Surface microbubble nucleation in bulk nano/microbubble water and its impacts on flotation

• The dissolution of bulk nano/microbubbles facilitates the nucleation of surface microbubbles. • Contact lengths of surface microbubbles play an important role in the particle-bubble attachment process. • Contact lengths of surface microbubbles increase more rapidly on hydrophobic surfaces compared to hydrophilic surfaces. • Surface microbubbles can deteriorate the flotation performance of hydrophilic particles. The high Laplace pressure of bulk nano/microbubbles drives air molecules to dissolve into the surrounding liquid, thereby creating an air-oversaturated environment that promotes the nucleation of surface microbubbles on mineral surfaces. In this study, the dissolved oxygen concentration in the bulk nano/microbubble water was measured. Microflotation tests were carried out using graphite, quartz, and esterified quartz particles. Bubble collision and pick-up experiments were performed to evaluate particle floatability with and without surface bubble nucleation. Additionally, the nucleation and growth of individual microbubbles at artificial microcavities under hydrodynamic conditions were recorded using a microscopic camera. The flotation, bubble collision, and pick-up experiments confirmed that surface microbubbles promote particle attachment to carrier bubbles and facilitate the formation of agglomerations, thereby improving flotation recovery. Pick-up experiments further revealed that the contact length of surface microbubbles on particle surfaces is a critical factor governing particle-bubble attachment. Notably, the presence of microbubbles on hydrophilic particles was found to hinder their flotation. Microscopic observations revealed a faster increase in the contact length of surface microbubbles and a longer bubble growth time on hydrophobic surfaces compared to hydrophilic ones. These differences are key factors contributing to the enhanced flotation selectivity of hydrophobic particles.