title: Synergy in Extraction System Chemistry: Combining Configurational Entropy, Film Bending, and Perturbation of Complexation.
abstract: Iron-uranium selectivity in liquid-liquid extraction depends not only on the mole fraction of extractants, but also on the nature of the diluent used, even if the diluent has no complexation interaction with the extracted ions. Modeling strong nonlinearity is difficult to parametrize without a large number of parameters, interpreted as "apparent constants". We determine in this paper the synergy curve versus mole fraction of HDEHP-TOPO (di(2-ethylexyl) phosphoric acid/tri-n-octyl phosphine oxide) and compare the free energy of aggregation to the free energy of extraction in various diluents. There is always a concomitant maximum of the two quantities, but with a gradual influence on intensity. The diluent is wetting the chains of the reverse aggregates responsible of the extraction. We show here that the intensity of the unexplained synergy peak is strongly dependent on the "penetrating" or "nonpenetrating" nature of the diluent. This experimental determination allows us to attribute the synergy to a combination of entropic effects favoring extraction, opposed to perturbation of the first coordination sphere by penetration as well as surfactant film bending energy.
authors.affiliation: †ICSM/LTSM, CEA/CNRS/UM2/ENSCM UMR5257, Site de Marcoule, Bat. 426, 30207 Bagnols sur Cèze, France.
authors.forename: J
authors.initials: J
authors.lastname: Rey
authors.affiliation: †ICSM/LTSM, CEA/CNRS/UM2/ENSCM UMR5257, Site de Marcoule, Bat. 426, 30207 Bagnols sur Cèze, France.
authors.forename: S
authors.initials: S
authors.lastname: Dourdain
authors.forename: L
authors.initials: L
authors.lastname: Berthon
authors.affiliation: §Laboratoire Léon Brillouin CEA/CNRS, CEA Saclay, 91191 Gif-sur-Yvette, France.
authors.forename: J
authors.initials: J
authors.lastname: Jestin
authors.affiliation: †ICSM/LTSM, CEA/CNRS/UM2/ENSCM UMR5257, Site de Marcoule, Bat. 426, 30207 Bagnols sur Cèze, France.
authors.forename: S
authors.initials: S
authors.lastname: Pellet-Rostaing
authors.affiliation: †ICSM/LTSM, CEA/CNRS/UM2/ENSCM UMR5257, Site de Marcoule, Bat. 426, 30207 Bagnols sur Cèze, France.
authors.forename: T
authors.initials: T
authors.lastname: Zemb
mesh_terms: D019277:Entropy; D007501:Iron / Q000302:isolation & purification; D059625:Liquid-Liquid Extraction / Q000379:methods*; D010720:Phosphines / Q000737:chemistry; D010756:Phosphoric Acids / Q000737:chemistry; D014501:Uranium / Q000302:isolation & purification
chemical_list: D010720:Phosphines; D010756:Phosphoric Acids; D014501:Uranium; D007501:Iron; C030242:phosphoric acid