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

DOI: 10.1021/acs.est.9b02292 DOI Help

Authors: William R. Bower (University of Manchester; The University of Helsinki) , Katherine Morris (University of Manchester) , Francis R. Livens (The University of Manchester) , J. Frederick W. Mosselmans (Diamond Light Source) , Connaugh M. Fallon (The University of Manchester) , Adam J. Fuller (The University of Manchester) , Louise S. Natrajan (The University of Manchester) , Christopher Boothman (The University of Manchester) , Jonathan R. Lloyd (The University of Manchester) , Satoshi Utsunomiya (Kyushu University) , Daniel Grolimund (Swiss Light Source) , Dario Ferreira Sanchez (Swiss Light Source) , Tom Jilbert (The University of Helsinki) , Julia E. Parker (Diamond Light Source) , Thomas S. Neill (University of Manchester) , Gareth T. W. Law (The University of Manchester; The University of Helsinki)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Environmental Science & Technology

State: Published (Approved)
Published: July 2019
Diamond Proposal Number(s): 15085 , 17270 , 13559 , 18053

Abstract: 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.

Subject Areas: Chemistry, Environment

Instruments: B18-Core EXAFS , I14-Hard X-ray Nanoprobe , I18-Microfocus Spectroscopy

Other Facilities: Swiss Light Source