X-rays used to better illuminate how uranium moves in deep underground environments

6 Jan 2020 10:26 AM

New research involving x-rays has enabled UK scientists to find a way to improve our understanding of uranium biogeochemistry. This has the potential to help us better store or dispose of radioactive materials in the future.

The team worked at the UK’s national synchrotron, Diamond Light Source, to better understand how uranium interacts with and moves through its environment, casting light on the best way to store or dispose of radioactive waste, or clean up nuclear sites or mines. The researchers looked at the oxidation state of uranium and how biogeochemical reactions – the way that uranium behaves when dissolved or on different mineral surfaces or with biological activity - can alter this and alter how it moves in its environment.

With its substantial nuclear legacy, the UK has a need for a deeper understanding of the complex systems that affect the mobility of uranium. In contaminated land and geodisposal systems, interactions with iron and sulphide minerals are important factors in controlling uranium mobility.

The team of researchers from the University of Manchester, Diamond Light Source and Radioactive Waste Management used an X-ray based method called X-ray Absorption Spectroscopy (XAS) to study samples of uranium when it sits at the surface of the mineral ferrihydrite. They found that a new uranium-sulphide complex can form under conditions representative of a deep underground environment.  This complex then transforms further into highly immobile uranium oxide nanoparticles.

Physical Science Director at Diamond, Professor Laurent Chapon says the beamlines at Diamond allowed a real insight into how the environment in which this new uranium-sulphur complex is found has an effect on its behaviour. He said: “This is another example of how Diamond’s state of the art analytical tools are enabling scientists to follow complex processes and help them to tackle 21st century challenges.”

Professor Katherine Morris, Associate Dean for Research Facilities in the Faculty of Science and Engineering, University of Manchester and the Research Director for the BNFL Research Centre in Radwaste Disposal says studying these chemical complexes will help us understand and deal with radioactive waste. She explained: “To be able to predict the behaviour of the uranium during geological disposal, we need to take into account that it may have interacted with other processes taking place in the ground. These so-called biogeochemical reactions are often a complex set of interactions between dissolved chemical species, mineral surfaces, and microorganisms.”

The data from the XAS spectroscopy method, in combination with computational modelling and geochemical analyses allowed the researchers to track and understand uranium behaviour. The researchers used highly controlled sulphidation experiments that mimic biogeochemical processes in the deep underground environment.

Callum Richardson, University of Manchester, PhD student demonstrating the loading a sample containing uranium onto Diamond’s I20-scanning beamline. Credit: Diamond Light Source.

NOTES:

The research is published in Environmental Science & Technology in a paper called Formation of a U(VI)-persulfide complex during environmentally relevant sulfidation of iron (oxyhydr)oxides and the authors, from the University of Manchester, Diamond Light Source and Radioactive Waste Management, are: Luke Townsend, Samuel Shaw; Naomi Ofili,  Nikolas Kaltsoyannis ; Alex Walton,  Frederick J. Mosselmans; Thomas Neill, Jonathan Lloyd; Sarah Heath; Rosemary Hibberd; Katherine Morris

The work is funded by EPSRC and Radioactive Waste Management and was performed by Luke Townsend and the team using I20 and B18 beamlines at Diamond.

Diamond Light Source is the UK’s national synchrotron, providing industrial and academic user communities with access to state-of-the-art analytical tools to enable world-changing science. Shaped like a huge ring, it works like a giant microscope, accelerating electrons to near light speeds, to produce a light 10 billion times brighter than the Sun, which is then directed off into 33 laboratories known as ‘beamlines’. In addition to these, Diamond offer access to several integrated laboratories including the Electron Bio-imaging Centre (eBIC) and the Electron Physical Science Imaging Centre (ePSIC).

Funded by the UK Government through the Science and Technology Facilities Council (STFC), and by the Wellcome Trust, Diamond is one of the most advanced scientific facilities in the world, and its pioneering capabilities are helping to keep the UK at the forefront of scientific research.