Adsorption of Eu(III) onto Minerals in the Presence of Humic Acids: Effects of Various Solution Parameters and Sorptive Fractionation on Modelling and Spectroscopy
Résumé
Adsorption of metals on minerals with humic acids is always under predicted [1]. The case of Eu(III) in ternary system including purified Aldrich humic acid (PAHA) and alpha-Al2O3 was measured, modelled and probed using time-resolved laser-induced luminescence spectroscopy (TRLS). Each binary system was studied independently [2,3,4], and the luminescence properties of Eu(III), luminescence spectra and decay times (%), were aquired and compared [5]. Influence of ionic strength and PAHA concentration was also evaluated.The typical luminescence behaviour of Eu(III)-HA system, showing a bi-exponential decay, was also found in the ternary system Eu(III)/PAHA/'- Al2O3, but with marked differences. Luminescence spectra and faster decay %1 are the same in both system at pH < 6, but with higher %2 indicating a rigid environment for Eu(III). For pH > 6, modifications of Eu(III) luminescence spectra and decrease of %2 are showing a progressive influence of '-Al2O3. The non-variation of %1suggests the on-going influence of PAHA, notwithstanding its progressive desorption. Comparing with previous data on sorptive fractionation of PAHA [2,3,6], and with the TRLS evolution of the system [5], an operational modelling was proposed [4], which implies that alumina-sorbed PAHA is showing a stronger interaction towards Eu(III) compared with non-sorbed PAHA even at pH > 7. This stronger interaction is due to the sorptive fractionation which reveals stronger binding sites [1,4,7].
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