Acid drainage: the global environmental crisis you’ve never heard of

A gold rush brings in lots of money in the short-term, but leaves a toxic legacy

Stephen Tuffnell
Wednesday 13 September 2017 12:19
Acid mine drainage has led to severe environmental problems due to the heavy metal concentrations in the Rio Tinto river
Acid mine drainage has led to severe environmental problems due to the heavy metal concentrations in the Rio Tinto river

Romania’s Prime Minister, Mihai Tudose, recently raised the prospect of reopening the country’s huge Rosia Montana goldfield. The area had been mined from Roman times until the last state-run operation closed in 2006. An application by a previous government to make the area a Unesco world heritage site has now been withdrawn, paving the way for new development.

Rosia Montana is nestled in the Carpathian mountains and, with 314 tons of gold, is home to Europe’s largest known deposits. A short-term mining bonanza promises employment for thousands of labourers and hundreds of millions of Romanian leu in investment in the EU’s fastest-growing economy. But is the boom really worth it? After all, gold mining has historically resulted in long-term, chronic environmental problems. Rosia Montana is big, but the threats posed by acid mine drainage are bigger.

The problem is, if completed, the project would use “cyanide amalgamation” to extract the gold from its ore body. This is the same cyanide used to poison people, fish and elephants. It has a toxic past in Rosia Montana, too: back in the 1970s, a copper mine in the area needed somewhere to store its cyanide-contaminated waste and the nearby village of Geamana was evacuated and flooded. It has been submerged under toxic waters ever since.

Geamana is one of Romania’s greatest ecological disasters, surpassed only in 2000 when a gold mine in Baia Mare in the north of the country spilled an estimated 100 tons of cyanide into a river. The latter incident was described as Europe’s worst environmental disaster since Chernobyl. No wonder that when the government first mooted the resumption of mining in 2013, it led to weeks of protests – protests which now threaten to erupt again.

Gold’s dirty secret

Cyanidation was the breakthrough gold mining technology of the 1890s, when it enabled Anglo mining conglomerates to make colossal profits from low grade ores. Simply put: cyanidation involves mixing finely crushed ores (referred to as “sands” or, when water-based, “slimes”) in a weak cyanide solution (usually calcium cyanide). This solution is then mixed in large tanks and the gold separated from its ore body.

The process increases yields of gold but produces immense quantities of highly-toxic waste that releases acid and metals into the environment. Around 90% of all gold extracted worldwide uses this method.

The waste from cyanidation is a fine rock solution that is left in open air ponds while the concentration of acid is reduced to legal limits. The risk here is from dam failure or breakages in the lining of waste ponds, which can lead to catastrophic spills or leakage through the porous land surface into the water table.

Waste water from a gold mine flows into the forest in Guyana, South America

In nearly all metal mines, and some coal mines, acid drainage occurs because of the oxidation of iron ore found alongside precious mineral deposits. Uncovered by the mining process, the iron reacts with the air and releases sulphuric acid into the water. This process can last centuries. Spills from cyanidation waste are more short-lived, but more highly toxic than acid mine drainage occurring through iron oxidation.

The ratio of waste to metal recovered in gold mining is vastly disproportionate: the Fimiston Super Pit, near the Western Australian town of Kalgoorlie, and until recently the largest open cut mine in the world, has returned approximately 1,640 tons of gold since operations began there in 1989. But that’s only a small portion of the 15 million tons of rock extracted per year. On a more personal scale, a single gold wedding ring generates 20 tons of waste.

The river runs yellow

Cyanidation poses catastrophic ecological risks because cyanide leaks so easily into groundwater. Historical parallels suggest the Romanian proposal will most likely leave a toxic legacy.

In 2015, as the US Environmental Protection Agency attempted to drain polluted water from the Gold King Mine in Colorado, which was closed in 1920, more than 3 million gallons were accidentally spilled into the Animas River. The polluted plume turned the entire river a deep mustard yellow. Water acidity levels increased 100-fold, and in some places a thousand times over levels considered safe for wildlife.

The Animas River as normal, on the day of the Gold King Mine spill, and a day later

The spill only posed no threat to fish in the Animas because ongoing pollution had already killed them. But the plume drained into the San Juan, a larger and cleaner river that flows into the spectacular Glen Canyon and, eventually, the Grand Canyon. There, the pollution threatened rare birds and endangered fish like the Colorado pikeminnow and razorback sucker.

EPA chief Scott Pruitt returned to the site at the beginning of August this year vowing to complete the clean-up after the agency had “walked away” from the problem. At a water treatment plant installed on the site, 500 gallons of mercury and arsenic-laced water a minute flow from the Gold King Mine. The clean-up could take a decade and has already cost the EPA $29m (£21m). The EPA has estimated that the cost of cleaning up just 156 mines in the US could be between $7bnand $24bn. Clean-up on most sites will take decades – those with acid drainage will require water treatment in perpetuity.

A global crisis

Acid drainage is a little-known global crisis. The UN has even labelled it the second biggest problem facing the world after global warming. In the US, an estimated 22,000 kilometres of streams and 180,000 acres of freshwater reservoirs are affected by acid mine drainage. Rivers and lakes in Arizona, Patagonia, Guangdong in China, Ontario, Papua New Guinea, and at Rio Tinto in Spain, to name just a few, have all been polluted by acid mine drainage. In South Africa, the problem is chronic.

Illegal gold mining in South Africa

These threats are prescient. Brazil recently announced a huge reserve in the Amazon rainforest has been earmarked for mining, including gold. In New Zealand, local activists fear the Karangahake Gorge is now under threat after a large, high-quality gold seam was found in the region. Around the Yellowstone National Park, mining companies are positively salivating at the possibility that Obama-era restrictions will be lifted, granting access to 3,000 tons of proven in-ground gold reserves. In Peru, marines have been dispatched to wage war against illegal mining on the River Santiago in the northern Amazon, which has done enormous damage to the region’s bio-diversity and placed the livelihoods of 70,000 indigenous Awajuns and Wampis at risk.

Multinationals hold out the promise of sustainable development through mining. But without careful forethought we’ll find ourselves dealing with chronic pollution for centuries.

Stephen Tuffnell is an associate professor of modern US history at the University of Oxford. This article was originally published on The Conversation (

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