Engineering News and Mining Weekly
PhD research looks into Joburg’s vast tailings dumps
Geometallurgy research by Stellenbosch University (SU) PhD graduate Dr Steve Chingwaru points to a “massive invisible gold source” and the potential to unlock as much as R450-billion through the reprocessing of legacy tailings dumps around Johannesburg, South Africa, reports SU.
Gold tailings from the gold-rich Witwatersrand basin, in Gauteng, contain over six-billion tonnes of material.
SU reports that Chingwaru’s calculations, the first of their kind to be undertaken by a scholar, point towards the possibility of these tailings dumps containing up to 460 tonnes of gold.
Chingwaru’s research, originally for his master’s degree, which has subsequently been upgraded to a PhD along the way, aimed to calculate and characterise these tailings-hosted gold reserves.
“Historically, the low concentration of gold inside tailings was considered below the economic cutoff to be of feasible value. But, now that extensive mining has depleted most of the high-grade concentration of [ore-hosted] gold, it’s becoming unfeasible to mine [ore]. Some shafts are already reaching 4 km underground.
“[This means that] looking for gold in low-concentration sources is becoming more viable,” Chingwaru notes.
Some major mining companies have started to process tailings to extract the leftover gold, but traditional methods of extraction, most using cyanide, are not very effective and also damaging to the environment, Chingwaru points out.
Further, he notes that traditional extraction is damaging to the environment. In particular, oxidised sulphides produce sulphuric acid, which can easily contaminate groundwater, thus increasing the mobility of several toxic elements in natural water courses.
He explains that groundwater becoming polluted by tailings-related acid mine drainage (AMD) is a significant problem and worry in some parts of Johannesburg.
“That’s why I’m passionate about highlighting the economic potential, as well as the environmental benefits of reprocessing tailings dumps efficiently,” Chingwaru enthuses.
“Typically, they manage to extract just 30% of the gold through this process. So, in my PhD research, I asked where the remaining 70% is, and how it can be safely removed from the pyrite.”
During his research, Chingwaru also explored ways to extract the gold efficiently while addressing environmental concerns related to the tailings, such as the release of AMD owing to pyrite oxidation.
The gold mineralisation present in old tailings dumps is not readily visible to the naked eye. This type of gold is typically dispersed within other minerals and is challenging to extract. Therefore, advanced techniques may be required to extract it economically.
“If you process the pyrite, you are taking out the key cause of AMD, plus you’re getting economic value from it. The process has the potential to recover additional valuable byproducts such as copper, cobalt and nickel, and reduce or even eliminate the heavy metal pollution and AMD associated with tailings dumping,” Chingwaru says.
Academic acclaim
Chingwaru’s research has garnered interest from mining companies around the globe.
His research has been published in industry journals including Mineral Processing and Extractive Metallurgy Review and Minerals Engineering.
At the end of 2023, Chingwaru was invited to a meeting hosted by the Public Protector in Johannesburg to discuss the environmental impact of illegal mining.
Chingwaru’s research was also voted the third best at the Prospectors and Developers Association of Canada’s Society of Economic Geologists Student Minerals Colloquium, where he presented his work.
Chingwaru is the grandson of the legendary prospector George Nolan, who discovered lithium in Zimbabwe and even wrote a book – Road to Lithium Lodge – about his adventures looking for precious metals in the wilderness of what was then southern Rhodesia.