Predicting bubble coarsening in flotation froth: Effect of contact angle and particle size

A froth model has been developed from first principles to predict bubble coarsening and to better understand the complex mechanisms involved in froth stability. The model is based on predicting the kinetics of film thinning and the critical rupture thickness using the Reynolds lubrication theory and the capillary wave model, respectively. The macroscopic capillary pressure that drives initial film thinning has been corrected for the local capillary pressures in the menisci around the particles adsorbed in lamella films. It has been found that the latter varies with contact angle (theta) and particle size. At theta < 90 degrees, the local capillary pressure constitutes a resistance to film thinning, which in turn varies with particle loading. The model shows that a froth acquires a kinetic stability when film thinning slows down due to the presence of particles despite the negative disjoining pressures of the film segments that are free of particles. A series of flotation tests conducted with 35 mu m glass spheres in the presence of 10(-5) M MIBC show that bubble coarsening as measured by the ratio between the bubble sizes at the top and bottom of a froth phase is minimum at theta = 70 degrees, which corresponds to the experimental data obtained in the present work and by others. The tests conducted with glass spheres with theta = 40 degrees show that bubble coarsening increases with particle size due to the high probability of particle detachment. Thus, the model is capable of predicting bubble coarsening in froth phase as functions of different physical, chemical, and operational variables.