An investigation of resuspension and gas transfer in flooded mine tailings

The use of a shallow water cover (up to 2m) to flood reactive sulfide mine tailings is a popular method of acid drainage prevention used by the mining industry. In addition to reduced solubility and diffusivity the water cover creates a reducing environment suitable for supporting sulphate reducing micro-organisms in the tailings where soluble metals may precipitate as sulphides. In flooded tailings, however, wind induced turbulence at the air-water interface can increase the oxygen flux from air into the water and also resuspend the tailings particles.; The critical shear stress causing the onset of sediment motion for tailings was measured experimentally in a rotating flume. Existing theoretical formulations were also used to calculate this critical shear stress and found to over predict the critical shear stress. These theoretical formulations may not be accurate for determining the onset of sediment motion for cohesive mine tailings. Experimental determination may be the only reliable method. Theoretical formulations were also developed to calculate the shear stress acting on the surface of tailings caused by the action of wind-waves and currents for a particular fetch, wind speed and water depth. When the calculated shear stress equals the critical shear stress sediment motion is initiated.; The experimental data and the numerical simulations showed that resuspension of tailings drastically increases the rate of tailings oxidation and significant release of metals the water cover. The rate of tailings oxidation is accelerated by the amount of resuspended tailings in the water cover and the degree of mixing (turbulent and mean kinetic energy in the water cover). Oxygen plays the major role as an oxidant in the initial stages to lower the pH of the water cover. Once the pH is below 3.5 ferric iron is the major oxidant and the reaction between the ferric iron and the sulphide minerals is accelerated by the degree of mixing. Only resuspended tailings were found to oxidize substantially. The oxidation rate of the undisturbed tailings were found to be lower or equal to that of tailings below a static water cover. The metals from the water cover did not infiltrate into the pore water of the tailings. This was found to occur as long as the surface of tailings was not severely disturbed. The precipitation and/or adsorption of metals was found to increase with the amount of tailings resuspended in the water cover and the degree of mixing.; The influence of depth of water on the mass transfer of oxygen from air into water due to wind-induced waves was investigated in a gas transfer flume (GTF). The results from the GTF experiments showed that the mass transfer velocity of oxygen increases non-linearly with wind speed at any depth of water. (Abstract shortened by UMI.)...