Freisetzung von Metallen bei der Oxidation von Schlämmen : umweltchemische Aspekte der Baggergutdeponierung

Oxidation of sulfide minerals and organic substances, partially mediated by bacteria, affects mobilization of critical trace elements such as cadmium from reduced sludges both in terrestrial and aquatic environments. Chemical extraction experiments indicate, that during short-term aeration of sediment slurries a transformation takes place for cadmium from sulfidic/organic to easily reductible phases; after freeze drying or oven drying (60 °C) carbonatic and exchangeable associations are formed, which are easily soluble under various hydrochemical conditions. Investigations on a vertical profile of a tidally affected freshwater mud flat in the Elbe estuary suggest that Cd is in part remobilized from surface sediments by processes involving oxidative pumping. At higher salinity cadmium contents remobilized were partly kept in solution by the mechanism of chloro-complexation. The rates of mobilization depend upon the availability of Cd from the binding sites formed after the oxidation of the sulfidic phases.
Disposal of reduced sludges in estuaries should be avoided as well as areal dispersal of contaminated sediments in shallow marine areas due to remobilization effects. Chemical stabilization of critical metal components can be achieved by additon of calcium carbonate (land disposal of less buffered sludges) or by storage under permanently anoxic conditions out of the range of productive zones, e.g. in near-coast sub-sediment deposits.

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Freisetzung von Metallen bei der Oxidation von Schlämmen : umweltchemische Aspekte der Baggergutdeponierung