Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

Dr. Ernest K. Yanful

Abstract

Proper management of sulphide rich reactive mine tailings is a growing concern for mining industries. Oxidation of tailings can release acids and toxic metals into the surroundings, which can potentially pollute the ecosystem. Confining tailings under shallow water covers is one of the most successfully applied technologies for long-term storage. The water has lower solubility and diffusivity of oxygen than air and can significantly reduce the influx of oxygen to the bed tailings. However, wind-induced waves and currents in the water can resuspend bed tailings and ultimately result in oxidation.

Extensive field investigations were carried out to evaluate the performance of the existing Shebandowan tailings storage facility, Thunder Bay, Ontario, Canada. Sediment traps and optical backscatter sensor data showed some amount of resuspension occurring at this site under existing conditions. The role of wind induced circulation currents in the resuspension was not clear from previous studies. A semi empirical approach was used to determine the total bed shear stress in the tailings pond, where the current fraction of the bed shear stress was obtained by fitting the Log-Law to mean velocity profiles measured using acoustic Doppler current profiler (ADCP). This was the first study, where the actual currents were measured in a tailings pond. The results showed that wave-current interactions increased the total bed shear stress. A graphical approach was developed to obtain the critical shear stress and erosion rate characteristics of the bed tailings using field recorded resuspension. Previous studies obtained these parameters from laboratory column and flume experiments that did not necessarily represent field conditions.

Based on the field investigations, some major improvements were made to an existing model of water cover design and the results show that wave-current interactions significantly increase the required depth of water from 3.9 m in the absence of wave-current interaction to 6.3 m to completely eliminate tailings resuspension in the west cell of the tailings pond. However, the optimized water depths of less than 2.2 m, 1.1 m, and 2.0 m for the west, middle and east cells were sufficient to reduce tailings concentration to values within the regulatory limit of 15 mg/L, respectively.




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