Fine grinding: How mill type affects particle shape characteristics and mineral liberation

In minerals beneficiation applications, the main function of comminution circuits is to liberate valuable minerals to facilitate downstream separation processes such as flotation. Traditionally, design and optimisation of comminution circuits was based on the production of a target particle size distribution at an optimised throughput with consideration of energy efficiency and equipment wear rates. However, research in flotation and process mineralogy is leading to queries as to whether more should be demanded from the comminution circuit in terms of particle preparation. For example if particle shape affects hydrophobicity, can mill operating conditions be adjusted to produce particles with shape characteristics which are more amenable to flotation? For this work UG2 ore (a South African platinum group mineral ore) was milled in a laboratory ball mill and stirred mill. To supplement the laboratory study, samples were taken from the fine grinding circuit of an operational UG2 concentrator. Automated Scanning Electron Microscopy with Energy Dispersive X-ray Spectrometry (Auto-SEM-EDS) was used for mineralogical and particle shape analysis of feed and product samples. Although the laboratory test work indicated a significant difference in product particle shape characteristics for the two mill types, the difference was not evident in the plant data.