A new approach to characterizing the mixing evolution and mass transport patterns in big flotation cells was developed. The procedure consists of using a non-invasive radioisotope tracer technique which allows for the continuous measurement of the local concentration of liquid and solid phases at different points in the cell. This approach was developed to characterize the mixing performance of a 130 m(3) self-aerated flotation cell at El Teniente copper concentrator, Codelco, Chile. Short-term mixing was experimentally characterized by using appropriate radioisotope tracers for liquid and solids. (82)Br in solution was used as liquid tracer and (24)Na was used to trace the solid, considering three particle size classes: +150, -150+45 and -45 mu m, for non-floatable gangue mineral. From the experimental data, a dynamic mixing model was developed to represent the internal short time mixing, as well as the overall mixing conditions in the pulp and froth zones in a big flotation cell. Results showed a mixing time of around 100 s, for liquid and solids, while the pulp mean residence time was 350 s. It was found that the feed pulp circulates 1.4 times through the impeller zone before reaching a well mixed condition in the cell. Also the feed pulp, on average, circulates approximately 5.0 times through the impeller zone, before leaving the cell into the tailings flowrate. From grade and solid percent axial profiles measurement, it was also shown that the pulp zone was reasonably well mixed with minor segregation of coarse minerals, and a very distinctive pulp-froth interface was clearly observed showing the significant Cu and Mo upgrading in the froth zone. (C) 2008 Elsevier B.V. All rights reserved.