The Mercury Problem in Artisanal and Small-Scale Gold Mining

Abstract

Mercury-dependent artisanal and small-scale gold mining (ASGM) is the largest source of mercury pollution on Earth. In this practice, elemental mercury is used to extract gold from ore as an amalgam. The amalgam is typically isolated by hand and then heated-often with a torch or over a stove-to distill the mercury and isolate the gold. Mercury release from tailings and vaporized mercury exceed 1000 tonnes each year from ASGM. The health effects on the miners are dire, with inhaled mercury leading to neurological damage and other health issues. The communities near these mines are also affected due to mercury contamination of water and soil and subsequent accumulation in food staples, such as fish-a major source of dietary protein in many ASGM regions. The risks to children are also substantial, with mercury emissions from ASGM resulting in both physical and mental disabilities and compromised development. Between 10 and 19 million people use mercury to mine for gold in more than 70 countries, making mercury pollution from ASGM a global issue. With the Minamata Convention on Mercury entering force this year, there is political motivation to help overcome the problem of mercury in ASGM. In this effort, chemists can play a central role. Here, the problem of mercury in ASGM is reviewed with a discussion on how the chemistry community can contribute solutions. Introducing portable and low-cost mercury sensors, inexpensive and scalable remediation technologies, novel methods to prevent mercury uptake in fish and food crops, and efficient and easy-to-use mercury-free mining techniques are all ways in which the chemistry community can help. To meet these challenges, it is critical that new technologies or techniques are low-cost and adaptable to the remote and under-resourced areas in which ASGM is most common. The problem of mercury pollution in ASGM is inherently a chemistry problem. We therefore encourage the chemistry community to consider and address this issue that affects the health of millions of people.

Keywords: Minamata convention; artisanal and small-scale gold mining (ASGM); gold; mercury; mining.

Figure 1

Estimated annual mercury use in artisanal and small‐scale gold mining (ASGM).1b, 4, 6c, 10

Figure 2

Liquid mercury is used in artisanal and small‐scale gold mining. a) Trommels are used to crush rock and mix mercury with ore. b) As much as 1 kg of liquid mercury is added to each trommel along with water and 20 kg of ore. c) Excess mercury is recovered, but mercury‐rich mine tailings are often released directly into the environment. d) Additional mercury is used on the mercury–gold concentrate to form a solid amalgam, which may be isolated by hand. e) The mercury–gold amalgam is heated with a torch to distill the mercury and allow isolation of gold. f) A sample of gold isolated in an artisanal mine. All images are used with permission from Yayasan Tambuhak Sinta (YTS) and Pure Earth.

Figure 3

A) When mercury is pulverized in mills, it can form tiny beads that bind to soil. A simulated sample of mercury flour (top right) is shown in which the mercury does not coalesce and it is not visible to the naked eye. The soil containing the floured mercury appears very similar in appearance to mercury‐free soil (top left). B) The floured mercury is observable in the SEM image as microbeads bound to soil. C) A polymer made from sulfur and recycled cooking oil is effective at removing floured mercury from the soil sample. The procedure requires mixing the polymer and soil directly. The polymer changes colour to black as metacinnabar is formed. The polymer‐bound mercury can be isolated by sieving. Neither the polymer nor the polymer bound to mercury are toxic to cells. Images were adapted under a Creative Commons (CC) license.45

Figure 4

A summary of ways in which the chemistry community can support artisanal gold miners’ health and livelihood. In proposing a solution to any one of these problems and challenges, it is essential that the technique, chemistry, and any equipment be low cost, require minimal capital outlay, operate in remote locations, and be easy to use. It is also important that the benefit to the miners be immediately obvious, so expediency in financial returns and health benefits are critical.