Minerals processed with a concentration technique generate tailings that must be stored in facilities designed according to specific technical, economic, legal, environmental and social requirements. During the operational life of tailings dams, the impact on the environment and on the surrounding communities is monitored through programs included in the mandatory environmental certifications. Once the mining operation is completed, the closure stage during which the tailings storage facility is rehabilitated, is launched.
When closing a tailings dam, consideration is given to factors such as the location, physical and chemical properties of the tailings, method of construction of the reservoir, and the behaviour of the tailings in the long term. For this, it is important to predict the reaction of the tailings when in contact with oxygen and water, as well as its capacity to generate acidity and leach metals.
The closure plan of the tailings dam must ensure physical, chemical, hydrological and biological stability in the post-closure period. One of the most significant challenges in achieving stability of mining waste with potential for acidity generation is contact with oxygen and water; therefore, to achieve chemical stability, the use of impermeable or semi-permeable barriers may be necessary. Each alternative comprises a series of closure activities which generate different direct and indirect costs.
In mining operations that use ore concentration, the cost of the tailings facility closure typically represents 21% of the total closure budget. The proposed solution to assure the chemical stability in the closure of the TSF is to add impermeable covers. These consist of a clay or geosynthetic clay liner placed over the tailings, on top of which a layer of drainage material is placed to direct water to an organic soil cover that sustains vegetation.
The main closure considerations within the budget to rehabilitate the tailing dams are physical, chemical and hydrological stability as well as revegetation. In the case of TSFs with the potential to generate acidity, the chemical stability typically accounts for 75% of the direct cost of dam closure.
