Disposal of a growing amount of fly ash creates environmental problems due to the leachability of their heavy metal content. However, fly ash is shown to be efficient in the removal of heavy metallic ions in the aqueous phase, for example, in the polluted wastewater resulting from desulfurization treatment in power plants. The objectives of this work were to study the removal of CU2+ and Zn2+ in water by sorption onto fly ash and fly ash mixture. The stability of the resulting cake was also approached in terms of leaching capability. Experimental design methodology was used in order to identify influential parameters and to evaluate their interactions. Temperature, fly ash to ion concentration ratio, and ash quality were particularly studied. Different ashes and a fly ash mixture were investigated. They each have alkaline reaction with water to a different extent, and this allows the control of the pH solution without lime addition. Final metal ion concentration in solution, sorption capacity and ion leaching were determined. The results are discussed in order to get the optimal operating parameters in terms of ion control to develop industrial techniques to remove and stabilize heavy metal ions present in wastewater. (C) 2001 Elsevier Science Ltd. All rights reserved.