**2. Results and applications**

Residence time distribution measurements have been developed for flotation cells of 45, 100, 130, 160, 250 and 300 m3; this has allowed the evaluation of the mean residence time for liquid and solid per size classes. Also, internal properties such as mixing regime, mixing time, froth mean residence time and mineral entrainment in large industrial flotation cells have been characterized by using radioactive tracers. The measurement of RTD in parallel industrial flotation circuits allowed the identification of uneven pulp flowrate distribution. Applications and results of using radioisotopes to characterize the hydrodynamic behaviour of industrial flotation machines are presented as follows.
