Investigating arsenic speciation in the JEB Tailings Management Facility at McClean Lake, Saskatchewan using X-ray absorption spectroscopy

AREVA Resources Canada operates the McClean Lake Operation (MLO), a uranium mine and processing facility located in northern Saskatchewan. Uranium-containing ores processed at the MLO contain high concentrations of arsenic that is oxidized to soluble arsenite and arsenate species when leaching and recovering uranium. To reduce the environmental impact of AREVA's mining operations, AREVA has developed a tailings preparation process designed to trap arsenic in a mineral form before the tailings are permanently deposited in the JEB Tailings Management Facility (TMF). Scorodite (FeAsO4·2H2O) is predicted to be the primary arsenic species produced from the tailings preparation process. However, scorodite has never been observed in aged tailings samples. Confirming the presence of scorodite in the tailings is important in verifying that the tailings preparation process at the MLO can isolate high concentrations of arsenic from the environment in the form of stable minerals. Herein, X-ray Absorption Near-Edge Structure (XANES) spectroscopy was used to investigate arsenic speciation in a series of samples collected from the JEB TMF in 2013. Arsenic K-edge XANES analysis confirmed that most (86 wt%) of the arsenic content in the tailings samples consisted of iron-containing arsenates. Of these, crystalline scorodite was the most abundant arsenate species followed by poorly crystalline arsenates in the form of poorly crystalline ferric arsenate (FeAsO4·xH2O) and arsenate adsorbed on ferrihydrite (AsO4-FeOOH). Arsenite adsorbed on ferrihydrite (AsO3-FeOOH), and gersdorffite (NiAsS) were also identified as minor arsenic species in the tailings samples. The abundance and distribution of scorodite in the TMF suggests that it is the major arsenic species produced in the tailings preparation process.