Turbulence-Driven Metal Release from Resuspended Pyrrhotite Tailings

Abstract

The use of shallow water covers (up to 2 m) to flood reactive sulfide mine tailings is a common method of reducing the environmental impact of mining. It relies on the low solubility and diffusivity of oxygen in water. In actual tailings ponds, however, wind-induced waves and turbulent mixing can lead to tailings resuspension and increased oxygen transfer. Laboratory experiments and numerical modeling were performed to examine the impact of resuspension on metal release from sulfide mine tailings, and to elucidate the nature of the flow field. The results indicated that resuspended tailings oxidized and released acidity and metals considerably more than tailings at rest. The oxidation and metal release rates increased with an increase in the degree of turbulence-induced mixing in the water cover. Computed wall shear stresses on the surface of the tailings ranged from 0.14 to 0.42 N/m², which were close to, but slightly above, the critical shear stresses of the tailings (0.12–0.17 N/m²). The flow energy was found to be positively correlated to the cumulative release of metals (zinc, nickel, copper, and ferric iron) and sulfate.