Stabilization of Centrifuged Fluid Fine Tailings Using Native Vegetation
Creators: Laberge, Scott L
Publisher: name: University of Alberta Library
Year: 2022

<p>Managing fluid fine tailings (FFT) is a defining challenge of the oil sands industry in Alberta due to low solids content, and extremely slow self-weight consolidation. One technology to increase the solids content of these tailings is centrifugation to produce centrifuged fluid fine tailings (CFFT). Although centrifugation results in a tailings product with a much greater solids content than raw FFT, deposits of CFFT can take centuries to densify under self-weight conditions. This research aims to assess the potential for four native plant species: Carex spp., Salix interior, Elymus trachycaulus, and Rumex occidentalis to dewater a centrifuged tailings product from an oil sands mine operator. This assessment was conducted on five one cubic meter totes, each containing approximately 600L of tailings that were located outside at a research facility in Peace River, AB. Several geotechnical parameters were collected through the study which lasted two years from June 2018 to October 2019 including: solids content, undrained shear strength, water table height, settlement, matric suction and volumetric water content. In addition, plant data including above and below ground biomass, as well as LAI were determined to allow assessment of the impact the plant species have on dewatering and strength gain in the samples of CFFT.<br>
    The study shows these species can successfully grow and establish in these tailings in a region with similar climate conditions to the oil sands in northeastern Alberta. In general, the totes with vegetation did show  a modest increase in solids content and shear strength when compared to the control tote that contained no plants. The greatest biomass generation in addition to strength and solids content gains were observed in totes containing Salix interior and Elymus trachycaulus. All totes experienced similar settlement in the first year, with an equivalent settlement attributable to freeze-thaw over the winter period. In Year 2, only the totes containing vegetation showed notable settlement, with nearly no additional settlement measured in the control tote. One challenge identified was the susceptibility of these tailings to rewetting. Significant precipitation events could contribute to swelling of the tailings in the totes, and subsequent loss of solids content and strength gain. This swell was found to be the most pronounced in the control tote, suggesting the plant species may have allowed the totes to weather these water influxes more successfully. <br>
    The findings indicate that planting species of Salix interior and Elymus trachycaulus will likely result in the greatest geotechnical performance gains in these types of tailings material. Undrained shear strength, strain, and solids content gain was greatest in totes containing these two species (in combination). Any application of plants as a dewatering method should be supported by a robust water management plan. This would minimize the risk from rewetting of the tailings that can result in a complete loss of previous shear strength and solids content gains in these tailings. It should also be noted that the material properties of the tailings such as clay content, hydraulic conductivity, and chemistry (among others), will also have a significant impact on plant growth and related dewatering potential.</p>