The formation of bubble clusters in flotation cells

Abstract We describe experiments in which the sizes of bubbles generated in a flotation cell were measured using high-speed video images. It was observed that in the presence of floatable solids, bubble clusters would form, held together by particles that attach to two or more bubbles and form stable bridges between them. The characteristics of clusters formed in the flotation of silica with dodecylamine (DDA) as collector, are reported. The size of the clusters is found to increase with increasing concentration of collector, probably because of its influence on the hydrophobicity of the silica. The mean size of bubbles within the clusters was generally higher than those that had not aggregated, suggesting that the rate of aggregation increases with increasing bubble diameter. The fraction of bubbles that were involved in clusters was found to increase with increasing DDA addition, reaching as high as 68 percent. There was a strong correlation between the fraction in clusters, and published values of the contact angle of DDA solutions and quartz. Previously unpublished photographs of bubble clusters rising out of industrial flotation cells are presented, that provide further evidence of cluster formation. The mechanics of cluster formation are discussed, and the implications for the modelling of the flotation process, and the performance of flotation cells, are explored. Clusters would be expected to lead to increased entrainment of non-floating particles into the froth in industrial cells, resulting in reduced product purity or grade. Cluster formation would be expected to increase the flotation recovery of coarse particles.

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