Exposure time risk assessment for filtered tailings facilities generating acid mine drainage

Tailings filtration reduces the geotechnical risks of tailings storage facilities by minimizing water management requirements compared to conventional tailings stored as slurry. However, prolonged exposure of sulfide tailings to the atmosphere may increase geochemical risks by generating acid mine drainage. This study identifies the main risks associated with prolonged exposure of acid generating filtered tailings through both qualitative and quantitative risk assessment. A workshop was conducted in collaboration with sector experts from two mining sites with filtered stockpiles. Results indicate that deposition may be delayed due to operational geotechnical constraints, and reclamation work were identified as the most critical stage regarding tailings exposure time. Additionally, a quantitative risk assessment was performed using site production data, material properties, and various deposition scenarios to estimate the time required for sufficient tailings cover to reduce oxygen flux. Quantitative risk assessments can help determine the parameters most susceptible to prolonged exposure, enabling the optimization of stockpile design to mitigate risks. • A critical time of 100 days, i.e., the period before tailings generate acidic porewater, is considered acceptable for planning deposition in a filtered tailings stockpile. • The workshop classified operational uncertainties as a minor risk and operational geotechnical constraints as a medium risk for delaying tailings deposition, and the implementation of reclamation as a high risk, as it may lead to prolonged exposure. • Managing exposure time variability is key to controlling acid mine drainage risk in filtered tailings stockpiles. The design should account for tailings production variability and incorporate deposition area, protective cover thickness, and deposition parameters.