Particle shape effects in flotation. Part 1: Microscale experimental observations

Abstract

There has long been speculation as to whether some particle shapes are more ‘floatable’ than others, which might be due to differences in the induction period required to achieve attachment between the particles and the air bubbles in the pulp. To resolve this, we used the Milli-Timer apparatus to directly observe the process of particle–bubble interaction and attachment by means of a magnified, high-speed video recording, thus providing a direct measure of the induction period for attachment.To assess the influence of particle shape on induction time we used two varieties of methylated borosilicate glass particles — spheres and angular ‘frit’ — in a range of tightly-sized fractions. Other factors that could affect the induction time, such as the polar angle of sliding commencement, and approach velocity, are accounted for using multiple nonlinear regression.Our results illustrate the importance of particle shape on induction period, with angular particles exhibiting induction periods that were an order of magnitude lower than those of spheres. Furthermore, the induction period was seen to decrease with increasing particle velocity, or kinetic energy on approach, but increased as the trajectory approached the limit of just grazing the bubble. These results indicate that attention should be paid to the shape of particles obtained from the grinding operation, besides particle size.