New approach to removing elements from nuclear waste

Scientists from the University of Manchester have found that arsenic molecules could be used to extract the most toxic elements from radioactive waste.

The researchers have reported the first examples of thorium – a radioactive actinide metal – forming multiple bonds to arsenic at ambient temperatures. This means arsenic could, in principle, be used in organic molecules that bond to metal atoms and improve extraction processes.

Elizabeth Wildman, a PhD student in a research group led by Professor Stephen Liddle at the  University, said: “In order to find ways of separating, recycling and reducing the volume of nuclear waste, research has focused on developing our understanding of how elements like thorium and uranium interact with elements from around the periodic table to potentially help improve nuclear waste clean-up.”

The study managed to achieve multi-gram quantities of thorium-arsenic complexes at ambient temperatures – instead of much smaller quantities at 3-10°K. This research follows on from previous work carried out at the University.

Professor Stephen Liddle, co-director of the centre for radiochemistry research at the University of Manchester, said: “There is currently significant interest in using organic molecules to extract, selectively, metal ions from the ‘soup’ of nuclear waste and fish out the more radioactive and toxic ones and leave the rest behind.”

He said: “This requires an understanding of chemical bonding and how the organic extractants bind to different metals. There is mounting evidence that the molecules that are best at this contain soft donor atoms to the metals. Arsenic is a soft donor, so we have prepared model complexes with it to understand the nature of the bonding.”

This research was carried out between the universities of Manchester and Regensburg, funded by institutions including the Royal Society and European Research Council. The study was published in Nature Communications.