Abstract
The sorption mechanism of inorganic C-14(CO32-) was investigated using batch sorption experiments, XPS analyses, and zeta potential measurements. The results suggested that C-14 was adsorbed onto the cement surface by an electrostatic force, due to the reaction between SiO2 and CaO contained in the cementitious composition. That is, SiO2 was originally negatively charged (SiO-) in cement, but became positively charged (SiO-Ca+) through the interaction of Ca2+. These positive sites on the SiO2 surface adsorbed inorganic C-14. Based on these investigations, the sorption mechanisms of Cs-134, Co-60 and Am-241 were clarified from the view point of electrostatic adsorption. The results suggested Cs was adsorbed by negative sites (SiO-) in cement, while Co-60 and Am-241 were adsorbed by the reaction product between SiO2 and CaO in cement.
Ordinary Portland cement (OPC) did not contain enough SiO- compared with its CaO content to produce sufficient numbers of adsorption sites. In order to raise the distribution coefficient (Kd) of each radionuclide, blast furnace slag, which produces enough SiO-, was added to optimize the Ca2+/SiO- ratio in cement. All Kd values were increased by adding 50 wt% blast furnace slag into OPC.
