SORPTION BEHAVIOR OF ACTINOIDS ON WEATHERED MINERALS

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Understanding the sorption behavior of nuclides having long-term radiological toxicity onto geological materials is central to the safety assessment of underground disposal of radioactive waste. In order to see the effect of crystal structure, crystallinity and surface conditions of various oxides and hydrous oxides on the sorption of metal ions, the sorption of tracer concentrations of Np(V) on naturally occurring iron and alumiun minerals, synthetic oxide powders and laboratory-prepared hydrous oxides was studied as a function of pH.The orders of their abilities to sorb Np(V) were hydrous oxides including oxyhydroxides and hydroxides > synthetic oxide powders > minerals (hematite, magnetite and corundum). These results suggest that the sorption of tracer concentrations of actinoids is controlled primarily by their crystal structures and subsidiarily by their surface areas, indicating that the transformation of oxides and hydrous oxides of iron and aluminum occurring in natural enviro … More nments will give a serious influence on the migration of radionuclides. The effects of metal ion saturation on the sorption of Eu(III) and Co(II) on goethite, gibbsite and laboratory-prepared amorphous iron and aluminum oxides were studied as a function of pH over a wide range of metal ion concentrations. When the metal ion concentrations were low, a simple Langmuir equation, assuming a single binding constant, was capable of describing sorption on these hydrous oxides. At high metal ion concentrations, sorption on goethite and gibbsite exhibited clear saturation maxima, indicating that sorption on these minerals was controlled by a simple one-to-one interaction between the metal ion and a binding site. Conversely, sorption on laboratory-prepared hydrous oxides continued to increase even at high metal ion concentrations, indicating that sorption on amorphous hydrous oxides proceeds through a somewhat different pathway, such as the formation of a pricipitate or a solid solution at the binding surface. Less