Sorption of Ni And Eu in a multi-element system

Laboratory studies on the retardation of radionuclides in the far-field of a radioactive waste repository are often performed using a single metal in the presence of the solid surfaces in solution. However, in the event of failure in the engineered barrier system (EBS), groundwater flowing pass the EBS will likely contain more than one long live radionuclide. The aim of this paper is to understand sorption in systems containing more than one radionuclide in solution. The work presented is carried out to understand how the presence of Ni or Eu in solution will affect the sorption of each other. Static batch sorption experiments of Ni and Eu sorption to different granitic materials have been performed. Radiometric analysis was done using Cobra (II) Auto gamma for 152Eu and TriCarb liquid scintillation for Ni63. Experimental results were described initially using the empirical models from which Rd values were obtained for sorption in single systems of Ni and Eu, and of multi-element systems of Ni and Eu. The experimental data was fitted to the surface complexation using JChess Geochemical Code to obtained complexation constants for the interactions between Ni and Eu and the solid surfaces. The effect on sorption in a multi-element system was expressed by the ratio of the sorption capacity of one metal ions in the presence of the other metal ions Qmix to the sorption capacity of same metal ions when it is present alone in solution Qsing. s in 1 m ix g Q Q > , the sorption is promoted by the presence of other metal ions, whereas if: sin 1 mix g Q Q = , there appears to be no observable effect, and if: s in 1 m ix g Q Q < , it would indicate that sorption is suppressed by the presence of other metal ions in solution. Results obtained showed that sorption was suppressed in systems containing Eu and Ni. Ratios of Qmix and Qsing were calculated as approximately 1and Eu sorption to Muscovite Mica and for Ni sorption to Plagioclase Feldspar, showing that there was no effect on the sorption capacity. The ratio was calculated as < 1 for Eu sorption to Granite Adamellite, Rose Quartz, Plagioclase Feldspar and Muscovite Mica, showing that sorption of Eu in the presence of both Ni was suppressed. Results also showed suppression of Ni sorption in the presence of Eu with the most suppression occurring with for Ni sorption to Rose Quartz in the presence of Eu with a mixed/single ratio << 1. A correlation between the Rd and determined surface complexation constant is determined for the granitic minerals.