Survey for effects of natural organic substances on sorption of radionuclides

In order to clarify an issue concerning the effects of natural organic substances on sorption of radionuclides, the author carried out the survey of technical and research papers. Consequently, the following conclusion was obtained. The sorption ratio of transition elements (Fe, Mn, Co and Ni) and actinide elements (Th, U, Pu, Am and Np) on geological media are susceptible to decrease by forming complexes with soluble humic and fulvic acids, however, alkali metal (K, Cs) and alkaline-earth metal (Ca, Sr) are hardly influenced by soluble organics. On the contrary, the sorption ratio of radionuclides may have increased by forming colloids with insoluble and polymeric natural organics. Especially, transuranic radionuclides (Pu, Am and Np) are more subject to be adsorbed by reductive form of organic and carbonate. In addition, some kinds of adsorbed chemical form of radionuclides on geological media have been indicated such as aluminum silicates, oxidized form of Fe and Mn. As mentioned above, natural organic may have a capacity to advance the mobility and/or the immobility of radionuclides. In the chemical reaction of coexistence with organic, radionuclides and geological media, the important factors of affecting the adsorption of radionuclides have been indicates as follows: redox condition, pH and ionic strength of solution, differences in concentration between dissolved organic ligands and radionuclides, species of geological sorbent, initial chemical form of radionuclide. However, the variation of sorption of radionuclides geological media in coexistence with natural organic substances (humic and fulvic acids) has not been identified qualitatively and/or quantitatively. Therefore, it will be important to study the experiment methods and assessment methods for the identification and the quantification which are concerning the interaction among natural organics, radionuclides and geological media, and the variation of radionuclide sorption. (author)