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Radium Sorption on Sandy and Clayey Sediments of the Upper Saxon Elbe River ValleyBaraniak, L.; Thieme, M.; Funke, H.; Bernhard, G.; Nindel, K.; Schreyer, J.; Nitsche, H.
The interaction of radium with characteristic sediments of the upper Saxon Elbe river valley was investigated with a two-fold aim: to provide key data for transport modelling within the framework of mining site restoration and to study the influence of barium-radium-sulfate coprecipitation on the radium adsorption behaviour. For this purpose sorption measurements were carried out on site-specific sediments (different kinds of sandstone, claystone and lime marl) using (1) original low-mineralized groundwater of this area, (2) typical acidic mine water coming from sulfuric acid residues of a former in-situ leaching process (~3 g/L SO42-, pH _ 2.5) and (3) groundwater which was contaminated by 2% mine water. The distribution ratios (Rd) were determined by batch experiments using an 8 weeks' equilibration at aquifer temperature (14C).
Radium sorption from pure and slightly contaminated groundwater onto limonite-rich turonian sandstone is characterized by relatively low distribution ratios (60-180 mL/g). When contacted with mine water, the sorption was enhanced by more than 20-fold compared to the pure and contaminated groundwaters. For the typical lime marl, the strongest sorption occured from the groundwater (390-520 mL/g) and a slightly reduced sorption took place from the acidic mine water.
In addition, the radium sorption was studied as a function of the Ba2+ and SO42- concentration. The results were discussed in terms of the ion product and the solubility product. Conclusions were drawn regarding the predominant sorption mechanisms: coprecipitation, surface complexation and ion exchange.
The long-term migration behaviour in the aquifers of the south-east Saxon Elbe basin was calculated on the basis of Hadermanns' equation, considering convection, dispersion, retardation and radioactive decay.
4 th International Conference on Nuclear and Radiochemistry, Saint Malo, France, Sept.8-13, 1996