Formation and aggregation of polymorphs in continuous precipitation .2. Kinetics of CaCO3 precipitation

Experiments with the continuous precipitation of calcium carbonate are reported in this study. Particle size distributions were measured on-line and interpreted by means of the simultaneous nucleation and the transformation models developed in part 1 of this sequence. Three regimes of precipitation are reported in this study, governed by the supersaturation and liquid phase [Ca2+]/[CO32-] ionic ratio. These comprise of a heterogeneous regime involving calcite and vaterite nucleation at moderate [Ca2+]/[CO32-] ionic ratio in an unsealed reactor, homogeneous nucleation of vaterite followed by transformation to calcite in a scaled reactor at low and moderate [Ca2+]/[CO32-] ratio, and formation of stable vaterite at high [Ca2+]/[CO32-] ratio. The particle size distributions in the different regimes are well fitted by the applicable model from part 1 or earlier studies of single-species precipitation. Where appropriate, kinetic parameters obtained from the fits are correlated with supersaturation by power law models.