Uranium Isotope Fractionation during Adsorption, (Co)precipitation, and Biotic Reduction

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• 作者：Duc Huy Dang ; Breda Novotnik ; Wei Wang ; R. Bastian Georg ; R. Douglas Evans
• 刊名：Environmental Science & Technology
• 出版年：2016
• 出版时间：December 6, 2016
• 年：2016
• 卷：50
• 期：23
• 页码：12695-12704
• 全文大小：565K
• ISSN：1520-5851

文摘

Uranium contamination of surface environments is a problem associated with both U-ore extraction/processing and situations in which groundwater comes into contact with geological formations high in uranium. Apart from the environmental concerns about U contamination, its accumulation and isotope composition have been used in marine sediments as a paleoproxy of the Earth’s oxygenation history. Understanding U isotope geochemistry is then essential either to develop sustainable remediation procedures as well as for use in paleotracer applications. We report on parameters controlling U immobilization and U isotope fractionation by adsorption onto Mn/Fe oxides, precipitation with phosphate, and biotic reduction. The light U isotope (²³⁵U) is preferentially adsorbed on Mn/Fe oxides in an oxic system. When adsorbed onto Mn/Fe oxides, dissolved organic carbon and carbonate are the most efficient ligands limiting U binding resulting in slight differences in U isotope composition (δ²³⁸U = 0.22 ± 0.06‰) compared to the DOC/DIC-free configuration (δ²³⁸U = 0.39 ± 0.04‰). Uranium precipitation with phosphate does not induce isotope fractionation. In contrast, during U biotic reduction, the heavy U isotope (²³⁸U) is accumulated in reduced species (δ²³⁸U up to −1‰). The different trends of U isotope fractionation in oxic and anoxic environments makes its isotope composition a useful tracer for both environmental and paleogeochemical applications.