Tailings are one of the major categories of industrial wastes, whose disposal is problematic from environmental viewpoint. Weathering of sulfide bearing waste materials commonly generate acidity and dissolved metals to the environment creating acid mine drainage (AMD). Typically, the chosen protective solutions emphasize low construction costs over environmental and technical sustainability.
Cover liners are constructed in mine sites over tailings impoundments as part of the closure works. A wide range of protective solutions have been designed and constructed on mine facilities globally for the purpose. The specifics of the solutions are dictated by the waste covered, the environment of the mine, climate conditions, and the governing regulations. The objective of the solutions range from various aspects and should account specific physical, chemical and biological processes in cold regions. The aim of the work was to analyze economical, technical and environmental aspects of five alternative cover scenarios.
The proposed method provides structural steps of multiple-criteria decision analysis (MCDA) to compare and contextually evaluate the implications of cover liner alternatives. Analytical Hierarchy Process (AHP) was applied as a MCDA approach for structuring complex problems and assisting decision makers to choose the best alternative among a discrete set of scenarios. MCDA can process competing and conflicting objectives in addition to quantitative and qualitative criteria, hence providing a holistic and interdisciplinary approach to the complex problem. Life-Cycle Assessment (LCA) was used for evaluating environmental impacts concerning emissions and energy demand. The proposed method combines LCA with AHP. In addition, hydraulic conductivity, material availability, waste recycling, and encapsulation characteristics were accounted as sub-criteria.
A case study on five different cover structure options in tailings pond of Pyhäsalmi mine demonstrates the framework. The study compares performance of the moraine based cover, bioash /steel slag cover, stabilization with portland cement or with composite binder, and use of advanced hardpan cover liner (AHCL). The AHCL comprises two different reacting stabilizing layers in addition to two moraine layers. Overall, the results from this study show that the AHCL was preferred over the other alternatives when the weighting of the main technical, environmental and economic criteria was equal (33%). Higher weighting of environmental and technical impacts (50%) favored stabilization with composite binder while higher weighting (50%) of costs favored moraine cover. The results from this project can be used to help to develop remediation strategies to reduce the environmental risks associated with mine wastes.
