Large quantities of green rust are rarely present at any given moment due to it's very high level of reactivity. On the other hand, it's easy to make. Green rust will form if iron sulphate and caustic soda are present in water. But it won't last long. As soon as oxygen is added to the mix, the rust will become ordinary red rust, known by its ochre characteristics.
Experiments demonstrating green rust's ability to immobilize neptunium have been conducted partly at SKB Swedish Nuclear Fuel and Waste Management's full scale pilot research facility at Okskarshamn on the Swedish east coast and also in part at the Karlsruhe Institute of Technology in Germany.
Typically, radioactive waste is disposed of in iron-lined copper canisters. This is suitable as long as the canisters are surrounded by water. However, any future ice-age will draw water levels downwards. Should the copper dry, it will begin to decay. And as the copper disappears, it will only take a short time for the iron to begin rusting away. Ultimately, the radioactive waste gains entry to the groundwater. Therefore, to ensure the security of radioactive waste, green rust could be established to surround the canisters.
"Green rust is no quick-fix to clean up after pollution that suddenly presents itself. But our experiments have shown the surprising result that nature can help to clean itself. Even when the pollution is with a substance as serious as neptunium," says Bo Christiansen who expects the results to inform and be applied to the design and modeling of future radioactive storage.
|Contact: Jes Andersen|
University of Copenhagen