A Franco-American collaboration has used X-rays to study the chemistry behind separating radioactive ions from nuclear waste.

Separating f-block elements is a long-standing challenge in chemistry and is particularly significant for nuclear waste reprocessing, according to Mark Antonio from the Argonne National Laboratory, Illinois. With colleagues from the Commissariat à l'Energie Atomique, France, he set out to investigate how liquid-liquid extraction separates radioactive actinide ions from inactive lanthanide ions. This is especially difficult as they have similar sizes and identical charges.

'Atomic-level insights are pivotal to a predictive understanding of the metal-ligand interactions responsible for the selectivity of the method and, ultimately, to advances in 4f and 5f element separations,' Antonio said.

The separation involves mixing an aqueous solution of the actinides and lanthanides with an organic phase containing two extractant ligands. The group used X-ray absorption and infrared spectroscopy to study the different coordination environments around the metal ions. Antonio explained that the success of the extraction is due to the conformational flexibility afforded by the presence of both ligands.

'Our research is of practical importance to heavy metal chemistry and to environmentally related issues arising from the separation and disposal or radioactive materials,' said Antonio. In particular, much effort is needed to prevent damage to the environment by long-lived radionuclides caused by recycling nuclear fuels, he said.

Jenna Wilson