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Effect of Diluent Levels on Greenhouse Gases and Reduced Sulfur Compound Emissions from Oil Sands Tailings Open Access


Other title
Greenhouse gas emissions
Sulfur emissions
Oil sands tailings
Hydrogen sulfide
Methane emissions
Type of item
Degree grantor
University of Alberta
Author or creator
Gee, Kathleen F.M.D.
Supervisor and department
Ulrich, Ania (Dept. of Civil and Environmental Engineering)
Hashisho, Zaher (Dept. of Civil and Environmental Engineering)
Examining committee member and department
Wilson, Ward (Dept. of Civil and Environmental Engineering)
Department of Civil and Environmental Engineering
Environmental Engineering
Date accepted
Graduation date
Master of Science
Degree level
A well-known issue of tailings is that they have poor consolidation properties, which, in situ, may require several decades or more before the material can be reclaimed. With the accumulation of tailings in the tailings ponds, one unintended consequence of this long-term storage is the evolution of emissions in the ponds. Studies in the last decade have indicated that methane, a greenhouse gas, is produced by methanogen microorganisms in the tailings and that emissions are more readily stimulated by the hydrocarbons in naphtha diluent that is leftover from the bitumen extraction process. More recent studies have also found black, sulfidic zones in the tailings where toxic, hydrogen sulfide gas may be being produced in considerable amounts, but it is unknown how much hydrogen sulfide or other reduced sulfur compound emissions are being released from the ponds or whether these emissions are also stimulated by naphtha diluent. The objectives of this study were as follows: 1) Determine whether there are advantages to further reducing the diluent concentrations in the tailings with respect to methane, carbon dioxide, and reduced sulfur compound emissions; 2) Between methane, carbon dioxide, and reduced sulfur compound emissions, which are the most concerning quantity wise under a worst case, high diluent scenario; and 3) Aside from diluent, are there other chemical factors that play a role in the types of emissions generated from tailings. A mesocosm experiment was conducted using Suncor Energy Inc. Pond 2/3 mature fine tailings, pond water (Pond 2/3 or surrogate pond water), with naphtha diluent amendments of 0% w/v, 0.2% w/v, 0.8% w/v, and 1.5% w/v. Chromatography gas analysis revealed that all greenhouse gases and reduced sulfur compound emissions increased with increasing naphtha diluent concentrations. Therefore, further reducing the concentration of residual diluent in the tailings ponds is anticipated to decrease the amount of greenhouse gases and reduced sulfur compound emissions that are produced in tailings. With respect to the quantities of emissions produced, at a worst-case diluent scenario of 1.5% w/v, methane emissions were the highest, followed by carbon dioxide, and then the combined amount of reduced sulfur compounds. Within the reduced sulfur compounds, amounts emitted from highest to lowest were in the order of hydrogen sulfide and 2-methylthiophene > 2,5-dimethylthiophene > 3-methylthiophene > thiofuran > butyl mercaptan > carbonyl sulfide, with hydrogen sulfide and 2-methylthiophene combined making up 81% of the total reduced sulfur compound emissions. The remaining sulfate concentrations within the tailings samples was also an important factor with regards to the types of emissions produced as there was a system shift from sulfur emissions production to methanogenesis after sulfate became depleted. Lastly, our results indicated that hydrogen sulfide, methane, and carbon dioxide were produced from biological sources associated with the mature fine tailings whereas the remaining reduced sulfur compounds appeared to originate from the naphtha diluent. In conclusion, this study has provided further insights to gas evolution in tailings that contain naphtha diluent.
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