Characterization of different coal fly ashes for their application in the synthesis of zeolite X as cation exchanger for soil remediation

Four different coal fly ashes have been characterized for their potential application in the synthesis of Zeolite X for its use as cation exchanger for the remediation of heavy metal-polluted soils. Their chemical composition, with particular attention to the concentration of trace elements potentially toxic for the environment, has been determined by total dissolution and ICP-OES analysis. The relative amount of Zeolite X synthesized after 4 days of incubation at 60 degrees C starting from fly ash and the possible synthesis of other minerals has been investigated by means of X-ray diffraction. The fly ashes have been evaluated by their morphology (SEM analysis), granulometry (laser granulometry) and loss on ignition (L.O.I.). Moreover, the fraction of potentially toxic elements, such as As, Cd, Cr, Cu, Pb and Zn, which can be released in solution during the synthetic process, has been quantified. Among the coal fly ash varieties analyzed, one resulted to possess suitable properties for the synthesis of environmentally applicable Zeolite X, since it showed higher yield, no by-products, lower mean particle size (useful for a quicker dissolution of the ash), and very low concentrations of potentially toxic elements. Finally, this coal fly ash has been fully characterized with regards to its chemical composition (major and minor constituents) by total dissolution and ICP-OES analysis, but also X-ray fluorescence of its fused powder.