Around 1.5 million people are directly engaged in Tanzania’s Artisanal and Small-Scale Gold Mining (ASGM) sector, which is regarded as the country’s largest source of mercury emissions. Tanzania has signed the Minamata Convention on Mercury, which aims to reduce and, when possible, eliminate mercury use in ASGM. Several alternatives have been developed, such as gravity concentrators (Gemini tables, Gold Kacha concentrators), direct smelting, the borax method, and cyanidation (VAT and CIP/CIL leaching).
Miners in ASGM typically prefer using mercury due to its simplicity, low cost, and quick returns. In contrast, many mercury-free technologies have failed to deliver these benefits to ASGM miners, making adoption difficult.
Cyanidation, given its strong adoption in Tanzania, presents a viable alternative to mercury. Cyanidation is practiced in two ways: amalgamation followed by cyanidation and full cyanidation. However, amalgamation followed by cyanidation risks releasing mercury-cyanide (Hg-cyanide) compounds, which are more toxic than sodium cyanide, contaminating water bodies and harming aquatic life such as fish.
Cyanidation has a clear edge over mercury in terms of recovery and process efficiency. Mercury typically recovers only 30-45% of the gold, while a well-operated cyanidation process can achieve recoveries of 90-95%. Unlike mercury, cyanide does not persist in the environment; when properly handled, it has a minimal environmental impact. Natural physical, chemical, and biological processes break down cyanide into less toxic compounds.
Although cyanidation offers many benefits, it also comes with challenges. Cleaner cyanidation plants are expensive and require technical expertise to operate. Furthermore, when cyanidation is poorly managed, especially in cases of inadequate tailings management, it can lead to significant environmental harm.
For successful cyanidation, three areas must be addressed: financial, technical, and environmental (including health) considerations. Cyanidation, being more complex than amalgamation, requires technical simplifications to suit typical ASGM miners. Moreover, miners accustomed to quick returns from mercury-based methods need adequate financial support to transition sustainably to cyanidation. Lastly, the environmental and health impacts of cyanide should be communicated to ASGM stakeholders, and compliance must be closely monitored.
Tanzania, through government institutions and NGOs, has been working to raise awareness about the dangers of mercury while educating ASGM stakeholders on the benefits of cyanidation and proper handling of the process. Additionally, there have been efforts to provide funding to ASGM miners through banks, although progress has been slow due to the lack of bankable geological and technical reports demonstrating the economic viability of mining areas.
Technologically, continuous improvements have been made since the introduction of VAT-leaching plants in the mid-2000s. Then followed by the construction of simplified low-tonnage CIP/CIL plants in areas like Geita, Shinyanga, Mbeya, Songwe, and Singida. These new CIP/CIL plants offer higher recovery rates than traditional VAT leaching.
In summary, we are well-prepared in terms of environmental awareness, halfway there with technology, but still lagging in financing the transition.
To ensure the successful transition to mercury-free technologies, ASGM sites must be de-risked through sufficient geological data, as only 16% of Tanzania has undergone high-resolution airborne geophysical surveys, and expanding these surveys would be beneficial. Additionally, ASGM miners need better information on handling cyanidation tailings, particularly at the VAT leaching level. The National Environmental Management Council (NEMC), in collaboration with the Mining Commission, should propose simplified tailings storage strategies for low-capital VAT leaching plants. Furthermore, contractors building CIP/CIL plants must ensure that the project capacities are aligned with ASGM production levels, considering ore grades and mineral properties to enhance efficiency and sustainability.
