We and our members support the International Cyanide Management Code
The World Gold Council and its members are committed to responsible mining practices that minimise short-term impact on the environment. The processes involved in gold mining, extraction and smelting can pose a risk to the environment and members take steps to minimise these wherever possible.
One of the issues to which our members are committed is the responsible management of cyanide in the extraction process.
Role of cyanide in extracting gold
The use of cyanide is important to the gold mining process. Due to its inherent dangers, it is an aspect that needs careful management.
This section explains why cyanide is used in gold mining, its risks and how those risks are managed.
Cyanide is used to extract gold from ore. This is done by leaching the rock on lined pads or by crushing the rock to the consistency of sand (milling), then adding water to form a slurry. The slurry is mixed with a cyanide solution; gold particles bond with the cyanide in solution and are extracted from the slurry.
The slurry of crushed rock left after processing is called tailings. Low-grade ore is treated differently because of the cost of milling. It is broken into smaller pieces and placed in layers on a leach pad made of an engineered and compacted clay lined with high density polyethylene liners.
A weak cyanide solution is dripped onto the leach pad to extract the gold. The resultant gold-laden solution is collected on the lining at the bottom of the pad and flows to double – or triple – lined ponds for processing. Leach pads are specially designed and constructed to ensure the solution is contained to prevent any leakage into ground and surface water.
The risks of using cyanide
The management and disposal of cyanide solutions used to dissolve and extract gold from ore is an environmental concern. Cyanide is a well known poison; hydrogen cyanide is acutely toxic to humans in its gaseous state and can be fatal at exposure levels of 100 to 300 parts per million (ppm).
Cyanide is also harmful to wildlife; mammals, birds and fish all have acute toxicity reactions to even low cyanide exposures. Cyanide does not, however, accumulate or biomagnify, so prolonged exposure to sub-toxic levels does not, in most cases, appear to pose health risks.
There are two significant environmental risks from cyanide solutions used in gold mining. The first is the possible leaching into soil and ground water at toxic concentrations; the second is the risk of catastrophic spills that might inundate an ecosystem with toxic levels of cyanide.
Managing cyanide responsibly
The World Gold Council and its members support the International Cyanide Management Code, a voluntary industry programme that promotes the responsible management of cyanide used in gold mining, enhancing the protection of human health and reducing the potential for environmental impacts. Developed in 2000 under the auspices of the United Nations Environmental Program (UNEP) and the former International Council on Metals and the Environment (ICME), the Code is the product of a multi-stakeholder steering committee that included a number of World Gold Council members, governments, NGOs, cyanide producers and other stakeholders.
Mining operations in the US take precautions to prevent the cyanide solution from escaping into the environment; the layers of ore and ground rock are contained in special leach pads lined with a plastic membrane to prevent cyanide from leaching into the soil. The cyanide is captured and recycled.
In order to minimize the environmental impact of cyanide that is not recycled, mining facilities treat cyanide waste through several processes, allowing it to degrade naturally through sunlight (photodegradation), hydrolysis and oxidation, among other natural processes. Mine managers often seek to enhance this natural degradation by use of non-natural methods to accelerate cyanide breakdown.