Deviation from Young-Laplace theory in predicting bubble detachment in flotation

• Developed a novel experimental approach to investigate bubble-surface detachment. • Identified bubble necking as the primary detachment mechanism. • Demonstrated significant deviation from the predictions of classical Young-Laplace theory. • Highlighted the potential role of Gibbs-Marangoni flow in influencing the detachment. Bubble-particle (BP) detachment is a critical mechanism in flotation, particularly for enhancing coarse particle recovery. The Young-Laplace theory (YLT) has long served as the foundation for modeling BP interactions and predicting detachment behavior, typically assuming detachment occurs at the three-phase contact line (TPCL). Here, we conducted novel bubble detachment experiments by manipulating capillary forces via surfactant addition, which lowered surface tension while maintaining constant bubble volume and buoyancy. The experiments reaffirm that detachment consistently occurs at the bubble neck, not at the TPCL. The bubble detachment was quantified by applying the YLT to solve the Young-Laplace equation and fitting the result to the experimental bubble shapes. Unexpectedly, the fitted capillary lengths were found to increase with time in the late stage near the detachment point − departing from values predicted based on bulk surfactant concentrations. We attribute this discrepancy to a combination of Gibbs-Marangoni flow, arising from non-uniform surfactant distribution, and inertial effects, while ruling out contributions from dynamic surface tension or interfacial rheology. This study reveals key limitations in the conventional application of YLT and offers new insights into the complex physics governing BP detachment dynamics.