Assessment of true flotation and entrainment in the flotation of submicron particles by fine bubbles

Entrainment can make an important contribution to recovery in the flotation of fine particles. This paper presents an experimental study into the recovery by true flotation and by entrainment, of colloidal silica and alumina particles with a size range from 40 to 160 nm in diameter. The flotation experiments were carried out in a small laboratory column-type cell with fine bubbles with typical average diameter of about 150 μm. No wash water was used. Cetyltrimethylammonium bromide and Dowfroth 250 were used as the collector and frother, respectively. The particle concentration in the pulp was about 1% by weight. In these experiments the total recovery of particles was low, typically 54% after 50 min. Four techniques, including three previously described in the literature and one newly developed in this study, were used to assess the true flotation due to the bubble-particle collection mechanism, and the entrainment. All employed techniques show that the proportion of the colloidal particles recovered by true flotation was quite high, varying from about 79–86% of the total recovery. The paper also discusses the mechanisms of minimising the entrainment of the colloidal particles in the laminar flow flotation regime with fine bubbles.