Formation of Calcium Carbonate Sub-Micron Particles in a High Shear Stress Three-Phase Reactor

The production of precipitated calcium carbonate (PCC) was investigated experimentally under industrially relevant conditions, i.e. at high solid concentrations and increasing amount of solid product in the slurry. Temperature is an important parameter since it determines the crystal structure, the particle shape and, as a consequence, the viscosity of the slurry. Of course, the mass concentration of the raw material also has an important influence on the viscosity. From the particle size distributions of primary particles and agglomerates, it can be concluded that the nucleation process is governed by primary nucleation. Also, heterogeneous nucleation occurs on solid calcium hydroxide particles that are present in the slurry. Especially if the raw material contains impurities heterogeneous nucleation occurs and large and unwanted particles are formed. If the slurry is not stabilized, strong agglomeration occurs that can be influenced by the shear stress introduced to the slurry: a high shear stress which is linked to the viscosity of the slurry limits the upper particle diameter and leads to a steep particle size distribution of the product.