文摘
Two zeolitization processes, hydrothermal and molten-salt, were used to examine the effect of zeolitizationof circulating fluidized-bed combustion (CFBC) fly ash on the immobilization of Cu2+, Pb2+, and Cr3+ inthis study. As a consequence of zeolitization, most of the dissolved Cu2+, Pb2+, and Cr3+ had been immobilizedin the synthetic aluminosilicate-aggregates-enriched matrixes under hydrothermal conditions, reaching maximumimmobilization efficiencies of ~89.1%, ~82.4%, and ~99.1%, respectively; whereas under molten-saltconditions, the synthetic cancrinite-enriched matrixes were most effective to immobilize Cu2+, Pb2+, andCr3+ with maximum immobilization efficiencies of ~94.5%, ~50.7%, and ~38.3%, respectively. Examinationsof the synthetic matrixes by X-ray diffraction (XRD), scanning electron microscopy/energy-dispersive X-rayspectrometry (SEM/EDS), and sequential EDTA extractions suggest that physicochemical reactions responsiblefor the immobilization of heavy metal ions were ascribed to the speciation of insoluble species such ascarbonates/silicates, hydroxides, and oxides and especially to the encapsulation of such species inaluminosilicates aggregates or cancrinite-enriched agglomerates. Furthermore, it is also proved that thespeciation of soluble chromate in molten-salt processes contributed to the unexpected low immobilizationefficiency of Cr3+ and that the Ca-enriched CFBC fly ash is an appropriate candidate for immobilization ofCu2+ and Pb2+. Both zeolitization processes could be employed in solidification/stabilization of soils andsediments contaminated by heavy metals.