Influence of natural organic matter and mineral surfaces upon the radionuclide speciation in an environmental context

This study deals with interactions occurring in a ternary europium(III)/humic acid(HA)/α Al2O3 system, depending on solution conditions (pH, ionic strength, organic concentration). These interactions were studied at a macroscopic scale - quantifying Eu(III) and/or HA adsorption onto the mineral surface - and using Time-Resolved Luminescence Spectroscopy. Presence of HA modifies Eu(III) behavior toward the mineral surface. The analysis showed a Eu(III)-HA complexation in the ternary system, in all the conditions studied. However, Eu(III) complexation with the mineral surface is occurring at high pH and ionic strength only. Spectrophotometric titrations were validated as a method to study HA reactivity at environmental relevant concentrations. They have been used to determine modifications of HA reactivity after adsorption onto the alumina surface depending on initial HA concentration. These results have then be used to model Eu(III) speciation in the ternary system, using the CD-MUSIC and NICA-Donnan models for mineral and organic complexation, respectively.