Interactions of NaCl with frother surfactants in producing microbubbles through modifying air/water interfacial energy and interfacial charge

Abstract

The interactions of NaCl with flotation frothers (i.e., weak surfactants) were investigated in the production of microbubbles at low frother concentrations far below their critical micelle concentrations. Two widely used flotation frothers, methyl isobutyl carbinol (MIBC) which is an alcohol-based frother and Dowfroth 250 (DF250) which is a polyglycol ether-based frother were studied. While in-situ measurements of microbubble number and size distribution were carried out to indicate the production of microbubbles, interfacial energy and interfacial charge were determined to understand the generation and stabilization of microbubbles. It was found that a synergy occurred between NaCl and the tested frothers in producing microbubbles. However, the significant synergistic effect was only observed at a low frother concentration. In the case of MIBC, the synergistic effect was weakened at the tested high MIBC concentrations of 16 and 40 mg/L. In the case of DF250, the synergy turned antagonistic as the addition of NaCl slightly enlarged the bubble size and significantly reduced the number of microbubbles at the tested high DF250 concentrations of 16 and 40 mg/L. The effects were explained through possible interactions of NaCl with interfacial water molecules and with the tested frothers as well as through the NaCl’s effect of compressing the electrical double layers of air bubbles.