Microscale measurements of oxygen diffusion and consumption in subaqueous sulfide tailings

The disposal of sulfide mine tailings in an environmentally sound, yet cost-effective, manner is an issue facing most metal mines. Subaqueous tailing disposal is considered an attractive option for disposal that limits oxygen (O2) availability within sulfide mine tailings and controlling sulfide oxidation and the resultant acid mine drainage (AMD). Assuming that O2 profiles represent steady-state conditions, we aim to evaluate the depth-dependent and temperature-dependent rates of O2 consumption in saturated mine tailings. Measurements include microscale O2 gradients and diffusivity profiles within columns representing undisturbed mine tailing profiles from an impoundment near Nanisivik Mine in northern Canada. Measurements were made across the diffusive boundary layer (DBL) above the tailing-water interface as well as in the tailings below. Laboratory measurements of O2 profiles are compared to in situ profiles. From the laboratory results it is possible to evaluate the O2 flux across the DBL and the depth-integrated O2 uptake. The results are compared with the average sulfate production rate over 3 months. O2 uptake in saturated tailings is discussed in relation to O2 uptake measured in columns after free drainage. The methods applied provide consistent O2 consumption rates as well as reliable predictions for controlling AMD by keeping tailings under water. Copyright © 2001 Elsevier Science Ltd