Reactivity of oxidized sulfidic mine tailings during lime treatment

Lime amendment is a common method for neutralizing the accumulated acidity and sequestering metals in oxidized mine tailings. This study assessed the reactivity of sulfide oxidation products during lime treatment of tailings samples from the Kam Kotia mine site in Timmins, Ontario. The contributions of several alkalinity consumption mechanisms to the lime requirements were compared. Methods involved lime treatment tests, multiple water extractions, sequential extractions, analytical scanning electron microscopy, and X-ray diffractometry. The majority of the alkalinity consumption was due to the reaction of water-insoluble Fe-oxyhydroxysulfate minerals (including K-jarosite, Na-jarosite, H-jarosite, and schwertmannite) with lime to form Fe-oxyhydroxides (including goethite) and gypsum. The cation exchange capacity of the oxidized tailings contributed a minor proportion to the alkalinity consumption. Measurements of water-soluble acidity underestimated lime requirements by more than 50% on average.