Radiostrontium sorption on natural glauconite sands of the Neogene-Paleogene formations in Belgium

The Neogene-Paleogene glauconite sands are investigated for radionuclide sorption in the framework of the Belgian radioactive waste disposal program. This study was set up to measure the adsorption of radiostrontium (⁸⁵Sr) on the sands and on glauconite fractions to identify factors explaining variable sorption among different formations. Batch ⁸⁵Sr sorption experiments were set up with 45 different glauconite sands and glauconite fractions (125-250 μm) in a background solution of 1 mM CaCl₂.H₂O and 0.5 mM KCl. The distribution coefficients (K_D) for ⁸⁵Sr²⁺ ranged 23-65 L kg^-1 for the intact sands and ranged 50-144 L kg^-1 for the glauconite fractions. The K_D values strongly correlated with the CEC (R² = 0.62 for sands and 0.82 for glauconite fractions) and corresponded well with CEC based predictions based on two existing models calibrated to soils. The K_D on the complete sand is proportional to the glauconite content and the K_D of the glauconite fraction if no other clay minerals are present in significant amounts. Sorption equilibrium was reached within 48 h in the complete sands, in milled complete sands, in glauconite fractions and in milled glauconite fractions, suggesting no diffusive boundaries in the glauconite pellets. It is concluded that glauconite sands have a suitably high retention of radiostrontium and the sorption strength is in line with that of other geological barriers when judged from the CEC.