Long-term environmental impact of tailings deposits

Abstract

This paper, within the MiMi project, explains the models and the modelling used in the performance assessment (long-term) calculations for the remediation of sulphidic mine tailings. The long-term impact of tailing deposits on the environment is addressed for two types of cover: soil and water covers. Oxygen intrusion is the process that determines the sulphide oxidation and the generation of acid mine drainage containing toxic metals. The primary acidity generated in the tailings from the sulphide oxidation is to a large extent neutralised by the buffering minerals in the deposit. However, when the water leaves the deposit, more acidity is generated due to the oxidation of mainly the ferrous iron (latent acidity). For soil covers, the generated acidity and dissolved metals flow downward with the infiltrating water. However, in a water cover, the reaction products formed may diffuse upwards into the water covering the deposit. Therefore, the acidity is not neutralised in the interior of the deposit. The behaviour of metals/metalloids such as Cu, Pb, Cd and As are also studied. They may be sorbed on the mineral surfaces of the minerals and retained in the deposit for a long time. Some of them may dissolve the more soluble sulphides (e.g., pyrrhotite) and precipitates as secondary sulphides. The data were selected based on experience from primarily Kristineberg (northern Sweden) but also from other sites.