A feasibility study on the use of desulphurized tailings to control acid mine drainage

CIM Bulletin, Vol. 98, No. 1087, 2005

D. Bois, M. Benzaazoua, B. Bussière, M. Kongolo and P. Poirier

Environmental desulphurization is an attractive alternative for the management of acid generating tailings. Sulphide bulk flotation is the most commonly used method to produce desulphurized tailings, as shown from many previous works. This process can reduce the volume of problematic tailings to manage by making a sulphide fraction concentrate. The desulphurized tailings can then be used as construction material for an engineered cover to prevent acid mine drainage. Results from different laboratory and pilot-scale flotation tests are presented in this paper confirming that low-sulphide, non-acid generating tailings can be produced by froth flotation. This paper also demonstrates that sulphide concentrates obtained from desulphurization, mixed with the appropriate binders, can be used as feed material for paste backfill. From previous work on the evaluation of operating and capital costs of the desulphurization process for different ore types, the use of desulphurization as a tailings management approach was studied for several scenarios. The desulphurization process was then compared with other technologies (underwater disposal and engineered soil cover) currently used to prevent acid drainage (AD) for a new mining operation. Results show that partial or complete desulphurization is a technically and economically viable option to manage tailings during mine operation. Mine waste managers should consider desulphurization as an efficient technology. Considering that the models and design hypotheses used for this study are representative of the majority of existing sites and can be applied to future mining projects, the results from this study show that: Partial desulphurization of tailings presents savings opportunities especially when the tailings pond location is characterized by flat terrain and a soft foundation, a situation that increases the dam construction cost. Underwater disposal is the most economical option, when topography of the site and foundation conditions are favourable. However, the cost difference between this option and the partial desulphurization option is very small, especially for tailings with low neutralization potentials. The construction cost of dry cover with capillary barrier effect (CCBE) can vary significantly from one site to another, depending on the proximity of construction materials. Complete desulphurization of tailings remains a viable economic option when it becomes expensive to build low-permeability tailings dams. There is a wide range of field conditions where the four different scenarios are comparable from an economic point of view. The desulphurization techniques, particularly when combined with paste backfill, should be considered as an integrated management technique throughout the mine life that will facilitate rehabilitation at the end of mine life. Desulphurization may facilitate permitting for new mine projects, particularly in regions with restrictive environmental regulations. The comparison of tailings management methods presented in this paper is based solely on economic considerations. Risk aspects and long-term liabilities were not taken into account. This study opens the door for further work on risk analysis, life cycle analysis, and development of better integration between the upstream metallurgical process for value recovery and the downstream desulphurization process for environmental purposes.

Keywords: Desulphurized tailings, Acid mine drainage, Dry cover, Water covers, Paste backfill.