The residence time of liquid and solid was determined in flotation banks of mechanical cells and flotation columns at Salvador Division, Codelco-Chile. The estimation was developed from residence time distribution (RTD) measurements using radioactive tracers. Results allowed the estimation of effective pulp volumes in flotation banks and columns. It was found that industrial flotation banks are properly modeled by a number of perfect mixers in series equivalent to the number of cells in the bank. However, large size flotation columns are closer to a perfect mixer. Measurement of RTD also allowed the identification of operating control problems such as solid sedimentation and excessive tailings valves manipulation.