Gold is still in high demand internationally, but especially in areas that are difficult to access, it cannot be mined with heavy equipment but can only be mined by hand as far as possible. What initially sounds like the more environmentally friendly option is actually more harmful than large-scale mechanical gold extraction, as researchers have now discovered. Accordingly, small-scale mining releases an average of 0.2 kilograms of mercury and 16 tons of CO per kilogram of gold extracted2 free. The research team is therefore calling for it to be more closely regulated by law.
In order to meet the global demand for gold, around 3,600 tons of the precious metal are mined every year, 700 of them in so-called artisanal mining - a type of small-scale mining in which the workers work largely by hand and without heavy machines. It occurs primarily in remote, difficult-to-access areas such as the Tapajós River basin in the Brazilian Amazon. However, this also makes it harder to monitor than the mechanical version, which is why there are numerous illegal mines in this and other such regions.
Hunting for gold with mercury
Just like mechanical gold mining, small-scale mining is not exactly good for the environment. In the past it has been criticized, among other things, because it releases large amounts of mercury into the environment and poisons the air, water and soil. The workers use the liquid metal to access the gold particles in the rock and sediment that they previously extracted from riverbeds. The mercury forms a so-called amalgam alloy with the gold, which allows the precious metal to be specifically removed from the ore lumps. If you then heat the amalgam, the mercury evaporates and what is left is largely pure gold. In order to prevent this mercury vapor from accumulating in the environment, so-called retorts are now usually used. These distillers capture the vaporous mercury and, so to speak, recycle it for the next round.
Until now, however, it was unclear how effectively the retorts actually work. It was also unclear how much CO2 The diesel and gasoline engines required for mining are thrown into the air when they drive vehicles or pumps, for example. Researchers led by Benjamin Fritz from Pforzheim University have now determined both for the first time. To do this, they visited around 50 mines in the Tapajós River basin in the Brazilian rainforest. While some of the mines operated legally, there were also illegal mining sites and those that operated in legal gray areas. On site, Fritz and his colleagues conducted interviews with the local miners and examined how much CO2 and mercury they release into the environment during gold mining.
Artisanal gold mining is more harmful than mechanical gold mining
The result: Even if the workers used distillers, an average of 0.2 kilograms of mercury and 16 tons of CO were still released per kilogram of gold mined2 into the environment, as the researchers report. “Gold mining is not climate-friendly, nor is artisanal mining. At 16 tons per kilo, gold's carbon footprint is one of the highest among metals. In comparison, the value for copper is only three kilograms of CO2“, says project manager Mario Schmidt. As for mercury emissions, the team calculated that around 2.5 tons of the toxic metal are released into the environment each year in the Tapajós River Basin alone. This is not only harmful to nature, but also to the health of the gold diggers.
Fritz and his colleagues found that the climate impacts of artisanal gold mining are often even more severe than those of large-scale mining. They attribute the phenomenon to the fact that machine processes work more efficiently and are also monitored more closely. However, the researchers do not want to encourage anyone to venture into remote areas with heavy equipment. “This could lead to a classic rebound effect, which means that more mines and therefore more area in the rainforest will be opened.” Instead, Fritz and his team are calling for informal mining in the Amazon region to be more closely regulated by law and for further work on technical solutions. that reduce the use of mercury.
Source: Pforzheim University; Specialist article: Nature Sustainability, doi: 10.1038/s41893-023-01242-1