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Please join us for our first weekly seminar of the academic year on Friday September 8th at 3:30 pm in Rm 155 Geology

Posted on 2017-09-05 in Events
Sep 8, 2017

You are invited to attend the first of our weekly seminars for this academic year next Friday September 8 at 3:30 and 4:00 pm in rm 155 Geology:

3:30 pm:

MSc candidate Carlo Cilia


This research aims to characterize the physical and chemical transport processes driving the distribution of dissolved salts in experimental reclamation scenarios implementing CFT, petroleum coke, and reclamation material. Six field lysimeters were constructed at an oil sands mine near Fort McMurray, Alberta to assess various layering alternatives under different degrees of saturation. Physical characteristics (temperature, water content), pore water geochemistry, and bulk mineralogy were characterized through collection of samples via multi-level monitoring wells, cores, and data loggers. Complimentary laboratory column experiments were set up to monitor the migration of dissolved ions over time, and conservative transport models developed as a means of assessing the major mass transport processes controlling salt distribution. Logger data and pore water chemistry revealed that self-weight consolidation and seasonal freeze-thaw cycles facilitate a volume change in the CFT that translates to an advective release of pore water toward the surface. Depth profiles of major ions and electrical conductivity consistently demonstrate that dissolved salt concentrations become elevated at the surface of saturated systems without a reclamation cover due to evaporation. Data suggests petroleum coke can mitigate salt movement via ion exchange reactions to an extent, however the presence of physical evaporation overshadows this. No measurable analyte concentrations were observed near the surface of unsaturated systems with petroleum coke, due to a lack of available pore water to act as a vehicle for salt movement. Column experiments support the field data, suggesting that the saturated arrangements are at greater risk of surface soil salinization than unsaturated complements. A comparison of Na and Cl concentrations reveal that exchange reactions in the petroleum coke decreases the magnitude of mass transport. Modeling results support the idea that advection - hydrodynamic dispersion is the primary transport regime in early time due to initially large settlement of CFT. In the long-term, transport transitions to primarily diffusion dominated.

4:00 pm:

MSc candidate Lawrence Swerhone

“Trace Element Mobility in Layered Oil Sands Mine Wastes”

Potential closure systems consisting of oil sands tailings and upgrading by-products were studied at the Syncrude Mildred Lake Mine in Northern Alberta, Canada. This research aimed to identify the geochemical implications of storing several different mine wastes together in integrated closure systems, with special focus on the behaviour of trace elements in associated porewater. To imitate such systems, layered assemblages of petroleum coke, centrifuged fine tailings (CFT), tailings sand, and peat-mineral mix soil were placed in large, hydraulically contained lysimeters. Three layering schemes were chosen for the study: one with a peat-mineral mix/petroleum coke cover overlying CFT, one with only petroleum coke overlying CFT, and one with uncovered CFT overlying a tailings sand unit – each having a duplicate to allow comparisons between saturated and partially-saturated systems. Each closure system’s geochemical behaviour was monitored with porewater samples obtained by continuous coring and by pumping multi-level piezometers installed throughout the depth of each lysimeter. Field measurements indicated that porewaters were sub-alkaline (7.7 ± 0.29 pH) with high specific conductivity (4.9 ± 1.9 mS cm 1). Oxidation-reduction potential typically decreased with depth, with saturated systems exhibiting more reduced conditions than their partially-saturated duplicate. Porewater trace element compositions were dominated by Mo (220 ± 350 μg L 1), V (110 ± 200 μg L 1), As (59 ± 42 μg L 1), Ni (7.8 ± 13 μg L 1), and Se (4.5 ± 9.0 μg L 1). Additional sequential extraction studies showed that porewater elevated in exchangeable cations and inorganic anions produced during the dewatering of CFT could influence the release of trace elements bound to petroleum coke and associated mineral surfaces. The results of this study indicate that the dual-cover closure systems performed better with respect to trace element mobility at surface compared with the single-cover and uncovered systems.

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