1 tank dip process
The tank leaching process is mainly for the chalcopyrite concentrate after flotation, and the reaction tank is generally provided with a stirring device. By increasing the reaction temperature in the stirred tank (40-60 ° C), adding moderately thermophilic leaching microorganisms, and continuously charging carbon dioxide and oxygen, the leaching rate of chalcopyrite can reach 70 within 6-10 days. %the above. A one-year semi-industrial experiment of agitated leaching of chalcopyrite concentrates was carried out at the Mt. Lyell copper mine in Australia. The technology used in the experiment was the BioCOPTM process designed by BHP Billiton. However, the specific experimental data and results did not report that the tank dipping process can better control the leaching parameters and effectively improve the bioleaching rate and leaching rate of chalcopyrite. However, the investment costs and operating costs involved in industrial applications are much higher than the heap leaching process, so when the market price of copper is not ideal, this process is difficult to obtain practical application.
2 heap leaching process
The heap leaching process is one of the most widely used technologies in the microbial metallurgical industry. It refers to spraying (drip) the leaching solution containing leaching microorganisms onto the ore or waste rock pile. During the diafiltration process, the microorganisms are adsorbed to the surface of the ore and continuously grow and propagate under suitable conditions. The "contact" or "non-contact" mechanism selectively dissolves and leachs the useful metal components of the ore or waste rock pile and transfers them to the product solution for further extraction and recovery (see Figure 5-1). Subsequently, the application of high temperature microorganisms in biometallurgy, the bioleaching process of primary sulfide ore chalcopyrite began to develop gradually. One of the most typical immersion fields is the heap leaching of Quebrada Blanca in northern Chile. The yard is located on the Alti Plano mountain at an altitude of 4,400 m. The average temperature is below 15 °C. The oxygen concentration in the air is relatively low. It is generally considered unrealistic to implement bio-dumping. The heap leaching field will break the ore particle size by 100% to less than 9 mm. Then, the ore is made of hot water and sulfuric acid, and the pile is transported into a 5-6 m high pile, and the gas pipeline is laid on the bottom of the pile for aeration to increase the activity of the leaching microorganisms; the top of the pile is covered with a heat insulating cloth. , the heap to reduce heat diffusion; initial extract intervals water spray, to increase temperature of the stack, to improve the rate of microbial growth; leaching the ore to be late, pyrite and other exothermic decomposition, leading to the heap When the temperature rises, the hot water can be stopped. Finally, the heap leaching process successfully processed the 17,000 t/d ore and obtained a higher copper leaching rate and leaching rate.
At present, there are few reports on the industrial application of chalcopyrite bioreactors. However, according to the heap leaching process of secondary copper sulfide ore and copper oxide ore, the study of chalcopyrite bioleaching parameters should also focus on the following aspects: Dip height, ore particle size, spray system, aeration intensity, etc. These aspects of research have important guiding significance for improving the leaching rate and leaching rate of copper in heap leaching.
A mine pile height
The height of the heap is one of the main factors affecting the heap. When the ore heap is too high, the ore density is too large, the solution seepage is prone to short circuit, the leaching area of ​​the lower part of the heap is reduced, the ore is not in contact with the leachate, and the copper leaching rate is reduced; at the same time, the height increase easily leads to the leachate flow to the heap. The lack of sufficient oxygen at the bottom reduces the transfer of oxygen in the heap, causing the leaching reaction to drop until it becomes unreactive. Therefore, in the heap leaching production, the ore height should be determined according to the nature of the ore, so as to ensure the ore processing capacity and ensure better leaching index and leaching period. For ore with high strength, low mud content and good permeability, the height of the heap can be relatively increased, and the height of the pile is generally 8-12m. For ore with high mud and poor permeability. The height of the heap should be controlled at 2-5m.
B ore particle size
The ore particle size not only affects the rate of chemical reaction in heap leaching, but also affects the mass transfer rate. The larger the specific surface area of ​​the ore particle size than the fine ore particle, the larger the contact surface of the leach solution with the ore, the better the leaching effect, and the shorter the injection cycle. However, if the ore particle size is too small, it is easy to increase the mud content of the ore heap, and then the knot is formed, which easily leads to channeling, affects the permeability of the leachate, and causes the local ore to form a dead angle, which is not conducive to bioleaching. Moreover, excessive crushing of ore can lead to greater production costs.
Tang Quan et al. analyzed the effect of ore particle size on heap leaching of a uranium ore. The sample ore is broken into four sizes of -30 mm, -20 mm, -10 mm, and -5 mm. The results of leaching experiments show that reducing the ore particle size helps to increase the leaching rate of uranium and shorten the leaching period. The particle size of -10mm and -5mm is similar, the leaching rate of uranium is above 90%, and the injection cycle is about 60 days, which is significantly higher than the other two particle sizes. However, the particle size of -5 mm requires more crushing costs, which greatly increases the energy consumption and material consumption of industrial production. Therefore, the use of a particle size of -10 mm is relatively economical.
C sprinkler system
At present, the liquid distribution system used in the bio-heap reactor in China usually includes three methods: irrigation pond liquid, shower cloth liquid and drip cloth liquid, and the main equipment is sprayer. This is because the pond is The irrigated cloth liquid system is not conducive to the flow of air in the heap, which is easy to cause low oxygen content in the heap, and the drip-type cloth installation work is large, and the dead space of the pile is easy to occur, and the liquid distributor is blocked. It is not easy to be discovered afterwards. Therefore, the shower cloth liquid is superior to the first two liquid distribution methods in terms of the uniformity of the cloth liquid and the fluidity of the air.
Two types of sprinklers are commonly used for sprinkler liquids: rotary swing nozzles and rotary diffuser nozzles. The rotating rocking nozzle is relatively heavy in mass, and the rotating body and the supporting body are easily worn. When the wear is severe, the resistance will increase, the rotation will be inflexible or even not rotate, so that the liquid can not be dispersed to form a water column to be ejected, and the distribution area of ​​the leachate is greatly reduced, thereby affecting the copper leaching rate. The use of such nozzles must be replaced frequently, increasing the cost of stacking. The rotary diffusing nozzle has a relatively small rotating body and is light in weight, and generally does not cause the nozzle to rotate inflexibly, and can ensure uniform scattering of the leaching solution. Although diffused spray heads require large working pressures and inlet sizes, they are still recommended by many stackers.
When using spray cloth, choosing the right spray intensity is a necessary part of bio-dump. Spray strength directly affects copper recovery and total cost. Properly increasing the spray intensity can enhance the relative motion of the solution between the ore and enhance the diffusion. However, when the spray intensity is too large, it is not suitable for the adsorption and diffusion of ions on the surface of the mineral particles. At this time, most of the solution containing the reactant ions flows in the channels between the mineral particles, and the volume of the liquid permeated in the voids of the mineral particles is small; The high flow rate makes the shear force between the inter-void fluid and the channel fluid interface too large, which is not conducive to material transportation and exchange [54].
D inflatable strength
The oxygen content of the heap mainly depends on the dissolved oxygen in the spray liquid, natural air infiltration and artificial inflation. The dissolved oxygen content of the spray liquid is less than 1%, and the concentration of metal ions in the solution increases. The amount of dissolved oxygen will decrease; natural air can bring in a certain amount of oxygen through siphoning, but when the heap is large and covers a large area, the center of the heap cannot rely on siphoning to bring in enough oxygen. Especially in the bio-disseping copper sulfide ore, due to the liberation of some minerals, the temperature in the center of the reactor is high, and the dissolved oxygen is drastically reduced, which is not conducive to the survival of the leaching microorganisms, thereby delaying the leaching of microorganisms and reducing the leaching rate of copper and Leach rate. Therefore, the gas pipeline should be laid at the bottom of the pile during the pile-up process, and the pile body is inflated intermittently, which is beneficial to increase the dissolved oxygen amount of the pile, thereby improving the bioleaching ability.
Wu Aixiang et al. found that in the low permeability coal mine immersion porosity improvement study, in the middle and late leaching, due to the vigorous biochemical reaction, the mineral mechanical properties deteriorated, resulting in secondary particles, which significantly reduced the porosity and seriously affected the heap penetration. Sex. At this time, by increasing the aeration intensity, an air wave is formed, which acts on the pore wall by the transmission of waves, thereby effectively reducing the viscous resistance and internal friction between the particles, thereby improving the fluidity of the particles in the pores and maintaining the pores. Smooth.
ML Heetor studied the effect of aeration intensity on copper leaching rate and microbial activity in chalcopyrite heap leaching. The total ore of the experimental ore heap is 62,500 tons, and the pile height is about 6.2 m. An oxygen content test instrument was placed at lm, 3 m, and 5 m from the bottom pad to measure oxygen levels at different leaching periods and at different heights. In the experiment of more than two months, it was found that the bottom of the heap was nearly saturated due to the large amount of oxygen in the air. However, when the air rises upward with the pores of the ore, it is continuously consumed by the leaching microorganisms, and the oxygen content is continuously lowered. When approaching the top of the stack (approximately 1 m difference), oxygen consumption is exhausted. Large oxygen consumption indicates that the amount of microorganisms is large, the activity is high, and the leaching ability is enhanced, thereby contributing to the improvement of copper leaching rate and leaching rate.
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