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Gold extraction methods from ore

2022-03-05 Xinhai (261)

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Extracting gold from ore is a poisonous business. The most common method is cyanide leaching, where cyanide salts in solution are used to suck the gold out from its ore. You get gold, but you also get highly toxic byproducts.

Cyanide leaching to extract gold

The cyanide leaching process is mainly used in places where the earth has high gold concentrations and therefore deserves industrial development. In the process, gold-bearing rocks are crushed into sand and dust. The cuttings (stacked in piles, columns or stored in tanks) are then mixed with a sodium cyanide solution (the sodium salt of hydrogen cyanide HCN). The acid separates the gold from the rock dust and is transported in the acid percolate in chemically bound form. Subsequently, the gold was filtered out of the leaching solution by adding zinc dust, washed out of the muddy substrate, and finally dried. The recovered raw gold is then refined into pure gold. There are major reservations about this extraction method due to the release of highly toxic and flammable hydrogen cyanide acid,


Gold extraction by amalgam process

The amalgam process is the oldest technical method of extracting gold and was used in ancient times. Gold-bearing rocks are likewise crushed into fine sand through the amalgam process. Mercury is then added to the cuttings. Gold has properties that allow it to bond with the surface of mercury. Gold-rich mercury forms a silvery alloy solution known as amalgam. The amalgam collects at the bottom of the mixing vessel and is easily separated from other minerals. The amalgam is then heated until the mercury evaporates, leaving behind pure gold. This method also involves health and environmental hazards when evaporating highly toxic mercury.


Gold Extraction Using Electrolytic Deposition Process

Meanwhile, electrolysis is a commonly used process in which gold is extracted without the use of toxic substances. The method uses electrochemical methods. This advantage can be taken advantage of when extracting other precious metals such as iron copper or zinc, and small amounts of gold are also found in the extracted rocks. During the electrolytic cleaning of rock sludge, the anode activates the rock sludge containing precious metals. The cathode is made from a piece of pure metal. During electrolysis, the gold in the original rock material does not dissolve and collects in the form of sludge under the anode. Along with gold, other precious metals (iron silver, copper, lead, tin) are concentrated in this anode sludge and are easily skimmed off. The individual precious metals are then separated from each other using a suitable process.


Gold extraction using the borax process

The borax process is also an environmentally friendly method of gold extraction. Here, gold-bearing rock material is placed in a melting crucible, followed by borax (sodium borate). Borax lowers the melting point of the ore mixture, making the melt more fluid. Thus, the low melting point enables gold to be melted using a cost-effective low-power heat source to extract gold. Gold sinks to the bottom of the crucible, while other rocky materials such as silicon, quartz, ores or generally all oxides rise to the top.


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