| Title | Geotechnical properties determination of thickened Fluid fine tailings |
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| Author | Demoz, A |
| Source | Geotechnical and Geological Engineering 2022 p. 1-12, https://doi.org/10.1007/s10706-021-01998-3  Open Access |
| Image |  |
| Year | 2022 |
| Alt Series | Natural Resources Canada, Contribution Series 20210733 |
| Publisher | Springer |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Subjects | general geology; tailings; tailings analyses; oil sands; hydraulic conductivity |
| Illustrations | tables; graphs; plots |
| Program | CanmetENERGY - Devon Director, Upstream and Environmental Impacts - Upstream and Environmental Impacts Operations |
| Released | 2022 02 22 |
| Abstract | Fluid fine tailings (FFT) comprising clayey-silt solids pose environmental and financial challenges. Currently, mining operators are depositing thickened FFT in deep-pits counting on self-weight
consolidation to form stable ground. The motivation of this study is to model the long-term prospects of such deposits utilizing consolidation and direct shear strength measurements. The tests were conducted using scroll decanter centrifuge separated
FFT sediment referred to as cake. Drained direct shear tests of the cake gave a linear Mohr-Coulomb failure envelope of 1.2 kPa cohesion intercept and 9 internal friction angle for normal stresses up to 1 MPa. Hydraulic conductivity of the cake was
non-linear with normal stress decreasing to 1.7 9 10-11 m/s at 300 kPa. Consolidation results confirmed that the cake exhibits properties similar to those of active clay minerals. The cake compression index is governed by the same relationship as for
active clays. The coefficient of consolidation for the cake was nearly constant and had a mean value of 2.25 9 10-3 m2/y, also similar to that of active clays. The void ratio- effective stress-hydraulic conductivity power law empirical relations were
used to simulate settlement with a finite-strain model. Numerical results show that the top portion of an FFT deep-pit deposit remains in the liquid state while the lower portion whose maximum solids content converges to 74% is in plastic state.
These mean that options that improve hydraulic conductivity and increase the shear strength of the thickened FFT should be integrated prior to final placement in order to create stable ground. |
| Summary | (Plain Language Summary, not published)
Terrestrial reclamation of oil sands tailing ponds starts with a necessary step of dewatering the fluid fine tailing (FFT) using chemical additives known
as coagulant and flocculant. The dewatered (thickened) FFT deposit at the final disposal site is then expected to form stable landscape over time due to compression. This work investigated the feasibility of thickened FFT solids forming reclaimable
deposit using two methods; shear strength and consolidation measurements on centrifuge separated fluid fine tailing (FFT) samples called cake. The cake represents the physical state of all FFT through its consolidation progress. The shear strength
indicates whether the deposit can support machinery and the consolidation indicates how fast the deposits compress and also provide inputs for model calculations that predict settlement. The shear strength measurements conducted under conditions
simulating real deposits showed that the fines do not have cohesive structures. The deposit also shears easily because the particles slide over each other without much resistance (because friction angle is low; <9 degrees). The cake permeability was
very low and in the same range as impermeable clays that are laid at the base of containment structures to stop leakage. Lower permeability means higher rate of water retention and slower consolidation. Empirical constants obtained from the
consolidation measurements were used as inputs of a modelling software for settlement. Model calculations show that even after hundreds of years of consolidation, the top part of a deep deposit remains high in water content. The test results in
totality mean that self-weight consolidation of thickened FFT can't be relied upon to form reclaimable deposits. Options that will increase the shear strength and water permeability of thickened FFT have to be integrated in the process prior to
discharge at final deposit site. Modifications necessary to increase cake permeability and shear strength are being pursued. |
| GEOSCAN ID | 329880 |
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