In this research on the solid products of the Elcogas IGCC plant (Puertollano, Spain) the influence of the two fuels, coal and pet coke, on the composition of the fly ashes and slag is demonstrated and how the majority of the elements are provided by the coal and only some as V, Ni and Mo are provided by the pet coke. The different nature of slag and fly ashes is highlighted and how the different elements are distributed between them that in general follow the indications of the mathematical models. The passage of the elements into gaseous phase is calculated. The fly ashes are some products of very fine granulometry that present problems of solubilization of a series of elements and therefore of deposition. Their inertization has been investigated by calcination at 1000 degrees C and with additives. Some good results have been obtained. (c) 2006 Elsevier Ltd. All rights reserved.