SORPTION OF URANIUM(VI) TO GRAPHITE UNDER POTENTIAL NUCLEAR REPOSITORY CONDITIONS
The sorption and desorption behavior of uranium(VI) was examined through a series of batch experiments to examine the equilibrium sorption and reaction kinetics across a range of potential repository conditions. Uranium(VI) showed pH dependent sorption behavior with pH varied from 2-10 with maximum values being recorded in the near-neutral and slightly acidic pH region (Kd ranging from 0 – 125 mL/g). Sorption behavior was also found to behave in a non-linear fashion with changing U(VI) concentration in solution, best fit by a Freundlich isotherm. Ionic strength was not observed to have a significant effect on the sorption up to 4 molal NaCl. Sorption was also strongly dependent on the solution concentration of dissolved carbonate with elevated dissolved carbonate being able to completely suppress sorption in previously identified high sorbing regions and reduced dissolved carbonate concentrations enhancing sorption in areas where sorption had been previously minimized. Sorption and desorption kinetics were examined revealing significant differences in the sorption and desorption rates, as well as incomplete desorption of the uranium from the graphite over the experiment duration.