Study of Secondary Nucleation by Attrition of Potassium Alum Crystals Suspended in Different Solvents

Abstract

Secondary nucleation by attrition was studied in a milliliter-scale reactor, where the effects of different stirring rates and of different solvents were investigated. The experiments in suspension were performed in a Crystal16 system, and the evolution of the attrition process was monitored through transmissivity measurements, which can be qualitatively correlated to the number of attrition fragments produced, thus giving information about the extent of secondary nucleation by attrition, if other crystallization phenomena are not present. Higher stirring intensities correspond to faster and more intense production of attrition fragments, as expected. In order to explain the transmissivity measurements in the case of different solvents, an interpretation involving the difference between fluid and crystal densities, and polarity was developed, which is consistent with the experimental evidence. The difference in density between the crystals and the solvent influences the amount and the rate of production of fines (buoyancy and breakage), while polarity affects agglomeration. The determination of a secondary nucleation rate from the attrition experiments is not straightforward, and it has not been performed in this work, since the final result is a superposition of different effects, i.e., production of fines and agglomeration, depending on the fluid dynamics and the operating conditions of the system.