Recovering and refining gold can be both difficult and costly – particularly when the grade or concentration of gold in a deposit is low. However, even when the concentration of gold is so low that it’s invisible to the naked eye, this precious metal can be recovered safely and economically through chemical processing.
Cyanide processing and management facilities at Newmont’s Boddington gold mine in Australia.
The most essential ingredient in chemical processing of gold is cyanide, which, when in the form of a very dilute sodium cyanide solution, dissolves and separates gold from finely crushed rock. Although cyanide can be toxic, what many people don’t know about this chemical is that it is naturally occurring and, in some forms and concentrations, it is nontoxic. In fact, cyanide is produced in the human body and exhaled in extremely low concentrations with each breath. It’s also released into the environment by more than 1,000 plant species.
At Newmont, carefully managing the use, transportation and storage of cyanide is part of our commitment to providing a safe workplace and protecting the environment and communities near our operations. With the intention of holding ourselves and the industry to even higher standards, in 2005 we became one of the first companies to sign the newly developed International Cyanide Management Code (ICMC), a voluntary initiative for the gold mining industry created to complement an operation’s existing regulatory requirements. Today, there are more than 150 signatories that operate to the Code’s standards of practice, including gold miners, cyanide producers and transporters.
Cyanide tanks on site at Waihi are painted purple, the internationally recognized color for any infrastructure that handles the chemical.
Used in mining, sodium cyanide is added to a semi-liquid mixture of ore and water, known as slurry, where it separates the gold from the ore. The slurry then moves through a series of tanks where carbon granules are added. The gold coats the carbon granules, which are removed from the tanks and washed with superheated water that effectively separates the gold from the carbon. During this process – and as an added measure of safety – all tanks, pipes or containers through which cyanide passes or is stored are either clearly labeled or painted purple, the internationally recognized color for cyanide. After the gold has been separated from the ore, the leftover slurry and residual cyanide, also known as tailings, is pumped to an onsite storage facility where the tailings consolidate over time. At many operations, water treatment includes the use of tailings ponds lined with natural or synthetic materials to prevent seepage into the groundwater. In the ponds, residual cyanide breaks down until the concentration of cyanide is deemed safe according to state and federal standards. In addition to complying with statutes and laws, Newmont follows its own strict standards for protecting the environment, including routinely monitoring surface runoff and subsurface drainage near all tailings facilities to ensure no cyanide is present in the water. We also closely study the local bird, fish and wildlife populations to make certain there are no signs of cyanide exposure.
Transportation of the chemical to our facilities is also carefully monitored. Double-skinned tankers carrying cyanide in pellet or liquid form travel only during daylight hours on strategically planned routes. When the trucks arrive at our operations, the pellets are converted into liquid and pumped into double-skinned storage tanks surrounded by concrete. Before departing, the tanker trucks are cleaned and flushed on site.
While the safe and responsible management of cyanide is a priority at Newmont, all chemicals used at our operations are handled in a manner intended to protect our employees and preserve the environment. By participating in and leading initiatives like the International Cyanide Management Code, we hope to continually improve our safety performance as well as our contribution to sustainable development .