The discrete element method for fine grinding scale-up in Hicom mills

The Hicom mill is a high-intensity grinding mill in which the grinding media tumbles in a strong centrifugal acceleration field. Typical applications include wet or dry fine grinding, liberation and concentration of diamonds, and breaking up mineral agglomerates and clay balls. When fine grinding, the intense grinding environment results in a rapid production of very fine material from most mineral ores, down to below 10 mu m However, scale-up from laboratory size data to industrial sized mills becomes increasingly difficult as the product size becomes finer. The discrete element method (DEM) is a computation technique which models the movement of collections of separate particles. DEM can be used to track individual collisions as particles tumble over each other, and to calculate the energy associated with each collision. It is shown how DEM techniques can be applied to the grinding media in a Hicom mill to produce frequency distribution plots of collision energies under different mill operating conditions, including ball size and density, mill speed and mill diameter. These results are shown to be well-correlated with conventional experimental and theoretical results for Hicom mills. The efficiency of fine grinding in the Hicom mill can be correlated with collision energies calculated by DEM. This has resulted in improved scale-up methods for fine grinding in the Hicom mill. (C) 1999 Elsevier Science S.A. All rights reserved.