Unveiling the role of anionic polyacrylamide flocculants in nanobubble generation and stabilization

Nanobubbles (NBs) are gaining prominence in mineral processing due to their ability to enhance mineral separation, reduce reagent consumption and improve overall process efficiency. Although the role of surfactants in NB generation and stabilization is well documented, the impact of flocculants, despite their structural similarities and extensive use in mineral systems, has received little attention. This study investigated the potential of two anionic polyacrylamide (APAM) flocculants, AN 934 and its higher molecular weight variant AN 934 VHM, to promote NB formation and stability. Remarkably, both flocculants produced NB concentrations comparable to those generated by the conventional anionic surfactant sodium oleate (NaOL), despite exhibiting negligible surface activity and minimal surface tension reduction. Instead, their stabilizing effect was driven by two key mechanisms: enhanced electrostatic repulsion indicated by significantly more negative zeta potentials, and increased solution viscosity which inhibited gas diffusion and bubble coalescence. AN 934 VHM demonstrated superior performance due to its higher molecular weight, yielding greater charge stabilization and viscosity enhancement, and thus more persistent NB populations. These findings reveal an unrecognized capability of APAM flocculants in NB stabilization, opening new avenues for their strategic use in flotation, tailings dewatering and other particle–bubble interaction-driven processes in mineral processing.