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Stability, composition and core-shell particle structure of uranium(IV)-silicate colloids

DOI: 10.1021/acs.est.8b01756 DOI Help

Authors: Thomas S. Neill (The University of Manchester) , Katherine Morris (The University of Manchester) , Carolyn I. Pearce (Pacific Northwest National Laboratory) , Nicholas K. Sherriff (National Nuclear Laboratory) , M. Grace Burke (The University of Manchester) , Philip A. Chater (Diamond Light Source) , Arne Janssen (The University of Manchester; Diamond Light Source) , Louise Natrajan (The University of Manchester) , Samuel Shaw (The University of Manchester)
Co-authored by industrial partner: Yes

Type: Journal Paper
Journal: Environmental Science & Technology

State: Published (Approved)
Published: July 2018
Diamond Proposal Number(s): 12704 , 13559 , 15276 , 15966

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 stabilise 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 UO2-rich core and a U-silicate shell. U(IV)-silicate colloids formation correlates with the formation of U(OH)3(H3SiO4)32- complexes in solution indicating they are likely particle precursors. Finally, these colloids form under a range of condition relevant to nuclear fuel storage and geological disposal of radioactive waste and represent a potential pathway for U mobility in these systems.

Journal Keywords: Colloids; uranium(IV); core-shell; uranium silicate; nuclear fuel storage; EXAFS; SAXS

Subject Areas: Environment, Chemistry, Materials

Instruments: B18-Core EXAFS , I15-Extreme Conditions , I22-Small angle scattering & Diffraction