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Effects of weathering on chemical and mineralogical properties of the Mount Polley mine tailings : preliminary implications for long-term ecosystem health Evans, Elana


The Mount Polley Mine’s tailings storage facility failure deposited large amounts of relatively unweathered material of a range of mineralogical and chemical composition over the Hazeltine Creek channel in Secwepemc territory. Reclamation efforts focus on the present chemical composition and sequential extractability of metals in the tailings. This precursory research focuses on the surface reactions of the tailings material and the effect that acids have on altering surface chemistry of these fresh tailings deposits in relation to environmental risk standards. Through laboratory simulation experiments, acid ammonium oxalate, hydrochloric acid, and aqua regia treatments, tailings composition under simulated acid weathered conditions were examined. The deposited tailings are characterized by low aeration and porosity, alkaline pH and very limited organic matter. Cu and V were readily available in concentrations that exceed the CSR regulations for the protection of soil invertebrates and plants. Exploratory PCA analysis suggested that the chemical composition of the tailings is not depth dependent, but spatial and material segregations were evident. XRD diagrams of tailings under simulated weathering conditions illustrate that the material has variable susceptibility to weathering. Calcite, magnetite and chlorite group minerals were removed by acid ammonium oxalate and hydrochloric acid treatments, while the more stable feldspar group minerals (albite, microcline), muscovite and quartz persisted despite treatment with the strong acid, aqua regia. Apatite group minerals were found in the majority of the raw samples. Elemental analysis revealed high concentrations of extractable P in the tailings. Longer-term monitoring of the receiving aquatic environments is recommended. Removal of tailings from the Hazeltine Creek channel is encouraged as is combining remnant tailings with organic material and till to improve aeration, porosity and structure, promote metal complexation and provide N for re-vegetation.

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