Detailed characterisation and separation of fly ash fed to the Inverted Reflux Classifier

This paper provides a detailed analysis of the separation of valuable cenospheres from different fly ash feeds using the Inverted Reflux Classifier (IRC). Even though the IRC was found to be effective in recovering cenospheres [A. Kiani, J. Zhou, K.P. Galvin, Upgrading of positively buoyant particles using an Inverted Reflux Classifier, Advance Powder Technology. 26 (2015a) 119–125], the separation performance can vary depending on the cenospheres and fly ash properties. A typical fly ash feed sample was characterised in terms of surface morphology, elemental composition, density and size distribution, providing more detail of the fly ash feed properties and their possible effects on the separation performance. The separation of cenospheres from three different fly ash feeds (Feed 1, Feed 2 and Feed 3) with the cenosphere concentrations at about 0.51 wt.%, 0.85 wt.% and 1.14 wt.%, respectively, was then examined using the IRC. Under the same operating conditions, about 64 wt.% and 93 wt.% of the cenospheres were recovered from the fly ash Feeds 2 and 3, respectively. For the fly ash Feed 1, only 49 wt.% of cenospheres was recovered despite the fact that the feed rate was lower. The results support the proposition that by increasing the cenosphere concentrations in the fly ash feed, the positively buoyant particles are more likely to form streaming structures and can be separated much more effectively from the negatively buoyant fly ash particles [A. Kiani, J. Zhou, K.P. Galvin, Enhanced recovery and concentration of positively buoyant cenospheres from negatively buoyant fly ash particles using the Inverted Reflux Classifier, Minerals Engineering, 79 (2015b) 1–9]. Moreover, the separation of cenosphere particles in Feed 3 was further promoted by the presence of larger particles, achieving a recovery of about 93 wt.% and grade of 80 wt.% at a high solids throughput of 4.9 t/(m² h).