Apart from the generation of fly ash, brine (hyper-saline wastewater) is also a waste material gen-erated in South African power stations as a result of water re-use. These waste materials contain major spe-cies such as Al, Si, Na, K, Ca, Mg, Cl and SO 4 . The co-disposal of fly ash and brine has been practiced by some power stations in South Africa with the aim of utilizing the fly ash to capture the salts in brine. The effect of the chemical interaction of the species contained in both fly ash and brine, when co-disposed, on the mobility of species in the fly ash–brine systems is the focus of this study. The up-flow percolation test was employed to determine the mobility of some major species in the fly ash–brine systems. The results of the analysed elu-ates from the up-flow percolation tests revealed that some species such as Al, Ca and Na were leached from the fly ash into the brine solution while some species such as Mg, Cl and SO 4 were removed to some extent from the brine solution during the interaction with fly ash. The pH of the up-flow percolation systems was observed to play a significant role on the mobility of major species from the fly ash–brine systems. The study showed that some major species such as Mg, Cl and SO 4 could be removed from brine solution using fly ash when certain amount of brine percolates through the ash.