Hematite can lock the door on uranium contamination

X-ray spectroscopy techniques at Diamond have given scientists a new insight into the behaviour of uranium during deep disposal of radioactive waste.

The common iron oxide hematite is ubiquitous in waste management scenarios, and is likely to hold a particular importance here due to its long-term stability. With the prospect of exposure to heat-yielding radioactive waste and geothermal fluctuations, hematite could be important in uranium immobilisation as it can be locked up within the mineral structure.

The team of researchers from the University of Manchester and Diamond Light Source used spectroscopy techniques on Diamond’s B18 beamline to explore these processes. Combining X-ray Absorption Spectroscopy alongside chemical extraction and transmission electron microscopy techniques at the labs in Manchester, they have been able to gather the first evidence for how absorbed U(VI) – uranium in its more mobile oxidation state – becomes incorporated into hematite. The Extended X-ray Absorption Fine Structure (EXAFS) technique also allowed the exact mechanism of uranium incorporation to be determined, showing that it directly substitutes for iron, with little distortion of the surrounding crystalline structure.

The combined results of the study have afforded a full mechanistic understanding of uranium incorporation into hematite, and the nature of uranium bonding within the mineral structure. Together these findings highlight that minerals can be used to lock away radioactive contaminants and thus may contribute to controlling the environmental impact of radioactive waste disposal.

The full news article available on the diamond website here.

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Image: Adsorption of uranium onto the surface of ferrihydrite, an amorphous iron oxyhydroxide, leads to incorporation of uranium into the structure of the iron oxide hematite during crystallisation.

Marshall, T. A., Morris, K., Law, G. T. W., Livens, F. R., Mosslemans, J. F. W., Bots, P., Shaw, S. Incorporation of uranium into hematite during crystallization from ferrihydrite. Environ. Sci. Technol., 201448, 3724–3731. DOI: 10.1021/es500212a

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