Nanoparticulate iron (oxyhydr)oxides are well known to sequester trace metals, including radionuclides, from solution in a range of engineered and natural environments. Radioactive species present in acidic solutions containing Fe(III) can be removed by raising the solution pH, causing the precipitation of an iron (oxyhydr)oxide floc which effectively sequesters most radionuclides. This process can be utilised to inhibit the mobility of contaminant metals within the environment or to process waste from industrial waste treatment plants, amongst other applications. The Enhanced Actinide Removal Plant (EARP) facility (Sellafield, UK) can decontaminate up to ~500 m3/day waste effluent by inducing iron hydrolysis and the subsequent precipitation of 2-line ferrihydrite1,2. A deeper understanding of the mechanism(s) by which radionuclides are removed from solution during this process is required as plant operations move towards decommissioning. The removal of U(VI) from solution during iron hydrolysis was characterised under experimental conditions relevant to the EARP process. Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy was used to determine the atomic-scale bonding environment of U(VI) associated with the solid ferrihydrite phase. When aged at 40°C the ferrihydrite floc transforms to a more crystalline hematite phase (α-Fe2O3) and various techniques including EXAFS were used to determine the fate of the associated U(VI) during this aging process. Our results show that during iron hydrolysis U(VI) is removed from solution by surface adsorption to 2-line ferrihydrite across a wide range of U(VI) concentrations (0.42 to 1050μm). During the aging induced evolution of the iron (oxyhydr)oxide phase, U(VI) becomes increasingly incorporated within the solid structure. This work provides new insights into the fundamental mechanisms of radionuclide removal by iron hydrolysis within such a dynamic system.

Uranium(VI) uptake during iron(III) (oxyhydr)oxide formation: Underpinning radioactive effluent treatment

255th National Meeting (2018)

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