Trapping CO2

The world’s largest diamond producer has announced plans to operate a carbon-neutral mine within just a few years. De Beers, majority owned by Anglo American, intends to implement a carbon capture and storage (CCS) project by storing carbon dioxide in kimberlite rock, abundant at most diamond mines. Minestories spoke to Stuart Haszeldine, professor of carbon capture and storage at the University of Edinburgh’s School of Geosciences, about CCS and what it may mean for mines in the future.

Q: Briefly explain the basic tenets of CCS for miners and mine sites.

A: CCS is the collective name for a group of technologies and actions that are trying to reduce the rate at which greenhouse gases such as CO2 are added to the atmosphere by human activity. It is well established from basic physics that increasing CO2 content acts as a thermal blanket around the Earth, increasing temperatures by a measurable 0.9 degrees Celsius.

The mining industry produces large quantities of CO2 emissions from the fuels used by heavy equipment moving rock and earth, and also by the crushing, purification and separation processes used in many mining operations. In some places mines are sitting on a valuable asset – the excavated or crushed rock associated with ores or products. Some of these rocks types, particularly those associated with igneous bodies, are chemically reactive with CO2. Over time, those minerals will naturally undergo weathering by reaction with atmospheric CO2 and combine that CO2 into new minerals – carbonates, clays, serpentine or soluble salts. So the mining industry wastes – rubble, tailings and fines – can be ideal materials for reaction with rainwater or river water carrying atmospheric CO2.

Q: So mine sites make good storage venues?

A: Yes, there is a huge resource of reactive rock, which has been crushed finely and so is ready to react. There is an industrial infrastructure that can divert water flow through the relevant rock debris where CO2 can be absorbed. And there are monitoring and clean-up facilities which can catch pollution episodes with enough engagement, speed and understanding to ensure that a new method of operating more cleanly is promoted rapidly.

Q: De Beers plans to store carbon in kimberlite tailings. Why are kimberlite tailings a particularly good choice for carbon storage, and can other mines – not just diamond mines – find success using their tailings as well?

A: Kimberlites are rich in mafic reactive minerals that contain iron, calcium and magnesium, such as forsterite olivine or magnesian ilmenite. These are particularly suited to rapid reactions with CO2 and may form serpentine, with methane as a by-product. Most igneous mines can produce minerals that have suitable reactions to absorb CO2. For example, granites contain feldspars, which react with CO2 to form clay minerals.