Confined particle bed comminution under compressive loads

Abstract

Eight minerals and ores were comminuted batchwise in a piston-die press under defined conditions that eliminated geometrical effects of the particle bed. The influence of bed pressure, material hardness and feed size on energy absorption, energy utilization and product size distributions was investigated. A set of compaction equations is proposed which provides explicit analytical expressions for relating pressure with piston travel distance, volume fraction of solids in the compressed bed and energy invested in the range of pressures studied. An energy utilization index is derived by coupling Rumpf's similarity law of fracture mechanics with self-similar size distributions of ground particles. It is suggested that this index is a consistent and meaningful measure of the grindability of a solid, whether it is ground in the particle bed or crushed in the single-particle mode. The mean ratio of grindabilities in the two modes for eight minerals and ores is about 0.46, which is in reasonable agreement with alternate estimates. Grinding virtually comes to a halt at higher pressures. Using the limiting values of fines produced and a characteristic energy parameter, the cumulative amount of fines passing a given size can be correlated with the energy expended by a single equation which is valid for all passing sizes and solids tested.