Abraham, Jillian2026-04-222026-04-222026-04-22http://hdl.handle.net/10393/51558https://doi.org/10.20381/ruor-31874The Giant Mine, located near Yellowknife, NWT, produced over 220 tonnes of gold (Au) from 1948-1999. The ore roasting process created over 237,000 tonnes of As₂O₃-containing roaster waste (ATRW) in the form of dust that is stored in underground chambers. Current plans are to freeze the surrounding ground to prevent groundwater leaching of As₂O₃ into nearby Great Slave Lake. Freezing requires constant maintenance, so this research explores a potentially maintenance-free, safe and permanent alternative. The overall objective is to chemically alter As₂O₃ into a thermodynamically-stable, low-solubility As₂S₃ that could be disposed of safely, deep in the underground mine workings. Specific objectives addressed in this paper are 1) aqueous extraction of As₂O₃ from the ATRW which is necessary prior to sulfidation and 2) characterization of the extraction residues. Extractions were conducted in pure water with a microwave at water-solid ratios ranging from 20-100 and temperatures from 140 °C - 220 °C. The residues were characterized with chemical and x-ray analytical techniques. Complete extraction of the As₂O₃ was accomplished at all temperatures using a water-solid ratio of 100, but small amounts (< 10%) of As₂O₃ remained at lower ratios. In extractions with full As₂O₃ dissolution, residues contain ~1-14 wt% As. Synchrotron (XANES and XRD) analyses of these residues indicate that As is present predominantly as As(V) with lesser As(III), associated with iron (Fe) minerals including goethite, maghemite and hematite. The research demonstrates that complete extraction of As₂O₃ from the waste is possible in water at temperatures ranging from 140 °C - 220 °C. The resulting aqueous As is then amenable to sulfidation to form As₂S₃.enAttribution 4.0 Internationalhttp://creativecommons.org/licenses/by/4.0/Giant MineRemediationAs₂O₃Arsenic trioxideThesis