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Oxidation rates of low sulphide (< 0.5 wt.%) gneissic waste rock from the Cluff lake U mine, northern Saskatchewan, Canada were determined using 3 independent methods: O 2 consumption rates in kinetic cells, SO 4 measurements of kinetic cell effluent and humidity cell SO 4 release rates. The O 2 consumption measurements demonstrated that the oxidation of pyrite was strongly dependent on grain size and moderately dependent on water content, temperature and microbiology. Oxygen consumption rates were highest at water contents of 5-10 wt.% (12-25% saturation). Measured SO 4 release rates (3.1-91 mg SO 4 kg -1 wk -1 ) for the kinetic cells were comparable to rates calculated from the O 2 consumption values (6.9-70 mg SO 4 kg -1 wk -1 ). Sulphate release rates determined from humidity cells were generally higher than those obtained from the kinetic cells, ranging from 6 to 64 mg SO 4 kg -1 wk -1 for the coarsest and finest fraction, respectively. These differences were attributed to sample heterogeneity. |
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