A statistical approach has been utilised to characterise the structural and chemical properties of vitrified model sewage sludge combustion ashes. A d-optimal design has been applied to determine the effects of the compositional variability of vitrified wastes on iron redox and coordination as measured by ~(57)Fe Mossbauer spectroscopy. Several Fe sites have been observed through the deconvolution of Mossbauer spectra, representing the Fe~(2+) oxidation state and tetrahedrally and octahedrally coordinated Fe~(3+) ions. The interdependency of iron redox and iron coordination is demonstrated, and suggests that conversion oftetrahedral Fe~(3+) to octahedral Fe~(3+) preferentially occurs upon increasing Fe~(2+)/EFe. For Fe~(2+)/ΣFe=0.30-0.89, the abundance of octahedrally coordinated Fe~(3+) remains approximately constant whilst tetrahedrally coordinated Fe~(3+) exhibits a linear decrease in its abundance with increasing Fe~(3+)/ΣFe ratio.
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