Simulation, aggregation and thermal analysis of nanostructured calcite obtained in a controlled multiphase process

Abstract

In the present experiments, the carbonation process in multiphase system was carried out using the reactor with rotating discs. Calcite was produced by controlled fast precipitation through gaseous CO2 adsorption in Ca(OH)2 slurry. Furthermore, the reaction kinetics' were controlled by disc's revolution speed in the range from 80 rpm through 120 to 160 rpm. Initial concentration of the slurry ranged between 54 and 110 mM L-1. The aggregates of crystals precipitated in the aqueous solution were of sub-micrometric size. Dynamic light scattering method showed that mean aggregate diameter decreased with the higher mixing rate as long as the mixing condition was homogenous (up to 160 rpm). Thermogravimetric analysis revealed that the surface of calcite was polluted by unwanted, different compounds amount of which depends on the initial concentration of the slurry. Therefore, in order to obtain chemically pure calcite, CaCO3 powder was heated up in the laboratory oven. In order to explain the mechanism of calcite particles' aggregation, the simulation of the aggregates formation has been performed based on the new model taking into account kinetics of the multiphase reaction, crystal growth and their agglomeration. The obtained data on crystal morphology during the precipitation process have been compared with the model simulation results. The internally consistent model very well describes both the formation and the aggregation of the calcite nanoparticles, and the same can be used and recommended for accurate calculations of the particle and aggregates' sizes as well as their distribution in the reactor.