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Using Co-Disposal Techniques to Achieve Stable “Dry-Stacked” Tailings: Geotechnical Properties of Blended Waste Rock and Tailings in Oil Sands and Metal Mining
- Author / Creator
- Burden, Ralph
Mine “tailings”, waste produced by the extraction process, are most typically stored in impoundments behind dams which are often constructed from the tailings themselves. These structures pose a serious geotechnical risk and are difficult to successfully reclaim at the end of mining. As highly destructive, tragic failures of tailings dams continue to occur, the mining industry and society at large seek more sustainable methods of waste management. In response, an increasingly common alternative to traditional tailings disposal is “dry stacking”: the placement of dewatered tailings in a self-supporting stack. This thesis investigates the application of co-disposal techniques, the blending of waste rock and tailings, to dry stacking. Two distinct applications are considered: blending filtered gold tailings with waste rock to improve the geotechnical performance of the stack and blending of oil sands tailings with Clearwater shale overburden material.
The addition of waste rock to a filtered tailings stack by blending the rock and tailings has the potential to offer significant advantage over established dry stacking methods. A conceptual model was developed to describe the behaviour of filtered tailings and waste rock blends, based upon particle packing arrangement. The model may be used to predict the structure and behaviour of the blend, based on mix ratio and density. In addition, the thesis presents the results of experimental investigations on filtered tailings and waste rock blends. The compression behaviour and pore pressure response under self-weight consolidation of blends at a range of mix ratios was investigated using an innovative methodology that was developed to simulate the placement of stacks, using a controlled rate of loading test. Large scale direct shear tests were undertaken to investigate the
relationship between shear strength and mix ratio. Blends of waste rock and tailings were observed that have higher drained shear strength than waste rock alone. Shear strength was observed to increase with rock content, up to a limiting value of 1 : 1 rock to tailings by dry mass. At higher stresses, or with weaker rocks, the strength of the blend has the potential to be higher than rockfill alone. The addition of waste rock to filtered tailings reduces the build-up of pore pressure when loaded in compression with an incrementally increasing load. This suggests that co-disposal of filtered tailings with rock will reduce the build-up of pore pressure during stacking, improving stability and allowing more rapid deposition or deposition in higher lifts. The oil sands of Northern Alberta present their own unique waste management challenge: very large volumes of fluid fine tailings (FFT) that are challenging to dewater by normal methods. A promising solution to this problem is co-disposal of FFT with the clay shale overburden found in the area. It has been demonstrated that clay shale overburden can be blended with FFT to create trafficable deposits. This study investigates the compression behaviour and pore pressure response of stacked clay shale – FFT blends, using the sample consolidation cell used in the filtered gold tailings study. Volume change behaviour and pore pressure response of Clearwater shale – FFT blends were found to be a complex, time-dependent process, governed by both consolidation and by transfer of moisture from the FFT into the shale lumps. Further study is recommended to characterise this process, including development of an unsaturated, double-porosity consolidation numerical consolidation model.
- Graduation date
- Fall 2021
- Type of Item
- Doctor of Philosophy
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.