Structural studies of iron in vitrified toxic wastes

Mossbauer spectroscopy and X-ray absorption spectroscopy (XAS) have been used to obtain information on the redox and coordination of iron in glasses made by the vitrification of simulated and actual sewage sludge combustion ashes. Mossbauer spectra have been deconvoluted using three extended Voigt-based profiles to allow quantitative analysis of multiple Fe3+ coordination environments. XAS Fe pre-K-edge absorption peaks have been analysed and fitted against reference standards to yield complementary analyses and provide validation of the Mossbauer results. Correlations are noted between the iron redox and the Fe3+ coordination. Tetrahedral Fe3+ is much more likely to take part in any redox reaction whilst octahedral Fe3+ appears to be more resistant to reduction to the ferrous state. Results from XAS also suggest that Fe2+ ions occupy both four-and six-fold coordination environments. Neither technique has provided any clear evidence for the existence of Fe2+ or Fe3+ in five-fold symmetry in the glasses studied.