A study of the Lilla Bredsjön tailings impoundment in mid-Sweden—a comparison of observations with RATAP model simulations

Representative core samples have been collected from the Lilla Bredsjön tailings impoundment, Sweden. The results of geochemical and mineralogical analyses are compared with the RATAP model. The study shows that the tailings can be divided into distinct zones. The oxidation zone is characterized by oxidizing and acidic conditions associated with high concentrations of Fe, SO4 and other metal species in the pore solution. Acid-neutralization by carbonates and hydraulic conditions in the tailings lead to abrupt changes in redox potential and sharp decreases in aqueous metal concentrations in the intermediate zone. A hardpan layer, 2–4 cm thick, was identified. The concomitant precipitation of gypsum, jarosite, goethite and ferrihydrite contribute to the formation of the hardpan. The low rate of water percolation and the hardpan provide multiple-controls on the formation of an oxidation barrier, leading to low sulfide oxidation in the tailings. This study shows that the RATAP model is a useful tool to assist in predicting the impact of sulfidic tailings on the environment, especially in tailings with clear zoning characteristics.