Finnie et al. [Finnie, G.J., Kruyt, N.P., Ye M., Zeilstra, C., Kuipers, J.A.M., 2005. Longitudinal and transverse mixing in rotary kilns: a discrete element method approach. Chemical Engineering Science 60, 4083-4091] developed a discrete elemental model to simulate the mixing of solids in a rotary kiln. It is interesting to analyse and compare their results to those obtained through experimental observations such as those by Henein et al. [Henein, H., Brimacombe, J.K., Watkinson, A.P., 1983. Experimental study of transverse bed motion in rotary kilns. Metallurgical Transactions B 1413, 191-205] Van Puyvelde et al. [Van Puyvelde, D.R., Young, B.R., Wilson, M.A., Schmitd, S.J., 1999. Experimental determination of transverse mixing kinetics in a rolling drum by image analysis. Powder Technology 106, 183-191; 2000. Modelling transverse mixing in a rolling drum. Canadian Journal of Chemical Engineering 78, 635-642] and Mellmann [Mellmam, J., 2001. The transverse motion of solids in rotating cylinders-forms of motion and transition behavior. Powder Technology 118, 251-270]. (c) 2006 Elsevier Ltd. All rights reserved.