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The surprising power of cyanide: Why is it the first choice for modern gold extraction?
In today's plastic world, gold is not only a metal that symbolizes wealth, but also an indispensable material in many fields such as electronic products, medical equipment and aerospace technology. However, as the demand for gold increases, the process of extracting the metal becomes more important. Among the many extraction methods, the use of cyanide has become the main choice for gold mining, and its amazing chemical ability makes gold extraction possible.
According to research data, the world produces about 3,600 tons of gold each year, and another 300 tons are recycled. Since the 20th century, the main method of extracting gold has been cyanide leaching. The method centres on combining a cyanide solution with mineral, allowing gold to be extracted from the dilute ore.
However, this process is not just a simple combination of chemical reactions; it involves a variety of operating techniques, such as grinding (shredding), leaching and adsorption steps, forming a mature and efficient extraction process.
Types of gold ore
Gold exists mainly in the form of natural gold, which is sometimes alloyed with silver to form so-called electric gold. Typically, gold is found in alluvial deposits as small, fine particles, or embedded in rock minerals in the form of grains or tiny particles. It is important to note that some ores have contaminants that interfere with the ability to extract cyanide, so understanding the different types of ores is crucial.
During the extraction process, certain ores are known as "pre-robbed ores" and these ores may contain materials such as carbon that will bind to the gold and prevent normal cyanide extraction.
Process of Cyanide Leaching
In the cyanide leaching process, the ore is first crushed to increase the surface area for more efficient exposure to the extraction solution. This process may use a variety of techniques, including heap leaching and impregnation. When the crushed ore comes into contact with the cyanide solution, metallic gold enters the solution in the form of gold cyanide.
Cyanide is now produced commercially at a rate of several billion tonnes per year, primarily to support the gold extraction process.
Other extraction methods
In addition to cyanide leaching, another older extraction method is the use of mercury for alloying. Although this process has declined in scale due to the toxicity of mercury, it can still be found in some small-scale artisanal mining operations. The mercury is alloyed with gold to form an amalgam, and the gold is then extracted by removing the mercury through evaporation. However, this method has caused serious pollution to the environment and has become a controversial issue today.
This is how environmental problems arose in California, where millions of pounds of mercury were released into waterways during gold mining, causing ongoing ecological harm.
From intractable ore to extractable gold
Some ores are called "refractory gold ores" because they contain gold particles dispersed in a very fine manner among other minerals, making them difficult to recover using standard cyanide leaching methods. Such ores usually require pretreatment, which may include calcination, bio-oxidation or pressure oxidation, in order to improve gold recovery.
Challenges of gold refining
Once the gold is extracted, the next step is the refining process, which usually uses various methods to remove other metals such as silver that coexist with the gold to obtain pure gold of commercial trade standards.
ConclusionThe typical Miller's law is to extract gold by passing chlorine gas into the molten alloy, because the chemical properties of gold make it not react with chlorine, but other metals will form low-density slag, which helps separation.
The use of cyanide has revolutionized the history of gold extraction, both from ore and from recycling, and its practicality and effectiveness cannot be overstated. However, faced with challenges in environmental impact and sustainability, do we need to rethink the future direction of this extraction method and explore other greener alternatives?
