Oxidation state and local environment of iron and hydrolytic stability of multicomponent aluminum-iron-phosphate glasses for immobilization of high-level waste

Resumo

The nuclear gamma resonance (Mössbauer effect) is used to determine the oxidation state and the coordination environment of iron ions in model glasses that simulate vitrified high-level waste. A major fraction of iron is present in the samples with relatively low contents of transition metal oxides as Fe(III) in the octahedral oxygen environment. When the content of transition metal oxides is high, iron is distributed between a glassy phase (10–15%) and a crystalline phase (85–90%). Iron in the first phase exists predominantly as Fe(III) in the octahedral environment, while in the second phase it is present as Fe(II) and Fe(III) ions as well in a form of octahedrally coordinated and participating ions in a “fast” electron exchange proceeding as mFe³⁺ + nFe²⁺ ↔ mFe²⁺ + nFe³⁺. The leach rate of Cs ions from boron-free glasses amounts to ~1 × 10^–5 g/(cm² day) and lower, and the value for Fe is three orders of magnitude lower. Upon annealing, both the rate and the degree of leaching increase by several times, while the boron-containing glasses exhibit lower hydrolytic durability. Both the rate and the degree of leaching of iron change insignificantly after annealing.