In this article, we provide a brief overview of the use of cyanide in the recovery of gold from ores. While the use of cyanide is critical to the modern gold mining industry, Omori understands the concerns about the use of this sodium cyanide reagent for gold extraction and through this discussion provides information on how to safely and effectively use sodium cyanide from Extract gold from ore. Technical references to the use of cyanide in gold ore processing are noted at the end of the article.
For over 130 years, chemicals containing “cyanide” (a combination of carbon and nitrogen) have been used safely and effectively to efficiently extract and recover gold and silver from ore. Cyanide is used in a variety of other applications both within and outside the mining industry.
It is true that cyanide is a highly toxic chemical under certain conditions and at sufficiently high concentrations, but when it is properly managed and controlled, it can continue to be used safely and without harming humans or the environment.
The role of cyanide in ore processing
The process known as “cyanidation” or cyanide leaching has been the primary gold extraction technology since the 1970s. In this process, sodium cyanide is used in a dilute solution of 100 ppm to 500 ppm or 0.01% to 0.05% cyanide to selectively dissolve gold from the ore. The two most common processes for recovering gold using cyanide are heap leaching and milling, also known as carbon leaching (CIL).
Despite extensive scientific research over the years, no other chemical reagent has been found to demonstrate superior economic and environmental qualities to cyanide in the recovery of precious metals.
As part of best practice, mines use as little cyanide as possible for environmental, safety and economic reasons. The cyanide leaching process is usually performed after other physical processes such as crushing and grinding. Once the gold is dissolved, the solution is further processed to recover the gold, which is then smelted into gold bars.
Tailings slurries and solutions containing leached material, water and residual cyanide are treated with different chemical and physical methods to reduce or remove cyanide left over from the gold dissolution process before discharge to the tailings facility. In addition, different technologies are used to recover and reuse residual cyanide in the aforementioned processing circuits.
Solutions collected in tailings facilities often contain cyanide concentrations that are not harmful to people, birds or animals. While cyanide concentrations must be below 50 ppm to comply with international cyanide management practices to protect wildlife, many mining operations achieve cyanide concentrations below 10 ppm at their tailings facilities.
After discharge, residual cyanide is rapidly diluted and destroyed through natural processes such as oxidation and UV catalysis (by sunlight). Local, state and national regulations limit the amount and concentration of cyanide that may be discharged into a tailings facility. These regulations vary by jurisdiction.
Dasen mining explained:
Cyanide has been used effectively and safely for gold and silver recovery in the mining industry for over 130 years;
Mining consumes only 6% of the total amount of cyanide produced globally;
Cyanides are generally not persistent in the environment and degrade to naturally occurring products including carbon dioxide, ammonia and nitrates;
Mining facilities using cyanide are designed to contain and dispose of the solution so that environmental impact is minimized;
Release of cyanide into the environment is subject to local, state and national regulations;
Mining companies and mining companies using cyanide are fully regulated and encouraged to be certified through the International Cyanide Management Code for the Manufacture, Transport and Use of Cyanide in Gold Production to ensure safe operating practices and transparent community relations.
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