Bottom ashes from the Tuncbilek power plant have been characterized by size fraction, X-ray diffraction and X-ray Fluorescence. These samples are potentially of class F type and have significant amounts of unburned coal. The unburned coal specimens studied using Fourier Transform Infrared Spectroscopy indicated a significant loss of the aliphatic hydrocarbon groups (C-H) and the carbon bond C=C during their stay in the combustion environment. In contrast, they indicated insignificant levels of carbonyl group, C=O, possibly due to the loss of CO2 to air as well as carboxylic ions to disposal water. The effects of various operating variables on the combustible recovery and ash content determined using column flotation were limited due to severely oxidized state of unburned coal. Best set of results was obtained with the bottom ash sample from unit 3, which brought the ash content from 77.6% down to 42.6% at a combustible recovery of 53.8%, and the calorific value was increased from 1270 kcal/kg to 3840 kcal/kg. (C) 2007 Elsevier Ltd. All rights reserved.