GEOCHEMICAL IMPLICATIONS OF GYPSUM ADDITION TO OIL SANDS FLUID FINE TAILINGS: LABORATORY BATCH AND COLUMN EXPERIMENTS
Large inventories of tailings in the Alberta Oil Sands have created the need for technologies that can accelerate dewatering of fluid tailings; however, knowledge of long-term implications from these technologies is limited. This research was split into two studies, examining: 1) temporal changes in porewater chemistry and gas production in gypsum-amended Fluid Fine Tailings (FFT), and 2) temporal and spatial changes in porewater chemistry in Centrifuged Fine Tailings (CFT) during successive freeze-thaw-evaporation cycles. An anoxic laboratory batch experiment was conducted, where differing gypsum amendments were added to FFT, and destructively sampled over 64 weeks. Methane measured in the headspace showed inconclusive results for the effect of gypsum on methanogenesis. Gypsum-amended FFT showed an increase in dissolved salts, with Na increasing up to 1.3 times (820–1,100 mg L−1) and Mg increasing up to 4.2 times (9.55–39.9 mg L−1) compared to the control. In the second experiment, six columns filled with CFT were subjected to three consecutive freeze thaw evaporation cycles, and sacrificially sampled before each thaw and evaporative period. Column mass decreased an average total of 28.5 kg with 72% of this attributed to runoff following the first thaw period. After this time, dissolved salts began accumulating in near the CFT surface, with Cl increasing up to 5.8 times (379–2,200 mg L−1), Na increasing up to 6.9 times (772–5,353 mg L−1), K increasing up to 15.6 times (16.1–251 mg L−1), and Mg increasing up to 94 times (22.0–2,069 mg L−1) compared to the initial CFT. Both studies revealed elevated porewater salt concentrations in gypsum-amended tailings, which could pose challenges for long-term reclamation of the oil sands tailings.
geochemistry oil sands tailings geology environmental
Master of Science (M.Sc.)