Nucleation control in precipitation processes by ultrasound

Abstract

The effect of an ultrasonic field on the precipitation process of barium sulphate has been investigated. Experiments in a semi-batch precipitator showed that small crystal sizes with narrow distribution are obtained with ultrasound in a very reproducible way; however, this effect could not be assigned to an improvement in micromixing. Experiments on continuous precipitation of barium sulphate in two reactors in series were carried out in order to characterise the effect of ultrasound on precipitation, by separating the nucleation and growth processes. It was concluded that the main effect of ultrasound is an enhancement of secondary contact nucleation by acoustic cavitation. This change in the precipitation process allows small crystals with uniform size and shape to be obtained without effect of mechanical mixing. It is only necessary to sonicate the mixing volume of the reactants with a low level of ultrasonic power: this is very promising for industrial applications.