Viability of commercial olivine mixtures for enhanced weathering in seawater: Dissolution kinetics, CO₂ sequestration, and metal release assessment

Enhanced silicate weathering (ESW) shows promise in converting atmospheric CO₂ into inorganic carbonates via mineral weathering. This study investigates the potential of utilizing olivine containing mineral mixtures from waste rock and tailings (olivine purity ∼ 55% and mean particle size ∼ 39 µm) for ESW in seawater. A decrease in olivine weathering rate over time was observed in the form of diminishing Mg release rates due to the formation of passivating layers at the mineral surface. Quantitative mineralogical analysis revealed a reduction in the olivine percentage (up to 8.6%) in the reacted mineral mixture indicating a reaction that results in CO₂ sequestration. However, there was also simultaneous precipitation of 2:1 layer silicates and a possible amorphous clay mineral (a CO₂-releasing process known as reverse weathering). The highest deployed material dosages released significant amounts of nickel (Ni) and cobalt (Co) into the solution, emphasizing the need for careful consideration in large-scale ESW deployment. The CO₂ sequestration rate measured at 90 days of the olivine-mineral mixture was calculated to be 3.80 × 10⁻¹² mol CO₂ m⁻² s⁻¹, equating to 14.43 kg of CO₂ sequestered per ton of olivine-mineral mixture per year. As rates decline non-linearly, this value reflects short-term kinetics, highlighting the need for Monitoring Reporting and Verification (MRV) based on windowed rates and cumulative uptake. These findings suggest that olivine containing mineral mixtures from mine waste and tailings represent a durable carbon storage, characterized by high early fluxes that decline over time, with material dosage critical for efficiency and metal risks.