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

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 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.

Insight into chromium adsorption from contaminated soil using Mg/Al LDH-zeolite

“…The fixation of e-Cr onto MALZ is significantly influenced by carbonate precipitation within the interlayer regions of the LDH. This process is supported by the work of [ 48 ], which demonstrated the leaching of Mg 2+ from hydrotalcite and the ready interchange of interlayer carbonate with the adjacent solution, resulting in the generation of uranyl carbonate complexes. Besides, Misol et al (2022) [ 49 ] highlighted the difficulty in preventing the integration of carbonate anions into the interlayer space when using the coprecipitation method, underscoring the strong tendency of carbonate to associate with LDH layers.…”

Interaction between Uranyl Cations and Layered Double Hydroxide Nanoparticles: Implications for Nuclear Wastewater Management

“…This information is directly relevant to the systems where Mg–Al LDH phases are present in U-contaminated natural and engineered systems, including legacy storage facilities at Sellafield, U.K. For example, Sellafield legacy spent nuclear fuel ponds (SNFPs) have highly heterogeneous inventories, which include SNF, cementitious materials, microbes, pond furniture, and extraneous debris. In these systems, Mg–Al LDH phases have the potential to form via the corrosion of Mg-rich fuel cladding, including their potential to form a colloidal phase within these uranium-containing systems . This study clearly illustrates the effect of changing chemical conditions on the colloidal stability of LDH and ULDH particles and can be used to help predict the extent and duration of colloidal formation in a wide range of systems.…”

“…In the present study, building on similar previous investigations of U-colloid interaction, , we investigate the interaction of UO 2 2+ (0.01 M as UO 2 (CH 3 CO 2 ) 2 ) with Mg–Al LDH colloids under two different conditions; first, where LDH was formed via coprecipitation in the presence of 10% of the stoichiometrically required Mg 2+ substituted by UO 2 2+ (ULDH), and the second where the UO 2 2+ was added to a neoformed LDH precipitate (LDHU). The colloid chemistry and behavior of the two uranyl-bearing LDH systems were then compared with a similarly prepared reference UO 2 2+ -free LDH.…”

Clay-Catalyzed Ozonation of Hydrotalcite-Extracted Lactic Acid Potential Application for Preventing Milk Fermentation Inhibition

“…Interestingly, this beneficial effect of strong convection appears to be limited by the appearance of a plateau with an almost constant 90-93% LA conversion yield between 5 and 15 min ozonation. This must be due to a detrimental pH decrease during ozonation that is supposed to alter the stability of the colloidal Ht suspension [ 66 ]. This is known to promote clay coagulation–flocculation, accentuated by LA protonation and the rise of hydrophobic aggregation of Ht lamellae.…”