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Determination of the free-ion concentration of rare earth elements by an ion-exchange technique: implementation, evaluation and limits.

Leguay, Sébastien; Campbell, Peter G. C.; Fortin, Claude (2016). Determination of the free-ion concentration of rare earth elements by an ion-exchange technique: implementation, evaluation and limits. Environmental Chemistry , vol. 13 , nº 3. p. 478-488. DOI: 10.1071/EN15136.

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An ion-exchange technique that employs a polystyrene sulphonate ion-exchange resin was developed for determining environmentally relevant free-ion concentrations of Ce, Eu, La and Nd. Owing to the high affinity of rare earth elements (REE) for the selected resin, this method requires the addition of an inert salt to increase the concentration of the counter-ions (i.e. cations that are exchanged with REE bound to the resin). The use of a batch equilibration approach to calibrate the resin allowed the implementation of the ion-exchange technique at reasonably low ionic strength (I = 0.1 M). Several ligands were used to test the selectivity of the method, which proved to be highly selective for the free metal ion in presence of the tested cationic and anionic complexes (REE–nitrate, REE–malic acid and REE–nitrilotriacetic acid systems) and operational for very low proportions of REE3+, owing to the strong REE–resin interactions. The ion-exchange technique was also implemented to determine [Eu]inorg in the presence of natural humic matter (Suwannee River Humic Acid) and the results were compared with those obtained using equilibrium dialysis and those calculated with chemical equilibrium models. At pH 4.00, the measured [Eu]inorg values were in fairly good agreement with those predicted with the Windermere Humic Aqueous Model and Stockholm Humic Model, whereas the Non-Ideal Competitive Absorption model appeared to underestimate the [Eu]inorg. However, the inorganic europium concentrations were strongly underestimated (4 < [Eu]inorg, IET/[Eu]inorg, calc < 18) with the three prediction models at higher pH (5.3 and 6.2).

Type de document: Article
Mots-clés libres: free metal ions; humic acid; lanthanides; speciation
Centre: Centre Eau Terre Environnement
Date de dépôt: 09 avr. 2018 17:38
Dernière modification: 09 avr. 2018 17:38
URI: http://espace.inrs.ca/id/eprint/4699

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