Characterization and column flotation of bottom ashes from Tuncbilek power plant U. Demir, A. Yamik, S. Kelebek * ,1 , B. Oteyaka, A. Ucar, O. Sahbaz DPU, Faculty of Engineering, Department of Mining Engineering Kutahya, Turkey Received 19 February 2007; received in revised form 10 May 2007; accepted 18 May 2007 Available online 28 June 2007 Abstract 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 CO 2 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. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Bottom ash characterization; Unburned coal; Column flotation 1. Introduction Coals have the largest share of available fossil fuel reserves in the world and thus they are expected to play an important role in energy production in future [1]. While the use of coal increases, waste issues associated with coal production are attracting more and more attention. Solid products originating from coal combustion process include bottom ash, slag, fly ash and unburned carbon. Ashes con- taining slag and unburned coal represent a common waste in many countries and very often they end up in refuse ponds. The ashes contain oxides (Al 2 O 3 , Fe 2 O 3 , CaO, MgO etc.) which are potential ingredients for use as addi- tive in many applications such as cement/concrete, cera- mic, glass production, geotechnical (road construction, dam building etc.) and agricultural industries. Ashes also contain organic micropollutants hazardous to environment due to their high toxicity and heavy metals. Unburned car- bon in ash is the main source of micro pollutants. There- fore, separation of unburned coal serves a dual purpose: namely improving the quality of the non-combustible part, i.e., oxides and recycling of energy by the recovery of com- bustible part, i.e., unburned combustibles. There have been various studies carried out on the recovery of combustibles from ash materials. For example, Neiewiodomski et al. [2] used a flotation device called air-sparged hydrocyclone and reported a recovery of about 54% at a 35% combustible grade using a fly ash sample from coal burning power plant. More recently, Huang et al. [3] reported removal of unburned carbon using a 55 cm tall flotation column with a 61.2 % recovery at a pH around 6, which dropped to a recovery of 25.4% at a pH of 7. Column flotation is an important method of mineral processing technology. It is regarded to have reached its maturity and offers some advantages over the conventional flotation. The advantages include the requirement of less 0016-2361/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2007.05.040 * Corresponding author. E-mail address: kelebek-s@mine.queensu.ca (S. Kelebek). 1 On leave from Queen’s University, Kingston, ON, Canada K7L 3N6. www.fuelfirst.com Available online at www.sciencedirect.com Fuel 87 (2008) 666–672