Adsorption characteristics of cesium onto calcium-silicate-hydrate in concrete powder and block

The concrete building and paved roads in the urban areas can be exposed to cesium (Cs⁺) in case of the accidental release to environment. The adsorption kinetics of Cs⁺ onto concrete powder was well-represented by the pseudo-second-order kinetic model and intra-particle diffusion model. Both Langmuir and Freundlich isotherm models adequately described the adsorption of Cs⁺ onto the concrete powder. Lower temperature favored the adsorption of Cs⁺, and the activation energy was estimated as 1.57 kJ/mol, which indicates a physical adsorption process. Additionally, the adsorption of Cs⁺ onto the concrete powder was spontaneous (ΔG<0), exothermic (ΔH<0), and its adsorption formed a stable arrangement onto the concrete powder (ΔS<0). The adsorption of Cs⁺ onto the concrete block was similar to that onto the powder, where the activation energy was 25.64 kJ/mol indicating physical adsorption. The presence of Na⁺ enhanced the adsorption of Cs⁺ because Na⁺ lowered the competitive inhibition of K⁺ on the adsorption of Cs⁺ based on hydrated radius and hydration enthalpy. The amounts of Cs⁺ adsorbed onto C–S–H gel were not substantial and the adsorption was slow, but it should be considered in an urban area due to a huge coverage of concrete.