A model of disjoining film rupture is presented in the context of bubble/particle flotation with viscous, surface tension, London-van der Waals dispersion, and hydrophobic attraction forces considered, Evolution equations are derived for three types of boundary conditions : (1) free bubble surface, (2) tangentially immobile bubble surface, and (3) nonconstant surface tension, Examples are shown where the film disjoins (stabilizes) and where the film drains and ruptures. A critical film height is related to the interaction parameters and the characteristic perturbation wavelength, Film rupture times are calculated in terms of both the magnitude of the hydrophobic attraction and the characteristic wavelength, An argument is given for associating the characteristic wavelength with particle dimension : the model predicts particles of intermediate sizes are preferentially floated, as observed in many flotation systems.