Interannual and spatial variations in acid-soluble trace elements in snow: comparison with the mineralogy of dusts from open pit bitumen mining

Abstract

There is ongoing concern about trace element (TE) emissions to the global environment from the dusts generated by open pit mining of coal, iron ore, stone quarries, and aggregate extraction. However, the chemical composition and acid solubility of these dusts is highly variable. Here, TEs were determined in snow collected in 2016 and 2017 in the vicinity of open-pit bitumen mines in northern Alberta, Canada. Acid solubility was assessed quantitatively by comparing TE concentrations in leachates and acid digests. The mineralogical composition of the particles extracted from the snow was examined using SEM-EDS. The data is reproducible from one year to the next. TE concentrations were greater throughout the industrial zone compared to the reference location (UTK), with the midpoint between the two central upgraders being especially impacted. Regardless of their geochemical class (lithophile: Al, Be, Cs, La, Li, Sr, Th; chalcophile: As, Cd, Pb, Sb, Tl; or enriched in bitumen: Mo, Ni, V), all TEs showed strong, positive correlations with Y, a conservative element which serves as a surrogate for the abundance of mineral particles. The ratio V:Ni in the snow is less than the corresponding values for bitumen and petcoke, but similar to that of local road dust. The ratio La:Al in snow is elevated, relative to the earth's crust, suggesting an enrichment of heavy minerals monazite and zircon. The predominance of quartz and other stable silicates helps to explain the limited chemical solubility of the dusts, and predicts a low bioaccessibility of these TEs in the environment.