The Role of Particle Shape in Size Analysis and the Evaluation of Comminution Processes

Abstract

The shape of the particles produced by comminution is affected by the kind of breakage action employed. Furthermore, the procedures used to determine product particle size are themselves influenced by shape. Illustrative examples of the effects of shape on particle size analysis and of shape variations in comminuted material are presented. Light scattering size measurements on narrow sieve fractions were found to indicate size distributions that were significantly broader than the sieve size range, especially for irregularly shaped particles. The distributions were also shifted to coarser sizes for the irregular particles but not for spheres. The apparent size shift is attributed to differences in the definition of size, while it is proposed that the apparent broadening of the distribution is a result of orientation effects. It is shown that broadening is relatively insignificant for broad, continuous distributions due to compensation effects. Applications to the determination of composite distributions by combining sieving and light scattering data are described. Distributions of particle shape descriptors, obtained by image analysis of comminution products, are shown to depend on the comminution method used. A slight variation with size was observed for coal particles but not for quartz. The implications of the size/shape interaction on the evaluation of comminution process performance are discussed.