Assessing soil properties governing radiosamarium sorption in soils: Can trivalent lanthanides and actinides be considered as analogues?

The interaction of radiosamarium (RSm), represented here by the 151Sm isotope, a trivalent lanthanide radioisotope of particular concern due to its presence in radioactive waste, was evaluated in 30 soils with contrasting characteristics by determining sorption and desorption parameters. Solid-liquid distribution coefficients (Kd) were in the range of 102  –105 L kg− 1 and desorbed fractions were always < 2%, which demonstrated that RSm was, in general, strongly and irreversibly sorbed in soils. The statistical analyses performed allowed us to identify pH, specific surface area (BET) and soil organic matter content as the soil properties controlling RSm sorption in the soils. From these, the sorption mechanisms responsible for the RSm-soil interaction were suggested. Two models, a multiple linear regression with BET and pH, and a partial least square regression-based model, were successfully developed and externally validated enabling to accurately predict Kd (RSm) values directly from soil properties. It was also evidenced that RSm and Am sorption is controlled by the same soil properties, and that Kd (RSm) values can be successfully predicted through the application of prediction models calibrated with Am data. Thus, the chemical analogy among trivalent actinides and trivalent lanthanides in terms of soil interaction and the feasibility of using interchangeably Kd data of both element families to predict their interaction in soils was demonstrated.