CO2 mineral sequestration: physically activated dissolution of serpentine and pH swing process

The effect of the physical activation on the dissolution of serpentine was investigated and a pH swing scheme was developed to improve the overall conversion of the CO2 mineral sequestration process. Various methods of the surface agitation such as ultrasound, acoustic, and internal (in-situ) grinding were examined for their effectiveness in removing the diffusion limiting SiO2 layer in order to promote further dissolution of the inner MgO layer of serpentine. It was found that the fluidization of the serpentine slurry with 2 mm glass beads was most effective in refreshing the surface of the serpentine particles during the dissolution process. Unlike the external attrition grinding, this method could be much less energy intensive. It was also found that the mechanical agitation via the internal grinding alone did not enhance the dissolution of serpentine, while the combination of the internal grinding and Mg leaching solvent resulted in rapid serpentine dissolution. Using the proposed pH swing scheme, the overall conversion of the mineral carbonation radically improved. By controlling the pH of the system, three solid products were generated from the mineral carbonation process: SiO2-rich solids, iron oxide and MgCO3*3H2O. Since the iron oxide and MgCO3 produced were highly pure, these value-added products could eventually reduce the overall cost of the carbon sequestration process.