Out of 121 applicants from 22 countries, a team from Pure Earth Colombia has emerged as one of the top 13 finalists selected for a $1 million challenge prize to protect the Amazon from impacts of artisanal and small-scale gold mining (ASGM). Pure Earth’s project uses silver-coated copper plates to decontaminate ASGM waste tailings that contain toxic mercury.
The technique works by taking advantage of silver’s chemical affinity with mercury. When the plates are inclined in a sluice box used by miners, the silver captures the mercury used in the mining process, forming an amalgam on the surface of the plates.
With the support of the U.S. Department of State, Pure Earth has been working with artisanal miners in Colombia to test and refine this technology over the past two years. To date, the technique has enabled the project team to recover up to 80% of mercury from the tailings!
[Watch this news report about Pure Earth and other innovators working to reduce the impact of gold mining in the Amazon]
Pure Earth is testing out this novel technology in Colombia in part because the country suffers among the worst mercury pollution in the world, releasing between 50 to 100 tons into the environment every year, according to estimates made by the Colombian government.
As reported in The Chemical Engineer, Pure Earth has been working with artisanal miners like Juan Torres and María, who come from a culture with a long history of mining. Their great-grandparents were miners, and they plan to pass the tradition on to their children, Camilo and Nicolás.
María is a “Chatarrera” – a term for women miners who sift through piles of gold-bearing rocks discarded by other miners and companies. Juan processes the ore, grinding it into a fine dust and mixing it with water and mercury to amalgamate the gold. Together, they recover about 2 grams (mass) per day (g/d) of gold, scraping out a meagre profit that goes directly to supporting their children. Meanwhile, the mercury they use is released as vapor when the amalgam is burned and as effluent into waterways, often in residential areas.
Mercury amalgamation typically only recovers less than half of the gold, leaving the remaining gold (and mercury) in the tailings. Capitalizing on this deficit, Juan was performing cyanidation on the gold-rich tailings, giving himself an advantage over other artisanal miners.
Using cyanidation on tailings that contain mercury can yield even more dangerous mercury-cyanide complexes. When disposed of improperly, this process releases mercury-cyanide complexes into waterways, which are highly bioavailable and pose a big threat to downstream aquatic life.
If this technique can remove mercury from the tailings before cyanidation, tailings reprocessing could become an economically viable means of cleaning up mercury contamination in Colombia. The prize will help Pure Earth experts work towards this goal.
This effort is part of Pure Earth’s work to reduce mercury pollution in Colombia. In 2020, the planetGOLD Colombia project commissioned Pure Earth to investigate the worst toxic mercury sites in Colombia with the aim of removing 20 tonnes of mercury from the environment and avoiding its use in mining in the next years. Pure Earth investigated 30 contaminated areas and 30 tailings (mining waste) piles, spanning 14 municipalities and four departments across the country.
Watch the video above to learn more about our work in Colombia.
Trapping a Slippery Foe, The Chemical Engineer, Aug, 2021.