AngloGold Ashanti in its just released 2020 Sustainability report says it is rolling out a novel in-situ water remediation project at the Geita mine in Tanzania, working with a local Tanzanian/German joint venture partner that will use a process where naturally occurring bacteria directly remediates sulphate in groundwater. The technology – known as in-situ TSF bioremediation – AGA says is groundbreaking.
The AngloGold Ashanti team worked to adapt it to the mining context, making them the first to introduce it on a mine site. The fact that the remediation takes place at the site of contamination is key, as it means the process has a very low environmental impact. It can be used instead of more intrusive water remediation solutions such as constructing a water processing plant, digging trenches and pumping the water back to a TSF.
With a successful concept study completed, the project is to be rolled out in three phases at Geita. This in-situ remediation approach has scope to be applied at other sites where it could be used not only at TSFs, but around pits as part of decommissioning. The process uses naturally occurring bacteria in the groundwater to remove contaminants such as sulphate and nitrate and because the bacteria is in-situ, the process, once established, will become self-sustaining after a few years.
For the process to work, a carbon source – in this instance, vegetable oil – is introduced to the impacted area, providing food for the micro bacteria. A combination of sulphur, sulphate and nitrate reducing bacteria carry out the remediation. After acclimatising, the bacteria convert the nitrates to nitrogen gas and precipitate the sulphates to physical sulphides. Vegetable oil is added over the course of a few months, while the team determines how much, and how often, this needs to take place in order to sustain the contamination-busting bacteria. This process will, over time, build a barrier that prevents the spread of sulphate enriched water beyond the reaction zone.