Comparison of methods for the estimation of pyrite oxidation rate in a waste rock pile at Mine Doyon site, Quebec, Canada |
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| Authors: | Ondra Sracek Pierre Glinas Ren Lefebvre Ronald V Nicholson |
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| Institution: | Ondra Sracek, Pierre Gélinas, René Lefebvre,Ronald V. Nicholson, |
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| Abstract: | Several methods were evaluated and compared for the estimation of pyrite oxidation rates (POR) in waste rock at Mine Doyon, Quebec, Canada. Methods based on data collected in situ, such as the interpretation of temperature and oxygen concentration profiles (TOP) measured in the waste rock pile and pyrite mass balance (PMB) on solid phase samples were compared with the oxygen consumption measurements (OCM) in closed chamber in the laboratory. A 1-D analytical solution to a gas and heat transport equation used temperature and oxygen profiles (TOP) measured in the pile for the preliminary POR estimates at a site close to the slope of the pile (Site 6) and in the core of the pile (Site 7). Resulting POR values were 1.1 × 10− 9 mol(O2) kg− 1 s− 1 and 1.0 × 10− 10 mol(O2) kg− 1 s− 1 for the slope site and the core site, respectively. Oxidation rates based on pyrite mass balance (PMB) calculations for solid samples were 2.21 × 10− 9 mol(O2) kg− 1 s− 1 and 2.03 × 10− 9 mol(O2) kg− 1 s− 1, respectively, for the same slope and core sites, but the difference between sites was within the error margin. The OCM measurements in the laboratory on fresh waste rock samples yielded higher POR values than field methods, with average oxidation rate of 6.7 × 10− 8 mol(O2) kg− 1 s− 1. However, the OCM results on weathered and decomposed material from the rock stockpile (average oxidation rate 3.4 × 10− 9 mol(O2) kg− 1 s− 1) were consistent with results from the field-based estimates. When POR values based on fresh material are excluded, the remaining POR values for all methods range from 1.0 × 10− 10 to 3.4 × 10− 9 mol(O2) kg− 1 s− 1. The lowest estimated value (1.0 × 10− 10 mol(O2) kg− 1 s− 1) was based on TOP estimates in the interior of the pile where oxygen transport was limited by diffusion from the surface. These results suggest that small-scale OCM laboratory experiments may provide relatively representative values of POR in the zones of waste rock piles in which oxygen transport is not dominated by diffusion. |
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| Keywords: | Waste rock pile Pyrite oxidation rate Oxygen transport Temperature and oxygen profiles Pyrite mass balance Oxygen consumption measurement |
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