Optimizing the management of quarry fines for on-site carbon removal: Implications of grain size and mineralogy on CO2 mineralization

Weathering of basaltic quarry fines can enable quarries to remove CO₂ by optimizing the management of underutilized rock fines. In this study, basaltic fines from two quarries in Scotland are used as potential feedstocks for ERW. Using column experiments, fines from both sites were placed into columns as layers with varying thicknesses (1 cm and 5 cm) and grain sizes (bulk and <100 μm). Fines were saturated (≈60 % pore water) and exposed to ambient UK conditions (10 °C, 0.04 % CO₂) and accelerated carbonation conditions (50 °C, 20 % CO₂). Quarry site 1 experienced negligible increases in TIC within bulk fines under ambient conditions, yet fines <100 μm experienced carbonation equivalent to 440 g CO₂/m²/yr. However, the total inorganic carbon content (TIC) nearly doubled in the bulk fines from quarry site 2 (5 cm) under ambient conditions, equivalent to 570 g CO₂/m²/yr. In the sieved fines from the same site the TIC content nearly tripled, equivalent to 1330 g CO₂/m²/yr. At site 2, if the bulk fines could be deposited over 0.8 km² of land in 5 cm thicknesses, approximately 460 t CO₂/yr could be sequestered with minimal management practices in place. Using fresh fines that have not previously weathered in stockpiles is important for maximizing the carbon dioxide removal potential. Despite higher carbon offsets within the sieved material, the energy and cost required to crush rock from bulk to <100 μm is not economically feasible, as it exceeds the value of carbon which it could be sold for.