The settling behaviour and rheological properties of microbubble-laden froth

In resource processing plants, dewatering froth concentrates is typically challenging due to the strong network structure of particles formed at the plateau borders of stable froth as observed in previous studies. However, these studies have overlooked the impact of bubbles which are essential components of froth. Given the unique properties of microbubbles, such as their ability to reduce the diffusion rate of core gas and withstand mechanical stresses, the objectives of this study were to determine whether microbubbles exist in stable froth and to assess their effect on froth settling. Through settling tests and microscopy analysis, we confirmed the presence of microbubbles (<100 μm) alongside macrobubbles (>100 μm) in stable froth. The results revealed that macrobubble-laden froth readily coalesced during settling, whereas microbubble-laden froth maintained its integrity and moved upwards. Structural analysis further demonstrated that microbubble-laden froth, in contrast to macrobubble-laden froth, was densely packed with finer particles. The small radii of the microbubbles enhanced capillary forces, promoting particle adhesion to bubble surfaces and reducing the likelihood of particle detachment. In addition, amplitude sweep analysis in the oscillatory rheology measurement discovered that the unsettled microbubble-laden froth exhibited a wider linear viscoelastic (LVE) range and lower complex modulus (G*), indicating the froth possessing greater structural resilience with less rigidity under deformation. Meanwhile, frequency sweep analysis discovered lower storage modulus (G′) and loss modulus (G″) values of the unsettled microbubble-laden froth, suggesting that the froth, despite displaying a solid-like behaviour, was characterized by weaker particle interactions and a softer structural framework. These results indicated that the microbubble-laden froth possessed greater adaptability and structural compliance, enabling it to maintain integrity during the settlement process as the root cause of the difficult settling of stable froth. • Microbubbles were identified in flotation froth embedded around macrobubbles. • Dense microbubble-particle packing formed a highly resilient froth structure. • Strong capillary forces from microbubbles prevented particle detachment. • Microbubble-laden froth showed weaker interactions but higher structural adaptability. • Microbubble-laden froth maintained structural integrity and resistance to collapse.