Novel speciation method based on Diffusive Gradients in Thin Films for in situ measurement of uranium in the vicinity of the former uranium mining sites.

The Diffusive Gradients in Thin Films (DGT) technique using PIWBA resin (The Dow Chemical Company) was developed and validated for the measurement of uranium (U) concentration in natural and uranium mining influenced waters. The U uptake on the PIWBA resin gel was 97.3 ± 0.4% (batch method; Vsol = 5 mL; [U] = 20 µg L(-1); 0.01 M NaNO3; pH = 7.0 ± 0.2). The optimal eluent was found to be HNO3conc/70 °C with an elution efficiency of 88.9 ± 1.4%. The laboratory DGT investigation demonstrated that the PIWBA resin gel exhibits a very good performance across a wide range of pH (3-9) and ionic strength (0.001-0.7 M NaNO3) at different time intervals. Neither effect of PO4(3-) (up to 1.72 × 10(-4) M), nor of HCO3(-) (up to 8.20 × 10(-3) M) on the quantitative measurement of uranium by DGT-PIWBA method were observed. Only at very high Ca(2+) (2.66 × 10(-4) M), and SO4(2-) (5.55 × 10(-4) M) concentration, the U uptake on DGT-PIWBA was appreciably lessened. In-situ DGT field evaluation was carried out in the vicinity of three former uranium mining sites in France (Loire-Atlantique and Herault departments), which employ different water treatment technologies and have different natural geochemical characteristics. There was a similar or inferior U uptake on DGT-Chelex(®)-100 in comparison with the U accumulation on a DGT-PIWBA sampler. Most likely, the performance of Chelex(®)-100 was negatively affected by a highly complex matrix of mining waters. The high concentration and identity of co-accumulating analytes, typical for the mining environment, did not have a substantial impact on the quantitative uptake of labile U species on DGT- PIWBA. The use of the polyphenol impregnated anion exchange resin leads to a significant advancement in the application and development of the DGT technique for determination of U in the vicinity of the former uranium mining sites.

DGT as a useful monitoring tool for radionuclides and trace metals in environments impacted by uranium mining: Case study of the Sagnes wetland in France.

The Diffusive Gradients in Thin films (DGT) technique was used to analyse U, (226)Ra and other trace metals in stream water and soil porewater in a wetland in France impacted by uranium mining. High resolution profiles of metals in soil porewater obtained by DGT could be measured for the first time up to a depth of 75 cm by the construction of a novel DGT holder. In stream water, the DGT technique was compared to speciation carried out by filtration (0.45 µm) and ultrafiltration (UF) (500 kDa/100 kDa/10 kDa) and DGT porewater profiles were compared with piezometer data obtained in a parallel study. An increase in the trace concentrations of dissolved (0.45 µm) and particulate U, (226)Ra, and elements such as Al, Fe, Mn and Ba was observed in the stream water as it passes through the bog as a results of mobilization from the wetland. The porewater results indicate DGT labile metals species to be present in porewater and mobilization of uranium and other elements linked to the presence of enriched clays. In stream water, colloids and particles govern the behavior of U, Al and Fe, whereas Mn, Ba and Ra are essentially transported as truly dissolved metal species with DGT labile concentrations accounting for 100% of the dissolved fraction. The combined approaches of DGT and UF allow us to obtain a better understanding on the biogeochemical processes involved in the retention and mobility of U and (226)Ra in the wetland.

Uranium aqueous speciation in the vicinity of the former uranium mining sites using the diffusive gradients in thin films and ultrafiltration techniques.

The performance of the Diffusive Gradients in Thin films (DGT) technique with Chelex(®)-100, Metsorb™ and Diphonix(®) as binding phases was evaluated in the vicinity of the former uranium mining sites of Chardon and L'Ecarpière (Loire-Atlantique department in western France). This is the first time that the DGT technique with three different binding agents was employed for the aqueous U determination in the context of uranium mining environments. The fractionation and speciation of uranium were investigated using a multi-methodological approach using filtration (0.45 µm, 0.2 µm), ultrafiltration (500 kDa, 100 kDa and 10 kDa) coupled to geochemical speciation modelling (PhreeQC) and the DGT technique. The ultrafiltration data showed that at each sampling point uranium was present mostly in the 10 kDa truly dissolved fraction and the geochemical modelling speciation calculations indicated that U speciation was markedly predominated by CaUO2(CO3)3(2-). In natural waters, no significant difference was observed in terms of U uptake between Chelex(®)-100 and Metsorb™, while similar or inferior U uptake was observed on Diphonix(®) resin. In turn, at mining influenced sampling spots, the U accumulation on DGT-Diphonix(®) was higher than on DGT-Chelex(®)-100 and DGT-Metsorb™, probably because their performance was disturbed by the extreme composition of the mining waters. The use of Diphonix(®) resin leads to a significant advance in the application and development of the DGT technique for determination of U in mining influenced environments. This investigation demonstrated that such multi-technique approach provides a better picture of U speciation and enables to assess more accurately the potentially bioavailable U pool.

Evaluation and application of Diffusive Gradients in Thin Films (DGT) technique using Chelex®-100, Metsorb™ and Diphonix® binding phases in uranium mining environments.

A new resin- Diphonix(®) in Diffusive Gradients in Thin Films (DGT) technique for the determination of uranium was investigated and compared with previously used binding phases for uranium, Chelex(®)-100 and Metsorb™. The DGT gel preparation and the elution procedure were optimized for the new resin. The U uptake on Diphonix(®) resin gel was 97.4 ± 1.5% (batch method; [U] = 20 µg L(-1); 0.01 M NaNO3; pH = 7.0 ± 0.2). The optimal eluent was found to be 1 M 1-hydroxyethane-1, 1-diphosphonic acid (HEDPA) with an elution efficiency of 80 ± 4.2%. Laboratory DGT study on U accumulation using a DGT samplers with Diphonix(®) resin showed a very good performance across a wide range of pH (3-9) and ionic strength (0.001-0.7 M NaNO3). Diffusion coefficients of uranium at different pH were determined using both, a diffusion cell and the DGT time-series, demonstrating the necessity of the implementation of the effective diffusion coefficients into U-DGT calculations. Diphonix(®) resin gel exhibits greater U capacity than Chelex(®)-100 and Metsorb™ binding phase gels (a Diphonix(®) gel disc is not saturated, even with loading of 10.5 µmol U). Possible interferences with Ca(2+) (up to 1.33 × 10(-2) M), PO4(3-) (up to 1.72 × 10(-4) M), SO4(2-) (up to 4.44 × 10(-3) M) and HCO3(-) (up to 8.20 × 10(-3) M) on U-DGT uptake ([U] = 20 µg L(-1)) were investigated. No effect or minor effect of Ca(2+), PO4(3-), SO4(2-), and HCO3(-) on the quantitative measurement of U by Diphonix(®)-DGT was observed. The results of this study demonstrated the DGT technique with Diphonix(®) resin is a reliable and robust method for the measurement of labile uranium species under laboratory conditions.