Both colloidal plutonium (Pu) and oxidized Pu(V) are considered to be mobile in the groundwater system. However, few studies have been designed to compare the mobility of the two Pu species simultaneously and distinguish the major species contributing to Pu transport. To fill this gap, the influence of Pu species on their mobility through a granite fracture was experimentally investigated to assess the transport ability of different Pu species. First, initial Pu(IV) and Pu(V) were added to a highly saline groundwater, and distributions of Pu species were determined at different times using an ultrafiltration and solvent extraction method. The results showed that initial Pu(IV) was transformed into colloidal Pu and soluble Pu(V), while in the initial Pu(V) system, soluble Pu(V) was the dominant species. Second, Pu solutions at different equilibrium times were fed into the granite fracture, and the Pu species distribution in each effluent fraction was analyzed using solvent extraction methods. Fracture transport experiments and analysis of Pu species in the effluent revealed that both colloidal Pu and soluble Pu(V) migrated through. For transport velocity (Retardation factor, Rf) and recovery (R) of each Pu species, results indicated the following transport velocity order for Pu species: Pu-coll > Pu(V) ≈ H2O > Pu(IV). The recoveries of Pu-coll (R = 27.1% ± 7.8%) and Pu(V) (R = 24.0% ± 3.5%) indicate that both species possess comparable migration capabilities, and the order of transport recovery for Pu species is Pu-coll ≈ Pu(V) > > Pu(IV). The simultaneous transport of colloidal Pu and soluble Pu(V) should be considered for Pu migration modelling.
Keywords: Colloid-facilitated transport; Fracture flow; Pu species; Recovery; Retardation factor.
Copyright © 2026 Elsevier B.V. All rights reserved.