Fluidized bed desliming in fine particle flotation – Part III flotation of difficult to clean coal

•The novel Reflux Flotation Cell is tested using industrial coal flotation feeds.•Separation and concentration of coal was achieved beyond the flooding condition.•Recovery and product ash results closely aligned with the Tree Flotation Curve.•Intense hydrodynamics selectively recovers the more hydrophobic particles.

A novel flotation system was used to process fine coal feeds supplied from coal preparation plants. The system consisted of an inverted fluidized bed arranged above a system of inclined channels. High fluidization (wash water) fluxes were imposed through a distributor enclosing the free-surface, producing strong positive bias of up to 2.4 cm/s, ideal for desliming. High gas fluxes of up to 2.6 cm/s, in excess of the flooding condition, were also imposed. The presence of the inclined channels prevented the entrainment of gas bubbles into the tailings stream. This paper, which is the third in a series, examines, for the first time, the hydrodynamic performance of this system on two actual plant feeds, each known to be difficult to wash. The first feed was a poorly liberated coal with particle size <260 μm and 69% feed ash. The second was a well liberated coal with nominal size <125 μm and 83% less than 38 μm. The product ash was shown to decrease significantly with an increasing fluidization flux to gas flux ratio. The single stage flotation system demonstrated a performance capable of matching the Tree Flotation Curve with some cases in fact surpassing this result.

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