Flotation separation processes important to paper recycling were studied using high-speed and high-magnification visualization techniques. Toner ink and model particle interactions with stationary and flowing bubbles in several system chemistries and flow facilities are discussed. Visualizations and image analysis results relate particle and bubble adhesion to particle and bubble properties, surfactants, calcium concentration, and flow parameters. Estimates for the probabilities of particle to bubble collisions, adhesion, and stable attachment determined experimentally were found to differ from probabilities based on predictive modeling.