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In the Lusatian Lignite Mining District a number of dump purification plants are in operation. The iron rich and partly acid swamp waters are mainly treated with white fine lime and white fine hydrate. The sludge generation during water treatment processes in Lusatian dumps amounts to approximately 13mio m³/a. At present, the sludge is considered as waste product and mainly gets disposed.

However, novel possibilities to use this iron sludge are currently being discovered. Therefore, the sludge needs to be characterised chemically. According to the quality of the untreated water and the conditioning technology, the sludges differ considerably in their chemical and mineralogical character. These special characteristics require the development of costumized analytical methods. The origin of the sludges and their interaction with the aquatic environment can be described and predicted very well by means of hydrogeochemical models. Thus, hydrogeochemical modelling is an important instrument for planning the application of iron hydroxide sludges. The chemical characteristics of the sludges allow an environmental-safe utilisation, particularly to neutralise acidic open-pit lakes. Due to calcite and surface complexation, the raw sludge of dump water purification plants acts as acid buffer. Older sludges, that have been stored in stocking places, have a considerable buffering capacity as well. The sludges´ high phosphate and arsenic adsorption capacity offers the possibility to use them for the treatment of eutrophic and contaminated water bodies.

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