Froth flotation is a widely used process of particle separation exploiting differences in surface properties. The froth performance in a flotation cell is expected to be affected by the froth rheology, as it affects the froth residence time that determines the probability of recovery of valuable minerals in the froth phase. Flotation froths have a similar structure to the gas-liquid foams whose rheology has been widely studied. However, to date, very little work has been done in the rheology of flotation froths owing to their instability and the presence of solid particles (on bubble surfaces and in the Plateau borders) that are believed to influence froth rheology and complicate any investigation. In this paper, the effects of froth properties on froth rheology were studied by examining the results of 33 flotation tests performed under various conditions that resulted in changes in the froth properties and, consequently, the froth rheology. The experiments were performed in a 20 L continuous flotation cell. It was found that the bubble size and the fraction of lamellae covered by solids defined the froth rheology, while the presence of particles in the Plateau borders contributed very little to the froth rheology. A model structure was developed by taking into account froth properties to predict froth viscosity.
In froth flotation, the degree of entrainment affects the concentrate grade and it is often assumed to be only a function of particle size in models. Literature suggests that other variables might also have a significant impact on the degree of entrainment. In this study, a factorial batch flotation experiment using a mixture of liberated chalcopyrite and two liberated gangue minerals, quartz and hematite, was performed to investigate the effects of these other variables (including impeller speed, gas flowrate, froth height and the specific gravity of gangue mineral) on the degree of entrainment. Results show that the degree of entrainment varied significantly as the flotation test conditions changed. Particle density and the interaction between gas flowrate and froth height had a statistically significant effect on the average degree of entrainment measured for the entire test. The degree of entrainment also significantly changed with flotation time throughout each experiment. It is hypothesised that these effects are a consequence of the degree of entrainment being affected by the weight of particles (not just their size) because of its effect on particle settling as well as the froth structure which provides varying resistance to particle drainage. It is concluded that models for the degree of entrainment that incorporate only particle size are not sufficient to predict gangue recovery and concentrate grade in an industrial application.
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