Enhanced cation release via acid pretreatment for gigaton-scale geologic CO2 sequestration in basalt

Abstract

Basalt-based CO₂ mineralization offers gigaton-scale capacity for sequestering anthropogenic CO₂, but it faces challenges such as low cation productivity and formation of pore-clogging clays. A potential solution is to treat the basalt with aqueous acids such as HCl, a by-product of some electrochemical CO₂ removal processes. To date, our understanding of basalt-acid interactions is limited to extrapolations from higher pH environments, and therefore little is known about the mechanisms of the reaction at acidic conditions. To address this knowledge gap, far-from-equilibrium dissolution rates of basaltic glass and crystalline basalt were measured in mixed flow reactors at pH 0 to 9, and temperatures from 23 to 60 °C, with a specific focus on the low-pH region. Measured geometric surface area-normalized dissolution rates can be described according to: $k=10^{-(5.6\pm 0.5)}\cdot exp\left(\left(\frac{-42.2\pm 2.0}{R}\right)\cdot \left(\frac{1}{T}-\frac{1}{T_r}\right)\right)\cdot a_{H^{+}}^{(0.81\pm 0.02)}+10^{-(10.9\pm 0.3)}\cdot exp\left(\left(\frac{-32.5\pm 1.1}{R}\right)\cdot \left(\frac{1}{T}-\frac{1}{T_r}\right)\right)\cdot a_{H^{+}}^{-(0.15\pm 0.01)}$ where $k$ is the rate constant (mol m⁻² s⁻¹) at any temperature $T$ (Kelvin) and ${\text{H}}^{+}$ activity ($a_{{\text{H}}^{+}}$), $T_r$ is the reference temperature (298.15 K), and $R$ is the ideal gas constant (8.314 $\times$ 10^-3 kJ mol⁻¹ K⁻¹). The combined results of kinetic experiments and geochemical modeling indicate that acid reaction with basalt yield orders of magnitude faster cation release rates, effectively neutralizes fluid pH, and limits clay formation by limiting Si release into the system.