The surface energy and surface charge of microbubbles generated by frother surfactants

Abstract

Microbubbles (MBs) in froth flotation have the important function of facilitating the collision and attachment between air bubbles and hydrophobic materials and subsequently recovering the hydrophobic materials. However, whether MBs can be generated in a flotation cell by adding frother surfactants is unknown. This study was designed to determine whether the two widely used frothers, methyl isobutylcarbinol (MIBC), representing alcohol frothers, and Dowfroth 250 (DF250), representing polyglycol ether frothers, could help generate MBs in a mechanical flotation cell. The underpinning air/water interfacial properties were also studied in the presence of the two frothers. The real time bubble size measurement demonstrated that MBs could be generated in the mechanical flotation cell in the presence of MIBC or DF250, and DF250 produced more and smaller MBs than MIBC. Air/water interfacial tension and microbubble zeta potential measurements indicated that the generation of MBs by MIBC and DF250 was primarily controlled by their ability in reducing surface tension. While DF250 formed premicellar aggregates at air/water interfaces and reduced surface tension significantly, MIBC only formed monolayers at air/water interfaces and reduced surface tension slightly. However, the slower adsorption of DF250 at air/water interfaces inhibited the generation of MBs to some extent. Compared with surface tension, surface charge played a secondary role in generating MBs. The adsorption of MIBC reduced the magnitude of surface charge of MBs, thus inhibiting the generation of MBs, while the adsorption of DF250 increased the magnitude of surface charge of MBs, enhancing the generation of MBs. The different behaviours of MIBC and DF250 in modifying interfacial properties and forming MBs were attributed to their unique structures. DF250 possesses a larger hydrophilic head and a longer hydrophobic chain than MIBC, and thus has a stronger ability to assist with the generation of MBs.