04 September 2023

Undoing carbon emissions with crushed basalt rock

Thousands of tonnes of crushed basalt rock from Aberdeenshire Council's quarries are being spread across local farms to improve soil quality and remove carbon dioxide from the atmosphere.

Aberdeenshire Council has three quarries, Balmedie, Pitcaple, and Craiglash, which produce more than 200,000 tonnes of aggregates and coated materials per year for internal and external customers.

During the crushing and screening processes, rock dust is produced that is often seen as a waste material—until a nature-based carbon removal company, UNDO, approached with a sustainable use for the basalt.

With the right conditions, it is estimated that for every four tonnes of basalt dust spread, one tonne of carbon dioxide is removed from the atmosphere. The heat-trapping greenhouse gas then stays locked away for hundreds of thousands of years.

UNDO is concentrating its efforts on Aberdeenshire Council’s Balmedie and Pitcaple quarries as the basalt they contain has nutrients such as phosphorus, potassium, and magnesium. Once spread, the crushed basalt dust should improve soil health and reduce the need for chemical fertilisers.

For millions of years, carbon dioxide has been combined with rainwater to form carbonic acid. When this dilute acid falls on mountains, forests, and grassland, the carbon dioxide interacts with the rocks and soil and mineralises—safely storing it in carbonate form.

UNDO enhances and accelerates that process by spreading crushed basalt rock on farmland, increasing the surface area of the rock and giving it immediate contact with carbon dioxide produced by plant roots and soil microbes. This process reduces the timescale from millions of years to just decades.

The locally sourced crushed basalt rock is spread using existing farming machinery, enabling local people to do carbon removal in their community. The basalt rock is offered free of charge to farmers in close proximity to quarries, with UNDO paying for and managing the spreading of it across farmland.

Because the crushed basalt rock is spread on farms local to the quarries, transportation is kept to a minimum and, so far, UNDO has hauled more than 15,600 tonnes from Aberdeenshire Council’s quarries.

Aberdeenshire Council’s Infrastructure Services Committee Chair, Councillor Alan Turner, said: “The great thing about this process is that it's not just reducing carbon emissions in one area of a supply chain in favour of another. It is actually removing carbon dioxide from the air. On a human timescale, it's essentially permanently stored and in a manner that also helps our local farming community.”

Vice-chair Councillor Isobel Davidson added: “To the quarry, this material is essentially waste. It’s encouraging to see a sustainable business model created from waste that helps the region on its journey towards decarbonisation.”

Jennifer Brodie, UNDO’s Agriculture Business Development Manager for Northern Scotland said: “In addition to permanent carbon removal, basalt is a mineral-rich volcanic rock full of nutrients and trace elements. We have an ever-extending range of field trials underway to scientifically quantify the benefits we are bringing to the soil and crops and the potential savings to farmers for expensive fertilisers and lime.”

Farmers can learn more about how their farms can remove carbon on UNDO’s website.