In this study the influence of impeller speed and superficial gas velocity on hydrodynamic parameters, bubble-particle collision frequency and efficiency using pure quartz particles of different sizes in an aerated Denver flotation cell was investigated. Collision frequency in different parts of cell was calculated by local turbulent energy dissipation rate measurements. Collision efficiency due to gravitational, inertial, interceptional and turbulence mechanism was determined. The overall collision efficiency (E-c) was also investigated. The results showed that the bubble-particle frequencies for different particle sizes in the turbulent zone were 10-12 times higher than in the quiescent zone. Under various hydrodynamic conditions, minimum and maximum values of E-c were observed for - 38 gm and - 300 + 212 mu m particles, respectively. The turbulence mechanism was the main collision mechanism for fine particles. The collision efficiency of coarse particles was mainly influenced by gravitational, inertial and interceptional mechanisms.