Carbon Capture, Utilization and Storage (CCUS) via Innovative Mineralization Pathways

Ever increasing anthropogenic CO₂ emission is one of the most urgent and difficult challenges faced by the global society. A wide range of carbon capture and storage technologies have been developed but the unprecedented scale of industrial CO₂ emission limits the number of viable options. Ocean and alkaline rocks are two large natural sinks for CO₂ but their uptake rates are currently not sufficient to keep up with increased CO₂ emissions. Thus, the acceleration pathways of mineral carbonation have been investigated to capture and fix CO₂ into thermodynamically stable solid carbonates. In-situ carbon mineralization in geologic formations has been suggested to lower the long-term monitoring costs, whereas ex-situ mineral carbonation is particularly interesting since they can use both alkaline rocks and alkaline industrial wastes. Moreover, ex-situ carbonation allows the formation of value-added products and their use can further offset the greenhouse gas emissions. In this study, Mg- and Ca-bearing minerals (e.g., serpentine) and industrial wastes (e.g., steel slags) have been engineered and activated to effectively leach out alkaline metals and to form carbonates with controlled chemical and physical properties. The use of Mg- and Si-targeting ligands as well as chemical or P_CO2 (partial pressure of CO₂) swing and internal grinding have been investigated in terms of the extent of mineral dissolution and carbonation. First, Mg and other components are leached from minerals and industrial wastes via rapid ion exchange with proton, but Mg extraction is eventually limited by the formation of Si-rich passivation layer induced by non-stoichiometric dissolution (Mg and Si) and re-precipitation of amorphous silica on the reactive mineral surface. In order to extract additional Mg from the solid residue, internal grinding and chemical ligand systems are studied. Mechanical abrasion of the passivation layer significantly improved the overall leaching of Mg, particularly when this method is combined with ligands. A modified core-shell model has been developed and the simulation results agree with the experimental data and well predicts the regime transition from kinetically to mass transfer limited reaction regimes of mineral dissolution. Findings from this study suggests that the dissolution and carbonation of alkaline minerals and industrial wastes can be significantly accelerated to capture and store CO₂ and mineralized carbon can also create unique large-scale utilization options for anthropogenic CO₂ such as construction materials.