On the thermal stability of vitrified industrial wastes using microscale synchrotron radiation based techniques

Abstract

The effect of annealing on the local coordination of Fe in a series of vitrified industrial wastes is studied by means of x-ray fluorescence mapping, and micro- and conventional x-ray absorption fine structure (XAFS) spectroscopies. It is demonstrated that annealing causes the formation of Fe- and Pb-rich microcrystallites which are embedded in the glass matrix. The local coordination of the Fe ion depends on the local variations of its concentration, i.e., Fe occupies octahedral sites in the Fe-rich crystalline regions and tetrahedral sites into the vitreous network. The percentage of the Fe atoms that belong to the crystalline inclusions depends on the waste content and the annealing temperature, and the stability of the vitrified product is discussed in relation to the nature of the formed microcrystallites. More specifically, when the microcrystallites are mixed Pb and Fe oxides, the material is safe since Pb is trapped both in the crystalline and vitreous regions. Finally, the effect of the different types of crystalline phases and crystalline ratio on the characteristics of the preedge peak in the near edge XAFS spectra is also discussed.