Stability, Composition, and Core–Shell Particle Structure of Uranium(IV)-Silicate Colloids

Abstract

Uranium is typically the most abundant radionuclide by mass in radioactive wastes and is a significant component of effluent streams at nuclear facilities. Actinide(IV) (An(IV)) colloids formed via various pathways, including corrosion of spent nuclear fuel, have the potential to greatly enhance the mobility of poorly soluble An(IV) forms, including uranium. This is particularly important in conditions relevant to decommissioning of nuclear facilities and the geological disposal of radioactive waste. Previous studies have suggested that silicate could stabilize U(IV) colloids. Here the formation, composition, and structure of U(IV)-silicate colloids under the alkaline conditions relevant to spent nuclear fuel storage and disposal were investigated using a range of state of the art techniques. The colloids are formed across a range of pH conditions (9-10.5) and silicate concentrations (2-4 mM) and have a primary particle size 1-10 nm, also forming suspended aggregates <220 nm. X-ray absorption spectroscopy, ultrafiltration, and scanning transmission electron microscopy confirm the particles are U(IV)-silicates. Additional evidence from X-ray diffraction and pair distribution function data suggests the primary particles are composed of a UO-rich core and a U-silicate shell. U(IV)-silicate colloids formation correlates with the formation of U(OH)(HSiO) complexes in solution indicating they are likely particle precursors. Finally, these colloids form under a range of conditions relevant to nuclear fuel storage and geological disposal of radioactive waste and represent a potential pathway for U mobility in these systems.

Formation of plutonium(iv) silicate species in very alkaline reactive media

“…The two next peaks have been attributed to silicon atoms in the second coordination sphere of plutonium and correspond to the presence of bidentate and monodentate silicate groups. Consistently with previous hypotheses from Hennig et al 2 , Neill et al 23 and Husar et al…”

I22: SAXS/WAXS beamline at Diamond Light Source – an overview of 10 years operation

“…These are characteristic of living organisms and also many complex materials such as polymers and colloids. Relevant active research in the UK encompasses the fields of medicine (Ma et al, 2016;Burton et al, 2019;Coudrillier et al, 2016;Al-Jaibaji et al, 2018;Kudsiova et al, 2019), biology (Troilo et al, 2016;McGeehan et al, 2011;Arnold et al, 2011;Salamah et al, 2018), the environment (Neill et al, 2018;Seddon et al, 2016) and materials (Summerton et al, 2019;Wychowaniec et al, 2018;Burton et al, 2017), and includes studies of supramolecular organization in biomechanical systems (Xi et al, 2018;Kampourakis et al, 2018;Sui et al, 2014), corneal transparency (Morgan et al, 2018;Hayes et al, 2017), biological membranes (Barriga et al, 2016;Slatter et al, 2018;, polymer processing (Stasiak et al, 2015;Wan et al, 2018;Heeley et al, 2013;Toolan et al, 2017), colloids (Calabrese et al, 2019;Poulos et al, 2016;Mable et al, 2016), inorganic aggregates (Raine et al, 2018;Bennett et al, 2015;Zhou et al, 2018), liquid crystals (Hallett et al, 2014;Prehm et al, 2018;Lehmann et al, 2018) and devices (Xia et al, 2018;Barrows et al, 2016).…”

Radiation Tolerance of Pseudanabaena catenata, a Cyanobacterium Relevant to the First Generation Magnox Storage Pond

“…Cationic metals are able to adsorb to negatively charged functional groups on the surfaces of the microorganisms and polysaccharide containing mucilage of some cyanobacteria at neutral to alkaline pH (Gadd, 1990(Gadd, , 2009Javanbakht et al, 2014;Decho and Gutierrez, 2017). Extracellular polymeric substances also have the ability to trap organic and inorganic colloids and nanoparticles, which are thought to be present in the pond (Maher et al, 2016;Decho and Gutierrez, 2017;Neil et al, 2018). The same experimental set-up described in this study was used recently to investigate the interaction of 90 Sr with the cell free medium from irradiated and control cultures (Ashworth et al, 2018).…”