Using Oxygen Consumption Rates as a Guide to Scale Up Laboratory Kinetic Data to Field Conditions

摘要

Field and modelling studies of sulfide oxidation in waste rock from the scientific literature indicate that O_2 penetration is typically less than about 50 m and commonly less than 20 to 30 m due to consumption by reactions with sulfide minerals. A compilation of data from a range of field and simulation modelling efforts indicates a consistent trend of increase in the intrinsic oxidation rate (IOR) with temperature over range of 2 to 57°C, yielding an activation energy of 91 kJ/mole. This value is consistent with the value of 92 kj/mole determined for pyrite oxidation by ferric ion. This activation energy indicates an increase in IOR of about 3.7 times per increase in temperature of 10°C.The O2 consumption rate data provide a potential guide to scaling kinetic data collected in laboratory experiments to field conditions. A comparison of the field data to O_2 consumption rates for 594 laboratory tests from the International Kinetic Database (Morin et al. 1995) shows that ratios of the laboratory IOR to field IOR range from 23 at the 25~(th) percentile to 58 at the 50~(th) percentile to 206 at the 75~(th) percentile or about one order of magnitude. If the potential exists for a waste rock to increase in temperature by 20°C due to exothermic oxidation reactions, the potential increase in IOR based on an activation energy of 91 kj/mole is about 13.7 times. If this factor of temperature increase is considered in the scaling approach, the range in ratios of laboratory IORs to field IORs decreases to 1.7 to 15 at the 25~(th) to 75~(th) percentiles. With this scaling approach, no other scaling factors are needed because the IOR values here are based on field data and therefore include the various effects of particle size, water-rock ratio, and elemental content.