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.
APRIL 2018 MINING MIRROR [ 19 ]