Heap Leaching (Mining) Heap leaching is a chemical process used to extract precious and other metals from vast amounts of earth and rock material. Tiny gold and silver particles dispersed throughout massive ore bodies can be economically recovered by leaching operations. However, due to the reactive nature of the chemicals used, environmental hazards may be created if care is not taken. Large quantities of naturally-occurring heavy metals and mineral salts are exposed and concentrated through this mining process. In the case of gold mining, a dilute cyanide solution is sprinkled over heaps of crushed rock, underlain by synthetic liners. The cyanide chemically bonds with the microscopic gold particles, which are then collected at the bottom of the heap in plastic liners for further processing. When the gold has been removed by this process, the heaps become a waste product requiring management and control well into the future. Heaps are typically full of residual dilute cyanide solution which, along with precipitation directly on the heap, will continue to drain through the heap. Because the heaps may contain residual cyanide, selenium, arsenic, mercury and various salts, the drainage solution may be hazardous to surface and groundwater supplies and the environment. Quite often, the least-costly manner in which to dispose of this continuous heap drainage is through a leach field and into the ground, where it may have adverse affects on the quality of groundwater, potentially contaminating water supplies for agriculture, human consumption and wildlife.
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Author of the Water Words Dictionary source of text: Gary A. Horton
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