In this work, a new method is presented to track discrete tracer particles in a two fluid model (TFM). This method is particularly useful for studying features of discrete particles, such as solids mixing. Following the implementation and verification of this method, its accuracy was studied. The results showed that the new method fulfills the continuity equation and it can represent individual solids motion very well. This method may suffer from false diffusion, which can be diminished by selecting a sufficiently small grid size. In addition, it has several advantages over other techniques, like simplicity, ease of implementation, straightforward processing and enabling the calculation of a mixing index based on the initial neighbor distance concept. Moreover, this method can open a new way to combine the TFM with Lagrangian approaches. After analyzing the strengths and drawbacks of our method and finding the proper simulation settings, the effects of superficial gas velocity and restitution coefficient on solids mixing were investigated. The results showed that the solids mixing is enhanced by increasing the gas velocity and/or decreasing the restitution coefficient. The observed trends can be attributed to altered bubble formation and dynamics. These results also confirm our earlier findings on the solids temperature distribution in fluidized beds for polyolefins production (Banaei et al., 2017). (C) 2018 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.