an example, from 2011 to 2013, the proportion of ore produced by China's aluminum industry accounted for only 48.84%, 50.84%, and 51.30% of the ore. It still needs a large amount of purchased and imported bauxite. However, due to factors such as Indonesia's bauxite export restrictions and other factors, the strategic safety of China's aluminum bauxite resources is difficult to guarantee, resulting in a serious squeeze on the profit margin of alumina production. At the same time, the shallow resources are gradually depleted, and the reserves of bauxite suitable for open pit mining are gradually reduced and cannot meet the needs of large-scale production. So far, China's bauxite underground mining mines are still relatively small [1-5], basically small and medium-sized underground mines below 150,000 t/a, mainly distributed in Shandong, Guizhou, Chongqing and other places, in addition, In other regions, there are only sporadic mining, such as Jiajiatun and Duicun Leigou bauxite in western Henan [6-10]. At the same time, there are many underground bauxite mines under construction in Henan, Guizhou, Shanxi and Chongqing. In the mountains, it can be seen that the production capacity of China's underground bauxite mines is bound to increase. In recent years, there have been few related achievements in the underground mining method of bauxite, and the experience of deep underground resources mining is lacking. A considerable part of the deep mining design is not perfect, which leads to accidents such as roadway collapse and filming in production. For the entire bauxite system in the country, underground mining is still in the exploratory stage.
Therefore, this study is suitable for the analysis of wall caving method, room column method and long arm single layer caving method for bauxite underground mining, and provides reference for promoting safe and efficient mining of bauxite deep.
1 Bauxite underground mining method
1.1 wall caving method
The engineering layout of the bauxite underground wall caving method is shown in Figure 1. The method mainly relies on natural caving or blasting to break the ore. The ore loading method is based on the inclination of the ore body using electric shovel, slag slag machine, scraper, etc.; the support can be supported by conventional wood, steel, hydraulic or hydraulic support or “well†type concrete precast block. The lane is protected; the mine is transported by traditional mine car or car. The method has the advantages of simple system and good ventilation conditions. The disadvantage is that the pit wood is consumed more, and the support roof is complicated to be managed. It is suitable for the gently inclined ore body where the surrounding rock is easy to collapse, the thickness is not large, and the surface is allowed to collapse [11-17].
1.2 room column method
The engineering layout of the underground mining of bauxite by the room-pillar method is shown in Figure 2. The method has a length of 80-150m and a width of 40-60m. The blasting method is used to break the mine. It is not supported or supported by bolts. When the stability of the roof is poor, a ceiling of 0.5~1m should be reserved. The method of loading and transporting and the method of caving is basically the same, and it is suitable for the stable level of ore rock or the gently inclined ore body [18-19].
1.3 Longwall loose blasting comprehensive mechanized mining method
Loose mechanized longwall mining method is blasting in recent years, domestic scholars to explore large-scale mining methods using mining technology of coal mining bauxite mine proposed, according to the number and manner of use of hydraulic props can be divided into single hydraulic support There are two types of roof protection and hydraulic support. Among them, the engineering arrangement of the single hydraulic prop support roof mining method is shown in Figure 3.
The innovation of this method is that the method of strengthening loose blasting is proposed in view of the low efficiency and poor blasting effect of the traditional blasting method. The implementation method is shown in Fig. 4.
The size of the mine can reach 1000m in length and 120m in width, depending on the size of the ore body. With the long-wall arrangement, it is also possible to adjust the long-wall arrangement according to the mine development arrangement, but the inclination angle is generally not more than 16°. Imitate the arrangement of coal mining according to the occurrence of harmful gas in the ore body, adopt one-to-one "U" type ventilation, or two-in-one "W" type arrangement. The fresh air flow and the personnel enter the work surface from the auxiliary transport roadway from the chute, and the wind is transported by the belt conveyor. The operation is carried out by means of continuous mining, blasting, slag or scraper loading, belt conveyor transporting ore, support by single hydraulic props, natural caving or treatment of mining areas by caving.
Although the method uses the continuous operation method to greatly improve the production capacity and efficiency, since the application of the method is still in the initial stage, and the occurrence of different underground bauxite is different from the rock mass, there are such as shipping and support equipment. High investment issues.
2 Bauxite underground mining difficulties
(1) Ore body production. The continuity and integrity of the ore body are weak, and the bottom of the ore body is undulating and uneven. The traditional mining method has high labor intensity, high loss rate of ore depletion rate, low recovery rate, and recovery rate is only 30% to 50%. It is difficult to meet the “Bauxite mining rights access conditions†standard, and it is difficult to achieve large-scale In the recovery, there is still a big gap compared with other countries in the world. When the ore body is relatively steep (more than 30°), the embers are unsafe, and the scraper is difficult to use when mining thin ore bodies, resulting in low mining efficiency.
(2) Supporting process and cost. Since bauxite is mostly sedimentary deposits, the direct roof is mostly bauxite clay, clay shale , carbonaceous shale or coal line, which is soft and extremely unstable. Once the free surface is exposed, it is easy to be weathered and disintegrated. indirect limestone or sandstone roof; direct plate generally claystone, iron clays rocks, clay and rock and bauxite, iron
The layer boundary is obvious, and the indirect bottom plate is dolomitic limestone, argillaceous limestone or breccia limestone. Top and bottom seam layers slate lower strength, poor stability, are weak - semi-hard rock, rock mostly weakness, bonding of mud water easily, arching, pressed and management difficulties, difficulties ore.
(3) Mineral rock properties. The properties of the ore rock vary greatly, and some ore bodies have large hardness, which is not convenient for mechanical cutting. The blasting process is complicated, the labor intensity is high, the labor productivity is low, the mining cost is high, some ore bodies are loose and broken, and it is difficult to support. The support rate is as high as 100%. And the laneway repair rate is high.
3 Discussion
At present, the underground mining of bauxite is still in the exploratory stage. Due to the low value of bauxite and its soft nature, its occurrence conditions are relatively simple compared with coal mines. Therefore, it can be properly borrowed from the well-developed coal mining technology for mining. Successful experience in the mining of underground mines in France, Hungary, and Northern Ural Bauxite Mines (active trials and the use of modern mining equipment, mechanized operations, while improving the profitability of bauxite mining, improving productivity and safety, and improving The working conditions of the machine, the application of the mechanical device makes it unnecessary for the worker to approach the dangerous area of ​​the working face, and accelerates the work schedule and shortens the ore recovery time). The types of bauxite deposits in China and even the world are geographically distinctly zoning. The bauxite deposits, ore-bearing strata, ore thickness and geological conditions of the top and bottom of the strata have different differences in different regions. The adoption of new technologies based on different mining technology conditions and resource characteristics is the only way to ensure the safe and efficient underground mining of bauxite mines in China.
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Author: Luo Gan Hua, Wu Aixiang; School of Civil and Environmental Engineering, Beijing University of Technology, Laboratory of efficient mining and metal mining Security, Ministry of Education;
Article source: "Modern Mining"; 2016.8;
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