IMPACT OF HIGH ALUMINUM LOADING ON A SMALL CATCHMENT-AREA (THURINGIA SLATE MINING AREA) GEOCHEMICAL TRANSFORMATIONS AND HYDROLOGICAL TRANSPORT

A field study was performed on the effects of acid mine leachate from slate mine tailings seeping into a small river passing through the tai lings. Before entering the tailings the river water has high alkalinit y which neutralizes acidity upon mixing with leachate within the taili ngs. Downstreams of the tailings the pH of the river water ranges abou t pH = 8, the water contains high concentrations of sulfate (approxima te to 1500 mu mol/l) and particulate bound aluminium (approximate to 8 0 mu mol/l), but low concentrations of dissolved aluminium (approximat e to 3 mu mol/l). It is therefore assumed that Al(OH)(3) colloids are precipitated during the neutralisation process and transported out of the tailings. The concentration of particulate bound aluminium along t he river shows a strong correlation with the concentration of sulfate, which indicates that particulate bound aluminium is conservative. It therefore seems that under dry weather conditions (under most of the s ampling was performed) no chemical retention mechanism exists which co nfines the distribution of aluminium to a restricted part of the catch ment area. In contrast, the white river sediment is rich in both alumi nium and sulfate, which suggests the temporary formation of aluminium hydroxosulfate minerals. Favorable (i.e. acidic) conditions may prevai l at high discharges where the acidity accumulated in the tailings is flushed into the river with its subsequent acidification.