Understanding the mechanism of froth flotation of molybdenite using oily collectors from a perspective of thinning and rupture of thin liquid film

Froth flotation of molybdenite is commonly achieved using hydrocarbon oils as the collector. The insoluble hydrocarbon oils adsorb on molybdenite surfaces, resulting in an increase in its surface hydrophobicity and thereby its flotation recovery. However, the underlying mechanism on a microscopic scale was poorly understood. In this study, the effect of insoluble oily collectors on thinning and rupture of thin liquid films (TLFs) between air bubbles and molybdenite face surfaces has been investigated by monitoring the spatial and temporal evolution of the TLFs using a synchronized tri-wavelength reflection interferometry microscope (STRIM) as well as by drop size and contact angle measurements. Two hydrocarbon oils, namely kerosene and dodecane, have been studied. The result from the STRIM measurements shows that the TLF is stable in a 1 mM NaCl solution between an air bubble and a molybdenite face surface despite the molybdenite face being hydrophobic. The TLF becomes unstable when the surface is treated in both dodecane and kerosene emulsion solutions and ruptures at a critical rupture thickness of 60-340 nm. The film rupture is predominantly attributed to the instability of the TLFs between air bubbles and oil droplets adsorbed on the molybdenite surfaces. It is found that both the thinning kinetics and the rupture thicknesses of the TLFs correlate with both the coverage and sizes of the oil droplets on molybdenite surfaces. Kerosene exhibits a better dispersibility in DI water than dodecane, and therefore performs better as the collector than dodecane from a perspective of film stability. The present work provides new insight into the underlying mechanism of oily collectors in the froth flotation of molybdenite and other naturally hydrophobic minerals. The result obtained from this study enables the development of new oil collectors in the future.