Understanding fine ore breakage in a laboratory scale ball mill using DEM Paul W. Cleary a, ⇑ , Rob D.Morrison b a CSIRO Mathematics, Informatics and Statistics, Private Bag 33, Clayton South 3168, Australia b JKMRC,The University of Queensland, 4068,Australia a r t i c l e i n f o Article history: Available online 1 February 2011 Keywords: DEM Breakage Ball mill Fine grinding Comminution a b s t r a c t DEM models of fine grinding in ball and stirred mills have to date almost entirely focused on the motion of the media and their interaction with the mill configuration. For SAG mills,a large fraction of the feed material can now be accurately represented in DEM models. However,for other mill types with much finer feed materials, such as the second chamber of a cement ball mill, the vast numbers of feed particles makes their explicit inclusion in the models prohibitive. However,it is now feasible to model a periodic section of a laboratory scale ball mill and include the coarser end of the ore size distribution directly in the DEM model. This provides the opportunity to better understand the effect of media on the interstitial bed of powder and of the effect of the powder on the media. The effect of the powder fill level, which is varied between 0% and 150% of the pore space in the media charge, is explored.The distribution of the powder, its effect on power draw and the way in which it contributes to the pattern of energy utilisation is assessed.The simulation results are compared with experimental results from a test at similar ball loading and rotation rate and for several size fractions of ore at a range of powder fill fractions. Tracking the collision histories of specific ore particles within the charge allows estimates of the probability (per unit time) of collision between media and ore particles (the ‘‘Selection’’ function) and of the intensity of each collision which can be used to estimate the severity of breakage using the JKMRC breakage model (the ‘‘Breakage’’ function). The energy spectra indicate that for a typical ore, only very few collisions are large enough to cause damage to the body of each particle. This provides an estimate of the energy effi- ciency which is less than 10% at even the best operating conditions. Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved. 1. Introduction Many researchers have used DEM to estimate media motion in ball mills, but the huge numbers of ore particles have often pre- cluded their inclusion in these simulations. The earliest two dimensionalDEM work on media only motion in ball mills was by Mishra and Rajamani (1992, 1994). Cleary (1998,2001a,b) in- cluded coarse feed into more detailed two dimensional ball mill models. These are most analogous to ball mills being used for coarse ore re-grinding or the first chamber of a cement (clinker) ball mill which has a coarse feed. Cleary and Sawley (2002) used a three dimensional slice model to explore the same type of coarse feed ball mill. Djordjevic (2003,2005) used 3D simulation to esti- mate the effect of charge size distribution and liner variations on power draw.Axial transport and grate discharge of a coarse rock and in a ball mill were also studied by Cleary (2006). Cleary et al. (2008) then used a slice modelto explore the effect of different coarse cement feed sizes in a first chamber ball mill. More recently, Cleary (2009a) used DEM to predict ball motion in both the first and second chamber of a full 13 m long by 4.4 m diameter cement ball mill. In contrast, for SAG mills which were first modelled by Rajama- ni and Mishra (1996) and subsequently by others (Cleary, 2001a,c; Herbst and Nordell, 2001; Morrison et al., 2001; Morrison and Cleary,2008) at least some fraction of the rock ore has been in- cluded. Cleary (2004) showed that modelling the complete mill with 95% of the rock size distribution was already possible at 1.8 m pilot scale. Cleary et al. (2008) presented 1.2 million particle slice model of a 36 0 SAG mill with a minimum particle size of 6 mm.With increasing computational power, full models of large SAG mills are now becoming possible. The fineness of the particles and their large numbers still repre- sents a major obstacle to including feed in fine grinding applica- tions. Cleary et al. (2008) included a coarse over-size feed in a slice model around one disk of an IsaMill to determine that the feed particles pack densely into the pore space between the media starting at the shell and filling inwards. For ball mills with a fine feed size, little is known about its distribution within the mill charge,its transport or the breakage environment that the fine powder is exposed to.The inclusion of powder is now computa- tionally feasible at laboratory or smallpilot mill scale.Here we 0892-6875/$ - see front matter Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2010.12.013 ⇑ Corresponding author. E-mail address: Paul.Cleary@csiro.au (P.W. Cleary). Minerals Engineering 24 (2011) 352–366 Contents lists available at ScienceDirect Minerals Engineering j o u r n a l h o me pa ge : w w w . e l s e v i e r . c o m / l o c a t e / m i n e n g