Hydrotalcite Colloidal Stability and Interactions with Uranium(VI) at Neutral to Alkaline pH

Autor: Chris Foster, Samuel Shaw, Thomas S. Neill, Nick Bryan, Nick Sherriff, Louise S. Natrajan, Hannah Wilson, Laura Lopez-Odriozola, Bruce Rigby, Sarah J. Haigh, Yi-Chao Zou, Robert Harrison, Katherine Morris
Rok vydání: 2022
Předmět:
Zdroj: Foster, C, Shaw, S, Neill, T, Bryan, N, Sherriff, N, Natrajan, L S, Wilson, H, Lopez Odriozola, L, Rigby, B, Haigh, S J, Zou, Y C, Harrison, R & Morris, K 2022, ' Hydrotalcite colloid stability and interactions with uranium(VI) at neutral to alkaline pH. ', Langmuir, vol. 383, no. 8, pp. 2576–2589 . https://doi.org/10.1021/acs.langmuir.1c03179
ISSN: 1520-5827
0743-7463
Popis: In the UK, 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 it’s 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 solution in the presence of hydrotalcite, regardless of pH and U loading, although the sorption mode was affected by both pH and U concentration. 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 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 uranium behaviour in environments where hydrotalcite and other LDHs may be present.
Databáze: OpenAIRE
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