Dissertation
Geochemical Modelling of Acid Mine Drainage (AMD) and Processes Controlling the Fate and Transport of AMD Pollutants in Groundwater Around Kansanshi Mine Site in Solwezi Town, Zambia
Washington State University
Doctor of Philosophy (PhD), Washington State University
2023
DOI:
https://doi.org/10.7273/000005218
Abstract
Complex geochemical reaction processes that occur within the tailings impoundments control the chemistry of resulting seepage or drainage water. In this dissertation, the second chapter focuses on simulating seepage water chemistry from the main sulphide tailings storage facility (TSF) around Kansanshi mine site in Zambia and its geochemical evolution in the underlying unconfined schist aquifer. The result of this study indicates that seepage water chemistry from the main sulphide TSF is likely to be within near neutral range (6.3 to 6.6) with elevated concentrations of sulphate and low concentration of Fe and Mn. The presence of calcite, dolomite and aluminosilicate minerals in the tailings helps to buffer the pH of the simulated seepage water within near neutral range favorable for the removal of metals from the solution through precipitation. Elevated sulphate levels in simulated seepage water results from the dissolution of both gypsum and pyrite. As the tailings water seeps into the shallow unconfined schist aquifer, geochemical simulations suggests that the presence of pyrite in the aquifer can moderately contribute to elevated concentrations of sulphate along the groundwater flow path with decreasing thickness of the capillary fringe or depth to water due to oxidation promoted by the increased rate of oxygen diffusion. The third chapter investigated the influence of fracture zones on solute (SO42-, Fe and Mn) transport from the main TSF using Equivalent Porous Media (EPM) approach, focusing on sulphate since it is the least reactive and can migrate far from the source. Two solute transport models were developed; one involving an EPM-only representation of the mapped fracture zones, and one including hypothetical fractures as high hydraulic conductivity zones to explore how unmapped fractures could impact solute transport. Results of the simulations revealed that only the model which incorporated hypothetical fractures to intersect wells that consistently show elevated sulphate concentrations show some degree of a match between the simulated and observed sulphate concentrations especially with boreholes KE03 and KE04 situated downstream of the main TSF, with the sulphate plume (>100mg/L) elongated along all fracture zones cutting across the dam. This demonstrates that fractures have a greater effect on solute transport than unfractured representation of the porous matrix, suggesting a simple EPM-based conceptual model may not be able to realistically represent transport behaviors in this system. However, in both cases, results from both solute transport models show that both Fe and Mn are restricted to the main TSF footprint and thus are not likely to be of concern from the facility.
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Details
- Title
- Geochemical Modelling of Acid Mine Drainage (AMD) and Processes Controlling the Fate and Transport of AMD Pollutants in Groundwater Around Kansanshi Mine Site in Solwezi Town, Zambia
- Creators
- Kenny Nyirenda
- Contributors
- Nicholas Engdahl (Advisor)Tim Ginn (Advisor)Md Akram Hossain (Committee Member)Joan Wu (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Civil and Environmental Engineering, Department of
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 128
- Identifiers
- 99901019837901842
- Language
- English
- Resource Type
- Dissertation