Kinetics, energy characteristics, and intensification of crystallization processes in chemical precipitation of hardness ions

Abstract

An analysis of the literature data on the solubility and kinetics of the chemical (reagent) precipitation of calcium carbonate and magnesium hydroxide is performed. The possible causes of the significant discrepancy in the available data are considered. The kinetics of the homogeneous and heterogeneous crystallization of calcium carbonate and magnesium hydroxide in reagent precipitation is studied using different methods. It is shown that the use of heterogeneous crystallization on seed particles pretreated in an ultrasonic field raises the rate of crystallization by an order of magnitude. The kinetics of nucleation is studied; the effect of supersaturation and temperature on the induction period in the homogeneous and heterogeneous nucleation of CaCO3 and Mg(OH)2 crystals is investigated. The energy characteristics of nucleation, namely, the interfacial tension (surface energy) and activation energy, are determined. The use of fine-dispersed particles activated by ultrasound makes it possible to considerably reduce the energy barrier for nucleation.