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.