Controls on CO2 Mineralization Using Natural and Industrial Alkaline Solids under Ambient Conditions

The extent to which carbon dioxide (CO2) mineralization (“carbonation”) using alkaline solids can reduce atmospheric CO2 concentrations is dictated by the rate of divalent alkaline metal release from such solids. These solids have distinct reactivities, that is, bulk dissolution rates, which dictate their rates of carbonation. To assess the feasibility of utilizing alkaline solids to mitigate CO2 emissions at scale, assessments of practical carbonation potentials under ambient conditions, which are often distinct from their stoichiometric carbonation potential as described by their bulk chemical composition, are needed. Therefore, the carbonation (or “CO2 mineralization”) potentials of 16 naturally occurring (mafic and ultramafic) rocks and industrial alkaline solids (fly ashes and slags) were quantified. In general, the extent of carbonation for the pulverized and as-received solids which is achievable under ambient conditions [25 °C, 1 bar]—in the presence of excess CO2 and water—that is, the carbonation potential, is correlated with the CaO and MgO content and varies inversely with the SiO2 content. Particularly, the carbonation efficiency (i.e., the ratio of the measured to the stoichiometric carbonation potential) is controlled by the atomic topology (network connectivity) of the solid reactant—suggesting that network rupture is the rate-controlling step of dissolution and, hence, carbonation. Based on our data, we offer estimates of CO2 removal that can be achieved under ambient exposure conditions to assess the controls and capacity of ambient CO2 mineralization as a carbon dioxide removal strategy.