Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

Dr. Julie Q. Shang

Abstract

The management of fine oil sands tailings, known as mature fine tailings (MFT), is a major challenge for the oil industry in the Northern Alberta, Canada. Dewatering and consolidation of MFT are slow and time consuming due to high water content and low permeability of MFT. The electrokinetic (EK) dewatering treatment has shown to be effective on oil sands tailings based on the results of previous researches. Therefore, this thesis is focusing on experimental and numerical studies of EK dewatering of oil sands tailings. The thesis includes three parts, i.e., EK dewatering of oil sands tailings and kaolinite slurry, EK and chemical (quicklime and Portland cement) combined treatment, and development of a one-dimensional large strain EK consolidation model.

In the first part, the EK dewatering experiments are designed and executed on oil sands tailings and slurries of kaolinite, which is the major clay mineral in the Alberta oil sands tailings, with vertically installed electrodes. The analyses are carried to obtain the regression equations of the dewatering trends for the results of oil sands tailings and kaolinite slurries, including the water drainage, water/solid content, energy consumptions, etc. The effects of applied voltage gradient and initial water content on EK dewatering are studied via the regression equations. The material saturation, especially at the anode, is found to be the key factor controlling the water flow generated by electrokinetics. Once the degree of saturation of the material at the anode drops below 80%, the most efficient stage for EK dewatering will end.

The effects of EK and chemical combined treatment of MFT are evaluated in the 2nd part in this research. The addition of quicklime or Portland cement minimizes the difference of water content and undrained shear strength of MFT between the anode and cathode, whereas it also reduces EK induced water flow. It is concluded that EK and chemical combined treatment of MFT may be beneficial at a low chemical dosage (1% quicklime or cement).

In the 3rd part of this study, a one-dimensional large strain EK consolidation model (LSEK-1D) is developed for oil sands tailings. The model predictions are in consistency with the experimental results in terms of the final settlements and consolidation times. Moreover, the effects of sample initial heights and applied current densities on consolidation times are evaluated via the model. The results indicate that the consolidation times of oil sands tailings are shorter than those based on the conventional small strain consolidation theory, and the application of EK combined with surcharge pressure can significantly reduce the consolidation time of oil sands tailings.

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