Maximizing Carbon Sequestration by Modeling Rock-CO2(g) Reaction with Basalts of Varying Composition from Nevada

Mineral carbonation is a process whereby carbon dioxide reacts with minerals or rocks to store the carbon permanently in synthetic minerals. The amount of carbon sequestered generally increases with Mg and Fe content in a rock, thereby focusing most mineral carbonation studies on ultramafic rocks. Although Nevada has minimal concentrations of ultramafic rocks, it has large volumes of mafic volcanic and plutonic rocks. Thus, the purpose of this study is to model the rock-CO₂(g) reaction for basalts from Nevada at various temperatures using the EQ3/6 reaction path code. Preliminary work has tested the sensitivity of the carbonation reaction to changes in temperature and the basalt compositions that result in maximized carbon sequestration.

This study modeled experimental conditions for wet mineral carbonation of forsterite (O'Connor et al., 2002). The experimental procedure from that study used a solution of 1.0 molar NaCl and 0.64 molar NaHCO₃, and reacted it with forsterite (crushed to 37 μm) at 185°C in the presence of 15 MPa CO₂(g). In the modeled system, a similar solution containing sodium, chloride, and bicarbonate ions was reacted with a basalt with CO₂ fugacity fixed at 150 bars. CIPW norms calculated for several Nevada basalts served as input basalt mineralogies. Models were run from 0 to 200°C at 25°C intervals for each basalt.

Preliminary results indicate that the amount of carbon sequestered by mineral carbonation is sensitive to temperature. Optimum reaction temperature varies with basalt composition, suggesting each mineral carbonation reaction should have its own optimum temperature based on basalt mineralogy. In the models, carbon is sequestered in four phases: siderite, magnesite, dolomite, and dawsonite. However, relative abundances of carbonate-bearing product minerals vary as a function of reaction temperature and basalt mineralogy.