Offering an alternative to full-ore mercury amalgamation

Only a few kilometres from the border of Kenya, after a few bumpy roads and with fertile agricultural land wherever you turn, is the remote and scattered village of Tiira in the Busia District of eastern Uganda. Artisanal and small-scale gold mining represents a crucial livelihood for the local population and is an activity deeply engrained in its identity, dating back almost a hundred years. 

miners waiting for the ore to be extracted impact facility
Miners waiting for the ore to be extracted

Traditional Gold Mining and Processing 

Gold-bearing rocks buried deep in the earth are mined using primitive tools such as pickaxes, spades and hammers. The recovered ore is sorted, dried in the sun, and once dry, fed into the crusher. The crushed ore is now a powder, several microns in size. This is added to water to make a slurry which is left to slide slowly down a sluice box using heavy sacks to capture fine gold particles.

Gold is left on the sacks, with the tailings (waste) flowing away into the ponds. The sacks are removed and washed in a big basin of water. Now this is where mercury comes into play. The infamous substance naturally binds gold along with other precious metals such as silver, acting as a glue separating out gold from worthless waste rock during the so-called washing/panning process. The concentrate captured during sluicing is mixed with mercury, and gets stirred around using bare hands – traditionally by women or children. After several minutes, a small ball of gold and mercury forms. This amalgam is then burnt over a hot flame on a spoon: the mercury vaporises, leaving behind a gold sponge. Mercury amalgamation is fast, easy and the substance is readily available, making this process very attractive to the local population.

The long-term consequences of mercury use, however, are most severe, causing disabilities, miscarriages and even death.

Awareness of the dangers of mercury use is on the rise, and the leaders of local mining organisations wanted to adopt mercury-free processing alternatives. 

pure mercury impact facility
pure mercury

The Impact Facility creates value

With the goal of receiving much needed equipment and training, Tiira’s mining organisations agreed to work with The Impact Facility and deliver measurable and sustainable development impact. For more than two years, The Impact Facility has supported the mines with business and governance training, awareness campaigns around safety at work and child labour, understanding of the dangers of mercury use, and capacity development for efficient gold mining methods and environmental stewardship. Today, all four mines have successfully formalised, holding all relevant permits, and boasting improved health and safety standards at the mines. 

In response to the organisations’ efforts and commitment to continuous improvement, The Impact Facility installed a centrally-located gold processing plant, offering a means of mercury-free gold processing to the group of miners. This process makes the gold recovery more efficient, recovering up to 95% of gold from the ore, compared to just about 60% estimated recovery when traditional methods are used. It also significantly speeds up the process. 

installation of the processing plant in June 2019
Installation of the processing plant in June 2019.

The mechanics of Mercury-free gold processing

Before the process can begin, the ore must be crushed or milled. Once the milled material is relatively consistent (similar in size), the material is fed into the gold katcha, which is a concentrating centrifugal machine which, capturing the heavier elements, such as gold, while washing away the lighter waste rock onto a tailings heap.

Next, the shaker table further concentrates the gold, using vibration to further separate heavy particles from lighter ones. Lighter minerals are washed away on the side while the gold is trapped by grooves in the table and directed to a collection point. It is a very effective machine and specially designed for the recovery of fine gold to a directly smeltable concentrate. 

This mechanical process makes gold recovery not only more efficient, doubling recovery rate compared to the traditional method with sluice mats and panning (up to 95% of gold is recovered) but it also dramatically speeds up the process, while simultaneously reducing reliance on the use of mercury to wash the ore.

By adding a smelting unit to the above process, the miners will be able to fully eliminate mercury use during the processing of their ore. However, to make smelting viable, the mines first need to increase their production volumes, currently challenged by heavy rainfall.

the impact facility shaker table
The Impact Facility Shaker Table

Benefits

By applying a pay-per-use scheme, none of the organisations face the debt burden of the underlying $55,000 outlay while shared use of the plant maximises both its investment and its positive impact. This model also reduces the barrier to engagement formerly posed by the high investment price, offering miners a chance to test out the system without needing to make a long-term financial commitment themselves. The plant is operated and maintained by locally-recruited, trained Impact Facility staff, ensuring that the plant remains in use and functional. 

The provision of capacity-building training and access to improved mining equipment enables ASM miners to generate a sustainable income with safe and efficient mining practices for responsibly mined ASM gold.  Economic prosperity will increase using this method and child labour in ASM communities may also be reduced. 

kids playing near the mines impact facility
kids playing near the mines