Coagulative colloidal gas aphrons generated from polyaluminum chloride (PACl)/dodecyl dimethyl betaine (BS-12) solution: Interfacial characteristics and flotation potential

•PACl/(BS-12) complex sheds lights on its application in bubble functionalization.•Inorganic polymeric coagulant is effectively surface modified on microbubbles.•PACl concentration is key to stability of coagulative CGAs and nanosilica removal.•Flotation performs better at higher stability of coagulative CGAs.•Coagulant is dosed during bubble creation and no chemical-addition unit is needed.

Bubble surface functionalization is promising in flotation in terms of stronger bubble-particle interaction, less chemical consumption, more flexible and pollutant-oriented. In this study, the coagulant-modified microbubbles were generated via colloidal gas aphrons (CGAs) technique; the specific bubble characteristics and flotation efficiency in removing nanosilica were investigated. The coagulative CGAs were generated from a mixed system consisting of zwitterionic surfactant (dodecyl dimethyl betaine, BS-12) and inorganic polymer coagulants (polyaluminium chloride, PACl). Results denoted that the bubble generation capability of the mixed solution was well maintained; meanwhile, the observed large aggregates indicated the possible interaction between PACl and BS-12. The generated PACl-modified CGAs exhibited a typical CGA morphology with the averaged diameter of 46-100 μm. It should be noted that the stability of these positively surface-charged bubbles was strongly influenced by the PACl concentration. The half-life reached ∼100 s at the optimum PACl concentration range of 0.92-1.17 mmol Al/L. The interaction mechanisms between PACl and BS-12 as well as CGAs were speculated: one the one hand, the monomer Al species might interact with the BS-12 molecules and coat on the CGA surface; on the other hand, the polymerized Al species probably acted as bridge/net in which the BS-12 micelles and CGAs were embedded. Particularly, the coagulative CGA-involved flotation could remove approximately 81% of nanosilica, and a reinforced flotation process was thus achieved.

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