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Matlock, Blaise

Mines generate millions of tonnes of waste rock over their lifespan, most of which will be stored in large piles exposed to the environment. Weathering of these waste rock piles over decades to millennia will release heavy metals and metalloids into the environment, potentially causing significant long-term environmental contamination. This is particularly a concern for waste rock with a high sulphide content, as oxidation of sulphidic waste rocks releases acidity and significant quantities of metals and metalloids. One inexpensive, simple, and effective method of contaminant attenuation in waste rock piles is the strategic layering of different waste rock types. This method utilizes geochemical processes that rely on the order infiltrating water encounters waste rock to minimize effluent contaminant concentrations. However, many geochemical mechanisms governing order-of-encounter effects are poorly understood. To develop a better understanding of the processes affecting metal and metalloid release and attenuation under neutral pH conditions and particularly of order-of-encounter effects, a reactive transport model was developed using MIN3P for the stacked waste rock barrels previously studied by Hirsche (2012) at the Antamina mine, Peru. A secondary objective of this model was to determine whether the geochemical mechanisms posited by Hirsche (2012) could explain the observed effluent lead, molybdenum, and zinc concentrations. The reactive transport model was also applied to the data-scarce Phu Thap Fah mine, Thailand, which has an extensive history of environmental contamination, to identify orders-of-encounter that could reduce effluent contaminant concentrations. Simulation results indicate that the reactive transport model is able to capture the main geochemical processes governing metal release and attenuation at Antamina, although the model has several limitations and did not predict all observed order-of-encounter effects. Some critical findings of the model are that silicate formation, as posited by Hirsche (2012), could explain the observed concentrations of zinc at Antamina, that copper surface complexation could be an important copper attenuation process at Antamina, and that lead and arsenic could be co-precipitating as the mineral mimetite (Pb5(AsO4)3Cl) at Antamina. When applied at Phu Thap Fah, the reactive transport model identified that layering sulphidic waste rock above calcite above gossan could result in improved effluent quality over the current waste rock management system. However, these results must be viewed with caution, since experimental data or field observations were not available to constrain the model.

Text

University of British Columbia. ENVR 449

Vancouver : University of British Columbia Library

10.14288/1.0432711

Science, Faculty of; Earth, Ocean and Atmospheric Sciences, Department of

Undergraduate

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