A Novel Approach for Improving Column Flotation of Fine and Coarse Coal

Abstract

Froth flotation, applied to the separation of solid particulates, has been practiced commercially for a long time in the coal and mineral industries. The potential benefits of establishing a deep froth, especially in column flotation have been shown by a number of researchers and that includes demonstrating that the froth phase is much more efficient at mineral upgrading than is the pulp phase. This approach could be useful in where the particles have difficulty in reporting from pulp phase to froth phase. Hence, it is expected that introduction of particles into the froth phase will significantly improve the grade and recovery of particles. In this article, a novel way of operating a flotation column was implemented, and the results were compared to those when operating the same column in the conventional fashion. Tests were conducted with both fine and coarse coals. Feeding into the froth zone enhances bubble-particle contact as observed by a higher product yield of 79.4% compared to a conventional column flotation yield of 73.4%, both at about 9% product ash. It was also observed that the novel froth feed improved the recovery of coarse (+1 mm) coal particles from 0.9 wt% to 2.2 wt% compared to the conventional way of feeding slurry to pulp. Similarly, recovery of 1 × 0.6 mm particles improved from 4.6 wt% to 8.3 wt% at the same ash level. Positive results were also obtained by external reflux of a portion of the concentrate back into the top of the column. The potential to simultaneously achieve improvement in both recovery and grade can be explained by application of conventional mass transfer concepts, analogous to developments in two-phase foam fractionation.