Dear EarthTalk: Most gold mining operations use cyanide to extract gold from surrounding rock. What are the environmental implications of this, and are there alternatives?
— J. Pelton, via e-mail
Although “cyanidation”—the use of a sodium cyanide compound to separate a precious metal from finely ground rock—has become less common in other forms of mining, it is still the dominant practice in gold mining. Some 90 percent of gold mines around the world employ cyanidation to harvest their loot.
“In gold mining, a diluted cyanide solution is sprayed on crushed ore that is placed in piles or mixed with ore in enclosed vats,” reports the State Environmental Resource Center (SERC), a project of the non-profit Defenders of Wildlife. “The cyanide attaches to minute particles of gold to form a water-soluble, gold-cyanide compound from which the gold can be recovered.”
But of course not all the cyanide gets recovered. Some of it gets spilled, and some is left within mine waste that is often buried underground woefully close to groundwater, leaving neighbors and public health officials worried about its effects on drinking water and on surrounding ecosystems and local wildlife.
“Mining and regulatory documents often state that cyanide in water rapidly breaks down in the presence of sunlight into largely harmless substances, such as carbon dioxide and nitrate or ammonia,” reports Earthworks, a Washington, DC-based non-profit. “However, cyanide also tends to react readily with many other chemical elements and is known to form, at a minimum, hundreds of different compounds.” While many of these compounds are less toxic than the original cyanide, says Earthworks, they can still persist in the environment and accumulate in fish and plant tissues, wreaking havoc on up the food chain.
In 2000, a breach in a tailings (mining waste) dam at a gold mine in Baia Mare, Romania resulted in the release of 100,000 cubic meters of cyanide-rich waste into the surrounding watershed. Nearly all aquatic life in nearby waters died, while drinking water supplies were cut off for some 2.5 million people.
In the wake of this accident, gold miners around the world have been taking steps to deal with tailings in a safer manner, through the use of special systems designed to prevent cyanide or its breakdown compounds from escaping into the environment. But such precautions at present are only voluntary. Regulators in the U.S.—the third largest gold producer after South Africa and Australia—don’t require mine operators to monitor cyanide and its breakdown compounds in nearby groundwater and water bodies, so no one knows just how big a problem might be.
One promising alternative to using cyanide in gold mines is the Haber Gold Process, a non-toxic extraction system that tests have shown can result in more gold recovery over a shorter period than cyanidation. Another alternative is YES Technologies’ biocatalyzed leaching process which proponents say is 200 times less toxic than cyanide. But with cyanidation well-entrenched in the industry and regulators looking the other way, these alternatives face an uphill battle in gaining widespread adoption.