Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

Julie Q. Shang

Abstract

This thesis addresses two challenges facing the management of mature fine tailings (MFT) from oil sand processing. The first challenge is the high concentration of residual bitumen in tailings ponds, which poses a hazard to aquatic biota and impact to the environment. A laboratory scale study is carried out to assess the suitability of electro-flotation (EF) for removal of bitumen from oil sand tailings slurry. The results of the study confirm that EF is effective to reduce bitumen contents of tailings slurry. At a current density 150 A/m2, the bitumen concentration is reduced from 106.8 mg/L to less than 10 mg/L within 90 minutes. The electrolysis voltage has direct impact to the operating cost of an EF system, hence an electrochemical model is developed to predict the total electrolysis voltage required for an EF cell. Good agreement is found between the simulation results and experimental data from both this study and the literature. Hence the model derived can be used to predict the total electrolysis voltage required for an EF cell and to optimize operating conditions of an EF cell to reduce the operating cost. The performance of EF is strongly influenced by the size of O2 and H2 bubbles. Therefore, in this study the bubble sizes are measured in a lab scale EF cell using a high-speed camera. The mean bubble size is found to vary in the range of 32.7–68.6 μm under different operating conditions. This study shows that the electrode material, current density, water pH, ionic strength, and frother (Tennafroth 250) concentration are important factors in controlling the bubble size. Furthermore, four mathematical distributions (normal, log-normal, Weibull and gamma distributions) are fitted to the experimental data, among which the log-normal distribution is found to be the best fit based on the lower Anderson-Darling (AD) value.

The second major challenge is to thicken and consolidate the MFT for water recycling and land reclamation. The suitability of electrokinetic (EK) sedimentation to accelerate sedimentation of MFT is investigated in this study. Based on the experimental data, an electric field intensity of 150V/m along with an initial tailings solid concentration of no more than 5% are the optimum operating condition for EK sedimentation of MFT, in terms of reducing the overall sedimentation time and increasing the final solid concentration. The results show that the current density of EK sedimentation for MFT should not be more than 20 A/m2 to control the bubble effect and reduce power consumption.


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