Effect of Salt on the Stability of Microbubbles in the Presence of Micro–Nanoparticles: Substantial Adsorption in the Separation of Particles by Flotation

This work presents the study of the stability of microbubbles based on the assemblage at air–water and liquid–solid interfaces with prominence on the systems containing surface-active agents and micro- or nanoparticles. Sodium chloride, lithium chloride, and cesium chloride salts in the presence of sodium dodecyl sulfate (an anionic surface-active agent) are efficient in decreasing the interfacial tension of air–water. For systems involving salt–water interfaces, the addition of salt effectively lowers the surface tension by reducing the critical micelle concentration (cmc) of the surface-active agent. The present observation shows the maximum decrease in the cmc with the addition of salt obtained in the order: CsCl > LiCl > NaCl. The insertion of negatively charged hydrophilic copper oxide nanoparticles (size < 50 nm, transmission electron microscopy) increases the efficacy of the microbubbles formulated with ionic surface-active molecules. This efficacy is due to the repulsive Coulomb interactions at the interfaces, which cause the adsorption at the interfaces. The stability of microbubbles increased with the increase in the concentration of salt in the case of CsCl, while it decreased for NaCl, and a mixed effect was observed with LiCl.