Abstract: In the process of fine mineral flotation， hydrophilic gangue minerals report into concentrate by froth entrainment， which leads to the decrease of concentrate grade. To reveal the theories of water drainage and gangue particles drainage will provide theoretical basis for the research of foam structure and foam entrainment behavior in flotation. The froth entrainment of gangue is a common phenomenon in the process of flotation. There is a liner relationship between recovery of gangue entrainment and recovery of concentrate water. Two-phase foam drainage is controlled by gravity， capillary force （surface tension） and viscous force. The water drainage of two-phase foam with different liquid content follows different drainage formula. The drainage of gangue particles of three-phase foam follows the convection-diffusion model； the entrainment recovery rate of gangue is controlled by the water drainage and the concentration distribution of gangue particles. Flotation operation conditions， hydrophilic gangue characteristics， slurry characteristics and foam structure are the main factors affecting foam entrainment. Optimization of flotation operation conditions， change of flotation flow sheet and reagent scheme can effectively reduce the foam entrainment of gangue and improve flotation selectivity. In the future， it is necessary to develop methods， devices or instruments to characterize three-phase flotation froth. The structure and morphology of three-phase froth， the movement path and distribution law of hydrophobic mineral particles and hydrophilic gangue particles in the froth， the mathematical model of water drainage and gangue drainage in three-phase flotation froth also need to be detailed studied. In addition， although the technologies developed could effectively reduce the foam entrainment of gangue， it is still difficult to eliminate the froth entrainment of gangue， thus some revolutionary technologies must be developed.

Key words: Froth entrainment, Affecting factors, Two-phase foam, Three-phase froth