Calcium carbonate particle formation through precipitation in a stagnant bubble and a bubble column reactor

The precipitation of CaCO3 via CO2 bubbling using well-defined membranes was used in this study to produce particles of a variety of structures. Studies into the mechanisms of particle formation via this method are limited and are mainly specific to hollow structures. Using a range of analytical techniques, particles produced with a stagnant bubble and in bubbling systems (crossflow and vertical flow) were investigated. The stagnant bubble work concluded that the particles are produced both in bulk but also at the gas/liquid interface which then fall down and collect at the base of the bubble, whereas in a dynamic system the bubble wake has an important role in precipitation of such particles. Precipitation occurs as the solution pH drops due to CO2 bubbling (acidic gas), and these particles are initially comprised of a solid core. As the pH drops further, these particles transform to ones with a hollow core and the pH plays an important role in controlling the particle shell thickness. Allowing the particles to age in solution allows for transformation of such particles from vaterite to calcite. Finally, the particle structure can also be altered by changing the bubbling set up as having a recirculation loop leading to the formation of particles exhibiting a stacked cube.