Mechanisms of Se(IV) and U(VI) uptake in chuckanovite (Fe2(OH)2CO3)

The aim of the project is to investigate the uptake of Se(IV) and U(VI) in chuckanovite (Fe2(OH)2CO3), an Fe(II)-carbonate hydroxide mineral, which can be formed under redox reducing conditions at the interface between the steel container and the bentonite clay barrier in a high-level radioactive waste repository. The characterisation of synthesised chuckanovite confirmed a 100% of Fe(II) in the structure. Batch sorption experiments, demonstrated that chuckanovite exhibits a high retention capacity for Se(IV) and U(VI) at pH 8.2, even in the presence of carbonates. The high Fe(II) content (which enhances redox reduction) and the presence of structural CO32- (which facilitates anionic exchange) can both contribute to the effective retention of radionuclides (RN). However, the formation of other surface complexes cannot be ruled out. Access to ROBL-BM20 beam line is deemed essential for the surface analysis of Se and U-chuckanovite samples and the understanding of retention mechanisms.