Study of annealing induced devitrification of stabilized industrial waste glasses by means of micro-X-ray fluorescence mapping and absorption fine structure spectroscopy

The distribution of Fe in as-casted and annealed vitrified Pb- and Fe-rich solid industrial waste is studied by means of X-ray fluorescence mapping and micro-X-ray absorption fine structure spectroscopy. The studied samples were produced by co-melting of lead and iron contaminated ash with the appropriate quantities of vitrifying (SiO2) and flux (Na2O) agents at high temperatures (1400 °C) and were subjected to thermal treatment in the temperature range 400–800 °C for 2 h. It is demonstrated that annealing at temperatures higher than the glass transition temperature (440 °C) induces loss of homogeneity in the sample and promotes the formation of Fe-rich crystalline regions, embedded into the glass matrix. In addition to that, annealing modifies the coordination environment around the Fe3+ atom, which occupies octahedral sites in the crystalline regions and tetrahedral sites in the amorphous, glassy phase where it acts as a network former. Finally, the effect of the coordination environment of Fe on the chemical stability of vitreous and vitroceramic materials containing industrial wastes is disclosed.