Influence of impact velocity on fragmentation and the energy efficiency of comminution

Abstract

Comminution processes such as crushing and grinding are essential stages in mining and mineral processing operations to reduce the size of ore and rock, and to liberate the valuable mineral for beneficiation. Comminution is energy-intensive and responsible for most of the energy used during mineral recovery. Energy efficiency is very low since almost all the energy is dissipated as heat instead of generating new surface area. This paper reports on studies conducted on strain rates achieved by various velocities of impacts that enhance energy efficiency and mineral liberation. The research focuses on understanding comminution fracture mechanics and on quantifying the distribution of energy with respect to generating new surface area. In interpreting breakage energy phenomena, accurate measurements of surface roughness and surface area are essential. A novel approach to measure surface roughness and surface area based on a fractal analysis procedure has been developed. Changes in surface roughness of broken specimens under variable loading rates were studied using a laser probe to generate 3D topographical maps of the fracture surfaces. The results indicate that surface roughness and hence, specific surface area, increase with increasing loading rate by several orders of magnitude as particle size decreases to ∼1 μm. Below this limit, surface roughness begins to diminish from particle–particle attrition. An apparatus to measure the quantitative parameters of impact at different velocities on aggregated rock samples is proposed. Experiments are being carried out at projectile velocities up to 500 m s −1 utilizing a compressed-air device. The results suggest possible efficiency improvements in breakage under the velocity of impact.