Sorption of Co, Cs, Sr and I onto argillaceous rock as studied by radiotracers

Sorption of 60Co, 85Sr, 137Cs and 125I have been studied on samples originated from Boda (siltstone-) claystone formation (BCF) (Hungary). The distribution of Kd values have been determined in static batch experiments using natural groundwater. The order of sorption of isotopes was Co>Cs>Sr>I, where iodine exhibits sorption properties in a modest extent. The sorption isotherm was determined for Cs from measurements carried out in 10-5-10-1M initial concentration range. The isotherm can be described with non-linear Freundlich approximation in the range of 10-7-10-4M equilibrium concentration. At concentrations >10-2M the isotherm achieves saturation. Hence, it is suggested that sorption of Cs on BCF is dominated by cation-exchange reactions on the illite mineral component. In the case of Co and Sr, precipitation reactions occurred during the experiments performed with carrier-containing solutions. This can be attributed to the low values of solubility product constants of SrCO3, SrSO4 and Co(OH)2, formed from anions present in the natural groundwater. (author)