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TitleGeoenvironmental characterization of ferroniobium slag, Saint Lawrence Columbium Mine, Oka, Québec
LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorDesbarats, A JORCID logo; Percival, J BORCID logo; Pelchat, P; Sekerka, J; Bilot, I; Girard, IORCID logo; Gammon, P
SourceGeological Survey of Canada, Open File 8752, 2020, 69 pages, Open Access logo Open Access
PublisherNatural Resources Canada
Documentopen file
Mediaon-line; digital
RelatedNRCan photo(s) in this publication
RelatedThis publication is related to Geoenvironmental characterization of carbonatite tailings, Saint Lawrence Columbium Mine, Oka, Québec
File formatreadme
File formatpdf; rtf; xlsx (Microsoft® Excel®)
NTS31G/08; 31G/09; 31H/05; 31H/12
Lat/Long WENS -74.1333 -73.9500 45.6000 45.4333
Subjectsenvironmental geology; hydrogeology; geochemistry; geophysics; mineralogy; economic geology; Nature and Environment; Science and Technology; Economics and Industry; groundwater resources; groundwater pollution; water quality; environmental impacts; mineral deposits; metals; niobium; mining; mineral processing; concentrates; mine waste products; radioactive waste; slag; pyrochlore; weathering; meteorology; precipitation; leaching; pollutants; uranium; thorium; host rocks; bedrock geology; lithology; igneous rocks; intrusive rocks; carbonatites; trace element analyses; geophysical surveys; radiometric surveys, ground; radioisotopes; climate; physiography; Saint Lawrence Columbium Mine; Oka Complex; Mining industry; Waste water; Resource development; mitigation; Mitigation; Climate change; Methodology; cumulative effects
Illustrationsphotographs; tables; satellite images; geoscientific sketch maps; plots; profiles
ProgramEnvironmental Geoscience Cumulative effects in cobalt watersheds
Released2020 11 19; 2021 01 08
Between 1961 and 1976, the St. Lawrence Columbium mine produced pyrochlore concentrate from a niobium-bearing carbonatite deposit near Oka, Québec. Beginning in 1971, the pyrochlore concentrate was converted into ferroniobium alloy through an aluminothermic reduction process, which also yielded slag as a waste product. Uranium and thorium occurring as impurities within the pyrochlore were preferentially sequestered in the slag. As a result, the slag represents Technologically Enhanced Naturally Occurring Radioactive Material (TENORM) requiring a long-term management solution.
Slag at the mine was deposited on the surface and has been exposed to the elements for approximately 45 years. Much of the slag exhibits an advanced degree of weathering. The slag consists of an assemblage of high-temperature mineral phases including hibonite, grossite, and perovskite, as well as amorphous glass. The minerals deviate significantly from their ideal compositions as they incorporate rare earth and other trace elements including uranium and thorium. Geochemically, the slag is composed mainly of aluminum, calcium, and sodium from reagents, and impurities from the pyrochlore concentrate including titanium, silicon, zirconium, uranium, thorium, and rare earth elements, as well as unrecovered niobium.
A ground-based spectral radiometric survey was conducted on a longitudinal transect through the slag disposal area. Equivalent uranium concentrations ranged between 455 and 1616 ppm, with a median value of 1069 ppm. Equivalent thorium concentrations ranged between 607 and 5059 ppm, with a median value of 2101 ppm. Assuming secular equilibrium within the decay series, total activity concentrations of the slag varied between 126 and 417 Bq/g, with a median of 304 Bq/g. These results are consistent with detailed radiological analyses for U-238, U-235, Th-232 and their daughter products performed on three selected slag samples.
An on-site field-scale leach test was conducted on three 220 L barrels of coarse vesicular slag open to natural precipitation. The experiment ran from June of 2017 to November of 2018 during which time collected leachate was sampled six times. The leachate had a near constant pH of 9.2 while specific conductance values varied between 1191 and 3280 µS/cm. Leachate chemistry did not stabilize during the test, likely because seasonal freeze-thaw cracking of the slag was regularly exposing fresh surfaces to chemical weathering. The main solutes were sodium and bicarbonate. Fluoride concentrations varied between 16.8 and 45.6 mg/L. Dissolved aluminum and uranium concentrations reached as high as 8173 and 65 µg/L, respectively. Although uranium is hosted by most minerals in the slag, it is released mainly by the weathering of unstable glass phases.
This investigation of slag geochemistry at the former St. Lawrence Columbium mine, provides new geoscience data and knowledge useful for the environmental assessment of future carbonatite-hosted niobium mining projects. The information will allow proponents and other stakeholders to anticipate potential environmental impacts associated with new resource development and to plan appropriate mitigation measures accordingly.
Summary(Plain Language Summary, not published)
New technologies are driving a strong demand for critical metals found in carbonatite deposits such as rare earth elements and niobium. However, little is known about the environmental characteristics of mine wastes from carbonatites. This study investigates the mineralogy, geochemistry, and radioactivity of slag from the processing of niobium ore at the former St-Lawrence Columbium mine in Oka, Quebec. Niobium (Nb) occurs in the mineral pyrochlore, which also contains uranium (U) and thorium (Th). The conversion of pyrochlore concentrate to ferroniobium alloy yields a slag enriched in U and Th. The slag contains enough U and Th to be classified as a radioactive hazard. Slag leachate contains high concentrations of dissolved aluminum and fluoride. Results of this study provide open access benchmark data for environmental impact assessments of carbonatite-hosted critical metal deposits developed in the future.

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