Investigations of the role of colloids in radionuclide migration
thesisposted on 25.11.2011, 13:00 authored by Silvia Anton Gascon
The mobility of radionuclides through the Geosphere depends greatly on the sorption of radionuclides to the host rock. However, the presence of colloidal particles may influence the transport of radionuclides. Given a stable and mobile colloidal suspension which sorbs radionuclides onto its surface, the radionuclide may be transported along with the colloidal suspension. Given an irreversible interaction, radionuclides may be transported until the colloids flocculate. A reversible interaction, may lead to a scenario where the radionuclide is immobilised by sorption to the host rock. The work presented herein provides insight to the reversibility of the interaction of Cs+, Ni2+ and Eu3+ with two colloidal suspensions, boehmite and montmorillonite. The main difference between the colloidal phase and the solid phase of a mineral is the surface area to mass ratio, greater for the colloidal phase, as shown by the results herein. Assuming equal chemistry between colloidal and solid surface, sorption experiments have been carried out to relate the distribution ratio, Rd, for colloids and for solids with the ratios between surface areas. An attempt to develop a mathematical expression was made. The effect of humic acid on the sorption of metals onto colloidal boehmite was investigated. In all cases, the sorption of metals onto boehmite was hindered by the presence of humic acid. The linear additive model was tested on the experimental results. The transport of radionuclides associated to inorganic colloids has been assessed by means of column experiments. A radiometric technique consisting of radiolabelling inorganic silica colloids with 152Eu spike was used to detect and quantify the migration of silica colloids through a sand column. Furthermore,the same method was used to investigate the migration of 137Cs associated to silica colloids through a sand column. The mobility of the radionuclide was found to be enhanced by the silica colloids.