This study aims atIn this work, modelling of Eu(iii) speciation in a ternary system, i.e., in presence of purified Aldrich humic acid (PAHA) and α‑Al2O3., is presented. First, the mineral surface charge is measured by potentiometric titrations and then described using the CD‑MUSIC model. This model is also used to describe Eu(iii) binding to thisthe α‑Al2O3 surface at different pH values, ionic strengthsstrength and mineral concentrations. Then, Eu(iii) binding to PAHA is studied at pH 4 and different humic concentrations by Time-resolved luminescence spectroscopy (TRLS).) is then used to study the binding of Eu(iii) to PAHA at pH 4 with different humic acid concentrations. The spectra are used to calculate a spectroscopic “titration curve”, allowingused to determine Eu(iii)/PAHA binding parameters in the NICA-Donnan model. These information are then used to describe Eu(iii) interactions in the ternary system. Following a previous study (Janot et al., Water Res. 46, 731-740), the modelling of the ternary system is based upon the definition of two PAHA fractions,pools where one fraction remains in solution and one the other is adsorbed onto the mineral surface, with each one withpossessing different proton and europium(iii)metal binding parameters. The modificationsmodification of protonation behaviour offor both fractions are obtained fromis examined using spectrophotometric titrations of the non-adsorbed PAHA fraction at different organic/mineral ratios. These data are then used to describe Eu(iii) interactions in the ternary system: Eu(iii) repartitionrepartitioning in the ternary system is calculated for different pH, ionic strength and PAHA concentrationconcentrations, and results are compared to experimental observations. Results of modelling areThe model is in good agreement with experiments, even if further adjustments would be needed, especiallyexperimental data, except at high PAHA fractionation rates. Results show the dominance ofthat organic complexation throughdominates over a large pH range, with predominance ofthe predominant species existing as the surface-bound fraction. Above pH 8, Eu(iii) seems to be mostly complexed to the mineral surface, which is in agreement with previous spectroscopic observations (Janot et al., Environ. Sci. Technol. 45, 3224-3230).

Modelling Eu(iii) speciation in a Eu(iii)/PAHA/αAl2O3 ternary system

249th National Meeting (2015)

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