BUBBLE-PARTICLE ATTACHMENT

Bubble-particle attachment efficiencies have been determined by measuring the collection efficiencies of single bubbles, with diameters between 0.75 and 2.0 mm and methylated quartz particles, whose diameters ranged from 5 to 80 mu m, as a function of particle-water advancing contact angle and ionic strength. By performing experiments under conditions where the bubble-particle aggregate was stable and using a model for collision efficiency, both attachment efficiency and induction time were calculated. Smaller bubbles have larger attachment efficiencies than do larger bubbles for all particle sizes over a wide range of contact angles and ionic strengths. Induction times generally decrease with increasing attachment efficiency, except for fine particles with diameters less than about 10 mu m, where they increase. Induction-time trends may be qualitatively interpreted in terms of thin-film drainage time as well as the time of formation of a stable wetting perimeter. The elementary steps in the bubble-particle attachment process are not properly described by existing models.