Formation and Aggregation of Polymorphs in Continuous Precipitation. 2. Kinetics of CaCO₃ Precipitation

Abstract

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+]/[CO3 2-] ionic ratio. These comprise of a heterogeneous regime involving calcite and vaterite nucleation at moderate [Ca2+]/[CO3 2-] ionic ratio in an unscaled reactor, homogeneous nucleation of vaterite followed by transformation to calcite in a scaled reactor at low and moderate [Ca2+]/[CO3 2-] ratio, and formation of stable vaterite at high [Ca2+]/[CO3 2-] 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.

Synthesis of CaCO3 nanoparticles by controlled precipitation of saturated carbonate and calcium nitrate aqueous solutions

“…They reported that increasing the agitation speed of the precipitation It is easily shown that the average particle size decreased as Ca 2+ 0 increased, reaching a size of 25 nm at 0.2 M of calcium ions. This could be explained by the supersaturation level S as defined by Equation (5) and the concentration ratio Ca 2+ t CO 2− 3 t of calcium and carbonate ions involved in the reaction medium at a given precipitation time as reported by Chakraborty and Bhatia (1996) when they described the liquidphase supersaturation for precipitation of CaCO 3 :…”

Contribution of Aggregation to the Growth Mechanism of Seeded Calcium Carbonate Precipitation in the Presence of Polyacrylic Acid

“…However understanding of the precipitation mechanism is still lacking at the higher supersaturations. Early models to describe the precipitation paths consider the nucleation of different polymorphs and hydrates, which then transform into more stable modifications 17,18 that can also be influenced by the presence of additive molecules. 19,20 New characterization tools such as cryogenic-TEM (cryo-TEM) or X-ray microscopy demonstrate the precipitation starts with particles ∼30 nm in size, which then transform into calcite or vaterite phases, [21][22][23][24] probably via agglomeration mechanisms involving amorphous calcium carbonate prenucleation clusters.…”

Simulation of CaCO3 Crystal Growth in Multiphase Reaction

“…That is why, a kinetic model should account for their simultaneous presence in the solution (Chakraborty & Bhatia, 1996). Usually, because of the complexity and difficulty of such calculations, the considerations are limited only to calcite.…”