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UBC Theses and Dissertations

Characterization of arsenic in a tailings impoundment under post depositional conditions Meilleur, Desiree


Arsenic is found naturally in the gold ores extracted from the Red Lake Mine in Balmertown, Ontario. Milling of ores produced arsenic-rich tailings that have been disposed of in different locations around the site through the over 50 years of mine operations. The composition of the tailings depended upon the mineral processing methods (cyanidation, sulphide flotation, and roasting) used at the time. The primary objective of this thesis was to characterize the forms, stability, and mobility of arsenic in the different wastes located around the mine site. In addition, a potential method to reduce arsenic transport from tailings pond sediments into the overlying pond waters was investigated. Whole rock analysis, Scanning Electron Microscopy (SEM), Rietveld refined powder X-ray diffraction, sequential extractions, and X-ray Absorption Near Edge Structure (XANES) using a Synchrotron light source were used to mineralogically characterize the various tailings types. Experiments were conducted to investigate the behaviour of arsenic in several tailings types under various conditions with the objective of determining if arsenic could be stabilized under reducing conditions, ideally in the form of arsenopyrite or arsenian pyrite. High aqueous arsenic concentrations were found to be associated with oxidized arsenic bearing mineral phases (i.e. arsenic bearing iron oxyhydroxides contained in historical roaster-derived tailings and tailings pond sediments). Mobilization of a significant fraction of the arsenic contained within these wastes is likely to continue as a result of the reducing conditions that these wastes are stored under. Arsenic is found at relatively low concentrations in the freshly produced tailings, primarily in the form of arsenopyrite, and is likely to remain immobile as long as saturated conditions exist. In order to minimize arsenic mobilization from solid wastes, oxidized arsenic bearing phases (e.g. arsenic bearing iron oxyhydroxides) should be kept dry and dissolved organic carbon influxes should be limited. Reduced arsenic bearing mineral phases (e.g. arsenopyrite, arsenian pyrite), however, should be maintained under saturated conditions. During field and laboratory experiments it appears as if arsenic was immobilized as a reduced sulphide phase under strongly reducing conditions, however further work is required to determine the mechanism and stability of the produced phase.

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