Zeolitic material was synthesised from fly ash using two different conversion methodologies. The two conversion products obtained were: (a) impure zeolitic material obtained by direct conversion from different Spanish fly ashes, and (b) a high purity 4A-X zeolite blend synthesised from the silica extracts obtained from the Meirama fly ash (NW Spain). The zeolitic material was tested for potential application as an ion exchanger to decontaminate waters containing high concentrations of ammonium and heavy metals. Preliminary results show high cation uptake efficiencies (up to 4.7 meq g(-1)) which allowed fast decontamination of different types of industrial or acidic mine waste waters. The CO2, SO2 and NH3 sorption capacity of several zeolitic products was also determined and very promising results were obtained for the A4-X blend. Sorption capacity values of up to 74, 297, and 111 mg g(-1) for CO2, SO2 and NH3 respectively were obtained for the zeolitic material synthesised from silica extracts from fly ash and a high-aluminate waste water.