Kinetic and Equilibrium Studies of Cesium and Strontium Adsorption on a Natural Sand Soil

Abstract

Modeling radionuclide migration is important to understand both environmental effects and develop remediation strategies. The key factors for modeling are the physical and chemical interactions of radionuclides with soil components, which depend on soil types and geochemical conditions. Although radionuclide adsorption on many soils has been studied, their migration behaviour is still not well understood due to the complexity of the environment.Radioactive cesium and strontium are present as fission products ¹³⁷Cs and ⁹⁰Sr in nuclear wastes and spent fuels, and pose a major concern to pollution control because of their biological activity and long decay half-lives. This paper will present bench top test results and discussions on the kinetics and equilibrium of the adsorption of inactive Cs⁺ and Sr²⁺ ions on a natural sand soil under a pH range of 3 to 10, temperatures (25 to 50 ^°C) and concentrations (10^-8 to 10^-3 mol/kg). It was found that the adsorption of Cs⁺ and Sr²⁺ followed second order reaction kinetics and generally required more than a week to reach equilibrium. The adsorption equilibria of Cs⁺ followed a Freundlich isotherm, while those of Sr²⁺ followed a Langmuir isotherm, suggesting different adsorption mechanisms. Adsorption increased with increasing pH for both ions at all temperatures studied, which is likely due to an increasingly negative surface charge on the sand soil. The desorption tests suggest that Cs⁺ is more tightly bound than Sr²⁺ to the surface of the adsorbent under the same chemistry conditions and that Cs⁺ is less mobile than Sr²⁺ in natural sand soil.