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

Abstract

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 Ca2+ (up to 1.33 × 10−2 M), PO43− (up to 1.72 × 10−4 M), SO42− (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 Ca2+, PO43−, SO42−, 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.