Sorption of Heavy Metals and Radionuclides on Zeolites and Clays

The sorption of zinc, strontium, technetium, cadmium, caesium, mercury, lead, plutonium and americium from their aqueous solutions by natural zeolitic materials from Metaxades (Greece), Nižný Hrabovec (Slovakia), synthetic zeolites Nalsit and Ysit (VURUP, Slovakia) and bentonites from Melos Island (Greece) and Jelsový Potok (Slovakia) was investigated using a batch-type procedure and radiotracer techniques. The metal uptake and the distribution coefficient (K_d) values determined for the materials of different origin were correlated with their mineralogical composition and their gross cation exchange capacity (CEC). The identification of specific uptake sites was attempted on the basis of the sorption isotherms and the exchangeable cation content. The experimental results provide information on the suitability of the individual materials for the treatment of radioactive waste and their application as a backfill in potential nuclear waste repositories. It was found, that the zeolites (natural and synthetic) are very efficient sorbents for caesium. The removal of lead from aqueous solutions by the investigated natural zeolites was almost as effective as the removal of caesium, whereas the materials were less effective for the removal of other heavy metal ions. The sorption of radionuclides (239Pu, 241Am, 90Sr, 99Tc, 137Cs) on zeolites and bentonites was correlated with their Gross Annual Stopping Power (GASP). The comparison of the obtained data indicated, that the Slovak synthetic zeolite NaY shows the best sorption characteristics among the studied materials.