Geotechnical Investigation of Uranium Tailings
With the increasing uranium demand for power generation, the mining industry is considering expansion of existing facilities. The management of tailings, generated as a by-product of ore beneficiation, in containment structures is particularly important to minimize the environmental footprint. A clear understanding of slurry behavior is required at the onset of deposition in the containment facility. The main purpose of this research was to understand the geotechnical behaviour (index properties, segregation, dewatering) of uranium tailings under field and laboratory conditions. The historical data of tailings characteristics in the Deilmann Tailings Management Facility (DTMF) at Key Lake, Saskatchewan, were analyzed to investigate the geotechnical performance of uranium tailings in the containment facility. Analyses of borehole data indicated that the high water content (100% to 250%) at the tailings surface gradually decreased with depth and reached around 60% to 80% at the DTMF bottom. The corresponding solids content values were found to be 30 ± 5% at the surface and 60 ± 5% at the bottom. The grain size data correlated well with both the water content and the solids content profiles, that is, an increase in fines content or a decrease in coarse content was associated with an increase in water content (decrease in solids content) and vice versa. The investigated tailings generally exhibited segregation within a narrow range of + 2% to – 2% when scaled with respect to the average solids content for a borehole. A fines water ratio of around 50 ± 5% was found to be associated with negligible segregation. The effective stress was found to be up to 600 kPa at the DTMF bottom. At low effective stress (around 5 kPa), void ratio variation was high (3.0 to 5.0) and the data generally merged at high effective stress (around 600 kPa) to void ratios of 0.5 to 1.0. Detailed laboratory investigations were conducted on tailings (4%, 5%, and 6% mill feed) from the Key Lake operation of Cameco Inc. Results indicated that uranium tailings are mainly silty-sand type materials and that their depositional characteristics are governed by the initial solids content. The investigated tailings showed insignificant segregation between 25% and 40% initial solids content. The initial hydraulic conductivity during settling was found to be around 10-2 cm/s at ei = 4 and was increased by a half order of magnitude for 4% mill feed and almost two orders of magnitude for 5% and 6% mill feeds at ei = 8. Over the same range of initial void ratio, the settling potential was found to increase three-fold: from 8% to 24% for 4% mill feed and from 12% to 36% for 5% and 6% mill feeds.
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Faculty of Graduate Studies and Research, University of Regina