Dodecylamine-promoted persistence of ultrasonication-generated microbubbles and its implications for quartz flotation

Dodecylamine (DDA), a cationic surfactant widely used in quartz flotation, can promote microbubble formation during ultrasonication; however, these ultrasonication-generated (UG) microbubbles may rapidly dissolve once the ultrasonic field is removed. This study hypothesizes that combining DDA with air oversaturation can markedly suppress post-ultrasonication microbubble dissolution and thereby enhance quartz flotation. UG bulk and surface microbubbles were characterized using dissolved-air measurements and optical imaging, while surface tension and contact angle measurements were used to elucidate the role of DDA. Flotation performance was evaluated using bubble pick-up and micro-flotation tests. DDA markedly increases the population of persistent UG microbubbles under air-oversaturated conditions, whereas no clear DDA-induced increase is observed under non-oversaturated conditions. This behavior is consistent with the coupled effects of air oversaturation and the DDA-induced reduction in gas-liquid interfacial tension, which together enhance the diffusive stability of microbubbles. The unexpectedly rapid decrease in bubble contact angle following bubble-solid contact in DDA solution suggests possible interfacial redistribution of DDA from the solid surface to the gas-liquid interface, which may accelerate the local reduction in gas-liquid interfacial tension. The resulting larger population of persistent microbubbles markedly enhances quartz-particle attachment to carrier bubbles and improves flotation recovery, highlighting the coupled roles of air oversaturation and surfactant adsorption in ultrasound-assisted flotation.