UBC Theses and Dissertations
Reactive transport modeling of waste rock weathering in permafrost environments Yi, Xueying
Developing an understanding of the thermo-hydrological-chemical (THC) behavior of waste rock piles (WRPs) at mine sites in cold-region climates is important for anticipating contaminated drainage. In cold-region climates, freeze-thaw cycles and the possible development of permafrost within WRPs add to the complexity of the coupled processes occurring in WRPs but also provide opportunity for reclamation strategies, in particular through the placement of thermal covers to isolate the waste rock from weathering. Reactive transport modeling (RTM) has proven a versatile tool that can help characterize the coupled processes within mine waste. In this thesis, RTM code MIN3P-HPC has been enhanced to account for the effects of seasonal freeze-thaw cycles on the weathering behavior of WRPs with specific focus on the development of permafrost and drainage quality. The code was used to perform a sensitivity analysis for a hypothetical full-scale sulfide-bearing WRP to assess the influence of two key factors: climate warming and sulfide reactivity. Simulation results indicate that for some WRPs hosting permafrost under present-day conditions, a marginally warmer climate has the potential to lead to self-heating of the pile and substantially increase the mass loadings. Moreover, even if permafrost within a WRP persists in a long term, the results illustrate that a warming climate can increase mass loadings significantly due to an increased active layer thickness and a longer duration of thawed conditions. Subsequently, the code was used to evaluate the effectiveness of thermal covers at mine sites in cold-region climates, constrained by observational laboratory and field data from the Meadowbank mine, located in the Kivialliq region. Favorable agreement of simulated and measured thermal data provides confidence in the utility of the numerical model to simulate coupled processes within a covered pile subjected to freeze-thaw cycles. The model was expanded to interpret the long-term functionality and effectiveness of the cover as a function of cover thickness. The results of this research demonstrate the capabilities of MIN3P-HPC for simulating problems in permafrost environments affected by seasonal freeze-thaw cycles and to evaluate weathering of WRPs in such environments. This modeling tool has potential to assist with the design of reclamation strategies.
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