Adsorption of Cerium Salts and Cerium Oxide Nanoparticles on Microbubbles Can Be Induced by a Fluorocarbon Gas

Retrieving heavy metals from wastewaters has become an important environmental challenge. We report that exposing dilute aqueous solutions or dispersions of cerium compounds (CeO2, Ce­(SO4)2, CeF4) to perfluorohexane-saturated air results in substantial adsorption of these salts at the air/water interface, as consistently reflected by a marked decrease in interfacial tension, as assessed by bubble-shape profile analysis tensiometry. No detectable adsorption is observed in the absence of the fluorocarbon. Adsorption to the interface is also achieved when, and only when, CeO2 nanoparticle dispersions are exposed to the fluorocarbon vapor. We also found that microbubbles could be generated in cerium salt solutions and CeO2 nanoparticle dispersions when they are formed in the presence of perfluorohexane-saturated air, without need for any surfactant or chelating agent. Optical microscopy, static light scattering, and ζ potential measurements were used to establish the ability for the fluorocarbon to induce the formation and stabilize these microbubbles. These findings could provide the basis for a new approach to heavy metal (including radioactive element) recovery and recycling from industrial and other effluents that would combine ionic flotation and fluorocarbon gas-driven adsorption on microbubbles. Extraction of critical raw materials from dilute solutions could also be considered.