The permeability of the heap deteriorates for some of the following reasons: The temperature has an important influence on the reproductive growth and leaching efficiency of the leaching bacteria. At the same time as the leaching reaction of the sulphide minerals, the heat is released. The reaction rate is different at each immersion pile, and the rate of heat release is also different, and the heat conduction and radiation in the pile are added. The difference in the process creates an imbalance in temperature.
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2.1 Mine pile permeability is poor
(1) The heap is compacted. After repeated crushing of shovel-mounted equipment, Ma Chunhua, et al.: Overview of research and application of leaching mining technology 34
The ore surface will be compacted, and the ore in the middle and lower part of the pile will be subjected to greater compressive force, even being fractured and crushed [17];
(2) The mud content is too large. The ore pile or the waste rock pile contains a large amount of soil because the ore body contains a muddy interlayer that is difficult to separate or when the surface soil is mixed during open pit mining;
(3) It is affected by weathering. Under the conditions of wind, sun and rain, some ores are more likely to weather and disintegrate, and the particle size becomes smaller and dissolves, precipitates and cements [18].
2.2 The uneven distribution of the leaching solution in the heap The heterogeneity of the heap can cause the coarse particles to be distributed in the upper part, while the fine particles are mostly distributed in the lower part, and the ore permeability of different particle sizes is also different. When the leaching solution flows through a region with strong water conductivity, the flow rate is fast, the contact time with the ore is short, and the reaction is incomplete, which affects the leaching effect of the ore [19]. In addition, due to the high flow rate of the solution in some regions, the rate of solution renewal in other regions is slow, and the mineral is not easily dissolved in time and the leaching dead angle occurs.
2.3 Low oxygen content in the heap The oxygen is indispensable during the bioleaching process. The oxidation reaction in the leaching process and the reproductive growth of the leaching microorganisms require the participation of oxygen and carbon dioxide. Therefore, the oxygen concentration in the reactor is very large. To a certain extent, the rate of leaching reaction of sulfide minerals is restricted. Oxygen piles with poor permeability and permeability, it is difficult for oxygen to enter the inner part of the pile through convection, but can only enter the pile slowly by molecular diffusion, so that the oxygen content in the pile is low.
2.4 Unbalanced temperature in the heap
In addition, leaching mining in China still has small scale, mechanization, automation and low level of automatic monitoring [20].
3 Development trend of leaching mining technology Leaching mining is a mining method with broad prospects and has achieved rapid development in China [21]. With rich theoretical basis of research and practical experience, it will be more widely used in various metal mining deposits. The future research direction of leaching mining mainly has the following three aspects [22].
(1) Study on the structural characterization of pore fracture network in leaching system. The leaching system has a complex pore-fracture structure and is a typical dynamic unstable structure, which is difficult to quantify. To this end, CT, image processing and three-dimensional reconstruction techniques are often used to obtain the microscopic structural parameters of the ore body and to construct a pore-fracture network space model. At present, research in this area is still lacking [23]. On the other hand, through the in-situ scanning test of the ore leaching process, the dynamic structural parameters of the pores in different leaching stages were analyzed to determine its temporal and spatial evolution.
(2) Response characteristics of the leaching process in a multi-phase multi-field environment. Under the direct or indirect interaction of gas phase, liquid phase, solid phase and temperature field, seepage field and concentration field, the response characteristics of the leaching process are complex. Therefore, the law of gas-liquid two-phase percolation and solid-liquid interaction under multi-field coupling is further studied, and the variation law of ore leaching behavior in multi-phase and multi-field environment is analyzed.
(3) Study on the mechanism of multi-field coupling in leaching system. Because the temperature, concentration, and flow rate of the leaching system are complex in spatial distribution, and the external environment is easy to affect it, it is difficult to make a clear explanation for the multi-field coupling mechanism. To this end, it is necessary to further explore the following aspects: chemical reaction, gas-liquid flow on the generation, transfer, dissipation and temperature field distribution of the reaction exothermic; migration mechanism of solute under the influence of temperature gradient and concentration gradient; seepage The coupling law of field and temperature field and concentration field; the spatial distribution characteristics and evolution law of solution saturation and seepage rate; the influence of solution seepage and heat transfer on the distribution characteristics of concentration field.
4 Conclusion Compared with traditional mining methods, leaching mining has outstanding advantages: low energy consumption, safe operation and good working conditions [24]; low cost, low capital construction, fast construction, high degree of automation; green Environmental protection; high resource recycling rate [25].
However, from the research application, the basic theory of leaching mining technology is still very weak [26], more theory needs to be done in the multi-factor strong correlation mechanism of bulk seepage kinetics, efficient strain cultivation and enhanced leaching. Research to change the long leaching period and low leaching rate of leaching mining technology, making it the best method for metal deposit mining.
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Article source: Mining Technology, 2013, 13 (3)
Author: Ma Chunhua, Huang governance can; Yunnan Jinding Zinc Industry Co., Ltd., Nujiang 671 400
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On the "Overview of the Research and Application of Leaching Mining Technology (I)"