Kinetic and equilibrium studies of Cs(I), Sr(II) and Eu(III) adsorption on a natural sandy soil

Radioactive cesium, strontium and europium can be released as fission products during nuclear incidents and pose a major concern to contamination control because of their biological activity and long decay half-lives. Experiments were performed to study the kinetics and equilibrium of the adsorption of inactive Cs(I), Sr(II) and Eu(III) ions on a natural sandy soil. It was found that the adsorption of Cs(I), Sr(II) and Eu(III) had a second order reaction kinetics and generally reached equilibrium within 7 days. The adsorption equilibria of Cs(I) follows a Freundlich isotherm, while those of Sr(II) and Eu(III) follows a Langmuir isotherm. Adsorption increases with increasing pH for these cations studied at temperatures from 25 to 50 C. In general, the temperature effect on cation adsorption is small under these test conditions suggesting that the enthalpy change for adsorption is not significant. Tests of mixed Cs(I) and Sr(II) adsorption suggested that these cations likely adsorb on different sites on the surface of sandy soil. The desorption tests in NaCl and CaCl₂ solutions show that Eu(III) and Cs(I) are more tightly bound and less mobile in natural sandy soil than Sr(II) under the same test conditions. Tests of Cs(I), Sr(II) and Eu(III) in a column under a flowing condition revealed that these cations mainly adsorbed within the depth of 2 cm below the surface of sandy soil.