In its recent advisory on Africa’s gold sector, the US State Department has bemoaned the increasing use of mercury in ASGM despite the existence of mercury-free gold recovery methods and projects that seek to reduce the use of mercury in ASGM. According to the agency, the artisanal and small scale gold mining (ASGM) sector is the largest source of mercury pollution in the world with an estimated 844 metric tons annual pollution.
The US State Department has raised public health concerns and dangers in the use of mercury and other chemicals such as cyanide in the ASGM sector in sub-Saharan Africa. In its 2021 Human Rights reports, the US State Department highlighted how individuals working in the ASGM sector especially children in Ghana, Mali, Sudan and Zimbabwe were exposed to mercury and its related negative health impact.
The use of mercury to recover gold is a common practice in the ASGM sector. In a paper published in the journal PNAS Nexus, Zhencheng Xing and co-authors reported that about 1800 megagrams of mercury are emitted annually with most of these global emissions linked to the smelting and pressing of non-ferrous metals, particularly during artisanal and small-scale gold mining. In both South America and sub-Saharan Africa, the ASGM sector is the major contributor to mercury emissions.
Artisanal gold miners depend on mercury to amalgamate gold, which is a process where the mercury is combined (mixed with the hand) with the ore concentrate to separate the gold from other minerals. Mercury in this process, binds to gold and some other metals to form the amalgam—a soft alloy of approximately 50% mercury and 50% gold. Cyanide is further used to extract the remaining gold in mercury-contaminated tailings.
The danger of mercury use in mining is demonstrated by how the chemical is handled and disposed by artisanal and small-scale miners. Mercury that is vaporized during amalgam heating, is either inhaled by miners—harmful to their respiratory, immune and digestive systems—or goes into the atmosphere where it then condenses over time and falls down as ‘mercury rain’ polluting the soil, river bodies and food crops. Mercury from mine tails and mine water runoff also get into water bodies.
Mercury is known for several negative health effects: neurological damage, kidney problems, memory loss, miscarriages, arthritis, psychotic reactions, and even death. Mercury is also corrosive to the skin and eyes. Foetuses and children exposed to mercury become vulnerable to malformations and cognitive defects. Moreover, mercury is carcinogenic meaning it has the potential to cause cancer.
Reducing Mercury and Cyanide Usage
The US State Department has called on industry participants to conduct due diligence in mitigating and addressing environmental concerns and as well as supporting initiatives that aim at reducing mercury and cyanide usage in the ASGM sector in sub-Saharan Africa.
“Individuals and entities should conduct specific due diligence with respect to environmental concerns to avoid commercial risks related to relevant red flags from responsible sourcing initiatives and reputational risks associated with contributing to these harms. Industry participants should seek opportunities for mitigation and continuous improvement when identifying these risks in their supply chains, including through identifying opportunities for supporting alternatives to, and reduction of, mercury and cyanide usage.”
In Ghana and other West African countries, Commodity Monitor Limited’s mercury-free mineral processing technology has proven to be a gamechanger in the ASGM sector in enabling miners minimize negative environmental impact while achieving high gold recovery. Currently, the machines are operating in all the mining regions in the country and some West African countries such as Cote D’Ivoire, Burkina Faso, Togo, and Nigeria.
The plants are manufactured to specifically remediate mercury contaminated areas, usually recovering significant quantities of gold in the process. The plants crush using the Jaw Crusher. It then mills using impact crusher and then concentrates the ore using the GoldKacha. The concentrates are further passed through the concentrate upgrader known as the GoldKonka which is simple to use and able to recover the finest gold particles. The GoldKonka comes with 3 consecutive sluice trays with a re-circulative water pump system. Heavy gold-bearing particles are caught on the surface of each tray which are then washed off with water into wash basins. The gold particles can therefore be smelted using the smelter furnace part of the mercury-free processing technology.