Use of multi-dimensional sorption data-sets to constrain models of radionuclide-solid interactions

In order to adequately constrain surface complexation models for radionuclide sorption, large 'multi-dimensional' data-sets, showing the dependence of sorption on numerous experimental parameters, are required. This paper describes how large sorption databases were used to develop surface complexation models of U(VI) uptake on kaolinite and ferrihydrite. It is shown that the shape of U uptake curves as a function of pH and total U (ΣU) can be used to distinguish between U adsorption and the precipitation of amorphous uranyl hydroxide. The U sorption data-set obtained in this work also includes the effects of several complexing ligands, including phosphate. The dependence of U uptake on these variables can be used to assess the formation of various types of surface complexes (including ternary surface complexes) and the possibility of precipitation reactions. Adsorption experiments with different sorbing materials were also useful in developing models for U sorption and for excluding some possible surface and precipitation reactions. This study shows how combining multi-dimensional sorption databases with advanced spectroscopic or microscopic techniques (such as EXAFS or AEM) can lead to improved models of interactions at mineral-water interfaces. Copyright (2001) Material Research Society