Summary
The seepage of water polluted with arsenic and heavy metals from mine pits and tips into groundwater has a significant impact on the environment. While the closing of active mines lowers the high concentration of pollutants, their long-term concentration levels are difficult to predict. Thus, passive methods are used for contaminant retention and containment based on geochemical barrier reactions. Because such pit and tip seepage water contains Fe and Al, it possesses an intrinsic self-cleaning potential for the binding and separation of loading elements such as As, Pb, Cd, Co, Cu, Ni, Mn and Zn through the use of hydroxide precipitation. On this basis, the aim of the current project was to initiate the process of precipitation of hydroxidic Fe phases and Al hydroxides within the mine, and for the hydroxides enriched with contaminants to be deploy a deposition option within the flooded mine pit. Particular attention was paid to the development of a method based on the adsorption of hydroxide precipitation, to be tested under real conditions (also in respect to long-term use) with the prospect for successful transfer to other suitable problem cases.
Results:
- The precipitation of Fe and Al hydroxide led to a reduction of the dissolved components of the loading elements by about 90 %.
- The essential material parameters on the yield of precipitation/depletion include the pH value, O2 concentration, the concentration of Fe and Al and their relationship to the loading elements, and the content of F-.
- The residual content of the arsenic and iron discharged from the mine water is transported almost exclusively in particulate form.
- The stable situation of the three-year pilot study showed that the storage conditions did not cause remobilisation of sediments and that the method is therefore suitable for ongoing operation.
