The ability to bind with gold turns mercury into a useful tool in mining, but this method also carries many risks.
Mercury has been used to extract precious metals such as gold and silver since 750 BC. Although the technique has many variations throughout different periods worldwide, the use of amalgamation (the alloying of mercury with another metal) historically shares many similarities with today’s processes, according to IFL Science.
Mercury is the only metal that is liquid at room temperature. (Photo: MarcelClemens)
But how can a liquid metal like mercury be used to separate gold flakes from rock? The process is typically performed with gold-bearing ore, where the gold flakes are so fine that other separation methods are less effective. Liquid mercury is mixed with the rock and dissolves the gold flakes, leaving behind the rock mass and creating an amalgam of gold and mercury known as gold amalgam.
Next, the raw gold amalgam needs to be separated from the unreacted mercury. This can be done by pouring the liquid through a porous material such as chamois leather made from the hide of the mountain goat species Rupicapra rupicapra. This type of leather is commonly used due to its porous nature, durability, and smooth surface. The liquid after filtration is the pure form of gold amalgam. To transform the amalgam into pure gold, the mixture is heated to over 356.7 degrees Celsius. At this temperature, mercury turns into a gaseous form, leaving the gold, which has a much higher boiling point of 2,836 degrees Celsius.
However, the extraction method produces an extremely toxic form of evaporated mercury, which can harm the respiratory system, gastrointestinal tract, and central nervous system. Symptoms of mercury vapor inhalation include shortness of breath, vomiting, and headaches. For this reason, mercury is currently less used as an industrial method for gold extraction.
Although the process is no longer used on an industrial scale, mercury remains prevalent in artisanal and small-scale gold mining, but its harmful effects have not diminished. According to a 2018 report, current activities are the largest source of mercury pollution on Earth, with over 1,000 tons of mercury vapor released annually.
Furthermore, areas still applying such extraction methods often include many impoverished and exploited communities. Approximately 10 to 19 million people use mercury for gold mining in over 70 countries. Evaporated mercury not only affects the health of miners but also impacts ecosystems through water, soil, wildlife, and food contamination.
However, there are measures to reduce the amount of evaporated mercury. Efforts to install low-cost mobile mercury sensors contribute to reducing exposure risks for miners. With the help of scientists, environmentalists, public health officials, cost-effective mining techniques that do not use mercury and are easy to scale are being introduced, alongside measures to prevent mercury from affecting fish and crops.
