Hydrogeochemical characterisation of surface water, sorption of metal(loid)s on sediments and exchange processes within
Lengenfeld in Saxony, Germany, was the first uranium milling and processing site of the former Wismut SAG. In 1954 a dam collapse happened and roughly 50.000 m3 of tailings were spilled into the low lands of the Plohnbach river forming several wetland are
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Abstract. Lengenfeld in Saxony, Germany, was the first uranium milling and
processing site ofthe former Wismut SAG. In 1954 a dam collapse happened and roughly 50.000 m3 of tailings were spilled into the low lands of the Plohnbach river forming several wetland areas. Both sediments as well as surface and seepage water were investigated downstream of the tailing dam with special respect to uranium and arsenic. It was shown that arsenic speciation (As(III), As(V), Monoand Dimethylarsenic) is highly dependent from seasonal variation. Arsenic is strongly bound to ironhydroxides and thus removed effectively from the water. However, for uranium no removal happens to occur in the Lengenfeld wetland since a major part ofthe uranium in the sediment is readily exchangeable.
lntroduction After the end of the Second World War uranium ore deposits within the Erzgebirge and Vogtland areas received more and more economic importance. Mining and processing was operated by the Wismut SAG. In 1947 Wismut opened their first uranium processing plant in Lengenfeld, a small town in the Bastern Vogtland/ Germany (Fig. 1). Ores were delivered from mines in the Vogtland area as well as from the Erzgebirge and in the late 1950s also from Thuringia (Ronneburg). The ores, which showed exclusively low uranium concentrations (0.03-0.5%, Schall 1995), were processed mechanically at first and later by alkaline or acid leaching. During the first period of mechanical processing heaps were deposited along a small river
B. J. Merkel et al. (eds.), Uranium in the Aquatic Environment © Springer-Verlag Berlin Heidelberg 2002
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named "Plohnbach". During the later stages of leaching a settling pondwas built up. The tailings deposited vary considerably in grain size and chemistry due to the testing of different processing methods. Of the total 1.5 Mio m3 residues from the uranium ore processing, 890 000 m3 of tailing material were deposited (Wismut 1992).
Lengemeld
Plohn
Fig. 1. Location of the tailing site (IAA) northeast of the town Lengenfeld, Eastem Vogtland I Germany
In 1954, the main dam of the uranium tailing collapsed during a flooding event. Tailing material (roughly 50.000 m3) swept into the wide Plohnbach river valley. The fine tailings, deposited up to four kilometres south of the tailing to the former Iake "Lenkteich", as a 1ow permeability layer, dammed both river and tailing water and created an extensive wetland area within the Plohnbach valley. After the uranium processing was abandoned at Lengenfeld and shifted to the big tailing and milling sites Crossen and Seeligenstedt, the "Fluorite and Baryte GmbH" took over in 1961 and covered the tailings with 5-8 m of residues from fluorite and barite processing. Current investigations of the wetland and the nearby surrounding were focused on water and sediment samples, taking into account existing data from examinations by the "Radiation Protection Agency" (BfS) and the engineer enterprise "C&E Chernnitz".
Hydrogeology Background
The study area is located at the
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