Mining Weekly

The Council for Geoscience (CGS) is currently investigating several options for the development of appropriate measures to address environmental challenges associated with acid mine drainage (AMD).

CGS intern Leahn Pieterse points out that, each year, the mining industry generates a signifi- cant amount of mine tailings. “Storage of these tailings occupies large areas of land and leads to high monetary, environmental and ecological costs,” she says.

However, the CGS is running a project that is based on the hypothesis that future AMD prevention could be achieved if gold mine tailings were used as starting aluminosilicate sources for the synthesis of geopolymeric materials and subsequent stabilisation.

Pieterse explains that geopolymers are mineral binders which can be used, for instance, in cement manufacturing.

“Australia’s roads authority, VicRoads, has recognised geopolymer concretes as being an equivalent of ordinary Portland cement (OPC) for nonstructural applications.

“This is of great significance when one considers that concrete made from OPC is the second-largest commo- dity used worldwide,” she highlights.

Pieterse says that there are currently several countries with pilot or demonstrated geopolymerisation plants, noting that high-performance geopolymer concretes have already been commercialised.

She contends that the benefits of the use of this technology in South Africa are numerous, as it would assist in the recycling of highly problematic gold tailings into useful and valuable commercial-grade products. It would also simultaneously prevent AMD from occurring, Pieterse adds.

She says that, in addition to the “obvious economic benefits” that would arise from this approach, the practice would also create a signi- ficant opportunity to reduce global carbon dioxide emissions.

Pieterse remarks that the abundance of silicon and aluminium in starting materials used for geopolymerisation is a prerequisite to the synthesis of high-quality geopolymeric materials.

“Most South African gold mine tailings are characterised by a silicon-to-aluminium ratio varying between 3 and 11, which is similar to ratios found at vanadium and copper mine tailings dumps,” she notes.

Pieterse says the CGS has examined tailings from gold mining company Giyani Gold’s Klein Letaba gold mine, in Limpopo, which exhibited a particularly promising composition.

Conversely, she states that most tailings samples taken from the abandoned Nestor gold mine, in Mpumalanga, exhibited a “very limited potential” for geopolymerisation because of elevated silicon dioxide contents (up to 94.7%) and their very low aluminium oxide content (as low as 2.1%).

Pieterse adds that the tailings that have been tested locally by the CGS also exhibited mineralogical similarities with tailings of mines in other countries, such as the predominance of quartz.