Metaschoepite dissolution in sediment column systems – implications for uranium speciation and transport

William Bower, Katherine Morris, Francis R. Livens, J. Frederick Willem Mosselmans, Connaugh M Fallon, Adam J Fuller, Louise S. Natrajan, Christopher Boothman, Jonathan Lloyd, Satoshi Utsunomiya, Daniel Grolimund, Dario Ferreira Sanchez, Tom Jilbert, Julia E. Parker, Thomas Neill, Gareth T.w. Law (Corresponding)

    Research output: Contribution to journalArticlepeer-review


    Metaschoepite is commonly found in U contaminated environments and metaschoepite-bearing wastes may be managed via shallow or deep disposal. Understanding metaschoepite dissolution and tracking the fate of any liberated U is thus important. Here, discrete horizons of metaschoepite (UO3●nH2O) particles were emplaced in flowing sediment/groundwater columns representative of the UK Sellafield site. The column systems either remained oxic or became anoxic due to electron donor additions, and the columns were sacrificed after 6- and 12-months for analysis. Solution chemistry, extractions, and bulk and micro-/nano-focus X-ray spectroscopies were used to track changes in U distribution and behavior. In the oxic columns, U migration was extensive, with UO22+ identified in effluents after 6-months of reaction using fluorescence spectroscopy. Unusually, in the electron-donor amended columns, during microbially-mediated sulfate reduction, significant amounts of UO2-like colloids (>60% of the added U) were found in the effluents using TEM. XAS analysis of the U remaining associated with the reduced sediments confirmed the presence of trace U(VI), non-crystalline U(IV), and biogenic UO2, with UO2 becoming more dominant with time. This study highlights the potential for U(IV) colloid production from U(VI) solids under reducing conditions and the complexity of U biogeochemistry in dynamic systems.
    Original languageEnglish
    Pages (from-to)9915–9925
    JournalEnvironmental Science & Technology
    Issue number16
    Early online date18 Jul 2019
    Publication statusPublished - 2019


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