Seepage water and drainage water geochemistry (pH, EC, O 2 , redox, alkalinity, dissolved cations and trace metals, major anions, total element concentrations) were studied at two active sulphide mine tailings impoundments in Finland (the Hitura Ni mine and Luikonlahti Cu mine/talc processing plant). The data were used to assess the factors influencing tailings seepage quality and to identify constraints for water treatment. Changes in seepage water quality after equilibration with atmospheric conditions were evaluated based on geochemical modelling. At Luikonlahti, annual and seasonal changes were also studied. Seepage quality was largely influenced by the tailings mineralogy, and the serpentinerich, low sulphide Hitura tailings produced neutral mine drainage with high Ni. In contrast, drainage from the high sulphide, multi-metal tailings of Luikonlahti represented typical acid mine drainage with elevated contents of Zn, Ni, Cu, and Co. Other factors affecting the seepage quality included weathering of the tailings along the seepage flow path, process water input, local hydrological settings, and structural changes in the tailings impoundment. Geochemical modelling showed that pH increased and some heavy metals were adsorbed to Fe precipitates after net alkaline waters equilibrated with the atmosphere. In the net acidic waters, pH decreased and no adsorption occurred. A combination of aerobic and anaerobic treatments is proposed for Hitura seepages to decrease the sulphate and metal loading. For Luikonlahti, prolonged monitoring of the seepage quality is suggested instead of treatment, since the water quality is still adjusting to recent modifications to the tailings impoundment.
Tailings-derived mine drainage water that is neutral in character, has a high electrical conductivity and contains elevated sulphate, chloride and nickel concentrations, has caused deterioration in groundwater and surface water quality in the mining area of Hitura in Western Finland. This deterioration, and thereby the location of the contaminant plume, was recognized in the water chemistry in the form of a gradual change in ion composition from Ca-HCO 3 -type water towards a Mg-SO 4 -rich type. It was possible to define the extent of the pollution by using cluster analysis to distinguish between hydrochemically different regimes and performing an electrical sounding survey. The results indicated that contamination is most intense close to the tailings impoundment and is related to an esker complex running across this area. Nevertheless, the water in the eastern and southern parts of the area upgradient of the hydraulic head is uncontaminated and suitable for water supply purposes.
The names of some of the authors of this section were inadvertently omitted in the original publication. We regret this omission and provide all of the authors' names here:
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