Microwave-assisted acid digestion (MW-AD) followed by atomic spectrometries such as inductively coupled plasma-atomic emission spectrometry (ICP-AES) was examined for the determination of major and trace elements in coal fly ash (CFA). Effective digestion conditions were studied using four certified reference materials of CFA, with particular focus on the composition of acid mixture and the removal of HF after MW-AD. When MW-AD was conducted without using HF (HNO3 + H202), the tested dements yielded fairly poor recoveries. When MW-AD with HF (HNO3 + HF + H2Oz) was carried out, two methods for HF removal were attempted, H3BO3 addition and evaporation of acids. In the former method, while the recoveries of major elements (A1, Ca, Fe, and Mg) were satisfactory, those of trace elements were not satisfactory; in particular, the recovery of Pb was fairly low. In the latter method, the recoveries of AI, Ca, and Mg were extremely poor; however, those of other elements including the trace elements (Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn) were satisfactory. In this paper, the optimization of the digestion method for ICP-AES is discussed. Further, the advantages and limitations of ICP-AES in the determination of elements in CFA are assessed. Kantiranis, N. et al. Fuel. 2006, 85, (3), 360 366. EPI-type zeolite was synthesized from Greek sulphocaleic lignite fly ashes. They consist mainly of SiO2, CaO and AI20> while the SiO2/ A1203 ratio was found to be 2,74. The activation was performed by 30% HzO2 in an open system. Zeolite formation was observed only when activated products aged at 95°C. The resulting materials were characterized by means of PXRD, FT-IR and SEM-EDS. PXRD and FT-IR results are in good agreement, confirming the zeolite formation. The role of H202 as a dominant factor in the zeolite synthesis is attributed to the oxidation of Fe(II) to Fe(III) and to the oxidative action on the unburned organic mater of the fly ash to prevent the reduction of Fe(III) to Fe(II). Fe(III) is proposed to participate in the reaction with Si-OH and HO-A1 groups in the preliminary steps, resulting to the formation of an intermediate group [Fe-(H+)O(O-Si)-A1] which then gives Si-O-A1 groups and Si-O-Fe groups to a lesser extent, both of which lead to a zeolite structure. Formation of the latter group explains the presence of Fe(III) in the zeolite crystal structure.
06•02109 EPI-type zeolite synthesis from Greek sulphocaicic fly ashes promoted by H202 solutions