Mossbauer studies of phosphate glasses for the immobilisation of toxic and nuclear wastes

Various iron-containing phosphate glasses were investigated by Mossbauer spectroscopy. Iron was found to occur predominantly as Fe 31 in all glasses, and largely occupied sites with distorted octahedral coordination for both redox states. Using a base glass of nominal composition 60 P2O5-40 Fe2O3 (mol%), stepwise molar replacement of Fe2O3 by (0.67 Na(2)Ox0.33 Al2O3) increased the redox ratio, Fe2+/Sigma Fe, from 0.13 at 40% Fe2O3 to 0.25 at 10% Fe2O3. The centre shift increased and quadrupole splitting decreased by up to similar to 20% over this range, interpreted as a decrease in the average distortion of Fe sites from cubic symmetry, and an increase in average iron coordination. Literature revealed that recoil-free fraction ratio f (Fe3+)/f (Fe2+)approximate to 1.3 in iron phosphate glasses, and this was considered when assessing redox. Mossbauer parameters of these and other glasses demonstrated a combination of structural stability and compositional flexibility which makes them so suitable for waste immobilisation.