It is important to determine the contaminant retention characteristics of materials when assessing their suitability for use as liners in landfill sites. Sand–bentonite mixtures are commonly used as liners in the construction of landfill sites for industrial and hazardous wastes. Sand is considered to be a passive material with a negligible chemical retention capacity; fly ash, however, offers the additional advantage of adsorbing the heavy metals present in landfill leachates. There have been few studies of the contaminant retention characteristics of fly ash–bentonite mixes. The study reported here determined the contaminant retention characteristics of different fly ashes, bentonite and selected fly ash–bentonite mixes for Pb²⁺ using 24 h batch tests. The tests were conducted by varying the initial concentrations of metal ions under uncontrolled pH conditions. The efficiency of the removal of Pb²⁺ by the different types of fly ash and fly ash–bentonite mixes was studied. The influence of multiple sources of fly ash on the retention characteristics of fly ash–bentonite mixes was investigated.