Assessment of the leaching potential of flotation tailings from rare earth mineral extraction in cold climates

Costis, Sophie; Coudert, Lucie; Mueller, Kristin K.; Cecchi, Emmanuelle; Neculita, Carmen Mihaela; Blais, Jean-Francois

Assessment of the leaching potential of flotation tailings from rare earth mineral extraction in cold climates

2020

Increasing use of rare earth elements (REEs) in modern technologies and existing or expected imbalances between demand and supply have led many countries, including Canada, to consider the exploitation of their own REEs primary sources. The objective of this study is a thorough characterization of the flotation tailings generated during the pre-concentration of REEs from a carbonatite type deposit with the aim of predicting their geochemical behaviour over time. These tailings were characterized based on physicochemical and mineralogical properties. Weathering cells were also used to assess the impact of temperature (3 and 19 °C) on the geochemical behaviour of the tailings exposed to a sub-arctic climate. Because the tailings consisted mainly of carbonates (97.4%) and had very high neutralization potential (859 kg CaCO₃/t) relative to their acidity potential (3.94 kg CaCO₃/t), no acid mine drainage (AMD) is anticipated. Compared to regional environmental standards and guidelines, the concentrations of Cd (0.20 μg/l), Zn (17 μg/l), and Pb (close to 4 μg/l) in leachates obtained during kinetic testing may be considered as potentially problematic. Finally, the results of the weathering cells at 3 °C indicate that the exposure to low temperatures may increase the concentrations of elements leached from the tailings. This study confirms that low temperatures and freeze-thaw events, which occur readily in a sub-arctic climate, may impact the geochemical behaviour of tailings produced from the extraction of REEs from carbonatite type deposit.

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