Effect of organic complexing agents on the interactions of Cs+, Sr2+ and UO22+ with silica and natural sand

Sorption processes play a key role in controlling radionuclide migration through subsurface environments and can be affected by the presence of anthropogenic organic complexing agents found at contaminated sites. The effect of these complexing agents on radionuclide–solid phase interactions is not well known. Therefore the aim of this study was to examine the processes by which EDTA, NTA and picolinate affect the sorption kinetics and equilibria of Cs+, Sr2+ and UO22+ onto natural sand. The caesium sorption rate and equilibrium were unaffected by the complexing agents. Strontium however showed greater interaction with EDTA and NTA in the presence of desorbed matrix cations than geochemical modelling predicted, with SrNTA− enhancing sorption and SrEDTA2− showing lower sorption than Sr2+. Complexing agents reduced UO22+ sorption to silica and enhanced the sorption rate in the natural sand system. Elevated concentrations of picolinate reduced the sorption of Sr2+ and increased the sorption rate of UO22+, demonstrating the potential importance of this complexing agent. These experiments provide a direct comparison of the sorption behaviour of Cs+, Sr2+ and UO22+onto natural sand and an assessment of the relative effects of EDTA, NTA and picolinate on the selected elements.

► EDTA and NTA affected Sr2+ and UO22+ sorption to both silica and sand.
► NTA enhanced, and EDTA and picolinate reduced, Sr2+ sorption to sand.
► All complexing agents enhanced the rate of UO22+ sorption to sand.
► The relative effect of the ligands is summarised for the selected elements.