Effect of Carbon Dioxide Pressure on Mineral Carbonation in Acidic Solutions

Magnesium silicate minerals such as serpentine [Mg3Si2O5(OH)(4)] have a high potential for the sequestration of CO2; thus, their reactivity toward dissolution under CO2-free and CO2-containing conditions in acidic solvents is a critical process with respect to their carbonation reactions. To examine the carbonation efficiency and dissolution mechanism of serpentine, hydrothermal treatment was performed to the starting material via a modified direct aqueous carbonation process at 100 and 150 degrees C. The serpentine dissolution experiments were conducted in H2SO4 solution with concentration range of 0.3-1 M and at a CO2 partial pressure of 3 MPa. The initial pH of the solution was adjusted to 13 for the carbonation process. Under CO2-free and CO2-containing conditions, the carbonation efficiency increased in proportion to the concentration of H2SO4 and the reaction temperature. The leaching rate under CO2-containing conditions was higher than that under CO2-free conditions. This suggests that shows the presence of CO2 affects the carbonation reaction. The leaching and carbonation efficiencies at 150 degrees C in 1 M H2SO4 solution under CO2-containing conditions were 85 and 84%, respectively. The dissolution rate of Mg was higher than that of Si, such that the Mg : Si ratio of the reacted serpentine decreased from the inner part (approximately 1.5) to the outer part (less than 0.1). The resultant silica-rich layer of the reaction product ultimately changed through the Mg-depleted skeletal phase and the pseudo-serpentine phase to the amorphous silica phase. A passivating silica layer was not observed on the outer surface of the reacted serpentine.