CO2 removal by enhanced rock weathering

By: Miriam Davies

Enhanced rock weathering, a natural form of carbon dioxide recovery, is a hot topic right now, considered by many as a very promising nature-based way of removing carbon from the atmosphere. Its added benefits and potential for fast adoption globally is a promising and exciting pathway to sequester significant amounts of CO2.

Rock weathering is a natural geological process where rocks break down over time as they are exposed to weather. When rainwater falls on the rock, it begins to break down into smaller particles and minerals releasing essential nutrients for plants.

Crushed basalt applied at the Glandwr Forest

Some rocks with high silica (containing silicon and oxygen) content, such as basalt, sequester CO2 from the air as a part of a chemical reaction, triggered by rainwater. Calcium combines with CO2 from the air to create calcium carbonate (also known as limescale), removing the polluting gas from the atmosphere and locking it into soil and water. We can assess the amount of CO2 captured by measuring the amount of carbonate in the soil water, as the rocks break down. Research shows this process is a very efficient and effective way to remove CO2 from the air.

We can enhance this natural process of rock weathering, by crushing the rocks first, increasing the surface area exposed to the weather and accelerating carbon sequestration. Calcium carbonate in water flows eventually into the oceans where it can be stored 100,000 years and therefore shows great promise as a means to capture carbon over the long term. (Beerling 2020)

Enhanced rock weathering has additional benefits. Due to increasing CO2 levels, acidification of the ocean is continuing, which endangers corals and shellfish. Enhanced rock weathering counters acidification, and therefore helps to restore our oceans at the same time.

Crushed basalt can be deployed by a lime spreader. This one was specially modified for the application at the Glandwr Forest.

This process also holds great potential for farmlands and forestry as it can improve crop production, help protect crops from pests and diseases, and can restore fertility of the soil and its structure. Croplands worldwide are already equipped to deal with this type of process and so rapid adoption is feasible, which also brings financial incentives for adoption worldwide. The basalt rock dust itself is a bi-product of mining – basalt is mainly used for making asphalt in our roads – and far more dust is produced than there is a market for.

The Carbon Community sources its basalt from Builth Quarry in Llanelwedd, 20 miles from our test site. This ability to source locally helps to reduce total carbon emissions for the overall project. For the test plots with basalt addition, the basalt is spread in advance of tree planting at 4 kg per square metre (40 tonnes per hectare).

This test is a world first deploying crushed basalt at scale with tree planting which, if successful, may revolutionize the way that trees are planted, and draw down significant quantities of CO2 that is already in the atmosphere.