Sorption of uranium and lead on CSH

The sorption of selected elements on a CSH (Calcium Silicate Hydrate) cement phase, the main sorbing phase in cements, was carried out in different conditions (temperature, addition of EDTA as a selected representative of the organic substances present in the waste). The sorption behaviour of the element is described by the distribution ratio (R_d) between the liquid and solid phases (L/S) or with sorption isotherm. The sorption of U and Pb on the synthetic cement phase CSH with Ca/Si ratio 1 was studied in a set of equilibrium and kinetic sorption experiments held within range of L/S = 100-800 L/kg and temperature range 22-80°C with ²³³U and stable Pb in an inert atmosphere. The aim of the study was to compare behaviour of these elements with previous study which was done on real cementitious materials and describe the sorption from several point of view: distribution ratio or the isotherm shape under the influence of temperature or addition of EDTA. The measurement of ²³³U was done with an LSC detector. The Pb concentration in the solution was measured by AAS. Where possible with regard to the experimental setup, the reaction enthalpy, entropy and apparent activation energy were also determined. The sorption experiments with the synthesized CSH phase in comparison with a real cementitious material in different conditions confirmed the dominant role of CSH in the sorption of selected radionuclides in cementitious materials in line with the higher R_d values of sorption on CSH than on real cementitious materials. The sorption of uranium and lead is strong, associated with high R_d values (in the order of about 10⁵ L/kg). Pb sorption is more sensitive to the presence of EDTA