No abstract

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.

Petroleum hydrocarbons (PHCs) react with oxygen by low temperature oxidation (LTO) to produce a coke-like solid residue, carbon oxide gases, and vaporized hydrocarbons. The feasibility of using LTO to remediate sandy soil contaminated with motor oil has been investigated in a plug flow reactor operated at temperatures between 150 and 221 °C and with air injection fluxes ranging from 0.40 to 2.28 m3(ST)·m–2·h–1. Low temperature oxidation occurred in three successive periods: the induction period during which the oxygen depletion in the reactor exit stream remained small, the middle period characterized by peaks in oxygen depletion and carbon oxide concentrations, and the tailing period corresponding to very gradual decreases in oxygen depletion and carbon oxide concentrations. The extents of oxidation measured in our tests ranged from 29 to 37 moles O2/kg oil. Soil samples treated at temperatures between 167 and 176 °C met all the Tier 1 levels of the Canada Wide Standard for PHCs in coarse-grained surface soils, except those for soil contact and protection of ground water. Concentrations of individual polycyclic aromatic hydrocarbons (PAHs) in the soil samples treated at 167 and 176 °C complied with the Canadian Environmental Quality Guidelines for all soil types. Key words: low temperature oxidation, petroleum hydrocarbons, remediation, soil, motor oil.