When building multi-layered ore piles, it is necessary to avoid compaction of the surface of each layer of ore. Some mines use ripper to loosen the compacted material, and some are considering using a belt transport system to prevent the vehicle from driving on the pile.
3) Slope pile-up method This is a better method of pile-up, that is, first use a waste rock to build a slope of 0.6-0.9m higher than the pile. Trucks carrying ore are only driving on this road. Use a bulldozer to push the ore to both sides of the ramp. The track of the bulldozer does not compact the ore like a truck. This method of pile-up allows the surface of the immersion pile to withstand less pressure (Figure 6).
4) Mobile Bridge Crane Building Method The Ozty Mine in New Mexico, USA, uses a unique mobile crane to build a heap. This method is characterized by reducing the compaction of the heap and ensuring good permeability of the heap (Figure 7).
5) mobile conveyors STACKING this method is reported to transport building heap of heap leaching beneficial, United States RA Hansen designed and manufactured by the company, in Pigg Seuss gold company (Pegasus Gold Corp) Florida Valley, the world's longest A fully mobile transport aircraft has recently been put into operation with a length of 457m for pile-up operations in heap leaching production. [next]
The use of such a mobile transporter to build a pile not only reduces production costs, but also reduces the degree of compaction of the heap, and will speed up the leaching rate of gold and increase the recovery rate of gold.
The built ore pile has a diameter of 914m and a height of 18m. The ore mining speed is 600-700t/h. A tracked walking mechanism is available to keep the conveyor level and accurate when moving or climbing (15% maximum slope). The unloader can move the ore along the same slewing conveyor to move along the entire length of the machine. When the front edge of the heap moves forward, the entire conveyor moves to a certain angle along the curved side by its own power. The whole ore heap is layered and piled up with a height of 2m. In order to build a uniform pile, there are other control systems that jointly control the speed and method of moving the unloader and transporter (Figure 8).
   4. Heap leaching method
The heap leaching method can be divided into three basic heap leaching methods according to the type of ore, the characteristics of the site and the treatment conditions of the slag, and the utilization of the immersion pad, namely, the multiplexed dip pad method, the expanded dip pad method, and the valley heap leaching method. .
1) Multiplex Dip Pad Mode The multiplex pad method involves periodic loading, leaching, and unloading from a durable dip pad, as well as washing and neutralizing the soaked waste ore to meet environmental requirements.
The multiplex padding method requires the construction of a durable set of dip pads. The prepared ore is loaded onto these dips for leaching, washing, neutralization (if necessary) and unloading in the heap (Figure 9).
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The design of the multiplexed dip pad system requires consideration of the leaching recovery and consistency of the ore. The size of the dip pad and the number of dip pads are determined by the rate of ore mining and the time required to leach the metal. The leaching speed of the ore is relatively constant.
In general, the leaching time is preferably less than 60d. The longer the leaching time, the larger the required dip mat area, because the residence time is extended for a certain productivity. For a particular production process, when planning a leaching cycle, you also need to consider the time frame over which an ore can be leached. Therefore, it is not possible for various ores to achieve the required recovery rates over the leaching period.
Repeated loading and unloading requires a durable pad on the dip pad to withstand the stresses encountered. Some typical gasket materials such as asphalt , concrete, etc. can be used. The choice of liner method should be mainly adapted to the mining method used during unloading. If the unwinding can be precisely controlled to ensure that the liner remains in its original position, a film liner can be used.
The multiplex padding method does have great advantages, mainly because the ore can be leached in a limited area. The more times the dip pad is reused, the lower the initial capital cost per ton of ore. The size of the solution tank is only determined by the area of ​​the multiplex pad, which limits the water circulation and can control the height of the solution. It is suitable for low mountain areas with high rainfall and fast evaporation.
In summary, the multiplex padding method is most suitable for those gold mines where the leaching time is short, the ore leaching characteristics are consistent, and the area of ​​the immersion pad used for leaching is small, but there is a suitable waste disposal site.
2) Extended dip pad method The expansion dip pad method involves the preparation and placement of ore on the dip pad. After the leaching, the ore remains in place (Figure 10). The ore is then re-leached or washed and neutralized (if needed). The deposit can then be added to the heap or trimmed.
This method requires a fairly large, suitable terrain, and the dip pad expands in a phased manner. Generally, the ground slope should be less than 10%, preferably less than 5%.
Compared to the multiplex pad method, the method uses a larger area, thus increasing the impact of the climate on the water cycle. Larger ponds are generally required to store the amount of water that is lowered during a storm.
The extended dip pad method has no limitation on the length of the leaching period, and can deal with ore with a long or variable leaching period without affecting the subsequent production. The ore can be leached for several cycles before being discarded. [next]
Once the build is completed, the pad of the dip pad is no longer subjected to working stress. In general, the installation of a film liner is primarily intended to withstand the stresses that are generated when the ore is initially placed. In this method, a low permeability natural material or an improved soil can also be used. Some expansion dips that are currently in operation have a stack height of more than 30m.
Since the facility is a phased building, the initial investment cost is relatively low. The construction cost of the dip pad per ton of leached ore is certain, depending on the number of layers placed.
All in all, the extended dip pad method is suitable for all types of ore. Larger, relatively flat areas are required and there should be climatic conditions for net evaporation to maintain no liquid discharge.
3) Valley Leach Method
The valley leaching method prepares and places ore behind a dyke, and uses the ore layer that is subsequently stacked on the slope to carry out leaching of the ore. Most of the ore and leachate remain in contact during operation. After the leaching is over, the ore remains in place for repair, just like the treatment of the waste rock pile (Figure 11).
The applicability of the valley heap leaching method depends on the strength of the ore and its ability to maintain permeability under the stress of continuously placing the ore. The main advantage of this method is that it can be applied to steep terrain and complex weather conditions. The liquid storage capacity of the pores in the ore is often used to preserve the precious liquid, replacing the need for a precious liquid pool. Storage of the solution in the heap requires a high degree of padding system. In general, the liner system is composed of a combination of a synthetic material and a low permeability or improved soil material. At present, in the heap leaching of the valley, the maximum height of the heap is more than 60m.
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