Open AccessHydrotalcite Colloidal Stability and Interactions with Uranium(VI) at Neutral to Alkaline pH
Author(s) -
Chris Foster,
Samuel Shaw,
Thomas Neill,
Nicholas Bryan,
Nick Sherriff,
Louise S. Natrajan,
Hannah Wilson,
Laura Lopez-Odriozola,
Bruce Rigby,
Sarah J. Haigh,
Yichao Zou,
R. W. Harrison,
Katherine Morris
Publication year - 2022
Publication title -
langmuir
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.042
H-Index - 333
eISSN - 1520-5827
pISSN - 0743-7463
DOI - 10.1021/acs.langmuir.1c03179
Subject(s) - hydrotalcite , colloid , leaching (pedology) , chemistry , hydroxide , uranium , sorption , carbonate , inorganic chemistry , actinide , nuclear chemistry , metallurgy , adsorption , materials science , geology , catalysis , organic chemistry , soil science , soil water
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 Mg 2+ 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, Mg 2+ 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(UO 2 (CO 3 ) 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.