A new paradigm of bubble-particle detachment interaction: How and where do the bubble and the particle detach?
The flotation of coarse in particular partially liberated particles has attracted both industry and research interests in recent years as it can bring several benefits to existing operations, including the decrease in grinding energy and media consumption, the increase in plant throughput, and environmental benefits. The bubble-particle detachment is critical to this flotation process. Here, we have investigated the physics underlying the bubbleparticle detachment and discovered a new paradigm, i.e., the bubble and particle do not detach at the threephase gas-liquid-solid contact (TPC) line between the bubble and the particle, which contradicts the conventional consideration in the available theories. Our high-speed video movies show that the bubble-particle detachment does take place at a capillary neck of the air-water interface near the solid surface. The detachment always leaves a tiny residual volume of gas on the solid surface. Our experiments also show that the detachment interaction does not simply follow the slip mode of the TPC motion but rather a combined slip-stick mode of the TPC line relaxation. We rationalize our observations by considering the contact angle hysteresis, which always exists on the real particle surfaces having morphological roughness and chemical heterogeneity. The new evidence challenges the existing theories about the bubble-particle detachment interaction in flotation and urges further investigations to overcome the inconsistent predictions.