2 results found
Kirby M, Simperler A, Krevor S, et al., 2018, Computational tools for calculating log β values of geochemically relevant uranium organometallic complexes, Journal of Physical Chemistry A, Vol: 122, Pages: 8007-8019, ISSN: 1089-5639
Uranium (UVI) interacts with organic ligands, subsequently controlling its aqueous chemistry. It is therefore imperative to assess the binding ability of natural organic molecules. We evidence that density functional theory (DFT) can be used as a practical protocol for predicting the stability of UVI organic ligand complexes, allowing for the development of a relative stability series for organic complexes with limited experimental data. Solvation methods and DFT settings were benchmarked to suggest a suitable off-the-shelf solution. The results indicate that the IEFPCM solvation method should be employed. A mixed solvation approach improves the accuracy of the calculated stability constant (log β); however, the calculated log β are approximately five times more favorable than experimental data. Different basis sets, functionals, and effective core potentials were tested to check that there were no major changes in molecular geometries and ΔrG. The recommended method employed is the B3LYP functional, aug-cc-pVDZ basis set for ligands, MDF60 ECP and basis set for UVI, and the IEFPCM solvation model. Using the fitting approach employed in the literature with these updated DFT settings allows fitting of 1:1 UVI complexes with root-mean-square deviation of 1.38 log β units. Fitting multiple bound carboxylate ligands indicates a second, separate fitting for 1:2 and 1:3 complexes.
Kenney J, Kirby, Cuadros J, et al., 2017, A conceptual model to predict uranium removal from aqueous solutions in water–rock systems associated with low- and intermediate-level radioactive waste disposal, RSC Advances, Vol: 7, Pages: 7876-7884, ISSN: 2046-2069
Global stores of radioactive waste are housed in surface stores where actinides are susceptible to environmental release. It is imperative that waste disposal facilities are built to safely contain this waste. However, to do this we must ensure that the engineered and natural barriers are sufficient to prevent the buried materials from migrating through to the surface. Solutions migrating from repositories (ILW and LLW) will have a wide range of chemical compositions and conceptual models constraining the key mineral-water interactions with realistic lithologies are urgently needed. To this end, we conducted experiments to study U removal from solution via mineral-surface interactions with quartz, sandstone, and volcanic rock over a pH range of 2-12, with varying concentrations of U (10 ppb, 0.1 ppm, 1 ppm, and 10 ppm) and with and without bicarbonate added (2 mM) with 0.1 M NaCl electrolyte. We observed that the U concentration in solution had little effect on the extent of U removal from solution as a function of pH or bicarbonate concentration 2with quartz and sandstone but was important for volcanic rocks, where removal ofU, due to adsorption, decreased with increasing U concentration between pH 4 and 8. When bicarbonate was added to solution then the quartz, sandstone, and volcanicrock geomaterials acted similarly in their abilities to immobilize uranium, with an adsorption envelope from pH 4-8 followed by an increase in U removal, likely via precipitation, at high pH. When bicarbonate was not added,the removal of U from solution was more controlled by the geomaterial. Bicarbonate addition at pH 6 -10 lowered adsorption. However, the addition of bicarbonate in experiments with 10 ppm U at pH 10 -12 allowed for precipitation of U at the rock surface, making bicarbonate
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