Fast flotation of coal at low pulp density using the Reflux Flotation Cell

•Fast flotation was investigated in a novel single-stage flotation cell.•Fast flotation maximises flotation kinetics, segregation, and interfacial flux.•Inclined channels enhance segregation, permitting extreme feed and gas fluxes.•Separation occurred using an extremely low cell residence time of 25 s.•Good recovery of fine coal particles was achieved from very low pulp density feed.

Fast particle flotation is accomplished by maximising three fundamental aspects: the kinetics of particle–bubble attachment, the bubble interfacial flux for particle extraction, and the rate of bubble–liquid segregation. In practice, it has been impossible to extend all three aspects simultaneously using conventional flotation devices. Hence, significantly higher processing rates using a single flotation cell has not been possible. Here, the Reflux Flotation Cell has been used in this work to address all three aspects in unison in a single stage of separation. This novel system permits throughput rates well beyond conventional flotation standards. Stable operation using extreme gas and feed fluxes is accomplished using a system of parallel inclined channels located below the vertical portion of the cell. In this paper a highly diluted coal feed comprised of well-liberated coal particles at 0.35 wt% solids, was prepared from hydrocyclone overflow. The volumetric feed flux was increased to nearly 10 times the typical conventional level, achieving an extremely low cell residence time, in the order of 25 s. Very good combustible recoveries were obtained, with the +38 μm portion increasing from 92.3% to 98.5% with increasing gas flux. The partitioning of particles below 38 μm decreased with decreasing particle size until separation became governed by hydraulic entrainment, clearly evident at a particle diameter of ∼1.65 μm.

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