Stability of a thin film of water formed between a bubble and a quartz surface with acoustic sound

Froth flotation, a versatile particle separation technology, is widely used for beneficiation of minerals. Central to the flotation process is the bubble-particle interaction. Recent research progress showed that flotation efficiency could be improved by acoustic sound, which was attributed to increased froth stability, but it was not clear as to whether the acoustic sound would also enhance the bubble-particle interaction. To fill this gap of knowledge, this paper explores the effect of acoustic sound on the stability of thin water film confined between an air bubble and a flat quartz substrate. The film lifetimes were measured by analyzing the optical images of the films recorded. The study considered three variables: sound frequency (in the range of 0.5–20 kHz), substrate hydrophobicity (with contact angle ranging from less than 5° to about 35°) and bubble size (0.7, 1.1, 1.4 and 1.7 mm). For any substrate hydrophobicity and bubble size tested, use of acoustic sound at frequencies of 3–20 kHz while keeping the same sound amplitude (88 ± 3 dB) would decrease the film lifetime, in favor of flotation; in contrast, mixed trends were observed at frequencies of 0.5–2 kHz, reflecting the complexity of the system. With or without the sound, the film lifetime would decrease with increasing substrate hydrophobicity or decreasing bubble size. The present work provides new insights into improvement of flotation with acoustic sound.