Negative emission technologiesCould South African Mine Wastes Provide a Feasible Storage Method for Millions of Tons of CO2?

By Liam Bullock, Zakhele Nkosi and Maxwell Amponsah-Dacosta

Published 8 April 2021

Mine sites are literally well-oiled machines, and it is easy to witness both the pros and cons that sites have on our society. However, hidden in plain sight among the hectic operations is perhaps the biggest untapped source of material that could help us in our ongoing battle with climate change. A material often perceived as having a negative effect on the environment – mine wastes known as tailings.

Having visited just a few of the many metal and diamond mines of South Africa, my colleagues and I are never short of astonishment of the sheer scale and efficiency of the operations.

Some stretch for tens of kilometers in length, width and even depth. The size of the mines, coupled with the riches in the ground that are targeted, require town-sized populations coming on and off-site 24 hours a day, as the Earth is upheaved, moved, crushed, and divided for the valuable commodities.

Moving from the rock faces through to the concentrators and beyond, one cannot help but be both impressed and intimidated by the volumes of material that is cascading through the system.

Mine sites are literally well-oiled machines, and it is easy to witness both the pros and cons that sites have on our society. However, hidden in plain sight among the hectic operations is perhaps the biggest untapped source of material that could help us in our ongoing battle with climate change. A material often perceived as having a negative effect on the environment – mine wastes known as tailings.

Negative Emissions Technologies
The means of climate mitigation that could be met here is through the implementation of “negative emissions technologies” (NETs) at mine sites. These methods aim to remove carbon dioxide (CO2) from the atmosphere, addressing one of the biggest societal challenges we face as a collective.

The gathering movement to NETs and CO2 removal forms part of a greater global response to limit temperature increase to well below 2 °C over the next few decades, as outlined by the Intergovernmental Panel on Climate Change (IPCC).

There are several possible NET methods of CO2 removal, including the advancing notion of utilizing “enhanced weathering of rocks”. The method involves speeding up the chemical breakdown of rocks, a natural process that converts atmospheric CO2 into carbonate minerals or hydrogen carbonate and carbonate ions (“alkalinity”).

Basalt, a common fast-weathering volcanic rock at the Earth’s surface, has been marked as a highly appropriate rock type for both direct CO2 injection (as demonstrated by the pioneering CarbFix Project) and deployment through spreading crushed basaltic rocks on croplands. South Africa is built upon similarly reactive rocks, and the mining industry of the nation has delivered a ready-made batch of finely ground rock for any future CO2 removal strategies.

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