Weathering is a natural geological process whereby atmospheric CO2 dissolved in rainwater attacks rocks, partly dissolving them. The CO₂ is converted into alkalinity or carbonate minerals that securely store carbon on timescales of >10,000 years. Modelling studies show that if weathering rates can be increased (by selecting the most reactive rocks, increasing reactive surface area), up to an additional 2 Gt CO₂ yr^-1 could be removed from the atmosphere, ~40% of the amount required by 2100 to meet the Paris Agreement target.

The mining industry extracts gigatonnes of rock each year, generating large amounts of freshly exposed, reactive surface area that could be used as a feedstock for enhanced weathering. Ore deposits with the highest CO₂ removal capacity are those mined in high quantities that have an abundance of calcium- and magnesium-bearing silicate minerals [1]. Here, we report the results of an investigation into the reactivity of serpentinised peridotite samples  from the Sakatti Cu-Ni-PGE deposit (Finland). The deposit consists of both disseminated and massive sulphides hosted within a large olivine-cumulate  body [2]. The material consists primarily of serpentine [Mg₃Si₂O₅(OH)₄] and olivine [Mg₂SiO₄] minerals that have a high potential for CO₂ removal via enhanced weathering.

We have conducted a series of laboratory experiments whereby crushed peridotite samples were reacted with CO₂-enriched solutions at 25 °C and 50 °C, and 1 bar CO₂ (100% CO₂).  Surface area normalised dissolution rates were determined for various grain sizes,  temperatures, mineral compositions (degree of serpentinization) and solution chemistry (with/without a chelating agent).