£2,000 / 5 Tonnes CO2e Removed
 
Enhanced rock weathering (ERW) accelerates the natural process of silicate rock weathering, which naturally removes and mineralizes atmospheric CO₂. This acceleration is achieved by dispersing crushed silicate rocks, greatly increasing the reactive surface area.
 
During this process, atmospheric and soil CO₂ is transformed into dissolved bicarbonate ions. These ions can subsequently react with other minerals to form rocks, or they can be transported to the ocean where they remain stable for over 1000 years.
 
When applied to agricultural soils, ERW offers several additional benefits, including the provision of essential nutrients for crop growth and the neutralization of soil and ocean acidity. Suitable rock sources are generally abundant worldwide, and the obstacles to expanding this technology are minimal.
 
The Science
Silicate rocks are rich in cations such as calcium and magnesium. When these cations dissolve, they increase alkalinity and through a series of chemical reactions, converts CO₂ into dissolved inorganic carbon, predominantly, bicarbonate ions (HCO₃ -) (Equation 1). One mole of Ca₂+ results in 2 moles of CO₂ removed.
 
1) CaSiO₃ + 2CO₂ + 3H₂O -> H₄SiO₄ + 2HCO₃⁻ + Ca²⁺
 
The purpose of ERW is to promote mineral dissolution, whereby the weathering products are then transported to the oceans where they increase ocean alkalinity and in turn, drawdown atmospheric CO₂.
 
Depending on the conditions in the soil and drainage waters, precipitation of solid carbonates can occur releasing one mole of CO₂ in the process (Equation 2).
 
2) Ca²⁺ + 2HCO₃⁻ -> CaCO₃ + CO₂ +H₂O
 
In general, ERW is most efficient in areas with high rainfall, warmer temperatures and slightly acidic soils. Even in ideal conditions, there will still be some CO₂ leakage due to the precipitation of carbonates and pH-dependent equilibration while the alkalinity makes its way to the ocean.