Mining in focus
The pre-oxidation method serves to better enable the leach amenability of the ore . In other words , if you get a highly variable ore source , you need to sustain gold leach efficiencies through the pre-oxidation of the ore , followed by carbon-in-leach .
Leon Louw complex metallurgical recovery processes to liberate it . These ores are naturally resistant to recovery by standard cyanidation and carbon adsorption processes . These refractory ores usually require pre-treatment of some sort for cyanidation or other leaching methods to be effective .
Over time , various gold recovery methodologies have been developed . In ancient times , technology only allowed for visible free gold to be recovered by gravity concentration methods and then smelting . In the more recent past , a better understanding of the mineral and metallurgical properties of the gold-bearing ores has encouraged more sophisticated methods of recovery . Owing to the nature of technological advancement today , the greater demand for cost efficiencies , and higher recovery performance , more effective and creative technology advancements are being developed .
Historical processing methodologies
Historically , gravity concentration has been the most important way of extracting the native metal using pans or washing tables . Gravity concentration separates minerals based on differences in specific gravity . Various concentrator equipment has evolved over time to simulate and automate the panning methods used by the ‘ old timers ’, but now the recovery of even finer particles of free gold is possible . Once a gravity concentrate is produced , this can undergo direct smelting to produce gold metal but , as would be expected , the gold is of a lower purity .
Similarly , gold amalgamation processes were used . Amalgamation is a concentrating process in which metallic gold is mixed with mercury , either in an amalgamation drum or table . Here the precious metal bonds with the mercury to form the metal-laden mercury amalgam and the waste ( barren ) ore pulp is caused to travel different paths to effect separation . Refractory or sulphide precious metal ores are difficult to amalgamate using mercury , due to the complex iron-sulphur-gold and other metals present , which do not allow the gold to come into contact with the mercury . The mercury vapour generated is highly toxic and , therefore , special care has been taken , over time , to develop methods of retorting the mercury . Retorting means distilling the mercury from the amalgam and it is done in a cast iron retort or steel retort . A retort is a vessel having a cover that can be fastened on so tightly that no fumes of mercury escape , except through the condenser , which leads from the cover to a vessel containing water , where the fumes of mercury are condensed to a metallic state . These methods are still very common among artisanal gold miners across the world .
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