Study of caesium adsorption onto alluvial sediments from the Italian Po Plain

The study investigates the adsorption processes of caesium onto alluvial sediments from the Po Plain (northern Italy). Understanding these adsorption processes is crucial for assessing the safety of low- and intermediate-level radioactive waste repositories, including the proposed Italian repository. Adsorption kinetics and equilibrium experiments on sandy samples were conducted with the aim of evaluating how even small differences in clay content and mineralogy can affect kinetics and equilibrium adsorption behaviour. The obtained data were compared with literature studies and confirmed the significant affinity of caesium for sandy sediments, even for a mud content of less than 5%. Kinetics analysis revealed that a pseudo-second-order model best described the process, suggesting two-site occupancy adsorption kinetics attributed to the presence of illite and characterised by various different sites for caesium adsorption. Samples with higher clay and micaceous minerals content, cation exchange capacity and specific surface area exhibit faster kinetics and higher affinity for caesium. The study shows a significant variation in partition coefficient values, ranging from 57 to 750 mg L-1. This finding emphasises the importance of sediment composition in caesium adsorption, which is crucial for developing accurate environmental protection and safety assessment models.