EVALUATION OF SULFIDE OXIDATION RATES - A LABORATORY STUDY COMPARING OXYGEN FLUXES AND RATES OF OXIDATION-PRODUCT RELEASE

A series of column experiments were conducted to evaluate three methods to determine sulphide oxidation rates in mine tailings. Measurements were made of (i) the flux of oxygen across the surface of the tailings, (ii) the oxygen consumption rates at the tailings surface, and (iii) the total sulphate produced in the pore water over time. Two columns were prepared with a mixture of quartz sand and pyrrhotite and overlain with varying thicknesses and grain sizes of a nonreactive layer. The impact of nonreactive layers with varying water-table depths on the overall oxidation rate was also evaluated. Modelling was applied to verify the importance of diffusion and kinetic control of the different column configurations. The results indicate that the overall rate of oxidation is reduced when fine-grain layers are applied. This is due to the high water saturation conditions generated by the fine material regardless of the depth to the water table. The consistency and precision of the methods used to measure relative oxidation rates were noted and a new practical field mapping tool is recommended. The new method provides rapid measurements of relative oxidation rates that can be applied to existing tailings rehabilitation with soil-type covers to show spatial and temporal trends.