Characterization of arsenic-hosting solid phases in Giant mine tailings and tailings dust
Dust from the tailings at Giant mine, an abandoned mine in northern Canada, has been a concern among local residents, particularly those from Ndilo, a community of Yellowknives Dene First Nations located approximately 2.5km southeast of the site. The arsenic-bearing tailings at Giant mine are left vulnerable to high velocity winds after snow melt in the late spring, when it is too cold to apply a dust suppressant to the tailings. The main objective of this research is to characterize the fine fraction of the tailings (particles <63µm in diameter) and dust that could be inhaled or ingested from Giant mine to identify the As-hosting solid phases therein. Surface tailings material was sampled from three of the tailings impoundments on site, and sieved to <63µm. From May to July of 2016, a total suspended particulate (TSP) high volume air sampler was set up to continuously sample airborne material coming from the tailings. Bulk chemical data was determined via inductively coupled plasma-optical emission spectrometry (ICP-OES) and -mass spectrometry (ICP-MS); mineralogical data via scanning electron microscope (SEM)-based automated mineralogy, electron microprobe analysis (EMPA), and synchrotron-based micro X-ray diffraction (µXRD), micro X-ray fluorescence (µXRF); and oxidation state data for As via X-ray absorption near edge structure (XANES). Bulk chemical data show elevated concentrations of As, Sb, Zn, Pb, Cu, and Ni. The As in the tailings is a mix of As(I-), As(V), and As(III), and is more concentrated in the <63µm fraction (3000 – 9300 ppm As) than in the unsieved tailings. Roaster-generated Fe-oxides (maghemite), Ca-Fe arsenate, and arsenopyrite comprise the majority of As-bearing particles in the surface tailings; Ca-Fe arsenate poses the greatest risk to human health of these three as it is the most bioaccessible. Fe-oxides were the only As-host found in the dust. Very little arsenic trioxide was found in the tailings, and no arsenic trioxide was found in the dust samples. However, previous studies have shown that the soils near the Giant mine tailings do contain arsenic trioxide from historic stack emissions, indicating that these soils might actually present a higher risk than the tailings themselves.