Comminution studies have been carried out by grinding narrowly sized fractions of single mineral feeds. Under these conditions, the mill environment remains self-similar and invariant which is a characteristic of the mill/material system. On the other hand, in industry, feed to the mill comprises oversize recycle and new feed that is highly heterogeneous and widely distributed in size. The objective of the present work is to compare the breakage kinetics and energetics of grinding coarse size feed in the presence of deliberately added fines for different material systems. Quartz, dolomite, and limestone mineral systems were selected as feed in order to study these phenomena for minerals whose hardness ranges from hard to soft, approximately from 7 to 3 on Moh's Scale of hardness, at different coarse/fine ratios. It was found that the cumulative breakage distribution functions for this situation do not change with mixture compositions for the three materials. On the other hand, the initial breakage rate function of the coarse particles increases with increasing proportion of fines in the mixture. It was also shown that the fines produced, and the coarse material retained on the top sieve were normalizable with respect to the specific energy consumed by the coarse fractions. A modified breakage rate function was used to simulate the grinding operation of the three material systems using the linear population balance model. As a result, reasonable agreement between the experimental data and the corresponding calculated values was achieved. (C) 2011 Elsevier B.V. All rights reserved.