The effect of froth on the dewatering of coals – An oscillatory rheology study

Abstract

Dewatering of fine coal flotation products is discouraged by the presence of stable coal froth, which is becoming a common problem in coal preparation plants, however, the underpinning mechanism is still unclear. In this study, the dewatering behaviours of fine coal flotation products in both thickening and filtration were investigated and compared with those of coal slurry under the same condition. The mechanism that how coal froth influenced dewatering was investigated by analysing the froth properties using oscillatory rheology in conjunction with the characterization of particle arrangements on the air-water interface using Scanning Electron Microscopy (SEM). It was found that, in the presence of air, particle interactions in coal froth were stronger than those in coal slurry, which was caused by the capillary attractive force between particles on the air-water interface. In addition, particles in coal froth were arranged regularly, while particles in coal slurry were distributed randomly. Strong particle interactions and well organised structures in coal froth made the capillary radii smaller, and as a result, a large amount of froth stabilized on top of water during settling and the final moisture of filter cake was high in filtration.