Crystallization of (Na2O-MgO)-CaO-Al2O3-SiO2 glassy systems formulated from waste products

Aluminosilicate and silicate glass-ceramics were obtained from controlled devitrification of CaO-Al2O3-SiO2 glassy systems starting from Spanish and Italian coal fly ash or Italian municipal incinerator slag mixed with other byproducts, such as glass cullet and dolomite, The nucleation mechanism and the crystallization kinetics were investigated by thermal, diffractometric, and microstructural measurements. Moreover, the experimentally observed devitrification and the identification of the crystalline phases formed were compared with the indications derived from Ginsberg, Raschin-Tschetveritkov, and Lebedeva diagrams used for petrological glass-ceramics. All the glasses showed a good crystallization tendency with the formation of dendritic pyroxene and acicular wollastonite together with feldspar and iron spinels starting from the surface. The activation energy values for crystallization ranging from 472 to 832 kJ.mol(-1) were found to be close to those typical for aluminosilicate glasses; moreover, the possibility to vitrify and devitrify up to 100 wt% of slag and up to 40-50 wt% of ash mixed with glass cullet and dolomite makes the vitrification treatment a suitable disposal procedure.