A cascading sequence of two Reflux Classifiers was used to beneficiate fine coal less than 2 mm in size; firstly to achieve a gravity concentration of the coal, and secondly to remove the clays and mineral matter present in the first stage product. This work was motivated by the need to recover coal down to sizes approaching 0.10 mm, and by the need to produce a high quality slime free product. Although screen technology has improved, the capacity of screens at this aperture size is relatively low, and wear continues to be a significant concern. Hydrodynamic methods provide a solution, however these are strongly influenced by particle density, and hence the separation size of the coal is always far greater than that for the slimes. In the present study, a new and powerful gravity separation mechanism was applied using closely spaced inclined channels in a Reflux Classifier. This allowed gravity separation performance to be extended over a much broader size range than has been previously observed. The usual upper to lower size ratio, previously about eight fold, was increased to more than 30 fold. With this significant extension of the particle size range, much of the classification was achieved via the gravity separation stage, allowing the remaining classification stage to be applied to the relatively fine mineral matter, typically less than 0.038 mm. The net result of this approach was the achievement of clean coal separations at target sizes ranging from 0.040 to 0.25 mm.
Thirteenth Australian Coal Preparation Conference. Proceedings of the Thirteenth Australian Coal Preparation Conference: Advancing Coal Preparation Technologies for our Future (Mackay, QLD 12-17 September, 2010) p. 224-235