Abstract
Environmental hazards are caused by uranium mining legacies and enhanced radioactivity in utilized groundwater and surface water resources. Knowledge of uranium speciation in these waters is essential for predicting radionuclide migration and for installing effective water purification technology.The validity of the thermodynamic data for the environmental media affected by uranium mining legacies is of utmost importance. Therefore, a comprehensive and consistent database was established according to current knowledge. The uranium data included in the database is based on the NEA TDB (Guillaumont et al., 2003) and is modified or supplemented as necessary e.g. for calcium and magnesium uranyl carbonates. The specific ion interaction theory (Brönsted, 1922) is used to estimate activity constants, which is sufficient for the considered low ionic strengths. The success of this approach was evaluated by comparative experimental investigations and model calculations (PHREEQC (Parkhurst and Appelo, 1999)) for several model systems. The waters differ in pH (2.7–9.8), uranium concentration (10−9-10−4 mol/L) and ionic strength (0.002–0.2 mol/L). We used chemical extraction experiments, ESI-Orbitrap-MS and time-resolved laser-induced fluorescence spectroscopy (TRLFS) to measure the uranium speciation. The latter method is nonintrusive and therefore does not change the chemical composition of the investigated waters. This is very important, because any change of the system under study may also change the speciation.
Highlights
The environmental hazard posed by geogenically increased radioactivity (NORM - Naturally Occurring Radioactive Material) in usable water resources is not limited to the remediation of contaminated sites of former uranium mining in Saxony and Thuringia or in Central Asia (Bernhard et al, 1998; Meinrath et al, 1999)
The polymeric species are weighted with respect to their number of uranyl units
It has been found that common thermodynamic databases for geochemical modelling software differ strongly in completeness, consistency and recent knowledge about uranium speciation in aquatic environments
Summary
The environmental hazard posed by geogenically increased radioactivity (NORM - Naturally Occurring Radioactive Material) in usable water resources is not limited to the remediation of contaminated sites of former uranium mining in Saxony and Thuringia or in Central Asia (Bernhard et al, 1998; Meinrath et al, 1999). THEREDA is a work in progress and more elements, reactions and interaction parameters will be included All of these databases are based on the NEA TDB (Guillaumont et al, 2003). The selected thermodynamic standard data (“selected values”) and ion interaction coefficients compiled in the NEA-TDB form a consistent database (Grenthe et al, 1992; Guillaumont et al, 2003). This work attempts to optimize the thermodynamic database and confirm the calculation results by measuring the speciation of uranium in the different solutions representing a broad range of natural groundwaters with high dissolved uranium using time-resolved laserinduced fluorescence spectroscopy, ion extraction on a resin, and electrospray ionization mass spectrometry
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