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Hydrotalcite colloidal stability and interactions with uranium(VI) at neutral to alkaline pH

DOI: 10.1021/acs.langmuir.1c03179 DOI Help

Authors: Chris Foster (The University of Manchester) , Samuel Shaw (The University of Manchester) , Thomas Neill (The University of Manchester) , Nick Bryan (The University of Manchester; National Nuclear Laboratory) , Nick Sherriff (National Nuclear Laboratory) , Louise S. Natrajan (The University of Manchester) , Hannah Wilson (The University of Manchester) , Laura Lopez-Odriozola (The University of Manchester) , Bruce Rigby (Sellafield Ltd) , Sarah J. Haigh (The University of Manchester) , Yi-Chao Zou (The University of Manchester) , Robert Harrison (The University of Manchester) , Katherine Morris (The University of Manchester)
Co-authored by industrial partner: Yes

Type: Journal Paper
Journal: Langmuir , VOL 5

State: Published (Approved)
Published: February 2022
Diamond Proposal Number(s): 17243 , 21441

Abstract: In the United Kingdom, decommissioning of legacy spent fuel storage facilities involves the retrieval of radioactive sludges that have formed as a result of corrosion of Magnox nuclear fuel. Retrieval of sludges may re-suspend a colloidal fraction of the sludge, thereby potentially enhancing the mobility of radionuclides including uranium. The colloidal properties of the layered double hydroxide (LDH) phase hydrotalcite, a key product of Magnox fuel corrosion, and its interactions with U(VI) are of interest. This is because colloidal hydrotalcite is a potential transport vector for U(VI) under the neutral-to-alkaline conditions characteristic of the legacy storage facilities and other nuclear decommissioning scenarios. Here, a multi-technique approach was used to investigate the colloidal stability of hydrotalcite and the U(VI) sorption mechanism(s) across pH 7–11.5 and with variable U(VI) surface loadings (0.01–1 wt %). Overall, hydrotalcite was found to form stable colloidal suspensions between pH 7 and 11.5, with some evidence for Mg2+ leaching from hydrotalcite colloids at pH ≤ 9. For systems with U present, >98% of U(VI) was removed from the solution in the presence of hydrotalcite, regardless of pH and U loading, although the sorption mode was affected by both pH and U concentrations. Under alkaline conditions, U(VI) surface precipitates formed on the colloidal hydrotalcite nanoparticle surface. Under more circumneutral conditions, Mg2+ leaching from hydrotalcite and more facile exchange of interlayer carbonate with the surrounding solution led to the formation of uranyl carbonate species (e.g., Mg(UO2(CO3)3)2–(aq)). Both X-ray absorption spectroscopy (XAS) and luminescence analysis confirmed that these negatively charged species sorbed as both outer- and inner-sphere tertiary complexes on the hydrotalcite surface. These results demonstrate that hydrotalcite can form pseudo-colloids with U(VI) under a wide range of pH conditions and have clear implications for understanding the uranium behavior in environments where hydrotalcite and other LDHs may be present.

Journal Keywords: Sorption; Luminescence; Nanoparticles; Inorganic carbon compounds; Cations

Subject Areas: Materials, Chemistry, Environment

Instruments: B18-Core EXAFS , I20-Scanning-X-ray spectroscopy (XAS/XES)

Added On: 17/02/2022 15:20

Discipline Tags:

Desertification & Pollution Earth Sciences & Environment Radioactive Materials Chemistry Materials Science Nuclear Waste Inorganic Chemistry

Technical Tags:

Spectroscopy X-ray Absorption Spectroscopy (XAS) Extended X-ray Absorption Fine Structure (EXAFS)