Full definition
Heap leaching is a hydrometallurgical process utilized for extracting valuable metals from ore, particularly in the mining industry. This technique involves stacking crushed or run-of-mine ore on lined pads and then applying a leaching solution that percolates through the heap to dissolve the targeted metals. The process is typically used for metals like copper, gold, and silver, each requiring specific leaching solutions and environmental conditions. For copper extraction, a dilute sulfuric acid solution is commonly used, while cyanide solutions are employed for the leaching of gold and silver. The efficiency of this method often hinges on the mineral composition of the ore and the operational parameters applied during leaching.
The heap leaching process generally operates under specific pH conditions that are critical for optimal metal recovery. For copper, the pH level is maintained between 0.5 and 2, which enhances the solubility of copper ions in the leaching solution. In contrast, for gold and silver extraction, the pH is adjusted to a range of 10 to 11, which is conducive to cyanide complexation. This method boasts a lower capital cost compared to traditional agitated tank leaching systems, making it an attractive option for large-scale mining operations.
Recovery rates are a vital aspect of heap leaching performance, with copper recoveries typically ranging between 60% and 80%, while gold recoveries can achieve rates of 70% to 90%. The pregnant leach solution (PLS), which contains the dissolved metals, is subsequently directed to an electrowinning process where the metals are recovered in a solid form. The operational efficiency of heap leaching can be influenced by various factors such as heap height, irrigation rate, and the composition of the ore itself, necessitating careful monitoring and management to optimize output.