Geochemical Characterisation of Seepage and Drainage Water Quality from Two Sulphide Mine Tailings Impoundments: Acid Mine Drainage versus Neutral Mine Drainage |
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Authors: | P M Heikkinen M L Räisänen R H Johnson |
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Affiliation: | (1) Geological Survey of Finland, P.O. Box 1237, 70211 Kuopio, Finland;(2) US Geological Survey, Denver Federal Center, P.O. Box 25046, MS 964D, Denver, CO 80225, USA |
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Abstract: | Seepage water and drainage water geochemistry (pH, EC, O2, 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 serpentine-rich, 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. |
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Keywords: | Seepage waters Drainage waters Tailings Sulphide mining Heavy metals As Sulphate Water quality Environmental geochemistry Geochemical modelling Hitura Luikonlahti Finland |
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