page_title: Gold extraction
section_title: Concentration
hierarchical_section_title: Gold extraction / Concentration
caption_attribution_description: English: Gold Nuggets Found by Rod Fitzhugh and Ted Scott in Arizona, on March 26th 2006.
context_page_description: Gold extraction refers to the processes required to extract gold from its ores. This may require a combination of comminution, mineral processing, hydrometallurgical, and pyrometallurgical processes to be performed on the ore.
  Gold mining from alluvium ores was once achieved by techniques associated with placer mining such as simple gold panning and sluicing, resulting in direct recovery of small gold nuggets and flakes. Placer mining techniques since the mid to late 20th century have generally only been the practice of artisan miners. Hydraulic mining was used widely in the Californian gold rush, and involved breaking down alluvial deposits with high-pressure jets of water. Hard rock ores have formed the basis of the majority of commercial gold recovery operations since the middle of the 20th century where open pit and or sub-surface mining techniques are used.
  Once the ore is mined it can be treated as a whole ore using a dump leaching or heap leaching processes. This is typical of low-grade, oxide deposits. Normally, the ore is crushed and agglomerated prior to heap leaching.
context_section_description: Gravity concentration has been historically the most important way of extracting the native metal using pans or washing tables. Amalgamation with mercury was used to enhance recovery, often by adding it directly to the riffle tables, and mercury is still widely used in small diggings across the world. However, froth flotation processes may also be used to concentrate the gold. In some cases, particularly when the gold is present in the ore as discrete coarse particles, a gravity concentrate can be directly smelted to form gold bars.  In other cases, particularly when the gold is present in the ore as fine particles or is not sufficiently liberated from the host rock, the concentrates are treated with cyanide salts, a process known as cyanidation leaching, followed by recovery from the leach solution.  Recovery from solution typically involves adsorption on activated carbon then stripping (eluting) the gold from the carbon and passing the pregnant solution through electrowinning and then onto the smelting process.
  Froth flotation is usually applied when the gold present in an ore is closely associated with sulfide minerals such as pyrite, chalcopyrite or arsenopyrite, and when such sulfides are present in large quantities in the ore.  In this case, concentration of the sulfides results in concentration of gold values.  Generally, recovery of the gold from the sulfide concentrates requires further processing, usually by roasting or wet pressure oxidation.  These pyrometallurgical or hydrometallurgical treatments are themselves usually followed by cyanidation and carbon adsorption techniques for final recovery of the gold.
  Sometimes gold is present as a minor constituent in a base metal (e.g. copper) concentrate, and is recovered as a by-product during production of the base metal.  For example, it can be recovered in the anode slime during the electrorefining process.
  The results of laboratory and bench experimental studies can be used with sufficient accuracy to implement adhesive gold dressing of fine and nano-size particles within a “few hundred microns – a few tens of nanometers”.
caption: Gold Nuggets found in Arizona.
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