Why is mercury used to mine gold?

Mercury has been used to mine precious metals such as gold and silver since 750 BC. Although the technique has many variations in different periods around the world, the use of the amalgam process (an alloy of mercury with other metals) in history has many similarities with the process today, according to IFL Science.

But how exactly can liquid metals like mercury be used to separate gold scraps from rocks? The process is often performed with gold-bearing rocks, where the gold scrap is so fine that other separation methods are less effective. Liquid mercury is mixed with the rock and dissolves the gold scrap, leaving behind the rock mass and creating a gold-mercury alloy called gold amalgam.

Next, the crude gold amalgam needs to be separated from the unreacted mercury. This can be done by pouring liquid through a porous material such as a chamois hide made from the skin of the mountain goat called chamois (Rupicapra rupicapra). This type of leather is very popular due to its porosity, flexibility and smooth surface. The filtered liquid is the pure form of golden amalgam. To turn amalgam into pure gold, the mixture is heated to more than 356.7 degrees Celsius. At that temperature, mercury turns into a gas, leaving behind gold, which has a much higher boiling point of 2,836 degrees Celsius.

However, the above separation method produces an extremely toxic form of evaporated mercury, which can damage the respiratory, gastrointestinal and central nervous systems. Symptoms of inhaling mercury vapor include difficulty breathing, vomiting, and headaches. For this reason, mercury is now less commonly used as an industrial method for separating gold.

Although the process is no longer used on an industrial scale, mercury is still common in artisanal and small-scale gold mining, but its harmful effects have not diminished. According to a 2018 article, this activity is currently the largest source of mercury pollution on Earth, with more than 1,000 tons of evaporated mercury released annually.

Additionally, the areas that still practice such segregation include many impoverished and exploited communities. About 10 – 19 million people use mercury to mine gold in more than 70 countries. Volatile mercury not only affects the health of miners but also the ecosystem through contamination of water, soil, wildlife and food.

However, there are a number of measures to reduce the amount of mercury that evaporates. Efforts to install low-cost, portable mercury sensors contribute to lowering the risk of exposure for miners. With the help of scientists, environmentalists, and public health officials, low-cost, mercury-free, and easily scalable mining techniques are being introduced, along with mercury containment measures. affects fish and crops.