The push to mine gold without mercury
Tue Nov 26 2024
In the Philippines, as in many places across the globe, mercury has long been central to how small-scale gold miners earn their living. Used as an easy way to separate gold from other minerals they mine, the heavy metal is highly toxic and can cause neurological damage, defects in utero, and even death.
A 2013 international treaty named after Minamata, Japan, a town where mercury-tainted water poisoned thousands of people, called upon countries to enact national plans to “reduce and where possible eliminate” mercury from small-scale, or artisanal, mining, the leading source of mercury pollution.
The Philippines outlawed mercury’s use in gold mining in 2012. Yet unregistered artisanal miners in the country continue to rely on the chemical for their day-to-day earnings. For them, a sense of denial prevails, despite learning about health hazards and even premature death experienced by people working in the sector.
Allan Francisco, a mine owner and lender to miners, operates a small facility that excavates ore from shafts dug deep below his property and processes it in grinding mills. He tips in a few spoonfuls of mercury every time the mills are fired up.
Artisanal miners use mercury because it is simple. When mercury is mixed with ore, it binds with the gold, creating an amalgam of roughly equal parts of the two metals. The mercury is then typically burned off, leaving behind gold but also creating a toxic vapor that many miners inadvertently inhale.
“I have no choice,” Francisco says about using mercury to support his family of four. He explains that he recently had to close a shaft and then invest in a new tunnel after a cyclone caused flooding.
He becomes emotional when asked about his family, noting that his work has allowed him to send one of his children to university. She is the first in his family of miners to go on to higher education.
Mercury-contaminated water is everywhere at the site, including in a small pool where miners use the toxic substance to pan for gold in ore that is diverted from the mill. The pool is surrounded by sandbags and sits just meters away from a river where young children fish.
“I know that mercury is very dangerous,” Francisco admits. Roughly a dozen men work around him at different stations in the complex, and another 10 are busy extracting ore underfoot. ”I tell the workers not to use it if they have scars,” he says, to avoid absorption into the bloodstream.
The visit to Francisco’s plant is part of a press trip organized by a United Nations–led program, planetGOLD, that works to help small-scale gold miners comply with the treaty, the Minamata Convention on Mercury. Reporters visited mines and processing plants that are at various stages of a transition away from mercury.
It was clear from the visits that a transition will happen only if miners become more aware of risks and get help from authorities to find viable alternative methods of extracting gold. For now, many miners are finding a solution in another dangerous chemical: sodium cyanide.
Encouraging change
Ever since Spanish colonists began searching for gold in the Philippines in the late 16th century, poor artisanal miners have been drawn to the industry, particularly during surges in the price of gold. Like half the population living around Paracale, Francisco has worked all his life in the sector. In 2020, he inherited the mine from his father.
As global uncertainty drives investors toward safe-haven assets and the energy transition increases the demand for gold and other minerals, gold prices have risen—by roughly 10% in 2024 alone—drawing more people to this line of work.
The UN estimates that 15 million people—including 4 million–5 million children and women—are employed in over 80 countries in small-scale mining operations that yield roughly 20% of the world’s output of the metal. Providing a source of income for people in remote areas where few other options exist, this artisanal gold mining releases some 2,000 metric tons (t) of mercury annually into the environment.
Since the Minamata Convention entered into force 7 years ago, planetGOLD has been working with authorities, miners, financiers, and local communities to change the way gold is extracted and processed. Efforts include building awareness of mercury’s risks while helping to adapt mercury-free mining and processing methods to local needs. Individual planetGold programs typically last 5 years, after which efforts are continued by communities and local authorities.
planetGOLD has operated in over 20 countries in Africa, Asia, and Latin America. In the program’s 2022–23 annual report, analysts estimated that its efforts had to date prevented the use of 31.4 t of mercury in six of the countries where it operates. In several countries, including Colombia, Peru, and Burkina Faso, planetGOLD encourages local financial organizations to provide credit to miners to help them adopt mercury-free processing technologies.
In Paracale, one of two sites in the Philippines where planetGOLD is present, a $500,000 mercury-free processing plant awaits official certification to begin operations in early 2025, when ownership will be transferred to miners and planetGOLD will retreat. Built on a hill above the town to take advantage of gravity in separating and milling of the ore, it will assist members of the local miners association, which goes by the acronym SMBC.
The mercury-free processing system developed by the government’s Mining and Geosciences Bureau (MGB) uses a cyanide-glycine mixture as an alternative to mercury. It is expected to process 2–4 t of ore daily.
In gold cyanidation, regularly used in large-scale mining, miners create a slurry of crushed ore and water and add sodium cyanide, which dissolves the gold. Activated carbon is added, acting as a sponge to soak up the gold-cyanide complex. The gold-laden carbon particles, which are larger than the bits of ore, are then separated using a wire mesh. Gold is recovered with the addition of more cyanide or via smelting.
Unlike mercury, which persists in the environment, the cyanide can be detoxified through oxidation with hydrogen peroxide or sodium metabisulfite.
Bernardo Bitanga, chief engineer in MGB’s metallurgical technology division, explains that the cyanide-glycine process has been shown during test runs to recover roughly 80% of the gold in the ore, a sharp improvement from the 25–30% recovery achieved with mercury. On the basis of laboratory studies and large-scale mining operations, researchers have found that using glycine in cyanidation can reduce cyanide consumption compared to using cyanide alone. Like cyanide, the amino acid helps dissolve gold.
“It will make a world of difference,” Bitanga says.
Authorized miners from outside of SMBC will also be able to bring their ore to the Paracale plant for processing, says Abigail Ocate, national project manager for planetGOLD Philippines.
The plant is expected to provide a model to the local community of what could be achieved without mercury. The higher recovery rates would allow any miners interested in duplicating the project to recoup construction costs within 3 years. Ocate acknowledges that adopters will need access to capital. “But if a mining association would like to replicate the Paracale mining site, they can do so by getting the information from the MGB,” she says. “It’s all open source.”
planetGOLD has implemented other projects to improve gold-processing plants in Mongolia and in Sagada, the Philippines.
And if launched widely, the MGB technology could have a big impact. In Ecuador, where 85% of gold production is done by 100,000 artisanal miners, a 2021 UN study found that $80 million in annual health and environmental costs caused by mercury contamination could be avoided, and miner revenues increased, by transferring processing to larger cyanide-based plants.
The alternative technology being launched at the new site in Paracale is not without risks.
Widely used in industrial gold mining, cyanide is highly toxic. While mercury persists in nature and can travel long distances, cyanide spills may result in major fish kills, water contamination, and harm to agriculture. In humans, poisoning by the chemical can occur through inhalation, ingestion, or skin or eye contact.
planetGOLD’s organizers maintain that the program does not advocate the use of cyanide and that the methods its projects adopt depend on what is accepted by local mining communities. “What we have seen is that cyanide has really taken off,” says Jennifer Wilmore Scroggins, the organization’s global communications manager. If this is what miners are going to use, planetGOLD needs to make sure that they understand the risks and that they use the substance safely, she says.
At the new operation in Sagada, Indigenous community members and artisanal miners agreed to eliminate all processing chemicals on site. planetGOLD provided shaking tables, gravity separators, and other equipment to isolate some gold mechanically. Remaining tailings will be sent to a cyanide leaching plant 5 h away in Benguet, an industrial mining center.
Some miners and processors who are trying to move away from mercury have run into other issues. Not far from Francisco’s operation in Paracale, Regi Elnar owns a small gold-processing plant where cyanide is used. Workers unload dozens of bags of ore delivered by individual artisanal miners into a large vat, where the contents are rinsed before being added to the cyanidation tanks. But much of what the workers refine is preprocessed with mercury before it gets to Elnar’s plant.
Meters away, a furnace burns the resulting gold-cyanide-mercury mixture. A large tailing pond meant to retain discarded minerals has been dug into a slope below the plant and directly above a few homes, a brook, and lush vegetation.
“It’s not an ideal scenario,” Wilmore Scroggins says about the plant and tailing pond. “When you apply cyanide to mercury-containing tailings, it’s even more toxic and considered a worst practice under the Minamata Convention.”
“Mercury is hazardous. We are aware of that,” Elnar says.
But as cyanide increasingly overlaps mercury during the transition away from the liquid metal, the mixing problem becomes inevitable. “It’s part of the process,” Wilmore Scroggins says.
Source: https://cen.acs.org/