Uranyl acetate speciation in aqueous solutions-An XAS study between 25°C and 250°C

Bailey, E. H.; Mosselmans, J. F.W.; Schofield, P. F.

Abstract

Speciation of uranium (VI) in acetate solutions between 25 and 250°C, at pH values between 1.8 and 3.8 and acetate/uranium (Ac/U) ratios of 0.5 to 100 has been investigated using uranium LIII-edge X-ray absorption spectroscopy. With increasing pH the UO2(Ac)20 species becomes more important than UO2(Ac)+ species, which is predominant below pH 2. It remains the dominant species as pH is further increased to 3.8 at an Ac/U ratio of 20. Decrease in U-Oeq bond distance and coordination number with increasing solution age indicates that steric/kinetic factors are important and that equilibrium is attained slowly in this system with initial acetate coordination to the uranyl ion being monodentate or pseudo-bridging before slow conversion to bidentate chelation. Acetate coordination to the uranyl ion appears to decrease as temperature is increased from room temperature to ∼100°C before increasing in solutions of Ac/U > 2. For solutions where Ac/U ≤ 2 at pH 2.1, there is no evidence for uranyl acetate speciation at low temperatures, but at elevated temperature bidentate uranyl-acetate ion-pairing is evident. The existence of the uranyl acetate species in the temperature range 200 to 240°C demonstrates the importance of including acetate and other organic ligands in models of uranium transport at elevated temperatures. © 2004 Elsevier Ltd.

• Journal Article Type: Article
• Acceptance Date: Aug 4, 2003
• Online Publication Date: Apr 7, 2004
• Publication Date: Apr 15, 2004
• Deposit Date: Apr 25, 2021
• Journal: Geochimica et Cosmochimica Acta
• Print ISSN: 0016-7037
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 68
• Issue: 8
• Pages: 1711-1722
• DOI: https://doi.org/10.1016/j.gca.2003.08.024
• Public URL: https://nottingham-repository.worktribe.com/output/5160851
• Publisher URL: https://www.sciencedirect.com/science/article/abs/pii/S001670370300752X?via%3Dihub