Long-term evolution of pH and metals (Al, Fe, Mn, U) in pyrite-bearing waste rocks using reactive transport modeling: Dealing with stock and process uncertainties

Hydrogeochemical management of mine effluents is essential to ensure a responsible and sustainable mining industry. These effluents can be heavily affected by acid mine drainage (AMD) over time spans that often extend over decades, during which continuous monitoring and treatment are required. However, significant uncertainties typically remain regarding the duration and evolution of AMD, as the source terms are often poorly characterized—particularly in the case of old or legacy mines. For mining operators, reducing these uncertainties represents a key advantage for optimizing long-term treatment and operational strategies, both technically and economically. In this study, we use reactive transport (RT) modeling to interpret 30 years of monitoring data from the former Bertholène uranium mine in France. Our results show that metal loadings have steadily decreased (Al, Fe, Mn, and U) to reach levels below regulatory limits for U (<1.8 mg/L), in parallel with a general decline in sulfide oxidation rates. This improved understanding will contribute to the development of a treatment strategy. In the coming decades, treatment will focus on addressing the remaining acidity, rather than on metals or radionuclides whose pre-treatment concentrations should comply with regulatory requirements.