Sequential Separation of Uranium, Hafnium and Neodymium from Natural Waters Concentrated by Iron Coprecipitation

A new ion exchange chromatography method is presented for the isolation of high field-strength elements (HFSE) from freshwater and seawater samples that have undergone iron coprecipitation. Large volumes of water can be condensed through the application of iron coprecipitation, but clean separation of elements from the precipitate proves difficult. The technique described is a five-column process designed to separate the HFSE, including rare earth elements such as neodymium and hafnium, before removing the iron and isolating uranium. Subsequent isolation of Nd and Hf was achieved using established ion exchange chromatography methods. The efficacy of our chemistry was verified by measurements of analytical reference materials – both reference solutions and seawater samples – subjected to the chemical separation methods described. Elution results indicate high yields (> 90%) determined by concentration measurements of a known reference material added to each column. Measurement results for isotopic compositions of seawater (U, Nd) and reference solutions (NIST SRM 960, U) were identical within uncertainty to previously published values. Compositions were identical between solutions (Spex CLMS3, Spex PLND2) that underwent different iron coprecipitation procedures. Isotopic determinations for reference materials JNdi-1 and NIST SRM 960 measured with the mass spectrometers used in this study were in agreement with universally accepted values for these materials, and indicate high precision. Une nouvelle methode de chromatographie echangeuse d'ions est presentee pour la separation des elements a champ electrostatique eleve («HFSE») a partir d’echantillons d'eau douce et d'eau de mer ayant subi une co-precipitation du fer. De grandes quantites d'eau peuvent etre condensees grâce a la co-precipitation du fer, mais une separation nette des elements du precipite se revele difficile. La technique decrite est un procede cinq colonnes destine a separer les «HFSE», y compris les terres rares tels que le neodyme et l'hafnium, avant d'enlever le fer et de separer l'uranium. La separation subsequente de Nd et Hf a ete realisee a l'aide demethodes bien etablies de chromatographie echangeused'ions. L'efficacite de notre chimie a ete verifiee par l'analyse de materiaux de reference –a la fois des solutions standards et des echantillons d'eau de mer - soumis aux procedes de separation chimique decrits. Les resultats des elutions indiquent des rendements eleves (> 90%) determinees par des mesures de concentration d'un materiau de reference connu ajoutedans chaque colonne. Les resultats des mesures de la composition isotopique de l'eau de mer (U, Nd), et des solutions standards (NIST SRM 960, U) sont identiques dans l'intervalle d'incertitude des valeurs precedemment publiees. Les compositions sont identiques entre les solutions (Spex CLMS3, Spex PLND2) ayant subi differentes procedures de co-precipitation du fer. Les determinations isotopiques pour les materiaux de reference JNDI-1 et NIST SRM 960 mesurees avec les spectrometres de masse utilises dans cette etude sont en accord avec les valeurs universellement acceptees pour ces materiaux, et indiquent en outre une grande precision.