Tricking the fractal nature of granular materials subjected to crushing

Abstract

When a confined granular material fractures under a high compressive load, its particle size distribution (PSD) evolves to reach the fractal distribution. Small particles fill the volume between the bigger ones. Next, even smaller particles fill the remaining space, repeating this pattern across different scales. Diversification of particle sizes is favourable for packing the material in a small volume which explains the occurrence of such a phenomenon. Here we show that the fractal nature of granular material subjected to crushing can be ‘tricked‘by substituting some of the original grains with uncrushable particles. During the compression, the PSD of such a mixture follows the same rule as the purely crushable material. That means the actual PSD, without uncrushable particles, is modified in a particular manner: unbreakable particles of a given size diminish the number of brittle particles of the same size in the fractured mixture. Our results demonstrate that the PSD of the crushed material can be easily controlled, hence optimized to increase the content of eligible fractions in the final product. We believe this method lays the foundations for developing new comminution techniques applicable to various fields of industry, such as mineral processing or recycling.