Combating climate change with olivine

Australia is very rich in silicate rocks, which may hold the key to unlocking new climate solutions. As world leaders in mining technology, we have the capacity to lead the charge in using silicate rocks to absorb CO₂ establishing Australia not only as a leader in renewable systems, but also nature-based climate solutions. Below, Tim Flannery discusses an exciting mineral, olivine, and how it can be used to tackle climate change.

When I was about 16 years old, I was quite taken by a farmer who collected rocks from a scoria (a volcanic rock) quarry on the side of a volcano. He picked up a piece of lava which was around the size and shape of a football; a ‘volcanic bomb’ which had been ejected out of the volcano when it had last erupted thousands of years ago. He broke the bomb open, and in the centre glowed a mass of beautiful green crystals. This was olivine, which the volcano had brought up from Earth’s upper mantle, then ejected with great force - the lava surrounding it solidifying into its distinctive shape as it flew. The Australian Museum has specimens in its collection from a volcano in Western Victoria which is very similar to the one I saw (Figure 1).

Peridot is another name for the crystalline mineral most commonly known as olivine. Olivine is just one of a group of minerals known as silicates, which all share a characteristic that makes them important in the fight against climate change. As olivine rocks decompose, they absorb atmospheric CO₂ and bind it into carbonates in the soil, thereby removing it permanently from the atmosphere. Olivine and some other silicate minerals are so efficient at capturing CO₂ as they degrade that less than a litre of crushed olivine can capture the CO₂ released by burning a litre of oil. To capture carbon, atmospheric CO₂ must combine with water to create carbonic acid. When this acid interacts with silicate minerals it triggers an Urey reaction^[1], which traps the CO₂ in soil carbonates.

While the Earth was still young and its atmosphere filled with CO₂, the Urey reaction reduced atmospheric CO₂ to levels that made the planet habitable. Over geological time, the Urey reaction responds to planetary warmth and balances the release and absorption of CO₂, keeping atmospheric CO₂ at low levels. The Urey reaction will eventually absorb the CO₂ that humans have put into the atmosphere, but that will take hundreds of thousands of years – too long to save us from catastrophic climate change. What we need is to speed up the Urey reaction; but how?

Some scientists think that olivine and related minerals might be the answer to combatting climate change. In the coming decades, we will need to draw vast volumes of CO₂ out of the atmosphere, and silicate rocks like olivine offer one of the most efficient ways of doing so. These scientists estimate that if we of it, crush it up and spread it on Earth’s beaches and agricultural fields, we could speed up the Urey reaction and be drawing down gigatons of atmospheric CO₂ by 2100.^[2]

Unfortunately, there is an impediment: to use these rocks, they must be blasted, transported and crushed to the consistency of sand, a process which currently burns a great deal of fossil fuel. Most of the CO₂ emissions associated with using silicate rocks come from transport. In one study where the rock quarry was 65km from the field where the crushed rock was spread, the process took 110g of CO₂ emissions for every kilogram of CO₂ removed from the atmosphere.^[2] But the study warns that if the rock needs to be transported more than around 600km, then as much CO₂ will be emitted as the rock will absorb. Until we can use clean energy to quarry and crush silicate rocks, we can’t take full advantage of their amazing ability to absorb CO₂ and store it in the earth.

Australia is very rich in silicate rocks, and we are world leaders in mining technology. We also have an exceptionally large agricultural industry. In addition to absorbing carbon from our atmosphere, minerals like olivine return elements to depleted soils, benefiting agricultural operations.^[4] A recent study has shown that if we added crushed basalt to the agricultural land of China, India, the United States and Brazil, we would draw down 2 gigatonnes of CO₂ per year!^[5] When the benefits of using this material are so varied, it is a wonder why we are not improving our mining operations to maximize the use of silicate rocks. If we green our energy and transport systems quickly, we could become a world leader in using silicate rocks to absorb CO₂. Thus, olivine may hold the key to establishing Australia as a leader in renewable, nature-based climate solutions.