Abstract:The synergistic extraction of alkaline earth (Ca 2þ , Sr 2þ , Ba 2þ and Ra 2þ ) and actinide (Am 3þ , UO 2 2þ and Th 4þ ) cations from aqueous nitric acid solutions by mixtures of P,P 0 -di (2-ethylhexyl) Downloaded by [Erciyes University] at 07:34 26 December 2014 methylene-(H 2 DEH[MDP]), ethylene-(H 2 DEH[EDP]), and butylene-(H 2 DEH[BuDP]) diphosphonic acids and neutral extractants in o-xylene has been investigated. The cis-syn-cis and cis-anti-cis stereoisomers of dicyclohexano-18-crown-6 (DCH18C6), th… Show more
“…In solvent extraction studies, molecular associations between extractants are often considered as responsible for antagonistic effects, implying that less chelating sites are available. However, such associations are seldom fully characterized, while they could also induce a specific organization which could also favor metal ions extraction. − Few groups have performed a detailed characterization of the organic phase organization from the atomic scale to the supramolecular scale of the self-assembled aggregates. − To our knowledge, the role of a preorganization of the solution prior to any contact with the target ions has never been evaluated to explain the synergistic mechanisms.…”
Among the proposed mechanisms to predict and understand synergism in solvent extraction, the possibility of a preorganization of the mixture of extractant molecules has never been considered. Whether involving synergistic aggregation as for solubilization enhancement with reverse micelles or favored molecular interaction between the extractant molecules, evaluation of this hypothesis requires characterization of the aggregates formed by the extractant molecules at different scales. We investigate here the HDEHP/TOPO couple of extractant with methods ranging from vibrational spectroscopy and ESI-MS spectrometry to vapor pressure osmometry and neutron and X-ray scattering to cover both molecular and supramolecular scales. These experimental methods are subjected to DFT calculations and molecular dynamics calculations, allowing a rationalization of the results through the different scales. Performed in the absence of any cation, this original study allows a decorrelation of the mechanisms at the origin of synergy: it appears that no clear preorganization of the extractants can explain the synergy and therefore that the synergistic aggregation observed in the presence of cations is rather due to the chelation mechanisms than to intrinsic properties of the extractant molecules.
“…In solvent extraction studies, molecular associations between extractants are often considered as responsible for antagonistic effects, implying that less chelating sites are available. However, such associations are seldom fully characterized, while they could also induce a specific organization which could also favor metal ions extraction. − Few groups have performed a detailed characterization of the organic phase organization from the atomic scale to the supramolecular scale of the self-assembled aggregates. − To our knowledge, the role of a preorganization of the solution prior to any contact with the target ions has never been evaluated to explain the synergistic mechanisms.…”
Among the proposed mechanisms to predict and understand synergism in solvent extraction, the possibility of a preorganization of the mixture of extractant molecules has never been considered. Whether involving synergistic aggregation as for solubilization enhancement with reverse micelles or favored molecular interaction between the extractant molecules, evaluation of this hypothesis requires characterization of the aggregates formed by the extractant molecules at different scales. We investigate here the HDEHP/TOPO couple of extractant with methods ranging from vibrational spectroscopy and ESI-MS spectrometry to vapor pressure osmometry and neutron and X-ray scattering to cover both molecular and supramolecular scales. These experimental methods are subjected to DFT calculations and molecular dynamics calculations, allowing a rationalization of the results through the different scales. Performed in the absence of any cation, this original study allows a decorrelation of the mechanisms at the origin of synergy: it appears that no clear preorganization of the extractants can explain the synergy and therefore that the synergistic aggregation observed in the presence of cations is rather due to the chelation mechanisms than to intrinsic properties of the extractant molecules.
“…The solvent extraction of thorium (IV) and uranium (VI) was investigated by Meera and Reddy (2004) using mixtures of para-substituted 1-phenyl-3-methyl-4-aroyl-5-pyrazolones and crown ethers. Similar work was also done on lanthanoids (Ensor and Reynolds, 1989;Pavithran et al, 2003;Reddy et al, 2006); alkaline earth metals (Chiarizia, et al, 2003;McAlister et al, 2002); vanadium (Remya et al, 2005) and copper (Torkestani et al, 1996). In all the works examined, multiple solvent systems were found to exhibit synergism with respect to the species being extracted.…”
“…26) and DtBuCH18C6. 27 Other than using single extractant, a combination of different extractants is useful for Sr(II) extraction, e.g., both 18C6 derivatives with didodecylnaphthalene sulfonic acid, 28 versatic acid, 28,29 cobalt dicarbolide, [30][31][32] di-n-octylphosphoric acid, 33,34 and di(2ethylhexyl)alkylenediphosphonic acid 35,36 are used for synergistic extraction. A better understanding of a given extraction process leads to optimize the extraction system.…”
The solvent extraction of Sr(ii) was carried out using DCH18C6, and two HFC mixed solvents composed of organic solvents and HFC-43 (HFC-43: 1,1,1,2,2,3,4,5,5,5-decafluoropentane), and two acids (nitric acid and H2PFTOUD).
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