Geochemistry of decades-old spodumene mine tailings under a humid continental climate

Transports electrification efforts currently increase global demand for lithium, but literature about the environmental geochemistry of spodumene mine tailings is very scarce. Mine tailings from the former Que acute accent bec Lithium Corporation site in La Corne, Que acute accent bec, Canada, were submitted to a suite of geochemical and mineralogical characterizations to evaluate metals distribution and mobility 55 years after deposition. From 1955 to 1965, production of spodumene concentrate, lithium carbonate and other lithium salts from a spodumenepegmatite ore left behind about 750,000 tons of non-sulfidic tailings (mostly from flotation). Core samples of the tailings were collected from 5 boreholes ranging from 5.13 to 9.75 m in depth. Results show that grain size and metals distribution is heterogeneous, with elements groups (Li-Ta-U or K-Rb) being enriched or depleted in coincident strata and zones. The mineralogical assemblage is dominated by quartz, albite and other feldspars, unrecovered spodumene (up to 12 wt%), and micas, displaying few to no signs of weathering. Sequential extraction results indicate that for most elements surveyed, including Li and Be, secondary retention mechanisms like precipitation, sorption, and ion exchange, almost exert no control on their mobility within the tailings. Silicate-hosted elements (Al, Li, Be, K, Rb) were proportionally among the least extractable. The most extractable elements are either ubiquitous in the environment (Fe, Mn) or hosted in metamict minerals (U). Apart from paste pH which tends to be relatively lower close to the surface, no relation is evident between depth or the water table level and any physical or geochemical parameter. Despite the tailings being almost unweathered, the surrounding waters contain Li concentrations up to the mg/L range. This study gives environmentally-relevant insights into the geochemistry of non-sulfidic spodumene-pegmatite mine tailings as surging worldwide demand for Li attracts interest towards new spodumene mining projects.