Graphical abstract Highlights • Optimum SNP removal and CCGA stability were achieved at the pH near the IEP(C15B). • Additional salt content should be low for high CCGA stability and SNP removal. • The CCGA-induced flocs were of sphere-like morphology and smooth surface. • The regular chemical-dosing unit could be omitted from the CCGA-flotation. • Modifying PACl on CGAs led to higher SNP removal than adding it directly in water. Abstract The present work used the coagulative colloidal gas aphron (CCGA)-involved flotation as a robust technology to efficiently remove the typical engineered nanoparticles – silica nanoparticles (SNPs) from water. The inorganic polymer coagulant – polyaluminum chloride (PACl) was used to surface-functionalize the zwitterionic surfactant (C15B)-based CGAs. Results denote that the physicochemical conditions of PACl/C15B mixed solution markedly influenced the flotation behaviors by changing the properties of CCGAs. The C15B molecules showed different dissociated states and interaction behaviors with Al species with the variation of pH. The addition of salt into the PACl/C15B mixed solution decreased the foamability of solution, and the bubbles collapsed before they could efficiently capture SNPs in their rising trajectory. The optimum SNP removal (87.2%) was obtained when the pH and the additional ionic strength of PACl/C15B mixed solution were ∼4.7 and ≤ 1.0 g NaCl/L, individually, and the pH of SNP suspension was ∼9.4. Importantly, modifying PACl on microbubbles took greater advantages than directly using it as coagulant in terms of SNP removal and PACl utlization. The CCGAs were robust since their colloidal attraction and collision efficiency with SNPs were simultaneously enhanced. The PACl was more efficiently utilized during flotation whilst the regular chemical-dosing unit was omitted. [ABSTRACT FROM AUTHOR]