The application of PEPT has allowed a detailed study of the motion of media in a stirred grinding mill. Further analysis of this motion has identified the main differences between this media motion and the classical theory of motion within fluid mixing. Three regions have been classified within the mill and it was found that the impeller speed altered the relative position of these regions. Three different impellers were also studied which gave different forms of motion. This fundamental knowledge was then applied to the mode of breakage within the mill. Results have shown that the size of these regions influences the breakage process. (C) 2002 Elsevier Science Ltd. All rights reserved.