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Zeolitic material was synthesised from¯y ash using two different conversion methodologies. The two conversion products obtained were: (a) impure zeolitic material obtained by direct conversion from different Spanish¯y ashes, and (b) a high purity 4A±X zeolite blend synthesised from the silica extracts obtained from the Meirama¯y 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 ef®ciencies (up to 4.7 meq g À1 ) which allowed fast decontamination of different types of industrial or acidic mine waste waters. The CO 2 , SO 2 and NH 3 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 À1 for CO 2 , SO 2 and NH 3 respectively were obtained for the zeolitic material synthesised from silica extracts from¯y ash and a high-aluminate waste water.

A high Al±Si Chinese¯y ash from Dou He power plant (Tangshan city, Hebei Province, Eastern China) was selected as starting material of the zeolitisation process. Zeolitic material was obtained by conventional alkaline activation using NaOH and KOH solutions. The process of synthesis was optimised by applying a wide range of reaction temperature, time and activation reagent concentrations. A high solution/¯y ash ratio was used in order to dissolve highly resistant Al±Si phases such as mullite. High yields were obtained with both KOH and NaOH solutions. Final products reached a cation exchange capacity (CEC) of up to 2.3 meq g À1