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TitleCharacterization of uranium and REE mobility downstream of a uranium tailings impoundment near Bancroft, Ontario
AuthorLaidlow, A M; Parsons, M BORCID logo; Jamieson, H E; Gault, A G
SourceGeological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Programs with Abstracts vol. 36, 2013 p. 126 Open Access logo Open Access
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20120415
PublisherGeological Association of Canada - Mineralogical Association of Canada (GAC MAC)
MeetingGeological Association of Canada - Mineralogical Association of Canada Joint Annual Meeting; Winnipeg; CA; May 22-24, 2013
File formatpdf
AreaBancroft; Duparquet district
Lat/Long WENS -78.5000 -78.0000 45.0000 44.7500
Subjectsenvironmental geology; Archean; greenstone belts; tailings; tailings geochemistry; tailings analyses; uranium; rare earths; rare earths geochemistry; heavy metals contamination; pollutants; Abitibi Greenstone Belt; Bicroft Mine
ProgramEnvironmental Geoscience Tools for environmental impacts and adaptation for metal mining
AbstractAttenuation of uranium (U) and rare earth elements (REEs) has been observed in stream and wetland sediments, but the processes involved in sequestering these elements in natural systems are not well understood. The decommissioned Bicroft Uranium Mine near
Bancroft, ON uses a modified stream and wetland system to reduce the concentrations of U and other metals in tailings pond effluent to levels below the Provincial Water Quality Objectives. The Bicroft Mine was operated from 1957 to 1963, and processed low-grade, isseminated U hosted by pegmatite dykes in amphibolite gneiss. In this study, we used tangential flow filtration (TFF), ICP-ES/MS, canning electron microscopy, and synchrotron techniques (bulk and µ-XANES, µ-XRF, and µ-XRD) to characterize sediment, tailings and colloid samples. In conducting TFF on waters downstream of the tailings impoundments, orange-brown staining of the filter membrane was
observed, suggesting that dissolved Fe(II) was oxidized and precipitated during TFF processing. TFF reservoir mass balance alculations identified losses of Fe, Mn, and Al on the filter membrane, as well as similar losses of REEs (Ce and La). In contrast, U present at concentrations of 18-27 µg/L (median = 21 µg/L; <0.45 µm fraction), showed little to no filter loss during TFF, which suggests that U is not
primarily associated with colloidal Fe- and Mn-oxy-hydroxides in solution. These results indicate that reduced forms of Fe and Mn
remain in solution at least 200 m downstream of the Bicroft tailings impoundments, and that the mobility of U and REEs may be governed
by different processes. Analyses of colloids by SEM, µ-XRF, and µ-XRD confirm that REEs are strongly associated with Fe- and Mn-oxyhydroxides, including goethite, lepidocrocite, 2-line ferrihydrite, and birnessite.
The lack of diffraction under the micro-focused synchrotron beam and poor element correlation between U and Fe- and Mn-xyhydroxides
suggests that U is most likely present in coarser detrital crystals, such as the primary ore minerals uraninite [UO2] and uranothorite [(Th,U)SiO4]. Micro-XANES analyses show that U in the colloids from Bicroft is primarily (80%) U(IV), providing further evidence that U is mainly hosted in detrital minerals and has not been extensively oxidized and re-precipitated in the colloids. This observation is important, as U(IV) is relatively insoluble in neutral pH environments and less mobile than oxidized hexavalent U(VI) species. The results of this study will help to develop better monitoring strategies for U tailings sites and should reduce the impacts of future U mining operations.

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