page_title: Hydrometallurgy
section_title: Heap leaching
hierarchical_section_title: Hydrometallurgy / Leaching / Heap leaching
context_page_description: Hydrometallurgy is a technique within the field of extractive metallurgy, the obtaining of metals from their ores. Hydrometallurgy involve the use of aqueous solutions for the recovery of metals from ores, concentrates, and recycled or residual materials. Processing techniques that complement hydrometallurgy are pyrometallurgy, vapour metallurgy, and molten salt electrometallurgy. Hydrometallurgy is typically divided into three general areas:
  Leaching
  Solution concentration and purification
  Metal or metal compound recovery
context_section_description: In heap leaching processes, crushed (and sometimes agglomerated) ore is piled in a heap which is lined with an impervious layer.  Leach solution is sprayed over the top of the heap, and allowed to percolate downward through the heap.  The heap design usually incorporates collection sumps, which allow the "pregnant" leach solution (i.e. solution with dissolved valuable metals) to be pumped for further processing.  An example is gold cyanidation, where pulverized ores are extracted with a solution of sodium cyanide, which, in the presence of air, dissolves the gold, leaving behind the nonprecious residue.
caption: Ball-and-stick model of the aurocyanide or dicyanoaurate(I) complex anion, [Au(CN)2]−.[6]
exif: {}