Redox Interactions of Tc(VII), U(VI), and Np(V) with Microbially Reduced Biotite and Chlorite

• Published in: Environmental science & technology Vol. 49; no. 22; pp. 13139 - 13148
• Main Authors: Brookshaw, Diana R, Pattrick, Richard A. D, Bots, Pieter, Law, Gareth T. W, Lloyd, Jonathan R, Mosselmans, J. Fredrick W, Vaughan, David J, Dardenne, Kathy, Morris, Katherine
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 17.11.2015
• Subjects: Aluminum Silicates - metabolism; Bacteria - metabolism; Chemical precipitation; Chemicals; Chlorides - metabolism; Ferrous Compounds - metabolism; Minerals; Minerals - chemistry; Neptunium - chemistry; Neptunium - isolation & purification; Oxidation-Reduction; Radioactivity; Solutions; Sorption; Spectrum analysis; Technetium - chemistry; Technetium - isolation & purification; Uranium; Uranium - chemistry; Uranium - isolation & purification; X-Ray Absorption Spectroscopy
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.5b03463

Technetium, uranium, and neptunium are contaminants that cause concern at nuclear facilities due to their long half-life, environmental mobility, and radiotoxicity. Here we investigate the impact of microbial reduction of Fe­(III) in biotite and chlorite and the role that this has in enhancing mineral reactivity toward soluble TcO4 –, UO2 2+, and NpO2 +. When reacted with unaltered biotite and chlorite, significant sorption of U­(VI) occurred in low carbonate (0.2 mM) buffer, while U­(VI), Tc­(VII), and Np­(V) showed low reactivity in high carbonate (30 mM) buffer. On reaction with the microbially reduced minerals, all radionuclides were removed from solution with U­(VI) reactivity influenced by carbonate. Analysis by X-ray absorption spectroscopy (XAS) confirmed reductive precipitation to poorly soluble U­(IV) in low carbonate conditions and both Tc­(VII) and Np­(V) in high carbonate buffer were also fully reduced to poorly soluble Tc­(IV) and Np­(IV) phases. U­(VI) reduction was inhibited under high carbonate conditions. Furthermore, EXAFS analysis suggested that in the reaction products, Tc­(IV) was associated with Fe, Np­(IV) formed nanoparticulate NpO2, and U­(IV) formed nanoparticulate UO2 in chlorite and was associated with silica in biotite. Overall, microbial reduction of the Fe­(III) associated with biotite and chlorite primed the minerals for reductive scavenging of radionuclides: this has clear implications for the fate of radionuclides in the environment.