The efficiency of different digestion methods (six microwave decomposition methods and a wet acid digestion method) in the solubilisation of six metals (Cr, Ni, Cu, Pb, Cd, Zn), for their determination in fly ashes, was compared. Five different mineral acid mixtures and two different microwave systems were tested. The study was carried out by analyzing two highly homogenised fly ash samples (from sewage sludge and city waste incineration) provided by the Joint Research Centre of Ispra. Determinations were performed by atomic absorption spectrometry and by inductively coupled plasma atomic emission spectrometry. The analytical performance of the laboratory was evaluated using the 1633a Coal Fly Ash Standard Reference Material of National Bureau of Standards (NBS SRM 1633a).Results showed that a HNO3 microwave treatment was strong enough to solubilise metals from the considered fly ashes. Moreover, microwave methods generally provided higher release than the classical aqua regia method, whereas no significant advantage was observed using a high performance microwave unit. Copyright (C) 1999 Elsevier Science B.V.

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