Mean residence time (MRT) in a flotation cell is one of the most important parameters especially in terms of designing aspect and also as a key factor on recovery. The objective of determining MRT was to evaluate the effectiveness of this factor on industrial flotation cells as well as its role on 8% and 4% reduction on rougher and final flotation cells recoveries at Sarcheshmeh concentrator, respectively. Therefore, this paper was aimed to determine it by taking advantage of salt tracer. Results showed that, MRT in rougher cells at feed rate of 225 t/h and 280 t/h were 11.79 and 10.00 minutes, respectively. Also, the results indicated that the mixing condition of slurry inside the rougher cells follows N-Mixer model. RTD curves along with size-by-size copper recovery analysis of particles in different cells pointed out that, decreased residence time around 15% was the major cause of the lower recovery.